RADIATION-INDUCED IRREVERSIBLE G(0) G(1) BLOCK IS ABOLISHED IN HUMAN-DIPLOID FIBROBLASTS TRANSFECTED WITH THE HUMAN PAPILLOMA-VIRUS E6 GENE- IMPLICATION OF THE P53-CIP1 WAF1 PATHWAY

It has been shown previously with human diploid fibroblasts that a fra ction of cells remains irreversibly blocked in the G(0)/G(1) phase of the cell cycle when the cells are irradiated in confluent, density-inh ibited cultures and released by subculture to low density. In the pres ent study we demonstrate that this G(0)/G(1) block is abolished when a human fibroblast cell strain is transfected with the human papilloma virus 16 E6 gene. Corresponding to the abolition of the G(0)/G(1) bloc k in the E6-transfected cells, the expression of both the p53 and WAF1 genes is also abolished, suggesting that the p53 pathway of DNA damag e response may be involved in this phenomenon.