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J. Biol. Chem., Vol. 282, Issue 47, 34167-34175, November 23, 2007
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From the
Institute for Genetics, University of Cologne, Zülpicher Strasse 47, D-50674 Cologne, Germany, the
Center for Molecular Medicine Cologne, University of Cologne, Zülpicher Strasse 47, D-50674 Cologne, Germany, the ¶Bioinformatics Department, Miltenyi Biotec GmbH, MACSmolecular Business Unit, Nattermannallee 1, D-50829 Cologne, Germany, and the ||Department of Biochemistry and Molecular Biology, Thomas Jefferson University, Philadelphia, Pennsylvania 19107
Posttranslational protein modification with small ubiquitin-related modifier (SUMO) is an important regulatory mechanism implicated in many cellular processes, including several of biomedical relevance. We report that inhibition of the proteasome leads to accumulation of proteins that are simultaneously conjugated to both SUMO and ubiquitin in yeast and in human cells. A similar accumulation of such conjugates was detected in Saccharomyces cerevisiae ubc4 ubc5 cells as well as in mutants lacking two RING finger proteins, Ris1 and Hex3/Slx5-Slx8, that bind to SUMO as well as to the ubiquitin-conjugating enzyme Ubc4. In vitro, Hex3-Slx8 complexes promote Ubc4-dependent ubiquitylation. Together these data identify a previously unrecognized pathway that mediates the proteolytic down-regulation of sumoylated proteins. Formation of substrate-linked SUMO chains promotes targeting of SUMO-modified substrates for ubiquitin-mediated proteolysis. Genetic and biochemical evidence indicates that SUMO conjugation can ultimately lead to inactivation of sumoylated substrates by polysumoylation and/or ubiquitin-dependent degradation. Simultaneous inhibition of both mechanisms leads to severe phenotypic defects.
Received for publication, April 17, 2007 , and in revised form, August 21, 2007.
* This work was supported in part by National Institutes of Health Grant GM62268 (to E. S. J.), European Union Grant MERG-CT-2004-006344 (to G. J. K. P.), and Deutsche Forschungsgemeinschaft Grant SFB635 (to R. J. D.). The costs of publication of this article were defrayed in part by the payment of page charges. This article must therefore be hereby marked "advertisement" in accordance with 18 U.S.C. Section 1734 solely to indicate this fact.
The on-line version of this article (available at http://www.jbc.org) contains supplemental Figs. S1–S5 and supplemental Tables S1 and S2.
1 Supported by a Deutsche Forschungsgemeinschaft Graduate Program "Genetics of Cellular Systems" predoctoral fellowship. Present address: Research Institute of Molecular Pathology, Dr. Bohrgasse 7, A-1030 Vienna, Austria.
2 Supported by a Center for Molecular Medicine Cologne predoctoral fellowship.
3 Supported by a North Rhine-Westphalia Graduate School "Functional Genetics and Genomics" predoctoral fellowship. Present address: Center for Neurologic Diseases, Brigham and Women's Hospital, Harvard Medical School, Boston, MA 02115.
4 To whom correspondence should be addressed: Institute for Genetics, University of Cologne, Zülpicher Str. 47, D-50674 Cologne, Germany. Tel.: 49-221-470-4862; E-mail: j.dohmen{at}uni-koeln.de.
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