Epstein–Barr virus latent membrane protein 2A mimics B-cell receptor-dependent virus reactivation

Abstract

Latent membrane protein 2A (LMP2A) of Epstein-Barr virus (EBV) shares protein motifs with the B-cell receptor that play a role in B-cell receptor signalling and has been shown to mimic an activated B-cell receptor by providing a survival signal for mature B cells in transgenic mice. Conversely, LMP2A has been reported not to support but to inhibit B-cell receptor signalling with respect to virus reactivation and to block lytic virus induction after anti-Ig treatment of EBV-infected B cells. To solve this apparent paradox, the role of LMP2A in lytic-cycle induction was re-examined in B cells conditionally immortalized by EBV. It was shown that, in the absence of other stimuli, LMP2A expression alone could lead to induction of the virus lytic cycle. Similarly to B-cell receptor stimulation by anti-Ig treatment, this LMP2A-mediated reactivation was dependent on the mitogen-activated protein kinase pathway and could be inhibited by the viral LMP1. Our data reinforce the notion that LMP2A is a functional homologue of the B-cell receptor, not only with respect to B-cell survival but also with respect to regulation of the lytic cycle. INTRODUCTIONEpstein-Barr virus (EBV) is a ubiquitous human lymphotropic herpesvirus. In the vast majority of cases, viral infection is benign, yet EBV is associated with a number of human malignancies, including Burkitt's lymphoma, nasopharyngeal carcinoma, lymphoproliferative diseases in immunocompromised individuals and Hodgkin's disease (Rickinson & Kieff, 2001). After primary infection, EBV persists for the life of the host in the peripheral blood in resting memory B cells (Thorley-Lawson, 2001). Virus reactivation from these cells is strictly controlled and mainly observed in immunocompromised individuals (Lam et al., 1991;Decker et al., 1996; Babcock et al., 1999). Latent membrane protein 2A (LMP2A) transcripts have been detected in memory B cells, the site of EBV persistence in the periphery, by RT-PCR (Qu & Rowe, 1992;Tierney et al., 1994;Miyashita et al., 1997;Babcock et al., 1998 Babcock et al., , 1999), yet analysis of the EBV latent geneexpression pattern at the single-cell level has revealed that none of the viral latent genes is expressed in latently infected memory B cells (Hochberg et al., 2004a, b). In contrast to peripheral EBV-positive B cells, memory B cells in tonsils exhibit consistent expression of LMP2A together with the latent viral nuclear protein EBNA1 and the viral LMP1 . The expression of LMP2A and LMP1 in tonsillar memory B cells is believed to provide a survival signal to peripheral latently EBV-infected cells and to rescue the cells from apoptosis when they migrate through secondary lymphoid organs. LMP1 and LMP2A may thus contribute significantly to long-term survival of EBV-positive memory B cells in vivo.LMP2A is an integral membrane protein with 12 hydrophobic transmembrane domains and cytoplasmic N and C termini (Laux et al., 1988(Laux et al., , 1989Rowe et al., 1990). Similarly to the intracellular domain of the B-cell receptor, the N terminus of ...

Epstein-Barr Virus LMP2A Enhances B-Cell Responses In Vivo and In Vitro

“…The possibility that LMP2A promotes plasma cell differentiation is interesting, in that Thorley-Lawson and colleagues have provided evidence that lytic reactivation requires differentiation into plasma cells (15). When combined with recent evidence that LMP2A may act as a BCR mimic to promote lytic reactivation (27), the data together suggest that LMP2A may be important for viral reactivation by promoting plasma cell differentiation when stimulated through the BCR and CD40.…”

“…More recent studies indicate that LMP2A may allow BCR signaling (28) and even act as a BCR mimic to induce lytic reactivation (27). Therefore, additional models are needed to dissect the effect of LMP2A on B cells.…”

Epstein-Barr Virus Latent Membrane Protein 2B (LMP2B) Modulates LMP2A Activity

“…The expression of LMP2B may be essential at this phase of the virus life cycle to regulate LMP2A activity to ensure that cells do not undergo lytic replication. In particular, previous studies have suggested that LMP2A expression can activate virus lytic replication (87). Thus, the strength of the LMP2A signal may have very diverse effects.…”

Epstein-Barr virus latent membrane protein 2A is a B-cell receptor mimic and essential for B-cell survival

“…32 LMP2A has been reported to prevent EBV-infected cells from entering the lytic and productive phase of EBV's life cycle, 11 but this issue is controversial. 33,34 We therefore asked whether in vitro, growth-transformed LCLs depend on sustained LMP2A signaling. Mixed populations of BCR ϩ/Ϫ primary B cells were infected with 2190 EBV, which carries its LMP2A allele flanked by 2 loxP sites ( Figure 2A) or with 2089 WT EBV.…”