Modulation in Cell Cycle and Cyclin B1 Expression in Irradiated HeLa Cells and Normal Human Skin Fibroblasts Treated with Staurosporine and Caffeine

Abstract

The comparative effects of staurosporine or caffeine on G2-phase arrest and cyclin B1 expression in human skin fibroblasts (HSF) and transformed HeLa cells following γ-irradiation were examined by flow cytometry. Contrary to some earlier reports with HeLa cells, the arrest in G2after irradiation was accompanied by an increase in cyclin B1 levels in both asynchronous and synchronized HeLa cells irradiated in early S phase. Caffeine and staurosporine were equally effective in attenuating both the radiation-induced increase in cyclin B1 expression and the prolongation of G2in synchronous and asynchronous HeLa cell populations. Staurosporine treatment was less effective in down-regulating cyclin B1 expression in asynchronous HeLa cells at earlier time points following irradiation when compared to caffeine-treated cells. In synchronized HeLa cells, down-regulation of an irradiation-induced increase in cyclin B1 expression was similar to either staurosporine or caffeine treatments, with caffeine being more effective at later time points. An increase in cyclin B1 expression was also observed in irradiated HSF cells (synchronous and asynchronous), which decreased when the cells were treated with staurosporine or caffeine. However, staurosporine was ineffective in attenuating the radiation-induced prolongation of G2in synchronous and asynchronous HSF cells, whereas treatment of irradiated synchronous or asynchronous HSF cells with caffeine significantly reduced the prolongation of G2. These results suggest that both staurosporine and caffeine treatments act on different pathways of cell cycle control in normal and transformed cells, in terms of attenuation of G2block and diminution of elevated levels of cyclin B1 expression, in response to radiation.