POLDIP3 facilitates the activation and maintenance of DNA damage checkpoint in response to replication stress

The replication stress response is crucial for the maintenance of a stable genome. POLDIP3 was initially identified as one of the DNA polymerase δ (Pol δ) interacting proteins almost twenty years ago. Using a variety of in vitro biochemical assays, we previously established that POLDIP3 is a key regulator of the enzymatic activity of Pol δ. However, the in vivo function of POLDIP3 has been elusive for a long time. Here, we first generated POLDIP3 knockout (KO) cells using the CRISPR technology and investigated its biological functions in vivo. We showed that though the POLDIP3-KO cells manifest no pronounced defect in the global DNA synthesis under non-stress conditions, they are sensitive to a variety of replication fork blockers. Intriguingly, we found that POLDIP3 plays a crucial role in the activation and maintenance of the DNA damage checkpoint in response to exogenous as well as endogenous replication stress. Our results thus indicate that when the DNA replication fork is blocked, POLDIP3 can be recruited to the stalled replication fork and functions to bridge the early DNA damage checkpoint response and the later replication fork repair/restart.