CONTROL OF MEMBRANE PHOSPHATIDYLCHOLINE BIOSYNTHESIS BY DIACYLGLYCEROL LEVELS IN NEURONAL CELLS UNDERGOING NEURITE OUTGROWTH

Phospholipids are the major components of cell membranes and are requi red for cellular growth. We studied membrane phosphatidylcholine (PtdC ho) biosynthesis in neuronal cells undergoing neurite outgrowth, by us ing PC12 cells as a model system. When neurite outgrowth was induced b y exposing PC12 cells to nerve growth factor for 2 and 4 days, the amo unts of [C-14]phosphatidyl-choline per cell (i.e., per DNA) increased approximately 5- and 10-fold, respectively, as compared with control c ells, reflecting increased in the rate of PtdCho biosynthesis. [C-14]c holine uptake was not affected. Analysis of the three major PtdCho bio synthetic enzymes showed that the activity of CDPcholine:1,2-diacylgly cerol cholinephosphotransferase was increased by approximately 50% aft er nerve growth factor treatment, but the activities of choline kinase or choline-phosphate cytidylyltransferase were unaltered; the choline phosphotransferase displayed a high K-m value (approximate to 1,200 mu M) for diacylglycerol. Moreover, free cellular diacylglycerol levels increased by approximately 1.5- and 4-fold on the second and fourth da ys, respectively. These data indicate that PtdCho biosynthesis is enha nced when PC12 cells sprout neurites, and the enhancement is mediated primarily by changes in cholinephosphotransferase activity and its sat uration with diacylglycerol. This suggests a novel regulatory role for diacylglycerol in membrane phospholipid biosynthesis.