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Research Articles: Therapeutics, Targets, and Development

Disrupting Skp2-cyclin A interaction with a blocking peptide induces selective cancer cell killing

Department of Developmental and Molecular Biology and Medicine, The Albert Einstein Comprehensive Cancer Center and Liver Research Center, Albert Einstein College of Medicine, Bronx, New York

Requests for reprints: Liang Zhu, Department of Developmental and Molecular Biology, Albert Einstein College of Medicine, 1300 Morris Park Avenue, Room U-521, Bronx, NY 10461. Phone: 718-430-3320; Fax: 718-430-8975. E-mail: lizhu{at}aecom.yu.edu

Abstract

Skp2 fulfills the definition of an oncoprotein with its frequent overexpression in cancer cells and oncogenic activity in various laboratory assays and therefore is a potential cancer therapy target. The best-known function of Skp2 is that of an F-box protein of the SCF^Skp2-Roc1 E3 ubiquitin ligase targeting the cyclin-dependent kinase inhibitor p27^Kip1. Knockdown of Skp2 generally leads to accumulation of p27 but its effects on cancer cells are less certain. Another function of Skp2 is its stable interaction with cyclin A, which directly protects cyclin A from inhibition by p27 in in vitro kinase assays. Here, we report that an 18-residue blocking peptide of Skp2-cyclin A interaction can indirectly inhibit cyclin A/Cdk2 kinase activity dependent on the presence of p27 in in vitro kinase assays. Transmembrane delivery of this blocking peptide can induce cell death in a panel of four cancer cell lines in which Skp2 knockdown only have mild inhibitory effects. This Skp2-cyclin A interaction blocking peptide can synergize with a previously identified E2F1-derived LDL peptide, which blocks its access to cyclin A, in killing cancer cells. IC₅₀ of the Skp2-cyclin A blocking peptide correlated with abundance of Skp2, its intended target, in cancer cells. These results suggest that Skp2-cyclin A interaction plays an important role in cancer cell survival and is an attractive target for cancer drug discovery. [Mol Cancer Ther 2007;6(2):684–91]

Grant support: NIH (National Cancer Institute, National Institutes of Diabetes, Digestive and Kidney Diseases), Albert Einstein Comprehensive Cancer Research Center and Liver Research Center (core facility support), and the Irma T. Hirschl Career Scientist Award (L. Zhu).

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: P.J.'s current address is Whitehead Institute, 9 Cambridge Center, Room 611, Cambridge, MA 02142.

Received 8/29/06; revised 11/16/06; accepted 12/21/06.