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TORC1 specifically inhibits microautophagy through ESCRT-0.
Riko Hatakeyama1, Claudio De Virgilio2
1Department of Biology, University of Fribourg, 1700, Fribourg, Switzerland.
Current Genetics
|May 2, 2019
Summary
Nutrient starvation triggers protein degradation via multivesicular body (MVB) and microautophagy pathways, both needing Vps27. Target of rapamycin complex 1 (TORC1) specifically inhibits microautophagy by phosphorylating Vps27.
Area of Science:
- Cellular Biology
- Molecular Biology
- Biochemistry
Background:
- Nutrient starvation induces protein degradation via the multivesicular body (MVB) pathway and microautophagy.
- Both pathways depend on the Vps27 protein, a component of the endosomal sorting complex required for transport (ESCRT-0).
- The target of rapamycin complex 1 (TORC1) regulates cell growth and antagonizes Vps27 function in microautophagy via phosphorylation.
Purpose of the Study:
- To investigate whether TORC1-mediated phosphorylation of Vps27 also restrains MVB sorting at endosomes.
- To elucidate the specific mechanisms by which TORC1 controls protein degradation pathways.
Main Methods:
- Utilized a Vps277D variant mimicking TORC1-phosphorylated Vps27.
- Assessed the degradation of plasma membrane proteins (Mup1, Itr1) via MVB and vacuolar membrane proteins (Vph1) via microautophagy.
- Compared the sensitivity of cargo sorting to TORC1-modified Vps27 in different pathways.
Main Results:
- TORC1 inhibits both MVB-driven turnover of Mup1 and Itr1, and microautophagy-dependent degradation of Vph1.
- Cargo sorting of Vph1 at the vacuolar membrane is sensitive to TORC1-controlled Vps27 modifications.
- Cargo sorting of Mup1 and Itr1 at endosomes is not sensitive to these modifications, indicating alternative control mechanisms.
Conclusions:
- TORC1 specifically modulates microautophagy through Vps27 phosphorylation.
- TORC1 controls MVB sorting through mechanisms independent of Vps27 phosphorylation.
- This study reveals pathway-specific regulation of protein degradation by TORC1.
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