Dysregulation of Dual-Specificity Phosphatases by Epstein-Barr Virus LMP1 and Its Impact on Lymphoblastoid Cell Line Survival.

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 of how the virus tempers the growth program of the host cells have not been fully elucidated. The mitogen-activated protein kinases 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 mitogen-activated protein kinases (MAPKs), during EBV infection and immortalization. Thirteen DUSPs, including ten typical and three atypical types of DUSPs, were tested. Most of them were down-regulated post EBV infection. Herein, a role of the viral oncogene latent membrane protein 1 (LMP1) in limiting DUSP6 and DUSP8 expression was identified. Using MAPK inhibitors, we found that LMP1 activates 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 study provides the first description of the interplay between EB viral genes and DUSPs and contributes considerably to the interpretation of MAPK regulation in EBV immortalization. Importance The infection of ubiquitous Epstein-Barr virus (EBV) is 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) exert great ability in regulating MAPK activities for their abilities to dephosphorylate MAPKs. In this study, we found that DUSPs generally are down-regulated post EBV infection. EBV oncogenic latent membrane protein 1 (LMP1) suppresses DUSP6 and DUSP8 expression via MAPK pathway. In this way, LMP1-mediated MAPK activation could be continuously activated. Furthermore, DUSP down-regulation contributes greatly to prevent apoptosis of EBV infected cells. To sum up, this study sheds light on a novel molecular mechanism on how EBV maintains the unlimited proliferation status of the immortalized cells and provides a new link to understand EBV-induced B cell survival.