AKT-mediated phosphorylation of TSC2 controls stimulus- and tissue-specific mTORC1 signaling and organ growth

Area of Science:

• Cellular Biology
• Molecular Biology
• Physiology

Background:

• Mechanistic target of rapamycin (mTOR) complex 1 (mTORC1) is a central regulator of cell and tissue growth, integrating various growth signals.
• The precise physiological function of mTORC1 regulation, particularly the role of specific protein modifications like tuberous sclerosis complex 2 (TSC2) phosphorylation, in mammalian tissues remains incompletely understood.

Purpose of the Study:

• To investigate the in vivo physiological role of TSC2 phosphorylation sites targeted by AKT in regulating mTORC1 signaling.
• To characterize a novel mouse model (TSC2-5A) lacking these critical TSC2 phosphorylation sites.

Main Methods:

• Generation and analysis of a genetic mouse model (TSC2-5A) with mutations at five AKT-mediated phosphorylation sites on TSC2.
• Assessment of body weight, organ weight, and mTORC1 signaling pathway activity in TSC2-5A mice under physiological conditions.

Main Results:

• TSC2-5A mice are developmentally normal but exhibit reduced body weight and organ weights (e.g., brain, skeletal muscle).
• These mice show cell-intrinsic reductions in growth factor-stimulated mTORC1 signaling.
• The study confirms TSC2 phosphorylation as a significant, though not universal, mechanism for mediating exogenous signal-induced mTORC1 regulation in specific tissues.

Conclusions:

• TSC2 phosphorylation by AKT is a critical physiological mechanism controlling mTORC1 signaling in response to growth factors in certain mammalian tissues.
• The developed TSC2-5A mouse model serves as a valuable genetic tool for further research into the physiological regulation of mTORC1 signaling pathways in vivo.