Graduate Institute of Microbiology, College of Medicine, National Taiwan University, Taipei, Taiwan;
Research Center for Emerging Viral Infections and Department of Medical Biotechnology and Laboratory Science, College of Medicine, Chang Gung University, Tao-Yuan, Taiwan; Division of Hepatogastroenterology, Department of Internal Medicine, Chang Gung Memorial Hospital, Tao-Yuan, Taiwan;
Blood. 2016 Sep 22;128(12):1578-89. doi: 10.1182/blood-2016-02-702530. Epub 2016 Jun 23.
Epstein-Barr virus (EBV), an oncogenic human virus, is associated with several lymphoproliferative disorders, including Burkitt lymphoma, Hodgkin disease, diffuse large B-cell lymphoma (DLBCL), and posttransplant lymphoproliferative disorder (PTLD). In vitro, EBV transforms primary B cells into lymphoblastoid cell lines (LCLs). Recently, several studies have shown that receptor tyrosine kinases (RTKs) play important roles in EBV-associated neoplasia. However, details of the involvement of RTKs in EBV-regulated B-cell neoplasia and malignancies remain largely unclear. Here, we found that erythropoietin-producing hepatocellular receptor A4 (EphA4), which belongs to the largest RTK Eph family, was downregulated in primary B cells post-EBV infection at the transcriptional and translational levels. Overexpression and knockdown experiments confirmed that EBV-encoded latent membrane protein 1 (LMP1) was responsible for this EphA4 suppression. Mechanistically, LMP1 triggered the extracellular signal-regulated kinase (ERK) pathway and promoted Sp1 to suppress EphA4 promoter activity. Functionally, overexpression of EphA4 prevented LCLs from proliferation. Pathologically, the expression of EphA4 was detected in EBV(-) tonsils but not in EBV(+) PTLD. In addition, an inverse correlation of EphA4 expression and EBV presence was verified by immunochemical staining of EBV(+) and EBV(-) DLBCL, suggesting EBV infection was associated with reduced EphA4 expression. Analysis of a public data set showed that lower EphA4 expression was correlated with a poor survival rate of DLBCL patients. Our findings provide a novel mechanism by which EphA4 can be regulated by an oncogenic LMP1 protein and explore its possible function in B cells. The results provide new insights into the role of EphA4 in EBV(+) PTLD and DLBCL.
EB 病毒（EBV）是一种致癌的人类病毒，与多种淋巴增殖性疾病有关，包括伯基特淋巴瘤、霍奇金病、弥漫性大 B 细胞淋巴瘤（DLBCL）和移植后淋巴增殖性疾病（PTLD）。在体外，EBV 将原代 B 细胞转化为淋巴母细胞系（LCL）。最近，几项研究表明，受体酪氨酸激酶（RTKs）在 EBV 相关肿瘤中发挥重要作用。然而，RTKs 参与 EBV 调节的 B 细胞肿瘤和恶性肿瘤的详细情况在很大程度上仍不清楚。在这里，我们发现属于最大的 RTK Eph 家族的促红细胞生成素产生肝细胞受体 A4（EphA4）在 EBV 感染后原代 B 细胞中转录和翻译水平下调。过表达和敲低实验证实，EBV 编码的潜伏膜蛋白 1（LMP1）是导致 EphA4 抑制的原因。在机制上，LMP1 触发细胞外信号调节激酶（ERK）途径并促进 Sp1 抑制 EphA4 启动子活性。在功能上，EphA4 的过表达可阻止 LCL 增殖。在病理上，EphA4 的表达在 EBV（-）扁桃体中检测到，但在 EBV（+）PTLD 中未检测到。此外，通过 EBV（+）和 EBV（-）DLBCL 的免疫化学染色验证了 EphA4 表达与 EBV 存在的反比关系，表明 EBV 感染与 EphA4 表达降低有关。对公共数据集的分析表明，EphA4 表达水平较低与 DLBCL 患者的生存率降低相关。我们的研究结果提供了一种新的机制，即致癌 LMP1 蛋白可调节 EphA4，并探讨了其在 B 细胞中的可能功能。研究结果为 EphA4 在 EBV（+）PTLD 和 DLBCL 中的作用提供了新的见解。
