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 G(0)/G(1) 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 G(0)/G(1) 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. (C) 2000 Elsevier Science Inc.