NUCLEAR ADP-RIBOSYLATION FACTOR (ARF)-DEPENDENT AND OLEATE-DEPENDENT PHOSPHOLIPASE-D (PLD) IN RAT-LIVER CELLS - INCREASES OF ARF-DEPENDENT PLD ACTIVITY IN REGENERATING LIVER-CELLS

Two forms of phospholipase D (PLD) have been found to be present in nu clei isolated from rat hepatocytes by measuring phosphatidylbutanol pr oduced from exogenous radiolabeled phosphatidylcholine in the presence of butanol. In nuclear lysates from either rat liver or ascites hepat oma AH 7974 cells, the PLD activity was markedly stimulated by a recom binant ADP-ribosylation factor (rARF) in the presence of the guanosine 5'-O-(3-thiotriphosphate) (GTP gamma S) and phosphatidylinositol 4,5- bisphosphate. ATP and phorbol-12-myristate 13-acetate had no synergist ic effect on this PLD activity. On the other hand, the nuclear PLD was stimulated by unsaturated fatty acids, especially by oleic acid. The ARF-dependent nuclear PLD activity was increased in the S-phase of the regenerating rat liver after partial hepatectomy and also was much hi gher in AH 7974 cells than in the resting rat liver. In contrast, the levels of the oleate-dependent PLD activity remained constant througho ut the cell cycle in liver regeneration. The intranuclear levels of th e stimulating proteins of the nuclear PLD activity, e.g. ARF, RhoA, an d protein kinase C delta increased in the S-phase of the regenerating liver. These results suggested that the nuclear ARF-dependent PLD acti vity may be associated with cell proliferation.