Smad7 and Smad6 Differentially Modulate Transforming Growth Factor β-induced Inhibition of Embryonic Lung Morphogenesis

Jingsong Zhao,Wei Shi,Hui Chen,David Warburton

doi:10.1074/jbc.m002433200

Jingsong Zhao, Wei Shi + Show 2 more

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https://doi.org/10.1074/jbc.m002433200

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Abstract

Transforming growth factors beta (TGF-beta) are known negative regulators of lung development, and excessive TGF-beta production has been noted in pulmonary hypoplasia associated with lung fibrosis. Inhibitory Smad7 was recently identified to antagonize TGF-beta family signaling by interfering with the activation of TGF-beta signal-transducing Smad complexes. To investigate whether Smad7 can regulate TGF-beta-induced inhibition of lung morphogenesis, ectopic overexpression of Smad7 was introduced into embryonic mouse lungs in culture using a recombinant adenovirus containing Smad7 cDNA. Although exogenous TGF-beta efficiently reduced epithelial lung branching morphogenesis in control virus-infected lung culture, TGF-beta-induced branching inhibition was abolished after epithelial transfer of the Smad7 gene into lungs in culture. Smad7 also prevented TGF-beta-mediated down-regulation of surfactant protein C gene expression, a marker of bronchial epithelial differentiation, in cultured embryonic lungs. Moreover, we found that Smad7 transgene expression blocked Smad2 phosphorylation induced by exogenous TGF-beta ligand in lung culture, indicating that Smad7 exerts its inhibitory effect on both lung growth and epithelial cell differentiation through modulation of TGF-beta pathway-restricted Smad activity. However, the above anti-TGF-beta signal transduction effects were not observed in cultured embryonic lungs with Smad6 adenoviral gene transfer, suggesting that Smad7 and Smad6 differentially regulate TGF-beta signaling in developing lungs. Our data therefore provide direct evidence that Smad7, but not Smad6, prevents TGF-beta-mediated inhibition of both lung branching morphogenesis and cytodifferentiation, establishing the mechanistic basis for Smad7 as a novel target to ameliorate aberrant TGF-beta signaling during lung development, injury, and repair.

Highlights

Transforming growth factor ␤ (TGF-␤)1 family members elicit a diverse range of cellular responses including cell proliferation, differentiation, migration, organization, and apoptosis [1]
We have recently shown that Smad7 gene is predominantly expressed in distal airway epithelium and that abrogation of endogenous Smad7 gene expression using a Smad7 antisense oligodeoxynucleotide increased the TGF-␤-mediated negative effect on embryonic mouse lung branching morphogenesis in culture [19]
Overexpression of Smad7 or Smad6 Transgene in Embryonic Mouse Lungs in Culture—To evaluate the biological function of inhibitory Smads during early lung development, we began our study by assessing the adenoviruses expressing full-length murine Smad7 (AdSmad7) and AdSmad6 for their ability to overexpress the corresponding transgenes in embryonic mouse lungs in culture

Summary

Introduction

Transforming growth factor ␤ (TGF-␤) family members elicit a diverse range of cellular responses including cell proliferation, differentiation, migration, organization, and apoptosis [1]. The TGF-␤-signaling pathway has been implicated in the normal temporo-spatial pattern of lung morphogenesis and concomitant pulmonary-specific gene expression. Both addition of exogenous TGF-␤1 and TGF-␤2 to embryonic mouse lungs in culture and organ-specific overexpression of TGF-␤1 in transgenic mice bearing a chimeric surfactant protein-C (SP-C) promoter-directed TGF-␤1 expression construct result in hypoplastic phenotypes [7,8,9], indicating that exogenous TGF-␤ ligands exert negative regulatory influences on lung development. We have recently shown that Smad gene is predominantly expressed in distal airway epithelium and that abrogation of endogenous Smad gene expression using a Smad antisense oligodeoxynucleotide increased the TGF-␤-mediated negative effect on embryonic mouse lung branching morphogenesis in culture [19]. Smad appears to be a novel molecule to reduce excessive TGF-␤ signaling during lung morphogenesis, development, injury, and repair

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