title: Apollo contributes to G overhang maintenance and protects leading-end telomeres.
abstract: 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.
authors.affiliation: Laboratory for Cell Biology and Genetics, The Rockefeller University, 1230 York Avenue, New York, NY 10065, USA.
authors.forename: Peng
authors.initials: P
authors.lastname: Wu
authors.forename: Megan
authors.initials: M
authors.lastname: van Overbeek
authors.forename: Sean
authors.initials: S
authors.lastname: Rooney
authors.forename: Titia
authors.initials: T
authors.lastname: de Lange
mesh_terms: D020816:Amino Acid Motifs; D000818:Animals; D064007:Ataxia Telangiectasia Mutated Proteins; D018797:Cell Cycle Proteins / Q000378:metabolism; D002460:Cell Line; D004249:DNA Damage; D004261:DNA Replication; D004268:DNA-Binding Proteins / Q000378:metabolism; D004789:Enzyme Activation; D005090:Exodeoxyribonucleases; D005347:Fibroblasts / Q000201:enzymology*; D016195:G2 Phase; D050939:Gene Fusion; D005838:Genotype; D051379:Mice; D008810:Mice, Inbred C57BL; D018345:Mice, Knockout; D009154:Mutation; D009690:Nucleic Acid Conformation; D010641:Phenotype; D017346:Protein Serine-Threonine Kinases / Q000378:metabolism; D034622:RNA Interference; D016196:S Phase; D016615:Telomere / Q000737:chemistry / Q000378:metabolism*; D034501:Telomere-Binding Proteins / Q000737:chemistry / Q000172:deficiency / Q000235:genetics / Q000378:metabolism*; D035341:Telomeric Repeat Binding Protein 2 / Q000378:metabolism; D013997:Time Factors; D025521:Tumor Suppressor Proteins / Q000378:metabolism
chemical_list: D018797:Cell Cycle Proteins; D004268:DNA-Binding Proteins; C534796:TRF2 protein, mouse; D034501:Telomere-Binding Proteins; D035341:Telomeric Repeat Binding Protein 2; D025521:Tumor Suppressor Proteins; D064007:Ataxia Telangiectasia Mutated Proteins; C576325:Atm protein, mouse; D017346:Protein Serine-Threonine Kinases; C551250:Dclre1b protein, mouse; D005090:Exodeoxyribonucleases