PPP1R15B encodes CReP (constitutive repressor of eIF2alpha phosphorylation), the constitutively expressed, short-lived paralog of GADD34 (PPP1R15A) and a non-catalytic regulatory subunit of protein phosphatase 1. CReP binds the PP1 catalytic subunit through a C-terminal PP1-binding region and captures the trimeric eIF2 substrate through a largely disordered central recruitment module whose helical elements clamp eIF2gamma and the C-terminal domain of eIF2alpha, far from the Ser51 phosphosite, presenting it to PP1 for dephosphorylation. The resulting holophosphatase keeps basal eIF2alpha phosphorylation low in unstressed cells; loss of CReP raises phospho-eIF2alpha and activates the integrated stress response. The CReP-PP1 complex is a target of the eIF2alpha dephosphorylation inhibitor salubrinal. Biallelic PPP1R15B variants that impair PP1 or eIF2 binding cause a syndrome of microcephaly, short stature, intellectual disability and impaired glucose metabolism.
| GO Term | Evidence | Action | Reason |
|---|---|---|---|
| GO:0000164 protein phosphatase type 1 complex | IBA GO_REF:0000033 | ACCEPT | Summary: IBA (PTN001046909, PPP1R15 family) for PP1 complex membership. Reason: PPP1R15B (CReP) is the constitutive PP1 regulatory subunit of an eIF2alpha holophosphatase; patient-cell co-IP confirms the PPP1R15B-PPP1C complex. Supporting Evidence: PMID:26307080 Reciprocal co-immunoprecipitation experiments showed a strong interaction of PPP1R15B with PPP1C in control lymphoblast cells and very little interaction with non-specific IgG, indicating the specificity of the immunoprecipitation reactions |
| GO:0000164 protein phosphatase type 1 complex | IDA PMID:26307080 Homozygous mutation in the eukaryotic translation initiation... | ACCEPT | Summary: Co-immunoprecipitation of PPP1R15B with PPP1C in human lymphoblasts; the R658C patient variant in the PP1-binding site reduces it. Reason: Direct evidence for the PPP1R15B-PP1 holoenzyme. Supporting Evidence: PMID:26307080 We show that patient cells have greatly diminished levels of PPP1R15B-PPP1C interaction, which results in increased eIF2Ξ± phosphorylation and resistance to cellular stress. |
| GO:0000164 protein phosphatase type 1 complex | IEA GO_REF:0000107 | ACCEPT | Summary: Ensembl ortholog transfer from mouse Ppp1r15b. Reason: Consistent with direct human evidence. Supporting Evidence: PMID:26307080 PPP1R15A and PPP1R15B function by recruiting the phosphatase PPP1C to eIF2 (3β6). |
| GO:0000164 protein phosphatase type 1 complex | IPI PMID:34847777 Substrate recognition determinants of human eIF2Ξ± phosphatas... | ACCEPT | Summary: IPI (DisProt) placing PPP1R15B in the PP1 complex; WITH/FROM lists PPP1CA and Q9BY44. Reason: The holoenzyme claim is right. The WITH/FROM UniProtKB:Q9BY44 is EIF2A (eIF-2A), not the eIF2alpha subunit EIF2S1 (P05198) that the paper studies. Supporting Evidence: PMID:34847777 The phosphatases are composed of the catalytic subunit PP1 and one of two related non-catalytic subunits, PPP1R15A or PPP1R15B (R15A or R15B). |
| GO:0000164 protein phosphatase type 1 complex | IPI PMID:38159565 Recruitment of trimeric eIF2 by phosphatase non-catalytic su... | ACCEPT | Summary: IPI (DisProt) placing PPP1R15B in the PP1 complex with trimeric eIF2; WITH/FROM lists PPP1CA and Q9BY44. Reason: The holoenzyme claim is right. The WITH/FROM Q9BY44 (EIF2A, eIF-2A) is wrong; the paper's substrate is trimeric eIF2, whose R15B contacts lie on eIF2gamma (EIF2S3) and the C-terminal domain of eIF2alpha (EIF2S1). Supporting Evidence: PMID:38159565 The protein phosphatase PP1 is the catalytic subunit of many holoenzymes that dephosphorylate serine/threonine residues. |
| GO:0000164 protein phosphatase type 1 complex | ISS GO_REF:0000024 | ACCEPT | Summary: ISS from mouse Ppp1r15b. Reason: Consistent with direct human evidence. Supporting Evidence: PMID:26307080 PPP1R15A and PPP1R15B function by recruiting the phosphatase PPP1C to eIF2 (3β6). |
| GO:0001933 negative regulation of protein phosphorylation | IMP PMID:26307080 Homozygous mutation in the eukaryotic translation initiation... | MODIFY | Summary: Patient R658C cells with impaired PPP1R15B-PPP1C binding show increased eIF2alpha phosphorylation. Reason: The observation is real, but PPP1R15B lowers phospho-eIF2alpha by promoting its dephosphorylation, not by restraining phosphorylation. The precise process is GO:0036496 regulation of translational initiation by eIF2 alpha dephosphorylation (lateral correction). Proposed replacements: regulation of translational initiation by eIF2 alpha dephosphorylation Supporting Evidence: PMID:26307080 We show that patient cells have greatly diminished levels of PPP1R15B-PPP1C interaction, which results in increased eIF2Ξ± phosphorylation and resistance to cellular stress. PMID:14638860 Here, we report on identification of a regulatory subunit of a constitutive eIF2Ξ± phosphatase complex that regulates basal levels of eIF2Ξ± phosphorylation. |
| GO:0005515 protein binding | IPI PMID:15231748 Functional proteomics mapping of a human signaling pathway. | MODIFY | Summary: Two-hybrid interaction with PPP1CA (Smad-pathway interactome). Reason: Binding the PP1 catalytic subunit is the defining interaction of a PP1 regulatory subunit; replaced with protein phosphatase 1 binding. Proposed replacements: protein phosphatase 1 binding Supporting Evidence: PMID:26307080 PPP1R15B functions by association with PPP1C through a binding site comprising residues 513β713 (4); the familial variant is located within this critical domain. |
| GO:0005515 protein binding | IPI PMID:21382349 Identification of the human testis protein phosphatase 1 int... | MODIFY | Summary: Testis PP1 interactome (PPP1CA). Reason: Replaced with protein phosphatase 1 binding. Proposed replacements: protein phosphatase 1 binding Supporting Evidence: PMID:21382349 Identification of the human testis protein phosphatase 1 interactome. |
| GO:0005515 protein binding | IPI PMID:22321011 Protein phosphatase 1Ξ± interacting proteins in the human bra... | MODIFY | Summary: Brain PP1alpha interactome (PPP1CA). Reason: Replaced with protein phosphatase 1 binding. Proposed replacements: protein phosphatase 1 binding Supporting Evidence: PMID:22321011 Protein phosphatase 1Ξ± interacting proteins in the human brain. |
| GO:0005515 protein binding | IPI PMID:26307080 Homozygous mutation in the eukaryotic translation initiation... | MODIFY | Summary: PPP1CC interaction in the patient-variant study. Reason: PPP1CC is a PP1 catalytic isoform; replaced with protein phosphatase 1 binding. Proposed replacements: protein phosphatase 1 binding Supporting Evidence: PMID:26307080 Reciprocal co-immunoprecipitation experiments showed a strong interaction of PPP1R15B with PPP1C in control lymphoblast cells |
| GO:0005515 protein binding | IPI PMID:28330616 Systematic Analysis of Human Protein Phosphatase Interaction... | MODIFY | Summary: Phosphatase interactome (PPP1CC). Reason: Replaced with protein phosphatase 1 binding. Proposed replacements: protein phosphatase 1 binding Supporting Evidence: PMID:28330616 Systematic Analysis of Human Protein Phosphatase Interactions and Dynamics. |
| GO:0005515 protein binding | IPI PMID:28330616 Systematic Analysis of Human Protein Phosphatase Interaction... | MODIFY | Summary: Phosphatase interactome (PPP1CA). Reason: Replaced with protein phosphatase 1 binding. Proposed replacements: protein phosphatase 1 binding Supporting Evidence: PMID:28330616 Systematic Analysis of Human Protein Phosphatase Interactions and Dynamics. |
| GO:0005515 protein binding | IPI PMID:32296183 A reference map of the human binary protein interactome. | REMOVE | Summary: HuRI binary interaction with TRIM23. Reason: Uninformative protein binding from a high-throughput screen; no function identified. Removal does not dispute the interaction. 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... | MODIFY | Summary: Proteome-scale interaction with PPP1CC. Reason: Replaced with protein phosphatase 1 binding. Proposed replacements: protein phosphatase 1 binding Supporting Evidence: PMID:33961781 Dual proteome-scale networks reveal cell-specific remodeling of the human interactome. |
| GO:0005783 endoplasmic reticulum | IBA GO_REF:0000033 | KEEP AS NON CORE | Summary: IBA (PTN001046909) ER, is_active_in; seeds are Drosophila and human GADD34. Reason: The PAINT node rests on GADD34-type ER targeting by an N-terminal amphipathic helix; no PPP1R15B-specific localization was in the sources reviewed here, and the patient study reports no change in its localization without naming the compartment. The organelle claim is plausible by descent but unverified for CReP itself, so it is kept as non-core rather than core. Supporting Evidence: PMID:26307080 Immunodetection of PPP1R15B in control and patient lymphoblast cell lines demonstrated no overt changes in PPP1R15B localization. |
| GO:0008157 protein phosphatase 1 binding | IPI PMID:34847777 Substrate recognition determinants of human eIF2Ξ± phosphatas... | ACCEPT | Summary: IPI (DisProt) PP1 binding of R15B fragments. Reason: Core interaction. Supporting Evidence: PMID:34847777 Activity assays in cells showed that R15A325-674 and R15B340-713, encompassing the substrate-binding region and the PP1-binding region, exhibit wild-type activity. |
| GO:0008157 protein phosphatase 1 binding | IPI PMID:38159565 Recruitment of trimeric eIF2 by phosphatase non-catalytic su... | ACCEPT | Summary: IPI PP1 binding in the R15B-eIF2 recruitment study. Reason: Core interaction. Supporting Evidence: PMID:38159565 How these enzymes recruit their substrates is largely unknown. |
| GO:0019888 protein phosphatase regulator activity | IBA GO_REF:0000033 | ACCEPT | Summary: IBA protein phosphatase regulator activity (PTN001046909). Reason: Core activity of the PPP1R15 family; CReP directs PP1 to eIF2alpha. Supporting Evidence: PMID:14638860 Here, we report on identification of a regulatory subunit of a constitutive eIF2Ξ± phosphatase complex that regulates basal levels of eIF2Ξ± phosphorylation. |
| GO:0019888 protein phosphatase regulator activity | IEA GO_REF:0000107 | ACCEPT | Summary: Ensembl ortholog transfer from mouse. Reason: Consistent with direct evidence. Supporting Evidence: file:human/PPP1R15B/PPP1R15B-uniprot.txt Maintains low levels of EIF2S1 phosphorylation in unstressed cells by promoting its dephosphorylation by PP1. |
| GO:0019888 protein phosphatase regulator activity | IEP PMID:34847777 Substrate recognition determinants of human eIF2Ξ± phosphatas... | ACCEPT | Summary: IEP (DisProt) for regulator activity from R15 truncation activity assays. Reason: The term is right; IEP is an odd code for an MF, but the paper's activity assays support it. Supporting Evidence: PMID:34847777 Activity assays in cells showed that R15A325-674 and R15B340-713, encompassing the substrate-binding region and the PP1-binding region, exhibit wild-type activity. |
| GO:0019888 protein phosphatase regulator activity | IMP PMID:38159565 Recruitment of trimeric eIF2 by phosphatase non-catalytic su... | ACCEPT | Summary: IMP; the N423D patient variant reduces substrate binding and dephosphorylation. Reason: Direct mutational evidence for R15B-directed eIF2 dephosphorylation. Supporting Evidence: PMID:38159565 A homozygous N423D variant, adjacent to H1, reducing substrate binding and dephosphorylation was discovered in a rare syndrome with microcephaly, developmental delay, and intellectual disability. |
| GO:0034976 response to endoplasmic reticulum stress | IBA GO_REF:0000033 | KEEP AS NON CORE | Summary: IBA response to ER stress. Reason: CReP is constitutive and sets basal eIF2alpha phosphorylation; knockdown or salubrinal inhibition of CReP-PP1 protects cells from ER (and oxidative) stress, so it does influence the ER stress response, but this is peripheral to its basal role. Supporting Evidence: PMID:14638860 Blocking CReP expression activated the ISR and protected cells from oxidative, nitrosative, and ER stress |
| GO:0051246 regulation of protein metabolic process | IEA GO_REF:0000117 | TOO GENERAL | Summary: ARBA-based IEA for regulation of protein metabolic process. Reason: True but uninformative beside regulation of translational initiation by eIF2 alpha dephosphorylation (proposed replacement for the IMP row). Supporting Evidence: file:human/PPP1R15B/PPP1R15B-uniprot.txt Maintains low levels of EIF2S1 phosphorylation in unstressed cells by promoting its dephosphorylation by PP1. |
| GO:0060090 molecular adaptor activity | IDA PMID:15705855 A selective inhibitor of eIF2alpha dephosphorylation protect... | MODIFY | Summary: Molecular adaptor activity (IDA) cited to the salubrinal paper (abstract-only). Reason: R15B bridges PP1 and its substrate eIF2; it binds trimeric eIF2 with high affinity independently of PP1 and presents it for dephosphorylation. That is GO:0140767 enzyme-substrate adaptor activity, an is_a descendant of molecular adaptor activity. Proposed replacements: enzyme-substrate adaptor activity Supporting Evidence: PMID:38159565 These findings explain how R15B captures its 125 kDa substrate by binding the far end of the complex relative to the phosphosite to present it for dephosphorylation by PP1, a paradigm of broad relevance. PMID:15705855 we identified salubrinal, a selective inhibitor of cellular complexes that dephosphorylate eukaryotic translation initiation factor 2 subunit alpha (eIF2alpha) |
| GO:0071074 eukaryotic initiation factor eIF2 binding | EXP PMID:38159565 Recruitment of trimeric eIF2 by phosphatase non-catalytic su... | ACCEPT | Summary: EXP binding of R15B to trimeric eIF2 (HDX-MS, binding assays). Reason: Direct evidence for eIF2 substrate binding, core to function. Supporting Evidence: PMID:38159565 We found that R15B binds eIF2 with high affinity, without requiring PP1 or any other factors. |
| GO:0071074 eukaryotic initiation factor eIF2 binding | IMP PMID:38159565 Recruitment of trimeric eIF2 by phosphatase non-catalytic su... | ACCEPT | Summary: IMP; H1/H2 clamp mutants and N423D reduce eIF2 binding. Reason: Direct mutational evidence. Supporting Evidence: PMID:38159565 H1 and H2 form a clamp that grasps the substrate in a region remote from the phosphorylated residue. |
| GO:0071074 eukaryotic initiation factor eIF2 binding | IPI PMID:34847777 Substrate recognition determinants of human eIF2Ξ± phosphatas... | ACCEPT | Summary: IPI (DisProt) eIF2 binding; WITH/FROM lists Q9BY44. Reason: Substrate-trapping R15B fragments bind phospho-eIF2alpha. The WITH/FROM Q9BY44 (EIF2A, eIF-2A) is not the eIF2alpha studied (EIF2S1, P05198). Supporting Evidence: PMID:34847777 Fragments containing the substrate-binding regions but lacking the PP1-binding motif trapped the phospho-substrate and caused accumulation of phosphorylated eIF2Ξ± in unstressed cells. |
| GO:0071074 eukaryotic initiation factor eIF2 binding | IPI PMID:38159565 Recruitment of trimeric eIF2 by phosphatase non-catalytic su... | ACCEPT | Summary: IPI (DisProt) eIF2 binding in the trimeric-eIF2 recruitment study; WITH/FROM lists Q9BY44. Reason: Binding to eIF2 is directly shown. The WITH/FROM Q9BY44 (EIF2A) is wrong; the contacts are on eIF2gamma (EIF2S3) and the eIF2alpha (EIF2S1) C-terminal domain. Supporting Evidence: PMID:38159565 Thus, we identified and used a fragment of R15B to reconstitute substrate recognition with the full trimeric eIF2 to demonstrate that R15B binds eIF2 with high affinity, without requiring PP1 or any other factor. |
| GO:1903898 negative regulation of PERK-mediated unfolded protein response | TAS PMID:22013210 The unfolded protein response: integrating stress signals th... | KEEP AS NON CORE | Summary: TAS (IRE1 review) for negative regulation of PERK-mediated UPR. Reason: CReP-PP1 dephosphorylates eIF2alpha constitutively and so opposes the PERK translational arm, but it is not the stress-induced feedback (that is GADD34); its effect on the UPR is a consequence of setting basal phospho-eIF2alpha. Non-core. Supporting Evidence: PMID:14638860 Blocking CReP expression activated the ISR and protected cells from oxidative, nitrosative, and ER stress |
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Download this section (compressed HTML)Q: Where in the cell does endogenous CReP act? The ER is assigned only by phylogenetic inference from GADD34-type N-terminal targeting; is CReP ER-membrane-associated in human cells?
Experiment: Localize endogenous PPP1R15B (tagged at the native locus) by imaging and fractionation with ER and mitochondrial markers, and test whether its N-terminal region is required for membrane association and basal eIF2alpha dephosphorylation.
Hypothesis: CReP, like GADD34, is targeted to the cytoplasmic face of the ER by its N-terminal region, and this targeting is needed for efficient basal dephosphorylation.
What is not known β curated, literature-grounded statements of the open unknowns (the inverse of core functions).
Gap: The subcellular site where CReP-PP1 dephosphorylates eIF2alpha in human cells is not established.
OPEN BIOLOGY RESIDUAL_SUBGAP
Provenance (the field's own admissions):
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