Disease relevance of LMP-2A

• We have previously shown that the EBV latent genes LMP-1 and LMP-2A (for latent membrane proteins 1 and 2A), transactivate a human endogenous retrovirus (HERV), HERV-K18, in infected B lymphocytes [1].
• When the new assays were used to screen a collection of endemic Burkitt's lymphoma tumours, abundant Qp-driven EBNA1 expression was found, whereas the other latent transcripts (with the exception of LMP2A) were either absent or detectable only at trace levels [2].
• To determine whether these two virus-encoded cytoplasmic domains are endowed with signalling functions, we constructed chimeric proteins by replacing the cytoplasmic tail of CD8-alpha with that of either BLV gp30 or EBV LMP2A [3].
• One of the few viral transcripts expressed in EBV-positive Hodgkin/Reed-Sternberg (HRS) cells of Hodgkin lymphoma is latent membrane protein 2A (LMP2A) [4].
• These antibodies were applied to the immunohistochemical detection of LMP2A in Hodgkin's disease (HD) [5].

High impact information on LMP-2A

• Transcription of the latent EBV gene products, EBV nuclear antigen 1, LMP-1, LMP-2A, and the BamHI-A fragment, was detected in most of the samples [6].
• Epstein-Barr virus LMP2A drives B cell development and survival in the absence of normal B cell receptor signals [7].
• Furthermore, spontaneous germinal centers developed in gut-associated lymphoid tissue of LMP2A mice, indicating that microbial antigens can promote germinal centers independently of BCR-mediated antigen recognition [8].
• Using a novel mouse model we have identified the intracellular adaptor protein Src homology 2 (SH2) domain-containing leukocyte protein (SLP)-65 as a critical downstream effector of LMP2A in vivo [9].
• This modulation of STAT activity correlated with the ability of LMP2A to inhibit the autocrine secretion of IL-6 from carcinoma cell lines [10].

Chemical compound and disease context of LMP-2A

• Furthermore, 5-Azacytidine induced upregulation of the latent EBV genes LMP2A, LMP2B, and EBNA2 in a similar fashion as observed following switching of latent to lytic EBV upon cross-linking of the B-cell receptor [11].
• However, it is established that EBV latent membrane protein 2A (LMP2A) blocks signaling in EBV-bearing cells by interaction with cellular tyrosine kinases [12].
• Lysine-independent ubiquitination of Epstein-Barr virus LMP2A [13].

Biological context of LMP-2A

• LMP-2A interferes with membrane signal transduction through phosphorylation of its hydrophilic N-terminal domain and binding of the cellular tyrosine kinases encoded by fyn and lyn [14].
• Latent membrane protein 2A (LMP-2A) of Epstein-Barr virus (EBV) mimics a constitutively active B-cell receptor (BCR) and plays a key role in viral latency and EBV pathogenesis [15].
• The expression of LMP2B did not alter the cellular localization of LMP2A but did bind to and prevent the phosphorylation of LMP2A [16].
• EBV signaling (through EBNA2, LMP1 and LMP2A) and NF-kB activation correlated with upregulation of target proteins: cMYC, JunB, CCL22, TRAF1 and IRF4 [17].
• Epstein-Barr virus-encoded LMP2A regulates viral and cellular gene expression by modulation of the NF-kappaB transcription factor pathway [10].

Anatomical context of LMP-2A

• Expression of LMP2A may be of therapeutic interest because it may make such cases amenable to immunotherapy with EBV-specific cytotoxic T cells [18].
• LMP2A also associates with rafts and is palmitoylated but does not associate with the cell cytoskeleton [19].
• In lymphoid tissues from patients with acute infectious mononucleosis (IM), interfollicular immunoblasts were shown to express LMP2A [5].
• Epstein-Barr Virus (EBV) LMP2A induces alterations in gene transcription similar to those observed in Reed-Sternberg cells of Hodgkin lymphoma [4].
• Previously, we demonstrated LMP2A triggers epithelial cell migration [20].

Associations of LMP-2A with chemical compounds

• To assess the function of LMP-2A, we have utilized a colony formation assay for the progenitor B cells that uses the B-cell proliferation factor IL-7 [15].
• 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 [16].
• Interestingly, the LMP2A(222-230) epitope could be efficiently generated from incomplete EBV-LMP2A fragments that were produced by puromycin treatment or gene-engineered shortened EBV-LMP2A lacking some of its hydrophobic domains [21].
• We also show that the juxtamembrane cysteine repeats in the LMP2A C terminus are the major targets for palmitoylation but that this acylation is not required for targeting of LMP2A to detergent-insoluble glycolipid-enriched membrane microdomains [22].
• Deletion and site-specific mutation of LMP2A indicates that LMP2A is ubiquitinated at its amino-terminus and is not ubiquitinated on lysine residues [13].
• Utilization by Shb of the LMP2A ITAM motif regulates stability of the Syk tyrosine kinase in LMP2A-expressing cells [23].

Physical interactions of LMP-2A

• Their substitution with six membrane-spanning domains from the LMP-2A protein of EBV yields a derivative which neither coimmunoprecipitates with LMP-1 nor signals to increase the activity of NF-kappaB as does wild-type LMP-1 [24].

Co-localisations of LMP-2A

• Epstein-Barr virus latent membrane protein 2B (LMP2B) co-localizes with LMP2A in perinuclear regions in transiently transfected cells [25].

Regulatory relationships of LMP-2A

• Interestingly, when LMP2B was expressed in conjunction with LMP2A, there was a restoration of normal BCR signal transduction upon BCR cross-linking [16].
• Tyrosine phosphorylation, calcium mobilization, and induction of BZLF1 expression were no longer blocked in the LMP2A ITAM mutant LCLs following BCR cross-linking [26].
• We report that LMP2A protein controls the expression of TRAF2 mRNA, which in turn is necessary for signaling by LMP1 [27].

Other interactions of LMP-2A

• Since these mRNAs are readily detected in largely latently infected cells and do not increase in abundance with EBV replication, these putative latent-infection membrane proteins are tentatively designated LMP-2A and LMP-2B, respectively [28].
• In addition, we also detected other latent EBV transcripts (ie., BARF0-, LMP2A-, and Q/K-driven EBNA1 transcripts in these carcinomas using reverse transcription-PCR analysis [29].
• In long-term virus carriers, the mononuclear cells were again positive for latent (EBER1) and negative for lytic (BZLF1) markers; Cp/Wp-initiated RNAs were not detected in these samples, but in several individuals it was possible to amplify both Fp-initiated EBNA1 mRNA and LMP2A mRNA signals [30].
• EBNA1 and BamHI-A rightward transcripts (BART) were detected in 7 of 7 and LMP2A transcripts in 5 of 7 tumors with well-preserved RNA [31].

Analytical, diagnostic and therapeutic context of LMP-2A

• 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 [16].
• LMP2A interacts with Syk as demonstrated by coimmunoprecipitation and confocal microscopy [20].
• Confirmation of mutant LMP2A protein expression was by immunofluorescence and immunoblotting with a newly identified rat monoclonal antibody that recognizes each of the LMP2A deletion mutations [32].
• Sequence analysis of LMP2 cDNAs obtained from two NPC specimens revealed four mutations in exon 1 of the LMP2A transcript, which were present in both tumors and which resulted in nonconservative amino acid changes [33].
• The presence of each mutation, LMP2A delta 21-36, LMP2A delta 21-64, and LMP2A delta 21-85, in EBV-infected transformed lymphoblastoid cell lines was confirmed by PCR analysis and Southern blot hybridization [32].

References