The Mre11 complex (Mre11, Rad50, and Nbs1) is a central component of the DNA damage response (DDR), governing both double-strand break repair and DDR signaling. Rad50 contains a highly conserved Zn(2+)-dependent homodimerization interface, the Rad50 hook domain. Mutations that inactivate the hook domain produce a null phenotype. In this study, we analyzed mutants with reduced hook domain function in an effort to stratify hook-dependent Mre11 complex functions. One of these alleles, Rad50(46), conferred reduced Zn(2+) affinity and dimerization efficiency. Homozygous Rad50(46/46) mutations were lethal in mice. However, in the presence of wild-type Rad50, Rad50(46) exerted a dominant gain-of-function phenotype associated with chronic DDR signaling. At the organismal level, Rad50(+/46) exhibited hydrocephalus, liver tumorigenesis, and defects in primitive hematopoietic and gametogenic cells. These outcomes were dependent on ATM, as all phenotypes were mitigated in Rad50(+/46) Atm(+/-) mice. These data reveal that the murine Rad50 hook domain strongly influences Mre11 complex-dependent DDR signaling, tissue homeostasis, and tumorigenesis.
Keywords: ATM; Mre11 complex; Rad50; double-strand breaks.