Abstract
Ether phospholipids are synthesized by a series of enzymes localized in peroxisomes, the endoplasmic reticulum (ER), and the Golgi apparatus. During this process, the lipid intermediate alkylacylglycerol (AAG) synthesized in the ER is transferred from the site of its synthesis to the Golgi apparatus. In this study, we determined whether ceramide transport protein (CERT) is a candidate for AAG transfer. A lipid transfer assay revealed that CERT can mediate AAG transfer between phospholipid liposomes. AAG transport activity was markedly inhibited by the CERT inhibitor HPA-12 and reduced when the lipid transport domain of CERT was deleted. Suppression of CERT in HEK293 cells resulted in increased levels of plasmanyl-PC, which is synthesized by the ER-residing choline/ethanolamine phosphotransferase 1 (CEPT1). The mRNA levels and enzymatic activity of plasmanyl-PC synthesizing enzymes were not increased in CERT-deficient cells, indicating that the increase in plasmanyl-PC results from AAG accumulation in the ER. Re-introduction of CERT into CERT-deficient cells caused a decrease in plasmanyl-PC. Taken together, our findings suggest for the first time that CERT is involved in the transfer of AAG from the ER to the Golgi apparatus and plays a role in the biosynthesis of ether phospholipids.