Covalent Modification of the Transcriptional Repressor Tramtrack by the Ubiquitin-Related Protein Smt3 in <i>Drosophila</i> Flies

Lehembre, François; Badenhorst, Paul; Müller, Stefan; Travers, Andrew; Schweisguth, François; Dejean, Anne

doi:10.1128/mcb.20.3.1072-1082.2000

Cited by 94 publications

(91 citation statements)

References 48 publications

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“…Anti-SUMO staining of Drosophila cells reveals punctate nuclear dots above a diffuse background of SUMO throughout the nucleus. These dots may represent the Drosophila counterpart of the PODs (70). Interestingly, we find that when SUMO is excluded from the nucleus by interference with Ulp1 expression, the dots relocalize to the cytoplasm.…”

Section: Sumo Deconjugation As a Means Tomentioning

confidence: 78%

Drosophila Ulp1, a Nuclear Pore-associated SUMO Protease, Prevents Accumulation of Cytoplasmic SUMO Conjugates

Smith

Bhaskar

Fernandez

et al. 2004

Journal of Biological Chemistry

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SUMO is a small ubiquitin-like protein that becomes covalently conjugated to a variety of target proteins, the large majority of which are found in the nucleus. Ulp1 is a member of a family of proteases that control SUMO function positively, by catalyzing the proteolytic processing of SUMO to its mature form, and negatively, by catalyzing SUMO deconjugation. In Drosophila S2 cells, depletion of Ulp1 by RNA interference results in a dramatic change in the overall spectrum of SUMO conjugates, indicating that SUMO deconjugation is substratespecific and plays a critical role in determining the steady state targets of SUMO conjugation. Ulp1 normally serves to prevent the accumulation of SUMO-conjugated forms of a number of proteins, including the aminoacyl-tRNA synthetase EPRS. In the presence of Ulp1, most SUMO conjugates reside in the nucleus. However, in its absence, SUMO-conjugated EPRS accumulates in the cytoplasm, contributing to an overall shift of SUMO from the nucleus to the cytoplasm. The ability of Ulp1 to restrict SUMO conjugates to the nucleus is independent of its role as a SUMO-processing enzyme because Ulp1-dependent nuclear localization of SUMO is even observed when SUMO is expressed in a preprocessed form. Studies of a Ulp1-GFP fusion protein suggest that Ulp1 localizes to the nucleoplasmic face of the nuclear pore complex. We hypothesize that, as a component of the nuclear pore complex, Ulp1 may prevent proteins from leaving the nucleus with SUMO still attached.The regulation of protein function by reversible post-translational modification is an effective means for regulating protein stability, activity, subcellular localization, and interaction specificity. One such modification involves the covalent attachment of the small ubiquitin-like modifier protein (SUMO) 1 (also called Smt3), to its target proteins via a series of enzymatic steps that closely resemble the reactions of the ubiquitylation pathway (1-3).Despite the sequence and structural homology between SUMO and ubiquitin, it is clear that sumoylation and ubiquitylation have distinct functional consequences. Ubiquitylation most frequently results in degradation of the substrate protein through targeting to the 26 S proteasome (4). The consequences of sumoylation are diverse and target-specific, with no evidence to suggest a role in promoting protein degradation. Conjugation of SUMO to RanGAP1 is required to target it to the nuclear pore complex (NPC), where it makes a stable interaction with the Ran-binding protein RanBP2 (5-7). Sumoylation of PML is essential for its recruitment to discrete intranuclear foci called PML oncogenic domains (PODs) (8 -11). For some sumoylation targets, including Smad4 and IB␣, this modification appears to increase protein stability by blocking ubiquitin-mediated degradation (12, 13). Finally, an increasing number of DNA binding transcription factors have been identified as substrates for sumoylation (14,15). Sumoylation of transcription factors can alter their activity in multiple ways. For example, in the ca...

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Section: Sumo Deconjugation As a Means Tomentioning

confidence: 78%

Drosophila Ulp1, a Nuclear Pore-associated SUMO Protease, Prevents Accumulation of Cytoplasmic SUMO Conjugates

Smith

Bhaskar

Fernandez

et al. 2004

Journal of Biological Chemistry

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“…In Drosophila polytene chromosomes, the SUMO moiety was detected in many euchromatic sites and the chromocenter (40), suggesting that histone (chromatin) sumoylation plays a role in both euchromatic transcriptional repression and heterochromatic gene silencing. Future work should clarify the precise roles of histone͞chromatin sumoylation in the regulation of chromatin function.…”

Section: Discussionmentioning

confidence: 99%

Histone sumoylation is associated with transcriptional repression

Shiio

Eisenman

2003

Proc. Natl. Acad. Sci. U.S.A.

604

444

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Histone proteins are subject to modifications, such as acetylation, methylation, phosphorylation, ubiquitination, glycosylation, and ADP ribosylation, some of which are known to play important roles in the regulation of chromatin structure and function. Here we report that histone H4 is modified by small ubiquitin-related modifier (SUMO) family proteins both in vivo and in vitro. H4 binds to the SUMO-conjugating enzyme (E2), UBC9, and can be sumoylated in an E1 (SUMO-activating enzyme)-and E2-dependent manner. We present evidence suggesting that histone sumoylation mediates gene silencing through recruitment of histone deacetylase and heterochromatin protein 1.C hromatin is composed of nucleosomes in which 146 bp of DNA are wrapped around a core histone octamer. The octamer consists of a (H3-H4) 2 tetramer associated with two H2A-H2B dimers. The C-terminal globular domains of core histones bind to each other to form the octamer whereas core histone N-terminal tails protrude from the nucleosome and are accessible to the enzymatic modification machineries that catalyze acetylation, methylation, phosphorylation, glycosylation, and ADP ribosylation (for reviews see refs. 1 and 2). Over the last several years, rapid progress has been made in the field of histone modification, owing largely to the discoveries that histone acetyltransferases and histone deacetylases function as transcriptional coactivators and corepressors, respectively (3). These discoveries were followed by analyses of the mechanism and effects of acetylation and the identification of other histone modifications including phosphorylation, methylation, and ubiquitination as regulators of transcription.Small ubiquitin-related modifier (SUMO) is the bestcharacterized member of a growing family of ubiquitin-like proteins involved in posttranslational modifications (for reviews see refs. 4-6). In mammals, there are three members of the SUMO protein family: SUMO-1, SUMO-2 (SMT3a), and SUMO-3 (SMT3b), which are implicated in partly overlapping, yet distinct functions (7,8). SUMO is covalently attached to other proteins through the activities of an enzyme cascade (E1-E2-E3) similar to that for ubiquitination. There is only one known SUMO-activating enzyme, E1 (a heterodimer of SAE1 and SAE2) and only one known SUMO-conjugating enzyme, E2 (UBC9). There appear to be a number of different SUMO ligases (E3s) in higher eukaryotes such as PIAS family proteins (9-11), RanBP2 (12), and the polycomb protein Pc2 (13). To date, dozens of proteins from different species have been identified as sumoylation substrates. Among these are the RanGTPase-activating protein, RanGAP1 (14), PML (15), I B␣ (16), p53 (17, 18), and MDM2 (19). Unlike ubiquitination, sumoylation of proteins has not been linked to protein degradation. Proposed functions for sumoylation include regulation of protein-protein interaction and localization, inhibition of ubiquitin-mediated degradation, and enhancement of transcriptional activity.Histone proteins have been long known to be ubiquitinated (20),...

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“…This domain is present in a variety of proteins that interact with histone deacetylase complexes and mediate transcriptional repression (14). A founding member of the protein family defining the BTB/POZ domains, the Drosophila protein Tramtrack 69 is a bona fide SUMO substrate (15).…”

Section: Resultsmentioning

confidence: 99%

Broad Spectrum Identification of Cellular Small Ubiquitin-related Modifier (SUMO) Substrate Proteins

Zhao

Kwon

Anselmo

et al. 2004

Journal of Biological Chemistry

123

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Reversible covalent modification of proteins with a small ubiquitin-related modifier (SUMO) is emerging as an important system contributing to dynamic regulation of protein function. To enhance our understanding of the cell regulatory systems impacted by sumoylation, we used affinity chromatography-coupled high pressure liquid chromatography/tandem mass spectrometry for unbiased identification of candidate cellular SUMO substrate proteins. Here we describe the identification of 21 candidate sumoylated proteins from whole-cell lysates of HEK-293 cells. The nature of the proteins identified is consistent with a role for sumoylation in diverse cell regulatory systems but highlights regulation of chromatin organization and gene expression as major systems targeted by the sumoylation machinery.In addition to the well recognized role of protein phosphorylation, dynamic post-translational regulation of protein function can be achieved through a combination of a variety of other reversible covalent modifications including methylation, acetylation, ubiquitination, and sumoylation. Ubiquitination and sumoylation involve the ligation of ubiquitin family small polypeptides to one or more lysines of the target protein. Ubiquitination has long been recognized as an address code that sends proteins to the proteasome for degradation. However, apart from its role in protein degradation, ubiquitination also participates in the regulation of gene expression, signal transduction, and intracellular transport. The consequences of sumoylation on target proteins are relatively obscure; although based on the growing list of identified sumoylated proteins, sumoylation has been implicated in a diverse array of cell regulatory functions including the regulation of chromatin structure, subcellular compartmentalization, transcription factor activity, DNA binding, and protein complex assembly (1-3).There are three known small ubiquitin-like modifier (SUMO) 1 family members in mammalian cells: SUMO1, -2, and -3. The biochemical pathway mediating protein sumoylation has been characterized and is analogous to that defined for ubiquitination. Namely, the combined action of three proteins (an E1 activating enzyme, an E2 conjugating enzyme, and an E3 ligase) mediates isopeptide bond formation between SUMO and the target lysine on the substrate protein. Importantly, sumoylation is reversible, and a number of SUMO proteases that can cleave SUMO from specific target proteins have been identified (1-3).The bulk of present knowledge of the role of sumoylation in the regulation of cell behavior has been inferred from the nature of identified SUMO substrate proteins (3). The list of known SUMO substrates has been compiled by a combination of serendipitous observations and direct candidate analysis. It is not at all clear how well this list reflects the contribution of dynamic sumoylation to cell regulatory events. Therefore, we wished to assess the feasibility of a proteomics-based approach for an unbiased sampling of cellular SUMO target proteins. Here, ...

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Covalent Modification of the Transcriptional Repressor Tramtrack by the Ubiquitin-Related Protein Smt3 in Drosophila Flies

Cited by 94 publications

References 48 publications

Drosophila Ulp1, a Nuclear Pore-associated SUMO Protease, Prevents Accumulation of Cytoplasmic SUMO Conjugates

Drosophila Ulp1, a Nuclear Pore-associated SUMO Protease, Prevents Accumulation of Cytoplasmic SUMO Conjugates

Histone sumoylation is associated with transcriptional repression

Broad Spectrum Identification of Cellular Small Ubiquitin-related Modifier (SUMO) Substrate Proteins

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