INCREASE IN POSTIRRADIATION SURVIVAL OF RAT 3Y1 FIBROBLASTS BY A PROTEIN-KINASE INHIBITOR, STAUROSPORINE

Protein kinases play an important role in the response of mammalian ce lls to ionizing radiation. In this study, we examined the effect of st aurosporine, a potent inhibitor of protein kinases, on cell survival a fter X-irradiation, using the normal rat fibroblast line 3Y1. Treatmen t with 30 ng/ml staurosporine Ih before irradiation resulted in the in crease in survival of 3Y1 cells. This phenomenon was drug dose-depende nt and maximal reduction of radiation-induced cell killing occurred wh en more than, or equal to, 30 ng/ml staurosporine was added. In contra st, treatment with 30 ng/ml staurosporine after irradiation did not in crease cell survival. There was no change in cell cycle distribution b y treatment for 1 h with 30 ng/ml staurosporine. These data suggest th at the inhibition of protein kinase activities by staurosporine influe nces the radiosensitivity of 3Y1 cells.