Previous work from our laboratory had demonstrated that deletion of TGL3 encoding the major yeast triacylglycerol (TAG) lipase resulted in decreased mobilization of TAG, a sporulation defect and a changed pattern of fatty acids, especially increased amounts of C22:0 and C26:0 very long chain fatty acids in the TAG fraction [K. Athenstaedt and G. Daum, J. Biol. Chem. 278 (2003) 23317-23323]. To study a possible link between TAG lipolysis and membrane lipid biosynthesis, we carried out metabolic labeling experiments with wild type and deletion strains bearing defects in the three major yeast TAG lipases, Tgl3p, Tgl4p and Tgl5p. Using [(3)H]inositol, [(32)P]orthophosphate, [(3)H]palmitate and [(14)C]acetate as precursors for complex lipids we demonstrated that tgl mutants had a lower level of sphingolipids and glycerophospholipids than wild type. ESI-MS/MS analyses confirmed that TAG accumulation in these mutant cells resulted in reduced amounts of phospholipids and sphingolipids. In vitro and in vivo experiments revealed that TAG lipolysis markedly affected the metabolic flux of long chain fatty acids and very long chain fatty acids required for sphingolipid and glycerophospholipid synthesis. Activity and expression level of fatty acid elongases, Elo1p and Elo2p were enhanced as a consequence of reduced TAG lipolysis. Finally, the pattern of phosphatidylcholine, phosphatidylethanolamine and phosphatidylserine molecular species was altered in tgl deletion strain underlining the important role of TAG turnover in maintaining the pool size of these compounds and the remodeling of complex membrane lipids.
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