Glucose Depletion Rapidly Inhibits Translation Initiation in Yeast

Abstract

Glucose performs key functions as a signaling molecule in the yeast Saccharomyces cerevisiae. Glucose depletion is known to regulate gene expression via pathways that lead to derepression of genes at the transcriptional level. In this study, we have investigated the effect of glucose depletion on protein synthesis. We discovered that glucose withdrawal from the growth medium led to a rapid inhibition of protein synthesis and that this effect was readily reversed upon readdition of glucose. Neither the inhibition nor the reactivation of translation required new transcription. This inhibition also did not require activation of the amino acid starvation pathway or inactivation of the TOR kinase pathway. However, mutants in the glucose repression (reg1, glc7, hxk2, and ssn6), hexose transporter induction (snf3 rgt2), and cAMP-dependent protein kinase (tpk1(w) and tpk2(w)) pathways were resistant to the inhibitory effects of glucose withdrawal on translation. These findings highlight the intimate connection between the nutrient status of the cell and its translational capacity. They also help to define a new area of posttranscriptional regulation in yeast.

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

“…In the presence of antimycin A, repolarization did not occur in the absence of glucose ( Figure 4A; and B, left) but was rapid and extensive at each glucose concentration tested ( Figure 4A; and B, right). Similar results have been obtained for the regulation of translation initiation after glucose readdition to starved cells (Ashe et al, 2000). Thus, both actin polarization and translation initiation are simultaneously regulated by glucose, and this synchronous regulation can be divided into three individual processes: 1) the rapid shutdown immediately after glucose removal, 2) the slow adaptation in the absence of glucose, and 3) the rapid recovery after readdition of glucose.…”

“…We then investigated whether translation initiation resumes after glucose removal, judging this by the polysome/monosome ratio, which has been observed to decrease in several mutants defective in translation initiation (Hartwell and McLaughlin, 1969;Valasek et al, 1998). The polysome/monosome ratio was markedly reduced 30 min after glucose removal ( Figure 3D), as reported previously (Ashe et al, 2000). However, after 5 h in an aerated culture, high-molecular-weight materials increased, whereas monosomes decreased ( Figure 3D).…”

“…This is consistent with the transient depolarization observed here, because ϳ20% of cells contained repolarized actin 2 h after glucose removal ( Figure 2B). The timing of actin depolarization upon glucose deprivation closely resembled that observed for translation inhibition (Ashe et al, 2000), suggesting that glucose deprivation simultaneously regulates both actin polarization and translation initiation. In addition, the specificity for carbon source on actin depolarization (see above) is similar to that found for the regulation of gene repression/derepression or translation initiation (Thevelein, 1994;Ashe et al, 2000).…”

“…Glucose deprivation also rapidly inhibits translation initiation (Martinez-Pastor and Estruch, 1996;Ashe et al, 2000). Ashe et al (2000) reported that several mutants affected in the glucose-sensing signal transduction pathways are resistant to the inhibitory effect of glucose removal on translation initiation. This indicates that these pathways are involved in the regulation of translation initiation as well as the transcriptional control of glucose-regulated genes.…”

Reversible induction of translational isoforms of p53 in glucose deprivation

“…Methionine synthase, a key enzyme that clears intracellular homocysteine, is induced by its cofactor, vitamin B12, at a translational level through an IRES in the 5'UTR of the mRNA. 26 In response to glucose deprivation, haploid Saccharomyces cerevisiae cells dramatically downregulate translation of most cellular messages, 27,28 but several yeast genes required for invasive growth, a developmental pathway induced by nutrient limitation, contain potent IRESs. 29 Serum starvation of mammalian cell cultures showed induction of Bcl-2 IRES 30 and activated translation of XIAP mRNA.…”