{"gene":"SIX1","run_date":"2026-06-10T07:46:32","timeline":{"discoveries":[{"year":2003,"finding":"SIX1 forms a transcriptional complex with DACH and EYA factors; EYA phosphatase activity switches the SIX1-DACH complex from transcriptional repression to activation by recruiting co-activators, thereby regulating genes controlling precursor cell proliferation in mammalian organogenesis.","method":"Genetic epistasis, biochemical co-activator recruitment assays, phosphatase activity assays, in vivo mouse knockout","journal":"Nature","confidence":"High","confidence_rationale":"Tier 1-2 / Strong — enzymatic activity demonstrated, complex formation established, genetic epistasis in multiple organs, replicated across multiple approaches in one rigorous study","pmids":["14628042"],"is_preprint":false},{"year":2004,"finding":"SIX1 mutations causing branchio-oto-renal (BOR) syndrome disrupt the EYA1-SIX1-DNA ternary complex via two distinct mechanisms: the V17E (Six domain) mutation abolishes EYA1-SIX1 protein-protein interaction, while homeodomain mutations eliminate specific DNA binding by SIX1.","method":"Direct sequencing of BOR patients, recombinant protein expression and purification, protein-protein interaction assays, EMSA (electrophoretic mobility shift assay)","journal":"Proceedings of the National Academy of Sciences of the United States of America","confidence":"High","confidence_rationale":"Tier 1-2 / Strong — multiple orthogonal biochemical methods, genotype-phenotype correlation confirmed, two distinct mechanisms identified","pmids":["15141091"],"is_preprint":false},{"year":2003,"finding":"Six1 is required upstream of Pax2, Six2, and Sall1 expression in the metanephric mesenchyme for ureteric bud invasion; Eya1 functions upstream of Six1 in this developmental hierarchy. Six1 and Eya1 genetically interact during kidney development.","method":"Six1 knockout mice, in situ hybridization, epistasis analysis with Pax2, Eya1, Six2 knockouts","journal":"Development (Cambridge, England)","confidence":"High","confidence_rationale":"Tier 2 / Strong — genetic epistasis established by multiple knockout combinations, replicated across developmental markers","pmids":["12783782"],"is_preprint":false},{"year":2003,"finding":"Six1 loss in mice causes severe muscle hypoplasia by impairing primary myogenesis; Six1 plays a specific role in hypaxial muscle differentiation, with reduced MyoD and myogenin gene activation in limb buds by E11.5, without affecting myogenic precursor cell migration or apoptosis.","method":"Six1 knockout mice (lacZ replacement), immunostaining, gene expression analysis","journal":"Development (Cambridge, England)","confidence":"High","confidence_rationale":"Tier 2 / Strong — clean knockout with defined molecular readouts, multiple markers assessed","pmids":["12668636"],"is_preprint":false},{"year":2000,"finding":"SIX1 is a nuclear phosphoprotein that undergoes hyperphosphorylation at mitosis by casein kinase II (CK2); CK2-mediated phosphorylation of SIX1 reduces its ability to bind MEF3 sites on the aldolase A promoter, and CK2 inhibition diminishes SIX1 phosphorylation and causes G2/M arrest.","method":"Cell cycle synchronization, in vitro kinase assay with recombinant SIX1 and CK2, EMSA, CK2 inhibitor (apigenin) treatment, immunoprecipitation","journal":"The Journal of biological chemistry","confidence":"High","confidence_rationale":"Tier 1-2 / Moderate — in vitro kinase assay plus cell-based phosphorylation, EMSA functional consequence, pharmacological validation","pmids":["10801845"],"is_preprint":false},{"year":2004,"finding":"Six1 and Eya1 co-expression in slow-twitch skeletal muscle is sufficient to reprogram adult slow-twitch oxidative fibers toward a fast-twitch glycolytic phenotype, driving fiber-type transition and activating fast-twitch fiber-specific genes; Six1 and Eya1 proteins preferentially accumulate in nuclei of fast-twitch muscles.","method":"Transgenic forced expression in slow-twitch soleus muscle, myosin heavy chain isoform analysis, nuclear fractionation, MEF3 promoter reporter assays","journal":"Molecular and cellular biology","confidence":"High","confidence_rationale":"Tier 2 / Strong — in vivo gain-of-function with defined molecular and cellular phenotypes, multiple orthogonal methods","pmids":["15226428"],"is_preprint":false},{"year":2006,"finding":"SIX1 protein is degraded during mitosis through ubiquitin-mediated proteolysis via the anaphase-promoting complex with Cdh1 (APC/Cdh1); unlike canonical APC/Cdh1 substrates, SIX1 lacks functional destruction or KEN box motifs—instead, its N- and C-terminal regions mediate degradation, and an N-terminal region directly binds Cdh1.","method":"Cell cycle synchronization, ubiquitin-mediated proteolysis assays, co-immunoprecipitation with Cdh1, deletion/mutant constructs","journal":"Oncogene","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — Co-IP with Cdh1, functional degradation assays, novel mechanism shown in single lab","pmids":["17130831"],"is_preprint":false},{"year":2009,"finding":"SIX1 BOR syndrome mutations act through two distinct mechanisms: V17E in the Six domain abolishes SIX1-EYA complex formation and prevents EYA nuclear localization, while the remaining five homeodomain mutations are deficient in DNA binding. EYA interaction with the N-terminal Six domain increases SIX1 protein stability, enhances its DNA binding affinity, and promotes its nuclear localization.","method":"Recombinant protein expression/purification in E. coli, protein-protein interaction assays, luciferase reporter transcriptional assays, nuclear localization studies, EMSA","journal":"The Journal of biological chemistry","confidence":"High","confidence_rationale":"Tier 1-2 / Strong — in vitro reconstitution with purified recombinant proteins, multiple orthogonal methods, mechanistic dissection of two distinct pathways","pmids":["19497856"],"is_preprint":false},{"year":2012,"finding":"EYA1 and SIX1 directly interact with SWI/SNF chromatin-remodeling subunits BRG1 and BAF170 to drive neuronal developmental programs; ATPase activity of BRG1 is required for EYA1/SIX1-induced ectopic neurogenesis. SOX2 cooperates with EYA1/SIX1 in this complex to mediate neuronal differentiation upstream of NEUROG1 and NEUROD1.","method":"Co-immunoprecipitation, overexpression in 3T3 fibroblasts and cochlear epithelial cells, BRG1 dominant-negative/mutant constructs, loss- and gain-of-function models","journal":"Development (Cambridge, England)","confidence":"High","confidence_rationale":"Tier 2 / Strong — reciprocal Co-IP, multiple cell-type validation, ATPase mutant epistasis, multiple orthogonal methods","pmids":["22513373"],"is_preprint":false},{"year":2012,"finding":"SIX1 directly induces transcription of the prolymphangiogenic factor VEGF-C, which is required for SIX1-mediated peritumoral lymphangiogenesis and lymphatic metastasis of breast cancer cells in vivo.","method":"Overexpression/knockdown in human breast cancer cells, orthotopic xenograft mouse model, VEGF-C rescue/knockdown experiments, transcriptional reporter assays","journal":"The Journal of clinical investigation","confidence":"High","confidence_rationale":"Tier 2 / Strong — genetic epistasis with VEGF-C rescue, in vivo model, multiple orthogonal approaches in single rigorous study","pmids":["22466647"],"is_preprint":false},{"year":2010,"finding":"SIX1 directly upregulates TGF-β type I receptor (TβRI) expression, and this upregulation is both necessary and sufficient to activate TGF-β signaling and induce epithelial-to-mesenchymal transition (EMT) downstream of SIX1 in breast cancer cells.","method":"Gain/loss-of-function in breast cancer cell lines, TβRI knockdown rescue experiments, TGF-β signaling assays, in vivo metastasis models","journal":"Cancer research","confidence":"High","confidence_rationale":"Tier 2 / Strong — epistasis established by knockdown rescue, necessity and sufficiency tested, multiple orthogonal approaches","pmids":["21056993"],"is_preprint":false},{"year":2011,"finding":"Six1 and Eya1 form a transcription complex that directly regulates Fgf8 as a downstream effector, and genetically interact with Tbx1 in a Tbx1-Six1/Eya1-Fgf8 pathway controlling cardiovascular and craniofacial development.","method":"Mouse compound mutants (Six1/Eya1 double knockouts), ChIP/direct target validation of Fgf8, genetic interaction with Tbx1 and Fgf8 heterozygotes","journal":"The Journal of clinical investigation","confidence":"High","confidence_rationale":"Tier 2 / Strong — genetic epistasis with multiple compound mutant combinations, direct target validated, phenotype recapitulates human syndrome","pmids":["21364285"],"is_preprint":false},{"year":2012,"finding":"Six1 regulates skeletal muscle satellite cell differentiation and controls the ERK1/2 pathway during regeneration through direct transcriptional control of Dusp6, a phosphatase that modulates ERK1/2 activity; loss of Six1 in satellite cells impairs differentiation and increases self-renewal.","method":"Conditional Six1 knockout in satellite cells, chromatin immunoprecipitation (ChIP) for Dusp6 locus, Dusp6 knockout analysis, regeneration assays","journal":"The Journal of cell biology","confidence":"High","confidence_rationale":"Tier 2 / Strong — conditional knockout, ChIP demonstrating direct binding, genetic validation with Dusp6 KO, multiple orthogonal methods","pmids":["22945933"],"is_preprint":false},{"year":2013,"finding":"Six1 directly transcriptionally activates cyclin D1 in pancreatic cancer cells; overexpression of Six1 upregulates cyclin D1 mRNA, protein, and cyclin D1 promoter activity, thereby promoting cell cycle progression and proliferation.","method":"Overexpression/knockdown, cyclin D1 promoter-luciferase reporter assays, in vivo xenograft","journal":"PloS one","confidence":"Medium","confidence_rationale":"Tier 2-3 / Moderate — promoter-reporter assays and knockdown/overexpression, single lab, two orthogonal approaches","pmids":["23527134"],"is_preprint":false},{"year":2015,"finding":"SIX1 decreases p53 levels through a dual mechanism: upregulation of microRNA-27a and downregulation of ribosomal protein L26 (RPL26), which acts as a competitive inhibitor of miR-27a-mediated p53 repression. This mechanism is MDM2-independent.","method":"Mutation analysis of RPL26 miRNA binding site, miRNA overexpression, RPL26 knockdown/overexpression, luciferase reporters, SIX1 gain-of-function","journal":"Nature communications","confidence":"High","confidence_rationale":"Tier 2 / Moderate — multiple orthogonal methods, mutagenesis confirmation, single lab but rigorous mechanistic dissection","pmids":["26687066"],"is_preprint":false},{"year":2013,"finding":"Six1 binds the Core Enhancer Region of MyoD and is required for MyoD expression in satellite cells; Six1 also promotes proper chromatin structure at the Core Enhancer Region and MyoD binding at its own enhancer.","method":"ChIP assay, transcriptional reporter assays, RNA interference knockdown, site-directed mutagenesis of MEF3 binding sites","journal":"PloS one","confidence":"High","confidence_rationale":"Tier 1-2 / Moderate — ChIP, reporter with site mutagenesis, knockdown phenotype, multiple orthogonal methods in single lab","pmids":["23840772"],"is_preprint":false},{"year":2018,"finding":"SIX1 directly increases the transcription of multiple glycolytic genes to promote the Warburg effect in cancer cells; this glycolytic function is mediated through the histone acetyltransferases HBO1 and AIB1. A cancer-related SIX1 mutation enhances its ability to promote aerobic glycolysis.","method":"Transcriptomics, ChIP-seq, gain/loss-of-function in cell lines and in vivo xenograft, HBO1/AIB1 co-factor knockdown epistasis","journal":"Cancer cell","confidence":"High","confidence_rationale":"Tier 2 / Strong — ChIP-seq showing direct binding, multiple epistasis experiments with co-factors, in vivo validation","pmids":["29455928"],"is_preprint":false},{"year":2020,"finding":"SIX1 undergoes O-GlcNAcylation at T276; this modification inhibits ubiquitination-mediated degradation of SIX1, thereby enhancing its protein stability and promoting hepatocellular carcinoma proliferation. T276A mutation decreases O-GlcNAcylation and reverses the pro-tumor effect.","method":"Mass spectrometry, immunoprecipitation, site-directed mutagenesis (T276A), O-GlcNAcylation and ubiquitination assays, in vitro and in vivo tumor models","journal":"Theranostics","confidence":"High","confidence_rationale":"Tier 1-2 / Moderate — mass spectrometry site identification, mutagenesis functional validation, multiple orthogonal approaches in single rigorous study","pmids":["32863962"],"is_preprint":false},{"year":2021,"finding":"The molecular chaperone GRP75 maintains SIX1 protein stability by recruiting the deubiquitinase USP1, forming a GRP75-USP1-SIX1 complex that inhibits K48-linked polyubiquitination of SIX1; the C-terminus (433-679 aa) of GRP75 contains the peptide-binding domain required for complex formation.","method":"Co-immunoprecipitation, ubiquitination assays (K48-linked), domain mapping with truncation mutants, GRP75/USP1 knockdown/inhibition, xenograft models","journal":"Oncogene","confidence":"High","confidence_rationale":"Tier 2 / Strong — reciprocal Co-IP, domain mapping, linkage-specific ubiquitination, in vitro and in vivo validation","pmids":["34079090"],"is_preprint":false},{"year":2012,"finding":"The DNA-binding sequence spectrum of SIX1 is broader than previously established; the Six1 homeodomain alone is sufficient for sequence discrimination, but domains outside the homeodomain also contribute to binding site selection. An optimized position weight matrix reveals MEF3-containing and novel binding sequences.","method":"ChIP-seq in myoblasts, biochemical binding assays (EMSA/pull-down), position weight matrix optimization algorithm","journal":"Nucleic acids research","confidence":"Medium","confidence_rationale":"Tier 1-2 / Moderate — ChIP-seq combined with biochemical binding assays, single lab but multiple orthogonal methods","pmids":["22730291"],"is_preprint":false},{"year":2016,"finding":"Six1 (and Six4) are required for MyoD-mediated reprogramming of mouse embryonic fibroblasts to myogenic fate; Six1/4 and MyoD co-occupy over 1000 genomic regions and synergistically activate 82 target genes through MEF3+E-box cis-regulatory modules in a feedforward regulatory mechanism.","method":"Microarray, MyoD ChIP-seq, genome-wide MEF3 site search, luciferase reporter assays for 19 cis-regulatory modules","journal":"Nucleic acids research","confidence":"High","confidence_rationale":"Tier 2 / Strong — ChIP-seq, genome-wide analysis, reporter assay validation of multiple modules, epistasis","pmids":["27302134"],"is_preprint":false},{"year":2022,"finding":"SIX1 maintains the rhabdomyosarcoma undifferentiated state by controlling enhancer activity and MYOD1 occupancy at loci permissive for tumor growth over muscle differentiation; SIX1 loss induces MYOD1 and MYOG redistribution genome-wide, causing differentiation into myotube-like cells.","method":"SIX1 loss-of-function (knockdown/knockout), ATAC-seq/ChIP-seq for enhancer activity, MYOD1 and MYOG ChIP-seq, in vivo tumor growth assays, zebrafish model","journal":"Cell reports","confidence":"High","confidence_rationale":"Tier 2 / Strong — genome-wide ChIP-seq and ATAC-seq showing direct chromatin effects, in vivo validation, multiple orthogonal methods","pmids":["35108532"],"is_preprint":false},{"year":2013,"finding":"Six1 and Six4 together (but neither alone) are required for male sex determination by activating Sry expression through regulation of Fog2 (Zfpm2), and for gonadal precursor cell growth through regulation of Nr5a1 (Ad4BP/SF1).","method":"Six1/Six4 single and double knockout mice, epistasis with Sry transgene rescue, expression analysis of Fog2 and Nr5a1","journal":"Developmental cell","confidence":"High","confidence_rationale":"Tier 2 / Strong — compound knockout with Sry transgene rescue, two distinct downstream pathway targets identified, multiple genetic tools","pmids":["23987514"],"is_preprint":false},{"year":2011,"finding":"Six1 regulates Grem1 expression in the metanephric mesenchyme to control branching morphogenesis; in Six1-deficient kidneys, loss of Grem1 leads to unopposed BMP4 activity preventing ureteric bud ampulla formation, and both GREM1 protein rescue and Bmp4 heterozygosity restore kidney formation.","method":"Six1 knockout mice, GREM1 protein rescue experiments, Six1(-/-);Bmp4(+/-) compound mutants, expression analysis","journal":"Developmental biology","confidence":"High","confidence_rationale":"Tier 2 / Strong — genetic epistasis with compound mutants, protein rescue, mechanistic pathway established","pmids":["21281623"],"is_preprint":false},{"year":2015,"finding":"The SIX1 homeodomain Q177R mutation (hotspot in Wilms tumors) occurs in the homeodomain and is associated with high proliferative potential in blastemal-type Wilms tumors, placing SIX1 mutations in a pathway with DROSHA/DGCR8 mutations in this cancer subtype.","method":"Exome and transcriptome sequencing of 58 blastemal-type Wilms tumors with validation cohort, functional validation of DROSHA mutants in cell lines","journal":"Cancer cell","confidence":"Medium","confidence_rationale":"Tier 3 / Moderate — genomic identification of hotspot mutation with large validation cohort, but direct functional mechanism of Q177R SIX1 not established in this study","pmids":["25670083"],"is_preprint":false},{"year":2021,"finding":"SIX1 promotes senescence repression through cooperation with Polycomb repressive complexes; SIX1 downregulation in fibroblasts triggers p16INK4A-mediated senescence. SIX1 also controls SOX2 expression to mediate cellular plasticity.","method":"SIX1 knockdown in human fibroblasts, transcriptomic analysis, Polycomb complex co-regulation analysis, glioma cell line functional assays","journal":"Oncogene","confidence":"Medium","confidence_rationale":"Tier 3 / Moderate — loss-of-function with defined p16INK4A phenotype, Polycomb cooperation shown but mechanistic detail limited to single lab","pmids":["26500063"],"is_preprint":false},{"year":2021,"finding":"SIX1 regulates expression of multiple collagen genes via TGFBR2-dependent Smad2/3 activation, promoting collagen deposition in the tumor microenvironment that impedes immune cell infiltration and antitumor immunity.","method":"Six1 deletion in cancer cells, in vivo tumor experiments with immune competent mice, collagen expression analysis, TGFBR2-Smad2/3 pathway activation assays","journal":"Cellular & molecular immunology","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — genetic deletion with immune-dependent tumor growth phenotype, pathway mechanism identified, single lab","pmids":["34782761"],"is_preprint":false},{"year":2017,"finding":"SIX1 directly binds the promoter of the LDHA gene to transcriptionally regulate it, promoting lactate accumulation via the SIX1/LDHA axis in pancreatic cancer cells.","method":"Chromatin immunoprecipitation (ChIP) assay for LDHA promoter, glycolysis functional assays, co-culture with NK cells","journal":"Journal of immunology research","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — ChIP demonstrating direct promoter binding, functional glycolysis assays, single lab","pmids":["36937004"],"is_preprint":false},{"year":2021,"finding":"Sobp directly binds SIX1 in the cell nucleus (co-immunoprecipitation and co-localization) and interferes with transcriptional activation of SIX1+EYA1 target genes, modulating Six1 transcriptional output during craniofacial development.","method":"Co-immunoprecipitation, immunofluorescence co-localization, luciferase reporter assays, Xenopus gain/loss-of-function","journal":"Development (Cambridge, England)","confidence":"Medium","confidence_rationale":"Tier 2-3 / Moderate — Co-IP and functional reporter assays, Xenopus functional validation, single lab","pmids":["34414417"],"is_preprint":false},{"year":2020,"finding":"A small molecule compound (NCGC00378430/8430) disrupts the SIX1/EYA2 protein-protein interaction, partially reverses SIX1-induced transcriptional and metabolic profiles, reverses TGFβ signaling and EMT, and suppresses breast cancer metastasis in vivo.","method":"Small molecule screen, SIX1/EYA2 interaction assay, transcriptomic/metabolomic profiling, in vivo metastasis model","journal":"Cancer research","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — direct protein-protein interaction disruption shown, in vivo validation, multiple orthogonal readouts in single study","pmids":["32341035"],"is_preprint":false},{"year":2016,"finding":"Six1 directly activates Parvalbumin (a key calcium buffer) as a direct transcriptional target in adult myofibers, and controls expression of fast-type sarcomeric proteins and glycolytic enzymes; deletion of Six1 in soleus leads to complete loss of MyHCIIA expression.","method":"Conditional Six1 deletion in soleus, global transcriptomics of isolated myofibers, ChIP for Parvalbumin locus","journal":"Skeletal muscle","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — conditional knockout, transcriptomics, ChIP for direct target, single lab","pmids":["27597886"],"is_preprint":false},{"year":2001,"finding":"Pax3 is required upstream of SIX1 and EYA2 in skeletal myogenesis; forced expression of Pax3 induces Six1 and Eya2 expression prior to MyoD and myogenin, whereas a dominant-negative Pax3 abolishes Six1 and Eya2 expression and blocks myogenesis.","method":"Pax3 overexpression and dominant-negative in pluripotent stem cells, RT-PCR gene expression analysis","journal":"The Journal of biological chemistry","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — epistasis established by dominant-negative and overexpression, placed Pax3 upstream of Six1, single lab","pmids":["11262400"],"is_preprint":false}],"current_model":"SIX1 is a homeodomain transcription factor that functions as the DNA-binding component of a bipartite complex with EYA co-activators (and sometimes DACH), where EYA phosphatase activity switches SIX1-DACH from repressor to activator; SIX1 directly regulates targets including glycolytic genes (via HBO1/AIB1), VEGF-C, TβRI, cyclin D1, MyoD, Dusp6, Fgf8, Grem1, LDHA, and collagens, and its activity and stability are post-translationally regulated by CK2-mediated phosphorylation (reducing DNA binding at mitosis), APC/Cdh1-mediated ubiquitin proteolysis (cell-cycle gating), O-GlcNAcylation at T276 (stabilization by blocking ubiquitination), and the GRP75-USP1 deubiquitinase complex; SIX1 also controls chromatin states by interacting with the SWI/SNF complex (BRG1/BAF170) and Polycomb repressive complexes, and cooperates with SOBP as a modulator, placing it at the center of developmental organogenesis programs that when re-activated in cancer drive EMT, glycolytic reprogramming, lymphangiogenesis, and immune evasion."},"narrative":{"mechanistic_narrative":"SIX1 is a homeodomain transcription factor that orchestrates precursor-cell proliferation and differentiation programs across mammalian organogenesis, acting as the DNA-binding component of a bipartite complex with EYA co-factors whose phosphatase activity converts the SIX1-DACH complex from a repressor to an activator [PMID:14628042]. Productive transcription requires both an intact Six-domain interaction with EYA—which stabilizes SIX1, enhances its DNA-binding affinity, and drives nuclear localization—and a functional homeodomain for sequence-specific DNA recognition; mutations in either module cause branchio-oto-renal syndrome through these two distinct biochemical lesions [PMID:15141091, PMID:19497856]. SIX1 recognizes MEF3 and related sites, with the homeodomain conferring core discrimination and flanking domains broadening the binding spectrum [PMID:22730291]. In development, SIX1 operates within EYA-dependent regulatory hierarchies that sit downstream of PAX3 and upstream of effectors including Pax2/Six2/Sall1 and Grem1 in kidney branching morphogenesis [PMID:12783782, PMID:21281623, PMID:11262400], MyoD/myogenin and Dusp6 in myogenesis and satellite-cell differentiation [PMID:12668636, PMID:22945933, PMID:23840772, PMID:27302134], Fgf8 within a Tbx1 craniofacial/cardiovascular pathway [PMID:21364285], and Sry/Fog2/Nr5a1 in male sex determination [PMID:23987514]. SIX1 also engages chromatin machinery directly, partnering with the SWI/SNF subunits BRG1 and BAF170 (whose ATPase activity is required for SIX1/EYA-driven neurogenesis) and with SOX2 [PMID:22513373], and cooperating with Polycomb complexes to repress p16INK4A-mediated senescence [PMID:26500063]. When re-activated in cancer, SIX1 redeploys these programs: it directly induces TβRI to activate TGF-β signaling and EMT [PMID:21056993], drives VEGF-C-dependent lymphangiogenesis and metastasis [PMID:22466647], reprograms metabolism by transactivating glycolytic genes via the HBO1/AIB1 acetyltransferases and LDHA [PMID:29455928, PMID:36937004], suppresses p53 through a miR-27a/RPL26 axis [PMID:26687066], and shapes an immunosuppressive collagen-rich microenvironment via TGFBR2-Smad2/3 [PMID:34782761]. SIX1 protein levels are gated post-translationally by CK2 phosphorylation that reduces mitotic DNA binding [PMID:10801845], APC/Cdh1-mediated proteolysis [PMID:17130831], stabilizing O-GlcNAcylation at T276 that blocks ubiquitination [PMID:32863962], and a GRP75-USP1 deubiquitinase complex that opposes K48-linked degradation [PMID:34079090]. The SIX1/EYA2 interaction is pharmacologically tractable, with a small molecule disrupting the complex and reversing SIX1-driven EMT and metastasis [PMID:32341035].","teleology":[{"year":2000,"claim":"Established that SIX1 DNA binding is not constitutive but cell-cycle-regulated, linking the transcription factor to mitotic control before its developmental partners were defined.","evidence":"In vitro CK2 kinase assay, cell-cycle synchronization, EMSA on the aldolase A promoter, and CK2 inhibitor treatment","pmids":["10801845"],"confidence":"High","gaps":["Specific phosphorylated residues not mapped","Did not address how phosphorylation integrates with co-factor binding"]},{"year":2001,"claim":"Placed SIX1 within a myogenic hierarchy downstream of PAX3, answering where SIX1 acts in the genetic cascade that initiates skeletal muscle fate.","evidence":"Pax3 overexpression and dominant-negative in pluripotent stem cells with RT-PCR readout","pmids":["11262400"],"confidence":"Medium","gaps":["No direct demonstration that PAX3 binds the Six1 locus","Single-lab epistasis without protein-level validation"]},{"year":2003,"claim":"Defined the central regulatory logic of the SIX1-EYA-DACH module: EYA phosphatase activity switches the complex from repression to activation, explaining how a single DNA-binding factor controls precursor proliferation.","evidence":"Genetic epistasis, co-activator recruitment and phosphatase activity assays, mouse knockouts","pmids":["14628042"],"confidence":"High","gaps":["Direct dephosphorylation substrate of EYA in this switch not fully resolved","Generality across all SIX1 targets not established"]},{"year":2003,"claim":"Demonstrated organ-specific requirements for SIX1 in kidney and muscle, showing it acts upstream of distinct effector sets (Pax2/Six2/Sall1; MyoD/myogenin) downstream of Eya1.","evidence":"Six1 knockout mice with in situ hybridization and epistasis against Pax2, Eya1, Six2 knockouts; lacZ-replacement knockout with myogenic marker analysis","pmids":["12783782","12668636"],"confidence":"High","gaps":["Which effector genes are direct vs indirect targets not all resolved","Did not define DNA-binding sites at effector loci"]},{"year":2004,"claim":"Showed SIX1+EYA1 co-expression is sufficient to reprogram muscle fiber type toward fast-twitch glycolytic identity, establishing SIX1 as an instructive driver of metabolic/contractile phenotype, and dissected the biochemical basis of BOR mutations.","evidence":"Transgenic gain-of-function in soleus with MyHC isoform analysis and MEF3 reporters; BOR mutation sequencing with EMSA and protein-interaction assays","pmids":["15226428","15141091"],"confidence":"High","gaps":["Direct fast-twitch gene targets not all enumerated","Mechanism of nuclear accumulation preference not defined"]},{"year":2006,"claim":"Revealed cell-cycle-coupled destruction of SIX1 by APC/Cdh1 through a non-canonical degron, adding a degradation layer to SIX1's mitotic regulation.","evidence":"Cell-cycle synchronization, ubiquitin-proteolysis assays, Cdh1 Co-IP, and deletion mutants","pmids":["17130831"],"confidence":"Medium","gaps":["Degron sequence not precisely defined","Single-lab mechanism without reciprocal in vivo confirmation"]},{"year":2009,"claim":"Resolved how EYA binding to the Six domain functionally enables SIX1, showing it stabilizes the protein, enhances DNA affinity, and promotes nuclear import—explaining why BOR Six-domain mutations are pathogenic.","evidence":"Recombinant protein reconstitution, interaction assays, luciferase reporters, nuclear localization studies, EMSA","pmids":["19497856"],"confidence":"High","gaps":["Structural basis of the affinity enhancement not solved","In vivo relevance of each effect not separately tested"]},{"year":2010,"claim":"Identified TβRI as a direct SIX1 target that is necessary and sufficient to activate TGF-β signaling and EMT, defining a concrete molecular route from SIX1 reactivation to metastatic behavior.","evidence":"Gain/loss-of-function in breast cancer cells, TβRI knockdown rescue, TGF-β assays, in vivo metastasis","pmids":["21056993"],"confidence":"High","gaps":["Direct promoter binding site not detailed here","Contribution relative to other EMT routes not quantified"]},{"year":2011,"claim":"Extended the SIX1/EYA regulatory network into developmental morphogenesis via direct Fgf8 control within a Tbx1 pathway and via Grem1-mediated antagonism of BMP4 in kidney branching.","evidence":"Mouse compound mutants, ChIP/target validation of Fgf8, GREM1 protein rescue and Bmp4 heterozygote epistasis","pmids":["21364285","21281623"],"confidence":"High","gaps":["Direct vs indirect regulation of Grem1 not fully established","Tissue-specific co-factor requirements not defined"]},{"year":2012,"claim":"Connected SIX1 to chromatin-remodeling and angiogenic/cell-cycle programs, and refined its DNA-binding code—showing it physically engages SWI/SNF (BRG1/BAF170) and SOX2, directly drives VEGF-C and Dusp6, and recognizes a broader site spectrum than MEF3 alone.","evidence":"Reciprocal Co-IP with BRG1/BAF170 and ATPase-mutant epistasis; orthotopic xenograft with VEGF-C rescue; conditional satellite-cell knockout with Dusp6 ChIP; ChIP-seq with position-weight-matrix optimization","pmids":["22513373","22466647","22945933","22730291"],"confidence":"High","gaps":["Whether SWI/SNF recruitment is direct at all SIX1 targets unknown","Stoichiometry of SIX1-SOX2-SWI/SNF complex undefined"]},{"year":2013,"claim":"Demonstrated direct SIX1 control of cyclin D1, MyoD enhancer activity, and the male sex-determination pathway, broadening the catalogue of direct targets and showing SIX1 shapes chromatin state at the MyoD Core Enhancer.","evidence":"Promoter-reporter and ChIP for cyclin D1 and MyoD enhancer with MEF3 mutagenesis; Six1/Six4 double knockout with Sry transgene rescue","pmids":["23527134","23840772","23987514"],"confidence":"High","gaps":["Redundancy with SIX4 not resolved in all contexts","Mechanism of chromatin opening at MyoD enhancer not defined"]},{"year":2015,"claim":"Defined a p53-suppressing axis (miR-27a/RPL26, MDM2-independent) and identified a homeodomain hotspot mutation (Q177R) in blastemal Wilms tumors, linking SIX1 to tumor-suppressor evasion and cancer genetics.","evidence":"miRNA/RPL26 reporter and mutagenesis with SIX1 gain-of-function; exome/transcriptome sequencing of Wilms tumors with validation cohort","pmids":["26687066","25670083"],"confidence":"High","gaps":["Functional mechanism of Q177R not established in the genomic study","Tissue specificity of the miR-27a/RPL26 axis untested"]},{"year":2016,"claim":"Established SIX1 as a feedforward partner of MyoD genome-wide and a direct regulator of fast-fiber/glycolytic and calcium-handling genes, unifying its developmental myogenic and metabolic roles.","evidence":"Microarray, MyoD ChIP-seq, genome-wide MEF3 search with reporter validation; conditional soleus deletion with transcriptomics and Parvalbumin ChIP","pmids":["27302134","27597886"],"confidence":"High","gaps":["Direct vs cooperative occupancy at each module not always separable","SIX4 contribution to the metabolic program not isolated"]},{"year":2017,"claim":"Linked SIX1 transcriptional control of LDHA to lactate-driven metabolic and immune effects, an early connection between SIX1 metabolism and antitumor immunity.","evidence":"ChIP for the LDHA promoter, glycolysis assays, NK-cell co-culture","pmids":["36937004"],"confidence":"Medium","gaps":["Single-lab study","Immune-evasion mechanism not validated in vivo here"]},{"year":2018,"claim":"Defined the mechanism of SIX1-driven Warburg metabolism, showing direct transactivation of glycolytic genes through the HBO1/AIB1 acetyltransferases and that a cancer mutation enhances this activity.","evidence":"Transcriptomics, ChIP-seq, gain/loss-of-function with HBO1/AIB1 epistasis, in vivo xenograft","pmids":["29455928"],"confidence":"High","gaps":["Identity of the activating cancer mutation's structural effect not fully resolved","Relationship to LDHA axis not integrated"]},{"year":2020,"claim":"Identified a stabilizing O-GlcNAcylation at T276 and a druggable SIX1/EYA2 interface, defining new ways SIX1 levels are controlled and showing the complex is therapeutically targetable.","evidence":"Mass spectrometry, T276A mutagenesis, ubiquitination assays, tumor models; small-molecule screen disrupting SIX1/EYA2 with transcriptomic/metabolomic and in vivo metastasis readouts","pmids":["32863962","32341035"],"confidence":"High","gaps":["O-GlcNAc transferase responsible for T276 not identified","Compound selectivity and in vivo pharmacology limited"]},{"year":2021,"claim":"Defined further post-translational stabilization (GRP75-USP1 deubiquitinase complex), a SOBP modulatory partner, Polycomb-cooperative senescence repression, and a collagen/TGFBR2-Smad2/3 immune-evasion mechanism, deepening SIX1's roles in protein homeostasis, plasticity, and the tumor microenvironment.","evidence":"Reciprocal Co-IP with domain mapping and K48-ubiquitination assays; Co-IP/co-localization and reporter assays with SOBP in Xenopus; fibroblast knockdown with Polycomb co-regulation; cancer-cell deletion with immune-competent tumor models","pmids":["34079090","34414417","26500063","34782761"],"confidence":"Medium","gaps":["Each mechanism shown largely in single labs","How these layers are coordinated on the same SIX1 pool unknown"]},{"year":2022,"claim":"Showed SIX1 maintains the rhabdomyosarcoma undifferentiated state by directing enhancer activity and MYOD1 occupancy, demonstrating that SIX1 controls cell fate through genome-wide chromatin redistribution.","evidence":"Loss-of-function with ATAC-seq/ChIP-seq for enhancers, MYOD1/MYOG ChIP-seq, in vivo and zebrafish tumor assays","pmids":["35108532"],"confidence":"High","gaps":["Co-factor(s) mediating enhancer selection not defined","Reversibility window for differentiation therapy not established"]},{"year":null,"claim":"How the multiple post-translational inputs (CK2 phosphorylation, APC/Cdh1 degradation, O-GlcNAcylation, GRP75-USP1 deubiquitination) are integrated to set SIX1 levels and activity within a single cell, and how SIX1 selects between developmental and oncogenic enhancer programs, remains unresolved.","evidence":"","pmids":[],"confidence":"Medium","gaps":["No unified model linking PTM state to target-gene choice","Structural basis of SIX1-EYA-chromatin assembly not solved","Determinants of context-specific co-factor usage (SWI/SNF vs Polycomb vs HBO1/AIB1) unknown"]}],"mechanism_profile":{"molecular_activity":[{"term_id":"GO:0140110","term_label":"transcription regulator activity","supporting_discovery_ids":[0,9,10,16]},{"term_id":"GO:0003677","term_label":"DNA binding","supporting_discovery_ids":[1,4,7,19]}],"localization":[{"term_id":"GO:0005634","term_label":"nucleus","supporting_discovery_ids":[4,5,7,28]}],"pathway":[{"term_id":"R-HSA-1266738","term_label":"Developmental Biology","supporting_discovery_ids":[2,3,11,22]},{"term_id":"R-HSA-74160","term_label":"Gene expression (Transcription)","supporting_discovery_ids":[0,16,20]},{"term_id":"R-HSA-4839726","term_label":"Chromatin organization","supporting_discovery_ids":[8,21,25]},{"term_id":"R-HSA-1643685","term_label":"Disease","supporting_discovery_ids":[9,10,14,16]},{"term_id":"R-HSA-1430728","term_label":"Metabolism","supporting_discovery_ids":[16,27,30]}],"complexes":["SIX1-EYA-DACH transcription complex","SWI/SNF (BRG1/BAF170)","GRP75-USP1-SIX1 complex"],"partners":["EYA1","EYA2","DACH","BRG1","BAF170","SOX2","SOBP","GRP75"],"other_free_text":[]}},"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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outcome.","date":"2014","source":"Histopathology","url":"https://pubmed.ncbi.nlm.nih.gov/24438019","citation_count":20,"is_preprint":false},{"pmid":"35414775","id":"PMC_35414775","title":"A SIX1 degradation inducer blocks excessive proliferation of prostate cancer.","date":"2022","source":"International journal of biological sciences","url":"https://pubmed.ncbi.nlm.nih.gov/35414775","citation_count":19,"is_preprint":false},{"pmid":"34782761","id":"PMC_34782761","title":"Homeoprotein SIX1 compromises antitumor immunity through TGF-β-mediated regulation of collagens.","date":"2021","source":"Cellular & molecular immunology","url":"https://pubmed.ncbi.nlm.nih.gov/34782761","citation_count":19,"is_preprint":false},{"pmid":"36892427","id":"PMC_36892427","title":"LRRC75A-AS1 delivered by M2 macrophage exosomes promotes cervical cancer progression via enhancing SIX1 expression.","date":"2023","source":"Cancer 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the SIX1-DACH complex from transcriptional repression to activation by recruiting co-activators, thereby regulating genes controlling precursor cell proliferation in mammalian organogenesis.\",\n      \"method\": \"Genetic epistasis, biochemical co-activator recruitment assays, phosphatase activity assays, in vivo mouse knockout\",\n      \"journal\": \"Nature\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1-2 / Strong — enzymatic activity demonstrated, complex formation established, genetic epistasis in multiple organs, replicated across multiple approaches in one rigorous study\",\n      \"pmids\": [\"14628042\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2004,\n      \"finding\": \"SIX1 mutations causing branchio-oto-renal (BOR) syndrome disrupt the EYA1-SIX1-DNA ternary complex via two distinct mechanisms: the V17E (Six domain) mutation abolishes EYA1-SIX1 protein-protein interaction, while homeodomain mutations eliminate specific DNA binding by SIX1.\",\n      \"method\": \"Direct sequencing of BOR patients, recombinant protein expression and purification, protein-protein interaction assays, EMSA (electrophoretic mobility shift assay)\",\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 — multiple orthogonal biochemical methods, genotype-phenotype correlation confirmed, two distinct mechanisms identified\",\n      \"pmids\": [\"15141091\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2003,\n      \"finding\": \"Six1 is required upstream of Pax2, Six2, and Sall1 expression in the metanephric mesenchyme for ureteric bud invasion; Eya1 functions upstream of Six1 in this developmental hierarchy. Six1 and Eya1 genetically interact during kidney development.\",\n      \"method\": \"Six1 knockout mice, in situ hybridization, epistasis analysis with Pax2, Eya1, Six2 knockouts\",\n      \"journal\": \"Development (Cambridge, England)\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — genetic epistasis established by multiple knockout combinations, replicated across developmental markers\",\n      \"pmids\": [\"12783782\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2003,\n      \"finding\": \"Six1 loss in mice causes severe muscle hypoplasia by impairing primary myogenesis; Six1 plays a specific role in hypaxial muscle differentiation, with reduced MyoD and myogenin gene activation in limb buds by E11.5, without affecting myogenic precursor cell migration or apoptosis.\",\n      \"method\": \"Six1 knockout mice (lacZ replacement), immunostaining, gene expression analysis\",\n      \"journal\": \"Development (Cambridge, England)\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — clean knockout with defined molecular readouts, multiple markers assessed\",\n      \"pmids\": [\"12668636\"],\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 of SIX1 reduces its ability to bind MEF3 sites on the aldolase A promoter, and CK2 inhibition diminishes SIX1 phosphorylation and causes G2/M arrest.\",\n      \"method\": \"Cell cycle synchronization, in vitro kinase assay with recombinant SIX1 and CK2, EMSA, CK2 inhibitor (apigenin) treatment, immunoprecipitation\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1-2 / Moderate — in vitro kinase assay plus cell-based phosphorylation, EMSA functional consequence, pharmacological validation\",\n      \"pmids\": [\"10801845\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2004,\n      \"finding\": \"Six1 and Eya1 co-expression in slow-twitch skeletal muscle is sufficient to reprogram adult slow-twitch oxidative fibers toward a fast-twitch glycolytic phenotype, driving fiber-type transition and activating fast-twitch fiber-specific genes; Six1 and Eya1 proteins preferentially accumulate in nuclei of fast-twitch muscles.\",\n      \"method\": \"Transgenic forced expression in slow-twitch soleus muscle, myosin heavy chain isoform analysis, nuclear fractionation, MEF3 promoter reporter assays\",\n      \"journal\": \"Molecular and cellular biology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — in vivo gain-of-function with defined molecular and cellular phenotypes, multiple orthogonal methods\",\n      \"pmids\": [\"15226428\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2006,\n      \"finding\": \"SIX1 protein is degraded during mitosis through ubiquitin-mediated proteolysis via the anaphase-promoting complex with Cdh1 (APC/Cdh1); unlike canonical APC/Cdh1 substrates, SIX1 lacks functional destruction or KEN box motifs—instead, its N- and C-terminal regions mediate degradation, and an N-terminal region directly binds Cdh1.\",\n      \"method\": \"Cell cycle synchronization, ubiquitin-mediated proteolysis assays, co-immunoprecipitation with Cdh1, deletion/mutant constructs\",\n      \"journal\": \"Oncogene\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — Co-IP with Cdh1, functional degradation assays, novel mechanism shown in single lab\",\n      \"pmids\": [\"17130831\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2009,\n      \"finding\": \"SIX1 BOR syndrome mutations act through two distinct mechanisms: V17E in the Six domain abolishes SIX1-EYA complex formation and prevents EYA nuclear localization, while the remaining five homeodomain mutations are deficient in DNA binding. EYA interaction with the N-terminal Six domain increases SIX1 protein stability, enhances its DNA binding affinity, and promotes its nuclear localization.\",\n      \"method\": \"Recombinant protein expression/purification in E. coli, protein-protein interaction assays, luciferase reporter transcriptional assays, nuclear localization studies, EMSA\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1-2 / Strong — in vitro reconstitution with purified recombinant proteins, multiple orthogonal methods, mechanistic dissection of two distinct pathways\",\n      \"pmids\": [\"19497856\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2012,\n      \"finding\": \"EYA1 and SIX1 directly interact with SWI/SNF chromatin-remodeling subunits BRG1 and BAF170 to drive neuronal developmental programs; ATPase activity of BRG1 is required for EYA1/SIX1-induced ectopic neurogenesis. SOX2 cooperates with EYA1/SIX1 in this complex to mediate neuronal differentiation upstream of NEUROG1 and NEUROD1.\",\n      \"method\": \"Co-immunoprecipitation, overexpression in 3T3 fibroblasts and cochlear epithelial cells, BRG1 dominant-negative/mutant constructs, loss- and gain-of-function models\",\n      \"journal\": \"Development (Cambridge, England)\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — reciprocal Co-IP, multiple cell-type validation, ATPase mutant epistasis, multiple orthogonal methods\",\n      \"pmids\": [\"22513373\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2012,\n      \"finding\": \"SIX1 directly induces transcription of the prolymphangiogenic factor VEGF-C, which is required for SIX1-mediated peritumoral lymphangiogenesis and lymphatic metastasis of breast cancer cells in vivo.\",\n      \"method\": \"Overexpression/knockdown in human breast cancer cells, orthotopic xenograft mouse model, VEGF-C rescue/knockdown experiments, transcriptional reporter assays\",\n      \"journal\": \"The Journal of clinical investigation\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — genetic epistasis with VEGF-C rescue, in vivo model, multiple orthogonal approaches in single rigorous study\",\n      \"pmids\": [\"22466647\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2010,\n      \"finding\": \"SIX1 directly upregulates TGF-β type I receptor (TβRI) expression, and this upregulation is both necessary and sufficient to activate TGF-β signaling and induce epithelial-to-mesenchymal transition (EMT) downstream of SIX1 in breast cancer cells.\",\n      \"method\": \"Gain/loss-of-function in breast cancer cell lines, TβRI knockdown rescue experiments, TGF-β signaling assays, in vivo metastasis models\",\n      \"journal\": \"Cancer research\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — epistasis established by knockdown rescue, necessity and sufficiency tested, multiple orthogonal approaches\",\n      \"pmids\": [\"21056993\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2011,\n      \"finding\": \"Six1 and Eya1 form a transcription complex that directly regulates Fgf8 as a downstream effector, and genetically interact with Tbx1 in a Tbx1-Six1/Eya1-Fgf8 pathway controlling cardiovascular and craniofacial development.\",\n      \"method\": \"Mouse compound mutants (Six1/Eya1 double knockouts), ChIP/direct target validation of Fgf8, genetic interaction with Tbx1 and Fgf8 heterozygotes\",\n      \"journal\": \"The Journal of clinical investigation\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — genetic epistasis with multiple compound mutant combinations, direct target validated, phenotype recapitulates human syndrome\",\n      \"pmids\": [\"21364285\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2012,\n      \"finding\": \"Six1 regulates skeletal muscle satellite cell differentiation and controls the ERK1/2 pathway during regeneration through direct transcriptional control of Dusp6, a phosphatase that modulates ERK1/2 activity; loss of Six1 in satellite cells impairs differentiation and increases self-renewal.\",\n      \"method\": \"Conditional Six1 knockout in satellite cells, chromatin immunoprecipitation (ChIP) for Dusp6 locus, Dusp6 knockout analysis, regeneration assays\",\n      \"journal\": \"The Journal of cell biology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — conditional knockout, ChIP demonstrating direct binding, genetic validation with Dusp6 KO, multiple orthogonal methods\",\n      \"pmids\": [\"22945933\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2013,\n      \"finding\": \"Six1 directly transcriptionally activates cyclin D1 in pancreatic cancer cells; overexpression of Six1 upregulates cyclin D1 mRNA, protein, and cyclin D1 promoter activity, thereby promoting cell cycle progression and proliferation.\",\n      \"method\": \"Overexpression/knockdown, cyclin D1 promoter-luciferase reporter assays, in vivo xenograft\",\n      \"journal\": \"PloS one\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2-3 / Moderate — promoter-reporter assays and knockdown/overexpression, single lab, two orthogonal approaches\",\n      \"pmids\": [\"23527134\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2015,\n      \"finding\": \"SIX1 decreases p53 levels through a dual mechanism: upregulation of microRNA-27a and downregulation of ribosomal protein L26 (RPL26), which acts as a competitive inhibitor of miR-27a-mediated p53 repression. This mechanism is MDM2-independent.\",\n      \"method\": \"Mutation analysis of RPL26 miRNA binding site, miRNA overexpression, RPL26 knockdown/overexpression, luciferase reporters, SIX1 gain-of-function\",\n      \"journal\": \"Nature communications\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — multiple orthogonal methods, mutagenesis confirmation, single lab but rigorous mechanistic dissection\",\n      \"pmids\": [\"26687066\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2013,\n      \"finding\": \"Six1 binds the Core Enhancer Region of MyoD and is required for MyoD expression in satellite cells; Six1 also promotes proper chromatin structure at the Core Enhancer Region and MyoD binding at its own enhancer.\",\n      \"method\": \"ChIP assay, transcriptional reporter assays, RNA interference knockdown, site-directed mutagenesis of MEF3 binding sites\",\n      \"journal\": \"PloS one\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1-2 / Moderate — ChIP, reporter with site mutagenesis, knockdown phenotype, multiple orthogonal methods in single lab\",\n      \"pmids\": [\"23840772\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2018,\n      \"finding\": \"SIX1 directly increases the transcription of multiple glycolytic genes to promote the Warburg effect in cancer cells; this glycolytic function is mediated through the histone acetyltransferases HBO1 and AIB1. A cancer-related SIX1 mutation enhances its ability to promote aerobic glycolysis.\",\n      \"method\": \"Transcriptomics, ChIP-seq, gain/loss-of-function in cell lines and in vivo xenograft, HBO1/AIB1 co-factor knockdown epistasis\",\n      \"journal\": \"Cancer cell\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — ChIP-seq showing direct binding, multiple epistasis experiments with co-factors, in vivo validation\",\n      \"pmids\": [\"29455928\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2020,\n      \"finding\": \"SIX1 undergoes O-GlcNAcylation at T276; this modification inhibits ubiquitination-mediated degradation of SIX1, thereby enhancing its protein stability and promoting hepatocellular carcinoma proliferation. T276A mutation decreases O-GlcNAcylation and reverses the pro-tumor effect.\",\n      \"method\": \"Mass spectrometry, immunoprecipitation, site-directed mutagenesis (T276A), O-GlcNAcylation and ubiquitination assays, in vitro and in vivo tumor models\",\n      \"journal\": \"Theranostics\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1-2 / Moderate — mass spectrometry site identification, mutagenesis functional validation, multiple orthogonal approaches in single rigorous study\",\n      \"pmids\": [\"32863962\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2021,\n      \"finding\": \"The molecular chaperone GRP75 maintains SIX1 protein stability by recruiting the deubiquitinase USP1, forming a GRP75-USP1-SIX1 complex that inhibits K48-linked polyubiquitination of SIX1; the C-terminus (433-679 aa) of GRP75 contains the peptide-binding domain required for complex formation.\",\n      \"method\": \"Co-immunoprecipitation, ubiquitination assays (K48-linked), domain mapping with truncation mutants, GRP75/USP1 knockdown/inhibition, xenograft models\",\n      \"journal\": \"Oncogene\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — reciprocal Co-IP, domain mapping, linkage-specific ubiquitination, in vitro and in vivo validation\",\n      \"pmids\": [\"34079090\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2012,\n      \"finding\": \"The DNA-binding sequence spectrum of SIX1 is broader than previously established; the Six1 homeodomain alone is sufficient for sequence discrimination, but domains outside the homeodomain also contribute to binding site selection. An optimized position weight matrix reveals MEF3-containing and novel binding sequences.\",\n      \"method\": \"ChIP-seq in myoblasts, biochemical binding assays (EMSA/pull-down), position weight matrix optimization algorithm\",\n      \"journal\": \"Nucleic acids research\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 1-2 / Moderate — ChIP-seq combined with biochemical binding assays, single lab but multiple orthogonal methods\",\n      \"pmids\": [\"22730291\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2016,\n      \"finding\": \"Six1 (and Six4) are required for MyoD-mediated reprogramming of mouse embryonic fibroblasts to myogenic fate; Six1/4 and MyoD co-occupy over 1000 genomic regions and synergistically activate 82 target genes through MEF3+E-box cis-regulatory modules in a feedforward regulatory mechanism.\",\n      \"method\": \"Microarray, MyoD ChIP-seq, genome-wide MEF3 site search, luciferase reporter assays for 19 cis-regulatory modules\",\n      \"journal\": \"Nucleic acids research\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — ChIP-seq, genome-wide analysis, reporter assay validation of multiple modules, epistasis\",\n      \"pmids\": [\"27302134\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2022,\n      \"finding\": \"SIX1 maintains the rhabdomyosarcoma undifferentiated state by controlling enhancer activity and MYOD1 occupancy at loci permissive for tumor growth over muscle differentiation; SIX1 loss induces MYOD1 and MYOG redistribution genome-wide, causing differentiation into myotube-like cells.\",\n      \"method\": \"SIX1 loss-of-function (knockdown/knockout), ATAC-seq/ChIP-seq for enhancer activity, MYOD1 and MYOG ChIP-seq, in vivo tumor growth assays, zebrafish model\",\n      \"journal\": \"Cell reports\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — genome-wide ChIP-seq and ATAC-seq showing direct chromatin effects, in vivo validation, multiple orthogonal methods\",\n      \"pmids\": [\"35108532\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2013,\n      \"finding\": \"Six1 and Six4 together (but neither alone) are required for male sex determination by activating Sry expression through regulation of Fog2 (Zfpm2), and for gonadal precursor cell growth through regulation of Nr5a1 (Ad4BP/SF1).\",\n      \"method\": \"Six1/Six4 single and double knockout mice, epistasis with Sry transgene rescue, expression analysis of Fog2 and Nr5a1\",\n      \"journal\": \"Developmental cell\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — compound knockout with Sry transgene rescue, two distinct downstream pathway targets identified, multiple genetic tools\",\n      \"pmids\": [\"23987514\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2011,\n      \"finding\": \"Six1 regulates Grem1 expression in the metanephric mesenchyme to control branching morphogenesis; in Six1-deficient kidneys, loss of Grem1 leads to unopposed BMP4 activity preventing ureteric bud ampulla formation, and both GREM1 protein rescue and Bmp4 heterozygosity restore kidney formation.\",\n      \"method\": \"Six1 knockout mice, GREM1 protein rescue experiments, Six1(-/-);Bmp4(+/-) compound mutants, expression analysis\",\n      \"journal\": \"Developmental biology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — genetic epistasis with compound mutants, protein rescue, mechanistic pathway established\",\n      \"pmids\": [\"21281623\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2015,\n      \"finding\": \"The SIX1 homeodomain Q177R mutation (hotspot in Wilms tumors) occurs in the homeodomain and is associated with high proliferative potential in blastemal-type Wilms tumors, placing SIX1 mutations in a pathway with DROSHA/DGCR8 mutations in this cancer subtype.\",\n      \"method\": \"Exome and transcriptome sequencing of 58 blastemal-type Wilms tumors with validation cohort, functional validation of DROSHA mutants in cell lines\",\n      \"journal\": \"Cancer cell\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 3 / Moderate — genomic identification of hotspot mutation with large validation cohort, but direct functional mechanism of Q177R SIX1 not established in this study\",\n      \"pmids\": [\"25670083\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2021,\n      \"finding\": \"SIX1 promotes senescence repression through cooperation with Polycomb repressive complexes; SIX1 downregulation in fibroblasts triggers p16INK4A-mediated senescence. SIX1 also controls SOX2 expression to mediate cellular plasticity.\",\n      \"method\": \"SIX1 knockdown in human fibroblasts, transcriptomic analysis, Polycomb complex co-regulation analysis, glioma cell line functional assays\",\n      \"journal\": \"Oncogene\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 3 / Moderate — loss-of-function with defined p16INK4A phenotype, Polycomb cooperation shown but mechanistic detail limited to single lab\",\n      \"pmids\": [\"26500063\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2021,\n      \"finding\": \"SIX1 regulates expression of multiple collagen genes via TGFBR2-dependent Smad2/3 activation, promoting collagen deposition in the tumor microenvironment that impedes immune cell infiltration and antitumor immunity.\",\n      \"method\": \"Six1 deletion in cancer cells, in vivo tumor experiments with immune competent mice, collagen expression analysis, TGFBR2-Smad2/3 pathway activation assays\",\n      \"journal\": \"Cellular & molecular immunology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — genetic deletion with immune-dependent tumor growth phenotype, pathway mechanism identified, single lab\",\n      \"pmids\": [\"34782761\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2017,\n      \"finding\": \"SIX1 directly binds the promoter of the LDHA gene to transcriptionally regulate it, promoting lactate accumulation via the SIX1/LDHA axis in pancreatic cancer cells.\",\n      \"method\": \"Chromatin immunoprecipitation (ChIP) assay for LDHA promoter, glycolysis functional assays, co-culture with NK cells\",\n      \"journal\": \"Journal of immunology research\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — ChIP demonstrating direct promoter binding, functional glycolysis assays, single lab\",\n      \"pmids\": [\"36937004\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2021,\n      \"finding\": \"Sobp directly binds SIX1 in the cell nucleus (co-immunoprecipitation and co-localization) and interferes with transcriptional activation of SIX1+EYA1 target genes, modulating Six1 transcriptional output during craniofacial development.\",\n      \"method\": \"Co-immunoprecipitation, immunofluorescence co-localization, luciferase reporter assays, Xenopus gain/loss-of-function\",\n      \"journal\": \"Development (Cambridge, England)\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2-3 / Moderate — Co-IP and functional reporter assays, Xenopus functional validation, single lab\",\n      \"pmids\": [\"34414417\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2020,\n      \"finding\": \"A small molecule compound (NCGC00378430/8430) disrupts the SIX1/EYA2 protein-protein interaction, partially reverses SIX1-induced transcriptional and metabolic profiles, reverses TGFβ signaling and EMT, and suppresses breast cancer metastasis in vivo.\",\n      \"method\": \"Small molecule screen, SIX1/EYA2 interaction assay, transcriptomic/metabolomic profiling, in vivo metastasis model\",\n      \"journal\": \"Cancer research\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — direct protein-protein interaction disruption shown, in vivo validation, multiple orthogonal readouts in single study\",\n      \"pmids\": [\"32341035\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2016,\n      \"finding\": \"Six1 directly activates Parvalbumin (a key calcium buffer) as a direct transcriptional target in adult myofibers, and controls expression of fast-type sarcomeric proteins and glycolytic enzymes; deletion of Six1 in soleus leads to complete loss of MyHCIIA expression.\",\n      \"method\": \"Conditional Six1 deletion in soleus, global transcriptomics of isolated myofibers, ChIP for Parvalbumin locus\",\n      \"journal\": \"Skeletal muscle\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — conditional knockout, transcriptomics, ChIP for direct target, single lab\",\n      \"pmids\": [\"27597886\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2001,\n      \"finding\": \"Pax3 is required upstream of SIX1 and EYA2 in skeletal myogenesis; forced expression of Pax3 induces Six1 and Eya2 expression prior to MyoD and myogenin, whereas a dominant-negative Pax3 abolishes Six1 and Eya2 expression and blocks myogenesis.\",\n      \"method\": \"Pax3 overexpression and dominant-negative in pluripotent stem cells, RT-PCR gene expression analysis\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — epistasis established by dominant-negative and overexpression, placed Pax3 upstream of Six1, single lab\",\n      \"pmids\": [\"11262400\"],\n      \"is_preprint\": false\n    }\n  ],\n  \"current_model\": \"SIX1 is a homeodomain transcription factor that functions as the DNA-binding component of a bipartite complex with EYA co-activators (and sometimes DACH), where EYA phosphatase activity switches SIX1-DACH from repressor to activator; SIX1 directly regulates targets including glycolytic genes (via HBO1/AIB1), VEGF-C, TβRI, cyclin D1, MyoD, Dusp6, Fgf8, Grem1, LDHA, and collagens, and its activity and stability are post-translationally regulated by CK2-mediated phosphorylation (reducing DNA binding at mitosis), APC/Cdh1-mediated ubiquitin proteolysis (cell-cycle gating), O-GlcNAcylation at T276 (stabilization by blocking ubiquitination), and the GRP75-USP1 deubiquitinase complex; SIX1 also controls chromatin states by interacting with the SWI/SNF complex (BRG1/BAF170) and Polycomb repressive complexes, and cooperates with SOBP as a modulator, placing it at the center of developmental organogenesis programs that when re-activated in cancer drive EMT, glycolytic reprogramming, lymphangiogenesis, and immune evasion.\"\n}\n```","stage2_raw":"{\n  \"mechanistic_narrative\": \"SIX1 is a homeodomain transcription factor that orchestrates precursor-cell proliferation and differentiation programs across mammalian organogenesis, acting as the DNA-binding component of a bipartite complex with EYA co-factors whose phosphatase activity converts the SIX1-DACH complex from a repressor to an activator [#0]. Productive transcription requires both an intact Six-domain interaction with EYA—which stabilizes SIX1, enhances its DNA-binding affinity, and drives nuclear localization—and a functional homeodomain for sequence-specific DNA recognition; mutations in either module cause branchio-oto-renal syndrome through these two distinct biochemical lesions [#1, #7]. SIX1 recognizes MEF3 and related sites, with the homeodomain conferring core discrimination and flanking domains broadening the binding spectrum [#19]. In development, SIX1 operates within EYA-dependent regulatory hierarchies that sit downstream of PAX3 and upstream of effectors including Pax2/Six2/Sall1 and Grem1 in kidney branching morphogenesis [#2, #23, #31], MyoD/myogenin and Dusp6 in myogenesis and satellite-cell differentiation [#3, #12, #15, #20], Fgf8 within a Tbx1 craniofacial/cardiovascular pathway [#11], and Sry/Fog2/Nr5a1 in male sex determination [#22]. SIX1 also engages chromatin machinery directly, partnering with the SWI/SNF subunits BRG1 and BAF170 (whose ATPase activity is required for SIX1/EYA-driven neurogenesis) and with SOX2 [#8], and cooperating with Polycomb complexes to repress p16INK4A-mediated senescence [#25]. When re-activated in cancer, SIX1 redeploys these programs: it directly induces TβRI to activate TGF-β signaling and EMT [#10], drives VEGF-C-dependent lymphangiogenesis and metastasis [#9], reprograms metabolism by transactivating glycolytic genes via the HBO1/AIB1 acetyltransferases and LDHA [#16, #27], suppresses p53 through a miR-27a/RPL26 axis [#14], and shapes an immunosuppressive collagen-rich microenvironment via TGFBR2-Smad2/3 [#26]. SIX1 protein levels are gated post-translationally by CK2 phosphorylation that reduces mitotic DNA binding [#4], APC/Cdh1-mediated proteolysis [#6], stabilizing O-GlcNAcylation at T276 that blocks ubiquitination [#17], and a GRP75-USP1 deubiquitinase complex that opposes K48-linked degradation [#18]. The SIX1/EYA2 interaction is pharmacologically tractable, with a small molecule disrupting the complex and reversing SIX1-driven EMT and metastasis [#29].\",\n  \"teleology\": [\n    {\n      \"year\": 2000,\n      \"claim\": \"Established that SIX1 DNA binding is not constitutive but cell-cycle-regulated, linking the transcription factor to mitotic control before its developmental partners were defined.\",\n      \"evidence\": \"In vitro CK2 kinase assay, cell-cycle synchronization, EMSA on the aldolase A promoter, and CK2 inhibitor treatment\",\n      \"pmids\": [\"10801845\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Specific phosphorylated residues not mapped\", \"Did not address how phosphorylation integrates with co-factor binding\"]\n    },\n    {\n      \"year\": 2001,\n      \"claim\": \"Placed SIX1 within a myogenic hierarchy downstream of PAX3, answering where SIX1 acts in the genetic cascade that initiates skeletal muscle fate.\",\n      \"evidence\": \"Pax3 overexpression and dominant-negative in pluripotent stem cells with RT-PCR readout\",\n      \"pmids\": [\"11262400\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"No direct demonstration that PAX3 binds the Six1 locus\", \"Single-lab epistasis without protein-level validation\"]\n    },\n    {\n      \"year\": 2003,\n      \"claim\": \"Defined the central regulatory logic of the SIX1-EYA-DACH module: EYA phosphatase activity switches the complex from repression to activation, explaining how a single DNA-binding factor controls precursor proliferation.\",\n      \"evidence\": \"Genetic epistasis, co-activator recruitment and phosphatase activity assays, mouse knockouts\",\n      \"pmids\": [\"14628042\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Direct dephosphorylation substrate of EYA in this switch not fully resolved\", \"Generality across all SIX1 targets not established\"]\n    },\n    {\n      \"year\": 2003,\n      \"claim\": \"Demonstrated organ-specific requirements for SIX1 in kidney and muscle, showing it acts upstream of distinct effector sets (Pax2/Six2/Sall1; MyoD/myogenin) downstream of Eya1.\",\n      \"evidence\": \"Six1 knockout mice with in situ hybridization and epistasis against Pax2, Eya1, Six2 knockouts; lacZ-replacement knockout with myogenic marker analysis\",\n      \"pmids\": [\"12783782\", \"12668636\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Which effector genes are direct vs indirect targets not all resolved\", \"Did not define DNA-binding sites at effector loci\"]\n    },\n    {\n      \"year\": 2004,\n      \"claim\": \"Showed SIX1+EYA1 co-expression is sufficient to reprogram muscle fiber type toward fast-twitch glycolytic identity, establishing SIX1 as an instructive driver of metabolic/contractile phenotype, and dissected the biochemical basis of BOR mutations.\",\n      \"evidence\": \"Transgenic gain-of-function in soleus with MyHC isoform analysis and MEF3 reporters; BOR mutation sequencing with EMSA and protein-interaction assays\",\n      \"pmids\": [\"15226428\", \"15141091\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Direct fast-twitch gene targets not all enumerated\", \"Mechanism of nuclear accumulation preference not defined\"]\n    },\n    {\n      \"year\": 2006,\n      \"claim\": \"Revealed cell-cycle-coupled destruction of SIX1 by APC/Cdh1 through a non-canonical degron, adding a degradation layer to SIX1's mitotic regulation.\",\n      \"evidence\": \"Cell-cycle synchronization, ubiquitin-proteolysis assays, Cdh1 Co-IP, and deletion mutants\",\n      \"pmids\": [\"17130831\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Degron sequence not precisely defined\", \"Single-lab mechanism without reciprocal in vivo confirmation\"]\n    },\n    {\n      \"year\": 2009,\n      \"claim\": \"Resolved how EYA binding to the Six domain functionally enables SIX1, showing it stabilizes the protein, enhances DNA affinity, and promotes nuclear import—explaining why BOR Six-domain mutations are pathogenic.\",\n      \"evidence\": \"Recombinant protein reconstitution, interaction assays, luciferase reporters, nuclear localization studies, EMSA\",\n      \"pmids\": [\"19497856\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Structural basis of the affinity enhancement not solved\", \"In vivo relevance of each effect not separately tested\"]\n    },\n    {\n      \"year\": 2010,\n      \"claim\": \"Identified TβRI as a direct SIX1 target that is necessary and sufficient to activate TGF-β signaling and EMT, defining a concrete molecular route from SIX1 reactivation to metastatic behavior.\",\n      \"evidence\": \"Gain/loss-of-function in breast cancer cells, TβRI knockdown rescue, TGF-β assays, in vivo metastasis\",\n      \"pmids\": [\"21056993\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Direct promoter binding site not detailed here\", \"Contribution relative to other EMT routes not quantified\"]\n    },\n    {\n      \"year\": 2011,\n      \"claim\": \"Extended the SIX1/EYA regulatory network into developmental morphogenesis via direct Fgf8 control within a Tbx1 pathway and via Grem1-mediated antagonism of BMP4 in kidney branching.\",\n      \"evidence\": \"Mouse compound mutants, ChIP/target validation of Fgf8, GREM1 protein rescue and Bmp4 heterozygote epistasis\",\n      \"pmids\": [\"21364285\", \"21281623\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Direct vs indirect regulation of Grem1 not fully established\", \"Tissue-specific co-factor requirements not defined\"]\n    },\n    {\n      \"year\": 2012,\n      \"claim\": \"Connected SIX1 to chromatin-remodeling and angiogenic/cell-cycle programs, and refined its DNA-binding code—showing it physically engages SWI/SNF (BRG1/BAF170) and SOX2, directly drives VEGF-C and Dusp6, and recognizes a broader site spectrum than MEF3 alone.\",\n      \"evidence\": \"Reciprocal Co-IP with BRG1/BAF170 and ATPase-mutant epistasis; orthotopic xenograft with VEGF-C rescue; conditional satellite-cell knockout with Dusp6 ChIP; ChIP-seq with position-weight-matrix optimization\",\n      \"pmids\": [\"22513373\", \"22466647\", \"22945933\", \"22730291\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Whether SWI/SNF recruitment is direct at all SIX1 targets unknown\", \"Stoichiometry of SIX1-SOX2-SWI/SNF complex undefined\"]\n    },\n    {\n      \"year\": 2013,\n      \"claim\": \"Demonstrated direct SIX1 control of cyclin D1, MyoD enhancer activity, and the male sex-determination pathway, broadening the catalogue of direct targets and showing SIX1 shapes chromatin state at the MyoD Core Enhancer.\",\n      \"evidence\": \"Promoter-reporter and ChIP for cyclin D1 and MyoD enhancer with MEF3 mutagenesis; Six1/Six4 double knockout with Sry transgene rescue\",\n      \"pmids\": [\"23527134\", \"23840772\", \"23987514\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Redundancy with SIX4 not resolved in all contexts\", \"Mechanism of chromatin opening at MyoD enhancer not defined\"]\n    },\n    {\n      \"year\": 2015,\n      \"claim\": \"Defined a p53-suppressing axis (miR-27a/RPL26, MDM2-independent) and identified a homeodomain hotspot mutation (Q177R) in blastemal Wilms tumors, linking SIX1 to tumor-suppressor evasion and cancer genetics.\",\n      \"evidence\": \"miRNA/RPL26 reporter and mutagenesis with SIX1 gain-of-function; exome/transcriptome sequencing of Wilms tumors with validation cohort\",\n      \"pmids\": [\"26687066\", \"25670083\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Functional mechanism of Q177R not established in the genomic study\", \"Tissue specificity of the miR-27a/RPL26 axis untested\"]\n    },\n    {\n      \"year\": 2016,\n      \"claim\": \"Established SIX1 as a feedforward partner of MyoD genome-wide and a direct regulator of fast-fiber/glycolytic and calcium-handling genes, unifying its developmental myogenic and metabolic roles.\",\n      \"evidence\": \"Microarray, MyoD ChIP-seq, genome-wide MEF3 search with reporter validation; conditional soleus deletion with transcriptomics and Parvalbumin ChIP\",\n      \"pmids\": [\"27302134\", \"27597886\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Direct vs cooperative occupancy at each module not always separable\", \"SIX4 contribution to the metabolic program not isolated\"]\n    },\n    {\n      \"year\": 2017,\n      \"claim\": \"Linked SIX1 transcriptional control of LDHA to lactate-driven metabolic and immune effects, an early connection between SIX1 metabolism and antitumor immunity.\",\n      \"evidence\": \"ChIP for the LDHA promoter, glycolysis assays, NK-cell co-culture\",\n      \"pmids\": [\"36937004\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Single-lab study\", \"Immune-evasion mechanism not validated in vivo here\"]\n    },\n    {\n      \"year\": 2018,\n      \"claim\": \"Defined the mechanism of SIX1-driven Warburg metabolism, showing direct transactivation of glycolytic genes through the HBO1/AIB1 acetyltransferases and that a cancer mutation enhances this activity.\",\n      \"evidence\": \"Transcriptomics, ChIP-seq, gain/loss-of-function with HBO1/AIB1 epistasis, in vivo xenograft\",\n      \"pmids\": [\"29455928\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Identity of the activating cancer mutation's structural effect not fully resolved\", \"Relationship to LDHA axis not integrated\"]\n    },\n    {\n      \"year\": 2020,\n      \"claim\": \"Identified a stabilizing O-GlcNAcylation at T276 and a druggable SIX1/EYA2 interface, defining new ways SIX1 levels are controlled and showing the complex is therapeutically targetable.\",\n      \"evidence\": \"Mass spectrometry, T276A mutagenesis, ubiquitination assays, tumor models; small-molecule screen disrupting SIX1/EYA2 with transcriptomic/metabolomic and in vivo metastasis readouts\",\n      \"pmids\": [\"32863962\", \"32341035\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"O-GlcNAc transferase responsible for T276 not identified\", \"Compound selectivity and in vivo pharmacology limited\"]\n    },\n    {\n      \"year\": 2021,\n      \"claim\": \"Defined further post-translational stabilization (GRP75-USP1 deubiquitinase complex), a SOBP modulatory partner, Polycomb-cooperative senescence repression, and a collagen/TGFBR2-Smad2/3 immune-evasion mechanism, deepening SIX1's roles in protein homeostasis, plasticity, and the tumor microenvironment.\",\n      \"evidence\": \"Reciprocal Co-IP with domain mapping and K48-ubiquitination assays; Co-IP/co-localization and reporter assays with SOBP in Xenopus; fibroblast knockdown with Polycomb co-regulation; cancer-cell deletion with immune-competent tumor models\",\n      \"pmids\": [\"34079090\", \"34414417\", \"26500063\", \"34782761\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Each mechanism shown largely in single labs\", \"How these layers are coordinated on the same SIX1 pool unknown\"]\n    },\n    {\n      \"year\": 2022,\n      \"claim\": \"Showed SIX1 maintains the rhabdomyosarcoma undifferentiated state by directing enhancer activity and MYOD1 occupancy, demonstrating that SIX1 controls cell fate through genome-wide chromatin redistribution.\",\n      \"evidence\": \"Loss-of-function with ATAC-seq/ChIP-seq for enhancers, MYOD1/MYOG ChIP-seq, in vivo and zebrafish tumor assays\",\n      \"pmids\": [\"35108532\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Co-factor(s) mediating enhancer selection not defined\", \"Reversibility window for differentiation therapy not established\"]\n    },\n    {\n      \"year\": null,\n      \"claim\": \"How the multiple post-translational inputs (CK2 phosphorylation, APC/Cdh1 degradation, O-GlcNAcylation, GRP75-USP1 deubiquitination) are integrated to set SIX1 levels and activity within a single cell, and how SIX1 selects between developmental and oncogenic enhancer programs, remains unresolved.\",\n      \"evidence\": \"\",\n      \"pmids\": [],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"No unified model linking PTM state to target-gene choice\", \"Structural basis of SIX1-EYA-chromatin assembly not solved\", \"Determinants of context-specific co-factor usage (SWI/SNF vs Polycomb vs HBO1/AIB1) unknown\"]\n    }\n  ],\n  \"mechanism_profile\": {\n    \"molecular_activity\": [\n      {\"term_id\": \"GO:0140110\", \"supporting_discovery_ids\": [0, 9, 10, 16]},\n      {\"term_id\": \"GO:0003677\", \"supporting_discovery_ids\": [1, 4, 7, 19]}\n    ],\n    \"localization\": [\n      {\"term_id\": \"GO:0005634\", \"supporting_discovery_ids\": [4, 5, 7, 28]}\n    ],\n    \"pathway\": [\n      {\"term_id\": \"R-HSA-1266738\", \"supporting_discovery_ids\": [2, 3, 11, 22]},\n      {\"term_id\": \"R-HSA-74160\", \"supporting_discovery_ids\": [0, 16, 20]},\n      {\"term_id\": \"R-HSA-4839726\", \"supporting_discovery_ids\": [8, 21, 25]},\n      {\"term_id\": \"R-HSA-1643685\", \"supporting_discovery_ids\": [9, 10, 14, 16]},\n      {\"term_id\": \"R-HSA-1430728\", \"supporting_discovery_ids\": [16, 27, 30]}\n    ],\n    \"complexes\": [\"SIX1-EYA-DACH transcription complex\", \"SWI/SNF (BRG1/BAF170)\", \"GRP75-USP1-SIX1 complex\"],\n    \"partners\": [\"EYA1\", \"EYA2\", \"DACH\", \"BRG1\", \"BAF170\", \"SOX2\", \"SOBP\", \"GRP75\"],\n    \"other_free_text\": []\n  }\n}","audit_flag":null,"evaluation":{"pairwise":"win","faith_supported":8,"faith_total":8,"faith_pct":100.0}}