CORRECTION BY THE ERCC2 GENE OF UV SENSITIVITY AND REPAIR DEFICIENCY PHENOTYPE IN A SUBSET OF TRICHOTHIODYSTROPHY CELLS

Trichothiodystrophy (TTD) is a rare genetic disease with heterogeneous clinical features associated with specific deficiencies in nucleotide excision repair. Patients have brittle hair due to a reduced content of cysteine-rich matrix proteins, About 50% of the cases reported in t he literature are photosensitive. In these patients an altered cellula r response to UV, due to a specific deficiency in nucleotide excision repair, has been observed. The majority of repair-defective TTD patien ts have been assigned by complementation analysis to group D of xerode rma pigmentosum (XP). Recently, the human excision repair gene ERCC2 h as been shown to correct the UV sensitivity of XP-D fibroblasts. In th is work we describe the effect of ERCC2 on the DNA repair deficient ph enotype of XP-D and on two repair-defective TTD cell strains (TTD1VI a nd TTD2VI) assigned by complementation analysis to group D of XP. ERCC 2 cDNA, cloned into a mammalian expression vector, was introduced into TTD and XP fibroblasts via DNA-mediated transfection or microneedle i njection. UV sensitivity and cellular DNA repair properties, including unscheduled DNA synthesis and reactivation of a UV-irradiated plasmid ;containing the chloramphenicol acetyltransferase reporter gene (pRSVC at), were corrected to wild-type level in both TTD and XP-D cells. The se data show that a functional ERCC2 gene is sufficient to reestablish a wild-type DNA repair phenotype in TTD1VI and TTD2VI cells, confirmi ng the genetic relationship between TTD and XP-D. Furthermore, our fin dings suggest that mutations at the ERCC2 locus are responsible for ca using a similar phenotype in TTD and XP-D cells in response to UV irra diation, but produce quite different clinical symptoms.