The Epstein-Barr Virus EBNA-LP Protein Preferentially Coactivates EBNA2-Mediated Stimulation of Latent Membrane Proteins Expressed from the Viral Divergent Promoter

Abstract

The mechanistic contribution of the Epstein-Barr virus (EBV) EBNA-LP protein to B-cell immortalization remains an enigma. However, previous studies have indicated that EBNA-LP may contribute to immortalization by enhancing EBNA2-mediated transcriptional activation of the LMP-1 gene. To gain further insight into the potential role EBNA-LP has in EBV-mediated B-cell immortalization, we asked whether it is a global or gene-specific coactivator of EBNA2 and whether coactivation requires interaction between these proteins. In type I Burkitt's lymphoma cells, we found that EBNA-LP strongly coactivated EBNA2 stimulation of LMP-1 and LMP2B RNAs, which are expressed from the viral divergent promoter. Surprisingly, the viral LMP2A gene and cellular CD21 and Hes-1 genes were induced by EBNA2 but showed no further induction after EBNA-LP coexpression. We also found that EBNA-LP did not stably interact with EBNA2 in coimmunoprecipitation assays, even though the conditions were adequate to observe specific interactions between EBNA2 and its cellular cofactor, CBF1. Colocalization between EBNA2 and EBNA-LP was not detectable in EBV-transformed cell lines or transfected type I Burkitt's cells. Finally, no significant interactions between EBNA2 and EBNA-LP were found with mammalian two-hybrid assays. From this data, we conclude that EBNA-LP is not a global coactivator of EBNA2 targets, but it preferentially coactivates EBNA2 stimulation of the viral divergent promoter. While this may require specific transient interactions between these proteins that only occur in the context of the divergent promoter, our data strongly suggest that EBNA-LP also cooperates with EBNA2 through mechanisms that do not require direct or indirect complex formation between these proteins.

Mechanisms of cell immortalization mediated by EB viral activation of telomerase in nasopharyngeal carcinoma

“…EBV may cause the NPC cell oncogenic clonal evolution by interfering with several intracellular mechanisms in the npg infected cells [1,[7][8][9][10][11]. Recently, evidence suggests that the enzyme telomerase required for cell immortalization is activated in NPC and the EBV proteins are involved in regulating telomerase activity [12][13][14], consistent with the findings that EBV proteins also play a key role in immortalization of infected B-lymphocyte [15][16][17]. Here we review the recent progress in our understanding of regulation of telomerase activity by EBV proteins, a critical step in cell immortalization.…”

EBV nuclear antigen EBNALP dismisses transcription repressors NCoR and RBPJ from enhancers and EBNA2 increases NCoR-deficient RBPJ DNA binding

“…These effects can be strong. EBNA2 and EBNALP coactivation of hes1 in BJAB cells was greater than observed in transiently transfected BL cells (51).…”

Truncated Form of the Epstein-Barr Virus Protein EBNA-LP Protects against Caspase-Dependent Apoptosis by Inhibiting Protein Phosphatase 2A

“…EBNA-LP is known to enhance the EBNA2-mediated transcriptional activation of various cellular (cyclin D2) and viral (LMP-1 and LMP-2B) genes (10,30,31,33,42). Three functionally conserved regions (CR1, CR2, and CR3) have been identified in the W1W2 domains: CR1 and CR2 constitute a bipartite nuclear localization signal, which, together with CR3, is critical for the transcriptional coactivation function of EBNA-LP.…”