MTOR and cancer: Methionine scarcity impairs cancer cells' proliferation (55), and methionine dependency is controlled by PI3K/AKT/mTOR pathway through the induction of the expression of cyst(e)ine/glutamate antiporter xc- (xCT; SLC7A11 gene) (56), ensuring that the levels of cysteine won't limit the bioavailability of methionine, since cysteine uptake downregulates TSP.