title: Sumoylation of internally initiated Sp3 isoforms regulates transcriptional repression via a Trichostatin A-insensitive mechanism.
abstract: Sp3 is a ubiquitously expressed member of the Sp family of transcription factors that encodes three proteins, Sp3, M1 and M2, with differing capacities to stimulate or repress transcription. As part of ongoing efforts to study the functions of Sp3 isoforms, we employed a yeast "two-hybrid" screen to identify Sp3-binding proteins. This screen resulted in the identification of Ubc9, a SUMO-1 conjugating enzyme, as an M2-binding protein, and consistent with these results sequence analyses identified consensus sumoylation motifs within several Sp family members. Western blots probed with anti-Sp3 detected a high molecular weight Sp3 isoform that is stabilized by a SUMO-1 hydrolase inhibitor, and this protein is also bound by anti-SUMO-1 antiserum. Transient transfection assays with epitope-tagged-SUMO-1 and GFP-SUMO-1 fusion proteins confirmed that Sp3, M1 and M2 proteins are sumoylated in vivo. Substitution of arginine for lysine at one putative site of sumoylation, lysine(551), blocked sumoylation of all Sp3 isoforms in vivo and led to a marginal increase in Sp3-mediated trans-activation in insect and mammalian cells. In contrast, introduction of this amino acid substitution within M1 converted it into a potent transcriptional trans-activator. We conclude that Sp3 isoforms are sumoylated in vivo and this post-translational modification plays an important role in the regulation of Sp3-mediated transcription.
authors.affiliation: Department of Pharmacology and Therapeutics, Roswell Park Cancer Institute, Buffalo, NY, USA.
authors.forename: Mary L
authors.initials: ML
authors.lastname: Spengler
authors.forename: Sarah B
authors.initials: SB
authors.lastname: Kennett
authors.forename: K Scott
authors.initials: KS
authors.lastname: Moorefield
authors.forename: Steven O
authors.initials: SO
authors.lastname: Simmons
authors.forename: Michael G
authors.initials: MG
authors.lastname: Brattain
authors.forename: Jonathan M
authors.initials: JM
authors.lastname: Horowitz
mesh_terms: D019943:Amino Acid Substitution; D000818:Animals; D015153:Blotting, Western; D019556:COS Cells; D002460:Cell Line; D045744:Cell Line, Tumor; D002467:Cell Nucleus / Q000737:chemistry / Q000378:metabolism; D002522:Chlorocebus aethiops; D004268:DNA-Binding Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D004791:Enzyme Inhibitors / Q000494:pharmacology; D005033:Ethylmaleimide / Q000737:chemistry; D006801:Humans; D006877:Hydroxamic Acids / Q000494:pharmacology*; D007150:Immunohistochemistry; D008239:Lysine / Q000378:metabolism; D009363:Neoplasm Proteins / Q000235:genetics / Q000378:metabolism; D009687:Nuclear Proteins / Q000235:genetics / Q000378:metabolism; D011401:Promoter Regions, Genetic / Q000235:genetics; D000071156:Promyelocytic Leukemia Protein; D017430:Prostate-Specific Antigen / Q000235:genetics; D020033:Protein Isoforms / Q000235:genetics / Q000378:metabolism; D025842:SUMO-1 Protein / Q000235:genetics / Q000378:metabolism*; D016329:Sp1 Transcription Factor / Q000737:chemistry / Q000378:metabolism; D051705:Sp3 Transcription Factor; D013762:Tetrahydrofolate Dehydrogenase / Q000235:genetics; D014157:Transcription Factors / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D015533:Transcriptional Activation / Q000187:drug effects; D014162:Transfection; D025521:Tumor Suppressor Proteins; D020798:Two-Hybrid System Techniques; D044763:Ubiquitin-Conjugating Enzymes / Q000378:metabolism; D000098843:Ubiquitin-Conjugating Enzyme UBC9
chemical_list: D004268:DNA-Binding Proteins; D004791:Enzyme Inhibitors; D006877:Hydroxamic Acids; D009363:Neoplasm Proteins; D009687:Nuclear Proteins; D000071156:Promyelocytic Leukemia Protein; D020033:Protein Isoforms; C497121:SP3 protein, human; D025842:SUMO-1 Protein; D016329:Sp1 Transcription Factor; D014157:Transcription Factors; D025521:Tumor Suppressor Proteins; C070576:PML protein, human; D051705:Sp3 Transcription Factor; C012589:trichostatin A; D013762:Tetrahydrofolate Dehydrogenase; D044763:Ubiquitin-Conjugating Enzymes; D017430:Prostate-Specific Antigen; D000098843:Ubiquitin-Conjugating Enzyme UBC9; D008239:Lysine; D005033:Ethylmaleimide