Author response: Ragulator and GATOR1 complexes promote fission yeast growth by attenuating TOR complex 1 through Rag GTPases

Abstract

TOR complex 1 (TORC1) is an evolutionarily conserved protein kinase complex that promotes cellular macromolecular synthesis and suppresses autophagy. Amino-acid-induced activation of mammalian TORC1 is initiated by its recruitment to the RagA/B-RagC/D GTPase heterodimer, which is anchored to lysosomal membranes through the Ragulator complex. We have identified in the model organism Schizosaccharomyces pombe a Ragulator-like complex that tethers the Gtr1-Gtr2 Rag heterodimer to the membranes of vacuoles, the lysosome equivalent in yeasts. Unexpectedly, the Ragulator-Rag complex is not required for the vacuolar targeting of TORC1, but the complex plays a crucial role in attenuating TORC1 activity independently of the Tsc1-Tsc2 complex, a known negative regulator of TORC1 signaling. The GATOR1 complex, which functions as Gtr1 GAP, is essential for the TORC1 attenuation by the Ragulator-Rag complex, suggesting that Gtr1 GDP -Gtr2 on vacuolar membranes moderates TORC1 signaling for optimal cellular response to nutrients.

The S. pombe CDK5 ortholog Pef1 regulates sexual differentiation through control of the TORC1 pathway and autophagy

“…As shown in Fig. 5C-E, after nitrogen starvation, the Psk1 phosphorylation levels were low in gtr2Δ, lam4Δ and npr2Δ cells, as previously reported (Chia et al, 2017). However, phosphorylation levels were significantly increased in the each double mutant with pef1 and gtr2, lam4 or npr2 deletion (Fig.…”

“…Under eutrophic conditions, TORC1 generally promotes cell growth through interactions with its regulators, such as GATOR1, Rag and Ragulator. In S. pombe, it has been proposed that Gtr2 (mammalian ortholog RagC and RagD), Lam4 (mammalian ortholog LAMTOR4) and Npr2 (mammalian ortholog NPRL2) are required for maintaining adequate TORC1 activity and normal growth (Chia et al, 2017). Therefore, the disruption of these genes should lead to an imbalance in TORC1 activity, resulting in growth defects.…”

“…In addition to the GATOR1, Rag and Ragulator complex, the TSC/ Rheb pathway is also conserved in S. pombe (Chia et al, 2017;Ma et al, 2013;Matsumoto et al, 2002;Murai et al, 2009;Urano et al, 2005Urano et al, , 2007Uritani et al, 2006;van Slegtenhorst et al, 2004). Notably, previous studies have reported that pas1, which encodes the predicted activating subunit of Pef1, genetically interacts with tsc2, and is involved in the regulation of amino acid uptake and the G1 arrest of the cell cycle (van Slegtenhorst et al, 2005).…”

“…Similar to the regulation of TORC1 in mammals, TORC1 in S. pombe localizes on the surface of vacuole (yeast lysosome), and is activated through interactions with Rhb1 (in mammals, Rheb GTPase), an essential activator of TORC1 in response to nitrogen sources (Murai et al, 2009;Urano et al, 2005Urano et al, , 2007Uritani et al, 2006;Valbuena et al, 2012). The TSC complex, which is comprised of Tsc1 and Tsc2, negatively regulates TORC1, as it acts as a GTPase-activating protein (GAP) for Rhb1 (Chia et al, 2017;Ma et al, 2013;Matsumoto et al, 2002;van Slegtenhorst et al, 2004). Rag GTPases and Ragulator are essential for anchoring TORC1 to the lysosome and vacuole membrane in mammals and budding yeast, respectively.…”

“…Rag GTPases and Ragulator are essential for anchoring TORC1 to the lysosome and vacuole membrane in mammals and budding yeast, respectively. However, a recent study suggested that in fission yeast, the Rag GTPases Gtr1 and Gtr2 and Ragulator components Lam1-Lam4 are dispensable for the vacuolar localization of TORC1 and attenuate TORC1 activity to maintain the normal growth of cells (Chia et al, 2017). In addition to these TORC1 regulatory systems, recent reports suggest that tRNA precursors regulate TORC1 activity in response to nutrients to prevent the initiation of sexual differentiation (Otsubo et al, 2018).…”