EXIT FROM G(2) PHASE AFTER 2 GY GAMMA-IRRADIATION IS FASTER IN RADIOSENSITIVE HUMAN-CELLS WITH HIGH EXPRESSION OF THE RAF1 PROTOONCOGENE

We have previously noted that high endogenous expression of the protei n product of the full-length RAF1 proto-oncogene is related to relativ e intrinsic cellular radiosensitivity in 19 human cell lines in vitro. This appeared to be unrelated to the parameters of cell kinetics. In rodent and human cell lines transfected with dominant oncogenes, inclu ding Myc and MYC, Hras and HRAS and SV40, increased radioresistance ha s been accompanied by increased delay in progress through the G(2) pha se of the cell cycle after irradiation. We have thus examined the puta tive relationship between RAF1 expression and postirradiation perturba tion of G, phase in six of the human cell lines for which data have be en reported previously. These lines exhibit a wide range of both radio sensitivity and Raf1 protein levels as measured previously by Western blotting, We report here that the cell lines whose cells appear to exi t more rapidly from G(2) phase are more radiosensitive (r = 0.91, P = 0.01) and express high levels of Raf1 protein (r = -0.93, P = 0.006). (C) 1996 by Radiation Research Society