SMCHD1 Promotes ATM-dependent DNA Damage Signaling and Repair of Uncapped Telomeres
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ABSTRACT:
SUBMITTER: Dr. Alexandra Vancevska
PROVIDER: S-SCDT-EMBOJ-2019-102668 | biostudies-other |
REPOSITORIES: biostudies-other
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Project description:Structural maintenance of chromosomes flexible hinge domain-containing protein 1 (SMCHD1) has been implicated in X-chromosome inactivation, imprinting, and DNA damage repair, and mutations in SMCHD1 can cause facioscapulohumeral muscular dystrophy. More recently, SMCHD1 has also been identified as a component of telomeric chromatin. Here, we report that SMCHD1 is required for DNA damage signaling and non-homologous end joining (NHEJ) at unprotected telomeres. Co-depletion of SMCHD1 and the shelterin subunit TRF2 reduced telomeric 3'-overhang removal in time-course experiments, as well as the number of chromosome end fusions. SMCHD1-deficient cells displayed reduced ATM S1981 phosphorylation and diminished formation of γH2AX foci and of 53BP1-containing telomere dysfunction-induced foci (TIFs), indicating defects in DNA damage checkpoint signaling. Removal of TPP1 and subsequent activation of ATR signaling rescued telomere fusion events in TRF2-depleted SMCHD1 knockout cells. Together, these data indicate that SMCHD1 depletion reduces telomere fusions in TRF2-depleted cells due to defects in ATM-dependent checkpoint signaling and that SMCHD1 mediates DNA damage response activation upstream of ATM phosphorylation at uncapped telomeres.
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Project description:In response to DNA damage, cells undergo either cell-cycle arrest or apoptosis, depending on the extent of damage and the cell's capacity for DNA repair. Cell-cycle arrest induced by double-stranded DNA breaks depends on activation of the ataxia-telangiectasia (ATM) protein kinase, which phosphorylates cell-cycle effectors such as Chk2 and p53 to inhibit cell-cycle progression. ATM is recruited to double-stranded DNA breaks by a complex of sensor proteins, including Mre11/Rad50/Nbs1, resulting in autophosphorylation, monomerization, and activation of ATM kinase.In characterizing Aven protein, a previously reported apoptotic inhibitor, we have found that Aven can function as an ATM activator to inhibit G2/M progression. Aven bound to ATM and Aven overexpressed in cycling Xenopus egg extracts prevented mitotic entry and induced phosphorylation of ATM and its substrates. Immunodepletion of endogenous Aven allowed mitotic entry even in the presence of damaged DNA, and RNAi-mediated knockdown of Aven in human cells prevented autophosphorylation of ATM at an activating site (S1981) in response to DNA damage. Interestingly, Aven is also a substrate of the ATM kinase. Mutation of ATM-mediated phosphorylation sites on Aven reduced its ability to activate ATM, suggesting that Aven activation of ATM after DNA damage is enhanced by ATM-mediated Aven phosphorylation.These results identify Aven as a new ATM activator and describe a positive feedback loop operating between Aven and ATM. In aggregate, these findings place Aven, a known apoptotic inhibitor, as a critical transducer of the DNA-damage signal.
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