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

Abstract

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. E pstein-Barr virus (EBV) is a cause of infectious mononucleosis and is associated with both B lymphocyte and epithelial cell malignancies. EBV encodes a number of proteins that trigger cell signaling pathways, such as AP-1, JAK-STAT, NF-B, and phosphatidylinositol 3-kinase (PI3K)/Akt, which are critical for cell survival, virus latency, and growth transformation (1-6). For example, EBV latent membrane protein 1 (LMP1) mimics CD40 signaling and is important for EBV-induced B cell growth proliferation, inhibition of apoptosis, and EBV transformation. LMP1 interacts with tumor necrosis factor receptor-associated factors (TRAFs), leading to activation of NF-B, c-Jun N-terminal kinase (JNK), p38 mitogen-activated protein kinase (MAPK), PI3K/Akt, and STAT3 (7-12). EBV LMP2A mimics B cell receptor signaling and contributes to the long-term survival of B cells (13-16). LMP2A activates extracellular signal-related protein kinase (ERK), PI3K/Akt, and JNK (17) and downregulates NF-B and STAT signaling pathways (18). The EBV immediate early protein BZLF1 activates virus reactivation from latency (19-21). BZLF1 activates p38 and JNK to turn on the ATF2 transcription factor (22). BRLF1, another EBV immediate early protein, activates the AP-1 pathway by increasing the levels of phosphorylated p38, JNK, and ERK (22, 23) and induces phosphorylation of Akt through the PI3K pathway (24). Activation of Akt, ERK, and p38 signaling is required for EBV reactivation from latency (25-28).To identify additional EBV proteins important for regulating cell signaling, we used a proteomic approach to screen viral proteins for AP-1 promoter activity in AP-1-luciferase reporter assays. We found that the EBV tegument protein BGLF2 induced AP-1 reporter activity and activated p38 and JNK. BGLF2 promoted EBV reactivation by enhancing BZLF1 expression and EBV production, and p38 activation by BGLF2 was required for these activities. Citation Liu X, Cohen JI. 2016. Epstein-Barr virus (EBV) tegument protein BGLF2 promotes EBV reactivation through activation of the p38 mitogen-activated protein kinase.

Domain Interaction Studies of Herpes Simplex Virus 1 Tegument Protein UL16 Reveal Its Interaction with Mitochondria

“…Indeed, studies of the UL16 homolog from a gammaherpesvirus (Epstein-Barr virus) have shown that it can multimerize in transfected cells (61). We used coimmunoprecipitation and colocalization assays to look for interactions among tagged derivatives of full-length UL16, but these experiments did not yield convincing results (not shown).…”

Epstein‐Barr virus tegument protein BGLF2 inhibits NF‐κB activity by preventing p65 Ser536 phosphorylation

“…BGLF2 is a tegument protein that expressed with late kinetics in EBV-infected cells (33,64,65). Recently, BGLF2 has been shown to activate p38 and JNK signaling pathways and enhance AP-1-dependent transcription (34,35). Several orthologs of BGLF2, such as Kaposi's sarcomaassociated herpesvirus ORF33 (66,67), varicella-zoster virus ORF44 (68), and cytomegalovirus (CMV) unique long 94 (UL94) (69), are essential for viral replication.…”

“…As a potential tegument protein, BGLF2 is important for the re-envelopment of EBV in the cytoplasm or plasma membrane, which can be detected in the mature virions (33). It has been reported that BGLF2 can increase EBV infectivity by activating the AP-1 signaling pathway through phosphorylation of p38 and JNK (34,35). However, whether BGLF2 is involved in regulating NF-kB signaling is still unknown.…”

Epstein-Barr virus lytic reactivation regulation and its pathogenic role in carcinogenesis

“…In an earlier study, the BMRF1 protein was found to directly interact with Zta in vitro as well as in vivo , enhancing transcription from their common early BHLF1 promoter 76. Similarly, EBV tegument protein BGLF2, encoded in the late phase of the lytic cycle, was suggested to enhance Zta expression through activation of the p38 signaling pathway 77.…”