Association of deficient DNA repair during G2 phase with progression from benign to malignant state in a line of human skin keratinocytes transfected with ras oncogene

Human skin keratinocytes after malignant neoplastic transformationby infection with Kirsten murine sarcoma virus (KiMSV) or transfectionwith pSV² ras (containing an activated c-Ha-ras oncogene) showeda DNA repair deficiency(ies). The repair deficiency was manifestas an abnormally high frequency of chromatid breaks and gapspersisting after X-ray-induced DNA damage inflicted during theG₂ phase of the cell cycle. Non-tumorigenic control cells atthat time were clearly repair-efficient. By analyzing benignand malignant tumorigenic HaCaT-ras clones, we could excluderas p21 oncoprotein expression as the causal mechanism for repairdeficiency, since both clone types expressed similar levelsof the mutated protein and only the malignant tumorigenlc cellsshowed repair deficiency. The results suggest that mutated p21ras provided the human keratinocytes with a growth advantagein vivo (benign tumor growth), but acquisition of repair deficiencyis required for progression from benign to malignant state.