DIFFERENTIAL-EFFECTS OF PLATELET-DERIVED GROWTH-FACTOR, SERUM AND BOMBESIN ON PHOSPHOLIPASE D-MEDIATED HYDROLYSIS OF PHOSPHATIDYLETHANOLAMINE IN NIH 3T3 FIBROBLASTS

In previous studies, activators of protein kinase C, sphingosine, ATP and various oncogenes were each found to enhance phospholipase D-mediated hydrolysis of phosphatidylethanolamine (PtdEtn) in NIH 3T3 fibroblasts. Here I examined possible stimulation of PtdEtn hydrolysis by various growth-stimulatory agents, including serum, bombesin, platelet-derived growth factor (PDGF), fibroblast growth factor (FGF) and insulin. Treatment of NIH 3T3 fibroblasts, prelabelled with [C-14]Etn or [P-32]PtdEtn, with PDGF-BB resulted in enhanced formation of [C-14]Etn or [P-32]phosphatidic acid from the respective labelled cellular pools of PtdEtn. A maximal effect (approximately 3-fold stimulation) on PtdEtn hydrolysis was obtained with 50 ng of PDGF/ml after 5 min of treatment. Phosphatidylcholine (PtdCho) was also hydrolysed, although less extensively than PtdEtn, in PDGF-stimulated cells. PDGF-stimulated hydrolysis of both PtdEtn and PtdCho was prevented by prolonged (30 h) treatment of cells with 400 nm-phorbol 12-myristate 13-acetate (PMA). Similar to PDGF, fetal calf serum (1-10 %) also stimulated PtdEtn hydrolysis. However, in contrast to PDGF, the effect of serum on PtdEtn hydrolysis (i) was not diminished by pretreatment with PMA, and (ii) was synergistic with that of PMA after a 1 h incubation. Compared with PDGF and serum, bombesin had less effect on PtdEtn hydrolysis, while FGF and insulin had no effects at all. In contrast to PDGF or serum, bombesin inhibited the effect of PMA on PtdEtn hydrolysis.