Calmodulin enhances mTORC1 signaling by preventing TSC2-Rheb binding

Area of Science:

• Cellular Biology
• Molecular Signaling
• Biochemistry

Background:

• The mechanistic target of rapamycin complex 1 (mTORC1) is crucial for cell growth and proliferation.
• Intracellular calcium ion (Ca2+) concentration modulates mTORC1 via calmodulin (CaM) binding to tuberous sclerosis complex 2 (TSC2).
• The exact molecular mechanism of Ca2+/CaM regulation of mTORC1 remains unclear.

Purpose of the Study:

• To elucidate the molecular mechanism by which Ca2+/CaM modulates mTORC1 activity.
• To investigate the interaction between TSC2, CaM, and Rheb in response to Ca2+.
• To understand how Ca2+ signaling influences TSC2 localization and mTORC1 activation.

Main Methods:

• Nano-luciferase reconstitution assay to detect TSC2-Rheb interactions.
• Live-cell imaging to analyze CaM-TSC2 binding.
• Treatment with carbachol and CaM inhibitors to assess mTORC1 pathway activation.
• Analysis of TSC2 dissociation from lysosomes.

Main Results:

• CaM inhibited TSC2-Rheb binding in a Ca2+-dependent manner.
• Elevated intracellular Ca2+ increased CaM binding to TSC2.
• Carbachol treatment activated mTORC1, an effect blocked by CaM inhibitors.
• Increased Ca2+ promoted TSC2 dissociation from lysosomes independently of Akt phosphorylation.

Conclusions:

• Ca2+/CaM binding to TSC2 inhibits its interaction with Rheb, a key activator of mTORC1.
• This Ca2+/CaM-mediated regulation of TSC2 is distinct from established Akt-dependent mechanisms.
• The findings provide mechanistic insights into how Ca2+ signaling activates the mTORC1 pathway through TSC2-Rheb regulation.