A TBX2-HLX Regulatory Axis Is Associated with Advanced Prostate Cancer.

Background: Homeobox transcription factors regulate developmental programs, cellular plasticity, and tumor progression, yet the role of H2.0-like homeobox (HLX) in prostate cancer (PCa) remains poorly defined. We investigated the clinical significance of HLX and its relationship to the pro-metastatic transcription factor TBX2. Methods: Transcriptomic and clinical datasets from TCGA, MET500, and SU2C/PCF cohorts were analyzed to assess HLX expression, clinicopathologic associations, and its relationship with TBX2. Functional studies in human PCa cell lines included TBX2 gain- and loss-of-function, HLX knockdown, chromatin immunoprecipitation (ChIP), and expression analyses. Shared HLX- and TBX2-associated pathways were evaluated by Reactome enrichment analysis, and Hallmark Gene Set Enrichment Analysis compared castration-resistant prostate cancer (CRPC) bone metastases with high versus low HLX expression (GSE77930; n = 5/group). In vivo relevance was assessed in an orthotopic TBX2 dominant-negative PCa xenograft model. Results: Human PCa datasets showed that HLX expression was elevated in PCa versus normal prostate tissue and associated with higher Gleason grade, lymph node involvement, aggressive molecular subtypes, and shorter disease-free survival. HLX expression also positively correlated with TBX2 across human PCa cohorts. HLX- and TBX2-associated transcriptional programs converged on extracellular matrix organization, cell adhesion, NOTCH, and VEGF-MAPK signaling pathways. Furthermore, HLX-high CRPC bone metastases were enriched for epithelial-mesenchymal transition, NOTCH, TGF-β, inflammatory, angiogenic, hypoxic, and KRAS signaling pathways. Mechanistic studies showed that HLX knockdown suppressed extracellular matrix-associated genes and key NOTCH pathway components. ChIP demonstrated direct TBX2 binding to the HLX promoter, and genetic modulation of TBX2 expression established HLX as a downstream target of TBX2. Consistent with these findings, reduced HLX expression in orthotopic TBX2 dominant-negative xenografts was associated with loss of metastatic progression. Conclusions: HLX is a candidate biomarker of aggressive PCa and a direct transcriptional target of TBX2. These findings identify a previously unrecognized TBX2-HLX regulatory axis associated with metastatic transcriptional programs and aggressive disease in advanced PCa.