Regulation of mammalian nucleotide metabolism and biosynthesis

Abstract

Nucleotides are required for a wide variety of biological processes and are constantly synthesized de novo in all cells. When cells proliferate, increased nucleotide synthesis is necessary for DNA replication and for RNA production to support protein synthesis at different stages of the cell cycle, during which these events are regulated at multiple levels. Therefore the synthesis of the precursor nucleotides is also strongly regulated at multiple levels. Nucleotide synthesis is an energy intensive process that uses multiple metabolic pathways across different cell compartments and several sources of carbon and nitrogen. The processes are regulated at the transcription level by a set of master transcription factors but also at the enzyme level by allosteric regulation and feedback inhibition. Here we review the cellular demands of nucleotide biosynthesis, their metabolic pathways and mechanisms of regulation during the cell cycle. The use of stable isotope tracers for delineating the biosynthetic routes of the multiple intersecting pathways and how these are quantitatively controlled under different conditions is also highlighted. Moreover, the importance of nucleotide synthesis for cell viability is discussed and how this may lead to potential new approaches to drug development in diseases such as cancer.

Glutaminase and poly(ADP-ribose) polymerase inhibitors suppress pyrimidine synthesis and VHL-deficient renal cancers

“…GLS1, glutaminase 1; CPSII, carbamoyl phosphate synthetase II; ACTase, aspartate transcarbamoylase; OMP, orotidine monophosphate; UMP, uridine monophosphate; PRPP, 5-phosphoribosyl pyrophosphate. orotase steps of UMP synthesis, and its activity is allosterically regulated at multiple levels to mediate de novo pyrimidine biosynthesis in a cell cycle-dependent manner (27,29,30 (28). CAD is the trifunctional enzyme that comprises the CPSII, ACTase, and dehydro- C 6 ]glucose with or without 2 μM BPTES for 48 hours, and the metabolite enrichment was measured by GC-MS. Effect of BPTES on the contribution of glucose oxidation, determined by the level of M2-enriched (E) and M3-enriched (F) TCA cycle intermediates, and of citrate enrichment (G).…”

Erratum: From Krebs to clinic: glutamine metabolism to cancer therapy

“…While carbon from glutamine is used for amino acid and fatty acid synthesis, nitrogen from glutamine contributes directly to both de novo purine and pyrimidine biosynthesis 118 . The importance of glutamine as a nitrogen reservoir is underscored by the fact that glutaminedeprived cancer cells undergo cell cycle arrest that cannot be rescued by TCA-cycle intermediates such as oxaloacetate but can be rescued by exogenous nucleotides 118,119 . In fact, synthesis of nucleotides from exogenous glutamine has been observed in human primary lung cancer samples cultured ex vivo 120 .…”

“…Aspartate derived from glutamine via the TCA cycle and transamination (Figures 2,3) serves as a crucial source of carbon for purine and pyrimidine synthesis 84,85 , and provision of aspartate can rescue cell cycle arrest caused by glutamine deprivation 86 . Additionally, glutamine dependent mTOR signaling may activate the enzyme carbamoyl-phosphate synthetase 2, aspartate transcarbamylase, and dihydroorotase (CAD), which catalyzes the incorporation of glutamine derived nitrogen into pyrimidine precursors 118,121,122 . It has been suggested that NADPH produced downstream of glutamine metabolism and flux through the malic enzymes can further support nucleotide synthesis 31 .…”

Molecular Basis of Nucleobase Transport Systems in Mammals

“…The de novo pathway assembles nucleotides from basic materials such as amino acids, bicarbonate, and ribose, and the salvage pathway utilizes purine nucleobases generated from the degradation of nucleosides and nucleotides. 2,3) The latter is advantageous in saving energy and materials for nucleotide production, which many types of cells physiologically adopt. This pathway can salvage not only intracellular purine nucleobases and nucleosides but also extracellular ones from dietary sources and those overproduced in other cells by the de novo pathway.…”