Epithelial cell α3β1 integrin links β-catenin and Smad signaling to promote myofibroblast formation and pulmonary fibrosis

Pulmonary and Critical Care Division, Department of Medicine, and Cardiovascular Research Institute, UCSF, San Francisco, CA 94143, USA.
Journal of Clinical Investigation (Impact Factor: 13.22). 01/2009; 119(1):213-24. DOI: 10.1172/JCI36940
Source: PubMed


Pulmonary fibrosis, in particular idiopathic pulmonary fibrosis (IPF), results from aberrant wound healing and scarification. One population of fibroblasts involved in the fibrotic process is thought to originate from lung epithelial cells via epithelial-mesenchymal transition (EMT). Indeed, alveolar epithelial cells (AECs) undergo EMT in vivo during experimental fibrosis and ex vivo in response to TGF-beta1. As the ECM critically regulates AEC responses to TGF-beta1, we explored the role of the prominent epithelial integrin alpha3beta1 in experimental fibrosis by generating mice with lung epithelial cell-specific loss of alpha3 integrin expression. These mice had a normal acute response to bleomycin injury, but they exhibited markedly decreased accumulation of lung myofibroblasts and type I collagen and did not progress to fibrosis. Signaling through beta-catenin has been implicated in EMT; we found that in primary AECs, alpha3 integrin was required for beta-catenin phosphorylation at tyrosine residue 654 (Y654), formation of the pY654-beta-catenin/pSmad2 complex, and initiation of EMT, both in vitro and in vivo during the fibrotic phase following bleomycin injury. Finally, analysis of lung tissue from IPF patients revealed the presence of pY654-beta-catenin/pSmad2 complexes and showed accumulation of pY654-beta-catenin in myofibroblasts. These findings demonstrate epithelial integrin-dependent profibrotic crosstalk between beta-catenin and Smad signaling and support the hypothesis that EMT is an important contributor to pathologic fibrosis.

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Available from: Paul J Wolters, Dec 09, 2014
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    • "EMT is triggered by a variety of soluble factors including epidermal growth factor (EGF), hepatocyte growth factor (HGF), fibroblast growth factor (FGF), and TGFβ [55,78-85]. Other stimuli, such as hypoxia [86,87] and adhesion to ECM components can also induce EMT [69,88,89]. TGFβ, a ubiquitously expressed cytokine, is a potent inducer of EMT and is regarded as a key mediator of wound healing [90,91], fibrosis [92,93], and cancer [94,95]. "
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