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Control of the SCFSkp2–Cks1 ubiquitin ligase by the APC/CCdh1 ubiquitin ligase


Skp2 and its cofactor Cks1 are the substrate-targeting subunits of the SCFSkp2–Cks1 (Skp1/Cul1/F-box protein) ubiquitin ligase complex that regulates entry into S phase by inducing the degradation of the cyclin-dependent kinase inhibitors p21 and p27 (ref. 1). Skp2 is an oncoprotein that often shows increased expression in human cancers2; however, the mechanism that regulates its cellular abundance is not well understood. Here we show that both Skp2 and Cks1 proteins are unstable in G1 and that their degradation is mediated by the ubiquitin ligase APC/CCdh1 (anaphase-promoting complex/cyclosome and its activator Cdh1). Silencing of Cdh1 by RNA interference in G1 cells stabilizes Skp2 and Cks1, with a consequent increase in p21 and p27 proteolysis. Depletion of Cdh1 also increases the percentage of cells in S phase, whereas concomitant downregulation of Skp2 reverses this effect, showing that Skp2 is an essential target of APC/CCdh1. Expression of a stable Skp2 mutant that cannot bind APC/CCdh1 induces premature entry into S phase. Thus, the induction of Skp2 and Cks1 degradation in G1 represents a principal mechanism by which APC/CCdh1 prevents the unscheduled degradation of SCFSkp2–Cks1 substrates and maintains the G1 state.

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Figure 1: In vivo degradation of Skp2 and Cks1 is stimulated by Cdh1.
Figure 2: Cdh1 silencing stabilizes Skp2 and Cks1 in G1 and G0.
Figure 3: Requirements for APC/CCdh1-mediated degradation of Skp2 and Cks1.
Figure 4: Biological relevance of Skp2 degradation.


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We thank A. Hershko for contributing to this work; W. Kaelin and M. Kirschner for communicating results before publication; J. Bloom, T. Cardozo, L. Gardner, A. Hershko and E. Oxelmark for critically reading the manuscript; and M. Brandeis, B. Dynlacht, G. Draetta, K. Helin and J. Lukas for reagents. M.P. is grateful to T. M. Thor for continuous support. This work was supported by a fellowship from the New York State Breast Cancer Research and Education fund to T.B.; a Federazione Italiana Ricerca sul Cancro fellowship to N.V.D.; a Human Frontiers Science Program fellowship to V.A.; an Italian American Cancer Foundation fellowship and a Susan Komen Breast Cancer Foundation fellowship to D.G.; and a Irma Hirschl Scholarship and NIH grants to M.P.

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Correspondence to Michele Pagano.

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Bashir, T., Dorrello, N., Amador, V. et al. Control of the SCFSkp2–Cks1 ubiquitin ligase by the APC/CCdh1 ubiquitin ligase. Nature 428, 190–193 (2004).

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