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TGF-beta 1 induces human alveolar epithelial to mesenchymal cell transition (EMT)

By H Kasai, JT Allen, RM Mason, T Kamimura and Z Zhang


Background: Fibroblastic foci are characteristic features in lung parenchyma of patients with idiopathic pulmonary fibrosis (IPF). They comprise aggregates of mesenchymal cells which underlie sites of unresolved epithelial injury and are associated with progression of fibrosis. However, the cellular origins of these mesenchymal phenotypes remain unclear. We examined whether the potent fibrogenic cytokine TGF-β1 could induce epithelial mesenchymal transition (EMT) in the human alveolar epithelial cell line, A549, and investigated the signaling pathway of TGF-β1-mediated EMT.\ud \ud Methods: A549 cells were examined for evidence of EMT after treatment with TGF-β1. EMT was assessed by: morphology under phase-contrast microscopy; Western analysis of cell lysates for expression of mesenchymal phenotypic markers including fibronectin EDA (Fn-EDA), and expression of epithelial phenotypic markers including E-cadherin (E-cad). Markers of fibrogenesis, including collagens and connective tissue growth factor (CTGF) were also evaluated by measuring mRNA level using RT-PCR, and protein by immunofluorescence or Western blotting. Signaling pathways for EMT were characterized by Western analysis of cell lysates using monoclonal antibodies to detect phosphorylated Erk1/2 and Smad2 after TGF-β1 treatment in the presence or absence of MEK inhibitors. The role of Smad2 in TGF-β1-mediated EMT was investigated using siRNA.\ud \ud Results: The data showed that TGF-β1, but not TNF-α or IL-1β, induced A549 cells with an alveolar epithelial type II cell phenotype to undergo EMT in a time-and concentration-dependent manner. The process of EMT was accompanied by morphological alteration and expression of the fibroblast phenotypic markers Fn-EDA and vimentin, concomitant with a downregulation of the epithelial phenotype marker E-cad. Furthermore, cells that had undergone EMT showed enhanced expression of markers of fibrogenesis including collagens type I and III and CTGF. MMP-2 expression was also evidenced. TGF-β1-induced EMT occurred through phosphorylation of Smad2 and was inhibited by Smad2 gene silencing; MEK inhibitors failed to attenuate either EMT-associated Smad2 phosphorylation or the observed phenotypic changes.\ud \ud Conclusion: Our study shows that TGF-β1 induces A549 alveolar epithelial cells to undergo EMT via Smad2 activation. Our data support the concept of EMT in lung epithelial cells, and suggest the need for further studies to investigate the phenomenon

Topics: Q1, R1, QH301, health_and_wellbeing, other
Publisher: BioMed Central
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  1. a cytokine released by activated mononuclear cells, induces epithelial cell-myofibroblast transdifferentiation via Jak/Stat pathway
  2. (2001). A: Idiopathic pulmonary fibrosis: prevailing and evolving hypotheses about its pathogenesis and implications for therapy. Ann Intern Med
  3. (1997). Adenovectormediated Gene Transfer of Active Transforming
  4. (2003). Adenoviral gene transfer of connective tissue growth factor in the lung induces transient fibrosis. Am J Respir Crit Care Med
  5. (1989). AS: Collagen synthesis by normal and fibrotic human lung fibroblasts and the effect of transforming growth factor-beta. Am Rev Respir Dis
  6. (1998). Audus KL: Characterization of the A549 cell line as a type II pulmonary epithelial cell model for drug metabolism. Exp Cell Res
  7. (2000). Brigstock DR: Connective tissue growth factor: what's in a name? Mol Genet Metab doi
  8. (1999). Cadherins and tissue formation: integrating adhesion and signaling. Bioessays
  9. (2001). Cherniack RM: Idiopathic pulmonary fibrosis: relationship between histopathologic features and mortality. Am J Respir Crit Care Med
  10. (2005). Connective tissue growth factor (CTGF, CCN2) interacts with and activates the tyrosine kinase receptor TrkA. J Am Soc Nephrol doi
  11. (1997). Connective tissue growth factor: a mediator of TGF-beta action on fibroblasts. Cytokine Growth Factor Rev doi
  12. (1994). Derynck R: TGF-beta induced transdifferentiation of mammary epithelial cells to mesenchymal cells: involvement of type I receptors.
  13. (2001). Dissection of key events in tubular epithelial to myofibroblast transition and its implications in renal interstitial fibrosis.
  14. (2004). DW: Fibroblast growth factor-10 attenuates H2O2-induced alveolar epithelial cell DNA damage: role of MAPK activation and DNA repair.
  15. (2002). DW: Interleukin-1β induces human proximal tubule cell injury, α-smooth muscle actin expression and fibronectin production. Kidney Int
  16. (1999). Effect of adenovirus E1A on ICAM-1 promoter activity in human alveolar and bronchial epithelial cells. Gene Expr
  17. (2003). EG: Epithelial-mesenchymal transition and its implications for fibrosis.
  18. (1999). Enhanced insulin-like growth factor binding protein-related protein 2 (Connective tissue growth factor) expression in patients with idiopathic pulmonary fibrosis and pulmonary sarcoidosis. doi
  19. (2004). Epithelial to mesenchymal transition in renal fibrogenesis: pathologic significance, molecular mechanism, and therapeutic intervention.
  20. (1995). Factors influencing myofibroblast differentiation during wound healing and fibrosis. Cell Biol Int
  21. (1997). Feng XH: TGF-β receptor signaling. Biochim Biophys Acta
  22. (2003). G: Normal and pathologic soft tissue remodeling: role of the myofibroblast, with special emphasis on liver and kidney fibrosis. Lab Invest
  23. (1997). Gespach C: Evidence for a role of Rho-like GTPase and stress-activated protein kinase/ c-Jun-N-terminal kinase (SAPK/JNK) in transforming growth factorβ-mediated signaling.
  24. (1991). Greenberg AH: Increased production and immunohistochemical localization of transforming growth factor-beta in idiopathic pulmonary fibrosis.
  25. (2001). Hara N: Upregulation of Fas-signalling molecules in lung epithelial cells from patients with idiopathic pulmonary fibrosis. Eur Respir J
  26. (2005). HB: Role of reactive oxygen species in TGF-beta1-induced mitogen-activated protein kinase activation and epithelial-mesenchymal transition in renal tubular epitheliasl cells.
  27. (1999). Heldin CH, ten Dijke P: TGF-(beta) type I receptor/ALK-5 and Smad proteins mediate epithelial to mesenchymal transdifferentation in NMuMG breast epithelial cells.
  28. (2001). HL: Transforming growth factor-beta1 mediates epithelial to mesenchymal transdifferentiation through a RhoA-dependent mechanism. Mol Biol Cell
  29. (2001). Horie T: Transforming growth factor-β1 induces phenotypic modulation of human lung fibroblasts to myofibroblast through a cJun-NH2-terminal kinase-dependent pathway. Am J Respir Crit Care Med
  30. (2001). Hunninghake GW: Idiopathic pulmonary fibrosis.
  31. (2001). Interleukin-1 induces tubular epithelial-myofibroblast transdifferentiation through a transforming growth factorβ1-dependent mechanism in vitro.
  32. (1999). Intestinal subepithelial myofibroblasts.
  33. (1995). Isaacs WB: Chromosome 5 suppresses tumorigenicity of PC3 prostate cancer cells: correction with reexpression of alpha-catenin and restoration of E-cadherin function. Cancer Res
  34. (1988). Lazo JS: Alterations in pulmonary mRNA encoding procollagens, fibronectin, and transforming growth factor-β precedes bleomycin-induced pulmonary fibrosis in mice. J Pharmacol Exp Ther
  35. (2002). M: TGF-beta signaling in renal disease.
  36. (1998). Mooseker MS: Unconventional myosins in cell movement, membrane traffic, and signal transduction. Science
  37. (1999). MP: Factors produced by activated leukocytes alter renal epithelial cell differentiation. Kidney Int
  38. (2002). Neilson EG: Role of basic fibroblast growth factor-2 in epithelial-mesenchymal transformation. Kidney Int
  39. (2002). Pardo A: Idiopathic pulmonary fibrosis: an epithelial/ fibroblastic cross-talk disorder. Respir Res
  40. (2002). PJ: A new direction in the pathogenesis of idiopathic pulmonary fibrosis? Respir Res
  41. (2003). Re-evaluation of fibrogenic cytokines in lung fibrosis. Curr Pharm Des
  42. (2001). Regulation of the effects of TGF-beta 1 by activation of latent TGF-beta 1 and differential expression of TGF-beta receptors (T beta R-I and T beta R-II) in idiopathic pulmonary fibrosis. Thorax
  43. (2001). RM: Role of connective tissue growth factor in the pathogenesis of diabetic nephropathy.
  44. (2001). Sawai T: Type II alveolar epithelial cells and interstitial fibroblasts express connective tissue growth factor in IPF. Eur Respir J doi
  45. (1998). Smads and early developmental signaling by the TGFβ superfamily. Genes Dev
  46. (2002). Spiteri MA: Growth factors in idiopathic pulmonary fibrosis: relative roles. Respir Res
  47. (2004). Tang HF: TGF-beta1 induces alveolar epithelial to mesenchymal transition in vitro. Life Sci
  48. (1996). Umruh H: TGF-β1, but not TGF-β2 or TGF-β3, is differentially present in epithelial cells of advanced pulmonary fibrosis: an immunohistochemical study.
  49. (2004). West AB:Page 14 of 15 (page number not for citation purposes) activation. J Am Soc Nephrol
  50. (2005). Zhang Z: RhoGTPase activation is a key step in renal epithelial mesenchymal transdifferentiation.

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