Persistent membrane translocation of protein kinase C alpha during 12-O-tetradecanoylphorbol-13-acetate-induced apoptosis of LNCaP human prostate cancer cells

Others have reported that the phorbol ester 12-O-tetradecanoylphorbol-13-acetate (TPA), an activator and down-regulator of most protein kinase C (PKC) isozymes, can induce apoptotic cell death of androgen-sensitive LNCaP but not androgen-insensitive PC-3 or DU 145 human prostate cancer cells. As a first step toward uncovering the mechanism by which TPA induces apoptosis of LNCaP cells, we quantified expression of PKC isozyme mRNAs in unmodified and TPA-resistant LNCaP cells and in naturally TPA-resistant PC-3, PC-3M, and DU 145 cells, All of the cell lines and normal prostate expressed RNAs for PKC alpha, delta, epsilon, eta, and mu; only DU 145 cells and normal prostate expressed PKC beta and theta RNAs, and none expressed PKC gamma. The amount of PKC alpha RNA and protein was 6- to 38-fold lower, and PKC mu RNA was 4.5- to 16.5-fold higher in unmodified and TPA-resistant LNCaP cells than in the androgen-independent cells. We examined the effects of TPA on PKC alpha and mu mRNA levels and on membrane translocation of PKC alpha. Incubation with TPA for 6 h or more induced 95% inhibition of cell growth, a transient 12-fold increase and 5-fold decrease in PKC alpha and mu mRNA levels, respectively, and prolonged translocation of PKC alpha to non-nuclear membranes in unmodified LNCaP cells and in TPA-resistant LNCaP cells from which TPA had been removed for 10 days, TPA-resistant LNCaP cells in the continuous presence of TPA, or 24 h after removal of TPA, had down-regulated PKC alpha and remained resistant to re-addition of TPA, These data demonstrate a strong correlation of the presence and absence of membrane PKC alpha with apoptosis and resistance to apoptosis, respectively.