human telomeres are hypersensitive to uv-induced dna damage and refractory to repair人类染色体端粒是高度敏感uv-induced dna损伤修复和耐火材料.pdfVIP

Human Telomeres Are Hypersensitive to UV-Induced DNA Damage and Refractory to Repair Patrick J. Rochette1,2¤, Douglas E. Brash1,2,3,4* 1 Department of Therapeutic Radiology, Yale School of Medicine, New Haven, Connecticut, United States of America, 2 Yale Comprehensive Cancer Center, Yale School of Medicine, New Haven, Connecticut, United States of America, 3 Department of Genetics, Yale School of Medicine, New Haven, Connecticut, United States of America, 4 Department of Dermatology, Yale School of Medicine, New Haven, Connecticut, United States of America Abstract Telomeric repeats preserve genome integrity by stabilizing chromosomes, a function that appears to be important for both cancer and aging. In view of this critical role in genomic integrity, the telomere’s own integrity should be of paramount importance to the cell. Ultraviolet light (UV), the preeminent risk factor in skin cancer development, induces mainly cyclobutane pyrimidine dimers (CPD) which are both mutagenic and lethal. The human telomeric repeat unit (59TTAGGG/ CCCTAA39) is nearly optimal for acquiring UV-induced CPD, which form at dipyrimidine sites. We developed a ChIP–based technique, immunoprecipitation of DNA damage (IPoD), to simultaneously study DNA damage and repair in the telomere and in the coding regions of p53, 28S rDNA, and mitochondrial DNA. We find that human telomeres in vivo are 7-fold hypersensitive to UV-induced DNA damage. In double-stranded oligonucleotides, this hypersensitivity is a property of both telomeric and non-telomeric repeats; in a series of telomeric repeat oligonucleotides, a phase change conferring UV- sensitivity occurs above 4 repeats. Furthermore, CPD removal in the telomere is almost absent, matching the rate in mitochondria known to lack nucleotide excision repair. Cells containing pe