MTOR and central nervous system cancer: Two tumor suppressors in the PI3K-mTOR pathway altered in the majority of human gliomas [20]–[23], PI3K regulatory subunit pi3kr1 and the tsc1 repressor of mTOR, were decreased in expression level in the Tg(flk1:RFP)is18 tumors (Fig. 5A and S7 Table).