title: Integration of transcriptional and posttranslational regulation in a glucose signal transduction pathway in Saccharomyces cerevisiae.
abstract: Expression of the HXT genes encoding glucose transporters in the budding yeast Saccharomyces cerevisiae is regulated by two interconnected glucose-signaling pathways: the Snf3/Rgt2-Rgt1 glucose induction pathway and the Snf1-Mig1 glucose repression pathway. The Snf3 and Rgt2 glucose sensors in the membrane generate a signal in the presence of glucose that inhibits the functions of Std1 and Mth1, paralogous proteins that regulate the function of the Rgt1 transcription factor, which binds to the HXT promoters. It is well established that glucose induces degradation of Mth1, but the fate of its paralogue Std1 has been less clear. We present evidence that glucose-induced degradation of Std1 via the SCF(Grr1) ubiquitin-protein ligase and the 26S proteasome is obscured by feedback regulation of STD1 expression. Disappearance of Std1 in response to glucose is accelerated when glucose induction of STD1 expression due to feedback regulation by Rgt1 is prevented. The consequence of relieving feedback regulation of STD1 expression is that reestablishment of repression of HXT1 expression upon removal of glucose is delayed. In contrast, degradation of Mth1 is reinforced by glucose repression of MTH1 expression: disappearance of Mth1 is slowed when glucose repression of MTH1 expression is prevented, and this results in a delay in induction of HXT3 expression in response to glucose. Thus, the cellular levels of Std1 and Mth1, and, as a consequence, the kinetics of induction and repression of HXT gene expression, are closely regulated by interwoven transcriptional and posttranslational controls mediated by two different glucose-sensing pathways.
authors.affiliation: Department of Genetics, Campus Box 8232, Washington University School of Medicine, 660 S. Euclid Avenue, St. Louis, Missouri 63110, USA.
authors.forename: Jeong-Ho
authors.initials: JH
authors.lastname: Kim
authors.forename: Valérie
authors.initials: V
authors.lastname: Brachet
authors.forename: Hisao
authors.initials: H
authors.lastname: Moriya
authors.forename: Mark
authors.initials: M
authors.lastname: Johnston
mesh_terms: D048868:Adaptor Proteins, Signal Transducing; D002843:Chromatin / Q000378:metabolism; D004268:DNA-Binding Proteins; D015966:Gene Expression Regulation, Fungal / Q000187:drug effects; D005947:Glucose / Q000378:metabolism* / Q000494:pharmacology; D051246:Glucose Transport Proteins, Facilitative; D047908:Intracellular Signaling Peptides and Proteins; D008565:Membrane Proteins / Q000378:metabolism; D009004:Monosaccharide Transport Proteins / Q000235:genetics; D009154:Mutation / Q000235:genetics; D011401:Promoter Regions, Genetic; D011499:Protein Processing, Post-Translational / Q000187:drug effects; D012097:Repressor Proteins / Q000378:metabolism; D044843:SKP Cullin F-Box Protein Ligases / Q000378:metabolism; D012441:Saccharomyces cerevisiae / Q000187:drug effects / Q000235:genetics* / Q000378:metabolism*; D029701:Saccharomyces cerevisiae Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D015398:Signal Transduction / Q000187:drug effects; D015534:Trans-Activators / Q000378:metabolism; D014157:Transcription Factors; D014158:Transcription, Genetic / Q000187:drug effects; D025801:Ubiquitin / Q000378:metabolism
chemical_list: D048868:Adaptor Proteins, Signal Transducing; D002843:Chromatin; D004268:DNA-Binding Proteins; D051246:Glucose Transport Proteins, Facilitative; C090595:HXT3 protein, S cerevisiae; D047908:Intracellular Signaling Peptides and Proteins; C118806:MTH1 protein, S cerevisiae; D008565:Membrane Proteins; D009004:Monosaccharide Transport Proteins; C102114:RGT1 protein, S cerevisiae; D012097:Repressor Proteins; C081335:STD1 protein, S cerevisiae; D029701:Saccharomyces cerevisiae Proteins; D015534:Trans-Activators; D014157:Transcription Factors; D025801:Ubiquitin; D044843:SKP Cullin F-Box Protein Ligases; D005947:Glucose