Β-catenin regulates NF-κB activity and inflammatory cytokine expression in bronchial epithelial cells treated with lipopolysaccharide.

Abstract

In the present study, we demonstrate that lipopolysaccharide (LPS) induces the expression of inflammatory cytokines, including interleukin (IL)-6, IL-8, IL-1β, tumor necrosis factor (TNF)-α and monocyte chemoattractant protein (MCP)-1 in BEAS-2B human bronchial epithelial cells in a dose- and time-dependent manner. This increase was accompanied by an increased activity of nuclear factor (NF)‑κB. When the expression of β-catenin was analyzed following treatment with LPS, the mRNA level was unaltered; however, the β-catenin protein levels increased with a decrease in phosphorylation at the serine 33/37 residues. Nuclear β-catenin protein levels also increased along with the reporter activity of a β-catenin-responsive TOPFlash vector. To elucidate the regulatory role of β-catenin in the LPS-induced inflammatory response of bronchial epithelial cells, β-catenin production was knocked down using siRNA. Our results revealed that β-catenin protein levels and TOPFlash vector reporter activity were reduced to basal levels by siRNA transfection. In this experimental condition, NF-κB activity, measured by enzyme-linked immunosorbent assay (ELISA), electrophoretic mobility shift assay (EMSA) and an NF-κB responsive reporter assay, was reduced to basal levels. Similarly, LPS-induced inflammatory cytokine expression was reduced almost to basal levels following transfection with β-catenin siRNA. These results demonstrate that β-catenin positively regulates NF-κB activity, as well as the expression of inflammatory cytokines in the inflammatory response of LPS-treated bronchial epithelial cells.