Checkpoint Kinase-Dependent Regulation of DNA Repair and Genome Instability in Breast Cancer

摘要

The DNA damage response (DDR) functions as a tumorigenesis barrier. It is activated in precancerous lesions, potentially as a consequence of aberrant DNA replication. The genetic alterations that create this genomic instability are poorly defined. Using a functional genomic screen in human cells we identified seventy-four genes that when silenced by RNAi activate the DDR. Using a series of secondary assays we determined that many have DNA replication-associated genome maintenance activities. In particular, we identified DDB1 as a genome maintenance gene, and further demonstrated that the replicationdependent genome maintenance activity of DDB1 involves the ubiquitin- mediated degradation of the replication protein CDT1. Our RNAi screen also identified CDK2-interacting protein (CINP) as a genome maintenance gene. Further characterization of CINP revealed this protein is a novel regulator of the ATR-mediated DDR pathway. CINP binds ATR through the ATRinteracting protein (ATRIP), and regulates ATR-dependent CHK1 phosphorylation and maintenance of the G2 checkpoint. Approximately seventeen of the seventy-four genome maintenance genes are known or putative tumor suppressors, including six that were identified as being mutated in breast and colorectal cancers by a cancer genome sequencing effort. Our results suggest that loss of these gene functions may promote tumorigenesis by causing genomic instability.