Complete restoration of normal DNA repair characteristics in group F xeroderma pigmentosum cells by over-expression of transfected XPF cDNA.

XP-F cDNA was cloned into a mammalian expression vector plasmid, and introduced into group F xeroderma pigmentosum (XP-F) cells. Several cell clones possessing transfected XPF cDNA were randomly isolated, and DNA repair characteristics of a clone, XP-FR2, were extensively analyzed. The XP-FR2 cells expressed high level of XPF protein as well as ERCC1 protein, although their parental XP-F cells expressed extremely low level of both proteins. The XP-FR2 cells showed UV resistance comparable to normal human cells, and had normal levels of UV-induced unscheduled DNA synthesis and normal capability to remove cyclobutane pyrimidine dimers and (6-4) photoproducts. Frequencies and types of UV-induced mutations examined by shuttle vector plasmids in XP-FR2 cells were similar to those in normal human cells. These results demonstrate that excision repair defect in XP-F cells is fully corrected by over-expression of XPF cDNA alone, although only partial correction of the cells by XPF cDNA has been reported before.