title: Long patch base excision repair in mammalian mitochondrial genomes.
abstract: The mitochondrial genome is highly susceptible to damage by reactive oxygen species (ROS) generated endogenously as a byproduct of respiration. ROS-induced DNA lesions, including oxidized bases, abasic (AP) sites, and oxidized AP sites, cause DNA strand breaks and are repaired via the base excision repair (BER) pathway in both the nucleus and mitochondria. Repair of damaged bases and AP sites involving 1-nucleotide incorporation, named single nucleotide (SN)-BER, was observed with mitochondrial and nuclear extracts. During SN-BER, the 5'-phosphodeoxyribose (dRP) moiety, generated by AP-endonuclease (APE1), is removed by the lyase activity of DNA polymerase gamma (pol gamma) and polymerase beta in the mitochondria and nucleus, respectively. However, the repair of oxidized deoxyribose fragments at the 5' terminus after strand break would require 5'-exo/endonuclease activity that is provided by the flap endonuclease (FEN-1) in the nucleus, resulting in multinucleotide repair patch (long patch (LP)-BER). Here we show the presence of a 5'-exo/endonuclease in the mitochondrial extracts of mouse and human cells that is involved in the repair of a lyase-resistant AP site analog via multinucleotide incorporation, upstream and downstream to the lesion site. We conclude that LP-BER also occurs in the mitochondria requiring the 5'-exo/endonuclease and pol gamma with 3'-exonuclease activity. Although a FEN-1 antibody cross-reacting species was detected in the mitochondria, it was absent in the LP-BER-proficient APE1 immunocomplex isolated from the mitochondrial extract that contains APE1, pol gamma, and DNA ligase 3. The LP-BER activity was marginally affected in FEN-1-depleted mitochondrial extracts, further supporting the involvement of an unidentified 5'-exo/endonuclease in mitochondrial LP-BER.
authors.affiliation: Department of Biochemistry and Molecular Biology, University of Texas Medical Branch, Galveston, Texas 77555, USA.
authors.forename: Bartosz
authors.initials: B
authors.lastname: Szczesny
authors.forename: Anne W
authors.initials: AW
authors.lastname: Tann
authors.forename: Matthew J
authors.initials: MJ
authors.lastname: Longley
authors.forename: William C
authors.initials: WC
authors.lastname: Copeland
authors.forename: Sankar
authors.initials: S
authors.lastname: Mitra
mesh_terms: D000818:Animals; D045744:Cell Line, Tumor; D002467:Cell Nucleus / Q000201:enzymology; D004249:DNA Damage / Q000502:physiology*; D004258:DNA Polymerase III / Q000378:metabolism; D000074002:DNA Polymerase gamma; D004260:DNA Repair / Q000502:physiology*; D043603:DNA-(Apurinic or Apyrimidinic Site) Lyase / Q000378:metabolism*; D004259:DNA-Directed DNA Polymerase / Q000378:metabolism*; D045585:Flap Endonucleases / Q000378:metabolism*; D054629:Genome, Mitochondrial / Q000502:physiology*; D006801:Humans; D051379:Mice; D008807:Mice, Inbred BALB C; D008930:Mitochondria, Liver / Q000201:enzymology*; D010084:Oxidation-Reduction; D017382:Reactive Oxygen Species / Q000378:metabolism
chemical_list: D017382:Reactive Oxygen Species; D004258:DNA Polymerase III; D000074002:DNA Polymerase gamma; D004259:DNA-Directed DNA Polymerase; D045585:Flap Endonucleases; C468317:FEN1 protein, human; C085108:APEX1 protein, human; C486216:Apex1 protein, mouse; D043603:DNA-(Apurinic or Apyrimidinic Site) Lyase