DNA2 nuclease inactivation induces DNA damage through a potential protein trapping mechanism.

DNA2 is a combined nuclease and helicase that processes long 5' flaps and other structures that occur during DNA replication and repair. Current models invoke an essential function of DNA2 in processing stalled replication forks to dampen toxic recombination based restart. As an essential replication stress response factor, DNA2 has been proposed as an anti-cancer drug target with several tool compounds developed. Here we sought to model inhibited DNA2 states using dominant genetics with separation-of-function alleles to identify the optimal mechanisms for DNA2 targeting. We find that expression of DNA2 nuclease-dead alleles exert dominant effects on fitness and DNA damage repair that are dependent on its helicase and RPA binding activities. These mutants are retained on chromatin, suggesting a protein trapping mechanism, perhaps associated with extensive helicase activity. Furthermore, we find an imperfect but interesting link wherein a subset of ALT tumor models are hypersensitive to the presence of DNA2-nuclease dead protein. Together, our data suggests that selectively targeting the nuclease activity of DNA2 in particular cancers may be an effective therapeutic strategy through a protein trapping mechanism.