Abstract 1705: SPOP: An essential gene for normal and prostate tumor cells

Abstract

Abstract Background: Prostate cancer (PC) is the single most common and second-most lethal cancer in men, with over 268,000 estimated cases and over 34,500 estimated deaths in the US in 2022. The Speckle-Type POZ protein (SPOP) mutant subclass of PC accounts for 10% to 15% of all primary PC cases. SPOP is an adaptor for Cullin3/Ring (CUL3-RING)-type E3 ubiquitin ligase complexes and provides substrate specificity. The Cancer Genome Atlas (TCGA) studies show that SPOP is the most frequently mutated gene in primary prostate cancer (PC). Interestingly, PC-associated SPOP mutations are always missense and occur in a heterozygous fashion. The current gap in knowledge is the lack of understanding of the role of wildtype SPOP in PC. Methods: By utilizing prostate specific SPOP knockout (KO) mice, we recently reported increased levels of AR and MYC protein and increased cellular turnover (both proliferation and apoptosis) in the prostate luminal epithelium compared to wildtype prostates. We now characterized these mice for the expression of Cre protein and SPOP mRNA at different age using immunohistochemistry and RNA in situ hybridization. Furthermore, we performed RNA-sequencing analysis in the SPOP knockout mice and matched control littermates. Moreover, we performed RNA-seq in LNCaP, LNCaP-Abl, and RWPE1 cells following SPOP inhibition via siRNA targeting SPOP. Finally, we compared our SPOP inhibition signature from in vitro cell lines and prostate specific SPOP knockout murine model to gain insights about the role of wildtype SPOP protein in the prostate epithelium. Result: Using our Spopfl/fl;PBCre+ model, we observed SPOP floxed cells are rapidly lost and the murine prostate epithelium was repopulated with SPOP wildtype carrying cells. Similarly, knockdown (KD) of SPOP through siRNA treatment in a panel of PC cell lines resulted in a significant reduction in cell viability. These observations suggest that SPOP is important for the normal prostate cell viability. Further transcriptomic profiling of SPOP KO (from transgenic murine model) as well as siSPOP treated in vitro prostate cell lines revealed a significant reduction in the transcriptional activity of the AR. Conclusion: Our data illustrate for the first time a critical role for SPOP in the growth and survival of the prostate epithelium and prostate cancer cell. Our findings further validates SPOP as a important therapeutic target for the treatment of prostate cancer. Citation Format: Kinza Rizwan, Darlene Skapura, Cammy Mason, Cristian Coarfa, Nicholas Mitsiades, Damian Young, Salma Kaochar. SPOP: An essential gene for normal and prostate tumor cells [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 1705.