INPROTEOLYS

Crosstalk between SUMO and ubiquitin

Posttranslational modifications play a major role in cellular functions. Among them ubiquitination and the related modification with SUMO (small ubiquitin related modifier) have gained in significance in the past years. Ubiquitination is primarily associated with proteasome dependent protein degradation (Hershko and Ciechanover 1998) but it also has non-proteolytic consequences in several other cellular processes like endosomal sorting (Hicke and Dunn 2003), histone modification (Osley 2004) and DNA repair (Hoege et al. 2002; Ulrich 2004). Sumoylation does not mediate degradation but plays an important role in processes like transcriptional regulation (Seeler and Dejean 2003; Yang et al. 2003; Girdwood et al. 2004), nucleo-cytoplasmatic transport (Pichler and Melchior 2002) or genome integrity (Muller et al. 2004). Both, modification with SUMO and with ubiquitin, are performed by an energy dependent enzymatic cascade: Ubiquitination involves a single E1 activating enzyme, several E2 conjugating enzymes and a large number of E3 ligating enzymes, which ensure substrate specificity (Figure 1). In the case of SUMO, only a single E1 and E2 and a few E3s are currently known (Figure 2). Both modifications are reversible involving a different set of enzymes for demodification, the isopeptidases. Recently, we could show that a ubiquitin conjugating enzyme (E2-25K) is a substrate for sumoylation (Pichler et al, 2005). The ubiquitin E2s have been linked to distinct biological functions including cell cycle regulation (cdc34/ubc3), ER associated degradation (Ubc6/7), histone modification (Ubc2/Rad6) and DNA repair (Ubc2/Rad6) (Jentsch 1992; Hochstrasser 1996; Pickart 2001). In the case of E2-25K, the biological role is not clearly understood. Different studies point to a role for E2-25K in Alzheimer disease (Song et al. 2003), as a regulator of huntingtin (Kalchman et al. 1996) and in antigen processing and representation (Lelouard et al. 2004) but no in vivo substrates or E3 ligases for E2-25K have been identified to date. In vitro, E2-25K sumoylation severely interferes with its interaction with the ubiquitin E1 resulting in highly reduced thioester formation. In vivo, however, the steady state level of sumoylation appears to be very low and this might result from two distinct scenarios: 1. Sumoylation of E2-25K acts as an inhibitor (Figure 3-A) and is strictly regulated or only takes place at a specific cellular location, after a given stimulus, during a certain cell cycle stage and/or in a defined tissue. 2. In another scenario, sumoylation of E2-25K acts as a positive regulator and E2-25K goes through rapid circles of modification and demodification, which may contribute to E2/E3 disassembly (Figure 3-B). Such a model is supported by the observation that the E2 N-terminus is not only involved in E1 but also in E3 interaction (Huang et al. 1999). At least in principle, E2 sumoylation could also contribute to E3 selection, because the sumoylated E2 can form thioester albeit at reduced rates, in vitro. Interestingly, a related model has been proposed for one subfamily of ubiquitin E3 ligases, which are regulated by another ubiquitin related modification (Cope & Deshaies, 2003, Wolf et al 2003).

Andrea Pichler

Katharina Mederböck

Lisa Kirschner

Helene Klug

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+43 (0) 1 4277 61711

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+43 (0) 1 4277 61712

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Dr. Bohrg. 9, A- 1030 Vienna

Center

Max F. Perutz Laboratories, Medical University of Vienna

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http://www.mfpl.ac.at/index.php?cid=574

Research Lines

Our main objective is to distinguish between these scenarios by addressing the following aims: 1. The biological function of sumoylated E2-25K To gain insights into the in vivo role of E2-25K sumoylation and to test the different hypotheses raised above, it will be important to identify substrates for E2-25K and its partner ubiquitin E3 ligases. 2. Identification of SUMO enzymes involved in regulating ubiquitin enzymes For a better understanding of E2-25K sumoylation and its physiological consequences, it will be important to identify the responsible SUMO enzymes. 3. Sumoylation of other E2 conjugating enzymes. One intriguing question is how many conjugating enzymes are sumoylated

Patents

Publications

Pubmed ID: 16275316

Title: A fluorescence resonance energy transfer-based assay to study SUMO modification in solution.

Authors: Guillaume Bossis , Katarzyna Chmielarska , Ulrike Gärtner , Andrea Pichler , Evelyn Stieger , Frauke Melchior ,

Year: 2005

Journal: Methods Enzymol volume: 398 pages: 20-32

Pubmed ID: 15723079

Title: SUMO modification of the ubiquitin-conjugating enzyme E2-25K.

Authors: Andrea Pichler , Puck Knipscheer , Edith Oberhofer , Willem J van Dijk , Roman Körner , Jesper Velgaard Olsen , Stefan Jentsch , Frauke Melchior , Titia K Sixma ,

Year: 2005

Journal: Nat Struct Mol Biol volume: 12 pages: 264-9

Pubmed ID: 15378033

Title: The RanBP2 SUMO E3 ligase is neither HECT- nor RING-type.

Authors: Andrea Pichler , Puck Knipscheer , Hisato Saitoh , Titia K Sixma , Frauke Melchior ,

Year: 2004

Journal: Nat Struct Mol Biol volume: 11 pages: 984-91

Pubmed ID: 14607092

Title: SUMO: ligases, isopeptidases and nuclear pores.

Authors: Frauke Melchior , Marion Schergaut , Andrea Pichler ,

Year: 2003

Journal: Trends Biochem Sci volume: 28 pages: 612-8

Pubmed ID: 12032081

Title: The SUMO E3 ligase RanBP2 promotes modification of the HDAC4 deacetylase.

Authors: Olivier Kirsh , Jacob-S Seeler , Andrea Pichler , Andreas Gast , Stefan Müller , Eric Miska , Marion Mathieu , Annick Harel-Bellan , Tony Kouzarides , Frauke Melchior , Anne Dejean ,

Year: 2002

Journal: EMBO J volume: 21 pages: 2682-91

Pubmed ID: 12010456

Title: Ubiquitin-related modifier SUMO1 and nucleocytoplasmic transport.

Authors: Andrea Pichler , Frauke Melchior ,

Year: 2002

Journal: Traffic volume: 3 pages: 381-7

Pubmed ID: 11792325

Title: The nucleoporin RanBP2 has SUMO1 E3 ligase activity.

Authors: Andrea Pichler , Andreas Gast , Jacob S Seeler , Anne Dejean , Frauke Melchior ,

Year: 2002

Journal: Cell volume: 108 pages: 109-20

Pubmed ID: 11731474

Title: PIASy, a nuclear matrix-associated SUMO E3 ligase, represses LEF1 activity by sequestration into nuclear bodies.

Authors: S Sachdev , L Bruhn , H Sieber , A Pichler , F Melchior , R Grosschedl ,

Year: 2001

Journal: Genes Dev volume: 15 pages: 3088-103

Collaborations

Dr. Tita Sixma Dr. Frauke Melchior Dr. Jesper Olsen

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