title: Chk1 mediates S and G2 arrests through Cdc25A degradation in response to DNA-damaging agents.
abstract: UV and ionizing radiation (IR) activate DNA damage checkpoints and induce Cdc25A degradation (Mailand, N., Falck, J., Lukas, C., Syljuasen, R. G., Welcker, M., Bartek, J., and Lukas, J. (2000) Science 288, 1425-1429; Falck, J., Mailand, N., Syljuasen, R. G., Bartek, J., and Lukas J. (2001) Nature 410, 842-847). The degradation of Cdc25A is abrogated by caffeine, which implicates Chk1 as the potential mediator (Mailand, N., Falck, J., Lukas, C., Syljuasen, R. G., Welcker, M., Bartek, J., and Lukas, J. (2000) Science 288, 1425-1429). However, the involvement of Chk1 is far from clear, because caffeine is a rather nonspecific inhibitor of the ATR/Chk1 signaling pathway. Additionally, it is not known whether DNA-damaging drugs commonly used in chemotherapy, which may activate different signal transduction pathways than UV or IR, also confer Cdc25A degradation. Herein, we show that camptothecin and doxorubicin, two widely used topoisomerase inhibitors conferring S and G2 arrest, respectively, cause the degradation of Cdc25A. Using a small interfering RNA that enables the specific elimination of Chk1 expression, we show that the observed proteolysis of Cdc25A is mediated through Chk1. Moreover, Cdc25A overexpression abrogates the Chk1-mediated degradation and overcomes the doxorubicin-induced G2 arrest through dephosphorylation and activation of Cdc2/Cdk1 in a dose-dependent manner. These results suggest that: (a) Cdc25A is involved in the G2/M transition in addition to its commonly accepted effect on G1/S progression, and (b) Chk1 mediates both S and G2 checkpoint and is thus a more ubiquitous cell cycle checkpoint mediator than previously thought.
authors.affiliation: Cancer Research, Abbott Laboratories, Abbott Park, Illinois 60064-6101, USA. zhan.ziao@abbott.com
authors.forename: Zhan
authors.initials: Z
authors.lastname: Xiao
authors.forename: Zehan
authors.initials: Z
authors.lastname: Chen
authors.forename: Angelo H
authors.initials: AH
authors.lastname: Gunasekera
authors.forename: Thomas J
authors.initials: TJ
authors.lastname: Sowin
authors.forename: Saul H
authors.initials: SH
authors.lastname: Rosenberg
authors.forename: Steve
authors.initials: S
authors.lastname: Fesik
authors.forename: Haiying
authors.initials: H
authors.lastname: Zhang
mesh_terms: D000972:Antineoplastic Agents, Phytogenic / Q000494:pharmacology; D015153:Blotting, Western; D002166:Camptothecin / Q000494:pharmacology; D002453:Cell Cycle; D002469:Cell Separation; D000071877:Checkpoint Kinase 1; D004249:DNA Damage / Q000187:drug effects; D004305:Dose-Response Relationship, Drug; D004317:Doxorubicin / Q000494:pharmacology; D004791:Enzyme Inhibitors / Q000494:pharmacology; D005434:Flow Cytometry; D016195:G2 Phase; D006801:Humans; D010766:Phosphorylation; D011494:Protein Kinases / Q000378:metabolism / Q000502:physiology*; D034741:RNA, Small Interfering / Q000378:metabolism; D016196:S Phase; D013997:Time Factors; D014162:Transfection; D014407:Tumor Cells, Cultured; D014443:Tyrosine / Q000378:metabolism; D014466:Ultraviolet Rays; D020687:cdc25 Phosphatases / Q000378:metabolism*
chemical_list: D000972:Antineoplastic Agents, Phytogenic; D004791:Enzyme Inhibitors; D034741:RNA, Small Interfering; D014443:Tyrosine; D004317:Doxorubicin; D011494:Protein Kinases; C000605867:CHEK1 protein, human; D000071877:Checkpoint Kinase 1; C517004:CDC25A protein, human; D020687:cdc25 Phosphatases; D002166:Camptothecin