Mitochondrial Structure, Function and Dynamics Are Temporally Controlled by c-Myc J. Anthony Graves1*, Yudong Wang2, Sunder Sims-Lucas3, Edward Cherok1, Kristi Rothermund 1 , Maria F. Branca4, Jennifer Elster1, Donna Beer-Stolz5,6, Bennett Van Houten7,8, Jerry Vockley2,9, Edward V. Prochownik1,7,10 1 Division of Hematology/Oncology, Department of Pediatrics, Children’s Hospital of Pittsburgh of UPMC, Pittsburgh, Pennsylvania, United States of America, 2 Division of Medical Genetics, Children’s Hospital of Pittsburgh of UPMC, Pittsburgh, Pennsylvania, United States of America, 3 Division of Nephrology, Children’s Hospital of Pittsburgh of UPMC, Pittsburgh, Pennsylvania, United States of America, 4 Department of Surgery, Children’s Hospital of Pittsburgh of UPMC, Pittsburgh, Pennsylvania, United States of America, 5 Department of Cell Biology and Physiology, The University of Pittsburgh, Pittsburgh, Pennsylvania, United States of America, 6 Center for Biological Imaging, The University of Pittsburgh, Pittsburgh, Pennsylvania, United States of America, 7 The University of Pittsburgh Cancer Institute, The University of Pittsburgh, Pittsburgh, Pennsylvania, United States of America, 8 Department of Pharmacology and Chemical Biology, The University of Pittsburgh, Pittsburgh, Pennsylvania, United States of America, 9 Department of Human Genetics, Graduate School of Public Health, The University of Pittsburgh, Pittsburgh, Pennsylvania, United States of America, 10 Department of Microbiology and Molecular Genetics, The University of Pittsburgh, Pittsburgh, Pennsylvania, United States of America Abstract Although the c-Myc (Myc) oncoprotein controls mitochondrial biogenesis and multiple enzymes involved in oxidative phosphorylation (OXPHOS), the coordination of these events and the mechanistic underpinnings of their regulation remain largely unexplored. We show here that re-expression of Myc in myc2/2 fibroblasts is accompanied by a gradual accumulation of mitochondrial biomass and by increases in membrane polarization and mitochondrial fusion. A correction of OXPHOS deficiency is also seen, although structural abnormalities in electron transport chain complexes (ETC) are not entirely normalized. Conversely, the down-regulation of Myc leads to a gradual decrease in mitochondrial mass and a more rapid loss of fusion and membrane potential. Increases in the levels of proteins specifically involved in mitochondrial fission and fusion support the idea that Myc affects mitochondrial mass by influencing both of these processes, albeit favoring the latter. The ETC defects that persist following Myc restoration may represent metabolic adaptations, as mitochondrial function is re-directed away from producing ATP to providing a source of metabolic precursors demanded by the transformed cell. Citation: Graves JA, Wang Y, Sims-Lucas S, Cherok E, Rothermund K, et al. (2012) Mitochondrial Structure, Function and Dynamics Are Temporally Controlled by c-Myc. PLoS ONE 7(5): e37699. doi:10.1371/journal.pone.0037699 Editor: Surinder K. Batra, University of Nebraska Medical Center, United States of America Received July 27, 2011; Accepted April 24, 2012; Published May 21, 2012 Copyright: 2012 Graves et al. This is an open-access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited. Funding: This work was supported by the following: JAG was supported by the Harold Amos Medical Faculty Development Program sponsored by the Robert Wood Johnson Foundation and the Hyundai Hope on Wheels Scholarship, JV and YW were supported in part by Public Health Service grant R01 DYKE 8775, BVH was supported by The University of Pittsburgh Cancer Institute and Commonwealth Universal Research Enhancement (C.U.R.E.) Program, Pennsylvania Settlement Fund, and EVP was supported by National Institutes of Health grants CA140624 and CA78259. The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript. Competing Interests: The authors have declared that no competing interests exist. * E-mail: gravja@chp.edu Introduction As one of the most frequently deregulated oncoproteins in human cancer [1,2] c-Myc (hereafter, Myc) exerts pleiotropic effects on proliferation, survival, cell cycle, size, differentiation, genomic stability, and metabolism [3,4,5,6]. As might be anticipated for a protein exerting such global influence, Myc regulates a large number of downstream target genes transcribed by RNA polymerases I–III [4,7,8,9,10,11]. A significant number of Myc’s Pol II-regulated transcripts encode proteins involved in ribosome biosynthesis, aerobic and anaerobic metabolism, and mitochondrial biogenesis [12,13,14,15]. It is believed that the proteins encoded by these genes are needed to sustain the high proliferative demands of transformed cells [16]. The metabolic reprogramming that results from Myc deregu- lation is exemplified by the ‘‘Warburg effect’’ whereby ATP originating from mitochondrial sources is largely supplanted by that derived from glycolysis, even in oxygen-rich environments [16]. Among the benefits thought to be afforded by the switch to this less efficient mode of energy generation is a redirecting of TCA intermediates away from ATP production and towards the synthesis of lipid, protein and nucleic acid precursors that serve the increased synthetic demands of the rapidly proliferating trans- formed cell [14,16,17,18]. The resultant increases in mitochon- drial biogenesis and metabolism that accompany this reprogram- ming are at least partly explained by the ability of Myc to regulate the expression of TFAM, a major determinant of mitochondrial DNA replication [12], as well as PGC-1a [19] and PGC-1b [15], which regulate mitochondrial mass and energy metabolism [20]. In addition to increased mitochondrial number, the fusion of pre-existing organelles could provide an independent means of increasing functional efficiency in the face of Myc deregulation. Normally, fusion is thought to allow the mixing and dilution of oxidatively damaged membranes and intra-mitochondrial contents whose excessive accumulation can otherwise lead to the compli- cations such as: the uncoupling of oxidative phosphorylation PLoS ONE | www.plosone.org 1 May 2012 | Volume 7 | Issue 5 | e37699