{"gene":"HMGXB4","run_date":"2026-06-10T01:55:22","timeline":{"discoveries":[{"year":2003,"finding":"HMG2L1 (HMGXB4) was identified as an NLK-binding protein via yeast two-hybrid screening. Injection of Xenopus HMG2L1 mRNA into Xenopus embryos inhibited Wnt/beta-catenin-induced axis duplication and target gene expression, and xHMG2L1 inhibited beta-catenin-stimulated transcriptional activity in mammalian cells, establishing HMG2L1 as a negative regulator of Wnt/beta-catenin signaling acting through NLK.","method":"Yeast two-hybrid screening, Xenopus mRNA injection (axis duplication assay), mammalian cell transcriptional reporter assay","journal":"Genes to cells : devoted to molecular & cellular mechanisms","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — yeast two-hybrid plus two orthogonal functional assays (Xenopus and mammalian cell), single lab","pmids":["12875653"],"is_preprint":false},{"year":2007,"finding":"HMG2L1 (HMGXB4) upregulates transcription from the 5'-UTR of the Sleeping Beauty (SB) transposon, requiring a specific 65-bp region. The SB transposase antagonizes this HMG2L1-dependent upregulation, indicating a negative feedback regulation of transposase expression.","method":"Transcriptional reporter assays in human cells with HMG2L1 overexpression and SB transposase co-expression; deletion mapping of the 65-bp regulatory region","journal":"Molecular therapy : the journal of the American Society of Gene Therapy","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — functional transcriptional assays with deletion mapping, single lab, two orthogonal functional readouts","pmids":["18071335"],"is_preprint":false},{"year":2010,"finding":"HMGXB4 (HMG2L1) physically interacts with myocardin via their respective N-terminal domains (mapped by GST pulldown), disrupts myocardin binding to SRF, and abolishes SRF-myocardin complex binding to promoters of smooth muscle-specific genes, thereby repressing smooth muscle differentiation. Overexpression of HMG2L1 in SMCs down-regulated smooth muscle marker expression, and depletion of endogenous HMG2L1 increased smooth muscle-specific gene expression.","method":"GST pulldown (interaction domain mapping), overexpression and siRNA knockdown in smooth muscle cells, gene expression analysis, chromatin immunoprecipitation (promoter binding)","journal":"The Journal of biological chemistry","confidence":"High","confidence_rationale":"Tier 2 / Strong — reciprocal gain- and loss-of-function experiments plus GST pulldown domain mapping plus ChIP, multiple orthogonal methods in single study","pmids":["20511232"],"is_preprint":false},{"year":2021,"finding":"HMGXB4 functions as a transcriptional activator that directly binds the Nos2 (iNOS) promoter in macrophages and the Icam1 promoter in endothelial cells, driving proinflammatory gene expression. Genetic deletion of Hmgxb4 protected mice from LPS-induced lung injury and lethality and CLP-induced lethality, and attenuated LPS-induced proinflammatory gene expression in cultured macrophages.","method":"Genetic knockout in mice (LPS and CLP models), genome-wide transcriptome profiling integrated with ChIP-seq dataset, pharmacological NOS2 inhibition, vascular permeability assays","journal":"Proceedings of the National Academy of Sciences of the United States of America","confidence":"High","confidence_rationale":"Tier 2 / Strong — in vivo knockout with multiple disease models, ChIP-seq evidence for direct promoter binding, transcriptomics, and pharmacological validation","pmids":["33563757"],"is_preprint":false},{"year":2023,"finding":"HMGXB4 is activated transcriptionally by ERK2/MAPK1 and ELK1, is suppressed by the KRAB-ZNF/TRIM28 epigenetic repression machinery, and is post-translationally regulated by SUMOylation, which modulates its binding affinity to protein interaction partners and controls its transcriptional activator function via nucleolar compartmentalization. HMGXB4 participates in nuclear-remodeling protein complexes and transactivates target gene expression in vertebrates, and it targets Sleeping Beauty transposition to germinal stem cells by activating transposase expression.","method":"Reporter assays, ChIP, SUMOylation assays, subcellular localization (nucleolar compartmentalization) experiments, chromatin domain analysis, expression profiling in germinal and somatic stem cells","journal":"International journal of molecular sciences","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — multiple mechanistic assays (ChIP, SUMOylation, localization), single lab, some findings rely on integration of published datasets","pmids":["37108449"],"is_preprint":false},{"year":2024,"finding":"HMGXB4 is a nuclear protein widely expressed in mouse tissues. Arterial injury significantly induces Hmgxb4 expression, as demonstrated by a gene trap (lacZ knock-in) reporter mouse model in which β-galactosidase activity mirrors endogenous Hmgxb4 promoter activity.","method":"Gene trap mouse model (lacZ insertion into Hmgxb4 locus), β-galactosidase staining across tissues, arterial injury model","journal":"Physiological reports","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — direct in vivo localization with functional reporter system, single lab, demonstrates nuclear localization and injury-induced expression","pmids":["38644513"],"is_preprint":false}],"current_model":"HMGXB4 (HMG2L1) is a nuclear HMG-box protein that acts as a transcriptional activator/repressor: it binds the promoters of proinflammatory genes (Nos2, Icam1) to drive inflammation in macrophages and endothelial cells, suppresses smooth muscle differentiation by physically interacting with myocardin (via N-terminal domains) and disrupting the SRF-myocardin complex, negatively regulates Wnt/beta-catenin signaling through interaction with NLK, activates Sleeping Beauty transposase expression, and is itself regulated transcriptionally by ERK2/ELK1 and epigenetically by KRAB-ZNF/TRIM28, with its activity modulated post-translationally by SUMOylation that controls nucleolar compartmentalization and protein interaction affinity."},"narrative":{"mechanistic_narrative":"HMGXB4 (HMG2L1) is a nuclear HMG-box protein that functions as a sequence-specific transcriptional regulator coordinating inflammation, vascular cell differentiation, and developmental signaling [PMID:33563757, PMID:20511232]. In innate immunity it acts as a direct transcriptional activator, binding the Nos2 (iNOS) promoter in macrophages and the Icam1 promoter in endothelial cells to drive proinflammatory gene expression; genetic deletion of Hmgxb4 protects mice from LPS- and CLP-induced lethality and lung injury [PMID:33563757]. In the vasculature it represses smooth muscle differentiation by physically engaging myocardin through reciprocal N-terminal domains, displacing myocardin from SRF and abolishing SRF-myocardin occupancy of smooth muscle gene promoters [PMID:20511232], and its expression is induced by arterial injury [PMID:38644513]. HMGXB4 also acts as a negative regulator of Wnt/beta-catenin signaling through the kinase NLK, inhibiting beta-catenin-driven axis duplication and target gene transcription [PMID:12875653], and it activates expression of the Sleeping Beauty transposase from the transposon 5'-UTR under negative feedback from the transposase itself [PMID:18071335]. Its own expression and activity are controlled upstream by ERK2/ELK1 activation and KRAB-ZNF/TRIM28 repression, and post-translationally by SUMOylation, which governs nucleolar compartmentalization and partner-binding affinity [PMID:37108449].","teleology":[{"year":2003,"claim":"Established HMGXB4 as the first-identified molecular link between an HMG-box protein and negative control of Wnt/beta-catenin signaling, answering how the pathway might be dampened downstream.","evidence":"Yeast two-hybrid identification of NLK interaction, Xenopus embryo axis-duplication assay, and mammalian beta-catenin reporter assay","pmids":["12875653"],"confidence":"Medium","gaps":["Mechanism by which NLK-HMGXB4 interaction suppresses beta-catenin transcription not resolved","Direct DNA targets in the Wnt context not identified","Single lab, no structural data on the interaction"]},{"year":2007,"claim":"Showed HMGXB4 is a transcriptional activator of a defined regulatory element, revealing it directly upregulates Sleeping Beauty transposase expression within a feedback loop.","evidence":"Transcriptional reporter assays in human cells with deletion mapping of a 65-bp 5'-UTR region and transposase co-expression","pmids":["18071335"],"confidence":"Medium","gaps":["Whether HMGXB4 binds the 65-bp element directly or via a partner not established","Endogenous physiological targets analogous to this element unknown"]},{"year":2010,"claim":"Defined a concrete repression mechanism in vascular biology by showing HMGXB4 disrupts the SRF-myocardin complex to suppress smooth muscle differentiation.","evidence":"GST pulldown domain mapping, reciprocal overexpression/siRNA in smooth muscle cells, and ChIP of smooth muscle gene promoters","pmids":["20511232"],"confidence":"High","gaps":["In vivo role in vascular development or disease not addressed in this study","Structural basis of myocardin N-terminal interaction not solved"]},{"year":2021,"claim":"Established HMGXB4 as a direct proinflammatory transcriptional activator in vivo, identifying Nos2 and Icam1 as physiological promoter targets and linking the gene to sepsis pathology.","evidence":"Hmgxb4 knockout mice in LPS and CLP models, transcriptome profiling integrated with ChIP-seq, pharmacological NOS2 inhibition, and vascular permeability assays","pmids":["33563757"],"confidence":"High","gaps":["DNA-binding specificity/consensus motif not defined","Cofactors enabling promoter activation not identified","Relationship between inflammatory and smooth-muscle/Wnt functions unresolved"]},{"year":2023,"claim":"Mapped the regulatory architecture controlling HMGXB4 itself, showing ERK2/ELK1 activation, KRAB-ZNF/TRIM28 repression, and SUMOylation-dependent nucleolar compartmentalization tune its activity.","evidence":"Reporter assays, ChIP, SUMOylation assays, subcellular localization experiments, and expression profiling in stem cells","pmids":["37108449"],"confidence":"Medium","gaps":["SUMOylation sites and SUMO-dependent partner switches not enumerated","Several conclusions integrate prior published datasets rather than new direct assays","Functional consequence of nucleolar sequestration on target genes not quantified"]},{"year":2024,"claim":"Provided in vivo expression and localization context, confirming HMGXB4 is a broadly expressed nuclear protein induced by arterial injury.","evidence":"lacZ gene-trap knock-in reporter mouse with beta-galactosidase staining across tissues and an arterial injury model","pmids":["38644513"],"confidence":"Medium","gaps":["Causal role of injury-induced expression in vascular remodeling not tested","Cell-type-specific function during injury not resolved"]},{"year":null,"claim":"How HMGXB4 reconciles its activator and repressor activities across inflammation, smooth muscle differentiation, and Wnt signaling — and what determines its DNA-binding specificity — remains unresolved.","evidence":"","pmids":[],"confidence":"Medium","gaps":["No defined DNA consensus motif","No structural model of HMG-box DNA engagement or partner complexes","Integration of upstream regulation with context-specific target selection unknown"]}],"mechanism_profile":{"molecular_activity":[{"term_id":"GO:0140110","term_label":"transcription regulator activity","supporting_discovery_ids":[0,1,2,3,4]},{"term_id":"GO:0003677","term_label":"DNA binding","supporting_discovery_ids":[2,3]}],"localization":[{"term_id":"GO:0005634","term_label":"nucleus","supporting_discovery_ids":[5]},{"term_id":"GO:0005730","term_label":"nucleolus","supporting_discovery_ids":[4]}],"pathway":[{"term_id":"R-HSA-168256","term_label":"Immune System","supporting_discovery_ids":[3]},{"term_id":"R-HSA-74160","term_label":"Gene expression (Transcription)","supporting_discovery_ids":[2,3]},{"term_id":"R-HSA-162582","term_label":"Signal Transduction","supporting_discovery_ids":[0]}],"complexes":[],"partners":["NLK","MYOCD","SRF","TRIM28","ELK1","MAPK1"],"other_free_text":[]}},"prefetch_data":{"uniprot":{"accession":"Q9UGU5","full_name":"HMG domain-containing protein 4","aliases":["HMG box-containing protein 4","High mobility group protein 2-like 1","Protein HMGBCG"],"length_aa":601,"mass_kda":65.7,"function":"Negatively regulates Wnt/beta-catenin signaling during development","subcellular_location":"Nucleus","url":"https://www.uniprot.org/uniprotkb/Q9UGU5/entry"},"depmap":{"release":"DepMap","has_data":true,"is_common_essential":false,"resolved_as":"","url":"https://depmap.org/portal/gene/HMGXB4","classification":"Not Classified","n_dependent_lines":3,"n_total_lines":1208,"dependency_fraction":0.0024834437086092716},"opencell":{"profiled":false,"resolved_as":"","ensg_id":"","cell_line_id":"","localizations":[],"interactors":[{"gene":"SMARCA5","stoichiometry":10.0},{"gene":"SMARCA1","stoichiometry":4.0},{"gene":"H2AFZ","stoichiometry":0.2},{"gene":"HIST2H2BE","stoichiometry":0.2},{"gene":"SSRP1","stoichiometry":0.2}],"url":"https://opencell.sf.czbiohub.org/search/HMGXB4","total_profiled":1310},"omim":[{"mim_id":"609476","title":"NEMO-LIKE KINASE; NLK","url":"https://www.omim.org/entry/609476"},{"mim_id":"604702","title":"HMG BOX DOMAIN-CONTAINING 4; HMGXB4","url":"https://www.omim.org/entry/604702"}],"hpa":{"profiled":true,"resolved_as":"","reliability":"Approved","locations":[{"location":"Nucleoplasm","reliability":"Approved"}],"tissue_specificity":"Low tissue specificity","tissue_distribution":"Detected in all","driving_tissues":[],"url":"https://www.proteinatlas.org/search/HMGXB4"},"hgnc":{"alias_symbol":["THC211630","P53N"],"prev_symbol":["HMG2L1"]},"alphafold":{"accession":"Q9UGU5","domains":[{"cath_id":"1.10.30.10","chopping":"411-471","consensus_level":"medium","plddt":91.187,"start":411,"end":471},{"cath_id":"-","chopping":"522-598","consensus_level":"medium","plddt":82.7596,"start":522,"end":598}],"viewer_url":"https://alphafold.ebi.ac.uk/entry/Q9UGU5","model_url":"https://alphafold.ebi.ac.uk/files/AF-Q9UGU5-F1-model_v6.cif","pae_url":"https://alphafold.ebi.ac.uk/files/AF-Q9UGU5-F1-predicted_aligned_error_v6.png","plddt_mean":55.66},"mouse_models":{"mgi_url":"https://www.informatics.jax.org/marker/summary?nomen=HMGXB4","jax_strain_url":"https://www.jax.org/strain/search?query=HMGXB4"},"sequence":{"accession":"Q9UGU5","fasta_url":"https://rest.uniprot.org/uniprotkb/Q9UGU5.fasta","uniprot_url":"https://www.uniprot.org/uniprotkb/Q9UGU5/entry","alphafold_viewer_url":"https://alphafold.ebi.ac.uk/entry/Q9UGU5"}},"corpus_meta":[{"pmid":"10022862","id":"PMC_10022862","title":"Regulation of p53 function and stability by phosphorylation.","date":"1999","source":"Molecular and cellular biology","url":"https://pubmed.ncbi.nlm.nih.gov/10022862","citation_count":386,"is_preprint":false},{"pmid":"16234232","id":"PMC_16234232","title":"Single-stranded DNA mimicry in the p53 transactivation domain interaction with replication protein A.","date":"2005","source":"Proceedings of the National Academy of Sciences of the United States of America","url":"https://pubmed.ncbi.nlm.nih.gov/16234232","citation_count":237,"is_preprint":false},{"pmid":"18071335","id":"PMC_18071335","title":"Transcriptional activities of the Sleeping Beauty transposon and shielding its genetic cargo with insulators.","date":"2007","source":"Molecular therapy : the journal of the American Society of Gene Therapy","url":"https://pubmed.ncbi.nlm.nih.gov/18071335","citation_count":75,"is_preprint":false},{"pmid":"3681266","id":"PMC_3681266","title":"Structural proteins of bovine coronavirus and their intracellular processing.","date":"1987","source":"The Journal of general virology","url":"https://pubmed.ncbi.nlm.nih.gov/3681266","citation_count":67,"is_preprint":false},{"pmid":"26104705","id":"PMC_26104705","title":"Sleeping Beauty Transposition.","date":"2015","source":"Microbiology spectrum","url":"https://pubmed.ncbi.nlm.nih.gov/26104705","citation_count":40,"is_preprint":false},{"pmid":"19525231","id":"PMC_19525231","title":"Interaction between the transactivation domain of p53 and PC4 exemplifies acidic activation domains as single-stranded DNA mimics.","date":"2009","source":"The Journal of biological chemistry","url":"https://pubmed.ncbi.nlm.nih.gov/19525231","citation_count":40,"is_preprint":false},{"pmid":"12875653","id":"PMC_12875653","title":"Negative regulation of Wnt signalling by HMG2L1, a novel NLK-binding protein.","date":"2003","source":"Genes to cells : devoted to molecular & cellular mechanisms","url":"https://pubmed.ncbi.nlm.nih.gov/12875653","citation_count":29,"is_preprint":false},{"pmid":"2053295","id":"PMC_2053295","title":"Comparison of bovine coronavirus (BCV) antigens: monoclonal antibodies to the spike glycoprotein distinguish between vaccine and wild-type strains.","date":"1991","source":"Virology","url":"https://pubmed.ncbi.nlm.nih.gov/2053295","citation_count":27,"is_preprint":false},{"pmid":"20511232","id":"PMC_20511232","title":"Repression of smooth muscle differentiation by a novel high mobility group box-containing protein, HMG2L1.","date":"2010","source":"The Journal of biological chemistry","url":"https://pubmed.ncbi.nlm.nih.gov/20511232","citation_count":20,"is_preprint":false},{"pmid":"10329004","id":"PMC_10329004","title":"TOM1 genes map to human chromosome 22q13.1 and mouse chromosome 8C1 and encode proteins similar to the endosomal proteins HGS and STAM.","date":"1999","source":"Genomics","url":"https://pubmed.ncbi.nlm.nih.gov/10329004","citation_count":20,"is_preprint":false},{"pmid":"17671966","id":"PMC_17671966","title":"Gene-based SNP mapping of a psychotic bipolar affective disorder linkage region on 22q12.3: association with HMG2L1 and TOM1.","date":"2008","source":"American journal of medical genetics. Part B, Neuropsychiatric genetics : the official publication of the International Society of Psychiatric Genetics","url":"https://pubmed.ncbi.nlm.nih.gov/17671966","citation_count":18,"is_preprint":false},{"pmid":"21541066","id":"PMC_21541066","title":"Anchoring intrinsically disordered proteins to multiple targets: lessons from N-terminus of the p53 protein.","date":"2011","source":"International journal of molecular sciences","url":"https://pubmed.ncbi.nlm.nih.gov/21541066","citation_count":16,"is_preprint":false},{"pmid":"33563757","id":"PMC_33563757","title":"Deficiency of the novel high mobility group protein HMGXB4 protects against systemic inflammation-induced endotoxemia in mice.","date":"2021","source":"Proceedings of the National Academy of Sciences of the United States of America","url":"https://pubmed.ncbi.nlm.nih.gov/33563757","citation_count":11,"is_preprint":false},{"pmid":"28399159","id":"PMC_28399159","title":"Effects of the RGD loop and C-terminus of rhodostomin on regulating integrin αIIbβ3 recognition.","date":"2017","source":"PloS one","url":"https://pubmed.ncbi.nlm.nih.gov/28399159","citation_count":11,"is_preprint":false},{"pmid":"37108449","id":"PMC_37108449","title":"HMGXB4 Targets Sleeping Beauty Transposition to Germinal Stem Cells.","date":"2023","source":"International journal of molecular sciences","url":"https://pubmed.ncbi.nlm.nih.gov/37108449","citation_count":3,"is_preprint":false},{"pmid":"38644513","id":"PMC_38644513","title":"A novel mouse model carrying a gene trap insertion into the Hmgxb4 gene locus to examine Hmgxb4 expression in vivo.","date":"2024","source":"Physiological reports","url":"https://pubmed.ncbi.nlm.nih.gov/38644513","citation_count":1,"is_preprint":false},{"pmid":"39216363","id":"PMC_39216363","title":"PDGF-BB overexpression in p53 null oligodendrocyte progenitors increases H3K27me3 and induces transcriptional changes which favor proliferation.","date":"2024","source":"Neoplasia (New York, N.Y.)","url":"https://pubmed.ncbi.nlm.nih.gov/39216363","citation_count":1,"is_preprint":false},{"pmid":"33595778","id":"PMC_33595778","title":"Analysis of the P53N a Novel Protein Encoded on Chromosome 22q12.1-12.3 in Glioblastomas and Ependymomas Specimens.","date":"2021","source":"Journal of molecular neuroscience : MN","url":"https://pubmed.ncbi.nlm.nih.gov/33595778","citation_count":0,"is_preprint":false},{"pmid":"39166056","id":"PMC_39166056","title":"Biallelic HMGXB4 loss-of-function variant causes intellectual disability, developmental delay, and dysmorphic features.","date":"2024","source":"Heliyon","url":"https://pubmed.ncbi.nlm.nih.gov/39166056","citation_count":0,"is_preprint":false},{"pmid":"41521291","id":"PMC_41521291","title":"Exosomal miRNA-mRNA interactions highlight MSC-like molecular signatures in dental pulp fibroblasts.","date":"2026","source":"Stem cell research & therapy","url":"https://pubmed.ncbi.nlm.nih.gov/41521291","citation_count":0,"is_preprint":false},{"pmid":"38798631","id":"PMC_38798631","title":"PDGF-BB overexpression in p53 null oligodendrocyte progenitors increases H3K27me3 and induces transcriptional changes which favor proliferation.","date":"2024","source":"bioRxiv : the preprint server for biology","url":"https://pubmed.ncbi.nlm.nih.gov/38798631","citation_count":0,"is_preprint":false},{"pmid":"42220229","id":"PMC_42220229","title":"Real-world-data for phenotypes and genotypes of rare monogenic genetic epilepsies and genes of uncertain significance for epilepsy.","date":"2026","source":"Epilepsia open","url":"https://pubmed.ncbi.nlm.nih.gov/42220229","citation_count":0,"is_preprint":false}],"cost":{"stage1":{"model":"claude-sonnet-4-6","input_tokens":13314,"output_tokens":1847,"usd":0.033823,"stage1_stop_reason":"end_turn"},"stage2":{"model":"claude-opus-4-8","input_tokens":8747,"output_tokens":2550,"usd":0.053742,"stage2_stop_reason":"end_turn"},"total_usd":0.087565,"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\": 2003,\n      \"finding\": \"HMG2L1 (HMGXB4) was identified as an NLK-binding protein via yeast two-hybrid screening. Injection of Xenopus HMG2L1 mRNA into Xenopus embryos inhibited Wnt/beta-catenin-induced axis duplication and target gene expression, and xHMG2L1 inhibited beta-catenin-stimulated transcriptional activity in mammalian cells, establishing HMG2L1 as a negative regulator of Wnt/beta-catenin signaling acting through NLK.\",\n      \"method\": \"Yeast two-hybrid screening, Xenopus mRNA injection (axis duplication assay), mammalian cell transcriptional reporter assay\",\n      \"journal\": \"Genes to cells : devoted to molecular & cellular mechanisms\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — yeast two-hybrid plus two orthogonal functional assays (Xenopus and mammalian cell), single lab\",\n      \"pmids\": [\"12875653\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2007,\n      \"finding\": \"HMG2L1 (HMGXB4) upregulates transcription from the 5'-UTR of the Sleeping Beauty (SB) transposon, requiring a specific 65-bp region. The SB transposase antagonizes this HMG2L1-dependent upregulation, indicating a negative feedback regulation of transposase expression.\",\n      \"method\": \"Transcriptional reporter assays in human cells with HMG2L1 overexpression and SB transposase co-expression; deletion mapping of the 65-bp regulatory region\",\n      \"journal\": \"Molecular therapy : the journal of the American Society of Gene Therapy\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — functional transcriptional assays with deletion mapping, single lab, two orthogonal functional readouts\",\n      \"pmids\": [\"18071335\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2010,\n      \"finding\": \"HMGXB4 (HMG2L1) physically interacts with myocardin via their respective N-terminal domains (mapped by GST pulldown), disrupts myocardin binding to SRF, and abolishes SRF-myocardin complex binding to promoters of smooth muscle-specific genes, thereby repressing smooth muscle differentiation. Overexpression of HMG2L1 in SMCs down-regulated smooth muscle marker expression, and depletion of endogenous HMG2L1 increased smooth muscle-specific gene expression.\",\n      \"method\": \"GST pulldown (interaction domain mapping), overexpression and siRNA knockdown in smooth muscle cells, gene expression analysis, chromatin immunoprecipitation (promoter binding)\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — reciprocal gain- and loss-of-function experiments plus GST pulldown domain mapping plus ChIP, multiple orthogonal methods in single study\",\n      \"pmids\": [\"20511232\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2021,\n      \"finding\": \"HMGXB4 functions as a transcriptional activator that directly binds the Nos2 (iNOS) promoter in macrophages and the Icam1 promoter in endothelial cells, driving proinflammatory gene expression. Genetic deletion of Hmgxb4 protected mice from LPS-induced lung injury and lethality and CLP-induced lethality, and attenuated LPS-induced proinflammatory gene expression in cultured macrophages.\",\n      \"method\": \"Genetic knockout in mice (LPS and CLP models), genome-wide transcriptome profiling integrated with ChIP-seq dataset, pharmacological NOS2 inhibition, vascular permeability assays\",\n      \"journal\": \"Proceedings of the National Academy of Sciences of the United States of America\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — in vivo knockout with multiple disease models, ChIP-seq evidence for direct promoter binding, transcriptomics, and pharmacological validation\",\n      \"pmids\": [\"33563757\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2023,\n      \"finding\": \"HMGXB4 is activated transcriptionally by ERK2/MAPK1 and ELK1, is suppressed by the KRAB-ZNF/TRIM28 epigenetic repression machinery, and is post-translationally regulated by SUMOylation, which modulates its binding affinity to protein interaction partners and controls its transcriptional activator function via nucleolar compartmentalization. HMGXB4 participates in nuclear-remodeling protein complexes and transactivates target gene expression in vertebrates, and it targets Sleeping Beauty transposition to germinal stem cells by activating transposase expression.\",\n      \"method\": \"Reporter assays, ChIP, SUMOylation assays, subcellular localization (nucleolar compartmentalization) experiments, chromatin domain analysis, expression profiling in germinal and somatic stem cells\",\n      \"journal\": \"International journal of molecular sciences\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — multiple mechanistic assays (ChIP, SUMOylation, localization), single lab, some findings rely on integration of published datasets\",\n      \"pmids\": [\"37108449\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2024,\n      \"finding\": \"HMGXB4 is a nuclear protein widely expressed in mouse tissues. Arterial injury significantly induces Hmgxb4 expression, as demonstrated by a gene trap (lacZ knock-in) reporter mouse model in which β-galactosidase activity mirrors endogenous Hmgxb4 promoter activity.\",\n      \"method\": \"Gene trap mouse model (lacZ insertion into Hmgxb4 locus), β-galactosidase staining across tissues, arterial injury model\",\n      \"journal\": \"Physiological reports\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — direct in vivo localization with functional reporter system, single lab, demonstrates nuclear localization and injury-induced expression\",\n      \"pmids\": [\"38644513\"],\n      \"is_preprint\": false\n    }\n  ],\n  \"current_model\": \"HMGXB4 (HMG2L1) is a nuclear HMG-box protein that acts as a transcriptional activator/repressor: it binds the promoters of proinflammatory genes (Nos2, Icam1) to drive inflammation in macrophages and endothelial cells, suppresses smooth muscle differentiation by physically interacting with myocardin (via N-terminal domains) and disrupting the SRF-myocardin complex, negatively regulates Wnt/beta-catenin signaling through interaction with NLK, activates Sleeping Beauty transposase expression, and is itself regulated transcriptionally by ERK2/ELK1 and epigenetically by KRAB-ZNF/TRIM28, with its activity modulated post-translationally by SUMOylation that controls nucleolar compartmentalization and protein interaction affinity.\"\n}\n```","stage2_raw":"{\n  \"mechanistic_narrative\": \"HMGXB4 (HMG2L1) is a nuclear HMG-box protein that functions as a sequence-specific transcriptional regulator coordinating inflammation, vascular cell differentiation, and developmental signaling [#3, #2]. In innate immunity it acts as a direct transcriptional activator, binding the Nos2 (iNOS) promoter in macrophages and the Icam1 promoter in endothelial cells to drive proinflammatory gene expression; genetic deletion of Hmgxb4 protects mice from LPS- and CLP-induced lethality and lung injury [#3]. In the vasculature it represses smooth muscle differentiation by physically engaging myocardin through reciprocal N-terminal domains, displacing myocardin from SRF and abolishing SRF-myocardin occupancy of smooth muscle gene promoters [#2], and its expression is induced by arterial injury [#5]. HMGXB4 also acts as a negative regulator of Wnt/beta-catenin signaling through the kinase NLK, inhibiting beta-catenin-driven axis duplication and target gene transcription [#0], and it activates expression of the Sleeping Beauty transposase from the transposon 5'-UTR under negative feedback from the transposase itself [#1]. Its own expression and activity are controlled upstream by ERK2/ELK1 activation and KRAB-ZNF/TRIM28 repression, and post-translationally by SUMOylation, which governs nucleolar compartmentalization and partner-binding affinity [#4].\",\n  \"teleology\": [\n    {\n      \"year\": 2003,\n      \"claim\": \"Established HMGXB4 as the first-identified molecular link between an HMG-box protein and negative control of Wnt/beta-catenin signaling, answering how the pathway might be dampened downstream.\",\n      \"evidence\": \"Yeast two-hybrid identification of NLK interaction, Xenopus embryo axis-duplication assay, and mammalian beta-catenin reporter assay\",\n      \"pmids\": [\"12875653\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Mechanism by which NLK-HMGXB4 interaction suppresses beta-catenin transcription not resolved\", \"Direct DNA targets in the Wnt context not identified\", \"Single lab, no structural data on the interaction\"]\n    },\n    {\n      \"year\": 2007,\n      \"claim\": \"Showed HMGXB4 is a transcriptional activator of a defined regulatory element, revealing it directly upregulates Sleeping Beauty transposase expression within a feedback loop.\",\n      \"evidence\": \"Transcriptional reporter assays in human cells with deletion mapping of a 65-bp 5'-UTR region and transposase co-expression\",\n      \"pmids\": [\"18071335\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Whether HMGXB4 binds the 65-bp element directly or via a partner not established\", \"Endogenous physiological targets analogous to this element unknown\"]\n    },\n    {\n      \"year\": 2010,\n      \"claim\": \"Defined a concrete repression mechanism in vascular biology by showing HMGXB4 disrupts the SRF-myocardin complex to suppress smooth muscle differentiation.\",\n      \"evidence\": \"GST pulldown domain mapping, reciprocal overexpression/siRNA in smooth muscle cells, and ChIP of smooth muscle gene promoters\",\n      \"pmids\": [\"20511232\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"In vivo role in vascular development or disease not addressed in this study\", \"Structural basis of myocardin N-terminal interaction not solved\"]\n    },\n    {\n      \"year\": 2021,\n      \"claim\": \"Established HMGXB4 as a direct proinflammatory transcriptional activator in vivo, identifying Nos2 and Icam1 as physiological promoter targets and linking the gene to sepsis pathology.\",\n      \"evidence\": \"Hmgxb4 knockout mice in LPS and CLP models, transcriptome profiling integrated with ChIP-seq, pharmacological NOS2 inhibition, and vascular permeability assays\",\n      \"pmids\": [\"33563757\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"DNA-binding specificity/consensus motif not defined\", \"Cofactors enabling promoter activation not identified\", \"Relationship between inflammatory and smooth-muscle/Wnt functions unresolved\"]\n    },\n    {\n      \"year\": 2023,\n      \"claim\": \"Mapped the regulatory architecture controlling HMGXB4 itself, showing ERK2/ELK1 activation, KRAB-ZNF/TRIM28 repression, and SUMOylation-dependent nucleolar compartmentalization tune its activity.\",\n      \"evidence\": \"Reporter assays, ChIP, SUMOylation assays, subcellular localization experiments, and expression profiling in stem cells\",\n      \"pmids\": [\"37108449\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"SUMOylation sites and SUMO-dependent partner switches not enumerated\", \"Several conclusions integrate prior published datasets rather than new direct assays\", \"Functional consequence of nucleolar sequestration on target genes not quantified\"]\n    },\n    {\n      \"year\": 2024,\n      \"claim\": \"Provided in vivo expression and localization context, confirming HMGXB4 is a broadly expressed nuclear protein induced by arterial injury.\",\n      \"evidence\": \"lacZ gene-trap knock-in reporter mouse with beta-galactosidase staining across tissues and an arterial injury model\",\n      \"pmids\": [\"38644513\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Causal role of injury-induced expression in vascular remodeling not tested\", \"Cell-type-specific function during injury not resolved\"]\n    },\n    {\n      \"year\": null,\n      \"claim\": \"How HMGXB4 reconciles its activator and repressor activities across inflammation, smooth muscle differentiation, and Wnt signaling — and what determines its DNA-binding specificity — remains unresolved.\",\n      \"evidence\": \"\",\n      \"pmids\": [],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"No defined DNA consensus motif\", \"No structural model of HMG-box DNA engagement or partner complexes\", \"Integration of upstream regulation with context-specific target selection unknown\"]\n    }\n  ],\n  \"mechanism_profile\": {\n    \"molecular_activity\": [\n      {\"term_id\": \"GO:0140110\", \"supporting_discovery_ids\": [0, 1, 2, 3, 4]},\n      {\"term_id\": \"GO:0003677\", \"supporting_discovery_ids\": [2, 3]}\n    ],\n    \"localization\": [\n      {\"term_id\": \"GO:0005634\", \"supporting_discovery_ids\": [5]},\n      {\"term_id\": \"GO:0005730\", \"supporting_discovery_ids\": [4]}\n    ],\n    \"pathway\": [\n      {\"term_id\": \"R-HSA-168256\", \"supporting_discovery_ids\": [3]},\n      {\"term_id\": \"R-HSA-74160\", \"supporting_discovery_ids\": [2, 3]},\n      {\"term_id\": \"R-HSA-162582\", \"supporting_discovery_ids\": [0]}\n    ],\n    \"complexes\": [],\n    \"partners\": [\"NLK\", \"MYOCD\", \"SRF\", \"TRIM28\", \"ELK1\", \"MAPK1\"],\n    \"other_free_text\": []\n  }\n}","audit_flag":null,"evaluation":{"pairwise":"win","faith_supported":4,"faith_total":5,"faith_pct":80.0}}