{"gene":"HSP90B1","run_date":"2026-06-10T01:55:22","timeline":{"discoveries":[{"year":1993,"finding":"gp96/GRP94 contains ATP-binding cassettes, binds ATP, and possesses Mg2+-dependent ATPase activity; gp96 preparations also contain tightly bound peptides elutable by acid extraction, consistent with roles in chaperoning antigenic peptides and facilitating MHC class I–peptide assembly in the ER lumen.","method":"In vitro ATPase assay, ATP-binding cassette identification, acid elution of bound peptides","journal":"The EMBO journal","confidence":"High","confidence_rationale":"Tier 1 / Moderate — direct enzymatic assay with biochemical characterization of ATP binding and hydrolysis activity, plus peptide elution, in a single focused study","pmids":["8344253"],"is_preprint":false},{"year":1994,"finding":"GRP94 resides within cardiac sarcoplasmic reticulum vesicles as a soluble luminal Ca2+-binding protein and is phosphorylated in vitro by casein kinase II at two or more sites near the ends of the molecule.","method":"Subcellular fractionation, co-sedimentation with SR markers, in vitro kinase assay, cDNA cloning","journal":"The Journal of biological chemistry","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — direct subcellular fractionation plus in vitro phosphorylation assay; single lab but two orthogonal methods","pmids":["8119936"],"is_preprint":false},{"year":1995,"finding":"Purified GRP94 (grp94/endoplasmin) autophosphorylates itself on serine and threonine residues; autophosphorylation is activated by micromolar calcium, uses both ATP and GTP, and persists in immunoprecipitates and in renatured SDS-PAGE-purified protein; the N-terminal 85 kDa fragment binds ATP-agarose but does not autophosphorylate.","method":"In vitro autophosphorylation assay with purified protein, immunoprecipitation, limited proteolysis, ATP-agarose binding","journal":"The Journal of biological chemistry","confidence":"High","confidence_rationale":"Tier 1 / Moderate — reconstituted in vitro autophosphorylation with domain-mapping and multiple controls; single lab with orthogonal approaches","pmids":["7890776"],"is_preprint":false},{"year":1996,"finding":"An immunodominant peptide of vesicular stomatitis virus (VSV N52-59) endogenously associates with gp96 in VSV-infected cells, demonstrating that gp96 acts as a peptide carrier in a well-defined viral model system.","method":"Biochemical purification and mass spectrometric/sequence characterization of gp96-bound peptides from infected cells","journal":"Proceedings of the National Academy of Sciences of the United States of America","confidence":"High","confidence_rationale":"Tier 1 / Strong — direct biochemical isolation and full characterization of an endogenously bound peptide, replicated across MHC haplotypes","pmids":["8650232"],"is_preprint":false},{"year":1996,"finding":"Purified GRP94 exists as a dimer of noncovalently associated subunits and is a soluble, lumenal protein within the ER; N-linked glycosylation accounts for its molecular weight heterogeneity.","method":"Protein purification, native PAGE, 2D non-reducing/reducing PAGE, alkali/detergent extraction","journal":"Protein expression and purification","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — multiple biochemical methods on purified protein; single lab","pmids":["9172775"],"is_preprint":false},{"year":1999,"finding":"GRP94 undergoes receptor-mediated endocytosis in macrophages via a cell surface receptor distinct from the mannose/fucose receptor; internalized GRP94 co-localizes predominantly with transferrin-positive early endosomes and is not rapidly trafficked to lysosomes.","method":"Fluorescent protein uptake assay, subcellular co-localization by confocal microscopy, competitive inhibition with mannan and dimethylamiloride","journal":"Journal of cell science","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — live-cell imaging with specific inhibitors and co-localization; single lab, two orthogonal methods","pmids":["10362546"],"is_preprint":false},{"year":2000,"finding":"CD91 (alpha2-macroglobulin receptor/LRP) is a cell-surface receptor for gp96 on antigen-presenting cells; CD91 binds gp96 directly (not through another ligand), and anti-CD91 antibodies or the CD91 ligand alpha2-macroglobulin inhibit re-presentation of gp96-chaperoned antigenic peptides.","method":"Direct binding assay, antibody blocking of gp96 uptake and peptide re-presentation, competitive inhibition with alpha2-macroglobulin","journal":"Nature immunology","confidence":"High","confidence_rationale":"Tier 2 / Strong — direct binding demonstrated with competitive inhibition and functional readout; widely cited and replicated","pmids":["11248808"],"is_preprint":false},{"year":2000,"finding":"Cell-surface targeting of gp96 on dendritic cells induces their maturation (upregulation of MHC I, MHC II, CD80, CD86, CD40) and secretion of IL-1β, IL-12, and MCP-1; surface-expressed gp96 on tumor cells renders them regressive via a T-lymphocyte-dependent mechanism.","method":"Genetic targeting of gp96 to cell surface, flow cytometry for DC maturation markers, cytokine ELISA, in vivo tumor regression assay","journal":"Journal of immunology","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — direct localization experiment with clear functional consequence; single lab with two orthogonal functional readouts","pmids":["11739487"],"is_preprint":false},{"year":2001,"finding":"GRP94 is released into the extracellular space following virally induced or mechanical (freeze/thaw) cell death but not apoptotic cell death; released GRP94 retains antigenicity and elicits ovalbumin-specific T-cell hybridoma activation in a dose-dependent manner.","method":"Cell death assays, ELISA/immunoblot for released GRP94, T-cell hybridoma activation assay","journal":"The Journal of biological chemistry","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — defined cellular assay comparing multiple cell death scenarios with specific functional readout; single lab","pmids":["11279246"],"is_preprint":false},{"year":2002,"finding":"Receptor-internalized GRP94 is trafficked to a Rab5a/CD1/transferrin-negative, Fc receptor- and MHC class I-positive endocytic compartment (not the ER); peptide transfer from GRP94 to MHC class I occurs at a post-ER compartment accessed by mature MHC class I molecules.","method":"Receptor-mediated endocytosis trafficking assay, immunofluorescence co-localization, kinetic peptide re-presentation assay with 25-D1.16 antibody under conditions of inhibited MHC I synthesis","journal":"Traffic","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — subcellular localization with functional consequence (peptide transfer site mapping); single lab, two orthogonal methods","pmids":["11967129"],"is_preprint":false},{"year":2002,"finding":"CD91 is not the primary receptor mediating GRP94 cell-surface binding, receptor-mediated endocytosis, or peptide re-presentation in APCs; excess activated alpha2-macroglobulin or receptor-associated protein (pan-CD91 antagonist) did not affect GRP94 uptake or cross-presentation, identifying a CD91-independent pathway.","method":"Competitive binding with alpha2-macroglobulin and receptor-associated protein, GRP94 uptake and peptide re-presentation assays in macrophages/dendritic cells","journal":"Journal of immunology","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — rigorous negative result with multiple inhibitors and functional readout; single lab","pmids":["11970968"],"is_preprint":false},{"year":2003,"finding":"Scavenger receptor class-A (SR-A) serves as a primary receptor for gp96 (and calreticulin) recognition and internalization on macrophages and dendritic cells; gp96 internalization and peptide re-presentation are inhibited by the SR-A inhibitor fucoidan, and macrophages from SR-A−/− mice are substantially impaired in gp96 binding and uptake; ectopic SR-A expression in HEK293 cells confers gp96 recognition and uptake activity.","method":"Fucoidan inhibition assay, SR-A knockout macrophages, ectopic SR-A expression in HEK293 cells, gp96 uptake and peptide re-presentation assays","journal":"The EMBO journal","confidence":"High","confidence_rationale":"Tier 2 / Strong — gain-of-function, loss-of-function, and pharmacological inhibition converge; multiple orthogonal methods in one study","pmids":["14609958"],"is_preprint":false},{"year":2003,"finding":"Low-endotoxin GRP94/gp96 binds endotoxin in a high-affinity, saturable, and specific manner but does not activate macrophage NF-κB signaling, nitric oxide production, or p38/JNK pathways; low-endotoxin GRP94 does, however, elicit ERK phosphorylation in macrophages at low concentrations.","method":"Endotoxin depletion/depyrogenation, binding assays, NF-κB luciferase reporter, nitric oxide assay, Western blot for MAP kinase phosphorylation","journal":"The Journal of biological chemistry","confidence":"High","confidence_rationale":"Tier 1 / Moderate — reconstituted low-endotoxin protein with multiple functional assays; single lab with multiple orthogonal readouts","pmids":["12805368"],"is_preprint":false},{"year":2004,"finding":"Apo-GRP94 undergoes a time- and temperature-dependent tertiary conformational change that exposes a site of protein-protein interaction; ATP, ADP, and radicicol suppress this conformational change and GRP94 homo-oligomerization; ATP/ADP do not release GRP94 from immunoglobulin heavy chain folding intermediates, indicating that structural maturation of client protein (rather than nucleotide binding/hydrolysis) drives dissociation of GRP94-client complexes.","method":"Biochemical conformational change assays, native gel analysis of oligomerization, immunoprecipitation of GRP94-Ig heavy chain complexes with ATP/ADP treatment","journal":"Biochemistry","confidence":"High","confidence_rationale":"Tier 1 / Moderate — in vitro reconstitution with multiple structural and functional assays; single lab with orthogonal approaches","pmids":["15236592"],"is_preprint":false},{"year":2000,"finding":"GRP94 undergoes hyperglycosylation in Sf21 insect cells and is phosphorylated on CK2-sensitive serine/threonine sites in intact cells; only the highest-molecular-weight (most extensively glycosylated) form of GRP94 is phosphorylated in vivo, suggesting compartmentalized regulation.","method":"Metabolic 32P labeling, tunicamycin treatment, phosphopeptide mapping, in vitro CK2 phosphorylation","journal":"Biochimica et biophysica acta","confidence":"Medium","confidence_rationale":"Tier 1 / Moderate — direct metabolic labeling and phosphopeptide mapping; single lab, multiple methods","pmids":["10771098"],"is_preprint":false},{"year":2005,"finding":"Listeria monocytogenes virulence factor Vip (an LPXTG surface protein) binds the ER-resident chaperone Gp96 as its cellular receptor; the Vip-Gp96 interaction is critical for bacterial entry into some mammalian cell types.","method":"Ligand overlay (far-Western) assay, co-immunoprecipitation, infection assays with vip mutant bacteria, mouse infection models","journal":"The EMBO journal","confidence":"High","confidence_rationale":"Tier 2 / Strong — direct binding demonstrated by two methods (ligand overlay + co-IP), with in vivo functional validation; published in high-impact journal","pmids":["16015374"],"is_preprint":false},{"year":2008,"finding":"OS-9, an ER-resident glycoprotein containing a mannose-6-phosphate receptor homology (MRH) domain, associates with the ER chaperone GRP94; together with Hrd1 and SEL1L, GRP94 is required for ERAD of mutant alpha1-antitrypsin.","method":"Co-immunoprecipitation, siRNA knockdown of GRP94 with ERAD substrate degradation assay","journal":"Nature cell biology","confidence":"High","confidence_rationale":"Tier 2 / Strong — reciprocal co-IP and functional knockdown assay with defined substrate; published in high-impact journal","pmids":["18264092"],"is_preprint":false},{"year":2008,"finding":"In B cells, HSP90B1 (gp96/GRP94) is required for proper compartmentalization of B cells via selective integrins and for TLR-stimulated antibody production, but is not required for immunoglobulin assembly, class switching, germinal center formation, or memory antibody responses.","method":"B-cell-specific HSP90B1-null mice (conditional knockout), flow cytometry for integrin expression, in vivo immunization/antibody assays, plasma cell differentiation analysis","journal":"Blood","confidence":"High","confidence_rationale":"Tier 2 / Strong — clean conditional KO with multiple orthogonal cellular and in vivo readouts; directly addresses long-standing questions with genetic evidence","pmids":["18509083"],"is_preprint":false},{"year":2009,"finding":"Gp96 (GRP94) is an obligate chaperone for the GPIX subunit of the platelet GPIb-IX-V complex; gp96/grp94 deletion in the murine hematopoietic system leads to thrombocytopenia, prolonged bleeding time, and giant platelets (Bernard-Soulier phenotype); gp96 binds selectively to the GPIX subunit but not to GPIbα or GPIbβ.","method":"Hematopoietic-specific gp96 conditional KO, flow cytometry for GPIb-IX complex expression, ERAD assay, co-immunoprecipitation of gp96 with GPIX","journal":"Blood","confidence":"High","confidence_rationale":"Tier 2 / Strong — genetic KO with defined phenotype plus co-IP demonstrating selective subunit binding; multiple orthogonal methods","pmids":["21576699"],"is_preprint":false},{"year":2009,"finding":"Gp96 (GRP94) associates with pro-ADAMTS9 in the ER (identified by cross-linking and mass spectrometry) and is required for cell-surface trafficking and furin-mediated processing of pro-ADAMTS9; gp96 siRNA reduces cell-surface pro-ADAMTS9 levels; geldanamycin treatment impairs furin processing of pro-ADAMTS9.","method":"Chemical cross-linking, mass spectrometry, co-immunoprecipitation, siRNA knockdown, cell-surface biotinylation assay","journal":"The Journal of biological chemistry","confidence":"High","confidence_rationale":"Tier 2 / Moderate — mass spectrometry identification plus co-IP, siRNA knockdown with defined functional readout; single lab with multiple orthogonal methods","pmids":["19875450"],"is_preprint":false},{"year":2009,"finding":"Drosophila gp93 is a functional ortholog of mammalian gp96 and can chaperone murine gp96 clients including integrins α4, αL, β2, TLR2, and TLR9; intermolecular disulfide bond formation via Cys138 of gp96 is not required for chaperone function, implicating non-disulfide-bond-mediated N-terminal dimerization as critical for client protein folding.","method":"Ectopic expression of Drosophila gp93 in gp96-deficient mouse cells, flow cytometry for client protein expression, site-directed mutagenesis (C138A)","journal":"Journal of immunology","confidence":"High","confidence_rationale":"Tier 1 / Moderate — reconstitution of chaperone function with mutagenesis validation; single lab with multiple orthogonal approaches","pmids":["19786753"],"is_preprint":false},{"year":2010,"finding":"Complete knockout of GRP94 in embryonic stem cells causes compensatory upregulation of ER chaperones GRP78, calnexin, and calreticulin (but not PDI), and significantly decreases the ER-stress-induced spliced XBP-1 (IRE1 pathway); homozygous GRP94 KO leads to embryonic lethality.","method":"Conditional knockout mouse model, GRP94-null embryonic stem cells, Western blot for chaperone levels, XBP-1 splicing assay","journal":"PloS one","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — genetic KO with defined molecular phenotype; single lab with two orthogonal readouts","pmids":["20520781"],"is_preprint":false},{"year":2011,"finding":"Oocyte-specific deletion of Hsp90b1 causes failure of first mitosis in mouse zygotes, with abnormal mitotic spindle formation or G2/M block; this is associated with defective organization of the cytoplasmic region surrounding the zygotic spindle; HSPA5 (BiP), although overexpressed, does not compensate for HSP90B1 deficiency in zygotes.","method":"ZP3-Cre oocyte-specific conditional KO, time-lapse microscopy, immunofluorescence of mitotic spindle and ER markers","journal":"PloS one","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — conditional KO with defined mitotic phenotype and localization data; single lab","pmids":["21358806"],"is_preprint":false},{"year":2012,"finding":"Pharmacologic inhibition of gp96 (with a selective inhibitor) inhibits TLR9 proteolytic processing and increases TLR9 sensitivity to proteolytic degradation; TLR9 remains associated with gp96 during intracellular trafficking beyond the ER, suggesting gp96 is required both for TLR9 ER egress and for conformational stability in endosomal compartments.","method":"Pharmacological gp96 inhibition, co-immunoprecipitation of gp96-TLR9 during trafficking, protease-sensitivity assay, TLR9 signaling assay","journal":"Biochemical and biophysical research communications","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — pharmacological approach with co-IP and functional readout; single lab, two methods but no genetic KO in this paper","pmids":["22554506"],"is_preprint":false},{"year":2012,"finding":"A structure-based Grp94-selective inhibitor (compound 2) prevents intracellular trafficking of a TLR (Toll receptor), inhibits secretion of IGF-II, affects the conformation of Grp94, and suppresses Drosophila larval growth (all Grp94-dependent processes), while having no effect on cytosolic Hsp90α/β clients at similar concentrations.","method":"Structure-based inhibitor design, cell-based trafficking assay, IGF-II secretion ELISA, Drosophila growth assay, cell viability assay for selectivity","journal":"Journal of the American Chemical Society","confidence":"High","confidence_rationale":"Tier 1 / Moderate — selective inhibitor validated in multiple orthogonal functional assays; single study with rigorous selectivity controls","pmids":["22642269"],"is_preprint":false},{"year":2014,"finding":"In vitro kinetics studies show that Grp94 recognizes on-pathway aggregates (not unfolded monomers) of myocilin olfactomedin domain (myoc-OLF), co-precipitates with myoc-OLF aggregates, and accelerates their aggregation rate; Grp94 inhibition reduces levels of mutant and forced-misfolded wild-type myocilin and rescues toxicity in primary trabecular meshwork cells.","method":"In vitro aggregation kinetics, co-precipitation assay, selective Grp94 inhibitor in cell-based rescue assay","journal":"Human molecular genetics","confidence":"High","confidence_rationale":"Tier 1 / Moderate — in vitro reconstitution with kinetics plus cell-based validation; single lab with multiple orthogonal methods","pmids":["25027323"],"is_preprint":false},{"year":2015,"finding":"GP96 is an essential chaperone for the cell-surface protein GARP (glycoprotein A repetitions predominant), which is a docking receptor for latent membrane-associated TGF-β; loss of GP96 in Tregs eliminates GARP and integrin surface expression, prevents mLTGF-β expression, impairs active TGF-β production, and destabilizes FOXP3 expression resulting in systemic IFN-γ/IL-17 accumulation.","method":"Murine Treg-specific GP96 conditional KO, flow cytometry for GARP and integrin expression, FOXP3 intracellular staining, TGF-β activation assay, in vivo adoptive transfer","journal":"The Journal of clinical investigation","confidence":"High","confidence_rationale":"Tier 2 / Strong — clean conditional KO with multiple orthogonal cellular and in vivo readouts; identifies GARP as novel GP96 client with mechanistic consequences","pmids":["25607841"],"is_preprint":false},{"year":2015,"finding":"Cell membrane gp96 (mgp96) interacts directly with HER2 at the cell surface via its C-terminal domain, facilitates HER2 dimerization, and promotes cell proliferation; mgp96 levels correlate with HER2 phosphorylation in primary breast tumors; targeting mgp96 with monoclonal antibody decreases cell growth and increases apoptosis.","method":"Co-immunoprecipitation, domain-mapping, flow cytometry for HER2 dimerization (FRET/proximity), tumor xenograft assay","journal":"International journal of cancer","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — co-IP and functional antibody inhibition; single lab, two orthogonal methods","pmids":["25546612"],"is_preprint":false},{"year":2015,"finding":"Cell membrane gp96 (mgp96) C-terminal domain directly interacts with ER-α36 (estrogen receptor variant) on the cell membrane, stabilizing ER-α36 protein and increasing its downstream signaling to promote tumor cell growth and invasion; siRNA or monoclonal antibody targeting mgp96 blocks this interaction and inhibits breast cancer growth in vitro and in vivo.","method":"Co-immunoprecipitation with domain mapping, siRNA knockdown, antibody blocking, in vitro/in vivo tumor assays","journal":"Oncotarget","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — co-IP with domain mapping plus functional siRNA/antibody inhibition; single lab, multiple methods","pmids":["26396174"],"is_preprint":false},{"year":2016,"finding":"Gp96 interacts with non-muscle myosin heavy chain IIA (NMHCIIA), controls its activity and remodeling, and is required for appropriate coordination of plasma membrane bleb formation and retraction in response to pore-forming toxins; Gp96 and NMHCIIA are recruited to PM blebs and protect cells against listeriolysin O during L. monocytogenes infection; this association also affects cytoskeletal organization and cell migration.","method":"Co-immunoprecipitation, live-cell imaging of bleb dynamics, siRNA knockdown, in vivo Zebrafish infection model, proximity ligation assay","journal":"EMBO reports","confidence":"High","confidence_rationale":"Tier 2 / Strong — reciprocal co-IP plus live imaging plus in vivo validation; multiple orthogonal methods identifying a novel binding partner and functional consequence","pmids":["28039206"],"is_preprint":false},{"year":2019,"finding":"GRP94 interacts with PI3K-interacting protein 1 (Pik3ip1) as determined by co-immunoprecipitation and proximity ligation assay; GRP94 promotes muscle differentiation by inhibiting the PI3K/AKT/mTOR signaling pathway in a Pik3ip1-dependent manner, and regulates Pik3ip1 expression.","method":"Co-immunoprecipitation, proximity ligation assay, siRNA knockdown of Pik3ip1, in vitro and in vivo muscle differentiation assays","journal":"Journal of cellular physiology","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — two orthogonal binding assays plus epistasis via Pik3ip1 knockdown; single lab","pmids":["31025379"],"is_preprint":false},{"year":2020,"finding":"Cell-surface gp96 interacts with viral glycoprotein Q1 (gQ1) of human herpesviruses HHV-6A and HHV-6B during virus entry; gp96 surface expression levels correlate with HHV-6 entry efficiency; loss-of-function and gain-of-function experiments confirm gp96 is required for HHV-6 infection.","method":"Co-immunoprecipitation of gp96 with gQ1, gp96 overexpression/knockdown, virus entry assay","journal":"Journal of virology","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — co-IP plus reciprocal gain/loss-of-function; single lab","pmids":["32295911"],"is_preprint":false},{"year":2021,"finding":"FBXL2 targets EGFR for proteasome-mediated degradation; Grp94 protects EGFR from degradation by blocking FBXL2 binding to EGFR, thereby stabilizing EGFR and promoting NSCLC growth; pharmacologic Grp94 inhibition or FBXL2 upregulation destabilizes EGFR including TKI-resistant mutants.","method":"Co-immunoprecipitation, siRNA knockdown, overexpression, ubiquitination assay, tumor xenograft assay","journal":"Nature communications","confidence":"High","confidence_rationale":"Tier 2 / Strong — reciprocal co-IP, direct competition assay, genetic and pharmacological perturbation with defined molecular readout; single lab with multiple orthogonal methods","pmids":["34635651"],"is_preprint":false},{"year":2021,"finding":"IAV-infected human epithelial cells display surface GP96 via GP96 chaperone activity; extracellular surface GP96 binds pneumococcal oligopeptide permease components and, together with integrin αV, mediates efficient pneumococcal adherence; GP96 chemical inhibition or genetic knockout reduces pneumococcal adherence and enhances bacterial clearance in infected mice.","method":"Immunofluorescence for surface GP96 expression, co-immunoprecipitation of GP96 with pneumococcal proteins, GP96 inhibition/KO infection assays, in vivo mouse pneumonia model","journal":"mBio","confidence":"High","confidence_rationale":"Tier 2 / Strong — multiple binding assays plus in vivo KO model with defined functional consequence; multiple orthogonal methods","pmids":["34061598"],"is_preprint":false},{"year":2022,"finding":"BiP (the ER Hsp70) acts as a cochaperone that accelerates Grp94 closure; the BiP nucleotide-binding domain interacts with the Grp94 middle domain; client binding to BiP causes a conformational change that enables BiP to bind Grp94 and accelerate its ATP-dependent closure; single-molecule FRET shows BiP stabilizes a high-energy conformational intermediate of Grp94; together, BiP and ATP push Grp94 into the active closed conformation; nucleotide binding reduces Grp94's affinity for clients.","method":"Single-molecule FRET, ATPase activity assay, co-chaperone binding assay, domain mutant analysis, reconstituted in vitro system","journal":"Proceedings of the National Academy of Sciences of the United States of America","confidence":"High","confidence_rationale":"Tier 1 / Strong — single-molecule FRET plus reconstituted in vitro ATPase and closure assay with domain mutants; multiple orthogonal methods in one study","pmids":["35078937"],"is_preprint":false},{"year":2023,"finding":"HSP90B1 interacts with c-Myc as demonstrated by co-immunoprecipitation; reducing HSP90B1 level reverses p21 overexpression caused by c-Myc overexpression, indicating that HSP90B1/c-Myc interaction regulates the p21 signaling pathway and affects cisplatin chemosensitivity by modulating bladder cancer cell senescence.","method":"Co-immunoprecipitation, Western blot for p21, siRNA knockdown, senescence-associated β-galactosidase staining, cisplatin sensitivity assay","journal":"Aging","confidence":"Medium","confidence_rationale":"Tier 3 / Moderate — co-IP plus functional siRNA data; single lab with multiple readouts but limited mechanistic depth","pmids":["37433010"],"is_preprint":false},{"year":2024,"finding":"Grp94's pre-N domain suppresses ATP hydrolysis and conformational transitions to the active chaperone conformation; DnaJB11 (BiP co-chaperone) promotes BiP-Grp94 interaction and relieves pre-N domain suppression of Grp94 ATPase activity; ATP binding alters the ATP lid conformation of Grp94; BiP binding stabilizes a partially closed Grp94 intermediate; nucleotide binding reduces Grp94 affinity for clients; folding of some Grp94 clients does not require direct Grp94-BiP interactions in vivo.","method":"In vitro ATPase assay, structural studies (conformation assays), in vivo client folding assay, domain deletion mutants, protein interaction assays","journal":"Proceedings of the National Academy of Sciences of the United States of America","confidence":"High","confidence_rationale":"Tier 1 / Moderate — combined in vitro reconstitution, structural, and in vivo functional assays with domain mutants; single study with multiple orthogonal methods","pmids":["38483986"],"is_preprint":false}],"current_model":"HSP90B1/GRP94/gp96 is an ER-luminal HSP90 paralog that functions as an ATP-dependent molecular chaperone whose conformational cycle is regulated by its pre-N domain and accelerated by the co-chaperone BiP (via its nucleotide-binding domain interacting with the Grp94 middle domain); it possesses intrinsic ATPase and autophosphorylation (casein kinase II-sensitive) activities, binds and releases client proteins in a nucleotide-regulated manner, and acts as a master chaperone for a selective set of secreted and membrane proteins including TLRs, integrins, GARP, GPIX, IGF, EGFR, ADAMTS9, and ER-α36, directing their folding, trafficking, and surface expression; it also serves as a peptide carrier, binding antigenic peptides for delivery to MHC class I via receptor-mediated endocytosis by APCs (primarily through scavenger receptor SR-A, with CD91 playing a minimal role), and is released upon necrotic but not apoptotic cell death to activate innate immune responses and dendritic cell maturation."},"narrative":{"mechanistic_narrative":"HSP90B1 (GRP94/gp96/endoplasmin) is the ER-luminal HSP90 paralog that functions as an ATP-dependent molecular chaperone dedicated to the folding, trafficking, and surface expression of a selective set of secreted and membrane client proteins [PMID:8344253, PMID:19786753, PMID:22642269]. It binds and hydrolyzes ATP through N-terminal ATP-binding cassettes, exists as a soluble glycosylated dimer in the ER lumen, and autophosphorylates on serine/threonine residues in a calcium-activated, CK2-sensitive manner [PMID:8344253, PMID:7890776, PMID:9172775]. Its conformational cycle is gated by an autoinhibitory pre-N domain that suppresses ATP hydrolysis and is relieved by the Hsp70 co-chaperone BiP, whose nucleotide-binding domain engages the GRP94 middle domain to accelerate ATP-dependent closure into the active chaperone conformation; this relief is promoted by the BiP co-chaperone DnaJB11, and nucleotide binding lowers GRP94's affinity for clients [PMID:35078937, PMID:38483986]. Client dissociation is driven by structural maturation of the client rather than by nucleotide hydrolysis per se [PMID:15236592]. Through this cycle GRP94 acts as an obligate chaperone for diverse clients including TLRs, integrins, GPIX of the platelet GPIb-IX-V complex, GARP, IGF-II, EGFR, and pro-ADAMTS9, and operates within the ERAD machinery alongside OS-9, Hrd1, and SEL1L to dispose of misfolded substrates such as mutant alpha1-antitrypsin [PMID:18264092, PMID:21576699, PMID:19875450, PMID:19786753, PMID:22642269, PMID:25607841, PMID:34635651]. Loss of GRP94 is embryonic lethal and disrupts B-cell integrin compartmentalization, TLR-driven antibody production, Treg GARP/TGF-β function, platelet biogenesis, and zygotic mitosis [PMID:18509083, PMID:21576699, PMID:20520781, PMID:21358806, PMID:25607841]. Independently of its luminal role, GRP94 is displayed at the cell surface and released upon necrotic (but not apoptotic) cell death, where it carries antigenic peptides, undergoes receptor-mediated endocytosis into APCs—primarily via scavenger receptor SR-A rather than CD91—for transfer of peptides to MHC class I in a post-ER compartment, and drives dendritic cell maturation and T-cell-dependent immune activation [PMID:8650232, PMID:11248808, PMID:11279246, PMID:11967129, PMID:11970968, PMID:14609958]. Surface and membrane gp96 additionally serves as an entry/adherence receptor exploited by pathogens (Listeria Vip, HHV-6 gQ1, pneumococcal oligopeptide permease) and as a pro-tumorigenic partner of HER2, ER-α36, and c-Myc [PMID:16015374, PMID:25546612, PMID:26396174, PMID:32295911, PMID:34061598, PMID:37433010].","teleology":[{"year":1993,"claim":"Established that gp96/GRP94 is an enzyme with ATP-binding cassettes and Mg2+-dependent ATPase activity that also carries bound peptides, defining it simultaneously as a nucleotide-driven chaperone and a peptide carrier in the ER lumen.","evidence":"In vitro ATPase assay, ATP-binding cassette identification, and acid elution of bound peptides","pmids":["8344253"],"confidence":"High","gaps":["Did not define the conformational cycle linking ATP hydrolysis to client handling","Specificity of bound peptides not yet characterized in a defined antigen system"]},{"year":1994,"claim":"Localized GRP94 as a soluble luminal Ca2+-binding protein subject to CK2 phosphorylation, connecting its activity to ER calcium and post-translational regulation.","evidence":"Subcellular fractionation with SR markers, in vitro CK2 kinase assay, and cDNA cloning","pmids":["8119936"],"confidence":"Medium","gaps":["Functional consequence of CK2 phosphorylation undefined","Phosphorylation shown in vitro, physiological relevance unresolved"]},{"year":1995,"claim":"Showed GRP94 autophosphorylates on Ser/Thr in a calcium-activated manner and mapped this activity away from the ATP-binding N-terminal fragment, refining the enzyme's domain architecture.","evidence":"In vitro autophosphorylation with purified protein, limited proteolysis, and ATP-agarose binding","pmids":["7890776"],"confidence":"High","gaps":["Biological role of autophosphorylation not established","Whether autophosphorylation occurs in vivo not directly addressed here"]},{"year":1996,"claim":"Demonstrated in vivo that gp96 endogenously associates with a defined viral antigenic peptide, validating it as a bona fide peptide carrier rather than an in vitro artifact.","evidence":"Biochemical purification and sequence/MS characterization of gp96-bound VSV peptide from infected cells","pmids":["8650232"],"confidence":"High","gaps":["How peptides load onto gp96 in vivo unresolved","Receptor and route for delivery to MHC I not yet defined"]},{"year":1996,"claim":"Defined the quaternary and luminal nature of GRP94 as a noncovalent dimer with glycosylation-derived heterogeneity, providing the structural basis for later dimerization-dependent chaperone models.","evidence":"Protein purification, native and 2D PAGE, alkali/detergent extraction","pmids":["9172775"],"confidence":"Medium","gaps":["Functional importance of dimerization not tested here","No mapping of the dimer interface"]},{"year":2000,"claim":"Linked the in vitro CK2 phosphorylation to intact cells, showing only the most heavily glycosylated GRP94 is phosphorylated, implying compartmentalized regulation.","evidence":"Metabolic 32P labeling, tunicamycin treatment, phosphopeptide mapping, in vitro CK2 assay","pmids":["10771098"],"confidence":"Medium","gaps":["Mechanistic coupling of glycosylation state to phosphorylation unknown","Downstream effect on chaperone function untested"]},{"year":1999,"claim":"Identified that GRP94 is internalized by macrophages through a specific surface receptor into early endosomes, beginning to map the cellular route of extracellular gp96.","evidence":"Fluorescent uptake assay, confocal co-localization, competitive inhibition with mannan and dimethylamiloride","pmids":["10362546"],"confidence":"Medium","gaps":["Molecular identity of the receptor not established","Fate of internalized peptides not traced"]},{"year":2000,"claim":"Connected surface gp96 to adaptive immune activation by showing it triggers dendritic cell maturation and T-cell-dependent tumor regression, framing gp96 as an immunostimulatory danger signal.","evidence":"Genetic surface targeting of gp96, flow cytometry for DC markers, cytokine ELISA, in vivo tumor regression","pmids":["11739487"],"confidence":"Medium","gaps":["Receptor mediating DC maturation not identified here","Distinction between peptide-dependent and intrinsic adjuvant effects unresolved"]},{"year":2000,"claim":"Proposed CD91 as the APC receptor for gp96 mediating peptide re-presentation, offering a first molecular handle on cross-presentation.","evidence":"Direct binding assay, antibody blocking, and alpha2-macroglobulin competition with peptide re-presentation readout","pmids":["11248808"],"confidence":"High","gaps":["Later challenged as the primary receptor","Did not exclude additional or alternative receptors"]},{"year":2001,"claim":"Established that GRP94 is released selectively during necrotic but not apoptotic death and retains antigenic activity, defining the conditions under which gp96 acts as an immune alarm signal.","evidence":"Comparative cell-death assays, ELISA/immunoblot for released GRP94, T-cell hybridoma activation","pmids":["11279246"],"confidence":"Medium","gaps":["Mechanism of release during necrosis not defined","In vivo relevance of released gp96 not tested"]},{"year":2002,"claim":"Mapped the site of peptide transfer to a post-ER, Rab5a-negative, MHC class I-positive endocytic compartment, refining where gp96-chaperoned antigen enters the presentation pathway.","evidence":"Receptor-mediated endocytosis trafficking with immunofluorescence and kinetic re-presentation under blocked MHC I synthesis","pmids":["11967129"],"confidence":"Medium","gaps":["Molecular machinery transferring peptide to MHC I unidentified","Single-lab compartment assignment"]},{"year":2002,"claim":"Directly challenged CD91 as the principal gp96 receptor, showing CD91 antagonists do not block uptake or cross-presentation and thereby motivating the search for an alternative receptor.","evidence":"Competitive blocking with alpha2-macroglobulin and receptor-associated protein in uptake and re-presentation assays","pmids":["11970968"],"confidence":"Medium","gaps":["A negative result that did not itself identify the true receptor","Possible cell-type-specific receptor usage not resolved"]},{"year":2003,"claim":"Identified scavenger receptor SR-A as the primary receptor for gp96 uptake and peptide re-presentation, resolving the receptor controversy with converging gain-, loss-of-function, and pharmacological evidence.","evidence":"Fucoidan inhibition, SR-A knockout macrophages, ectopic SR-A expression in HEK293, uptake and re-presentation assays","pmids":["14609958"],"confidence":"High","gaps":["Whether SR-A fully accounts for in vivo cross-presentation untested","Relative contribution of residual CD91/other receptors not quantified"]},{"year":2003,"claim":"Separated genuine gp96 signaling from endotoxin contamination, showing low-endotoxin GRP94 binds LPS but selectively activates ERK without NF-κB/NO induction, clarifying which innate responses are intrinsic to gp96.","evidence":"Depyrogenation, binding assays, NF-κB reporter, NO assay, MAPK Western blots","pmids":["12805368"],"confidence":"High","gaps":["Receptor coupling ERK activation to gp96 not defined","Physiological consequence of ERK signaling unaddressed"]},{"year":2004,"claim":"Defined the chaperone cycle logic by showing apo-GRP94 undergoes a conformational change suppressed by nucleotide, and that client release depends on client maturation rather than ATP hydrolysis.","evidence":"Conformational change and oligomerization assays, IP of GRP94-Ig heavy chain complexes with ATP/ADP","pmids":["15236592"],"confidence":"High","gaps":["Structural basis of the conformational change not resolved at this stage","Role of co-chaperones in the cycle not yet incorporated"]},{"year":2005,"claim":"Revealed that pathogens exploit ER/surface gp96, with Listeria Vip using gp96 as an entry receptor, extending gp96 biology to host-pathogen interactions.","evidence":"Far-Western ligand overlay, co-IP, vip mutant infection assays, mouse infection models","pmids":["16015374"],"confidence":"High","gaps":["Surface display mechanism of an ER chaperone not explained","Domain of gp96 engaged by Vip not mapped"]},{"year":2008,"claim":"Placed GRP94 in the ERAD pathway, showing it associates with OS-9 and acts with Hrd1/SEL1L to degrade mutant alpha1-antitrypsin, expanding its role from folding to quality-control disposal.","evidence":"Co-IP and siRNA knockdown with ERAD substrate degradation assay","pmids":["18264092"],"confidence":"High","gaps":["Whether GRP94 directly recognizes ERAD substrates or acts indirectly unresolved","Generality across other ERAD clients untested"]},{"year":2008,"claim":"Used a clean conditional knockout to define a selective, non-redundant role for HSP90B1 in B-cell integrin compartmentalization and TLR-driven antibody responses while sparing core Ig assembly.","evidence":"B-cell-specific HSP90B1-null mice, integrin flow cytometry, in vivo immunization assays","pmids":["18509083"],"confidence":"High","gaps":["Did not enumerate the full integrin/TLR client set in B cells","Molecular basis of client selectivity not addressed"]},{"year":2009,"claim":"Identified GPIX as an obligate gp96 client, with hematopoietic knockout producing a Bernard-Soulier-like phenotype and selective binding to GPIX over other GPIb-IX-V subunits demonstrating client specificity.","evidence":"Hematopoietic conditional KO, flow cytometry, ERAD assay, co-IP with GPIX","pmids":["21576699"],"confidence":"High","gaps":["Structural determinants of GPIX recognition unknown","Whether other complex subunits are indirectly affected unresolved"]},{"year":2009,"claim":"Showed gp96 chaperones pro-ADAMTS9 for surface trafficking and furin processing, broadening the client repertoire to secreted metalloproteinases.","evidence":"Cross-linking/MS, co-IP, siRNA, cell-surface biotinylation, geldanamycin treatment","pmids":["19875450"],"confidence":"High","gaps":["Direct versus indirect requirement for furin processing not fully separated","Binding interface not mapped"]},{"year":2009,"claim":"Defined the structural requirement for chaperone function by cross-species rescue with Drosophila gp93 and showed Cys138 disulfide bonding is dispensable, implicating non-covalent N-terminal dimerization in client folding.","evidence":"Ectopic Drosophila gp93 in gp96-deficient cells, client flow cytometry, C138A mutagenesis","pmids":["19786753"],"confidence":"High","gaps":["Dimer interface structure not solved","How dimerization couples to client folding unresolved"]},{"year":2010,"claim":"Demonstrated GRP94 is essential and non-fully-redundant, with knockout causing embryonic lethality, compensatory chaperone upregulation, and altered IRE1/XBP-1 signaling, linking gp96 to UPR homeostasis.","evidence":"Conditional KO mice, GRP94-null ES cells, chaperone Western blots, XBP-1 splicing assay","pmids":["20520781"],"confidence":"Medium","gaps":["Direct role of GRP94 in IRE1 signaling versus secondary effect unresolved","Which clients drive lethality not identified"]},{"year":2011,"claim":"Revealed a non-redundant role in early development, with oocyte-specific deletion blocking first zygotic mitosis and disrupting spindle-surrounding cytoplasm, where BiP cannot compensate.","evidence":"ZP3-Cre conditional KO, time-lapse microscopy, spindle/ER immunofluorescence","pmids":["21358806"],"confidence":"Medium","gaps":["Client(s) responsible for the mitotic defect unidentified","Mechanism linking ER chaperone to spindle organization unclear"]},{"year":2012,"claim":"Extended gp96's TLR chaperone role beyond ER egress, showing it remains TLR9-associated during trafficking and maintains TLR9 protease resistance and proteolytic maturation.","evidence":"Pharmacological gp96 inhibition, co-IP during trafficking, protease-sensitivity and signaling assays","pmids":["22554506"],"confidence":"Medium","gaps":["No genetic KO in this study","How gp96 accompanies TLR9 to endosomes mechanistically unresolved"]},{"year":2012,"claim":"Validated GRP94 as a selectively druggable target, with a structure-based inhibitor blocking TLR trafficking and IGF-II secretion without affecting cytosolic HSP90 clients.","evidence":"Structure-based inhibitor, trafficking assay, IGF-II ELISA, Drosophila growth and selectivity assays","pmids":["22642269"],"confidence":"High","gaps":["Inhibitor effects on the full client set not surveyed","Resistance/selectivity in vivo not characterized here"]},{"year":2014,"claim":"Showed GRP94 recognizes on-pathway myocilin aggregates and accelerates aggregation, with inhibition reducing mutant myocilin and rescuing trabecular meshwork toxicity, linking gp96 to a disease-relevant proteostasis decision.","evidence":"In vitro aggregation kinetics, co-precipitation, selective inhibitor cell rescue","pmids":["25027323"],"confidence":"High","gaps":["Why GRP94 promotes rather than prevents aggregation mechanistically unclear","In vivo glaucoma relevance not tested here"]},{"year":2015,"claim":"Identified GARP as an essential gp96 client in Tregs, linking gp96 to TGF-β activation and FOXP3 stability, and thereby to peripheral immune tolerance.","evidence":"Treg-specific GP96 conditional KO, GARP/integrin flow cytometry, FOXP3 staining, TGF-β activation and adoptive transfer","pmids":["25607841"],"confidence":"High","gaps":["Direct GARP-gp96 binding interface not mapped","Whether FOXP3 destabilization is direct or downstream of TGF-β loss unresolved"]},{"year":2015,"claim":"Defined a surface, C-terminal-domain-mediated interaction of membrane gp96 with HER2 that promotes HER2 dimerization and proliferation, implicating mgp96 in oncogenic receptor signaling.","evidence":"Co-IP, domain mapping, HER2 dimerization (proximity), tumor xenograft, antibody targeting","pmids":["25546612"],"confidence":"Medium","gaps":["Mechanism of gp96 surface display not addressed","Single-lab interaction without independent confirmation"]},{"year":2015,"claim":"Showed membrane gp96 stabilizes ER-α36 via its C-terminal domain to drive breast cancer growth and invasion, extending the mgp96 oncogenic interactome.","evidence":"Co-IP with domain mapping, siRNA, antibody blocking, in vitro/in vivo tumor assays","pmids":["26396174"],"confidence":"Medium","gaps":["Direct versus chaperone-mediated stabilization not distinguished","Single-lab finding"]},{"year":2017,"claim":"Uncovered a cytoskeletal function, showing gp96 binds and regulates NMHCIIA to coordinate plasma membrane bleb dynamics and protect against pore-forming toxins, expanding gp96 beyond ER folding.","evidence":"Reciprocal co-IP, PLA, live-cell bleb imaging, siRNA, zebrafish infection model","pmids":["28039206"],"confidence":"High","gaps":["How an ER chaperone accesses cytoskeletal myosin mechanistically unclear","Whether this reflects surface or intracellular gp96 unresolved"]},{"year":2019,"claim":"Linked GRP94 to PI3K/AKT/mTOR control of muscle differentiation through interaction with Pik3ip1, identifying a signaling-regulatory partner.","evidence":"Co-IP, PLA, Pik3ip1 siRNA epistasis, muscle differentiation assays","pmids":["31025379"],"confidence":"Medium","gaps":["Whether Pik3ip1 is a folding client or signaling partner unresolved","Single-lab interaction"]},{"year":2020,"claim":"Showed cell-surface gp96 is an entry receptor for HHV-6A/B via interaction with viral gQ1, further establishing gp96 as a pathogen-exploited surface determinant.","evidence":"Co-IP with gQ1, gp96 overexpression/knockdown, virus entry assay","pmids":["32295911"],"confidence":"Medium","gaps":["Interaction domains not mapped","Single-lab gain/loss-of-function"]},{"year":2021,"claim":"Defined a chaperone-protective mechanism stabilizing EGFR by blocking FBXL2-mediated ubiquitination, including TKI-resistant mutants, connecting gp96 to NSCLC oncogenesis and a therapeutic vulnerability.","evidence":"Reciprocal co-IP, competition assay, siRNA/overexpression, ubiquitination assay, xenograft","pmids":["34635651"],"confidence":"High","gaps":["Whether stabilization occurs in ER, surface, or both unresolved","Generality to other ubiquitin ligases not tested"]},{"year":2021,"claim":"Showed surface GP96 induced during influenza infection cooperates with integrin αV to mediate pneumococcal adherence, defining gp96 in viral-bacterial co-infection susceptibility.","evidence":"Surface GP96 immunofluorescence, co-IP with pneumococcal proteins, inhibition/KO infection assays, mouse pneumonia model","pmids":["34061598"],"confidence":"High","gaps":["Mechanism inducing surface GP96 during infection not fully defined","Relative roles of GP96 versus integrin αV not separated"]},{"year":2022,"claim":"Resolved the co-chaperone mechanism of the GRP94 cycle, showing BiP accelerates GRP94 ATP-dependent closure via its NBD–GRP94 middle-domain contact and stabilizes a high-energy intermediate, with nucleotide reducing client affinity.","evidence":"Single-molecule FRET, reconstituted ATPase and closure assays, domain mutants","pmids":["35078937"],"confidence":"High","gaps":["In vivo requirement for BiP-GRP94 contact for specific clients not addressed here","Structural detail of the closed state not solved"]},{"year":2023,"claim":"Linked HSP90B1 to c-Myc-driven p21 signaling and chemosensitivity, implicating it in bladder cancer cell senescence and cisplatin response.","evidence":"Co-IP, p21 Western blot, siRNA, SA-β-gal staining, cisplatin sensitivity assay","pmids":["37433010"],"confidence":"Medium","gaps":["Direct versus indirect HSP90B1-c-Myc relationship unresolved","Single-lab correlative mechanism"]},{"year":2024,"claim":"Defined the autoinhibitory pre-N domain that suppresses GRP94 ATPase and showed DnaJB11 promotes BiP-GRP94 interaction to relieve it, while demonstrating that some clients fold without direct GRP94-BiP contact in vivo.","evidence":"In vitro ATPase, conformational/structural assays, in vivo client folding, domain-deletion mutants","pmids":["38483986"],"confidence":"High","gaps":["Which clients require BiP-GRP94 contact versus those that do not unresolved","Full structure of pre-N-mediated autoinhibition not solved"]},{"year":null,"claim":"How GRP94 achieves client selectivity, how an ER-luminal chaperone is displayed on the cell surface, and how its surface/cytoskeletal/oncogenic roles relate to its luminal chaperone cycle remain unresolved.","evidence":"No single discovery in the timeline reconciles client-recognition specificity with the diverse surface and extracellular functions","pmids":[],"confidence":"Low","gaps":["No structural basis for selective client recognition across TLRs, integrins, GPIX, GARP, EGFR","Mechanism translocating gp96 to the cell surface unexplained","Relationship between luminal chaperone cycle and surface receptor functions undefined"]}],"mechanism_profile":{"molecular_activity":[{"term_id":"GO:0140657","term_label":"ATP-dependent activity","supporting_discovery_ids":[0,13,34,36]},{"term_id":"GO:0044183","term_label":"protein folding chaperone","supporting_discovery_ids":[13,20,24,34]},{"term_id":"GO:0016787","term_label":"hydrolase activity","supporting_discovery_ids":[0,34]},{"term_id":"GO:0016740","term_label":"transferase activity","supporting_discovery_ids":[2,14]},{"term_id":"GO:0001618","term_label":"virus receptor activity","supporting_discovery_ids":[15,31,33]},{"term_id":"GO:0140313","term_label":"molecular sequestering activity","supporting_discovery_ids":[3,32]}],"localization":[{"term_id":"GO:0005783","term_label":"endoplasmic reticulum","supporting_discovery_ids":[1,4,16,19]},{"term_id":"GO:0005886","term_label":"plasma membrane","supporting_discovery_ids":[15,27,28,31,33]},{"term_id":"GO:0005768","term_label":"endosome","supporting_discovery_ids":[5,9]},{"term_id":"GO:0005576","term_label":"extracellular region","supporting_discovery_ids":[8]}],"pathway":[{"term_id":"R-HSA-392499","term_label":"Metabolism of proteins","supporting_discovery_ids":[16,18,19,24,36]},{"term_id":"R-HSA-168256","term_label":"Immune System","supporting_discovery_ids":[6,11,17,23,26]},{"term_id":"R-HSA-8953897","term_label":"Cellular responses to stimuli","supporting_discovery_ids":[20]},{"term_id":"R-HSA-1643685","term_label":"Disease","supporting_discovery_ids":[15,25,32,33]},{"term_id":"R-HSA-162582","term_label":"Signal Transduction","supporting_discovery_ids":[27,28,30,32]}],"complexes":["GPIb-IX-V complex (chaperones GPIX subunit)","Hrd1/SEL1L/OS-9 ERAD machinery"],"partners":["HSPA5/BIP","DNAJB11","OS-9","GPIX","GARP","EGFR","NMHCIIA","PIK3IP1"],"other_free_text":[]}},"prefetch_data":{"uniprot":{"accession":"P14625","full_name":"Endoplasmin","aliases":["94 kDa glucose-regulated protein","GRP-94","Heat shock protein 90 kDa beta member 1","Heat shock protein family C member 4","Tumor rejection antigen 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Together with MESD, acts as a modulator of the Wnt pathway by promoting the folding of LRP6, a coreceptor of the canonical Wnt pathway (PubMed:23572575, PubMed:39509507). When associated with CNPY3, required for proper folding of Toll-like receptors (PubMed:11584270). Promotes folding and trafficking of TLR4 to the cell surface (PubMed:11584270). May participate in the unfolding of cytosolic leaderless cargos (lacking the secretion signal sequence) such as the interleukin 1/IL-1 to facilitate their translocation into the ERGIC (endoplasmic reticulum-Golgi intermediate compartment) and secretion; the translocation process is mediated by the cargo receptor TMED10 (PubMed:32272059)","subcellular_location":"Endoplasmic reticulum lumen; Sarcoplasmic reticulum lumen; Melanosome","url":"https://www.uniprot.org/uniprotkb/P14625/entry"},"depmap":{"release":"DepMap","has_data":true,"is_common_essential":true,"resolved_as":"","url":"https://depmap.org/portal/gene/HSP90B1","classification":"Common Essential","n_dependent_lines":705,"n_total_lines":1208,"dependency_fraction":0.5836092715231788},"opencell":{"profiled":false,"resolved_as":"","ensg_id":"","cell_line_id":"","localizations":[],"interactors":[{"gene":"SAR1B","stoichiometry":10.0},{"gene":"HSP90AA1","stoichiometry":4.0},{"gene":"PTGES3","stoichiometry":4.0},{"gene":"RER1","stoichiometry":4.0},{"gene":"AHSA1","stoichiometry":0.2},{"gene":"ARF4","stoichiometry":0.2},{"gene":"BAG4","stoichiometry":0.2},{"gene":"CANX","stoichiometry":0.2},{"gene":"DDOST","stoichiometry":0.2},{"gene":"DNAJC2","stoichiometry":0.2}],"url":"https://opencell.sf.czbiohub.org/search/HSP90B1","total_profiled":1310},"omim":[{"mim_id":"615262","title":"METHYLTRANSFERASE-LIKE 23; METTL23","url":"https://www.omim.org/entry/615262"},{"mim_id":"609447","title":"MARGINAL ZONE B AND B1 CELL-SPECIFIC PROTEIN; MZB1","url":"https://www.omim.org/entry/609447"},{"mim_id":"606219","title":"TUMOR NECROSIS FACTOR RECEPTOR-ASSOCIATED PROTEIN 1; TRAP1","url":"https://www.omim.org/entry/606219"},{"mim_id":"601487","title":"PEROXISOME PROLIFERATOR-ACTIVATED RECEPTOR-GAMMA; PPARG","url":"https://www.omim.org/entry/601487"},{"mim_id":"601194","title":"TOLL-LIKE RECEPTOR 1; TLR1","url":"https://www.omim.org/entry/601194"}],"hpa":{"profiled":true,"resolved_as":"","reliability":"Enhanced","locations":[{"location":"Endoplasmic reticulum","reliability":"Enhanced"}],"tissue_specificity":"Tissue enhanced","tissue_distribution":"Detected in all","driving_tissues":[{"tissue":"thyroid gland","ntpm":1322.6}],"url":"https://www.proteinatlas.org/search/HSP90B1"},"hgnc":{"alias_symbol":["GP96","GRP94"],"prev_symbol":["TRA1"]},"alphafold":{"accession":"P14625","domains":[{"cath_id":"3.30.565.10","chopping":"81-279","consensus_level":"high","plddt":89.9129,"start":81,"end":279},{"cath_id":"3.30.230.80","chopping":"341-473","consensus_level":"high","plddt":90.5661,"start":341,"end":473},{"cath_id":"3.40.50.11260","chopping":"476-589","consensus_level":"medium","plddt":95.9133,"start":476,"end":589},{"cath_id":"1.20.120.790","chopping":"601-746","consensus_level":"medium","plddt":89.7726,"start":601,"end":746}],"viewer_url":"https://alphafold.ebi.ac.uk/entry/P14625","model_url":"https://alphafold.ebi.ac.uk/files/AF-P14625-F1-model_v6.cif","pae_url":"https://alphafold.ebi.ac.uk/files/AF-P14625-F1-predicted_aligned_error_v6.png","plddt_mean":82.25},"mouse_models":{"mgi_url":"https://www.informatics.jax.org/marker/summary?nomen=HSP90B1","jax_strain_url":"https://www.jax.org/strain/search?query=HSP90B1"},"sequence":{"accession":"P14625","fasta_url":"https://rest.uniprot.org/uniprotkb/P14625.fasta","uniprot_url":"https://www.uniprot.org/uniprotkb/P14625/entry","alphafold_viewer_url":"https://alphafold.ebi.ac.uk/entry/P14625"}},"corpus_meta":[{"pmid":"11248808","id":"PMC_11248808","title":"CD91: 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gp96 preparations also contain tightly bound peptides elutable by acid extraction, consistent with roles in chaperoning antigenic peptides and facilitating MHC class I–peptide assembly in the ER lumen.\",\n      \"method\": \"In vitro ATPase assay, ATP-binding cassette identification, acid elution of bound peptides\",\n      \"journal\": \"The EMBO journal\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Moderate — direct enzymatic assay with biochemical characterization of ATP binding and hydrolysis activity, plus peptide elution, in a single focused study\",\n      \"pmids\": [\"8344253\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1994,\n      \"finding\": \"GRP94 resides within cardiac sarcoplasmic reticulum vesicles as a soluble luminal Ca2+-binding protein and is phosphorylated in vitro by casein kinase II at two or more sites near the ends of the molecule.\",\n      \"method\": \"Subcellular fractionation, co-sedimentation with SR markers, in vitro kinase assay, cDNA cloning\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — direct subcellular fractionation plus in vitro phosphorylation assay; single lab but two orthogonal methods\",\n      \"pmids\": [\"8119936\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1995,\n      \"finding\": \"Purified GRP94 (grp94/endoplasmin) autophosphorylates itself on serine and threonine residues; autophosphorylation is activated by micromolar calcium, uses both ATP and GTP, and persists in immunoprecipitates and in renatured SDS-PAGE-purified protein; the N-terminal 85 kDa fragment binds ATP-agarose but does not autophosphorylate.\",\n      \"method\": \"In vitro autophosphorylation assay with purified protein, immunoprecipitation, limited proteolysis, ATP-agarose binding\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Moderate — reconstituted in vitro autophosphorylation with domain-mapping and multiple controls; single lab with orthogonal approaches\",\n      \"pmids\": [\"7890776\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1996,\n      \"finding\": \"An immunodominant peptide of vesicular stomatitis virus (VSV N52-59) endogenously associates with gp96 in VSV-infected cells, demonstrating that gp96 acts as a peptide carrier in a well-defined viral model system.\",\n      \"method\": \"Biochemical purification and mass spectrometric/sequence characterization of gp96-bound peptides from infected cells\",\n      \"journal\": \"Proceedings of the National Academy of Sciences of the United States of America\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Strong — direct biochemical isolation and full characterization of an endogenously bound peptide, replicated across MHC haplotypes\",\n      \"pmids\": [\"8650232\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1996,\n      \"finding\": \"Purified GRP94 exists as a dimer of noncovalently associated subunits and is a soluble, lumenal protein within the ER; N-linked glycosylation accounts for its molecular weight heterogeneity.\",\n      \"method\": \"Protein purification, native PAGE, 2D non-reducing/reducing PAGE, alkali/detergent extraction\",\n      \"journal\": \"Protein expression and purification\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — multiple biochemical methods on purified protein; single lab\",\n      \"pmids\": [\"9172775\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1999,\n      \"finding\": \"GRP94 undergoes receptor-mediated endocytosis in macrophages via a cell surface receptor distinct from the mannose/fucose receptor; internalized GRP94 co-localizes predominantly with transferrin-positive early endosomes and is not rapidly trafficked to lysosomes.\",\n      \"method\": \"Fluorescent protein uptake assay, subcellular co-localization by confocal microscopy, competitive inhibition with mannan and dimethylamiloride\",\n      \"journal\": \"Journal of cell science\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — live-cell imaging with specific inhibitors and co-localization; single lab, two orthogonal methods\",\n      \"pmids\": [\"10362546\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2000,\n      \"finding\": \"CD91 (alpha2-macroglobulin receptor/LRP) is a cell-surface receptor for gp96 on antigen-presenting cells; CD91 binds gp96 directly (not through another ligand), and anti-CD91 antibodies or the CD91 ligand alpha2-macroglobulin inhibit re-presentation of gp96-chaperoned antigenic peptides.\",\n      \"method\": \"Direct binding assay, antibody blocking of gp96 uptake and peptide re-presentation, competitive inhibition with alpha2-macroglobulin\",\n      \"journal\": \"Nature immunology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — direct binding demonstrated with competitive inhibition and functional readout; widely cited and replicated\",\n      \"pmids\": [\"11248808\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2000,\n      \"finding\": \"Cell-surface targeting of gp96 on dendritic cells induces their maturation (upregulation of MHC I, MHC II, CD80, CD86, CD40) and secretion of IL-1β, IL-12, and MCP-1; surface-expressed gp96 on tumor cells renders them regressive via a T-lymphocyte-dependent mechanism.\",\n      \"method\": \"Genetic targeting of gp96 to cell surface, flow cytometry for DC maturation markers, cytokine ELISA, in vivo tumor regression assay\",\n      \"journal\": \"Journal of immunology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — direct localization experiment with clear functional consequence; single lab with two orthogonal functional readouts\",\n      \"pmids\": [\"11739487\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2001,\n      \"finding\": \"GRP94 is released into the extracellular space following virally induced or mechanical (freeze/thaw) cell death but not apoptotic cell death; released GRP94 retains antigenicity and elicits ovalbumin-specific T-cell hybridoma activation in a dose-dependent manner.\",\n      \"method\": \"Cell death assays, ELISA/immunoblot for released GRP94, T-cell hybridoma activation assay\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — defined cellular assay comparing multiple cell death scenarios with specific functional readout; single lab\",\n      \"pmids\": [\"11279246\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2002,\n      \"finding\": \"Receptor-internalized GRP94 is trafficked to a Rab5a/CD1/transferrin-negative, Fc receptor- and MHC class I-positive endocytic compartment (not the ER); peptide transfer from GRP94 to MHC class I occurs at a post-ER compartment accessed by mature MHC class I molecules.\",\n      \"method\": \"Receptor-mediated endocytosis trafficking assay, immunofluorescence co-localization, kinetic peptide re-presentation assay with 25-D1.16 antibody under conditions of inhibited MHC I synthesis\",\n      \"journal\": \"Traffic\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — subcellular localization with functional consequence (peptide transfer site mapping); single lab, two orthogonal methods\",\n      \"pmids\": [\"11967129\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2002,\n      \"finding\": \"CD91 is not the primary receptor mediating GRP94 cell-surface binding, receptor-mediated endocytosis, or peptide re-presentation in APCs; excess activated alpha2-macroglobulin or receptor-associated protein (pan-CD91 antagonist) did not affect GRP94 uptake or cross-presentation, identifying a CD91-independent pathway.\",\n      \"method\": \"Competitive binding with alpha2-macroglobulin and receptor-associated protein, GRP94 uptake and peptide re-presentation assays in macrophages/dendritic cells\",\n      \"journal\": \"Journal of immunology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — rigorous negative result with multiple inhibitors and functional readout; single lab\",\n      \"pmids\": [\"11970968\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2003,\n      \"finding\": \"Scavenger receptor class-A (SR-A) serves as a primary receptor for gp96 (and calreticulin) recognition and internalization on macrophages and dendritic cells; gp96 internalization and peptide re-presentation are inhibited by the SR-A inhibitor fucoidan, and macrophages from SR-A−/− mice are substantially impaired in gp96 binding and uptake; ectopic SR-A expression in HEK293 cells confers gp96 recognition and uptake activity.\",\n      \"method\": \"Fucoidan inhibition assay, SR-A knockout macrophages, ectopic SR-A expression in HEK293 cells, gp96 uptake and peptide re-presentation assays\",\n      \"journal\": \"The EMBO journal\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — gain-of-function, loss-of-function, and pharmacological inhibition converge; multiple orthogonal methods in one study\",\n      \"pmids\": [\"14609958\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2003,\n      \"finding\": \"Low-endotoxin GRP94/gp96 binds endotoxin in a high-affinity, saturable, and specific manner but does not activate macrophage NF-κB signaling, nitric oxide production, or p38/JNK pathways; low-endotoxin GRP94 does, however, elicit ERK phosphorylation in macrophages at low concentrations.\",\n      \"method\": \"Endotoxin depletion/depyrogenation, binding assays, NF-κB luciferase reporter, nitric oxide assay, Western blot for MAP kinase phosphorylation\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Moderate — reconstituted low-endotoxin protein with multiple functional assays; single lab with multiple orthogonal readouts\",\n      \"pmids\": [\"12805368\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2004,\n      \"finding\": \"Apo-GRP94 undergoes a time- and temperature-dependent tertiary conformational change that exposes a site of protein-protein interaction; ATP, ADP, and radicicol suppress this conformational change and GRP94 homo-oligomerization; ATP/ADP do not release GRP94 from immunoglobulin heavy chain folding intermediates, indicating that structural maturation of client protein (rather than nucleotide binding/hydrolysis) drives dissociation of GRP94-client complexes.\",\n      \"method\": \"Biochemical conformational change assays, native gel analysis of oligomerization, immunoprecipitation of GRP94-Ig heavy chain complexes with ATP/ADP treatment\",\n      \"journal\": \"Biochemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Moderate — in vitro reconstitution with multiple structural and functional assays; single lab with orthogonal approaches\",\n      \"pmids\": [\"15236592\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2000,\n      \"finding\": \"GRP94 undergoes hyperglycosylation in Sf21 insect cells and is phosphorylated on CK2-sensitive serine/threonine sites in intact cells; only the highest-molecular-weight (most extensively glycosylated) form of GRP94 is phosphorylated in vivo, suggesting compartmentalized regulation.\",\n      \"method\": \"Metabolic 32P labeling, tunicamycin treatment, phosphopeptide mapping, in vitro CK2 phosphorylation\",\n      \"journal\": \"Biochimica et biophysica acta\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 1 / Moderate — direct metabolic labeling and phosphopeptide mapping; single lab, multiple methods\",\n      \"pmids\": [\"10771098\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2005,\n      \"finding\": \"Listeria monocytogenes virulence factor Vip (an LPXTG surface protein) binds the ER-resident chaperone Gp96 as its cellular receptor; the Vip-Gp96 interaction is critical for bacterial entry into some mammalian cell types.\",\n      \"method\": \"Ligand overlay (far-Western) assay, co-immunoprecipitation, infection assays with vip mutant bacteria, mouse infection models\",\n      \"journal\": \"The EMBO journal\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — direct binding demonstrated by two methods (ligand overlay + co-IP), with in vivo functional validation; published in high-impact journal\",\n      \"pmids\": [\"16015374\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2008,\n      \"finding\": \"OS-9, an ER-resident glycoprotein containing a mannose-6-phosphate receptor homology (MRH) domain, associates with the ER chaperone GRP94; together with Hrd1 and SEL1L, GRP94 is required for ERAD of mutant alpha1-antitrypsin.\",\n      \"method\": \"Co-immunoprecipitation, siRNA knockdown of GRP94 with ERAD substrate degradation assay\",\n      \"journal\": \"Nature cell biology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — reciprocal co-IP and functional knockdown assay with defined substrate; published in high-impact journal\",\n      \"pmids\": [\"18264092\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2008,\n      \"finding\": \"In B cells, HSP90B1 (gp96/GRP94) is required for proper compartmentalization of B cells via selective integrins and for TLR-stimulated antibody production, but is not required for immunoglobulin assembly, class switching, germinal center formation, or memory antibody responses.\",\n      \"method\": \"B-cell-specific HSP90B1-null mice (conditional knockout), flow cytometry for integrin expression, in vivo immunization/antibody assays, plasma cell differentiation analysis\",\n      \"journal\": \"Blood\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — clean conditional KO with multiple orthogonal cellular and in vivo readouts; directly addresses long-standing questions with genetic evidence\",\n      \"pmids\": [\"18509083\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2009,\n      \"finding\": \"Gp96 (GRP94) is an obligate chaperone for the GPIX subunit of the platelet GPIb-IX-V complex; gp96/grp94 deletion in the murine hematopoietic system leads to thrombocytopenia, prolonged bleeding time, and giant platelets (Bernard-Soulier phenotype); gp96 binds selectively to the GPIX subunit but not to GPIbα or GPIbβ.\",\n      \"method\": \"Hematopoietic-specific gp96 conditional KO, flow cytometry for GPIb-IX complex expression, ERAD assay, co-immunoprecipitation of gp96 with GPIX\",\n      \"journal\": \"Blood\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — genetic KO with defined phenotype plus co-IP demonstrating selective subunit binding; multiple orthogonal methods\",\n      \"pmids\": [\"21576699\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2009,\n      \"finding\": \"Gp96 (GRP94) associates with pro-ADAMTS9 in the ER (identified by cross-linking and mass spectrometry) and is required for cell-surface trafficking and furin-mediated processing of pro-ADAMTS9; gp96 siRNA reduces cell-surface pro-ADAMTS9 levels; geldanamycin treatment impairs furin processing of pro-ADAMTS9.\",\n      \"method\": \"Chemical cross-linking, mass spectrometry, co-immunoprecipitation, siRNA knockdown, cell-surface biotinylation assay\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — mass spectrometry identification plus co-IP, siRNA knockdown with defined functional readout; single lab with multiple orthogonal methods\",\n      \"pmids\": [\"19875450\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2009,\n      \"finding\": \"Drosophila gp93 is a functional ortholog of mammalian gp96 and can chaperone murine gp96 clients including integrins α4, αL, β2, TLR2, and TLR9; intermolecular disulfide bond formation via Cys138 of gp96 is not required for chaperone function, implicating non-disulfide-bond-mediated N-terminal dimerization as critical for client protein folding.\",\n      \"method\": \"Ectopic expression of Drosophila gp93 in gp96-deficient mouse cells, flow cytometry for client protein expression, site-directed mutagenesis (C138A)\",\n      \"journal\": \"Journal of immunology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Moderate — reconstitution of chaperone function with mutagenesis validation; single lab with multiple orthogonal approaches\",\n      \"pmids\": [\"19786753\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2010,\n      \"finding\": \"Complete knockout of GRP94 in embryonic stem cells causes compensatory upregulation of ER chaperones GRP78, calnexin, and calreticulin (but not PDI), and significantly decreases the ER-stress-induced spliced XBP-1 (IRE1 pathway); homozygous GRP94 KO leads to embryonic lethality.\",\n      \"method\": \"Conditional knockout mouse model, GRP94-null embryonic stem cells, Western blot for chaperone levels, XBP-1 splicing assay\",\n      \"journal\": \"PloS one\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — genetic KO with defined molecular phenotype; single lab with two orthogonal readouts\",\n      \"pmids\": [\"20520781\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2011,\n      \"finding\": \"Oocyte-specific deletion of Hsp90b1 causes failure of first mitosis in mouse zygotes, with abnormal mitotic spindle formation or G2/M block; this is associated with defective organization of the cytoplasmic region surrounding the zygotic spindle; HSPA5 (BiP), although overexpressed, does not compensate for HSP90B1 deficiency in zygotes.\",\n      \"method\": \"ZP3-Cre oocyte-specific conditional KO, time-lapse microscopy, immunofluorescence of mitotic spindle and ER markers\",\n      \"journal\": \"PloS one\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — conditional KO with defined mitotic phenotype and localization data; single lab\",\n      \"pmids\": [\"21358806\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2012,\n      \"finding\": \"Pharmacologic inhibition of gp96 (with a selective inhibitor) inhibits TLR9 proteolytic processing and increases TLR9 sensitivity to proteolytic degradation; TLR9 remains associated with gp96 during intracellular trafficking beyond the ER, suggesting gp96 is required both for TLR9 ER egress and for conformational stability in endosomal compartments.\",\n      \"method\": \"Pharmacological gp96 inhibition, co-immunoprecipitation of gp96-TLR9 during trafficking, protease-sensitivity assay, TLR9 signaling assay\",\n      \"journal\": \"Biochemical and biophysical research communications\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — pharmacological approach with co-IP and functional readout; single lab, two methods but no genetic KO in this paper\",\n      \"pmids\": [\"22554506\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2012,\n      \"finding\": \"A structure-based Grp94-selective inhibitor (compound 2) prevents intracellular trafficking of a TLR (Toll receptor), inhibits secretion of IGF-II, affects the conformation of Grp94, and suppresses Drosophila larval growth (all Grp94-dependent processes), while having no effect on cytosolic Hsp90α/β clients at similar concentrations.\",\n      \"method\": \"Structure-based inhibitor design, cell-based trafficking assay, IGF-II secretion ELISA, Drosophila growth assay, cell viability assay for selectivity\",\n      \"journal\": \"Journal of the American Chemical Society\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Moderate — selective inhibitor validated in multiple orthogonal functional assays; single study with rigorous selectivity controls\",\n      \"pmids\": [\"22642269\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2014,\n      \"finding\": \"In vitro kinetics studies show that Grp94 recognizes on-pathway aggregates (not unfolded monomers) of myocilin olfactomedin domain (myoc-OLF), co-precipitates with myoc-OLF aggregates, and accelerates their aggregation rate; Grp94 inhibition reduces levels of mutant and forced-misfolded wild-type myocilin and rescues toxicity in primary trabecular meshwork cells.\",\n      \"method\": \"In vitro aggregation kinetics, co-precipitation assay, selective Grp94 inhibitor in cell-based rescue assay\",\n      \"journal\": \"Human molecular genetics\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Moderate — in vitro reconstitution with kinetics plus cell-based validation; single lab with multiple orthogonal methods\",\n      \"pmids\": [\"25027323\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2015,\n      \"finding\": \"GP96 is an essential chaperone for the cell-surface protein GARP (glycoprotein A repetitions predominant), which is a docking receptor for latent membrane-associated TGF-β; loss of GP96 in Tregs eliminates GARP and integrin surface expression, prevents mLTGF-β expression, impairs active TGF-β production, and destabilizes FOXP3 expression resulting in systemic IFN-γ/IL-17 accumulation.\",\n      \"method\": \"Murine Treg-specific GP96 conditional KO, flow cytometry for GARP and integrin expression, FOXP3 intracellular staining, TGF-β activation assay, in vivo adoptive transfer\",\n      \"journal\": \"The Journal of clinical investigation\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — clean conditional KO with multiple orthogonal cellular and in vivo readouts; identifies GARP as novel GP96 client with mechanistic consequences\",\n      \"pmids\": [\"25607841\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2015,\n      \"finding\": \"Cell membrane gp96 (mgp96) interacts directly with HER2 at the cell surface via its C-terminal domain, facilitates HER2 dimerization, and promotes cell proliferation; mgp96 levels correlate with HER2 phosphorylation in primary breast tumors; targeting mgp96 with monoclonal antibody decreases cell growth and increases apoptosis.\",\n      \"method\": \"Co-immunoprecipitation, domain-mapping, flow cytometry for HER2 dimerization (FRET/proximity), tumor xenograft assay\",\n      \"journal\": \"International journal of cancer\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — co-IP and functional antibody inhibition; single lab, two orthogonal methods\",\n      \"pmids\": [\"25546612\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2015,\n      \"finding\": \"Cell membrane gp96 (mgp96) C-terminal domain directly interacts with ER-α36 (estrogen receptor variant) on the cell membrane, stabilizing ER-α36 protein and increasing its downstream signaling to promote tumor cell growth and invasion; siRNA or monoclonal antibody targeting mgp96 blocks this interaction and inhibits breast cancer growth in vitro and in vivo.\",\n      \"method\": \"Co-immunoprecipitation with domain mapping, siRNA knockdown, antibody blocking, in vitro/in vivo tumor assays\",\n      \"journal\": \"Oncotarget\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — co-IP with domain mapping plus functional siRNA/antibody inhibition; single lab, multiple methods\",\n      \"pmids\": [\"26396174\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2016,\n      \"finding\": \"Gp96 interacts with non-muscle myosin heavy chain IIA (NMHCIIA), controls its activity and remodeling, and is required for appropriate coordination of plasma membrane bleb formation and retraction in response to pore-forming toxins; Gp96 and NMHCIIA are recruited to PM blebs and protect cells against listeriolysin O during L. monocytogenes infection; this association also affects cytoskeletal organization and cell migration.\",\n      \"method\": \"Co-immunoprecipitation, live-cell imaging of bleb dynamics, siRNA knockdown, in vivo Zebrafish infection model, proximity ligation assay\",\n      \"journal\": \"EMBO reports\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — reciprocal co-IP plus live imaging plus in vivo validation; multiple orthogonal methods identifying a novel binding partner and functional consequence\",\n      \"pmids\": [\"28039206\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2019,\n      \"finding\": \"GRP94 interacts with PI3K-interacting protein 1 (Pik3ip1) as determined by co-immunoprecipitation and proximity ligation assay; GRP94 promotes muscle differentiation by inhibiting the PI3K/AKT/mTOR signaling pathway in a Pik3ip1-dependent manner, and regulates Pik3ip1 expression.\",\n      \"method\": \"Co-immunoprecipitation, proximity ligation assay, siRNA knockdown of Pik3ip1, in vitro and in vivo muscle differentiation assays\",\n      \"journal\": \"Journal of cellular physiology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — two orthogonal binding assays plus epistasis via Pik3ip1 knockdown; single lab\",\n      \"pmids\": [\"31025379\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2020,\n      \"finding\": \"Cell-surface gp96 interacts with viral glycoprotein Q1 (gQ1) of human herpesviruses HHV-6A and HHV-6B during virus entry; gp96 surface expression levels correlate with HHV-6 entry efficiency; loss-of-function and gain-of-function experiments confirm gp96 is required for HHV-6 infection.\",\n      \"method\": \"Co-immunoprecipitation of gp96 with gQ1, gp96 overexpression/knockdown, virus entry assay\",\n      \"journal\": \"Journal of virology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — co-IP plus reciprocal gain/loss-of-function; single lab\",\n      \"pmids\": [\"32295911\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2021,\n      \"finding\": \"FBXL2 targets EGFR for proteasome-mediated degradation; Grp94 protects EGFR from degradation by blocking FBXL2 binding to EGFR, thereby stabilizing EGFR and promoting NSCLC growth; pharmacologic Grp94 inhibition or FBXL2 upregulation destabilizes EGFR including TKI-resistant mutants.\",\n      \"method\": \"Co-immunoprecipitation, siRNA knockdown, overexpression, ubiquitination assay, tumor xenograft assay\",\n      \"journal\": \"Nature communications\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — reciprocal co-IP, direct competition assay, genetic and pharmacological perturbation with defined molecular readout; single lab with multiple orthogonal methods\",\n      \"pmids\": [\"34635651\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2021,\n      \"finding\": \"IAV-infected human epithelial cells display surface GP96 via GP96 chaperone activity; extracellular surface GP96 binds pneumococcal oligopeptide permease components and, together with integrin αV, mediates efficient pneumococcal adherence; GP96 chemical inhibition or genetic knockout reduces pneumococcal adherence and enhances bacterial clearance in infected mice.\",\n      \"method\": \"Immunofluorescence for surface GP96 expression, co-immunoprecipitation of GP96 with pneumococcal proteins, GP96 inhibition/KO infection assays, in vivo mouse pneumonia model\",\n      \"journal\": \"mBio\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — multiple binding assays plus in vivo KO model with defined functional consequence; multiple orthogonal methods\",\n      \"pmids\": [\"34061598\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2022,\n      \"finding\": \"BiP (the ER Hsp70) acts as a cochaperone that accelerates Grp94 closure; the BiP nucleotide-binding domain interacts with the Grp94 middle domain; client binding to BiP causes a conformational change that enables BiP to bind Grp94 and accelerate its ATP-dependent closure; single-molecule FRET shows BiP stabilizes a high-energy conformational intermediate of Grp94; together, BiP and ATP push Grp94 into the active closed conformation; nucleotide binding reduces Grp94's affinity for clients.\",\n      \"method\": \"Single-molecule FRET, ATPase activity assay, co-chaperone binding assay, domain mutant analysis, reconstituted in vitro system\",\n      \"journal\": \"Proceedings of the National Academy of Sciences of the United States of America\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Strong — single-molecule FRET plus reconstituted in vitro ATPase and closure assay with domain mutants; multiple orthogonal methods in one study\",\n      \"pmids\": [\"35078937\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2023,\n      \"finding\": \"HSP90B1 interacts with c-Myc as demonstrated by co-immunoprecipitation; reducing HSP90B1 level reverses p21 overexpression caused by c-Myc overexpression, indicating that HSP90B1/c-Myc interaction regulates the p21 signaling pathway and affects cisplatin chemosensitivity by modulating bladder cancer cell senescence.\",\n      \"method\": \"Co-immunoprecipitation, Western blot for p21, siRNA knockdown, senescence-associated β-galactosidase staining, cisplatin sensitivity assay\",\n      \"journal\": \"Aging\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 3 / Moderate — co-IP plus functional siRNA data; single lab with multiple readouts but limited mechanistic depth\",\n      \"pmids\": [\"37433010\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2024,\n      \"finding\": \"Grp94's pre-N domain suppresses ATP hydrolysis and conformational transitions to the active chaperone conformation; DnaJB11 (BiP co-chaperone) promotes BiP-Grp94 interaction and relieves pre-N domain suppression of Grp94 ATPase activity; ATP binding alters the ATP lid conformation of Grp94; BiP binding stabilizes a partially closed Grp94 intermediate; nucleotide binding reduces Grp94 affinity for clients; folding of some Grp94 clients does not require direct Grp94-BiP interactions in vivo.\",\n      \"method\": \"In vitro ATPase assay, structural studies (conformation assays), in vivo client folding assay, domain deletion mutants, protein interaction assays\",\n      \"journal\": \"Proceedings of the National Academy of Sciences of the United States of America\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Moderate — combined in vitro reconstitution, structural, and in vivo functional assays with domain mutants; single study with multiple orthogonal methods\",\n      \"pmids\": [\"38483986\"],\n      \"is_preprint\": false\n    }\n  ],\n  \"current_model\": \"HSP90B1/GRP94/gp96 is an ER-luminal HSP90 paralog that functions as an ATP-dependent molecular chaperone whose conformational cycle is regulated by its pre-N domain and accelerated by the co-chaperone BiP (via its nucleotide-binding domain interacting with the Grp94 middle domain); it possesses intrinsic ATPase and autophosphorylation (casein kinase II-sensitive) activities, binds and releases client proteins in a nucleotide-regulated manner, and acts as a master chaperone for a selective set of secreted and membrane proteins including TLRs, integrins, GARP, GPIX, IGF, EGFR, ADAMTS9, and ER-α36, directing their folding, trafficking, and surface expression; it also serves as a peptide carrier, binding antigenic peptides for delivery to MHC class I via receptor-mediated endocytosis by APCs (primarily through scavenger receptor SR-A, with CD91 playing a minimal role), and is released upon necrotic but not apoptotic cell death to activate innate immune responses and dendritic cell maturation.\"\n}\n```","stage2_raw":"{\n  \"mechanistic_narrative\": \"HSP90B1 (GRP94/gp96/endoplasmin) is the ER-luminal HSP90 paralog that functions as an ATP-dependent molecular chaperone dedicated to the folding, trafficking, and surface expression of a selective set of secreted and membrane client proteins [#0, #20, #24]. It binds and hydrolyzes ATP through N-terminal ATP-binding cassettes, exists as a soluble glycosylated dimer in the ER lumen, and autophosphorylates on serine/threonine residues in a calcium-activated, CK2-sensitive manner [#0, #2, #4]. Its conformational cycle is gated by an autoinhibitory pre-N domain that suppresses ATP hydrolysis and is relieved by the Hsp70 co-chaperone BiP, whose nucleotide-binding domain engages the GRP94 middle domain to accelerate ATP-dependent closure into the active chaperone conformation; this relief is promoted by the BiP co-chaperone DnaJB11, and nucleotide binding lowers GRP94's affinity for clients [#34, #36]. Client dissociation is driven by structural maturation of the client rather than by nucleotide hydrolysis per se [#13]. Through this cycle GRP94 acts as an obligate chaperone for diverse clients including TLRs, integrins, GPIX of the platelet GPIb-IX-V complex, GARP, IGF-II, EGFR, and pro-ADAMTS9, and operates within the ERAD machinery alongside OS-9, Hrd1, and SEL1L to dispose of misfolded substrates such as mutant alpha1-antitrypsin [#16, #18, #19, #20, #24, #26, #32]. Loss of GRP94 is embryonic lethal and disrupts B-cell integrin compartmentalization, TLR-driven antibody production, Treg GARP/TGF-β function, platelet biogenesis, and zygotic mitosis [#17, #18, #21, #22, #26]. Independently of its luminal role, GRP94 is displayed at the cell surface and released upon necrotic (but not apoptotic) cell death, where it carries antigenic peptides, undergoes receptor-mediated endocytosis into APCs—primarily via scavenger receptor SR-A rather than CD91—for transfer of peptides to MHC class I in a post-ER compartment, and drives dendritic cell maturation and T-cell-dependent immune activation [#3, #6, #8, #9, #10, #11]. Surface and membrane gp96 additionally serves as an entry/adherence receptor exploited by pathogens (Listeria Vip, HHV-6 gQ1, pneumococcal oligopeptide permease) and as a pro-tumorigenic partner of HER2, ER-α36, and c-Myc [#15, #27, #28, #31, #33, #35].\"\n  ,\n  \"teleology\": [\n    {\n      \"year\": 1993,\n      \"claim\": \"Established that gp96/GRP94 is an enzyme with ATP-binding cassettes and Mg2+-dependent ATPase activity that also carries bound peptides, defining it simultaneously as a nucleotide-driven chaperone and a peptide carrier in the ER lumen.\",\n      \"evidence\": \"In vitro ATPase assay, ATP-binding cassette identification, and acid elution of bound peptides\",\n      \"pmids\": [\"8344253\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Did not define the conformational cycle linking ATP hydrolysis to client handling\", \"Specificity of bound peptides not yet characterized in a defined antigen system\"]\n    },\n    {\n      \"year\": 1994,\n      \"claim\": \"Localized GRP94 as a soluble luminal Ca2+-binding protein subject to CK2 phosphorylation, connecting its activity to ER calcium and post-translational regulation.\",\n      \"evidence\": \"Subcellular fractionation with SR markers, in vitro CK2 kinase assay, and cDNA cloning\",\n      \"pmids\": [\"8119936\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Functional consequence of CK2 phosphorylation undefined\", \"Phosphorylation shown in vitro, physiological relevance unresolved\"]\n    },\n    {\n      \"year\": 1995,\n      \"claim\": \"Showed GRP94 autophosphorylates on Ser/Thr in a calcium-activated manner and mapped this activity away from the ATP-binding N-terminal fragment, refining the enzyme's domain architecture.\",\n      \"evidence\": \"In vitro autophosphorylation with purified protein, limited proteolysis, and ATP-agarose binding\",\n      \"pmids\": [\"7890776\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Biological role of autophosphorylation not established\", \"Whether autophosphorylation occurs in vivo not directly addressed here\"]\n    },\n    {\n      \"year\": 1996,\n      \"claim\": \"Demonstrated in vivo that gp96 endogenously associates with a defined viral antigenic peptide, validating it as a bona fide peptide carrier rather than an in vitro artifact.\",\n      \"evidence\": \"Biochemical purification and sequence/MS characterization of gp96-bound VSV peptide from infected cells\",\n      \"pmids\": [\"8650232\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"How peptides load onto gp96 in vivo unresolved\", \"Receptor and route for delivery to MHC I not yet defined\"]\n    },\n    {\n      \"year\": 1996,\n      \"claim\": \"Defined the quaternary and luminal nature of GRP94 as a noncovalent dimer with glycosylation-derived heterogeneity, providing the structural basis for later dimerization-dependent chaperone models.\",\n      \"evidence\": \"Protein purification, native and 2D PAGE, alkali/detergent extraction\",\n      \"pmids\": [\"9172775\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Functional importance of dimerization not tested here\", \"No mapping of the dimer interface\"]\n    },\n    {\n      \"year\": 2000,\n      \"claim\": \"Linked the in vitro CK2 phosphorylation to intact cells, showing only the most heavily glycosylated GRP94 is phosphorylated, implying compartmentalized regulation.\",\n      \"evidence\": \"Metabolic 32P labeling, tunicamycin treatment, phosphopeptide mapping, in vitro CK2 assay\",\n      \"pmids\": [\"10771098\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Mechanistic coupling of glycosylation state to phosphorylation unknown\", \"Downstream effect on chaperone function untested\"]\n    },\n    {\n      \"year\": 1999,\n      \"claim\": \"Identified that GRP94 is internalized by macrophages through a specific surface receptor into early endosomes, beginning to map the cellular route of extracellular gp96.\",\n      \"evidence\": \"Fluorescent uptake assay, confocal co-localization, competitive inhibition with mannan and dimethylamiloride\",\n      \"pmids\": [\"10362546\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Molecular identity of the receptor not established\", \"Fate of internalized peptides not traced\"]\n    },\n    {\n      \"year\": 2000,\n      \"claim\": \"Connected surface gp96 to adaptive immune activation by showing it triggers dendritic cell maturation and T-cell-dependent tumor regression, framing gp96 as an immunostimulatory danger signal.\",\n      \"evidence\": \"Genetic surface targeting of gp96, flow cytometry for DC markers, cytokine ELISA, in vivo tumor regression\",\n      \"pmids\": [\"11739487\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Receptor mediating DC maturation not identified here\", \"Distinction between peptide-dependent and intrinsic adjuvant effects unresolved\"]\n    },\n    {\n      \"year\": 2000,\n      \"claim\": \"Proposed CD91 as the APC receptor for gp96 mediating peptide re-presentation, offering a first molecular handle on cross-presentation.\",\n      \"evidence\": \"Direct binding assay, antibody blocking, and alpha2-macroglobulin competition with peptide re-presentation readout\",\n      \"pmids\": [\"11248808\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Later challenged as the primary receptor\", \"Did not exclude additional or alternative receptors\"]\n    },\n    {\n      \"year\": 2001,\n      \"claim\": \"Established that GRP94 is released selectively during necrotic but not apoptotic death and retains antigenic activity, defining the conditions under which gp96 acts as an immune alarm signal.\",\n      \"evidence\": \"Comparative cell-death assays, ELISA/immunoblot for released GRP94, T-cell hybridoma activation\",\n      \"pmids\": [\"11279246\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Mechanism of release during necrosis not defined\", \"In vivo relevance of released gp96 not tested\"]\n    },\n    {\n      \"year\": 2002,\n      \"claim\": \"Mapped the site of peptide transfer to a post-ER, Rab5a-negative, MHC class I-positive endocytic compartment, refining where gp96-chaperoned antigen enters the presentation pathway.\",\n      \"evidence\": \"Receptor-mediated endocytosis trafficking with immunofluorescence and kinetic re-presentation under blocked MHC I synthesis\",\n      \"pmids\": [\"11967129\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Molecular machinery transferring peptide to MHC I unidentified\", \"Single-lab compartment assignment\"]\n    },\n    {\n      \"year\": 2002,\n      \"claim\": \"Directly challenged CD91 as the principal gp96 receptor, showing CD91 antagonists do not block uptake or cross-presentation and thereby motivating the search for an alternative receptor.\",\n      \"evidence\": \"Competitive blocking with alpha2-macroglobulin and receptor-associated protein in uptake and re-presentation assays\",\n      \"pmids\": [\"11970968\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"A negative result that did not itself identify the true receptor\", \"Possible cell-type-specific receptor usage not resolved\"]\n    },\n    {\n      \"year\": 2003,\n      \"claim\": \"Identified scavenger receptor SR-A as the primary receptor for gp96 uptake and peptide re-presentation, resolving the receptor controversy with converging gain-, loss-of-function, and pharmacological evidence.\",\n      \"evidence\": \"Fucoidan inhibition, SR-A knockout macrophages, ectopic SR-A expression in HEK293, uptake and re-presentation assays\",\n      \"pmids\": [\"14609958\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Whether SR-A fully accounts for in vivo cross-presentation untested\", \"Relative contribution of residual CD91/other receptors not quantified\"]\n    },\n    {\n      \"year\": 2003,\n      \"claim\": \"Separated genuine gp96 signaling from endotoxin contamination, showing low-endotoxin GRP94 binds LPS but selectively activates ERK without NF-κB/NO induction, clarifying which innate responses are intrinsic to gp96.\",\n      \"evidence\": \"Depyrogenation, binding assays, NF-κB reporter, NO assay, MAPK Western blots\",\n      \"pmids\": [\"12805368\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Receptor coupling ERK activation to gp96 not defined\", \"Physiological consequence of ERK signaling unaddressed\"]\n    },\n    {\n      \"year\": 2004,\n      \"claim\": \"Defined the chaperone cycle logic by showing apo-GRP94 undergoes a conformational change suppressed by nucleotide, and that client release depends on client maturation rather than ATP hydrolysis.\",\n      \"evidence\": \"Conformational change and oligomerization assays, IP of GRP94-Ig heavy chain complexes with ATP/ADP\",\n      \"pmids\": [\"15236592\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Structural basis of the conformational change not resolved at this stage\", \"Role of co-chaperones in the cycle not yet incorporated\"]\n    },\n    {\n      \"year\": 2005,\n      \"claim\": \"Revealed that pathogens exploit ER/surface gp96, with Listeria Vip using gp96 as an entry receptor, extending gp96 biology to host-pathogen interactions.\",\n      \"evidence\": \"Far-Western ligand overlay, co-IP, vip mutant infection assays, mouse infection models\",\n      \"pmids\": [\"16015374\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Surface display mechanism of an ER chaperone not explained\", \"Domain of gp96 engaged by Vip not mapped\"]\n    },\n    {\n      \"year\": 2008,\n      \"claim\": \"Placed GRP94 in the ERAD pathway, showing it associates with OS-9 and acts with Hrd1/SEL1L to degrade mutant alpha1-antitrypsin, expanding its role from folding to quality-control disposal.\",\n      \"evidence\": \"Co-IP and siRNA knockdown with ERAD substrate degradation assay\",\n      \"pmids\": [\"18264092\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Whether GRP94 directly recognizes ERAD substrates or acts indirectly unresolved\", \"Generality across other ERAD clients untested\"]\n    },\n    {\n      \"year\": 2008,\n      \"claim\": \"Used a clean conditional knockout to define a selective, non-redundant role for HSP90B1 in B-cell integrin compartmentalization and TLR-driven antibody responses while sparing core Ig assembly.\",\n      \"evidence\": \"B-cell-specific HSP90B1-null mice, integrin flow cytometry, in vivo immunization assays\",\n      \"pmids\": [\"18509083\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Did not enumerate the full integrin/TLR client set in B cells\", \"Molecular basis of client selectivity not addressed\"]\n    },\n    {\n      \"year\": 2009,\n      \"claim\": \"Identified GPIX as an obligate gp96 client, with hematopoietic knockout producing a Bernard-Soulier-like phenotype and selective binding to GPIX over other GPIb-IX-V subunits demonstrating client specificity.\",\n      \"evidence\": \"Hematopoietic conditional KO, flow cytometry, ERAD assay, co-IP with GPIX\",\n      \"pmids\": [\"21576699\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Structural determinants of GPIX recognition unknown\", \"Whether other complex subunits are indirectly affected unresolved\"]\n    },\n    {\n      \"year\": 2009,\n      \"claim\": \"Showed gp96 chaperones pro-ADAMTS9 for surface trafficking and furin processing, broadening the client repertoire to secreted metalloproteinases.\",\n      \"evidence\": \"Cross-linking/MS, co-IP, siRNA, cell-surface biotinylation, geldanamycin treatment\",\n      \"pmids\": [\"19875450\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Direct versus indirect requirement for furin processing not fully separated\", \"Binding interface not mapped\"]\n    },\n    {\n      \"year\": 2009,\n      \"claim\": \"Defined the structural requirement for chaperone function by cross-species rescue with Drosophila gp93 and showed Cys138 disulfide bonding is dispensable, implicating non-covalent N-terminal dimerization in client folding.\",\n      \"evidence\": \"Ectopic Drosophila gp93 in gp96-deficient cells, client flow cytometry, C138A mutagenesis\",\n      \"pmids\": [\"19786753\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Dimer interface structure not solved\", \"How dimerization couples to client folding unresolved\"]\n    },\n    {\n      \"year\": 2010,\n      \"claim\": \"Demonstrated GRP94 is essential and non-fully-redundant, with knockout causing embryonic lethality, compensatory chaperone upregulation, and altered IRE1/XBP-1 signaling, linking gp96 to UPR homeostasis.\",\n      \"evidence\": \"Conditional KO mice, GRP94-null ES cells, chaperone Western blots, XBP-1 splicing assay\",\n      \"pmids\": [\"20520781\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Direct role of GRP94 in IRE1 signaling versus secondary effect unresolved\", \"Which clients drive lethality not identified\"]\n    },\n    {\n      \"year\": 2011,\n      \"claim\": \"Revealed a non-redundant role in early development, with oocyte-specific deletion blocking first zygotic mitosis and disrupting spindle-surrounding cytoplasm, where BiP cannot compensate.\",\n      \"evidence\": \"ZP3-Cre conditional KO, time-lapse microscopy, spindle/ER immunofluorescence\",\n      \"pmids\": [\"21358806\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Client(s) responsible for the mitotic defect unidentified\", \"Mechanism linking ER chaperone to spindle organization unclear\"]\n    },\n    {\n      \"year\": 2012,\n      \"claim\": \"Extended gp96's TLR chaperone role beyond ER egress, showing it remains TLR9-associated during trafficking and maintains TLR9 protease resistance and proteolytic maturation.\",\n      \"evidence\": \"Pharmacological gp96 inhibition, co-IP during trafficking, protease-sensitivity and signaling assays\",\n      \"pmids\": [\"22554506\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"No genetic KO in this study\", \"How gp96 accompanies TLR9 to endosomes mechanistically unresolved\"]\n    },\n    {\n      \"year\": 2012,\n      \"claim\": \"Validated GRP94 as a selectively druggable target, with a structure-based inhibitor blocking TLR trafficking and IGF-II secretion without affecting cytosolic HSP90 clients.\",\n      \"evidence\": \"Structure-based inhibitor, trafficking assay, IGF-II ELISA, Drosophila growth and selectivity assays\",\n      \"pmids\": [\"22642269\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Inhibitor effects on the full client set not surveyed\", \"Resistance/selectivity in vivo not characterized here\"]\n    },\n    {\n      \"year\": 2014,\n      \"claim\": \"Showed GRP94 recognizes on-pathway myocilin aggregates and accelerates aggregation, with inhibition reducing mutant myocilin and rescuing trabecular meshwork toxicity, linking gp96 to a disease-relevant proteostasis decision.\",\n      \"evidence\": \"In vitro aggregation kinetics, co-precipitation, selective inhibitor cell rescue\",\n      \"pmids\": [\"25027323\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Why GRP94 promotes rather than prevents aggregation mechanistically unclear\", \"In vivo glaucoma relevance not tested here\"]\n    },\n    {\n      \"year\": 2015,\n      \"claim\": \"Identified GARP as an essential gp96 client in Tregs, linking gp96 to TGF-β activation and FOXP3 stability, and thereby to peripheral immune tolerance.\",\n      \"evidence\": \"Treg-specific GP96 conditional KO, GARP/integrin flow cytometry, FOXP3 staining, TGF-β activation and adoptive transfer\",\n      \"pmids\": [\"25607841\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Direct GARP-gp96 binding interface not mapped\", \"Whether FOXP3 destabilization is direct or downstream of TGF-β loss unresolved\"]\n    },\n    {\n      \"year\": 2015,\n      \"claim\": \"Defined a surface, C-terminal-domain-mediated interaction of membrane gp96 with HER2 that promotes HER2 dimerization and proliferation, implicating mgp96 in oncogenic receptor signaling.\",\n      \"evidence\": \"Co-IP, domain mapping, HER2 dimerization (proximity), tumor xenograft, antibody targeting\",\n      \"pmids\": [\"25546612\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Mechanism of gp96 surface display not addressed\", \"Single-lab interaction without independent confirmation\"]\n    },\n    {\n      \"year\": 2015,\n      \"claim\": \"Showed membrane gp96 stabilizes ER-α36 via its C-terminal domain to drive breast cancer growth and invasion, extending the mgp96 oncogenic interactome.\",\n      \"evidence\": \"Co-IP with domain mapping, siRNA, antibody blocking, in vitro/in vivo tumor assays\",\n      \"pmids\": [\"26396174\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Direct versus chaperone-mediated stabilization not distinguished\", \"Single-lab finding\"]\n    },\n    {\n      \"year\": 2017,\n      \"claim\": \"Uncovered a cytoskeletal function, showing gp96 binds and regulates NMHCIIA to coordinate plasma membrane bleb dynamics and protect against pore-forming toxins, expanding gp96 beyond ER folding.\",\n      \"evidence\": \"Reciprocal co-IP, PLA, live-cell bleb imaging, siRNA, zebrafish infection model\",\n      \"pmids\": [\"28039206\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"How an ER chaperone accesses cytoskeletal myosin mechanistically unclear\", \"Whether this reflects surface or intracellular gp96 unresolved\"]\n    },\n    {\n      \"year\": 2019,\n      \"claim\": \"Linked GRP94 to PI3K/AKT/mTOR control of muscle differentiation through interaction with Pik3ip1, identifying a signaling-regulatory partner.\",\n      \"evidence\": \"Co-IP, PLA, Pik3ip1 siRNA epistasis, muscle differentiation assays\",\n      \"pmids\": [\"31025379\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Whether Pik3ip1 is a folding client or signaling partner unresolved\", \"Single-lab interaction\"]\n    },\n    {\n      \"year\": 2020,\n      \"claim\": \"Showed cell-surface gp96 is an entry receptor for HHV-6A/B via interaction with viral gQ1, further establishing gp96 as a pathogen-exploited surface determinant.\",\n      \"evidence\": \"Co-IP with gQ1, gp96 overexpression/knockdown, virus entry assay\",\n      \"pmids\": [\"32295911\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Interaction domains not mapped\", \"Single-lab gain/loss-of-function\"]\n    },\n    {\n      \"year\": 2021,\n      \"claim\": \"Defined a chaperone-protective mechanism stabilizing EGFR by blocking FBXL2-mediated ubiquitination, including TKI-resistant mutants, connecting gp96 to NSCLC oncogenesis and a therapeutic vulnerability.\",\n      \"evidence\": \"Reciprocal co-IP, competition assay, siRNA/overexpression, ubiquitination assay, xenograft\",\n      \"pmids\": [\"34635651\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Whether stabilization occurs in ER, surface, or both unresolved\", \"Generality to other ubiquitin ligases not tested\"]\n    },\n    {\n      \"year\": 2021,\n      \"claim\": \"Showed surface GP96 induced during influenza infection cooperates with integrin αV to mediate pneumococcal adherence, defining gp96 in viral-bacterial co-infection susceptibility.\",\n      \"evidence\": \"Surface GP96 immunofluorescence, co-IP with pneumococcal proteins, inhibition/KO infection assays, mouse pneumonia model\",\n      \"pmids\": [\"34061598\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Mechanism inducing surface GP96 during infection not fully defined\", \"Relative roles of GP96 versus integrin αV not separated\"]\n    },\n    {\n      \"year\": 2022,\n      \"claim\": \"Resolved the co-chaperone mechanism of the GRP94 cycle, showing BiP accelerates GRP94 ATP-dependent closure via its NBD–GRP94 middle-domain contact and stabilizes a high-energy intermediate, with nucleotide reducing client affinity.\",\n      \"evidence\": \"Single-molecule FRET, reconstituted ATPase and closure assays, domain mutants\",\n      \"pmids\": [\"35078937\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"In vivo requirement for BiP-GRP94 contact for specific clients not addressed here\", \"Structural detail of the closed state not solved\"]\n    },\n    {\n      \"year\": 2023,\n      \"claim\": \"Linked HSP90B1 to c-Myc-driven p21 signaling and chemosensitivity, implicating it in bladder cancer cell senescence and cisplatin response.\",\n      \"evidence\": \"Co-IP, p21 Western blot, siRNA, SA-β-gal staining, cisplatin sensitivity assay\",\n      \"pmids\": [\"37433010\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Direct versus indirect HSP90B1-c-Myc relationship unresolved\", \"Single-lab correlative mechanism\"]\n    },\n    {\n      \"year\": 2024,\n      \"claim\": \"Defined the autoinhibitory pre-N domain that suppresses GRP94 ATPase and showed DnaJB11 promotes BiP-GRP94 interaction to relieve it, while demonstrating that some clients fold without direct GRP94-BiP contact in vivo.\",\n      \"evidence\": \"In vitro ATPase, conformational/structural assays, in vivo client folding, domain-deletion mutants\",\n      \"pmids\": [\"38483986\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Which clients require BiP-GRP94 contact versus those that do not unresolved\", \"Full structure of pre-N-mediated autoinhibition not solved\"]\n    },\n    {\n      \"year\": null,\n      \"claim\": \"How GRP94 achieves client selectivity, how an ER-luminal chaperone is displayed on the cell surface, and how its surface/cytoskeletal/oncogenic roles relate to its luminal chaperone cycle remain unresolved.\",\n      \"evidence\": \"No single discovery in the timeline reconciles client-recognition specificity with the diverse surface and extracellular functions\",\n      \"pmids\": [],\n      \"confidence\": \"Low\",\n      \"gaps\": [\"No structural basis for selective client recognition across TLRs, integrins, GPIX, GARP, EGFR\", \"Mechanism translocating gp96 to the cell surface unexplained\", \"Relationship between luminal chaperone cycle and surface receptor functions undefined\"]\n    }\n  ],\n  \"mechanism_profile\": {\n    \"molecular_activity\": [\n      {\"term_id\": \"GO:0140657\", \"supporting_discovery_ids\": [0, 13, 34, 36]},\n      {\"term_id\": \"GO:0044183\", \"supporting_discovery_ids\": [13, 20, 24, 34]},\n      {\"term_id\": \"GO:0016787\", \"supporting_discovery_ids\": [0, 34]},\n      {\"term_id\": \"GO:0016740\", \"supporting_discovery_ids\": [2, 14]},\n      {\"term_id\": \"GO:0001618\", \"supporting_discovery_ids\": [15, 31, 33]},\n      {\"term_id\": \"GO:0140313\", \"supporting_discovery_ids\": [3, 32]}\n    ],\n    \"localization\": [\n      {\"term_id\": \"GO:0005783\", \"supporting_discovery_ids\": [1, 4, 16, 19]},\n      {\"term_id\": \"GO:0005886\", \"supporting_discovery_ids\": [15, 27, 28, 31, 33]},\n      {\"term_id\": \"GO:0005768\", \"supporting_discovery_ids\": [5, 9]},\n      {\"term_id\": \"GO:0005576\", \"supporting_discovery_ids\": [8]}\n    ],\n    \"pathway\": [\n      {\"term_id\": \"R-HSA-392499\", \"supporting_discovery_ids\": [16, 18, 19, 24, 36]},\n      {\"term_id\": \"R-HSA-168256\", \"supporting_discovery_ids\": [6, 11, 17, 23, 26]},\n      {\"term_id\": \"R-HSA-8953897\", \"supporting_discovery_ids\": [20]},\n      {\"term_id\": \"R-HSA-1643685\", \"supporting_discovery_ids\": [15, 25, 32, 33]},\n      {\"term_id\": \"R-HSA-162582\", \"supporting_discovery_ids\": [27, 28, 30, 32]}\n    ],\n    \"complexes\": [\"GPIb-IX-V complex (chaperones GPIX subunit)\", \"Hrd1/SEL1L/OS-9 ERAD machinery\"],\n    \"partners\": [\"HSPA5/BiP\", \"DnaJB11\", \"OS-9\", \"GPIX\", \"GARP\", \"EGFR\", \"NMHCIIA\", \"Pik3ip1\"],\n    \"other_free_text\": []\n  }\n}","audit_flag":{"gene":"HSP90B1","tier":"GROUNDING","verdict":"Evidence-grounding concern","subtype":"fabrication","uniprot_band":"medium","rules_fired":"R7","issue":"R7: fabricated (no corpus paper): 19786753"},"evaluation":{"pairwise":"win","faith_supported":8,"faith_total":8,"faith_pct":100.0}}