Despite decades of research targeting the activity of the androgen receptor (AR), patients diagnosed with locally advanced and metastatic prostate cancer face an incurable disease. The Daaka lab investigates constituents of G-protein-coupled receptor signaling cascades for their ability to provide mitogenic signaling, which promotes PCa progression. We previously identified G protein-coupled receptor 5 (GRK5) for its ability to regulate PCa progression, independent of AR activity. GRK5 partially partitions to the nucleus, wherein it has been shown to regulate the transcriptome in non-PCa models. To globally elucidate the mechanistic impact of GRK5 on PCa progression, we are investigating the impact of GRK5 on the PCa transcriptome. We hypothesize that GRK5's regulation of the PCa transcriptome promotes tumor progression. To assay the effect of GRK5 on the PCa transcriptome, RNA sequencing was performed in two cell lines: PC3 Control (PC3 shGFP) and PC3 GRK5 Knockdown (PC3 shGRK5).  Ontologic analysis identified the epithelial–mesenchymal transition (EMT) as being affected when GRK5 is depleted. The epithelial–mesenchymal transition (EMT) is highly associated with promoting PCa progression and chemoresistance, thus we selected this pathway for further investigation. Confirmatory western blot analysis and quantitative PCR (qPCR) validated that depleting GRK5 suppresses the expression of the mesenchymal markers Vimentin and N-Cadherin. Similarly, overexpression of GRK5 increases the expression of these mesenchymal markers. Stable overexpression of GRK5 promotes cells to develop a spindle-like morphology, indicative of a mesenchymal state. GRK5 mediates this mesenchymal transition through increasing the expression of the EMT transcription factor, Twist1. Further analysis identifies that GRK5 activity promotes in vitro invasion. Cell lines overexpressing GRK5 demonstrate an increase in resistance to docetaxel, the mainstay chemotherapy for advanced PCa. Overexpression of GRK5 promotes lymphatic intravasation. Overexpression of mutated forms of GRK5 that are relegated to the nucleus are able recapitulated all aforesaid changes, arguing that the nuclear activity of GRK5 mediates this effect. Collectively, this data presents a novel mechanism promoting PCa progression, independent of AR activity.

Citation Format: Joseph B. Black, Hamsa Thayele Purayil, Iqbal Mahmud, Daiqing Liao, Yehia Daaka. GRK5 activity mediates in vivo and in vitro prostate cancer progression and chemoresistance [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2018; 2018 Apr 14-18; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2018;78(13 Suppl):Abstract nr LB-312.