Relationship between x-ray exposure and malignant transformation in C3H 10T1/2 cells.

Abstract

The appearance of transformed foci after x-irradiation of the C3H 10T1/2 line of murine cells requires extensive proliferation followed by prolonged incubation under conditions of confluence. When the progeny of irradiated cells are resuspended and plated to determine the number of potential transformed foci, the absolute yield is constant over a wide range of dilutions and is similar to that observed in cultures that have not been resuspended. For cells exposed to a given X-ray dose, the number of transformed foci per dish is independent of the number of irradiated cells. Apparently, few, if any, of the transformed clones occur as a direct consequence of the X-ray exposure, challenging the hypothesis that transformed foci are the clonal products of occasional cells that have experienced an X-ray-induced mutational change. It appears that at least 2 steps are involved. Exposure to X-rays may result in a change, for example, the induction or expression of some cell function, in many or all of the cells and this change may be transmitted to the progeny of the surviving cells; a consequence of this change would be an enhanced probability of the occurrence of a 2nd step, transformation, when these cells are maintained under conditions of confluence.