Inhibitory effect of epidermal growth factor on resveratrol-induced apoptosis in prostate cancer cells is mediated by protein kinase C-A

Resveratrol, a naturally occurring stilbene with antitumor properties, caused mitogen-activated protein kinase [MAPK, extracellular signal-regulated kinase 1/2 (ERK1/2)] activation, nuclear translocation of Ser-phosphorylated p53, and p53-dependent apoptosis in hormone-insensitive DU145 prostate cancer cells. Exposure of these cells to epidermal growth factor (EGF) for up to 4 hours resulted in brief activation of MAPK followed by inhibition of resveratrol-induced signal transduction, p53 phosphorylation, and apoptosis. Resveratrol stimulated c-fos and c-jun expression in DU145 cells, an effect also suppressed by EGF. An inhibitor of protein kinase C (PKC)-A, -B, and -; (CGP41251) enhanced Ser phosphorylation of p53 by resveratrol in the absence of EGF and blocked EGF inhibition of the resveratrol effect. EGF caused PKC-A/B phosphorylation in DU145 cells, an effect reversed by CGP41251. Activation of PKC by phorbol ester (phorbol 12-myristate 13-acetate) enhanced EGF action on ERK1/2 phosphorylation without significantly altering p53 phosphorylation by resveratrol. DU145 cells transfected with a dominant-negative PKC-A construct showed resveratrolinduced ERK1/2 phosphorylation and Ser phosphorylation of p53 but were unresponsive to EGF. Thus, resveratrol and EGF activate MAPK by discrete mechanisms in DU145 cells. The stilbene promoted p53dependent apoptosis, whereas EGF opposed induction of apoptosis by resveratrol via a PKC-A-mediated mechanism. Resveratrol also induced p53 phosphorylation in LNCaP prostate cancer cells, an effect also inhibited by EGF. Inhibition of PKC activation in LNCaP cells, however, resulted in a reduction, rather than increase, in p53 activation and apoptosis, suggesting that resveratrol-induced apoptosis in these two cell lines occurs through different PKC-mediated and MAPK-dependent pathways. [Mol Cancer Ther 2004;3(11):1355–63]