DNA damage checkpoints operate throughout the cell cycle to monitor and maintain genomic stability. The checkpoints ensure that damaged DNA is not replicated or segregated to daughter cells until repair. I have examined the relative contribution of CHK1 and CHK2 on Adriamycin-induced checkpoint. Several lines of evidence including dominant negative mutants, downregulation by shRNA, and gene knockout indicated that CHK1 plays a more important role than CHK2 for Adriamycin-induced checkpoint....[ Read more ]

DNA damage checkpoints operate throughout the cell cycle to monitor and maintain genomic stability. The checkpoints ensure that damaged DNA is not replicated or segregated to daughter cells until repair. I have examined the relative contribution of CHK1 and CHK2 on Adriamycin-induced checkpoint. Several lines of evidence including dominant negative mutants, downregulation by shRNA, and gene knockout indicated that CHK1 plays a more important role than CHK2 for Adriamycin-induced checkpoint.

Both stalled replication block and DNA damage induce the tumor suppressor p53, but the downstream effectors and upstream regulators of p53 during replication blockade remain to be deciphered. I have examined the relationship between the replication checkpoint and p53 as well as the effectors and regulators of p53 during the replication checkpoint. I found that the levels of p53 and p21CIP1/WAF1 attained after HU treatment were significantly lower than that after DNA damage. Down-regulation of p21CIP1/WAF1 with short hairpin RNA (shRNA) indicated that p21CIP1/WAF1 was not required for the p53-dependent replication checkpoint. Down-regulation of CHK1 by shRNA or knockout of the CHK2 gene in mouse embryonic fibroblasts did not abolish p53 induction. This illustrated that neither CHK1 nor CHK2 is essential for the induction of p53 during the replication checkpoint. While cells from patients with genetic disorders Nijimegen breakage syndrome (NBS) and Bloom syndrome (BS) show defect in induction of p53 upon replication block. These data reveal that the downstream effectors and upstream regulators of p53 during replication checkpoint are very different from that after DNA damage.