Effects of oxidative stress on the expression of 8-oxoguanine and its eliminating enzymes in human keratinocytes and squamous carcinoma cells.

Abstract: Purpose of the research: An oxidized form of guanine, 8-oxoGua, is known to have a potential to induce genetic mutations, thereby causing carcinogenesis. Mammalian cells hence have various mechanisms to eliminate 8-oxoGua in DNA and nucleotide pools. Since MutT-related enzymes, MTH1 and NUDT5, can hydrolyze 8-oxoGua-containing nucleotides in nucleotide pools, the expressions of MTH1 and NUDT5 are likely to be involved in controlling oxidation-induced carcinogenesis. In the present study, we examined the expressions of 8-oxoGua, MTH1, and NUDT5 in human normal keratinocytes and human oral squamous carcinoma cells treated with H₂O₂. Principal results: The immunofluorescent study demonstrated that the localization of 8-oxo-dGTP changed from cytoplasm to nucleus in the treatment with H₂O₂ in both cell types. The Western blotting analysis as well as RT-PCR revealed that H₂O₂ enhanced the expression of NUDT5, but not MTH1, in normal keratinocytes. The increased NUDT5 proteins were also detected in the nuclear extracts of keratinocytes treated with H₂O₂. In contrast, H₂O₂ had no effects on the expressions of NUDT5 and MTH1 in squamous carcinoma cells. Major conclusions: NUDT5 may thus be involved in preventing carcinogenic mutations in keratinocytes under oxidative stress, and its impaired expression may promote their carcinogenesis. [Copyright &y& Elsevier]