Analyses on Mechanisms for Multistep Transcriptional Regulation via Inducible Factors

由首席研究员发现的IκB-ζ是在调节炎症反应中起双重作用的关键分子。IκB-ζ是由多种微生物物质刺激先天免疫系统诱导的，是二级应答基因如白细胞介素(IL)-6、IL-12和转录因子C/EBP-δ转录所必需的，抑制肿瘤坏死因子(TNF)-α等一级应答基因的转录。在本研究中，我们研究了IκB-ζ的转录调控机制。我们发现，启动子区域的NF-κB结合位点和C/EBP结合位点对于i -κB -ζ在人β-防御素2和中性粒细胞明胶酶相关的脂质蛋白基因中的转录激活是必不可少的。另一方面，IκB-ζ抑制含有典型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NF-κB形成复合物，并结合到含有NF-κB结合位点和C/EBP位点的启动子上，在那里它激活转录。IL-1β和LPS均能诱导i - κ b -ζ的表达，TNF-α不能。我们分析了IκB-ζ诱导的机制，并表明IκB-ζ mRNA在LPS/IL-1β刺激下特异性稳定。在本研究中，我们在IκB-ζ mRNA中寻找转录后调控所必需的元件，并发现在3'-非翻译区有165个核苷酸序列是调控所必需的和足够的。我们进一步研究了IκB-ζ在B细胞中的诱导作用，发现它是在B细胞抗原受体的刺激下诱导的。我们还发现，这种诱导被抑制Fc受体的共同刺激所抑制。这些结果强烈表明，κ b -ζ在适应性免疫系统中起关键作用。

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.