Samanta M, Iwakiri D, Takada K
Department of Tumor Virology, Institute for Genetic Medicine, Hokkaido University, Sapporo, Japan.
Oncogene. 2008 Jul 10;27(30):4150-60. doi: 10.1038/onc.2008.75. Epub 2008 Mar 24.
Epstein-Barr virus-encoded small RNA (EBER) is nonpolyadenylated, noncoding RNA, forms stem-loop structure by intermolecular base-pairing giving rise to double-stranded RNA (dsRNA)-like molecule and exists abundantly in EBV-infected cells. EBER induces IL-10 and thus supports the growth of Burkitt's lymphoma (BL) cells. In this study, the mechanism of IL-10 induction by EBER was analysed in the context of dsRNA signaling pathway. Knockdown of retinoic acid-inducible gene I (RIG-I) by small interfering RNA (siRNA), and expression of dominant-negative RIG-I downregulated IL-10 induction in EBER(+) EBV-infected and EBER plasmid-transfected BL cells. Transfection of EBER-expressing plasmid or in vitro synthesized EBER induced IL-10 in RIG-I-expressing cell clones, and activation of IL-10 promoter by EBER was blocked by dominant-negative RIG-I. Blocking of nuclear factor (NF)-kappaB by dominant-negative IkappaB-alpha plasmid did not block IL-10 expression, whereas knockdown of IRF-3 by siRNA resulted in downregulation of IL-10 in EBER(+) BL cells. NF-kappaB is reported to function downstream of RIG-I signaling pathway and is involved in the induction of proinflammatory cytokines. Our results indicate that EBER induces an anti-inflammatory cytokine IL-10 through RIG-I-mediated IRF-3 but not NF-kappaB signaling. These findings suggest a new mechanism of dsRNA signaling pathway that triggers the expression of IL-10, which acts as an autocrine growth factor in BL cells.
爱泼斯坦-巴尔病毒编码的小RNA（EBER）是一种非多聚腺苷酸化的非编码RNA，通过分子间碱基配对形成茎环结构，产生双链RNA（dsRNA）样分子，并大量存在于爱泼斯坦-巴尔病毒感染的细胞中。EBER可诱导白细胞介素-10（IL-10），从而支持伯基特淋巴瘤（BL）细胞的生长。在本研究中，在dsRNA信号通路的背景下分析了EBER诱导IL-10的机制。用小干扰RNA（siRNA）敲低视黄酸诱导基因I（RIG-I），以及显性负性RIG-I的表达下调了EBER(+)爱泼斯坦-巴尔病毒感染和EBER质粒转染的BL细胞中IL-10的诱导。表达EBER的质粒转染或体外合成的EBER在表达RIG-I的细胞克隆中诱导IL-10，并且显性负性RIG-I阻断了EBER对IL-10启动子的激活。显性负性IκB-α质粒阻断核因子（NF）-κB并不阻断IL-10的表达，而用siRNA敲低IRF-3导致EBER(+) BL细胞中IL-10的下调。据报道，NF-κB在RIG-I信号通路的下游发挥作用，并参与促炎细胞因子的诱导。我们的结果表明，EBER通过RIG-I介导的IRF-3而非NF-κB信号诱导抗炎细胞因子IL-10。这些发现提示了dsRNA信号通路触发IL-10表达的新机制，IL-10在BL细胞中作为自分泌生长因子发挥作用。
