Gene-specific DNA repair of UV-induced cyclobutane pyrimidine dimers in some cancer-prone and premature-aging human syndromes.

We have examined the gene-specific DNA repair of UV-induced cyclobutane pyrimidine dimers (CPDs) in fibroblasts from the following cancer prone syndromes: familial dysplastic nevus syndrome (DNS), Gardner's syndrome (GS), and Bloom's syndrome (BS). These heritable human syndromes are associated with DNA damage hypersensitivity and have been considered as potentially DNA repair deficient. Previous determinations of DNA repair in these cell strains have been done solely at the level of the overall genome. That approach is not sensitive enough to detect deficiencies in repair at the level of the gene. Defective preferential repair of active genes may impair survival and affect genomic stability. This is exemplified by the disorder Cockayne's syndrome (CS) which is associated with a selective deficiency in the preferential repair of active genes. In this study, we have used a Cockayne's syndrome cell strain and also a normal human fibroblast cell line as a control. Repair was studied in the transcriptionally active gene dihydrofolate reductase (DHFR), the inactive delta globin gene, and in the c-myc protooncogene. In the DNS, GS and BS cell lines, we find preferential repair similar to that in normal cells. In Cockayne's syndrome cells, there is no preferential repair of the DHFR gene.