EXPRESSION OF WILD-TYPE P53 IS REQUIRED FOR EFFICIENT GLOBAL GENOMIC NUCLEOTIDE EXCISION-REPAIR IN UV-IRRADIATED HUMAN FIBROBLASTS

We have shown previously that Li-Fraumeni syndrome fibroblasts homozyg ous for p53 mutations are deficient in the removal of UV-induced cyclo butane pyrimidine dimers from genomic DNA, but still proficient in the transcription-coupled repair pathway (Ford, J. M., and Hanawalt, P. C . (1995) Proc, Natl, Acad. Sci, U. S. A. 92, 8876-8880), We have now u tilized monoclonal antibodies specific for cyclobutane pyrimidine dime rs or 6-4 photoproducts, respectively, to measure their repair in UV-i rradiated human fibroblasts, Cells homozygous for p53 mutations were d eficient in the repair of both photoproducts, whereas cells heterozygo us for mutant p53 exhibited normal repair of 6-4 photoproducts, but de creased initial rates of removal of cyclobutane pyrimidine dimers, com pared with normal cells, The specificity of the effect of wild-type p5 3 on nucleotide excision repair was demonstrated in a p53 homozygous m utant cell line containing a tetracycline-regulated wild-type p53 gene , Wild-type p53 expression and activity were suppressed in the presenc e of tetracycline, whereas withdrawal of tetracycline resulted in the induction of p53 expression, cell cycle checkpoint activation, and DNA damage-induced apoptosis, The regulated expression of wild-type p53 r esulted in the recovery of normal levels of repair of both cyclobutane pyrimidine dimers and 6-4 photoproducts in genomic DNA, but did not a lter the transcription-coupled repair of cyclobutane pyrimidine dimers , Therefore, the wild-type p53 gene product is an important determinan t of nucleotide excision repair activity in human cells.