Fig. 1

Formate overflow is controlled by the cell redox state in vitro. a Diagram of mammalian one-carbon metabolism with serine as the major substrate for both anabolic and catabolic processes. b Correlation of formate release with the cell redox state estimated by the NAD⁺/NADH ratio. Symbols indicate different cell lines (see legend and Supplementary Table 1). Black symbols indicate standard cell culture conditions, red symbols indicate treatment with the complex I inhibitor rotenone (250 nM). The line represents a linear fit excluding outlier (triangle down). c–f Metabolic profile of HAP1 cells growing in regular medium or medium with galactose (Gal) instead of glucose (Ctrl). g–j Metabolic profile of HAP1 untreated cells (Ctrl) and cells treated with 50 nM MTX. Significant growth repression upon MTX is illustrated in Supplementary Fig. S1c. k–n Metabolic profile of HAP1 cells under ambient oxygen (21%) or moderate (1%) and deep (0.1%) hypoxia. o–r Metabolic profile of HAP1 parental, ΔSHMT1 and ΔSHMT2 cells. For knockout validation and growth analysis see Supplementary Fig. S2. Each dot indicates one independent experiment performed with triplicate wells. Each experiment was performed at least three times. Error bars indicate s.e.m. p-values are calculated using an unpaired t-test with Welch’s correction. PCC Pearsson correlation coefficient