Epstein-Barr Virus (EBV) Tegument Protein BGLF2 Promotes EBV Reactivation through Activation of the p38 Mitogen-Activated Protein Kinase.

UNLABELLED Epstein-Barr virus (EBV) is a ubiquitous gammaherpesvirus associated with both B cell and epithelial cell malignancies. EBV infection of B cells triggers activation of several signaling pathways that are critical for cell survival, virus latency, and growth transformation. To identify EBV proteins important for regulating cell signaling, we used a proteomic approach to screen viral proteins for AP-1 and NF-κB promoter activity in AP-1- and NF-κB-luciferase reporter assays. We found that EBV BGLF2 activated AP-1 but not NF-κB reporter activity. Expression of EBV BGLF2 in cells activated p38 and c-Jun N-terminal kinase (JNK), both of which are important for mitogen-activated protein kinase (MAPK) signaling. Deletion of the carboxyl-terminal 66 amino acids of BGLF2 reduced the ability of BGLF2 to activate JNK and p38. Expression of BGLF2 enhanced BZLF1 expression in latently EBV-infected lymphoblastoid cell lines, and knockdown of BGLF2 reduced EBV reactivation induced by IgG cross-linking. Expression of BGLF2 induced BZLF1 expression and virus production in EBV-infected gastric carcinoma cells. BGLF2 enhanced BZLF1 expression and EBV production by activating p38; chemical inhibition of p38 and MAPK/ERK kinases 1 and 2 (MEK1/2) reduced expression of BZLF1 and virus production induced by BGLF2. In summary, the EBV tegument protein BGLF2, which is delivered to the cell at the onset of virus infection, activates the AP-1 pathway and enhances EBV reactivation and virus production. IMPORTANCE Epstein-Barr virus (EBV) is associated with both B cell and epithelial cell malignancies, and the virus activates multiple signaling pathways important for its persistence in latently infected cells. We identified a viral tegument protein, BGLF2, which activates members of the mitogen-activated protein kinase signaling pathway. Expression of BGLF2 increased expression of EBV BZLF1, which activates a switch from latent to lytic virus infection, and increased production of EBV. Inhibition of BGFL2 expression or inhibition of p38/MAPK, which is activated by BGLF2, reduced virus reactivation from latency. These results indicate that a viral tegument protein which is delivered to cells upon infection activates signaling pathways to enhance virus production and facilitate virus reactivation from latency.