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Research Articles: Therapeutics, Targets, and Development

Defective p53 signaling in p53 wild-type tumors attenuates p21^waf1 induction and cyclin B repression rendering them sensitive to Chk1 inhibitors that abrogate DNA damage-induced S and G₂ arrest

Department of Pharmacology and Toxicology and Norris Cotton Cancer Center, Dartmouth Medical School, Lebanon, New Hampshire

Requests for reprints: Alan Eastman, Department of Pharmacology and Toxicology and Norris Cotton Cancer Center, Dartmouth Medical School, Rubin Building Level 6, One Medical Center Drive, Lebanon, NH 03756. Phone: 603-653-9981; Fax: 603-653-9952. E-mail: alan.r.eastman{at}dartmouth.edu

Abstract

DNA damage induces cell cycle arrest to provide time for repair and enhance cell survival. The Chk1 inhibitor 7-hydroxystaurosporine (UCN-01) can overcome both S and G₂ arrest and drive cells through a lethal mitosis. S-phase arrest induced by the topoisomerase I inhibitor SN38 results from activation of Chk1 and degradation of Cdc25A phosphatase that occurs independent of p53 status. However, p53-mediated induction of p21^waf1 and repression of cyclin B prevent abrogation of S and G₂ arrest, respectively. Surprisingly, incubation of MCF10A immortalized breast cells with UCN-01 fails to elevate Cdc25A protein due to p53-mediated inhibition of Cdc25A transcription. Suppression of p21^waf1 in MCF10A cells overcame this transcriptional inhibition, and the S-phase-arrested cells became sensitive to UCN-01, although they now arrested in G₂ as cyclin B expression remained suppressed. We also compared the response of p53 wild-type tumors to the combination of SN38 and UCN-01. In CAKI-1, U87MG, and SUM102, SN38 induced p21^waf1 and the cells were resistant to UCN-01. In contrast, HCT116 and MCF7 cells had markedly attenuated induction of p21^waf1 and failed to repress cyclin B. Accordingly, these cells were susceptible to UCN-01-mediated abrogation of both S and G₂ arrest. SN38 induced expression of another p53-inducible gene, 14-3-3, suggesting selective dysregulation of p53 response genes. In summary, several cell lines commonly considered wild-type for p53 appear to have defects in expression of selected p53 response genes following DNA damage, and this makes them sensitive to the combination of DNA damage plus Chk1 inhibitor. [Mol Cancer Ther 2008;7(2):252–62]

Grant support: NIH CA117874, Cancer Center Support Grant NIH CA23108 (Norris Cotton Cancer Center), and PhRMA Foundation fellowship (A.A. Levesque).

The costs of publication of this article were defrayed in part by the payment of page charges. This article must therefore be hereby marked advertisement in accordance with 18 U.S.C. Section 1734 solely to indicate this fact.

Note: Current address for A.A. Levesque: Department of Biology, University of Hartford, 200 Bloomfield Avenue, West Hartford, CT 06117.

¹ A. Poh and A. Eastman, unpublished observations.

² Supplementary material for this article is available at Molecular Cancer Therapeutics Online (http://mct.aacrjournals.org/).

Received 9/11/07; revised 11/ 9/07; accepted 11/27/07.