Abstract 5730: CDX1 binding to the <i>PVT1</i> exon 9-associated promoter drives oncogenic <i>PVT1</i> exon 9 overexpression in aggressive prostate cancer

Abstract This study elucidates a previously uncharacterized epigenetic-transcriptional regulatory axis involving the transcription factor CDX1 and the PVT1 exon 9-associated promoter (PEAP) that governs PVT1 exon 9 overexpression in aggressive prostate cancer. The long noncoding RNA (lncRNA) PVT1, located at the 8q24 oncogenic locus, has been implicated in prostate tumorigenesis and progression; however, the molecular mechanisms underlying its exon-specific transcriptional activation remains obscure. Through in silico motif discovery using FIMO analysis, we identified a high-affinity CDX1 consensus binding site within the PEAP sequence, suggesting a potential transcriptional regulatory role. DNA methylation profiling of matched prostate tumor and adjacent normal tissues from prostate cancer patients demonstrated promoter hypomethylation at PEAP, concomitant with a significant upregulation of PVT1 exon 9. While siRNA-mediated CDX1 silencing in PVT1 exon 9 overexpressing cells (MDA-PCa-2b and C22OH) attenuated PVT1 exon 9 expression, CDX1 overexpression in RWPE-1 cells enhanced PVT1 exon 9 transcription. Immunohistochemical and immunofluorescence analysis corroborated the nuclear localization and elevated expression of CDX1 in high-Gleason-grade tumors, underscoring its role as a transcriptional activator. Using digital PCR, CRISPR-mediated base editing of the CDX1 binding sequence on PEAP in MDA-PCa-2b and C22OH revealed drastic reduction in PVT1 exon 9 copy number compared to scramble. Collectively, these findings delineate a CDX1-PEAP-PVT1 signaling axis that is dependent on CDX1 binding to PEAP, thereby driving oncogenic PVT1 exon 9 overexpression. This mechanistic insight provides a novel framework for understanding PVT1 exon-specific regulation and positions the CDX1-PEAP interaction as a promising molecular target for therapeutic interventions in PVT1 exon 9 overexpressing prostate cancers. Citation Format: Chinedum C. Udekwu, Siti K. Nuraziza, Seidu Adams, Rachel E. Bonnaci, E. Oluwabunmi Olapade-Olaopa, Olorunseun O. Ogunwobi. CDX1 binding to the PVT1 exon 9-associated promoter drives oncogenic PVT1 exon 9 overexpression in aggressive prostate cancer [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2026; Part 1 (Regular Abstracts); 2026 Apr 17-22; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2026;86(7 Suppl):Abstract nr 5730.