The ROCK-ezrin signaling pathway mediates LPS-induced cytokine production in pulmonary alveolar epithelial cells

Abstract

Abstract Background Ezrin/radixin/moesin (ERM) proteins are members of the protein 4.1 superfamily and function as linkers that connect the actin cytoskeleton to the plasma membrane of cells. ERM also play critical role in the Lipopolysaccharide (LPS)-induced inflammatory response. However, the signaling mechanisms involved in this process remain unclear. In this study, we aimed to investigate the potential role of the rho-associated coiled-coil containing protein kinase (ROCK) pathway in LPS-induced ezrin phosphorylation and cytokine production in pulmonary alveolar epithelial cells. Methods Cultured A549 and HPAEpiC cells were treated with LPS. The expression and localization of ezrin in A549 and HPAEpiC cells were then analyzed by western blotting and immunoflurescence. Activation of RhoA/ROCK was assessed by western blotting and RhoA activity assays. The interaction of ezrin with Syk and myeloid differentiation factor 88 (MyD88)/IL-1R-associated kinase 1 (IRAK-1) was investigated by co-immunoprecipitation. The activation of nuclear factor-κB (NF-κB) and mitogen-activated protein kinase (MAPK) was measured with electrophoretic mobility shift assays and by western blotting. ELISA and western blotting were performed to detect the levels of tumor necrosis factor-α (TNF-α), interleukin-1β (IL-1β), and high mobility group box 1 protein (HMGB1) release into the culture supernatant, and cellular HMGB1 levels. Results LPS induced ezrin phosphorylation in a concentration- and time-dependent manner. The blockade of RhoA/ROCK inhibited LPS-induced ezrin phosphorylation and its translocation from the cytoplasm to the cell membrane. Co-immunoprecipitation assays further revealed that ezrin associated with Syk constitutively, but only associated with MyD88/IRAK-1 upon LPS challenge. Moreover, LPS-induced p38 and nuclear NF-κB activation was found to be ezrin dependent. The suppression of ezrin by siRNA or the blockade of ROCK activation with Y-27632 reduced the production of TNF-α, IL-1β, and HMGB1 in response to LPS. Conclusions Our findings reveal a novel regulatory mechanism involving ezrin in the LPS-induced production of pro-inflammatory cytokines, and highlight the importance of the RhoA/ROCK-ezrin/Syk-MyD88/IRAK1 axis. Data presented in this manuscript provide novel insights into the signaling pathways activated in pulmonary alveolar epithelial cells by LPS.