Pseudosubstrate regulation of the SCFβ-TrCP ubiquitin ligase by hnRNP-U
- Matti Davis1,
- Ada Hatzubai1,
- Jens S. Andersen2,
- Etti Ben-Shushan1,
- Gregory Zvi Fisher1,
- Avraham Yaron1,
- Asne Bauskin3,
- Frank Mercurio4,
- Matthias Mann2, and
- Yinon Ben-Neriah1,5
- 1The Lautenberg Center for Immunology, The Hebrew University–Hadassah Medical School, Jerusalem 91120, Israel; 2Protein Interaction Laboratory, University of Southern Denmark, DK-5230 Odense M, Denmark; 3Centre for Immunology, St. Vincent's Hospital and University of New South Wales, Sydney 2010, Australia; 4Signal Research Division, Celgene Corp., San Diego, California 92121, USA
Abstract
β-TrCP/E3RS (E3RS) is the F-box protein that functions as the receptor subunit of the SCFβ-TrCP ubiquitin ligase (E3). Surprisingly, although its two recognized substrates, IκBα and β-catenin, are present in the cytoplasm, we have found that E3RS is located predominantly in the nucleus. Here we report the isolation of the major E3RS-associated protein, hnRNP-U, an abundant nuclear phosphoprotein. This protein occupies E3RS in a specific and stoichiometric manner, stabilizes the E3 component, and is likely responsible for its nuclear localization. hnRNP-U binding was abolished by competition with a pIκBα peptide, or by a specific point mutation in the E3RS WD region, indicating an E3–substrate-type interaction. However, unlike pIκBα, which is targeted by SCFβ-TrCP for degradation, the E3-bound hnRNP-U is stable and is, therefore, a pseudosubstrate. Consequently, hnRNP-U engages a highly neddylated active SCFβ-TrCP, which dissociates in the presence of a high-affinity substrate, resulting in ubiquitination of the latter. Our study points to a novel regulatory mechanism, which secures the localization, stability, substrate binding threshold, and efficacy of a specific protein-ubiquitin ligase.
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Footnotes
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↵5 Corresponding author.
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E-MAIL yinon{at}cc.huji.ac.il; FAX 972-2-642-4653.
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Article and publication are at http://www.genesdev.org/cgi/doi/10.1101/gad.218702.
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- Received October 15, 2001.
- Accepted December 15, 2001.
- Cold Spring Harbor Laboratory Press