Effect of fumonisin B₁ on phosphatidylethanolamine biosynthesis in Chinese hamster ovary cells

Fumonisin B₁ has been shown to inhibit dihydroceramide synthesis and elevate cellular sphinganine levels in several cultured cell lines. In Chinese hamster ovary (CHO)-K1 cells, 20 μM fumonisin B₁ inhibited sphingomyelin synthesis by 75% after 5 h, but stimulated [³H]serine incorporation into PtdEtn by 5- to 7-fold. Fumonisin caused a 10-20% increase in [³H]serine labelling of PtdSer. While fumonisin (20 μM) caused sustained inhibition of sphingomyelin synthesis, PtdEtn labelling peaked at 7-fold above controls at 12 h and declined to 4-fold by 24 h. Fumonisin treatment for 12 h increased the in vitro activity of PtdSer synthase by 62% and inhibited PtdSer decarboxylase by 35%, suggesting that increased PtdEtn labelling by [³H]serine is not by this pathway. An ethanolamine 'trap' experiment was performed to assess the contribution of phosphoethanolamine from sphinganine degradation for PtdEtn labelling. Stimulation of [³H]serine incorporation into PtdEtn by fumonisin could be reduced by 60% with the inclusion of 50 μM unlabelled ethanolamine in the culture medium. The ethanolamine-mediated reduction in [³H]serine incorporation into PtdEtn was accompanied by 4-fold increase in cellular [³H]phosphoethanolamine. In control cells labelled with [³H]serine, 50 μM ethanolamine did not cause [³H]phosphoethanolamine to accumulate. Consistent with elevated phosphoethanolamine production in fumonisin-treated cells, [³H]ethanolamine incorporation into PtdEtn was inhibited by 75% after 12 h. The degradation of endogenous long-chain bases to phosphoethanolamine and entry into the CDP-ethanolamine pathway appears to be a major pathway for PtdEtn synthesis in fumonisin-treated CHO-K1 cells.