The double-stranded RNA induces IL-33 expression through activation of EGFR, ERK, p38 and TBK-1 in normal human epidermal keratinocytes

Abstract

The epidermis is the first line of innate host defense against external stimulus, which is mainly composed of keratinocyte. IL-33 is a member of IL-1 cytokine family that constitutively expressed in endothelial cells and epithelial cells of tissues. Viral infection is known to induce Toll-like receptor 3 (TLR3) activation through double-stranded RNA (dsRNA). We have previously reported that ultraviolet (UV) B irradiation induced IL-33 expression in normal human epidermal keratinocytes (NHEKs). We aimed to investigate whether TLR3 activation induces IL-33 expression in normal human epidermal keratinocytes and examine the mechanism of its induction. We also tried to investigate if the IL-33 which was induced by ultraviolet (UV) B irradiation can be suppressed by blocking TLR3 signal. NHEKs were stimulated with Poly I:C, the ligand for TLR3. The expression levels of mRNA for IL-33 and IFN-beta were assayed using quantitative real-time PCR. The expression of IL-33 was induced in NHEKs with the stimulation of Poly I:C and UVB which both were suppressed by the addition of TLR3 inhibitor. The induction of IL-33 by Poly I:C was dose- and time-dependent. The expression of IL-33 stimulated by Poly I:C peaked at 8 h, was suppressed at 24 through 48 h. IFN-beta were strongly induced by Poly I:C, which peaked at 4 h. We used anti-IFN-beta antibody aiming at blocking each signal, but the induction of IL-33 was not suppressed. Inhibitors for phosphorylation of extracellular signal regulated kinase (ERK), epidermal growth factor receptor (EGFR), p38 and TANK-binding kinase 1 (TBK-1) inhibited the induction of IL-33 efficiently. These results suggested that IL33 was induced through EGFR, ERK, p38, TBK-1 activation, but not through the production of IFNs by Poly I:C.