Telomere Dysfunction and DNA-PKcs Deficiency: Characterization and Consequence

• Published in: Cancer research (Chicago, Ill.) Vol. 69; no. 5; pp. 2100 - 2107
• Main Authors: WILLIAMS, Eli S, KLINGLER, Rebekah, PONNAIYA, Brian, HARDT, Tanja, SCHROCK, Evelin, LEES-MILLER, Susan P, MEEK, Katheryn, ULLRICH, Robert L, BAILEY, Susan M
• Format: Journal Article
• Language: English
• Published: Philadelphia, PA American Association for Cancer Research 01.03.2009
• Subjects: Animals; Antineoplastic agents; Biological and medical sciences; DNA Breaks, Double-Stranded; DNA Ligase ATP; DNA Ligases - physiology; DNA-Activated Protein Kinase - deficiency; DNA-Binding Proteins - deficiency; Female; Genomic Instability; Medical sciences; Mice; Mice, Inbred BALB C; Mice, Inbred C57BL; Nuclear Proteins - deficiency; Pharmacology. Drug treatments; Phosphorylation; Telomere - physiology; Tumors; Characterization; Protein kinase C; Enzyme; Dysfunction; Transferases; DNA; Deficiency; Telomere
• ISSN: 0008-5472; 1538-7445
• DOI: 10.1158/0008-5472.can-08-2854

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.