The tumor suppressor p53 can reduce stable transfection in the presence ofirradiation

The tumor suppressor p53 is believed to play an essential role in maintaini ng genome stability, Although it is currently unknown how p53 is involved i n this important biological safeguard, several previous publications indica te that p53 can help to maintain genome integrity through the recombination -mediated DNA repair process. The integration of linearized plasmid DNA int o the host chromosome utilizes the same repair process, and the frequency c an be measured by clonogenic assays in which cells that were stably transfe cted by plasmid integration can be scored by their colony-forming abilities . To gain insight into whether p53 has a direct role in plasmid integration into the host chromosome, we determined the frequency of stable transfecti on with CHO cells expressing either wild-type or mutant p53 in the presence and absence of irradiation. We found that low-dose irradiation (similar to 50 to 100 cGy) increased stable transfection frequencies in CHO cells rega rdless of their p53 status. However, the increase of transfection frequency was significantly lower in CHO cells expressing wild-type p53. Our data th us suggest that wild-type p53 can suppress plasmid DNA integration into the host genome. This p53 function may play a direct and significant role in m aintaining genome stability.