Two waves of the nuclear phospholipase C activity in serum-stimulated HL-60 cells during G(1) phase of the cell cycle.
Phosphatidylinositol-specific phospholipase C (PI-PLC) is activated in cell nuclei during the cell cycle progression. We have previously demonstrated two peaks of an increase in the nuclear PI-PLC activities in nocodazole-synchronized HL-60 cells. In this study, the activity of nuclear PI-PLC was investigated in serum-stimulated HL-60 cells. In serum-starved HL-60 cells, two peaks of the activity of nuclear PI-PLC were detected at 30 min and 11 h after the re-addition of serum with no parallel increase in PLC activity in cytosol, postnuclear membranes or total cell lysates. An increase in the serine phosphorylation of b splicing variant of PI-PLCbeta(1) was detected with no change in the amount of PI-PLCbeta(1b) in nuclei isolated at 30 min and 11 h after the addition of serum. PI-PLC inhibitor ET-18-OCH(3) and MEK inhibitor PD 98059 completely abolished serum-mediated increase at both time-points. The addition of inhibitors either immediately or 6 h after the addition of serum had inhibitory effects on the number of cells entering S phase. These results demonstrate that two waves of nuclear PI-PLCbeta(1b) activity occur in serum-stimulated cells during G(1) phase of the cell cycle and that the later increase in the PLC activity is equally important for the progression into the S phase.
Lukinovic-Skudar
Vesna
V
Department of Physiology and Croatian Institute for Brain Research, School of Medicine, University of Zagreb, Salata 3, Zagreb, Croatia.
Matkovic
Katarina
K
Banfic
Hrvoje
H
Visnjic
Dora
D
D000818:Animals; D002417:Cattle; D002467:Cell Nucleus / Q000187:drug effects / Q000201:enzymology*; D004791:Enzyme Inhibitors / Q000494:pharmacology; D016193:G1 Phase / Q000187:drug effects; D018922:HL-60 Cells; D006801:Humans; D043265:Phosphatidylinositol Diacylglycerol-Lyase / Q000037:antagonists & inhibitors / Q000378:metabolism*; D054801:Phosphoinositide Phospholipase C; D010768:Phosphoserine / Q000378:metabolism; D044967:Serum / Q000378:metabolism*; D013347:Subcellular Fractions / Q000187:drug effects / Q000201:enzymology; D013997:Time Factors
D004791:Enzyme Inhibitors; D010768:Phosphoserine; D054801:Phosphoinositide Phospholipase C; D043265:Phosphatidylinositol Diacylglycerol-Lyase