Purine Biosynthesis Regulates Mtorc1 By Modulating Rheb Gtpase Activity

The mechanistic target of rapamycin complex 1 (mTORC1) regulates protein synthesis through effects on mRNA translation and ribosome biogenesis. Emerging evidence suggests that active mTORC1 also stimulates the de novo biosynthesis of purine and pyrimidine nucleotides. Here, using pharmacologic and genetic tools, we demonstrate that mTORC1 signaling is modulated by cellular purine nucleotide pools arising from the metabolic processes that generate ATP and GTP. Inhibition of GARFT, the enzyme that catalyzes the first folate-dependent step in purine synthesis, by the specific inhibitor AG2037, dramatically inhibits mTORC1 signaling via an AMPK-independent mechanism. GARFT inhibition suppresses the level of the activated form of the Rheb GTPase, a requisite upstream activator of mTORC1, through a global reduction in intracellular guanine-based nucleotides, and subsequently reduces Rheb protein farnesylation. Moreover, we demonstrate that mTORC1 blockade resulting from AG2037-mediated inhibition of GARFT impacts both translation initiation and pyrimidine biosynthesis and results in robust tumor growth inhibition of non-small cell lung cancer (NSCLC) xenografts. Our findings indicate that the regulatory relationship between mTORC1 activity and purine nucleotide pool is bidirectional, and suggest that mTORC1 inhibition contributes to the clinically established antiproliferative effects of purine biosynthesis inhibitors in cancer and inflammatory diseases. Citation Format: Kezi Unsal-Kacmaz, Natasha Emmanuel, Shoba Ragunathan, Qin Shan, Fang Wang, Andreas Giannakou, Nanni Huser, Guixian Jin, Jeremy Myers, Robert T. Abraham. Purine biosynthesis regulates mTORC1 by modulating Rheb GTPase activity [abstract]. In: Proceedings of the AACR-NCI-EORTC International Conference: Molecular Targets and Cancer Therapeutics; 2017 Oct 26-30; Philadelphia, PA. Philadelphia (PA): AACR; Mol Cancer Ther 2018;17(1 Suppl):Abstract nr B025.