| Research Abstract |
Our identified limitin has a sequence homology with type I IFNs and displays antiviral activity against several viruses. In addition, it can bind to IFN-α/βR and induces some effectors as IFN-α and IFN-β. Based on these facts, limitin has been considered as a novel type I IFN with the designation of IFN-ζ by the Nomenclature Committee of the International Society for Interferon and Cytokine Research. Both IFN-ζ/limitin and IFN-α were titrated with a cytopathic effect dye binding assay in encephalo myocarditis virus-infected L929 cells. Half-maximal protection was achieved with 30 pg/ml of IFN-ζ/limitin and with 30-300 pg/ml of several subtypes of IFN-αs. These titrated IFNs were used for point-by-point comparison of their biological activities and signals. IFN-ζ/limitin showed antitumor, immunomodulatory, and antiviral activities as strong as IFN-α. However, IFN-ζ/limitin did not suppress CFU-GM or BFU-E colony formation while IFN-α did. Much higher concentrations of IFN-ζ/limitin than
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IFN-α were required for the suppression of CFU-IL7 and CFU-Meg colony formation. Similarly, approximately 30% of CFU-GM and 50% of BFU-E in bone marrow were reduced when 4,000 international unit (IU)/body/day of IFN-α was injected, while there was no influence on these progenitors even when IFN-ζ/limitin was injected at 40,000 IU/body/day. With regard to signaling, similar signaling molecules are used between IFN-ζ/limitin and IFN-α, but there are some differences. In fibroblasts, IRF-1-dependent pathway is more critical for IFN-ζ/limitin than IFN-α to induce antiviral state and to induce ISRE promoter activity. In addition, higher dose of IFN-ζ/limitin is required for the induction of Daxx in megakaryocytes than IFN-α. We also analyzed a role of Daxx in apoptosis, in addition, identified DMAP1 and TSG101 as novel Daxx-associated proteins. As described above, we have clarified characters of IFN-ζ/limitin in biological activities and signaling. To our regret, we could not isolate the human homologue of IFN-ζ/limitin. To make an engineered cytokine with some features of IFN-ζ/limitin, we have constructed IFN-a cDNA with mutations based on the differences of sequence between IFN-ζ/limitin and IFN-α. Less
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