{"gene":"PBX2","run_date":"2026-06-10T05:19:53","timeline":{"discoveries":[{"year":1991,"finding":"PBX2 encodes a homeodomain protein with 92% identity to PBX1 over a 266-amino acid region spanning and flanking the homeodomain; unlike PBX1 and PBX3, PBX2 mRNA is not alternatively spliced.","method":"cDNA cloning, sequence analysis, Northern blotting","journal":"Molecular and cellular biology","confidence":"High","confidence_rationale":"Tier 1 / Strong — direct sequence and structural characterization, replicated across subsequent work","pmids":["1682799"],"is_preprint":false},{"year":1995,"finding":"PBX2 binds cooperatively to DNA with Hoxb-7 and Hoxb-8; the Hox hexapeptide and its linker to the homeodomain are required for this cooperative DNA binding with PBX1 and PBX2.","method":"Electrophoretic mobility shift assay (EMSA), in vitro DNA binding assays, deletion mutagenesis of hexapeptide and linker","journal":"Proceedings of the National Academy of Sciences of the United States of America; Mechanisms of development","confidence":"High","confidence_rationale":"Tier 1 / Strong — reconstituted in vitro cooperative binding, confirmed by mutagenesis, replicated in two independent papers","pmids":["7568094","7577680"],"is_preprint":false},{"year":1999,"finding":"In myeloid cells, PBX2 forms trimeric complexes with HOXA9 and MEIS1; MEIS1 enhances HOXA9-PBX2 complex formation in the absence of DNA, and all three proteins co-immunoprecipitate from myeloid nuclear extracts and co-localize in nuclear speckles.","method":"EMSA, co-immunoprecipitation from cell extracts, nuclear fractionation, immunofluorescence colocalization","journal":"Molecular and cellular biology","confidence":"High","confidence_rationale":"Tier 2 / Strong — reciprocal Co-IP from endogenous nuclear extracts combined with EMSA and colocalization, multiple orthogonal methods","pmids":["10082572"],"is_preprint":false},{"year":2002,"finding":"A PBX2-containing complex (also including PREP1) binds a specific regulatory element (PRE-1048) in the HOX11 promoter and activates HOX11 transcription in K562 cells, representing the first report of a homeobox gene regulated specifically by PBX2.","method":"Reporter gene assays, EMSA/DNA binding assays, promoter deletion analysis","journal":"Biochemical and biophysical research communications","confidence":"Medium","confidence_rationale":"Tier 2 / Weak — functional reporter assay with EMSA, single lab, single study","pmids":["12054735"],"is_preprint":false},{"year":2002,"finding":"A PBX2-PREP1 heterodimer binds the UGT2B17 promoter Pbx site and interferes with HNF1α binding to an adjacent site, thereby down-regulating HNF1α-mediated transcriptional activation of UGT2B17.","method":"Gel shift assays (EMSA), promoter-reporter functional assays, competition binding experiments","journal":"Molecular pharmacology","confidence":"Medium","confidence_rationale":"Tier 2 / Weak — EMSA and functional reporter assay, single lab, single study","pmids":["12065766"],"is_preprint":false},{"year":2003,"finding":"PREP1 overexpression stabilizes PBX2 protein by preventing its proteasomal degradation; dimerization with PREP1 protects PBX2 from proteasome-dependent decay, thereby increasing PBX2-PREP1 DNA binding activity.","method":"Cycloheximide chase assay, proteasome inhibitor (MG132) treatment, immunoblotting, DNA binding (EMSA) in stable transfectants","journal":"The Journal of biological chemistry","confidence":"High","confidence_rationale":"Tier 1 / Moderate — protein stability assay with cycloheximide and MG132, multiple orthogonal methods in single lab","pmids":["12871956"],"is_preprint":false},{"year":2004,"finding":"Retinoic acid (RA) induces PBX2 mRNA as a primary response (not requiring new protein synthesis) in a RAR-dependent manner, and RA treatment extends the half-life of PBX2 protein, at least partly through increased association with MEIS proteins and decreased proteasomal degradation.","method":"Northern blotting, protein stability assay, cycloheximide and transcription inhibitor treatment, immunoblotting in P19 cells","journal":"Journal of cellular biochemistry","confidence":"Medium","confidence_rationale":"Tier 2 / Weak — multiple methods (mRNA kinetics, protein stability) in single lab with P19 cell model","pmids":["15095411"],"is_preprint":false},{"year":2004,"finding":"Pbx2 is functionally redundant with Pbx1 in mouse development; Pbx2-null mice are viable and fertile with no detectable developmental abnormalities, but Pbx2 is the predominant high-MW Pbx isoform in postnatal bone marrow and thymus.","method":"Genetic knockout (Pbx2−/− mice), immunoblotting, histological and hematopoietic analysis","journal":"Molecular and cellular biology","confidence":"High","confidence_rationale":"Tier 2 / Strong — clean knockout mouse with thorough phenotypic characterization including hematopoiesis and development","pmids":["15169896"],"is_preprint":false},{"year":2006,"finding":"Pbx1 and Pbx2 are co-expressed in lateral plate and early limb field mesoderm; compound loss-of-function (Pbx1−/−; Pbx2+/−) reveals that Pbx1/Pbx2 are required for distal limb patterning via hierarchical control of Hox gene spatial distribution and Shh expression in the ZPA.","method":"Genetic loss-of-function mouse model (compound mutants), in situ hybridization, gene expression analysis","journal":"Development (Cambridge, England)","confidence":"High","confidence_rationale":"Tier 2 / Strong — epistasis established through compound genetic mutants with defined molecular readouts (Hox expression, Shh), multiple genotypes tested","pmids":["16672333"],"is_preprint":false},{"year":2008,"finding":"Pbx1/Pbx2 govern axial skeletal patterning by genetically controlling Polycomb and Hox expression/distribution in paraxial mesoderm and Pax1/Pax9 expression in sclerotome; decreasing Pbx2 dosage in Pbx1-null background severely worsens vertebral column identity loss.","method":"Compound genetic loss-of-function mouse model, in situ hybridization, immunohistochemistry","journal":"Developmental biology","confidence":"High","confidence_rationale":"Tier 2 / Strong — epistasis via compound genetic mutants, multiple molecular readouts (Polycomb, Hox, Pax1/Pax9 expression)","pmids":["18691704"],"is_preprint":false},{"year":2008,"finding":"Prep1/Pbx2 complexes preferentially bind the -2578 G allele of the CCL2 promoter and suppress basal CCL2 transcription; upon IL-1β stimulation, the complex maintains binding but does not suppress inducible transcription, resulting in higher fold induction from G allele promoters.","method":"EMSA, promoter-reporter functional assays, allele-specific binding experiments in astrocyte cell lines","journal":"Genes and immunity","confidence":"Medium","confidence_rationale":"Tier 2 / Weak — EMSA and functional reporter assay, allele-specific binding, single lab","pmids":["18480829"],"is_preprint":false},{"year":2013,"finding":"The HOXB7/PBX2 dimer acts as a positive transcriptional regulator of miR-221 and miR-222 in melanoma; abrogation of HOXB7/PBX2 dimerization (using the HXR9 peptide antagonist) reduces miR-221/222 transcription and elevates c-FOS expression, leading to cell death.","method":"HOX/PBX dimerization antagonist (HXR9) treatment, luciferase reporter assays, miRNA expression analysis, apoptosis assays","journal":"International journal of cancer","confidence":"Medium","confidence_rationale":"Tier 2 / Weak — functional reporter and pharmacological disruption in single lab, mechanistic chain established but relies on peptide inhibitor","pmids":["23400877"],"is_preprint":false},{"year":2015,"finding":"PBX2 is a direct post-transcriptional target of miR-1915-3p; miR-1915-3p binds the 3′-UTR of PBX2 mRNA, reduces PBX2 mRNA and protein levels, and knockdown of PBX2 contributes to the anti-apoptotic effect of miR-1915-3p in lung cancer cells.","method":"3′-UTR luciferase reporter assay, miRNA overexpression/rescue experiments, immunoblotting in lung cancer cell lines","journal":"Molecular medicine reports","confidence":"Medium","confidence_rationale":"Tier 2 / Weak — 3′-UTR reporter plus rescue experiment, single lab, single study","pmids":["26572100"],"is_preprint":false},{"year":2021,"finding":"HOXA6 physically interacts with PBX2 and stabilizes PBX2 protein in gastric cancer cells; co-expression of HOXA6 and PBX2 promotes migration and invasion in vitro and enhances metastasis in vivo.","method":"Co-immunoprecipitation, siRNA knockdown, overexpression, in vitro migration/invasion assays, orthotopic mouse model","journal":"Aging","confidence":"Medium","confidence_rationale":"Tier 2 / Weak — Co-IP with functional follow-up, single lab, single study","pmids":["33535170"],"is_preprint":false},{"year":2021,"finding":"PBX2 transcriptionally activates circTLK1 expression in glioma cells, which in turn activates JAK/STAT signaling via the miR-452-5p/SSR1 axis to promote glioma progression.","method":"ChIP assay (or promoter binding), RNA pull-down, AGO2-RIP, luciferase reporter, knockdown experiments in glioma cells","journal":"Frontiers in genetics","confidence":"Low","confidence_rationale":"Tier 3 / Weak — single lab, upstream transcriptional role of PBX2 on circRNA inferred from reporter and knockdown, limited direct mechanistic validation of PBX2 binding","pmids":["34721518"],"is_preprint":false},{"year":2023,"finding":"PBX2, but not other PBX family members, is specifically dephosphorylated downstream of mTORC1 activity; GSK3 is the kinase responsible for PBX2 phosphorylation and PP1 is the phosphatase responsible for its dephosphorylation, with their antagonistic activities determining PBX2 phosphorylation status.","method":"Large-scale phosphoproteomics re-analysis, pharmacological inhibition of mTORC1 (rapamycin), GSK3, and PP1, gene knockdown experiments, immunoblotting with phospho-specific readout","journal":"Journal of biochemistry","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — phosphoproteomics plus pharmacological and genetic confirmation, multiple orthogonal approaches in single lab","pmids":["36477205"],"is_preprint":false},{"year":2023,"finding":"HOXB9 interacts with PBX2 to form a heterodimer that transcriptionally upregulates CDK6 in gastric cancer cells; this HOXB9/PBX2 complex drives G1-phase cell cycle progression and cytoskeletal organization downstream of E2F1.","method":"Co-immunoprecipitation, ChIP assay, reporter assays, siRNA knockdown, cell cycle analysis in gastric cancer cell lines","journal":"The Journal of pathology","confidence":"Medium","confidence_rationale":"Tier 2 / Weak — Co-IP and ChIP with functional knockdown, single lab, single study","pmids":["37272544"],"is_preprint":false}],"current_model":"PBX2 is a TALE-class homeodomain transcription factor that functions primarily as a DNA-binding cofactor, forming heterodimers with PREP1/MEIS proteins (which protect it from proteasomal degradation) and cooperative complexes with HOX proteins (requiring the HOX hexapeptide-linker) to regulate target gene transcription; its phosphorylation state is governed by the antagonistic actions of GSK3 (kinase) and PP1 (phosphatase) downstream of mTORC1, and compound loss-of-function with Pbx1 in mice establishes essential roles in limb and axial skeletal patterning through hierarchical control of Hox, Polycomb, Shh, and Pax gene expression."},"narrative":{"mechanistic_narrative":"PBX2 is a TALE-class homeodomain transcription factor that functions as a DNA-binding cofactor, regulating target gene expression through combinatorial complexes with HOX and PREP1/MEIS partners [PMID:1682799, PMID:7568094, PMID:7577680, PMID:10082572]. It binds DNA cooperatively with HOX proteins (including Hoxb-7, Hoxb-8, and HOXA9) in a manner that requires the HOX hexapeptide and its linker to the homeodomain [PMID:7568094, PMID:7577680], and forms higher-order trimeric complexes with HOXA9 and MEIS1 that co-localize in nuclear speckles [PMID:10082572]. Dimerization with PREP1 stabilizes PBX2 by preventing its proteasomal degradation, thereby increasing its DNA-binding activity; retinoic acid induces PBX2 as a primary transcriptional response and further extends PBX2 protein half-life via increased MEIS association [PMID:12871956, PMID:15095411]. Through these complexes PBX2 directly regulates transcription of target promoters, acting either as an activator (HOX11) or as a repressor that interferes with neighboring factor binding (UGT2B17, CCL2) [PMID:12054735, PMID:12065766, PMID:18480829]. Genetic analysis in mice establishes that PBX2 is functionally redundant with PBX1: Pbx2-null mice are viable and normal, but compound loss with Pbx1 reveals essential roles in distal limb and axial skeletal patterning through hierarchical control of Hox, Polycomb, Shh, and Pax1/Pax9 gene expression [PMID:15169896, PMID:16672333, PMID:18691704]. PBX2 phosphorylation is set by the antagonistic activities of GSK3 (kinase) and PP1 (phosphatase) downstream of mTORC1 [PMID:36477205]. In cancer, HOX/PBX2 dimers drive pro-tumorigenic transcriptional programs in melanoma, gastric cancer, and other contexts [PMID:23400877, PMID:33535170, PMID:37272544].","teleology":[{"year":1991,"claim":"Establishing that PBX2 is a distinct homeodomain protein closely related to PBX1 defined it as a candidate DNA-binding transcription factor and member of a multigene family.","evidence":"cDNA cloning, sequence analysis, and Northern blotting","pmids":["1682799"],"confidence":"High","gaps":["Did not define DNA-binding partners or target genes","No functional or in vivo role established"]},{"year":1995,"claim":"Demonstrating cooperative DNA binding with HOX proteins answered how PBX2 achieves binding specificity and identified the HOX hexapeptide-linker as the docking determinant.","evidence":"EMSA and deletion mutagenesis of the HOX hexapeptide and linker in vitro","pmids":["7568094","7577680"],"confidence":"High","gaps":["In vitro binding only; cellular target genes not identified","Did not address higher-order complex composition"]},{"year":1999,"claim":"Identifying trimeric PBX2-HOXA9-MEIS1 complexes in myeloid cells showed PBX2 operates within multimeric assemblies and that MEIS1 promotes complex formation independent of DNA.","evidence":"EMSA, reciprocal Co-IP from endogenous myeloid nuclear extracts, and immunofluorescence colocalization in nuclear speckles","pmids":["10082572"],"confidence":"High","gaps":["Direct transcriptional targets of the trimeric complex not defined","Functional consequence in hematopoiesis not tested here"]},{"year":2002,"claim":"Linking PBX2-PREP1 complexes to specific promoters established PBX2 as both an activator and a repressor depending on context.","evidence":"Reporter assays, EMSA, and competition binding on HOX11 and UGT2B17 promoters","pmids":["12054735","12065766"],"confidence":"Medium","gaps":["Single-lab functional reporter studies","Endogenous regulation not confirmed in vivo"]},{"year":2003,"claim":"Showing PREP1 stabilizes PBX2 against proteasomal degradation answered how PBX2 abundance and DNA-binding activity are controlled post-translationally.","evidence":"Cycloheximide chase, MG132 treatment, immunoblotting, and EMSA in stable transfectants","pmids":["12871956"],"confidence":"High","gaps":["E3 ligase and degradation signal not identified","Mechanism by which dimerization shields PBX2 unresolved"]},{"year":2004,"claim":"Defining PBX2 as a primary retinoic-acid-inducible gene whose protein is stabilized by MEIS association connected PBX2 to RA signaling and reinforced the partner-dependent stability model.","evidence":"Northern blotting, protein stability and inhibitor assays in P19 cells","pmids":["15095411"],"confidence":"Medium","gaps":["RARE in the PBX2 promoter not mapped","Single cell-model system"]},{"year":2004,"claim":"The Pbx2 knockout revealed functional redundancy with Pbx1, showing PBX2 alone is dispensable for development despite being the predominant high-MW Pbx isoform in bone marrow and thymus.","evidence":"Pbx2-null mice with histological and hematopoietic characterization and immunoblotting","pmids":["15169896"],"confidence":"High","gaps":["Redundant partner identity inferred but not directly tested here","Tissue-specific roles masked by compensation"]},{"year":2006,"claim":"Compound Pbx1/Pbx2 mutants established an essential, dosage-sensitive role in distal limb patterning via hierarchical control of Hox spatial distribution and Shh in the ZPA.","evidence":"Compound loss-of-function mouse genetics with in situ hybridization","pmids":["16672333"],"confidence":"High","gaps":["Direct PBX2 target promoters in limb mesoderm not identified","Separation of PBX1 vs PBX2 contributions limited"]},{"year":2008,"claim":"Extending the genetic analysis to axial skeleton showed Pbx1/Pbx2 control Polycomb, Hox, and Pax1/Pax9 expression, placing PBX upstream of vertebral identity programs.","evidence":"Compound genetic mutants with in situ hybridization and immunohistochemistry","pmids":["18691704"],"confidence":"High","gaps":["Direct vs indirect regulation of Polycomb/Pax genes not distinguished","Binding sites not mapped"]},{"year":2008,"claim":"Allele-specific Prep1/Pbx2 binding at the CCL2 promoter demonstrated PBX2 can act as a basal repressor whose activity is sensitive to promoter polymorphism and inflammatory stimulation.","evidence":"EMSA, allele-specific binding, and reporter assays in astrocyte lines","pmids":["18480829"],"confidence":"Medium","gaps":["Endogenous CCL2 regulation by PBX2 not confirmed","Single-lab study"]},{"year":2013,"claim":"Pharmacological disruption of HOXB7/PBX2 dimers in melanoma linked the complex to miR-221/222 transcription and survival, implicating PBX2 in tumor cell viability.","evidence":"HXR9 antagonist treatment, luciferase reporters, miRNA expression, and apoptosis assays","pmids":["23400877"],"confidence":"Medium","gaps":["Relies on peptide inhibitor specificity","Direct PBX2 binding at miR-221/222 loci not shown"]},{"year":2015,"claim":"Identifying PBX2 as a miR-1915-3p target showed PBX2 levels are post-transcriptionally regulated and contribute to apoptosis control in lung cancer.","evidence":"3'-UTR luciferase reporter and miRNA rescue experiments in lung cancer lines","pmids":["26572100"],"confidence":"Medium","gaps":["Single study","Downstream transcriptional effectors of PBX2 in this context not defined"]},{"year":2021,"claim":"Demonstrating HOXA6-mediated stabilization of PBX2 driving gastric cancer metastasis reinforced the partner-dependent stability theme in a tumorigenic setting.","evidence":"Co-IP, knockdown/overexpression, migration/invasion assays, and orthotopic mouse model","pmids":["33535170"],"confidence":"Medium","gaps":["Stabilization mechanism not molecularly resolved","Single-lab study"]},{"year":2021,"claim":"PBX2 was placed upstream of a circTLK1/JAK-STAT axis in glioma, extending its transcriptional reach to non-coding RNA targets.","evidence":"ChIP/promoter binding, RNA pull-down, AGO2-RIP, reporters, and knockdown in glioma cells","pmids":["34721518"],"confidence":"Low","gaps":["Limited direct validation of PBX2 binding at the circTLK1 locus","Single-lab, inferred upstream role"]},{"year":2023,"claim":"Identifying GSK3 and PP1 as the antagonistic kinase/phosphatase acting downstream of mTORC1 defined a specific signaling input controlling PBX2 phosphorylation, uniquely among PBX members.","evidence":"Phosphoproteomics re-analysis with rapamycin, GSK3, and PP1 inhibition plus knockdowns and phospho-immunoblotting","pmids":["36477205"],"confidence":"Medium","gaps":["Functional consequence of phosphorylation on PBX2 activity not established","Phosphosite-resolved effects on DNA binding/complex formation unknown"]},{"year":2023,"claim":"The HOXB9/PBX2 dimer was shown to transcriptionally activate CDK6 and drive G1 progression, connecting PBX2 to cell-cycle control in gastric cancer.","evidence":"Co-IP, ChIP, reporter assays, knockdown, and cell cycle analysis in gastric cancer lines","pmids":["37272544"],"confidence":"Medium","gaps":["Single-lab study","Generality across cancers not tested"]},{"year":null,"claim":"How PBX2 phosphorylation status mechanistically alters its DNA binding, partner selection, or transcriptional output remains unresolved.","evidence":"","pmids":[],"confidence":"Medium","gaps":["No phosphosite-to-function link established","Genome-wide PBX2 binding landscape not defined","Direct target gene catalog incomplete"]}],"mechanism_profile":{"molecular_activity":[{"term_id":"GO:0140110","term_label":"transcription regulator activity","supporting_discovery_ids":[3,4,10,16]},{"term_id":"GO:0003677","term_label":"DNA binding","supporting_discovery_ids":[1,2,10]}],"localization":[{"term_id":"GO:0005634","term_label":"nucleus","supporting_discovery_ids":[2]}],"pathway":[{"term_id":"R-HSA-74160","term_label":"Gene expression (Transcription)","supporting_discovery_ids":[3,4,10,16]},{"term_id":"R-HSA-1266738","term_label":"Developmental Biology","supporting_discovery_ids":[8,9]}],"complexes":["PBX2-PREP1 heterodimer","PBX2-HOXA9-MEIS1 trimeric complex"],"partners":["PREP1","MEIS1","HOXA9","HOXB7","HOXB9","HOXA6","PBX1","GSK3"],"other_free_text":[]}},"prefetch_data":{"uniprot":{"accession":"P40425","full_name":"Pre-B-cell leukemia transcription factor 2","aliases":["Homeobox protein PBX2","Protein G17"],"length_aa":430,"mass_kda":45.9,"function":"Transcriptional activator that binds the sequence 5'-ATCAATCAA-3'. Activates transcription of PF4 in complex with MEIS1","subcellular_location":"Nucleus","url":"https://www.uniprot.org/uniprotkb/P40425/entry"},"depmap":{"release":"DepMap","has_data":true,"is_common_essential":false,"resolved_as":"","url":"https://depmap.org/portal/gene/PBX2","classification":"Not Classified","n_dependent_lines":105,"n_total_lines":1208,"dependency_fraction":0.0869205298013245},"opencell":{"profiled":false,"resolved_as":"","ensg_id":"","cell_line_id":"","localizations":[],"interactors":[],"url":"https://opencell.sf.czbiohub.org/search/PBX2","total_profiled":1310},"omim":[{"mim_id":"618774","title":"CEBALID SYNDROME; CEBALID","url":"https://www.omim.org/entry/618774"},{"mim_id":"603099","title":"1-@ACYLGLYCEROL-3-PHOSPHATE O-ACYLTRANSFERASE 1; AGPAT1","url":"https://www.omim.org/entry/603099"},{"mim_id":"602100","title":"PBX/KNOTTED 1 HOMEOBOX 1; PKNOX1","url":"https://www.omim.org/entry/602100"},{"mim_id":"600214","title":"ADVANCED GLYCOSYLATION END PRODUCT-SPECIFIC RECEPTOR; AGER","url":"https://www.omim.org/entry/600214"},{"mim_id":"176312","title":"PRE-B-CELL LEUKEMIA TRANSCRIPTION FACTOR 3; PBX3","url":"https://www.omim.org/entry/176312"}],"hpa":{"profiled":true,"resolved_as":"","reliability":"Supported","locations":[{"location":"Nucleoplasm","reliability":"Supported"}],"tissue_specificity":"Low tissue specificity","tissue_distribution":"Detected in all","driving_tissues":[],"url":"https://www.proteinatlas.org/search/PBX2"},"hgnc":{"alias_symbol":["G17","HOX12","PBX2MHC"],"prev_symbol":[]},"alphafold":{"accession":"P40425","domains":[{"cath_id":"-","chopping":"65-99","consensus_level":"medium","plddt":85.7274,"start":65,"end":99},{"cath_id":"-","chopping":"112-129_153-245","consensus_level":"high","plddt":89.6593,"start":112,"end":245},{"cath_id":"1.10.10.60","chopping":"252-323","consensus_level":"high","plddt":93.0199,"start":252,"end":323}],"viewer_url":"https://alphafold.ebi.ac.uk/entry/P40425","model_url":"https://alphafold.ebi.ac.uk/files/AF-P40425-F1-model_v6.cif","pae_url":"https://alphafold.ebi.ac.uk/files/AF-P40425-F1-predicted_aligned_error_v6.png","plddt_mean":69.06},"mouse_models":{"mgi_url":"https://www.informatics.jax.org/marker/summary?nomen=PBX2","jax_strain_url":"https://www.jax.org/strain/search?query=PBX2"},"sequence":{"accession":"P40425","fasta_url":"https://rest.uniprot.org/uniprotkb/P40425.fasta","uniprot_url":"https://www.uniprot.org/uniprotkb/P40425/entry","alphafold_viewer_url":"https://alphafold.ebi.ac.uk/entry/P40425"}},"corpus_meta":[{"pmid":"1682799","id":"PMC_1682799","title":"PBX2 and PBX3, new homeobox genes with extensive homology to the human proto-oncogene PBX1.","date":"1991","source":"Molecular and cellular biology","url":"https://pubmed.ncbi.nlm.nih.gov/1682799","citation_count":272,"is_preprint":false},{"pmid":"7835890","id":"PMC_7835890","title":"Three genes in the human MHC class III region near the junction with the class II: gene for receptor of advanced glycosylation end products, PBX2 homeobox gene and a notch homolog, human counterpart of mouse mammary tumor gene int-3.","date":"1994","source":"Genomics","url":"https://pubmed.ncbi.nlm.nih.gov/7835890","citation_count":211,"is_preprint":false},{"pmid":"10082572","id":"PMC_10082572","title":"HOXA9 forms triple complexes with PBX2 and MEIS1 in myeloid cells.","date":"1999","source":"Molecular and cellular biology","url":"https://pubmed.ncbi.nlm.nih.gov/10082572","citation_count":206,"is_preprint":false},{"pmid":"16672333","id":"PMC_16672333","title":"Pbx1/Pbx2 requirement for distal limb patterning 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survival.","date":"2004","source":"Molecular and cellular biology","url":"https://pubmed.ncbi.nlm.nih.gov/15169896","citation_count":75,"is_preprint":false},{"pmid":"26977084","id":"PMC_26977084","title":"Rice HOX12 Regulates Panicle Exsertion by Directly Modulating the Expression of ELONGATED UPPERMOST INTERNODE1.","date":"2016","source":"The Plant cell","url":"https://pubmed.ncbi.nlm.nih.gov/26977084","citation_count":74,"is_preprint":false},{"pmid":"23400877","id":"PMC_23400877","title":"The abrogation of the HOXB7/PBX2 complex induces apoptosis in melanoma through the miR-221&222-c-FOS pathway.","date":"2013","source":"International journal of cancer","url":"https://pubmed.ncbi.nlm.nih.gov/23400877","citation_count":55,"is_preprint":false},{"pmid":"15095411","id":"PMC_15095411","title":"Retinoic acid regulates the expression of PBX1, PBX2, and PBX3 in P19 cells both transcriptionally and post-translationally.","date":"2004","source":"Journal of cellular 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prevents the apoptosis of lung cancer cells by downregulating DRG2 and PBX2.","date":"2015","source":"Molecular medicine reports","url":"https://pubmed.ncbi.nlm.nih.gov/26572100","citation_count":12,"is_preprint":false},{"pmid":"33905146","id":"PMC_33905146","title":"Association of genomic variants at PAX8 and PBX2 with cervical cancer risk.","date":"2021","source":"International journal of cancer","url":"https://pubmed.ncbi.nlm.nih.gov/33905146","citation_count":11,"is_preprint":false},{"pmid":"34721518","id":"PMC_34721518","title":"PBX2-Mediated circTLK1 Activates JAK/STAT Signaling to Promote Gliomagenesis via miR-452-5p/SSR1 Axis.","date":"2021","source":"Frontiers in genetics","url":"https://pubmed.ncbi.nlm.nih.gov/34721518","citation_count":10,"is_preprint":false},{"pmid":"12054735","id":"PMC_12054735","title":"A complex containing PBX2 contributes to activation of the proto-oncogene HOX11.","date":"2002","source":"Biochemical and biophysical research communications","url":"https://pubmed.ncbi.nlm.nih.gov/12054735","citation_count":10,"is_preprint":false},{"pmid":"26852910","id":"PMC_26852910","title":"Variant of PBX2 gene in the 6p21.3 asthma susceptibility locus is associated with allergic rhinitis in Chinese subjects.","date":"2016","source":"International forum of allergy & rhinology","url":"https://pubmed.ncbi.nlm.nih.gov/26852910","citation_count":6,"is_preprint":false},{"pmid":"29160311","id":"PMC_29160311","title":"Microstructure variations induced by excess PbX2 or AX within perovskite thin films.","date":"2017","source":"Chemical communications (Cambridge, England)","url":"https://pubmed.ncbi.nlm.nih.gov/29160311","citation_count":4,"is_preprint":false},{"pmid":"36477205","id":"PMC_36477205","title":"Phosphorylation of PBX2, a novel downstream target of mTORC1, is determined by GSK3 and PP1.","date":"2023","source":"Journal of biochemistry","url":"https://pubmed.ncbi.nlm.nih.gov/36477205","citation_count":1,"is_preprint":false},{"pmid":null,"id":"bio_10.1101_2025.01.02.25319933","title":"Identifying Potential Drug Targets for Prostate Cancer from a Genetic Perspective: A Mendelian Randomization Study","date":"2025-01-03","source":"bioRxiv","url":"https://doi.org/10.1101/2025.01.02.25319933","citation_count":0,"is_preprint":true}],"cost":{"stage1":{"model":"claude-sonnet-4-6","input_tokens":15129,"output_tokens":3825,"usd":0.051381,"stage1_stop_reason":"end_turn"},"stage2":{"model":"claude-opus-4-8","input_tokens":11508,"output_tokens":4486,"usd":0.084845,"stage2_stop_reason":"end_turn"},"total_usd":0.136226,"stage1_batch_id":"msgbatch_013a8chtv3AWyTqv4z4sEF4C","stage2_batch_id":"msgbatch_01AHsuW63vinsvuTgzmQ3n62","note":"batch pricing = 50% of standard"},"stage1_raw":"```json\n{\n  \"discoveries\": [\n    {\n      \"year\": 1991,\n      \"finding\": \"PBX2 encodes a homeodomain protein with 92% identity to PBX1 over a 266-amino acid region spanning and flanking the homeodomain; unlike PBX1 and PBX3, PBX2 mRNA is not alternatively spliced.\",\n      \"method\": \"cDNA cloning, sequence analysis, Northern blotting\",\n      \"journal\": \"Molecular and cellular biology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Strong — direct sequence and structural characterization, replicated across subsequent work\",\n      \"pmids\": [\"1682799\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1995,\n      \"finding\": \"PBX2 binds cooperatively to DNA with Hoxb-7 and Hoxb-8; the Hox hexapeptide and its linker to the homeodomain are required for this cooperative DNA binding with PBX1 and PBX2.\",\n      \"method\": \"Electrophoretic mobility shift assay (EMSA), in vitro DNA binding assays, deletion mutagenesis of hexapeptide and linker\",\n      \"journal\": \"Proceedings of the National Academy of Sciences of the United States of America; Mechanisms of development\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Strong — reconstituted in vitro cooperative binding, confirmed by mutagenesis, replicated in two independent papers\",\n      \"pmids\": [\"7568094\", \"7577680\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1999,\n      \"finding\": \"In myeloid cells, PBX2 forms trimeric complexes with HOXA9 and MEIS1; MEIS1 enhances HOXA9-PBX2 complex formation in the absence of DNA, and all three proteins co-immunoprecipitate from myeloid nuclear extracts and co-localize in nuclear speckles.\",\n      \"method\": \"EMSA, co-immunoprecipitation from cell extracts, nuclear fractionation, immunofluorescence colocalization\",\n      \"journal\": \"Molecular and cellular biology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — reciprocal Co-IP from endogenous nuclear extracts combined with EMSA and colocalization, multiple orthogonal methods\",\n      \"pmids\": [\"10082572\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2002,\n      \"finding\": \"A PBX2-containing complex (also including PREP1) binds a specific regulatory element (PRE-1048) in the HOX11 promoter and activates HOX11 transcription in K562 cells, representing the first report of a homeobox gene regulated specifically by PBX2.\",\n      \"method\": \"Reporter gene assays, EMSA/DNA binding assays, promoter deletion analysis\",\n      \"journal\": \"Biochemical and biophysical research communications\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Weak — functional reporter assay with EMSA, single lab, single study\",\n      \"pmids\": [\"12054735\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2002,\n      \"finding\": \"A PBX2-PREP1 heterodimer binds the UGT2B17 promoter Pbx site and interferes with HNF1α binding to an adjacent site, thereby down-regulating HNF1α-mediated transcriptional activation of UGT2B17.\",\n      \"method\": \"Gel shift assays (EMSA), promoter-reporter functional assays, competition binding experiments\",\n      \"journal\": \"Molecular pharmacology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Weak — EMSA and functional reporter assay, single lab, single study\",\n      \"pmids\": [\"12065766\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2003,\n      \"finding\": \"PREP1 overexpression stabilizes PBX2 protein by preventing its proteasomal degradation; dimerization with PREP1 protects PBX2 from proteasome-dependent decay, thereby increasing PBX2-PREP1 DNA binding activity.\",\n      \"method\": \"Cycloheximide chase assay, proteasome inhibitor (MG132) treatment, immunoblotting, DNA binding (EMSA) in stable transfectants\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Moderate — protein stability assay with cycloheximide and MG132, multiple orthogonal methods in single lab\",\n      \"pmids\": [\"12871956\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2004,\n      \"finding\": \"Retinoic acid (RA) induces PBX2 mRNA as a primary response (not requiring new protein synthesis) in a RAR-dependent manner, and RA treatment extends the half-life of PBX2 protein, at least partly through increased association with MEIS proteins and decreased proteasomal degradation.\",\n      \"method\": \"Northern blotting, protein stability assay, cycloheximide and transcription inhibitor treatment, immunoblotting in P19 cells\",\n      \"journal\": \"Journal of cellular biochemistry\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Weak — multiple methods (mRNA kinetics, protein stability) in single lab with P19 cell model\",\n      \"pmids\": [\"15095411\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2004,\n      \"finding\": \"Pbx2 is functionally redundant with Pbx1 in mouse development; Pbx2-null mice are viable and fertile with no detectable developmental abnormalities, but Pbx2 is the predominant high-MW Pbx isoform in postnatal bone marrow and thymus.\",\n      \"method\": \"Genetic knockout (Pbx2−/− mice), immunoblotting, histological and hematopoietic analysis\",\n      \"journal\": \"Molecular and cellular biology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — clean knockout mouse with thorough phenotypic characterization including hematopoiesis and development\",\n      \"pmids\": [\"15169896\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2006,\n      \"finding\": \"Pbx1 and Pbx2 are co-expressed in lateral plate and early limb field mesoderm; compound loss-of-function (Pbx1−/−; Pbx2+/−) reveals that Pbx1/Pbx2 are required for distal limb patterning via hierarchical control of Hox gene spatial distribution and Shh expression in the ZPA.\",\n      \"method\": \"Genetic loss-of-function mouse model (compound mutants), in situ hybridization, gene expression analysis\",\n      \"journal\": \"Development (Cambridge, England)\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — epistasis established through compound genetic mutants with defined molecular readouts (Hox expression, Shh), multiple genotypes tested\",\n      \"pmids\": [\"16672333\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2008,\n      \"finding\": \"Pbx1/Pbx2 govern axial skeletal patterning by genetically controlling Polycomb and Hox expression/distribution in paraxial mesoderm and Pax1/Pax9 expression in sclerotome; decreasing Pbx2 dosage in Pbx1-null background severely worsens vertebral column identity loss.\",\n      \"method\": \"Compound genetic loss-of-function mouse model, in situ hybridization, immunohistochemistry\",\n      \"journal\": \"Developmental biology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — epistasis via compound genetic mutants, multiple molecular readouts (Polycomb, Hox, Pax1/Pax9 expression)\",\n      \"pmids\": [\"18691704\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2008,\n      \"finding\": \"Prep1/Pbx2 complexes preferentially bind the -2578 G allele of the CCL2 promoter and suppress basal CCL2 transcription; upon IL-1β stimulation, the complex maintains binding but does not suppress inducible transcription, resulting in higher fold induction from G allele promoters.\",\n      \"method\": \"EMSA, promoter-reporter functional assays, allele-specific binding experiments in astrocyte cell lines\",\n      \"journal\": \"Genes and immunity\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Weak — EMSA and functional reporter assay, allele-specific binding, single lab\",\n      \"pmids\": [\"18480829\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2013,\n      \"finding\": \"The HOXB7/PBX2 dimer acts as a positive transcriptional regulator of miR-221 and miR-222 in melanoma; abrogation of HOXB7/PBX2 dimerization (using the HXR9 peptide antagonist) reduces miR-221/222 transcription and elevates c-FOS expression, leading to cell death.\",\n      \"method\": \"HOX/PBX dimerization antagonist (HXR9) treatment, luciferase reporter assays, miRNA expression analysis, apoptosis assays\",\n      \"journal\": \"International journal of cancer\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Weak — functional reporter and pharmacological disruption in single lab, mechanistic chain established but relies on peptide inhibitor\",\n      \"pmids\": [\"23400877\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2015,\n      \"finding\": \"PBX2 is a direct post-transcriptional target of miR-1915-3p; miR-1915-3p binds the 3′-UTR of PBX2 mRNA, reduces PBX2 mRNA and protein levels, and knockdown of PBX2 contributes to the anti-apoptotic effect of miR-1915-3p in lung cancer cells.\",\n      \"method\": \"3′-UTR luciferase reporter assay, miRNA overexpression/rescue experiments, immunoblotting in lung cancer cell lines\",\n      \"journal\": \"Molecular medicine reports\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Weak — 3′-UTR reporter plus rescue experiment, single lab, single study\",\n      \"pmids\": [\"26572100\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2021,\n      \"finding\": \"HOXA6 physically interacts with PBX2 and stabilizes PBX2 protein in gastric cancer cells; co-expression of HOXA6 and PBX2 promotes migration and invasion in vitro and enhances metastasis in vivo.\",\n      \"method\": \"Co-immunoprecipitation, siRNA knockdown, overexpression, in vitro migration/invasion assays, orthotopic mouse model\",\n      \"journal\": \"Aging\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Weak — Co-IP with functional follow-up, single lab, single study\",\n      \"pmids\": [\"33535170\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2021,\n      \"finding\": \"PBX2 transcriptionally activates circTLK1 expression in glioma cells, which in turn activates JAK/STAT signaling via the miR-452-5p/SSR1 axis to promote glioma progression.\",\n      \"method\": \"ChIP assay (or promoter binding), RNA pull-down, AGO2-RIP, luciferase reporter, knockdown experiments in glioma cells\",\n      \"journal\": \"Frontiers in genetics\",\n      \"confidence\": \"Low\",\n      \"confidence_rationale\": \"Tier 3 / Weak — single lab, upstream transcriptional role of PBX2 on circRNA inferred from reporter and knockdown, limited direct mechanistic validation of PBX2 binding\",\n      \"pmids\": [\"34721518\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2023,\n      \"finding\": \"PBX2, but not other PBX family members, is specifically dephosphorylated downstream of mTORC1 activity; GSK3 is the kinase responsible for PBX2 phosphorylation and PP1 is the phosphatase responsible for its dephosphorylation, with their antagonistic activities determining PBX2 phosphorylation status.\",\n      \"method\": \"Large-scale phosphoproteomics re-analysis, pharmacological inhibition of mTORC1 (rapamycin), GSK3, and PP1, gene knockdown experiments, immunoblotting with phospho-specific readout\",\n      \"journal\": \"Journal of biochemistry\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — phosphoproteomics plus pharmacological and genetic confirmation, multiple orthogonal approaches in single lab\",\n      \"pmids\": [\"36477205\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2023,\n      \"finding\": \"HOXB9 interacts with PBX2 to form a heterodimer that transcriptionally upregulates CDK6 in gastric cancer cells; this HOXB9/PBX2 complex drives G1-phase cell cycle progression and cytoskeletal organization downstream of E2F1.\",\n      \"method\": \"Co-immunoprecipitation, ChIP assay, reporter assays, siRNA knockdown, cell cycle analysis in gastric cancer cell lines\",\n      \"journal\": \"The Journal of pathology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Weak — Co-IP and ChIP with functional knockdown, single lab, single study\",\n      \"pmids\": [\"37272544\"],\n      \"is_preprint\": false\n    }\n  ],\n  \"current_model\": \"PBX2 is a TALE-class homeodomain transcription factor that functions primarily as a DNA-binding cofactor, forming heterodimers with PREP1/MEIS proteins (which protect it from proteasomal degradation) and cooperative complexes with HOX proteins (requiring the HOX hexapeptide-linker) to regulate target gene transcription; its phosphorylation state is governed by the antagonistic actions of GSK3 (kinase) and PP1 (phosphatase) downstream of mTORC1, and compound loss-of-function with Pbx1 in mice establishes essential roles in limb and axial skeletal patterning through hierarchical control of Hox, Polycomb, Shh, and Pax gene expression.\"\n}\n```","stage2_raw":"{\n  \"mechanistic_narrative\": \"PBX2 is a TALE-class homeodomain transcription factor that functions as a DNA-binding cofactor, regulating target gene expression through combinatorial complexes with HOX and PREP1/MEIS partners [#0, #1, #2]. It binds DNA cooperatively with HOX proteins (including Hoxb-7, Hoxb-8, and HOXA9) in a manner that requires the HOX hexapeptide and its linker to the homeodomain [#1], and forms higher-order trimeric complexes with HOXA9 and MEIS1 that co-localize in nuclear speckles [#2]. Dimerization with PREP1 stabilizes PBX2 by preventing its proteasomal degradation, thereby increasing its DNA-binding activity; retinoic acid induces PBX2 as a primary transcriptional response and further extends PBX2 protein half-life via increased MEIS association [#5, #6]. Through these complexes PBX2 directly regulates transcription of target promoters, acting either as an activator (HOX11) or as a repressor that interferes with neighboring factor binding (UGT2B17, CCL2) [#3, #4, #10]. Genetic analysis in mice establishes that PBX2 is functionally redundant with PBX1: Pbx2-null mice are viable and normal, but compound loss with Pbx1 reveals essential roles in distal limb and axial skeletal patterning through hierarchical control of Hox, Polycomb, Shh, and Pax1/Pax9 gene expression [#7, #8, #9]. PBX2 phosphorylation is set by the antagonistic activities of GSK3 (kinase) and PP1 (phosphatase) downstream of mTORC1 [#15]. In cancer, HOX/PBX2 dimers drive pro-tumorigenic transcriptional programs in melanoma, gastric cancer, and other contexts [#11, #13, #16].\",\n  \"teleology\": [\n    {\n      \"year\": 1991,\n      \"claim\": \"Establishing that PBX2 is a distinct homeodomain protein closely related to PBX1 defined it as a candidate DNA-binding transcription factor and member of a multigene family.\",\n      \"evidence\": \"cDNA cloning, sequence analysis, and Northern blotting\",\n      \"pmids\": [\"1682799\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Did not define DNA-binding partners or target genes\", \"No functional or in vivo role established\"]\n    },\n    {\n      \"year\": 1995,\n      \"claim\": \"Demonstrating cooperative DNA binding with HOX proteins answered how PBX2 achieves binding specificity and identified the HOX hexapeptide-linker as the docking determinant.\",\n      \"evidence\": \"EMSA and deletion mutagenesis of the HOX hexapeptide and linker in vitro\",\n      \"pmids\": [\"7568094\", \"7577680\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"In vitro binding only; cellular target genes not identified\", \"Did not address higher-order complex composition\"]\n    },\n    {\n      \"year\": 1999,\n      \"claim\": \"Identifying trimeric PBX2-HOXA9-MEIS1 complexes in myeloid cells showed PBX2 operates within multimeric assemblies and that MEIS1 promotes complex formation independent of DNA.\",\n      \"evidence\": \"EMSA, reciprocal Co-IP from endogenous myeloid nuclear extracts, and immunofluorescence colocalization in nuclear speckles\",\n      \"pmids\": [\"10082572\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Direct transcriptional targets of the trimeric complex not defined\", \"Functional consequence in hematopoiesis not tested here\"]\n    },\n    {\n      \"year\": 2002,\n      \"claim\": \"Linking PBX2-PREP1 complexes to specific promoters established PBX2 as both an activator and a repressor depending on context.\",\n      \"evidence\": \"Reporter assays, EMSA, and competition binding on HOX11 and UGT2B17 promoters\",\n      \"pmids\": [\"12054735\", \"12065766\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Single-lab functional reporter studies\", \"Endogenous regulation not confirmed in vivo\"]\n    },\n    {\n      \"year\": 2003,\n      \"claim\": \"Showing PREP1 stabilizes PBX2 against proteasomal degradation answered how PBX2 abundance and DNA-binding activity are controlled post-translationally.\",\n      \"evidence\": \"Cycloheximide chase, MG132 treatment, immunoblotting, and EMSA in stable transfectants\",\n      \"pmids\": [\"12871956\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"E3 ligase and degradation signal not identified\", \"Mechanism by which dimerization shields PBX2 unresolved\"]\n    },\n    {\n      \"year\": 2004,\n      \"claim\": \"Defining PBX2 as a primary retinoic-acid-inducible gene whose protein is stabilized by MEIS association connected PBX2 to RA signaling and reinforced the partner-dependent stability model.\",\n      \"evidence\": \"Northern blotting, protein stability and inhibitor assays in P19 cells\",\n      \"pmids\": [\"15095411\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"RARE in the PBX2 promoter not mapped\", \"Single cell-model system\"]\n    },\n    {\n      \"year\": 2004,\n      \"claim\": \"The Pbx2 knockout revealed functional redundancy with Pbx1, showing PBX2 alone is dispensable for development despite being the predominant high-MW Pbx isoform in bone marrow and thymus.\",\n      \"evidence\": \"Pbx2-null mice with histological and hematopoietic characterization and immunoblotting\",\n      \"pmids\": [\"15169896\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Redundant partner identity inferred but not directly tested here\", \"Tissue-specific roles masked by compensation\"]\n    },\n    {\n      \"year\": 2006,\n      \"claim\": \"Compound Pbx1/Pbx2 mutants established an essential, dosage-sensitive role in distal limb patterning via hierarchical control of Hox spatial distribution and Shh in the ZPA.\",\n      \"evidence\": \"Compound loss-of-function mouse genetics with in situ hybridization\",\n      \"pmids\": [\"16672333\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Direct PBX2 target promoters in limb mesoderm not identified\", \"Separation of PBX1 vs PBX2 contributions limited\"]\n    },\n    {\n      \"year\": 2008,\n      \"claim\": \"Extending the genetic analysis to axial skeleton showed Pbx1/Pbx2 control Polycomb, Hox, and Pax1/Pax9 expression, placing PBX upstream of vertebral identity programs.\",\n      \"evidence\": \"Compound genetic mutants with in situ hybridization and immunohistochemistry\",\n      \"pmids\": [\"18691704\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Direct vs indirect regulation of Polycomb/Pax genes not distinguished\", \"Binding sites not mapped\"]\n    },\n    {\n      \"year\": 2008,\n      \"claim\": \"Allele-specific Prep1/Pbx2 binding at the CCL2 promoter demonstrated PBX2 can act as a basal repressor whose activity is sensitive to promoter polymorphism and inflammatory stimulation.\",\n      \"evidence\": \"EMSA, allele-specific binding, and reporter assays in astrocyte lines\",\n      \"pmids\": [\"18480829\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Endogenous CCL2 regulation by PBX2 not confirmed\", \"Single-lab study\"]\n    },\n    {\n      \"year\": 2013,\n      \"claim\": \"Pharmacological disruption of HOXB7/PBX2 dimers in melanoma linked the complex to miR-221/222 transcription and survival, implicating PBX2 in tumor cell viability.\",\n      \"evidence\": \"HXR9 antagonist treatment, luciferase reporters, miRNA expression, and apoptosis assays\",\n      \"pmids\": [\"23400877\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Relies on peptide inhibitor specificity\", \"Direct PBX2 binding at miR-221/222 loci not shown\"]\n    },\n    {\n      \"year\": 2015,\n      \"claim\": \"Identifying PBX2 as a miR-1915-3p target showed PBX2 levels are post-transcriptionally regulated and contribute to apoptosis control in lung cancer.\",\n      \"evidence\": \"3'-UTR luciferase reporter and miRNA rescue experiments in lung cancer lines\",\n      \"pmids\": [\"26572100\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Single study\", \"Downstream transcriptional effectors of PBX2 in this context not defined\"]\n    },\n    {\n      \"year\": 2021,\n      \"claim\": \"Demonstrating HOXA6-mediated stabilization of PBX2 driving gastric cancer metastasis reinforced the partner-dependent stability theme in a tumorigenic setting.\",\n      \"evidence\": \"Co-IP, knockdown/overexpression, migration/invasion assays, and orthotopic mouse model\",\n      \"pmids\": [\"33535170\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Stabilization mechanism not molecularly resolved\", \"Single-lab study\"]\n    },\n    {\n      \"year\": 2021,\n      \"claim\": \"PBX2 was placed upstream of a circTLK1/JAK-STAT axis in glioma, extending its transcriptional reach to non-coding RNA targets.\",\n      \"evidence\": \"ChIP/promoter binding, RNA pull-down, AGO2-RIP, reporters, and knockdown in glioma cells\",\n      \"pmids\": [\"34721518\"],\n      \"confidence\": \"Low\",\n      \"gaps\": [\"Limited direct validation of PBX2 binding at the circTLK1 locus\", \"Single-lab, inferred upstream role\"]\n    },\n    {\n      \"year\": 2023,\n      \"claim\": \"Identifying GSK3 and PP1 as the antagonistic kinase/phosphatase acting downstream of mTORC1 defined a specific signaling input controlling PBX2 phosphorylation, uniquely among PBX members.\",\n      \"evidence\": \"Phosphoproteomics re-analysis with rapamycin, GSK3, and PP1 inhibition plus knockdowns and phospho-immunoblotting\",\n      \"pmids\": [\"36477205\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Functional consequence of phosphorylation on PBX2 activity not established\", \"Phosphosite-resolved effects on DNA binding/complex formation unknown\"]\n    },\n    {\n      \"year\": 2023,\n      \"claim\": \"The HOXB9/PBX2 dimer was shown to transcriptionally activate CDK6 and drive G1 progression, connecting PBX2 to cell-cycle control in gastric cancer.\",\n      \"evidence\": \"Co-IP, ChIP, reporter assays, knockdown, and cell cycle analysis in gastric cancer lines\",\n      \"pmids\": [\"37272544\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Single-lab study\", \"Generality across cancers not tested\"]\n    },\n    {\n      \"year\": null,\n      \"claim\": \"How PBX2 phosphorylation status mechanistically alters its DNA binding, partner selection, or transcriptional output remains unresolved.\",\n      \"evidence\": \"\",\n      \"pmids\": [],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"No phosphosite-to-function link established\", \"Genome-wide PBX2 binding landscape not defined\", \"Direct target gene catalog incomplete\"]\n    }\n  ],\n  \"mechanism_profile\": {\n    \"molecular_activity\": [\n      {\"term_id\": \"GO:0140110\", \"supporting_discovery_ids\": [3, 4, 10, 16]},\n      {\"term_id\": \"GO:0003677\", \"supporting_discovery_ids\": [1, 2, 10]},\n      {\"term_id\": \"GO:0003700\", \"supporting_discovery_ids\": []}\n    ],\n    \"localization\": [\n      {\"term_id\": \"GO:0005634\", \"supporting_discovery_ids\": [2]}\n    ],\n    \"pathway\": [\n      {\"term_id\": \"R-HSA-74160\", \"supporting_discovery_ids\": [3, 4, 10, 16]},\n      {\"term_id\": \"R-HSA-1266738\", \"supporting_discovery_ids\": [8, 9]}\n    ],\n    \"complexes\": [\n      \"PBX2-PREP1 heterodimer\",\n      \"PBX2-HOXA9-MEIS1 trimeric complex\"\n    ],\n    \"partners\": [\n      \"PREP1\",\n      \"MEIS1\",\n      \"HOXA9\",\n      \"HOXB7\",\n      \"HOXB9\",\n      \"HOXA6\",\n      \"PBX1\",\n      \"GSK3\"\n    ],\n    \"other_free_text\": []\n  }\n}","audit_flag":null,"evaluation":{"pairwise":"win","faith_supported":7,"faith_total":7,"faith_pct":100.0}}