The mTOR proteins, an abbreviation for mammalian target of rapamycin, also known as mechanistic target of rapamycin, are two proteins that are involved in cell signaling pathways implicated in tumorigenesis.
The mTOR proteins are serine/threonine protein kinases that combine with several other proteins to form two large complexes (mTORC1 and mTORC2) 1. Regulation of mTOR proteins occurs via a complex balance of stimulatory and inhibitory pathways, with activation resulting in protein translation, cell growth, proliferation, and survival via several signaling pathways 2.
Loss of inhibition of mTOR is the basis for tumor formation in tuberous sclerosis. Normally, the hamartin (encoded by the TSC1 gene on chromosome 9q32-34) and tuberin (encoded by the TSC2 gene on chromosome 16p13.3) act as a complex which inactivate the Rheb (Ras homologue enriched in brain) protein. In its active state Rheb stimulates mTORC1. Thus, a mutation in either the TSC1 or TSC2 tumor suppressor genes results in overactivation of the mTOR pathway 1.
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