Voleti Bhavya, Agrawal Alok
Department of Pharmacology, James H. Quillen College of Medicine, East Tennessee State University, Johnson City, TN 37614, USA.
J Immunol. 2005 Sep 1;175(5):3386-90. doi: 10.4049/jimmunol.175.5.3386.
C-reactive protein (CRP) is an acute phase protein produced by hepatocytes. A minor elevation in the baseline levels of serum CRP is considered an indicator of chronic inflammation. In hepatoma Hep3B cells, IL-6 induces CRP expression by activating transcription factors STAT3 and C/EBPbeta. IL-1 synergistically enhances the effects of IL-6. The first 157 bp of the CRP promoter are sufficient for IL-1 synergy. Previously, NF-kappaB, a transcription factor activated by IL-1beta in Hep3B cells, has been shown to increase endogenous CRP expression. The purpose of this study was to investigate the possible action of NF-kappaB on the 157 bp of the proximal promoter. In this study we show that NF-kappaB requires and acts synergistically with C/EBPbeta on the CRP-proximal promoter to regulate CRP expression. We located the regulatory element that consisted of overlapping binding sites for NF-kappaB (p50-p50 and p50-p65) and OCT-1. The kappaB site was responsible for the synergy between NF-kappaB and C/EBPbeta and was also necessary for the CRP transactivation by C/EBPbeta through the C/EBP site. Mutation of the kappaB site decreased the synergistic effect of IL-1beta on IL-6-induced CRP expression. Basal CRP expression increased dramatically when binding of both OCT-1 and NF-kappaB was abolished. Combined data from luciferase transactivation assays and EMSA lead us to conclude that the binding of OCT-1 to the promoter, facilitated by p50-p50 in a novel way, represses, whereas replacement of OCT-1 by p50-p65 induces CRP transcription in cooperation with C/EBPbeta. This model for CRP expression favors the variation seen in baseline serum CRP levels in a normal healthy population.
C反应蛋白（CRP）是一种由肝细胞产生的急性期蛋白。血清CRP基线水平的轻微升高被认为是慢性炎症的一个指标。在肝癌Hep3B细胞中，白细胞介素-6（IL-6）通过激活转录因子信号转导和转录激活因子3（STAT3）和CCAAT/增强子结合蛋白β（C/EBPβ）来诱导CRP表达。白细胞介素-1（IL-1）协同增强IL-6的作用。CRP启动子的前157个碱基对足以实现IL-1的协同作用。此前，在Hep3B细胞中被IL-1β激活的转录因子核因子κB（NF-κB）已被证明可增加内源性CRP表达。本研究的目的是探讨NF-κB对近端启动子157个碱基对可能的作用。在本研究中，我们表明NF-κB需要与C/EBPβ在CRP近端启动子上协同作用以调节CRP表达。我们定位了由NF-κB（p50-p50和p50-p65）和八聚体转录因子1（OCT-1）的重叠结合位点组成的调控元件。κB位点负责NF-κB与C/EBPβ之间的协同作用，也是C/EBPβ通过C/EBP位点对CRP进行反式激活所必需的。κB位点的突变降低了IL-1β对IL-6诱导的CRP表达的协同作用。当OCT-1和NF-κB的结合都被消除时，基础CRP表达显著增加。来自荧光素酶反式激活分析和电泳迁移率变动分析（EMSA）的综合数据使我们得出结论，OCT-1以一种新的方式由p50-p50促进与启动子的结合，从而抑制转录，而p50-p65取代OCT-1则与C/EBPβ协同诱导CRP转录。这种CRP表达模型有利于正常健康人群中基线血清CRP水平的变化。
