Protein kinase C inhibitors and PAF stimulate phosphatidylserine synthesis in human leucocytes

To study the regulation and turnover of phosphatidylserine (PtdSer) in human leucocytes, we investigated the effect of 12-O-tetradecanoylphorbol 13-acetate (TPA), I-O-octadecyl-2-O-methyl-rac-glycero-3-phosphocholine (ET-18-OCH3 or edelfosine), staurosporine and platelet activating factor (PAF) on [14C]serine incorporation into phospholipids. More than 80% of lipid radioactivity was in PtdSer. ET-18-OCH3 stimulated incorporation into PtdSer 5-fold, without increasing incorporation into other lipids. PAF stimulated PtdSer synthesis 3-fold after 1 h, while staurosporine stimulated the synthesis 2-fold after 3 h. TPA inhibited PtdSer synthesis. It abolished the ET-18-OCH3 stimulation, and reduced the staurosporine stimulation. ET-18-OCH3 and TPA did not significantly alter the incorporation of [14C]arachidonic acid into PtdSer, and did not increase PtdSer turnover judged from chase and stability experiments. The results demonstrate that PKC inhibitors and PAF induce increased incorporation of [14C]serine into PtdSer, while TPA inhibits stimulated PtdSer synthesis. This suggests that modulation of PtdSer synthesis may regulate PKC activity in PMN cells.