Morishita Hideaki, Saito Fumiji, Kayama Hisako, Atarashi Koji, Kuwata Hirotaka, Yamamoto Masahiro, Takeda Kiyoshi
Department of Molecular Genetics, Medical Institute of Bioregulation, Kyushu University, Fukuoka, Japan.
Int Immunol. 2009 Apr;21(4):457-65. doi: 10.1093/intimm/dxp015. Epub 2009 Feb 27.
Stimulation of macrophages with a Toll-like receptor ligand, LPS, facilitates gene expression. The activator protein-1 (AP-1) family of transcription factors mediates these responses. However, c-Fos, a member of the AP-1 family, has been shown to inhibit LPS-induced gene expression in macrophages. In this study, we analyzed the role of Fos-related antigen-1 (Fra-1), another member of the AP-1 family of transcription factors, in LPS-induced responses in RAW264.7 macrophages. Fra-1 was induced in LPS-stimulated macrophages with delayed time kinetics compared with c-Fos. Lentiviral introduction of Fra-1 blocked LPS-induced expression of pro-inflammatory mediators at the protein and mRNA levels. A Fra-1 mutant, which lacks the basic leucine zipper domain required for heterodimer formation and DNA binding, did not inhibit LPS-induced responses. c-Fos bound to the AP-1-binding site early, but afterward it was replaced by Fra-1 in LPS-stimulated macrophages. Over-expression of Fra-1 induced its association with Jun proteins and stable DNA binding from an early time point following LPS stimulation. These findings indicate that Fra-1 suppresses LPS-induced mRNA expression by binding to the AP-1-binding site. RNAi-mediated knockdown of Fra-1 in RAW264.7 macrophages resulted in enhanced LPS-induced expression of a subset of genes. Thus, like c-Fos, Fra-1 negatively regulates LPS-induced responses in RAW264.7 macrophages.
用Toll样受体配体脂多糖（LPS）刺激巨噬细胞可促进基因表达。转录因子激活蛋白-1（AP-1）家族介导这些反应。然而，AP-1家族成员之一的c-Fos已被证明可抑制巨噬细胞中LPS诱导的基因表达。在本研究中，我们分析了转录因子AP-1家族的另一个成员Fos相关抗原-1（Fra-1）在RAW264.7巨噬细胞LPS诱导反应中的作用。与c-Fos相比，Fra-1在LPS刺激的巨噬细胞中以延迟的时间动力学被诱导。通过慢病毒导入Fra-1可在蛋白质和mRNA水平阻断LPS诱导的促炎介质表达。一种缺乏异二聚体形成和DNA结合所需的碱性亮氨酸拉链结构域的Fra-1突变体，不抑制LPS诱导的反应。c-Fos早期与AP-1结合位点结合，但随后在LPS刺激的巨噬细胞中被Fra-1取代。Fra-1的过表达从LPS刺激后的早期时间点就诱导其与Jun蛋白结合并稳定结合DNA。这些发现表明，Fra-1通过与AP-1结合位点结合来抑制LPS诱导的mRNA表达。RNAi介导的RAW264.7巨噬细胞中Fra-1的敲低导致LPS诱导的一组基因表达增强。因此，与c-Fos一样，Fra-1在RAW264.7巨噬细胞中对LPS诱导的反应起负调节作用。
