Alterations of phospholipid metabolism by phorbol esters and fatty acids occur by different intracellular mechanisms in cultured glioma, neuroblastoma, and hybrid cells

Differences between the influences of phorbol esters (such as 4β-12-O-tetradecanoylphorbol 13-acetate) and of fatty acids (such as oleic acid) on the synthesis and turnover of phosphatidylcholine (PtdCho) and other phospholipids have been studied in glioma (C₆), neuroblastoma (N1E-115), and hybrid (NG108-15) cells in culture using [methyl-³H]choline, [³²P]P(i), [1,2-¹⁴C]ethanolamine, or 1-¹⁴C-labeled fatty acids as lipid precursors. 100-500 μM oleic acid stimulated PtdCho synthesis 3- to 5-fold in all three cell lines, but had little influence on chase of choline label following a 25-h pulse. Phorbol ester (50-200 nM) stimulated PtdCho synthesis 1.5- to 3-fold in C₆ cells, was without effect in N1E-115 cells, and had intermediate effects on NG108-15 cells. Phorbol ester stimulated both uptake of extracellular choline and synthesis of PtdCho, whereas fatty acid stimulated only synthesis. Release of radioactivity from 24-h pulse-labeled PtdCho to the medium was enhanced by phorbol ester in C₆ cells. Incorporation of [³²P]P(i), primarily into PtdCho, was stimulated, whereas utilization of [1,2-¹⁴C]ethanolamine or 1-¹⁴C-fatty acid was little altered by phorbol ester. C₆ cells 'down-regulated' with phorbol ester lost the stimulatory response of subsequent treatment with phorbol esters on PtdCho synthesis, but the response to fatty acid was enhanced. Fatty acid had little influence on the relative binding of phorbol ester or 'translocation' of phorbol ester binding sites. Accordingly, metabolism of phospholipids in these cultured cells of neural origin is markedly influenced by cell type, phospholipid class, condition of incubation medium, and nature of stimulator. Phorbol esters and fatty acids appear to enhance phospholipid synthesis and turnover by distinct intracellular mechanisms.