Kühnel F, Zender L, Paul Y, Tietze M K, Trautwein C, Manns M, Kubicka S
Department of Gastroenterology and Hepatology, Medizinische Hochschule, 30625 Hannover, Germany.
J Biol Chem. 2000 Mar 3;275(9):6421-7. doi: 10.1074/jbc.275.9.6421.
NFkappaB is an essential survival factor in several physiological conditions such as embryonal liver development and liver regeneration. However, NFkappaB is also a main mediator of the cellular response to a variety of extracellular stress stimuli, and it has been shown that some viral-induced host cell apoptosis appears to be dependent on NFkappaB activation. The activation of NFkappaB upon viral infection may be a rapid way of initiating an innate immune response against the viral particles. We have assessed the role of NFkB during the early phase of adenoviral hepatitis in a nude mouse model using an adenoviral vector expressing a mutant form of IkappaBalpha. Administration of a LacZ-expressing adenoviral vector induces NFkB DNA and correlates with the up-regulation of Fas (CD95) mRNA, but not FasL (CD95L) mRNA, during the early phase of adenoviral hepatitis. The rapid increase in NFkappaB DNA binding after adenoviral infection of the liver could be very effectively inhibited by IkappaBalpha. Compared with the LacZ control virus, the IkappaBalpha-expressing adenoviral vector inhibits the increase of Fas (CD95) mRNA expression, in particular in the very early phase of the hepatitis. Reporter gene experiments in hepatoma cell lines with a Fas promoter-luciferase construct indicated that the repression of Fas (CD95) mRNA by IkappaBalpha was transcriptionally mediated. The functional relevance of the NFkappaB-dependent increase in Fas (CD95) transcription was assessed by caspase 3 assays and terminal dUTP nick-end labeling tests. Compared with the control, IkappaBalpha adenoviral infection resulted in reduced caspase 3 activity during the early phase of viral hepatitis and in a prevention of liver cell apoptosis 24 h after adenoviral administration. Therefore our study demonstrates a new pro-apoptotic function of NFkappaB in Fas (CD95)-mediated apoptosis of hepatocytes. Interestingly, NFkappaB mediates liver cell apoptosis upon viral infection even in a phase where tumor necrosis factor-alpha is already induced, as shown by the time curves of tumor necrosis factor-alpha serum levels. Therefore, the pro- or anti-apoptotic role of NFkappaB appears to be more determined by the nature of the death stimulus than by the origin of the tissue.
核因子κB（NFκB）在多种生理状况下，如胚胎肝脏发育和肝脏再生过程中，是一种至关重要的存活因子。然而，NFκB也是细胞对多种细胞外应激刺激作出反应的主要介质，并且已经表明，一些病毒诱导的宿主细胞凋亡似乎依赖于NFκB的激活。病毒感染时NFκB的激活可能是启动针对病毒颗粒的先天性免疫反应的一种快速方式。我们使用表达突变形式的IκBα的腺病毒载体，在裸鼠模型中评估了NFκB在腺病毒性肝炎早期阶段的作用。在腺病毒性肝炎的早期阶段，给予表达LacZ的腺病毒载体可诱导NFκB DNA，并与Fas（CD95）mRNA的上调相关，但与FasL（CD95L）mRNA的上调无关。肝脏腺病毒感染后NFκB DNA结合的快速增加可被IκBα非常有效地抑制。与LacZ对照病毒相比，表达IκBα的腺病毒载体抑制Fas（CD95）mRNA表达的增加，尤其是在肝炎的极早期阶段。用Fas启动子 - 荧光素酶构建体在肝癌细胞系中进行的报告基因实验表明，IκBα对Fas（CD95）mRNA的抑制是由转录介导的。通过半胱天冬酶3测定和末端脱氧核苷酸转移酶介导的缺口末端标记试验评估了Fas（CD95）转录中NFκB依赖性增加的功能相关性。与对照相比，IκBα腺病毒感染导致病毒性肝炎早期阶段半胱天冬酶3活性降低，并在腺病毒给药后24小时预防肝细胞凋亡。因此，我们的研究证明了NFκB在Fas（CD95）介导的肝细胞凋亡中具有一种新的促凋亡功能。有趣的是，如肿瘤坏死因子 - α血清水平的时间曲线所示，即使在肿瘤坏死因子 - α已经被诱导的阶段，NFκB在病毒感染时也介导肝细胞凋亡。因此，NFκB的促凋亡或抗凋亡作用似乎更多地取决于死亡刺激的性质，而不是组织的来源。
