Abstract
Overexpression of XPA genes, both wild type and a missense mutant, which code for a damage-specific, DNA-binding protein, increased the survival of repair-deficient and -competent human cells to levels above that of normal cells that did not overexpress XPA. The first 3 h after cells were damaged were most critical to achieving this increased survival. The dose at which 37% of the irradiated population survives could be restored to about one-half that of normal cells, with no detectable genome-wide repair of pyrimidine dimers or (6-4) photoproducts, suggesting that intermediate levels of XPA gene expression can direct repair to restricted critical regions of the genome. Current views of repair implicate transcriptionally active genes as a major component of such critical regions. Consistent with this interpretation, the repair of a transfected, actively expressed luciferase gene was higher than that of genomic DNA at intermediate and higher levels of XPA expression. High levels of XPA expression resulted in increased repair at early times after irradiation and extensive repair of (6-4) photoproducts but little, if any, pyrimidine dimer repair in the whole genome. At the highest level of expression, some clonal cell lines acquired resistance to radiation that corresponded to a dose at which 37% of the irradiated population survives that was about 1.5 to 2 times that of normal cells. The XPA gene product, therefore, can influence levels of DNA repair and radiation sensitivity quantitatively by contributing to selective repair at certain sites in the genome.
Footnotes
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↵1 This work was supported by the Office of Health and Environmental Research, United States Department of Energy, contract DE-AC03-76-SF01012, and by NIH Grant CA04484-34, National Institute of Environmental Health Sciences Grant ES05914, and American Cancer Society Grant S19-14.
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↵2 To whom requests for reprints should be addressed, at Laboratory of Radiobiology and Environmental Health, Box 0750, University of California, San Francisco, CA 94143-0750. Phone: (415) 476-4563; Fax: (415) 476-0721.
- Received December 8, 1994.
- Accepted October 13, 1995.
- ©1995 American Association for Cancer Research.