[Structural Basis of the Multifunctional Hub Protein and Identification of a Small-molecule Compound for Drug...

Translesion DNA synthesis (TLS) is an emergency system activated to inhibit cell death caused by DNA damage-induced replication arrest. Thus, TLS enables cancer cells to acquire resistance to alkylate anticancer drugs. REV7 functions as the hub protein that interacts with both the inserter DNA polymerase REV1 and the extender DNA polymerase REV3 in TLS. REV7-mediated protein-protein interactions (PPIs) are essential for the activation of TLS, and are therefore attractive targets for anticancer drug development. To clarify the REV7-REV3 and REV7-REV1 PPIs, we determined the structures of REV7-REV3 and REV7-REV3-REV1 complexes. In the structures of REV7-REV3 and REV7-REV3-REV1 complexes, REV7 wraps around the REV3 fragment, and the REV1-binding interface is distinct from the REV3-binding site of REV7. We also identified a novel REV7 binding protein, transcription factor II-I (TFII-I), which is required for TLS. Of note, TFII-I binds the REV7-REV3-REV1 complex, suggesting that REV7-TFII-I PPIs are independent of other REV7-mediated PPIs. Furthermore, we found a small-molecule compound that inhibits TLS by targeting the REV7-REV3 PPIs. Lastly, we determined the structure of REV7 in complex with chromosome alignment maintaining phosphoprotein (CAMP), a known kinetochore-microtubule attachment protein. The overall structure of the REV7-CAMP complex is similar to that of the REV7-REV3 complex, but the REV7-CAMP PPIs are markedly different from the REV7-REV3 PPIs. These findings improve our understanding of multifunctional hub proteins, and are helpful for designing small-molecule compounds for novel anticancer drug development.