Activity of the antimutagenic enzyme 8-oxo-2 '-deoxyguanosine 5 '-triphosphate pyrophosphohydrolase (8-oxo-dGTPase) in cultured Chinese hamster ovarycells: 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 ro le 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 investig ated the effect of cell population density, proliferation rate, and cell cy cle phase on 8-oxo-dGTPase specific activity in cultured Chinese hamster ov ary K1-BH4 (CHO) cells. With increasing cell population density (from 30 to 95% confluence), the activity of 8-oxo-dGTPase per milligram protein decre ased 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 a ctivity were observed within cell populations of different cell cycle phase s separated by centrifugal elutriation. Thus, the present results exclude c ell cycle-dependent regulation of 8-oxo-dGTPase activity in CHO cells or it s simple dependence on proliferation rate. The observed decrease of 8-oxo-d GTPase activity with increasing cell population density might be related to augmentation of cell-to-cell contact. (C) 2000 Elsevier Science Inc.