The strongest evidence of the oncogenicity of Epstein-Barr virus (EBV) in vitro is its ability to immortalize human primary B lymphocytes into lymphoblastoid cell lines (LCLs). Yet the underlying mechanisms explaining how the virus tempers the growth program of the host cells have not been fully elucidated. The mitogen-activated protein kinases (MAPKs) are implicated in many cellular processes and are constitutively activated in LCLs. We questioned the expression and regulation of the dual-specificity phosphatases (DUSPs), the main negative regulator of MAPKs, during EBV infection and immortalization. Thirteen DUSPs, including 10 typical and 3 atypical types of DUSPs, were tested. Most of them were downregulated after EBV infection. Here, a role of viral oncogene latent membrane protein 1 (LMP1) in limiting DUSP6 and DUSP8 expression was identified. Using MAPK inhibitors, we found that LMP1 activates extracellular signal-regulated kinase (ERK) or p38 to repress the expression of DUSP6 and DUSP8, with corresponding substrate specificity. Morphologically, overexpression of DUSP6 and DUSP8 attenuates the ability of EBV-immortalized LCL cells to clump together. Mechanistically, apoptosis induced by restoring DUSP6 and DUSP8 in LCLs indicated a novel mechanism for LMP1 to provide a survival signal during EBV immortalization. Collectively, this report provides the first description of the interplay between EBV genes and DUSPs and contributes considerably to the interpretation of MAPK regulation in EBV immortalization.IMPORTANCE Infections by the ubiquitous Epstein-Barr virus (EBV) are associated with a wide spectrum of lymphomas and carcinomas. It has been well documented that activation levels of MAPKs are found in cancer cells to translate various external or intrinsic stimuli into cellular responses. Physiologically, the dual-specificity phosphates (DUSPs) exhibit great ability in regulating MAPK activities with respect to their capability of dephosphorylating MAPKs. In this study, we found that DUSPs were generally downregulated after EBV infection. EBV oncogenic latent membrane protein 1 (LMP1) suppressed DUSP6 and DUSP8 expression via MAPK pathway. In this way, LMP1-mediated MAPK activation was a continuous process. Furthermore, DUSP downregulation was found to contribute greatly to prevent apoptosis of EBV-infected cells. To sum up, this report sheds light on a novel molecular mechanism explaining how EBV maintains the unlimited proliferation status of the immortalized cells and provides a new link to understand EBV-induced B cell survival.

中文翻译：

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爱泼斯坦-巴尔病毒LMP1对双特异性磷酸酶的失调及其对淋巴母细胞存活的影响。

爱泼斯坦-巴尔病毒（EBV）体外致癌性的最有力证据是其将人类原代B淋巴细胞永生成淋巴母细胞样细胞系（LCL）的能力。尚未完全阐明解释病毒如何调节宿主细胞生长程序的潜在机制。丝裂原激活的蛋白激酶（MAPK）与许多细胞过程有关，并在LCL中被组成性激活。我们质疑在EBV感染和永生化过程中MAPKs的主要负调节剂-双特异性磷酸酶（DUSPs）的表达和调控。测试了13种DUSP，包括10种典型和3种非典型类型的DUSP。多数在EBV感染后被下调。这里，确定了病毒癌基因潜伏膜蛋白1（LMP1）在限制DUSP6和DUSP8表达中的作用。使用MAPK抑制剂，我们发现LMP1激活细胞外信号调节激酶（ERK）或p38以抑制DUSP6和DUSP8的表达，并具有相应的底物特异性。在形态上，DUSP6和DUSP8的过表达减弱了EBV永生化LCL细胞聚集在一起的能力。从机制上讲，通过在LCL中恢复DUSP6和DUSP8诱导的细胞凋亡表明LMP1在EBV永生化期间提供生存信号的新机制。总的来说，该报告首次描述了EBV基因与DUSP之间的相互作用，并为EBV永生化中MAPK调控的解释做出了重要贡献。重要信息普遍存在的爱泼斯坦-巴尔病毒（EBV）感染与多种淋巴瘤和癌相关。业已充分证明，在癌细胞中发现MAPKs的激活水平可将各种外部或固有刺激转化为细胞反应。从生理上讲，双特异性磷酸酯（DUSPs）表现出极大的调节MAPK活性的能力，因为它们使MAPKs脱磷酸。在这项研究中，我们发现EBV感染后DUSP通常被下调。EBV致癌潜伏膜蛋白1（LMP1）通过MAPK途径抑制DUSP6和DUSP8的表达。这样，LMP1介导的MAPK激活是一个连续的过程。此外，发现DUSP的下调在防止被EBV感染的细胞凋亡中起很大作用。总结一下，