Nuclear sphingomyelin-synthase and protein kinase C δ in melanoma cells

The aim of this research is to study the influence of protein kinase C 6 on the nuclear phospholipids metabolism. Murine and human melanoma cells, in which overexpression of protein kinase 8 was induced, were used. After purification of the nuclei, the phosphatidylcholine-dependent phospholipase Q sphingomyelin-synthase, and sphingomyelinase activities were measured. The results showed that the nuclear sphingomyelin-synthase activity increased and sphingomyelinase activity decreased in the protein kinase C delta overexpressive cells with respect to the controls. As a consequence, the ceramide pool decreased and diacylglycerol pool increased; this effect was not due to the phosphatidylcholine-dependent phospholipase C activity that did not change. The inhibition of sphingomyelinase could be due to protein kinase C 6 as well as to existence of a sort of nuclear self-regulation between sphingomyelin-synthase and sphingomyelinase. The possible role of nuclear sphingomyelin-synthase in cell proliferation is discussed.