Analysis of the structure of interleukin 1 receptor and the mechanism of IL-1 signal transduction

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The structural and functional relaionship of the intracellular portion of mouse interleukin 1 receptor (IL-1R)type I was examined with regard to activation of the human IL-8 gene in the Jurkat T cell line. We found that C-terminal boundary for the function of the receptor is localized between 28-42 amino acids from C-terminal end, and that the large region of IL-1R cytoplasmic portion is required for the function to transmit IL-1 signal. In addition, the cytoplasmic region of IL-1R possess the segment homologous to gp130, beta chain of IL-6R, including box 1 and 2-like elements, and mutations within the gp130 homologous segments, abolishied the capacity to induce IL-8 gene expression, suggesting similar structural requirements in the cytoplasmic portion of several cytokine receptors.To investigate the molecular mechanism of IL-1 reaceptor mediated signal transduction, we examined the IL-1 responsive elements on the 5'-flanking region of the human IL-8 gene. We found that the three cis elements on the IL-8 promoter, NFkB, C/EBP and AP-1 binding sites are required for IL-1 induced IL-8 gene activation. Interestingly, in fibrosarcoma 8387 cells, NFkB and C/EBP binding sites are necessary for the responsiveness to IL-1, whereas in gastric cancer derived MKN45 cells, AP-1 and NFkB binding sites, are indispensable, indicationg that the relative importance of these three sites is different among cell types. In addition synergistic action between TNF and IFNgamma was observed for the IL-8 production and the activation of IL-8 promoter. Gel retardation analysis revealed that TNF and IFNgamma synergistically induced the activation of NFkB binding activity, suggesting that IFNgamma enhance the activation of IL-8 gene by TNF through augmenting NFkB activation.