DNA polymerase β: A missing link of the base excision repair machinery in mammalian mitochondria

Abstract

Mitochondrial genome integrity is fundamental to mammalian cell viability. Since mitochondrial DNA is constantly under attack from oxygen radicals released during ATP production, DNA repair is vital in removing oxidatively generated lesions in mitochondrial DNA, but the presence of a strong base excision repair system has not been demonstrated. Here, we addressed the presence of such a system in mammalian mitochondria involving the primary base lesion repair enzyme DNA polymerase (pol) β. Pol β was localized to mammalian mitochondria by electron microscopic-immunogold staining, immunofluorescence co-localization and biochemical experiments. Extracts from purified mitochondria exhibited base excision repair activity that was dependent on pol β. Mitochondria from pol β-deficient mouse fibroblasts had compromised DNA repair and showed elevated levels of superoxide radicals after hydrogen peroxide treatment. Mitochondria in pol β-deficient fibroblasts displayed altered morphology by electron microscopy. These results indicate that mammalian mitochondria contain an efficient base lesion repair system mediated in part by pol β and thus pol β plays a role in preserving mitochondrial genome stability.

Defective base excision repair in the response to DNA damaging agents in triple negative breast cancer

“…Previous studies showed that POL β stability may depend on interactions with XRCC1 [41–43], and XRCC1 localization has been previously observed to be primarily nuclear [26]. POL β functions in both nuclear and mitochondrial BER and is observed within the cytoplasm, mitochondria, and nucleus of cells [27, 44].…”

“…However, the TNBC cells also showed altered localization of POL β that did not correlate with altered XRCC1 localization. The MDA-157 and MDA-231 cells showed low nuclear content of POL β, whereas HCC1806 and MDA-468 showed nuclear POL β enrichment [27, 44]. Loss of POL β does not induce the same level of hypersensitivity to DNA damaging agents as loss of XRCC1 [52, 62, 63].…”

Mitochondrial DNA: Epigenetics and environment

“…Transcription of mtDNA is initiated at one of three promoter regions, two located on the heavy strand (HSP1 and HSP2) and one located on the light strand (LSP), where an overwhelming majority of transcripts are produced by transcription from HSP1 ( Fig. Only 7 of the 11 known DNA glycosylases that initiate BER have been identified in the mitochondria and recently, evidence presented by the Wilson and Bohr groups indicated that the resynthesis step after damage removal can be performed by DNA polymerase beta during repair of mtDNA (Prasad et al, 2017;Sykora et al, 2017;reviewed in Prakash and Doublié, 2015). Of the mitochondrial transcription components, TFAM appears to be regulated via post-translational modifications, where the precise implications of these modifications on epigenetic regulation of mitochondrial transcription are unknown (Lu et al, 2013;King et al, 2018).…”

“…For instance, the base excision repair (BER) pathway appears to be the most abundant pathway within the mitochondria and repairs small, nonbulky lesions such as alkylated and oxidized DNA bases (reviewed in Prakash and Doublié, 2015;Saki and Prakash, 2017). Only 7 of the 11 known DNA glycosylases that initiate BER have been identified in the mitochondria and recently, evidence presented by the Wilson and Bohr groups indicated that the resynthesis step after damage removal can be performed by DNA polymerase beta during repair of mtDNA (Prasad et al, 2017;Sykora et al, 2017;reviewed in Prakash and Doublié, 2015). Various proteins involved in homologous recombination and translesion DNA synthesis have also been identified within the mitochondria (Sage et al, 2010;Dmitrieva et al, 2011;García-Gómez et al, 2013;Singh et al, 2015).…”

Hippocampal tau oligomerization early in tau pathology coincides with a transient alteration of mitochondrial homeostasis and DNA repair in a mouse model of tauopathy

“…Recent reports have shown the presence of the major nuclear BER DNA polymerase, DNA polymerase β (Polβ), in mitochondria in the brain [65,76], with a likely role in mtDNA repair. 3xTgAD mice with a 50% reduction of Polβ (3xTg AD/Polβ +/− ), which also contain a mutated version of human tau, display exacerbated AD phenotypes with impaired cellular bioenergetics and mitochondrial dysfunction [58,77].…”