Immunochemical detection of unrepaired cyclobutane-type pyrimidine dimers of DNAs extracted from human skin tumours.

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.