Flagellin and lipopolysaccharide up-regulation of IL-6 and CXCLi2 gene expression in chicken heterophils is mediated by ERK1/2-dependent activation of AP-1 and NF-κB signaling pathways

The Toll-like receptor agonists, flagellin (FLG) and lipopolysaccharide (LPS), stimulate chicken heterophils to induce the expression and secretion of pro-inflammatory cytokines by a mechanism involving the triggering of differential MEK-ERK signaling cascades. However, the translocation and activation of transcription factors potentially involved in the control of cytokine gene expression remains unknown. Herein, we examined the effects of FLG and LPS on the activation of the transcription factors NF-κB and AP-1 and their role in regulating heterophil activation leading to cytokine gene expression. Treatment of heterophils with either FLG or LPS induced a significant increase in DNA binding by the NF-κB family members p50, c-Rel, and RelB. Likewise, FLG and LPS induced a significant increase in DNA binding by the AP-1 family members c-Jun and JunD. The activation of both NF-κB and AP-1 was inhibited following treatment of heterophils with specific inhibitors of ERK1/2 (U0126 and PD098059), NF-κB (Bay 11-7086 and the cell-permeable NF-κB peptide, SN50), and AP-1 (Tanshinone IIA). Likewise, the up-regulation of gene expression of the pro-inflammatory cytokine, IL-6, and the inflammatory chemokine, CXCLi2, were inhibited when heterophils were treated with the same specific inhibitors. Taken together these data demonstrate that FLG and LPS stimulate the up-regulation of expression of IL-6 and CXCLi2 through an ERK1/2-dependent activation of both NF-κB and AP-1.