An integral membrane protein (LMP2) blocks reactivation of Epstein-Barr virus from latency following surface immunoglobulin crosslinking.

Abstract

The role of latent membrane protein 2 (LMP2) in Epstein-Barr virus (EBV) infection was evaluated by using latently infected primary B lymphocytes that had been growth transformed by wild-type or specifically mutated EBV recombinants. LMP2 null mutant recombinant EBV-infected cells were similar to normal B lymphocytes in their rapid increase in intracellular free calcium after surface immunoglobulin crosslinking. These cells also became more permissive for lytic EBV replication. In sharp contrast, wild-ype control infected cells had little or no increase in intracellular free calcium or in permissivity for EBV replication. The block to surface immunoglobulin crosslinking-induced permissivity in cells expressing wild-type LMP2 could be bypassed by raising intracellular free calcium levels with an ionophore and by activating protein kinase C with phorbol 12-myristate 13-acetate. LMP2A, not LMP2B, mediates this effect on calcium mobilization. Genetic and biochemical data are consistent with these effects being due to the interaction of the LMP2A N-terminal cytoplasmic domain with B lymphocyte src family tyrosine kinases.Epstein-Barr virus (EBV) is a herpes virus that establishes latency in B lymphocytes during primary infection. Latent infection of B lymphocytes is likely to be essential for perpetuation of this virus in human populations, since virus reactivation from latency is the major reservoir of virus for infection of susceptible hosts. In latent infection, the virus can express six nuclear proteins [EBV nuclear antigens (EBNAs)], two integral membrane proteins [latent membrane proteins (LMPs)], and two small RNAs, thereby causing proliferation of the infected lymphocyte (1-3). Latently infected lymphocytes can cause a lymphoproliferative disease in immunodeficient individuals (4-6). The EBNAs and LMPs are being intensively studied since they are likely to be involved in the maintenance or regulation of latency or of the concomitant effects on cell proliferation. This report focuses on LMP2, the protein(s) most recently discovered to be expressed in latently infected B lymphocytes (7-9).Two forms of LMP2 (designated LMP2A and -2B) are expressed in latently infected B lymphocytes. Both forms are encoded by highly related mRNAs composed of eight exons with a single long open reading frame, differing only in their first exons (10-12). The first exon of LMP2A encodes a 119-amino acid hydrophilic N terminus that is unique to LMP2A. The promoter for LMP2B is in the first LMP2A intron, and the first LMP2B exon is noncoding. The first codon of the second exon in LMP2A and -2B is a methionine codon, at which translation of LMP2B initiates. That methionine is followed by 12 predicted hydrophobic transmembrane domains separated by short reverse turns and a 27-

Transcriptional analysis of Epstein-Barr virus gene expression in EBV-positive gastric carcinoma: unique viral latency in the tumour cells

“…In addition, although EBV latency can be disrupted as epithelial cells differentiate, as shown by observations in OHL , none of the gastric carcinomas with various differentiations showed any evidence of virus production. LMP2A, detectably expressed in three of our seven cases, was shown to block calcium mobilisation in B cells, thereby suppressing EBV replication (Miller et al, 1993(Miller et al, , 1994. It is unknown whether the finding can be extended to epithelial cells; however, at least in certain EBV-positive gastric carcinomas, the absence of tumour cells entering the lytic cycle may be associated with LMP2A expression.…”

Syk Tyrosine Kinase Mediates Epstein-Barr Virus Latent Membrane Protein 2A-induced Cell Migration in Epithelial Cells

“…Similarly, LMP2A can have diverse effects depending on the cell types tested. LMP2A can block BCR signaling when expressed in EBV-transformed B cells grown in cell culture (23,47). In contrast, in primary murine B cells LMP2A does not block BCR signaling but alters normal B cell signaling and confers survival and developmental signals to BCR-negative B cells (25,27,48,49).…”

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

“…LMP2A mimics BCR signaling and contributes to the long-term survival of B-cells [67]. In latent infected B-cells, BCR is blocked, and a series of events renders the necessary survival signals to prevent viral replication and promote B-cell differentiation into resting memory cells [68][69][70]. The role of LMP2 in malignancy remains an enigma.…”