Abstract 2353: Biphasic regulation of MYB by androgen signaling mediates its growth-promoting and repressive effects in prostate cancer cells
Authors: Acharya Srijan , Anand Shashi , Khan Mohammad Aslam , Zubair Haseeb , Srivastava Sanjeev Kumar , Singh Seema , Singh Ajay Pratap 
Published: June 2022

Abstract
Prostate cancer is the most frequently diagnosed malignancy affecting millions of men worldwide. It is also the second leading cause of cancer-related death in American men. Androgen signaling plays a central role in prostate cancer development but results in growth inhibition at high doses. Mechanisms underlying such biphasic effect of androgens are not well understood. We recently identified MYB as an aberrantly expressed gene in prostate cancer cells, which promoted their growth and aggressive behavior. We also observed that MYB induced ligand-independent activation of androgen receptor (AR) and influenced its binding to selective target genes to promote castration-resistance. The goal of the present study was to examine the regulatory crosstalk between MYB and AR in prostate cancer cells. We observed that while MYB had no significant effect on AR expression, androgen (dihydrotestosterone, DHT) treatment resulted in a dose-dependent biphasic regulation of MYB at both transcript and protein levels correlating with its effect on the growth of prostate cancer cells. Interestingly, we observed that the treatment of prostate cancer cells with either low (1 nM) or high (100 nM) doses of DHT enhanced the transcriptional activity of MYB promoter. In silico analysis identified two potential androgen-responsive elements (AREs) in MYB promoter and AR bound more efficiently to the proximal sequence as determined by chromatin immunoprecipitation (ChIP). In a time-course experiment, we observed that both low and high doses of DHT increased MYB transcript and protein levels at early time points, which decreased sharply after 12 h in high dose DHT-treated prostate cancer cells. RNA stability assay following treatment with actinomycin D (inhibitor of transcription) showed decreased MYB mRNA half-life in prostate cancer cells at late time points when treated with high dose DHT. Profiling of MYB-targeted miRNAs showed significantly greater induction of miR-150 in high-dose DHT-treated prostate cancer cells than those treated with low-dose DHT. Two AREs were predicted in the 1000 bp upstream sequence of miR-150 transcription start site and AR binding was confirmed by ChIP assay. Functional inhibition of miR-150 using anti-miR relieved MYB suppression by high-dose DHT and promoted the growth of prostate cancer cells. Further, transfection of prostate cancer cells by miR-150 mimic reduced endogenous MYB levels and led to repression of growth of prostate cancer cells. Overall, our findings reveal a novel mechanism of MYB regulation that mediates, at least in part, the biphasic effect of androgens on the growth of prostate cancer cells.
Citation Format: Srijan Acharya, Shashi Anand, Mohammad Aslam Khan, Haseeb Zubair, Sanjeev Kumar Srivastava, Seema Singh, Ajay Pratap Singh. Biphasic regulation of MYB by androgen signaling mediates its growth-promoting and repressive effects in prostate cancer cells [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2022; 2022 Apr 8-13. Philadelphia (PA): AACR; Cancer Res 2022;82(12_Suppl):Abstract nr 2353.