Airway epithelial cells express toll-like receptor 3 and its ligand stimulates inflammatory cytokines and chemokines through NF-kB and IRF3

Abstract

Rationale Double-stranded RNA (dsRNA) is known to be synthesized during replication of many viruses and a ligand of Toll-like receptor 3. We hypothesized that dsRNA may mimic viral infection and induce cytokines/chemokines expression in airway epithelial cells and next focused our studies on the molecular mechanisms. Methods Airway epithelial cell line BEAS-2B and normal human bronchial epithelial cells were used in vitro study. Levels of mRNA and protein expression were determined with real time-PCR and ELISA. Mechanisms of transcriptional regulation were assessed by electrophoretic mobility shift assay, pull-down western blot assay and dual luciferase assay using promoter-luciferase reporter plasmids. Results Airway epithelial cell lines and normal human bronchial epithelial cells constitutively expressed Toll-like receptor 3. Its ligand dsRNA upregulated RANTES, IP-10, IL-8, IL-12 and IL-1b mRNA and protein synthesis in the airway epithelial cells. Activation of NF-kB and IFN regulatory factor 3 (IRF3) by dsRNA was confirmed by nuclear protein binding to a DNA probe. While activity of the promoter which consists of binding sites for these two transcription factors was increased by dsRNA, other promoter such as for AP-1, CREB and SRE, was not activated. RANTES promoter was also activated by dsRNA and this activity was inhibited in the promoter which were mutated at the sites for NF-kB and/or IRF. Conclusions These results imply that dsRNA activates NF-kB and IRF3 and these transcription factors activate transcription of the RANTES and other inflammatory cytokines/chemokines promoter.