Ceramide inhibits cell proliferation through Akt/PKB inactivation and decreases melanin synthesis in Mel-Ab cells

Ceramide is a bioactive sphingolipid that mediates a variety of cell functi ons, However, the effects of ceramide on cell growth and the melanogenesis of melanocytes are not known, In the present study, we investigated the act ions of cell-permeable ceramide and its possible role in the signaling path way of a spontaneously immortalized mouse melanocyte cell line, Mel-Ab, Our results show that C-2-ceramide inhibits DNA synthesis in Mel-Ab cells and G361 human melanoma cells in a dose-dependent manner, Cell cycle analysis c onfirmed the inhibition of DNA synthesis by a reduction in the S phase, To investigate the ceramide signaling pathway, we studied whether C-2-ceramide is able to influence extracellular signal-regulated kinase (ERK) and/or Ak t/protein kinase B (PKB) activation. We demonstrated that phosphorylated Ak t/PKB is decreased by C-2-ceramide, whereas phosphorylated ERK was only sli ghtly affected, Therefore, the C-2-ceramide-induced inactivation of Akt/PKB may be closely related to the reduced cell proliferation of Mel-Ab cells, Furthermore, we assessed the effects of C-2-ceramide on the pigmentation of Mel-Ab cells, The results obtained showed that the melanin content of cell s was significantly reduced by C-2-ceramide at concentrations in the range of 1-10 muM, and that the pigmentation-inhibiting effect of C-2-ceramide is much greater than that of kojic acid at 1-100 muM. In addition, we found t hat the activity of tyrosinase is reduced by C-2-ceramide treatment. Our re sults demonstrate that C-2-ceramide reduces the pigmentation of Mel-Ab cell s by inhibiting tyrosinase activity.