Effect of growth phase on phospholipid biosynthesis in Saccharomyces cerevisiae

Phosphatidylglycerophosphate synthase catalyzes the committed step in the synthesis of the mitochondrial phospholipid cardiolipin. We showed previously that phosphatidylglycerophosphate synthase activity in Saccharomyces cerevisiae is increased in conditions favoring mitochondrial development and during growth in the absence of inositol. Interestingly, the regulatory effects of inositol were not altered in ino2, ino4, or opi1 mutants suggesting that regulation in response to inositol is not at the level of gene transcription. We report here that steady state mRNA levels of the PGS1 gene, which encodes phosphatidylglycerophosphate synthase, were not altered by inositol or choline. Growth in the presence of the inositol-depleting drug valproate led to an increase in phosphatidylglycerophosphate synthase activity unaccompanied by increased PGS1 mRNA. PGS1 mRNA abundance was not decreased in ino2 or ino4 mutants and was unaffected in an opi1 mutant. Therefore, regulation of phosphatidylglycerophosphate synthase by inositol is not mediated at the level of mRNA abundance and does not require the INO2-INO4-OPI1 regulatory circuit. PGS1 was increased in glycerol/ethanol compared with glucose media and was maximally expressed as cells entered the stationary phase. Deletion of the mitochondrial genome did not affect PGS1 expression. Thus, whereas inositol controls phosphatidylglycerophosphate synthase activity, regulation of PGS1 expression occurs primarily in response to mitochondrial development cues.

Section: Pgs1 Expression Peaks In the Early Stationarymentioning

confidence: 73%

Regulation of Phosphatidylglycerophosphate Synthase by Inositol in Saccharomyces cerevisiae Is Not at the Level of PGS1 mRNA Abundance

Zhong

Greenberg

2003

“…This enzyme is regulated by genetic and biochemical mechanisms that influence the synthesis of phospholipids via the CDP-DAG pathway as well as the synthesis of PI (13,25,123). The expression of CHO1 is repressed by water-soluble phospholipid precursors (67,100,103,104) and in the stationary phase of growth (124,125). The PS synthase enzyme is activated by DGPP, PA, PC, and PI but inhibited by cardiolipin, diacylglycerol, sphingoid bases, inositol, and CTP (20,34,38,40,126).…”

Section: Discussionmentioning

confidence: 99%

Regulation of Phospholipid Synthesis in Saccharomyces cerevisiae by Zinc

Iwanyshyn

Han

Carman

2004

156

Zinc is an essential nutrient required for the growth and metabolism of eukaryotic cells. In this work, we examined the effects of zinc depletion on the regulation of phospholipid synthesis in the yeast Saccharomyces cerevisiae. Zinc depletion resulted in a decrease in the activity levels of the CDP-diacylglycerol pathway enzymes phosphatidylserine synthase, phosphatidylserine decarboxylase, phosphatidylethanolamine methyltransferase, and phospholipid methyltransferase. In contrast, the activity of phosphatidylinositol synthase was elevated in response to zinc depletion. The level of Aut7p, a marker for the induction of autophagy, was also elevated in zinc-depleted cells. For the CHO1-encoded phosphatidylserine synthase, the reduction in activity in response to zinc depletion was controlled at the level of transcription. This regulation was mediated through the UAS INO element and by the transcription factors Ino2p, Ino4p, and Opi1p that are responsible for the inositol-mediated regulation of UAS INO -containing genes involved in phospholipid synthesis. Analysis of the cellular composition of the major membrane phospholipids showed that zinc depletion resulted in a 66% decrease in phosphatidylethanolamine and a 29% increase in phosphatidylinositol. A zrt1⌬ zrt2⌬ mutant (defective in the plasma membrane zinc transporters Zrt1p and Zrt2p) grown in the presence of zinc exhibited a phospholipid composition similar to that of wild type cells depleted for zinc. These results indicated that a decrease in the cytoplasmic levels of zinc was responsible for the alterations in phospholipid composition.

“…nutrient deprivation) by regulating the expression of enzyme activities including those involved in phospholipid synthesis (4,27,40,40,43,66,67). In particular, the stress condition of zinc depletion results in an increase in PI content which is attributed to elevated expression of PI synthase activity (40).…”

Section: Discussionmentioning

confidence: 99%

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

Han

Iwanyshyn

et al. 2005

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 ...