Nakahira Masakiyo, Ahn Hyun-Jong, Park Woong-Ryeon, Gao Ping, Tomura Michio, Park Cheung-Seog, Hamaoka Toshiyuki, Ohta Tsunetaka, Kurimoto Masashi, Fujiwara Hiromi
Department of Oncology, Osaka University Graduate School of Medicine, 2-2, Yamada-oka, Suita, Osaka 565-0871, Japan.
J Immunol. 2002 Feb 1;168(3):1146-53. doi: 10.4049/jimmunol.168.3.1146.
IL-12 and IL-18 synergistically enhance IFN-gamma mRNA transcription by activating STAT4 and AP-1, respectively. However, it is still unknown how STAT4/AP-1 elicit IFN-gamma promoter activation. Using an IL-12/IL-18-responsive T cell clone, we investigated the mechanisms underlying synergistic enhancement of IFN-gamma mRNA expression induced by these two cytokines. Synergy was observed in a reporter gene assay using an IFN-gamma promoter fragment that binds AP-1, but not STAT4. An increase in c-Jun, a component of AP-1, in the nuclear compartment was elicited by stimulation with either IL-12 or IL-18, but accumulation of serine-phosphorylated c-Jun was induced only by IL-18 capable of activating c-Jun N-terminal kinase. The binding of AP-1 to the relevant promoter sequence depended on the presence of STAT4. STAT4 bound with c-Jun, and a phosphorylated c-Jun-STAT4 complex most efficiently interacted with the AP-1-relevant promoter sequence. Enhanced cobinding of STAT4 and c-Jun to the AP-1 sequence was also observed when activated lymph node T cells were exposed to IL-12 plus IL-18. These results show that STAT4 up-regulates AP-1-mediated IFN-gamma promoter activation without directly binding to the promoter sequence, providing a mechanistic explanation for IL-12/IL-18-induced synergistic enhancement of IFN-gamma gene expression.
白细胞介素-12（IL-12）和白细胞介素-18（IL-18）分别通过激活信号转导和转录激活因子4（STAT4）和活化蛋白-1（AP-1），协同增强γ-干扰素（IFN-γ）信使核糖核酸（mRNA）的转录。然而，STAT4/AP-1如何引发IFN-γ启动子激活仍不清楚。我们使用一个对IL-12/IL-18有反应的T细胞克隆，研究了这两种细胞因子诱导IFN-γ mRNA表达协同增强的潜在机制。在使用与AP-1结合但不与STAT4结合的IFN-γ启动子片段的报告基因检测中观察到了协同作用。用IL-12或IL-18刺激可引起核内AP-1组分c-Jun增加，但只有能够激活c-Jun N端激酶的IL-18能诱导丝氨酸磷酸化的c-Jun积累。AP-1与相关启动子序列的结合取决于STAT4的存在。STAT4与c-Jun结合，磷酸化的c-Jun-STAT4复合物与AP-1相关启动子序列的相互作用最为有效。当活化的淋巴结T细胞暴露于IL-12加IL-18时，也观察到STAT4和c-Jun与AP-1序列的共结合增强。这些结果表明，STAT4上调AP-1介导的IFN-γ启动子激活，而不直接与启动子序列结合，这为IL-12/IL-18诱导的IFN-γ基因表达协同增强提供了机制解释。
