Mre11 Dimers Coordinate DNA End Bridging and Nuclease Processing in Double-Strand-Break Repair

Abstract

SUMMARY Mre11 forms the core of the multifunctional Mre11-Rad50-Nbs1 (MRN) complex that detects DNA double-strand breaks (DSBs), activates the ATM checkpoint kinase, and initiates homologous recombination (HR) repair of DSBs. To de?ne the roles of Mre11 in both DNA bridging and nucleolytic processing during initiation of DSB repair, we combined small-angle X-ray scattering (SAXS) and crystal structures of Pyrococcus furiosus Mre11 dimers bound to DNA with mutational analyses of ?ssion yeast Mre11. The Mre11 dimer adopts a four-lobed U-shaped structure that is critical for proper MRN complex assembly and for binding and aligning DNA ends. Further, mutations blocking Mre11 endonuclease activity impair cell survival after DSB induction without compromising MRN complex assembly or Mre11-dependant recruitment of Ctp1, an HR factor, to DSBs. These results show how Mre11 dimerization and nuclease activities initiate repair of DSBs and collapsed replication forks, as well as provide a molecular foundation for understanding cancer-causing Mre11 mutations in ataxia telangiectasia-like disorder (ATLD).

PKB/Akt promotes DSB repair in cancer cells through upregulating Mre11 expression following ionizing radiation

“…Mre11, one of important DSB repair elements, is required for DNA-DSB repair including non-homologous end-joining repair system and homologous recombination repair system. Ding et al, 2006;Williams et al, 2007Williams et al, , 2008. It also can stabilize Rad50 and Nbs1 polypeptides and act as a chaperone for the MRN complex (Takemura et al, 2006).…”

The Rad50 hook domain regulates DNA damage signaling and tumorigenesis

“…Indeed, studies in yeast have shown that the dimerization function of the hook domain underlies the influence of this domain on DSB repair, telomere maintenance, and meiotic DSB formation (Wiltzius et al 2005). In cis, the globular domain could bridge two DNA ends in a manner that would promote NHEJ (Williams et al 2008). In this mode, end-to-end DNA bridging is effected by adjacent monomeric components of the dimeric globular domain (Lammens et al 2011;Lim et al 2011).…”

“…With respect its role in HDR, genetic and physical evidence suggests that the primary function of the Mre11 complex is to promote HDR between sister chromatids via the hook and coiled-coil domains of Rad50 (Bressan et al 1999;Hartsuiker et al 2001;Gonzalez-Barrera et al 2003;Wiltzius et al 2005;Hohl et al 2011). Mre11 complex-mediated NHEJ appears to be primarily dependent on DNA-binding sites in the globular domain (Williams et al 2008(Williams et al , 2009), although we showed that the hook and coiled-coil domains also influence this process, presumably via long-range effects on the disposition of globular domain components (Hohl et al 2011). …”

The MRE11 GAR motif regulates DNA double-strand break processing and ATR activation

“…The MRN complex tethers the DNA ends [10,11], leading to the recruitment and activation of the ATM kinase [12,13]. The MRN complex is also thought to participate in ATR-CHK1 kinase activation by facilitating DNA end resection [14][15][16][17][18].…”

“…MRE11 is a conserved protein with an N-terminal nuclease domain [11,34] and a DNA-binding region [10,35] encompassing the GAR motif [36]. MRE11 nucleasedefective mice have been generated (Mre11 H129N/H129N ), defining a physiological role of the MRE11 nuclease activity in homologous recombination and the maintenance of genomic stability [30].…”