RON Receptor Tyrosine Kinase Regulates Epithelial Mesenchymal Transition and the Expression of Pro-Fibrotic Markers via Src/Smad Signaling in HK-2 and NRK49F Cells

Receptor tyrosine kinases (RTKs) play important roles in the pathogenic processes of kidney fibrosis. However, the pathophysiological roles of recepteur d’origine nantais (RON), one of the receptor tyrosine kinases, have not yet been defined. We investigated whether the activation or sequence-specific small interfering RNA (siRNA) suppression of RON could regulate epithelial mesenchymal transition (EMT) and the expression of pro-fibrotic markers, and its underlying molecular mechanisms. Stable cell lines and transient transfection for RON and the transfected cells of siRNA for RON were developed to investigate the molecular mechanisms in human kidney proximal tubular epithelial (HK-2) and interstitial fibroblasts (NRK49F) cells. RON overexpression induced EMT and increased expression of fibrosis-related proteins such as N-cadherin, vimentin, transforming growth factor-β (TGFβ), αSMA, and fibronectin in HK-2 and NRK49F cells. RON overexpression increased various RTKs and the phosphorylation of Src (Y416) and Smad, while inhibition of RON by siRNA attenuated the expression of EMT- and fibrosis-related proteins and decreased RTKs such as insulin-like growth factor receptor (IGFR), fibroblast growth factor receptor 1 (FGFR1), vascular endothelial growth factor receptor (VEGFR), and platelet-derived growth factor receptor (PDGFR), as well as the phosphorylation of Src and Smad pathways. siRNA silencing of Src also attenuated the expression of IGFR, FGFR1, VEGFR, and PDGFR. Inhibition of RON can exert an anti-fibrotic effect by the inhibition of EMT and other RTKs through control of Src and Smad pathways in HK-2 and NRK49F cells.