title: TGF-β₂ decreases baseline and IL-13-stimulated mucin production by primary human bronchial epithelial cells.
abstract: BACKGROUND
  Mucus hypersecretion is a major contributor to asthma pathology and occurs as part of a spectrum of structural changes termed airway wall remodeling. Transforming growth factor (TGF)-β is proposed to play a key role in regulating airway matrix remodeling although less is known about the specific action of TGF-β isoforms in regulating mucus production.
  
  
  METHODS
  Primary human bronchial epithelial (HBE) cells cultured at air-liquid interface were treated with exogenous TGF-β(1), TGF-β(2), and/or a Th2 cytokine, interleukin (IL)-13. Expression and production of respiratory mucins, MUC5AC and MUC5B, were analyzed by real-time PCR, agarose gel electrophoresis, and western blotting. A murine-transformed Clara cell line (mtCC1-2) transfected with a luciferase reporter driven by the Muc5ac promoter containing Smad4 site-mutated cis sequences was used to determine whether exogenous TGF-β(2) affects Muc5ac promoter function.
  
  
  RESULTS
  Surprisingly, TGF-β(1) showed no measurable effect on MUC5AC or MUC5B production by HBE cells whereas TGF-β(2) caused a decrease in both MUC5AC and MUC5B mRNA and protein. Dual treatment with TGF-β(2) and IL-13 partially attenuated the increase in mucin production found with IL-13 alone. This effect was confirmed by using mtCC1-2 cells where addition of TGF-β(2) reduced the ability of IL-13/EGF to induce Muc5ac promoter expression in wild-type cells; however, this decrease was absent in mutant promoter-transfected cells.
  
  
  CONCLUSIONS
  Findings suggest that normal regulation of MUC5AC and MUC5B production by HBE cells is TGF-β isoform-specific and that TGF-β(2) downregulates both MUC5AC and MUC5B. Furthermore, TGF-β(2) controls baseline and IL-13-driven Muc5ac promoter function in murine Clara cells via an endogenous Smad4 recognition motif.
authors.affiliation: Wellcome Trust Centre for Cell-Matrix Research, Faculty of Life Sciences, The University of Manchester, Manchester, UK.
authors.forename: Ceri A
authors.initials: CA
authors.lastname: Harrop
authors.forename: Robin B
authors.initials: RB
authors.lastname: Gore
authors.forename: Christopher M
authors.initials: CM
authors.lastname: Evans
authors.forename: David J
authors.initials: DJ
authors.lastname: Thornton
authors.forename: Sarah E
authors.initials: SE
authors.lastname: Herrick
mesh_terms: D000818:Animals; D002461:Cell Line, Transformed; D002478:Cells, Cultured; D015870:Gene Expression / Q000187:drug effects; D006801:Humans; D018793:Interleukin-13 / Q000494:pharmacology*; D008168:Lung / Q000187:drug effects* / Q000378:metabolism / Q000473:pathology; D051379:Mice; D055271:Mucin 5AC / Q000235:genetics / Q000378:metabolism*; D055257:Mucin-5B / Q000235:genetics / Q000378:metabolism*; D020545:Respiratory Mucosa / Q000187:drug effects* / Q000378:metabolism / Q000473:pathology; D014162:Transfection; D053781:Transforming Growth Factor beta2 / Q000494:pharmacology*
chemical_list: C578095:IL13 protein, human; D018793:Interleukin-13; C524678:MUC5AC protein, human; C524578:MUC5B protein, human; D055271:Mucin 5AC; D055257:Mucin-5B; D053781:Transforming Growth Factor beta2