Human Nuclease/Helicase DNA2 Alleviates Replication Stress by Promoting DNA End Resection

Abstract

In precancerous and cancerous lesions, excessive growth signals resulting from activation of oncogenes or loss of tumor suppressor genes lead to intensive replication stress, which is recognized by a high level of replication-associated DNA double-strand breaks (DSBs). However, the molecular mechanism by which cells alleviate excessive replication stress remains unclear. In this study, we report that the human nuclease/helicase DNA2 facilitates homologous recombination to repair replication-associated DNA double-strand breaks (DSBs), thereby providing cells with survival advantages under conditions of replication stress. The nuclease activity of DNA2 was required for DSB end resection, which allowed subsequent recruitment of RPA and RAD51 to repair DSBs and restart replication. More importantly, DNA2 expression was significantly increased in human cancers and its expression correlated with patient outcome. Our findings therefore indicate that enhanced activity of DSB resection likely constitutes one mechanism whereby precancerous and cancerous cells might alleviate replication stress.

DNA Damage Sensing by the ATM and ATR Kinases

“…Consistent with the idea that DSB resection is important for ATR activation, depletion, or inactivation of ATM, Mre11, CtIP, Exo1, and Dna2 all lead to diminished ATR responses to DSBs (Fig. 4) (Adams et al 2006;Jazayeri et al 2006;Myers and Cortez 2006;Sartori et al 2007;Peng et al 2012;Tomimatsu et al 2012). …”

“…Based on studies using yeast, Xenopus, and human cells, several conserved nucleases have been implicated in the generation of ssDNA at DSBs through a process called resection (Symington and Gautier 2011). These nucleases include the MRN complex and its associated protein CtIP (Limbo et al 2007;Sartori et al 2007;You et al 2009), Exo1 (Tomimatsu et al 2012), and Dna2 (Wawrousek et al 2010;Peng et al 2012). ATM is also required for efficient resection, possibly through CtIP and Exo1 regulation (You et al 2009;Bolderson et al 2010).…”

Okazaki Fragment Processing-independent Role for Human Dna2 Enzyme during DNA Replication

“…This toxicity depends on its helicase activity, suggesting that both activities need to be coupled within a single Dna2 molecule to act on its substrates in vivo. This is in contrast to Dna2 function in 5Ј end resection during DSB repair where only the nuclease activity of Dna2 participates in this process (24,28,29,53).…”

Nuclease activity of Saccharomyces cerevisiae Dna2 inhibits its potent DNA helicase activity

“…Dna2 was also shown to function in telomere maintenance (15), aging (16), long-patch base excision repair (17), and prevention of reversal of stalled replication forks (18). The expression of human DNA2 was increased in human cancers and negatively correlated with disease outcome, indicating that DNA2 function is relevant for human health (19). However, the role of Dna2/DNA2 in these latter processes remains poorly defined.…”