Characterization of RagC phosphorylation sites reveals self-regulation of mTOR complex 1

Yang G1, Murashige D2, Francis D1, Wang Q1,3, Humphrey S1, Neely G1 and James D1

  1. The University of Sydney, School of Life and Environmental Sciences, Charles Perkins Centre, Sydney.
  2. University of Pennsylvania, Perelman School of Medicine, Philadelphia, PA 19104, USA.
  3. Sun Yat-sen University, School of Pharmaceutical Sciences (Shenzhen), Guangzhou 510275, China.

The mechanistic target of rapamycin complex1 (mTORC1) controls cell growth, proliferation and metabolism in response to diverse stimuli. Two major parallel pathways are implicated in mTORC1 regulation including a growth factor-responsive pathway mediated via TSC2/Rheb, and an amino acid-responsive pathway mediated via the Rag GTPases. Here we identify and characterize three highly conserved growth factor-responsive phosphorylation sites on RagC, a component of the Rag heterodimer, implicating cross talk between amino acid and growth factor-mediated regulation of mTORC1. We find that RagC phosphorylation is associated with destabilization of mTORC1, and is essential for both growth factor and amino acid-induced mTORC1 activation. Functionally, phosphorylation of RagC suppresses starvation-induced autophagy, and genetic studies in Drosophila reveal that RagC phosphorylation plays an essential role in regulation of cell growth. Finally, we identify mTORC1 as an upstream kinase of RagC on Ser21. Our data highlight the convergence of amino acid and growth factor pathways at the level of the RagC GTPase, and identify a previously unappreciated auto-regulatory mechanism of mTORC1 activity.