We have shown previously that
Li-Fraumeni syndrome fibroblasts homozygous for p53 mutations are deficient in the removal of UV-induced
cyclobutane 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 utilized
monoclonal antibodies specific for
cyclobutane pyrimidine dimers or 6-4 photoproducts, respectively, to measure their repair in UV-irradiated human fibroblasts. Cells homozygous for p53 mutations were deficient in the repair of both photoproducts, whereas cells heterozygous for mutant p53 exhibited normal repair of 6-4 photoproducts, but decreased initial rates of removal of
cyclobutane pyrimidine dimers, compared with normal cells. The specificity of the effect of wild-type p53 on nucleotide excision repair was demonstrated in a p53 homozygous mutant cell line containing a
tetracycline-regulated wild-type p53 gene. Wild-type p53 expression and activity were suppressed in the presence 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 resulted in the recovery of normal levels of repair of both
cyclobutane pyrimidine dimers and 6-4 photoproducts in genomic
DNA, but did not alter the transcription-coupled repair of
cyclobutane pyrimidine dimers. Therefore, the wild-type p53 gene product is an important determinant of nucleotide excision repair activity in human cells.