Ataxia-telangiectasia mutated kinase regulates ribonucleotide reductase and mitochondrial homeostasis
Jana S. Eaton, Z. Ping Lin, Alan C. Sartorelli, Nicholas D. Bonawitz, Gerald S. Shadel
Jana S. Eaton, Z. Ping Lin, Alan C. Sartorelli, Nicholas D. Bonawitz, Gerald S. Shadel
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Research Article Genetics

Ataxia-telangiectasia mutated kinase regulates ribonucleotide reductase and mitochondrial homeostasis

Abstract

Ataxia-telangiectasia mutated (ATM) kinase orchestrates nuclear DNA damage responses but is proposed to be involved in other important and clinically relevant functions. Here, we provide evidence for what we believe are 2 novel and intertwined roles for ATM: the regulation of ribonucleotide reductase (RR), the rate-limiting enzyme in the de novo synthesis of deoxyribonucleoside triphosphates, and control of mitochondrial homeostasis. Ataxia-telangiectasia (A-T) patient fibroblasts, wild-type fibroblasts treated with the ATM inhibitor KU-55933, and cells in which RR is inhibited pharmacologically or by RNA interference (RNAi) each lead to mitochondrial DNA (mtDNA) depletion under normal growth conditions. Disruption of ATM signaling in primary A-T fibroblasts also leads to global dysregulation of the R1, R2, and p53R2 subunits of RR, abrogation of RR-dependent upregulation of mtDNA in response to ionizing radiation, high mitochondrial transcription factor A (mtTFA)/mtDNA ratios, and increased resistance to inhibitors of mitochondrial respiration and translation. Finally, there are reduced expression of the R1 subunit of RR and tissue-specific alterations of mtDNA copy number in ATM null mouse tissues, the latter being recapitulated in tissues from human A-T patients. Based on these results, we propose that disruption of RR and mitochondrial homeostasis contributes to the complex pathology of A-T and that RR genes are candidate disease loci in mtDNA-depletion syndromes.

Authors

Jana S. Eaton, Z. Ping Lin, Alan C. Sartorelli, Nicholas D. Bonawitz, Gerald S. Shadel

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Figure 1

Inhibition of RR causes mtDNA depletion during proliferation.

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Inhibition of RR causes mtDNA depletion during proliferation. (A) Relati...
(A) Relative mtDNA copy number for wild-type primary fibroblasts treated with Triapine during high proliferation (0–24 hours) or reduced proliferation (24–48 hours) conditions. The ratio of the amount of mtDNA to nuclear DNA is plotted with the ratio in control cells arbitrarily set to 1.0. The mean ± SEM is plotted with significant statistical differences via Student’s t test indicated. (B) Relative mtDNA copy number of gemcitabine-treated wild-type primary fibroblasts. Cultures were maintained in the concentrations indicated for 48 hours with untreated (0 μM) arbitrarily set to 1.0. The mean ± SEM is shown. (C) Relative mtDNA copy number (plotted as in A) of HeLa cells with R2 or R1 expression knocked down compared with vector or short hairpin RNA control cells, respectively. R2 was reduced 50% and R1 was undetectable via Western blot. The mean ± SEM is plotted with significant statistical differences via Student’s t test indicated.