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

Abstract

Latent membrane protein 2A (LMP2A) and LMP2B are viral proteins expressed during Epstein-Barr virus (EBV) latency in EBV-infected B cells both in cell culture and in vivo. LMP2A has important roles in modulating B-cell receptor (BCR) signal transduction by associating with the cellular tyrosine kinases Lyn and Syk via specific phosphotyrosine motifs found within the LMP2A N-terminal tail domain. LMP2A has been shown to alter normal BCR signal transduction in B cells by reducing levels of Lyn and by blocking tyrosine phosphorylation and calcium mobilization following BCR cross-linking. Although little is currently known about the function of LMP2B in B cells, the similarity in structure between LMP2A and LMP2B suggests that they may localize to the same cellular compartments. To investigate the function of LMP2B, B-cell lines expressing LMP2A, LMP2B, LMP2A/LMP2B, and the relevant vector controls were analyzed. As was previously shown, cells expressing LMP2A had a dramatic block in normal BCR signal transduction as measured by calcium mobilization and tyrosine phosphorylation. There was no effect on BCR signal transduction in cells expressing LMP2B. Interestingly, when LMP2B was expressed in conjunction with LMP2A, there was a restoration of normal BCR signal transduction upon BCR cross-linking. The expression of LMP2B did not alter the cellular localization of LMP2A but did bind to and prevent the phosphorylation of LMP2A. A restoration of Lyn levels, but not a change in LMP2A levels, was also observed in cells coexpressing LMP2B with LMP2A. From these results, we conclude that LMP2B modulates LMP2A activity.

The signaling pathways of Epstein-Barr virus-encoded latent membrane protein 2A (LMP2A) in latency and cancer

“…A recent study suggested that LMP2B modulates LMP2A activity. When LMP2B was expressed in conjunction with LMP2A, there was a restoration of normal B-cell receptor (BCR) signal transduction upon BCR cross-linking [37]. The expression of LMP2B did not alter the cellular localization of LMP2A, but did bind to and prevent the phosphorylation of LMP2A [37].…”

“…When LMP2B was expressed in conjunction with LMP2A, there was a restoration of normal B-cell receptor (BCR) signal transduction upon BCR cross-linking [37]. The expression of LMP2B did not alter the cellular localization of LMP2A, but did bind to and prevent the phosphorylation of LMP2A [37]. However, further in-depth studies are required to scrutinize the effect of LMP2B expression on LMP2A, because the loss of function of LMP2A does not appear to be dependant solely on the heterodimerazation of LMP2A and LMP2B [37].…”

“…Since LMP2A and LMP2B are coded by the same gene, they are identical except for the first exon. Therefore, it is speculated that both proteins might possess some common functions and might localize to the same cellular compartments [36,37]. A recent study suggested that LMP2B modulates LMP2A activity.…”

Latent Membrane Protein 2B Regulates Susceptibility to Induction of Lytic Epstein-Barr Virus Infection

“…Given that no specific antibody against LMP2B exists, we chose to tag LMP2B with a 3ϫ FLAG sequence at the N terminus. The tag was placed at the N terminus, since it has been suggested that clustering of LMP2A and LMP2B occurs over the common C termini and that LMP2B influences the activity of its LMP2A isoform only when they colocalize (18,29). As the transfection efficiency of B cells is low with common protocols, we decided to establish Akata cell pools stably overexpressing LMP2B, LMP2A, or a control vector.…”

“…LMP2B colocalized with LMP2A in the membrane where the C terminus of both splice variants can interact and regulate the activity of each other (17). Furthermore, LMP2B was shown to negatively regulate LMP2A activity by interfering with its aggregation (29). Another study revealed protein domains of LMP2B which are required for intra-and extracellular localization and self-aggregation (37), which raised the question of whether the function of LMP2B in EBV is bound to its localization independently of LMP2A.…”