Effects of a Tumor Promoter on Phospholipid Metabolism in HeLa Cells¹

The tumor promoter 12-O-tetradecanoylphorbol-13-acetate (TPA) caused a marked stimulation of inorganic [³²P]orthophosphate incorporation into HeLa-cell phosphatidylcholine (PC), phosphatidylethanolamine (PE), and lysophosphatidylethanolamine. The increased incorporation of inorganic [³²P]orthophosphate into PE and lysophosphatidylethanolamine in the presence of TPA was not associated with an increase in PE synthesis as detected by the incorporation of [³H]serine or [³H]ethanolamine. The PC-specific exchange protein from beef liver was used to insert PC labeled with [³H]choline, inorganic [³²P]orthophosphate, or [¹⁴C]arachidonic acid plus [³H]palmitic acid into the outer monolayer of intact HeLa cell membranes. Radioactivity from the latter two compounds was rapidly incorporated into PE and lysophosphatidylethanolamine; the incorporation was stimulated by TPA. It was concluded that TPA stimulated the formation of PE by base exchange between ethanolamine and PC.