Amino acid-dependent NPRL2 interaction with Raptor determines mTOR Complex 1 activation

Area of Science:

• Cell Biology
• Molecular Biology
• Biochemistry

Background:

• The mechanistic target of rapamycin complex 1 (mTORC1) pathway is a central regulator of cell growth and metabolism.
• Amino acid availability is a key signal that modulates mTORC1 activity.
• The tumor suppressor NPRL2's role in nutrient sensing and mTORC1 regulation remains largely unexplored.

Purpose of the Study:

• To elucidate the novel function of the tumor suppressor NPRL2 in regulating mTORC1 activity.
• To investigate the molecular mechanisms by which NPRL2 senses and responds to amino acid availability.
• To characterize the interaction of NPRL2 with key components of the mTORC1 pathway, including Rag GTPases and Raptor.

Main Methods:

• Co-immunoprecipitation assays to study protein-protein interactions.
• Cellular localization studies using microscopy.
• Analysis of mTORC1 activity under varying amino acid conditions.
• Genetic manipulation of NPRL2, Rag GTPases, and Raptor.
• Drosophila melanogaster as an in vivo model system.

Main Results:

• NPRL2 was identified as a novel activator of mTORC1 activity.
• NPRL2 interacts with Raptor in amino acid-sufficient conditions to promote mTORC1 activation.
• NPRL2 interacts with Rag GTPases, particularly RagD, to inhibit mTORC1 activity during amino acid scarcity.
• A reciprocal binding relationship between NPRL2 and Rag GTPases/Raptor was observed, dependent on amino acid availability.
• NPRL2's positive effect on the mTORC1 pathway was validated in a Drosophila model.

Conclusions:

• NPRL2 functions as a critical sensor of amino acid availability, integrating nutrient signals to control mTORC1 activity.
• A 'seesaw' model is proposed, where NPRL2 dynamically switches its binding partners (Rag GTPases vs. Raptor) to dictate mTORC1 activation.
• These findings reveal a previously unknown role for the tumor suppressor NPRL2 in cellular nutrient sensing and metabolic regulation.