The ROCK-Ezrin Signaling Pathway Mediates LPS-Induced Cytokine Production in A549 Cells

Abstract Background: Ezrin/radixin/moesin proteins (ERMs) are members of the protein 4.1 superfamily and function as linkers that connect the actin cytoskeleton to the plasma membrane of cells. ERMs also play critical role in the Lipopolysaccharide (LPS)-induced inflammatory response. However, the signaling mechanisms involved remain unclear. This study aims 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 A549 cells. Methods: Cultured A549 cells were treated with LPS. The expression and localization of ezrin in A549 cells were analyzed by Western bloting and immunoflurescence. The activation of RhoA/ROCK was assessed by Western bloting 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 using co-immunoprecipitation. The activation of nuclear factor-κB (NF-κB) and mitogen-activated protein kinase (MAPK) was measured with electrophoretic mobility shift assay and Western blotting. ELISA and Western bloting were performed to detect 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: Here, we show that 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 LPS induced the production of pro-inflammatory cytokines, and highlight the importance of the RhoA/ROCK-MyD88/IRAK1-ezrin/Syk axis. Data presented in this manuscript provide novel insights into the signaling pathways activated in A549 cells by LPS.