Acute glucose starvation activates the nuclear localization signal of a stress-specific yeast transcription factor

Abstract

In yeast, environmental conditions control the transcription factor Msn2, the nuclear accumulation and function of which serve as a sensitive indicator of nutrient availablity and environmental stress load. We show here that the nuclear localization signal (NLS) of Msn2 is a direct target of cAMP-dependent protein kinase (cAPK). Genetic analysis suggests that Msn2-NLS function is inhibited by phosphorylation and activated by dephosphorylation. Msn2-NLS function is unaffected by many stress conditions that normally induce nuclear accumulation of full-length Msn2. The Msn2-NLS phosphorylation status is, however, highly sensitive to carbohydrate fluctuations during fermentative growth. Dephosphorylation occurs in >2 min after glucose withdrawal but the effect is reversed rapidly by refeeding with glucose. This response to glucose depletion is due to changes in cAPK activity rather than an increase in protein phosphatase activity. Surprisingly, the classical glucose-sensing systems are not connected to this rapid response system. Our results further imply that generic stress signals do not cause short-term depressions in cAPK activity. They operate on Msn2 by affecting an Msn5-dependent nuclear export and/or retention mechanism.

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

“…In strong support of this hypothesis, a reg1⌬ snf1⌬ double mutant depolarized as rapidly as wild type ( Figure 5, Aa and Ba). These results all parallel those obtained previously with respect to the rapid inhibition of translation initiation upon glucose removal (Ashe et al, 2000).In the cAPK pathway, cAPK negatively regulates the stress-responsive transcription factors Msn2p and Msn4p by inhibiting their nuclear import (Ruis and Schuller, 1995;Gö rner et al, 1998Gö rner et al, , 2002. A tpk1 w mutant (tpk1-1w tpk2⌬ tpk3⌬), which has a low level of cAPK activity, was largely resistant to actin depolarization upon glucose removal, whereas a tpk1⌬ tpk2⌬ tpk3⌬ msn2⌬ msn4⌬ strain depolarized as rapidly as wild type ( Figure 5, Ac and Bb).…”

“…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.…”

“…In the cAPK pathway, cAPK negatively regulates the stress-responsive transcription factors Msn2p and Msn4p by inhibiting their nuclear import (Ruis and Schuller, 1995;Gö rner et al, 1998Gö rner et al, , 2002. A tpk1 w mutant (tpk1-1w tpk2⌬ tpk3⌬), which has a low level of cAPK activity, was largely resistant to actin depolarization upon glucose removal, whereas a tpk1⌬ tpk2⌬ tpk3⌬ msn2⌬ msn4⌬ strain depolarized as rapidly as wild type ( Figure 5, Ac and Bb).…”

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

“…Upon glucose exhaustion, they are hyperphosphorylated and translocated to the nucleus, where they induce expression of the STREcontrolled genes. PKA inhibits nuclear import of Msn2/4, probably through direct phosphorylation of their nuclear localization signal (Gorner et al 1998(Gorner et al , 2002Garreau et al 2000). A second mechanism for PKA-mediated regulation of STRE-controlled gene expression involves the Ccr4-Not complex, a global transcriptional regulator that affects genes positively and negatively.…”

“…On the other hand, TORC1 inhibits the transcription of stress-responsive genes via a Rim15-independent, but Tap42-PP2A-dependent route, thereby promoting the phosphorylation and cytoplasmic retention of Msn2 (Beck and Hall 1999; Duvel et al 2003;Santhanam et al 2004). It is important to note that the latter is independent of the PKA-mediated phosphorylation of the Msn2/4 nuclear localization signal (Gorner et al 1998(Gorner et al , 2002Garreau et al 2000;Santhanam et al 2004).…”