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Phosphorylation by Akt1 promotes cytoplasmic localization of Skp2 and impairs APCCdh1-mediated Skp2 destruction

Nature Cell Biology volume 11, pages 397–408 (2009)Cite this article

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Abstract

Deregulated Skp2 function promotes cell transformation, and this is consistent with observations of Skp2 overexpression in many human cancers. However, the mechanisms underlying elevated Skp2 expression are still unknown. Here we show that the serine/threonine protein kinase Akt1, but not Akt2, directly controls Skp2 stability by a mechanism that involves degradation by the APC–Cdh1 ubiquitin ligase complex. We show further that Akt1 phosphorylates Skp2 at Ser 72, which is required to disrupt the interaction between Cdh1 and Skp2. In addition, we show that Ser 72 is localized within a putative nuclear localization sequence and that phosphorylation of Ser 72 by Akt leads to cytoplasmic translocation of Skp2. This finding expands our knowledge of how specific signalling kinase cascades influence proteolysis governed by APC–Cdh1 complexes, and provides evidence that elevated Akt activity and cytoplasmic Skp2 expression may be causative for cancer progression.

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Figure 1: Human Skp2 protein levels are regulated by the PTEN/PI(3)K/Akt pathway.
Figure 2: The PTEN/PI(3)K/Akt pathway regulates both Skp2 transcription and Skp2 stability.
Figure 3: The Skp2 protein contains a canonical Akt phosphorylation site at Ser 72 and interacts with Akt1, but not with Akt2, in vivo.
Figure 4: Akt phosphorylates the human Skp2 protein at Ser 72.
Figure 5: Phosphorylation of Skp2 at Ser 72 triggers the subsequent phosphorylation of Ser 75 by CKI.
Figure 6: Phosphorylation of Skp2 by Akt1 protects Skp2 from Cdh1-mediated destruction.
Figure 7: Phosphorylation of Skp2 at Ser 72 by Akt affects Skp2 protein stability.
Figure 8: Akt phosphorylation of Skp2 promotes its cytoplasmic translocation.

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Change history

  • 18 March 2009

    In the version of this article initially published online, Fig 6e had no separating lines between Akt1 and Akt2 or Cdh1 and Cdh1/Akt1. This error has now been corrected for the HTML and PDF versions of the article.

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Acknowledgements

We thank William Kaelin Jr, Lewis Cantley, Roya Khosravi-Far and Susan Glueck for critical reading of the manuscript; James DeCaprio, Christoph Geisen, Ronald DePinho, Laura Benjamin, Suzanne Conzen, John Blenis and Peter Jackson for providing reagents; Ross Tomaino for his kind assistance on the mass spectrum analysis; Isaac Robinovitz for his technical support on the fluorescence microscopy; Pier Paolo Pandolfi for sharing unpublished data; and members of the Wei and Toker laboratories for useful discussions. W.W. is a Leukemia and Lymphoma Society Special Fellow, Kimmel Scholar and V Scholar. This work was supported in part by the Harvard Medical School Milton Fund (W.W.) and the Emerald Foundation, and by grants from the National Institutes of Health (W.G.K., CA076120; A.T., CA122099) and the Susan G. Komen Breast Cancer Foundation (R.Y.C., 0706963).

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  1. Department of Pathology, Beth Israel Deaconess Medical Center, Harvard Medical School, Boston, 02215, Massachusetts, USA

    Daming Gao, Hiroyuki Inuzuka, Alan Tseng, Rebecca Y. Chin, Alex Toker & Wenyi Wei

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Contributions

D.G. and H.I. performed most of the experiments with the assistance of A.Tseng. R.Y.C. performed the shAkt1 and shAkt2 experiment to examine its effects on Skp2 Ser 72 phosphorylation. W.W. and A.T. designed the experiments. W.W. supervised the study. W.W. wrote the paper with the assistance of A.T. All authors commented on the manuscript.

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Correspondence to Wenyi Wei.

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Gao, D., Inuzuka, H., Tseng, A. et al. Phosphorylation by Akt1 promotes cytoplasmic localization of Skp2 and impairs APCCdh1-mediated Skp2 destruction. Nat Cell Biol 11, 397–408 (2009). https://doi.org/10.1038/ncb1847

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