Slowly Progressing Nucleotide Excision Repair in Trichothiodystrophy Group A Patient Fibroblasts

Abstract

Trichothiodystrophy (TTD) is a rare autosomal premature-ageing and neuroectodermal disease. The photohypersensitive form of TTD is caused by inherited mutations in three of the 10 subunits of the basal transcription factor TFIIH. TFIIH is an essential transcription initiation factor that is also pivotal for nucleotide excision repair (NER). Photosensitive TTD is explained by deficient NER, dedicated to removing UV-induced DNA lesions. TTD group A (TTD-A) patients carry mutations in the smallest TFIIH subunit, TTDA, which is an 8-kDa protein that dynamically interacts with TFIIH. TTD-A patients display a relatively mild TTD phenotype, and TTD-A primary fibroblasts exhibit moderate UV sensitivity despite a rather low level of UV-induced unscheduled DNA synthesis (UDS). To investigate the rationale of this seeming discrepancy, we studied the repair kinetics and the binding kinetics of TFIIH downstream NER factors to damaged sites in TTD-A cells. Our results show that TTD-A cells do repair UV lesions, although with reduced efficiency, and that the binding of downstream NER factors on damaged DNA is not completely abolished but only retarded. We conclude that in TTD-A cells repair is not fully compromised but only delayed, and we present a model that explains the relatively mild photosensitive phenotype observed in TTD-A patients.

ACKNOWLEDGMENTS

We thank K. Tanaka for kindly providing XPA antibody, M. Fousteri for help with the ChIP experiments, J. H. J. Hoeijmakers for helpful discussions, and A. Raams for technical assistance.

This study was financed by the Dutch Organization for Scientific Research (grants ZonMW 917-46-364 and 912-08-031; EU-FP6, IP DNA repair, and LSHG-CT-2005-512113; EU-FP6; and MRTN-CT-2003-503618 to W.V.), the Centre National de la Recherche Scientifique (CNRS contract no. 039438 to G.G.-M.), and the Institut National du Cancer (InCa contract no. 2009-001 to G.G.-M.).