Cells from XP-D and XP-D-CS patients exhibit equally inefficient repair of UV-induced damage in transcribed genes but different capacity to recover UV-inhibited transcription.
Xeroderma pigmentosum (XP) is a rare hereditary human disorder clinically associated with severe sun sensitivity and predisposition to skin cancer. Some XP patients also show clinical characteristics of Cockayne syndrome (CS), a disorder associated with defective preferential repair of DNA lesions in transcriptionally active genes. Cells from the two XP-patients who belong to complementation group D and exhibit additional clinical symptoms of CS are strikingly more sensitive to the cytotoxic effects of UV-light than cells from classical XP-D patients. To explain the severe UV-sensitivity it was suggested that XP-D-CS cells have a defect in preferential repair of UV-induced 6-4 photoproducts (6-4PP) in active genes. We investigated the capacity of XP-D and XP-D-CS cells to repair UV-induced DNA lesions in the active adenosine deaminase gene (ADA) and in the inactive 754 gene by determining (i) the removal of specific lesions, i.e. cyclobutane pyrimidine dimers (CPD) and 6-4PP, or (ii) the formation of BrdUrd-labeled repair patches. No differences in repair capacity were observed between XP-D and XP-D-CS cells. In both cell types repair of CPD was completely absent whereas 6-4PP were inefficiently removed from the ADA gene and the 754 gene with similar kinetics. However, whereas XP-D cells were able to restore UV-inhibited RNA synthesis after a UV-dose of 2 J/m2, RNA synthesis in XP-D-CS cells remained repressed up to 24 h after irradiation. Our results are inconsistent with the hypothesis that differences in the capacity to perform preferential repair of UV-induced photolesions in active genes between XP-D and XP-D-CS cells are the cause of the extreme UV-sensitivity of XP-D-CS cells. Rather, the enhanced sensitivity of XP-D-CS cells may be associated with a defect in transcription regulation superimposed on the repair defect.
van Hoffen
A
A
MGC, Department of Radiation Genetics and Chemical Mutagenesis, Leiden University, Wassenaarseweg 72, 2333 AL Leiden, The Netherlands.
Kalle
W H
WH
de Jong-Versteeg
A
A
Lehmann
A R
AR
van Zeeland
A A
AA
Mullenders
L H
LH
D000243:Adenosine Deaminase / Q000235:genetics; D002470:Cell Survival / Q000528:radiation effects; D002478:Cells, Cultured; D003057:Cockayne Syndrome / Q000235:genetics* / Q000473:pathology; D004249:DNA Damage / Q000235:genetics*; D004260:DNA Repair / Q000235:genetics*; D004307:Dose-Response Relationship, Radiation; D005347:Fibroblasts; D005816:Genetic Complementation Test; D006801:Humans; D011740:Pyrimidine Dimers / Q000378:metabolism; D012313:RNA / Q000096:biosynthesis; D011836:Radiation Tolerance; D013997:Time Factors; D014158:Transcription, Genetic / Q000235:genetics* / Q000528:radiation effects; D014466:Ultraviolet Rays; D014983:Xeroderma Pigmentosum / Q000235:genetics* / Q000473:pathology
D011740:Pyrimidine Dimers; C058406:pyrimidine-pyrimidone dimer; D012313:RNA; D000243:Adenosine Deaminase