LAUSR

Prostate cancer (PCa) is characterized by the complexity of oncogenic signaling and heterogeneity of transcriptional landscapes. Adaptor protein ABI1 is a tumor suppressor in PCa, as evidenced by its loss or downregulation in high-grade and metastatic tumors. STAT3 activation is a hallmark of high-risk prostate tumors. ABI1 loss is associated with STAT3 activation leading to transcriptional reprogramming and epithelial-mesenchymal-transition (EMT) of prostate cancer cells (Nath, Li et al. Cell Commun Signal. 2019). EMT changes involve several homeobox transcription factors. The fact that ABI1 contains a homeobox homology region (HHR) suggests the possibility that it plays a role in EMT by directly regulating transcriptional activity by DNA binding. To examine this hypothesis, we set out to analyze ABI1-DNA binding. Structural NMR studies and in-vitro protein-DNA binding assays confirmed ABI1 binding to DNA regulated by alternative spliced ABI1 Exon 4 region located on the C-terminus of ABI1 HHR. RNA-sequencing data and PCa cell lines qPCR assays reveal the alternative ABI1 Exon 4 spliced-in is enriched in high Gleason-scored PCa samples. ABI1 and STAT3 co-regulate their nuclear vs. cytoplasm localization, and the subsequent functional studies using PCa lines expressing wild type or HHR Exon 4 deletion mutant of ABI1 demonstrated that HHR regulates the STAT3 DNA binding patterns, STAT3 mediated chromatin structure programming as well as its transcription activities. We propose that ABI1 is a critical regulator of STAT3 activity during prostate cancer progression. Citation Format: Xiang Li, Neeru Arya, Baylee A. Porter, Allysa P. Kemraj, Xuesen Dong, Dominique Frueh, Alaji Bah, Leszek Kotula. ABI1 regulates STAT3 transcription through a DNA binding activity. [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2023; Part 1 (Regular and Invited Abstracts); 2023 Apr 14-19; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2023;83(7_Suppl):Abstract nr 3725.