Phosphorylated Rho-GDP directly activates mTORC2 kinase towards AKT through dimerization with Ras-GTP to regulate...

Area of Science:

• Cellular signaling pathways
• Molecular mechanisms of cell regulation
• Biochemistry and molecular biology

Background:

• The mechanistic target of rapamycin complex 2 (mTORC2) is crucial for cell survival, metabolism, and cytoskeletal dynamics.
• AKT phosphorylation by mTORC2 is a key event, but its regulation remains poorly understood.
• Small GTPases, like Rho, are typically considered active in their GTP-bound state.

Purpose of the Study:

• To elucidate the regulatory mechanism controlling mTORC2-mediated AKT phosphorylation.
• To investigate the role of small GTPases, specifically Rho, in mTORC2 activation.
• To challenge the conventional understanding of GDP-bound G protein function.

Main Methods:

• Biochemical reconstitution using purified proteins in Dictyostelium discoideum.
• Analysis of supercomplex formation involving Rho-GTPase, Ras-GTP, and mTORC2.
• Investigation of chemoattractant-induced phosphorylation of Rho-GDP at S192 by GSK-3.
• Functional rescue experiments in Rho-null cells.

Main Results:

• GDP-bound Rho GTPase (Rho-GDP) directly activates mTORC2 to phosphorylate AKT.
• Rho-GDP promotes AKT phosphorylation by forming a supercomplex with Ras-GTP and mTORC2.
• Phosphorylation of Rho-GDP at S192 by GSK-3 regulates supercomplex formation.
• Rho-GDP rescues mTORC2-AKT phosphorylation and directed cell migration defects in Rho-null cells.

Conclusions:

• The GDP-bound form of Rho GTPase is an active activator of mTORC2 signaling.
• This study uncovers a novel mechanism where Rho-GDP activates mTORC2-AKT phosphorylation.
• The findings redefine the role of GDP-bound G proteins in cellular signaling and cell migration.