title: Repression of Smad4 transcriptional activity by SUMO modification.
abstract: Smad4 plays a key role in TGF-beta (transforming growth factor beta)/Smad-mediated transcriptional responses. We show that Smad4 is sumoylated both in vivo and in vitro. Recent studies showed that sumoylation of Smad4 regulated its stability, but the effect of sumoylation on the intrinsic transcriptional activity of Smad4 was not defined. We show that overexpression of SUMO (small ubiquitin-related modifier)-1 and Ubc9 can inhibit a TGF-beta-responsive reporter gene, whereas co-transfection with SUMO-1 protease-1 (SuPr-1) can increase the TGF-beta response. We show further that mutation of the Smad4 sumoylation sites or co-transfection with SuPr-1 greatly increases Smad4 transcriptional activity. Moreover, direct fusion of SUMO-1 to the sumoylation mutant Smad4 potently inhibits its transcriptional activity. Thus, as it is being rapidly discovered that sumoylation inhibits the activities of many transcription factors, sumoylation also represses Smad4 transcriptional activity. The net effect of sumoylation of Smad4 can therefore be either stimulatory or inhibitory, depending on the target promoter that is analysed.
authors.affiliation: Center for Advanced Biotechnology and Medicine, Rutgers, the State University of New Jersey, 679 Hoes Lane, Piscataway, NJ 08854, USA.
authors.forename: Jianyin
authors.initials: J
authors.lastname: Long
authors.forename: Guannan
authors.initials: G
authors.lastname: Wang
authors.forename: Dongming
authors.initials: D
authors.lastname: He
authors.forename: Fang
authors.initials: F
authors.lastname: Liu
mesh_terms: D000818:Animals; D019556:COS Cells / Q000378:metabolism; D002522:Chlorocebus aethiops; D004268:DNA-Binding Proteins / Q000737:chemistry / Q000502:physiology*; D005786:Gene Expression Regulation; D017930:Genes, Reporter; D011401:Promoter Regions, Genetic; D011499:Protein Processing, Post-Translational; D011993:Recombinant Fusion Proteins / Q000378:metabolism; D025842:SUMO-1 Protein / Q000378:metabolism*; D012441:Saccharomyces cerevisiae / Q000235:genetics* / Q000378:metabolism; D029701:Saccharomyces cerevisiae Proteins / Q000737:chemistry / Q000502:physiology*; D015534:Trans-Activators / Q000737:chemistry / Q000502:physiology*; D014158:Transcription, Genetic; D014162:Transfection; D016212:Transforming Growth Factor beta / Q000494:pharmacology / Q000502:physiology; D020798:Two-Hybrid System Techniques; D025801:Ubiquitin / Q000378:metabolism; D044763:Ubiquitin-Conjugating Enzymes / Q000235:genetics / Q000378:metabolism; D000098843:Ubiquitin-Conjugating Enzyme UBC9
chemical_list: D004268:DNA-Binding Proteins; D011993:Recombinant Fusion Proteins; D025842:SUMO-1 Protein; D029701:Saccharomyces cerevisiae Proteins; D015534:Trans-Activators; D016212:Transforming Growth Factor beta; D025801:Ubiquitin; D044763:Ubiquitin-Conjugating Enzymes; D000098843:Ubiquitin-Conjugating Enzyme UBC9