id: O43301 gene_symbol: HSPA12A product_type: PROTEIN status: COMPLETE taxon: id: NCBITaxon:9606 label: Homo sapiens description: >- HSPA12A is an atypical and still poorly characterized HSP70-family protein. The strongest direct mechanistic evidence supports ATP/ADP-sensitive binding to the cytosolic tail of SORL1/SorLA and modulation of SorLA trafficking, while later disease- and tissue-specific studies suggest context-dependent signaling or scaffold-like roles rather than a conserved GO-ready core activity. Current evidence supports a narrow SorLA/SORL1-selective adaptor-like trafficking role and does not establish canonical ATP-dependent protein folding chaperone activity or another broad core proteostasis function for HSPA12A. existing_annotations: - term: id: GO:0005515 label: protein binding evidence_type: IPI original_reference_id: PMID:30679749 review: summary: MODIFY. PMID:30679749 demonstrates a specific, ATP/ADP-sensitive interaction between HSPA12A and the cytosolic tail of SORL1/SorLA together with delayed receptor internalization, so GO:0005515 should be replaced by more informative terms capturing receptor-tail binding and trafficking control. action: MODIFY reason: GO:0005515 is too generic for this evidence. The paper supports a selective SorLA cytoplasmic-domain interaction with a clear trafficking consequence, but it does not justify canonical HSP70 chaperone activity. I am using the conservative existing MF term GO:0019904 as the replacement and adding the trafficking consequence as a separate NEW BP annotation below. The more specific missing function is captured below as a proposed new receptor-tail binding term rather than overcalling HSPA12A as a canonical cargo adaptor. proposed_replacement_terms: - id: GO:0019904 label: protein domain specific binding supported_by: - reference_id: PMID:30679749 supporting_text: We have identified HSPA12A as a new adaptor protein that, among Vps10p-D receptors, selectively binds to SorLA in an ADP/ATP dependent manner. - reference_id: PMID:30679749 supporting_text: We also observed that the endocytic capacity of SorLA was lowered by HSPA12A expression (Fig. 7). - reference_id: file:human/HSPA12A/HSPA12A-uniprot.txt supporting_text: 'CC -!- FUNCTION: Adapter protein for SORL1, but not SORT1. Delays SORL1' - reference_id: file:human/HSPA12A/HSPA12A-deep-research-falcon.md supporting_text: >- HSPA12A was identified as a **specific SorLA cytosolic-tail interactor**; Y2H recovered C-terminal HSPA12A clones, GST-HSPA12A pulled down full-length SorLA, and binding mapped to SorLA cytosolic acidic clusters including E34-D38 and D47D48. HSPA12B was negative in Y2H, arguing against paralog transfer. - reference_id: file:human/HSPA12A/HSPA12A-deep-research-falcon.md supporting_text: >- HSPA12A **delays SorLA internalization/endocytosis**: surface SorLA staining persisted longer in HSPA12A-expressing cells, and labeled SorLA accumulated in HSPA12A-positive vesicles. - term: id: GO:0002091 label: negative regulation of receptor internalization evidence_type: IDA original_reference_id: PMID:30679749 review: summary: NEW. PMID:30679749 directly shows that HSPA12A expression delays SorLA/SORL1 internalization. action: NEW reason: This BP captures the trafficking consequence of the SorLA cytosolic-tail interaction. It should be added separately from the MF replacement for GO:0005515 rather than listed as a cross-aspect proposed replacement term. supported_by: - reference_id: PMID:30679749 supporting_text: We also observed that the endocytic capacity of SorLA was lowered by HSPA12A expression (Fig. 7). - reference_id: file:human/HSPA12A/HSPA12A-deep-research-falcon.md supporting_text: >- HSPA12A **delays SorLA internalization/endocytosis**: surface SorLA staining persisted longer in HSPA12A-expressing cells, and labeled SorLA accumulated in HSPA12A-positive vesicles. - term: id: GO:0005515 label: protein binding evidence_type: IPI original_reference_id: PMID:32296183 review: summary: MARK_AS_OVER_ANNOTATED. PMID:32296183 records a high-throughput HSPA12A-HSPA12B physical interaction. action: MARK_AS_OVER_ANNOTATED reason: Large-scale interaction mapping can support a physical association between HSPA12A and HSPA12B, but generic GO:0005515 remains uninformative and does not define a specific HSPA12A molecular function or proteostasis role. 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: MARK_AS_OVER_ANNOTATED. PMID:33961781 is a proteome-scale interactome study that records an HSPA12A-HSPA12B physical interaction. action: MARK_AS_OVER_ANNOTATED reason: This is high-throughput interaction evidence only. GO:0005515 is not a useful GO assertion here and does not justify a specific HSPA12A molecular function or core chaperone/proteostasis role. 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:40205054 review: summary: MARK_AS_OVER_ANNOTATED. PMID:40205054 is a multimodal cell-map study; the GOA row records an HSPA12A-HSPA12B physical interaction. action: MARK_AS_OVER_ANNOTATED reason: Another high-throughput interaction call. GO:0005515 remains too generic and does not establish a conserved HSPA12A-specific molecular function or core chaperone/proteostasis role. supported_by: - reference_id: PMID:40205054 supporting_text: Multimodal cell maps as a foundation for structural and functional genomics. - term: id: GO:0005634 label: nucleus evidence_type: IEA original_reference_id: GO_REF:0000044 review: summary: KEEP_AS_NON_CORE. Nuclear localization is a broad UniProt transfer, not a defining HSPA12A biology. action: KEEP_AS_NON_CORE reason: Retain conservatively as contextual localization only. Current direct literature is insufficient to make nucleus a distinctive or proteostasis-defining location for HSPA12A. supported_by: - reference_id: file:human/HSPA12A/HSPA12A-uniprot.txt supporting_text: 'CC -!- SUBCELLULAR LOCATION: Cytoplasm {ECO:0000250|UniProtKB:Q8K0U4}. Nucleus' - term: id: GO:0005737 label: cytoplasm evidence_type: IEA original_reference_id: GO_REF:0000044 review: summary: KEEP_AS_NON_CORE. Broad cytoplasmic localization is consistent with UniProt curation and with the SorLA study, which observed HSPA12A-SorLA co-localization in cytoplasm. action: KEEP_AS_NON_CORE reason: Useful contextual localization, but too broad to define core function and not specific evidence for a canonical proteostasis module. supported_by: - reference_id: file:human/HSPA12A/HSPA12A-uniprot.txt supporting_text: 'CC -!- SUBCELLULAR LOCATION: Cytoplasm {ECO:0000250|UniProtKB:Q8K0U4}. Nucleus' - reference_id: PMID:30679749 supporting_text: Co-localisation of SorLA and HSPA12A is here only demonstrated to take place in cytoplasm. - term: id: GO:0005634 label: nucleus evidence_type: ISS original_reference_id: GO_REF:0000024 review: summary: KEEP_AS_NON_CORE. Nuclear localization is a broad transferred localization, not a defining HSPA12A biology. action: KEEP_AS_NON_CORE reason: Retain conservatively as contextual localization only. Orthology-based transfer is plausible but too weak to support a core or proteostasis-specific conclusion. supported_by: - reference_id: file:human/HSPA12A/HSPA12A-uniprot.txt supporting_text: 'CC -!- SUBCELLULAR LOCATION: Cytoplasm {ECO:0000250|UniProtKB:Q8K0U4}. Nucleus' - term: id: GO:0005737 label: cytoplasm evidence_type: ISS original_reference_id: GO_REF:0000024 review: summary: KEEP_AS_NON_CORE. Cytoplasmic localization is compatible with both orthology-based transfer and the direct SorLA interaction study. action: KEEP_AS_NON_CORE reason: Broad intracellular context only. This does not by itself define HSPA12A's core function or argue for a canonical HSP70 proteostasis role. supported_by: - reference_id: file:human/HSPA12A/HSPA12A-uniprot.txt supporting_text: 'CC -!- SUBCELLULAR LOCATION: Cytoplasm {ECO:0000250|UniProtKB:Q8K0U4}. Nucleus' - reference_id: PMID:30679749 supporting_text: Co-localisation of SorLA and HSPA12A is here only demonstrated to take place in cytoplasm. - term: id: GO:0070062 label: extracellular exosome evidence_type: HDA original_reference_id: PMID:19056867 review: summary: KEEP_AS_NON_CORE. PMID:19056867 is a large-scale urinary exosome proteomics study that detected HSPA12A in exosome preparations. action: KEEP_AS_NON_CORE reason: This supports context-specific extracellular-vesicle association at the proteomics level, but it does not establish exosome biology as a core or proteostasis-defining function for HSPA12A. supported_by: - reference_id: PMID:19056867 supporting_text: Large-scale proteomics and phosphoproteomics of urinary exosomes. references: - id: file:human/HSPA12A/HSPA12A-deep-research-falcon.md title: Falcon deep research report for human HSPA12A findings: - statement: >- HSPA12A supports a narrow SorLA/SORL1 trafficking mechanism rather than established canonical HSP70 folding activity. supporting_text: >- Current evidence in retrieved primary literature is insufficient to support canonical HSP70 chaperone/protein-folding activity for HSPA12A. - statement: >- HSPA12A specifically binds the SorLA cytosolic tail with nucleotide sensitivity. supporting_text: >- HSPA12A was identified as a **specific SorLA cytosolic-tail interactor**; Y2H recovered C-terminal HSPA12A clones, GST-HSPA12A pulled down full-length SorLA, and binding mapped to SorLA cytosolic acidic clusters including E34-D38 and D47D48. HSPA12B was negative in Y2H, arguing against paralog transfer. - statement: >- HSPA12A delays SorLA internalization. supporting_text: >- HSPA12A **delays SorLA internalization/endocytosis**: surface SorLA staining persisted longer in HSPA12A-expressing cells, and labeled SorLA accumulated in HSPA12A-positive vesicles. - id: PMID:12552099 title: Two Hsp70 family members expressed in atherosclerotic lesions. findings: - statement: Han et al. place HSPA12A/HSPA12B as distant HSP70-family members with atypical ATPase-domain similarity. supporting_text: Both genes appear to contain an atypical Hsp70 ATPase domain. The BLAST search also revealed that both genes were more similar to primitive eukaryote and prokaryote than mammalian Hsp70s, making these two genes distant members of the mammalian Hsp70 family. - statement: The original HSPA12A/HSPA12B characterization cautions against assuming canonical HSP70 function from domain placement alone. supporting_text: Despite HspA12A and HspA12B localization to macrophages in lesions and their placement into the Hsp70 family by computer algorithms, we cannot be certain that they share any of the functions of Hsp70s. - id: PMID:32128976 title: Heat-Shock protein A12A is a novel PCNA-binding protein and promotes hepatocellular carcinoma growth. findings: - statement: Cheng et al. report a disease-context PCNA interaction, not canonical HSP70 folding or ATPase activity. supporting_text: HSPA12A directly binds to PCNA and promotes its trimerization, which is an essential functional conformation of PCNA for carcinogenesis. - id: GO_REF:0000024 title: Manual transfer of experimentally-verified manual GO annotation data to orthologs by curator judgment of sequence similarity findings: [] - id: GO_REF:0000044 title: Gene Ontology annotation based on UniProtKB/Swiss-Prot Subcellular Location vocabulary mapping, accompanied by conservative changes to GO terms applied by UniProt findings: [] - id: PMID:19056867 title: Large-scale proteomics and phosphoproteomics of urinary exosomes. findings: [] - id: PMID:30679749 title: HSPA12A targets the cytoplasmic domain and affects the trafficking of the Amyloid Precursor Protein receptor SorLA. findings: - statement: HSPA12A selectively binds the cytosolic tail of SorLA in an ADP/ATP-dependent manner supporting_text: We have identified HSPA12A as a new adaptor protein that, among Vps10p-D receptors, selectively binds to SorLA in an ADP/ATP dependent manner. - statement: SorLA is the first described substrate of HSPA12A in this study supporting_text: This is the first described substrate of HSPA12A. - statement: HSPA12A lowers SorLA internalization and alters its trafficking supporting_text: We also observed that the endocytic capacity of SorLA was lowered by HSPA12A expression (Fig. 7). Together, these data clearly show HSPA12A has cellular effects on SorLA localisation and trafficking. - id: PMID:32296183 title: A reference map of the human binary protein interactome. findings: [] - id: PMID:33961781 title: Dual proteome-scale networks reveal cell-specific remodeling of the human interactome. findings: [] - id: PMID:40205054 title: Multimodal cell maps as a foundation for structural and functional genomics. findings: [] - id: file:human/HSPA12A/HSPA12A-uniprot.txt title: UniProt entry for HSPA12A (O43301) findings: - statement: UniProt curates HSPA12A as an adapter protein for SORL1 and not SORT1 supporting_text: 'CC -!- FUNCTION: Adapter protein for SORL1, but not SORT1.' - id: file:human/HSPA12A/HSPA12A-notes.md title: Curator notes on HSPA12A PN context and conservative GO review findings: [] - id: file:human/HSPA12A/HSPA12A-hypotheses/hsp70-folding-machinery-check/openscientist.md title: 'OpenScientist hypothesis run: HSPA12A HSP70 folding-machinery check' findings: - statement: Confirms HSPA12A is a divergent non-canonical HSP70 for which GO:0140662 (ATP-dependent protein folding chaperone) should not be assigned - all three PROSITE HSP70 signatures, the substrate-binding domain, the interdomain linker, and the C-terminal EEVD are absent. Corroborates the PN workbook InterPro domain deficit (only the root ATPase fold is shared with canonical HSPA8). supporting_text: lacks the molecular machinery required for canonical ATP-dependent protein folding chaperone activity core_functions: - molecular_function: id: GO:0019904 label: protein domain specific binding description: HSPA12A's only directly characterized function is a selective, adaptor-like interaction with the cytoplasmic tail of the sorting receptor SORL1/SorLA. HSPA12A binds SorLA in an ADP/ATP-sensitive manner, alters SorLA subcellular distribution, and lowers SorLA internalization. This supports a narrow receptor-trafficking role, while canonical HSP70 protein-folding chaperone activity remains unestablished. supported_by: - reference_id: PMID:30679749 supporting_text: We have identified HSPA12A as a new adaptor protein that, among Vps10p-D receptors, selectively binds to SorLA in an ADP/ATP dependent manner. - reference_id: PMID:30679749 supporting_text: We also observed that the endocytic capacity of SorLA was lowered by HSPA12A expression (Fig. 7). - reference_id: file:human/HSPA12A/HSPA12A-uniprot.txt supporting_text: 'CC -!- FUNCTION: Adapter protein for SORL1, but not SORT1. Delays SORL1' - reference_id: file:human/HSPA12A/HSPA12A-deep-research-falcon.md supporting_text: >- Based on the retrieved evidence, HSPA12A should **not** be annotated as a canonical HSP70 chaperone (e.g., *ATP hydrolysis activity*, *unfolded protein binding*, *protein folding chaperone*) on experimental grounds alone; the strongest experimental support is instead **nucleotide-modulated binding** to a specific partner (SORL1/SorLA tail) - reference_id: file:human/HSPA12A/HSPA12A-deep-research-falcon.md supporting_text: >- HSPA12A **delays SorLA internalization/endocytosis**: surface SorLA staining persisted longer in HSPA12A-expressing cells, and labeled SorLA accumulated in HSPA12A-positive vesicles. directly_involved_in: - id: GO:0002091 label: negative regulation of receptor internalization proposed_new_terms: - proposed_name: sorting receptor cytoplasmic tail binding proposed_definition: Binding to the cytoplasmic domain of a sorting receptor, permitting selective regulation of receptor internalization or intracellular trafficking. justification: Current GO molecular function terms do not cleanly capture the experimentally demonstrated selectivity of HSPA12A for the SorLA/SORL1 cytoplasmic tail. GO:0019904 protein domain specific binding is usable but too generic, GO:0140355 cargo receptor ligand activity describes ligands that initiate endocytosis rather than cytosolic tail binders, and GO:0140312 cargo adaptor activity would overstate the evidence because direct bridging to coat scaffolds was not shown. proposed_parent: id: GO:0019904 label: protein domain specific binding supported_by: - reference_id: PMID:30679749 supporting_text: We have identified HSPA12A as a new adaptor protein that, among Vps10p-D receptors, selectively binds to SorLA in an ADP/ATP dependent manner. - reference_id: PMID:30679749 supporting_text: Accordingly, it is concluded that the 2 C-terminal acidic clusters both contributed to the binding between the SorLA-cd and HSPA12A. suggested_questions: - question: Does HSPA12A have intrinsic ATP binding/hydrolysis and client-folding behavior comparable to canonical HSP70 chaperones, or is it primarily a specialized adaptor/scaffold protein? - question: Which HSPA12A interactions are reproducible at endogenous levels in native neuronal or glial systems, and how much of the current literature reflects cell-type-specific stress phenotypes rather than a conserved core role? suggested_experiments: - description: Reconstitute recombinant HSPA12A in biochemical ATP-binding, ATPase, client-aggregation, and refolding assays alongside canonical HSP70 controls hypothesis: If HSPA12A is a bona fide HSP70-system chaperone, it should show measurable nucleotide handling and client-folding behavior rather than only receptor/adaptor interactions - description: Test endogenous HSPA12A-SORL1 interaction and trafficking effects in human neuronal or astrocytic models using knock-in tags or orthogonal co-immunoprecipitation/proximity labeling hypothesis: The best-supported direct HSPA12A function is SORL1/SorLA trafficking control, but this should be reproducible outside overexpression-heavy systems