The Rad50 hook domain regulates DNA damage signaling and tumorigenesis

Area of Science:

• Molecular Biology
• Genetics
• Cellular Biology

Background:

• The Mre11 complex (Mre11, Rad50, and Nbs1) is essential for DNA damage response (DDR), regulating double-strand break repair and signaling.
• Rad50's hook domain is a conserved Zn(2+)-dependent dimerization interface; its inactivation leads to a null phenotype.

Purpose of the Study:

• To investigate the functions of the Rad50 hook domain by analyzing mutants with reduced function.
• To stratify hook-dependent Mre11 complex functions and understand their impact on DDR signaling and organismal health.

Main Methods:

• Analysis of Rad50 hook domain mutants, including the Rad50(46) allele with reduced Zn(2+) affinity and dimerization.
• Generation and study of homozygous Rad50(46/46) lethal mice and heterozygous Rad50(+/46) mice.
• Assessment of phenotypes in Rad50(+/46) mice, including developmental defects and tumorigenesis, and their dependence on ATM kinase.

Main Results:

• The Rad50(46) allele conferred reduced Zn(2+) affinity and dimerization efficiency.
• Homozygous Rad50(46/46) mutations were lethal, while heterozygous Rad50(+/46) mice showed a dominant gain-of-function phenotype with chronic DDR signaling.
• Rad50(+/46) mice exhibited hydrocephalus, liver tumors, and defects in hematopoietic and gametogenic cells, which were mitigated in the absence of one ATM allele (Atm(+/-)).

Conclusions:

• The murine Rad50 hook domain plays a critical role in regulating Mre11 complex-dependent DDR signaling.
• Dysfunctional Rad50 hook domain can lead to chronic DDR signaling, impacting tissue homeostasis and promoting tumorigenesis.
• ATM kinase activity is essential for the manifestation of phenotypes associated with the Rad50(46) gain-of-function mutation.