Tumor-promoting phorbol ester-induced cell death and gene expression in a human prostate adenocarcinoma cell line

12-O-tetradecanoyl phorbol ester (TPA) has profound cytotoxic effects on a human prostate cancer cell line, LNCaP. The TPA effect may be mediated via a protein kinase C (PKC) pathway, since staurosporine, a potent PKC inhibitor, could reverse the cell-killing effect. Our studies, based on cellular fragmentation, chromatin condensation, and nuclear fragmentation, suggest that the cell-killing effect is due to apoptosis. Moreover, we also examined expression of early growth response genes and androgen-induced genes in association with TPA-induced apoptosis. Northern blot analysis demonstrated that androgen induction of human glandular kallikrein-1 (hKLK2) mRNA was repressed by TPA in a concentration-dependent manner. A time course study showed that both hKLK2 and c-myc mRNAs were repressed by TPA as early as four hours. In contrast, the steady state mRNA levels for c-fos, c-jun, nerve growth factor induced gene A, and the orphan steroid receptor nur77 were rapidly induced within the first two hours of the treatment. Furthermore, transient co-transfection experiments demonstrated that c-fos and c-jun could repress androgen receptor-mediated gene induction. The above studies suggest that (1) the repression of androgen induction of gene expression by TPA-activated PKC is at least in part due to overexpression of c-jun and c-fos and (2) PKC may be a negative growth regulator in prostate cells.