title: Disappearance of the telomere dysfunction-induced stress response in fully senescent cells.
abstract: Replicative senescence is a natural barrier to cellular proliferation that is triggered by telomere erosion and dysfunction. Here, we demonstrate that ATM activation and H2AX-gamma nuclear focus formation are sensitive markers of telomere dysfunction in primary human fibroblasts. Whereas the activated form of ATM and H2AX-gamma foci were rarely observed in early-passage cells, they were readily detected in late-passage cells. The ectopic expression of telomerase in late-passage cells abrogated ATM activation and H2AX-gamma focus formation, suggesting that these stress responses were the consequence of telomere dysfunction. ATM activation was induced in quiescent fibroblasts by inhibition of TRF2 binding to telomeres, indicating that telomere uncapping is sufficient to initiate the telomere signaling response; breakage of chromosomes with telomeric associations is not required for this activation. Although ATM activation and H2AX-gamma foci were readily observed in late-passage cells, they disappeared once cells became fully senescent, indicating that constitutive signaling from dysfunctional telomeres is not required for the maintenance of senescence.
authors.affiliation: Department of Hematology/Oncology, St Jude Children's Research Hospital, Memphis, Tennessee 38105, USA.
authors.forename: Christopher J
authors.initials: CJ
authors.lastname: Bakkenist
authors.forename: Rachid
authors.initials: R
authors.lastname: Drissi
authors.forename: Jing
authors.initials: J
authors.lastname: Wu
authors.forename: Michael B
authors.initials: MB
authors.lastname: Kastan
authors.forename: Jeffrey S
authors.initials: JS
authors.lastname: Dome
mesh_terms: D064007:Ataxia Telangiectasia Mutated Proteins; D018797:Cell Cycle Proteins; D002467:Cell Nucleus / Q000378:metabolism; D002478:Cells, Cultured; D016922:Cellular Senescence / Q000502:physiology*; D004268:DNA-Binding Proteins; D005347:Fibroblasts / Q000166:cytology / Q000648:ultrastructure; D006367:HeLa Cells; D006657:Histones / Q000378:metabolism; D006801:Humans; D008856:Microscopy, Fluorescence; D017346:Protein Serine-Threonine Kinases / Q000502:physiology; D015398:Signal Transduction / Q000502:physiology; D016615:Telomere / Q000502:physiology*; D016159:Tumor Suppressor Protein p53 / Q000378:metabolism; D025521:Tumor Suppressor Proteins
chemical_list: D018797:Cell Cycle Proteins; D004268:DNA-Binding Proteins; C468783:H2AX protein, human; D006657:Histones; D016159:Tumor Suppressor Protein p53; D025521:Tumor Suppressor Proteins; C576324:ATM protein, human; D064007:Ataxia Telangiectasia Mutated Proteins; D017346:Protein Serine-Threonine Kinases