In a previous study we found that transfection of a human melanoma cell line with the oncogene N-ras led to increased radiosensitivity as measured by clonogenic assays. Since a shift in radiosensitivity is often correlated with altered G2/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 transfected with the neomycin phosphotransferase gene only (IGRneo), were irradiated with 5 Gy and cell cycle distribution was measured at hourly time intervals by DNA staining with propidium iodide. Next, the effect of ionising radiation on the duration of the S-phase was determined by pulse labelling cells with BrdUrd before irradiation. Both cell lines showed a radiation induced G2/M delay, which was most prolonged for the ras transfected cell line. After 5 Gy, the S-phase duration was unaltered, although the shape of the relative movement (RM) curves was slightly different. No G1 delay was observed in either cell line. Ras transfection in a melanoma cell line leads to prolonged G2/M delay after radiotherapy. This prolongation is associated with increased radiosensitivity and not with radioresistance. These data throw doubt on the use of oncogene expression or G2/M delay as predictors of radiosensitivity.

Related Articles