Polyinosinic:polycytidylic acid causes epithelial-mesenchymal transition via BAFF expression in Beas-2B human...

The bronchial epithelium acts not only as the primary physical barrier but also as an active sensor that responds to exogenous materials such as bacteria and viruses, by producing various cytokines including B-cell activating factor (BAFF). Although BAFF is a well-known protein in B-cell functions, its role in bronchial cell function remains undefined. Polyinosinic-polycytidylic acid (Poly (I:C)), a synthetic double-stranded RNA, serves as a model for viral infection that binds to toll-like receptor (TLR) 3 to trigger intracellular signal pathways. In this study, we investigated the effect of Poly (I:C)-induced BAFF expression on airway cell migration using Beas-2B human bronchial epithelial cells. Poly (I:C) increased BAFF expression and cell migration, along with the increased expression of N-cadherin, Vimentin and Slug (SNAI2), which are three primary markers for epithelial-mesenchymal transition (EMT). Cell migration was attenuated by small interfering RNA (siRNA) against BAFF, which also inhibited the expression of these EMT markers. Phosphorylation of c-Jun N-terminal kinase (JNK) was enhanced by Poly (I:C) and inhibited by SP600125, JNK inhibitor, leading to a decreased expression of BAFF and aforementioned EMT markers. Poly (I:C) increased reactive oxygen species (ROS), resulting in a ROS-dependent up-regulation of antioxidants (Catalase, superoxide dismutase (SOD)1 and heme oxygenase (HMOX)1) and Nrf2. Pre-treatment with N-acetylcysteine (NAC), ROS scavenger, inhibited Nrf2 activation and JNK phosphorylation. The increase in Nrf2 levels induced by Poly (I:C) was also attenuated by SP600125. Additionally, while NAC treatment inhibited BAFF expression, it caused little change in the expression of the three EMT markers. Increased BAFF expression was confirmed by Nrf2 binding to the BAFF promoter or an increase in the luciferase activity of BAFF promoter co-transfected with Nrf2 plasmids. Treatment with recombinant BAFF protein also increased cell migration and EMT marker expression. Taken together, our results demonstrate that Poly (I:C) promotes a regenerative migration of bronchial epithelial cells by inducing BAFF expression through the ROS-dependent JNK-Nrf2 signaling axis.