Activity of the antimutagenic enzyme 8-oxo-2′-deoxyguanosine 5′-triphosphate pyrophosphohydrolase (8-oxo-dGTPase) in cultured Chinese hamster ovary cells: effects of cell cycle, proliferation rate, and population density

Mammalian 8-oxo-2′-deoxyguanosine 5′-triphosphate pyrophosphohydrolases (8-oxo-dGTPases), such as MTH1, are believed to play the same antimutagenic role as their bacterial homologues, like MutT. Both decompose promutagenic 8-oxo-dGTP, a product of active oxygen’s attack on dGTP. It is not known how 8-oxo-dGTPase expression and function are regulated. Therefore, we investigated the effect of cell population density, proliferation rate, and cell cycle phase on 8-oxo-dGTPase specific activity in cultured Chinese hamster ovary K1-BH4 (CHO) cells. With increasing cell population density (from 30 to 95% confluence), the activity of 8-oxo-dGTPase per milligram protein decreased by 33% (p = .007 by ANOVA) while cells shifted by 9% into the G0/G1 phase, with a 5% drop in cells in S phase. Importantly, inhibition of the cells’ proliferation rate by calf serum deprivation caused a more dramatic 23% shift toward the G0/G1 phase and a 25% drop in S phase, but had no effect on 8-oxo-dGTPase activity. Likewise, no differences in the enzyme activity were observed within cell populations of different cell cycle phases separated by centrifugal elutriation. Thus, the present results exclude cell cycle–dependent regulation of 8-oxo-dGTPase activity in CHO cells or its simple dependence on proliferation rate. The observed decrease of 8-oxo-dGTPase activity with increasing cell population density might be related to augmentation of cell-to-cell contact.