Journal
PROCEEDINGS OF THE NATIONAL ACADEMY OF SCIENCES OF THE UNITED STATES OF AMERICA
Volume 115, Issue 38, Pages 9545-9550Publisher
NATL ACAD SCIENCES
DOI: 10.1073/pnas.1811727115
Keywords
mTORC1; Ragulator; Rag GTPases; SLC38A9; guanine exchange factor
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Funding
- NIH [R01 CA103866, R01 CA129105, R37 AI047389]
- Department of Defense [W81XWH-15-1-0230]
- Lustgarten Foundation
- Life Sciences Research Foundation
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The mechanistic target of rapamycin complex 1 (mTORC1) growth pathway detects nutrients through a variety of sensors and regulators that converge on the Rag GTPases, which form heterodimers consisting of RagA or RagB tightly bound to RagC or RagD and control the subcellular localization of mTORC1. The Rag heterodimer uses a unique locking mechanism to stabilize its active ((GTP)RagA-RagC(GDP)) or inactive ((GDP)RagA-RagC(GTP)) nucleotide states. The Ragulator complex tethers the Rag heterodimer to the lysosomal surface, and the SLC38A9 transmembrane protein is a lysosomal arginine sensor that upon activation stimulates mTORC1 activity through the Rag GTPases. How Ragulator and SLC38A9 control the nucleotide loading state of the Rag GTPases remains incompletely understood. Here we find that Ragulator and SLC38A9 are each unique guanine exchange factors (GEFs) that collectively push the Rag GTPases toward the active state. Ragulator triggers GTP release from RagC, thus resolving the locked inactivated state of the Rag GTPases. Upon arginine binding, SLC38A9 converts RagA from the GDP-to the GTP-loaded state, and therefore activates the Rag GTPase heterodimer. Altogether, Ragulator and SLC38A9 act on the Rag GTPases to activate them TORC1 pathway in response to nutrient sufficiency.
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