Polymerase eta deficiency in the xeroderma pigmentosum variant uncovers an overlap between the S phase checkpoint and double-strand break repair.
The xeroderma pigmentosum variant (XPV) is a genetic disease involving high levels of solar-induced cancer that has normal excision repair but shows defective DNA replication after UV irradiation because of mutations in the damage-specific polymerase hRAD30. We previously found that the induction of sister chromatid exchanges by UV irradiation was greatly enhanced in transformed XPV cells, indicating the activation of a recombination pathway. We now have identified that XPV cells make use of a homologous recombination pathway involving the hMre11/hRad50/Nbs1 protein complex, but not the Rad51 recombination pathway. The hMre11 complexes form at arrested replication forks, in association with proliferating cell nuclear antigen. In x-ray-damaged cells, in contrast, there is no association between hMre11 and proliferating cell nuclear antigen. This recombination pathway assumes greater importance in transformed XPV cells that lack a functional p53 pathway and can be detected at lower frequencies in excision-defective XPA fibroblasts and normal cells. DNA replication arrest after UV damage, and the associated S phase checkpoint, is therefore a complex process that can recruit a recombination pathway that has a primary role in repair of double-strand breaks from x-rays. The symptoms of elevated solar carcinogenesis in XPV patients therefore may be associated with increased genomic rearrangements that result from double-strand breakage and rejoining in cells of the skin in which p53 is inactivated by UV-induced mutations.
Limoli
C L
CL
Departments of Radiology and Radiation Oncology, University of California, San Francisco, CA 94103-0806, USA.
Giedzinski
E
E
Morgan
W F
WF
Cleaver
J E
JE
D017766:Acid Anhydride Hydrolases; D017209:Apoptosis; D002461:Cell Line, Transformed; D004249:DNA Damage; D004260:DNA Repair; D045643:DNA Repair Enzymes; D004268:DNA-Binding Proteins / Q000302:isolation & purification; D004259:DNA-Directed DNA Polymerase / Q000172:deficiency*; D005347:Fibroblasts / Q000166:cytology; D005455:Fluorescent Antibody Technique; D006801:Humans; D000076228:MRE11 Homologue Protein; D009690:Nucleic Acid Conformation; D018809:Proliferating Cell Nuclear Antigen / Q000302:isolation & purification; D011995:Recombination, Genetic; D016196:S Phase; D012854:Sister Chromatid Exchange; D014466:Ultraviolet Rays; D014965:X-Rays; D014983:Xeroderma Pigmentosum / Q000201:enzymology* / Q000235:genetics; D000094769:DNA Polymerase iota; D000099270:Y-Family DNA Polymerases
D017766:Acid Anhydride Hydrolases; D045643:DNA Repair Enzymes; D004268:DNA-Binding Proteins; D004259:DNA-Directed DNA Polymerase; D000076228:MRE11 Homologue Protein; D018809:Proliferating Cell Nuclear Antigen; D000094769:DNA Polymerase iota; C121766:MRE11 protein, human; C112338:Rad30 protein; D000099270:Y-Family DNA Polymerases; C112158:RAD50 protein, human; C000722070:POLI protein, human