GPCR signaling inhibits mTORC1 via PKA phosphorylation of Raptor

Area of Science:

• Cellular signaling pathways
• Molecular biology
• Biochemistry

Background:

• The mammalian target of rapamycin complex 1 (mTORC1) is a key regulator of cell growth, metabolism, and autophagy.
• While activators of mTORC1 are well-studied, the signaling pathways that inhibit mTORC1 remain largely unknown.
• Understanding mTORC1 inhibition is crucial for addressing diseases characterized by its hyperactivation.

Purpose of the Study:

• To identify novel signaling pathways that directly inhibit mTORC1 activity.
• To elucidate the molecular mechanism by which G-protein coupled receptors (GPCRs) influence mTORC1.
• To explore the therapeutic potential of targeting GPCR-mediated mTORC1 inhibition.

Main Methods:

• Investigated the role of Gαs-coupled GPCRs in regulating mTORC1.
• Utilized cell-based assays to measure cyclic adenosine 3'5' monophosphate (cAMP) levels and protein kinase A (PKA) activity.
• Performed site-directed mutagenesis on the Raptor protein (Ser 791) to assess the role of phosphorylation.
• Examined mTORC1 inhibition in various cell lines and mouse tissues.

Main Results:

• Stimulation of Gαs-coupled GPCRs leads to increased cAMP levels, activating PKA.
• Activated PKA directly phosphorylates Raptor at Serine 791, resulting in mTORC1 inhibition.
• Mutating Raptor Serine 791 to Alanine partially rescues mTORC1 activity despite PKA activation.
• Gαs-coupled GPCRs effectively inhibit mTORC1 in diverse cellular and tissue contexts.

Conclusions:

• Discovered a novel signaling pathway where Gαs-coupled GPCRs inhibit mTORC1 via the cAMP-PKA-Raptor axis.
• PKA-mediated phosphorylation of Raptor at Ser 791 is a critical step in mTORC1 inhibition.
• Gαs-coupled GPCRs represent potential therapeutic targets for diseases associated with mTORC1 hyperactivation.