Inositide-specific phospholipase C signalling in the nucleus

The nucleus of eukaryotic cells contains all the information needed for cell proliferation and differentiation, however the initiation of these programmes are dependent on the signalling pathway elicited by different agonists. The existence of a nuclear phosphoinositide signalling stems from the early evidence that isolated nuclei posses the lipid kinases capable of phosphorylating phosphatidylinositol (PI) and phosphatidylinositol 4-phosphate (PIP). The synthesis of phosphatidylinositol 4,5- phosphate (PIP2) was clearly increased only in the nuclear fraction from Friend cells terminally differentiated towards erythrocytes (Cocco et al., 1987). On the contrary its amount along with that of PIP was decreased in nuclei of Swiss 3T3 cells stimulated to grow with insulin-like growth factor-I (IGFI) (Manzoli et al., 1989). Following these early observations we and others have demonstrated in several cell type the participation of the whole phosphoinositide cycle in the nucleus (Cocco et al., 1994; Martelli et al., 1992; Divecha et al., 1991; Martelli et al., 1994; Mazzoni et al., 1992). Here we review the most recent achievements on this issue.