Aherne Carol M, McMorrow Jason, Kane David, FitzGerald Oliver, Mix Kimberlee S, Murphy Evelyn P
College of Life Sciences, UCD Veterinary Sciences Centre, University College Dublin, Belfield, Dublin 4, Ireland.
Mol Immunol. 2009 Oct;46(16):3345-57. doi: 10.1016/j.molimm.2009.07.019. Epub 2009 Sep 3.
Expression of the orphan nuclear receptor NR4A2 is controlled by pro-inflammatory mediators, suggesting that NR4A2 may contribute to pathological processes in the inflammatory lesion. This study identifies the chemoattractant protein, interleukin 8 (IL-8/CXCL8), as a molecular target of NR4A2 in human inflammatory arthritis and examines the mechanism through which NR4A2 modulates IL-8 expression. In TNF-alpha-activated human synoviocyte cells, enhanced expression of IL-8 mRNA and protein correspond to temporal changes in NR4A2 transcription and nuclear distribution. Ectopic expression of NR4A2 leads to robust changes in endogenous IL-8 mRNA levels and co-treatment with TNF-alpha results in significant (p<0.001) secretion of IL-8 protein. Transcriptional effects of NR4A2 on the human IL-8 promoter are enhanced in the presence of TNF-alpha, suggesting molecular crosstalk between TNF-alpha signalling and NR4A2. A dominant negative IkappaB kinase antagonizes the combined effects of NR4A2 and TNF-alpha on IL-8 promoter activity. Co-expression of NR4A2 and the p65 subunit of NF-kappaB enhances IL-8 transcription and functional studies indicate that transactivation occurs independently of NR4A2 binding to DNA or heterodimerization with additional nuclear receptors. The IL-8 minimal promoter region is sufficient to support NR4A2 and NF-kappaB/p65 co-operative activity and NR4A2 can interact with NF-kappaB/p65 on a 39bp sequence within this region. In patients treated with methotrexate for active inflammatory arthritis, a reduction in NR4A2 synovial tissue levels correlate significantly (n=10, r=0.73, p=0.002) with changes in IL-8 expression. Collectively, these data delineate an important role for NR4A2 in modulating IL-8 expression and reveal novel transcriptional responses to TNF-alpha in human inflammatory joint disease.
孤儿核受体NR4A2的表达受促炎介质调控，提示NR4A2可能参与炎症病变的病理过程。本研究确定趋化因子蛋白白细胞介素8（IL-8/CXCL8）是NR4A2在人类炎性关节炎中的分子靶点，并探讨NR4A2调节IL-8表达的机制。在肿瘤坏死因子-α（TNF-α）激活的人滑膜细胞中，IL-8 mRNA和蛋白表达增强与NR4A2转录和核分布的时间变化相对应。NR4A2的异位表达导致内源性IL-8 mRNA水平发生显著变化，与TNF-α共同处理可导致IL-8蛋白大量分泌（p<0.001）。在TNF-α存在的情况下，NR4A2对人IL-8启动子的转录作用增强，提示TNF-α信号与NR4A2之间存在分子串扰。显性负性IκB激酶可拮抗NR4A2和TNF-α对IL-8启动子活性的联合作用。NR4A2与核因子-κB（NF-κB）的p65亚基共表达可增强IL-8转录，功能研究表明，反式激活独立于NR4A2与DNA的结合或与其他核受体的异源二聚化。IL-8最小启动子区域足以支持NR4A2与NF-κB/p65的协同活性，且NR4A2可在该区域内的一段39bp序列上与NF-κB/p65相互作用。在接受甲氨蝶呤治疗的活动性炎性关节炎患者中，NR4A2滑膜组织水平的降低与IL-8表达的变化显著相关（n=10，r=0.73，p=0.002）。总体而言，这些数据阐明了NR4A2在调节IL-8表达中的重要作用，并揭示了人类炎性关节疾病中对TNF-α的新型转录反应。
