Existing Annotations Review

GO Term	Evidence	Action	Reason
GO:0005783 endoplasmic reticulum	IBA GO_REF:0000033	ACCEPT	Summary: PGRMC2 localization to the ER is well-supported by multiple lines of evidence. The deep research confirms PGRMC2 localizes primarily to the endoplasmic reticulum and nuclear envelope [PMID:27754849]. This IBA annotation is phylogenetically appropriate and consistent with experimental data. Reason: ER localization is a core feature of PGRMC2 function as a heme chaperone that receives heme from mitochondria-bound PGRMC1 and delivers it to the nucleus. Multiple experimental studies confirm this localization. Supporting Evidence: PMID:27754849 Visualising PGRMC2 in the cell using immunofluorescence and confocal microscopy has shown the presence of PGRMC2 at the central ER, and, interestingly, at the nuclear envelope and the perinuclear ER. file:human/PGRMC2/PGRMC2-deep-research-perplexity.md The protein localizes primarily to the endoplasmic reticulum (ER) and nuclear envelope, with additional reported localization to mitochondria-associated membranes (MAMs).
GO:0012505 endomembrane system	IBA GO_REF:0000033	ACCEPT	Summary: PGRMC2 is a single-pass transmembrane protein localized to ER and nuclear envelope, which are part of the endomembrane system. This IBA annotation is appropriately broad and phylogenetically supported. Reason: As a membrane protein of the ER and nuclear envelope, PGRMC2 is correctly annotated to endomembrane system. This is consistent with its function in heme trafficking between cellular compartments. Supporting Evidence: file:human/PGRMC2/PGRMC2-deep-research-perplexity.md PGRMC2 appears to operate as the downstream component in a relay system where mitochondria-bound PGRMC1 first acquires heme from ferrochelatase at the mitochondrial outer membrane, then transfers this heme to PGRMC2 localized on the endoplasmic reticulum and nuclear envelope.
GO:0016020 membrane	IBA GO_REF:0000033	ACCEPT	Summary: PGRMC2 is a single-pass transmembrane protein. The membrane annotation is accurate but very general. Reason: UniProt confirms PGRMC2 has a transmembrane domain (residues 42-66). While this is a broad term, the IBA annotation is phylogenetically sound. Supporting Evidence: file:human/PGRMC2/PGRMC2-uniprot.txt TRANSMEM 42..66 /note="Helical"
GO:0005496 steroid binding	IEA GO_REF:0000120	MODIFY	Summary: The historical name "progesterone receptor membrane component" suggested steroid binding, but modern research shows PGRMC2 primarily binds heme, not progesterone. The deep research explicitly states this protein binds heme rather than progesterone with high affinity [PMID:28111073]. Reason: While PGRMC2 was initially characterized as a potential steroid receptor, current evidence strongly supports heme binding as its primary ligand interaction. The IEA annotation based on automated pipelines reflects outdated understanding. GO:0020037 (heme binding) is more accurate. Proposed replacements: heme binding Supporting Evidence: file:human/PGRMC2/PGRMC2-deep-research-perplexity.md This protein's discovery that it binds heme rather than progesterone with high affinity fundamentally reframed our understanding of non-classical steroid signaling. PMID:28111073 our initial studies point to heme-related molecules as potential candidates to serve this function
GO:0005576 extracellular region	IEA GO_REF:0000044	KEEP AS NON CORE	Summary: UniProt indicates PGRMC2 can be secreted, based on detection in urine [PMID:37453717]. However, this appears to be a minor localization rather than a primary functional site. Reason: The secreted form may represent a secondary localization. The primary function of PGRMC2 as a heme chaperone occurs intracellularly at the ER and nuclear envelope. Supporting Evidence: file:human/PGRMC2/PGRMC2-uniprot.txt Secreted {ECO:0000269\|PubMed:37453717}.
GO:0005635 nuclear envelope	IEA GO_REF:0000044	ACCEPT	Summary: Nuclear envelope localization is well-supported by experimental evidence showing PGRMC2 co-localizes with nucleoporin ALADIN at the NPC [PMID:27754849]. This IEA annotation is consistent with experimental data. Reason: Nuclear envelope localization is central to PGRMC2 function in delivering heme to the nucleus. This is supported by both the ALADIN interaction studies and Reactome pathway data. Supporting Evidence: PMID:27754849 We detected that PGRMC2 co-localises with ALADIN and with different FG-repeat NUPs [...] to the nuclear envelope and the perinuclear ER.
GO:0005783 endoplasmic reticulum	IEA GO_REF:0000044	ACCEPT	Summary: Duplicate of IBA annotation. ER localization is experimentally confirmed [PMID:27754849]. Reason: ER localization is well-supported and represents a core site of PGRMC2 function in the heme trafficking pathway. Supporting Evidence: PMID:27754849 Visualising PGRMC2 in the cell using immunofluorescence and confocal microscopy has shown the presence of PGRMC2 at the central ER, and, interestingly, at the nuclear envelope and the perinuclear ER.
GO:0008289 lipid binding	IEA GO_REF:0000043	MARK AS OVER ANNOTATED	Summary: This IEA annotation is based on UniProt keyword mapping. While PGRMC2 has a cytochrome b5-like domain that could theoretically bind lipids, the primary demonstrated binding activity is heme binding. Reason: There is no direct experimental evidence for lipid binding by PGRMC2. The primary ligand is heme. This annotation appears to be based on domain predictions rather than functional characterization. Recent reviews of the MAPR family explicitly caution that direct ligand-binding evidence outside heme is weaker for non-PGRMC1 MAPRs. Supporting Evidence: file:human/PGRMC2/PGRMC2-deep-research-perplexity.md PGRMC2 exhibits reversible heme binding characteristic of signaling proteins that require dynamic exchange of heme with other proteins. file:human/PGRMC2/PGRMC2-deep-research-falcon.md Reviews highlight that PGRMC2 is less well characterized than PGRMC1 (tissue specificity, interaction network, subcellular locations). Additionally, progesterone binding evidence is weaker for non-PGRMC1 MAPRs.
GO:0016020 membrane	IEA GO_REF:0000044	ACCEPT	Summary: Duplicate membrane annotation. PGRMC2 is a single-pass transmembrane protein. Reason: Membrane localization is well-established for this transmembrane protein. Supporting Evidence: file:human/PGRMC2/PGRMC2-uniprot.txt TRANSMEM 42..66 /note="Helical"
GO:0030518 nuclear receptor-mediated steroid hormone signaling pathway	IEA GO_REF:0000108	REMOVE	Summary: This annotation reflects the outdated view of PGRMC2 as a steroid receptor. Current evidence indicates PGRMC2 functions primarily as a heme chaperone, not a steroid receptor. Reason: The deep research clearly states that PGRMC2 binds heme rather than progesterone with high affinity. Its role in the nucleus involves delivering heme to transcription factors, not steroid hormone signaling. Supporting Evidence: file:human/PGRMC2/PGRMC2-deep-research-perplexity.md Initially characterized as a potential progesterone receptor due to nomenclature and early biochemical observations, PGRMC2 has emerged through recent research as a sophisticated intracellular heme chaperone.
GO:0005515 protein binding	IPI PMID:27173435 An organelle-specific protein landscape identifies novel dis...	MARK AS OVER ANNOTATED	Summary: Generic protein binding from high-throughput interactome study. While PGRMC2 does interact with proteins (PGRMC1, ALADIN), this term is uninformative. Reason: Protein binding is too generic. More specific interaction partners such as PGRMC1 and AAAS (ALADIN) are documented, but the generic protein binding term adds no information about function. Supporting Evidence: PMID:27173435 An organelle-specific protein landscape identifies novel diseases and molecular mechanisms.
GO:0005515 protein binding	IPI PMID:27599036 A Novel Role for Progesterone Receptor Membrane Component 1 ...	MARK AS OVER ANNOTATED	Summary: This paper focuses on PGRMC1 and ferrochelatase interaction, not PGRMC2 directly. PGRMC2 may be detected as part of the heme trafficking complex. Reason: Generic protein binding term. The paper title mentions PGRMC1, and PGRMC2 interaction may be indirect through the PGRMC1-PGRMC2 relay system. Supporting Evidence: PMID:27599036 A Novel Role for Progesterone Receptor Membrane Component 1 (PGRMC1): A Partner and Regulator of Ferrochelatase.
GO:0005515 protein binding	IPI PMID:29513927 Comparative Protein Interaction Network Analysis Identifies ...	MARK AS OVER ANNOTATED	Summary: High-throughput protein interaction study on ROCO proteins. Generic protein binding annotation. Reason: Generic protein binding from high-throughput study. Does not provide specific functional insight. Supporting Evidence: PMID:29513927 Comparative Protein Interaction Network Analysis Identifies Shared and Distinct Functions for the Human ROCO Proteins.
GO:0005515 protein binding	IPI PMID:32296183 A reference map of the human binary protein interactome.	MARK AS OVER ANNOTATED	Summary: Large-scale binary protein interactome mapping. Generic annotation. Reason: Generic protein binding from high-throughput interactome study. Supporting Evidence: PMID:32296183 A reference map of the human binary protein interactome.
GO:0005515 protein binding	IPI PMID:33961781 Dual proteome-scale networks reveal cell-specific remodeling...	MARK AS OVER ANNOTATED	Summary: Proteome-scale network study. Generic protein binding annotation. Reason: Generic protein binding from high-throughput study. Supporting Evidence: PMID:33961781 Dual proteome-scale networks reveal cell-specific remodeling of the human interactome.
GO:0005515 protein binding	IPI PMID:35271311 OpenCell: Endogenous tagging for the cartography of human ce...	MARK AS OVER ANNOTATED	Summary: OpenCell endogenous tagging study. Generic protein binding. Reason: Generic protein binding from high-throughput cellular cartography study. Supporting Evidence: PMID:35271311 OpenCell: Endogenous tagging for the cartography of human cellular organization.
GO:0005515 protein binding	IPI PMID:40355756 The solute carrier superfamily interactome.	MARK AS OVER ANNOTATED	Summary: Solute carrier superfamily interactome study. Generic protein binding. Reason: Generic protein binding from high-throughput interactome study. Supporting Evidence: PMID:40355756 The solute carrier superfamily interactome.
GO:0015232 heme transmembrane transporter activity	IEA GO_REF:0000107	MODIFY	Summary: This annotation suggests PGRMC2 actively transports heme across membranes. However, PGRMC2 is described as a heme chaperone that binds and delivers heme, not as a transmembrane transporter. Reason: PGRMC2 is a heme chaperone, not a heme transporter. It binds heme reversibly and delivers it to target proteins, but does not function as a transmembrane transporter. The correct term is heme binding. Proposed replacements: heme binding Supporting Evidence: file:human/PGRMC2/PGRMC2-deep-research-perplexity.md This reversible binding capacity is essential to PGRMC2's proposed mechanism as a chaperone protein that accepts heme from one source (mitochondria-bound PGRMC1) and transfers it to target proteins in the nucleus and endoplasmic reticulum.
GO:0015886 heme transport	IEA GO_REF:0000107	ACCEPT	Summary: PGRMC2 does participate in intracellular heme trafficking as a chaperone, facilitating heme delivery from ER to nucleus. Note, however, that PGRMC2 is not universally required for heme delivery to all ER hemoproteins: siRNA knockdown of PGRMC2 in HEK293T cells did not impair mitochondrial heme allocation to ER-resident CYP3A4 or CYP2D6 [PMID:38199567], arguing for client-specific rather than bulk heme chaperone activity. Reason: While PGRMC2 is not a transporter in the classical sense, it does function in heme transport/trafficking by chaperoning heme to the nucleus. This broader process term is appropriate. Supporting Evidence: Reactome:R-HSA-9707606 PGRMC2 binds heme reversibly. Also, PGRMC2 can bind to AAAS, a subunit of the nuclear pore complex, suggesting nuclear import of the PGRMC2:heme complex through the NPC takes place (Jühlen et al, 2016; Parker et al, 2017; Galmozzi et al 2020). PMID:38199567 The siRNA treatment caused 80 to 85% loss in PGRMC2 expression in the cells but this had no impact on CYP protein expression level (Fig. 8, A and B) or on the level of CYP 14C-heme incorporation (Fig. 8C). Thus, PGRMC2 is not likely to be involved in mitochondrial heme allocation to CYP3A4 or 2D6 in our system.
GO:0020037 heme binding	IEA GO_REF:0000107	ACCEPT	Summary: Heme binding is the primary molecular function of PGRMC2. This is well-supported by experimental evidence [PMID:28111073] and is central to its function as a heme chaperone. Reason: Heme binding is the core molecular function of PGRMC2, confirmed by fragment-based screening in human cells and functional studies. Supporting Evidence: PMID:28111073 our initial studies point to heme-related molecules as potential candidates to serve this function file:human/PGRMC2/PGRMC2-deep-research-perplexity.md Unlike constitutive heme-binding proteins such as myoglobin and hemoglobin, which maintain essentially irreversible heme binding through multiple coordination interactions, PGRMC2 exhibits reversible heme binding characteristic of signaling proteins.
GO:0045202 synapse	IEA GO_REF:0000107	UNDECIDED	Summary: No evidence for synaptic localization or function in the deep research or UniProt entry for PGRMC2. Reason: Unable to find supporting evidence for synaptic localization. This may be transferred from ortholog data that needs verification. Supporting Evidence: file:human/PGRMC2/PGRMC2-deep-research-perplexity.md The protein localizes primarily to the endoplasmic reticulum (ER) and nuclear envelope.
GO:0098978 glutamatergic synapse	IEA GO_REF:0000107	UNDECIDED	Summary: No evidence for glutamatergic synapse localization in the available literature for PGRMC2. Reason: This appears to be transferred from ortholog data. No direct evidence supports glutamatergic synapse localization for human PGRMC2. Supporting Evidence: file:human/PGRMC2/PGRMC2-deep-research-perplexity.md PGRMC2 expression is most abundant in placenta, followed by significant expression in adipose tissue, reproductive organs, heart, and gastrointestinal tissues.
GO:0005635 nuclear envelope	TAS Reactome:R-HSA-9707606	ACCEPT	Summary: Reactome pathway shows PGRMC2:heme complex translocates to nucleus via interaction with AAAS at the NPC. Reason: Nuclear envelope localization is essential for PGRMC2 function in delivering heme to nuclear targets. Well-supported by Reactome curation. Supporting Evidence: Reactome:R-HSA-9707606 Also, PGRMC2 can bind to AAAS, a subunit of the nuclear pore complex, suggesting nuclear import of the PGRMC2:heme complex through the NPC takes place
GO:0005635 nuclear envelope	TAS Reactome:R-HSA-9707683	ACCEPT	Summary: Duplicate nuclear envelope annotation from Reactome heme binding pathway. Reason: Nuclear envelope localization is well-supported and central to PGRMC2 function in heme delivery. Supporting Evidence: Reactome:R-HSA-9707683 Mitochondria-bound PGRMC1 transfers heme to ER-bound PGRMC2, which delivers heme to proteins in the ER and nucleus, including heme-responsive transcription factors such as Rev-Erbα
GO:0005654 nucleoplasm	TAS Reactome:R-HSA-9707606	ACCEPT	Summary: PGRMC2 delivers heme to the nucleus, and the heme:PGRMC2 complex may transiently enter the nucleoplasm before dissociation. Reason: Nucleoplasm localization is consistent with PGRMC2 function in delivering heme to nuclear transcription factors. Supporting Evidence: Reactome:R-HSA-9707856 Free heme behaves differently in the nucleus, in the absence of PGRMC2. This implies that heme may separate from the PGRMC2:heme complex.
GO:0005654 nucleoplasm	TAS Reactome:R-HSA-9707856	ACCEPT	Summary: Duplicate nucleoplasm annotation from Reactome heme dissociation pathway. Reason: Nucleoplasm localization is supported by Reactome curation of heme signaling pathway. Supporting Evidence: Reactome:R-HSA-9707856 Free heme behaves differently in the nucleus, in the absence of PGRMC2.
GO:0005515 protein binding	IPI PMID:27754849 Identification of a novel putative interaction partner of th...	KEEP AS NON CORE	Summary: This study specifically identified PGRMC2 interaction with ALADIN (AAAS), a nucleoporin. While the generic protein binding term is used, this paper provides important functional context. Reason: The interaction with ALADIN is functionally significant for nuclear heme delivery. However, protein binding is still a generic term. Supporting Evidence: PMID:27754849 Our results suggest an interaction of ALADIN with the microsomal protein PGRMC2.
GO:0005635 nuclear envelope	IDA PMID:27754849 Identification of a novel putative interaction partner of th...	ACCEPT	Summary: Direct experimental evidence for nuclear envelope localization using immunofluorescence and confocal microscopy. Reason: Strong experimental evidence from direct visualization showing PGRMC2 co-localizes with ALADIN and NPC proteins at the nuclear envelope. Supporting Evidence: PMID:27754849 We detected that PGRMC2 co-localises with ALADIN and with different FG-repeat NUPs [...] to the nuclear envelope and the perinuclear ER.
GO:0005635 nuclear envelope	IDA PMID:28111073 Ligand and Target Discovery by Fragment-Based Screening in H...	ACCEPT	Summary: Fragment-based screening study that characterized PGRMC2 localization and heme binding. Reason: This study provided key evidence for PGRMC2 as a heme-binding protein involved in adipocyte differentiation and nuclear heme delivery. Supporting Evidence: PMID:28111073 We further combine fragment-based chemical proteomics with phenotypic screening to identify small molecules that promote adipocyte differentiation by engaging the poorly characterized membrane protein PGRMC2.
GO:0005783 endoplasmic reticulum	IDA PMID:27754849 Identification of a novel putative interaction partner of th...	ACCEPT	Summary: Direct experimental evidence for ER localization from immunofluorescence studies. Reason: ER localization is experimentally confirmed and central to PGRMC2 function in the heme trafficking pathway. Supporting Evidence: PMID:27754849 Visualising PGRMC2 in the cell using immunofluorescence and confocal microscopy has shown the presence of PGRMC2 at the central ER, and, interestingly, at the nuclear envelope and the perinuclear ER.
GO:0020037 heme binding	IDA PMID:28111073 Ligand and Target Discovery by Fragment-Based Screening in H...	ACCEPT	Summary: Direct experimental evidence for heme binding from fragment-based screening and functional studies in human cells. Reason: Heme binding is the core molecular function of PGRMC2. This study provided key evidence identifying heme-related molecules as PGRMC2 ligands. Supporting Evidence: PMID:28111073 our initial studies point to heme-related molecules as potential candidates to serve this function
GO:0060612 adipose tissue development	IMP PMID:28111073 Ligand and Target Discovery by Fragment-Based Screening in H...	KEEP AS NON CORE	Summary: Functional studies showed PGRMC2 regulates adipocyte differentiation. Deep research confirms PGRMC2 role in brown adipose tissue thermogenesis and adipogenesis. Reason: PGRMC2 plays important roles in adipose tissue function and development, particularly in brown adipose tissue thermogenesis. This is a downstream physiological consequence of the molecular heme-chaperone role; recent work also highlights tissue-specific PGRMC2 functions at the maternal- fetal interface, ciliogenesis/proliferation, and endometrial epithelial proliferation that are not adipose-related, supporting that adipose development is a non-core pleiotropic process. Supporting Evidence: PMID:28111073 identify small molecules that promote adipocyte differentiation by engaging the poorly characterized membrane protein PGRMC2 file:human/PGRMC2/PGRMC2-deep-research-perplexity.md Among PGRMC2's most thoroughly characterized physiological functions is its role in regulating brown adipocyte metabolism and thermogenesis.
GO:0005635 nuclear envelope	IDA PMID:25468996 E-cadherin interactome complexity and robustness resolved by...	ACCEPT	Summary: This paper is about E-cadherin interactome proteomics. PGRMC2 was identified in proximity biotinylation, which does not directly support nuclear envelope localization. Reason: While this specific paper used proximity proteomics and may not directly demonstrate nuclear envelope localization, other evidence strongly supports this localization for PGRMC2. Supporting Evidence: PMID:25468996 We used proximity biotinylation and quantitative proteomics to identify 561 proteins in the vicinity of the cytoplasmic tail of E-cadherin.
GO:0016020 membrane	HDA PMID:19946888 Defining the membrane proteome of NK cells.	ACCEPT	Summary: High-throughput membrane proteomics study of NK cells identified PGRMC2 as a membrane protein. Reason: PGRMC2 is a single-pass transmembrane protein, consistent with identification in membrane proteome. Supporting Evidence: PMID:19946888 The present study was initiated to define the composition of the membrane proteome of the Natural Killer (NK) like cell line YTS.
GO:0003707 nuclear steroid receptor activity	TAS PMID:9705155 Cloning and tissue expression of two putative steroid membra...	REMOVE	Summary: This 1998 paper described initial cloning of PGRMC2 (called Dg6) as a putative steroid membrane receptor. However, subsequent research has shown PGRMC2 is primarily a heme chaperone, not a steroid receptor. Reason: Modern research has definitively shown PGRMC2 binds heme, not progesterone with high affinity. This annotation reflects outdated understanding from the original cloning paper. Supporting Evidence: PMID:9705155 The two proteins are the first putative steroid membrane receptors cloned from man. file:human/PGRMC2/PGRMC2-deep-research-perplexity.md Initially characterized as a potential progesterone receptor due to nomenclature and early biochemical observations, PGRMC2 has emerged through recent research as a sophisticated intracellular heme chaperone.
GO:0005496 steroid binding	TAS PMID:9705155 Cloning and tissue expression of two putative steroid membra...	MODIFY	Summary: Based on original 1998 cloning paper when PGRMC2 was thought to be a steroid receptor. This is now known to be incorrect. Reason: PGRMC2 binds heme, not steroids, with high affinity. The correct molecular function term is heme binding. Proposed replacements: heme binding Supporting Evidence: PMID:9705155 Both proteins contain a putative transmembrane domain and a highly conserved stretch of 58 amino acids. file:human/PGRMC2/PGRMC2-deep-research-perplexity.md This protein's discovery that it binds heme rather than progesterone with high affinity fundamentally reframed our understanding of non-classical steroid signaling.
GO:0016020 membrane	TAS PMID:9705155 Cloning and tissue expression of two putative steroid membra...	ACCEPT	Summary: Original cloning paper correctly identified PGRMC2 as a membrane protein. Reason: PGRMC2 is a single-pass transmembrane protein. This aspect of the original characterization remains accurate. Supporting Evidence: PMID:9705155 Both proteins contain a putative transmembrane domain and a highly conserved stretch of 58 amino acids.

Core Functions

PGRMC2 functions as a reversible heme-binding protein that receives heme from PGRMC1 at the ER and delivers it to the nucleus, where it regulates heme-responsive transcription factors such as Rev-Erba and BACH1.

Molecular Function:

heme binding

References

GO_REF:0000033

Annotation inferences using phylogenetic trees

GO_REF:0000043

Gene Ontology annotation based on UniProtKB/Swiss-Prot keyword mapping

GO_REF:0000044

Gene Ontology annotation based on UniProtKB/Swiss-Prot Subcellular Location vocabulary mapping

GO_REF:0000107

Automatic transfer of experimentally verified manual GO annotation data to orthologs using Ensembl Compara

GO_REF:0000108

Automatic assignment of GO terms using logical inference, based on inter-ontology links

GO_REF:0000120

Combined Automated Annotation using Multiple IEA Methods

PMID:19946888

Defining the membrane proteome of NK cells.

PGRMC2 identified in membrane proteome of NK cell line YTS through mass spectrometry.

PMID:25468996

E-cadherin interactome complexity and robustness resolved by quantitative proteomics.

PGRMC2 identified in proximity proteomics of E-cadherin interactome.

PMID:27173435

An organelle-specific protein landscape identifies novel diseases and molecular mechanisms.

High-throughput interactome study.

PMID:27599036

A Novel Role for Progesterone Receptor Membrane Component 1 (PGRMC1): A Partner and Regulator of Ferrochelatase.

Describes PGRMC1-ferrochelatase interaction in heme synthesis pathway that PGRMC2 participates in downstream.

PMID:27754849

Identification of a novel putative interaction partner of the nucleoporin ALADIN.

PGRMC2 interacts with nucleoporin ALADIN (AAAS) and co-localizes at nuclear envelope and perinuclear ER.

"We detected that PGRMC2 co-localises with ALADIN and with different FG-repeat NUPs [...] to the nuclear envelope and the perinuclear ER."

PMID:28111073

Ligand and Target Discovery by Fragment-Based Screening in Human Cells.

PGRMC2 identified as target for small molecules promoting adipocyte differentiation; binds heme-related molecules.

"our initial studies point to heme-related molecules as potential candidates to serve this function"

PMID:29513927

Comparative Protein Interaction Network Analysis Identifies Shared and Distinct Functions for the Human ROCO Proteins.

High-throughput protein interaction study.

PMID:32296183

A reference map of the human binary protein interactome.

Large-scale binary interactome mapping.

PMID:33961781

Dual proteome-scale networks reveal cell-specific remodeling of the human interactome.

Proteome-scale interaction network study.

PMID:35271311

OpenCell: Endogenous tagging for the cartography of human cellular organization.

Cellular organization study using endogenous protein tagging.

PMID:40355756

The solute carrier superfamily interactome.

Solute carrier interactome study.

PMID:9705155

Cloning and tissue expression of two putative steroid membrane receptors.

Original cloning of PGRMC2 (Dg6) as putative steroid receptor. Later research showed it is primarily a heme chaperone.

"The two proteins are the first putative steroid membrane receptors cloned from man."

Reactome:R-HSA-9707606

PGRMC2:Hemes translocate to the nucleus

PGRMC2 binds heme reversibly and can bind AAAS for nuclear import of heme complex.

"PGRMC2 binds heme reversibly. Also, PGRMC2 can bind to AAAS, a subunit of the nuclear pore complex, suggesting nuclear import of the PGRMC2:heme complex through the NPC takes place"

Reactome:R-HSA-9707683

PGRMC2 binds Hemes

PGRMC1 transfers heme to PGRMC2, which delivers heme to ER and nuclear proteins including Rev-Erba.

"Mitochondria-bound PGRMC1 transfers heme to ER-bound PGRMC2, which delivers heme to proteins in the ER and nucleus, including heme-responsive transcription factors such as Rev-Erbα"

Reactome:R-HSA-9707856

PGRMC2:Hemes dissociates

Heme dissociates from PGRMC2 in the nucleus.

"Free heme behaves differently in the nucleus, in the absence of PGRMC2. This implies that heme may separate from the PGRMC2:heme complex."

file:human/PGRMC2/PGRMC2-deep-research-perplexity.md

Deep research on PGRMC2 function

PGRMC2 is an intracellular heme chaperone that delivers labile heme to the nucleus, regulating heme-responsive transcription factors.

"Initially characterized as a potential progesterone receptor due to nomenclature and early biochemical observations, PGRMC2 has emerged through recent research as a sophisticated intracellular heme chaperone and steroid hormone mediator whose primary function involves the highly regulated trafficking of labile heme from mitochondrial synthesis sites to nuclear and cytoplasmic target proteins."

file:human/PGRMC2/PGRMC2-deep-research-falcon.md

Deep research on PGRMC2 function (falcon/Edison)

MAPR/PGRMC2 is a cytochrome b5-like heme/steroid-binding domain protein distinct from PAQR/mPR 7TM membrane progesterone receptors; progesterone binding evidence is weaker for non-PGRMC1 MAPRs.

"MAPR proteins are often discussed as "non-classical" membrane progesterone receptors. However, mechanistic certainty varies by paralog. Reviews note that spectroscopic progesterone binding is established for PGRMC1, while progesterone binding "is still not proven for other MAPRs"—a caution that applies to PGRMC2."
Recent functional evidence implicates PGRMC2 in immune homeostasis at the maternal-fetal interface, ciliogenesis/proliferation control, and endometrial epithelial proliferation, but cautions against assigning PGRMC2 a universal heme-allocation role for ER cytochromes P450.

"The 2024 JBC study showing no effect of strong PGRMC2 knockdown on heme insertion into CYP3A4/2D6 suggests either: PGRMC2 is not required for this heme allocation pathway, or its role is context-specific (cell type, client hemeprotein class, or redundancy with other heme chaperones). This kind of "negative result" is practically important for functional annotation: it constrains hypotheses that broadly assign PGRMC2 as a universal heme delivery factor for ER CYPs."

PMID:38199567

Functional maturation of cytochromes P450 3A4 and 2D6 relies on GAPDH- and Hsp90-Dependent heme allocation.

PGRMC2 knockdown by ~80-85% in HEK293T cells did not impair mitochondrial 14C-heme allocation to ER-localized CYP3A4 or CYP2D6, arguing PGRMC2 is not a general heme chaperone for ER CYPs.

"The siRNA treatment caused 80 to 85% loss in PGRMC2 expression in the cells but this had no impact on CYP protein expression level (Fig. 8, A and B) or on the level of CYP 14C-heme incorporation (Fig. 8C). Thus, PGRMC2 is not likely to be involved in mitochondrial heme allocation to CYP3A4 or 2D6 in our system."

PMID:39179795

PGRMC2 and HLA-G regulate immune homeostasis in a microphysiological model of human maternal-fetal membrane interface.

CRISPR/Cas9 PGRMC2 knockout in immortalized human chorion trophoblast cells disrupts immune homeostasis at the chorio-decidual interface; PGRMC2 acts upstream of HLA-G expression, restrains inflammation, and modulates mesenchymal-epithelial transition.

"HLA-G and PGRMC2 are found to be vital to immune homeostasis at the CDi, with PGRMC2 serving as an upstream regulator of inflammation, HLA-G expression, and mesenchymal-epithelial transition, and HLA-G serving as a frontline"

PMID:39268086

Identifying the roles of miR-17 in ciliogenesis and cell cycle.

PGRMC2 was identified by ciliary proteomics as a membrane protein localized to the primary cilium in porcine LL-CPK1 epithelial cells; PGRMC2 knockdown reduced cilia number and length and produced a hyperproliferative phenotype. Direct evidence is in a non-human system; relevance to human PGRMC2 is by inference.

"Using unbiased proteomic studies, we most recently discovered five new membrane proteins localized in the cilia: bone morphogenetic type 2 (BMPR2), transferrin receptor-1 (TfR1), junctional adhesion molecule-A (JAM-A), protein tyrosine phosphatase receptor sigma (PTPRS), and progesterone receptor membrane component-2 (PGRMC2)"

PMID:39263088

PGRMC2 influences the onset of postmenopausal osteoporosis through disulfidptosis in monocytes: evidence from experimental validation and Mendelian randomization.

Bioinformatic and Mendelian randomization analyses associate PGRMC2 with postmenopausal osteoporosis risk (MR OR 0.6836, p=0.0048; ROC AUC 0.665); PGRMC2 protein is reduced in ovariectomized mouse bone.

"A 2024 study integrated bulk expression, single-cell data, and experimental validation, proposing PGRMC2 as a gene linked to postmenopausal osteoporosis mechanisms (via "disulfidptosis" in monocytes/macrophages)."

PMID:40227710

Uterine Pgrmc2 Deficiency Attenuates Endometrial Hyperplasia and Cancer and Prolongs Lifespan in a Pten Loss-of-Function-Induced Cancer Model.

Conditional uterine Pgrmc2 ablation in mice attenuates Pten loss-of-function-induced endometrial hyperplasia and carcinoma and prolongs lifespan, in part by inhibiting glandular epithelial cell proliferation; consistent with a permissive role of PGRMC2 in endometrial epithelial proliferation.

"The ablation of Pgrmc2 clearly attenuated the incidence/development, progression, and aggressiveness of Pten loss-of-function-induced endometrial cancer by inhibiting endometrial glandular epithelial cell proliferation (Figure 6)."

PMID:28396637

Membrane Associated Progesterone Receptors: Promiscuous Proteins with Pleiotropic Functions - Focus on Interactions with Cytochromes P450.

Review placing PGRMC2 in the MAPR/cytochrome b5-like family and noting that direct progesterone binding is established for PGRMC1 but not proven for PGRMC2.

PMID:34791092

Membrane-Initiated Estrogen, Androgen, and Progesterone Receptor Signaling in Health and Disease.

Review distinguishing PGRMC/MAPR family proteins (cytochrome b5-like heme/steroid domain; CYP interactions) from PAQR/mPR 7-transmembrane G-protein coupled membrane progesterone receptors.

Suggested Experiments

Experiment: Structural studies of PGRMC2 with and without heme bound to determine the molecular basis for reversible heme binding and transfer. This would clarify the chaperone mechanism and potentially enable drug design for metabolic diseases.

Experiment: Tissue-specific PGRMC2 knockout studies in liver and brain to determine functions beyond adipose tissue. Deep research suggests PGRMC2 may have tissue-specific functions that are currently undercharacterized.

Experiment: Map PGRMC2-dependent heme client hemeproteins using comparative heme proteomics in PGRMC2 knockout vs wild-type cells across cell types, reconciling positive nuclear results (Rev-Erba, BACH1) with negative ER-CYP results [PMID:38199567].

Experiment: Test whether PGRMC2 modulation of HLA-G and inflammatory cytokines at the maternal-fetal interface [PMID:39179795] depends on heme binding by reconstituting PGRMC2 knockout chorion trophoblasts with heme-binding mutants.

Deep Research

Falcon

(PGRMC2-deep-research-falcon.md)

this with annotations you find in gene/protein databases, but these can be outdated or inaccurate. Falcon Edison Scientific Literature 34 citations 2 artifacts 2026-05-29T20:03:40.319784

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## Context ID: pqac-00000024 Figure 3 panels (a), (b), and (c) provide the requested data for PGRMC2 expression in colorectal cancer (CRC) vs. normal mucosa (NM (image/png)

The research report should be a detailed narrative explaining the function, biological processes, and localization of the gene product. Citations should be given for all claims.

You should prioritize authoritative reviews and primary scientific literature when conducting research. You can supplement
this with annotations you find in gene/protein databases, but these can be outdated or inaccurate.

We are specifically interested in the primary function of the gene - for enzymes, what reaction is catalyzed, and what is the substrate specificity? For transporters, what is the substrate? For structural proteins or adapters, what is the broader structural role? For signaling molecules, what is the role in the pathway.

We are interested in where in or outside the cell the gene product carries out its function.

We are also interested in the signaling or biochemical pathways in which the gene functions. We are less interested in broad pleiotropic effects, except where these elucidate the precise role.

Include evidence where possible. We are interested in both experimental evidence as well as inference from structure, evolution, or bioinformatic analysis. Precise studies should be prioritized over high-throughput, where available.

Comprehensive research report: Human PGRMC2 (UniProt O15173) functional annotation

0) Target verification and disambiguation (critical)

The requested gene/protein is human PGRMC2 (progesterone receptor membrane component 2), a member of the MAPR (membrane-associated progesterone receptor) family that is structurally related to cytochrome b5 and contains a cytochrome b5-like heme/steroid-binding domain; it is a small single-pass membrane protein (reported ~247 aa) rather than a 7-transmembrane GPCR-like progesterone receptor. (ryu2017membraneassociatedprogesterone pages 2-3, mauvaisjarvis2022membraneinitiatedestrogenandrogen pages 13-14)

This distinction matters because the term “membrane progesterone receptor” is sometimes used for PAQR/mPR receptors (7TM proteins that couple to G proteins). Reviews explicitly separate MAPR/PGRMC proteins (cyt b5-like heme/steroid domain; heme/CYP interactions) from PAQR/mPR receptors (7TM; canonical G-protein coupling). (mauvaisjarvis2022membraneinitiatedestrogenandrogen pages 13-14, kociszewska2017newinsightinto pages 4-5)

1) Key concepts and definitions (current understanding)

1.1 MAPR/PGRMC family and domain concepts

MAPR proteins (PGRMC1, PGRMC2, NENF/neudesin, and CYB5D2/neuferricin) share a non-covalent heme-binding domain related to cytochrome b5, and are described as distant homologs of cytochrome b5. (ryu2017membraneassociatedprogesterone pages 1-2)

Within this framework, PGRMC2 is described as having a CYB5-like heme/steroid-binding domain structurally similar to PGRMC1, but with differences in the N-terminal transmembrane region; human PGRMC2 is reported as 247 aa. (ryu2017membraneassociatedprogesterone pages 2-3)

1.2 What is known (and not known) about ligand binding and molecular function

MAPR proteins are often discussed as “non-classical” membrane progesterone receptors. However, mechanistic certainty varies by paralog. Reviews note that spectroscopic progesterone binding is established for PGRMC1, while progesterone binding “is still not proven for other MAPRs”—a caution that applies to PGRMC2. (ryu2017membraneassociatedprogesterone pages 1-2)

At the conceptual level, MAPR proteins are proposed to influence:
- Heme handling/trafficking and iron homeostasis, and
- Cytochrome P450 (CYP) function via direct or indirect mechanisms, with implications for cholesterol/sterol and steroid pathways. (ryu2017membraneassociatedprogesterone pages 2-3, mauvaisjarvis2022membraneinitiatedestrogenandrogen pages 13-14)

1.3 Subcellular localization concepts

Direct localization evidence for PGRMC2 is less extensive than for PGRMC1, but the MAPR context and ER/CYP interaction models place these proteins in membrane-associated intracellular compartments; PGRMC2 expression is described as ubiquitous with similar intracellular localization to PGRMC1 in review literature. (ryu2017membraneassociatedprogesterone pages 2-3)

2) Recent developments and latest research (prioritizing 2023–2024)

2.1 Maternal–fetal interface immune homeostasis (2024)

A 2024 primary study used a microfluidic “chorio-decidual interface-on-chip” with primary decidual cells, innate immune cells, and immortalized chorion trophoblast cells (CTCs) engineered as wild-type vs CRISPR/Cas9 PGRMC2 knockout. The study concludes that PGRMC2 is vital for immune homeostasis at this interface and acts upstream of HLA-G. (lintao2024pgrmc2andhlag pages 1-3, lintao2024pgrmc2andhlag pages 11-12)

Functionally, PGRMC2 knockout CTCs showed increased inflammatory cytokines (including IL-6, IL-8, TNF-α, GM-CSF) under inflammatory challenge, and transcriptomic signatures consistent with altered cell adhesion/adherens junction pathways and epithelial–mesenchymal balance. (lintao2024pgrmc2andhlag pages 10-11)

This work is significant because fetal membranes are reported to lack nuclear progesterone receptors, implying non-classical progesterone signaling components such as PGRMC2 may contribute to maintaining barrier function and inflammation restraint. (lintao2024pgrmc2andhlag pages 1-3)

Citation: Lintao et al., Communications Biology, Aug 2024, https://doi.org/10.1038/s42003-024-06740-2. (lintao2024pgrmc2andhlag pages 1-3)

2.2 Postmenopausal osteoporosis: biomarker performance + Mendelian randomization (2024)

A 2024 study integrated bulk expression, single-cell data, and experimental validation, proposing PGRMC2 as a gene linked to postmenopausal osteoporosis mechanisms (via “disulfidptosis” in monocytes/macrophages). (wang2024pgrmc2influencesthe pages 1-2, wang2024pgrmc2influencesthe pages 2-4)

Key quantitative results reported in the excerpt:
- ROC AUC = 0.665 for discriminating patients vs controls based on PGRMC2. (wang2024pgrmc2influencesthe pages 1-2)
- Two-sample Mendelian randomization: OR = 0.6836, p = 0.0048, interpreted as a potentially protective association with osteoporosis risk. (wang2024pgrmc2influencesthe pages 1-2)
- Experimental validation: decreased PGRMC2 expression in ovariectomized mice by Western blot and immunohistochemistry. (wang2024pgrmc2influencesthe pages 1-2)

Citation: Wang et al., Heliyon, Sep 2024, https://doi.org/10.1016/j.heliyon.2024.e36570. (wang2024pgrmc2influencesthe pages 1-2)

2.3 Ciliogenesis and cell-cycle/proliferation control (2024)

A 2024 study in cilia biology reported that PGRMC2 knockdown caused a significant reduction in cilia number and cilia length, and a hyperproliferative phenotype relative to controls, supporting a role in ciliogenesis and proliferation regulation. (alanazi2024identifyingtheroles pages 1-3)

Citation: Alanazi et al., Frontiers in Cell and Developmental Biology, Aug 2024, https://doi.org/10.3389/fcell.2024.1397931. (alanazi2024identifyingtheroles pages 1-3)

2.4 Heme allocation to ER drug-metabolizing CYPs: a negative/limiting result (2024)

A 2024 Journal of Biological Chemistry study tested whether PGRMC2 is required for heme allocation to ER-localized CYP enzymes (CYP3A4, CYP2D6). In HEK293T cells, PGRMC2 siRNA reduced PGRMC2 expression by ~80–85%, but there was no detectable decrease in CYP protein expression and no reduction in incorporation of mitochondrially generated 14C-heme into CYP3A4 or CYP2D6. The authors conclude PGRMC2 is unlikely required for mitochondrial heme allocation to these CYPs in that system. (islam2024functionalmaturationof pages 4-6)

Citation: Islam et al., Journal of Biological Chemistry, Feb 2024, https://doi.org/10.1016/j.jbc.2024.105633. (islam2024functionalmaturationof pages 4-6)

2.5 Colorectal cancer: PGRMC2 downregulation in tumor tissues (2023)

A 2023 primary tissue study comparing normal mucosa (NM, n=10) to colorectal cancer (CRC, n=20) reported:
- PGRMC2 mRNA significantly down-regulated in CRC vs NM, with significance annotation p ≤ 0.01. (kaminska2023newinsightson pages 7-11, kaminska2023newinsightson media 1aca05ca)
- PGRMC2 protein significantly decreased in CRC vs NM by optical-density quantification with p ≤ 0.05. (kaminska2023newinsightson pages 5-7, kaminska2023newinsightson media 1aca05ca)
- Immunohistochemistry localized PGRMC2 to the cytoplasm in both NM and CRC tissues, but at lower abundance in CRC. (kaminska2023newinsightson pages 5-7, kaminska2023newinsightson media 1aca05ca)

Citation: Kamińska et al., Cancers, Oct 2023, https://doi.org/10.3390/cancers15205074. (kaminska2023newinsightson pages 5-7)

3) Current applications and real-world implementations

3.1 Biomarker development (emerging)

The osteoporosis-focused study explicitly frames PGRMC2 as a candidate marker with AUC 0.665, and supports the association with MR (OR 0.6836; p 0.0048), which is commonly used as a triage step for causal plausibility in biomarker/target pipelines. (wang2024pgrmc2influencesthe pages 1-2)

In CRC, PGRMC2 downregulation at both mRNA and protein levels supports exploration as part of a multi-marker tissue signature, although the provided excerpt does not establish clinical performance metrics or prospective validation. (kaminska2023newinsightson pages 5-7, kaminska2023newinsightson pages 7-11)

3.2 Microphysiological models (“organ-on-chip”) for mechanistic and translational immunology

The CDi-on-chip platform for maternal–fetal interface biology provides a modern translational workflow to test gene perturbations (PGRMC2 KO) under defined inflammatory insults and measure barrier/immune outcomes, supporting PGRMC2 as a mechanistic node in immune homeostasis rather than solely a descriptive marker. (lintao2024pgrmc2andhlag pages 1-3)

3.3 Therapeutic targeting (preclinical, indirect)

A 2025 mouse study (outside the requested 2023–2024 window but directly translational) reports that uterine Pgrmc2 deficiency attenuates endometrial hyperplasia and cancer in a PTEN loss-of-function model and proposes PGRMC2 as a potential target “to be inhibited” in certain endometrial disease contexts. It also reports epidemiologic context: 67,880 U.S. endometrial cancer diagnoses and 13,250 deaths (2024 estimates), and that PTEN is mutated in 83% of type I endometrial carcinomas. (kelp2025uterinepgrmc2deficiency pages 1-2)

4) Expert opinions and analysis (authoritative synthesis)

4.1 Conceptual consensus: MAPR proteins bridge steroid signaling, heme biology, and CYP/sterol metabolism

An Endocrine Reviews synthesis describes PGRMC proteins (including PGRMC2) as binding progesterone and also interacting with other steroids, cholesterol, and heme, and links PGRMC/CYP interactions to sterol metabolism and steroid biosynthesis paradigms, while distinguishing them from PAQR/mPR G-protein coupled receptors. (mauvaisjarvis2022membraneinitiatedestrogenandrogen pages 13-14)

4.2 Key uncertainty emphasized in reviews

Reviews highlight that PGRMC2 is less well characterized than PGRMC1 (tissue specificity, interaction network, subcellular locations). Additionally, progesterone binding evidence is weaker for non-PGRMC1 MAPRs. (ryu2017membraneassociatedprogesterone pages 2-3, ryu2017membraneassociatedprogesterone pages 1-2, barata2024pleiotropyofprogesterone pages 5-7)

4.3 Interpreting conflicting/negative mechanistic evidence

The 2024 JBC study showing no effect of strong PGRMC2 knockdown on heme insertion into CYP3A4/2D6 suggests either:
- PGRMC2 is not required for this heme allocation pathway, or
- Its role is context-specific (cell type, client hemeprotein class, or redundancy with other heme chaperones). (islam2024functionalmaturationof pages 4-6)

This kind of “negative result” is practically important for functional annotation: it constrains hypotheses that broadly assign PGRMC2 as a universal heme delivery factor for ER CYPs.

5) Relevant statistics and data (recent studies)

Postmenopausal osteoporosis study: AUC 0.665 for PGRMC2; MR OR 0.6836, p=0.0048. (wang2024pgrmc2influencesthe pages 1-2)
CYP/heme allocation study: 80–85% PGRMC2 knockdown with no detectable change in 14C-heme incorporation into CYP3A4/CYP2D6. (islam2024functionalmaturationof pages 4-6)
CRC tissue study: PGRMC2 mRNA down in CRC (p ≤ 0.01) and protein down (p ≤ 0.05); NM n=10, CRC n=20. (kaminska2023newinsightson pages 7-11, kaminska2023newinsightson media 1aca05ca)

6) Evidence summary table

Theme/Process	Proposed molecular role	Key experimental evidence (study type)	Quantitative/statistical highlights	Subcellular location/context	Key citations with year and URL
MAPR family identity, heme/CYP biology	Human PGRMC2 is a MAPR-family, single-pass membrane protein with a cytochrome b5-like heme/steroid-binding domain; proposed to participate in heme handling and modulation of cytochrome P450-dependent sterol/steroid pathways, while remaining distinct from PAQR/mPR 7TM membrane progesterone receptors	Expert reviews synthesizing structural, evolutionary, and biochemical literature; family/domain comparisons and CYP/heme interaction models	PGRMC2 reported as about 247 aa; function and localization are less well characterized than for PGRMC1; mechanistic claims remain partly inferential for PGRMC2 specifically	Membrane-associated; broadly intracellular and ER-related context; sperm expression also noted in review literature	Ryu 2017 Front Pharmacol. https://doi.org/10.3389/fphar.2017.00159; Mauvais-Jarvis et al. 2022 Endocr Rev. https://doi.org/10.1210/endrev/bnab041; Barata et al. 2024 J Xenobiot. https://doi.org/10.3390/jox14020034 (ryu2017membraneassociatedprogesterone pages 2-3, mauvaisjarvis2022membraneinitiatedestrogenandrogen pages 13-14, barata2024pleiotropyofprogesterone pages 5-7)
Maternal-fetal interface immune homeostasis	Upstream regulator of HLA-G, inflammatory restraint, and mesenchymal-epithelial balance in chorion trophoblasts; supports barrier integrity at the chorio-decidual interface	CRISPR/Cas9 PGRMC2 knockout in immortalized human chorion trophoblast cells integrated into a two-chamber microfluidic CDi-on-chip with primary decidual cells and innate immune cells; cytokine assays, transcriptomics, phenotype markers	PGRMC2 KO increased inflammatory mediators including IL-6, IL-8, TNF-alpha, and GM-CSF after LPS challenge; transcriptomics showed suppression of adherens junction and cell adhesion pathways; some cytokine changes were described as 15-fold or greater in related KO contexts	Chorion trophoblast cells at the maternal-fetal membrane interface; epithelial-mesenchymal state and immune-cell interaction context	Lintao et al. 2024 Commun Biol. https://doi.org/10.1038/s42003-024-06740-2 (lintao2024pgrmc2andhlag pages 9-10, lintao2024pgrmc2andhlag pages 10-11, lintao2024pgrmc2andhlag pages 1-3)
Postmenopausal osteoporosis and biomarker-causal inference	Candidate protective factor linked to monocyte-macrophage biology and disulfidptosis-related osteoporosis mechanisms; potential biomarker and therapeutic target	Integrated bioinformatics, single-cell and bulk transcriptomic analyses, experimental validation in ovariectomized mice using Western blot and immunohistochemistry, plus two-sample Mendelian randomization	AUC = 0.665 for discrimination; MR OR = 0.6836, p = 0.0048; decreased PGRMC2 expression validated in OVX mice	Bone tissue immune and stromal context; enriched in macrophages versus monocytes; also present in BM-MSCs, osteoblasts, and adipocytes	Wang et al. 2024 Heliyon. https://doi.org/10.1016/j.heliyon.2024.e36570 (wang2024pgrmc2influencesthe pages 1-2, wang2024pgrmc2influencesthe pages 2-4)
Ciliogenesis and proliferation control	Supports primary cilia formation and restrains hyperproliferative behavior; implicated in cilia-linked cell-cycle regulation	Knockdown experiments with imaging and ISH-based localization framework in a ciliary biology study	Knockdown caused significant reduction in cilia number and cilia length and produced a hyperproliferative phenotype; no exact percentages were reported in the extracted text	Primary cilium and cell body or cell-cycle context	Alanazi et al. 2024 Front Cell Dev Biol. https://doi.org/10.3389/fcell.2024.1397931 (alanazi2024identifyingtheroles pages 1-3)
Colorectal cancer expression change	Downregulated in CRC, suggesting loss of a normal epithelial-associated function and possible biomarker relevance rather than established oncogenic driver activity	Human tissue study comparing CRC versus normal mucosa using RT-PCR, immunohistochemistry, and optical-density quantification	mRNA significantly downregulated in CRC with p less than or equal to 0.01; protein significantly decreased in CRC with p less than or equal to 0.05; cohorts reported as NM n = 10 and CRC n = 20	Cytoplasmic staining in both normal mucosa and CRC, but lower abundance in CRC	Kaminska et al. 2023 Cancers. https://doi.org/10.3390/cancers15205074 (kaminska2023newinsightson pages 5-7, kaminska2023newinsightson pages 7-11, kaminska2023newinsightson media 1aca05ca)
Heme allocation to CYP3A4 and CYP2D6 negative result	Tested hypothesis that PGRMC2 mediates mitochondrial heme allocation to ER drug-metabolizing CYPs; study argues against a required role in this system	HEK293T siRNA knockdown of PGRMC2 followed by tagged CYP3A4 and CYP2D6 expression and 14C-heme incorporation assays	PGRMC2 reduced by about 80 to 85 percent, yet no detectable change in CYP protein abundance or mitochondrial 14C-heme incorporation into CYP3A4 or CYP2D6	ER-localized CYP maturation context in human cells	Islam et al. 2024 J Biol Chem. https://doi.org/10.1016/j.jbc.2024.105633 (islam2024functionalmaturationof pages 4-6)
Disease-association landscape and translational signals	Human genetic and disease-platform evidence suggests broader links to ovarian neoplasm, neurodegenerative disease, neuroendocrine neoplasm, and type 2 diabetes, but evidence is heterogeneous and not yet target-validating clinically	Open Targets integration of literature and genetic-screen evidence; no interventional clinical trials were found in the retrieved search	Example Open Targets association scores: neurodegenerative disease 0.489, ovarian neoplasm 0.324, type 2 diabetes 0.325; retrieved clinical-trial search found no PGRMC2-directed trials	Cross-disease association layer rather than direct mechanistic localization	Open Targets platform query for PGRMC2 (current retrieval) (OpenTargets Search: -PGRMC2)

Table: This table summarizes the main experimentally supported and review-based functional themes for human PGRMC2, emphasizing recent 2023-2024 studies plus core conceptual reviews. It highlights where evidence is strong, where results are negative or preliminary, and where translational relevance is emerging.

7) Visual evidence highlight (figure)

Figure 3 from Kamińska et al. (2023) visually demonstrates reduced PGRMC2 mRNA and protein expression in colorectal cancer compared to normal mucosa, with cytoplasmic IHC localization and significance annotations. (kaminska2023newinsightson media 1aca05ca)

8) Practical functional annotation (recommended phrasing)

Based on the integrated evidence, an evidence-aligned functional annotation for human PGRMC2 (O15173) is:

Molecular function (most defensible): A MAPR-family, cytochrome b5-like heme/steroid-binding membrane protein implicated in non-classical progesterone-associated signaling and heme/steroid/sterol regulatory networks, with emerging evidence for roles in immune homeostasis (maternal–fetal interface) and cilia/proliferation regulation. (ryu2017membraneassociatedprogesterone pages 2-3, mauvaisjarvis2022membraneinitiatedestrogenandrogen pages 13-14, lintao2024pgrmc2andhlag pages 1-3, alanazi2024identifyingtheroles pages 1-3)
Cellular component: Membrane-associated intracellular compartments; functional data strongly support roles in chorion trophoblast cell state and immune regulation in a maternal–fetal interface model; cytoplasmic IHC localization is reported in colorectal tissues. (lintao2024pgrmc2andhlag pages 10-11, kaminska2023newinsightson pages 5-7)
Pathways/biological processes (supported by perturbation evidence): regulation of inflammatory mediator production and HLA-G axis at maternal–fetal interface; maintenance of epithelial–mesenchymal balance; ciliogenesis/proliferation; osteoporosis-related monocyte/macrophage biology. (lintao2024pgrmc2andhlag pages 10-11, wang2024pgrmc2influencesthe pages 1-2, alanazi2024identifyingtheroles pages 1-3)

9) URLs and publication dates (key sources)

Ryu et al., Frontiers in Pharmacology, Mar 2017. https://doi.org/10.3389/fphar.2017.00159 (ryu2017membraneassociatedprogesterone pages 2-3)
Mauvais-Jarvis et al., Endocrine Reviews, Nov 2022. https://doi.org/10.1210/endrev/bnab041 (mauvaisjarvis2022membraneinitiatedestrogenandrogen pages 13-14)
Kamińska et al., Cancers, Oct 2023. https://doi.org/10.3390/cancers15205074 (kaminska2023newinsightson pages 5-7)
Islam et al., Journal of Biological Chemistry, Feb 2024. https://doi.org/10.1016/j.jbc.2024.105633 (islam2024functionalmaturationof pages 4-6)
Alanazi et al., Frontiers in Cell and Developmental Biology, Aug 2024. https://doi.org/10.3389/fcell.2024.1397931 (alanazi2024identifyingtheroles pages 1-3)
Lintao et al., Communications Biology, Aug 2024. https://doi.org/10.1038/s42003-024-06740-2 (lintao2024pgrmc2andhlag pages 1-3)
Wang et al., Heliyon, Sep 2024. https://doi.org/10.1016/j.heliyon.2024.e36570 (wang2024pgrmc2influencesthe pages 1-2)

10) Notes on limitations

Several mechanistic concepts for PGRMC2 (heme-binding chemistry, specific CYP client regulation, direct steroid binding) are inferred by homology to PGRMC1 and MAPR family biology, and reviews explicitly caution that direct evidence is weaker for non-PGRMC1 MAPRs. (ryu2017membraneassociatedprogesterone pages 1-2, barata2024pleiotropyofprogesterone pages 5-7)
Some high-impact PGRMC2 papers (e.g., specific trophoblast invasion studies) were not obtainable in the retrieved corpus; conclusions here are therefore limited to accessible full texts and extracted evidence. (lintao2024pgrmc2andhlag pages 1-3)
Open Targets associations provide a useful disease landscape but should be treated as hypothesis-generating unless supported by direct mechanistic/clinical validation. (OpenTargets Search: -PGRMC2)

References

(ryu2017membraneassociatedprogesterone pages 2-3): Chang S. Ryu, Kathrin Klein, and Ulrich M. Zanger. Membrane associated progesterone receptors: promiscuous proteins with pleiotropic functions – focus on interactions with cytochromes p450. Frontiers in Pharmacology, Mar 2017. URL: https://doi.org/10.3389/fphar.2017.00159, doi:10.3389/fphar.2017.00159. This article has 134 citations.
(mauvaisjarvis2022membraneinitiatedestrogenandrogen pages 13-14): Franck Mauvais-Jarvis, Carol A Lange, and Ellis R Levin. Membrane-initiated estrogen, androgen, and progesterone receptor signaling in health and disease. Endocrine Reviews, 43:720-742, Nov 2022. URL: https://doi.org/10.1210/endrev/bnab041, doi:10.1210/endrev/bnab041. This article has 105 citations and is from a domain leading peer-reviewed journal.
(kociszewska2017newinsightinto pages 4-5): Karolina Kociszewska and Piotr Czekaj. New insight into progesterone-dependent signalization. ArXiv, 4:11-22, Feb 2017. URL: https://doi.org/10.2174/1874844901704010011, doi:10.2174/1874844901704010011. This article has 2 citations.
(ryu2017membraneassociatedprogesterone pages 1-2): Chang S. Ryu, Kathrin Klein, and Ulrich M. Zanger. Membrane associated progesterone receptors: promiscuous proteins with pleiotropic functions – focus on interactions with cytochromes p450. Frontiers in Pharmacology, Mar 2017. URL: https://doi.org/10.3389/fphar.2017.00159, doi:10.3389/fphar.2017.00159. This article has 134 citations.
(lintao2024pgrmc2andhlag pages 1-3): Ryan C. V. Lintao, Lauren S. Richardson, Ananth Kumar Kammala, Jenieve Chapa, Dianne Aster Yunque-Yap, Kamil Khanipov, George Golovko, Leslie Michelle M. Dalmacio, and Ramkumar Menon. Pgrmc2 and hla-g regulate immune homeostasis in a microphysiological model of human maternal-fetal membrane interface. Communications Biology, Aug 2024. URL: https://doi.org/10.1038/s42003-024-06740-2, doi:10.1038/s42003-024-06740-2. This article has 17 citations and is from a peer-reviewed journal.
(lintao2024pgrmc2andhlag pages 11-12): Ryan C. V. Lintao, Lauren S. Richardson, Ananth Kumar Kammala, Jenieve Chapa, Dianne Aster Yunque-Yap, Kamil Khanipov, George Golovko, Leslie Michelle M. Dalmacio, and Ramkumar Menon. Pgrmc2 and hla-g regulate immune homeostasis in a microphysiological model of human maternal-fetal membrane interface. Communications Biology, Aug 2024. URL: https://doi.org/10.1038/s42003-024-06740-2, doi:10.1038/s42003-024-06740-2. This article has 17 citations and is from a peer-reviewed journal.
(lintao2024pgrmc2andhlag pages 10-11): Ryan C. V. Lintao, Lauren S. Richardson, Ananth Kumar Kammala, Jenieve Chapa, Dianne Aster Yunque-Yap, Kamil Khanipov, George Golovko, Leslie Michelle M. Dalmacio, and Ramkumar Menon. Pgrmc2 and hla-g regulate immune homeostasis in a microphysiological model of human maternal-fetal membrane interface. Communications Biology, Aug 2024. URL: https://doi.org/10.1038/s42003-024-06740-2, doi:10.1038/s42003-024-06740-2. This article has 17 citations and is from a peer-reviewed journal.
(wang2024pgrmc2influencesthe pages 1-2): Yao-sheng Wang, Hefang Xiao, Yi Chen, Xiaoyun Sheng, Zhi-wei Feng, Bo Peng, Zhongcheng Liu, Hongwei Zhan, Dejian Xiang, Chengjun Zhang, Yayi Xia, and Bin Geng. Pgrmc2 influences the onset of postmenopausal osteoporosis through disulfidptosis in monocytes: evidence from experimental validation and mendelian randomization. Sep 2024. URL: https://doi.org/10.1016/j.heliyon.2024.e36570, doi:10.1016/j.heliyon.2024.e36570. This article has 5 citations.
(wang2024pgrmc2influencesthe pages 2-4): Yao-sheng Wang, Hefang Xiao, Yi Chen, Xiaoyun Sheng, Zhi-wei Feng, Bo Peng, Zhongcheng Liu, Hongwei Zhan, Dejian Xiang, Chengjun Zhang, Yayi Xia, and Bin Geng. Pgrmc2 influences the onset of postmenopausal osteoporosis through disulfidptosis in monocytes: evidence from experimental validation and mendelian randomization. Sep 2024. URL: https://doi.org/10.1016/j.heliyon.2024.e36570, doi:10.1016/j.heliyon.2024.e36570. This article has 5 citations.
(alanazi2024identifyingtheroles pages 1-3): Ashwaq Alanazi, Ayan K. Barui, Ashraf M. Mohieldin, Ankan Gupta, Ramani Ramchandran, and Surya M. Nauli. Identifying the roles of mir-17 in ciliogenesis and cell cycle. Frontiers in Cell and Developmental Biology, Aug 2024. URL: https://doi.org/10.3389/fcell.2024.1397931, doi:10.3389/fcell.2024.1397931. This article has 6 citations.
(islam2024functionalmaturationof pages 4-6): Sidra Islam, Dhanya Thamaraparambil Jayaram, Pranjal Biswas, and Dennis J. Stuehr. Functional maturation of cytochromes p450 3a4 and 2d6 relies on gapdh- and hsp90-dependent heme allocation. Journal of Biological Chemistry, 300:105633, Feb 2024. URL: https://doi.org/10.1016/j.jbc.2024.105633, doi:10.1016/j.jbc.2024.105633. This article has 14 citations and is from a domain leading peer-reviewed journal.
(kaminska2023newinsightson pages 7-11): Joanna Kamińska, Olga Martyna Koper-Lenkiewicz, Donata Ponikwicka-Tyszko, Weronika Lebiedzińska, Ewelina Palak, Maria Sztachelska, Piotr Bernaczyk, Justyna Dorf, Katarzyna Guzińska-Ustymowicz, Konrad Zaręba, Sławomir Wołczyński, Nafis Ahmed Rahman, and Violetta Dymicka-Piekarska. New insights on the progesterone (p4) and pgrmc1/nenf complex interactions in colorectal cancer progression. Cancers, 15:5074, Oct 2023. URL: https://doi.org/10.3390/cancers15205074, doi:10.3390/cancers15205074. This article has 10 citations.
(kaminska2023newinsightson media 1aca05ca): Joanna Kamińska, Olga Martyna Koper-Lenkiewicz, Donata Ponikwicka-Tyszko, Weronika Lebiedzińska, Ewelina Palak, Maria Sztachelska, Piotr Bernaczyk, Justyna Dorf, Katarzyna Guzińska-Ustymowicz, Konrad Zaręba, Sławomir Wołczyński, Nafis Ahmed Rahman, and Violetta Dymicka-Piekarska. New insights on the progesterone (p4) and pgrmc1/nenf complex interactions in colorectal cancer progression. Cancers, 15:5074, Oct 2023. URL: https://doi.org/10.3390/cancers15205074, doi:10.3390/cancers15205074. This article has 10 citations.
(kaminska2023newinsightson pages 5-7): Joanna Kamińska, Olga Martyna Koper-Lenkiewicz, Donata Ponikwicka-Tyszko, Weronika Lebiedzińska, Ewelina Palak, Maria Sztachelska, Piotr Bernaczyk, Justyna Dorf, Katarzyna Guzińska-Ustymowicz, Konrad Zaręba, Sławomir Wołczyński, Nafis Ahmed Rahman, and Violetta Dymicka-Piekarska. New insights on the progesterone (p4) and pgrmc1/nenf complex interactions in colorectal cancer progression. Cancers, 15:5074, Oct 2023. URL: https://doi.org/10.3390/cancers15205074, doi:10.3390/cancers15205074. This article has 10 citations.
(kelp2025uterinepgrmc2deficiency pages 1-2): Nicole C. Kelp, Cindy A. Pru, Sandeep Paudel, John P. Lydon, J. Julie Kim, John J. Peluso, and James K. Pru. Uterine pgrmc2 deficiency attenuates endometrial hyperplasia and cancer and prolongs lifespan in a pten loss-of-function-induced cancer model. Cancers, 17:1178, Mar 2025. URL: https://doi.org/10.3390/cancers17071178, doi:10.3390/cancers17071178. This article has 1 citations.
(barata2024pleiotropyofprogesterone pages 5-7): Isabel S. Barata, José Rueff, Michel Kranendonk, and Francisco Esteves. Pleiotropy of progesterone receptor membrane component 1 in modulation of cytochrome p450 activity. Journal of Xenobiotics, 14:575-603, May 2024. URL: https://doi.org/10.3390/jox14020034, doi:10.3390/jox14020034. This article has 5 citations.
(lintao2024pgrmc2andhlag pages 9-10): Ryan C. V. Lintao, Lauren S. Richardson, Ananth Kumar Kammala, Jenieve Chapa, Dianne Aster Yunque-Yap, Kamil Khanipov, George Golovko, Leslie Michelle M. Dalmacio, and Ramkumar Menon. Pgrmc2 and hla-g regulate immune homeostasis in a microphysiological model of human maternal-fetal membrane interface. Communications Biology, Aug 2024. URL: https://doi.org/10.1038/s42003-024-06740-2, doi:10.1038/s42003-024-06740-2. This article has 17 citations and is from a peer-reviewed journal.
(OpenTargets Search: -PGRMC2): Open Targets Query (-PGRMC2, 5 results). Buniello, A. et al. (2025). Open Targets Platform: facilitating therapeutic hypotheses building in drug discovery. Nucleic Acids Research.

Artifacts

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Citations

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Perplexity

(PGRMC2-deep-research-perplexity.md)

Progesterone Receptor Membrane Component 2: A Critical Intracellular Heme Chaperone and Multifunctional Regulator of Metabolic, Reproductive, and Cardiac Physiology Perplexity sonar-deep-research 49 citations 2025-12-12T07:07:35.453683

Progesterone Receptor Membrane Component 2: A Critical Intracellular Heme Chaperone and Multifunctional Regulator of Metabolic, Reproductive, and Cardiac Physiology

PGRMC2 (Progesterone Receptor Membrane Component 2), encoded by the PGRMC2 gene on human chromosome 4 and identified by UniProt accession O15173, represents a pivotal yet historically understudied member of the membrane-associated progesterone receptor (MAPR) family with profound implications for understanding intracellular signaling, metabolic homeostasis, and reproductive biology. Initially characterized as a potential progesterone receptor due to nomenclature and early biochemical observations, PGRMC2 has emerged through recent research as a sophisticated intracellular heme chaperone and steroid hormone mediator whose primary function involves the highly regulated trafficking of labile heme from mitochondrial synthesis sites to nuclear and cytoplasmic target proteins. This protein's discovery that it binds heme rather than progesterone with high affinity fundamentally reframed our understanding of non-classical steroid signaling and revealed an ancient regulatory mechanism controlling fundamental cellular processes including adaptive thermogenesis, adipogenesis, cardiac pressure-volume homeostasis, reproductive senescence, and immune tolerance at the maternal-fetal interface. The emerging picture demonstrates that PGRMC2 serves as a critical node in multiple physiological systems, where its dysregulation correlates with metabolic disease, reproductive dysfunction, and altered cancer progression, making it an increasingly important target for therapeutic intervention and mechanistic study.

Molecular Classification, Structure, and Evolutionary Positioning

PGRMC2 belongs to the cytochrome b5-related membrane-associated progesterone receptor (MAPR) family, of which humans have four members including PGRMC1, PGRMC2, Neudesin, and Neuferricin[3]. The protein is a single-pass transmembrane protein comprising approximately 195 amino acids that exhibits characteristic structural features inherited from its evolutionary relationship to the cytochrome b5 superfamily. The defining structural element of PGRMC2 is its conserved cytochrome b5-like heme/steroid-binding domain, which represents the functional core enabling the protein's capacity to bind heme through non-covalent interactions[3][44]. The protein localizes primarily to the endoplasmic reticulum (ER) and nuclear envelope, with additional reported localization to mitochondria-associated membranes (MAMs), positioning it at critical junctions for intracellular signal transduction and metabolite trafficking[7][44]. Unlike PGRMC1, which displays broader tissue expression with highest levels in liver and kidney, PGRMC2 expression is most abundant in placenta, followed by significant expression in adipose tissue, reproductive organs, heart, and gastrointestinal tissues[55][58].

The evolutionary relationship between PGRMC1 and PGRMC2 indicates their descent from a common ancestral gene, with both proteins exhibiting two conserved introns that distinguish them from other MAPR family members[45]. This shared evolutionary origin is reflected in their functional overlap, yet evidence increasingly suggests specialized and sometimes opposing roles in different biological contexts. Phylogenetic analysis reveals that while PGRMC1 and PGRMC2 represent the most closely related pair within the MAPR family, Neudesin diverged earlier in animal evolution and maintains distinct structural features including non-conserved introns, marking it as less evolutionarily related to the PGRMC proteins despite membership in the same protein family[45]. The structural conservation of the heme-binding domain across all MAPR proteins, particularly the two critical tyrosine residues (Tyr131 and corresponding positions in other family members) essential for heme coordination, underscores the functional importance of heme binding as a fundamental property of this protein family[45][7].

Heme Binding, Trafficking, and Intracellular Localization

The discovery that PGRMC2 functions as a reversible heme-binding protein and intracellular heme chaperone represents a major conceptual advance in understanding its biological roles[7][8]. Unlike constitutive heme-binding proteins such as myoglobin and hemoglobin, which maintain essentially irreversible heme binding through multiple coordination interactions, PGRMC2 exhibits reversible heme binding characteristic of signaling proteins that require dynamic exchange of heme with other proteins[7][31][44]. This reversible binding capacity is essential to PGRMC2's proposed mechanism as a chaperone protein that accepts heme from one source (mitochondria-bound PGRMC1) and transfers it to target proteins in the nucleus and endoplasmic reticulum including heme-responsive transcription factors. The biochemical evidence for this transfer capability derives from cell-free assays where PGRMC2 efficiently transferred heme to apo-horseradish peroxidase, converting the inactive apoenzyme into the catalytically active holoenzyme form, thereby directly demonstrating that PGRMC2 can mobilize and transfer heme[7][31].

The trafficking pathway in which PGRMC2 functions emerged from studies characterizing the subcellular distribution of labile heme across different cellular compartments[7]. PGRMC2 appears to operate as the downstream component in a relay system where mitochondria-bound PGRMC1 first acquires heme from ferrochelatase (FECH) at the mitochondrial outer membrane, then transfers this heme to PGRMC2 localized on the endoplasmic reticulum and nuclear envelope[7][31][44]. This model is supported by evidence that PGRMC1 forms a stable complex with FECH at mitochondria-associated membranes, and that PGRMC2 interacts with PGRMC1 through or near the heme-binding domain[7][44]. The functional significance of this two-step transfer mechanism becomes apparent when examining the consequences of PGRMC2 depletion: cells lacking PGRMC2 exhibit substantially reduced labile heme accumulation in the nucleus despite normal mitochondrial heme synthesis, indicating that the protein is specifically required for nuclear heme delivery[7][31][44]. By contrast, PGRMC1 depletion reduces labile heme in all subcellular compartments including mitochondria, ER, cytosol, and nucleus, suggesting its broader role in initial heme mobilization[44].

The definition of "labile heme" represents an important conceptual distinction from structural heme bound as prosthetic groups in enzymes like cytochrome P450 or peroxidases. Labile heme refers to a dynamic pool of heme buffered by proteins, available for exchange and regulatory interactions with heme-responsive transcription factors and other signaling molecules[7][44]. This pool represents only a fraction of total cellular heme but possesses disproportionate regulatory importance because it mediates cellular sensing of heme status and triggers appropriate transcriptional responses[7]. The restoration of labile heme pools through PGRMC2 activation therefore provides a mechanism through which cells can rapidly adjust gene expression in response to metabolic demands and heme availability. Quantitative studies using fluorescent heme-reporter fusion proteins targeted to different cellular compartments revealed that PGRMC2 depletion primarily affects nuclear and, to a lesser extent, endoplasmic reticulum labile heme levels, consistent with its ER-nuclear envelope localization[7]. Importantly, this depletion did not prevent heme synthesis or incorporation into structural hemoproteins but specifically impaired the pool available for signaling functions, revealing the specialized physiological role of this trafficking mechanism[7][31].

Role in Adipose Tissue Thermogenesis and Metabolic Homeostasis

Among PGRMC2's most thoroughly characterized physiological functions is its role in regulating brown adipocyte metabolism and thermogenesis, discovered through studies of adipose-specific PGRMC2 knockout mice (PATKO) and validated through pharmacological approaches[7][8][31]. PGRMC2 is particularly enriched in brown adipose tissue (BAT), which maintains the highest metabolic demand for heme among all tissues due to the extraordinarily high mitochondrial content required for uncoupling protein 1 (UCP1)-mediated heat generation[7]. The discovery that PGRMC2 deletion specifically in brown adipocytes severely impaired adaptive thermogenesis illuminated a previously unappreciated link between intracellular heme dynamics and the thermogenic program[7]. When exposed to cold, PATKO mice failed to activate the heat-generating capacity of brown adipose tissue and showed a profoundly exaggerated metabolic deterioration when challenged with a high-fat diet compared to wild-type littermates[7]. This phenotype extended beyond thermogenesis to include broader dysregulation of adipocyte function, as PGRMC2-null brown adipocytes exhibited severe mitochondrial dysfunction manifest by reduced oxygen consumption, impaired ATP production, and dysregulated expression of genes required for mitochondrial biogenesis and function[7][31][44].

The mechanistic basis for PGRMC2's role in thermogenesis involves regulation of heme-responsive transcription factors, particularly Rev-Erbα and BACH1, which serve as key integrators of metabolic signaling[7][31]. These factors possess dual functionality: Rev-Erbα functions as a transcriptional repressor required early in adipogenesis but must be degraded for differentiation to proceed, while BACH1 serves broader roles in cellular redox homeostasis and metabolic programming[7]. Upon binding heme, both factors undergo rapid proteasomal degradation, removing their repressive effects on target genes[7][31]. In PATKO brown adipocytes, where nuclear labile heme is depleted, Rev-Erbα and BACH1 proteins accumulate to abnormally high levels due to their stabilization in the absence of heme-induced degradation signals[7][31]. This stabilization results in persistent repression of genes whose protein products are required for optimal mitochondrial function and metabolic activity, including genes encoding components of the electron transport chain, ATP synthase, and metabolic enzymes[7]. Enhanced analysis through transcriptomic approaches revealed that approximately 3.9 percent of the BAT transcriptome was dysregulated in PATKO mice, with particular enrichment of Rev-Erbα and BACH1 binding motifs in the promoters of downregulated genes, confirming the functional importance of these transcription factors in mediating PGRMC2's metabolic effects[7][31].

The metabolic dysfunction in PGRMC2-depleted adipocytes could be partially reversed by genetic deletion of both Rev-Erbα and BACH1, providing evidence that these factors mediate the major effects of PGRMC2-dependent heme trafficking[7][31]. Specifically, dual knockdown of Rev-Erbα and BACH1 substantially restored basal mitochondrial respiration in PGRMC2-null adipocytes, indicating that the stabilization of these repressor proteins accounts for a significant portion of the metabolic impairment[7]. This finding further supported the model that PGRMC2 regulates thermogenesis through a specific and measurable mechanism involving heme-dependent control of transcriptional repressor degradation. Conversely, pharmacological activation of PGRMC2 with a small-molecule gain-of-function ligand demonstrated the potential for therapeutic benefit in obesity and metabolic disease models[7][8]. Obese-diabetic mice treated with a PGRMC2 activator showed substantial improvement in multiple features of metabolic dysfunction including improved glucose homeostasis, enhanced insulin sensitivity, and reduced metabolic deterioration in response to high-fat feeding[7]. These findings collectively suggest that PGRMC2 represents a tractable therapeutic target for conditions of pathological metabolic dysregulation.

The role of heme in promoting adipogenesis extends beyond thermogenesis to white adipose tissue development, where addition of heme boosts the differentiation of precursor cells into mature adipocytes while inhibition of heme synthesis blocks differentiation[7][31]. This observation indicates that heme availability serves as a regulatory signal for the adipogenic program more broadly, not exclusively in the specialized context of thermogenic brown adipocytes. The dependency of adipogenesis on heme and its effects on Rev-Erbα suggests that heme-responsive transcription factors represent ancient regulatory mechanisms for integrating cellular metabolic status with differentiation programs. The enrichment of PGRMC2 in brown adipose tissue parallels the extreme metabolic specialization of this tissue type, where adaptive thermogenesis demands extraordinary mitochondrial activity and coordinated metabolic regulation. This specialization may explain why PGRMC2 demonstrates particularly critical roles in brown fat compared to other tissues, though the protein functions broadly across metabolic tissues to regulate heme-dependent processes.

Reproductive Function and Placental Development

PGRMC2 plays multifaceted and critically important roles throughout the female reproductive system, with particular significance during placentation, decidualization, and the maintenance of uterine histoarchitecture[17][18][55]. The expression pattern of PGRMC2 in reproductive tissues demonstrates distinct cell-type and cycle-dependent regulation that illuminates its function as a non-classical progesterone receptor mediating progesterone-dependent biological effects. In the endometrium, PGRMC2 expression shows the most consistent cross-species pattern of all MAPR family members, with expression elevated during the secretory phase of the menstrual cycle when progesterone levels peak[17][18]. Unlike PGRMC1, which exhibits highest expression during the proliferative phase and localizes primarily to stromal compartments, PGRMC2 remains abundant in both luminal and glandular epithelia during the secretory phase and appears to localize more prominently to epithelial compartments[17][18][21]. This inverse expression pattern between PGRMC1 and PGRMC2 across the menstrual cycle suggests complementary and stage-specific roles in endometrial function, with PGRMC1 facilitating proliferative responses during the proliferative phase while PGRMC2 inhibits proliferation and promotes differentiation during the secretory phase[23].

The role of PGRMC2 in extravillous trophoblast invasion during early placentation has emerged as a critical function with direct implications for successful pregnancy establishment[9][12]. In first-trimester placental tissue, PGRMC2 is highly expressed in syncytiotrophoblast but significantly downregulated in extravillous trophoblasts and cytotrophoblasts, indicating a divergent and stage-specific role in trophoblast biology[9]. Studies using trophoblast cell models revealed that attenuation of PGRMC2 expression promotes cell proliferation, invasion, and tube formation—hallmarks of proper placentation[9]. These effects were mediated through activation of hypoxia-inducible factor 1α (HIF1α) signaling, a master regulator of adaptive responses to the hypoxic environment of the developing placenta[9]. PGRMC2 knockdown cells exhibited increased HIF1α signaling and enhanced expression of vascular endothelial growth factor A (VEGFA), a key angiogenic factor essential for establishing placental blood supply[9]. The finding that culture supernatant from PGRMC2-depleted cells did not significantly affect extravillous trophoblast invasion suggests that the effects are mediated through intracellular mechanisms rather than secreted paracrine factors[9]. These results indicate that PGRMC2 functions as a brake on the invasive program, and its attenuation facilitates the phenotypic transition from proliferative cytotrophoblasts to invasive extravillous trophoblasts[9][12].

PGRMC2 deficiency has been associated with premature reproductive senescence and subfertility in mouse models, suggesting critical roles in maintaining long-term ovarian and reproductive tissue function[43][46]. Conditional ablation of PGRMC2 led initially to subfertility, with heterozygous knockout female mice producing 47 percent fewer pups per litter than wild-type controls[46]. These findings imply that PGRMC2 contributes to sustained reproductive capacity across the lifespan, potentially through effects on granulosa cell function, oocyte development, or endocrine signaling. The requirement of PGRMC2 for maintaining normal uterine histoarchitecture and female reproductive lifespan demonstrates that this protein participates in fundamental processes ensuring reproductive tissue health[55]. In the context of endometriosis, a pathological condition characterized by progesterone resistance and ectopic uterine tissue growth, PGRMC2 expression and localization are significantly disrupted[20][21][23]. Endometrial tissue from women with advanced-stage endometriosis shows markedly reduced PGRMC2 expression compared to disease-free controls, and the subcellular localization of remaining PGRMC2 protein is altered, with loss of the predominant cytoplasmic localization observed in normal cells[20][21]. These expression changes correlate with the well-documented progesterone resistance observed in endometriosis and suggest that PGRMC2 dysregulation contributes to the failure of progesterone-mediated suppression of inflammatory and proliferative responses characteristic of the disease[20][23].

The role of PGRMC2 in mediating progesterone signaling at the maternal-fetal interface has recently emerged as critical for maintaining immune homeostasis and fetal membrane integrity[60]. Recent sophisticated organ-on-chip technology modeling the chorion-decidua interface demonstrated that PGRMC2 serves as an upstream regulator of inflammation, HLA-G expression, and mesenchymal-epithelial transition (MET)[60]. PGRMC2 knockout chorion trophoblast cells exhibited increased vimentin expression indicating transition toward mesenchymal phenotype, a change associated with compromise of epithelial barrier function[60]. In response to inflammatory challenge with lipopolysaccharide or polyinosinic:polycytidylic acid (polyI:C), decidual tissues from PGRMC2-knockout systems showed exaggerated cytokine responses including elevated interleukin-6, interleukin-10, and tumor necrosis factor-α compared to wild-type systems[60]. PGRMC2 thereby functions to stabilize the fetal membrane barrier and suppress excessive maternal inflammatory responses that could compromise pregnancy. The intimate connection between PGRMC2 and HLA-G, a non-classical major histocompatibility complex molecule crucial for fetal immune protection, suggests a functional partnership in which PGRMC2 regulates the expression or function of this critical immunomodulatory molecule[60]. Defects in PGRMC2 function, whether through gene mutations, epigenetic silencing, or altered phosphorylation, could theoretically contribute to pregnancy complications characterized by fetal membrane dysfunction including preterm birth.

Cardiac Function and Pressure-Volume Regulation

Recent investigations have revealed previously unsuspected roles for PGRMC2 in cardiac physiology, specifically in regulating the pressure-volume relationship essential for normal myocardial function[14][27][38]. The discovery emerged from unbiased proteomic studies identifying associations between cardiac disease and PGRMC2, which prompted functional characterization through analysis of heart-specific PGRMC2 knockout mice (MyH6•Pgrmc2 flox/flox) in which the PGRMC2 gene is selectively deleted in cardiomyocytes[14][27][38]. The knockout hearts exhibit marked impairment in pressure-volume relationship in response to even modest hemodynamic stress, manifesting as abnormalities in left ventricular pressure and end-systolic volume[27][38]. Under hypoxic conditions, this pressure-volume dysregulation progresses to manifest as severe congestive left and right ventricular failure, demonstrating that PGRMC2 is particularly critical for maintaining normal cardiac physiology during stress conditions demanding compensatory mechanisms[27][38].

The mechanism through which PGRMC2 exerts its cardiac effects involves mediation of steroid hormone signaling for rapid calcium homeostasis in cardiomyocytes[14][27][38]. PGRMC2 functions as a membrane steroid receptor enabling rapid, non-genomic responses to steroid hormones including progesterone, estradiol, and hydrocortisone, which activate calcium signaling cascades essential for maintaining cardiac contraction[14][27][38]. Isolated cardiomyocytes from wild-type hearts exhibit robust increases in cytosolic calcium in response to physiological concentrations of steroid hormones, whereas cardiomyocytes from PGRMC2 knockout hearts show blunted or absent responses to these hormones[27][38]. Ectopic expression of PGRMC2 in knockout cardiomyocytes rescued the calcium response to steroid hormones, confirming the specificity of PGRMC2 in mediating this signaling pathway[27][38]. The critical nature of PGRMC2-dependent calcium signaling for maintaining adequate stroke volume and cardiac output emerges from analysis of heart function parameters, where PGRMC2-deficient hearts show impaired contractility manifest as reduced maximum rate of left ventricular pressure generation (LVP max) and altered end-systolic pressure[27][38].

The consequences of PGRMC2 deletion extend to broader systemic manifestations including pulmonary and systemic hemodynamic abnormalities[27][38]. PGRMC2 knockout mice subjected to hypoxic stress develop evidence of congestive heart failure including ascites (free abdominal fluid), indicating fluid retention due to hepatic congestion from right ventricular failure[27][38]. Pulmonary artery pressures and pulmonary vascular resistance increase significantly in knockout mice under hypoxia, indicating development of secondary pulmonary hypertension as a consequence of right ventricular dysfunction[27][38]. Exercise capacity is severely reduced in PGRMC2 knockout mice during hypoxic stress, with male knockout mice demonstrating greater exercise intolerance and faster exhaustion than females, a sex-dependent effect potentially related to differential fibrotic burden in male hearts[27][38]. These comprehensive physiological characterizations establish PGRMC2 as an essential component of the cardiac steroid hormone response system, whose dysfunction could predispose to or accelerate development of heart failure, particularly under conditions of metabolic stress such as hypoxia.

The requirement for acid-base homeostasis during hypoxic challenge also appears linked to PGRMC2 function, as knockout mice developed altered acid-base parameters[27][38]. Chronic hypoxia typically induces polycythemic responses with elevated hemoglobin and hematocrit, compensatory mechanisms aimed at improving tissue oxygen delivery[27]. PGRMC2 appears involved in regulating how effectively these compensatory mechanisms support cardiac function. The electrical abnormalities observable in PGRMC2-deficient hearts, including J wave abnormalities suggesting altered electrical propagation, likely reflect the structural remodeling including fibrosis and dilation that develops in these hearts[27][38]. This comprehensive cardiac phenotype suggests that PGRMC2-dependent steroid signaling integrates with multiple other regulatory systems to maintain normal cardiac pressure-volume dynamics, contractility, and electrical function.

Cytochrome P450 Interactions and Drug Metabolism

PGRMC2 shares with its homolog PGRMC1 the capacity to interact with cytochrome P450 (CYP450) enzymes, a family of critical drug-metabolizing and steroidogenic proteins[2][13][16]. These interactions have implications both for understanding steroidogenesis in steroid-producing tissues and for drug metabolism and potential drug-drug interactions in tissues expressing high levels of both PGRMC2 and CYP450 enzymes[2][13]. The evidence for stable physical interactions between PGRMC2 and CYP enzymes derives from coimmunoprecipitation studies demonstrating binding of PGRMC2 to CYP1A2, CYP3A4, and CYP21A2 in human embryonic kidney cells[13][16]. The functional consequences of these interactions for CYP enzyme activity remain incompletely characterized compared to PGRMC1, but available evidence suggests that PGRMC2 may modulate CYP function through mechanisms similar to those documented for its homolog[13]. The stoichiometry and physiological relevance of PGRMC2:CYP interactions in vivo remain uncertain given that most characterization has employed artificial conditions of protein overexpression, and tissue-specific abundances of PGRMC2 relative to its CYP interaction partners may limit the frequency of complex formation in some tissues.

The interaction with steroidogenic CYP enzymes is of particular significance in steroid-producing tissues such as adrenal gland, where both PGRMC2 and multiple steroidogenic CYP enzymes are expressed at potentially substantial levels. While detailed functional studies examining PGRMC2 modulation of steroidogenic CYP activity are limited compared to those for PGRMC1, the homology between these proteins and their shared capacity for CYP binding suggest similar functional potential. The importance of understanding PGRMC2:CYP interactions extends to clinical pharmacology, as dysregulation of PGRMC2 expression in tissues responsible for drug metabolism could theoretically alter the clearance rates of drugs metabolized by CYP enzymes with which PGRMC2 interacts.

Cell Cycle Regulation and Tumor-Suppressive Functions

PGRMC2 exhibits cell cycle regulatory functions that appear to suppress entry into the cell cycle, a role that contrasts with the proliferation-promoting effects commonly attributed to PGRMC1[32][39][42][54]. Studies in granulosa cells and other cell systems have demonstrated that depletion of PGRMC2 increases entry into the G1 phase of the cell cycle, suggesting that the protein normally functions to maintain cells in G0 quiescence[32][39][42]. The mechanism involves interaction of PGRMC2 with GTPase-activating protein-binding protein 2 (G3BP2), which forms a complex that suppresses NF-κB-mediated transcription of genes promoting cell cycle progression[32][42][54]. Dynamic changes in the PGRMC1:PGRMC2:G3BP2 complex regulate the timing of entry into G1, with disruption of these interactions leading to increased NF-κB transcriptional activity and accelerated cell cycle progression[32][39][42][54]. Additionally, PGRMC2 localizes to the mitotic spindle where it plays roles in regulating proper chromosome segregation, and its depletion leads to metaphase arrest and apoptosis in granulosa cells, suggesting important functions in ensuring proper mitotic progression[32][39][42].

The evidence for PGRMC2 functioning as a tumor suppressor emerges from observations that elevated PGRMC2 expression inhibits cell migration in ovarian cancer cells (SKOV-3 line), whereas decreased PGRMC2 expression promotes migration[25][28]. This contrasts with PGRMC1, which generally promotes cancer cell growth and chemoresistance, suggesting that PGRMC1 and PGRMC2 may possess opposite effects in the neoplastic setting[22][25][54]. The regulatory relationship between PGRMC1 and PGRMC2 expression appears to be important in determining the overall proliferative phenotype, as the ratio of these proteins rather than absolute levels of either may drive cancer cell behavior[23][54]. In the uterine endometrium, recent studies demonstrate that conditional ablation of PGRMC2 reduces incidence and severity of endometrial hyperplasia and cancer in mice with conditional PTEN heterozygosity or knockout, suggesting that PGRMC2 removal paradoxically reduces tumor burden by decreasing glandular epithelial proliferation[55]. This finding underscores the complexity of PGRMC2's roles in different cellular contexts and suggests that its tumor-suppressive potential may be particularly manifest in the endometrium.

Placental Expression and Trophoblast Biology

The pattern of PGRMC2 expression in placental tissues indicates high abundance in the outer syncytiotrophoblast layer but reduced expression in inner trophoblast compartments, suggesting stage-specific roles in trophoblast differentiation and placental maturation[4][9][12]. The syncytiotrophoblast, the terminally differentiated outer layer of placental villi in direct contact with maternal blood, shows strong PGRMC2 expression, while cytotrophoblasts and extravillous trophoblasts show significantly lower expression[9]. This expression pattern indicates that PGRMC2 may promote a differentiated, non-invasive trophoblast phenotype, consistent with the finding that PGRMC2 knockdown promotes the invasive properties characteristic of extravillous trophoblasts[9]. The angiogenic functions promoted by PGRMC2 attenuation through HIF1α activation are essential for placental vascularization and nutrient exchange, suggesting that the developmental downregulation of PGRMC2 in early extravillous trophoblasts facilitates the vascular remodeling necessary for placental expansion[9][12].

Spermatozoal Function and Male Reproductive Biology

PGRMC2 is expressed in spermatozoa, where it is believed to function as a steroid receptor and may participate in the progesterone-dependent sperm acrosome reaction[6][15]. The acrosome reaction represents a crucial step in fertilization in which the outer membrane of the sperm acrosome fuses and exocytoses enzymes necessary for penetrating the egg's protective layers. Although detailed mechanistic studies of PGRMC2's role in spermatozoal function remain limited, its expression in this specialized cell type and presumed receptor function suggest a role in mediating progesterone-dependent signaling required for proper fertilization capacity. The implications of PGRMC2 dysfunction in male fertility warrant investigation in the context of the documented subfertility phenotype associated with PGRMC2 knockout.

Fetal Membrane Physiology and Parturition

PGRMC2 expression in fetal membranes demonstrates dynamic regulation associated with the transition to labor, with significant downregulation occurring at term and in conditions associated with premature rupture of membranes (pPROM)[29]. Intact fetal membranes from term labor and preterm pPROM show significantly lower PGRMC2 expression compared to tissues from preterm birth without membrane rupture, suggesting that PGRMC2 downregulation may facilitate fetal membrane destabilization associated with labor onset[29]. This functional relationship is further supported by evidence that oxidative stress, which occurs both during normal parturition and in pathologic conditions like pPROM, induces cell-type-dependent changes in PGRMC2 expression[29]. In amnion and chorion cells exposed to cigarette smoke extract (a model of oxidative stress mimicking conditions at term labor), PGRMC2 expression was significantly reduced, indicating that oxidative stress contributes to PGRMC2 downregulation[29]. The functional significance of this downregulation may involve altered response to progesterone signaling, as PGRMC2 represents one of multiple membrane progesterone receptors contributing to functional progesterone withdrawal at parturition despite maintained circulating progesterone levels[29].

Protein Interactions and Signaling Complexes

PGRMC2 participates in multiple protein interaction networks that govern its localization, stability, and functional activities. The interaction with PGRMC1 represents a central relationship through which heme is transferred from mitochondria to distal cellular compartments[7][44]. Additionally, PGRMC2 interacts with G3BP2, a protein involved in regulating cell cycle progression and cellular stress responses, in a manner that appears to suppress NF-κB-mediated transcription[32][39][42][54]. The discovery that this PGRMC1:PGRMC2:G3BP2 complex regulates entry into the cell cycle reveals a mechanism through which progesterone signaling, mediated through these membrane receptors, exerts effects on fundamental cell biological processes including proliferation. Post-translational modifications including phosphorylation, ubiquitination, and sumoylation have been identified as regulating PGRMC2 localization, stability, and presumably function, though the detailed biochemistry of these modifications and their functional consequences remain incompletely understood[3][52]. Sumoylation appears particularly important for PGRMC1 translocation to the nucleus, and similar mechanisms may regulate PGRMC2 nuclear localization[3][52].

Conclusion and Future Perspectives

PGRMC2 has emerged through recent research as a sophisticated and multifunctional protein whose primary role as an intracellular heme chaperone illuminates a previously unappreciated regulatory axis controlling fundamental physiological processes. The discovery that this protein functions primarily through reversible heme binding rather than direct steroid hormone binding required a conceptual shift in understanding non-classical steroid signaling, revealing instead a mechanism through which heme availability serves as an ancient regulatory signal integrated with steroid hormone responses[7][8][31][44][50][52]. The protein's roles in regulating thermogenesis through heme-dependent control of transcriptional repressor degradation, mediating rapid steroid hormone effects on cardiac calcium homeostasis, and promoting proper placental development through suppression of trophoblast invasion collectively demonstrate its broad physiological importance[7][9][14][27][38].

The dysregulation of PGRMC2 in disease states including metabolic disease, endometriosis, endometrial cancer, and complications of pregnancy suggests that therapeutic modulation of PGRMC2 expression or activity represents a tractable approach to improving outcomes in multiple clinical contexts. The development of pharmacological activators of PGRMC2 that demonstrated beneficial metabolic effects in obese-diabetic mice provides proof-of-concept that PGRMC2 represents a viable therapeutic target[7][8]. However, significant gaps in knowledge remain regarding the precise molecular mechanisms through which PGRMC2 executes its diverse functions in different cellular and tissue contexts, the structural basis for its selectivity in transferring heme to specific target proteins, and the integration of PGRMC2 function with other regulatory systems controlling fundamental cellular processes.

Future investigations should prioritize detailed characterization of the PGRMC2 interactome in different tissue types, determining the kinetics and specificity of heme transfer to various target proteins, and understanding the signaling mechanisms through which PGRMC2-mediated heme delivery influences transcriptional programs and cellular phenotype. The creation of tissue-specific knockout models for additional tissues including liver, kidney, endocrine organs, and immune tissues would illuminate PGRMC2's roles in these contexts. Investigation of PGRMC2 mutations in human disease, particularly in reproductive disorders and metabolic disease, may identify loss-of-function mutations that would validate PGRMC2 as a disease-associated gene. Understanding how PGRMC2 integrates with other membrane steroid receptors and classical nuclear receptors to coordinate hormonal responses represents another frontier for investigation[56]. The recent discovery of PGRMC2's critical role in immune homeostasis at the maternal-fetal interface opens new avenues for exploring how dysregulation of this protein contributes to pregnancy complications[60]. These investigations will likely reveal PGRMC2 as a central regulatory hub whose dysfunction contributes to multiple pathological conditions, making it an important target for understanding fundamental principles of cellular regulation and for developing novel therapeutic interventions.

Citations

https://en.wikipedia.org/wiki/PGRMC2
https://pubmed.ncbi.nlm.nih.gov/23276631/
https://pmc.ncbi.nlm.nih.gov/articles/PMC7866220/
https://www.ncbi.nlm.nih.gov/gene/10424
https://maayanlab.cloud/Harmonizome/gene/PGRMC2
https://www.thermofisher.com/antibody/product/PGRMC2-Antibody-Polyclonal/PA5-59465
https://pmc.ncbi.nlm.nih.gov/articles/PMC6895438/
https://pubmed.ncbi.nlm.nih.gov/31748741/
https://pubmed.ncbi.nlm.nih.gov/37665239/
https://digitalcommons.unl.edu/cgi/viewcontent.cgi?article=1456&context=biochemfacpub
https://reactome.org/content/detail/R-HSA-9707683
https://academic.oup.com/biolreprod/article/109/5/759/7259344
https://pmc.ncbi.nlm.nih.gov/articles/PMC5366339/
https://www.nature.com/articles/s41467-025-57707-8
https://www.thermofisher.com/proteins/product/Human-PGRMC2-Control-Fragment-Recombinant-Protein/RP-95669
https://pmc.ncbi.nlm.nih.gov/articles/PMC6718323/
https://www.frontiersin.org/journals/neuroscience/articles/10.3389/fnins.2013.00168/full
https://pmc.ncbi.nlm.nih.gov/articles/PMC3776937/
https://www.ovid.com/journals/steri/pdf/10.1016/j.steroids.2012.12.002~pgrmc2-a-yet-uncharacterized-protein-with-potential-as-tumor
https://pubmed.ncbi.nlm.nih.gov/23793472/
https://pmc.ncbi.nlm.nih.gov/articles/PMC3358041/
https://www.emjreviews.com/reproductive-health/article/progesterone-resistance-in-endometriosis-j150122/
https://www.uniprot.org/uniprotkb/O15173/entry
https://pmc.ncbi.nlm.nih.gov/articles/PMC4632865/
https://pubmed.ncbi.nlm.nih.gov/23064006/
https://pmc.ncbi.nlm.nih.gov/articles/PMC7876665/
https://pmc.ncbi.nlm.nih.gov/articles/PMC4629436/
https://pmc.ncbi.nlm.nih.gov/articles/PMC4434922/
https://pmc.ncbi.nlm.nih.gov/articles/PMC10392766/
https://www.nature.com/articles/s42003-020-01202-x
https://genesdev.cshlp.org/content/27/3/234.full.html
https://pmc.ncbi.nlm.nih.gov/articles/PMC11897200/
https://academic.oup.com/biolreprod/article/91/5/104,%201-12/2434285
https://communities.springernature.com/posts/pgrmc2-the-discovery-of-pressure-volume-regulator
https://pmc.ncbi.nlm.nih.gov/articles/PMC4435414/
https://www.frontiersin.org/journals/molecular-biosciences/articles/10.3389/fmolb.2015.00024/full
https://academic.oup.com/endo/article/158/3/640/3053386
https://www.uniprot.org/uniprot/A0A3Q1J653
https://www3.botany.ubc.ca/keeling/PDF/20Hehenberger.pdf
https://patents.google.com/patent/US9724337B2/en
https://www.nature.com/articles/ncomms11030
https://portlandpress.com/biochemsoctrans/article/53/03/603/236126/Mechanisms-of-heme-transport-in-the-mitochondria
https://pmc.ncbi.nlm.nih.gov/articles/PMC9186309/
https://pmc.ncbi.nlm.nih.gov/articles/PMC11988108/
https://academic.oup.com/edrv/article/43/4/720/6428770
https://www.omicsdi.org/dataset/pride/PXD048494
https://www.proteinatlas.org/ENSG00000164040-PGRMC2
https://pmc.ncbi.nlm.nih.gov/articles/PMC8616056/
https://www.nature.com/articles/s42003-024-06740-2

📄 View Raw YAML

id: O15173
gene_symbol: PGRMC2
product_type: PROTEIN
taxon:
  id: NCBITaxon:9606
  label: Homo sapiens
description: >-
  PGRMC2 (Progesterone Receptor Membrane Component 2) is an intracellular heme
  chaperone belonging to the cytochrome b5 family MAPR subfamily. Despite its
  historical name suggesting progesterone receptor function, PGRMC2 primarily
  functions as a reversible heme-binding protein that delivers labile heme from
  the ER to the nucleus, where it regulates heme-responsive transcription factors
  such as Rev-Erba and BACH1. PGRMC2 localizes to the ER and nuclear envelope,
  interacts with nucleoporin ALADIN (AAAS), and plays roles in adipose tissue
  development, thermogenesis, and reproductive physiology. Recent work also
  implicates PGRMC2 in immune homeostasis at the maternal-fetal interface
  upstream of HLA-G [PMID:39179795] and in endometrial epithelial proliferation
  in Pten loss-of-function settings [PMID:40227710], while a 2024 study found
  PGRMC2 is not required for mitochondrial heme allocation to ER cytochromes
  P450 3A4 or 2D6 [PMID:38199567], suggesting client-specific rather than
  bulk ER heme chaperone activity.
existing_annotations:
  - term:
      id: GO:0005783
      label: endoplasmic reticulum
    evidence_type: IBA
    original_reference_id: GO_REF:0000033
    review:
      summary: >-
        PGRMC2 localization to the ER is well-supported by multiple lines of evidence.
        The deep research confirms PGRMC2 localizes primarily to the endoplasmic
        reticulum and nuclear envelope [PMID:27754849]. This IBA annotation is
        phylogenetically appropriate and consistent with experimental data.
      action: ACCEPT
      reason: >-
        ER localization is a core feature of PGRMC2 function as a heme chaperone
        that receives heme from mitochondria-bound PGRMC1 and delivers it to the
        nucleus. Multiple experimental studies confirm this localization.
      supported_by:
        - reference_id: PMID:27754849
          supporting_text: >-
            Visualising PGRMC2 in the cell using immunofluorescence and confocal
            microscopy has shown the presence of PGRMC2 at the central ER, and,
            interestingly, at the nuclear envelope and the perinuclear ER.
        - reference_id: file:human/PGRMC2/PGRMC2-deep-research-perplexity.md
          supporting_text: >-
            The protein localizes primarily to the endoplasmic reticulum (ER) and
            nuclear envelope, with additional reported localization to
            mitochondria-associated membranes (MAMs).
  - term:
      id: GO:0012505
      label: endomembrane system
    evidence_type: IBA
    original_reference_id: GO_REF:0000033
    review:
      summary: >-
        PGRMC2 is a single-pass transmembrane protein localized to ER and nuclear
        envelope, which are part of the endomembrane system. This IBA annotation
        is appropriately broad and phylogenetically supported.
      action: ACCEPT
      reason: >-
        As a membrane protein of the ER and nuclear envelope, PGRMC2 is correctly
        annotated to endomembrane system. This is consistent with its function in
        heme trafficking between cellular compartments.
      supported_by:
        - reference_id: file:human/PGRMC2/PGRMC2-deep-research-perplexity.md
          supporting_text: >-
            PGRMC2 appears to operate as the downstream component in a relay system
            where mitochondria-bound PGRMC1 first acquires heme from ferrochelatase
            at the mitochondrial outer membrane, then transfers this heme to PGRMC2
            localized on the endoplasmic reticulum and nuclear envelope.
  - term:
      id: GO:0016020
      label: membrane
    evidence_type: IBA
    original_reference_id: GO_REF:0000033
    review:
      summary: >-
        PGRMC2 is a single-pass transmembrane protein. The membrane annotation is
        accurate but very general.
      action: ACCEPT
      reason: >-
        UniProt confirms PGRMC2 has a transmembrane domain (residues 42-66). While
        this is a broad term, the IBA annotation is phylogenetically sound.
      supported_by:
        - reference_id: file:human/PGRMC2/PGRMC2-uniprot.txt
          supporting_text: >-
            TRANSMEM 42..66 /note="Helical"
  - term:
      id: GO:0005496
      label: steroid binding
    evidence_type: IEA
    original_reference_id: GO_REF:0000120
    review:
      summary: >-
        The historical name "progesterone receptor membrane component" suggested
        steroid binding, but modern research shows PGRMC2 primarily binds heme,
        not progesterone. The deep research explicitly states this protein binds
        heme rather than progesterone with high affinity [PMID:28111073].
      action: MODIFY
      reason: >-
        While PGRMC2 was initially characterized as a potential steroid receptor,
        current evidence strongly supports heme binding as its primary ligand
        interaction. The IEA annotation based on automated pipelines reflects
        outdated understanding. GO:0020037 (heme binding) is more accurate.
      proposed_replacement_terms:
        - id: GO:0020037
          label: heme binding
      supported_by:
        - reference_id: file:human/PGRMC2/PGRMC2-deep-research-perplexity.md
          supporting_text: >-
            This protein's discovery that it binds heme rather than progesterone
            with high affinity fundamentally reframed our understanding of
            non-classical steroid signaling.
        - reference_id: PMID:28111073
          supporting_text: >-
            our initial studies point to heme-related molecules as potential
            candidates to serve this function
  - term:
      id: GO:0005576
      label: extracellular region
    evidence_type: IEA
    original_reference_id: GO_REF:0000044
    review:
      summary: >-
        UniProt indicates PGRMC2 can be secreted, based on detection in urine
        [PMID:37453717]. However, this appears to be a minor localization rather
        than a primary functional site.
      action: KEEP_AS_NON_CORE
      reason: >-
        The secreted form may represent a secondary localization. The primary
        function of PGRMC2 as a heme chaperone occurs intracellularly at the ER
        and nuclear envelope.
      supported_by:
        - reference_id: file:human/PGRMC2/PGRMC2-uniprot.txt
          supporting_text: >-
            Secreted {ECO:0000269|PubMed:37453717}.
  - term:
      id: GO:0005635
      label: nuclear envelope
    evidence_type: IEA
    original_reference_id: GO_REF:0000044
    review:
      summary: >-
        Nuclear envelope localization is well-supported by experimental evidence
        showing PGRMC2 co-localizes with nucleoporin ALADIN at the NPC
        [PMID:27754849]. This IEA annotation is consistent with experimental data.
      action: ACCEPT
      reason: >-
        Nuclear envelope localization is central to PGRMC2 function in delivering
        heme to the nucleus. This is supported by both the ALADIN interaction
        studies and Reactome pathway data.
      supported_by:
        - reference_id: PMID:27754849
          supporting_text: >-
            We detected that PGRMC2 co-localises with ALADIN and with different
            FG-repeat NUPs [...] to the
            nuclear envelope and the perinuclear ER.
  - term:
      id: GO:0005783
      label: endoplasmic reticulum
    evidence_type: IEA
    original_reference_id: GO_REF:0000044
    review:
      summary: >-
        Duplicate of IBA annotation. ER localization is experimentally confirmed
        [PMID:27754849].
      action: ACCEPT
      reason: >-
        ER localization is well-supported and represents a core site of PGRMC2
        function in the heme trafficking pathway.
      supported_by:
        - reference_id: PMID:27754849
          supporting_text: >-
            Visualising PGRMC2 in the cell using immunofluorescence and confocal
            microscopy has shown the presence of PGRMC2 at the central ER, and,
            interestingly, at the nuclear envelope and the perinuclear ER.
  - term:
      id: GO:0008289
      label: lipid binding
    evidence_type: IEA
    original_reference_id: GO_REF:0000043
    review:
      summary: >-
        This IEA annotation is based on UniProt keyword mapping. While PGRMC2 has
        a cytochrome b5-like domain that could theoretically bind lipids, the
        primary demonstrated binding activity is heme binding.
      action: MARK_AS_OVER_ANNOTATED
      reason: >-
        There is no direct experimental evidence for lipid binding by PGRMC2.
        The primary ligand is heme. This annotation appears to be based on domain
        predictions rather than functional characterization. Recent reviews of
        the MAPR family explicitly caution that direct ligand-binding evidence
        outside heme is weaker for non-PGRMC1 MAPRs.
      supported_by:
        - reference_id: file:human/PGRMC2/PGRMC2-deep-research-perplexity.md
          supporting_text: >-
            PGRMC2 exhibits reversible heme binding characteristic of signaling
            proteins that require dynamic exchange of heme with other proteins.
        - reference_id: file:human/PGRMC2/PGRMC2-deep-research-falcon.md
          supporting_text: >-
            Reviews highlight that PGRMC2 is less well characterized than
            PGRMC1 (tissue specificity, interaction network, subcellular
            locations). Additionally, progesterone binding evidence is weaker
            for non-PGRMC1 MAPRs.
  - term:
      id: GO:0016020
      label: membrane
    evidence_type: IEA
    original_reference_id: GO_REF:0000044
    review:
      summary: >-
        Duplicate membrane annotation. PGRMC2 is a single-pass transmembrane protein.
      action: ACCEPT
      reason: >-
        Membrane localization is well-established for this transmembrane protein.
      supported_by:
        - reference_id: file:human/PGRMC2/PGRMC2-uniprot.txt
          supporting_text: >-
            TRANSMEM 42..66 /note="Helical"
  - term:
      id: GO:0030518
      label: nuclear receptor-mediated steroid hormone signaling pathway
    evidence_type: IEA
    original_reference_id: GO_REF:0000108
    review:
      summary: >-
        This annotation reflects the outdated view of PGRMC2 as a steroid
        receptor. Current evidence indicates PGRMC2 functions primarily as a
        heme chaperone, not a steroid receptor.
      action: REMOVE
      reason: >-
        The deep research clearly states that PGRMC2 binds heme rather than
        progesterone with high affinity. Its role in the nucleus involves
        delivering heme to transcription factors, not steroid hormone signaling.
      supported_by:
        - reference_id: file:human/PGRMC2/PGRMC2-deep-research-perplexity.md
          supporting_text: >-
            Initially characterized as a potential progesterone receptor due to
            nomenclature and early biochemical observations, PGRMC2 has emerged
            through recent research as a sophisticated intracellular heme chaperone.
  - term:
      id: GO:0005515
      label: protein binding
    evidence_type: IPI
    original_reference_id: PMID:27173435
    review:
      summary: >-
        Generic protein binding from high-throughput interactome study. While
        PGRMC2 does interact with proteins (PGRMC1, ALADIN), this term is
        uninformative.
      action: MARK_AS_OVER_ANNOTATED
      reason: >-
        Protein binding is too generic. More specific interaction partners such
        as PGRMC1 and AAAS (ALADIN) are documented, but the generic protein
        binding term adds no information about function.
      supported_by:
        - reference_id: PMID:27173435
          supporting_text: >-
            An organelle-specific protein landscape identifies novel diseases
            and molecular mechanisms.
  - term:
      id: GO:0005515
      label: protein binding
    evidence_type: IPI
    original_reference_id: PMID:27599036
    review:
      summary: >-
        This paper focuses on PGRMC1 and ferrochelatase interaction, not PGRMC2
        directly. PGRMC2 may be detected as part of the heme trafficking complex.
      action: MARK_AS_OVER_ANNOTATED
      reason: >-
        Generic protein binding term. The paper title mentions PGRMC1, and
        PGRMC2 interaction may be indirect through the PGRMC1-PGRMC2 relay system.
      supported_by:
        - reference_id: PMID:27599036
          supporting_text: >-
            A Novel Role for Progesterone Receptor Membrane Component 1 (PGRMC1):
            A Partner and Regulator of Ferrochelatase.
  - term:
      id: GO:0005515
      label: protein binding
    evidence_type: IPI
    original_reference_id: PMID:29513927
    review:
      summary: >-
        High-throughput protein interaction study on ROCO proteins. Generic
        protein binding annotation.
      action: MARK_AS_OVER_ANNOTATED
      reason: >-
        Generic protein binding from high-throughput study. Does not provide
        specific functional insight.
      supported_by:
        - reference_id: PMID:29513927
          supporting_text: >-
            Comparative Protein Interaction Network Analysis Identifies Shared
            and Distinct Functions for the Human ROCO Proteins.
  - term:
      id: GO:0005515
      label: protein binding
    evidence_type: IPI
    original_reference_id: PMID:32296183
    review:
      summary: >-
        Large-scale binary protein interactome mapping. Generic annotation.
      action: MARK_AS_OVER_ANNOTATED
      reason: >-
        Generic protein binding from high-throughput interactome study.
      supported_by:
        - reference_id: PMID:32296183
          supporting_text: >-
            A reference map of the human binary protein interactome.
  - term:
      id: GO:0005515
      label: protein binding
    evidence_type: IPI
    original_reference_id: PMID:33961781
    review:
      summary: >-
        Proteome-scale network study. Generic protein binding annotation.
      action: MARK_AS_OVER_ANNOTATED
      reason: >-
        Generic protein binding from high-throughput study.
      supported_by:
        - reference_id: PMID:33961781
          supporting_text: >-
            Dual proteome-scale networks reveal cell-specific remodeling of the
            human interactome.
  - term:
      id: GO:0005515
      label: protein binding
    evidence_type: IPI
    original_reference_id: PMID:35271311
    review:
      summary: >-
        OpenCell endogenous tagging study. Generic protein binding.
      action: MARK_AS_OVER_ANNOTATED
      reason: >-
        Generic protein binding from high-throughput cellular cartography study.
      supported_by:
        - reference_id: PMID:35271311
          supporting_text: >-
            OpenCell: Endogenous tagging for the cartography of human cellular
            organization.
  - term:
      id: GO:0005515
      label: protein binding
    evidence_type: IPI
    original_reference_id: PMID:40355756
    review:
      summary: >-
        Solute carrier superfamily interactome study. Generic protein binding.
      action: MARK_AS_OVER_ANNOTATED
      reason: >-
        Generic protein binding from high-throughput interactome study.
      supported_by:
        - reference_id: PMID:40355756
          supporting_text: >-
            The solute carrier superfamily interactome.
  - term:
      id: GO:0015232
      label: heme transmembrane transporter activity
    evidence_type: IEA
    original_reference_id: GO_REF:0000107
    review:
      summary: >-
        This annotation suggests PGRMC2 actively transports heme across membranes.
        However, PGRMC2 is described as a heme chaperone that binds and delivers
        heme, not as a transmembrane transporter.
      action: MODIFY
      reason: >-
        PGRMC2 is a heme chaperone, not a heme transporter. It binds heme
        reversibly and delivers it to target proteins, but does not function
        as a transmembrane transporter. The correct term is heme binding.
      proposed_replacement_terms:
        - id: GO:0020037
          label: heme binding
      supported_by:
        - reference_id: file:human/PGRMC2/PGRMC2-deep-research-perplexity.md
          supporting_text: >-
            This reversible binding capacity is essential to PGRMC2's proposed
            mechanism as a chaperone protein that accepts heme from one source
            (mitochondria-bound PGRMC1) and transfers it to target proteins in
            the nucleus and endoplasmic reticulum.
  - term:
      id: GO:0015886
      label: heme transport
    evidence_type: IEA
    original_reference_id: GO_REF:0000107
    review:
      summary: >-
        PGRMC2 does participate in intracellular heme trafficking as a chaperone,
        facilitating heme delivery from ER to nucleus. Note, however, that PGRMC2
        is not universally required for heme delivery to all ER hemoproteins:
        siRNA knockdown of PGRMC2 in HEK293T cells did not impair mitochondrial
        heme allocation to ER-resident CYP3A4 or CYP2D6 [PMID:38199567], arguing
        for client-specific rather than bulk heme chaperone activity.
      action: ACCEPT
      reason: >-
        While PGRMC2 is not a transporter in the classical sense, it does
        function in heme transport/trafficking by chaperoning heme to the
        nucleus. This broader process term is appropriate.
      supported_by:
        - reference_id: Reactome:R-HSA-9707606
          supporting_text: >-
            PGRMC2 binds heme reversibly. Also, PGRMC2 can bind to AAAS, a subunit of
            the nuclear pore complex, suggesting nuclear import of the PGRMC2:heme complex through
            the NPC takes place (Jühlen et al, 2016; Parker et al, 2017; Galmozzi et al 2020).
        - reference_id: PMID:38199567
          supporting_text: >-
            The siRNA treatment caused 80 to 85% loss in PGRMC2 expression in
            the cells but this had no impact on CYP protein expression level
            (Fig. 8, A and B) or on the level of CYP 14C-heme incorporation
            (Fig. 8C). Thus, PGRMC2 is not likely to be involved in
            mitochondrial heme allocation to CYP3A4 or 2D6 in our system.
  - term:
      id: GO:0020037
      label: heme binding
    evidence_type: IEA
    original_reference_id: GO_REF:0000107
    review:
      summary: >-
        Heme binding is the primary molecular function of PGRMC2. This is
        well-supported by experimental evidence [PMID:28111073] and is central
        to its function as a heme chaperone.
      action: ACCEPT
      reason: >-
        Heme binding is the core molecular function of PGRMC2, confirmed by
        fragment-based screening in human cells and functional studies.
      supported_by:
        - reference_id: PMID:28111073
          supporting_text: >-
            our initial studies point to heme-related molecules as potential
            candidates to serve this function
        - reference_id: file:human/PGRMC2/PGRMC2-deep-research-perplexity.md
          supporting_text: >-
            Unlike constitutive heme-binding proteins such as myoglobin and
            hemoglobin, which maintain essentially irreversible heme binding
            through multiple coordination interactions, PGRMC2 exhibits
            reversible heme binding characteristic of signaling proteins.
  - term:
      id: GO:0045202
      label: synapse
    evidence_type: IEA
    original_reference_id: GO_REF:0000107
    review:
      summary: >-
        No evidence for synaptic localization or function in the deep research
        or UniProt entry for PGRMC2.
      action: UNDECIDED
      reason: >-
        Unable to find supporting evidence for synaptic localization. This may
        be transferred from ortholog data that needs verification.
      supported_by:
        - reference_id: file:human/PGRMC2/PGRMC2-deep-research-perplexity.md
          supporting_text: >-
            The protein localizes primarily to the endoplasmic reticulum (ER)
            and nuclear envelope.
  - term:
      id: GO:0098978
      label: glutamatergic synapse
    evidence_type: IEA
    original_reference_id: GO_REF:0000107
    review:
      summary: >-
        No evidence for glutamatergic synapse localization in the available
        literature for PGRMC2.
      action: UNDECIDED
      reason: >-
        This appears to be transferred from ortholog data. No direct evidence
        supports glutamatergic synapse localization for human PGRMC2.
      supported_by:
        - reference_id: file:human/PGRMC2/PGRMC2-deep-research-perplexity.md
          supporting_text: >-
            PGRMC2 expression is most abundant in placenta, followed by
            significant expression in adipose tissue, reproductive organs,
            heart, and gastrointestinal tissues.
  - term:
      id: GO:0005635
      label: nuclear envelope
    evidence_type: TAS
    original_reference_id: Reactome:R-HSA-9707606
    review:
      summary: >-
        Reactome pathway shows PGRMC2:heme complex translocates to nucleus
        via interaction with AAAS at the NPC.
      action: ACCEPT
      reason: >-
        Nuclear envelope localization is essential for PGRMC2 function in
        delivering heme to nuclear targets. Well-supported by Reactome curation.
      supported_by:
        - reference_id: Reactome:R-HSA-9707606
          supporting_text: >-
            Also, PGRMC2 can bind to AAAS, a subunit of the nuclear pore complex, suggesting nuclear import of the PGRMC2:heme complex through the NPC takes place
  - term:
      id: GO:0005635
      label: nuclear envelope
    evidence_type: TAS
    original_reference_id: Reactome:R-HSA-9707683
    review:
      summary: >-
        Duplicate nuclear envelope annotation from Reactome heme binding pathway.
      action: ACCEPT
      reason: >-
        Nuclear envelope localization is well-supported and central to PGRMC2
        function in heme delivery.
      supported_by:
        - reference_id: Reactome:R-HSA-9707683
          supporting_text: >-
            Mitochondria-bound PGRMC1 transfers heme to ER-bound PGRMC2, which delivers
            heme to proteins in the ER and nucleus, including heme-responsive transcription
            factors such as Rev-Erbα
  - term:
      id: GO:0005654
      label: nucleoplasm
    evidence_type: TAS
    original_reference_id: Reactome:R-HSA-9707606
    review:
      summary: >-
        PGRMC2 delivers heme to the nucleus, and the heme:PGRMC2 complex may
        transiently enter the nucleoplasm before dissociation.
      action: ACCEPT
      reason: >-
        Nucleoplasm localization is consistent with PGRMC2 function in
        delivering heme to nuclear transcription factors.
      supported_by:
        - reference_id: Reactome:R-HSA-9707856
          supporting_text: >-
            Free heme behaves differently in the nucleus, in the absence of
            PGRMC2. This implies that heme may separate from the PGRMC2:heme
            complex.
  - term:
      id: GO:0005654
      label: nucleoplasm
    evidence_type: TAS
    original_reference_id: Reactome:R-HSA-9707856
    review:
      summary: >-
        Duplicate nucleoplasm annotation from Reactome heme dissociation pathway.
      action: ACCEPT
      reason: >-
        Nucleoplasm localization is supported by Reactome curation of heme
        signaling pathway.
      supported_by:
        - reference_id: Reactome:R-HSA-9707856
          supporting_text: >-
            Free heme behaves differently in the nucleus, in the absence of
            PGRMC2.
  - term:
      id: GO:0005515
      label: protein binding
    evidence_type: IPI
    original_reference_id: PMID:27754849
    review:
      summary: >-
        This study specifically identified PGRMC2 interaction with ALADIN (AAAS),
        a nucleoporin. While the generic protein binding term is used, this
        paper provides important functional context.
      action: KEEP_AS_NON_CORE
      reason: >-
        The interaction with ALADIN is functionally significant for nuclear
        heme delivery. However, protein binding is still a generic term.
      supported_by:
        - reference_id: PMID:27754849
          supporting_text: >-
            Our results suggest an interaction of ALADIN with the microsomal
            protein PGRMC2.
  - term:
      id: GO:0005635
      label: nuclear envelope
    evidence_type: IDA
    original_reference_id: PMID:27754849
    review:
      summary: >-
        Direct experimental evidence for nuclear envelope localization using
        immunofluorescence and confocal microscopy.
      action: ACCEPT
      reason: >-
        Strong experimental evidence from direct visualization showing PGRMC2
        co-localizes with ALADIN and NPC proteins at the nuclear envelope.
      supported_by:
        - reference_id: PMID:27754849
          supporting_text: >-
            We detected that PGRMC2 co-localises with ALADIN and with different
            FG-repeat NUPs [...] to the
            nuclear envelope and the perinuclear ER.
  - term:
      id: GO:0005635
      label: nuclear envelope
    evidence_type: IDA
    original_reference_id: PMID:28111073
    review:
      summary: >-
        Fragment-based screening study that characterized PGRMC2 localization
        and heme binding.
      action: ACCEPT
      reason: >-
        This study provided key evidence for PGRMC2 as a heme-binding protein
        involved in adipocyte differentiation and nuclear heme delivery.
      supported_by:
        - reference_id: PMID:28111073
          supporting_text: >-
            We further combine fragment-based chemical proteomics with
            phenotypic screening to identify small molecules that promote
            adipocyte differentiation by engaging the poorly characterized
            membrane protein PGRMC2.
  - term:
      id: GO:0005783
      label: endoplasmic reticulum
    evidence_type: IDA
    original_reference_id: PMID:27754849
    review:
      summary: >-
        Direct experimental evidence for ER localization from immunofluorescence
        studies.
      action: ACCEPT
      reason: >-
        ER localization is experimentally confirmed and central to PGRMC2
        function in the heme trafficking pathway.
      supported_by:
        - reference_id: PMID:27754849
          supporting_text: >-
            Visualising PGRMC2 in the cell using immunofluorescence and confocal
            microscopy has shown the presence of PGRMC2 at the central ER, and,
            interestingly, at the nuclear envelope and the perinuclear ER.
  - term:
      id: GO:0020037
      label: heme binding
    evidence_type: IDA
    original_reference_id: PMID:28111073
    review:
      summary: >-
        Direct experimental evidence for heme binding from fragment-based
        screening and functional studies in human cells.
      action: ACCEPT
      reason: >-
        Heme binding is the core molecular function of PGRMC2. This study
        provided key evidence identifying heme-related molecules as PGRMC2
        ligands.
      supported_by:
        - reference_id: PMID:28111073
          supporting_text: >-
            our initial studies point to heme-related molecules as potential
            candidates to serve this function
  - term:
      id: GO:0060612
      label: adipose tissue development
    evidence_type: IMP
    original_reference_id: PMID:28111073
    review:
      summary: >-
        Functional studies showed PGRMC2 regulates adipocyte differentiation.
        Deep research confirms PGRMC2 role in brown adipose tissue thermogenesis
        and adipogenesis.
      action: KEEP_AS_NON_CORE
      reason: >-
        PGRMC2 plays important roles in adipose tissue function and development,
        particularly in brown adipose tissue thermogenesis. This is a downstream
        physiological consequence of the molecular heme-chaperone role; recent
        work also highlights tissue-specific PGRMC2 functions at the maternal-
        fetal interface, ciliogenesis/proliferation, and endometrial epithelial
        proliferation that are not adipose-related, supporting that adipose
        development is a non-core pleiotropic process.
      supported_by:
        - reference_id: PMID:28111073
          supporting_text: >-
            identify small molecules that promote adipocyte differentiation by
            engaging the poorly characterized membrane protein PGRMC2
        - reference_id: file:human/PGRMC2/PGRMC2-deep-research-perplexity.md
          supporting_text: >-
            Among PGRMC2's most thoroughly characterized physiological functions
            is its role in regulating brown adipocyte metabolism and
            thermogenesis.
  - term:
      id: GO:0005635
      label: nuclear envelope
    evidence_type: IDA
    original_reference_id: PMID:25468996
    review:
      summary: >-
        This paper is about E-cadherin interactome proteomics. PGRMC2 was
        identified in proximity biotinylation, which does not directly support
        nuclear envelope localization.
      action: ACCEPT
      reason: >-
        While this specific paper used proximity proteomics and may not directly
        demonstrate nuclear envelope localization, other evidence strongly
        supports this localization for PGRMC2.
      supported_by:
        - reference_id: PMID:25468996
          supporting_text: >-
            We used proximity biotinylation and quantitative proteomics to
            identify 561 proteins in the vicinity of the cytoplasmic tail of
            E-cadherin.
  - term:
      id: GO:0016020
      label: membrane
    evidence_type: HDA
    original_reference_id: PMID:19946888
    review:
      summary: >-
        High-throughput membrane proteomics study of NK cells identified PGRMC2
        as a membrane protein.
      action: ACCEPT
      reason: >-
        PGRMC2 is a single-pass transmembrane protein, consistent with
        identification in membrane proteome.
      supported_by:
        - reference_id: PMID:19946888
          supporting_text: >-
            The present study was initiated to define the composition of the
            membrane proteome of the Natural Killer (NK) like cell line YTS.
  - term:
      id: GO:0003707
      label: nuclear steroid receptor activity
    evidence_type: TAS
    original_reference_id: PMID:9705155
    review:
      summary: >-
        This 1998 paper described initial cloning of PGRMC2 (called Dg6) as a
        putative steroid membrane receptor. However, subsequent research has
        shown PGRMC2 is primarily a heme chaperone, not a steroid receptor.
      action: REMOVE
      reason: >-
        Modern research has definitively shown PGRMC2 binds heme, not
        progesterone with high affinity. This annotation reflects outdated
        understanding from the original cloning paper.
      supported_by:
        - reference_id: PMID:9705155
          supporting_text: >-
            The two proteins are the first putative steroid membrane receptors
            cloned from man.
        - reference_id: file:human/PGRMC2/PGRMC2-deep-research-perplexity.md
          supporting_text: >-
            Initially characterized as a potential progesterone receptor due to
            nomenclature and early biochemical observations, PGRMC2 has emerged
            through recent research as a sophisticated intracellular heme
            chaperone.
  - term:
      id: GO:0005496
      label: steroid binding
    evidence_type: TAS
    original_reference_id: PMID:9705155
    review:
      summary: >-
        Based on original 1998 cloning paper when PGRMC2 was thought to be a
        steroid receptor. This is now known to be incorrect.
      action: MODIFY
      reason: >-
        PGRMC2 binds heme, not steroids, with high affinity. The correct
        molecular function term is heme binding.
      proposed_replacement_terms:
        - id: GO:0020037
          label: heme binding
      supported_by:
        - reference_id: PMID:9705155
          supporting_text: >-
            Both proteins contain a putative transmembrane domain and a highly
            conserved stretch of 58 amino acids.
        - reference_id: file:human/PGRMC2/PGRMC2-deep-research-perplexity.md
          supporting_text: >-
            This protein's discovery that it binds heme rather than progesterone
            with high affinity fundamentally reframed our understanding of
            non-classical steroid signaling.
  - term:
      id: GO:0016020
      label: membrane
    evidence_type: TAS
    original_reference_id: PMID:9705155
    review:
      summary: >-
        Original cloning paper correctly identified PGRMC2 as a membrane protein.
      action: ACCEPT
      reason: >-
        PGRMC2 is a single-pass transmembrane protein. This aspect of the
        original characterization remains accurate.
      supported_by:
        - reference_id: PMID:9705155
          supporting_text: >-
            Both proteins contain a putative transmembrane domain and a highly
            conserved stretch of 58 amino acids.
references:
  - id: GO_REF:0000033
    title: Annotation inferences using phylogenetic trees
    findings: []
  - id: GO_REF:0000043
    title: Gene Ontology annotation based on UniProtKB/Swiss-Prot keyword mapping
    findings: []
  - id: GO_REF:0000044
    title: >-
      Gene Ontology annotation based on UniProtKB/Swiss-Prot Subcellular
      Location vocabulary mapping
    findings: []
  - id: GO_REF:0000107
    title: >-
      Automatic transfer of experimentally verified manual GO annotation data
      to orthologs using Ensembl Compara
    findings: []
  - id: GO_REF:0000108
    title: >-
      Automatic assignment of GO terms using logical inference, based on
      inter-ontology links
    findings: []
  - id: GO_REF:0000120
    title: Combined Automated Annotation using Multiple IEA Methods
    findings: []
  - id: PMID:19946888
    title: Defining the membrane proteome of NK cells.
    findings:
      - statement: >-
          PGRMC2 identified in membrane proteome of NK cell line YTS through
          mass spectrometry.
  - id: PMID:25468996
    title: >-
      E-cadherin interactome complexity and robustness resolved by quantitative
      proteomics.
    findings:
      - statement: >-
          PGRMC2 identified in proximity proteomics of E-cadherin interactome.
  - id: PMID:27173435
    title: >-
      An organelle-specific protein landscape identifies novel diseases and
      molecular mechanisms.
    findings:
      - statement: High-throughput interactome study.
  - id: PMID:27599036
    title: >-
      A Novel Role for Progesterone Receptor Membrane Component 1 (PGRMC1): A
      Partner and Regulator of Ferrochelatase.
    findings:
      - statement: >-
          Describes PGRMC1-ferrochelatase interaction in heme synthesis pathway
          that PGRMC2 participates in downstream.
  - id: PMID:27754849
    title: >-
      Identification of a novel putative interaction partner of the nucleoporin
      ALADIN.
    findings:
      - statement: >-
          PGRMC2 interacts with nucleoporin ALADIN (AAAS) and co-localizes at
          nuclear envelope and perinuclear ER.
        supporting_text: >-
          We detected that PGRMC2 co-localises with ALADIN and with different
          FG-repeat NUPs [...] to the
          nuclear envelope and the perinuclear ER.
  - id: PMID:28111073
    title: Ligand and Target Discovery by Fragment-Based Screening in Human Cells.
    findings:
      - statement: >-
          PGRMC2 identified as target for small molecules promoting adipocyte
          differentiation; binds heme-related molecules.
        supporting_text: >-
          our initial studies point to heme-related molecules as potential
          candidates to serve this function
  - id: PMID:29513927
    title: >-
      Comparative Protein Interaction Network Analysis Identifies Shared and
      Distinct Functions for the Human ROCO Proteins.
    findings:
      - statement: High-throughput protein interaction study.
  - id: PMID:32296183
    title: A reference map of the human binary protein interactome.
    findings:
      - statement: Large-scale binary interactome mapping.
  - id: PMID:33961781
    title: >-
      Dual proteome-scale networks reveal cell-specific remodeling of the human
      interactome.
    findings:
      - statement: Proteome-scale interaction network study.
  - id: PMID:35271311
    title: >-
      OpenCell: Endogenous tagging for the cartography of human cellular
      organization.
    findings:
      - statement: Cellular organization study using endogenous protein tagging.
  - id: PMID:40355756
    title: The solute carrier superfamily interactome.
    findings:
      - statement: Solute carrier interactome study.
  - id: PMID:9705155
    title: Cloning and tissue expression of two putative steroid membrane receptors.
    findings:
      - statement: >-
          Original cloning of PGRMC2 (Dg6) as putative steroid receptor. Later
          research showed it is primarily a heme chaperone.
        supporting_text: >-
          The two proteins are the first putative steroid membrane receptors
          cloned from man.
  - id: Reactome:R-HSA-9707606
    title: PGRMC2:Hemes translocate to the nucleus
    findings:
      - statement: >-
          PGRMC2 binds heme reversibly and can bind AAAS for nuclear import of
          heme complex.
        supporting_text: >-
          PGRMC2 binds heme reversibly. Also, PGRMC2 can bind to AAAS, a subunit of
          the nuclear pore complex, suggesting nuclear import of the PGRMC2:heme complex through
          the NPC takes place
  - id: Reactome:R-HSA-9707683
    title: PGRMC2 binds Hemes
    findings:
      - statement: >-
          PGRMC1 transfers heme to PGRMC2, which delivers heme to ER and nuclear
          proteins including Rev-Erba.
        supporting_text: >-
          Mitochondria-bound PGRMC1 transfers heme to ER-bound PGRMC2, which delivers
          heme to proteins in the ER and nucleus, including heme-responsive transcription
          factors such as Rev-Erbα
  - id: Reactome:R-HSA-9707856
    title: PGRMC2:Hemes dissociates
    findings:
      - statement: Heme dissociates from PGRMC2 in the nucleus.
        supporting_text: >-
          Free heme behaves differently in the nucleus, in the absence of PGRMC2.
          This implies that heme may separate from the PGRMC2:heme complex.
  - id: file:human/PGRMC2/PGRMC2-deep-research-perplexity.md
    title: Deep research on PGRMC2 function
    findings:
      - statement: >-
          PGRMC2 is an intracellular heme chaperone that delivers labile heme to
          the nucleus, regulating heme-responsive transcription factors.
        supporting_text: >-
          Initially characterized as a potential progesterone receptor due to
          nomenclature and early biochemical observations, PGRMC2 has emerged
          through recent research as a sophisticated intracellular heme chaperone
          and steroid hormone mediator whose primary function involves the highly
          regulated trafficking of labile heme from mitochondrial synthesis sites
          to nuclear and cytoplasmic target proteins.
  - id: file:human/PGRMC2/PGRMC2-deep-research-falcon.md
    title: Deep research on PGRMC2 function (falcon/Edison)
    findings:
      - statement: >-
          MAPR/PGRMC2 is a cytochrome b5-like heme/steroid-binding domain
          protein distinct from PAQR/mPR 7TM membrane progesterone receptors;
          progesterone binding evidence is weaker for non-PGRMC1 MAPRs.
        supporting_text: >-
          MAPR proteins are often discussed as "non-classical" membrane
          progesterone receptors. However, mechanistic certainty varies by
          paralog. Reviews note that spectroscopic progesterone binding is
          established for PGRMC1, while progesterone binding "is still not
          proven for other MAPRs"—a caution that applies to PGRMC2.
      - statement: >-
          Recent functional evidence implicates PGRMC2 in immune homeostasis at
          the maternal-fetal interface, ciliogenesis/proliferation control, and
          endometrial epithelial proliferation, but cautions against assigning
          PGRMC2 a universal heme-allocation role for ER cytochromes P450.
        supporting_text: >-
          The 2024 JBC study showing no effect of strong PGRMC2 knockdown on
          heme insertion into CYP3A4/2D6 suggests either: PGRMC2 is not
          required for this heme allocation pathway, or its role is
          context-specific (cell type, client hemeprotein class, or redundancy
          with other heme chaperones). This kind of "negative result" is
          practically important for functional annotation: it constrains
          hypotheses that broadly assign PGRMC2 as a universal heme delivery
          factor for ER CYPs.
  - id: PMID:38199567
    title: >-
      Functional maturation of cytochromes P450 3A4 and 2D6 relies on GAPDH-
      and Hsp90-Dependent heme allocation.
    findings:
      - statement: >-
          PGRMC2 knockdown by ~80-85% in HEK293T cells did not impair
          mitochondrial 14C-heme allocation to ER-localized CYP3A4 or CYP2D6,
          arguing PGRMC2 is not a general heme chaperone for ER CYPs.
        supporting_text: >-
          The siRNA treatment caused 80 to 85% loss in PGRMC2 expression in
          the cells but this had no impact on CYP protein expression level
          (Fig. 8, A and B) or on the level of CYP 14C-heme incorporation
          (Fig. 8C). Thus, PGRMC2 is not likely to be involved in
          mitochondrial heme allocation to CYP3A4 or 2D6 in our system.
  - id: PMID:39179795
    title: >-
      PGRMC2 and HLA-G regulate immune homeostasis in a microphysiological
      model of human maternal-fetal membrane interface.
    findings:
      - statement: >-
          CRISPR/Cas9 PGRMC2 knockout in immortalized human chorion trophoblast
          cells disrupts immune homeostasis at the chorio-decidual interface;
          PGRMC2 acts upstream of HLA-G expression, restrains inflammation, and
          modulates mesenchymal-epithelial transition.
        supporting_text: >-
          HLA-G and PGRMC2 are found to be vital to immune homeostasis at the
          CDi, with PGRMC2 serving as an upstream regulator of inflammation,
          HLA-G expression, and mesenchymal-epithelial transition, and HLA-G
          serving as a frontline
  - id: PMID:39268086
    title: Identifying the roles of miR-17 in ciliogenesis and cell cycle.
    findings:
      - statement: >-
          PGRMC2 was identified by ciliary proteomics as a membrane protein
          localized to the primary cilium in porcine LL-CPK1 epithelial cells;
          PGRMC2 knockdown reduced cilia number and length and produced a
          hyperproliferative phenotype. Direct evidence is in a non-human
          system; relevance to human PGRMC2 is by inference.
        supporting_text: >-
          Using unbiased proteomic studies, we most recently discovered five
          new membrane proteins localized in the cilia: bone morphogenetic
          type 2 (BMPR2), transferrin receptor-1 (TfR1), junctional adhesion
          molecule-A (JAM-A), protein tyrosine phosphatase receptor sigma
          (PTPRS), and progesterone receptor membrane component-2 (PGRMC2)
  - id: PMID:39263088
    title: >-
      PGRMC2 influences the onset of postmenopausal osteoporosis through
      disulfidptosis in monocytes: evidence from experimental validation and
      Mendelian randomization.
    findings:
      - statement: >-
          Bioinformatic and Mendelian randomization analyses associate PGRMC2
          with postmenopausal osteoporosis risk (MR OR 0.6836, p=0.0048; ROC
          AUC 0.665); PGRMC2 protein is reduced in ovariectomized mouse bone.
        supporting_text: >-
          A 2024 study integrated bulk expression, single-cell data, and
          experimental validation, proposing PGRMC2 as a gene linked to
          postmenopausal osteoporosis mechanisms (via "disulfidptosis" in
          monocytes/macrophages).
  - id: PMID:40227710
    title: >-
      Uterine Pgrmc2 Deficiency Attenuates Endometrial Hyperplasia and Cancer
      and Prolongs Lifespan in a Pten Loss-of-Function-Induced Cancer Model.
    findings:
      - statement: >-
          Conditional uterine Pgrmc2 ablation in mice attenuates Pten
          loss-of-function-induced endometrial hyperplasia and carcinoma and
          prolongs lifespan, in part by inhibiting glandular epithelial cell
          proliferation; consistent with a permissive role of PGRMC2 in
          endometrial epithelial proliferation.
        supporting_text: >-
          The ablation of Pgrmc2 clearly attenuated the incidence/development,
          progression, and aggressiveness of Pten loss-of-function-induced
          endometrial cancer by inhibiting endometrial glandular epithelial
          cell proliferation (Figure 6).
  - id: PMID:28396637
    title: >-
      Membrane Associated Progesterone Receptors: Promiscuous Proteins with
      Pleiotropic Functions - Focus on Interactions with Cytochromes P450.
    findings:
      - statement: >-
          Review placing PGRMC2 in the MAPR/cytochrome b5-like family and
          noting that direct progesterone binding is established for PGRMC1
          but not proven for PGRMC2.
  - id: PMID:34791092
    title: >-
      Membrane-Initiated Estrogen, Androgen, and Progesterone Receptor
      Signaling in Health and Disease.
    findings:
      - statement: >-
          Review distinguishing PGRMC/MAPR family proteins (cytochrome
          b5-like heme/steroid domain; CYP interactions) from PAQR/mPR
          7-transmembrane G-protein coupled membrane progesterone receptors.
core_functions:
  - description: >-
      PGRMC2 functions as a reversible heme-binding protein that receives heme
      from PGRMC1 at the ER and delivers it to the nucleus, where it regulates
      heme-responsive transcription factors such as Rev-Erba and BACH1.
    molecular_function:
      id: GO:0020037
      label: heme binding
  # Second core_function entry for BAT thermogenesis / adipocyte
  # differentiation removed per PR #751 review feedback: contradicts the
  # explicit KEEP_AS_NON_CORE decision on GO:0060612 (adipose tissue
  # development) in existing_annotations. Adipose phenotypes are
  # downstream consequences of the heme-delivery role already captured
  # in the first core_function above.
suggested_questions:
  - question: >-
      What is the exact mechanism by which PGRMC2 transfers heme from PGRMC1 to
      nuclear transcription factors? The relay mechanism between PGRMC1 and
      PGRMC2 is central to understanding heme signaling, but structural details
      of the handoff are unclear.
  - question: >-
      Does PGRMC2 have any residual steroid binding activity, or is heme binding
      its exclusive ligand interaction? The historical characterization as a
      steroid receptor may have had some basis, but modern evidence strongly
      favors heme as the primary ligand.
  - question: >-
      Which specific hemeproteins (other than Rev-Erba/BACH1 in the nucleus)
      are bona fide clients of PGRMC2-mediated heme delivery? Negative results
      for CYP3A4 and CYP2D6 [PMID:38199567] argue PGRMC2 is not a generic ER
      heme chaperone and call for a defined client list.
  - question: >-
      How does PGRMC2 act upstream of HLA-G expression and restrain
      inflammation in chorion trophoblasts [PMID:39179795]? Is this a
      downstream consequence of heme-regulated transcription factor activity
      (e.g., BACH1, NRF2) or an independent function?
suggested_experiments:
  - description: >-
      Structural studies of PGRMC2 with and without heme bound to determine the
      molecular basis for reversible heme binding and transfer. This would
      clarify the chaperone mechanism and potentially enable drug design for
      metabolic diseases.
  - description: >-
      Tissue-specific PGRMC2 knockout studies in liver and brain to determine
      functions beyond adipose tissue. Deep research suggests PGRMC2 may have
      tissue-specific functions that are currently undercharacterized.
  - description: >-
      Map PGRMC2-dependent heme client hemeproteins using comparative heme
      proteomics in PGRMC2 knockout vs wild-type cells across cell types,
      reconciling positive nuclear results (Rev-Erba, BACH1) with negative
      ER-CYP results [PMID:38199567].
  - description: >-
      Test whether PGRMC2 modulation of HLA-G and inflammatory cytokines at
      the maternal-fetal interface [PMID:39179795] depends on heme binding by
      reconstituting PGRMC2 knockout chorion trophoblasts with heme-binding
      mutants.
status: COMPLETE

PGRMC2

Gene Description

Existing Annotations Review

Core Functions

PGRMC2 functions as a reversible heme-binding protein that receives heme from PGRMC1 at the ER and delivers it to the nucleus, where it regulates heme-responsive transcription factors such as Rev-Erba and BACH1.

References

Suggested Questions for Experts

Suggested Experiments

Deep Research

Falcon

Comprehensive research report: Human PGRMC2 (UniProt O15173) functional annotation

0) Target verification and disambiguation (critical)

1) Key concepts and definitions (current understanding)

1.1 MAPR/PGRMC family and domain concepts

1.2 What is known (and not known) about ligand binding and molecular function

1.3 Subcellular localization concepts

2) Recent developments and latest research (prioritizing 2023–2024)

2.1 Maternal–fetal interface immune homeostasis (2024)

2.2 Postmenopausal osteoporosis: biomarker performance + Mendelian randomization (2024)

2.3 Ciliogenesis and cell-cycle/proliferation control (2024)

2.4 Heme allocation to ER drug-metabolizing CYPs: a negative/limiting result (2024)

2.5 Colorectal cancer: PGRMC2 downregulation in tumor tissues (2023)

3) Current applications and real-world implementations

3.1 Biomarker development (emerging)

3.2 Microphysiological models (“organ-on-chip”) for mechanistic and translational immunology

3.3 Therapeutic targeting (preclinical, indirect)

4) Expert opinions and analysis (authoritative synthesis)

4.1 Conceptual consensus: MAPR proteins bridge steroid signaling, heme biology, and CYP/sterol metabolism

4.2 Key uncertainty emphasized in reviews

4.3 Interpreting conflicting/negative mechanistic evidence

5) Relevant statistics and data (recent studies)

6) Evidence summary table

7) Visual evidence highlight (figure)

8) Practical functional annotation (recommended phrasing)

9) URLs and publication dates (key sources)

10) Notes on limitations

Artifacts

Citations

Perplexity

Progesterone Receptor Membrane Component 2: A Critical Intracellular Heme Chaperone and Multifunctional Regulator of Metabolic, Reproductive, and Cardiac Physiology

Molecular Classification, Structure, and Evolutionary Positioning

Heme Binding, Trafficking, and Intracellular Localization

Role in Adipose Tissue Thermogenesis and Metabolic Homeostasis

Reproductive Function and Placental Development

Cardiac Function and Pressure-Volume Regulation

Cytochrome P450 Interactions and Drug Metabolism

Cell Cycle Regulation and Tumor-Suppressive Functions

Placental Expression and Trophoblast Biology

Spermatozoal Function and Male Reproductive Biology

Fetal Membrane Physiology and Parturition

Protein Interactions and Signaling Complexes

Conclusion and Future Perspectives

Citations

📄 View Raw YAML