Mitochondrial localization of MRN complex components in mammal cells

Abstract

Although the molecular mechanism that causes the formation and accumulation of deletions in the mtDNA is unknown, it has been proposed that somatic deletions result from incomplete or unresolved repair events, mainly during repair of double-strand breaks. Deletions in mtDNA are related to mitochondrial diseases like Kearns-Sayre syndrome and other complex diseases such as neurodegeneration and cancer. The molecular mechanisms of double strand break repair and the accumulation of lesions in the mtDNA are not as characterized as those that act on nuclear DNA. It is known that in the nucleus there are two pathways for double-strand breaks repair: non-homologous end joining and the homologous recombination pathway (HR). The HR pathway requires the MRN protein complex , formed by Mre11, Rad50, and Nbs1 subunits. Recently the presence of the Mre11 subunit has been observed in mouse kidney mitochondria, raising the possibility that the MRN complex may function in an analogous or similar manner as it does in the nucleus. To investigate such possibilities we will verify: (I) the presence of the Nbs1 subunit in HEK293T and HeLa cell mitochondria through immunofluorescence and western blot assays; and (II) whether Nbs1 mitochondrial localization and expression are altered by treatment with hydrogen peroxide, an agent that causes double-strand breaks in DNA.