Regulation of phosphatidylethanolamine methyltransferase and phospholipid methyltransferase by phospholipid precursors in Saccharomyces cerevisiae

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117

194

In the yeast Saccharomyces cerevisiae, the transcription of many genes encoding enzymes of phospholipid biosynthesis are repressed in cells grown in the presence of the phospholipid precursors inositol and choline. A genome-wide approach using cDNA microarray technology was used to profile the changes in the expression of all genes in yeast that respond to the exogenous presence of inositol and choline. We report that the global response to inositol is completely distinct from the effect of choline. Whereas the effect of inositol on gene expression was primarily repressing, the effect of choline on gene expression was activating. Moreover, the combination of inositol and choline increased the number of repressed genes compared with inositol alone and enhanced the repression levels of a subset of genes that responded to inositol. In all, 110 genes were repressed in the presence of inositol and choline. Two distinct sets of genes exhibited differential expression in response to inositol or the combination of inositol and choline in wild-type cells. One set of genes contained the UAS INO sequence and were bound by Ino2p and Ino4p. Many of these genes were also negatively regulated by OPI1, suggesting a common regulatory mechanism for Ino2p, Ino4p, and Opi1p. Another nonoverlapping set of genes was coregulated by the unfolded protein response pathway, an ER-localized stress response pathway, but was not dependent on OPI1 and did not show further repression when choline was present together with inositol. These results suggest that inositol is the major effector of target gene expression, whereas choline plays a minor role.Phospholipids are the key structural elements of membranebounded organelles and play important roles in signaling and membrane trafficking pathways. Each membrane compartment is composed of a unique set of phospholipids whose biophysical properties contribute to the function of each organelle. Phospholipid metabolism is highly regulated by the cell, ensuring the biogenesis and growth of membranes by coordinating the relative rates of synthesis of individual phospholipids with numerous factors, such as the availability of exogenous supplies of phospholipid precursors, growth stage, and membrane trafficking (1, 2).

Section: Global Analysis Of Inositol and Choline On Gene Expressionsupporting

confidence: 81%

Section: A Mechanism For Regulating the Expression Of Inositol-responmentioning

confidence: 61%

Section: Analysis Of Genome-wide Expression Regulated By Inositolmentioning

confidence: 99%

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Genome-wide Analysis Reveals Inositol, Not Choline, as the Major Effector of Ino2p-Ino4p and Unfolded Protein Response Target Gene Expression in Yeast

Jesch

Zhao

Wells

et al. 2005

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117

194

“…1). The coordinate repression of the CDP-diacylglycerol pathway enzymes by inositol requires the ongoing synthesis of PC (73,74) and is en- 687-880 and 0, 25, 50, and 100 pmol of unlabeled oligonucleotide with the sequence for UAS ZRE 3 . C, the experiment was performed with 0.6 g of recombinant GST-Zap1p 687-880 and sequences for wild type (WT) and mutated forms of UAS ZRE 3 .…”

Section: Discussionmentioning

confidence: 99%

Regulation of the PIS1-encoded Phosphatidylinositol Synthase in Saccharomyces cerevisiae by Zinc

Han

Iwanyshyn

et al. 2005

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279, 21976 -21983).We examined the effects of zinc depletion on the regulation of the PIS1-encoded phosphatidylinositol synthase, the enzyme that catalyzes the formation of phosphatidylinositol from CDP-diacylglycerol and inositol. Phosphatidylinositol synthase activity increased when zinc was depleted from the growth medium. Analysis of a zrt1⌬ zrt2⌬ mutant defective in plasma membrane zinc transport indicated that the cytoplasmic levels of zinc were responsible for the regulation of phosphatidylinositol synthase. PIS1 mRNA, its encoded protein Pis1p, and the ␤-galactosidase activity driven by the P PIS1 -lacZ reporter gene were elevated in zinc-depleted cells. This indicated that the increase in phosphatidylinositol synthase activity was the result of a transcriptional mechanism. The zinc-mediated induction of the P PIS1 -lacZ reporter gene, Pis1p, and phosphatidylinositol synthase activity was lost in zap1⌬ mutant cells. These data indicated that the regulation of PIS1 gene expression by zinc depletion was mediated by the zinc-regulated transcription factor Zap1p. Direct interaction between glutathione S-transferase (GST)-Zap1p 687-880 and a putative upstream activating sequence (UAS) zinc-responsive element in the PIS1 promoter was demonstrated by electrophoretic mobility shift assays. Mutations in the UAS zinc-responsive element in the PIS1 promoter abolished the GSTZap1p 687-880 -DNA interaction in vitro and abolished the zinc-mediated regulation of the PIS1 gene in vivo. This work advances understanding of phospholipid synthesis regulation by zinc and the transcription control of the PIS1 gene. Phosphatidylinositol (PI)1 is the third most abundant phospholipid in the cellular membranes of the yeast Saccharomyces cerevisiae (1-3), and it is essential for the growth and metabolism of this model eukaryote (4 -6). In addition to being a major structural component of the membrane, PI serves as the precursor for sphingolipids (7,8), the D-3, D-4, and D-5 phosphoinositides (3, 9 -12), and glycosylphosphatidylinositol anchors (13, 14) (Fig. 1). Several of these PI-derived lipids and their metabolic products are prominent signaling molecules in S. cerevisiae and in higher eukaryotes that contribute to essential physiological functions (12,(15)(16)(17)(18)(19)(20).The enzyme responsible for the synthesis of PI in S. cerevisiae is the essential PIS1-encoded PI synthase (CDP-diacylglycerol:myo-inositol 3-phosphatidyltransferase, EC 2.7.8.11) (6, 21-23). This endoplasmic reticulum-associated (24) enzyme catalyzes the formation of PI and CMP from CDP-diacylglycerol and inositol (25) (Fig. 1). The regulation of PI synthase activity in vivo is largely governed by the availability of its substrates inositol and CDP-diacylglycerol (26 -28). Cellular inositol levels are controlled by expression of the INO1 gene encoding inositol-3-phosphate synthase and by inositol supplementation (26 -28). The levels of CDP-diacylglycerol are controlled through its utilization by the PI synthase enzyme itself and the competing activity of ...

“…Strains with deletions in OPI3 or CHO and CYB5 or OLE1 were obtained from Susan Henry (21) and Charles Martin (22,23), respectively. Synthetic genetic interactions with neutral lipid acyltransferase genes were determined from an ER-Golgi epistatic SGA map (24).…”

Section: Methodsmentioning

confidence: 99%

Sterol and Diacylglycerol Acyltransferase Deficiency Triggers Fatty Acid-mediated Cell Death

Garbarino

Padamsee

Wilcox

et al. 2009

143

157

Deletion of the acyltransferases responsible for triglyceride and steryl ester synthesis in Saccharomyces cerevisiae serves as a genetic model of diseases where lipid overload is a component. The yeast mutants lack detectable neutral lipids and cytoplasmic lipid droplets and are strikingly sensitive to unsaturated fatty acids. Expression of human diacylglycerol acyltransferase 2 in the yeast mutants was sufficient to reverse these phenotypes. Similar to mammalian cells, fatty acid-mediated death in yeast is apoptotic and presaged by transcriptional induction of stressresponse pathways, elevated oxidative stress, and activation of the unfolded protein response. To identify pathways that protect cells from lipid excess, we performed genetic interaction and transcriptional profiling screens with the yeast acyltransferase mutants. We thus identified diacylglycerol kinase-mediated phosphatidic acid biosynthesis and production of phosphatidylcholine via methylation of phosphatidylethanolamine as modifiers of lipotoxicity. Accordingly, the combined ablation of phospholipid and triglyceride biosynthesis increased sensitivity to saturated fatty acids. Similarly, normal sphingolipid biosynthesis and vesicular transport were required for optimal growth upon denudation of triglyceride biosynthesis and also mediated resistance to exogenous fatty acids. In metazoans, many of these processes are implicated in insulin secretion thus linking lipotoxicity with early aspects of pancreatic ␤-cell dysfunction, diabetes, and the metabolic syndrome.