MODULATION IN CELL-CYCLE AND CYCLIN B1 EXPRESSION IN IRRADIATED HELA-CELLS AND NORMAL HUMAN SKIN FIBROBLASTS TREATED WITH STAUROSPORINE ANDCAFFEINE

The comparative effects of staurosporine or caffeine on G(2)-phase arr est and cyclin B1 expression in human skin fibroblasts (HSF) and trans formed HeLa cells following gamma-irradiation were examined by flow cy tometry. Contrary to some earlier reports with HeLa cells, the arrest in G(2) after 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 at tenuating both the radiation-induced increase in cyclin B1 expression and the prolongation of G(2) in synchronous and asynchronous HeLa cell populations. Staurosporine treatment was less effective in down-regul ating 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 o r caffeine treatments, with caffeine being more effective at later tim e points. An increase in cyclin B1 expression was also observed in irr adiated HSF cells (synchronous and asynchronous), which decreased when the cells were treated with staurosporine or caffeine. However, staur osporine was ineffective in attenuating the radiation-induced prolonga tion of G(2) in synchronous and asynchronous HSF cells, whereas treatm ent of irradiated synchronous or asynchronous HSF cells with caffeine significantly reduced the prolongation of G(2). These results suggest that both staurosporine and caffeine treatments act on different pathw ays of cell cycle control in normal and transformed cells, in terms of attenuation of G(2) block and diminution of elevated levels of cyclin B1 expression, in response to radiation. (C) 1997 Academic Press.