The influence of the oncogene N-ras on cell cycle delay in a human melanoma cell line with reduced radioresistance

In a previous study we found that transfection of a human melanoma cell lin e with the oncogene N-ras led to increased radiosensitivity as measured by clonogenic assays. Since a shift in radiosensitivity is often correlated wi th altered G(2)/M delay, we investigated whether this was also the case in this oncogene containing melanoma cell line (IGRras). A human melanoma cell line, stably transfected with mutated N-ras, and its parental cell line tr ansfected with the neomycin phosphotransferase gene only (IGRneo), were irr adiated with 5 Gy and cell cycle distribution was measured at hourly time i ntervals by DNA staining with propidium iodide. Next, the effect of ionisin g radiation on the duration of the S-phase was determined by purse labellin g cells with BrdUrd before irradiation. Both cell lines showed a radiation induced G(2)/M delay, which was most prolonged for the ras transfected cell line. After 5 Gy, the S-phase duration was unaltered, although the shape o f the relative movement (RM) curves was slightly different. No G(1) delay w as observed in either cell line. Ras transfection in a melanoma cell line l eads to prolonged G(2)/M delay after radiotherapy. This prolongation is ass ociated with increased radiosensitivity and not with radioresistance. These data throw doubt on the use of oncogene expression or G(2)/M delay as pred ictors of radiosensitivity.