{"gene":"HOPX","run_date":"2026-06-10T01:55:22","timeline":{"discoveries":[{"year":2010,"finding":"HOPX physically interacts with HDAC2, and this complex mediates deacetylation of the non-histone transcription factor GATA4. HOPX stabilizes the HDAC2-GATA4 interaction, and Hopx/Hdac2-mediated deacetylation of GATA4 impairs its ability to transactivate cell cycle genes, thereby suppressing cardiac myocyte proliferation during embryonic development. Loss of both Hopx and Hdac2 leads to GATA4 hyperacetylation and increased cardiomyocyte proliferation.","method":"Co-immunoprecipitation (physical interaction), mouse genetic knockout (double mutant), in vitro deacetylation assays, gene expression analysis of Gata4 target genes","journal":"Developmental cell","confidence":"High","confidence_rationale":"Tier 1-2 / Strong — reciprocal Co-IP establishing physical complex, in vitro functional assays, genetic loss-of-function with defined cellular phenotype, multiple orthogonal methods in a single rigorous study","pmids":["20833366"],"is_preprint":false},{"year":2015,"finding":"HOPX coordinates BMP and Wnt signaling in cardiomyoblasts by physically interacting with activated SMAD proteins (downstream of BMP) to repress Wnt target genes, thereby promoting cardiomyocyte commitment. This mechanism positions HOPX as an integrator of niche signals that inhibits Wnt signaling to drive cardiomyogenesis.","method":"Co-immunoprecipitation (HOPX-SMAD interaction), genetic gain- and loss-of-function in vivo, reporter assays for Wnt signaling, lineage tracing","journal":"Science (New York, N.Y.)","confidence":"High","confidence_rationale":"Tier 1-2 / Strong — physical interaction established by Co-IP, genetic loss-of-function, Wnt reporter assays, multiple orthogonal methods in one study","pmids":["26113728"],"is_preprint":false},{"year":2009,"finding":"HOPX suppresses estrogen-stimulated proliferation in endometrial cancer cells by inhibiting serum response factor (SRF)-dependent transcription. Specifically, forced HOPX expression blocked E2-induced c-fos activation through the serum response element (SRE) of the c-fos promoter, and HOPX knockdown in immortalized endometrial cells accelerated proliferation.","method":"Forced expression and RNAi knockdown, SRE luciferase reporter assay, cell proliferation assay, in vivo tumorigenicity assay","journal":"International journal of cancer","confidence":"Medium","confidence_rationale":"Tier 2-3 / Moderate — SRE reporter assay and knockdown/overexpression, single lab, two orthogonal functional methods","pmids":["19173292"],"is_preprint":false},{"year":2007,"finding":"HOP/NECC1 negatively regulates serum response factor (SRF) transcriptional activity in trophoblasts. Forced expression of SRF in trophoblast stem cells induces differentiation into giant cells, and HOP/NECC1 binding to SRF contributes to restraining giant cell formation and promoting spongiotrophoblast formation. HOP/NECC1-null placenta exhibited excess giant cell layers and reduced spongiotrophoblast.","method":"Genetic knockout mouse model, forced expression in trophoblast stem cell lines, differentiation assays, analysis of SRF transcriptional activity","journal":"The Journal of biological chemistry","confidence":"Medium","confidence_rationale":"Tier 2-3 / Moderate — genetic KO with defined phenotype and forced expression studies, single lab, two orthogonal approaches","pmids":["17576768"],"is_preprint":false},{"year":2010,"finding":"HOPX is required for the survival and persistence of Th1 effector/memory cells by regulating genes involved in apoptosis and making them refractory to Fas-induced apoptosis. HOPX expression is induced by T-bet and upregulated upon repeated antigenic restimulation; Hopx-deficient murine Th1 cells fail to persist in vivo and cannot induce chronic colitis or arthritis.","method":"Adoptive transfer of Hopx-deficient Th1 cells in vivo, murine colitis and arthritis models, apoptosis assays (Fas-induced), gene expression profiling","journal":"European journal of immunology","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — in vivo adoptive transfer with defined immunopathological phenotype, apoptosis assays, single lab with multiple functional readouts","pmids":["21061432"],"is_preprint":false},{"year":2010,"finding":"HOPX (Hop) is required for the function of induced regulatory T cells (iTreg) generated by peripheral dendritic cells. Hopx-sufficient iTreg cells downregulate AP-1 complex expression and suppress other T cells, whereas Hopx-deficient iTreg cells show high AP-1 expression, proliferate abnormally, and fail to mediate T cell unresponsiveness to antigen rechallenge in vivo.","method":"Genetic loss-of-function (Hopx-deficient mice), DC-mediated iTreg induction assay, antigen rechallenge model in vivo, AP-1 expression analysis","journal":"Nature immunology","confidence":"High","confidence_rationale":"Tier 2 / Strong — clean genetic KO with defined cellular phenotype in vivo, mechanistic link to AP-1 suppression, published in high-impact journal with multiple functional readouts","pmids":["20802482"],"is_preprint":false},{"year":2015,"finding":"Hopx inhibits intrinsic IL-2 expression in peripherally induced regulatory T cells (pTregs) following antigenic rechallenge. In the absence of Hopx, increased IL-2 levels lead to death and decreased numbers of pTregs. Hopx+ pTregs converted by DCs are indispensable to sustain tolerance that prevents autoimmune responses in experimental encephalomyelitis.","method":"Genetic Hopx-deficiency in T cells, adoptive transfer, IL-2 measurement, EAE model in vivo","journal":"Journal of immunology (Baltimore, Md. : 1950)","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — genetic KO with defined molecular mechanism (IL-2 suppression) and disease model, single lab","pmids":["26170384"],"is_preprint":false},{"year":2013,"finding":"HOPX and GATA6 cooperatively limit metastatic competence of lung adenocarcinoma cells by modulating overlapping alveolar differentiation and invasogenic target genes. Functional experiments showed that these two lineage transcription factors act together to suppress invasion and metastasis.","method":"Gain- and loss-of-function in lung cancer cell lines, invasion assays, gene expression analysis, in vivo metastasis models","journal":"Cancer cell","confidence":"Medium","confidence_rationale":"Tier 2-3 / Moderate — functional cell-based assays and in vivo models with defined pathway context (cooperative action of GATA6 and HOPX), single lab","pmids":["23707782"],"is_preprint":false},{"year":2017,"finding":"HOPX acts as a tumor suppressor in nasopharyngeal carcinoma by epigenetically silencing SNAIL transcription through enhancement of histone H3K9 deacetylation at the SNAIL promoter. Restoring HOPX expression suppresses NPC cell metastasis and enhances chemosensitivity.","method":"Forced expression and knockdown in NPC cell lines, chromatin immunoprecipitation (H3K9 deacetylation at SNAIL promoter), in vitro migration/invasion assays, in vivo metastasis models","journal":"Nature communications","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — ChIP for histone modification, functional invasion assays, in vivo data, single lab","pmids":["28146149"],"is_preprint":false},{"year":2014,"finding":"HOPX exerts tumor-suppressive activity in lung cancer cells through oncogenic Ras-induced cellular senescence via activation of the MAPK pathway, leading to decreased MDM2 and increased p21. Knockdown of HOPX by siRNA reduced Ras activity, inactivated the MAPK pathway, decreased p21, and reduced senescence.","method":"Stable transfection with HOPX expression vector, siRNA knockdown, Ras activity assay, MAPK signaling analysis, senescence assays (SA-β-gal), p21/MDM2 western blot","journal":"The Journal of pathology","confidence":"Medium","confidence_rationale":"Tier 2-3 / Moderate — multiple orthogonal methods (overexpression, knockdown, Ras activity assay, downstream signaling), single lab","pmids":["25345926"],"is_preprint":false},{"year":2015,"finding":"Hopx is specifically expressed in radial glia-like (RGL) neural stem cells of the adult dentate gyrus (DG) but not in the lateral ventricle proliferative zone, distinguishing hippocampal NSCs from lateral ventricle NSCs. Hopx-null NSCs exhibit enhanced neurogenesis with increased BrdU+ cells and reduced quiescent Sox2+ NSCs. Hopx regulates hippocampal NSC quiescence at least partly by modulating Notch signaling (reduced Hes1, Hey2, and NICD in Hopx-null DG).","method":"Lineage tracing, genetic knockout (Hopx-null mice), BrdU labeling, doublecortin immunostaining, Notch target gene expression analysis, cleaved Notch1 (NICD) immunostaining","journal":"Stem cell research","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — genetic KO with defined neurogenesis phenotype and Notch pathway link, multiple histological methods, single lab","pmids":["26451648"],"is_preprint":false},{"year":2018,"finding":"HOPX is required for cardiomyocyte maturation during hPSC cardiac differentiation. Loss-of-function and gain-of-function experiments showed that hypertrophic signaling activates HOPX, which in turn activates downstream gene programs governing late-stage cardiomyocyte maturation. HOPX controls enhancer networks and cardiac gene programs associated with cardiomyocyte identity.","method":"Single-cell transcriptomics, genetic gain- and loss-of-function in hPSC-derived cardiomyocytes, gene expression profiling","journal":"Cell stem cell","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — genetic gain/loss of function in human stem cell model, single-cell transcriptomics, single lab","pmids":["30290179"],"is_preprint":false},{"year":2023,"finding":"HOPX (a non-DNA-binding homeodomain protein) interacts with and controls cardiac gene enhancer networks in cardiomyocytes. Upstream cell growth and proliferation signals control HOPX transcription, which regulates downstream gene programs underpinning cardiomyocyte identity and function. HOPX-regulated programs were validated in vitro, in organoids, and in zebrafish regeneration models.","method":"Genetic loss-of-function in hiPSC-derived cardiomyocytes, perturbation studies, ATAC-seq/ChIP-seq for enhancer analysis, zebrafish regeneration model, cardiac organoids","journal":"Developmental cell","confidence":"High","confidence_rationale":"Tier 1-2 / Strong — multiple orthogonal genomic and functional approaches (loss-of-function, enhancer profiling, organoid and in vivo zebrafish models) in a single rigorous study","pmids":["38091997"],"is_preprint":false},{"year":2017,"finding":"HOPX regulates primitive hematopoiesis by suppressing Wnt/β-catenin signaling in blood-forming endothelial cells. Using HOPX reporter and knockout hESCs, loss of HOPX markedly reduces primitive hematopoiesis while not affecting endothelial fate specification.","method":"HOPX reporter and knockout hESC lines, chromatin accessibility (ATAC-seq), transcriptional profiling, hematopoietic differentiation assays, Wnt/β-catenin signaling readout","journal":"Cell reports","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — HOPX KO hESC with defined hematopoietic phenotype, Wnt pathway link, chromatin and transcriptional analysis, single lab","pmids":["28813672"],"is_preprint":false},{"year":2020,"finding":"Hematopoietic-specific knockout of Hopx in mice leads to decreased HSC reconstitution ability, reduced HSC quiescence signatures, and downregulation of the Cxcl12-Cxcr4 axis. Hopx-/- HSCs show decreased CXCL12 and CXCR4 expression, implicating this pathway as a mechanism by which Hopx maintains HSC quiescence.","method":"Conditional hematopoietic Hopx knockout mouse model, serial transplantation assay, transcriptomic analysis of HSCs, CXCL12/CXCR4 expression measurement, AML model (MN1 overexpression)","journal":"Oncogene","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — conditional KO with defined HSC phenotype and molecular pathway (CXCL12-CXCR4), transcriptomic support, single lab","pmids":["32533098"],"is_preprint":false},{"year":2018,"finding":"Hopx is required for basal radial glial cell (bRGC) abundance in the developing mouse neocortex. Disruption of Hopx expression in mouse embryonic medial neocortex reduces bRGC numbers, and forced Hopx expression in lateral neocortex increases bRGC abundance to levels seen in gyrencephalic neocortex, demonstrating that Hopx is both necessary and sufficient for bRGC generation.","method":"Genetic disruption (CRISPR/electroporation in vivo), forced expression (in utero electroporation), quantitative histology of bRGC populations, lineage tracing","journal":"Development (Cambridge, England)","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — gain- and loss-of-function in vivo with defined cellular phenotype, single lab","pmids":["30266827"],"is_preprint":false},{"year":2010,"finding":"HOPX expression in human keratinocytes is induced through the PKC signaling pathway (activated by PMA), but not by the demethylating agent 5-aza-dC, suggesting its regulation is not associated with DNA methylation in this cell type. Knockdown of HOPX by RNAi increases differentiation markers (involucrin and loricrin), while forced exogenous HOPX downregulates differentiation marker genes in HaCaT cells.","method":"RNAi knockdown, forced expression, PKC pathway inhibition, differentiation marker gene expression (involucrin, loricrin), calcium-triggered differentiation assay","journal":"European journal of cell biology","confidence":"Medium","confidence_rationale":"Tier 2-3 / Moderate — knockdown and overexpression with defined differentiation marker readouts, pathway inhibition, single lab","pmids":["20226564"],"is_preprint":false},{"year":2003,"finding":"NECC1/HOPX (also called LAGY) encodes a small 73 amino acid homeodomain protein. Transfection of NECC1 into choriocarcinoma cell lines induces CSH1 (chorionic somatomammotropin hormone 1) expression and suppresses in vivo tumorigenesis, suggesting differentiation toward syncytiotrophoblasts.","method":"Transfection/forced expression in choriocarcinoma cell lines, in vivo xenograft tumorigenesis assay, expression profiling","journal":"Genomics","confidence":"Low","confidence_rationale":"Tier 3 / Weak — single forced-expression study without detailed mechanistic pathway delineation, single lab","pmids":["12573257"],"is_preprint":false},{"year":2008,"finding":"HOP/OB1/NECC1 (HOPX) has two promoters (A and B) encoding two isoforms (HOPα and HOPβ). HOPβ silencing is associated with dense CpG island methylation at promoter B in esophageal squamous cell carcinoma, and forced HOP expression suppresses tumorigenesis in soft agar assays in four different squamous cell carcinoma cell lines. RNA interference knockdown of HOP restores the oncogenic phenotype.","method":"Methylation-specific PCR (TaqMan), demethylating agent treatment (5-aza-dCR + TSA), forced expression and RNAi knockdown, soft agar colony formation assay","journal":"Molecular cancer research : MCR","confidence":"Medium","confidence_rationale":"Tier 2-3 / Moderate — matched forced expression and RNAi knockdown with functional readout, epigenetic mechanism identified, single lab","pmids":["18234960"],"is_preprint":false},{"year":2020,"finding":"EZH2 directly binds to the HOPX promoter region during normal growth and osteogenic differentiation (but not adipogenic conditions), thereby repressing HOPX. HOPX promotes BMSC proliferation and inhibits adipogenesis by suppressing adipogenic pathway genes (ADIPOQ, FABP4, PLIN1, PLIN4), as shown by gain- and loss-of-function studies and RNA-seq.","method":"ChIP (EZH2 binding to HOPX promoter), HOPX knockdown and overexpression in BMSCs, RNA-seq during adipogenesis, differentiation assays","journal":"Scientific reports","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — ChIP for direct EZH2-HOPX promoter binding, matched gain/loss-of-function, RNA-seq, single lab","pmids":["32647304"],"is_preprint":false},{"year":2016,"finding":"HOPX and KLF4 cooperate to activate claudin 4, 7, and 15 expression during colonic epithelial differentiation, as shown by correlation analysis, in vitro confirmatory methods, and chromatin immunoprecipitation identifying the Hopx/Klf4 cascade as a regulator of barrier gene expression.","method":"Gene expression microarray/correlation analysis, in vitro confirmatory assays, chromatin immunoprecipitation (ChIP), conditional knockout mice for validation","journal":"Tissue barriers","confidence":"Low","confidence_rationale":"Tier 3 / Weak — ChIP and correlation data for HOPX/Klf4, limited functional validation of HOPX's direct role vs. Klf4, single lab","pmids":["27583195"],"is_preprint":false},{"year":2024,"finding":"HOPX physically interacts with HDAC2 in AML cells (confirmed by endogenous and exogenous co-immunoprecipitation), and this HOPX-HDAC2 interaction induces differentiation blockage and malignant progression in AML. Low HOPX expression represses AML cell proliferation, anti-apoptotic activity, and differentiation blockage.","method":"Endogenous and exogenous Co-immunoprecipitation, flow cytometry (proliferation and apoptosis), MTT assay, bioinformatics analysis","journal":"Hematological oncology","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — reciprocal Co-IP for HOPX-HDAC2 interaction, functional assays, single lab","pmids":["39243399"],"is_preprint":false},{"year":2025,"finding":"In lung cancer drug-tolerant persister (DTP) cells, HOPX undergoes cytoplasmic-to-nuclear translocation upon targeted therapy treatment. Nuclear HOPX regulates NF-κB activation and repressive histone modifications. HOPX deletion significantly delays DTP regrowth, identifying HOPX as a regulator of DTP persistence through epigenetic and NF-κB-dependent mechanisms.","method":"scATAC-seq, HOPX deletion (CRISPR), subcellular fractionation/immunofluorescence for nuclear translocation, NF-κB activity assays, histone modification analysis, in vitro DTP regrowth assay","journal":"iScience","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — HOPX deletion with defined DTP phenotype, subcellular localization tracking, NF-κB and epigenetic readouts, single lab","pmids":["40352726"],"is_preprint":false},{"year":2021,"finding":"Hopx plays a critical role in epigenetic regulation through histone deacetylation in cardiomyocytes treated with antiretroviral drugs (ARVs). HOPX expression is significantly increased in ARV-treated cardiomyocytes and HIV patient heart tissue. HDAC inhibitor Trichostatin A restores histone 3 acetylation in the presence of ARVs, and HOPX is identified as mediating cellular hypertrophy via histone deacetylation.","method":"RNA-sequencing of ARV-treated neonatal rat cardiomyocytes, HDAC inhibitor rescue experiment (Trichostatin A), histone acetylation western blot, validation in HIV patient cardiac tissue","journal":"Cells","confidence":"Low","confidence_rationale":"Tier 3 / Weak — indirect evidence linking HOPX to histone deacetylation via HDAC inhibitor rescue, no direct HOPX knockdown/overexpression experiment reported in abstract, single lab","pmids":["34943964"],"is_preprint":false},{"year":2025,"finding":"Iron released from radiotherapy-induced tumor cell death triggers a Stat3-dependent pro-survival program in neighboring Hopx+ quiescent cancer stem cells, causing their activation. Activated Hopx+ cancer stem cells antagonize ferroptosis (which should be caused by iron overload) through inhibition of de novo lipid synthesis.","method":"Lineage-tracing (HopxCreERT2;RosatdTomato mice and organoids), BrdU pulse-chase, cell cycle analysis, apoptosis/necroptosis blockade experiments, human rectal cancer organoids and PDX models","journal":"Journal of advanced research","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — lineage tracing, multiple in vivo and organoid models, Stat3 pathway and lipid synthesis mechanistic link, single lab","pmids":["41325838"],"is_preprint":false},{"year":2026,"finding":"HOPX stabilizes β-catenin protein by directly inhibiting the interaction of β-catenin with UBA52, which targets β-catenin for ubiquitination-mediated degradation. High iron diet activates Wnt/β-catenin signaling in Hopx+ intestinal stem cells in a Hopx-dependent manner through this competitive binding mechanism.","method":"Co-immunoprecipitation (HOPX-UBA52 and HOPX-β-catenin interaction), ubiquitination assay, Hopx genetic models, Wnt/β-catenin signaling assays, high-iron diet mouse model","journal":"International journal of biological sciences","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — Co-IP for protein interactions, ubiquitination assay, genetic model, defined molecular mechanism, single lab","pmids":["42157941"],"is_preprint":false},{"year":2025,"finding":"DNMT3B directly methylates the HOPX promoter, downregulating HOPX expression in lung cancer cells. DNMT inhibitor SGI-1027 upregulates HOPX, and HOPX knockdown partially recovers the malignant phenotypes (proliferation, migration, invasion) suppressed by DNMT3B knockdown or SGI-1027 treatment, placing HOPX downstream of DNMT3B-mediated DNA methylation.","method":"DNMT3B overexpression and knockdown, DNMT inhibitor (SGI-1027) treatment, methylation analysis of HOPX promoter, HOPX knockdown rescue experiment, in vitro and in vivo functional assays","journal":"iScience","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — matched gain/loss-of-function with rescue, methylation analysis, functional readouts, single lab","pmids":["41660264"],"is_preprint":false},{"year":2025,"finding":"HOPX regulates hepatocellular carcinoma invasion and migration by suppressing SNAIL expression, thereby inhibiting epithelial-to-mesenchymal transition (EMT). HOPX inhibition of SNAIL was required for HOPX's metastasis-inhibitory activity in in vitro and in vivo HCC models.","method":"HOPX forced expression and knockdown, invasion/migration assays, SNAIL protein expression analysis, in vivo HCC metastasis mouse model, EMT marker analysis","journal":"Scientific reports","confidence":"Medium","confidence_rationale":"Tier 2-3 / Moderate — matched overexpression and loss-of-function, in vivo metastasis model, SNAIL pathway link, single lab","pmids":["40804282"],"is_preprint":false},{"year":2022,"finding":"GRHL3 transcriptionally regulates HOPX expression in the esophageal epithelium (ChIP-seq confirmed GRHL3 binding to the HOPX locus), and HOPX in turn limits Wnt/β-catenin signaling. Loss of GRHL3 reduces HOPX expression and increases Wnt/β-catenin activity, driving esophageal squamous cell carcinoma progression.","method":"ChIP-seq (GRHL3 binding to HOPX), conditional Grhl3 deletion in mice, RNA-seq, immunohistochemistry, Wnt/β-catenin pathway analysis, patient-derived ESCC validation","journal":"Cellular and molecular gastroenterology and hepatology","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — ChIP-seq for GRHL3-HOPX regulatory link, genetic mouse model, patient validation, single lab","pmids":["36442813"],"is_preprint":false},{"year":2024,"finding":"HOPX, operating downstream of GPR109A (activated by butyrate from gut microbiota), enhances CD8+ T cell cytotoxic killing of gastric cancer cells. GPR109A knockout significantly weakened butyrate's enhancement of CD8+ T cell function, and HOPX acted downstream in this GPR109A/HOPX axis.","method":"GPR109A knockout mouse model, butyrate supplementation during gastric cancer induction, co-culture of GC cells with CD8+ T cells or CAR-T cells, in vivo tumor-bearing studies, IFN-γ measurement","journal":"Gut microbes","confidence":"Low","confidence_rationale":"Tier 3 / Weak — HOPX's direct molecular role in the GPR109A signaling cascade is inferred from pathway position; direct HOPX mechanistic experiment not clearly described in abstract, single lab","pmids":["38319728"],"is_preprint":false}],"current_model":"HOPX is an atypical, non-DNA-binding homeodomain protein that functions as a transcriptional co-regulator by physically interacting with partners such as SRF, HDAC2, GATA4, activated SMADs, and UBA52 to modulate gene programs controlling cell proliferation, differentiation, and survival; in cardiac development it recruits HDAC2 to deacetylate GATA4 and integrates BMP/SMAD and Wnt signals to drive cardiomyocyte commitment, in stem cell niches it maintains quiescence partly through Notch and CXCL12-CXCR4 signaling, and in multiple cancers it suppresses metastasis via epigenetic silencing of SNAIL (H3K9 deacetylation) and modulation of Wnt/β-catenin stability, while in immune cells it suppresses AP-1 and IL-2 to sustain regulatory T cell function."},"narrative":{"mechanistic_narrative":"HOPX is a small, atypical non-DNA-binding homeodomain protein that functions as a transcriptional co-regulator, controlling cell proliferation, differentiation, and survival across cardiac, neural, hematopoietic, epithelial, immune, and tumor contexts [PMID:20833366, PMID:38091997]. A core mechanism is its partnership with HDAC2: in the developing heart HOPX recruits and stabilizes HDAC2 to deacetylate the transcription factor GATA4, blunting GATA4-driven cell-cycle gene transactivation and thereby restraining cardiomyocyte proliferation [PMID:20833366], while in acute myeloid leukemia the same HOPX-HDAC2 interaction enforces a differentiation block and drives malignant progression [PMID:39243399]. HOPX also represses serum response factor (SRF)-dependent transcription, suppressing estrogen-stimulated c-fos induction in endometrial cells and trophoblast giant-cell differentiation [PMID:19173292, PMID:17576768]. In cardiomyocyte commitment and maturation, HOPX integrates niche signals by binding activated SMAD proteins to repress Wnt targets and by controlling enhancer networks that define cardiomyocyte identity downstream of growth and hypertrophic signals [PMID:26113728, PMID:30290179, PMID:38091997]. Across stem/progenitor compartments HOPX maintains quiescence and lineage decisions: it limits Wnt/β-catenin signaling to support primitive hematopoiesis and hematopoietic stem cell quiescence via the CXCL12-CXCR4 axis [PMID:28813672, PMID:32533098], regulates dentate-gyrus neural stem cell quiescence through Notch signaling and is necessary and sufficient for basal radial glia generation in neocortex [PMID:26451648, PMID:30266827]. As a tumor suppressor, HOPX epigenetically silences SNAIL through enhanced H3K9 deacetylation to block EMT and metastasis, cooperates with GATA6 to limit metastatic competence, and promotes oncogenic Ras-induced senescence [PMID:23707782, PMID:28146149, PMID:25345926, PMID:40804282]. HOPX expression is itself controlled epigenetically by promoter methylation (DNMT3B) and CpG silencing, by EZH2-mediated repression, and by upstream transcription factors GRHL3 and KLF4 [PMID:18234960, PMID:32647304, PMID:41660264, PMID:36442813]. In immune cells HOPX sustains regulatory T cell function and Th1 persistence by suppressing the AP-1 complex and intrinsic IL-2 and by conferring resistance to Fas-induced apoptosis [PMID:21061432, PMID:20802482, PMID:26170384]. More recent work links HOPX to β-catenin stabilization via competitive inhibition of UBA52-mediated ubiquitination and to nuclear translocation that drives NF-κB activation in drug-tolerant persister cells [PMID:42157941, PMID:40352726].","teleology":[{"year":2003,"claim":"Establishing HOPX as a small homeodomain protein with differentiation-promoting, tumor-suppressive activity gave the first functional handle on an otherwise uncharacterized gene.","evidence":"Forced expression of NECC1/HOPX in choriocarcinoma lines with xenograft tumorigenesis assay","pmids":["12573257"],"confidence":"Low","gaps":["No molecular partner or mechanism defined","Single forced-expression study without pathway delineation"]},{"year":2007,"claim":"Identifying SRF as a functional target answered how HOPX restrains transcription without binding DNA, linking it to lineage decisions in the placenta.","evidence":"Genetic knockout mouse and forced expression in trophoblast stem cells with SRF activity analysis","pmids":["17576768"],"confidence":"Medium","gaps":["Direct HOPX-SRF binding not biochemically dissected here","Generalizability beyond trophoblast unclear"]},{"year":2010,"claim":"Discovery of the HOPX-HDAC2 complex deacetylating GATA4 explained at the biochemical level how HOPX suppresses cardiomyocyte proliferation, defining its prototypical co-repressor mechanism.","evidence":"Reciprocal Co-IP, double-knockout mice, and in vitro deacetylation assays on GATA4","pmids":["20833366"],"confidence":"High","gaps":["How HOPX selects GATA4 vs other substrates not defined","Structural basis of HDAC2 recruitment unknown"]},{"year":2010,"claim":"Demonstrating HOPX requirement in iTreg/Th1 cells extended its role from development to immune tolerance and effector persistence via AP-1 suppression and apoptosis resistance.","evidence":"Hopx-deficient mice, DC-mediated iTreg induction, adoptive transfer and Fas-apoptosis assays","pmids":["20802482","21061432"],"confidence":"High","gaps":["Mechanism of AP-1 downregulation not resolved","Direct transcriptional targets in T cells not mapped"]},{"year":2013,"claim":"Showing HOPX cooperates with GATA6 to suppress invasion positioned it as a lineage transcription factor limiting metastatic competence in solid tumors.","evidence":"Gain/loss-of-function in lung adenocarcinoma lines with invasion and in vivo metastasis models","pmids":["23707782"],"confidence":"Medium","gaps":["Direct HOPX-GATA6 physical interaction not established","Shared target genes only partially defined"]},{"year":2015,"claim":"Linking HOPX to SMAD binding and Wnt repression revealed it as a signaling integrator driving cardiomyocyte commitment, and parallel work tied IL-2 suppression to Treg maintenance.","evidence":"Co-IP of HOPX-SMAD, Wnt reporter assays, lineage tracing; Hopx-deficient pTreg IL-2 measurement in EAE model","pmids":["26113728","26170384"],"confidence":"High","gaps":["Specific Wnt target genes repressed not enumerated","Whether SMAD binding is direct or complex-mediated unresolved"]},{"year":2015,"claim":"Defining HOPX as a marker and regulator of adult dentate-gyrus NSC quiescence via Notch distinguished hippocampal from ventricular stem cells.","evidence":"Hopx-null mice, BrdU labeling, Notch target gene and NICD analysis","pmids":["26451648"],"confidence":"Medium","gaps":["How HOPX modulates Notch signaling mechanistically unknown","Direct transcriptional targets not identified"]},{"year":2017,"claim":"ChIP demonstration of H3K9 deacetylation at the SNAIL promoter gave a concrete epigenetic mechanism for HOPX's anti-metastatic function, complemented by Wnt suppression in hematopoiesis.","evidence":"ChIP at SNAIL promoter in NPC cells; HOPX-KO hESC with ATAC-seq and Wnt readout in blood-forming endothelium","pmids":["28146149","28813672"],"confidence":"Medium","gaps":["HDAC partner at SNAIL promoter not identified in NPC","Whether SNAIL silencing generalizes across tumor types tested separately"]},{"year":2018,"claim":"Genomic profiling established that HOPX governs enhancer networks and cardiomyocyte maturation downstream of hypertrophic/growth signals, and that it controls basal radial glia abundance in cortex.","evidence":"scRNA-seq and gain/loss-of-function in hPSC-cardiomyocytes; in vivo CRISPR and electroporation for bRGC quantification","pmids":["30290179","30266827"],"confidence":"Medium","gaps":["Enhancer recruitment mechanism for a non-DNA-binding protein unresolved","Co-factors directing HOPX to specific loci unknown"]},{"year":2020,"claim":"Conditional hematopoietic knockout connected HOPX to HSC quiescence and reconstitution through the CXCL12-CXCR4 axis, and EZH2 was shown to repress HOPX during BMSC differentiation.","evidence":"Conditional Hopx-KO mice, serial transplantation, transcriptomics; ChIP of EZH2 at HOPX promoter with BMSC gain/loss-of-function","pmids":["32533098","32647304"],"confidence":"Medium","gaps":["Whether HOPX directly regulates Cxcl12/Cxcr4 transcription not shown","Substrate/target specificity in HSCs undefined"]},{"year":2022,"claim":"Upstream regulatory architecture was clarified by showing GRHL3 transcriptionally activates HOPX, which then limits Wnt/β-catenin to suppress esophageal carcinoma progression.","evidence":"ChIP-seq for GRHL3 binding at HOPX, conditional Grhl3 mice, patient ESCC validation","pmids":["36442813"],"confidence":"Medium","gaps":["Mechanism by which HOPX limits Wnt in this context not biochemically defined"]},{"year":2024,"claim":"Re-demonstration of the HOPX-HDAC2 complex in AML reframed the same molecular interaction as oncogenic, enforcing a differentiation block.","evidence":"Endogenous and exogenous Co-IP with proliferation/apoptosis functional assays in AML cells","pmids":["39243399"],"confidence":"Medium","gaps":["Target genes/substrates of HOPX-HDAC2 in AML not identified","Why the same complex is suppressive in heart but oncogenic in AML unexplained"]},{"year":2025,"claim":"Recent work uncovered new HOPX behaviors: cytoplasmic-to-nuclear translocation driving NF-κB and repressive histone marks in drug-tolerant persisters, SNAIL suppression in HCC, and DNMT3B methylation controlling HOPX expression.","evidence":"scATAC-seq, CRISPR deletion, subcellular fractionation and NF-κB assays (DTP); forced expression/knockdown in HCC; DNMT3B gain/loss with HOPX rescue in lung cancer","pmids":["40352726","40804282","41660264"],"confidence":"Medium","gaps":["Trigger and machinery for HOPX nuclear translocation undefined","How HOPX engages NF-κB mechanistically unknown"]},{"year":2026,"claim":"Identification of UBA52 as a HOPX partner revealed a post-translational mechanism: HOPX competitively blocks UBA52-mediated β-catenin ubiquitination to stabilize β-catenin in iron-stimulated intestinal stem cells.","evidence":"Co-IP of HOPX-UBA52 and HOPX-β-catenin, ubiquitination assay, Hopx genetic models, high-iron diet","pmids":["42157941"],"confidence":"Medium","gaps":["Reconciliation with prior reports of HOPX limiting Wnt/β-catenin not addressed","Structural basis of competitive binding unknown"]},{"year":null,"claim":"How a non-DNA-binding homeodomain protein is recruited to context-specific enhancers and partners (HDAC2, SMAD, SRF, UBA52) to produce opposite outcomes (tumor suppression vs oncogenic persistence) remains unresolved.","evidence":"","pmids":[],"confidence":"Medium","gaps":["No structural model of HOPX-partner complexes","Determinants of cell-type-specific co-factor selection unknown","Mechanism switching HOPX between cytoplasmic and nuclear/repressive roles undefined"]}],"mechanism_profile":{"molecular_activity":[{"term_id":"GO:0140110","term_label":"transcription regulator activity","supporting_discovery_ids":[0,2,3,11,12]},{"term_id":"GO:0098772","term_label":"molecular function regulator activity","supporting_discovery_ids":[0,25]},{"term_id":"GO:0060090","term_label":"molecular adaptor activity","supporting_discovery_ids":[0,1,25]}],"localization":[{"term_id":"GO:0005634","term_label":"nucleus","supporting_discovery_ids":[0,22]},{"term_id":"GO:0005829","term_label":"cytosol","supporting_discovery_ids":[22]}],"pathway":[{"term_id":"R-HSA-4839726","term_label":"Chromatin organization","supporting_discovery_ids":[0,8,22]},{"term_id":"R-HSA-1266738","term_label":"Developmental Biology","supporting_discovery_ids":[1,11,12,15]},{"term_id":"R-HSA-162582","term_label":"Signal Transduction","supporting_discovery_ids":[1,13,25,28]},{"term_id":"R-HSA-168256","term_label":"Immune System","supporting_discovery_ids":[4,5,6]},{"term_id":"R-HSA-74160","term_label":"Gene expression (Transcription)","supporting_discovery_ids":[0,2,3,12]}],"complexes":[],"partners":["HDAC2","GATA4","SMAD","SRF","GATA6","UBA52","CTNNB1"],"other_free_text":[]}},"prefetch_data":{"uniprot":{"accession":"Q9BPY8","full_name":"Homeodomain-only protein","aliases":["Lung cancer-associated Y protein","Not expressed in choriocarcinoma protein 1","Odd homeobox protein 1"],"length_aa":73,"mass_kda":8.3,"function":"Atypical homeodomain protein which does not bind DNA and is required to modulate cardiac growth and development. Acts via its interaction with SRF, thereby modulating the expression of SRF-dependent cardiac-specific genes and cardiac development. Prevents SRF-dependent transcription either by inhibiting SRF binding to DNA or by recruiting histone deacetylase (HDAC) proteins that prevent transcription by SRF. Overexpression causes cardiac hypertrophy (By similarity). May act as a tumor suppressor. Acts as a co-chaperone for HSPA1A and HSPA1B chaperone proteins and assists in chaperone-mediated protein refolding (PubMed:27708256)","subcellular_location":"Nucleus; Cytoplasm","url":"https://www.uniprot.org/uniprotkb/Q9BPY8/entry"},"depmap":{"release":"DepMap","has_data":true,"is_common_essential":false,"resolved_as":"","url":"https://depmap.org/portal/gene/HOPX","classification":"Not Classified","n_dependent_lines":0,"n_total_lines":1208,"dependency_fraction":0.0},"opencell":{"profiled":false,"resolved_as":"","ensg_id":"","cell_line_id":"","localizations":[],"interactors":[],"url":"https://opencell.sf.czbiohub.org/search/HOPX","total_profiled":1310},"omim":[{"mim_id":"607275","title":"HOP HOMEOBOX; HOPX","url":"https://www.omim.org/entry/607275"}],"hpa":{"profiled":true,"resolved_as":"","reliability":"Approved","locations":[{"location":"Nuclear bodies","reliability":"Approved"},{"location":"Cytosol","reliability":"Additional"}],"tissue_specificity":"Tissue enhanced","tissue_distribution":"Detected in all","driving_tissues":[{"tissue":"esophagus","ntpm":712.1},{"tissue":"skin 1","ntpm":1401.9}],"url":"https://www.proteinatlas.org/search/HOPX"},"hgnc":{"alias_symbol":["LAGY","HOP","OB1","NECC1","SMAP31"],"prev_symbol":[]},"alphafold":{"accession":"Q9BPY8","domains":[{"cath_id":"1.10.10.60","chopping":"10-58","consensus_level":"high","plddt":92.411,"start":10,"end":58}],"viewer_url":"https://alphafold.ebi.ac.uk/entry/Q9BPY8","model_url":"https://alphafold.ebi.ac.uk/files/AF-Q9BPY8-F1-model_v6.cif","pae_url":"https://alphafold.ebi.ac.uk/files/AF-Q9BPY8-F1-predicted_aligned_error_v6.png","plddt_mean":82.69},"mouse_models":{"mgi_url":"https://www.informatics.jax.org/marker/summary?nomen=HOPX","jax_strain_url":"https://www.jax.org/strain/search?query=HOPX"},"sequence":{"accession":"Q9BPY8","fasta_url":"https://rest.uniprot.org/uniprotkb/Q9BPY8.fasta","uniprot_url":"https://www.uniprot.org/uniprotkb/Q9BPY8/entry","alphafold_viewer_url":"https://alphafold.ebi.ac.uk/entry/Q9BPY8"}},"corpus_meta":[{"pmid":"25865356","id":"PMC_25865356","title":"Plasticity of Hopx(+) type I alveolar cells to regenerate type II cells in the lung.","date":"2015","source":"Nature communications","url":"https://pubmed.ncbi.nlm.nih.gov/25865356","citation_count":236,"is_preprint":false},{"pmid":"30290179","id":"PMC_30290179","title":"Single-Cell Transcriptomic Analysis of Cardiac Differentiation from Human PSCs Reveals HOPX-Dependent Cardiomyocyte Maturation.","date":"2018","source":"Cell stem cell","url":"https://pubmed.ncbi.nlm.nih.gov/30290179","citation_count":198,"is_preprint":false},{"pmid":"20833366","id":"PMC_20833366","title":"Hopx and Hdac2 interact to modulate Gata4 acetylation and embryonic cardiac myocyte proliferation.","date":"2010","source":"Developmental cell","url":"https://pubmed.ncbi.nlm.nih.gov/20833366","citation_count":125,"is_preprint":false},{"pmid":"23707782","id":"PMC_23707782","title":"Control of alveolar differentiation by the lineage transcription factors GATA6 and HOPX inhibits lung adenocarcinoma metastasis.","date":"2013","source":"Cancer cell","url":"https://pubmed.ncbi.nlm.nih.gov/23707782","citation_count":124,"is_preprint":false},{"pmid":"26113728","id":"PMC_26113728","title":"HEART DEVELOPMENT. 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DCLK1 expression in normal canine intestine and in intestinal adenoma and adenocarcinoma.","date":"2022","source":"Veterinary pathology","url":"https://pubmed.ncbi.nlm.nih.gov/35220825","citation_count":7,"is_preprint":false},{"pmid":"25036325","id":"PMC_25036325","title":"Association between non-coding polymorphisms of HOPX gene and syncope in hypertrophic cardiomyopathy.","date":"2014","source":"Anadolu kardiyoloji dergisi : AKD = the Anatolian journal of cardiology","url":"https://pubmed.ncbi.nlm.nih.gov/25036325","citation_count":5,"is_preprint":false},{"pmid":"41325838","id":"PMC_41325838","title":"Paracrine iron activates Hopx+ rectal cancer stem cells to display radioresistance.","date":"2025","source":"Journal of advanced research","url":"https://pubmed.ncbi.nlm.nih.gov/41325838","citation_count":4,"is_preprint":false},{"pmid":"34805566","id":"PMC_34805566","title":"Landscape of Hopx expression in cells of the immune 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donors","date":"2024-07-16","source":"bioRxiv","url":"https://doi.org/10.1101/2024.07.15.24310447","citation_count":0,"is_preprint":true}],"cost":{"stage1":{"model":"claude-sonnet-4-6","input_tokens":35813,"output_tokens":7883,"usd":0.112842,"stage1_stop_reason":"end_turn"},"stage2":{"model":"claude-opus-4-8","input_tokens":17552,"output_tokens":4945,"usd":0.105692,"stage2_stop_reason":"end_turn"},"total_usd":0.218534,"stage1_batch_id":"msgbatch_01DUPACZi7AAWwuZiUjseQF4","stage2_batch_id":"msgbatch_018yt7chE3f48PEFtDwtj6AE","note":"batch pricing = 50% of standard"},"stage1_raw":"```json\n{\n  \"discoveries\": [\n    {\n      \"year\": 2010,\n      \"finding\": \"HOPX physically interacts with HDAC2, and this complex mediates deacetylation of the non-histone transcription factor GATA4. HOPX stabilizes the HDAC2-GATA4 interaction, and Hopx/Hdac2-mediated deacetylation of GATA4 impairs its ability to transactivate cell cycle genes, thereby suppressing cardiac myocyte proliferation during embryonic development. Loss of both Hopx and Hdac2 leads to GATA4 hyperacetylation and increased cardiomyocyte proliferation.\",\n      \"method\": \"Co-immunoprecipitation (physical interaction), mouse genetic knockout (double mutant), in vitro deacetylation assays, gene expression analysis of Gata4 target genes\",\n      \"journal\": \"Developmental cell\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1-2 / Strong — reciprocal Co-IP establishing physical complex, in vitro functional assays, genetic loss-of-function with defined cellular phenotype, multiple orthogonal methods in a single rigorous study\",\n      \"pmids\": [\"20833366\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2015,\n      \"finding\": \"HOPX coordinates BMP and Wnt signaling in cardiomyoblasts by physically interacting with activated SMAD proteins (downstream of BMP) to repress Wnt target genes, thereby promoting cardiomyocyte commitment. This mechanism positions HOPX as an integrator of niche signals that inhibits Wnt signaling to drive cardiomyogenesis.\",\n      \"method\": \"Co-immunoprecipitation (HOPX-SMAD interaction), genetic gain- and loss-of-function in vivo, reporter assays for Wnt signaling, lineage tracing\",\n      \"journal\": \"Science (New York, N.Y.)\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1-2 / Strong — physical interaction established by Co-IP, genetic loss-of-function, Wnt reporter assays, multiple orthogonal methods in one study\",\n      \"pmids\": [\"26113728\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2009,\n      \"finding\": \"HOPX suppresses estrogen-stimulated proliferation in endometrial cancer cells by inhibiting serum response factor (SRF)-dependent transcription. Specifically, forced HOPX expression blocked E2-induced c-fos activation through the serum response element (SRE) of the c-fos promoter, and HOPX knockdown in immortalized endometrial cells accelerated proliferation.\",\n      \"method\": \"Forced expression and RNAi knockdown, SRE luciferase reporter assay, cell proliferation assay, in vivo tumorigenicity assay\",\n      \"journal\": \"International journal of cancer\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2-3 / Moderate — SRE reporter assay and knockdown/overexpression, single lab, two orthogonal functional methods\",\n      \"pmids\": [\"19173292\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2007,\n      \"finding\": \"HOP/NECC1 negatively regulates serum response factor (SRF) transcriptional activity in trophoblasts. Forced expression of SRF in trophoblast stem cells induces differentiation into giant cells, and HOP/NECC1 binding to SRF contributes to restraining giant cell formation and promoting spongiotrophoblast formation. HOP/NECC1-null placenta exhibited excess giant cell layers and reduced spongiotrophoblast.\",\n      \"method\": \"Genetic knockout mouse model, forced expression in trophoblast stem cell lines, differentiation assays, analysis of SRF transcriptional activity\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2-3 / Moderate — genetic KO with defined phenotype and forced expression studies, single lab, two orthogonal approaches\",\n      \"pmids\": [\"17576768\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2010,\n      \"finding\": \"HOPX is required for the survival and persistence of Th1 effector/memory cells by regulating genes involved in apoptosis and making them refractory to Fas-induced apoptosis. HOPX expression is induced by T-bet and upregulated upon repeated antigenic restimulation; Hopx-deficient murine Th1 cells fail to persist in vivo and cannot induce chronic colitis or arthritis.\",\n      \"method\": \"Adoptive transfer of Hopx-deficient Th1 cells in vivo, murine colitis and arthritis models, apoptosis assays (Fas-induced), gene expression profiling\",\n      \"journal\": \"European journal of immunology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — in vivo adoptive transfer with defined immunopathological phenotype, apoptosis assays, single lab with multiple functional readouts\",\n      \"pmids\": [\"21061432\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2010,\n      \"finding\": \"HOPX (Hop) is required for the function of induced regulatory T cells (iTreg) generated by peripheral dendritic cells. Hopx-sufficient iTreg cells downregulate AP-1 complex expression and suppress other T cells, whereas Hopx-deficient iTreg cells show high AP-1 expression, proliferate abnormally, and fail to mediate T cell unresponsiveness to antigen rechallenge in vivo.\",\n      \"method\": \"Genetic loss-of-function (Hopx-deficient mice), DC-mediated iTreg induction assay, antigen rechallenge model in vivo, AP-1 expression analysis\",\n      \"journal\": \"Nature immunology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — clean genetic KO with defined cellular phenotype in vivo, mechanistic link to AP-1 suppression, published in high-impact journal with multiple functional readouts\",\n      \"pmids\": [\"20802482\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2015,\n      \"finding\": \"Hopx inhibits intrinsic IL-2 expression in peripherally induced regulatory T cells (pTregs) following antigenic rechallenge. In the absence of Hopx, increased IL-2 levels lead to death and decreased numbers of pTregs. Hopx+ pTregs converted by DCs are indispensable to sustain tolerance that prevents autoimmune responses in experimental encephalomyelitis.\",\n      \"method\": \"Genetic Hopx-deficiency in T cells, adoptive transfer, IL-2 measurement, EAE model in vivo\",\n      \"journal\": \"Journal of immunology (Baltimore, Md. : 1950)\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — genetic KO with defined molecular mechanism (IL-2 suppression) and disease model, single lab\",\n      \"pmids\": [\"26170384\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2013,\n      \"finding\": \"HOPX and GATA6 cooperatively limit metastatic competence of lung adenocarcinoma cells by modulating overlapping alveolar differentiation and invasogenic target genes. Functional experiments showed that these two lineage transcription factors act together to suppress invasion and metastasis.\",\n      \"method\": \"Gain- and loss-of-function in lung cancer cell lines, invasion assays, gene expression analysis, in vivo metastasis models\",\n      \"journal\": \"Cancer cell\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2-3 / Moderate — functional cell-based assays and in vivo models with defined pathway context (cooperative action of GATA6 and HOPX), single lab\",\n      \"pmids\": [\"23707782\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2017,\n      \"finding\": \"HOPX acts as a tumor suppressor in nasopharyngeal carcinoma by epigenetically silencing SNAIL transcription through enhancement of histone H3K9 deacetylation at the SNAIL promoter. Restoring HOPX expression suppresses NPC cell metastasis and enhances chemosensitivity.\",\n      \"method\": \"Forced expression and knockdown in NPC cell lines, chromatin immunoprecipitation (H3K9 deacetylation at SNAIL promoter), in vitro migration/invasion assays, in vivo metastasis models\",\n      \"journal\": \"Nature communications\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — ChIP for histone modification, functional invasion assays, in vivo data, single lab\",\n      \"pmids\": [\"28146149\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2014,\n      \"finding\": \"HOPX exerts tumor-suppressive activity in lung cancer cells through oncogenic Ras-induced cellular senescence via activation of the MAPK pathway, leading to decreased MDM2 and increased p21. Knockdown of HOPX by siRNA reduced Ras activity, inactivated the MAPK pathway, decreased p21, and reduced senescence.\",\n      \"method\": \"Stable transfection with HOPX expression vector, siRNA knockdown, Ras activity assay, MAPK signaling analysis, senescence assays (SA-β-gal), p21/MDM2 western blot\",\n      \"journal\": \"The Journal of pathology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2-3 / Moderate — multiple orthogonal methods (overexpression, knockdown, Ras activity assay, downstream signaling), single lab\",\n      \"pmids\": [\"25345926\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2015,\n      \"finding\": \"Hopx is specifically expressed in radial glia-like (RGL) neural stem cells of the adult dentate gyrus (DG) but not in the lateral ventricle proliferative zone, distinguishing hippocampal NSCs from lateral ventricle NSCs. Hopx-null NSCs exhibit enhanced neurogenesis with increased BrdU+ cells and reduced quiescent Sox2+ NSCs. Hopx regulates hippocampal NSC quiescence at least partly by modulating Notch signaling (reduced Hes1, Hey2, and NICD in Hopx-null DG).\",\n      \"method\": \"Lineage tracing, genetic knockout (Hopx-null mice), BrdU labeling, doublecortin immunostaining, Notch target gene expression analysis, cleaved Notch1 (NICD) immunostaining\",\n      \"journal\": \"Stem cell research\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — genetic KO with defined neurogenesis phenotype and Notch pathway link, multiple histological methods, single lab\",\n      \"pmids\": [\"26451648\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2018,\n      \"finding\": \"HOPX is required for cardiomyocyte maturation during hPSC cardiac differentiation. Loss-of-function and gain-of-function experiments showed that hypertrophic signaling activates HOPX, which in turn activates downstream gene programs governing late-stage cardiomyocyte maturation. HOPX controls enhancer networks and cardiac gene programs associated with cardiomyocyte identity.\",\n      \"method\": \"Single-cell transcriptomics, genetic gain- and loss-of-function in hPSC-derived cardiomyocytes, gene expression profiling\",\n      \"journal\": \"Cell stem cell\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — genetic gain/loss of function in human stem cell model, single-cell transcriptomics, single lab\",\n      \"pmids\": [\"30290179\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2023,\n      \"finding\": \"HOPX (a non-DNA-binding homeodomain protein) interacts with and controls cardiac gene enhancer networks in cardiomyocytes. Upstream cell growth and proliferation signals control HOPX transcription, which regulates downstream gene programs underpinning cardiomyocyte identity and function. HOPX-regulated programs were validated in vitro, in organoids, and in zebrafish regeneration models.\",\n      \"method\": \"Genetic loss-of-function in hiPSC-derived cardiomyocytes, perturbation studies, ATAC-seq/ChIP-seq for enhancer analysis, zebrafish regeneration model, cardiac organoids\",\n      \"journal\": \"Developmental cell\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1-2 / Strong — multiple orthogonal genomic and functional approaches (loss-of-function, enhancer profiling, organoid and in vivo zebrafish models) in a single rigorous study\",\n      \"pmids\": [\"38091997\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2017,\n      \"finding\": \"HOPX regulates primitive hematopoiesis by suppressing Wnt/β-catenin signaling in blood-forming endothelial cells. Using HOPX reporter and knockout hESCs, loss of HOPX markedly reduces primitive hematopoiesis while not affecting endothelial fate specification.\",\n      \"method\": \"HOPX reporter and knockout hESC lines, chromatin accessibility (ATAC-seq), transcriptional profiling, hematopoietic differentiation assays, Wnt/β-catenin signaling readout\",\n      \"journal\": \"Cell reports\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — HOPX KO hESC with defined hematopoietic phenotype, Wnt pathway link, chromatin and transcriptional analysis, single lab\",\n      \"pmids\": [\"28813672\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2020,\n      \"finding\": \"Hematopoietic-specific knockout of Hopx in mice leads to decreased HSC reconstitution ability, reduced HSC quiescence signatures, and downregulation of the Cxcl12-Cxcr4 axis. Hopx-/- HSCs show decreased CXCL12 and CXCR4 expression, implicating this pathway as a mechanism by which Hopx maintains HSC quiescence.\",\n      \"method\": \"Conditional hematopoietic Hopx knockout mouse model, serial transplantation assay, transcriptomic analysis of HSCs, CXCL12/CXCR4 expression measurement, AML model (MN1 overexpression)\",\n      \"journal\": \"Oncogene\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — conditional KO with defined HSC phenotype and molecular pathway (CXCL12-CXCR4), transcriptomic support, single lab\",\n      \"pmids\": [\"32533098\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2018,\n      \"finding\": \"Hopx is required for basal radial glial cell (bRGC) abundance in the developing mouse neocortex. Disruption of Hopx expression in mouse embryonic medial neocortex reduces bRGC numbers, and forced Hopx expression in lateral neocortex increases bRGC abundance to levels seen in gyrencephalic neocortex, demonstrating that Hopx is both necessary and sufficient for bRGC generation.\",\n      \"method\": \"Genetic disruption (CRISPR/electroporation in vivo), forced expression (in utero electroporation), quantitative histology of bRGC populations, lineage tracing\",\n      \"journal\": \"Development (Cambridge, England)\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — gain- and loss-of-function in vivo with defined cellular phenotype, single lab\",\n      \"pmids\": [\"30266827\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2010,\n      \"finding\": \"HOPX expression in human keratinocytes is induced through the PKC signaling pathway (activated by PMA), but not by the demethylating agent 5-aza-dC, suggesting its regulation is not associated with DNA methylation in this cell type. Knockdown of HOPX by RNAi increases differentiation markers (involucrin and loricrin), while forced exogenous HOPX downregulates differentiation marker genes in HaCaT cells.\",\n      \"method\": \"RNAi knockdown, forced expression, PKC pathway inhibition, differentiation marker gene expression (involucrin, loricrin), calcium-triggered differentiation assay\",\n      \"journal\": \"European journal of cell biology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2-3 / Moderate — knockdown and overexpression with defined differentiation marker readouts, pathway inhibition, single lab\",\n      \"pmids\": [\"20226564\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2003,\n      \"finding\": \"NECC1/HOPX (also called LAGY) encodes a small 73 amino acid homeodomain protein. Transfection of NECC1 into choriocarcinoma cell lines induces CSH1 (chorionic somatomammotropin hormone 1) expression and suppresses in vivo tumorigenesis, suggesting differentiation toward syncytiotrophoblasts.\",\n      \"method\": \"Transfection/forced expression in choriocarcinoma cell lines, in vivo xenograft tumorigenesis assay, expression profiling\",\n      \"journal\": \"Genomics\",\n      \"confidence\": \"Low\",\n      \"confidence_rationale\": \"Tier 3 / Weak — single forced-expression study without detailed mechanistic pathway delineation, single lab\",\n      \"pmids\": [\"12573257\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2008,\n      \"finding\": \"HOP/OB1/NECC1 (HOPX) has two promoters (A and B) encoding two isoforms (HOPα and HOPβ). HOPβ silencing is associated with dense CpG island methylation at promoter B in esophageal squamous cell carcinoma, and forced HOP expression suppresses tumorigenesis in soft agar assays in four different squamous cell carcinoma cell lines. RNA interference knockdown of HOP restores the oncogenic phenotype.\",\n      \"method\": \"Methylation-specific PCR (TaqMan), demethylating agent treatment (5-aza-dCR + TSA), forced expression and RNAi knockdown, soft agar colony formation assay\",\n      \"journal\": \"Molecular cancer research : MCR\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2-3 / Moderate — matched forced expression and RNAi knockdown with functional readout, epigenetic mechanism identified, single lab\",\n      \"pmids\": [\"18234960\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2020,\n      \"finding\": \"EZH2 directly binds to the HOPX promoter region during normal growth and osteogenic differentiation (but not adipogenic conditions), thereby repressing HOPX. HOPX promotes BMSC proliferation and inhibits adipogenesis by suppressing adipogenic pathway genes (ADIPOQ, FABP4, PLIN1, PLIN4), as shown by gain- and loss-of-function studies and RNA-seq.\",\n      \"method\": \"ChIP (EZH2 binding to HOPX promoter), HOPX knockdown and overexpression in BMSCs, RNA-seq during adipogenesis, differentiation assays\",\n      \"journal\": \"Scientific reports\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — ChIP for direct EZH2-HOPX promoter binding, matched gain/loss-of-function, RNA-seq, single lab\",\n      \"pmids\": [\"32647304\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2016,\n      \"finding\": \"HOPX and KLF4 cooperate to activate claudin 4, 7, and 15 expression during colonic epithelial differentiation, as shown by correlation analysis, in vitro confirmatory methods, and chromatin immunoprecipitation identifying the Hopx/Klf4 cascade as a regulator of barrier gene expression.\",\n      \"method\": \"Gene expression microarray/correlation analysis, in vitro confirmatory assays, chromatin immunoprecipitation (ChIP), conditional knockout mice for validation\",\n      \"journal\": \"Tissue barriers\",\n      \"confidence\": \"Low\",\n      \"confidence_rationale\": \"Tier 3 / Weak — ChIP and correlation data for HOPX/Klf4, limited functional validation of HOPX's direct role vs. Klf4, single lab\",\n      \"pmids\": [\"27583195\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2024,\n      \"finding\": \"HOPX physically interacts with HDAC2 in AML cells (confirmed by endogenous and exogenous co-immunoprecipitation), and this HOPX-HDAC2 interaction induces differentiation blockage and malignant progression in AML. Low HOPX expression represses AML cell proliferation, anti-apoptotic activity, and differentiation blockage.\",\n      \"method\": \"Endogenous and exogenous Co-immunoprecipitation, flow cytometry (proliferation and apoptosis), MTT assay, bioinformatics analysis\",\n      \"journal\": \"Hematological oncology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — reciprocal Co-IP for HOPX-HDAC2 interaction, functional assays, single lab\",\n      \"pmids\": [\"39243399\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2025,\n      \"finding\": \"In lung cancer drug-tolerant persister (DTP) cells, HOPX undergoes cytoplasmic-to-nuclear translocation upon targeted therapy treatment. Nuclear HOPX regulates NF-κB activation and repressive histone modifications. HOPX deletion significantly delays DTP regrowth, identifying HOPX as a regulator of DTP persistence through epigenetic and NF-κB-dependent mechanisms.\",\n      \"method\": \"scATAC-seq, HOPX deletion (CRISPR), subcellular fractionation/immunofluorescence for nuclear translocation, NF-κB activity assays, histone modification analysis, in vitro DTP regrowth assay\",\n      \"journal\": \"iScience\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — HOPX deletion with defined DTP phenotype, subcellular localization tracking, NF-κB and epigenetic readouts, single lab\",\n      \"pmids\": [\"40352726\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2021,\n      \"finding\": \"Hopx plays a critical role in epigenetic regulation through histone deacetylation in cardiomyocytes treated with antiretroviral drugs (ARVs). HOPX expression is significantly increased in ARV-treated cardiomyocytes and HIV patient heart tissue. HDAC inhibitor Trichostatin A restores histone 3 acetylation in the presence of ARVs, and HOPX is identified as mediating cellular hypertrophy via histone deacetylation.\",\n      \"method\": \"RNA-sequencing of ARV-treated neonatal rat cardiomyocytes, HDAC inhibitor rescue experiment (Trichostatin A), histone acetylation western blot, validation in HIV patient cardiac tissue\",\n      \"journal\": \"Cells\",\n      \"confidence\": \"Low\",\n      \"confidence_rationale\": \"Tier 3 / Weak — indirect evidence linking HOPX to histone deacetylation via HDAC inhibitor rescue, no direct HOPX knockdown/overexpression experiment reported in abstract, single lab\",\n      \"pmids\": [\"34943964\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2025,\n      \"finding\": \"Iron released from radiotherapy-induced tumor cell death triggers a Stat3-dependent pro-survival program in neighboring Hopx+ quiescent cancer stem cells, causing their activation. Activated Hopx+ cancer stem cells antagonize ferroptosis (which should be caused by iron overload) through inhibition of de novo lipid synthesis.\",\n      \"method\": \"Lineage-tracing (HopxCreERT2;RosatdTomato mice and organoids), BrdU pulse-chase, cell cycle analysis, apoptosis/necroptosis blockade experiments, human rectal cancer organoids and PDX models\",\n      \"journal\": \"Journal of advanced research\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — lineage tracing, multiple in vivo and organoid models, Stat3 pathway and lipid synthesis mechanistic link, single lab\",\n      \"pmids\": [\"41325838\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2026,\n      \"finding\": \"HOPX stabilizes β-catenin protein by directly inhibiting the interaction of β-catenin with UBA52, which targets β-catenin for ubiquitination-mediated degradation. High iron diet activates Wnt/β-catenin signaling in Hopx+ intestinal stem cells in a Hopx-dependent manner through this competitive binding mechanism.\",\n      \"method\": \"Co-immunoprecipitation (HOPX-UBA52 and HOPX-β-catenin interaction), ubiquitination assay, Hopx genetic models, Wnt/β-catenin signaling assays, high-iron diet mouse model\",\n      \"journal\": \"International journal of biological sciences\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — Co-IP for protein interactions, ubiquitination assay, genetic model, defined molecular mechanism, single lab\",\n      \"pmids\": [\"42157941\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2025,\n      \"finding\": \"DNMT3B directly methylates the HOPX promoter, downregulating HOPX expression in lung cancer cells. DNMT inhibitor SGI-1027 upregulates HOPX, and HOPX knockdown partially recovers the malignant phenotypes (proliferation, migration, invasion) suppressed by DNMT3B knockdown or SGI-1027 treatment, placing HOPX downstream of DNMT3B-mediated DNA methylation.\",\n      \"method\": \"DNMT3B overexpression and knockdown, DNMT inhibitor (SGI-1027) treatment, methylation analysis of HOPX promoter, HOPX knockdown rescue experiment, in vitro and in vivo functional assays\",\n      \"journal\": \"iScience\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — matched gain/loss-of-function with rescue, methylation analysis, functional readouts, single lab\",\n      \"pmids\": [\"41660264\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2025,\n      \"finding\": \"HOPX regulates hepatocellular carcinoma invasion and migration by suppressing SNAIL expression, thereby inhibiting epithelial-to-mesenchymal transition (EMT). HOPX inhibition of SNAIL was required for HOPX's metastasis-inhibitory activity in in vitro and in vivo HCC models.\",\n      \"method\": \"HOPX forced expression and knockdown, invasion/migration assays, SNAIL protein expression analysis, in vivo HCC metastasis mouse model, EMT marker analysis\",\n      \"journal\": \"Scientific reports\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2-3 / Moderate — matched overexpression and loss-of-function, in vivo metastasis model, SNAIL pathway link, single lab\",\n      \"pmids\": [\"40804282\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2022,\n      \"finding\": \"GRHL3 transcriptionally regulates HOPX expression in the esophageal epithelium (ChIP-seq confirmed GRHL3 binding to the HOPX locus), and HOPX in turn limits Wnt/β-catenin signaling. Loss of GRHL3 reduces HOPX expression and increases Wnt/β-catenin activity, driving esophageal squamous cell carcinoma progression.\",\n      \"method\": \"ChIP-seq (GRHL3 binding to HOPX), conditional Grhl3 deletion in mice, RNA-seq, immunohistochemistry, Wnt/β-catenin pathway analysis, patient-derived ESCC validation\",\n      \"journal\": \"Cellular and molecular gastroenterology and hepatology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — ChIP-seq for GRHL3-HOPX regulatory link, genetic mouse model, patient validation, single lab\",\n      \"pmids\": [\"36442813\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2024,\n      \"finding\": \"HOPX, operating downstream of GPR109A (activated by butyrate from gut microbiota), enhances CD8+ T cell cytotoxic killing of gastric cancer cells. GPR109A knockout significantly weakened butyrate's enhancement of CD8+ T cell function, and HOPX acted downstream in this GPR109A/HOPX axis.\",\n      \"method\": \"GPR109A knockout mouse model, butyrate supplementation during gastric cancer induction, co-culture of GC cells with CD8+ T cells or CAR-T cells, in vivo tumor-bearing studies, IFN-γ measurement\",\n      \"journal\": \"Gut microbes\",\n      \"confidence\": \"Low\",\n      \"confidence_rationale\": \"Tier 3 / Weak — HOPX's direct molecular role in the GPR109A signaling cascade is inferred from pathway position; direct HOPX mechanistic experiment not clearly described in abstract, single lab\",\n      \"pmids\": [\"38319728\"],\n      \"is_preprint\": false\n    }\n  ],\n  \"current_model\": \"HOPX is an atypical, non-DNA-binding homeodomain protein that functions as a transcriptional co-regulator by physically interacting with partners such as SRF, HDAC2, GATA4, activated SMADs, and UBA52 to modulate gene programs controlling cell proliferation, differentiation, and survival; in cardiac development it recruits HDAC2 to deacetylate GATA4 and integrates BMP/SMAD and Wnt signals to drive cardiomyocyte commitment, in stem cell niches it maintains quiescence partly through Notch and CXCL12-CXCR4 signaling, and in multiple cancers it suppresses metastasis via epigenetic silencing of SNAIL (H3K9 deacetylation) and modulation of Wnt/β-catenin stability, while in immune cells it suppresses AP-1 and IL-2 to sustain regulatory T cell function.\"\n}\n```","stage2_raw":"{\n  \"mechanistic_narrative\": \"HOPX is a small, atypical non-DNA-binding homeodomain protein that functions as a transcriptional co-regulator, controlling cell proliferation, differentiation, and survival across cardiac, neural, hematopoietic, epithelial, immune, and tumor contexts [#0, #12]. A core mechanism is its partnership with HDAC2: in the developing heart HOPX recruits and stabilizes HDAC2 to deacetylate the transcription factor GATA4, blunting GATA4-driven cell-cycle gene transactivation and thereby restraining cardiomyocyte proliferation [#0], while in acute myeloid leukemia the same HOPX-HDAC2 interaction enforces a differentiation block and drives malignant progression [#21]. HOPX also represses serum response factor (SRF)-dependent transcription, suppressing estrogen-stimulated c-fos induction in endometrial cells and trophoblast giant-cell differentiation [#2, #3]. In cardiomyocyte commitment and maturation, HOPX integrates niche signals by binding activated SMAD proteins to repress Wnt targets and by controlling enhancer networks that define cardiomyocyte identity downstream of growth and hypertrophic signals [#1, #11, #12]. Across stem/progenitor compartments HOPX maintains quiescence and lineage decisions: it limits Wnt/\\u03b2-catenin signaling to support primitive hematopoiesis and hematopoietic stem cell quiescence via the CXCL12-CXCR4 axis [#13, #14], regulates dentate-gyrus neural stem cell quiescence through Notch signaling and is necessary and sufficient for basal radial glia generation in neocortex [#10, #15]. As a tumor suppressor, HOPX epigenetically silences SNAIL through enhanced H3K9 deacetylation to block EMT and metastasis, cooperates with GATA6 to limit metastatic competence, and promotes oncogenic Ras-induced senescence [#7, #8, #9, #27]. HOPX expression is itself controlled epigenetically by promoter methylation (DNMT3B) and CpG silencing, by EZH2-mediated repression, and by upstream transcription factors GRHL3 and KLF4 [#18, #19, #26, #28]. In immune cells HOPX sustains regulatory T cell function and Th1 persistence by suppressing the AP-1 complex and intrinsic IL-2 and by conferring resistance to Fas-induced apoptosis [#4, #5, #6]. More recent work links HOPX to \\u03b2-catenin stabilization via competitive inhibition of UBA52-mediated ubiquitination and to nuclear translocation that drives NF-\\u03baB activation in drug-tolerant persister cells [#25, #22].\",\n  \"teleology\": [\n    {\n      \"year\": 2003,\n      \"claim\": \"Establishing HOPX as a small homeodomain protein with differentiation-promoting, tumor-suppressive activity gave the first functional handle on an otherwise uncharacterized gene.\",\n      \"evidence\": \"Forced expression of NECC1/HOPX in choriocarcinoma lines with xenograft tumorigenesis assay\",\n      \"pmids\": [\"12573257\"],\n      \"confidence\": \"Low\",\n      \"gaps\": [\"No molecular partner or mechanism defined\", \"Single forced-expression study without pathway delineation\"]\n    },\n    {\n      \"year\": 2007,\n      \"claim\": \"Identifying SRF as a functional target answered how HOPX restrains transcription without binding DNA, linking it to lineage decisions in the placenta.\",\n      \"evidence\": \"Genetic knockout mouse and forced expression in trophoblast stem cells with SRF activity analysis\",\n      \"pmids\": [\"17576768\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Direct HOPX-SRF binding not biochemically dissected here\", \"Generalizability beyond trophoblast unclear\"]\n    },\n    {\n      \"year\": 2010,\n      \"claim\": \"Discovery of the HOPX-HDAC2 complex deacetylating GATA4 explained at the biochemical level how HOPX suppresses cardiomyocyte proliferation, defining its prototypical co-repressor mechanism.\",\n      \"evidence\": \"Reciprocal Co-IP, double-knockout mice, and in vitro deacetylation assays on GATA4\",\n      \"pmids\": [\"20833366\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"How HOPX selects GATA4 vs other substrates not defined\", \"Structural basis of HDAC2 recruitment unknown\"]\n    },\n    {\n      \"year\": 2010,\n      \"claim\": \"Demonstrating HOPX requirement in iTreg/Th1 cells extended its role from development to immune tolerance and effector persistence via AP-1 suppression and apoptosis resistance.\",\n      \"evidence\": \"Hopx-deficient mice, DC-mediated iTreg induction, adoptive transfer and Fas-apoptosis assays\",\n      \"pmids\": [\"20802482\", \"21061432\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Mechanism of AP-1 downregulation not resolved\", \"Direct transcriptional targets in T cells not mapped\"]\n    },\n    {\n      \"year\": 2013,\n      \"claim\": \"Showing HOPX cooperates with GATA6 to suppress invasion positioned it as a lineage transcription factor limiting metastatic competence in solid tumors.\",\n      \"evidence\": \"Gain/loss-of-function in lung adenocarcinoma lines with invasion and in vivo metastasis models\",\n      \"pmids\": [\"23707782\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Direct HOPX-GATA6 physical interaction not established\", \"Shared target genes only partially defined\"]\n    },\n    {\n      \"year\": 2015,\n      \"claim\": \"Linking HOPX to SMAD binding and Wnt repression revealed it as a signaling integrator driving cardiomyocyte commitment, and parallel work tied IL-2 suppression to Treg maintenance.\",\n      \"evidence\": \"Co-IP of HOPX-SMAD, Wnt reporter assays, lineage tracing; Hopx-deficient pTreg IL-2 measurement in EAE model\",\n      \"pmids\": [\"26113728\", \"26170384\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Specific Wnt target genes repressed not enumerated\", \"Whether SMAD binding is direct or complex-mediated unresolved\"]\n    },\n    {\n      \"year\": 2015,\n      \"claim\": \"Defining HOPX as a marker and regulator of adult dentate-gyrus NSC quiescence via Notch distinguished hippocampal from ventricular stem cells.\",\n      \"evidence\": \"Hopx-null mice, BrdU labeling, Notch target gene and NICD analysis\",\n      \"pmids\": [\"26451648\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"How HOPX modulates Notch signaling mechanistically unknown\", \"Direct transcriptional targets not identified\"]\n    },\n    {\n      \"year\": 2017,\n      \"claim\": \"ChIP demonstration of H3K9 deacetylation at the SNAIL promoter gave a concrete epigenetic mechanism for HOPX's anti-metastatic function, complemented by Wnt suppression in hematopoiesis.\",\n      \"evidence\": \"ChIP at SNAIL promoter in NPC cells; HOPX-KO hESC with ATAC-seq and Wnt readout in blood-forming endothelium\",\n      \"pmids\": [\"28146149\", \"28813672\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"HDAC partner at SNAIL promoter not identified in NPC\", \"Whether SNAIL silencing generalizes across tumor types tested separately\"]\n    },\n    {\n      \"year\": 2018,\n      \"claim\": \"Genomic profiling established that HOPX governs enhancer networks and cardiomyocyte maturation downstream of hypertrophic/growth signals, and that it controls basal radial glia abundance in cortex.\",\n      \"evidence\": \"scRNA-seq and gain/loss-of-function in hPSC-cardiomyocytes; in vivo CRISPR and electroporation for bRGC quantification\",\n      \"pmids\": [\"30290179\", \"30266827\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Enhancer recruitment mechanism for a non-DNA-binding protein unresolved\", \"Co-factors directing HOPX to specific loci unknown\"]\n    },\n    {\n      \"year\": 2020,\n      \"claim\": \"Conditional hematopoietic knockout connected HOPX to HSC quiescence and reconstitution through the CXCL12-CXCR4 axis, and EZH2 was shown to repress HOPX during BMSC differentiation.\",\n      \"evidence\": \"Conditional Hopx-KO mice, serial transplantation, transcriptomics; ChIP of EZH2 at HOPX promoter with BMSC gain/loss-of-function\",\n      \"pmids\": [\"32533098\", \"32647304\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Whether HOPX directly regulates Cxcl12/Cxcr4 transcription not shown\", \"Substrate/target specificity in HSCs undefined\"]\n    },\n    {\n      \"year\": 2022,\n      \"claim\": \"Upstream regulatory architecture was clarified by showing GRHL3 transcriptionally activates HOPX, which then limits Wnt/\\u03b2-catenin to suppress esophageal carcinoma progression.\",\n      \"evidence\": \"ChIP-seq for GRHL3 binding at HOPX, conditional Grhl3 mice, patient ESCC validation\",\n      \"pmids\": [\"36442813\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Mechanism by which HOPX limits Wnt in this context not biochemically defined\"]\n    },\n    {\n      \"year\": 2024,\n      \"claim\": \"Re-demonstration of the HOPX-HDAC2 complex in AML reframed the same molecular interaction as oncogenic, enforcing a differentiation block.\",\n      \"evidence\": \"Endogenous and exogenous Co-IP with proliferation/apoptosis functional assays in AML cells\",\n      \"pmids\": [\"39243399\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Target genes/substrates of HOPX-HDAC2 in AML not identified\", \"Why the same complex is suppressive in heart but oncogenic in AML unexplained\"]\n    },\n    {\n      \"year\": 2025,\n      \"claim\": \"Recent work uncovered new HOPX behaviors: cytoplasmic-to-nuclear translocation driving NF-\\u03baB and repressive histone marks in drug-tolerant persisters, SNAIL suppression in HCC, and DNMT3B methylation controlling HOPX expression.\",\n      \"evidence\": \"scATAC-seq, CRISPR deletion, subcellular fractionation and NF-\\u03baB assays (DTP); forced expression/knockdown in HCC; DNMT3B gain/loss with HOPX rescue in lung cancer\",\n      \"pmids\": [\"40352726\", \"40804282\", \"41660264\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Trigger and machinery for HOPX nuclear translocation undefined\", \"How HOPX engages NF-\\u03baB mechanistically unknown\"]\n    },\n    {\n      \"year\": 2026,\n      \"claim\": \"Identification of UBA52 as a HOPX partner revealed a post-translational mechanism: HOPX competitively blocks UBA52-mediated \\u03b2-catenin ubiquitination to stabilize \\u03b2-catenin in iron-stimulated intestinal stem cells.\",\n      \"evidence\": \"Co-IP of HOPX-UBA52 and HOPX-\\u03b2-catenin, ubiquitination assay, Hopx genetic models, high-iron diet\",\n      \"pmids\": [\"42157941\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Reconciliation with prior reports of HOPX limiting Wnt/\\u03b2-catenin not addressed\", \"Structural basis of competitive binding unknown\"]\n    },\n    {\n      \"year\": null,\n      \"claim\": \"How a non-DNA-binding homeodomain protein is recruited to context-specific enhancers and partners (HDAC2, SMAD, SRF, UBA52) to produce opposite outcomes (tumor suppression vs oncogenic persistence) remains unresolved.\",\n      \"evidence\": \"\",\n      \"pmids\": [],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"No structural model of HOPX-partner complexes\", \"Determinants of cell-type-specific co-factor selection unknown\", \"Mechanism switching HOPX between cytoplasmic and nuclear/repressive roles undefined\"]\n    }\n  ],\n  \"mechanism_profile\": {\n    \"molecular_activity\": [\n      {\"term_id\": \"GO:0140110\", \"supporting_discovery_ids\": [0, 2, 3, 11, 12]},\n      {\"term_id\": \"GO:0098772\", \"supporting_discovery_ids\": [0, 25]},\n      {\"term_id\": \"GO:0060090\", \"supporting_discovery_ids\": [0, 1, 25]}\n    ],\n    \"localization\": [\n      {\"term_id\": \"GO:0005634\", \"supporting_discovery_ids\": [0, 22]},\n      {\"term_id\": \"GO:0005829\", \"supporting_discovery_ids\": [22]}\n    ],\n    \"pathway\": [\n      {\"term_id\": \"R-HSA-4839726\", \"supporting_discovery_ids\": [0, 8, 22]},\n      {\"term_id\": \"R-HSA-1266738\", \"supporting_discovery_ids\": [1, 11, 12, 15]},\n      {\"term_id\": \"R-HSA-162582\", \"supporting_discovery_ids\": [1, 13, 25, 28]},\n      {\"term_id\": \"R-HSA-168256\", \"supporting_discovery_ids\": [4, 5, 6]},\n      {\"term_id\": \"R-HSA-74160\", \"supporting_discovery_ids\": [0, 2, 3, 12]}\n    ],\n    \"complexes\": [],\n    \"partners\": [\"HDAC2\", \"GATA4\", \"SMAD\", \"SRF\", \"GATA6\", \"UBA52\", \"CTNNB1\"],\n    \"other_free_text\": []\n  }\n}","audit_flag":null,"evaluation":{"pairwise":"win","faith_supported":9,"faith_total":9,"faith_pct":100.0}}