Schwarz E M, Badorff C, Hiura T S, Wessely R, Badorff A, Verma I M, Knowlton K U
Laboratory of Genetics, The Salk Institute, San Diego, California 92186-5800, USA.
J Virol. 1998 Jul;72(7):5654-60. doi: 10.1128/JVI.72.7.5654-5660.1998.
Apoptosis is a central host defense mechanism to eliminate virus-infected cells. Activation of NF-kappaB suppresses apoptosis following some types of stimulation in vitro. To test the physiological importance of this pathway in vivo, we studied murine encephalomyocarditis virus (EMCV) infection in mice and cell lines defective in NF-kappaB1 (p50) signaling. As previously reported, we find that all p50 knockout (p50 -/-) mice survive an EMCV infection that readily kills normal mice. By introducing the p50 mutation into interferon (IFN) type I receptor knockout (IFNRI -/-) mice, we find that this resistance is not mediated by IFN-beta as previously thought. While no IFNRI -/- mice survive, the double-knockout mice survive 60% of the time. The survival is tightly linked to the animals' ability to clear the virus from the heart in vivo. Using murine embryonic fibroblasts (MEF) derived from wild-type, p50 -/-, and p65 -/- embryos, we found that NF-kappaB is not required for the replication cycle of EMCV. However, during these experiments we observed that p50 -/- and p65 -/- MEF infected with EMCV undergo enhanced, premature cytotoxicity. Upon examination of this cell death, we found that EMCV infection induced both plasma membrane and nuclear changes typical of apoptosis in all cell lines. These apoptotic processes occurred in an accelerated and pronounced way in the NF-kappaB-defective cells, as soon as 6 h after infection, when virus is beginning to be released. Previously, only the RelA (p65) subunit of NF-kappaB has been shown to play a role in suppressing apoptosis. In our studies, we find that p50 is equally important in suppressing apoptosis during EMCV infection. Additionally, we show that suppression of apoptosis by NF-kappaB1 is required for EMCV virulence in vivo. The attenuation in p50 -/- mice can be explained by rapid apoptosis of infected cells which allows host phagocytes to clear infected cells before the viral burst leading to a reduction of the viral burden and survival of the mice.
细胞凋亡是清除病毒感染细胞的一种核心宿主防御机制。在体外某些类型的刺激后，核因子-κB（NF-κB）的激活会抑制细胞凋亡。为了测试该通路在体内的生理重要性，我们研究了小鼠脑心肌炎病毒（EMCV）感染小鼠以及NF-κB1（p50）信号缺陷的细胞系的情况。如先前报道，我们发现所有p50基因敲除（p50 -/-）小鼠在EMCV感染中存活下来，而这种感染会轻易杀死正常小鼠。通过将p50突变引入I型干扰素（IFN）受体敲除（IFNRI -/-）小鼠，我们发现这种抗性并非如先前认为的那样由IFN-β介导。虽然没有IFNRI -/-小鼠存活，但双敲除小鼠有60%的存活率。存活率与动物在体内从心脏清除病毒的能力紧密相关。使用源自野生型、p50 -/-和p65 -/-胚胎的小鼠胚胎成纤维细胞（MEF），我们发现NF-κB对于EMCV的复制周期并非必需。然而，在这些实验过程中，我们观察到感染EMCV的p50 -/-和p65 -/- MEF会经历增强的、过早的细胞毒性。在检查这种细胞死亡时，我们发现EMCV感染在所有细胞系中均诱导了典型的细胞凋亡的质膜和核变化。这些凋亡过程在NF-κB缺陷细胞中以加速且显著的方式发生，在感染后6小时，即病毒开始释放时就出现了。此前，仅显示NF-κB的RelA（p65）亚基在抑制细胞凋亡中起作用。在我们的研究中，我们发现p50在EMCV感染期间抑制细胞凋亡方面同样重要。此外，我们表明NF-κB1对细胞凋亡的抑制是EMCV在体内致病力所必需的。p50 -/-小鼠中的毒力减弱可以通过受感染细胞的快速凋亡来解释，这使得宿主吞噬细胞能够在病毒爆发前清除受感染细胞，从而导致病毒载量降低以及小鼠存活。
