DELETION OF SPECIFIC PROTEIN-KINASE-C SUBSPECIES IN HUMAN-MELANOMA CELLS

It has been shown that tumor-promoting phorbol ester, 12-O-tetradecano ylphorbol-13-acetate (TPA), stimulates the proliferation of normal hum an melanocytes, whereas it inhibits the growth of human melanoma cell lines. The expression of protein kinase C (PKC) subspecies, the major intracellular receptors for TPA, was examined in normal melanocytes an d the four melanoma cell lines HM3KO, MeWo, HMV-I, and G361. PKC was p artially purified and then separated into subspecies by column chromat ography on Mono Q and hydroxyapatite successively, and finally subject ed to immunoblot analysis using antibodies specific for the PKC subspe cies. Of the PKC subspecies examined, delta-, epsilon-, and zeta-PKC w ere detected in both normal melanocytes and the four melanoma cell lin es. In contrast, both alpha-PKC and beta-PKC were expressed in normal melanocytes, whereas either alpha-PKC or beta-PKC was detected in mela noma cells. Specifically, HM3KO, MeWo, and HMV-I cells were shown to c ontain alpha-PKC but not beta-PKC, while G361 cells expressed beta-PKC but not alpha-PKC. The growth of these melanoma cells was suppressed by TPA treatment, and the growth of the G361 cells lacking alpha-PKC w as inhibited more efficiently than the other melanoma cell lines which lacked beta-PKC. It was further shown that beta-PKC was not detected in freshly isolated human primary or metastatic melanoma tissues. Thes e results suggest that the expression of alpha-PKC or beta-PKC may be altered during the malignant transformation of normal melanocytes and that loss of alpha-PKC or beta-PKC may be related to the inhibitory ef fect of TPA on the growth of melanoma cells. (C) 1996 Wiley-Liss, Inc.