Bcl2 inhibition of mitochondrial DNA repair.
BACKGROUND
Accumulation of mitochondrial DNA (mtDNA) damage could enhance the frequency of mitochondrial mutations and promote a variety of mitochondria-related diseases, including cancer. However, the mechanism(s) involved are not fully understood.


METHODS
Quantitative extended length PCR was used to compare mtDNA and nDNA damage in human lung H1299 cells expressing WT Bcl2 or vector-only control. mtAPE1 endonuclease activity was analyzed by AP oligonucleotide assay. mtDNA mutation was measured by single molecule PCR. Subcellular localization of Bcl2 and APE1 was analyzed by subcellular fractionation.


RESULTS
Bcl2, an anti-apoptotic molecule and oncoprotein, effectively inhibits the endonuclease activity of mitochondrial APE1 (mtAPE1), leading to significant retardation of mtDNA repair and enhanced frequency of mtDNA mutations following exposure of cells to hydrogen peroxide (H2O2) or nitrosamine 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone (NNK, a carcinogen in cigarette smoke). Inversely, depletion of endogenous Bcl2 by RNA interference increases mtAPE1 endonuclease activity leading to accelerated mtDNA repair and decreased mtDNA mutation. Higher levels of mtAPE1 were observed in human lung cancer cells than in normal human bronchial epithelial cells (i.e. BEAS-2B). Bcl2 partially co-localizes with APE1 in the mitochondria of human lung cancer cells. Bcl2 directly interacts with mtAPE1 via its BH domains. Removal of any of the BH domains from Bcl2 abolishes Bcl2's capacity to interact with mtAPE1 as well as its inhibitory effects on mtAPE1 activity and mtDNA repair.


CONCLUSIONS
Based our findings, we propose that Bcl2 suppression of mtDNA repair occurs through direct interaction with mtAPE1 and inhibition of its endonuclease activity in mitochondria, which may contribute to enhanced mtDNA mutations and carcinogenesis.
Division of Cancer Biology, Departments of Radiation Oncology, Emory University School of Medicine and Winship Cancer Institute of Emory University, Atlanta, GA, 30322, USA. mxie6@emory.edu.
Maohua
M
Xie
Division of Cancer Biology, Departments of Radiation Oncology, Emory University School of Medicine and Winship Cancer Institute of Emory University, Atlanta, GA, 30322, USA. medpwd@emory.edu.|Biochemistry, Emory University School of Medicine and Winship Cancer Institute of Emory University, Atlanta, GA, 30322, USA. medpwd@emory.edu.
Paul W
PW
Doetsch
Division of Cancer Biology, Departments of Radiation Oncology, Emory University School of Medicine and Winship Cancer Institute of Emory University, Atlanta, GA, 30322, USA. xdeng4@emory.edu.
Xingming
X
Deng
D045744:Cell Line, Tumor; D004249:DNA Damage / Q000235:genetics*; D004260:DNA Repair / Q000235:genetics*; D004272:DNA, Mitochondrial / Q000737:chemistry / Q000235:genetics* / Q000378:metabolism*; D043603:DNA-(Apurinic or Apyrimidinic Site) Lyase / Q000235:genetics / Q000378:metabolism; D006801:Humans; D006861:Hydrogen Peroxide; D009154:Mutation; D019253:Proto-Oncogene Proteins c-bcl-2 / Q000737:chemistry / Q000235:genetics* / Q000378:metabolism*
D004272:DNA, Mitochondrial; D019253:Proto-Oncogene Proteins c-bcl-2; D006861:Hydrogen Peroxide; C085108:APEX1 protein, human; D043603:DNA-(Apurinic or Apyrimidinic Site) Lyase