Disease relevance of EBNA-LP

• Mediation of Epstein-Barr virus EBNA-LP transcriptional coactivation by Sp100 [1].
• We show that the EBNA-5 protein (alternatively designated EBNA-LP) that is required for B-cell transformation can form a molecular complex with the retinoblastoma (RB) and p53 tumor suppressor proteins [2].
• Therefore, we have used a comparative approach by studying the EBNA-LP homologues from baboon and rhesus macaque lymphocryptoviruses (LCVs) (baboon LCV and rhesus LCV) [3].
• EBNA-LP is not expressed in an EBV-transformed marmoset lymphocyte cell (B95-8) or in one EBV-infected Burkitt tumor cell line (Raji) but is expressed in three other Burkitt tumor cell lines (Namalwa, P3HR-1, and Daudi) [4].
• The potential karyophilic signals within EBNA-LP CR1c and CR2 were also examined by introducing oligonucleotides encoding these positively charged amino acid groupings into a cytoplasmic test protein, herpes simplex virus DeltaIE175, and by examining the intracellular localization of the resulting proteins [5].

High impact information on EBNA-LP

• The Epstein-Barr virus (EBV) EBNA-LP protein is important for EBV-mediated B-cell immortalization and is a potent gene-specific coactivator of the viral transcriptional activator, EBNA2 [1].
• The mechanism(s) by which EBNA-LP functions as a coactivator remains an important question in the biology of EBV-induced B-cell immortalization [1].
• Protein kinase A catalytic subunit alpha (PKAcsalpha) is significantly associated with HA95 in the presence or absence of EBNA-LP [6].
• Marked decreases in the levels of EBV nuclear antigen-1 (EBNA-1), EBNA-2, and EBNA-LP antibodies correlated with the increase in EBV-infected PBL [7].
• However, previous studies have indicated that EBNA-LP may contribute to immortalization by enhancing EBNA2-mediated transcriptional activation of the LMP-1 gene [8].

Biological context of EBNA-LP

• Vectors encoding two viral genes, EBNA-2 and EBNA-LP, are sufficient to activate the expression of cyclin D2 in this system [9].
• These results indicated that the coactivator function of EBNA-LP is regulated by phosphorylation [10].
• The rhesus LCV EBNA-LP was able to further enhance rhesus LCV or EBV EBNA2 transactivation 5- to 12-fold [3].
• Expression of cyclin D2 is induced in primary B lymphocytes following infection with Epstein-Barr virus (EBV) or transfection of the EBV genes EBNA-LP and EBNA-2 [11].
• While EBNA-2's essential role in transformation as a transcriptional activatory is well documented, very little is known about EBNA-LP function except that recombinant viruses lacking the EBNA-LP Y1Y2 exons show reduced, but still detectable, transforming ability [12].

Anatomical context of EBNA-LP

• Several lymphoblastoid cell lines infected with the EBNA-LP mutant recombinant viruses had a high percentage of cells with bright cytoplasmic immunoglobulin staining, as is characteristic of cells undergoing plasmacytoid differentiation [13].
• We report here that EBNA-LP self-associates in vivo and the domain responsible for the homotypic association is a multifunctional domain mediating nuclear localization, nuclear matrix association, and EBNA-2-dependent coactivator function of the protein [14].
• (iii) When Flag epitope-tagged EBNA-LP with either one or two W1W2 repeats and EBNA-LP containing four W1W2 repeats were coexpressed in COS-7 cells, the latter was specifically coimmunoprecipitated with the former [14].
• EBNA-2 is essential for lymphocyte transformation, and EBNA-LP is at least critical [15].

Associations of EBNA-LP with chemical compounds

• Identification of evolutionarily conserved serine residues and regions in EBNA-LP homologues provides important clues for identifying the cellular cofactors and molecular mechanisms mediating these conserved viral functions [3].
• Clustered alanine mutations were introduced into CR1 to CR3, and the conserved serines were also changed to alanine residues in an EBNA-LP with two repeats, which is the minimal protein able to cooperate with EBNA2 [5].
• (ii) A purified chimeric protein consisting of glutathione S-transferase fused to EBNA-LP specifically formed complexes with EBNA-LP transiently expressed in COS-7 cells [14].
• Release from nocodazole G2/M block or treatment with phosphatase caused the more slowly migrating species of EBNA-LP to disappear [16].
• (iii) The EBNA-LP mutant with the arginine to alanine substitutions in NMTS was no longer localized not only to the nuclear matrix but also to the nucleus [17].

Physical interactions of EBNA-LP

• Epstein-Barr virus (EBV) nuclear antigen leader protein (EBNA-LP) forms complexes with a cellular anti-apoptosis protein Bcl-2 or its EBV counterpart BHRF1 through HS1-associated protein X-1 [18].

Regulatory relationships of EBNA-LP

• Identification of major phosphorylation sites of Epstein-Barr virus nuclear antigen leader protein (EBNA-LP): ability of EBNA-LP to induce latent membrane protein 1 cooperatively with EBNA-2 is regulated by phosphorylation [10].

Other interactions of EBNA-LP

• We have also found that the behavior of EBNA-3A in a cell fractionation procedure that distinguishes insoluble matrix from soluble cell fractions is modified by EBNA-LP, indicating a further novel level of interplay between the EBNA proteins [19].
• Consistent with this, the EBV-encoded conserved protein kinase BGLF4 specifically mediated the phosphorylation of EBNA-LP at Ser-35 [20].

Analytical, diagnostic and therapeutic context of EBNA-LP

• (v) Careful cell fractionation experiments of an EBV-infected lymphoblastoid cell line revealed that EBNA-LP is localized in the cytoplasm as well as in the nucleus [21].
• (vi) When EBNA-LP containing four W1W2 repeats was expressed in COS-7 cells, EBNA-LP was detected mainly in the nucleus by immunofluorescence assay [21].
• Finally, no significant interactions between EBNA2 and EBNA-LP were found with mammalian two-hybrid assays [8].
• Microarray analysis led to the identification of a cellular gene encoding the CC chemokine TARC as a novel target gene that was induced by EBNA-LP [22].
• Metabolic 32Pi-labeling of cells followed by two-dimensional gel electrophoresis showed that EBNA-LP could be resolved into multiple phosphorylated isoforms [23].

References