Nuclear lipid metabolism is involved in the regulation of cell proliferation. Modulation of the expression and activity of nuclear PI-phospholipase C (PI-PLC) has been reported during liver regeneration after partial hepatectomy, although it has not been determined whether different PLC isoforms play specific roles in the regulation of cell cycle progression. Here, we report evidence that the increased activity of nuclear PLCs in regenerating rat liver occurs before the peak of DNA replication and involves the enzyme activity associated to the chromatin and not that associated to the nuclear membrane. Immunocytochemical analyses indicate that PI-PLC beta(1) isoform is exclusively localized at the chromatin level, PI-PLC beta(1) co-localizes with DNA replication sites much more than PI-PLC gamma(1), which is also present at the nuclear envelope. These findings and the increased amount of PI-PLC gamma(1) occurring after the peak of DNA replication suggest that PI-PLC beta(1) and gamma(1) play different roles in cell cycle progression during regenerating liver. The increased activity of PI-PLC beta(1) constitutively present within the hepatocyte nucleus, should trigger DNA replication, whereas PI-PLC gamma(1) should be involved in G2/M phase transition through lamin phosphorylation.
Copyright 2003 Wiley-Liss, Inc.