PROLONGED P53 PROTEIN ACCUMULATION IN TRICHOTHIODYSTROPHY FIBROBLASTSDEPENDENT ON UNREPAIRED PYRIMIDINE DIMERS ON THE TRANSCRIBED STRANDS OF CELLULAR GENES

Trichothiodistrophy (TTD), xeroderma pigmentosum (XP), and Cockayne's syndrome (CS) are three distinct human diseases with sensitivity to ul traviolet (UV) radiation affected by mutations in genes involved in nu cleotide excision repair (NER). Among the many responses of human cell s to UV irradiation, both nuclear accumulation of p53, a tumor suppres sor protein, and alterations in cell-cycle checkpoints play crucial ro les. The purpose of this study was to define the signals transmitted a fter UV-C-induced DNA damage, which activates p53 accumulation in TTD/ XP-D fibroblasts, and compare this with XP-D cell lines that carry dif ferent mutations in the same gene, XPD. Our results showed that p53 wa s rapidly induced in the nuclei of TTD/XP-D and XP-D fibroblasts in a dose-dependent manner after UV-C irradiation, as seen in XP-A and CS-A fibroblasts, much lower doses being required for the protein accumula tion than in normal human fibroblasts, XP variant cells, and XP-C cell s. The kinetics of accumulation of p53 and two effector proteins invol ved in cell-cycle arrest, WAF1 a nd GAD D45, were also directly relate d to the repair potential of the cells, as in normal human fibroblasts the ir levels declined after 24 h, the time required for repair of UV -induced lesions, whereas NER-deficient TTD/XP-D cells showed p53, WAF 1, and GADD45 accumulation for over 72 h after irradiation. Our result s indicate that p53 accumulation followed by transcriptional activatio n of genes implicated in growth arrest is triggered in TTD/XP-D cells by the persistence of cyclobutane pyrimidine dimers, which are known t o block transcription, on the transcribed strands of active genes. (C) 1997 Wiley-Liss, Inc.