An RNA-binding protein αCP-1 is involved in the STAT3-mediated suppression of NF-κB transcriptional activity
An RNA-binding protein αCP-1 is involved in the STAT3-mediated suppression of NF-κB transcriptional activity
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DOI：
10.1093/intimm/dxm026
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发表时间：
2007-05-01
影响因子：
4.4
通讯作者：
Kobayashi, Takashi
中科院分区：
文献类型：
--
作者：
Nishinakamura, Hitomi;Minoda, Yasumasa;Kobayashi, Takashi
信号转导子和转录激活子3（STAT3）已显示介导IL-10的抗肿瘤作用。活化的STAT3抑制巨噬细胞和树突状细胞中LPS诱导的IL-6、肿瘤坏死因子-α和IL-12基因表达。然而，STAT3抑制Toll样受体（TLR）信号的机制尚未阐明。在这项研究中，我们研究了组成性激活的STAT3（STAT3C）对LPS诱导的核因子-κ B（NF-κ B）激活的影响。在HEK293/TLR4细胞中，STAT3 C的强制表达，但野生型STAT3和显性阴性形式的STAT3均不抑制LPS-TLR4介导的NF-κ B报告基因激活。STAT3C的过表达并不影响TLR 4的信号转导，如抑制性核因子-κ B α和丝裂原活化蛋白激酶的磷酸化以及NF-κ B的DNA结合活性。因此，STAT3C可以抑制NF-κ B的转录和/或翻译活性。为了确定分子机制，我们通过使用蛋白质组学方法搜索STAT3C结合蛋白，发现一种新的RNA结合蛋白α CP-1与STAT3C相互作用。α-CP-1是一种含有K-同源结构域的RNA结合蛋白，对富含C的嘧啶片段具有特异性。此类蛋白质在广泛的转录和翻译事件中发挥关键作用。α CP-1的过表达增强了STAT3C对HEK293/TLR4细胞中NF-κ B活化的抑制作用。此外，α CP-1的强制表达增强了IL-10对RAW264.7细胞中IL-6产生的拮抗作用，而针对α CP-1的小干扰RNA降低了IL-10对RAW264.7细胞中IL-6产生的拮抗作用。
Signal transducer and activator of transcription 3 (STAT3) has been shown to mediate the antiinflammatory effect of IL-10. Activated STAT3 suppresses LPS-induced IL-6, tumor necrosis factor-alpha and IL-12 gene expression in macrophages and dendritic cells. However, the mechanism of Toll-like receptor (TLR) signal suppression by STAT3 has not been clarified. In this study, we investigated the effect of constitutively activated STAT3 (STAT3C) on LPS-induced nuclear factor-KB (NF-KB) activation. The forced expression of STAT3C in HEK293/TLR4 cells, but neither wild-type STAT3 nor dominant-negative form of STAT3, suppressed LPS-TLR4-mediated NF-kappa B reporter activation. The over-expression of STAT3C did not affect the signal transduction of TLR4, such as the phosphorylation of inhibitory nuclear factor-kappa B alpha and mitogen-activated protein kinases and the DNA-binding activity of NF-KB. Thus, STAT3C could suppress the transcriptional and/or translational activity of NF-KB. To define the molecular mechanism, we searched STAT3C-binding proteins by using a proteomic approach and found that a novel RNA-binding protein, alpha CP-1, interacted with STAT3C. alpha-CP-1 is a K-homology domain-containing RNA-binding protein with specificity for C-rich pyrimidine tracts. Such proteins play pivotal roles in a broad-spectrum of transcriptional and translational events. The over-expression of alpha CP-1 augmented the suppressive effect of STAT3C on NF-KB activation in HEK293/TLR4 cells. Furthermore, the forced expression of alpha CP-1 enhanced the antagonistic effect of IL-10 on IL-6 production in RAW264.7 cells, while small interfering RNA against alpha CP-1 reduced it. These data suggest that alpha CP-1 is involved in the STAT3-mediated suppression of NF-KB activity.