Abstract 4803: A novel mitochondrial isoform of mammalian DNA methyltransferase 1

Abstract

Abstract Cancer cells, in contrast to normal cells and tissues, fulfill their energy requirements by increased glycolysis, with a distinct downregulation of oxidative phosphorylation in the mitochondria. Regulation of enzymes of the glycolytic pathway under the anoxic conditions prevalent in human solid tumors by stabilization of HIF1α have been intensely investigated; however, the mechanisms regulating transcription of the mitochondrial genome, and its coordinate regulation with the nuclear genome are less well understood. Eukaryotic mitochondrial DNA carries a low but significant level of cytosine methylation, but molecular mechanisms responsible for the generation of this modification and its role in mitochondrial function has not been studied. The mitochondrial genome encodes 13 polypeptides involved in oxidative phosphorylation, as well as the tRNAs and rRNAs required for mitochondrial translation. All other proteins required for mitochondrial function are encoded by the nuclear genome and translocated to the mitochondria using mitochondrial targeting sequences frequently located at the N-terminus. We have identified a novel isoform of mammalian DNA methyltransferase 1 (DNMT1) that translocates to the mitochondrion, using a conserved N-terminal mitochondrial targeting sequence; the mRNA encoding this isoform is expressed from an upstream transcription start site. De novo methyltransferases DNMT3a and DNMT3b are not found in mammalian mitochondria. Expression of the mitochondrial DNMT1 isoform (mtDNMT1) is regulated by nuclear respiratory factor 1 (NRF1) and coactivator PGC1α, which together upregulate several nuclear-encoded mitochondrial genes involved in the electron transport chain, following hypoxic stress. The mitochondrial isoform (mtDNMT1) is also preferentially upregulated following loss of p53 function, leading to specific effects on mitochondrial gene expression and potentially affecting mitochondrial function. We therefore suggest that mitochondrial DNA methylation, established and maintained by mtDNMT1, plays a role in coordination of mitochondrial gene expression and that the expression of the mtDNMT1 isoform is under the control of p53. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 101st Annual Meeting of the American Association for Cancer Research; 2010 Apr 17-21; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2010;70(8 Suppl):Abstract nr 4803.