An Essential Role of the Mitochondrial Electron Transport Chain in Cell Proliferation Is to Enable Aspartate Synthesis

The mitochondrial electron transport chain (ETC) enables many metabolic processes, but why its inhibition suppresses cell proliferation is unclear. It is also not well understood why pyruvate supplementation allows cells lacking ETC function to proliferate. We used a CRISPR-based genetic screen to identify genes whose loss sensitizes human cells to phenformin, a complex I inhibitor. The screen yielded GOT1, the cytosolic aspartate aminotransferase, loss of which kills cells upon ETC inhibition. GOT1 normally consumes aspartate to transfer electrons into mitochondria, but, upon ETC inhibition, it reverses to generate aspartate in the cytosol, which partially compensates for the loss of mitochondrial aspartate synthesis. Pyruvate stimulates aspartate synthesis in a GOT1-dependent fashion, which is required for pyruvate to rescue proliferation of cells with ETC dysfunction. Aspartate supplementation or overexpression of an aspartate transporter allows cells without ETC activity to proliferate. Thus, enabling aspartate synthesis is an essential role of the ETC in cell proliferation. [Display omitted] •A CRISPR-Cas9 genetic screen reveals that GOT1 loss kills cells upon ETC inhibition•In cells with ETC inhibition, GOT1 reverses flux to generate aspartate in the cytosol•Aspartate is limiting for proliferation in cells with ETC inhibition•Pyruvate reverses the effects of ETC inhibition by inducing aspartate synthesis Aspartate is a limiting metabolite for proliferation in cells with mitochondrial electron transport chain defects.