Differential Utilization of the Ethanolamine Moiety of Phosphatidylethanolamine Derived from Serine and Ethanolamine during NGF-Induced Neuritogenesis of PC12 Cells

Neurite elongation involves the expansion of the plasma membrane and phospholipid synthesis. We investigated membrane phosphatidylethanolamine (PE) biosynthesis in PC12 cells during neurite outgrowth induced by nerve growth factor (NGF). When PE was prelabeled with ³H]ethanolamine and the radioactivity was chased by incubation with 1 mM unlabeled ethanolamine, the radioactivity of ³H]PE steadily declined and ³H]ethanolamine was released into the medium in NGF-treated cells during neurite outgrowth; in the absence of unlabeled ethanolamine, the radioactivity of ³H]PE remained relatively constant for at least 24 hr. In undifferentiated cells but not in NGF-treated cells, ³H]phosphoethanolamine accumulated in significant amounts during pulse labeling, and was converted partly to PE but largely released into the medium irrespective of incubation with unlabeled ethanolamine. The decline in the radioactivity of ³H]PE and release of ³H]ethanolamine following incubation with unlabeled ethanolamine were also observed in undifferentiated cells. Thus, the ethanolamine moiety of PE derived from ethanolamine is actively recycled in both differentiated and undifferentiated cells. When PE was derived from ³H]serine through phosphatidylserine (PS) decarboxylation, the decrease in radioactivity of ³H]PE and release of ³H]ethanolamine into the medium following incubation with unlabeled ethanolamine were observed only in NGF-treated cells, but not in undifferentiated cells, indicating that the ethanolamine moiety of PE derived from PS is actively recycled only in the cells undergoing NGF-induced neuritogenesis. Thus, in PC12 cells, the ethanolamine moiety of PE derived from PS is regulated differently from that of PE derived from ethanolamine.