| Summary: | 博士 === 國立清華大學 === 生物資訊與結構生物研究所 === 103 === Abstract
Cdc7-Dbf4 kinase is not only required for DNA replication but plays important roles in S phase checkpoint signaling in eukaryotes. However, the mechanism underlying Cdc7-Dbf4 functions in the S phase checkpoint in mammals is elusive. Our previous data showed that ATM and ATR phosphorylate Dbf4 in response to DNA damages, but the kinase activity of Cdc7 is still remained. Therefore, we hypothesis that Cdc7-Dbf4 may act as a downstream effector of ATR to regulate the S-phase checkpoints and inhibit DNA replication. HSP90 is upregulated in various cancers and binds with HCLK2 to form a chaperone complex to stabilize all phosphatidylinositol 3-kinase-related kinases (PIKKs) including ATM and ATR. We demonstrated that Cdc7-Dbf4 interacts with HCLK2-HSP90 complex and phosphorylates HSP90 at the N-terminus under DNA damage response. PHA-767491, the inhibitor of Cdc7 kinase, disrupts the interaction of Cdc7-Dbf4 with HSP90-HCLK2 complex and prevents the HCLK2-HSP90 chaperone function, suggesting that the kinase activity of Cdc7 is important for the interaction and function of HCLK2-HSP90 complex. Furthermore, the phosphorylation of HSP90 affects the stability and function of the complex of ATR kinase, HCLK2, and Mre11-Rad50-NBS1. These results suggest that Cdc7-Dbf4 regulates S-phase checkpoint signaling via affecting the stability of ATR kinase through the phosphorylation toward HSP90, providing a rationale why overexpressed Cdc7-Dbf4 promotes cancer cells survival and provides a new insight for cancer therapy.
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