Target Gene regulated Interleukin 12 and transcription factor, STAT4

白细胞介素(IL)-12诱导酪氨酸磷酸化和信号转导和转录激活因子（STAT） 4的激活，刺激自然杀伤细胞（NK）的增殖，增强NK细胞介导的细胞溶解活性，诱导NK细胞产生干扰素(IFN)-γ。stat4缺陷小鼠表现出对IL-12缺乏反应性和NK细胞功能降低。孔形成蛋白穿孔蛋白是NK细胞和ctl介导的细胞溶解的关键效应蛋白。在IL-12的作用下，穿孔素基因在人NK细胞（NKL）中被诱导表达。人类穿孔蛋白基因的启动子区包含17个碱基间隔的STAT结合序列。利用含有穿孔蛋白启动子STAT结合序列的探针进行的电泳迁移分析（EMSA）表明，该区域与STAT4结合。串联STAT结合序列突变导致dna结合能力和启动子活性下调。这些结果表明，穿孔素是NK细胞IL-12/STAT4信号转导通路的直接靶基因，穿孔素启动子区的串联STAT结合位点对其表达起核心作用。我们的研究结果表明STAT4的四聚体与穿孔蛋白启动子结合。

Interleukin (IL)-12 induces tyrosine phosphorylation and activation of signal transducer and activator of transcription (STAT) 4, stimulates proliferation of natural killer (NK) cells, enhances NK cell-mediated cytolytic activity, and induces interferon (IFN)-γ production by NK cells. STAT4-deficient mice display lack of responsiveness to IL-12 and reduced NK cell function. The pore-forming protein perforin is a key effecter protein for NK cell and CTL-mediated cytolysis. In response to IL-12, expression of perforin gene was induced in human NK cell line, NKL. The promoter region of human perforin gene contained 17 bases spaced STAT binding sequences. Electrophoretic mobility shift assay (EMSA) analysis using a probe containing the STAT binding sequence of the perforin promoter showed that this region binds with STAT4. Mutation of either of tandem STAT binding sequences resulted in down-regulation of DNA-binding capacity and promoter activity. These results demonstrated that perforin is a direct target gene of IL-12/STAT4 signal transduction pathway in NK cells, and tandem STAT binding sites in perforin promoter region play a central role for the expression. Our results suggest that tetramer of STAT4 binds to perforin promoter.