A G2/M growth arrest response to low-dose intermittent H2O2 in normal uroepithelial cells

Studies in fibroblasts have shown that H2O2, as a model for oxidative damag e, leads to a G1 growth arrest phenotypically similar to senescence. These observations as well as the observation that bladder cancer is associated w ith deletions of CDKN2, a gene important in normal senescence, led us to ex amine normal urothelial cell response to H2O2. We hypothesized that low dos e H2O2 exposure would lead to p16 and/or p14(ARF) mediated senescence. We s how that H2O2 leads to endogenous beta-galactosidase expression similar to senescence, but instead of G1 arrest, it leads to G2/M growth arrest withou t induction of either p16 or p14(ARF). Lack of p21 induction and a similar G2/M growth arrest in E6 immortalized uroepithelial cells suggests that thi s response is independent of p53 as well. An increased level of cdc2 tyrosi ne-15 phosphorylation following H2O2 treatment suggests that the observed g rowth arrest is mediated by a G2 checkpoint mechanism.