Related Experiment Videos
The TOR nutrient signalling pathway phosphorylates NPR1 and inhibits turnover of the tryptophan permease
1Department of Biochemistry, Biozentrum, University of Basel, CH-4056 Basel, Switzerland.
Abstract:
The Saccharomyces cerevisiae targets of rapamycin, TOR1 and TOR2, signal activation of cell growth in response to nutrient availability. Loss of TOR or rapamycin treatment causes yeast cells to arrest growth in early G1 and to express several other physiological properties of starved (G0) cells. As part of this starvation response, high affinity amino acid permeases such as the tryptophan permease TAT2 are targeted to the vacuole and degraded. Here we show that the TOR signalling pathway phosphorylates the Ser/Thr kinase NPR1 and thereby inhibits the starvation-induced turnover of TAT2. Overexpression of NPR1 inhibits growth and induces the degradation of TAT2, whereas loss of NPR1 confers resistance to rapamycin and to FK506, an inhibitor of amino acid import. NPR1 is controlled by TOR and the type 2A phosphatase-associated protein TAP42. First, overexpression of NPR1 is toxic only when TOR function is reduced. Secondly, NPR1 is rapidly dephosphorylated in the absence of TOR. Thirdly, NPR1 dephosphorylation does not occur in a rapamycin-resistant tap42 mutant. Thus, the TOR nutrient signalling pathway also controls growth by inhibiting a stationary phase (G0) programme. The control of NPR1 by TOR is analogous to the control of p70 s6 kinase and 4E-BP1 by mTOR in mammalian cells.
Insights
The targets of rapamycin (TOR) pathway in yeast regulates cell growth by inhibiting starvation responses. This study reveals TOR signaling controls the NPR1 kinase, preventing degradation of key amino acid transporters during starvation.
Area of Science:
- Cell Biology
- Molecular Biology
- Biochemistry
Background:
- The targets of rapamycin (TOR) pathway in Saccharomyces cerevisiae is crucial for signaling cell growth in response to nutrient availability.
- TOR inactivation or rapamycin treatment induces cell cycle arrest and triggers starvation responses, including the degradation of high-affinity amino acid permeases like tryptophan permease TAT2.
- Understanding the molecular mechanisms by which TOR regulates starvation responses is essential for comprehending cell growth control.
Purpose of the Study:
- To investigate the role of the TOR signaling pathway in regulating the starvation-induced turnover of the tryptophan permease TAT2.
- To elucidate the function of the Ser/Thr kinase NPR1 within the TOR pathway and its impact on cell growth and starvation responses.
- To determine the relationship between TOR, NPR1, and TAP42 in controlling the transition to the stationary phase (G0).
Main Methods:
- Investigated the effect of TOR signaling on NPR1 phosphorylation and TAT2 stability.
- Utilized yeast genetics, including overexpression and loss-of-function mutants for NPR1 and TAP42.
- Assessed cell growth, TAT2 degradation, and NPR1 phosphorylation status under various conditions, including rapamycin treatment and altered TOR activity.
Main Results:
- The TOR signaling pathway phosphorylates NPR1, thereby inhibiting the starvation-induced degradation of TAT2.
- Overexpression of NPR1 leads to growth inhibition and TAT2 degradation, while NPR1 loss-of-function confers resistance to rapamycin and FK506.
- NPR1 phosphorylation is dependent on TOR activity and is regulated by the type 2A phosphatase-associated protein TAP42.
Conclusions:
- The TOR nutrient signaling pathway controls cell growth by inhibiting a stationary phase (G0) program through the regulation of NPR1.
- NPR1 acts as a key mediator in the TOR pathway, linking nutrient availability to the control of amino acid permease stability.
- The regulatory mechanism involving TOR, NPR1, and TAP42 in yeast is analogous to the regulation of p70 s6 kinase and 4E-BP1 by mTOR in mammalian cells, highlighting conserved pathways in growth control.