The Loss of PIN1 Deregulates Cyclin E and Sensitizes Mouse Embryo Fibroblasts to Genomic Instability

doi:10.1074/jbc.M505770200

The Loss of PIN1 Deregulates Cyclin E and Sensitizes Mouse Embryo Fibroblasts to Genomic Instability*

Department of Pharmacology and Cancer Biology, Duke University Medical Center, Durham, North Carolina 27710

2 To whom correspondence should be addressed: Dept. of Pharmacology and Cancer Biology, Duke University Medical Center, Box 3813, Durham, NC 27710-3813. Tel.: 919-681-6209; Fax: 919-681-7767; E-mail: means001{at}mc.duke.edu.

Abstract

During the G₀/G₁-S phase transition, the timely synthesis and degradation of key regulatory proteins is required for normal cell cycle progression. Two of these proteins, c-Myc and cyclin E, are recognized by the Cdc4 E3 ligase of the Skp1/Cul1/Rbx1 (SCF) complex. SCF^Cdc4 binds to a similar phosphodegron sequence in c-Myc and cyclin E proteins resulting in ubiquitylation and degradation of both proteins via the 26 S proteosome. Since the prolyl isomerase Pin1 binds the c-Myc phosphodegron and participates in regulation of c-Myc turnover, we hypothesized that Pin1 would bind to and regulate cyclin E turnover in a similar manner. Here we show that Pin1 regulates the turnover of cyclin E in mouse embryo fibroblasts. Pin1 binds to the cyclin E-Cdk2 complex in a manner that depends on Ser³⁸⁴ of cyclin E, which is phosphorylated by Cdk2. The absence of Pin1 results in an increased steady-state level of cyclin E and stalling of the cells in the G₁/S phase of the cell cycle. The cellular changes that result from the loss of Pin1 predispose Pin1 null mouse embryo fibroblasts to undergo more rapid genomic instability when immortalized by conditional inactivation of p53 and sensitizes these cells to more aggressive Ras-dependent transformation and tumorigenesis.

Footnotes

↵3 The abbreviations used are: SCF, Skp1/Cul1/Rbx1; MEF, mouse embryo fibroblast; GST, glutathione S-transferase; PBS, phosphate-buffered saline; BrdUrd, bromodeoxyuridine; WT, wild type; MMTV, murine mammary tumor virus.
↵* This work was supported by National Institutes of Health (NIH) Grant CA082845 (to A. R. M.). 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.
↵ The on-line version of this article (available at http://www.jbc.org) contains supplemental Figs. 1 and 2.
↵1 Supported in part by NCI, NIH, T32 Training Grant CA-059365 and a grant from the Milheim Foundation for Cancer Research.
- Received May 26, 2005.
- Revision received October 11, 2005.
The American Society for Biochemistry and Molecular Biology, Inc.