The key sensor of energy status, AMP-dependent kinase (AMPK), can be activated by intracellular ZMP generated directly from the aminoimidazolecarboxamide ribonucleoside (AICAR) or from inhibition of purine synthesis by the antifolate pemetrexed (PTX). In spite of this common mechanism, signaling from AMPK activated by PTX or AICAR differed: PTX-activated AMPK phosphorylated the mTORC1 component Raptor but not tuberin (TSC2), whereas AICAR-activated AMPK phosphorylated both targets. This dichotomy proved to be due to p53 function: although p53 accumulated after either treatment, AICAR robustly activated the transcriptional profile of p53, including expression of p53 target genes TSC2 and sestrin2 whereas, in PTX-treated cells, p53 was virtually inactive as a transcriptional activator. Accordingly, activation of AMPK by PTX initiated a cell growth inhibition that was p53 and TSC2 independent, whereas p53 and TSC2 wild-type HCT116 colon carcinoma cells were more sensitive to AICAR than isogenic cells null for p53 or both p53 and TSC2. Furthermore, in cells null for p53, mTORC1 was hyperactive, apparently caused by lower TSC2 function, higher Rheb bound to mTORC1, and a concomitantly lower inhibition of mTORC1 by PRAS40. Although TSC2 was deficient and mTORC1 activity enhanced in the absence of p53 function, Raptor phosphorylation by AMPK following PTX was robust and independent of both p53 and TSC2. This provides insight into the therapeutic activity of PTX against human lung cancers lacking p53 function and with hyperactive mTORC1, a feature atypical of other antifolates. We concluded that phosphorylation of Raptor by AMPK after PTX treatment was both necessary and sufficient to suppress the kinase activity of mTORC1, even under conditions of limited TSC2 and enhanced mTORC1 function, suggesting the use of pemetrexed for treatment of Tuberous Sclerosis.

Citation Format: Stuti Agarwal, Catherine M. Bell, Richard G. Moran. Phosphorylation of Raptor by pemetrexed-activated AMPK is sufficient to suppress mTORC1 activity promoted by loss of p53 and TSC2. [abstract]. In: Proceedings of the 105th Annual Meeting of the American Association for Cancer Research; 2014 Apr 5-9; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2014;74(19 Suppl):Abstract nr 2432. doi:10.1158/1538-7445.AM2014-2432