Protein Kinase A-mediated Phosphorylation of Pah1p Phosphatidate Phosphatase Functions in Conjunction with the Pho85p-Pho80p and Cdc28p-Cyclin B Kinases to Regulate Lipid Synthesis in Yeast

Abstract

Background: Pah1p, a phosphatidate phosphatase in yeast, produces diacylglycerol for lipid synthesis. Results: Phosphorylation of Pah1p by protein kinase A inhibited membrane association, phosphatidate phosphatase activity, and triacylglycerol synthesis. Conclusion: Protein kinase A functioned in conjunction with Pho85p-Pho80p and Cdc28p-cyclin B kinases to regulate Pah1p. Significance: Lipid synthesis is regulated through multiple phosphorylations of Pah1p phosphatidate phosphatase.

Phosphorylation Regulates the Ubiquitin-independent Degradation of Yeast Pah1 Phosphatidate Phosphatase by the 20S Proteasome

“…Ser-769) may play a role in stimulating enzyme degradation. In vivo, the S10A mutation destabilizes Pah1 abundance (41), whereas alanine mutations of the protein kinase C sites stabilize abundance, but only when Pah1 is not already phosphorylated by Pho85-Pho80 (42).…”

“…carrying Pah1 with alanine mutations for phosphorylation sites indicate that its abundance in vivo is stabilized through its phosphorylation by Pho85-Pho80 (40), Cdc28-cyclin B (39), or protein kinase A (41). In Pah1, the target phosphorylation sites of the protein kinases are located in the regions that are predicted to be unfolded (Fig.…”

“…With more than 30 phosphorylation sites (18, 46 -51), it is one of the most heavily phosphorylated proteins in S. cerevisiae and has been shown to be a target for multiple protein kinases in vitro (49,52). Pah1 as a bona fide substrate has been confirmed for Pho85-Pho80 (40), Cdc28-cyclin B (39), protein kinase A (41), and protein kinase C (42). The physiological relevance of Pah1 phosphorylation by these protein kinases has been shown by analysis of cells expressing phosphorylation-deficient mutant forms of the enzyme (18, 39 -43).…”

“…In this process, the acidic tail of Pah1 plays a role for interaction with Nem1-Spo7 (44), and its N-terminal amphipathic helix mediates association with the membrane surface (43). Phosphorylation of Pah1 by Pho85-Pho80 or protein kinase A inhibits PAP activity (40,41), whereas its dephosphorylation by Nem1-Spo7 stimulates the enzyme activity (54). Pah1 is also regulated for PAP activity by membrane-associated and cytosolic factors.…”

Conserved Residues in the N Terminus of Lipin-1 Are Required for Binding to Protein Phosphatase-1c, Nuclear Translocation, and Phosphatidate Phosphatase Activity

“…However, it is possible that there are serine/threonine residues on lipin-1 that can modulate PP-1c binding when phosphorylated. For example, there are three serines in the NLIP domain of yeast Pah1p, which are phosphorylated by protein kinase A (serine 10) and Pho85p-Pho80p protein kinase⅐cyclin complex (serines 110 and 114) (42,43). Phosphorylation at these sites decreases PAP activity, membrane association, and triacyglycerol synthesis (42,43).…”