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The deubiquitylase USP33 discriminates between RALB functions in autophagy and innate immune response

Nature Cell Biology volume 15, pages 12201230 (2013) | Download Citation

Abstract

The RAS-like GTPase RALB mediates cellular responses to nutrient availability or viral infection by respectively engaging two components of the exocyst complex, EXO84 and SEC5. RALB employs SEC5 to trigger innate immunity signalling, whereas RALB–EXO84 interaction induces autophagocytosis. How this differential interaction is achieved molecularly by the RAL GTPase remains unknown. We found that whereas GTP binding turns on RALB activity, ubiquitylation of RALB at Lys 47 tunes its activity towards a particular effector. Specifically, ubiquitylation at Lys 47 sterically inhibits RALB binding to EXO84, while facilitating its interaction with SEC5. Double-stranded RNA promotes RALB ubiquitylation and SEC5–TBK1 complex formation. In contrast, nutrient starvation induces RALB deubiquitylation by accumulation and relocalization of the deubiquitylase USP33 to RALB-positive vesicles. Deubiquitylated RALB promotes the assembly of the RALB–EXO84–beclin-1 complexes driving autophagosome formation. Thus, ubiquitylation within the effector-binding domain provides the switch for the dual functions of RALB in autophagy and innate immune responses.

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Acknowledgements

This work was supported by the VIB (A.A.S.), Swiss Bridge Award (A.A.S.), a PhD-student fellowship of the Research Foundation of Flanders (FWO) (M.S.), the KU Leuven Onderzoekstoelage Grant 13/097 (S.V.S.), FWO Project G.0709.12 (S.V.S.), FWO Project G.0864.10 (J.T.), and the Group-ID Multidisciplinary Research Partnership of Ghent University and the Belgian government, Interuniversity Attraction Poles Project P6/36 (J.T.).

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Affiliations

  1. VIB Center for the Biology of Disease, VIB, 3000 Leuven, Belgium

    • Michal Simicek
    • , Peter Kalev
    • , Maria Francesca Baietti
    •  & Anna A. Sablina
  2. Department of Human Genetics, KU Leuven, Herestraat 49, 3000 Leuven, Belgium

    • Michal Simicek
    • , Peter Kalev
    • , Maria Francesca Baietti
    •  & Anna A. Sablina
  3. Department of Medical Protein Research, VIB, 9000 Ghent, Belgium

    • Sam Lievens
    • , Mathias Laga
    • , Kris Gevaert
    •  & Jan Tavernier
  4. Department of Biochemistry, Ghent University, Albert Baertsoenkaai 3, 9000 Ghent, Belgium

    • Sam Lievens
    • , Mathias Laga
    • , Kris Gevaert
    •  & Jan Tavernier
  5. Department of Pharmaceutical and Pharmacological Sciences, KU Leuven, Herestraat 49, 3000 Leuven, Belgium

    • Dmytro Guzenko
    •  & Sergei V. Strelkov
  6. Institute of Carcinogenesis, N.N. Blokhin Russian Cancer Research Center, Kashirskoye Shosse 24, 115478 Moscow, Russia

    • Vasily N. Aushev

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Contributions

M.S. and A.A.S. conceived of the study. M.S. performed most of the experiments; S.L. and J.T. designed and performed the MAPPIT screen; M.L. and K.G. performed the mass spectrometry analysis; D.G. and S.V.S. carried out the Rosetta docking; P.K. and M.F.B. assisted with the fluorescence microscopy. V.N.A. assisted with ubiquitylation experiments. A.A.S. wrote the manuscript. All authors discussed results and commented on the manuscript.

Competing interests

The authors declare no competing financial interests.

Corresponding author

Correspondence to Anna A. Sablina.

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DOI

https://doi.org/10.1038/ncb2847

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