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PubMed2006

Sumoylation of the yeast Gcn5 protein.

Sumoylation, the process by which the ubiquitin-related SUMO protein is covalently attached to lysine side chains in other proteins, is involved in numerous processes in the eukaryotic cell, including transcriptional repression. In this study, we identify Gcn5, the histone-modifying subunit of the transcriptional regulatory complex SAGA, as a sumoylation substrate in yeast. In vitro, multiple sumoylation of recombinant Gcn5 alone or as a trimer with its interacting proteins Ada2 and Ada3 did not affect Gcn5's histone acetyltransferase (HAT) activity, suggesting that modification of Gcn5 with yeast SUMO (Smt3) may not directly regulate its HAT function. Through site-directed mutagenesis, the primary in vivo sumoylation site was identified as lysine-25, although an unsumoylatable K-to-R mutation of this residue led to no obvious in vivo effects. However, fusion of SUMO to the N-terminus of Gcn5 to mimic constitutive sumoylation resulted in defective growth on 3-aminotriazole media and reduced basal and activated transcription of the SAGA-dependent gene TRP3. Taken together with recent identification of multiple additional subunits of SAGA as sumoylated proteins in vivo, these data suggest that Gcn5 sumoylation may have an inhibitory role in transcriptional regulation.

Binding Sites↗

PubMed2005

Pias1 interaction and sumoylation of metabotropic glutamate receptor 8.

Group III presynaptic metabotropic glutamate receptors (mGluRs) play a central role in regulating presynaptic activity through G-protein effects on ion channels and signal transducing enzymes. Like all Class C G-protein-coupled receptors, mGluR8 has an extended intracellular C-terminal domain (CTD) presumed to allow for modulation of downstream signaling. In a yeast two-hybrid screen of an adult rat brain cDNA library with the CTDs of mGluR8a and 8b (mGluR8-C) as baits, we identified sumo1 and four different components of the sumoylation cascade (ube2a, Pias1, Piasgamma, Piasxbeta) as interacting proteins. Binding assays using recombinant GST fusion proteins confirmed that Pias1 interacts not only with mGluR8-C but also with all group III mGluR CTDs. Pias1 binding to mGluR8-C required a region N-terminal to a consensus sumoylation motif and was not affected by arginine substitution of the conserved lysine 882 within this motif. Co-transfection of fluorescently tagged mGluR8a-C, sumo1, and enzymes of the sumoylation cascade into HEK293 cells showed that mGluR8a-C can be sumoylated in vivo. Arginine substitution of lysine 882 within the consensus sumoylation motif, but not other conserved lysines within the CTD, abolished in vivo sumoylation. Our results are consistent with post-translational sumoylation providing a novel mechanism of group III mGluR regulation.

Amino Acid Motifs↗

PubMed2005

Control of MEF2 transcriptional activity by coordinated phosphorylation and sumoylation.

A eukaryotic protein is often subject to regulation by multiple modifications like phosphorylation, acetylation, ubiquitination, and sumoylation. How these modifications are coordinated in vivo is an important issue that is poorly understood but is relevant to many biological processes. We recently showed that human MEF2D (myocyte enhancer factor 2D) is sumoylated on Lys-439. Adjacent to the sumoylation motif is Ser-444, which like Lys-439 is highly conserved among MEF2 proteins from diverse species. Here we present [corrected] several lines of evidence to demonstrate that Ser-444 of MEF2D is required for sumoylation of Lys-439. Histone deacetylase 4 (HDAC4) stimulated this modification by acting through Ser-444. In addition, phosphorylation of Ser-444 by Cdk5, a cyclin-dependent kinase known to inhibit MEF2 transcriptional activity, stimulated sumoylation. Opposing the actions of HDAC4 and Cdk5, calcineurin (also known as protein phosphatase 2B) dephosphorylated Ser-444 and inhibited sumoylation of Lys-439. This phosphatase, however, exerted minimal effects on the phosphorylation catalyzed by ERK5, an extracellular signal-regulated kinase known to activate MEF2D. These results identify [corrected] an essential role for Ser-444 in MEF2D sumoylation and reveal [corrected] a novel mechanism by which calcineurin selectively "edits" phosphorylation at different sites, thereby reiterating that interplay between different modifications represents a general mechanism for coordinated regulation of eukaryotic protein functions in vivo.

Amino Acid Sequence↗

PubMed2006

Sumoylated SnoN represses transcription in a promoter-specific manner.

The transcriptional modulator SnoN controls a diverse set of biological processes, including cell proliferation and differentiation. The mechanisms by which SnoN regulates these processes remain incompletely understood. Recent studies have shown that SnoN exerts positive or negative regulatory effects on transcription. Because post-translational modification of proteins by small ubiquitin-like modifier (SUMO) represents an important mechanism in the control of the activity of transcriptional regulators, we asked if this modification regulates SnoN function. Here, we show that SnoN is sumoylated. Our data demonstrate that the SUMO-conjugating E2 enzyme Ubc9 is critical for SnoN sumoylation and that the SUMO E3 ligase PIAS1 selectively interacts with and enhances the sumoylation of SnoN. We identify lysine residues 50 and 383 as the SUMO acceptor sites in SnoN. Analyses of SUMO "loss-of-function" and "gain-of-function" SnoN mutants in transcriptional reporter assays reveal that sumoylation of SnoN contributes to the ability of SnoN to repress gene expression in a promoter-specific manner. Although this modification has little effect on SnoN repression of the plasminogen activator inhibitor-1 promoter and only modestly potentiates SnoN repression of the p21 promoter, SnoN sumoylation robustly augments the ability of SnoN to suppress transcription of the myogenesis master regulatory gene myogenin. In addition, we show that the SnoN SUMO E3 ligase, PIAS1, at its endogenous levels, suppresses myogenin transcription. Collectively, our findings suggest that SnoN is directly regulated by sumoylation leading to the enhancement of the ability of SnoN to repress transcription in a promoter-specific manner. Our study also points to a physiological role for SnoN sumoylation in the control of myogenin expression in differentiating muscle cells.

Amino Acid Sequence↗

PubMed2007

Transforming growth factor-beta-independent regulation of myogenesis by SnoN sumoylation.

Recent progress has been made on the role of oncoproteins c-Ski and related SnoN in the control of cellular transformation. c-Ski/SnoN potently repress transforming growth factor-beta (TGF-beta) antiproliferative signaling through physical interaction with signal transducers called Smads. Overexpression of c-Ski/SnoN also induces skeletal muscle differentiation, but how c-Ski/SnoN function in myogenesis is largely unknown. During our investigation on the role of sumoylation in TGF-beta signaling, we inadvertently found that SnoN is modified by small ubiquitin-like modifier-1 (SUMO-1). Here, we biochemically characterize SnoN sumoylation in detail and report the physiological function of the modification. Sumoylation occurs primarily at lysine 50 (Lys-50). PIAS1 and PIASx proteins physically interact with SnoN to stimulate its sumoylation, thus serving as SUMO-protein isopeptide ligases (E3) for SnoN sumoylation. SnoN sumoylation does not alter its metabolic stability or its ability to repress TGF-beta signaling. Notably, loss of sumoylation in the Lys-50 site (via a Lys-to-Arg point mutation) potently activates muscle-specific gene expression and enhances myotube formation. Our study suggests a novel role for SUMO modification in the regulation of myogenic differentiation.

Cell Line↗

PubMed2005

Association with class IIa histone deacetylases upregulates the sumoylation of MEF2 transcription factors.

The myocyte enhancer factor-2 (MEF2) family of transcription factors plays an important role in regulating cellular programs like muscle differentiation, neuronal survival, and T-cell apoptosis. Multisite phosphorylation is known to control the transcriptional activity of MEF2 proteins, but it is unclear whether other modifications are involved. Here, we report that human MEF2D, as well as MEF2C, is modified by SUMO2 and SUMO3 at a motif highly conserved among MEF2 proteins from diverse organisms. This motif is located within the C-terminal transcriptional activation domain, and its sumoylation inhibits transcription. As a transcriptional corepressor of MEF2, histone deacetylase 4 (HDAC4) potentiates sumoylation. This potentiation is dependent on the N-terminal region but not the C-terminal deacetylase domain of HDAC4 and is inhibited by the sumoylation of HDAC4 itself. Moreover, HDAC5, HDAC7, and an HDAC9 isoform also stimulate sumoylation of MEF2. Opposing the action of class IIa deacetylases, the SUMO protease SENP3 reverses the sumoylation to augment the transcriptional and myogenic activities of MEF2. Similarly, the calcium/calmodulin-dependent kinases [corrected] and extracellular signal-regulated kinase 5 signaling pathways negatively regulate the sumoylation. These results thus identify sumoylation as a novel regulatory mechanism for MEF2 and suggest that this modification interplays with phosphorylation to promote intramolecular signaling for coordinated regulation in vivo.

Amino Acid Motifs↗

PubMed2001

Intracellular targeting of proteins by sumoylation.

A novel host cell posttranslational modification system, termed sumoylation, has recently been characterized. Sumoylation is an enzymatic process that is biochemically analogous to, but functionally distinct from, ubiquitinylation. As in ubiquitinylation, sumoylation involves the covalent attachment of a small protein moiety, SUMO, to substrate proteins. However, conjugation of SUMO does not typically lead to degradation of the substrate and instead has a more diverse array of effects on substrate function. As the list of sumoylation substrates has expanded, a common theme is that many substrates exhibit sumoylation-dependent subcellular distribution. While the molecular mechanisms by which sumoylation targets protein localization are still poorly understood, it is clear that this modification system is an important regulator of intracellular protein localization, particularly involving nuclear uptake and punctate intranuclear accumulation.

Drosophila Proteins↗

PubMed2005

Differential interactions of the homeodomain-interacting protein kinase 2 (HIPK2) by phosphorylation-dependent sumoylation.

Homeodomain-interacting protein kinase 2 (HIPK2) interacts with and phosphorylates various transcription factors that are critical regulators of cell fate decisions and apoptosis during development. Here we show that lysine 25 of HIPK2 is the major sumoylation site, both in vitro and in vivo, and that the sumoylation of this site occurs in a phosphorylation-dependent manner. This became clear with the finding that kinase-dead HIPK2 (K221R) could not be efficiently sumoylated in vitro. The sumoylation of HIPK2 resulted in the disruption of its interaction with a Groucho corepressor. Consequently, sumoylation inhibited the regulatory activity of HIPK2 on the Groucho-mediated repression of transcription, whereas not on p53-mediated transactivation. These results suggest that phosphorylation-dependent sumoylation enables HIPK2 to drive different target gene transcription by means of differential interactions with its binding partners.

Basic Helix-Loop-Helix Proteins↗

PubMed2003

Opposed regulation of corepressor CtBP by SUMOylation and PDZ binding.

The transcription corepressor CtBP is often recruited to the target promoter via interaction with a conserved PxDLS motif in the interacting repressor. In this study, we demonstrate that CtBP1 was SUMOylated and that its SUMOylation profoundly affected its subcellular localization. SUMOylation occurred at a single Lys residue, Lys428, of CtBP1. CtBP2, a close homolog of CtBP1, lacked the SUMOylation site and was not modified by SUMO-1. Mutation of Lys428 into Arg (K428R) shifted CtBP1 from the nucleus to the cytoplasm, while it had little effect on its interaction with the PxDLS motif. Consistent with a change in localization, the K428R mutation abolished the ability of CtBP1 to repress the E-cadherin promoter activity. Notably, SUMOylation of CtBP1 was inhibited by the PDZ domain of nNOS, correlating with the known inhibitory effect of nNOS on the nuclear accumulation of CtBP1. This study identifies SUMOylation as a regulatory mechanism underlying CtBP1-dependent transcriptional repression.

Alcohol Oxidoreductases↗

PubMed2003

MDM2-ARF complex regulates p53 sumoylation.

The p53 tumor suppressor is regulated by MDM2-mediated ubiquitination and degradation. Ubiquitination of p53 is regulated by ARF, which binds to MDM2 and inhibits its E3 ligase function. P53 is also subjected to modification by conjugation of SUMO-1. We found that a p53 mutant deficient for MDM2 binding (p53(14Q19S)) is poorly sumoylated in vivo compared to wild-type p53. Overexpression of MDM2 increases the level of p53 sumoylation, which is further stimulated by expression of ARF. Stimulation of p53 sumoylation requires a highly conserved region (102-116) encoded by exon 2 of ARF and correlates with the ability of ARF to target p53 to the nucleolus. An MDM2 deletion mutant (MDM2(Delta222-437)) with activated cryptic nucleolar localization signal also targets p53 to the nucleolus and efficiently promotes p53 sumoylation in the absence of ARF. Direct targeting of p53 to the nucleolus enhances its sumoylation in an MDM2- and ARF-dependent fashion. These results show that p53 sumoylation is regulated by MDM2- and ARF-mediated nucleolar targeting.

ADP-Ribosylation Factors↗

PubMed2005

Sumoylation induced by the Arf tumor suppressor: a p53-independent function.

The mouse p19(Arf) protein has both p53-dependent and p53-independent tumor-suppressive activities. Arf triggers sumoylation of many cellular proteins, including Mdm2 and nucleophosmin (NPM/B23), with which p19(Arf) physically interacts in vivo, and this occurs equally well in cells expressing or lacking functional p53. In an Arf-null NIH 3T3 cell derivative (MT-Arf cells) engineered to reexpress an Arf transgene driven by a zinc-inducible metallothionein promoter, sumoylation of endogenous Mdm2 and NPM proteins was initiated as p19(Arf) was induced and was observed before p53-dependent cell cycle arrest. Predominately nucleoplasmic molecules visualized by immunofluorescence with antibodies to small ubiquitin-like modifier (SUMO) 1 localized to nucleoli as p19(Arf) accumulated there. Two Arf mutants, one of which binds to Mdm2 and NPM but is excluded from nucleoli and the other of which enters nucleoli but is handicapped in binding to Mdm2 and NPM, were defective in inducing sumoylation of these two target proteins and did not localize bulk sumoylated molecules to nucleoli. The CELO adenovirus protein, Gam1, which inhibits the SUMO activating enzyme (E1) and leads to down-regulation of the SUMO conjugating enzyme (E2/Ubc9), had no overt effect on the ability of p19(Arf) to activate p53 or the p53-responsive genes encoding Mdm2 and p21(Cip1), despite the fact that Arf-induced sumoylation of Mdm2 was blocked. Reduction of Ubc9 levels with short hairpin RNAs rendered similar results. We suggest that Arf's p53-independent effects on gene expression and tumor suppression might depend on Arf-induced sumoylation.

Animals↗

PubMed2003

Sumoylation of Smad4, the common Smad mediator of transforming growth factor-beta family signaling.

Transforming growth factor-beta (TGF-beta) and TGF-beta-related factors regulate cell growth, differentiation, and apoptosis, and play key roles in normal development and tumorigenesis. TGF-beta family-induced changes in gene expression are mediated by serine/threonine kinase receptors at the cell surface and Smads as intracellular effectors. Receptor-activated Smads combine with a common Smad4 to translocate into the nucleus where they cooperate with other transcription factors to activate or repress transcription. The activities of the receptor-activated Smads are controlled by post-translational modifications such as phosphorylation and ubiquitylation. Here we show that Smad4 is modified by sumoylation. Sumoylation of Smad4 was enhanced by the conjugating enzyme Ubc9 and members of the PIAS family of SUMO ligases. A major sumoylation site in Smad4 was localized to Lys-159 in its linker segment with an additional site at Lys-113 in the MH-1 domain. Increased sumoylation in the presence of the PIASy E3 ligase correlated with targeting of Smad4 to subnuclear speckles that contain SUMO-1 and PIASy. Replacement of lysines 159 and 113 by arginines or increased sumoylation enhanced the stability of Smad4, and transcription in mammalian cells and Xenopus embryos. These observations suggest a role for Smad4 sumoylation in the regulation of TGF-beta signaling through Smads.

Active Transport, Cell Nucleus↗

PubMed2004

Repression of the Transactivating Capacity of the Oncoprotein PLAG1 by SUMOylation.

Human pleomorphic adenoma gene 1 (PLAG1), a developmentally regulated proto-oncogene, is consistently rearranged and overexpressed in pleomorphic salivary gland adenomas and lipoblastomas with 8q12 translocations. Together with PLAGL1 and PLAGL2, PLAG1 belongs to a subfamily of C(2)H(2) zinc finger transcription factors that activate transcription through binding to the bipartite consensus sequence GRGGC(N)(6-8)GGG. Ectopic expression of PLAG1 deregulates target genes and presumably results in uncontrolled cell proliferation. To gain insight into molecular mechanisms regulating PLAG transcriptional capacity, we searched for interaction partners using the yeast two-hybrid system and confirmed these by glutathione S-transferase pull-down. Ubiquitin-conjugating enzyme 9 (UBC9) and protein inhibitor of activated STAT (PIAS) proteins were first identified as genuine interacting partners of mouse PlagL2. Because UBC9 and PIAS are components of the small ubiquitin-related modifier (SUMO) modification pathway, we hypothesized that PLAG proteins could be SUMOylated. Here, we report results obtained for founding family member PLAG1. Its endogenous SUMOylation was demonstrated, and SUMOylation of PLAG1 was further investigated in cells co-transfected with PLAG1 and SUMO-1 DNA or a SUMO-1 mutant form and similarly examined in the presence or absence of DNA encoding the various PIAS proteins. Using anti-PLAG1 antibodies, we discovered single and double SUMO-1-modified forms of PLAG1. By mutating predicted SUMO consensus sites, we defined two important target lysines for SUMOylation in PLAG1, Lys-244 and Lys-263. Moreover, mutation of both SUMO consensus sequences, resulting in inhibition of SUMOylation, led to a significant increase of the transactivation capacity of PLAG1. Nuclear distribution of PLAG1 was not measurably influenced. Our results suggest a direct repression of the transactivating capacity of the oncoprotein PLAG1 by SUMOylation.

DNA-Binding Proteins↗

PubMed2004

Dual role of sumoylation in the nuclear localization and transcriptional activation of NFAT1.

The nuclear import of nuclear factor of activated T cells (NFAT) transcription factors is critical for regulating NFAT activity. Here we demonstrate that the sumoylation of NFAT1 defines a novel mechanism of the nuclear anchorage and transcriptional activation downstream from the known mechanism of calcineurin-mediated dephosphorylation and nuclear import. We show that Lys(684) and Lys(897) of NFAT1 can be sumoylated. The sumoylation at Lys(684) is required for NFAT1 transcriptional activity and subsequent sumoylation of Lys(897), whereas the sumoylation of Lys(897) is only required for nuclear anchorage. Because Lys(897) of NFAT1 is not conserved among other members of the NFAT family, we propose that sumoylation of Lys(897) may provide a mechanism for NFAT1 isotype-specific regulation of nuclear anchorage and transcriptional activation. Furthermore, we found that treatment with both ionomycin and phorbol 12-myristate 13-acetate ensured efficient nuclear anchorage with the recruitment of NFAT1 into the SUMO-1 bodies, whereas treatment with ionomycin alone induced nuclear translocation of NFAT1 but not recruitment into the SUMO-1 bodies. Our results suggest that the recruitment of NFAT1 into SUMO-1 bodies may be required for the progressive transcriptional activity of NFAT1 upon co-stimulation with ionomycin and phorbol 12-myristate 13-acetate, whereas anergic transcription stimulated by ionomycin alone may occur without recruitment into the SUMO-1 bodies.

Animals↗

PubMed2006

Sumoylation inhibits cleavage of Sp1 N-terminal negative regulatory domain and inhibits Sp1-dependent transcription.

Sp1 is a ubiquitously expressed transcription factor that binds GC-rich cis elements. Many posttranslational modifications have been implicated in the regulation of Sp1 activity. We now provide evidence for a novel mechanism of Sp1 regulation involving the small ubiquitin-like modifier (SUMO-1). Western blot analysis revealed a high molecular mass Sp1 of 125 kDa that is stabilized by a selective SUMO hydrolase inhibitor and destabilized by a specific SUMO-1 hydrolase. The covalent modification of Sp1 by endogenous SUMO-1 and SUMO-1 that has been fused to green fluorescent protein was demonstrated using transient transfection assays. A high probability sumoylation consensus motif, VK(16)IE(18), is located within the N-terminal negative regulatory domain of Sp1. Either arginine substitution for lysine 16 (Sp1(K16R)) or alanine substitution for glutamic acid 18 (Sp1(E18A)), abrogated Sp1 sumoylation. In vitro SUMO-1 covalently bound affinity-purified GST-Sp1, but not GST-Sp1(K16R). In vivo Sp1 was determined to be N-terminally cleaved, while Sp1(K16R) could not be cleaved indicating that sumoylation and cleavage are coupled through the key regulatory lysine 16. This coupling was evident by the demonstration of an inverse relationship between cellular SUMO-modified Sp1 and N-terminally cleaved Sp1. Compared with Sp1, sumoylation-deficient Sp1(E18A) exhibited enhanced cleavage and was a better transcriptional activator, while constitutively SUMO-1-modified Sp1 was deficient in proteolytic processing and repressed Sp1 transcriptional activity. The repressive effect of sumoylation on Sp1 activity is emphasized through the use of a GAL4 based transactivation assay. A model is proposed defining a mechanism by which sumoylation preserves the integrity of a negative regulatory domain thereby allowing for the inhibition of Sp-dependent transcription.

Amino Acid Sequence↗

PubMed2004

A proteomic strategy for gaining insights into protein sumoylation in yeast.

Sumoylation represents a vital post-translational modification that pervades numerous aspects of cell biology, including protein targeting, transcriptional regulation, signal transduction, and cell division. However, despite its broad reaching effects, most biological outcomes of protein sumoylation remain poorly understood. In an effort to provide further insight into this complex process, a proteomics approach was undertaken to identify the targets of sumoylation en mass. Specifically, SUMO-conjugated proteins were isolated by a double-affinity purification procedure from a Saccharomyces cerevisiae strain engineered to express tagged SUMO. The components of the isolated protein mixture were then identified by subsequent LC-MS/MS analysis using an LTQ FT mass spectrometer. In this manner, 159 candidate sumoylated proteins were identified by two or more peptides. Furthermore, the high accuracy of the instrument, combined with stringent search criteria, enabled the identification of an additional 92 putative candidates by only one peptide. The validity of this proteomics approach was confirmed by performing subsequent Western blot experiments for numerous proteins and determining the actual sumoylation sites for several other substrates. These data combine with recent works to further our understanding of the breadth and impact of protein sumoylation in a diverse array of biological processes.

Amino Acid Sequence↗

PubMed2006

Sumoylation of the budding yeast kinetochore protein Ndc10 is required for Ndc10 spindle localization and regulation of anaphase spindle elongation.

Posttranslational modification by the ubiquitin-like protein SUMO (small ubiquitin-like modifier) is emerging as an important regulator in many cellular processes, including genome integrity. In this study, we show that the kinetochore proteins Ndc10, Bir1, Ndc80, and Cep3, which mediate the attachment of chromosomes to spindle microtubules, are sumoylated substrates in budding yeast. Furthermore, we show that Ndc10, Bir1, and Cep3 but not Ndc80 are desumoylated upon exposure to nocodazole, highlighting the possibility of distinct roles for sumoylation in modulating kinetochore protein function and of a potential link between the sumoylation of kinetochore proteins and mitotic checkpoint function. We find that lysine to arginine mutations that eliminate the sumoylation of Ndc10 cause chromosome instability, mislocalization of Ndc10 from the mitotic spindle, abnormal anaphase spindles, and a loss of Bir1 sumoylation. These data suggest that sumoylation of Ndc10 and other kinetochore proteins play a critical role during the mitotic process.

Anaphase↗

PubMed2005

TRAF7 sequesters c-Myb to the cytoplasm by stimulating its sumoylation.

Small ubiquitin-related modifiers (SUMOs) are proteins that are posttranslationally conjugated to diverse proteins. The c-myb proto-oncogene product (c-Myb) regulates proliferation and differentiation of hematopoietic cells. PIASy is the only known SUMO E3 ligase for c-Myb. Here, we report that TRAF7 binds to c-Myb and stimulates its sumoylation. TRAF7 bound to the DNA-binding domain of c-Myb via its WD40 repeats. TRAF7 has an E3 ubiquitin ligase activity for self-ubiquitination, but TRAF7 also stimulated the sumoylation of c-Myb at Lys-523 and Lys-499, which are the same sites as those used for PIASy-induced sumoylation. TRAF7 inhibited trans-activation induced by wild-type c-Myb, but not by the sumoylation site mutant of c-Myb. The expression of both c-myb and TRAF7 was down-regulated during differentiation of M1 cells. Endogenous TRAF7 localized to both the cytoplasm and nucleus of M1 cells. Consistent with this, significant amounts of sumoylated c-Myb were found in the cytoplasm of M1 cells, whereas nonsumoylated c-Myb was found predominantly in the nucleus. Overexpressed TRAF7 was localized in the cytoplasm of CV-1 cells, and sequestered c-Myb and SUMO1 in the cytosol, whereas PIASy was localized in the nucleus. Thus, TRAF7 negatively regulates c-Myb activity by sequestering c-Myb to the cytosol via sumoylation.

Animals↗