| Research Abstract |
We analyzed molecular functions, mechanisms for transcriptional regulation, and mechanisms for stimuli-specific induction of IκB-ζ, which function in both acceleration and inhibition of transcription of genes on inflammation. Firstly, we identified a nuclear localization signal in a region of amino acids 153-157 of IκB-ζ and a domain with transcriptional activation activity in a region of amino acids 329-402. Furthermore, we found that overexpression of IκB-ζ resulted in inhibition of tumor necrosis factor (TNF)-α production and acceleration of interleukin (IL)-6 production, on transcriptional level, upon stimulation with lipopolysaccharide (LPS). Analyses on IκB-ζ gene-disrupted mice revealed that IκB-ζ-deficient macrophages produced normal levels of TNF-α and nitric oxide in response to LPS, but IL-6 production was abolished, and that, in vivo, IL-12 production upon treatment with LPS was impaired whereas TNF-α production was strongly augmented. Secondly, promoter analyses of genes whose transcription is accelerated by IκB-ζ showed that NF-κB binding sites in the promoter is essential for the IκB-ζ-mediated transcriptional activation, but not sufficient and another cis-element is required for the activation. Thus, the presence of the cis-element determines the function of IκB-ζ on each promoter. Thirdly, regarding the mechanisms for stimuli-specific induction of IκB-ζ, we found that stability of IκB-ζ mRNA is strongly up-regulated upon stimulation with LPS or IL- 1β, but not with TNF-α. Furthermore, we found that a sequence in the 3'-untranslated region of IκB-ζ mRNA determines the stimuli-specific induction of IκB-ζ by post-transcriptional level. Therefore, IκB-ζ is one of key players in regulation of inflammatory responses, which is specifically induced upon stimulation of innate immunity, and is essential for the expression of a subset of inflammatory genes while it inhibits the expression of another subset of genes.
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