Telomere dysfunction and DNA-PKcs deficiency: characterization and consequence.
The mechanisms by which cells accurately distinguish between DNA double-strand break (DSB) ends and telomeric DNA ends remain poorly defined. Recent investigations have revealed intriguing interactions between DNA repair and telomeres. We were the first to report a requirement for the nonhomologous end-joining (NHEJ) protein DNA-dependent protein kinase (DNA-PK) in the effective end-capping of mammalian telomeres. Here, we report our continued characterization of uncapped (as opposed to shortened) dysfunctional telomeres in cells deficient for the catalytic subunit of DNA-PK (DNA-PKcs) and shed light on their consequence. We present evidence in support of our model that uncapped telomeres in this repair-deficient background are inappropriately detected and processed as DSBs and thus participate not only in spontaneous telomere-telomere fusion but, importantly, also in ionizing radiation-induced telomere-DSB fusion events. We show that phosphorylation of DNA-PKcs itself (Thr-2609 cluster) is a critical event for proper telomere end-processing and that ligase IV (NHEJ) is required for uncapped telomere fusion. We also find uncapped telomeres in cells from the BALB/c mouse, which harbors two single-nucleotide polymorphisms that result in reduced DNA-PKcs abundance and activity, most markedly in mammary tissue, and are both radiosensitive and susceptible to radiogenic mammary cancer. Our results suggest mechanistic links between uncapped/dysfunctional telomeres in DNA-PKcs-deficient backgrounds, radiation-induced instability, and breast cancer. These studies provide the first direct evidence of genetic susceptibility and environmental insult interactions leading to a unique and ongoing form of genomic instability capable of driving carcinogenesis.
Williams
Eli S
ES
Department of Environmental and Radiological Health Sciences, Colorado State University, Fort Collins, Colorado 80523-1618, USA.
Klingler
Rebekah
R
Ponnaiya
Brian
B
Hardt
Tanja
T
Schrock
Evelin
E
Lees-Miller
Susan P
SP
Meek
Katheryn
K
Ullrich
Robert L
RL
Bailey
Susan M
SM
D000818:Animals; D053903:DNA Breaks, Double-Stranded; D000072481:DNA Ligase ATP; D011088:DNA Ligases / Q000502:physiology; D051747:DNA-Activated Protein Kinase / Q000172:deficiency*; D004268:DNA-Binding Proteins / Q000172:deficiency*; D005260:Female; D042822:Genomic Instability; D051379:Mice; D008807:Mice, Inbred BALB C; D008810:Mice, Inbred C57BL; D009687:Nuclear Proteins / Q000172:deficiency*; D010766:Phosphorylation; D016615:Telomere / Q000502:physiology*
D004268:DNA-Binding Proteins; D009687:Nuclear Proteins; D051747:DNA-Activated Protein Kinase; C497264:Prkdc protein, mouse; D011088:DNA Ligases; D000072481:DNA Ligase ATP