NPHS2

Existing Annotations Review

GO Term	Evidence	Action	Reason
GO:0005886 plasma membrane	IBA GO_REF:0000033	ACCEPT	Summary: Podocin is a membrane-associated protein that localizes to the plasma membrane of podocytes at the slit diaphragm. The IBA annotation is well-supported by phylogenetic inference and extensive experimental evidence demonstrating plasma membrane localization [PMID:11786407]. Reason: Podocin is clearly established as a plasma membrane protein in podocytes. The deep research confirms that podocin is an integral membrane protein with a hairpin-like topology that positions both N- and C-termini in the cytoplasm while the central hydrophobic region associates with the plasma membrane [PMID:11786407]. UniProt also annotates isoform 1 to the cell membrane. This is a core localization for podocin function. Supporting Evidence: PMID:11786407 23 Using immunogold labeling and electron microsopy, we showed the podocin distribution at the base of the foot processes and precisely determined its localization on either side of the slit diaphragm, the slit membrane itself being unlabeled PMID:10742096 NPHS2 is almost exclusively expressed in the podocytes of fetal and mature kidney glomeruli, and encodes a new integral membrane protein, podocin, belonging to the stomatin protein family. PMID:14570703 We show that wild-type podocin is targeted to the plasma membrane, and forms homo-oligomers involving the carboxy and amino terminal cytoplasmic domains.
GO:0005783 endoplasmic reticulum	IEA GO_REF:0000044	KEEP AS NON CORE	Summary: The ER annotation is based on UniProt subcellular location vocabulary mapping. UniProt specifically notes that isoform 2 (Pod-short) localizes to the endoplasmic reticulum, not the main isoform 1. Reason: This annotation represents a trafficking/biosynthesis location rather than the functional site. The main isoform (isoform 1) localizes to the plasma membrane at the slit diaphragm, which is where podocin performs its core scaffolding function. The ER localization is specifically for isoform 2 according to UniProt. Disease-causing mutations often cause ER retention of misfolded podocin, but the ER is not the functional location for wild-type podocin. Supporting Evidence: file:human/NPHS2/NPHS2-deep-research-perplexity.md Disease-causing mutations that impair podocin trafficking result in accumulation of the mutant protein in these intracellular compartments. For instance, the P118L mutation causes predominant accumulation in the endoplasmic reticulum. PMID:38114895 Experiments in cell culture could show that this isoform is mostly retained in the endoplasmic reticulum, which is a pathogenic feature known from other disease causing mutations of podocin
GO:0005886 plasma membrane	IEA GO_REF:0000120	ACCEPT	Summary: Automated annotation to plasma membrane is correct and redundant with the IBA annotation. Well-supported by experimental evidence. Reason: Plasma membrane localization is a core feature of podocin function. This IEA annotation is consistent with extensive experimental evidence showing podocin at the cytoplasmic face of the plasma membrane at the slit diaphragm [PMID:11786407]. Supporting Evidence: PMID:11786407 Interestingly, both the C- and N-terminal domains of the protein identified by specific antibodies are co-localized at the cytoplasmic face of the plasma membrane, a finding in agreement with the hairpin-like predicted structure of podocin
GO:0016020 membrane	IEA GO_REF:0000002	MODIFY	Summary: Generic membrane annotation from InterPro. This is too general given that more specific localizations are well-established. Reason: The generic GO:0016020 membrane term is an over-generalization. Podocin has well-characterized localization to the plasma membrane, specifically at the slit diaphragm. The more specific term GO:0005886 plasma membrane should be preferred. Proposed replacements: plasma membrane Supporting Evidence: PMID:11786407 In the mature kidney, NPHS2 is exclusively expressed in the podocytes of mature glomeruli
GO:0005515 protein binding	IPI PMID:22662192 IQGAP1 interacts with components of the slit diaphragm compl...	REMOVE	Summary: This annotation is based on IQGAP1 interaction study showing podocin interacts with IQGAP1 and other slit diaphragm components via immunoprecipitation. Reason: The generic term GO:0005515 protein binding is uninformative and does not capture the specific scaffolding function of podocin. Podocin's protein interactions are integral to its scaffolding role at the slit diaphragm, recruiting nephrin, CD2AP, TRPC6, and other proteins into lipid raft microdomains. A more informative molecular function annotation such as scaffold protein binding or structural constituent activity would be preferable. Supporting Evidence: PMID:22662192 The In situ Proximity Ligation assay confirmed interactions between IQGAP1 and proteins of the slit diaphragm complex, nephrin, MAGI-1, CD2AP, podocin and NCK1/2
GO:0009898 cytoplasmic side of plasma membrane	IEA GO_REF:0000120	ACCEPT	Summary: Automated annotation correctly identifies podocin topology with cytoplasmic orientation. This is consistent with the hairpin membrane topology established by experimental studies. Reason: Podocin has a well-characterized hairpin-like membrane topology where both the N-terminal and C-terminal domains face the cytoplasm [PMID:11786407]. This is essential for its scaffolding function linking slit diaphragm components to the cytoskeleton. The annotation accurately reflects podocin's membrane topology. Supporting Evidence: PMID:11786407 Interestingly, both the C- and N-terminal domains of the protein identified by specific antibodies are co-localized at the cytoplasmic face of the plasma membrane, a finding in agreement with the hairpin-like predicted structure of podocin file:human/NPHS2/NPHS2-deep-research-perplexity.md The hairpin structure positions both the N-terminal region (amino acids 1-100) and the C-terminal region (amino acids 126-383) intracellularly within the cytoplasm. PMID:24596097 podocin and MEC-2 are membrane-associated proteins with a predicted hairpin-like structure and amino and carboxyl termini facing the cytoplasm
GO:0010467 gene expression	IEA GO_REF:0000107	REMOVE	Summary: Annotation to gene expression is based on ortholog transfer from Ensembl Compara. This is an extremely vague term that does not reflect podocin's actual function. Reason: GO:0010467 gene expression is an overly generic term that does not meaningfully describe podocin function. Podocin is a structural/scaffolding protein at the slit diaphragm, not a transcription factor or direct regulator of gene expression. This appears to be an erroneous or overly broad automated annotation that should be removed. Supporting Evidence: file:human/NPHS2/NPHS2-deep-research-perplexity.md The essential function of podocin is to position nephrin correctly within lipid raft microdomains, thereby enabling nephrin to participate in proper slit diaphragm assembly.
GO:0036057 slit diaphragm	IEA GO_REF:0000107	ACCEPT	Summary: Automated annotation to slit diaphragm is correct. This is a core localization for podocin that has been extensively validated by experimental studies. Reason: The slit diaphragm is the primary functional location of podocin in podocytes. Extensive experimental evidence from immunogold electron microscopy precisely localizes podocin to the cytoplasmic face of the slit diaphragm [PMID:11786407]. This annotation is a core localization representing where podocin performs its essential scaffolding function. Supporting Evidence: PMID:11786407 23 Using immunogold labeling and electron microsopy, we showed the podocin distribution at the base of the foot processes and precisely determined its localization on either side of the slit diaphragm, the slit membrane itself being unlabeled file:human/NPHS2/NPHS2-deep-research-perplexity.md Podocin is located at the base of the foot processes, at the insertion site of the slit diaphragm where it contacts the cytoplasm of the podocyte cell body. PMID:38114895 STED microscopy revealed the complete absence of podocin at the podocytes' slit diaphragm and severe morphological alterations of podocyte foot processes.
GO:0071944 cell periphery	IEA GO_REF:0000107	MODIFY	Summary: Cell periphery annotation is correct but less specific than plasma membrane. Reason: GO:0071944 cell periphery is a parent term of plasma membrane. Since podocin has well-established localization to the plasma membrane at the slit diaphragm, the more specific term GO:0005886 plasma membrane should be used. Proposed replacements: plasma membrane Supporting Evidence: PMID:11786407 Interestingly, both the C- and N-terminal domains of the protein identified by specific antibodies are co-localized at the cytoplasmic face of the plasma membrane, a finding in agreement with the hairpin-like predicted structure of podocin
GO:0003094 glomerular filtration	TAS PMID:10742096 NPHS2, encoding the glomerular protein podocin, is mutated i...	ACCEPT	Summary: This TAS annotation to glomerular filtration is well-supported by the original discovery paper demonstrating NPHS2 mutations cause nephrotic syndrome with disrupted glomerular filtration barrier function. Reason: Glomerular filtration is the core biological process that podocin is involved in. The original cloning paper [PMID:10742096] established that NPHS2 mutations cause steroid-resistant nephrotic syndrome with disrupted glomerular filtration, and podocin-deficient mice develop massive proteinuria demonstrating the essential role of podocin in glomerular filtration barrier function. Supporting Evidence: PMID:10742096 We found ten different NPHS2 mutations, comprising nonsense, frameshift and missense mutations, to segregate with the disease, demonstrating a crucial role for podocin in the function of the glomerular filtration barrier. file:human/NPHS2/NPHS2-deep-research-perplexity.md In podocin-deficient mice, extensive podocyte lesions develop and massive proteinuria appears before birth, leading to death from uremia within days of life.
GO:0070062 extracellular exosome	HDA PMID:23533145 In-depth proteomic analyses of exosomes isolated from expres...	KEEP AS NON CORE	Summary: High-throughput proteomics study detecting podocin in urinary exosomes from prostatic secretions. Reason: Detection in extracellular exosomes likely reflects the normal turnover and shedding of podocyte proteins rather than a core functional location. Podocin's primary function is at the slit diaphragm, not in exosomes. This annotation reflects proteomics detection but not functional localization. Supporting Evidence: file:human/NPHS2/NPHS2-deep-research-perplexity.md Podocin detected in urinary exosome proteomics studies reflects protein shedding rather than functional localization PMID:23533145 2013 Apr 23. In-depth proteomic analyses of exosomes isolated from expressed prostatic secretions in urine.
GO:0070062 extracellular exosome	HDA PMID:19056867 Large-scale proteomics and phosphoproteomics of urinary exos...	KEEP AS NON CORE	Summary: Large-scale proteomics study of urinary exosomes detecting podocin. Reason: Similar to the other exosome annotation, detection of podocin in urinary exosomes reflects protein shedding rather than functional localization. This is not a core functional location for podocin. Supporting Evidence: file:human/NPHS2/NPHS2-deep-research-perplexity.md Podocin detected in urinary exosome proteomics studies reflects protein shedding rather than functional localization PMID:19056867 2008 Dec 3. Large-scale proteomics and phosphoproteomics of urinary exosomes.
GO:0005886 plasma membrane	TAS Reactome:R-HSA-373734	ACCEPT	Summary: Reactome pathway annotation for nephrin-podocin interaction at the plasma membrane. This is consistent with the well-established slit diaphragm localization. Reason: The Reactome annotation correctly places podocin at the plasma membrane where it interacts with nephrin. This is consistent with extensive experimental evidence and represents a core localization for podocin function. Supporting Evidence: PMID:11786407 This suggests that podocin, as a membrane protein anchored to the plasma membrane, could interact with the intracellular domains of the transmembrane proteins localized in the slit diaphragm such as nephrin, P-cadherin, or FAT
GO:0036057 slit diaphragm	IDA PMID:11786407 Podocin localizes in the kidney to the slit diaphragm area.	ACCEPT	Summary: Direct experimental evidence from immunogold electron microscopy precisely localizing podocin to the slit diaphragm area in podocyte foot processes. Reason: This IDA annotation is supported by rigorous immunogold electron microscopy demonstrating podocin localization at the base of foot processes on either side of the slit diaphragm [PMID:11786407]. This is the core functional location for podocin where it organizes the slit diaphragm protein complex. Supporting Evidence: PMID:11786407 23 Using immunogold labeling and electron microsopy, we showed the podocin distribution at the base of the foot processes and precisely determined its localization on either side of the slit diaphragm, the slit membrane itself being unlabeled
GO:0009898 cytoplasmic side of plasma membrane	IDA PMID:11786407 Podocin localizes in the kidney to the slit diaphragm area.	ACCEPT	Summary: Direct experimental evidence demonstrating that both N- and C-terminal domains of podocin face the cytoplasm, establishing its hairpin membrane topology. Reason: The IDA annotation is directly supported by immunogold labeling using antibodies against both N- and C-terminal regions of podocin, showing both domains localize to the cytoplasmic face of the plasma membrane [PMID:11786407]. This topology is essential for podocin's scaffolding function. Supporting Evidence: PMID:11786407 Interestingly, both the C- and N-terminal domains of the protein identified by specific antibodies are co-localized at the cytoplasmic face of the plasma membrane, a finding in agreement with the hairpin-like predicted structure of podocin
GO:0072249 metanephric podocyte development	IEP PMID:11786407 Podocin localizes in the kidney to the slit diaphragm area.	ACCEPT	Summary: Expression pattern study showing NPHS2 is expressed during podocyte development in the metanephric kidney starting at the late S-shaped body stage. Reason: The IEP annotation is appropriately applied based on temporal expression data showing podocin expression during metanephric kidney development [PMID:11786407]. Podocin expression is first detected in metanephric podocytes at the late S-shaped body stage and persists through differentiation. This represents a legitimate developmental role for podocin. Supporting Evidence: PMID:11786407 In metanephric kidneys, the NPHS2 transcript was initially detected in the lower limb of the late S-shaped body, in the presumptive podocytes but not in future parietal epithelial cells
GO:0030036 actin cytoskeleton organization	IDA PMID:17675666 Podocin participates in the assembly of tight junctions betw...	KEEP AS NON CORE	Summary: Study showing podocin facilitates coalescence of lipid rafts and restricts their lateral mobility through dynamic actin reorganization and tethering of protein complexes to the cytoskeleton. Reason: Podocin's role in actin cytoskeleton organization is indirect, mediated through its scaffolding function and interaction with CD2AP which directly links to actin. The primary function of podocin is as a lipid raft organizer and scaffold protein. The actin cytoskeleton organization is a downstream consequence of podocin's scaffolding activity rather than a direct molecular function. Supporting Evidence: PMID:17675666 Consistent with this, we found that podociin facilitated the coalescence of preassembled lipid rafts containing CAR and restricted their lateral mobility, the latter likely a result of dynamic actin reorganization and subsequent tethering of CAR-podocin complexes to the cytoskeleton file:human/NPHS2/NPHS2-deep-research-perplexity.md Podocin localizes specifically to the non-contractile actin network within foot processes and serves to anchor this network to the slit diaphragm complex. The protein achieves this anchoring function through its interactions with CD2AP.
GO:0045121 membrane raft	IDA PMID:17675666 Podocin participates in the assembly of tight junctions betw...	ACCEPT	Summary: Study demonstrating podocin localizes to and organizes lipid raft microdomains, facilitating coalescence of preassembled rafts at podocyte junctions. Reason: Lipid raft organization is a core function of podocin. It localizes to detergent-resistant membrane fractions and organizes lipid raft microdomains that recruit slit diaphragm proteins including nephrin and TRPC6 [PMID:17675666]. Podocin binds cholesterol through its PHB domain and this cholesterol recruitment is essential for proper slit diaphragm assembly. Supporting Evidence: PMID:17675666 Consistent with this, we found that podociin facilitated the coalescence of preassembled lipid rafts containing CAR and restricted their lateral mobility, the latter likely a result of dynamic actin reorganization and subsequent tethering of CAR-podocin complexes to the cytoskeleton file:human/NPHS2/NPHS2-deep-research-perplexity.md Podocin localizes to detergent-resistant membrane (DRM) fractions, biochemical preparations enriched in lipid rafts that are resistant to extraction by non-ionic detergents such as Triton X-100. This lipid raft localization is functionally important; recruitment of nephrin into lipid rafts is dependent on functional podocin. PMID:14570703 The association of podocin with specialized lipid raft microdomains of the plasma membrane was a prerequisite for recruitment of nephrin into rafts. PMID:24596097 Podocin(P118L) and MEC-2(P134S) did not fractionate in detergent-resistant membrane domains.
GO:0005911 cell-cell junction	IDA PMID:17675666 Podocin participates in the assembly of tight junctions betw...	ACCEPT	Summary: Study showing podocin participates in assembly of tight junctions between foot processes in nephrotic podocytes, colocalizing with CAR and ZO-1 at cell-cell contacts. Reason: The slit diaphragm is a specialized cell-cell junction between podocyte foot processes. Podocin is recruited to sites of cell-cell contact and colocalizes with junction proteins CAR and ZO-1 [PMID:17675666]. This annotation appropriately captures podocin's localization at the specialized junction between podocytes. Supporting Evidence: PMID:17675666 In this study, we confirmed that podocin colocalizes with CAR and ZO-1 at the tight junction between foot processes in nephrotic rats
GO:0005515 protein binding	IPI PMID:17675666 Podocin participates in the assembly of tight junctions betw...	REMOVE	Summary: Evidence from co-immunoprecipitation showing podocin forms a multi-protein complex with CAR, ZO-1, and other junctional proteins. Reason: GO:0005515 protein binding is uninformative for a scaffolding protein like podocin. Podocin's interactions with multiple slit diaphragm proteins (nephrin, CD2AP, TRPC6, CAR, ZO-1) are integral to its scaffolding function but should be represented by more specific molecular function terms rather than generic protein binding. Supporting Evidence: PMID:17675666 Immunoprecipitation suggested that these three junctional proteins from a multi-protein complex
GO:0032991 protein-containing complex	IDA PMID:17675666 Podocin participates in the assembly of tight junctions betw...	ACCEPT	Summary: Evidence showing podocin forms a multi-protein complex with CAR, ZO-1, and cytoskeletal proteins. Reason: Podocin functions as part of a large multiprotein complex at the slit diaphragm. Proteomic analyses have identified podocin in macromolecular assemblies of 1.5-3 megadaltons containing nephrin, neph1, CD2AP, and many other proteins [PMID:17675666]. This annotation correctly reflects podocin's participation in protein complexes. Supporting Evidence: PMID:17675666 Immunoprecipitation suggested that these three junctional proteins from a multi-protein complex file:human/NPHS2/NPHS2-deep-research-perplexity.md Podocin is present in native slit diaphragms as part of macromolecular assemblies with apparent molecular weights in the range of 1.5-3 megadaltons. PMID:26792178 Podocin and its Caenorhabditis elegans orthologue MEC-2 have emerged as key components of mechanosensitive membrane protein signalling complexes. PMID:14570703 wild-type podocin is targeted to the plasma membrane, and forms homo-oligomers involving the carboxy and amino terminal cytoplasmic domains
GO:0005515 protein binding	IPI PMID:12424224 NEPH1 defines a novel family of podocin interacting proteins...	REMOVE	Summary: Evidence from pull-down assays demonstrating podocin interacts with NEPH1 family proteins through their C-terminal domain. Reason: The generic protein binding term is uninformative for podocin which is known to function as a scaffolding protein with specific interactions with nephrin, neph1, CD2AP, and TRPC6. These interactions should be captured by more specific MF terms if available, or the scaffolding role should be represented in BP annotations. Supporting Evidence: PMID:12424224 We report now that NEPH1 belongs to a family of three closely related proteins that interact with the C-terminal domain of podocin
GO:0005886 plasma membrane	TAS PMID:10742096 NPHS2, encoding the glomerular protein podocin, is mutated i...	ACCEPT	Summary: The original discovery paper describes podocin as an integral membrane protein with predicted plasma membrane localization based on sequence analysis. Reason: The original cloning paper [PMID:10742096] correctly identified podocin as an integral membrane protein belonging to the stomatin family, which are characteristically plasma membrane-associated proteins. This has been validated by subsequent experimental studies. Supporting Evidence: PMID:10742096 NPHS2 is almost exclusively expressed in the podocytes of fetal and mature kidney glomeruli, and encodes a new integral membrane protein, podocin, belonging to the stomatin protein family.
GO:0005198 structural molecule activity	TAS PMID:10742096 NPHS2, encoding the glomerular protein podocin, is mutated i...	NEW	Summary: Podocin functions as a structural scaffold at the slit diaphragm, organizing lipid raft microdomains and recruiting key proteins. This molecular function annotation captures podocin's essential role. Reason: Podocin's primary molecular function is as a structural scaffolding protein at the slit diaphragm. It does not have enzymatic activity but rather serves to organize the multiprotein complex at the slit diaphragm. The deep research extensively documents this scaffolding role. Supporting Evidence: file:human/NPHS2/NPHS2-deep-research-perplexity.md Our results suggest that podocin could serve to anchor directly or indirectly components of the slit diaphragm to the cytoskeleton. PMID:17675666 our data suggest that podocin may also serve as a scaffold that links tight junction proteins to the actin cytoskeleton in nephrotic foot processes PMID:10742096 NPHS2, encoding the glomerular protein podocin, is mutated in autosomal recessive steroid-resistant nephrotic syndrome.
GO:0015485 cholesterol binding	IDA PMID:24596097 A disease-causing mutation illuminates the protein membrane ...	NEW	Summary: Podocin binds cholesterol through its PHB domain, which is essential for lipid raft organization and TRPC6 channel regulation. Reason: Multiple studies have demonstrated that podocin directly binds cholesterol through residues in the PHB domain. This cholesterol binding is functionally critical for organizing lipid raft microdomains at the slit diaphragm and for proper regulation of the TRPC6 channel. Supporting Evidence: file:human/NPHS2/NPHS2-deep-research-perplexity.md Biochemical studies have demonstrated direct binding of cholesterol to podocin through residues in the PHB domain. Podocin lacking the PHB domain (PodocinDeltaPHB) fails to bind cholesterol and does not properly activate TRPC6. PMID:24596097 the carboxyl terminus of podocin/MEC-2 has to be placed at the inner leaflet of the plasma membrane to mediate cholesterol binding and contribute to ion channel activity, a prerequisite for mechanosensation and the integrity of the kidney filtration barrier.

Gene Description

Existing Annotations Review

Core Functions

Podocin directly binds cholesterol through its PHB domain. This cholesterol binding is essential for organizing lipid raft microdomains and regulating TRPC6 channel activity.

References

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Deep Research

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Perplexity

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