title: Activation of transforming growth factor-beta signaling by SUMO-1 modification of tumor suppressor Smad4/DPC4.
abstract: Smads are important intracellular effectors in signaling pathways of the transforming growth factor-beta (TGF-beta) superfamily. Upon activation by TGF-beta, receptor-phosphorylated Smads form a complex with tumor suppressor Smad4/DPC4, and the Smad complexes then are imported into the nucleus. Although diverse pathways regulate the activity and expression of receptor-phosphorylated and inhibitory Smads, cellular factors modulating the activity of the common Smad4 remain unidentified. Here we describe the involvement of the small ubiquitin-like modifier-1 (SUMO-1) conjugation pathway in regulating the growth inhibitory and transcriptional responses of Smad4. The MH1 domain of Smad4 was shown to associate physically with Ubc9, the ubiquitin carrier protein (E2) conjugating enzyme in sumoylation. In cultured cells, Smad4 is modified by SUMO-1 at the endogenous level. The sumoylation sites were identified as two evolutionarily conserved lysine residues, Lys-113 and Lys-159, in the MH1 domain. We found that the mutations at Lys-113 and Lys-159 did not alter the ability of Smad4 to form a complex with Smad2 and FAST on the Mix.2 promoter. Importantly, SUMO-1 overexpression enhanced TGF-beta-induced transcriptional responses. These findings identify sumoylation as a unique mechanism to modulate Smad4-dependent cellular responses.
authors.affiliation: Michael E. DeBakey Department of Surgery, Baylor College of Medicine, Houston, Texas 77030, USA.
authors.forename: Xia
authors.initials: X
authors.lastname: Lin
authors.forename: Min
authors.initials: M
authors.lastname: Liang
authors.forename: Yao-Yun
authors.initials: YY
authors.lastname: Liang
authors.forename: F Charles
authors.initials: FC
authors.lastname: Brunicardi
authors.forename: Frauke
authors.initials: F
authors.lastname: Melchior
authors.forename: Xin-Hua
authors.initials: XH
authors.lastname: Feng
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D016466:CHO Cells; D002460:Cell Line; D017124:Conserved Sequence; D006224:Cricetinae; D004268:DNA-Binding Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D004355:Drug Stability; D004622:Embryo, Mammalian; D017353:Gene Deletion; D016147:Genes, Tumor Suppressor; D006367:HeLa Cells; D006801:Humans; D007163:Immunosorbent Techniques; D007668:Kidney; D008025:Ligases / Q000235:genetics / Q000378:metabolism; D008156:Luciferases / Q000235:genetics; D008168:Lung; D008239:Lysine / Q000378:metabolism; D008907:Mink; D008969:Molecular Sequence Data; D016296:Mutagenesis; D011993:Recombinant Fusion Proteins; D020218:Response Elements; D025842:SUMO-1 Protein / Q000235:genetics / Q000378:metabolism / Q000494:pharmacology*; D012441:Saccharomyces cerevisiae / Q000235:genetics; D015398:Signal Transduction / Q000187:drug effects*; D051901:Smad4 Protein; D015534:Trans-Activators / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D014158:Transcription, Genetic; D014162:Transfection; D016212:Transforming Growth Factor beta / Q000494:pharmacology / Q000502:physiology*; D044763:Ubiquitin-Conjugating Enzymes; D000098843:Ubiquitin-Conjugating Enzyme UBC9
chemical_list: D004268:DNA-Binding Proteins; D011993:Recombinant Fusion Proteins; C497796:SMAD4 protein, human; D025842:SUMO-1 Protein; D051901:Smad4 Protein; D015534:Trans-Activators; D016212:Transforming Growth Factor beta; D008156:Luciferases; D044763:Ubiquitin-Conjugating Enzymes; D008025:Ligases; D000098843:Ubiquitin-Conjugating Enzyme UBC9; D008239:Lysine