Differential sensitivity to mitomycin C between human RSa cell line and its derivative UVr-1

To study cellular signaling factors responsible for the susceptibility of h uman cells to cel proliferation inhibition by anticancer drugs, human RSa c ell line and its ultraviolet-resistant derivative UVr-1 were compared with respect to their sensitivity to the anti-proliferative effects of mitomycin C (MMC), 5-fluorouracil, nimustine (ACNU), cisplatin, pirarubicin (THP), b leomycin, methotrexate and ifosfamide. RSa cells were found to be highly se nsitive to MMC by MTT assay compared to UVr-1 cells. The half maximum inhib ition concentration of MMC against proliferation of RSa cells was approxima tely 100 ng/ml while that of UVr-1 cells was greater than 1 mu g/ml. There was no significant difference observed between RSa and UVr-1 cells in the s ensitivity to other seven drugs examined. Analysis by flow cytometry reveal ed that the cell cycle of RSa was completely blocked at the G(2)/M phase 40 h after treatment wit MMC at a concentration of 100 ng/ml whereas a substa ntial proportion of UVr-1 cells was not arrested at that phase even in the presence of MMC. Further immunoblot analysis on MMC-induced signal transduc tion showed that the amounts of phosphorylated ERK MAP kinases wee increase d in UVr-1 cells to a greater extent than those in RSa cells after treatmen t with MMC for longer than 2 h. However, the increase in p21(Cip1) was obse rved in RSa cells 1 h after addition of MMC but was not observed in UVr-1 c ells. These distinct signaling pathways might account for the differences i n sensitivity to MMC between Ra and UVr-1 cells.