Hepatic glutamine synthetase controls N5-methylglutamine in homeostasis and cancer
Víctor H. Villar, Maria Francesca Allega, Ruhi Deshmukh, Tobias Ackermann, Mark A. Nakasone, Johan Vande Voorde, Thomas M. Drake, Janina Oetjen, Algernon Bloom, Colin Nixon, Miryam Müller, Stephanie May, Ee Hong Tan, Lars Vereecke, Maude Jans, Gillian Blancke, Daniel J. Murphy, Danny T. Huang, David Y. Lewis, Thomas G. Bird, Owen J. Sansom, Karen Blyth, David Sumpton, Saverio Tardito
Abstract
Abstract Glutamine synthetase (GS) activity is conserved from prokaryotes to humans, where the ATP-dependent production of glutamine from glutamate and ammonia is essential for neurotransmission and ammonia detoxification. Here, we show that mammalian GS uses glutamate and methylamine to produce a methylated glutamine analog, N 5 -methylglutamine. Untargeted metabolomics revealed that liver-specific GS deletion and its pharmacological inhibition in mice suppress hepatic and circulating levels of N 5 -methylglutamine. This alternative activity of GS was confirmed in human recombinant enzyme and cells, where a pathogenic mutation in the active site (R324C) promoted the synthesis of N 5 -methylglutamine over glutamine. N 5 -methylglutamine is detected in the circulation, and its levels are sustained by the microbiome, as demonstrated by using germ-free mice. Finally, we show that urine levels of N 5 -methylglutamine correlate with tumor burden and GS expression in a β-catenin-driven model of liver cancer, highlighting the translational potential of this uncharacterized metabolite.