Deletion of specific protein kinase C subspecies in human melanoma cells.

It has been shown that tumor-promoting phorbol ester, 12-O-tetradecanoylphorbol-13-acetate (TPA), stimulates the proliferation of normal human 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 and the four melanoma cell lines HM3KO, MeWo, HMV-1, and G361. PKC was partially purified and then separated into subspecies by column chromatography on Mono Q and hydroxyapatite successively, and finally subjected to immunoblot analysis using antibodies specific for the PKC subspecies. Of the PKC subspecies examined, δ-, ϵ-, and ζ-PKC were detected in both normal melanocytes and the four melanoma cell lines. In contrast, both α-PKC and β-PKC were expressed in normal melanocytes, whereas either α-PKC or β-PKC was detected in melanoma cells. Specifically, HM3KO, MeWo, and HMV-1 cells were shown to contain α-PKC but not β-PKC, while G361 cells expressed β-PKC but not α-PKC. The growth of these melanoma cells was suppressed by TPA treatment, and the growth of the G361 cells lacking α-PKC was inhibited more efficiently than the other melanoma cell lines which lacked β-PKC. It was further shown that β-PKC was not detected in freshly isolated human primary or metastatic melanoma tissues. These results suggest that the expression of α-PKC or β-PKC may be altered during the malignant transformation of normal melanocytes and that loss of α-PKC or β-PKC may be related to the inhibitory effect of TPA on the growth of melanoma cells. © 1996 Wiley-Liss, Inc.