RAS-mediated radiation resistance is not linked to MAP kinase activation in two bladder carcinoma cell lines

The expression of activated RAS oncogenes has been shown to increase radior esistance in a number of cell lines. The pathways by which RAS leads to rad ioresistance, however, are unknown. RAS activates several signal transducti on pathways, with the RAF-MAP2K-MAP kinase pathway perhaps the best studied . MAP kinase has also been shown to be activated by radiation through this pathway. Given the important role of MAP kinase in multiple signaling event s, we asked if radioresistance induced by RAS was mediated through the acti vation of MAPK. Cells of two human bladder carcinoma cell lines were used, one with a mutated oncogenic HRAS (T24) and other with a wild-type HRAS (RT 4). The surviving fraction after exposure to 2 Gy of radiation (SF2) for th e T24 cell lines was found to be 0.62, whereas that for RT4 cells was 0.40. Treatment with the farnesyl transferase inhibitor (FTI) L744,832, which in hibits RAS processing and activity, decreased the SF2 of T24 cells to 0.29, whereas the SF2 of RT4 cells remained unchanged after FTI treatment, thus demonstrating the importance of RAS activation to the radiosensitivity of c ells with mutated RAS. MAP kinase activation was found to be constitutive a nd dependent on RAS in T24 cells, while it was inducible by radiation and w as independent of RAS in RT4 cells. Treatment of both cell lines with the M AP2K inhibitor PD98059 inhibited MAPK activation; however, inhibiting MAPK activation had no effect on radiation survival of T24 or RT4 cells. These d ata indicate that MAPK activation does not contribute to RAS-induced radior esistance in this system. (C) 2000 by Radiation Research Society.