Cigarette smoke-induced EGFR activation promotes epithelial mesenchymal migration of human retinal pigment epithelial cells through regulation of the FAK-mediated Syk/Src pathway.

Epithelial-mesenchymal transition (EMT) of retinal pigment epithelial (RPE) cells is inevitable change of age­related macular degeneration (AMD). Smoking is a major risk factor for the development of EMT in several diseases, including lung cancer. Cigarette smoke­induced stress promotes the production of epidermal growth factor (EGF) in RPE cells. However, the underlying signaling pathways induced by aberrant EGF receptor (EGFR) expression in cigarette smoke-exposed RPE cells remain largely unknown. In the present study, the morphological transformation and production of EMT-associated cytokines were investigated to analyze the effect of smoking on the retina. Furthermore, EGF­treated or cigarette smoke­exposed RPE cells, as well as the downstream targets of EGFR, were investigated to identify the key molecules involved in EMT of cigarette smoke­stimulated RPE cells via immunoblotting. Exposure of RPE cells to cigarette smoke extract (CSE) induced secretion of VEGF and TGF­ß1, and increased the expression of EMT markers. CSE­mediated focal adhesion kinase (FAK) activation resulted in the phosphorylation and activation of spleen associated tyrosine kinase (Syk)/Src proto­oncogene, non­receptor tyrosine kinase (Src), leading to migration and invasion of RPE cells. Knockdown of FAK or pharmacological inhibition of Syk/Src abrogated CSE­mediated VEGF and TGF­ß1 production and blocked the phosphorylation of Smad2/3 in CSE­stimulated RPE cells. Erlotinib (an EGFR inhibitor) suppressed EGF and CSE­mediated switch from an epithelial to mesenchymal phenotype. Baicalein, an inhi-bitor of 12/15­lipooxygenase, also efficiently suppressed CSE­induced EMT processes by inhibiting EGFR­associated downstream signaling transduction. The results identified a novel signaling pathway mediated by EGFR in CSE­activated RPE cells, and suggest baicalein as a potential new therapeutic drug for CSE­associated retinopathy.