Interaction of nucleotide excision repair proteins with DNA containing bulky lesion and apurinic/apyrimidinic site

Interaction of Nucleotide Excision Repair Protein XPC-RAD23B with DNA Containing Benzo[a]pyrene-Derived Adduct and Apurinic/Apyrimidinic Site within a Cluster

The combined action of reactive metabolites of benzo[a]pyrene (B[a]P) and oxidative stress can lead to cluster-type DNA damage that includes both a bulky lesion and an apurinic/apyrimidinic (AP) site, which are repaired by the nucleotide and base excision repair mechanisms - NER and BER, respectively. Interaction of NER protein XPC-RAD23B providing primary damage recognition with DNA duplexes containing a B[a]P-derived residue linked to the exocyclic amino group of a guanine (BPDE-N(2)-dG) in the central position of one strand and AP site in different positions of the other strand was analyzed. It was found that XPC-RAD23B crosslinks to DNA containing (+)-trans-BPDE-N(2)-dG more effectively than to DNA containing cis-isomer, independently of the AP site position in the opposite strand; protein affinity to DNA containing one of the BPDE-N(2)-dG isomers depends on the AP site position in the opposite strand. The influence of XPC-RAD23B on hydrolysis of an AP site clustered with BPDE-N(2)-dG catalyzed by the apurinic/apyrimidinic endonuclease 1 (APE1) was examined. XPC-RAD23B was shown to stimulate the endonuclease and inhibit the 3'-5' exonuclease activity of APE1. These data demonstrate the possibility of cooperation of two proteins belonging to different DNA repair systems in the repair of cluster-type DNA damage.

Smoking cessation reverses DNA double-strand breaks in human mononuclear cells

OBJECTIVE

Cigarette smoking is a major risk factor for atherosclerotic cardiovascular disease, which is responsible for a significant proportion of smoking-related deaths. However, the precise mechanism whereby smoking induces this pathology has not been fully delineated. Based on observation of DNA double-strand breaks (DSBs), the most harmful type of DNA damage, in atherosclerotic lesions, we hypothesized that there is a direct association between smoking and DSBs. The goal of this study was to investigate whether smoking induces DSBs and smoking cessation reverses DSBs in vivo through examination of peripheral mononuclear cells (MNCs).

APPROACH AND RESULTS

Immunoreactivity of oxidative modification of DNA and DSBs were increased in human atherosclerotic lesions but not in the adjacent normal area. DSBs in human MNCs isolated from the blood of volunteers can be detected as cytologically visible "foci" using an antibody against the phosphorylated form of the histone H2AX (γ-H2AX). Young healthy active smokers (n = 15) showed increased γ-H2AX foci number when compared with non-smokers (n = 12) (foci number/cell: median, 0.37/cell; interquartile range [IQR], 0.31-0.58 vs. 4.36/cell; IQR, 3.09-7.39, p<0.0001). Smoking cessation for 1 month reduced the γ-H2AX foci number (median, 4.44/cell; IQR, 4.36-5.24 to 0.28/cell; IQR, 0.12-0.53, p<0.05). A positive correlation was noted between γ-H2AX foci number and exhaled carbon monoxide levels (r = 0.75, p<0.01).

CONCLUSIONS

Smoking induces DSBs in human MNCs in vivo, and importantly, smoking cessation for 1 month resulted in a decrease in DSBs to a level comparable to that seen in non-smokers. These data reinforce the notion that the cigarette smoking induces DSBs and highlight the importance of smoking cessation.