Phosphatidylcholine-specific phospholipase C in mitogen-stimulated fibroblasts.

To investigate expression, subcellular localization and mechanisms of translocation of phosphatidylcholine-specific phospholipase C (PC-PLC) during the cell proliferative response, biochemical, immunoblotting, and immunofluorescence analyses were performed on quiescent and mitogen-stimulated NIH-3T3 fibroblasts. Platelet-derived growth factor (PDGF), insulin and 12-O-tetradecanoylphorbol-13-acetate induced, in 10-60 min, PC-PLC translocation from a perinuclear cytoplasmic area to the plasma membrane. Following cell exposure to PDGF (60 min), the overall PC-PLC expression increased up to 2-3x, while the enzyme activity increased 5x in total cell lysates, 2x in the plasma membrane, and 4x in the nucleus; moreover, confocal laser scanning microscopy showed a progressive externalization of PC-PLC on the outer plasma membrane surface and its accumulation in the nuclear matrix. Pre-incubation of cells with the PC-PLC inhibitor tricyclodecan-9-yl potassium xanthate (D609), before PDGF-stimulation, not only reduced the enzyme activity in total cell lysates as well as in plasma membrane and nuclear fractions, but also blocked the mechanisms of PC-PLC subcellular redistribution. These effects were associated with a D609-induced long-lasting cell cycle block in Go.