Defective transcription/repair factor IIH recruitment to specific UV lesions in trichothiodystrophy syndrome.

Most trichothiodystrophy (TTD) patients present mutations in the xeroderma pigmentosum D (XPD) gene, coding for a subunit of the transcription/repair factor IIH (TFIIH) complex involved in nucleotide excision repair (NER) and transcription. After UV irradiation, most TTD/XPD patients are more severely affected in the NER of cyclobutane pyrimidine dimers (CPD) than of 6-4-photoproducts (6-4PP). The reasons for this differential DNA repair defect are unknown. Here we report the first study of NER in response to CPDs or 6-4PPs separately analyzed in primary fibroblasts. This was done by using heterologous photorepair; recombinant adenovirus vectors carrying photolyases enzymes that repair CPD or 6-4PP specifically by using the energy of light were introduced in different cell lines. The data presented here reveal that some TTD/XPD mutations affect the recruitment of TFIIH specifically to CPDs, but not to 6-4PPs. This deficiency is further confirmed by the inability of TTD/XPD cells to recruit, specifically for CPDs, NER factors that arrive in a TFIIH-dependent manner later in the NER pathway. For 6-4PPs, we show that TFIIH complexes carrying an NH(2)-terminal XPD mutated protein are also deficient in recruitment of NER proteins downstream of TFIIH. Treatment with the histone deacetylase inhibitor trichostatin A allows the recovery of TFIIH recruitment to CPDs in the studied TTD cells and, for COOH-terminal XPD mutations, increases the repair synthesis and survival after UV, suggesting that this defect can be partially related with accessibility of DNA damage in closed chromatin regions.