Tor signaling and nutrient-based signals converge on Mks1p phosphorylation to regulate expression of Rtg1.Rtg3p-dependent target genes.
The heterodimeric bZip/HLH transcription factors Rtg1p and Rtg3p regulate the expression of a concise set of metabolic genes (termed RTG target genes) required for de novo biosynthesis of glutamate and glutamine. Several components have now been identified that control both the intracellular localization as well as activity of the Rtg1p.Rtg3p complex, yet the precise upstream regulatory signals involved remain unclear. For example, it has been proposed that Rtg1p.Rtg3p activity is repressed by glutamate, acting through the mitochondrial retrograde response pathway or, alternatively, by glutamine, acting through the Tor kinase pathway. Here we demonstrate that RTG target gene regulation is remarkably complex, with glutamate and glutamine as well as ammonia collaborating as potentially distinct signals to regulate RTG target gene expression. We show that both Tor and these nutrient-based signals converge on Mks1p, the immediate upstream inhibitor of Rtg1p.Rtg3p, and that a direct correlation exists between the degree of Mks1p phosphorylation and the extent of RTG target gene repression. Finally, we find that Tor- and glutamine-mediated RTG-target gene repression can be experimentally uncoupled, indicating that glutamine and Tor act, at least in part, independently to inhibit this pathway.
Section of Molecular and Cellular Biology and Center for Genetics and Development, Division of Biological Sciences, University of California, Davis, California 95616, USA.
Ivanka
I
Dilova
Sofia
S
Aronova
Jenny C-Y
JC
Chen
Ted
T
Powers
D000641:Ammonia / Q000494:pharmacology; D051778:Basic Helix-Loop-Helix Leucine Zipper Transcription Factors; D015152:Blotting, Northern; D015153:Blotting, Western; D018076:DNA, Complementary / Q000378:metabolism; D019281:Dimerization; D004305:Dose-Response Relationship, Drug; D017353:Gene Deletion; D005786:Gene Expression Regulation; D005838:Genotype; D018698:Glutamic Acid / Q000378:metabolism; D005973:Glutamine / Q000378:metabolism; D006801:Humans; D008856:Microscopy, Fluorescence; D008928:Mitochondria / Q000378:metabolism; D008954:Models, Biological; D009584:Nitrogen / Q000378:metabolism; D020411:Oligonucleotide Array Sequence Analysis; D019869:Phosphatidylinositol 3-Kinases / Q000378:metabolism*; D010766:Phosphorylation; D017853:Phosphotransferases (Alcohol Group Acceptor) / Q000378:metabolism*; D012097:Repressor Proteins / Q000378:metabolism*; D012441:Saccharomyces cerevisiae / Q000378:metabolism; D029701:Saccharomyces cerevisiae Proteins / Q000378:metabolism*; D015398:Signal Transduction; D020123:Sirolimus / Q000494:pharmacology; D014157:Transcription Factors / Q000378:metabolism*
D000641:Ammonia; D051778:Basic Helix-Loop-Helix Leucine Zipper Transcription Factors; D018076:DNA, Complementary; D018698:Glutamic Acid; D005973:Glutamine; D009584:Nitrogen; D019869:Phosphatidylinositol 3-Kinases; D017853:Phosphotransferases (Alcohol Group Acceptor); D012097:Repressor Proteins; D029701:Saccharomyces cerevisiae Proteins; D020123:Sirolimus; D014157:Transcription Factors; C080921:MKS1 protein, S cerevisiae; C079378:RTG1 protein, S cerevisiae; C104438:RTG3 protein, S cerevisiae; C083324:TOR1 protein, S cerevisiae