Triacylglycerol as a precursor in phospholipid biosynthesis in cultured neuroblastoma cells: studies with labeled glucose, fatty acid, and triacylglycerol.

Neuroblastoma cells rapidly incorporate exogenous fatty acids into cellular triacylglycerol and relationships between triacylglycerol and phospholipid biosynthesis have been indicated by the relative time course of labeling of these lipids. To evaluate this further, neuroblastoma cells were labeled using potential precursors of phospholipid including radiolabeled triacyglycerol, glycerol, glucose, and fatty acid. With [2-3H]glycerol or a mixture of [2-3H]glycerol trioleate and glycerol tri[1-14C]oleate, phospholipids were labeled at very low levels (less than 0.1 and less than 0.5%, respectively). With [6-3H]glucose, labeling of lipids (0.5-3.5%) was greatest in medium containing 19 mM fructose, whereas labeling with [1-14C]18:2(n-6) was similar in media containing either 19 mM fructose or 25 mM glucose. Labeling of the glycerol moiety of triacylglycerol with [6-3H]glucose increased with 40-200 microM 18:2(n-6) present and occurred predominantly in 2 h. Some [6-3H]glucose label was in fatty acyl chains (chiefly 16:0) of triacylglycerol by 16 h, but was unaffected by exogenous 18:2(n-6). Triacylglycerol was the only lipid to increase in mass (threefold with 200 microM 18:2(n-6)). During the chase of cells pulsed with [6-3H]glucose, label in triacylglycerol declined within 0.5 h, whereas in phospholipid it increased transiently up to 2 h and then declined. Changes were inversely proportional to 18:2(n-6) levels in the chase medium and labeled acyl chains moved in parallel with the glycerol moiety. Thus, a major portion of acyl chain transfer from triacylglycerol was accompanied by glycerol.(ABSTRACT TRUNCATED AT 250 WORDS)