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

Purpose of the researchAn 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 resultsThe 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 conclusionsNUDT5 may thus be involved in preventing carcinogenic mutations in keratinocytes under oxidative stress, and its impaired expression may promote their carcinogenesis.