mTOR Signaling Pathway

The mechanistic target of rapamycin (mTOR) is a central regulator of cell growth, metabolism, autophagy, and aging. Dysregulation drives cancer, neurodegeneration, and accelerated aging.

Overview

mTOR exists in two complexes: mTORC1 (sensitive to rapamycin) and mTORC2 (partially rapamycin-resistant). mTORC1 integrates signals from growth factors (PI3K/Akt), amino acids (Rag GTPases), energy status (AMPK), and oxygen to control protein synthesis via S6K1 and 4E-BP1. When nutrients are abundant, mTORC1 promotes anabolic processes and suppresses autophagy. When inhibited, cells shift to catabolic metabolism and activate quality control mechanisms.

Key Steps

Growth factors activate PI3K → Akt, which phosphorylates TSC2, releasing Rheb to activate mTORC1
Amino acids (leucine) activate Rag GTPases, recruiting mTORC1 to lysosomal surface
Active mTORC1 phosphorylates S6K1 (protein synthesis) and 4E-BP1 (cap-dependent translation)
mTORC1 phosphorylates ULK1, suppressing autophagy initiation
AMPK senses low energy (high AMP:ATP ratio) and directly inhibits mTORC1 via TSC2 and Raptor phosphorylation
Rapamycin binds FKBP12, forming a complex that allosterically inhibits mTORC1

Disease Relevance

Cancer: Constitutive mTORC1 activation drives tumor cell growth. PI3K/Akt/mTOR is the most frequently mutated pathway in cancer. mTOR inhibitors (temsirolimus, everolimus) are FDA-approved for renal cell carcinoma and breast cancer.
Alzheimer's: mTOR hyperactivation impairs autophagy-mediated clearance of tau and amyloid-β aggregates. Rapamycin rescues cognitive function in AD mouse models.
Aging: mTOR inhibition extends lifespan in every organism tested (yeast, worms, flies, mice). The PEARL trial is testing rapamycin for human longevity.

Therapeutic Targets

Rapamycin: Allosteric mTORC1 inhibitor via FKBP12 binding
Metformin: Indirect mTOR inhibition via AMPK activation
Berberine: AMPK activator that suppresses mTORC1 signaling
Resveratrol: SIRT1 activator that modulates mTOR through AMPK