The conversion of formate into purines stimulates mTORC1 leading to CAD-dependent activation of pyrimidine synthesis
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RESEARCH
Open Access
The conversion of formate into purines stimulates mTORC1 leading to CADdependent activation of pyrimidine synthesis Jacqueline Tait-Mulder1, Kelly Hodge1, David Sumpton1, Sara Zanivan1,2 and Alexei Vazquez1,2*
Abstract Background: Mitochondrial serine catabolism to formate induces a metabolic switch to a hypermetabolic state with high rates of glycolysis, purine synthesis and pyrimidine synthesis. While formate is a purine precursor, it is not clear how formate induces pyrimidine synthesis. Methods: Here we combine phospho-proteome and metabolic profiling to determine how formate induces pyrimidine synthesis. Results: We discover that formate induces phosphorylation of carbamoyl phosphate synthetase (CAD), which is known to increase CAD enzymatic activity. Mechanistically, formate induces mechanistic target of rapamycin complex 1 (mTORC1) activity as quantified by phosphorylation of its targets S6, 4E-BP1, S6K1 and CAD. Treatment with the allosteric mTORC1 inhibitor rapamycin abrogates CAD phosphorylation and pyrimidine synthesis induced by formate. Furthermore, we show that the formate-dependent induction of mTOR signalling and CAD phosphorylation is dependent on an increase in purine synthesis. Conclusions: We conclude that formate activates mTORC1 and induces pyrimidine synthesis via the mTORC1dependent phosphorylation of CAD.
Background Cells activate metabolic pathways during differentiation and de-differentiation. The activation of one or more biochemical reactions can, in turn, trigger a cascade of metabolic changes leading to a distinct metabolic state. We have recently shown that the mitochondrialdependent oxidation of the third carbon of serine to formate triggers a metabolic switch [1]. This switch is characterized by an increase in metabolic fluxes associated with glycolysis, purine synthesis and pyrimidine synthesis. * Correspondence: [email protected] 1 Cancer Research UK Beatson Institute, Switchback Road, Bearsden, Glasgow G61 1BD, UK 2 Institute of Cancer Sciences, University of Glasgow, Glasgow, UK
Nevertheless, how formate induces pyrimidine synthesis is yet unclear. The formate-dependent induction of pyrimidine synthesis is characterized by a dramatic increase of dihydroorotate levels [1]. Dihydroorotate is the product of carbamoyl phosphate synthetase (CAD), the first step of pyrimidine synthesis. We hypothesized that the formate-dependent increase in adenosine triphosphate (ATP) levels stimulate the enzymatic activity of cytosolic CAD. Mammalian CAD has a half saturation constant for ATP in the mM range [2], which is the range of intracellular ATP levels. However, a theoretical analysis of the full range of behavior indicates that increased ATP is not sufficient to explain the dramatic increase in dihydroorotate levels. A necessary condition is that the maximum CAD activity exceeds the maximum
© The Author(s). 2020 Open Access This article is licensed under a Creative Commons Attribution 4.0 International License, which permits use, sharing, adaptat
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