Feedback Inhibition of the Rag GTPase GAP Complex Lst4-Lst7 Safeguards TORC1 from Hyperactivation by Amino Acid Signals

• Published in: Cell reports (Cambridge) 2017-07, Vol.20 (2), p.281-288
• Main Authors: Péli-Gulli, Marie-Pierre, Raucci, Serena, Hu, Zehan, Dengjel, Jörn, De Virgilio, Claudio
• Format: Article
• Language: English
• Subjects: amino acid signaling; growth control; Immunoprecipitation; Lst4-Lst7 GAP complex; Mass Spectrometry; Mechanistic Target of Rapamycin Complex 1 - genetics; Mechanistic Target of Rapamycin Complex 1 - metabolism; Microscopy, Fluorescence; Phosphorylation; Rag GTPases; Saccharomyces cerevisiae - enzymology; Saccharomyces cerevisiae - metabolism; Saccharomyces cerevisiae Proteins - genetics; Saccharomyces cerevisiae Proteins - metabolism; Signal Transduction - genetics; Signal Transduction - physiology; target of rapamycin complex 1; TORC1; Transcription Factors - genetics; Transcription Factors - metabolism; Vesicular Transport Proteins - genetics; Vesicular Transport Proteins - metabolism
• ISSN: 2211-1247; 2211-1247
• DOI: 10.1016/j.celrep.2017.06.058

Amino acids stimulate the eukaryotic target of rapamycin complex 1 (TORC1), and hence growth, through the Rag GTPases and their regulators. Among these, the yeast Lst4-Lst7 Rag GTPase GAP complex clusters, as we previously reported, at the vacuolar membrane upon amino acid starvation. In response to amino acid refeeding, it activates the Rag GTPase-TORC1 branch and is then dispersed from the vacuolar surface. Here, we show that the latter effect is driven by TORC1 itself, which directly phosphorylates several residues within the intra-DENN loop of Lst4 that, only in its non-phosphorylated state, tethers the Lst4-Lst7 complex to the vacuolar membrane. An Lst4 variant disrupting this feedback inhibition mechanism causes TORC1 hyperactivation and proliferation defects in cells grown on poor nitrogen sources. Thus, we identify Lst4 as a TORC1 target and key node of a homeostatic mechanism that adjusts TORC1 activity to the availability of amino acids. [Display omitted] •Amino acids activate the Lst4-Lst7-Rag GTPase-TORC1 branch at the vacuolar membrane•The Lst4 intra-DENN loop is required and sufficient for its membrane tethering•TORC1 phosphorylates this loop to disperse the Lst4-Lst7 complex from the vacuole•This feedback inhibition prevents TORC1 hyperactivation and is relevant for growth Amino acids activate Rag GTPase-TORC1 signaling in part through the conserved Lst4-Lst7 Rag GTPase GAP complex. Here, Péli-Gulli et al. show that the Lst4-Lst7 module is a direct TORC1 target and key node of a feedback mechanism that adjusts TORC1 activity to amino acid availability.