This Article Full Text Full Text (PDF) Alert me when this article is cited Alert me if a correction is posted Services Email this article to a friend Similar articles in this journal Similar articles in PubMed Alert me to new issues of the journal Download to citation manager Citing Articles Citing Articles via HighWire Citing Articles via Google Scholar Google Scholar Articles by Maude, S. L. Articles by Enders, G. H. Search for Related Content PubMed PubMed Citation Articles by Maude, S. L. Articles by Enders, G. H.

Cdk Inhibition in Human Cells Compromises Chk1 Function and Activates a DNA Damage Response

Department of Medicine, Gastroenterology Division, Department of Genetics, Abramson Cancer Center, and Cell and Molecular Biology Graduate Group, University of Pennsylvania, Philadelphia, Pennsylvania

Requests for reprints: Greg Enders, Department of Medicine/GI Division, University of Pennsylvania, 600 Clinical Research Building, 415 Curie Boulevard, Philadelphia, PA 19104. Phone: 215-898-0159; Fax: 215-573-2024; E-mail: endersgh{at}mail.med.upenn.edu.

Cyclin-dependent kinases (Cdk) promote cell proliferation, are often deregulated in human cancers, and are targets of ongoing cancer chemotherapy trials. We show here that Cdk activity is also required in human cells to maintain function of the Chk1 pathway, a key component of the response to DNA damage or stalled replication. Chk1 expression was markedly reduced in primary fibroblasts and U2OS osteogenic sarcoma cells by treatment with small molecule Cdk inhibitors or induction of a dominant-negative mutant of Cdk2. The findings of decreased Chk1 activity and accumulation of Cdc25A, a protein targeted for degradation by Chk1, confirmed that Chk1 function was impaired. Furthermore, Cdk inhibition triggered a DNA damage response, characterized by the accumulation of activated forms of ATM and Chk2 as well as nuclear foci containing phosphorylated substrates of ATM/ATR, including histone H2AX (H2AX). Time course experiments showed that the bulk of ATM activation followed Chk1 down-regulation. Chk1 RNA interference combined with partial inhibition of DNA replication was sufficient to evoke the DNA damage response. Conversely, ectopic expression of Chk1 blunted induction of H2AX foci by Cdk inhibitors, indicating that Chk1 down-regulation was necessary to elicit the full phenotype. Finally, both Cdk and Chk1 inhibitors enhanced the cytotoxity of etoposide, a DNA-damaging agent. These results define a pathway through which Cdk inhibition can mediate DNA damage and potentially enhance the efficacy of extant cancer chemotherapies.

Key Words: Cdks and Cdk inhibitors • cell cycle checkpoints • Chk1 • DNA damage • roscovitine

This article has been cited by other articles:

				H. Gali-Muhtasib, D. Kuester, C. Mawrin, K. Bajbouj, A. Diestel, M. Ocker, C. Habold, C. Foltzer-Jourdainne, P. Schoenfeld, B. Peters, et al. Thymoquinone Triggers Inactivation of the Stress Response Pathway Sensor CHEK1 and Contributes to Apoptosis in Colorectal Cancer Cells Cancer Res., July 15, 2008; 68(14): 5609 - 5618. [Abstract] [Full Text] [PDF]

				G. H. Enders Expanded Roles for Chk1 in Genome Maintenance J. Biol. Chem., June 27, 2008; 283(26): 17749 - 17752. [Abstract] [Full Text] [PDF]

				I. Malavazi, J. F. Lima, P. A. de Castro, M. Savoldi, M. H. de Souza Goldman, and G. H. Goldman Genetic Interactions of the Aspergillus nidulans atmAATM Homolog With Different Components of the DNA Damage Response Pathway Genetics, February 1, 2008; 178(2): 675 - 691. [Abstract] [Full Text] [PDF]

				J. S. Myers, R. Zhao, X. Xu, A.-J. L. Ham, and D. Cortez Cyclin-Dependent Kinase 2 Dependent Phosphorylation of ATRIP Regulates the G2-M Checkpoint Response to DNA Damage Cancer Res., July 15, 2007; 67(14): 6685 - 6690. [Abstract] [Full Text] [PDF]

				E. Olson, C. J. Nievera, V. Klimovich, E. Fanning, and X. Wu RPA2 Is a Direct Downstream Target for ATR to Regulate the S-phase Checkpoint J. Biol. Chem., December 22, 2006; 281(51): 39517 - 39533. [Abstract] [Full Text] [PDF]

				D. Cai, V. M. Latham Jr., X. Zhang, and G. I. Shapiro Combined depletion of cell cycle and transcriptional cyclin-dependent kinase activities induces apoptosis in cancer cells. Cancer Res., September 15, 2006; 66(18): 9270 - 9280. [Abstract] [Full Text] [PDF]

				A. J. Deans, K. K. Khanna, C. J. McNees, C. Mercurio, J. Heierhorst, and G. A. McArthur Cyclin-Dependent Kinase 2 Functions in Normal DNA Repair and Is a Therapeutic Target in BRCA1-Deficient Cancers Cancer Res., August 15, 2006; 66(16): 8219 - 8226. [Abstract] [Full Text] [PDF]

				D. Sampath, J. Cortes, Z. Estrov, M. Du, Z. Shi, M. Andreeff, V. Gandhi, and W. Plunkett Pharmacodynamics of cytarabine alone and in combination with 7-hydroxystaurosporine (UCN-01) in AML blasts in vitro and during a clinical trial Blood, March 15, 2006; 107(6): 2517 - 2524. [Abstract] [Full Text] [PDF]

				C. R. Barker, A. V. McNamara, S. A. Rackstraw, D. E. Nelson, M. R. White, A. J. M. Watson, and J. R. Jenkins Inhibition of Hsp90 acts synergistically with topoisomerase II poisons to increase the apoptotic killing of cells due to an increase in topoisomerase II mediated DNA damage Nucleic Acids Res., February 16, 2006; 34(4): 1148 - 1157. [Abstract] [Full Text] [PDF]

				O. M. Tirado, S. Mateo-Lozano, and V. Notario Roscovitine Is an Effective Inducer of Apoptosis of Ewing's Sarcoma Family Tumor Cells In vitro and In vivo Cancer Res., October 15, 2005; 65(20): 9320 - 9327. [Abstract] [Full Text] [PDF]