Background: Oxidative stress is a major causative agent of carcinogenesis, aging, and a number of diseases. 8-oxoG is the most stable and deleterious lesion of oxidative DNA damage. The 8-oxoG lesions can be eliminated by human repair systems consisting of three enzymes hMTH1, hOGG1, and hMYH homologous to E. coli MutT, MutM, and MutY proteins, respectively.
Material and Methods: Human cells (P1, P2, and P3) resistant to H2O2 were derived from the non-tumorigenic human breast cell line MCF10A by sequential treatment of the cells with H2O2. The protein expression levels of DNA repair enzymes were analyzed by Western blotting. The DNA binding and glycosylase activities of hMYH and hOGG1 were measured in the extracts of the H2O2 resistant cells.
Results: The H2O2 resistant cells displayed tremendously greater anchorage-independent growth capability and higher expression of the anti-apoptotic protein BCL-2 than the parental cells. H2O2 detoxification ability was elevated in P1 and P2 cells, but not in P3 cells, suggesting P3 cells might employ a different defense mechanism from P1 and P2 cells. In P3 cells, both hOGG1 and hMYH glycosylase activities were reduced but their protein levels increased. Two A/8-oxoG binding complexes were detected with cell extracts: the fast-migrating complex (bottom form) was dominated in MCF10A cells, and was greatly reduced in P3 cells. Interesting, the P3 cells showing the least amount of bottom form had the weakest hMYH glycosylase activity.
Conclusion: Our results demonstrated, for the first time, that alteration of base excision repair pathways is correlated to cell resistance to oxidative stress.

Keywords: DNA Repair, hMYH, hOGG1, Base excision repair, H2O2-resistance