PROCESSING OF 3 DIFFERENT TYPES OF DNA-DAMAGE IN CELL-LINES OF A CUTANEOUS SQUAMOUS-CELL CARCINOMA PROGRESSION MODEL

In order to study the role of DNA damage processing in the development of cutaneous squamous cell carcinoma (SCC), we assessed the ability o f six keratinocyte cell lines from a multistage-tumor progression mode l to repair three types of DNA damage: pyrimidine dimers, oxidative DN A lesions and DNA double strand breaks (DSB), The model comprised the spontaneously immortalized, non-tumorigenic human keratinocyte cell li ne HaCaT, four different c-Ha-rns transfectants of HaCaT (non-, benign - and two malignant-tumorigenic) and a SCC-derived cell line, Host cel l reactivation assays with UVB-treated plasmid vectors pRSVcat showed no significantly altered repair of UVB-induced pyrimidine dimers in th e tumorigenic cell lines, compared with the non-tumorigenic lines, Usi ng the singlet oxygen-treated plasmids pRSVcat the Ha-ras-HaCaT-clones and the SCC-cells, exerted a DNA repair efficiency that was not signi ficantly different from HaCaT cells, In order to assess the ability of the cells to ligate free DNA ends (repair of DSB), we used a plasmid shuttle vector assay with linearized plasmid pZ189, We found a signifi cant increase of DNA end joining ability in the non-tumorigenic, the b enign and in one of the malignant HaCaT-clones II-4, The malignant HaC aT-clone II-3, however, exerted a significantly lower rate of rejoinin g the linearized plasmid, This cell line also showed a highly and sign ificantly elevated rate of micronuclei, which reflects a pronounced ch romosomal instability, The SCC-cells exhibited a more efficient repair of DNA DSB than the HaCaT cells, We conclude that in the examined mod el, progression of human keratinocytes from the non-tumorigenic to the highly tumorigenic phenotype, is not accompanied by a decrease in the cell's capacity to repair UVB- and singlet oxygen-induced DNA lesions , However, an acquired deficiency in repairing DNA double strand break s can be one mechanism promoting progression towards malignancy, possi bly through impairing chromosomal stability.