Defects in triacylglycerol lipolysis affect synthesis of triacylglycerols and steryl esters in the yeast

Tgl3p, Tgl4p and Tgl5p are the major triacylglycerol lipases of the yeast Saccharomyces cerevisiae catalyzing degradation of triacylglycerols stored in lipid droplets. Previous results from our laboratory (Athenstaedt and Daum, 2005,J. Biol. Chem. 280,37301-37309) demonstrated that a yeast strain lacking all three triacylglycerol lipases accumulates not only triacylglycerols at high amount, but also steryl esters. Here we show a metabolic link between synthesis and mobilization of non-polar lipids. In particular, we demonstrate that a block in triacylglycerol degradation in a tgl3 Delta tgl4 Delta tgl5 Delta. triple mutant lacking all major triacylglycerol lipases causes marked changes in non-polar lipid synthesis. Under these conditions formation of triacylglycerols is reduced, whereas steryl ester synthesis is enhanced as shown by quantification of non-polar lipids, in vivo labeling oflipids using [C-14]oleic add and [C-14]acetic acid as precursors, and enzyme analyses in vitro. In summary, this study demonstrates that triacylglycerol metabolism and steryl ester metabblism are linked processes. The importance of balanced storage and degradation of these components for lipid homeostasis in the yeast is highlighted. (C) 2014 Elsevier B.V. All rights reserved.