Survival mechanisms induced by 12-O-tetradecanoylphorbol-13-acetate in normal human melanocytes include inhibition of apoptosis and increased Bcl-2 expression.

Abstract

Phorbol esters, which activate protein kinase C, stimulate the growth of normal human melanocytes yet inhibit the growth of most melanoma cells. We investigated whether apoptosis mediates the effects of 12-O-tetradecanoylphorbol-13-acetate (TPA) on melanocyte and melanoma cell growth. Few apoptotic cells were present when melanocytes were cultured with TPA. Upon removal of TPA, the number of apoptotic cells increased over 10 days. Addition of TPA did not induce apoptosis in a metastatic melanoma cell line, Demel, although it strongly inhibited its growth. Protection of normal melanocytes from apoptosis was associated with high levels of Bcl-2. Following withdrawal of TPA from melanocytes, the expression of Bcl-2 decreased steadily. Bax and Bcl-X(L) levels did not differ between melanoma cells or melanocytes and were unaffected by the addition of TPA. These results suggest that TPA plays an important role in stimulating the growth of melanocytes by promoting anti-apoptotic mechanisms associated with high levels of Bcl-2.