{"gene":"HSPB7","run_date":"2026-06-10T01:55:22","timeline":{"discoveries":[{"year":1999,"finding":"HSPB7 (cvHsp) interacts with alpha-filamin (actin-binding protein 280), with amino acid residues 56-119 of HSPB7 identified as important for this specific interaction with the C-terminal tail of alpha-filamin, as demonstrated by yeast two-hybrid and immunoprecipitation experiments.","method":"Yeast two-hybrid and co-immunoprecipitation","journal":"The Journal of biological chemistry","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — reciprocal yeast two-hybrid and immunoprecipitation with domain mapping, single lab","pmids":["10593960"],"is_preprint":false},{"year":2004,"finding":"Under ischemic conditions, HSPB7 (cvHsp) translocates from cytosol to the Z-/I-area of myofibrils in heart and skeletal muscle, with myofibrillar binding resisting extraction with 1 M NaSCN or 1 M urea, indicating tight association with myofibrillar components.","method":"Subcellular fractionation, immunohistochemistry, extraction assays","journal":"Histochemistry and cell biology","confidence":"Medium","confidence_rationale":"Tier 3 / Moderate — localization by immunostaining and biochemical fractionation, replicated across multiple sHSPs in same study","pmids":["15480735"],"is_preprint":false},{"year":2009,"finding":"HSPB7 constitutively localizes to SC35 splicing speckles in cells, driven by its N-terminus; unlike HSPB1 and HSPB5, HSPB7 does not support refolding of heat-unfolded substrates (negative result for classical chaperone activity), suggesting a non-chaperone role at SC35 speckles.","method":"Confocal microscopy (GFP-tagged constructs), luciferase refolding assay","journal":"Biochimica et biophysica acta","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — direct localization by imaging with domain mapping and functional chaperone assay, single lab, two orthogonal methods","pmids":["19464326"],"is_preprint":false},{"year":2010,"finding":"HSPB7 is the most potent polyQ aggregation suppressor within the HSPB family; it prevents polyQ aggregation and toxicity by a mechanism that requires active macroautophagy (ATG5-dependent), is independent of Hsp70 machinery and proteasomal activity, and does not involve refolding of heat-denatured substrates.","method":"Cell-based polyQ aggregation assay, ATG5-/- knockout cells, Drosophila eye degeneration model, luciferase refolding assay, inhibitor studies","journal":"Human molecular genetics","confidence":"High","confidence_rationale":"Tier 2 / Strong — multiple orthogonal methods including genetic KO, pharmacological inhibitors, in vivo Drosophila model, and cell-based assays; mechanistic pathway placement via ATG5 epistasis","pmids":["20843828"],"is_preprint":false},{"year":2011,"finding":"HSPB7 overexpression protects tachypaced atrial myocytes against calcium transient reduction and tachycardia remodeling by directly preventing F-actin stress fiber formation downstream of RhoA GTPase activation, independently of HSPB1.","method":"HL-1 atrial myocyte tachypacing model, calcium transient measurements, F-actin staining, ROCK inhibitor (Y27632), overexpression studies","journal":"PloS one","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — functional assay with pharmacological pathway dissection and overexpression, single lab","pmids":["21731611"],"is_preprint":false},{"year":2013,"finding":"HSPB7 expression in zebrafish is regulated by the transcription factor Gata4; depletion of Hspb7 disrupts Kupffer's vesicle morphology, impairs left-right axis establishment, and causes heart tube formation defects, with the yolk syncytial layer identified as a key site of action; genetic interaction with gata4 was confirmed.","method":"Zebrafish morpholino knockdown, genetic epistasis (gata4 interaction), confocal microscopy","journal":"Developmental biology","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — loss-of-function with specific developmental phenotypes, genetic epistasis in zebrafish, single lab","pmids":["23850773"],"is_preprint":false},{"year":2014,"finding":"HSPB7 expression is induced by p53 in a dose-dependent manner in renal cell carcinoma cells, placing HSPB7 in the p53 pathway; ectopic HSPB7 expression suppresses cancer cell growth.","method":"Dose-response transfection of p53, qPCR, cell growth assay","journal":"International journal of oncology","confidence":"Low","confidence_rationale":"Tier 3 / Weak — single lab, single method for p53 induction, limited mechanistic detail in abstract","pmids":["24585183"],"is_preprint":false},{"year":2016,"finding":"HSPB7 interacts specifically with dimerized filamin C (FLNC) in skeletal muscle; skeletal-muscle-specific ablation of HSPB7 causes progressive myopathy with FLNC aggregation and mislocalization, sarcomere disarray, muscle fibrosis, and abnormal upregulation/mislocalization of γ- and δ-sarcoglycan (but not dystrophin).","method":"Conditional knockout mouse model, co-immunoprecipitation, immunofluorescence","journal":"Journal of cell science","confidence":"High","confidence_rationale":"Tier 2 / Strong — conditional KO with defined phenotype, co-IP binding partner identification, immunofluorescence localization, multiple orthogonal readouts in single study","pmids":["26929074"],"is_preprint":false},{"year":2016,"finding":"MEF2A and AP-1 (Fra-2/c-Jun) transcription factors antagonistically regulate Hspb7 gene expression in skeletal muscle: MEF2A is required for dexamethasone-induced Hspb7 upregulation, while AP-1 suppresses it; Hspb7 levels affect muscle mass in vivo.","method":"ChIP-seq, siRNA knockdown, dexamethasone treatment, qPCR, in vivo muscle manipulation","journal":"Journal of cell science","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — ChIP-seq and siRNA with functional readout, single lab, multiple methods","pmids":["27632998"],"is_preprint":false},{"year":2017,"finding":"HSPB7 is indispensable for cardiac development; global or cardiac-specific HSPB7 KO results in embryonic lethality before E12.5; HSPB7 binds monomeric actin and represses actin polymerization, regulating thin filament length; KO hearts show longer actin/thin filaments, abnormal actin bundles cross-linking Z lines, upregulation of Lmod2, and mislocalization of Tmod1; genetic rescue showed abnormal actin bundles (not elongated filaments) caused lethality.","method":"Global and cardiac-specific KO mouse models, biochemical binding assays, in vitro actin polymerization assay, genetic rescue (HSPB7/Lmod2 double KO), immunofluorescence","journal":"Proceedings of the National Academy of Sciences of the United States of America","confidence":"High","confidence_rationale":"Tier 1–2 / Strong — reconstituted actin-binding in vitro, multiple KO models, genetic epistasis rescue, multiple orthogonal cellular readouts in single rigorous study","pmids":["29078393"],"is_preprint":false},{"year":2017,"finding":"Cardiac-specific inducible HSPB7 KO causes rapid heart failure and arrhythmia; loss of HSPB7 leads to structural disruption of intercalated discs, downregulation of connexin 43, mislocalization of desmoplakin and N-cadherin, and upregulation/aggregation of filamin C in cardiomyocytes, without disrupting sarcomere contractile protein organization.","method":"Cardiac-specific inducible KO mouse, ECG, immunofluorescence, Western blot","journal":"PLoS genetics","confidence":"High","confidence_rationale":"Tier 2 / Strong — conditional KO with specific cardiac phenotype, ECG functional readout, multiple protein localization analyses, single rigorous study","pmids":["28827800"],"is_preprint":false},{"year":2018,"finding":"Zebrafish Hspb7 is a kinetically privileged sensor for reactive electrophilic species (RES); a single conserved cysteine (C117 in zebrafish, conserved in human ortholog) reacts rapidly with native carbonyl-based RES at substoichiometric concentrations; RES adduction causes structural changes (increase in β-sheet content) detected by circular dichroism; a cancer-relevant missense mutation reduces this RES-sensing property.","method":"In vitro RES adduction kinetics, site-directed mutagenesis (C117), circular dichroism, cell-based RES sensing assay","journal":"ACS chemical biology","confidence":"High","confidence_rationale":"Tier 1 / Moderate — in vitro reconstitution with mutagenesis and structural (CD) analysis, validated in living cells, single lab","pmids":["29397684"],"is_preprint":false},{"year":2018,"finding":"Hspb7 binds FilaminC and Titin as interacting partners in cardiac cells; loss of Hspb7 in zebrafish causes focal cardiac fibrosis and sarcomeric abnormalities; HSPB7 loss stimulates autophagic pathways and Hspb5 expression; inhibiting autophagy in HSPB7 mutant human cardiomyocytes causes FilaminC aggregation and developmental cardiomyopathy, establishing that HSPB7 facilitates autophagic processing of damaged FilaminC to maintain sarcomeric homeostasis.","method":"Co-immunoprecipitation (FilaminC, Titin), zebrafish hspb7 mutants, human iPSC-derived cardiomyocytes with HSPB7 mutation, autophagy inhibition, autophagy flux assays","journal":"Developmental biology","confidence":"High","confidence_rationale":"Tier 2 / Strong — co-IP binding partners, genetic loss-of-function in two organisms (zebrafish and human cardiomyocytes), pharmacological epistasis via autophagy inhibition, multiple orthogonal methods","pmids":["29331499"],"is_preprint":false},{"year":2019,"finding":"The flexible N-terminal domain (NTD) of HSPB7 is both necessary and sufficient for association with and inhibition of polyQ aggregation; transplanting the HSPB7 NTD onto HSPB1 (which cannot suppress polyQ aggregation) confers anti-polyQ activity and reduces oligomer size; de-oligomerization of HSPB1 alone does not suffice to gain polyQ suppression activity.","method":"In vitro aggregation assay, domain-swap chimeric constructs (NTD transplant), immunoblotting, fluorescence microscopy, phospho-mimicking HSPB1 mutants","journal":"The Journal of biological chemistry","confidence":"High","confidence_rationale":"Tier 1–2 / Strong — in vitro reconstitution, domain deletion and chimeric mutagenesis, multiple orthogonal methods in single study","pmids":["31097540"],"is_preprint":false},{"year":2020,"finding":"HSPB7 knockdown promotes osteogenic differentiation of human adipose-derived stem cells (hASCs), while overexpression suppresses it; the mechanism involves regulation of the ERK signaling pathway, as inhibition of ERK with U0126 or ERK1/2 siRNA blocks the pro-osteogenic effect of HSPB7 knockdown.","method":"Lentiviral knockdown/overexpression, ERK inhibitor (U0126), ERK siRNA, ALP assay, Alizarin Red staining, in vivo ectopic bone formation","journal":"Stem cell research & therapy","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — loss- and gain-of-function with pharmacological and genetic pathway dissection, single lab","pmids":["33097082"],"is_preprint":false},{"year":2021,"finding":"Recombinant human HspB7 forms two oligomeric forms (dimers ~36 kDa and large oligomers >600 kDa); mild oxidation promotes large oligomer formation; modification of Cys126 by iodoacetamide prevents large oligomer formation; deletion of the first 13 residues or the polySer motif (residues 17-29) also prevents large oligomer formation; HspB7 can form heterodimers with HspB6 and HspB8 through a disulfide-mediated interface.","method":"Recombinant protein purification, size-exclusion chromatography, hydrophobic chromatography, chemical crosslinking, cysteine modification, domain deletion, co-immunoprecipitation","journal":"International journal of molecular sciences","confidence":"Medium","confidence_rationale":"Tier 1–2 / Moderate — in vitro biochemical reconstitution with mutagenesis/deletion analysis and co-IP, single lab","pmids":["34360542"],"is_preprint":false},{"year":2022,"finding":"HSPB7 is not a genuine actin-binding protein: blot overlay shows HspB7 can bind G- and F-actin at the C-terminal large core domain of actin, but ultracentrifugation pelleting is nonspecific (no saturation), HspB7 cannot retard or prevent heat-induced F-actin aggregation, and native gel electrophoresis and chemical crosslinking fail to detect G-actin/HspB7 complexes, unlike confirmed actin binders DNase I and cofilin-2.","method":"Blot overlay, ultracentrifugation co-sedimentation, native gel electrophoresis, chemical crosslinking, heat-induced aggregation assay","journal":"Biochimie","confidence":"Medium","confidence_rationale":"Tier 1 / Moderate — multiple in vitro methods with appropriate controls, single lab; this is a negative mechanistic result","pmids":["35977674"],"is_preprint":false},{"year":2022,"finding":"HDAC1 represses HSPB7 expression in oral squamous cell carcinoma cells through histone deacetylation of the HSPB7 promoter; sodium butyrate (NaB) inhibits HDAC1 and thereby upregulates HSPB7, suppressing cancer cell proliferation and invasion.","method":"ChIP assay (HDAC1 at HSPB7 promoter), Western blot, cell functional assays, in vivo xenograft","journal":"Neoplasma","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — ChIP-based epigenetic mechanism with functional cell assays and in vivo validation, single lab","pmids":["35652621"],"is_preprint":false},{"year":2023,"finding":"HSPB7 interacts with the transcription factor MECOM (which acts as a transcriptional regulator of HSPB7) and inhibits glycolysis in lung adenocarcinoma cells, reducing glucose consumption, lactic acid production, and levels of glycolytic enzymes LDHA, HK2, and PKM2.","method":"Co-immunoprecipitation, ChIP assay (MECOM at HSPB7 promoter), metabolic assays (glucose/lactate), Western blot, cell functional assays","journal":"Oncology reports","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — co-IP and ChIP with functional metabolic readouts, single lab","pmids":["37732539"],"is_preprint":false},{"year":2023,"finding":"HSPB7 silencing in bone marrow mesenchymal stromal cells (BMSCs) promotes adipogenesis while reducing osteogenic differentiation; overexpression enhances osteogenesis; both N-terminal and C-terminal domains are required for full osteoblastic potency; mechanistically, Activin A is identified as a downstream target mediating HSPB7 knockdown-induced osteogenic inhibition.","method":"Lentiviral knockdown/overexpression, domain deletion constructs, ALP/calcium/Alizarin Red/Oil Red O assays, Activin A antibody/SB431542 inhibition","journal":"Stem cell research & therapy","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — domain deletion analysis, pathway identification via ligand/inhibitor, multiple differentiation readouts, single lab","pmids":["37170285"],"is_preprint":false},{"year":2025,"finding":"HSPB7 and FLNC form a strong heterodimer whose structure was solved by X-ray crystallography; the HSPB7-FLNC heterodimer out-competes the FLNC homodimer interface; phosphorylation of FLNC at T2677 (cardiac stress-associated) favors FLNC homodimerization, while phosphorylation at Y2683 shifts equilibrium toward the HSPB7-FLNC heterodimer; HSPB7-FLNC heterodimerization is proposed to abrogate FLNC actin cross-linking and enhance FLNC diffusive mobility; this interaction arose evolutionarily around the time primitive hearts evolved in chordates.","method":"X-ray crystallography, quantitative binding assays, phospho-mimetic mutagenesis, FRAP (diffusive mobility), evolutionary ancestral sequence reconstruction","journal":"Nature communications","confidence":"High","confidence_rationale":"Tier 1 / Strong — crystal structure plus quantitative binding with phospho-mutants, functional diffusion measurements, single rigorous study with multiple orthogonal methods","pmids":["40312381"],"is_preprint":false},{"year":2025,"finding":"Among the five sHSPs tested (HspB1, phospho-mimicking HspB1 3D, HspB5, HspB6, HspB7, HspB8), only HspB7 forms complexes with the FLNC C-terminal fragment (Ig-like domains 19-24); the interaction is mediated by HspB7's α-crystallin domain binding to Ig-like domain 24 of FLNC; this binding induces dissociation of FLNC dimers.","method":"Size-exclusion chromatography, native gel electrophoresis, chemical crosslinking, immunochemistry","journal":"Biochemistry. Biokhimiia","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — multiple in vitro biochemical methods with selectivity panel, single lab","pmids":["41702738"],"is_preprint":false},{"year":2025,"finding":"Disease-causing mutations in FLNC domains 22-24 (EN/D in domain 22; ΔPGL and W2710X in domain 24) differentially reduce or abolish interaction with HspB7: WT~EN/D interact with HspB7 > ΔPGL; Wmut (W2710X) cannot interact with HspB7 or its α-crystallin domain; structural modeling indicates ΔPGL and Wmut expose a hydrophobic groove in domain 24 that reduces HspB7 binding.","method":"Size-exclusion chromatography, native gel electrophoresis, chemical crosslinking, AlphaFold 3 modeling, recombinant mutant proteins","journal":"International journal of molecular sciences","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — multiple in vitro biochemical methods with panel of disease mutants, computational structural support, single lab","pmids":["40564978"],"is_preprint":false}],"current_model":"HSPB7 is a muscle-enriched small heat shock protein that functions primarily as a molecular chaperone for the sarcomere: it binds monomeric actin to limit polymerization and regulate thin filament length, forms a structurally characterized heterodimer with filamin C (FLNC) that competes with the FLNC homodimer interface and is regulated by phosphorylation at the FLNC dimer interface, and supports autophagic processing of damaged sarcomeric proteins (including FLNC and titin) to maintain proteostasis; its N-terminal domain mediates polyQ aggregation suppression via an autophagy-dependent mechanism, it constitutively localizes to SC35 nuclear speckles (driven by its N-terminus) where it lacks classical chaperone-refolding activity, it contains a kinetically privileged reactive cysteine (C117) for electrophilic stress sensing, and loss of HSPB7 causes embryonic cardiac lethality in mice due to abnormal actin bundle formation, or in adult hearts causes intercalated disc disruption, arrhythmia, and heart failure."},"narrative":{"mechanistic_narrative":"HSPB7 is a muscle-enriched small heat shock protein that maintains sarcomeric and intercalated-disc proteostasis in the heart and skeletal muscle, where its loss is developmentally and clinically catastrophic [PMID:29078393, PMID:28827800]. Its central biochemical activity is selective recognition of filamin C (FLNC): HSPB7 binds dimerized FLNC and, via its α-crystallin domain engaging FLNC Ig-like domain 24, forms a crystallographically defined heterodimer that out-competes the FLNC homodimer interface and is tuned by FLNC phosphorylation (T2677 favoring homodimer, Y2683 favoring the HSPB7 heterodimer), thereby antagonizing FLNC actin cross-linking and enhancing its mobility [PMID:40312381, PMID:41702738]. This proteostatic role extends to autophagy: HSPB7 facilitates autophagic processing of damaged FLNC and titin, and its loss in zebrafish and human iPSC-cardiomyocytes drives FLNC aggregation and cardiomyopathy when autophagy is blocked [PMID:29331499]. Consistent with a chaperone-distinct activity, HSPB7 is the most potent polyQ aggregation suppressor of the HSPB family through a macroautophagy-dependent (ATG5-dependent), Hsp70- and proteasome-independent mechanism encoded by its N-terminal domain, which is necessary and sufficient and can transfer this activity onto HSPB1 [PMID:20843828, PMID:31097540]. In cardiomyocytes HSPB7 ablation disrupts intercalated discs with connexin 43 loss and desmoplakin/N-cadherin mislocalization, producing arrhythmia and heart failure, while embryonic loss yields lethal abnormal actin bundles cross-linking Z lines [PMID:29078393, PMID:28827800]. HSPB7 constitutively localizes to SC35 nuclear speckles via its N-terminus and lacks classical refolding activity [PMID:19464326], and it contains a kinetically privileged reactive cysteine (C117) that senses reactive electrophilic species [PMID:29397684]. Whether HSPB7 is a bona fide direct actin-binding protein is contested, with reconstitution studies reporting both repression of actin polymerization and failure to detect specific complexes [PMID:29078393, PMID:35977674]. Beyond muscle, HSPB7 is transcriptionally regulated (by GATA4, MEF2A/AP-1, p53, MECOM, and HDAC1) and modulates osteogenic/adipogenic differentiation and tumor cell metabolism in several contexts [PMID:23850773, PMID:27632998, PMID:37170285, PMID:37732539].","teleology":[{"year":1999,"claim":"Established the first molecular partner of HSPB7, linking it to the actin cytoskeletal scaffold by mapping a filamin-binding region.","evidence":"Yeast two-hybrid and co-IP with domain mapping (residues 56-119) against alpha-filamin C-terminal tail","pmids":["10593960"],"confidence":"Medium","gaps":["Filamin isoform specificity (FLNA vs FLNC) not resolved here","No functional consequence of the interaction defined","Structural basis not determined"]},{"year":2004,"claim":"Showed HSPB7 responds to cardiac/skeletal stress by stably redistributing to myofibrillar Z/I regions, indicating a sarcomeric site of action.","evidence":"Subcellular fractionation, immunohistochemistry, and chaotrope-resistant extraction in ischemic muscle","pmids":["15480735"],"confidence":"Medium","gaps":["Molecular target at the Z/I band not identified","Mechanism of translocation unknown"]},{"year":2009,"claim":"Revealed HSPB7 has a non-canonical, non-refolding role by localizing constitutively to SC35 nuclear speckles, separating it from classical chaperone sHSPs.","evidence":"Confocal imaging of GFP constructs with N-terminal domain mapping and luciferase refolding assay (negative)","pmids":["19464326"],"confidence":"Medium","gaps":["Functional role at SC35 speckles undefined","No splicing or RNA-processing partner identified"]},{"year":2010,"claim":"Defined a distinctive disposal mechanism: HSPB7 suppresses polyQ aggregation through macroautophagy rather than refolding or proteasomal routes.","evidence":"Cell-based polyQ assays, ATG5-/- cells, Drosophila eye model, inhibitor and refolding assays","pmids":["20843828"],"confidence":"High","gaps":["How HSPB7 routes substrates to autophagy is not molecularly defined","No direct autophagy-machinery partner identified"]},{"year":2011,"claim":"Connected HSPB7 to cytoskeletal stress signaling by showing it blocks RhoA/ROCK-driven F-actin stress fiber formation in atrial myocytes.","evidence":"HL-1 tachypacing model, calcium transient measurement, F-actin staining, ROCK inhibition, overexpression","pmids":["21731611"],"confidence":"Medium","gaps":["Direct versus indirect effect on actin not resolved","Mechanistic link to RhoA pathway not biochemically defined"]},{"year":2013,"claim":"Placed HSPB7 in a GATA4-controlled developmental program required for left-right axis and heart tube morphogenesis.","evidence":"Zebrafish morpholino knockdown with gata4 genetic epistasis and confocal imaging","pmids":["23850773"],"confidence":"Medium","gaps":["Morpholino specificity not corroborated by mutant","Molecular effector downstream of HSPB7 in Kupffer's vesicle unknown"]},{"year":2016,"claim":"Demonstrated in vivo that HSPB7 binds dimerized FLNC and is required to prevent FLNC aggregation and myopathy in skeletal muscle.","evidence":"Skeletal-muscle conditional KO mouse, co-IP, immunofluorescence","pmids":["26929074"],"confidence":"High","gaps":["Structural basis of FLNC-dimer selectivity not defined here","Mechanism linking FLNC binding to aggregation prevention unresolved"]},{"year":2016,"claim":"Identified the transcriptional logic controlling HSPB7 in muscle, with MEF2A activating and AP-1 repressing, tying expression to muscle mass.","evidence":"ChIP-seq, siRNA knockdown, dexamethasone treatment, in vivo muscle manipulation","pmids":["27632998"],"confidence":"Medium","gaps":["Direct promoter elements for each factor not fully mapped","Link between expression level and chaperone function not addressed"]},{"year":2017,"claim":"Showed HSPB7 is indispensable for cardiac development and regulates thin-filament length, with abnormal actin bundles—not filament elongation—causing lethality.","evidence":"Global and cardiac KO mice, in vitro actin polymerization/binding assays, HSPB7/Lmod2 double-KO rescue, immunofluorescence","pmids":["29078393"],"confidence":"High","gaps":["Direct actin binding later disputed","How HSPB7 limits actin bundling mechanistically unresolved"]},{"year":2017,"claim":"Established a postnatal cardiac requirement: inducible HSPB7 loss disrupts intercalated discs and causes arrhythmia and heart failure independent of sarcomere contractile organization.","evidence":"Cardiac-specific inducible KO mouse, ECG, immunofluorescence, Western blot","pmids":["28827800"],"confidence":"High","gaps":["Mechanism connecting HSPB7 loss to connexin 43/desmoplakin disruption not defined","Whether FLNC aggregation is cause or consequence unresolved"]},{"year":2018,"claim":"Defined a proteostasis mechanism in the heart: HSPB7 binds FLNC and titin and channels damaged FLNC into autophagy to sustain sarcomeric homeostasis.","evidence":"Co-IP, zebrafish mutants, HSPB7-mutant human iPSC-cardiomyocytes, autophagy inhibition and flux assays","pmids":["29331499"],"confidence":"High","gaps":["Direct autophagy-receptor partner not identified","How titin binding contributes mechanistically unclear"]},{"year":2018,"claim":"Revealed a redox-sensing function: a single conserved cysteine (C117) makes HSPB7 a kinetically privileged sensor of reactive electrophilic species.","evidence":"In vitro RES adduction kinetics, C117 mutagenesis, circular dichroism, cell-based sensing, cancer-relevant mutant","pmids":["29397684"],"confidence":"High","gaps":["Downstream signaling consequence of C117 adduction not defined","Physiological RES targets in muscle unknown"]},{"year":2019,"claim":"Localized the anti-aggregation activity to the flexible N-terminal domain, showing it is necessary, sufficient, and transferable to HSPB1.","evidence":"In vitro aggregation assays, NTD domain-swap chimeras, phospho-mimic mutants, microscopy","pmids":["31097540"],"confidence":"High","gaps":["Structural basis of NTD-polyQ recognition not determined","Connection of NTD activity to autophagy routing unresolved"]},{"year":2021,"claim":"Characterized HSPB7 oligomeric behavior, showing redox- and motif-dependent large-oligomer formation and disulfide-mediated heterodimers with HspB6/HspB8.","evidence":"Recombinant protein SEC, crosslinking, cysteine modification, domain deletion, co-IP","pmids":["34360542"],"confidence":"Medium","gaps":["Functional role of large oligomers unknown","Physiological relevance of HspB6/HspB8 heterodimers untested in vivo"]},{"year":2022,"claim":"Challenged the actin-binding model with a controlled negative study finding no specific, saturable G/F-actin complex.","evidence":"Blot overlay, co-sedimentation, native gels, crosslinking, heat-aggregation assay with positive controls","pmids":["35977674"],"confidence":"Medium","gaps":["Discrepancy with cellular actin-regulation data unresolved","Whether actin effects are indirect not established"]},{"year":2023,"claim":"Extended HSPB7 regulation and function to cancer, with transcriptional control by MECOM/HDAC1 and suppression of glycolysis and tumor growth.","evidence":"Co-IP, ChIP, metabolic assays, cell functional assays, xenograft (multiple tumor types)","pmids":["37732539","35652621"],"confidence":"Medium","gaps":["Mechanism linking HSPB7 to glycolytic enzyme levels undefined","Relationship to muscle chaperone role unclear"]},{"year":2025,"claim":"Provided the structural and biophysical basis of HSPB7-FLNC heterodimerization, defining phospho-regulation and the consequences for FLNC cross-linking and mobility.","evidence":"X-ray crystallography, quantitative binding with phospho-mimetic FLNC, FRAP, ancestral sequence reconstruction; plus SEC/native-gel mapping of α-crystallin domain to FLNC Ig24","pmids":["40312381","41702738"],"confidence":"High","gaps":["In vivo demonstration of phospho-switch in stressed myocardium pending","Quantitative balance of homo- vs heterodimer in cells not measured"]},{"year":2025,"claim":"Linked FLNC disease mutations directly to disrupted HSPB7 binding, providing a mechanistic basis for FLNC-associated myopathy via lost chaperone engagement.","evidence":"SEC, native gels, crosslinking, AlphaFold3 modeling of FLNC domain 22-24 disease mutants","pmids":["40564978"],"confidence":"Medium","gaps":["Functional rescue in patient cells not shown","Whether lost binding alone drives pathology not established"]},{"year":null,"claim":"It remains unresolved how HSPB7's distinct activities—FLNC heterodimerization, autophagic substrate routing, nuclear-speckle residence, and electrophile sensing—are integrated and whether a single biochemical mechanism underlies its non-canonical, non-refolding chaperone role.","evidence":"","pmids":[],"confidence":"Medium","gaps":["No unifying biochemical mechanism linking the four activities","Direct autophagy-receptor partner unidentified","Function at SC35 speckles still undefined"]}],"mechanism_profile":{"molecular_activity":[{"term_id":"GO:0140096","term_label":"catalytic activity, acting on a protein","supporting_discovery_ids":[20,21,16]},{"term_id":"GO:0140299","term_label":"molecular sensor activity","supporting_discovery_ids":[11]},{"term_id":"GO:0008092","term_label":"cytoskeletal protein binding","supporting_discovery_ids":[9,0]},{"term_id":"GO:0044183","term_label":"protein folding chaperone","supporting_discovery_ids":[3,13]}],"localization":[{"term_id":"GO:0005730","term_label":"nucleolus","supporting_discovery_ids":[2]},{"term_id":"GO:0005654","term_label":"nucleoplasm","supporting_discovery_ids":[2]},{"term_id":"GO:0005829","term_label":"cytosol","supporting_discovery_ids":[1]},{"term_id":"GO:0005856","term_label":"cytoskeleton","supporting_discovery_ids":[1,9]}],"pathway":[{"term_id":"R-HSA-9612973","term_label":"Autophagy","supporting_discovery_ids":[3,12]},{"term_id":"R-HSA-392499","term_label":"Metabolism of proteins","supporting_discovery_ids":[12,7]},{"term_id":"R-HSA-1266738","term_label":"Developmental Biology","supporting_discovery_ids":[5,9]},{"term_id":"R-HSA-8953897","term_label":"Cellular responses to stimuli","supporting_discovery_ids":[11]}],"complexes":["HSPB7-FLNC heterodimer","HSPB7-HSPB6 heterodimer","HSPB7-HSPB8 heterodimer"],"partners":["FLNC","FLNA","TTN","HSPB6","HSPB8","MECOM"],"other_free_text":[]}},"prefetch_data":{"uniprot":{"accession":"Q9UBY9","full_name":"Heat shock protein beta-7","aliases":["Cardiovascular heat shock protein","cvHsp"],"length_aa":170,"mass_kda":18.6,"function":"","subcellular_location":"Cytoplasm; Nucleus; Nucleus, Cajal body","url":"https://www.uniprot.org/uniprotkb/Q9UBY9/entry"},"depmap":{"release":"DepMap","has_data":true,"is_common_essential":false,"resolved_as":"","url":"https://depmap.org/portal/gene/HSPB7","classification":"Not Classified","n_dependent_lines":17,"n_total_lines":1208,"dependency_fraction":0.014072847682119206},"opencell":{"profiled":false,"resolved_as":"","ensg_id":"","cell_line_id":"","localizations":[],"interactors":[],"url":"https://opencell.sf.czbiohub.org/search/HSPB7","total_profiled":1310},"omim":[{"mim_id":"619448","title":"STEROID RECEPTOR-ASSOCIATED AND -REGULATED PROTEIN; SRARP","url":"https://www.omim.org/entry/619448"},{"mim_id":"610692","title":"HEAT-SHOCK 27-KD PROTEIN 7; HSPB7","url":"https://www.omim.org/entry/610692"}],"hpa":{"profiled":true,"resolved_as":"","reliability":"Approved","locations":[{"location":"Nucleoplasm","reliability":"Approved"}],"tissue_specificity":"Tissue enhanced","tissue_distribution":"Detected in many","driving_tissues":[{"tissue":"heart muscle","ntpm":3567.7},{"tissue":"skeletal muscle","ntpm":2065.4},{"tissue":"tongue","ntpm":1148.4}],"url":"https://www.proteinatlas.org/search/HSPB7"},"hgnc":{"alias_symbol":["cvHSP"],"prev_symbol":[]},"alphafold":{"accession":"Q9UBY9","domains":[{"cath_id":"2.60.40.790","chopping":"75-152","consensus_level":"medium","plddt":94.1385,"start":75,"end":152}],"viewer_url":"https://alphafold.ebi.ac.uk/entry/Q9UBY9","model_url":"https://alphafold.ebi.ac.uk/files/AF-Q9UBY9-F1-model_v6.cif","pae_url":"https://alphafold.ebi.ac.uk/files/AF-Q9UBY9-F1-predicted_aligned_error_v6.png","plddt_mean":73.31},"mouse_models":{"mgi_url":"https://www.informatics.jax.org/marker/summary?nomen=HSPB7","jax_strain_url":"https://www.jax.org/strain/search?query=HSPB7"},"sequence":{"accession":"Q9UBY9","fasta_url":"https://rest.uniprot.org/uniprotkb/Q9UBY9.fasta","uniprot_url":"https://www.uniprot.org/uniprotkb/Q9UBY9/entry","alphafold_viewer_url":"https://alphafold.ebi.ac.uk/entry/Q9UBY9"}},"corpus_meta":[{"pmid":"15480735","id":"PMC_15480735","title":"Comparison 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unlike HSPB1 and HSPB5, HSPB7 does not support refolding of heat-unfolded substrates (negative result for classical chaperone activity), suggesting a non-chaperone role at SC35 speckles.\",\n      \"method\": \"Confocal microscopy (GFP-tagged constructs), luciferase refolding assay\",\n      \"journal\": \"Biochimica et biophysica acta\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — direct localization by imaging with domain mapping and functional chaperone assay, single lab, two orthogonal methods\",\n      \"pmids\": [\"19464326\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2010,\n      \"finding\": \"HSPB7 is the most potent polyQ aggregation suppressor within the HSPB family; it prevents polyQ aggregation and toxicity by a mechanism that requires active macroautophagy (ATG5-dependent), is independent of Hsp70 machinery and proteasomal activity, and does not involve refolding of heat-denatured substrates.\",\n      \"method\": \"Cell-based polyQ aggregation assay, ATG5-/- knockout cells, Drosophila eye degeneration model, luciferase refolding assay, inhibitor studies\",\n      \"journal\": \"Human molecular genetics\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — multiple orthogonal methods including genetic KO, pharmacological inhibitors, in vivo Drosophila model, and cell-based assays; mechanistic pathway placement via ATG5 epistasis\",\n      \"pmids\": [\"20843828\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2011,\n      \"finding\": \"HSPB7 overexpression protects tachypaced atrial myocytes against calcium transient reduction and tachycardia remodeling by directly preventing F-actin stress fiber formation downstream of RhoA GTPase activation, independently of HSPB1.\",\n      \"method\": \"HL-1 atrial myocyte tachypacing model, calcium transient measurements, F-actin staining, ROCK inhibitor (Y27632), overexpression studies\",\n      \"journal\": \"PloS one\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — functional assay with pharmacological pathway dissection and overexpression, single lab\",\n      \"pmids\": [\"21731611\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2013,\n      \"finding\": \"HSPB7 expression in zebrafish is regulated by the transcription factor Gata4; depletion of Hspb7 disrupts Kupffer's vesicle morphology, impairs left-right axis establishment, and causes heart tube formation defects, with the yolk syncytial layer identified as a key site of action; genetic interaction with gata4 was confirmed.\",\n      \"method\": \"Zebrafish morpholino knockdown, genetic epistasis (gata4 interaction), confocal microscopy\",\n      \"journal\": \"Developmental biology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — loss-of-function with specific developmental phenotypes, genetic epistasis in zebrafish, single lab\",\n      \"pmids\": [\"23850773\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2014,\n      \"finding\": \"HSPB7 expression is induced by p53 in a dose-dependent manner in renal cell carcinoma cells, placing HSPB7 in the p53 pathway; ectopic HSPB7 expression suppresses cancer cell growth.\",\n      \"method\": \"Dose-response transfection of p53, qPCR, cell growth assay\",\n      \"journal\": \"International journal of oncology\",\n      \"confidence\": \"Low\",\n      \"confidence_rationale\": \"Tier 3 / Weak — single lab, single method for p53 induction, limited mechanistic detail in abstract\",\n      \"pmids\": [\"24585183\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2016,\n      \"finding\": \"HSPB7 interacts specifically with dimerized filamin C (FLNC) in skeletal muscle; skeletal-muscle-specific ablation of HSPB7 causes progressive myopathy with FLNC aggregation and mislocalization, sarcomere disarray, muscle fibrosis, and abnormal upregulation/mislocalization of γ- and δ-sarcoglycan (but not dystrophin).\",\n      \"method\": \"Conditional knockout mouse model, co-immunoprecipitation, immunofluorescence\",\n      \"journal\": \"Journal of cell science\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — conditional KO with defined phenotype, co-IP binding partner identification, immunofluorescence localization, multiple orthogonal readouts in single study\",\n      \"pmids\": [\"26929074\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2016,\n      \"finding\": \"MEF2A and AP-1 (Fra-2/c-Jun) transcription factors antagonistically regulate Hspb7 gene expression in skeletal muscle: MEF2A is required for dexamethasone-induced Hspb7 upregulation, while AP-1 suppresses it; Hspb7 levels affect muscle mass in vivo.\",\n      \"method\": \"ChIP-seq, siRNA knockdown, dexamethasone treatment, qPCR, in vivo muscle manipulation\",\n      \"journal\": \"Journal of cell science\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — ChIP-seq and siRNA with functional readout, single lab, multiple methods\",\n      \"pmids\": [\"27632998\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2017,\n      \"finding\": \"HSPB7 is indispensable for cardiac development; global or cardiac-specific HSPB7 KO results in embryonic lethality before E12.5; HSPB7 binds monomeric actin and represses actin polymerization, regulating thin filament length; KO hearts show longer actin/thin filaments, abnormal actin bundles cross-linking Z lines, upregulation of Lmod2, and mislocalization of Tmod1; genetic rescue showed abnormal actin bundles (not elongated filaments) caused lethality.\",\n      \"method\": \"Global and cardiac-specific KO mouse models, biochemical binding assays, in vitro actin polymerization assay, genetic rescue (HSPB7/Lmod2 double KO), immunofluorescence\",\n      \"journal\": \"Proceedings of the National Academy of Sciences of the United States of America\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1–2 / Strong — reconstituted actin-binding in vitro, multiple KO models, genetic epistasis rescue, multiple orthogonal cellular readouts in single rigorous study\",\n      \"pmids\": [\"29078393\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2017,\n      \"finding\": \"Cardiac-specific inducible HSPB7 KO causes rapid heart failure and arrhythmia; loss of HSPB7 leads to structural disruption of intercalated discs, downregulation of connexin 43, mislocalization of desmoplakin and N-cadherin, and upregulation/aggregation of filamin C in cardiomyocytes, without disrupting sarcomere contractile protein organization.\",\n      \"method\": \"Cardiac-specific inducible KO mouse, ECG, immunofluorescence, Western blot\",\n      \"journal\": \"PLoS genetics\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — conditional KO with specific cardiac phenotype, ECG functional readout, multiple protein localization analyses, single rigorous study\",\n      \"pmids\": [\"28827800\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2018,\n      \"finding\": \"Zebrafish Hspb7 is a kinetically privileged sensor for reactive electrophilic species (RES); a single conserved cysteine (C117 in zebrafish, conserved in human ortholog) reacts rapidly with native carbonyl-based RES at substoichiometric concentrations; RES adduction causes structural changes (increase in β-sheet content) detected by circular dichroism; a cancer-relevant missense mutation reduces this RES-sensing property.\",\n      \"method\": \"In vitro RES adduction kinetics, site-directed mutagenesis (C117), circular dichroism, cell-based RES sensing assay\",\n      \"journal\": \"ACS chemical biology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Moderate — in vitro reconstitution with mutagenesis and structural (CD) analysis, validated in living cells, single lab\",\n      \"pmids\": [\"29397684\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2018,\n      \"finding\": \"Hspb7 binds FilaminC and Titin as interacting partners in cardiac cells; loss of Hspb7 in zebrafish causes focal cardiac fibrosis and sarcomeric abnormalities; HSPB7 loss stimulates autophagic pathways and Hspb5 expression; inhibiting autophagy in HSPB7 mutant human cardiomyocytes causes FilaminC aggregation and developmental cardiomyopathy, establishing that HSPB7 facilitates autophagic processing of damaged FilaminC to maintain sarcomeric homeostasis.\",\n      \"method\": \"Co-immunoprecipitation (FilaminC, Titin), zebrafish hspb7 mutants, human iPSC-derived cardiomyocytes with HSPB7 mutation, autophagy inhibition, autophagy flux assays\",\n      \"journal\": \"Developmental biology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — co-IP binding partners, genetic loss-of-function in two organisms (zebrafish and human cardiomyocytes), pharmacological epistasis via autophagy inhibition, multiple orthogonal methods\",\n      \"pmids\": [\"29331499\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2019,\n      \"finding\": \"The flexible N-terminal domain (NTD) of HSPB7 is both necessary and sufficient for association with and inhibition of polyQ aggregation; transplanting the HSPB7 NTD onto HSPB1 (which cannot suppress polyQ aggregation) confers anti-polyQ activity and reduces oligomer size; de-oligomerization of HSPB1 alone does not suffice to gain polyQ suppression activity.\",\n      \"method\": \"In vitro aggregation assay, domain-swap chimeric constructs (NTD transplant), immunoblotting, fluorescence microscopy, phospho-mimicking HSPB1 mutants\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1–2 / Strong — in vitro reconstitution, domain deletion and chimeric mutagenesis, multiple orthogonal methods in single study\",\n      \"pmids\": [\"31097540\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2020,\n      \"finding\": \"HSPB7 knockdown promotes osteogenic differentiation of human adipose-derived stem cells (hASCs), while overexpression suppresses it; the mechanism involves regulation of the ERK signaling pathway, as inhibition of ERK with U0126 or ERK1/2 siRNA blocks the pro-osteogenic effect of HSPB7 knockdown.\",\n      \"method\": \"Lentiviral knockdown/overexpression, ERK inhibitor (U0126), ERK siRNA, ALP assay, Alizarin Red staining, in vivo ectopic bone formation\",\n      \"journal\": \"Stem cell research & therapy\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — loss- and gain-of-function with pharmacological and genetic pathway dissection, single lab\",\n      \"pmids\": [\"33097082\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2021,\n      \"finding\": \"Recombinant human HspB7 forms two oligomeric forms (dimers ~36 kDa and large oligomers >600 kDa); mild oxidation promotes large oligomer formation; modification of Cys126 by iodoacetamide prevents large oligomer formation; deletion of the first 13 residues or the polySer motif (residues 17-29) also prevents large oligomer formation; HspB7 can form heterodimers with HspB6 and HspB8 through a disulfide-mediated interface.\",\n      \"method\": \"Recombinant protein purification, size-exclusion chromatography, hydrophobic chromatography, chemical crosslinking, cysteine modification, domain deletion, co-immunoprecipitation\",\n      \"journal\": \"International journal of molecular sciences\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 1–2 / Moderate — in vitro biochemical reconstitution with mutagenesis/deletion analysis and co-IP, single lab\",\n      \"pmids\": [\"34360542\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2022,\n      \"finding\": \"HSPB7 is not a genuine actin-binding protein: blot overlay shows HspB7 can bind G- and F-actin at the C-terminal large core domain of actin, but ultracentrifugation pelleting is nonspecific (no saturation), HspB7 cannot retard or prevent heat-induced F-actin aggregation, and native gel electrophoresis and chemical crosslinking fail to detect G-actin/HspB7 complexes, unlike confirmed actin binders DNase I and cofilin-2.\",\n      \"method\": \"Blot overlay, ultracentrifugation co-sedimentation, native gel electrophoresis, chemical crosslinking, heat-induced aggregation assay\",\n      \"journal\": \"Biochimie\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 1 / Moderate — multiple in vitro methods with appropriate controls, single lab; this is a negative mechanistic result\",\n      \"pmids\": [\"35977674\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2022,\n      \"finding\": \"HDAC1 represses HSPB7 expression in oral squamous cell carcinoma cells through histone deacetylation of the HSPB7 promoter; sodium butyrate (NaB) inhibits HDAC1 and thereby upregulates HSPB7, suppressing cancer cell proliferation and invasion.\",\n      \"method\": \"ChIP assay (HDAC1 at HSPB7 promoter), Western blot, cell functional assays, in vivo xenograft\",\n      \"journal\": \"Neoplasma\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — ChIP-based epigenetic mechanism with functional cell assays and in vivo validation, single lab\",\n      \"pmids\": [\"35652621\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2023,\n      \"finding\": \"HSPB7 interacts with the transcription factor MECOM (which acts as a transcriptional regulator of HSPB7) and inhibits glycolysis in lung adenocarcinoma cells, reducing glucose consumption, lactic acid production, and levels of glycolytic enzymes LDHA, HK2, and PKM2.\",\n      \"method\": \"Co-immunoprecipitation, ChIP assay (MECOM at HSPB7 promoter), metabolic assays (glucose/lactate), Western blot, cell functional assays\",\n      \"journal\": \"Oncology reports\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — co-IP and ChIP with functional metabolic readouts, single lab\",\n      \"pmids\": [\"37732539\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2023,\n      \"finding\": \"HSPB7 silencing in bone marrow mesenchymal stromal cells (BMSCs) promotes adipogenesis while reducing osteogenic differentiation; overexpression enhances osteogenesis; both N-terminal and C-terminal domains are required for full osteoblastic potency; mechanistically, Activin A is identified as a downstream target mediating HSPB7 knockdown-induced osteogenic inhibition.\",\n      \"method\": \"Lentiviral knockdown/overexpression, domain deletion constructs, ALP/calcium/Alizarin Red/Oil Red O assays, Activin A antibody/SB431542 inhibition\",\n      \"journal\": \"Stem cell research & therapy\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — domain deletion analysis, pathway identification via ligand/inhibitor, multiple differentiation readouts, single lab\",\n      \"pmids\": [\"37170285\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2025,\n      \"finding\": \"HSPB7 and FLNC form a strong heterodimer whose structure was solved by X-ray crystallography; the HSPB7-FLNC heterodimer out-competes the FLNC homodimer interface; phosphorylation of FLNC at T2677 (cardiac stress-associated) favors FLNC homodimerization, while phosphorylation at Y2683 shifts equilibrium toward the HSPB7-FLNC heterodimer; HSPB7-FLNC heterodimerization is proposed to abrogate FLNC actin cross-linking and enhance FLNC diffusive mobility; this interaction arose evolutionarily around the time primitive hearts evolved in chordates.\",\n      \"method\": \"X-ray crystallography, quantitative binding assays, phospho-mimetic mutagenesis, FRAP (diffusive mobility), evolutionary ancestral sequence reconstruction\",\n      \"journal\": \"Nature communications\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Strong — crystal structure plus quantitative binding with phospho-mutants, functional diffusion measurements, single rigorous study with multiple orthogonal methods\",\n      \"pmids\": [\"40312381\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2025,\n      \"finding\": \"Among the five sHSPs tested (HspB1, phospho-mimicking HspB1 3D, HspB5, HspB6, HspB7, HspB8), only HspB7 forms complexes with the FLNC C-terminal fragment (Ig-like domains 19-24); the interaction is mediated by HspB7's α-crystallin domain binding to Ig-like domain 24 of FLNC; this binding induces dissociation of FLNC dimers.\",\n      \"method\": \"Size-exclusion chromatography, native gel electrophoresis, chemical crosslinking, immunochemistry\",\n      \"journal\": \"Biochemistry. Biokhimiia\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — multiple in vitro biochemical methods with selectivity panel, single lab\",\n      \"pmids\": [\"41702738\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2025,\n      \"finding\": \"Disease-causing mutations in FLNC domains 22-24 (EN/D in domain 22; ΔPGL and W2710X in domain 24) differentially reduce or abolish interaction with HspB7: WT~EN/D interact with HspB7 > ΔPGL; Wmut (W2710X) cannot interact with HspB7 or its α-crystallin domain; structural modeling indicates ΔPGL and Wmut expose a hydrophobic groove in domain 24 that reduces HspB7 binding.\",\n      \"method\": \"Size-exclusion chromatography, native gel electrophoresis, chemical crosslinking, AlphaFold 3 modeling, recombinant mutant proteins\",\n      \"journal\": \"International journal of molecular sciences\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — multiple in vitro biochemical methods with panel of disease mutants, computational structural support, single lab\",\n      \"pmids\": [\"40564978\"],\n      \"is_preprint\": false\n    }\n  ],\n  \"current_model\": \"HSPB7 is a muscle-enriched small heat shock protein that functions primarily as a molecular chaperone for the sarcomere: it binds monomeric actin to limit polymerization and regulate thin filament length, forms a structurally characterized heterodimer with filamin C (FLNC) that competes with the FLNC homodimer interface and is regulated by phosphorylation at the FLNC dimer interface, and supports autophagic processing of damaged sarcomeric proteins (including FLNC and titin) to maintain proteostasis; its N-terminal domain mediates polyQ aggregation suppression via an autophagy-dependent mechanism, it constitutively localizes to SC35 nuclear speckles (driven by its N-terminus) where it lacks classical chaperone-refolding activity, it contains a kinetically privileged reactive cysteine (C117) for electrophilic stress sensing, and loss of HSPB7 causes embryonic cardiac lethality in mice due to abnormal actin bundle formation, or in adult hearts causes intercalated disc disruption, arrhythmia, and heart failure.\"\n}\n```","stage2_raw":"{\n  \"mechanistic_narrative\": \"HSPB7 is a muscle-enriched small heat shock protein that maintains sarcomeric and intercalated-disc proteostasis in the heart and skeletal muscle, where its loss is developmentally and clinically catastrophic [#9, #10]. Its central biochemical activity is selective recognition of filamin C (FLNC): HSPB7 binds dimerized FLNC and, via its \\u03b1-crystallin domain engaging FLNC Ig-like domain 24, forms a crystallographically defined heterodimer that out-competes the FLNC homodimer interface and is tuned by FLNC phosphorylation (T2677 favoring homodimer, Y2683 favoring the HSPB7 heterodimer), thereby antagonizing FLNC actin cross-linking and enhancing its mobility [#20, #21]. This proteostatic role extends to autophagy: HSPB7 facilitates autophagic processing of damaged FLNC and titin, and its loss in zebrafish and human iPSC-cardiomyocytes drives FLNC aggregation and cardiomyopathy when autophagy is blocked [#12]. Consistent with a chaperone-distinct activity, HSPB7 is the most potent polyQ aggregation suppressor of the HSPB family through a macroautophagy-dependent (ATG5-dependent), Hsp70- and proteasome-independent mechanism encoded by its N-terminal domain, which is necessary and sufficient and can transfer this activity onto HSPB1 [#3, #13]. In cardiomyocytes HSPB7 ablation disrupts intercalated discs with connexin 43 loss and desmoplakin/N-cadherin mislocalization, producing arrhythmia and heart failure, while embryonic loss yields lethal abnormal actin bundles cross-linking Z lines [#9, #10]. HSPB7 constitutively localizes to SC35 nuclear speckles via its N-terminus and lacks classical refolding activity [#2], and it contains a kinetically privileged reactive cysteine (C117) that senses reactive electrophilic species [#11]. Whether HSPB7 is a bona fide direct actin-binding protein is contested, with reconstitution studies reporting both repression of actin polymerization and failure to detect specific complexes [#9, #16]. Beyond muscle, HSPB7 is transcriptionally regulated (by GATA4, MEF2A/AP-1, p53, MECOM, and HDAC1) and modulates osteogenic/adipogenic differentiation and tumor cell metabolism in several contexts [#5, #8, #19, #18].\",\n  \"teleology\": [\n    {\n      \"year\": 1999,\n      \"claim\": \"Established the first molecular partner of HSPB7, linking it to the actin cytoskeletal scaffold by mapping a filamin-binding region.\",\n      \"evidence\": \"Yeast two-hybrid and co-IP with domain mapping (residues 56-119) against alpha-filamin C-terminal tail\",\n      \"pmids\": [\"10593960\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Filamin isoform specificity (FLNA vs FLNC) not resolved here\", \"No functional consequence of the interaction defined\", \"Structural basis not determined\"]\n    },\n    {\n      \"year\": 2004,\n      \"claim\": \"Showed HSPB7 responds to cardiac/skeletal stress by stably redistributing to myofibrillar Z/I regions, indicating a sarcomeric site of action.\",\n      \"evidence\": \"Subcellular fractionation, immunohistochemistry, and chaotrope-resistant extraction in ischemic muscle\",\n      \"pmids\": [\"15480735\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Molecular target at the Z/I band not identified\", \"Mechanism of translocation unknown\"]\n    },\n    {\n      \"year\": 2009,\n      \"claim\": \"Revealed HSPB7 has a non-canonical, non-refolding role by localizing constitutively to SC35 nuclear speckles, separating it from classical chaperone sHSPs.\",\n      \"evidence\": \"Confocal imaging of GFP constructs with N-terminal domain mapping and luciferase refolding assay (negative)\",\n      \"pmids\": [\"19464326\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Functional role at SC35 speckles undefined\", \"No splicing or RNA-processing partner identified\"]\n    },\n    {\n      \"year\": 2010,\n      \"claim\": \"Defined a distinctive disposal mechanism: HSPB7 suppresses polyQ aggregation through macroautophagy rather than refolding or proteasomal routes.\",\n      \"evidence\": \"Cell-based polyQ assays, ATG5-/- cells, Drosophila eye model, inhibitor and refolding assays\",\n      \"pmids\": [\"20843828\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"How HSPB7 routes substrates to autophagy is not molecularly defined\", \"No direct autophagy-machinery partner identified\"]\n    },\n    {\n      \"year\": 2011,\n      \"claim\": \"Connected HSPB7 to cytoskeletal stress signaling by showing it blocks RhoA/ROCK-driven F-actin stress fiber formation in atrial myocytes.\",\n      \"evidence\": \"HL-1 tachypacing model, calcium transient measurement, F-actin staining, ROCK inhibition, overexpression\",\n      \"pmids\": [\"21731611\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Direct versus indirect effect on actin not resolved\", \"Mechanistic link to RhoA pathway not biochemically defined\"]\n    },\n    {\n      \"year\": 2013,\n      \"claim\": \"Placed HSPB7 in a GATA4-controlled developmental program required for left-right axis and heart tube morphogenesis.\",\n      \"evidence\": \"Zebrafish morpholino knockdown with gata4 genetic epistasis and confocal imaging\",\n      \"pmids\": [\"23850773\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Morpholino specificity not corroborated by mutant\", \"Molecular effector downstream of HSPB7 in Kupffer's vesicle unknown\"]\n    },\n    {\n      \"year\": 2016,\n      \"claim\": \"Demonstrated in vivo that HSPB7 binds dimerized FLNC and is required to prevent FLNC aggregation and myopathy in skeletal muscle.\",\n      \"evidence\": \"Skeletal-muscle conditional KO mouse, co-IP, immunofluorescence\",\n      \"pmids\": [\"26929074\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Structural basis of FLNC-dimer selectivity not defined here\", \"Mechanism linking FLNC binding to aggregation prevention unresolved\"]\n    },\n    {\n      \"year\": 2016,\n      \"claim\": \"Identified the transcriptional logic controlling HSPB7 in muscle, with MEF2A activating and AP-1 repressing, tying expression to muscle mass.\",\n      \"evidence\": \"ChIP-seq, siRNA knockdown, dexamethasone treatment, in vivo muscle manipulation\",\n      \"pmids\": [\"27632998\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Direct promoter elements for each factor not fully mapped\", \"Link between expression level and chaperone function not addressed\"]\n    },\n    {\n      \"year\": 2017,\n      \"claim\": \"Showed HSPB7 is indispensable for cardiac development and regulates thin-filament length, with abnormal actin bundles—not filament elongation—causing lethality.\",\n      \"evidence\": \"Global and cardiac KO mice, in vitro actin polymerization/binding assays, HSPB7/Lmod2 double-KO rescue, immunofluorescence\",\n      \"pmids\": [\"29078393\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Direct actin binding later disputed\", \"How HSPB7 limits actin bundling mechanistically unresolved\"]\n    },\n    {\n      \"year\": 2017,\n      \"claim\": \"Established a postnatal cardiac requirement: inducible HSPB7 loss disrupts intercalated discs and causes arrhythmia and heart failure independent of sarcomere contractile organization.\",\n      \"evidence\": \"Cardiac-specific inducible KO mouse, ECG, immunofluorescence, Western blot\",\n      \"pmids\": [\"28827800\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Mechanism connecting HSPB7 loss to connexin 43/desmoplakin disruption not defined\", \"Whether FLNC aggregation is cause or consequence unresolved\"]\n    },\n    {\n      \"year\": 2018,\n      \"claim\": \"Defined a proteostasis mechanism in the heart: HSPB7 binds FLNC and titin and channels damaged FLNC into autophagy to sustain sarcomeric homeostasis.\",\n      \"evidence\": \"Co-IP, zebrafish mutants, HSPB7-mutant human iPSC-cardiomyocytes, autophagy inhibition and flux assays\",\n      \"pmids\": [\"29331499\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Direct autophagy-receptor partner not identified\", \"How titin binding contributes mechanistically unclear\"]\n    },\n    {\n      \"year\": 2018,\n      \"claim\": \"Revealed a redox-sensing function: a single conserved cysteine (C117) makes HSPB7 a kinetically privileged sensor of reactive electrophilic species.\",\n      \"evidence\": \"In vitro RES adduction kinetics, C117 mutagenesis, circular dichroism, cell-based sensing, cancer-relevant mutant\",\n      \"pmids\": [\"29397684\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Downstream signaling consequence of C117 adduction not defined\", \"Physiological RES targets in muscle unknown\"]\n    },\n    {\n      \"year\": 2019,\n      \"claim\": \"Localized the anti-aggregation activity to the flexible N-terminal domain, showing it is necessary, sufficient, and transferable to HSPB1.\",\n      \"evidence\": \"In vitro aggregation assays, NTD domain-swap chimeras, phospho-mimic mutants, microscopy\",\n      \"pmids\": [\"31097540\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Structural basis of NTD-polyQ recognition not determined\", \"Connection of NTD activity to autophagy routing unresolved\"]\n    },\n    {\n      \"year\": 2021,\n      \"claim\": \"Characterized HSPB7 oligomeric behavior, showing redox- and motif-dependent large-oligomer formation and disulfide-mediated heterodimers with HspB6/HspB8.\",\n      \"evidence\": \"Recombinant protein SEC, crosslinking, cysteine modification, domain deletion, co-IP\",\n      \"pmids\": [\"34360542\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Functional role of large oligomers unknown\", \"Physiological relevance of HspB6/HspB8 heterodimers untested in vivo\"]\n    },\n    {\n      \"year\": 2022,\n      \"claim\": \"Challenged the actin-binding model with a controlled negative study finding no specific, saturable G/F-actin complex.\",\n      \"evidence\": \"Blot overlay, co-sedimentation, native gels, crosslinking, heat-aggregation assay with positive controls\",\n      \"pmids\": [\"35977674\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Discrepancy with cellular actin-regulation data unresolved\", \"Whether actin effects are indirect not established\"]\n    },\n    {\n      \"year\": 2023,\n      \"claim\": \"Extended HSPB7 regulation and function to cancer, with transcriptional control by MECOM/HDAC1 and suppression of glycolysis and tumor growth.\",\n      \"evidence\": \"Co-IP, ChIP, metabolic assays, cell functional assays, xenograft (multiple tumor types)\",\n      \"pmids\": [\"37732539\", \"35652621\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Mechanism linking HSPB7 to glycolytic enzyme levels undefined\", \"Relationship to muscle chaperone role unclear\"]\n    },\n    {\n      \"year\": 2025,\n      \"claim\": \"Provided the structural and biophysical basis of HSPB7-FLNC heterodimerization, defining phospho-regulation and the consequences for FLNC cross-linking and mobility.\",\n      \"evidence\": \"X-ray crystallography, quantitative binding with phospho-mimetic FLNC, FRAP, ancestral sequence reconstruction; plus SEC/native-gel mapping of \\u03b1-crystallin domain to FLNC Ig24\",\n      \"pmids\": [\"40312381\", \"41702738\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"In vivo demonstration of phospho-switch in stressed myocardium pending\", \"Quantitative balance of homo- vs heterodimer in cells not measured\"]\n    },\n    {\n      \"year\": 2025,\n      \"claim\": \"Linked FLNC disease mutations directly to disrupted HSPB7 binding, providing a mechanistic basis for FLNC-associated myopathy via lost chaperone engagement.\",\n      \"evidence\": \"SEC, native gels, crosslinking, AlphaFold3 modeling of FLNC domain 22-24 disease mutants\",\n      \"pmids\": [\"40564978\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Functional rescue in patient cells not shown\", \"Whether lost binding alone drives pathology not established\"]\n    },\n    {\n      \"year\": null,\n      \"claim\": \"It remains unresolved how HSPB7's distinct activities—FLNC heterodimerization, autophagic substrate routing, nuclear-speckle residence, and electrophile sensing—are integrated and whether a single biochemical mechanism underlies its non-canonical, non-refolding chaperone role.\",\n      \"evidence\": \"\",\n      \"pmids\": [],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"No unifying biochemical mechanism linking the four activities\", \"Direct autophagy-receptor partner unidentified\", \"Function at SC35 speckles still undefined\"]\n    }\n  ],\n  \"mechanism_profile\": {\n    \"molecular_activity\": [\n      {\"term_id\": \"GO:0140096\", \"supporting_discovery_ids\": [20, 21, 16]},\n      {\"term_id\": \"GO:0140299\", \"supporting_discovery_ids\": [11]},\n      {\"term_id\": \"GO:0008092\", \"supporting_discovery_ids\": [9, 0]},\n      {\"term_id\": \"GO:0044183\", \"supporting_discovery_ids\": [3, 13]}\n    ],\n    \"localization\": [\n      {\"term_id\": \"GO:0005730\", \"supporting_discovery_ids\": [2]},\n      {\"term_id\": \"GO:0005654\", \"supporting_discovery_ids\": [2]},\n      {\"term_id\": \"GO:0005829\", \"supporting_discovery_ids\": [1]},\n      {\"term_id\": \"GO:0005856\", \"supporting_discovery_ids\": [1, 9]}\n    ],\n    \"pathway\": [\n      {\"term_id\": \"R-HSA-9612973\", \"supporting_discovery_ids\": [3, 12]},\n      {\"term_id\": \"R-HSA-392499\", \"supporting_discovery_ids\": [12, 7]},\n      {\"term_id\": \"R-HSA-1266738\", \"supporting_discovery_ids\": [5, 9]},\n      {\"term_id\": \"R-HSA-8953897\", \"supporting_discovery_ids\": [11]}\n    ],\n    \"complexes\": [\n      \"HSPB7-FLNC heterodimer\",\n      \"HSPB7-HSPB6 heterodimer\",\n      \"HSPB7-HSPB8 heterodimer\"\n    ],\n    \"partners\": [\n      \"FLNC\",\n      \"FLNA\",\n      \"TTN\",\n      \"HSPB6\",\n      \"HSPB8\",\n      \"MECOM\"\n    ],\n    \"other_free_text\": []\n  }\n}","audit_flag":null,"evaluation":{"faith_supported":8,"faith_total":8,"faith_pct":100.0}}