The shelterin protein TRF2 inhibits Chk2 activity at telomeres in the absence of DNA damage.
The shelterin complex [1] shapes and protects telomeric DNA from being processed as double strand breaks (DSBs) [2, 3]. Here we show that in human undamaged cells, a fraction of the kinase Chk2, a downstream target of ATM and mediator of checkpoint responses and senescence [4, 5], physically interacts with the shelterin subunit TRF2 and colocalizes with this complex at chromosome ends. This interaction, enhanced by TRF2 binding to telomeric DNA, inhibits the activation and senescence-induced function of Chk2 by a mechanism in which TRF2 binding to the N terminus of Chk2 surrounding Thr68 hinders the phosphorylation of this priming site. In response to radiation-induced DSBs, but not chromatin-remodelling agents, the telomeric Chk2-TRF2 binding dissociates in a Chk2 activity-dependent manner. Moreover, active Chk2 phosphorylates TRF2 and decreases its binding to telomeric DNA repeats, corroborating the evidences on the specific TRF2 relocalization in presence of DSBs [6]. Altogether, the capacity of TRF2 to locally repress Chk2 provides an additional level of control by which shelterin restrains the DNA damage response from an unwanted activation [6, 7] and may explain why TRF2 overexpression acts as a telomerase-independent oncogenic stimulus [8].
Department of Experimental Oncology, Fondazione IRCCS Istituto Nazionale dei Tumori, Milan 20133, Italy.
Giacomo
G
Buscemi
Laura
L
Zannini
Enrico
E
Fontanella
Daniele
D
Lecis
Sofia
S
Lisanti
Domenico
D
Delia
D000818:Animals; D064007:Ataxia Telangiectasia Mutated Proteins; D018797:Cell Cycle Proteins / Q000235:genetics / Q000378:metabolism; D002460:Cell Line; D016922:Cellular Senescence; D064447:Checkpoint Kinase 2; D004249:DNA Damage; D004268:DNA-Binding Proteins / Q000235:genetics / Q000378:metabolism; D006801:Humans; D009369:Neoplasms / Q000378:metabolism; D017346:Protein Serine-Threonine Kinases / Q000235:genetics / Q000378:metabolism*; D017434:Protein Structure, Tertiary; D019098:Telomerase / Q000378:metabolism; D016615:Telomere / Q000378:metabolism*; D035341:Telomeric Repeat Binding Protein 2 / Q000235:genetics / Q000378:metabolism*; D025521:Tumor Suppressor Proteins / Q000235:genetics / Q000378:metabolism
D018797:Cell Cycle Proteins; D004268:DNA-Binding Proteins; D035341:Telomeric Repeat Binding Protein 2; D025521:Tumor Suppressor Proteins; D064447:Checkpoint Kinase 2; C576324:ATM protein, human; D064007:Ataxia Telangiectasia Mutated Proteins; C578634:CHEK2 protein, human; D017346:Protein Serine-Threonine Kinases; D019098:Telomerase