Rag Ubiquitination Recruits a GATOR1: Attenuation of Amino Acid-Induced mTORC1 Signaling

Area of Science:

• Cellular signaling
• Molecular biology
• Biochemistry

Background:

• The mechanistic target of rapamycin complex 1 (mTORC1) pathway is a central regulator of cell growth and metabolism.
• mTORC1 activity is tightly controlled by nutrient availability, particularly amino acids.
• Rag GTPases are key mediators linking amino acid sensing to mTORC1 activation.

Purpose of the Study:

• To elucidate the molecular mechanisms by which amino acid signals are translated to mTORC1 regulation.
• To identify novel regulators of Rag GTPase activity in response to amino acid availability.

Main Methods:

• Ubiquitination assays to detect K63-linked polyubiquitination of RagA.
• Co-immunoprecipitation assays to assess the interaction between RagA and GATOR1.
• Biochemical assays to measure the GTPase-activating protein (GAP) activity of GATOR1 towards RagA/B GTPases.
• Cellular assays to monitor mTORC1 signaling activity.

Main Results:

• Two independent reports identified that K63-linked polyubiquitination of RagA is a critical regulatory event.
• This polyubiquitination event facilitates the recruitment of the GATOR1 complex to RagA/B GTPases.
• GATOR1 acts as a GTPase-activating protein (GAP) for RagA/B, promoting GTP hydrolysis and attenuating mTORC1 signaling.

Conclusions:

• K63-linked RagA polyubiquitination serves as an inhibitory signal for mTORC1 activation.
• The recruitment of GATOR1 by ubiquitinated RagA provides a direct link between ubiquitination status and mTORC1 pathway output.
• These findings reveal a novel regulatory axis controlling amino acid-dependent mTORC1 signaling.