PACT is requisite for prostate cancer cell proliferation.

PACT (encoded by the PRKRA gene) is a double-stranded RNA binding protein with defined antiviral defense and cytoplasmic RNA-induced silencing actions in mammals. We previously described a further role for PACT as a modulator of nuclear receptor (NR)-regulated gene expression. Here, we investigated the role of PACT in prostate cancer (PCa) using a loss-of-function approach. Depletion of PACT in multiple PCa cell lines resulted in a reduction in cell proliferation, but viability was maintained. RNA-sequencing analysis of LNCaP PCa cells ± PACT revealed a depletion of biological processes involved in cell cycle, mitochondrial function, and NR-response pathways in the PACT knockout (KO) cells. In the PACT KO cells, downregulated genes included the androgen-regulated KLK3 (prostate specific antigen, PSA), together with H2AFJ, PSMD5, AQP3, TMEM45B, and SLC22A3, and siRNA-mediated knockdown of these genes reduced cell growth and proliferation in LNCaP cells. Further, reducing PACT or PSA induced cell cycle arrest at G0/G1. Additionally, the hormone-mediated upregulation and AR antagonist-driven downregulation of PSA gene expression were respectively attenuated and enhanced in PACT KO cells. Taken together, these data support a pro-proliferative role for PACT in PCa, and siRNA therapeutic targeting of PACT, or downregulated genes with PACT KO, could represent a new therapeutic approach.