Yeast models of mutations in the mitochondrial ATP6 gene found in human cancer cells.

Since the discovery of somatic mtDNA mutations in tumor cells, multiple studies have focused on establishing a causal relationship between those changes and alterations in energy metabolism, a hallmark of cancer cells. Yet the consequences of these mutations on mitochondrial function remain largely unknown. In this study, Saccharomyces cerevisiae has been used as a model to investigate the functional consequences of four cancer-associated missense mutations (8914C>A, 8932C>T, 8953A>G, 9131T>C) found in the mitochondrial MT-ATP6 gene. This gene encodes the a-subunit of F1FO-ATP synthase, which catalyzes the last steps of ATP production in mitochondria. Although the four studied mutations affected well-conserved residues of the a-subunit, only one of them (8932C>T) had a significant impact on mitochondrial function, due to a less efficient incorporation of the a-subunit into ATP synthase. Our findings indicate that these ATP6 genetic variants found in human tumors are neutral mitochondrial genome substitutions with a limited, if any, impact on the energetic function of mitochondria.

Defining the impact on yeast ATP synthase of two pathogenic human mitochondrial DNA mutations, T9185C and T9191C.

Mutations in the human mitochondrial ATP6 gene encoding ATP synthase subunit a/6 (referred to as Atp6p in yeast) are at the base of neurodegenerative disorders like Neurogenic Ataxia and Retinitis Pigmentosa (NARP), Leigh syndrome (LS), Charcot-Marie-Tooth (CMT), and ataxia telangiectasia. In previous studies, using the yeast Saccharomyces cerevisiae as a model we were able to better define how several of these mutations impact the ATP synthase. Here we report the construction of yeast models of two other ATP6 pathogenic mutations, T9185C and T9191C. The first one was reported as conferring a mild, sometimes reversible, CMT clinical phenotype; the second one has been described in a patient presenting with severe LS. We found that an equivalent of the T9185C mutation partially impaired the functioning of yeast ATP synthase, with only a 30% deficit in mitochondrial ATP production. An equivalent of the mutation T9191C had much more severe effects, with a nearly complete block in yeast Atp6p assembly and an >95% drop in the rate of ATP synthesis. These findings provide a molecular basis for the relative severities of the diseases induced by T9185C and T9191C.