MtDNMT1 and DNMT3b cooperate to methylate mitochondrial DNA and regulate mitochondrial transcription

Abstract

Mitochondria are dynamic modulators of cell physiology, rewiring their metabolic and signaling pathways to allow for rapid and flexible adaptions to environmental changes. Mitochondrial DNA (mtDNA) is packaged into DNA‐protein complexes called nucleoids, and the DNA is epigenetically modified (1,2). We, and others, have demonstrated that mtDNA methylation represents a powerful mechanism for regulating transcription of mtDNA‐encoded oxidative phosphorylation (OXPHOS) genes under conditions of cellular stress (1,3). We identified a mitochondrial (mt) isoform of DNA methyltransferase 1 (mtDNMT1) that translocates to the mt matrix, and binds to mtDNA in critical control regions (1). Our new data demonstrates that mtDNMT1 interacts with several proteins essential for proper functioning of mitochondria, including core components of the nucleoid. These findings place mtDNMT1 at the heart of mitochondrial nucleoid organization, and suggest that mtDNMT1 plays a critical role in regulating nucleoid structure and mitochondrial output, either as a consequence of, or independently from, its methylation activity. We now have evidence that mtDNMT1 is not working alone: DNMT3b works in concert with mtDNMT1 to methylate mtDNA and regulate mt transcription. CRISPR/Cas9‐mediated inactivation of mtDNMT1 and/or DNMT3b activity resulted in significant decrease in mitochondrial methylation across the heavy and light strand promoters of mtDNA, with a concomitant reduction in transcription of several mtDNA‐encoded OXPHOS genes. Cells lacking mtDNMT1 and/or DNMT3b exhibited a striking morphological change, undertaking an elongated, fibroblast‐like appearance with increased migration, reminiscent of cells undergoing epithelial‐to‐mesenchymal transition (EMT), a hallmark of cancer metastasis. These observations implicate mtDNA methylation in the phenotypic plasticity that occurs in response to changing cellular growth conditions, driving the initiation and progression of numerous pathologies. We propose that the mitochondrial DNA methylation machinery may constitute a novel target for therapeutic intervention.Support or Funding InformationMCB 1122018 (NSF) to Taylor, Start‐up funds (VCU Dept of Microbiology and Immunology) to Shock, IRG‐14‐192‐40 (ACS) to ShockThis abstract is from the Experimental Biology 2018 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.