Chen H, Lee J M, Wang Y, Huang D P, Ambinder R F, Hayward S D
Department of Pharmacology and Molecular Sciences, Johns Hopkins School of Medicine, Baltimore, MD 21205, USA.
Proc Natl Acad Sci U S A. 1999 Aug 3;96(16):9339-44. doi: 10.1073/pnas.96.16.9339.
In Epstein-Barr virus (EBV)-associated tumors in nonimmunocompromised patients, EBV gene expression is highly restricted. EBV-encoded nuclear antigen (EBNA)-1 is expressed, whereas the immunogenic and proliferative EBNAs are not. This pattern of EBNA expression is generated by usage of the BamHI-Q promoter (Qp). We have determined that the JAK/STAT pathway positively regulates Qp activity. In transient-transfection assays, a Qp-CAT reporter was activated by cotransfected JAK-1 and by treatment of cells with the cytokine IL-6. The ability of Qp to bind signal transducer and activator of transcription (STAT) proteins was directly demonstrated by electrophoretic mobility-shift assay, and mutation of potential STAT-binding sites reduced Qp responsiveness to Janus kinase (JAK)-1. Consistent with a role for STATs in Qp function, Qp using Burkitt's lymphoma Rael cells and cultured nasopharyngeal carcinoma (NPC) cells contained nuclear STAT protein. We investigated whether the inability to maintain EBV-positive NPC cell lines in culture was related to Qp activity. Passaging of the NPC cell line HK666 led to activation of expression of BZLF1, which encodes Zta and loss of Qp function. Transient expression assays linked Zta expression to the down-regulation of Qp. Cotransfection of Zta reduced Qp activity in reporter assays. This negative regulation required Zta DNA-binding activity. We provide evidence that Zta up-regulation of p53 leads to p53-mediated interference with JAK/STAT activation of Qp. The data imply that JAK/STAT signaling has a role in EBV-associated malignancies.
在非免疫功能低下患者的爱泼斯坦-巴尔病毒（EBV）相关肿瘤中，EBV基因表达受到高度限制。EBV编码的核抗原（EBNA）-1表达，而具有免疫原性和增殖性的EBNA则不表达。这种EBNA表达模式是由BamHI-Q启动子（Qp）的使用产生的。我们已经确定JAK/STAT信号通路正向调节Qp活性。在瞬时转染实验中，Qp-CAT报告基因被共转染的JAK-1以及用细胞因子IL-6处理细胞所激活。通过电泳迁移率变动分析直接证明了Qp与信号转导和转录激活因子（STAT）蛋白结合的能力，并且潜在STAT结合位点的突变降低了Qp对Janus激酶（JAK）-1的反应性。与STAT在Qp功能中的作用一致，使用伯基特淋巴瘤Rael细胞和培养的鼻咽癌（NPC）细胞的Qp含有核STAT蛋白。我们研究了在培养中无法维持EBV阳性NPC细胞系是否与Qp活性有关。NPC细胞系HK666的传代导致编码Zta的BZLF1表达激活以及Qp功能丧失。瞬时表达实验将Zta表达与Qp的下调联系起来。在报告基因实验中，Zta的共转染降低了Qp活性。这种负调控需要Zta的DNA结合活性。我们提供的证据表明，Zta对p53的上调导致p53介导的对JAK/STAT激活Qp的干扰。数据表明JAK/STAT信号在EBV相关恶性肿瘤中起作用。
