Bipartite binding and partial inhibition links DEPTOR and mTOR in a mutually antagonistic embrace

Area of Science:

• Biochemistry
• Cell Biology
• Molecular Oncology

Background:

• The mechanistic target of rapamycin complex 1 (mTORC1) is a key regulator of cell growth, proliferation, and survival.
• Dysregulation of DEPTOR, an endogenous inhibitor of mTORC1, is implicated in various cancers.

Purpose of the Study:

• To elucidate the functional mechanism of DEPTOR as an mTORC1 inhibitor.
• To understand the structural basis of the mTORC1-DEPTOR interaction and its implications in cancer.

Main Methods:

• Reconstitution of the mTORC1 complex with DEPTOR.
• Biochemical assays to assess inhibition.
• Structural analyses (e.g., X-ray crystallography) of the mTORC1/DEPTOR complex.

Main Results:

• DEPTOR functions as a unique partial inhibitor of mTORC1, potentially preserving PI3K feedback inhibition.
• mTORC1 activated by RHEB or oncogenic mutations exhibits enhanced sensitivity to DEPTOR inhibition.
• A mutual antagonism exists where mTORC1 phosphorylates DEPTOR, preventing inhibition, a process independent of external factors.
• Structural studies identified key interaction domains: DEPTOR's PDZ domain with mTOR's FAT region and the linker binding to the FRB domain, with N-terminal DEP domains also contributing.

Conclusions:

• DEPTOR's partial inhibition of mTORC1 and the mutual phosphorylation mechanism offer novel insights into cellular regulation.
• The structural framework of the mTORC1-DEPTOR complex provides a basis for understanding its role in cancer and for therapeutic targeting.