Role of protein kinase C-iota in transformed non-malignant RWPE-1 cells and androgen-independent prostate carcinoma DU-145 cells

Prostate cancer is one of the leading causes of death among men in the USA. In this study, we investigated the role of atypical protein kinase C-iota (PKC-iota) in androgen-independent prostate DU-145 carcinoma cells compared to transformed non-malignant prostate RWPE-1 cells. Western blotting and immunoprecipitations demonstrated that PKC-iota is associated with cyclin-dependent kinase activating kinase (CAK/Cdk7) in RWPE-1 cells, but not in DU-145 cells. Treatment of prostate RWPE-1 cells with PKC-iota silencing RNA (siRNA) decreased cell viability, cell-cycle accumulation at G(2)/M phase, and phosphorylation of Cdk7 and Cdk2. In addition, PKC-iota siRNA treatment caused less phosphorylation of Bad at ser-155, ser-136, and greater Bad/Bcl-x(L) heterodimerization, leading to apoptosis. In DU-145 cells, PKC-iota was anti-apoptotic and was required for cell survival. Treatment with PKC-iota siRNA blocked increase in cell number, and inhibited G(1)/S transition by accumulation of cells in G(0)/G(1) phase. In addition to cell-cycle arrest, both RWPE-1 and DU-145 cells underwent apoptosis due to mitochondrial dysfunction and apoptosis cascades, such as release of cytochrome c, activation of caspase-7, and poly (ADP-ribose) polymerase (PARP) cleavage. Our results suggest that PKC-iota is required for cell survival in both transformed non-malignant prostate RWPE-1 cells and androgen-independent malignant prostate DU-145 cells, whereas suppressing PKC-iota lead to apoptosis in DU-145 prostate cells.