p53-dependent regulation of nucleotide excision repair in murine epidermis in vivo

p53 protects the integrity of the genome by inducing programed cell death or by promoting DNA repair. We have previously shown that loss or mutation of p53 leads to reduced DNA repair in keratinocytes.

The hypothesis that p53 regulates repair of ultraviolet light-induced epidermal DNA damage in vivo was tested in mice.

An immunohistochemical assay for pyrimidine dimers and 6-4 photoproducts was performed on ultraviolet-irradiated skin from p53 null (-/-) and wild type (+/+) mice. Immunostaining for photoproducts was quantified using computer-assisted imaging. The level of DNA repair was then expressed as the percentage of positive cells remaining as compared to the zero hour time point.

p53+/+ mouse skin exposed to 1000 J/m2 retained ' 25% of epidermal cyclobutane dimers at 48 h, whereas approximately 50% remained in p53-/- cells. Using the same UV dose, p53+/+ mice retained 20% of detectable 6-4 photoproducts by 24 h, whereas about 50% remained in epidermal cells of p53-deficient mice.

Using in situ labelling of UV-damaged cells, we confirm our earlier conclusion that p53 regulates DNA repair within the epidermis after exposure to UV light.