Base excision repair of oxidative DNA damage coupled with removal of a CAG repeat hairpin attenuates trinucleotide repeat expansion

ABSTRACT DNAs harbored in both nuclei and mitochondria of eukaryotic cells are subject to continuous oxidative damage resulting from normal metabolic activities or environmental insults. Oxidative DNA damage is primarily reversed by the base excision repair (BER) pathway, initiated by N-glycosylase apurinic/apyrimidinic (AP) lyase proteins. To execute an appropriate repair response, BER components must be distributed to accommodate levels of genotoxic stress that may vary considerably between nuclei and mitochondria, depending on the growth state and stress environment of the cell. Numerous examples exist where cells respond to signals, resulting in relocalization of proteins involved in key biological transactions. To address whether such dynamic localization contributes to efficient organelle-specific DNA repair, we determined the intracellular localization of the Saccharomyces cerevisiae N-glycosylase/AP lyases, Ntg1 and Ntg2, in response to nuclear and mitochondrial oxidative stress. Fluorescence microscopy revealed that Ntg1 is differentially localized to nuclei and mitochondria, likely in response to the oxidative DNA damage status of the organelle. Sumoylation is associated with targeting of Ntg1 to nuclei containing oxidative DNA damage. These studies demonstrate that trafficking of DNA repair proteins to organelles containing high levels of oxidative DNA damage may be a central point for regulating BER in response to oxidative stress.

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Base excision repair of oxidative DNA damage and association with cancer and aging

Carcinogenesis ◽

10.1093/carcin/bgn250 ◽

2008 ◽

Vol 30 (1) ◽

pp. 2-10 ◽

Cited By ~ 344

Author(s):

S. Maynard ◽

S. H. Schurman ◽

C. Harboe ◽

N. C. de Souza-Pinto ◽

V. A. Bohr

Keyword(s):

Dna Damage ◽

Base Excision Repair ◽

Oxidative Dna Damage ◽

Excision Repair ◽

Base Excision

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R-loops promote trinucleotide repeat deletion through DNA base excision repair enzymatic activities

Journal of Biological Chemistry ◽

10.1074/jbc.ra120.014161 ◽

2020 ◽

Vol 295 (40) ◽

pp. 13902-13913

Author(s):

Eduardo E. Laverde ◽

Yanhao Lai ◽

Fenfei Leng ◽

Lata Balakrishnan ◽

Catherine H. Freudenreich ◽

...

Keyword(s):

Base Excision Repair ◽

Trinucleotide Repeat ◽

Excision Repair ◽

Enzymatic Activities ◽

Cag Repeat ◽

Abasic Site ◽

Dna Damage And Repair ◽

Dna Base Excision Repair ◽

Treatment And Prevention ◽

Base Excision

Trinucleotide repeat (TNR) expansion and deletion are responsible for over 40 neurodegenerative diseases and associated with cancer. TNRs can undergo somatic instability that is mediated by DNA damage and repair and gene transcription. Recent studies have pointed toward a role for R-loops in causing TNR expansion and deletion, and it has been shown that base excision repair (BER) can result in CAG repeat deletion from R-loops in yeast. However, it remains unknown how BER in R-loops can mediate TNR instability. In this study, using biochemical approaches, we examined BER enzymatic activities and their influence on TNR R-loops. We found that AP endonuclease 1 incised an abasic site on the nontemplate strand of a TNR R-loop, creating a double-flap intermediate containing an RNA:DNA hybrid that subsequently inhibited polymerase β (pol β) synthesis of TNRs. This stimulated flap endonuclease 1 (FEN1) cleavage of TNRs engaged in an R-loop. Moreover, we showed that FEN1 also efficiently cleaved the RNA strand, facilitating pol β loop/hairpin bypass synthesis and the resolution of TNR R-loops through BER. Consequently, this resulted in fewer TNRs synthesized by pol β than those removed by FEN1, thereby leading to repeat deletion. Our results indicate that TNR R-loops preferentially lead to repeat deletion during BER by disrupting the balance between the addition and removal of TNRs. Our discoveries open a new avenue for the treatment and prevention of repeat expansion diseases and cancer.

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The Effect ofMsh2Knockdown on Toxicity Induced bytert-Butyl-hydroperoxide, Potassium Bromate, and Hydrogen Peroxide in Base Excision Repair Proficient and Deficient Cells

BioMed Research International ◽

10.1155/2013/152909 ◽

2013 ◽

Vol 2013 ◽

pp. 1-9 ◽

Cited By ~ 3

Author(s):

N. Cooley ◽

R. H. Elder ◽

A. C. Povey

Keyword(s):

Dna Damage ◽

Base Excision Repair ◽

Oxidative Dna Damage ◽

Excision Repair ◽

Shrna Expression ◽

Cellular Toxicity ◽

Dna Mismatch ◽

Shrna Expression Vector ◽

Repair Systems ◽

Base Excision

The DNA mismatch repair (MMR) and base excision repair (BER) systems are important determinants of cellular toxicity following exposure to agents that cause oxidative DNA damage. To examine the interactions between these different repair systems, we examined whether toxicity, induced byt-BOOH and KBrO3, differs in BER proficient (Mpg+/+,Nth1+/+) and deficient (Mpg−/−,Nth1−/−) mouse embryonic fibroblasts (MEFs) followingMsh2knockdown of between 79 and 88% using an shRNA expression vector.Msh2knockdown inNth1+/+cells had no effect ont-BOOH and KBrO3induced toxicity as assessed by an MTT assay; knockdown inNth1−/−cells resulted in increased resistance tot-BOOH and KBrO3, a result consistent with Nth1 removing oxidised pyrimidines.Msh2knockdown inMpg+/+cells had no effect ont-BOOH toxicity but increased resistance to KBrO3; inMpg−/−cells,Msh2knockdown increased cellular sensitivity to KBrO3but increased resistance to t-BOOH, suggesting a role forMpgin removing DNA damage induced by these agents. MSH2 dependent and independent pathways then determine cellular toxicity induced by oxidising agents. A complex interaction between MMR and BER repair systems, that is, exposure dependent, also exists to determine cellular toxicity.

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