Apollo Contributes to G Overhang Maintenance and Protects Leading-End Telomeres

• Published in: Molecular cell Vol. 39; no. 4; pp. 606 - 617
• Main Authors: Wu, Peng, van Overbeek, Megan, Rooney, Sean, de Lange, Titia
• Format: Journal Article
• Language: English
• Published: United States Elsevier Inc 27.08.2010
• Subjects: Amino Acid Motifs; Animals; Ataxia Telangiectasia Mutated Proteins; Cell Cycle Proteins - metabolism; Cell Line; CELLCYCLE; DNA; DNA Damage; DNA Replication; DNA-Binding Proteins - metabolism; Enzyme Activation; Fibroblasts - enzymology; G2 Phase; Gene Fusion; Genotype; Mice; Mice, Inbred C57BL; Mice, Knockout; Mutation; Nucleic Acid Conformation; Phenotype; Protein-Serine-Threonine Kinases - metabolism; PROTEINS; RNA Interference; S Phase; Telomere - chemistry; Telomere - metabolism; Telomere-Binding Proteins - chemistry; Telomere-Binding Proteins - deficiency; Telomere-Binding Proteins - genetics; Telomere-Binding Proteins - metabolism; Telomeric Repeat Binding Protein 2 - metabolism; Time Factors; Tumor Suppressor Proteins - metabolism; PROTEINS; CELLCYCLE; DNA
• ISSN: 1097-2765; 1097-4164
• DOI: 10.1016/j.molcel.2010.06.031

Mammalian telomeres contain a single-stranded 3′ overhang that is thought to mediate telomere protection. Here we identify the TRF2-interacting factor Apollo as a nuclease that contributes to the generation/maintenance of this overhang. The function of mouse Apollo was determined using Cre-mediated gene deletion, complementation with Apollo mutants, and the TRF2-F120A mutant that cannot bind Apollo. Cells lacking Apollo activated the ATM kinase at their telomeres in S phase and showed leading-end telomere fusions. These telomere dysfunction phenotypes were accompanied by a reduction in the telomeric overhang signal. The telomeric functions of Apollo required its TRF2-interaction and nuclease motifs. Thus, TRF2 recruits the Apollo nuclease to process telomere ends synthesized by leading-strand DNA synthesis, thereby creating a terminal structure that avoids ATM activation and resists end-joining. These data establish that the telomeric overhang is required for the protection of telomeres from the DNA damage response. ► The shelterin-associated Apollo/SNM1B nuclease was removed from mouse telomeres ► Apollo removal diminished the 3′ overhang and activated the ATM kinase in S phase ► Without Apollo, telomeres generated by leading-strand synthesis underwent fusions ► Thus, shelterin recruits Apollo to protect newly synthesized leading-end telomeres