TitleThe E3 ubiquitin ligase Pib1 regulates effective gluconeogenic shutdown upon glucose availability.
Publication TypeJournal Article
Year of Publication2019
AuthorsVengayil V, Rashida Z, Laxman S
JournalJ Biol Chem
Date Published2019 Oct 11

Cells use multiple mechanisms to regulate their metabolic states in response to changes in their nutrient environment. One example is the response of cells to glucose. In S. cerevisiae growing in glucose-depleted medium, the re-availability of glucose leads to the downregulation of gluconeogenesis, and the activation of glycolysis, leading to 'glucose repression'. However, our knowledge of the mechanisms mediating the glucose dependent downregulation of the gluconeogenic transcription factors is limited. Using a major gluconeogenic transcription factor Rds2 as a candidate, here we identify a novel role for the E3 ubiquitin ligase Pib1 in regulating the stability and degradation of Rds2. Glucose addition to cells growing in glucose limitation results in rapid ubiquitination of Rds2, followed by its proteasomal degradation. Through in vivo and in vitro experiments, we establish Pib1 as the ubiquitin E3 ligase that regulates Rds2 ubiquitination and stability. Notably, this Pib1 mediated Rds2 ubiquitination, followed by proteasomal degradation, is specific to the presence of glucose. This Pib1 mediated ubiquitination of Rds2 depends on the phosphorylation state of Rds2, suggesting a cross-talk between ubiquitination and phosphorylation to achieve a metabolic state change. Using stable-isotope based metabolic flux experiments we find that the loss of Pib1 results in an imbalanced gluconeogenic state, regardless of glucose availability. Pib1 is required for complete glucose repression, and enables cells to optimally grow in competitive environments when glucose becomes re-available. Our results reveal the existence of a Pib1 mediated regulatory program that mediates glucose-repression when glucose availability is restored.

Alternate JournalJ. Biol. Chem.
PubMed ID31604822