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

Abstract

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 ...

Multiple Endoplasmic Reticulum-to-Nucleus Signaling Pathways Coordinate Phospholipid Metabolism with Gene Expression by Distinct Mechanisms

“…7). Both phosphate and zinc are important nutrients that play important roles in regulating phospholipid metabolism (57)(58)(59)(60)(61)(62)(63). Taken together, these results suggest that long term adaptation to growth in the presence of inositol may require reprogramming of a number of regulatory circuits that sense nutrient availability.…”

Regulation of phospholipid synthesis in yeast

“…As discussed above, the repression of UAS INO -containing genes in response to inositol supplementation or zinc depletion is attributed to the regulation of PI synthase activity or PIS1 gene expression, respectively (36,37). Previous studies have shown that the levels of PA phosphatase activity are elevated in inositol-supplemented (52) and zincdepleted (53) cells as well as in stationary phase cells (54).…”

“…This regulation that occurs in the absence of inositol supplementation is mediated by the zinc-sensing and zinc-inducible transcriptional activator Zap1 and the zinc-responsive cis-acting element (UAS ZRE ) of phospholipid synthesis genes (9). Zinc depletion results in an increase in PI synthesis through increased expression of the PIS1-encoded PI synthase (35,37) that is mediated by the interaction of Zap1 with a UAS ZRE in the PIS1 promoter (35, 37). As indicated above, the increase in PI synthesis causes a decrease in PA content.…”

Phosphatidic Acid Plays a Central Role in the Transcriptional Regulation of Glycerophospholipid Synthesis in Saccharomyces cerevisiae

“…The increase in PI synthesis in response to zinc depletion is not the result of elevated levels of inositol; INO1 is actually repressed under this growth condition (75). Instead, the increase in PI synthesis is due to the Zap1p-mediated induction of PIS1 gene expression (76). Furthermore, zinc depletion induces Mg 2ϩ -dependent PA phosphatase activity (77), and this would further reduce the PA pool.…”