Growth-state-dependent radiation-induced expression of the proto-oncogene c-fos in NIH 3T3 cells.

Expression of the proto-oncogene c-fos in response to ionizing radiation has been observed in some but not all cell lines tested. Here we report on delayed, transient c-fos expression in NIH 3T3 cells induced by 60Co gamma rays in the dose range 2-5 Gy. Induction of c-fos was significantly increased in cells irradiated in the density-arrested quiescent state compared to irradiation in the exponential growth phase. The enhancement correlated with the transition to quiescence as measured by the proliferation markers, proliferating cell nuclear antigen and bromodeoxyuridine. The observation of growth-state-dependent expression of c-fos after irradiation might indicate a functional relationship between c-fos and growth control in the DNA damage response, e.g. a potential role of c-fos in the control of replicative proteins.