Radiation-induced anchorage-independent growth and collagenase production in diploid human fibroblasts.

Early-passage human foreskin fibroblasts were exposed to X-ray doses ranging from 100 to 600 rad. The X-ray treatments resulted in cell killing in a dose-dependent manner as judged by the colony-forming efficiency of the cells. When cultures exposed to radiation were serially passaged and checked at various times for growth in semi-solid medium they showed the presence of cells with the ability to grow under anchorage-independent conditions (in agarose) at 24 population doublings. The frequencies of colonies with the ability to grow in agarose increased with increasing doses of X-rays above the levels observed for control cultures under similar conditions. When assayed for plasminogen activator levels, the X-ray-treated cultures at various passages showed insignificant differences from levels observed in control cultures. However, the amounts of collagenase (type IV collagen-specific) increased significantly by 32 population doublings in the X-ray-treated cultures compared with control cultures. Our results suggest that the production of type IV collagen-specific collagenase could be useful as an in vitro marker for the transformation of human diploid fibroblasts by X-irradiation.