Cdh1-Anaphase-Promoting Complex Targets Skp2 for Destruction in Transforming Growth Factor β-Induced Growth Inhibition

Abstract

As a subunit of a ubiquitin ligase, Skp2 is implicated in facilitating cell cycle progression via degradation of various protein targets. We report here that Skp2 is rapidly degraded following cellular stimulation by the cytokine transforming growth factor β (TGF-β) and that this degradation stabilizes the cell cycle arrest protein p27. The Skp2 degradation is mediated by Cdh1-anaphase-promoting complex (APC), as shown by depletion of Cdh1 with small interfering RNA, and by reconstitution of ubiquitylation reactions in a purified system. Blockage of Skp2 degradation greatly reduces TGF-β-induced cell cycle arrest, as does expression of a nondegradable Skp2 mutant. Furthermore, we demonstrate that TGF-β-induced Skp2 degradation is mediated by the Smad cascade. The degradation of Skp2 stabilizes p27, thereby ensuring TGF-β-induced cell cycle arrest. These results identify a novel mechanism for tumor suppression by TGF-β and explain why dysfunction of APC in the TGF-β pathway in responsive cells is associated with cancer.

SUPPLEMENTAL MATERIAL

We thank X. Liu, W. Malcolm, W. Kaelin, A. Weissman, and D. Zhang for cDNA clones. We are grateful to R. Wood and J. Brodsky and the members of our laboratory for critical reading of the manuscript. We thank D. Finley, R. Deshaies and J. Massague for discussions. This project was initiated from Marc W. Kirschner's laboratory.

This work is supported by NIH grants CA115943 and GM070681. Y.W. is a scholar of the American Cancer Society and V Cancer Research Foundation.