Phospholipid Metabolism Regulated by a Transcription Factor Sensing Phosphatidic Acid

Abstract

Cells regulate the biophysical properties of their membranes by coordinated synthesis of different classes of lipids. Here, we identified a highly dynamic feedback mechanism by which the budding yeast Saccharomyces cerevisiae can regulate phospholipid biosynthesis. Phosphatidic acid on the endoplasmic reticulum directly bound to the soluble transcriptional repressor Opi1p to maintain it as inactive outside the nucleus. After the addition of the lipid precursor inositol, this phosphatidic acid was rapidly consumed, releasing Opi1p from the endoplasmic reticulum and allowing its nuclear translocation and repression of target genes. Thus, phosphatidic acid appears to be both an essential ubiquitous metabolic intermediate and a signaling lipid.

Identification of Novel Membrane-binding Domains in Multiple Yeast Cdc42 Effectors

“…Except for the FAPP1 domain, which caused strong localization to Golgi membranes, each of the foreign domains restored Ste20 localization to bud tips and to shmoo tips in pheromone-treated cells ( Figure 5C). In addition, the Opi1 chimera showed strong nuclear localization, consistent with the dual targeting activity of the isolated Opi1 domain (Loewen et al, 2004). In pheromone response assays, signaling was restored to levels that agreed with the localization of each chimera ( Figure 5D).…”

“…Notably, the Gic1 BR domain (but not the Gic2 BR domain) also showed nuclear-targeting activity, the strength of which was influenced by adjacent sequences ( Figure 7B). Related dual targeting behavior has been found recently for similar domains in Opi1 and Ste5 (Loewen et al, 2004;, and was also weakly apparent for the Ste20 BR domain (see Figure 1A, vi and vii). In addition to their targeting activity as isolated motifs, the BR domains from both Gic1 and Gic2 could potently substitute for the Ste20 BR domain in pheromone response assays (Supplementary Figure S3).…”

“…We used PH domains from mammalian PLC␦ (which binds PIP 2 ), mammalian FAPP1 (which binds PI4P and PIP 2 ), and yeast Cla4 (which binds multiple phospholipids; Kavran et al, 1998;Levine and Munro, 2002;Wild et al, 2004), as well as BR motifs from yeast Spo20 (which prefers PA) and yeast Opi1 (which binds PA and mediates both membrane and nuclear localization; Loewen et al, 2004;Nakanishi et al, 2004). When expressed as isolated domains tagged with GFP, each of these domains localized in a manner consistent with previous studies (Figure 5B), although in several cases they showed polarized localization that was not reported previously (see Discussion).…”

Rearrangements of the transcriptional regulatory networks of metabolic pathways in fungi

“…Opi1 is a repressor that monitors imbalances in the phosphatidic acid pool, and when inositol is limiting it directly interacts with phosphatidic acid and is tethered in the endoplasmic reticulum. This derepresses the Ino2/4 activatory complex that can then turn on the transcription of biosynthetic enzyme genes [30,31]. The Ino4 and Ino2 proteins as well as the structural genes of the inositol/choline (IC) regulon are highly conserved between S. cerevisiae and C. albicans.…”

Role of phosphatidic acid in plant galactolipid synthesis

“…Since local concentration of Ca 2þ and Mg 2þ can fluctuate very rapidly in particular cellular condition, this chemical property of PA is an important feature to probe its environment. As a consequence PA can behave as a pH biosensor as notably reported in yeast for regulation of expression of phospholipid metabolic genes through PA-dependent sequestration in the ER of the transcription factor Opi1p [16,51,52]. Interestingly it has been recently demonstrated that during the first minutes of carbon deprivation the cytosolic pH of plant cells rises from 7.4 to stabilize at 7.8 and recovers to more acidic pH within 5 min after carbon repletion accompanying modification of level of soluble phosphorous metabolites [53].…”