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Mechanism of metabolic control. Target of rapamycin signaling links nitrogen quality to the activity of the Rtg1 and Rtg3 transcription factors.

Komeili A, Wedaman KP, O'Shea EK, Powers T - J. Cell Biol. (2000)

Bottom Line: Remarkably, nuclear accumulation of Rtg1/Rtg3, as well as expression of their target genes, is induced by addition of rapamycin, a specific inhibitor of the target of rapamycin (TOR) kinases.We demonstrate further that Rtg3 is a phosphoprotein and that its phosphorylation state changes after rapamycin treatment.Taken together, these results demonstrate that target of rapamycin signaling regulates specific anaplerotic reactions by coupling nitrogen quality to the activity and subcellular localization of distinct transcription factors.

View Article: PubMed Central - PubMed

Affiliation: Howard Hughes Medical Institute, University of California School of Medicine, San Francisco, California 94143, USA.

ABSTRACT
De novo biosynthesis of amino acids uses intermediates provided by the TCA cycle that must be replenished by anaplerotic reactions to maintain the respiratory competency of the cell. Genome-wide expression analyses in Saccharomyces cerevisiae reveal that many of the genes involved in these reactions are repressed in the presence of the preferred nitrogen sources glutamine or glutamate. Expression of these genes in media containing urea or ammonia as a sole nitrogen source requires the heterodimeric bZip transcription factors Rtg1 and Rtg3 and correlates with a redistribution of the Rtg1p/Rtg3 complex from a predominantly cytoplasmic to a predominantly nuclear location. Nuclear import of the complex requires the cytoplasmic protein Rtg2, a previously identified upstream regulator of Rtg1 and Rtg3, whereas export requires the importin-beta-family member Msn5. Remarkably, nuclear accumulation of Rtg1/Rtg3, as well as expression of their target genes, is induced by addition of rapamycin, a specific inhibitor of the target of rapamycin (TOR) kinases. We demonstrate further that Rtg3 is a phosphoprotein and that its phosphorylation state changes after rapamycin treatment. Taken together, these results demonstrate that target of rapamycin signaling regulates specific anaplerotic reactions by coupling nitrogen quality to the activity and subcellular localization of distinct transcription factors.

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Model for involvement of the TOR pathway in nitrogen-dependent regulation of the Rtg1 and Rtg3 transcription factors. See text for details.
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Figure 10: Model for involvement of the TOR pathway in nitrogen-dependent regulation of the Rtg1 and Rtg3 transcription factors. See text for details.

Mentions: Our results also shed light on the functional role of Rtg2 in regulating RTG-dependent gene expression, a previously identified upstream positive regulator of Rtg1 and Rtg3 (Liao and Butow 1993; Rothermel et al. 1997). Specifically, we find that Rtg2 is required for rapamycin-induced entry of the Rtg1/Rtg3 complex into the nucleus (Fig. 10). How Rtg2 acts mechanistically is unclear at present; however, we believe that Rtg2 is likely to be required for a step subsequent to the action of TOR, based upon the observation that rapamycin-induced changes in Rtg3 phosphorylation are observed in rtg2Δ mutant cells (Fig. 8 B). Furthermore, our examination of Rtg3 localization in rtg1Δ, rtg2Δ, and rtg1Δ rtg2Δ mutant cells suggests that Rtg2 may interact primarily with Rtg1 to regulate nuclear entry of the Rtg1/Rtg3 complex (Fig. 7, and data not shown).


Mechanism of metabolic control. Target of rapamycin signaling links nitrogen quality to the activity of the Rtg1 and Rtg3 transcription factors.

Komeili A, Wedaman KP, O'Shea EK, Powers T - J. Cell Biol. (2000)

Model for involvement of the TOR pathway in nitrogen-dependent regulation of the Rtg1 and Rtg3 transcription factors. See text for details.
© Copyright Policy
Related In: Results  -  Collection

Show All Figures
getmorefigures.php?uid=PMC2169436&req=5

Figure 10: Model for involvement of the TOR pathway in nitrogen-dependent regulation of the Rtg1 and Rtg3 transcription factors. See text for details.
Mentions: Our results also shed light on the functional role of Rtg2 in regulating RTG-dependent gene expression, a previously identified upstream positive regulator of Rtg1 and Rtg3 (Liao and Butow 1993; Rothermel et al. 1997). Specifically, we find that Rtg2 is required for rapamycin-induced entry of the Rtg1/Rtg3 complex into the nucleus (Fig. 10). How Rtg2 acts mechanistically is unclear at present; however, we believe that Rtg2 is likely to be required for a step subsequent to the action of TOR, based upon the observation that rapamycin-induced changes in Rtg3 phosphorylation are observed in rtg2Δ mutant cells (Fig. 8 B). Furthermore, our examination of Rtg3 localization in rtg1Δ, rtg2Δ, and rtg1Δ rtg2Δ mutant cells suggests that Rtg2 may interact primarily with Rtg1 to regulate nuclear entry of the Rtg1/Rtg3 complex (Fig. 7, and data not shown).

Bottom Line: Remarkably, nuclear accumulation of Rtg1/Rtg3, as well as expression of their target genes, is induced by addition of rapamycin, a specific inhibitor of the target of rapamycin (TOR) kinases.We demonstrate further that Rtg3 is a phosphoprotein and that its phosphorylation state changes after rapamycin treatment.Taken together, these results demonstrate that target of rapamycin signaling regulates specific anaplerotic reactions by coupling nitrogen quality to the activity and subcellular localization of distinct transcription factors.

View Article: PubMed Central - PubMed

Affiliation: Howard Hughes Medical Institute, University of California School of Medicine, San Francisco, California 94143, USA.

ABSTRACT
De novo biosynthesis of amino acids uses intermediates provided by the TCA cycle that must be replenished by anaplerotic reactions to maintain the respiratory competency of the cell. Genome-wide expression analyses in Saccharomyces cerevisiae reveal that many of the genes involved in these reactions are repressed in the presence of the preferred nitrogen sources glutamine or glutamate. Expression of these genes in media containing urea or ammonia as a sole nitrogen source requires the heterodimeric bZip transcription factors Rtg1 and Rtg3 and correlates with a redistribution of the Rtg1p/Rtg3 complex from a predominantly cytoplasmic to a predominantly nuclear location. Nuclear import of the complex requires the cytoplasmic protein Rtg2, a previously identified upstream regulator of Rtg1 and Rtg3, whereas export requires the importin-beta-family member Msn5. Remarkably, nuclear accumulation of Rtg1/Rtg3, as well as expression of their target genes, is induced by addition of rapamycin, a specific inhibitor of the target of rapamycin (TOR) kinases. We demonstrate further that Rtg3 is a phosphoprotein and that its phosphorylation state changes after rapamycin treatment. Taken together, these results demonstrate that target of rapamycin signaling regulates specific anaplerotic reactions by coupling nitrogen quality to the activity and subcellular localization of distinct transcription factors.

Show MeSH