The Role of EXD2 in the maintenance of mithocondrial homeostasis

Mitochondrial dysfunction arising from aberrant mitochondrial nucleic acid homeostasis has been associated with various pathologies. In this thesis, we aim to characterize a putative mitochondrial exonuclease, EXD2, and the consequences of its loss in cell metabolism. For that purpose we use three approaches: 1) Biochemical assays with bacterially purified EXD2 to study its enzymatic activity, 2) In vitro experiments with cell lines to study the phenotype of cells with altered EXD2-levels, and, 3) In vivo experiments with a mouse xenograft model and D.melanogaster to study the consequences of EXD2-loss in tumors and at the organismal level. Our work shows, that EXD2 is a uniquely versatile mammalian exonuclease able to bind and degrade various DNA and RNA substrates. We demonstrate that loss of EXD2 in cancer cells leads to alterations in mtDNA, various metabolic changes and aberrant hypoxia signaling. We also describe how, in vivo, this leads to inhibition of breast tumor growth and increased lifespan in fruitflies. Taken together, our observations provide a link between mitochondrial nucleic acid maintenance and large-scale metabolic alterations influencing tumor growth and aging. ; La disfunción mitocondrial que surge de la homeostasis de ácido nucleico mitocondrial aberrante se ha asociado con varias patologías. En esta tesis, se pretende caracterizar una exonucleasa putativo mitocondrial, EXD2, y las consecuencias de su pérdida en el metabolismo celular. Para ello utilizamos tres enfoques: 1) ensayos bioquímicos con EXD2 purificado de bacterias para estudiar su actividad enzimática, 2) los experimentos in vitro con líneas celulares para estudiar el fenotipo de las células con niveles de EXD2 alterados, y, 3) experimentos in vivo con modelo de xenotrasplante de ratón y D.melanogaster para estudiar las consecuencias de perdida de EXD2 en los tumores y en el nivel del organismo. Nuestro trabajo muestra que EXD2 es una exonucleasa mamíferos excepcionalmente versátil capaz de unirse y degradar diversos sustratos ...