Subcellular localization of the Snf1 kinase is regulated by specific β subunits and a novel glucose signaling mechanism

Abstract

The Snf1/AMP-activated protein kinase family has broad roles in transcriptional, metabolic, and developmental regulation in response to stress. In Saccharomyces cerevisiae, Snf1 is required for the response to glucose limitation. Snf1 kinase complexes contain the ␣ (catalytic) subunit Snf1, one of the three related ␤ subunits Gal83, Sip1, or Sip2, and the ␥ subunit Snf4. We present evidence that the ␤ subunits regulate the subcellular localization of the Snf1 kinase. Green fluorescent protein fusions to Gal83, Sip1, and Sip2 show different patterns of localization to the nucleus, vacuole, and/or cytoplasm. We show that Gal83 directs Snf1 to the nucleus in a glucose-regulated manner. We further identify a novel signaling pathway that controls this nuclear localization in response to glucose phosphorylation. This pathway is distinct from the glucose signaling pathway that inhibits Snf1 kinase activity and responds not only to glucose but also to galactose and sucrose. Such independent regulation of the localization and the activity of the Snf1 kinase, combined with the distinct localization of kinases containing different ␤ subunits, affords versatility in regulating physiological responses.

Simultaneous yet Independent Regulation of Actin Cytoskeletal Organization and Translation Initiation by Glucose inSaccharomyces cerevisiae

“…The other is the slow reactivation of both translation and actin polarization, possibly via gene expression changes brought about by Snf1p and Msn2p/4p, a hypothesis supported by the observation that both the snf1 and msn2/4 disruptants showed incomplete adaptation of actin polarization and translation initiation after glucose removal ( Figure 6). These two opposite reactions are likely to start at virtually the same time after glucose removal, because the shutdown is initiated after ϳ3 min (Figure 2), whereas Snf1p and Msn2p/4p are rapidly modified by phosphorylation and rapidly imported into the nucleus, respectively (Wilson et al, 1996;Vincent et al, 2001;Gö rner et al, 2002). As a result of the combination of these opposite reactions, the shutdown may occur only transiently.…”

Ubp8 and SAGA Regulate Snf1 AMP Kinase Activity

“…on April 8, 2019 by guest http://mcb.asm.org/ crease in the phosphorylation of these downstream targets (22,41). We show that SAGA, through the Ubp8 deubiquitinase, fine-tunes these activities, as hyperubiquitination of Snf1 decreases phosphorylation of both Snf1 and its downstream target, Gal83.…”

“…Therefore, it is likely that this isoform of the Snf1 complex is posttranslationally modified by Ubp8. In addition, Gal83 is phosphorylated by Snf1 in vivo and in vitro (22,41). Therefore, to determine if the hypophosphorylation of Snf1 that we observe in ubp8⌬ strains corresponds to a decrease in Snf1 activity, we monitored the phosphorylation status of Gal83 in wild-type, ubp8⌬, and snf1⌬ strains grown in activating (galactose) and nonactivating (glucose) carbon sources.…”

Life in the midst of scarcity: adaptations to nutrient availability in Saccharomyces cerevisiae

“…During growth on glucose medium, all Snf1 complexes are localized in the cytoplasm. However, upon glucose limitation, the Snf1-Sip1 complex translocates to the vacuole and the Snf1-Gal83 complex goes into the nucleus, whereas the Snf1-Sip2 complex remains in the cytoplasm (Vincent et al 2001). Certainly, the regulation of the nucleocytoplasmic distribution of Snf1-Gal83 is important, as Snf1 has such a great impact on gene expression.…”