Glucose-induced hyperaccumulation of cyclic AMP and defective glucose repression in yeast strains with reduced activity of cyclic AMP-dependent protein kinase.

Abstract

Addition of glucose or related fermentable sugars to derepressed cells of the yeast Saccharomyces cerevisiae triggers a RAS-mediated cyclic AMP (cAMP) signal that induces a protein phosphorylation cascade. In yeast mutants (tpklwl, tpk2", and tpk3w') containing reduced activity of cAMP-dependent protein kinase, fermentable sugars, as opposed to nonfermentable carbon sources, induced a permanent hyperaccumulation of cAMP. This finding confirms previous conclusions that fermentable sugars are specific stimulators of cAMP synthesis in yeast cells. Despite the huge cAMP levels present in these mutants, deletion of the gene (BCYI) coding for the regulatory subunit of cAMP-dependent protein kinase severely reduced hyperaccumulation of cAMP. Glucose-induced hyperaccumulation of cAMP was also observed in exponential-phase glucose-grown cells of the tpklwl and tpk2w' strains but not the tpk3w' strain even though addition of glucose to glucose-repressed wild-type cells did not induce a cAMP signal. Investigation of mitochondrial respiration by in vivo 31P nuclear magnetic resonance spectroscopy showed the tpklwl and tpk2wl strains, but not the tpk3Wl strain, to be defective in glucose repression. These results are consistent with the idea that the signal transmission pathway from glucose to adenyl cyclase contains a glucose-repressible protein. They also show that a certain level of cAMP-dependent protein phosphorylation is required for glucose repression. Investigation of the glucose-induced cAMP signal and glucose-induced activation of trehalase in derepressed cells of strains containing only one of the wild-type TPK genes indicates that the transient nature of the cAMP signal is due to feedback inhibition by cAMP-dependent protein kinase.Cells of the yeast Saccharomyces cerevisiae contain two RAS genes, RAS] and RAS2, which are homologs of the mammalian ras genes H-ras, K-ras, and N-ras (21). The RAS proteins are plasma membrane-bound G proteins that are generally considered to be signal transmitters. The yeast RAS proteins were shown to act as controlling elements of adenyl cyclase (21). The product of the yeast gene CDC25 is required for RAS activity and hence for cyclic AMP (cAMP) synthesis in vivo (2). Addition of glucose or related fermentable sugars to derepressed yeast cells triggers a transient increase in the cAMP level which is mediated by the CDC25 and RAS proteins (12, 13). The hormonelike effect of glucose on adenyl cyclase, which resembles the well-known hormone effects on adenyl cyclase in mammalian cells, induces a protein phosphorylation cascade that mobilizes the storage sugar trehalose and stimulates the switch of metabolism from gluconeogenic to fermentative (16).In yeast cells, three genes, TPKJ, TPK2, and TPK3, code for the catalytic subunit of cAMP-dependent protein kinase (19). The presence of one of the three is enough for viability. Recently, yeast mutants tpkl"', tpk2"', and tpk3"' that show greatly reduced activity of cAMP-dependent protein kinase were isolated (14). In these strains, two ...

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

“…This transient increase is strongly reduced in a strain with enhanced feedback inhibition of cAMP synthesis by elevated cAPK activity (Mbonyi et al, 1990;Colombo et al, 1998; Figure 1B), such as a bcy1 disruptant, which is also defective in the slow adaptation of the actin cytoskeleton in the absence of glucose (see above). In addition, the transient increase is also partially dependent on Gpr1p, a putative G protein-coupled receptor, and Gpa2p, a G protein subunit (Thevelein, 1984;Kü bler et al, 1997;Kraakman et al, 1999).…”

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

“…PKA itself is involved in this mechanism since basal cAMP levels are dramatically increased in strains with reduced activity of the kinase (Nikawa et al 1987a;Mbonyi et al 1990). cAMP is hydrolyzed by the low-and high-affinity phosphodiesterases, respectively, encoded by PDE1 and PDE2 (Sass et al 1986;Nikawa et al 1987b;Wilson and Tatchell 1988).…”

“…Another target for feedback regulation could be adenylate cyclase itself (Nikawa et al 1987a). Furthermore, feedback regulation may involve other carbon source-dependent pathways as well, for instance the main glucose repression pathway, since no glucose-induced cAMP increase was observed in a snf1D mutant (Arguelles et al 1990). Finally, it is important to note that PKA activity is further finetuned by modulation of its subcellular localization, phosphorylation state and abundance (Werner-Washburne et al 1991;Griffioen et al 2000Griffioen et al , 2001Schmelzle et al 2004; http://doc.rero.ch Portela and Moreno 2006).…”

The activity of the gluconate‐H+ symporter of Schizosaccharomyces pombe cells is down‐regulated by d‐glucose and exogenous cAMP

“…For S. pombe [15], as well as S. cerevisiae [27] expression [30]. To examine the involvement of this kinase, 9 " gluconate transport measurements were performed in the kinase-deficient strain JZ633 [16].…”