Unrepaired cyclobutane-type
pyrimidine dimers of
DNA extracted from human skin tumours were examined by an immunoblotting method using polyclonal
antibodies raised against UV-irradiated
calf thymus DNA. A total of 40
DNA samples extracted from seven SCC lesions, two AK lesions, two
lymphomas, one
basal cell epithelioma, one
eccrine poroma, one
neurofibroma of Recklinghausen's disease, on
verruca vulgaris, four femoral normal skins and white blood cells of 21 humans were studied by immunoblotting using this antibody. Two of the 40 DNAs examined, one from facial
actinic keratosis (AK) and one from a
squamous cell carcinoma (SCC) which developed form facial AK formed immunoprecipitates. It was found, using
photoreactivation enzyme plus visible light, that both immunoprecipitates were cyclobutane-type
pyrimidine dimers. In addition, immunofluorescent studies on AK tissue were positive in an immunoblotting assay and revealed that the unremoved photodamage in
DNA remained in the nucleus of AK cells. These findings indicate that these tumour cells may be deficient in the
enzyme function for repairing photoproduct damage. The unrepaired cyclobutane-type
pyrimidine dimer in AK cells might reflect the genetic process in multistage
carcinogenesis as well as in
xeroderma pigmentosum.