ABSTRACT
Checkpoint kinase 1 (Chk1) is a checkpoint gene that is activated after DNA damage. It phosphorylates and inactivates the Cdc2 activating phosphatase Cdc25C. This in turn inactivates Cdc2, which leads to G2/M arrest. We report that blocking Chk1 expression by antisense or ribozymes in mammalian cells induces apoptosis and interferes with the G2/M arrest induced by adriamycin. The Chk1 inhibitor UCN-01 also blocks the G2 arrest after DNA damage and renders cells more susceptible to adriamycin. These results indicate that Chk1 is an essential gene for the checkpoint mechanism during normal cell proliferation as well as in the DNA damage response.
Subject(s)
Apoptosis , Enzyme Inhibitors/pharmacology , G2 Phase/physiology , Oxazines , Protein Kinase Inhibitors , Xanthenes , Alkaloids/pharmacology , Antineoplastic Agents/pharmacology , Antineoplastic Agents, Phytogenic/pharmacology , Blotting, Western , Caspases/metabolism , Cell Cycle/drug effects , Checkpoint Kinase 1 , Coloring Agents , DNA Primers/chemistry , DNA, Antisense/pharmacology , Doxorubicin/pharmacology , Drug Resistance , Etoposide/pharmacology , Flow Cytometry , Humans , Lung Neoplasms/metabolism , Mitosis , Protein Kinases/metabolism , RNA, Catalytic/pharmacology , Staurosporine/analogs & derivatives , Tumor Cells, CulturedABSTRACT
BACKGROUND: Chkl is a checkpoint gene that is activated after DNA damage. It phosphorylates and inactivates Cdc25C at the late G2 phase. The inactivation of Cdc25C and consequently, the inactivation of Cdc2, are required for the G2 arrest induced by DNA damage. METHODS: We treated 184B5 cell line and its E6 transformed cell lines with adriamycin in the presence of staurosporine or UCNO1 and examined G2 arrest and cell death. RESULTS: We found that adriamycin induced a p53 and p21 response as well as a G1 arrest in 184B5 cells, but not in its E6 transformed cells. Staurosporine or UCNO1 abrogated the G2 arrest induced by adriamycin in both cell lines. In addition, staurosporine or UCNO1 specifically sensitized p53 incompetent cells to adriamycin. CONCLUSION: G2/M checkpoint abrogators can potentially enhance the cytotoxic effect of conventional chemotherapeutic reagents specifically to tumor cells.
