title: Telomere protection by TPP1 is mediated by POT1a and POT1b.
abstract: Mammalian telomeres are protected by the shelterin complex, which contains single-stranded telomeric DNA binding proteins (POT1a and POT1b in rodents, POT1 in other mammals). Mouse POT1a prevents the activation of the ATR kinase and contributes to the repression of the nonhomologous end-joining pathway (NHEJ) at newly replicated telomeres. POT1b represses unscheduled resection of the 5'-ended telomeric DNA strand, resulting in long 3' overhangs in POT1b KO cells. Both POT1 proteins bind TPP1, forming heterodimers that bind to other proteins in shelterin. Short hairpin RNA (shRNA)-mediated depletion had previously demonstrated that TPP1 contributes to the normal function of POT1a and POT1b. However, these experiments did not establish whether TPP1 has additional functions in shelterin. Here we report on the phenotypes of the conditional deletion of TPP1 from mouse embryo fibroblasts. TPP1 deletion resulted in the release of POT1a and POT1b from chromatin and loss of these proteins from telomeres, indicating that TPP1 is required for the telomere association of POT1a and POT1b but not for their stability. The telomere dysfunction phenotypes associated with deletion of TPP1 were identical to those of POT1a/POT1b DKO cells. No additional telomere dysfunction phenotypes were observed, establishing that the main role of TPP1 is to allow POT1a and POT1b to protect chromosome ends.
authors.affiliation: Laboratory for Cell Biology and Genetics, The Rockefeller University, 1230 York Avenue, New York, NY 10065-6399, USA.
authors.forename: Tatsuya
authors.initials: T
authors.lastname: Kibe
authors.forename: Gail A
authors.initials: GA
authors.lastname: Osawa
authors.forename: Catherine E
authors.initials: CE
authors.lastname: Keegan
authors.forename: Titia
authors.initials: T
authors.lastname: de Lange
mesh_terms: D000818:Animals; D064007:Ataxia Telangiectasia Mutated Proteins; D018797:Cell Cycle Proteins / Q000378:metabolism; D002460:Cell Line; D002872:Chromosome Deletion; D004249:DNA Damage; D004268:DNA-Binding Proteins / Q000235:genetics / Q000378:metabolism*; D051379:Mice; D008810:Mice, Inbred C57BL; D008815:Mice, Inbred Strains; D011485:Protein Binding; D034622:RNA Interference; D000089804:Shelterin Complex; D016615:Telomere / Q000235:genetics / Q000378:metabolism*; D034501:Telomere-Binding Proteins
chemical_list: C544060:Acd protein, mouse; D018797:Cell Cycle Proteins; D004268:DNA-Binding Proteins; C507326:POT1 protein, mouse; D000089804:Shelterin Complex; D034501:Telomere-Binding Proteins; C576897:Atr protein, mouse; D064007:Ataxia Telangiectasia Mutated Proteins