Effect of 1alpha,25-dihydroxyvitamin D3 in embryonic hippocampal cells.

Although the role of 1alpha,25-dihydroxyvitamin D3 in calcium homeostasis of bone tissue is clear, evidence of the involvement of vitamin D3 in the central nervous system functions is increasing. In fact, vitamin D3 regulates vitamin D receptor and nerve growth factor expression, modulates brain development, and reverses experimental autoimmune encephalomyelitis. Only few studies, however, address vitamin D3 effect on embryonic hippocampal cell differentiation. In this investigation, the HN9.10e cell line was used as experimental model; these cells, that are a somatic fusion product of hippocampal cells from embryonic day-18 C57BL/6 mice and N18TG2 neuroblastoma cells, show morphological and cytoskeletal features similar to their neuronal precursors. By this model, we have studied the time course of vitamin D3 localization in the nucleus and its effect on proteins involved in proliferation and/or differentiation. We found that the translocation of vitamin D3 from cytoplasm to the nucleus is transient, as the maximal nuclear concentration is reached after 10 h of incubation with (3)H-vitamin D3 and decreases to control values by 12 h. The appearance of differentiation markers such as Bcl2, NGF, STAT3, and the decrease of proliferation markers such as cyclin-1 and PCNA are late events. Moreover, physiological concentrations of vitamin D3 delay cell proliferation and induce cell differentiation of embryonic cells characterized by modification of soma lengthening and formation of axons and dendrites.

Nuclear sphingomyelin-synthase and protein kinase C delta in melanoma cells.

The aim of this research is to study the influence of protein kinase C delta on the nuclear phospholipids metabolism. Murine and human melanoma cells, in which overexpression of protein kinase delta was induced, were used. After purification of the nuclei, the phosphatidylcholine-dependent phospholipase C, 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 delta 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.