Induction of a Mesenchymal Expression Program in Lung Epithelial Cells by Wingless Protein (Wnt)/β-Catenin Requires the Presence of c-Jun N-Terminal Kinase–1 (JNK1)

Abstract

Recent studies suggest the importance of the transition of airway epithelial cells (EMT) in pulmonary fibrosis, and also indicate a role for Wingless protein (Wnt)/b-catenin signaling in idiopathic pulmonary fibrosis. We investigated the possible role of the Wnt signaling pathway in inducing EMT in lung epithelial cells, and sought to unravel the role of c-Jun-N-terminal-kinase-1 (JNK1). The exposure of C10 lung epithelial cells or primary mouse tracheal epithelial cells (MTECs) to Wnt3a resulted in increases in JNK phosphorylation and nuclear b-catenin content. Because the role of b-catenin as a transcriptional coactivator is well established, we investigated T-cell factor/lymphocyteenhancement factor (TCF/LEF) transcriptional activity in C10 lung epithelial cells after the activation of Wnt. TCF/LEF transcriptional activity was enhanced after the activation of Wnt, and this increase in TCF/LEF transcriptional activity was diminished after the small interfering (si)RNA-mediated ablation of JNK. The activation of the Wnt pathway by Wnt3a, or the expression of either wild-type or constitutively active b-catenin (S37A), led to the activation of an EMT transcriptome, manifested by the increased mRNA expression of CArG box-binding factor-A, fibroblast-specific protein (FSP)-1, a-smooth muscle actin (a-SMA), and vimentin, increases in the content of a-SMA and FSP1, and the concomitant loss of zona occludens-1. The siRNA-mediated ablation of b-catenin substantially decreased Wnt3a-induced EMT. The siRNA ablation of JNK1 largely abolished Wnt3a, b-catenin, and b-catenin S37a-induced EMT. In MTECs lacking Jnk1, Wnt3a-induced increases in nuclear b-catenin, EMT transcriptome, and the content of a-SMA or FSP1 were substantially diminished. These data show that the activation of the Wnt signaling pathway is capable of inducing an EMT program in lung epithelial cells through b-catenin, and that this process is controlled by JNK1.Keywords: lung; epithelium; Wnt3a; fibrosis; epithelial to mesenchymal transitionThe development of fibrosis represents an important feature of pulmonary remodeling, and the critical role of epithelial cells in fibrogenesis is emerging. Studies from our laboratory identified a critical role for c-Jun-N-terminal-kinase-1 (JNK1) in augmenting the profibrotic effects of TGF-b1, in association with the causation of a mesenchymal transition of airway epithelialcells (EMT) (1). EMT is an important process during embryonic development, tumor progression, and fibrotic tissue repair after injury (2). We recently demonstrated that JNK1-induced phosphorylation in the linker domain of SMAD3 enhanced its ability to induce an EMT transcriptome. Consequently, JNK1-dependent, TGF-b1-induced EMT was greatly diminished in epithelial cells expressing a variant of SMAD3 refractory to phosphorylation in the linker domain (3).Recent studies indicated a role of b-catenin signaling in the induction of EMT. Moreover, the Wingless protein (Wnt)/ b-catenin axis was recently implicated to play a role in the development of idio...

Airway Epithelial Barrier Dysfunction in Chronic Obstructive Pulmonary Disease: Role of Cigarette Smoke Exposure

“…Similarly, cigarette smoke has been shown to induce EMT in alveolar epithelial cells (61)(62)(63), which may impair alveolar re-epithelization upon damage (64,65), thus also having implications for the development of emphysema. Cigarette smoke affects WNT/b-catenin signaling and EMT in alveolar epithelial cells (66,67), although these studies show an inhibition of b-catenin signaling, which is not in line with previous studies showing the induction of EMT (68,69).…”

β-Catenin in the Alveolar Epithelium Protects from Lung Fibrosis after Intratracheal Bleomycin

“…Even with siRNA knockdown of b-catenin, TGFb1 exposure still reduced E-cadherin and zonula occludens 1 (ZO-1) expression and increased S100A4 expression. In contrast, TGFb1-induced expression of aSMA was attenuated with siRNA knockdown of b-catenin ( Figure E14), complementing recent studies by other investigators (26,27). Confocal immunofluorescence on lung sections from cell fate mapping mice revealed that total S100A41 and EMT-derived bgal1/S100A41 lung fibroblasts increased at 2 weeks after bleomycin ( Figure E15A).…”

Adipose tissue fibrosis in human cancer cachexia: the role of TGFβ pathway

“…Mechanical stress caused by excessive contractility leads to an aberrant wound-healing response and fibrosis [33]. In epithelial-mesenchymal cell transition (EMT), which occurs in pulmonary fibrosis, is seen the concomitant increased amounts of mRNA levels of α-SMA, FSP1 and vimentin [55]. According with this, our study showed enhanced immunolabeling of α-SMA in the subcutaneous AT of cancer cachectic group, as well as increased mRNA expression of FSP1.…”