{"gene":"SIX1","run_date":"2026-04-28T20:42:07","timeline":{"discoveries":[{"year":2003,"finding":"SIX1 forms a transcriptional complex with DACH and EYA proteins; EYA family members possess protein phosphatase activity, and this enzymatic activity switches the SIX1-DACH complex from transcriptional repression to activation by recruiting co-activators to specific gene targets regulating precursor cell proliferation.","method":"Biochemical phosphatase assays, co-immunoprecipitation, transcriptional reporter assays, genetic mouse knockouts","journal":"Nature","confidence":"High","confidence_rationale":"Tier 1-2 — enzymatic activity demonstrated in vitro, combined with genetic epistasis and transcriptional assays in a highly-cited foundational paper","pmids":["14628042"],"is_preprint":false},{"year":2004,"finding":"BOR syndrome-causing SIX1 mutations disrupt either EYA1-SIX1 protein-protein interaction or SIX1-DNA binding; all three identified mutations abolish transcriptional activation, establishing that the EYA1-SIX1-DNA complex is required for normal otic and renal development.","method":"Direct sequencing, protein-protein interaction assays, DNA binding assays (EMSA), transcriptional reporter assays","journal":"PNAS","confidence":"High","confidence_rationale":"Tier 1-2 — multiple orthogonal methods (binding assays + mutagenesis + transcription assays) on disease-causing mutants","pmids":["15141091"],"is_preprint":false},{"year":2000,"finding":"SIX1 is a nuclear phosphoprotein that undergoes hyperphosphorylation at mitosis by casein kinase II (CK2); CK2-mediated phosphorylation abolishes SIX1 binding to MEF3 sites in the aldolase A promoter, and CK2 inhibition arrests cells at G2/M.","method":"Cell cycle synchronization, in vitro kinase assay with CK2, EMSA for DNA binding, CK2 inhibitor (apigenin) treatment, immunoprecipitation","journal":"Journal of Biological Chemistry","confidence":"High","confidence_rationale":"Tier 1 — in vitro reconstitution of phosphorylation with direct functional readout (DNA binding loss), replicated with pharmacological inhibitor in cells","pmids":["10801845"],"is_preprint":false},{"year":2004,"finding":"SIX1 and EYA1 together reprogram adult slow-twitch oxidative muscle fibers toward a fast-twitch glycolytic phenotype; SIX1 and EYA1 proteins preferentially accumulate in nuclei of fast-twitch muscles, and the MEF3/Six DNA binding element in the aldolase A pM promoter mediates high-level activation specifically in fast-twitch fibers.","method":"Transgenic forced expression in soleus muscle, myosin heavy chain isoform analysis, promoter-reporter assays, immunolocalization","journal":"Molecular and Cellular Biology","confidence":"High","confidence_rationale":"Tier 2 — clean gain-of-function in vivo with defined molecular readout, multiple orthogonal assays","pmids":["15226428"],"is_preprint":false},{"year":2006,"finding":"SIX1 protein is degraded via ubiquitin-mediated proteolysis through the APC(Cdh1) complex at mitosis; unlike canonical APC targets, SIX1 lacks destruction or KEN box motifs, instead containing multiple N- and C-terminal sequences including an N-terminal region that binds Cdh1.","method":"Cell cycle synchronization, proteasome inhibitor assays, co-immunoprecipitation with Cdh1, deletion mutagenesis","journal":"Oncogene","confidence":"High","confidence_rationale":"Tier 2 — reciprocal co-IP with Cdh1, mutagenesis defining degradation sequences, cell-cycle-staged protein analysis","pmids":["17130831"],"is_preprint":false},{"year":2009,"finding":"SIX1 BOR syndrome mutations act through two distinct mechanisms: the V17E mutation in the Six domain abolishes SIX1-EYA complex formation and prevents nuclear localization of EYA, while the remaining five mutations retain EYA binding but are deficient in DNA binding; all mutants fail transcriptional activation. EYA interaction increases SIX1 protein stability and DNA binding affinity.","method":"Recombinant protein expression/purification in E. coli, in vitro binding assays, cellular localization studies, luciferase reporter assays","journal":"Journal of Biological Chemistry","confidence":"High","confidence_rationale":"Tier 1-2 — reconstituted protein interactions in vitro, mutagenesis, multiple orthogonal functional assays","pmids":["19497856"],"is_preprint":false},{"year":2010,"finding":"SIX1 promotes epithelial-mesenchymal transition (EMT) and metastasis through upregulation of TGF-β type I receptor (TβRI), which is both necessary and sufficient to activate TGF-β signaling and induce EMT properties; SIX1 overexpression is required to switch TGF-β from tumor-suppressive to pro-metastatic.","method":"Knockdown/overexpression in breast cancer cell lines, TβRI promoter-reporter assays, in vivo metastasis assays","journal":"Cancer Research","confidence":"High","confidence_rationale":"Tier 2 — identified direct transcriptional target (TβRI), rescue experiments, in vivo validation","pmids":["21056993"],"is_preprint":false},{"year":2011,"finding":"EYA2 is a required co-factor for SIX1 to mediate pro-metastatic functions including induction of TGF-β signaling, EMT, and cancer stem cell properties in breast cancer cells; knockdown of EYA2 reverses SIX1-induced phenotypes.","method":"siRNA knockdown, EMT marker analysis, TGF-β pathway reporter assays, cancer stem cell assays in MCF7 cells","journal":"Oncogene","confidence":"High","confidence_rationale":"Tier 2 — epistasis by co-knockdown, multiple phenotypic readouts establishing EYA2 dependency","pmids":["21706047"],"is_preprint":false},{"year":2012,"finding":"EYA1 and SIX1 interact directly with SWI/SNF chromatin-remodeling subunits BRG1 and BAF170 to drive neurogenesis; the ATPase activity of BRG1 is required for EYA1/SIX1-induced ectopic neurogenesis and normal neurogenesis in the otocyst. SOX2 cooperates with EYA1/SIX1 in this complex to mediate neuronal differentiation upstream of NEUROG1 and NEUROD1.","method":"Co-immunoprecipitation, overexpression in non-neuronal cells (3T3 fibroblasts), cochlear explants, otocyst gain-of-function, BRG1 ATPase-dead mutant","journal":"Development","confidence":"High","confidence_rationale":"Tier 2 — direct protein interaction (Co-IP), dominant-negative ATPase mutant, multiple cell-type validations","pmids":["22513373"],"is_preprint":false},{"year":2012,"finding":"EYA1/SIX1 coexpression in mouse cochlear explants is sufficient to induce hair cell fate in non-sensory epithelium by activating Atoh1-dependent and Atoh1-independent pathways; SOX2 cooperates with EYA1/SIX1 by direct binding to conserved Sox- and Six-binding sites in Atoh1 enhancers, and these proteins physically interact.","method":"Cochlear explant overexpression, Atoh1 enhancer reporter assays with site-directed mutagenesis, co-immunoprecipitation, conditional knockout mice","journal":"Developmental Cell","confidence":"High","confidence_rationale":"Tier 1-2 — physical interaction shown by Co-IP, enhancer binding validated by mutagenesis, gain-of-function sufficiency demonstrated","pmids":["22340499"],"is_preprint":false},{"year":2012,"finding":"SIX1 transcriptionally induces VEGF-C expression, promoting peritumoral and intratumoral lymphangiogenesis and lymphatic metastasis in breast cancer; VEGF-C induction is required for SIX1-mediated lymphangiogenesis but additional VEGF-C-independent pathways also contribute to metastasis.","method":"Xenograft models in immunocompromised mice, VEGF-C promoter-reporter assays, siRNA knockdown, in vivo lymphangiogenesis quantification","journal":"Journal of Clinical Investigation","confidence":"High","confidence_rationale":"Tier 2 — direct transcriptional target validated with promoter assays, in vivo rescue experiments","pmids":["22466647"],"is_preprint":false},{"year":2012,"finding":"SIX1 regulates skeletal muscle satellite cell differentiation and self-renewal via the ERK1/2 pathway through direct transcriptional control of Dusp6, a phosphatase that modulates ERK1/2 activity; genetic disruption of Six1 specifically in adult satellite cells impairs myofiber repair and increases stem cell self-renewal.","method":"Conditional Six1 knockout in adult satellite cells, chromatin immunoprecipitation (ChIP) for Dusp6, regeneration assays, Dusp6-null mice analysis","journal":"Journal of Cell Biology","confidence":"High","confidence_rationale":"Tier 2 — ChIP demonstrating direct binding to Dusp6, conditional knockout with defined phenotype, epistatic rescue via Dusp6 knockout","pmids":["22945933"],"is_preprint":false},{"year":2013,"finding":"SIX1 directly binds to the Core Enhancer Region of MyoD in muscle progenitor cells, is required for proper chromatin structure at this enhancer, and promotes MyoD binding at its own enhancer; Six1 knockdown reduces MyoD expression in myoblasts.","method":"Chromatin immunoprecipitation (ChIP), transcriptional reporter assays, siRNA knockdown, regenerating muscle analysis","journal":"PLoS One","confidence":"High","confidence_rationale":"Tier 2 — ChIP demonstrating direct binding plus functional reporter assays and chromatin accessibility analysis","pmids":["23840772"],"is_preprint":false},{"year":2013,"finding":"SIX1 directly transcriptionally activates cyclin D1, promoting cell cycle progression and proliferation; SIX1 overexpression upregulates cyclin D1 mRNA and protein and enhances cyclin D1 promoter activity in pancreatic cancer cells.","method":"Cyclin D1 promoter-luciferase reporter assays, qRT-PCR, western blot, xenograft assays","journal":"PLoS One","confidence":"Medium","confidence_rationale":"Tier 2-3 — promoter-reporter assay suggests direct transcription but no ChIP confirmation; single lab","pmids":["23527134"],"is_preprint":false},{"year":2014,"finding":"SIX1 coordinates TGF-β signals to upregulate VEGF-C expression in cervical cancer cells; SIX1 enhances TGF-β-induced SMAD2/3 activation and cooperates with the SMAD pathway to promote VEGF-C expression and lymphangiogenesis.","method":"SMAD2/3 phosphorylation analysis, VEGF-C promoter assays, in vitro lymphangiogenesis assays, knockdown/overexpression in tumor cells","journal":"Cancer Research","confidence":"Medium","confidence_rationale":"Tier 2-3 — pathway interaction established but mechanistic detail of SIX1-SMAD cooperation is inferred; single lab","pmids":["25142796"],"is_preprint":false},{"year":2015,"finding":"SIX1 decreases p53 levels through a dual mechanism: (1) upregulation of microRNA-27a-3p that targets p53, and (2) downregulation of RPL26, which normally inhibits miR-27a-mediated repression of p53; these mechanisms operate independently of MDM2.","method":"Transcriptional reporter assays, miRNA overexpression/knockdown, RPL26 mutation analysis, western blot for p53 pathway components","journal":"Nature Communications","confidence":"High","confidence_rationale":"Tier 2 — dual mechanism with mutation analysis confirming the RPL26-miR-27a competition; replicated across multiple cancer types","pmids":["26687066"],"is_preprint":false},{"year":2018,"finding":"SIX1 directly increases expression of many glycolytic genes to promote the Warburg effect; this transcriptional regulation of glycolysis occurs through HBO1 and AIB1 histone acetyltransferases; a cancer-related SIX1 mutation increases its ability to promote aerobic glycolysis.","method":"ChIP-seq for SIX1 binding at glycolytic gene promoters, HAT inhibitor studies, SIX1 mutant overexpression, metabolic flux assays, in vivo tumor growth","journal":"Cancer Cell","confidence":"High","confidence_rationale":"Tier 1-2 — genome-wide ChIP combined with functional metabolic assays and HAT-dependency experiments; highly cited","pmids":["29455928"],"is_preprint":false},{"year":2020,"finding":"O-GlcNAcylation of SIX1 at threonine 276 (T276) enhances its stability by inhibiting ubiquitin-mediated proteasomal degradation; SIX1 itself promotes O-GlcNAcylation levels, forming a feedback loop; T276A mutation reduces O-GlcNAcylation and reverses the pro-tumor effect.","method":"Mass spectrometry, immunoprecipitation, site-directed mutagenesis (T276A), ubiquitination assays, xenograft models","journal":"Theranostics","confidence":"High","confidence_rationale":"Tier 1-2 — modification site identified by mass spectrometry, confirmed by mutagenesis with functional consequence on ubiquitination and tumor growth","pmids":["32863962"],"is_preprint":false},{"year":2021,"finding":"GRP75 forms a trimeric complex with USP1 (a deubiquitinating enzyme) and SIX1; GRP75 provides a scaffold to recruit USP1, which inhibits K48-linked polyubiquitination of SIX1, thereby stabilizing SIX1 protein in prostate cancer cells; the C-terminus of GRP75 (433-679 aa) containing a peptide binding domain is required for complex formation.","method":"Co-immunoprecipitation, domain mapping, K48-ubiquitination assays, genetic and pharmacological inhibition, xenograft mouse models","journal":"Oncogene","confidence":"High","confidence_rationale":"Tier 2 — trimeric complex defined by domain mapping, specific ubiquitination linkage identified, in vivo validation","pmids":["34079090"],"is_preprint":false},{"year":2022,"finding":"USP1 deubiquitinase stabilizes SIX1 protein in hepatocellular carcinoma through the EGFR-AKT signaling axis; EGFR-AKT activation promotes USP1 expression, which in turn prevents SIX1 degradation; suppression of this axis with SNS-032 induces SIX1 degradation.","method":"Ubiquitination assays, USP1 knockdown/overexpression, EGFR inhibitor experiments, western blot, xenograft models","journal":"Acta Pharmacologica Sinica","confidence":"Medium","confidence_rationale":"Tier 2 — deubiquitinase-substrate relationship established with pathway context; single lab","pmids":["36261513"],"is_preprint":false},{"year":2020,"finding":"A small molecule (NCGC00378430/8430) that reduces the SIX1/EYA2 protein-protein interaction partially reverses SIX1-induced transcriptional and metabolic profiles, reverses TGF-β signaling and EMT, and suppresses breast cancer metastasis in vivo without affecting primary tumor growth.","method":"Small molecule screen, co-immunoprecipitation to assess complex disruption, transcriptome profiling, metabolic assays, in vivo metastasis model","journal":"Cancer Research","confidence":"High","confidence_rationale":"Tier 2 — pharmacological disruption of complex with multiple orthogonal functional readouts and in vivo validation","pmids":["32341035"],"is_preprint":false},{"year":2011,"finding":"SIX1 and EYA1 form a transcription complex that directly regulates Fgf8 expression, acting downstream of Tbx1 in a genetic pathway (Tbx1-Six1/Eya1-Fgf8) controlling cardiovascular and craniofacial development; Six1/Eya1 double mutant mice recapitulate human del22q11 syndrome features.","method":"Genetic epistasis in mouse double mutants, Fgf8 promoter assays, compound mutant rescue experiments","journal":"Journal of Clinical Investigation","confidence":"High","confidence_rationale":"Tier 2 — genetic epistasis with direct promoter evidence, multi-allele compound mutants establishing pathway order","pmids":["21364285"],"is_preprint":false},{"year":2011,"finding":"SIX1 acts in the metanephric mesenchyme as an upstream regulator of Grem1 expression; loss of Six1 abolishes Grem1 expression, leading to unopposed BMP4 activity that prevents ureteric bud ampulla formation; GREM1 protein treatment or genetic reduction of BMP4 restores branching morphogenesis in Six1-null kidneys.","method":"Six1 knockout mouse analysis, recombinant GREM1 treatment of kidney rudiments, genetic rescue (Six1−/−; Bmp4+/−), in vitro kidney culture","journal":"Developmental Biology","confidence":"High","confidence_rationale":"Tier 2 — genetic epistasis confirmed by protein rescue and compound genetics, pathway position unambiguously established","pmids":["21281623"],"is_preprint":false},{"year":2016,"finding":"Six1 and Six4 are both required for MyoD reprogramming of mouse embryonic fibroblasts toward myogenic fate; Six1/Six4 binding sites (MEF3 motifs) co-localize with MyoD binding sites on over 1000 genomic regions; Six1 and MyoD act synergistically in a feedforward transcriptional network to activate >80 co-regulated genes.","method":"MyoD-driven reprogramming of MEFs with Six1/Six4 knockdown, microarray gene expression, MyoD ChIP-seq analysis, genome-wide MEF3 site mapping, luciferase reporter assays","journal":"Nucleic Acids Research","confidence":"High","confidence_rationale":"Tier 2 — genome-wide ChIP-seq combined with functional reprogramming assays and reporter validation","pmids":["27302134"],"is_preprint":false},{"year":2012,"finding":"Six1 optimal DNA-binding sequence is broader than previously known; Six1 domains outside the homeodomain contribute to DNA binding site selection, and Six1 alone (without co-factors) is sufficient for sequence discrimination at MEF3-type sites.","method":"Genomic ChIP binding profile analysis in myoblasts, position weight matrix optimization, in vitro DNA binding assays","journal":"Nucleic Acids Research","confidence":"Medium","confidence_rationale":"Tier 2-3 — ChIP-seq combined with biochemical binding assays; single lab characterization","pmids":["22730291"],"is_preprint":false},{"year":2016,"finding":"Pa2G4 (Ebp1/Plfap) is a novel SIX1 co-factor that binds to SIX1 and interferes with the SIX1-EYA1 complex in human embryonic kidney cells; in Xenopus, Pa2G4 knockdown reduces neural crest and placodal gene expression and affects otocyst development.","method":"Co-immunoprecipitation in HEK cells, Xenopus gain- and loss-of-function, otocyst marker analysis","journal":"Developmental Biology","confidence":"Medium","confidence_rationale":"Tier 3 — single co-IP demonstrating interaction plus Xenopus functional data; single lab","pmids":["27940157"],"is_preprint":false},{"year":2018,"finding":"SIX1 expression in leukemic initiating cells is controlled by WNT/β-catenin signaling through TCF7L2; the oncofusion protein MLL-AF9 increases chromatin accessibility at TCF/LEF-binding elements controlling the Six1 locus, enabling TCF7L2-dependent transcriptional activation of Six1.","method":"ATAC-seq, transcriptome profiling, WNT inhibitor treatment, genetic deletion of Wntless (WLS) in mice, AML mouse model","journal":"EBioMedicine","confidence":"Medium","confidence_rationale":"Tier 2 — ATAC-seq + transcriptomics establishes chromatin accessibility mechanism; genetic and pharmacological validation","pmids":["30528456"],"is_preprint":false},{"year":2023,"finding":"SIX1 directly binds the LDHA promoter region to transcriptionally activate LDHA expression, promoting lactate accumulation in pancreatic cancer cells; SIX1-driven lactate production leads to NK cell dysfunction in the tumor microenvironment.","method":"Chromatin immunoprecipitation (ChIP) for SIX1 at LDHA promoter, metabolic assays, NK cell co-culture assays, xenograft models, LDHA inhibitor rescue experiments","journal":"Journal of Immunology Research","confidence":"Medium","confidence_rationale":"Tier 2-3 — ChIP demonstrates direct binding, functional rescue with LDHA inhibitor; single lab","pmids":["36937004"],"is_preprint":false},{"year":2017,"finding":"SIX1 regulates dorsal mandibular arch identity by inducing Jag1 expression and simultaneously inhibiting Edn1 (endothelin 1) expression in pharyngeal endoderm; loss of SIX1 leads to aberrant EDNRA signaling in the dorsal arch domain, resulting in partial mandibular duplication.","method":"Six1 conditional knockout mice, Edn1/Jag1 expression analysis by in situ hybridization, genetic epistasis with EDNRA pathway mutants","journal":"Development","confidence":"Medium","confidence_rationale":"Tier 2 — clean conditional knockout with defined molecular targets; pathway position established by genetic epistasis","pmids":["28455376"],"is_preprint":false}],"current_model":"SIX1 is a homeodomain transcription factor that binds MEF3-type DNA sequences (with the homeodomain and flanking domains contributing to site selection) and acts as a transcriptional activator or repressor depending on its co-factor context: interaction with EYA proteins (which contribute phosphatase activity) switches SIX1-DACH complexes from repression to activation by recruiting histone acetyltransferases (HBO1, AIB1), while interaction with SWI/SNF subunits (BRG1, BAF170) and SOX2 drives neurogenesis programs; SIX1 protein stability is regulated post-translationally by CK2-mediated phosphorylation (which reduces DNA binding), by APC(Cdh1)-mediated ubiquitin-proteasomal degradation at mitosis, and by O-GlcNAcylation at T276 and deubiquitination by USP1 (scaffolded by GRP75) which stabilize the protein; key direct transcriptional targets include glycolytic genes (via HBO1/AIB1), TGF-β type I receptor, VEGF-C, LDHA, cyclin D1, Fgf8, Grem1, MyoD, and Dusp6, placing SIX1 at the intersection of developmental organogenesis, metabolic reprogramming, and cancer metastasis pathways."},"narrative":{"teleology":[{"year":2000,"claim":"Establishing that SIX1 is a cell-cycle-regulated phosphoprotein answered how its DNA-binding activity is dynamically controlled: CK2-mediated hyperphosphorylation at mitosis abolishes MEF3 site binding, linking SIX1 transcriptional output to cell cycle state.","evidence":"In vitro CK2 kinase assay, EMSA for MEF3 binding, cell cycle synchronization, CK2 inhibitor treatment","pmids":["10801845"],"confidence":"High","gaps":["Specific CK2 phosphorylation sites on SIX1 not mapped","Whether phosphorylation also affects co-factor interactions unknown","In vivo physiological consequence of CK2 regulation of SIX1 not tested"]},{"year":2003,"claim":"The discovery that EYA proteins possess intrinsic phosphatase activity that switches the SIX1-DACH complex from repression to activation established the core molecular logic of the SIX regulatory network — co-factor enzymatic activity determines transcriptional output.","evidence":"Biochemical phosphatase assays, co-immunoprecipitation, transcriptional reporters, mouse knockouts","pmids":["14628042"],"confidence":"High","gaps":["Identity of the EYA phosphatase substrate(s) in the SIX1-DACH complex not defined","Structure of the ternary SIX1-DACH-EYA complex unknown"]},{"year":2004,"claim":"Demonstrating that BOR syndrome mutations either abolish SIX1-EYA1 interaction or SIX1-DNA binding — with both classes eliminating transcriptional activation — established that the intact EYA1-SIX1-DNA ternary complex is essential for otic and renal development.","evidence":"Patient mutation sequencing, EMSA, protein-protein interaction assays, luciferase reporters","pmids":["15141091"],"confidence":"High","gaps":["Whether different BOR mutations produce distinct clinical severities through graded biochemical defects not resolved","Downstream target genes mediating kidney and ear phenotypes not identified at this stage"]},{"year":2004,"claim":"Forced SIX1/EYA1 expression reprogramming slow-twitch to fast-twitch muscle fibers demonstrated that SIX1 specifies glycolytic muscle identity in vivo, extending its role beyond development to adult tissue homeostasis.","evidence":"Transgenic overexpression in soleus muscle, myosin heavy chain isoform analysis, MEF3 promoter reporters","pmids":["15226428"],"confidence":"High","gaps":["Whether endogenous SIX1 is required to maintain fast-twitch identity (loss-of-function) not shown","Direct transcriptional targets mediating fiber-type switch not catalogued"]},{"year":2006,"claim":"Identification of APC/Cdh1-mediated proteasomal degradation of SIX1 at mitosis revealed a novel non-canonical APC substrate mechanism, explaining how SIX1 protein levels are reset each cell cycle.","evidence":"Proteasome inhibitor treatment, Cdh1 co-immunoprecipitation, deletion mutagenesis, cell cycle staging","pmids":["17130831"],"confidence":"High","gaps":["Exact degron motifs replacing D-box/KEN-box not fully mapped","Relationship between CK2 phosphorylation and APC-mediated degradation not tested"]},{"year":2009,"claim":"Detailed biochemical analysis of six BOR mutations refined the two-class model and revealed that EYA interaction increases SIX1 protein stability and DNA-binding affinity, establishing EYA as both an enzymatic co-activator and a structural stabilizer of SIX1.","evidence":"Recombinant protein purification, in vitro binding assays, cellular localization, luciferase reporters","pmids":["19497856"],"confidence":"High","gaps":["Structural basis for how EYA binding enhances SIX1 stability not resolved","Whether EYA protects SIX1 from specific ubiquitin ligases not tested"]},{"year":2010,"claim":"Identifying TGF-β type I receptor as a direct SIX1 transcriptional target that switches TGF-β from tumor-suppressive to pro-metastatic established SIX1 as a master regulator of EMT and metastasis signaling.","evidence":"Knockdown/overexpression in breast cancer lines, TβRI promoter reporters, in vivo metastasis assays","pmids":["21056993"],"confidence":"High","gaps":["Whether SIX1 directly binds TβRI promoter (ChIP) not shown at this stage","Mechanism of signaling switch from tumor suppression to promotion not fully delineated"]},{"year":2011,"claim":"Three studies collectively placed SIX1 within defined developmental signaling cascades: SIX1/EYA1 directly activates Fgf8 downstream of Tbx1 in cardiovascular/craniofacial development, regulates Grem1 to antagonize BMP4 in kidney branching morphogenesis, and requires EYA2 for pro-metastatic TGF-β/EMT functions in cancer.","evidence":"Genetic epistasis in compound mutant mice, recombinant GREM1 rescue of Six1-null kidneys, EYA2 knockdown epistasis in breast cancer cells","pmids":["21364285","21281623","21706047"],"confidence":"High","gaps":["Whether SIX1 directly binds Grem1 regulatory elements not confirmed by ChIP","How SIX1/EYA1 vs SIX1/EYA2 co-factor choice is determined in different tissues unknown"]},{"year":2012,"claim":"A series of 2012 studies expanded SIX1's mechanisms in four directions: (1) SIX1/EYA1 recruit SWI/SNF (BRG1/BAF170) for neurogenesis, (2) SIX1/EYA1/SOX2 drive hair cell fate via Atoh1 enhancers, (3) SIX1 transcriptionally induces VEGF-C for lymphangiogenesis, (4) SIX1 directly activates Dusp6 to regulate satellite cell ERK signaling, and (5) SIX1's DNA-binding specificity extends beyond the homeodomain.","evidence":"Co-IP with BRG1/BAF170, BRG1 ATPase-dead mutant, Atoh1 enhancer mutagenesis, cochlear explants, VEGF-C promoter reporters plus xenograft lymphangiogenesis, Dusp6 ChIP in satellite cells, ChIP-seq binding profile optimization","pmids":["22513373","22340499","22466647","22945933","22730291"],"confidence":"High","gaps":["Whether SWI/SNF is recruited genome-wide or at specific SIX1 targets not determined","Relative contribution of VEGF-C-dependent vs independent SIX1 metastasis pathways unquantified","Structural basis of SIX1 DNA-binding site selection by non-homeodomain regions unknown"]},{"year":2013,"claim":"SIX1 was shown to directly bind the MyoD core enhancer to maintain chromatin accessibility and MyoD expression, and to activate cyclin D1 transcription for cell cycle progression, broadening the direct target gene repertoire.","evidence":"ChIP at MyoD enhancer in myoblasts, siRNA knockdown, cyclin D1 promoter-reporter assays in pancreatic cancer cells","pmids":["23840772","23527134"],"confidence":"High","gaps":["Cyclin D1 activation lacks ChIP confirmation of direct binding","Whether SIX1's role at MyoD enhancer requires EYA co-factors not tested"]},{"year":2015,"claim":"Discovery that SIX1 downregulates p53 through a miR-27a-3p/RPL26 dual mechanism, independent of MDM2, revealed a non-canonical route by which SIX1 suppresses tumor surveillance.","evidence":"miRNA overexpression/knockdown, RPL26 mutation analysis, western blot for p53 pathway components","pmids":["26687066"],"confidence":"High","gaps":["Whether SIX1 directly transcribes miR-27a-3p or acts indirectly not established","Physiological relevance during normal development unknown"]},{"year":2016,"claim":"Genome-wide analysis demonstrated that SIX1/Six4 MEF3 binding sites co-localize with MyoD sites at >1000 genomic loci, establishing a feedforward transcriptional network for myogenic reprogramming, and Pa2G4 was identified as a novel SIX1-binding co-factor that competes with EYA1.","evidence":"MyoD ChIP-seq with MEF3 motif mapping in reprogrammed MEFs, Pa2G4 co-IP in HEK cells, Xenopus knockdown","pmids":["27302134","27940157"],"confidence":"High","gaps":["Pa2G4-SIX1 interaction confirmed only by single co-IP direction","Whether Pa2G4 modulates SIX1 targets genome-wide not tested"]},{"year":2017,"claim":"SIX1 was found to regulate dorsal mandibular arch identity by inducing Jag1 and repressing Edn1, with loss causing aberrant EDNRA signaling and partial mandibular duplication — revealing a role in craniofacial patterning distinct from inner ear development.","evidence":"Conditional Six1 knockout, in situ hybridization, genetic epistasis with EDNRA pathway","pmids":["28455376"],"confidence":"Medium","gaps":["Whether SIX1 directly binds Jag1 and Edn1 regulatory regions not shown","Mechanism of SIX1-mediated repression of Edn1 unknown"]},{"year":2018,"claim":"ChIP-seq revealed that SIX1 directly occupies promoters of glycolytic genes and recruits HBO1/AIB1 histone acetyltransferases to drive aerobic glycolysis (Warburg effect), providing the mechanistic basis for SIX1's metabolic reprogramming function in cancer.","evidence":"ChIP-seq, HAT inhibitor studies, metabolic flux assays, cancer-associated SIX1 mutant analysis, in vivo tumor growth","pmids":["29455928"],"confidence":"High","gaps":["Whether HBO1/AIB1 recruitment is EYA-dependent or independent not fully resolved","Structural basis of SIX1-HAT interaction unknown"]},{"year":2020,"claim":"Two advances in 2020 addressed SIX1 protein stability and pharmacological targeting: O-GlcNAcylation at T276 was shown to inhibit ubiquitin-mediated degradation, and a small molecule disrupting SIX1-EYA2 interaction reversed EMT, TGF-β signaling, and metastasis in vivo.","evidence":"Mass spectrometry for O-GlcNAc site, T276A mutagenesis with ubiquitination assays; small-molecule screen with co-IP assessment, transcriptome profiling, in vivo metastasis model","pmids":["32863962","32341035"],"confidence":"High","gaps":["O-GlcNAc transferase responsible for T276 modification not identified","Small molecule's direct binding mode and selectivity not structurally characterized","Relationship between O-GlcNAcylation and APC/Cdh1-mediated degradation not tested"]},{"year":2021,"claim":"Identification of a GRP75-USP1-SIX1 trimeric complex revealed the deubiquitination mechanism that stabilizes SIX1: GRP75 scaffolds USP1 to remove K48-linked polyubiquitin chains from SIX1, directly opposing proteasomal degradation.","evidence":"Co-immunoprecipitation, domain mapping of GRP75 C-terminus, K48-ubiquitination assays, xenograft models","pmids":["34079090"],"confidence":"High","gaps":["Whether USP1-mediated stabilization operates during normal development or only in cancer contexts unknown","Specific lysine residues on SIX1 targeted by USP1 not mapped"]},{"year":2022,"claim":"Placing USP1-mediated SIX1 stabilization downstream of EGFR-AKT signaling revealed how growth factor signaling sustains SIX1 protein levels in hepatocellular carcinoma.","evidence":"USP1 knockdown/overexpression, EGFR inhibitor treatment, ubiquitination assays, xenograft models","pmids":["36261513"],"confidence":"Medium","gaps":["Whether AKT directly phosphorylates USP1 to regulate its activity not determined","Generalizability beyond hepatocellular carcinoma not tested"]},{"year":2023,"claim":"SIX1 was shown to directly bind the LDHA promoter and activate transcription, linking SIX1-driven lactate production to immune evasion via NK cell dysfunction in the tumor microenvironment.","evidence":"ChIP at LDHA promoter, metabolic assays, NK cell co-culture, LDHA inhibitor rescue, xenograft models","pmids":["36937004"],"confidence":"Medium","gaps":["Whether LDHA is activated through HBO1/AIB1 co-activators as for other glycolytic targets not tested","In vivo immune phenotype confirmation in immunocompetent models lacking"]},{"year":null,"claim":"Major unresolved questions include the structural basis of SIX1-EYA and SIX1-DACH complex assembly, how tissue-specific co-factor choice (EYA1 vs EYA2 vs Pa2G4) is determined, the identity of the E3 ubiquitin ligase(s) opposing USP1 at steady state, and whether the diverse post-translational regulatory mechanisms (CK2 phosphorylation, O-GlcNAcylation, APC/Cdh1 degradation, USP1 deubiquitination) are integrated or operate in distinct cellular contexts.","evidence":"","pmids":[],"confidence":"Low","gaps":["No crystal or cryo-EM structure of any SIX1-containing complex","Tissue-specific co-factor selectivity mechanism unknown","Identity of the E3 ligase(s) that ubiquitinate SIX1 outside of APC/Cdh1 not determined"]}],"mechanism_profile":{"molecular_activity":[{"term_id":"GO:0003677","term_label":"DNA binding","supporting_discovery_ids":[2,5,24]},{"term_id":"GO:0140110","term_label":"transcription regulator activity","supporting_discovery_ids":[0,6,12,16,23,27]}],"localization":[{"term_id":"GO:0005634","term_label":"nucleus","supporting_discovery_ids":[2,3,5]}],"pathway":[{"term_id":"R-HSA-74160","term_label":"Gene expression (Transcription)","supporting_discovery_ids":[0,12,16,23,27]},{"term_id":"R-HSA-1266738","term_label":"Developmental Biology","supporting_discovery_ids":[1,8,9,21,22,28]},{"term_id":"R-HSA-162582","term_label":"Signal Transduction","supporting_discovery_ids":[6,7,14]},{"term_id":"R-HSA-1430728","term_label":"Metabolism","supporting_discovery_ids":[3,16,27]},{"term_id":"R-HSA-1640170","term_label":"Cell Cycle","supporting_discovery_ids":[2,4]},{"term_id":"R-HSA-4839726","term_label":"Chromatin organization","supporting_discovery_ids":[8,12]}],"complexes":["SIX1-EYA1/EYA2-DACH","GRP75-USP1-SIX1","SIX1-EYA1-BRG1-BAF170 (SWI/SNF)"],"partners":["EYA1","EYA2","DACH1","SOX2","BRG1","GRP75","USP1","PA2G4"],"other_free_text":[]},"mechanistic_narrative":"SIX1 is a homeodomain transcription factor that orchestrates developmental organogenesis, muscle fiber-type specification, and metabolic reprogramming by binding MEF3-type DNA elements and assembling context-dependent transcriptional complexes. SIX1 forms obligate complexes with EYA family phosphatases, which switch SIX1-DACH repressor complexes to activation mode by recruiting histone acetyltransferases (HBO1, AIB1), directly driving glycolytic gene expression, VEGF-C, TGF-β type I receptor, Fgf8, MyoD, Dusp6, and other targets [PMID:14628042, PMID:29455928, PMID:21056993, PMID:22340499]. SIX1 protein stability is tightly controlled by CK2-mediated phosphorylation that abolishes DNA binding, APC/Cdh1-mediated ubiquitin-proteasomal degradation at mitosis, O-GlcNAcylation at T276 that inhibits ubiquitination, and USP1-mediated deubiquitination scaffolded by GRP75 [PMID:10801845, PMID:17130831, PMID:32863962, PMID:34079090]. Mutations in SIX1 that disrupt either EYA interaction or DNA binding cause branchio-oto-renal (BOR) syndrome, and SIX1 cooperates with SWI/SNF chromatin remodelers (BRG1, BAF170) and SOX2 to drive neurogenesis and hair cell fate in the inner ear [PMID:15141091, PMID:22513373, PMID:22340499]."},"prefetch_data":{"uniprot":{"accession":"Q15475","full_name":"Homeobox protein SIX1","aliases":["Sine oculis homeobox homolog 1"],"length_aa":284,"mass_kda":32.2,"function":"Transcription factor that is involved in the regulation of cell proliferation, apoptosis and embryonic development (By similarity). Plays an important role in the development of several organs, including kidney, muscle and inner ear (By similarity). Depending on context, functions as a transcriptional repressor or activator (By similarity). Lacks an activation domain, and requires interaction with EYA family members for transcription activation (PubMed:15141091). Mediates nuclear translocation of EYA1 and EYA2 (PubMed:19497856). Binds the 5'-TCA[AG][AG]TTNC-3' motif present in the MEF3 element in the MYOG promoter and CIDEA enhancer (PubMed:15141091, PubMed:19497856, PubMed:23435380, PubMed:27923061). Regulates the expression of numerous genes, including MYC, CCND1 and EZR (By similarity). Acts as an activator of the IGFBP5 promoter, probably coactivated by EYA2 (By similarity). Repression of precursor cell proliferation in myoblasts is switched to activation through recruitment of EYA3 to the SIX1-DACH1 complex (By similarity). During myogenesis, seems to act together with EYA2 and DACH2 (By similarity). Regulates the expression of CCNA1 (PubMed:15123840). Promotes brown adipocyte differentiation (By similarity)","subcellular_location":"Nucleus; Cytoplasm","url":"https://www.uniprot.org/uniprotkb/Q15475/entry"},"depmap":{"release":"DepMap","has_data":true,"is_common_essential":false,"resolved_as":"","url":"https://depmap.org/portal/gene/SIX1","classification":"Not Classified","n_dependent_lines":30,"n_total_lines":1208,"dependency_fraction":0.024834437086092714},"opencell":{"profiled":false,"resolved_as":"","ensg_id":"","cell_line_id":"","localizations":[],"interactors":[],"url":"https://opencell.sf.czbiohub.org/search/SIX1","total_profiled":1310},"omim":[{"mim_id":"617195","title":"MUSCULOSKELETAL EMBRYONIC NUCLEAR PROTEIN 1; MUSTN1","url":"https://www.omim.org/entry/617195"},{"mim_id":"615576","title":"MICRO RNA 185; MIR185","url":"https://www.omim.org/entry/615576"},{"mim_id":"614187","title":"HYPERTELORISM, PREAURICULAR SINUS, PUNCTAL PITS, AND DEAFNESS; HPPD","url":"https://www.omim.org/entry/614187"},{"mim_id":"610896","title":"BRANCHIOOTORENAL SYNDROME 2; BOR2","url":"https://www.omim.org/entry/610896"},{"mim_id":"608389","title":"BRANCHIOOTIC SYNDROME 3; BOS3","url":"https://www.omim.org/entry/608389"}],"hpa":{"profiled":true,"resolved_as":"","reliability":"Supported","locations":[{"location":"Nucleoplasm","reliability":"Supported"},{"location":"Nucleoli","reliability":"Additional"}],"tissue_specificity":"Tissue enhanced","tissue_distribution":"Detected in many","driving_tissues":[{"tissue":"parathyroid gland","ntpm":45.0},{"tissue":"salivary gland","ntpm":48.1},{"tissue":"skeletal muscle","ntpm":111.8},{"tissue":"tongue","ntpm":43.2}],"url":"https://www.proteinatlas.org/search/SIX1"},"hgnc":{"alias_symbol":[],"prev_symbol":["DFNA23"]},"alphafold":{"accession":"Q15475","domains":[{"cath_id":"1.10.10.60","chopping":"132-189","consensus_level":"high","plddt":87.849,"start":132,"end":189},{"cath_id":"1.25.40","chopping":"10-113","consensus_level":"medium","plddt":92.5209,"start":10,"end":113}],"viewer_url":"https://alphafold.ebi.ac.uk/entry/Q15475","model_url":"https://alphafold.ebi.ac.uk/files/AF-Q15475-F1-model_v6.cif","pae_url":"https://alphafold.ebi.ac.uk/files/AF-Q15475-F1-predicted_aligned_error_v6.png","plddt_mean":75.56},"mouse_models":{"mgi_url":"https://www.informatics.jax.org/marker/summary?nomen=SIX1","jax_strain_url":"https://www.jax.org/strain/search?query=SIX1"},"sequence":{"accession":"Q15475","fasta_url":"https://rest.uniprot.org/uniprotkb/Q15475.fasta","uniprot_url":"https://www.uniprot.org/uniprotkb/Q15475/entry","alphafold_viewer_url":"https://alphafold.ebi.ac.uk/entry/Q15475"}},"corpus_meta":[{"pmid":"14628042","id":"PMC_14628042","title":"Eya 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Laryngoscope","url":"https://pubmed.ncbi.nlm.nih.gov/22447252","citation_count":28,"is_preprint":false},{"pmid":"21281623","id":"PMC_21281623","title":"Six1 regulates Grem1 expression in the metanephric mesenchyme to initiate branching morphogenesis.","date":"2011","source":"Developmental biology","url":"https://pubmed.ncbi.nlm.nih.gov/21281623","citation_count":28,"is_preprint":false},{"pmid":"36937004","id":"PMC_36937004","title":"The SIX1/LDHA Axis Promotes Lactate Accumulation and Leads to NK Cell Dysfunction in Pancreatic Cancer.","date":"2023","source":"Journal of immunology research","url":"https://pubmed.ncbi.nlm.nih.gov/36937004","citation_count":27,"is_preprint":false},{"pmid":"31050834","id":"PMC_31050834","title":"Six1 regulates leukemia stem cell maintenance in acute myeloid leukemia.","date":"2019","source":"Cancer science","url":"https://pubmed.ncbi.nlm.nih.gov/31050834","citation_count":27,"is_preprint":false},{"pmid":"10777717","id":"PMC_10777717","title":"A novel locus (DFNA23) for prelingual autosomal dominant nonsyndromic hearing loss maps to 14q21-q22 in a Swiss German kindred.","date":"2000","source":"American journal of human genetics","url":"https://pubmed.ncbi.nlm.nih.gov/10777717","citation_count":27,"is_preprint":false},{"pmid":"23104013","id":"PMC_23104013","title":"EYA1-SIX1 complex in neurosensory cell fate induction in the mammalian inner ear.","date":"2012","source":"Hearing research","url":"https://pubmed.ncbi.nlm.nih.gov/23104013","citation_count":26,"is_preprint":false},{"pmid":"27302134","id":"PMC_27302134","title":"MyoD reprogramming requires Six1 and Six4 homeoproteins: genome-wide cis-regulatory module analysis.","date":"2016","source":"Nucleic acids research","url":"https://pubmed.ncbi.nlm.nih.gov/27302134","citation_count":25,"is_preprint":false},{"pmid":"26802027","id":"PMC_26802027","title":"Chromosomal anomalies at 1q, 3, 16q, and mutations of SIX1 and DROSHA genes underlie Wilms tumor recurrences.","date":"2016","source":"Oncotarget","url":"https://pubmed.ncbi.nlm.nih.gov/26802027","citation_count":25,"is_preprint":false},{"pmid":"29337851","id":"PMC_29337851","title":"Transcriptional Regulation by CpG Sites Methylation in the Core Promoter Region of the Bovine SIX1 Gene: Roles of Histone H4 and E2F2.","date":"2018","source":"International journal of molecular sciences","url":"https://pubmed.ncbi.nlm.nih.gov/29337851","citation_count":25,"is_preprint":false},{"pmid":"32065213","id":"PMC_32065213","title":"MiR-203a-3p regulates TGF-β1-induced epithelial-mesenchymal transition (EMT) in asthma by regulating Smad3 pathway through SIX1.","date":"2020","source":"Bioscience reports","url":"https://pubmed.ncbi.nlm.nih.gov/32065213","citation_count":24,"is_preprint":false},{"pmid":"21700001","id":"PMC_21700001","title":"A novel dominant mutation in SIX1, affecting a highly conserved residue, result in only auditory defects in humans.","date":"2011","source":"European journal of medical genetics","url":"https://pubmed.ncbi.nlm.nih.gov/21700001","citation_count":23,"is_preprint":false},{"pmid":"36261513","id":"PMC_36261513","title":"SNS-023 sensitizes hepatocellular carcinoma to sorafenib by inducing degradation of cancer drivers SIX1 and RPS16.","date":"2022","source":"Acta pharmacologica Sinica","url":"https://pubmed.ncbi.nlm.nih.gov/36261513","citation_count":23,"is_preprint":false},{"pmid":"22730291","id":"PMC_22730291","title":"Discovery, optimization and validation of an optimal DNA-binding sequence for the Six1 homeodomain transcription factor.","date":"2012","source":"Nucleic acids research","url":"https://pubmed.ncbi.nlm.nih.gov/22730291","citation_count":23,"is_preprint":false},{"pmid":"27940157","id":"PMC_27940157","title":"Pa2G4 is a novel Six1 co-factor that is required for neural crest and otic development.","date":"2016","source":"Developmental 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senescence and promotes SOX2-mediated cellular plasticity during tumorigenesis.","date":"2019","source":"Scientific reports","url":"https://pubmed.ncbi.nlm.nih.gov/30723235","citation_count":21,"is_preprint":false},{"pmid":"26175950","id":"PMC_26175950","title":"Six1 promotes glioblastoma cell proliferation and invasion by upregulation of connective tissue growth factor.","date":"2015","source":"American journal of cancer research","url":"https://pubmed.ncbi.nlm.nih.gov/26175950","citation_count":21,"is_preprint":false},{"pmid":"35527783","id":"PMC_35527783","title":"Tanshinone IIA inhibits cell growth by suppressing SIX1-induced aerobic glycolysis in non-small cell lung cancer cells.","date":"2022","source":"Oncology letters","url":"https://pubmed.ncbi.nlm.nih.gov/35527783","citation_count":21,"is_preprint":false},{"pmid":"32380038","id":"PMC_32380038","title":"FBXW7 promotes pathological cardiac hypertrophy by targeting EZH2-SIX1 signaling.","date":"2020","source":"Experimental cell 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the SIX1-DACH complex from transcriptional repression to activation by recruiting co-activators to specific gene targets regulating precursor cell proliferation.\",\n      \"method\": \"Biochemical phosphatase assays, co-immunoprecipitation, transcriptional reporter assays, genetic mouse knockouts\",\n      \"journal\": \"Nature\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1-2 — enzymatic activity demonstrated in vitro, combined with genetic epistasis and transcriptional assays in a highly-cited foundational paper\",\n      \"pmids\": [\"14628042\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2004,\n      \"finding\": \"BOR syndrome-causing SIX1 mutations disrupt either EYA1-SIX1 protein-protein interaction or SIX1-DNA binding; all three identified mutations abolish transcriptional activation, establishing that the EYA1-SIX1-DNA complex is required for normal otic and renal development.\",\n      \"method\": \"Direct sequencing, protein-protein interaction assays, DNA binding assays (EMSA), transcriptional reporter assays\",\n      \"journal\": \"PNAS\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1-2 — multiple orthogonal methods (binding assays + mutagenesis + transcription assays) on disease-causing mutants\",\n      \"pmids\": [\"15141091\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2000,\n      \"finding\": \"SIX1 is a nuclear phosphoprotein that undergoes hyperphosphorylation at mitosis by casein kinase II (CK2); CK2-mediated phosphorylation abolishes SIX1 binding to MEF3 sites in the aldolase A promoter, and CK2 inhibition arrests cells at G2/M.\",\n      \"method\": \"Cell cycle synchronization, in vitro kinase assay with CK2, EMSA for DNA binding, CK2 inhibitor (apigenin) treatment, immunoprecipitation\",\n      \"journal\": \"Journal of Biological Chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — in vitro reconstitution of phosphorylation with direct functional readout (DNA binding loss), replicated with pharmacological inhibitor in cells\",\n      \"pmids\": [\"10801845\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2004,\n      \"finding\": \"SIX1 and EYA1 together reprogram adult slow-twitch oxidative muscle fibers toward a fast-twitch glycolytic phenotype; SIX1 and EYA1 proteins preferentially accumulate in nuclei of fast-twitch muscles, and the MEF3/Six DNA binding element in the aldolase A pM promoter mediates high-level activation specifically in fast-twitch fibers.\",\n      \"method\": \"Transgenic forced expression in soleus muscle, myosin heavy chain isoform analysis, promoter-reporter assays, immunolocalization\",\n      \"journal\": \"Molecular and Cellular Biology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — clean gain-of-function in vivo with defined molecular readout, multiple orthogonal assays\",\n      \"pmids\": [\"15226428\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2006,\n      \"finding\": \"SIX1 protein is degraded via ubiquitin-mediated proteolysis through the APC(Cdh1) complex at mitosis; unlike canonical APC targets, SIX1 lacks destruction or KEN box motifs, instead containing multiple N- and C-terminal sequences including an N-terminal region that binds Cdh1.\",\n      \"method\": \"Cell cycle synchronization, proteasome inhibitor assays, co-immunoprecipitation with Cdh1, deletion mutagenesis\",\n      \"journal\": \"Oncogene\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — reciprocal co-IP with Cdh1, mutagenesis defining degradation sequences, cell-cycle-staged protein analysis\",\n      \"pmids\": [\"17130831\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2009,\n      \"finding\": \"SIX1 BOR syndrome mutations act through two distinct mechanisms: the V17E mutation in the Six domain abolishes SIX1-EYA complex formation and prevents nuclear localization of EYA, while the remaining five mutations retain EYA binding but are deficient in DNA binding; all mutants fail transcriptional activation. EYA interaction increases SIX1 protein stability and DNA binding affinity.\",\n      \"method\": \"Recombinant protein expression/purification in E. coli, in vitro binding assays, cellular localization studies, luciferase reporter assays\",\n      \"journal\": \"Journal of Biological Chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1-2 — reconstituted protein interactions in vitro, mutagenesis, multiple orthogonal functional assays\",\n      \"pmids\": [\"19497856\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2010,\n      \"finding\": \"SIX1 promotes epithelial-mesenchymal transition (EMT) and metastasis through upregulation of TGF-β type I receptor (TβRI), which is both necessary and sufficient to activate TGF-β signaling and induce EMT properties; SIX1 overexpression is required to switch TGF-β from tumor-suppressive to pro-metastatic.\",\n      \"method\": \"Knockdown/overexpression in breast cancer cell lines, TβRI promoter-reporter assays, in vivo metastasis assays\",\n      \"journal\": \"Cancer Research\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — identified direct transcriptional target (TβRI), rescue experiments, in vivo validation\",\n      \"pmids\": [\"21056993\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2011,\n      \"finding\": \"EYA2 is a required co-factor for SIX1 to mediate pro-metastatic functions including induction of TGF-β signaling, EMT, and cancer stem cell properties in breast cancer cells; knockdown of EYA2 reverses SIX1-induced phenotypes.\",\n      \"method\": \"siRNA knockdown, EMT marker analysis, TGF-β pathway reporter assays, cancer stem cell assays in MCF7 cells\",\n      \"journal\": \"Oncogene\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — epistasis by co-knockdown, multiple phenotypic readouts establishing EYA2 dependency\",\n      \"pmids\": [\"21706047\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2012,\n      \"finding\": \"EYA1 and SIX1 interact directly with SWI/SNF chromatin-remodeling subunits BRG1 and BAF170 to drive neurogenesis; the ATPase activity of BRG1 is required for EYA1/SIX1-induced ectopic neurogenesis and normal neurogenesis in the otocyst. SOX2 cooperates with EYA1/SIX1 in this complex to mediate neuronal differentiation upstream of NEUROG1 and NEUROD1.\",\n      \"method\": \"Co-immunoprecipitation, overexpression in non-neuronal cells (3T3 fibroblasts), cochlear explants, otocyst gain-of-function, BRG1 ATPase-dead mutant\",\n      \"journal\": \"Development\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — direct protein interaction (Co-IP), dominant-negative ATPase mutant, multiple cell-type validations\",\n      \"pmids\": [\"22513373\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2012,\n      \"finding\": \"EYA1/SIX1 coexpression in mouse cochlear explants is sufficient to induce hair cell fate in non-sensory epithelium by activating Atoh1-dependent and Atoh1-independent pathways; SOX2 cooperates with EYA1/SIX1 by direct binding to conserved Sox- and Six-binding sites in Atoh1 enhancers, and these proteins physically interact.\",\n      \"method\": \"Cochlear explant overexpression, Atoh1 enhancer reporter assays with site-directed mutagenesis, co-immunoprecipitation, conditional knockout mice\",\n      \"journal\": \"Developmental Cell\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1-2 — physical interaction shown by Co-IP, enhancer binding validated by mutagenesis, gain-of-function sufficiency demonstrated\",\n      \"pmids\": [\"22340499\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2012,\n      \"finding\": \"SIX1 transcriptionally induces VEGF-C expression, promoting peritumoral and intratumoral lymphangiogenesis and lymphatic metastasis in breast cancer; VEGF-C induction is required for SIX1-mediated lymphangiogenesis but additional VEGF-C-independent pathways also contribute to metastasis.\",\n      \"method\": \"Xenograft models in immunocompromised mice, VEGF-C promoter-reporter assays, siRNA knockdown, in vivo lymphangiogenesis quantification\",\n      \"journal\": \"Journal of Clinical Investigation\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — direct transcriptional target validated with promoter assays, in vivo rescue experiments\",\n      \"pmids\": [\"22466647\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2012,\n      \"finding\": \"SIX1 regulates skeletal muscle satellite cell differentiation and self-renewal via the ERK1/2 pathway through direct transcriptional control of Dusp6, a phosphatase that modulates ERK1/2 activity; genetic disruption of Six1 specifically in adult satellite cells impairs myofiber repair and increases stem cell self-renewal.\",\n      \"method\": \"Conditional Six1 knockout in adult satellite cells, chromatin immunoprecipitation (ChIP) for Dusp6, regeneration assays, Dusp6-null mice analysis\",\n      \"journal\": \"Journal of Cell Biology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — ChIP demonstrating direct binding to Dusp6, conditional knockout with defined phenotype, epistatic rescue via Dusp6 knockout\",\n      \"pmids\": [\"22945933\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2013,\n      \"finding\": \"SIX1 directly binds to the Core Enhancer Region of MyoD in muscle progenitor cells, is required for proper chromatin structure at this enhancer, and promotes MyoD binding at its own enhancer; Six1 knockdown reduces MyoD expression in myoblasts.\",\n      \"method\": \"Chromatin immunoprecipitation (ChIP), transcriptional reporter assays, siRNA knockdown, regenerating muscle analysis\",\n      \"journal\": \"PLoS One\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — ChIP demonstrating direct binding plus functional reporter assays and chromatin accessibility analysis\",\n      \"pmids\": [\"23840772\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2013,\n      \"finding\": \"SIX1 directly transcriptionally activates cyclin D1, promoting cell cycle progression and proliferation; SIX1 overexpression upregulates cyclin D1 mRNA and protein and enhances cyclin D1 promoter activity in pancreatic cancer cells.\",\n      \"method\": \"Cyclin D1 promoter-luciferase reporter assays, qRT-PCR, western blot, xenograft assays\",\n      \"journal\": \"PLoS One\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2-3 — promoter-reporter assay suggests direct transcription but no ChIP confirmation; single lab\",\n      \"pmids\": [\"23527134\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2014,\n      \"finding\": \"SIX1 coordinates TGF-β signals to upregulate VEGF-C expression in cervical cancer cells; SIX1 enhances TGF-β-induced SMAD2/3 activation and cooperates with the SMAD pathway to promote VEGF-C expression and lymphangiogenesis.\",\n      \"method\": \"SMAD2/3 phosphorylation analysis, VEGF-C promoter assays, in vitro lymphangiogenesis assays, knockdown/overexpression in tumor cells\",\n      \"journal\": \"Cancer Research\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2-3 — pathway interaction established but mechanistic detail of SIX1-SMAD cooperation is inferred; single lab\",\n      \"pmids\": [\"25142796\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2015,\n      \"finding\": \"SIX1 decreases p53 levels through a dual mechanism: (1) upregulation of microRNA-27a-3p that targets p53, and (2) downregulation of RPL26, which normally inhibits miR-27a-mediated repression of p53; these mechanisms operate independently of MDM2.\",\n      \"method\": \"Transcriptional reporter assays, miRNA overexpression/knockdown, RPL26 mutation analysis, western blot for p53 pathway components\",\n      \"journal\": \"Nature Communications\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — dual mechanism with mutation analysis confirming the RPL26-miR-27a competition; replicated across multiple cancer types\",\n      \"pmids\": [\"26687066\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2018,\n      \"finding\": \"SIX1 directly increases expression of many glycolytic genes to promote the Warburg effect; this transcriptional regulation of glycolysis occurs through HBO1 and AIB1 histone acetyltransferases; a cancer-related SIX1 mutation increases its ability to promote aerobic glycolysis.\",\n      \"method\": \"ChIP-seq for SIX1 binding at glycolytic gene promoters, HAT inhibitor studies, SIX1 mutant overexpression, metabolic flux assays, in vivo tumor growth\",\n      \"journal\": \"Cancer Cell\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1-2 — genome-wide ChIP combined with functional metabolic assays and HAT-dependency experiments; highly cited\",\n      \"pmids\": [\"29455928\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2020,\n      \"finding\": \"O-GlcNAcylation of SIX1 at threonine 276 (T276) enhances its stability by inhibiting ubiquitin-mediated proteasomal degradation; SIX1 itself promotes O-GlcNAcylation levels, forming a feedback loop; T276A mutation reduces O-GlcNAcylation and reverses the pro-tumor effect.\",\n      \"method\": \"Mass spectrometry, immunoprecipitation, site-directed mutagenesis (T276A), ubiquitination assays, xenograft models\",\n      \"journal\": \"Theranostics\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1-2 — modification site identified by mass spectrometry, confirmed by mutagenesis with functional consequence on ubiquitination and tumor growth\",\n      \"pmids\": [\"32863962\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2021,\n      \"finding\": \"GRP75 forms a trimeric complex with USP1 (a deubiquitinating enzyme) and SIX1; GRP75 provides a scaffold to recruit USP1, which inhibits K48-linked polyubiquitination of SIX1, thereby stabilizing SIX1 protein in prostate cancer cells; the C-terminus of GRP75 (433-679 aa) containing a peptide binding domain is required for complex formation.\",\n      \"method\": \"Co-immunoprecipitation, domain mapping, K48-ubiquitination assays, genetic and pharmacological inhibition, xenograft mouse models\",\n      \"journal\": \"Oncogene\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — trimeric complex defined by domain mapping, specific ubiquitination linkage identified, in vivo validation\",\n      \"pmids\": [\"34079090\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2022,\n      \"finding\": \"USP1 deubiquitinase stabilizes SIX1 protein in hepatocellular carcinoma through the EGFR-AKT signaling axis; EGFR-AKT activation promotes USP1 expression, which in turn prevents SIX1 degradation; suppression of this axis with SNS-032 induces SIX1 degradation.\",\n      \"method\": \"Ubiquitination assays, USP1 knockdown/overexpression, EGFR inhibitor experiments, western blot, xenograft models\",\n      \"journal\": \"Acta Pharmacologica Sinica\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — deubiquitinase-substrate relationship established with pathway context; single lab\",\n      \"pmids\": [\"36261513\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2020,\n      \"finding\": \"A small molecule (NCGC00378430/8430) that reduces the SIX1/EYA2 protein-protein interaction partially reverses SIX1-induced transcriptional and metabolic profiles, reverses TGF-β signaling and EMT, and suppresses breast cancer metastasis in vivo without affecting primary tumor growth.\",\n      \"method\": \"Small molecule screen, co-immunoprecipitation to assess complex disruption, transcriptome profiling, metabolic assays, in vivo metastasis model\",\n      \"journal\": \"Cancer Research\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — pharmacological disruption of complex with multiple orthogonal functional readouts and in vivo validation\",\n      \"pmids\": [\"32341035\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2011,\n      \"finding\": \"SIX1 and EYA1 form a transcription complex that directly regulates Fgf8 expression, acting downstream of Tbx1 in a genetic pathway (Tbx1-Six1/Eya1-Fgf8) controlling cardiovascular and craniofacial development; Six1/Eya1 double mutant mice recapitulate human del22q11 syndrome features.\",\n      \"method\": \"Genetic epistasis in mouse double mutants, Fgf8 promoter assays, compound mutant rescue experiments\",\n      \"journal\": \"Journal of Clinical Investigation\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — genetic epistasis with direct promoter evidence, multi-allele compound mutants establishing pathway order\",\n      \"pmids\": [\"21364285\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2011,\n      \"finding\": \"SIX1 acts in the metanephric mesenchyme as an upstream regulator of Grem1 expression; loss of Six1 abolishes Grem1 expression, leading to unopposed BMP4 activity that prevents ureteric bud ampulla formation; GREM1 protein treatment or genetic reduction of BMP4 restores branching morphogenesis in Six1-null kidneys.\",\n      \"method\": \"Six1 knockout mouse analysis, recombinant GREM1 treatment of kidney rudiments, genetic rescue (Six1−/−; Bmp4+/−), in vitro kidney culture\",\n      \"journal\": \"Developmental Biology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — genetic epistasis confirmed by protein rescue and compound genetics, pathway position unambiguously established\",\n      \"pmids\": [\"21281623\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2016,\n      \"finding\": \"Six1 and Six4 are both required for MyoD reprogramming of mouse embryonic fibroblasts toward myogenic fate; Six1/Six4 binding sites (MEF3 motifs) co-localize with MyoD binding sites on over 1000 genomic regions; Six1 and MyoD act synergistically in a feedforward transcriptional network to activate >80 co-regulated genes.\",\n      \"method\": \"MyoD-driven reprogramming of MEFs with Six1/Six4 knockdown, microarray gene expression, MyoD ChIP-seq analysis, genome-wide MEF3 site mapping, luciferase reporter assays\",\n      \"journal\": \"Nucleic Acids Research\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — genome-wide ChIP-seq combined with functional reprogramming assays and reporter validation\",\n      \"pmids\": [\"27302134\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2012,\n      \"finding\": \"Six1 optimal DNA-binding sequence is broader than previously known; Six1 domains outside the homeodomain contribute to DNA binding site selection, and Six1 alone (without co-factors) is sufficient for sequence discrimination at MEF3-type sites.\",\n      \"method\": \"Genomic ChIP binding profile analysis in myoblasts, position weight matrix optimization, in vitro DNA binding assays\",\n      \"journal\": \"Nucleic Acids Research\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2-3 — ChIP-seq combined with biochemical binding assays; single lab characterization\",\n      \"pmids\": [\"22730291\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2016,\n      \"finding\": \"Pa2G4 (Ebp1/Plfap) is a novel SIX1 co-factor that binds to SIX1 and interferes with the SIX1-EYA1 complex in human embryonic kidney cells; in Xenopus, Pa2G4 knockdown reduces neural crest and placodal gene expression and affects otocyst development.\",\n      \"method\": \"Co-immunoprecipitation in HEK cells, Xenopus gain- and loss-of-function, otocyst marker analysis\",\n      \"journal\": \"Developmental Biology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 3 — single co-IP demonstrating interaction plus Xenopus functional data; single lab\",\n      \"pmids\": [\"27940157\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2018,\n      \"finding\": \"SIX1 expression in leukemic initiating cells is controlled by WNT/β-catenin signaling through TCF7L2; the oncofusion protein MLL-AF9 increases chromatin accessibility at TCF/LEF-binding elements controlling the Six1 locus, enabling TCF7L2-dependent transcriptional activation of Six1.\",\n      \"method\": \"ATAC-seq, transcriptome profiling, WNT inhibitor treatment, genetic deletion of Wntless (WLS) in mice, AML mouse model\",\n      \"journal\": \"EBioMedicine\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — ATAC-seq + transcriptomics establishes chromatin accessibility mechanism; genetic and pharmacological validation\",\n      \"pmids\": [\"30528456\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2023,\n      \"finding\": \"SIX1 directly binds the LDHA promoter region to transcriptionally activate LDHA expression, promoting lactate accumulation in pancreatic cancer cells; SIX1-driven lactate production leads to NK cell dysfunction in the tumor microenvironment.\",\n      \"method\": \"Chromatin immunoprecipitation (ChIP) for SIX1 at LDHA promoter, metabolic assays, NK cell co-culture assays, xenograft models, LDHA inhibitor rescue experiments\",\n      \"journal\": \"Journal of Immunology Research\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2-3 — ChIP demonstrates direct binding, functional rescue with LDHA inhibitor; single lab\",\n      \"pmids\": [\"36937004\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2017,\n      \"finding\": \"SIX1 regulates dorsal mandibular arch identity by inducing Jag1 expression and simultaneously inhibiting Edn1 (endothelin 1) expression in pharyngeal endoderm; loss of SIX1 leads to aberrant EDNRA signaling in the dorsal arch domain, resulting in partial mandibular duplication.\",\n      \"method\": \"Six1 conditional knockout mice, Edn1/Jag1 expression analysis by in situ hybridization, genetic epistasis with EDNRA pathway mutants\",\n      \"journal\": \"Development\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — clean conditional knockout with defined molecular targets; pathway position established by genetic epistasis\",\n      \"pmids\": [\"28455376\"],\n      \"is_preprint\": false\n    }\n  ],\n  \"current_model\": \"SIX1 is a homeodomain transcription factor that binds MEF3-type DNA sequences (with the homeodomain and flanking domains contributing to site selection) and acts as a transcriptional activator or repressor depending on its co-factor context: interaction with EYA proteins (which contribute phosphatase activity) switches SIX1-DACH complexes from repression to activation by recruiting histone acetyltransferases (HBO1, AIB1), while interaction with SWI/SNF subunits (BRG1, BAF170) and SOX2 drives neurogenesis programs; SIX1 protein stability is regulated post-translationally by CK2-mediated phosphorylation (which reduces DNA binding), by APC(Cdh1)-mediated ubiquitin-proteasomal degradation at mitosis, and by O-GlcNAcylation at T276 and deubiquitination by USP1 (scaffolded by GRP75) which stabilize the protein; key direct transcriptional targets include glycolytic genes (via HBO1/AIB1), TGF-β type I receptor, VEGF-C, LDHA, cyclin D1, Fgf8, Grem1, MyoD, and Dusp6, placing SIX1 at the intersection of developmental organogenesis, metabolic reprogramming, and cancer metastasis pathways.\"\n}\n```","stage2_raw":"```json\n{\n  \"mechanistic_narrative\": \"SIX1 is a homeodomain transcription factor that orchestrates developmental organogenesis, muscle fiber-type specification, and metabolic reprogramming by binding MEF3-type DNA elements and assembling context-dependent transcriptional complexes. SIX1 forms obligate complexes with EYA family phosphatases, which switch SIX1-DACH repressor complexes to activation mode by recruiting histone acetyltransferases (HBO1, AIB1), directly driving glycolytic gene expression, VEGF-C, TGF-β type I receptor, Fgf8, MyoD, Dusp6, and other targets [PMID:14628042, PMID:29455928, PMID:21056993, PMID:22340499]. SIX1 protein stability is tightly controlled by CK2-mediated phosphorylation that abolishes DNA binding, APC/Cdh1-mediated ubiquitin-proteasomal degradation at mitosis, O-GlcNAcylation at T276 that inhibits ubiquitination, and USP1-mediated deubiquitination scaffolded by GRP75 [PMID:10801845, PMID:17130831, PMID:32863962, PMID:34079090]. Mutations in SIX1 that disrupt either EYA interaction or DNA binding cause branchio-oto-renal (BOR) syndrome, and SIX1 cooperates with SWI/SNF chromatin remodelers (BRG1, BAF170) and SOX2 to drive neurogenesis and hair cell fate in the inner ear [PMID:15141091, PMID:22513373, PMID:22340499].\",\n  \"teleology\": [\n    {\n      \"year\": 2000,\n      \"claim\": \"Establishing that SIX1 is a cell-cycle-regulated phosphoprotein answered how its DNA-binding activity is dynamically controlled: CK2-mediated hyperphosphorylation at mitosis abolishes MEF3 site binding, linking SIX1 transcriptional output to cell cycle state.\",\n      \"evidence\": \"In vitro CK2 kinase assay, EMSA for MEF3 binding, cell cycle synchronization, CK2 inhibitor treatment\",\n      \"pmids\": [\"10801845\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Specific CK2 phosphorylation sites on SIX1 not mapped\", \"Whether phosphorylation also affects co-factor interactions unknown\", \"In vivo physiological consequence of CK2 regulation of SIX1 not tested\"]\n    },\n    {\n      \"year\": 2003,\n      \"claim\": \"The discovery that EYA proteins possess intrinsic phosphatase activity that switches the SIX1-DACH complex from repression to activation established the core molecular logic of the SIX regulatory network — co-factor enzymatic activity determines transcriptional output.\",\n      \"evidence\": \"Biochemical phosphatase assays, co-immunoprecipitation, transcriptional reporters, mouse knockouts\",\n      \"pmids\": [\"14628042\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Identity of the EYA phosphatase substrate(s) in the SIX1-DACH complex not defined\", \"Structure of the ternary SIX1-DACH-EYA complex unknown\"]\n    },\n    {\n      \"year\": 2004,\n      \"claim\": \"Demonstrating that BOR syndrome mutations either abolish SIX1-EYA1 interaction or SIX1-DNA binding — with both classes eliminating transcriptional activation — established that the intact EYA1-SIX1-DNA ternary complex is essential for otic and renal development.\",\n      \"evidence\": \"Patient mutation sequencing, EMSA, protein-protein interaction assays, luciferase reporters\",\n      \"pmids\": [\"15141091\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Whether different BOR mutations produce distinct clinical severities through graded biochemical defects not resolved\", \"Downstream target genes mediating kidney and ear phenotypes not identified at this stage\"]\n    },\n    {\n      \"year\": 2004,\n      \"claim\": \"Forced SIX1/EYA1 expression reprogramming slow-twitch to fast-twitch muscle fibers demonstrated that SIX1 specifies glycolytic muscle identity in vivo, extending its role beyond development to adult tissue homeostasis.\",\n      \"evidence\": \"Transgenic overexpression in soleus muscle, myosin heavy chain isoform analysis, MEF3 promoter reporters\",\n      \"pmids\": [\"15226428\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Whether endogenous SIX1 is required to maintain fast-twitch identity (loss-of-function) not shown\", \"Direct transcriptional targets mediating fiber-type switch not catalogued\"]\n    },\n    {\n      \"year\": 2006,\n      \"claim\": \"Identification of APC/Cdh1-mediated proteasomal degradation of SIX1 at mitosis revealed a novel non-canonical APC substrate mechanism, explaining how SIX1 protein levels are reset each cell cycle.\",\n      \"evidence\": \"Proteasome inhibitor treatment, Cdh1 co-immunoprecipitation, deletion mutagenesis, cell cycle staging\",\n      \"pmids\": [\"17130831\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Exact degron motifs replacing D-box/KEN-box not fully mapped\", \"Relationship between CK2 phosphorylation and APC-mediated degradation not tested\"]\n    },\n    {\n      \"year\": 2009,\n      \"claim\": \"Detailed biochemical analysis of six BOR mutations refined the two-class model and revealed that EYA interaction increases SIX1 protein stability and DNA-binding affinity, establishing EYA as both an enzymatic co-activator and a structural stabilizer of SIX1.\",\n      \"evidence\": \"Recombinant protein purification, in vitro binding assays, cellular localization, luciferase reporters\",\n      \"pmids\": [\"19497856\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Structural basis for how EYA binding enhances SIX1 stability not resolved\", \"Whether EYA protects SIX1 from specific ubiquitin ligases not tested\"]\n    },\n    {\n      \"year\": 2010,\n      \"claim\": \"Identifying TGF-β type I receptor as a direct SIX1 transcriptional target that switches TGF-β from tumor-suppressive to pro-metastatic established SIX1 as a master regulator of EMT and metastasis signaling.\",\n      \"evidence\": \"Knockdown/overexpression in breast cancer lines, TβRI promoter reporters, in vivo metastasis assays\",\n      \"pmids\": [\"21056993\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Whether SIX1 directly binds TβRI promoter (ChIP) not shown at this stage\", \"Mechanism of signaling switch from tumor suppression to promotion not fully delineated\"]\n    },\n    {\n      \"year\": 2011,\n      \"claim\": \"Three studies collectively placed SIX1 within defined developmental signaling cascades: SIX1/EYA1 directly activates Fgf8 downstream of Tbx1 in cardiovascular/craniofacial development, regulates Grem1 to antagonize BMP4 in kidney branching morphogenesis, and requires EYA2 for pro-metastatic TGF-β/EMT functions in cancer.\",\n      \"evidence\": \"Genetic epistasis in compound mutant mice, recombinant GREM1 rescue of Six1-null kidneys, EYA2 knockdown epistasis in breast cancer cells\",\n      \"pmids\": [\"21364285\", \"21281623\", \"21706047\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Whether SIX1 directly binds Grem1 regulatory elements not confirmed by ChIP\", \"How SIX1/EYA1 vs SIX1/EYA2 co-factor choice is determined in different tissues unknown\"]\n    },\n    {\n      \"year\": 2012,\n      \"claim\": \"A series of 2012 studies expanded SIX1's mechanisms in four directions: (1) SIX1/EYA1 recruit SWI/SNF (BRG1/BAF170) for neurogenesis, (2) SIX1/EYA1/SOX2 drive hair cell fate via Atoh1 enhancers, (3) SIX1 transcriptionally induces VEGF-C for lymphangiogenesis, (4) SIX1 directly activates Dusp6 to regulate satellite cell ERK signaling, and (5) SIX1's DNA-binding specificity extends beyond the homeodomain.\",\n      \"evidence\": \"Co-IP with BRG1/BAF170, BRG1 ATPase-dead mutant, Atoh1 enhancer mutagenesis, cochlear explants, VEGF-C promoter reporters plus xenograft lymphangiogenesis, Dusp6 ChIP in satellite cells, ChIP-seq binding profile optimization\",\n      \"pmids\": [\"22513373\", \"22340499\", \"22466647\", \"22945933\", \"22730291\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Whether SWI/SNF is recruited genome-wide or at specific SIX1 targets not determined\", \"Relative contribution of VEGF-C-dependent vs independent SIX1 metastasis pathways unquantified\", \"Structural basis of SIX1 DNA-binding site selection by non-homeodomain regions unknown\"]\n    },\n    {\n      \"year\": 2013,\n      \"claim\": \"SIX1 was shown to directly bind the MyoD core enhancer to maintain chromatin accessibility and MyoD expression, and to activate cyclin D1 transcription for cell cycle progression, broadening the direct target gene repertoire.\",\n      \"evidence\": \"ChIP at MyoD enhancer in myoblasts, siRNA knockdown, cyclin D1 promoter-reporter assays in pancreatic cancer cells\",\n      \"pmids\": [\"23840772\", \"23527134\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Cyclin D1 activation lacks ChIP confirmation of direct binding\", \"Whether SIX1's role at MyoD enhancer requires EYA co-factors not tested\"]\n    },\n    {\n      \"year\": 2015,\n      \"claim\": \"Discovery that SIX1 downregulates p53 through a miR-27a-3p/RPL26 dual mechanism, independent of MDM2, revealed a non-canonical route by which SIX1 suppresses tumor surveillance.\",\n      \"evidence\": \"miRNA overexpression/knockdown, RPL26 mutation analysis, western blot for p53 pathway components\",\n      \"pmids\": [\"26687066\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Whether SIX1 directly transcribes miR-27a-3p or acts indirectly not established\", \"Physiological relevance during normal development unknown\"]\n    },\n    {\n      \"year\": 2016,\n      \"claim\": \"Genome-wide analysis demonstrated that SIX1/Six4 MEF3 binding sites co-localize with MyoD sites at >1000 genomic loci, establishing a feedforward transcriptional network for myogenic reprogramming, and Pa2G4 was identified as a novel SIX1-binding co-factor that competes with EYA1.\",\n      \"evidence\": \"MyoD ChIP-seq with MEF3 motif mapping in reprogrammed MEFs, Pa2G4 co-IP in HEK cells, Xenopus knockdown\",\n      \"pmids\": [\"27302134\", \"27940157\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Pa2G4-SIX1 interaction confirmed only by single co-IP direction\", \"Whether Pa2G4 modulates SIX1 targets genome-wide not tested\"]\n    },\n    {\n      \"year\": 2017,\n      \"claim\": \"SIX1 was found to regulate dorsal mandibular arch identity by inducing Jag1 and repressing Edn1, with loss causing aberrant EDNRA signaling and partial mandibular duplication — revealing a role in craniofacial patterning distinct from inner ear development.\",\n      \"evidence\": \"Conditional Six1 knockout, in situ hybridization, genetic epistasis with EDNRA pathway\",\n      \"pmids\": [\"28455376\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Whether SIX1 directly binds Jag1 and Edn1 regulatory regions not shown\", \"Mechanism of SIX1-mediated repression of Edn1 unknown\"]\n    },\n    {\n      \"year\": 2018,\n      \"claim\": \"ChIP-seq revealed that SIX1 directly occupies promoters of glycolytic genes and recruits HBO1/AIB1 histone acetyltransferases to drive aerobic glycolysis (Warburg effect), providing the mechanistic basis for SIX1's metabolic reprogramming function in cancer.\",\n      \"evidence\": \"ChIP-seq, HAT inhibitor studies, metabolic flux assays, cancer-associated SIX1 mutant analysis, in vivo tumor growth\",\n      \"pmids\": [\"29455928\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Whether HBO1/AIB1 recruitment is EYA-dependent or independent not fully resolved\", \"Structural basis of SIX1-HAT interaction unknown\"]\n    },\n    {\n      \"year\": 2020,\n      \"claim\": \"Two advances in 2020 addressed SIX1 protein stability and pharmacological targeting: O-GlcNAcylation at T276 was shown to inhibit ubiquitin-mediated degradation, and a small molecule disrupting SIX1-EYA2 interaction reversed EMT, TGF-β signaling, and metastasis in vivo.\",\n      \"evidence\": \"Mass spectrometry for O-GlcNAc site, T276A mutagenesis with ubiquitination assays; small-molecule screen with co-IP assessment, transcriptome profiling, in vivo metastasis model\",\n      \"pmids\": [\"32863962\", \"32341035\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"O-GlcNAc transferase responsible for T276 modification not identified\", \"Small molecule's direct binding mode and selectivity not structurally characterized\", \"Relationship between O-GlcNAcylation and APC/Cdh1-mediated degradation not tested\"]\n    },\n    {\n      \"year\": 2021,\n      \"claim\": \"Identification of a GRP75-USP1-SIX1 trimeric complex revealed the deubiquitination mechanism that stabilizes SIX1: GRP75 scaffolds USP1 to remove K48-linked polyubiquitin chains from SIX1, directly opposing proteasomal degradation.\",\n      \"evidence\": \"Co-immunoprecipitation, domain mapping of GRP75 C-terminus, K48-ubiquitination assays, xenograft models\",\n      \"pmids\": [\"34079090\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Whether USP1-mediated stabilization operates during normal development or only in cancer contexts unknown\", \"Specific lysine residues on SIX1 targeted by USP1 not mapped\"]\n    },\n    {\n      \"year\": 2022,\n      \"claim\": \"Placing USP1-mediated SIX1 stabilization downstream of EGFR-AKT signaling revealed how growth factor signaling sustains SIX1 protein levels in hepatocellular carcinoma.\",\n      \"evidence\": \"USP1 knockdown/overexpression, EGFR inhibitor treatment, ubiquitination assays, xenograft models\",\n      \"pmids\": [\"36261513\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Whether AKT directly phosphorylates USP1 to regulate its activity not determined\", \"Generalizability beyond hepatocellular carcinoma not tested\"]\n    },\n    {\n      \"year\": 2023,\n      \"claim\": \"SIX1 was shown to directly bind the LDHA promoter and activate transcription, linking SIX1-driven lactate production to immune evasion via NK cell dysfunction in the tumor microenvironment.\",\n      \"evidence\": \"ChIP at LDHA promoter, metabolic assays, NK cell co-culture, LDHA inhibitor rescue, xenograft models\",\n      \"pmids\": [\"36937004\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Whether LDHA is activated through HBO1/AIB1 co-activators as for other glycolytic targets not tested\", \"In vivo immune phenotype confirmation in immunocompetent models lacking\"]\n    },\n    {\n      \"year\": null,\n      \"claim\": \"Major unresolved questions include the structural basis of SIX1-EYA and SIX1-DACH complex assembly, how tissue-specific co-factor choice (EYA1 vs EYA2 vs Pa2G4) is determined, the identity of the E3 ubiquitin ligase(s) opposing USP1 at steady state, and whether the diverse post-translational regulatory mechanisms (CK2 phosphorylation, O-GlcNAcylation, APC/Cdh1 degradation, USP1 deubiquitination) are integrated or operate in distinct cellular contexts.\",\n      \"evidence\": \"\",\n      \"pmids\": [],\n      \"confidence\": \"Low\",\n      \"gaps\": [\"No crystal or cryo-EM structure of any SIX1-containing complex\", \"Tissue-specific co-factor selectivity mechanism unknown\", \"Identity of the E3 ligase(s) that ubiquitinate SIX1 outside of APC/Cdh1 not determined\"]\n    }\n  ],\n  \"mechanism_profile\": {\n    \"molecular_activity\": [\n      {\"term_id\": \"GO:0003677\", \"supporting_discovery_ids\": [2, 5, 24]},\n      {\"term_id\": \"GO:0140110\", \"supporting_discovery_ids\": [0, 6, 12, 16, 23, 27]}\n    ],\n    \"localization\": [\n      {\"term_id\": \"GO:0005634\", \"supporting_discovery_ids\": [2, 3, 5]}\n    ],\n    \"pathway\": [\n      {\"term_id\": \"R-HSA-74160\", \"supporting_discovery_ids\": [0, 12, 16, 23, 27]},\n      {\"term_id\": \"R-HSA-1266738\", \"supporting_discovery_ids\": [1, 8, 9, 21, 22, 28]},\n      {\"term_id\": \"R-HSA-162582\", \"supporting_discovery_ids\": [6, 7, 14]},\n      {\"term_id\": \"R-HSA-1430728\", \"supporting_discovery_ids\": [3, 16, 27]},\n      {\"term_id\": \"R-HSA-1640170\", \"supporting_discovery_ids\": [2, 4]},\n      {\"term_id\": \"R-HSA-4839726\", \"supporting_discovery_ids\": [8, 12]}\n    ],\n    \"complexes\": [\n      \"SIX1-EYA1/EYA2-DACH\",\n      \"GRP75-USP1-SIX1\",\n      \"SIX1-EYA1-BRG1-BAF170 (SWI/SNF)\"\n    ],\n    \"partners\": [\n      \"EYA1\",\n      \"EYA2\",\n      \"DACH1\",\n      \"SOX2\",\n      \"BRG1\",\n      \"GRP75\",\n      \"USP1\",\n      \"PA2G4\"\n    ],\n    \"other_free_text\": []\n  }\n}\n```"}