title: TGF-beta down-regulates IL-6 signaling in intestinal epithelial cells: critical role of SMAD-2.
abstract: Interleukin-6 (IL-6) is a pro-inflammatory cytokine that plays an important role in the pathogenesis of inflammatory bowel disease. TGF-beta, a multifunctional cytokine, is a potent negative regulator of mucosal inflammation in the intestine. The aim of the present study is to determine possible cross-talk between IL-6 and TGF-beta signaling pathways. Model intestinal epithelial cell lines, Caco2-BBE were used. We show that TGF-beta receptor Type II is predominantly present in the basolateral membrane of intestinal epithelial cells. TGF-beta1 induces a time-dependent phosphorylation of Smad2 and co-immunoprecipitation of SMAD-2 with Smad-4 and its subsequently translocation to the nucleus. We show that pretreatment of cells with TGF-beta1 is associated with a down-regulation of IL-6 induced tyrosine phosphorylation of STAT1 and STAT3 and suppression of ICAM-1 expression. Furthermore, TGF-beta1 pretreatment resulted in a significant inhibition of IL-6 induced ICAM-1 promoter activity. TGF-beta mediated inhibition of IL-6 induced ICAM-1 expression was reversed by transfection with dominant negative Smad2 constructs. In conclusion, we show that: 1) TGF-beta receptor Type II is predominantly located on basolateral membrane and receptor stimulation activates Smad pathway; 2) TGF-beta1 down-regulates IL-6-induced tyrosine phoshorylation of STAT1 and STAT3 and ICAM-1 expression; and 3) Smad2 is required for the down-regulation of IL-6 signaling by TGF-beta. Collectively, our data demonstrate a cross-talk between TGF-beta and IL-6, and TGF-beta may play a role in the negative regulation of IL-6 signaling in intestinal epithelial cells.
mesh_terms: D021581:Active Transport, Cell Nucleus; D018938:Caco-2 Cells; D002467:Cell Nucleus / Q000378:metabolism; D004268:DNA-Binding Proteins / Q000378:metabolism / Q000502:physiology*; D015536:Down-Regulation; D004847:Epithelial Cells / Q000737:chemistry / Q000187:drug effects / Q000378:metabolism; D006801:Humans; D018799:Intercellular Adhesion Molecule-1 / Q000096:biosynthesis; D007413:Intestinal Mucosa / Q000378:metabolism*; D008954:Models, Biological; D010766:Phosphorylation; D017346:Protein Serine-Threonine Kinases; D000077294:Receptor, Transforming Growth Factor-beta Type II; D018125:Receptors, Transforming Growth Factor beta / Q000032:analysis; D050796:STAT3 Transcription Factor; D015398:Signal Transduction / Q000187:drug effects; D051899:Smad2 Protein; D015534:Trans-Activators / Q000378:metabolism / Q000502:physiology*; D016212:Transforming Growth Factor beta / Q000494:pharmacology*; D053773:Transforming Growth Factor beta1; D000093242:Interleukin-6 Inhibitors
chemical_list: D004268:DNA-Binding Proteins; D018799:Intercellular Adhesion Molecule-1; D017346:Protein Serine-Threonine Kinases; D000077294:Receptor, Transforming Growth Factor-beta Type II; D018125:Receptors, Transforming Growth Factor beta; D050796:STAT3 Transcription Factor; D051899:Smad2 Protein; D015534:Trans-Activators; D016212:Transforming Growth Factor beta; D053773:Transforming Growth Factor beta1; D000093242:Interleukin-6 Inhibitors; C497782:SMAD2 protein, human; C494086:STAT3 protein, human; C508960:TGFB1 protein, human