Department of Molecular Immunology, The University of Tokyo, Komaba 4-6-1, Meguro-Ku, Tokyo 153-8505, Japan.
Biochem Biophys Res Commun. 2013 Jan 4;430(1):95-100. doi: 10.1016/j.bbrc.2012.11.006. Epub 2012 Nov 12.
The regulation of the Il12b gene, encoding the shared p40 subcomponent for IL-12 and IL-23, is critical for innate immune responses and subsequent T cell polarization. This gene is robustly induced upon Toll-like receptor (TLR) stimulation, wherein an enhancer located 10kb upstream of the transcription start site is required for promoter activity; however, the underlying mechanisms that regulate this enhancer in cooperation with the promoter has remained elusive. We show here that the Il12b enhancer contains functional ISREs for recognition by interferon regulatory factors (IRFs), and provide evidence that TLR-activated IRF5 mediates cooperativity of the enhancer with the promoter which also contains ISREs. By contrast, IRF3 activated by cytosolic RIG-I-like receptor (RLR) signaling binds to these ISREs and causes gene suppression. Consistently, IRF5 binding is accompanied with chromatin remodeling of both regulatory regions and the formation of a productive transcriptional complex containing other transcription factors, whereas these events are inhibited by IRF3 binding. We show that the ISREs embedded in the enhancer are indeed critical for its activation by IRF5. We also adduce evidence that the 5' sequences of the enhancer and promoter ISREs, all of which deviate from consensus ISREs, critically affect the function of IRF3. The dual commitment of these IRFs in the regulation of the Il12b enhancer and promoter is unique and may have implications for understanding the evolution of this gene.
编码 IL-12 和 IL-23 共享 p40 亚基的 Il12b 基因的调节对于先天免疫反应和随后的 T 细胞极化至关重要。该基因在 Toll 样受体 (TLR) 刺激下被强烈诱导，其中位于转录起始位点上游 10kb 的增强子对于启动子活性是必需的；然而，调节该增强子与启动子协同作用的潜在机制仍然难以捉摸。我们在这里表明，Il12b 增强子包含干扰素调节因子 (IRF) 识别的功能性 ISRE，并提供证据表明 TLR 激活的 IRF5 介导增强子与启动子的协同作用，该启动子也包含 ISRE。相比之下，细胞质 RIG-I 样受体 (RLR) 信号激活的 IRF3 结合这些 ISRE 并导致基因抑制。一致地，IRF5 结合伴随着两个调节区域的染色质重塑以及包含其他转录因子的有活力的转录复合物的形成，而这些事件被 IRF3 结合抑制。我们表明，增强子中嵌入的 ISRE 对于其被 IRF5 激活确实很重要。我们还提供了证据表明增强子和启动子 ISRE 的 5'序列，所有这些序列都偏离了共识 ISRE，对 IRF3 的功能有重要影响。这些 IRF 在 Il12b 增强子和启动子调节中的双重作用是独特的，可能对理解该基因的进化具有重要意义。
