Analyses on Mechanisms for Multistep Transcriptional Regulation via Inducible Factors

IκB-ζ是由首席研究员发现的一种在调节炎症反应中具有双重作用的关键分子。IκB-ζ是由多种刺激天然免疫系统的微生物物质诱导的，对IL-6、IL-12和转录因子C/eBP-δ等次级反应基因的转录是必需的，并抑制以肿瘤坏死因子-α为代表的初级反应基因的转录。在本研究中，我们研究了IκB-ζ的转录调控机制。我们发现，在人κ-Defensin2和中性粒细胞明胶酶相关的Lipocalin基因中，启动子区域的一个NF-κB结合位点和一个C/EBP结合位点对于IζB-β的转录激活是必不可少的。另一方面，IκB-ζ抑制含有典型的NF-κB结合位点的启动子的转录。这些结果表明，刺激诱导的I-κB-ζ与核因子-κB形成复合体，并与含有核因子-κB结合位点和C/EBP结合位点的启动子结合，在那里激活转录。I-κ-B-ζ可被IL-1β刺激和内毒素诱导，但不能被α诱导。我们已经分析了IκB-ζ的诱导机制，并证明IκB-ζ在β/IL-1刺激下特异性地稳定。在本研究中，我们搜索了IκB-ζ基因中转录后调控所必需的一个元件，发现3‘-非翻译区的165核苷酸序列对于调控是必要的和充分的。我们进一步检测了I-κB-ζ在B细胞中的诱导，发现它是在刺激B细胞抗原受体时诱导的。我们还发现，抑制的Fc受体的共同刺激抑制了这种诱导。这些结果有力地表明，I-κB-ζ在获得性免疫系统中起着关键作用。

IκB-ζ, which was discovered by the head investigator, is a key molecule playing dual roles in regulation of inflammatory reactions. IκB-ζ is induced by various microbial substances stimulating the innate immune system and is essential for transcription of secondary response genes such as interleukin (IL)-6, IL-12, and the transcription factor C/EBP-δ and suppresses those of primary response genes represented by tumor necrosis factor (TNF)-α. In the present study, we investigated mechanisms for transcriptional regulation by IκB-ζ. We found that both an NF-κB binding site and a C/EBP binding site in the promoter region are essential for the transcriptional activation by IκB-ζ in the human β-defensin 2 and neutrophil gelatinase-associated lipocalin genes. On the other hand, IκB-ζ inhibited transcription of a promoter harboring canonical NF-κB binding sites. These results indicated that IκB-ζ induced on stimulation forms a complex with NF-κB and binds to the promoters harboring an NF-κB binding site and a C/EBP sites, where it activates transcription. Induction of IκB-ζ is induced by IL-1β stimulation as well as LPS, but not by TNF-α. We have analyzed mechanisms for IκB-ζ induction and have shown that IκB-ζ mRNA is specifically stabilized upon LPS/IL-1β stimulation. In the present study, we searched for an element in the IκB-ζ mRNA that is essential for the post-transcriptional regulation, and found that a 165-nucleotide sequence in the 3'-untranslated region is essential and sufficient for the regulation. We furthermore examined induction of IκB-ζ in B cells and found that it is induced upon stimulation of B cell antigen receptor. We also found that the induction was inhibited by co-stimulation of the inhibitory Fc receptor. These results strongly suggest that IκB-ζ plays a critical role in the adaptive immune system.