The association of the cytoplasmic domains of interleukin 4 receptor alpha and interleukin 13 receptor alpha 2 regulates interleukin 4 signaling.

Interleukin-4 (IL-4) and Interleukin-13 (IL-13), key cytokines in the pathogenesis of allergic inflammatory disease, mediate their effects via a receptor composed of IL-13Rα1 and IL-4Rα. A third (decoy) receptor called IL-13Rα2 regulates interleukin signaling through this receptor complex. We employed a variety of biophysical and cell-based techniques to decipher the role of this decoy receptor in mediating IL-4 signaling though the IL-4Rα-IL-13Rα1 receptor complex. Surface plasmon resonance (SPR) analysis showed that IL-13Rα2 does not bind IL-4, and does not affect binding of IL-4 to IL-4Rα. These results indicate that the extracellular domains of IL-4Rα and IL-13Rα2 are not involved in the regulation of IL-4 signaling by IL-13Rα2. We next used a two-hybrid system to show that the cytoplasmic domains of IL-4Rα and IL-13Rα2 interact, and that the secondary structure of the IL-13Rα2 intracellular domain is critical for this interaction. The cellular relevance of this interaction was next investigated. BEAS-2B bronchial epithelial cells that stably express full length IL-13Rα2, or IL-13Rα2 lacking its cytoplasmic domain, were established. Over expression of IL-13Rα2 attenuated IL-4 and IL-13 mediated STAT6 phosphorylation. IL-13Rα2 lacking its cytoplasmic domain continued to attenuate IL-13-mediated signaling, but had no effect on IL-4-mediated STAT6 signaling. Our results suggest that the physical interaction between the cytoplasmic domains of IL-13Rα2 and IL-4Rα regulates IL-4 signaling through the IL-4Rα-IL-13Rα1 receptor complex.

The innate antiviral response upregulates IL-13 receptor α2 in bronchial fibroblasts.

BACKGROUND: IL-13 is key mediator of allergic inflammation in asthmatic patients. We have previously shown that the decoy receptor IL-13 receptor (IL-13R) α2 attenuates responses of fibroblasts to IL-13. Because the expression of IL-13Rα2 can be regulated by IFN-γ, a type II interferon, we hypothesized that innate antiviral responses characterized by type I interferon expression can also induce IL-13Rα2 expression. OBJECTIVE: We sought to induce an innate antiviral response in primary fibroblasts using exposure to double-stranded RNA (dsRNA) and to examine the expression and function of IL-13Rα2. METHODS: Primary human fibroblasts were cultured from endobronchial biopsy specimens obtained from healthy or asthmatic volunteers and challenged with dsRNA. Upregulation of IL-13Rα2 mRNA was measured by using real-time quantitative PCR, and cell-surface IL-13Rα2 protein expression was measured by using fluorescence-activated cell sorting. Eotaxin release was determined by means of ELISA. RESULTS: Direct treatment with IFN-ß led to an upregulation of IL-13Rα2. Exposure to dsRNA rapidly induced IFN-ß mRNA in fibroblasts, and this was followed by significant induction of IL-13Rα2 mRNA and cell-surface protein expression, which was dependent on de novo protein synthesis. A neutralizing antibody to the IFN-α/ß receptor blocked cell-surface expression of IL-13Rα2 in the presence of dsRNA. Pretreatment of fibroblasts with dsRNA led to attenuation of IL-13-stimulated eotaxin production. However, the presence of an IL-13Rα2 neutralizing antibody restored IL-13-stimulated eotaxin production in dsRNA-treated cells. CONCLUSION: IFN-ß induces IL-13Rα2 expression, leading to a consequential suppression of responsiveness to IL-13. These data suggest cross-talk between TH1 and TH2 pathways and point to an immunomodulatory role for IL-13Rα2 in human bronchial fibroblasts during viral infection.