Abstract
The cell division cycle 7 (Cdc7) is a serine-threonine kinase, conserved from yeast to human, whose activation requires the interaction with either one of the regulatory subunits dumb-bell forming factor 4 (Dbf4) or diaphanous-related formin 1 (Drf1). Cdc7-Dbf4 kinase participates in the initiation of DNA replication, replication fork stability, and the S-phase checkpoint upon replication stress. Our recent findings suggest that overexpression of Cdc7 accumulates double-stranded breaks (DSBs) to activate checkpoint signaling and enhances the capacity of homologous recombination (HR) repair. However, the detailed mechanism of how up-regulated Cdc7 promotes HR repair and tumorigenesis remains obscure. The critical control of the HR takes place at the initiation step, which entails nucleolytic resection of the DSB ends to generate ssDNA with 3’-termini. This resection process needs Mre11–Rad50–NBS1 (MRN) complex that has multiple roles in the DNA damage response (DDR) including direct detection of DSB and amplification of damage signal. In this study, we showed here that Cdc7-Dbf4 kinase interacts with Mre11. Interestingly, Mre11 phosphorylation upon DNA damage is dependent on the kinase activity of Cdc7 and ATR. However, Mre11 phosphorylation is indirectly regulated by Cdc7 according to in vitro kinase assay. We then found that inhibition of Cdc7 activity impairs the phosphorylation of RPA2 and Nbs1 by ATR and the recruitment of HR repair proteins such as Rad51 on chromatin in response to replication stress. Collectively, these results suggest a novel function of Cdc7-Dbf4 that regulates HR repair through ATR-mediated Mre11 phosphorylation following UV stress. This study sheds new light on the tumorigenic role of Cdc7-Dbf4 in regulating checkpoint activation and HR repair upon replication stress, which provides a new direction to cancer therapy combination.