Effect of adenosine treatment on HAP1 cells with a knockout of MTHFD1

Folate metabolism provides the building blocks of many classes of biomolecules including purine nucleotides, thymidylate, serine and methionine and is an important target of antimetabolite drugs. A central enzyme in the pathway is the trifunctional MTHFD1, that catalyzes the interconversion of folates by its formyltetrahydrofolate synthetase and methylenetetrahydrofolate dehydrogenase/methenyltetrahydrofolate cyclohydrolase domains. Here, we employ large-scale chemical and genome-wide genetic screens to investigate the chemical and genetic dependencies caused by MTHFD1 loss-of-function and uncover a central role of the enzyme in balancing the response to extracellular adenosine. We show that adenosine is essential in MTHFD1KO cells, where adenine-containing compounds counter AMPK activation and increase proliferation in a PARP8, ATF7 and PML-dependent manner. In contrast, adenosine supplementation causes strong toxicity in patient-derived MTHFD1-derived cells harboring dehydrogenase/cyclohydrolase domain mutations. This response, mediated by replication stress and activation of the DNA damage response, is dependent on the nucleotide salvage enzyme HRPT1 and on NUDT5, an enzyme involved in nuclear ATP generation. Our findings suggest an evolutionary rationale for integrating three distinct enzymatic activities within the single MTHFD1 protein and propose the application of dehydrogenase/cyclohydrolase inhibitors in tumors located in an adenosine-rich microenvironment. Overall design: RNAseq samples were performed in at least duplicates. All experiments contain respective control samples.