| First Author | Watanabe-Takano H | Year | 2015 |
| Journal | PLoS One | Volume | 10 |
| Issue | 5 | Pages | e0127888 |
| PubMed ID | 25996975 | Mgi Jnum | J:235411 |
| Mgi Id | MGI:5796248 | Doi | 10.1371/journal.pone.0127888 |
| Citation | Watanabe-Takano H, et al. (2015) DA-Raf-Mediated Suppression of the Ras--ERK Pathway Is Essential for TGF-beta1-Induced Epithelial-Mesenchymal Transition in Alveolar Epithelial Type 2 Cells. PLoS One 10(5):e0127888 |
| abstractText | Myofibroblasts play critical roles in the development of idiopathic pulmonary fibrosis by depositing components of extracellular matrix. One source of lung myofibroblasts is thought to be alveolar epithelial type 2 cells that undergo epithelial-mesenchymal transition (EMT). Rat RLE-6TN alveolar epithelial type 2 cells treated with transforming growth factor-beta1 (TGF-beta1) are converted into myofibroblasts through EMT. TGF-beta induces both canonical Smad signaling and non-canonical signaling, including the Ras-induced ERK pathway (Raf-MEK-ERK). However, the signaling mechanisms regulating TGF-beta1-induced EMT are not fully understood. Here, we show that the Ras-ERK pathway negatively regulates TGF-beta1-induced EMT in RLE-6TN cells and that DA-Raf1 (DA-Raf), a splicing isoform of A-Raf and a dominant-negative antagonist of the Ras-ERK pathway, plays an essential role in EMT. Stimulation of the cells with fibroblast growth factor 2 (FGF2), which activated the ERK pathway, prominently suppressed TGF-beta1-induced EMT. An inhibitor of MEK, but not an inhibitor of phosphatidylinositol 3-kinase, rescued the TGF-beta1-treated cells from the suppression of EMT by FGF2. Overexpression of a constitutively active mutant of a component of the Ras-ERK pathway, i.e., H-Ras, B-Raf, or MEK1, interfered with EMT. Knockdown of DA-Raf expression with siRNAs facilitated the activity of MEK and ERK, which were only weakly and transiently activated by TGF-beta1. Although DA-Raf knockdown abrogated TGF-beta1-induced EMT, the abrogation of EMT was reversed by the addition of the MEK inhibitor. Furthermore, DA-Raf knockdown impaired the TGF-beta1-induced nuclear translocation of Smad2, which mediates the transcription required for EMT. These results imply that intrinsic DA-Raf exerts essential functions for EMT by antagonizing the TGF-beta1-induced Ras-ERK pathway in RLE-6TN cells. |
