Epstein-Barr virus ensures B cell survival by uniquely modulating apoptosis at early and late times after infection

Abstract

Latent Epstein-Barr virus (EBV) infection is causally linked to several human cancers. EBV expresses viral oncogenes that promote cell growth and inhibit the apoptotic response to uncontrolled proliferation. The EBV oncoprotein LMP1 constitutively activates NFκB and is critical for survival of EBV-immortalized B cells. However, during early infection EBV induces rapid B cell proliferation with low levels of LMP1 and little apoptosis. Therefore, we sought to define the mechanism of survival in the absence of LMP1/NFκB early after infection. We used BH3 profiling to query mitochondrial regulation of apoptosis and defined a transition from uninfected B cells (BCL-2) to early-infected (MCL-1/BCL-2) and immortalized cells (BFL-1). This dynamic change in B cell survival mechanisms is unique to virus-infected cells and relies on regulation of MCL-1 mitochondrial localization and BFL-1 transcription by the viral EBNA3A protein. This study defines a new role for EBNA3A in the suppression of apoptosis with implications for EBV lymphomagenesis.DOI: http://dx.doi.org/10.7554/eLife.22509.001

Identification of Host Biomarkers of EBV Latency IIb and Latency III

“…Broad distribution of LMP1 within latency III populations makes these cells difficult to distinguish. As many EBV-positive tumors display cellular LMP1 heterogeneity (14, 15), it is important to determine whether these EBNA+/LMP1-cells are latency IIb or latency III as their immune recognition and response to chemotherapy may vary depending on viral gene expression (7, 10).…”

“…Early after infection, EBNA2 stimulates cellular proliferation by inducing the host transcription factor c-Myc through coordination of its upstream enhancer and chromatin looping (6). During this period, the cells are dependent upon MCL-1 and BCL-2 for survival in the absence of NFκB signaling (5, 7). Elevated levels of c-Myc early after infection antagonize LMP1 mRNA and protein expression (8).…”

“…By two to three weeks post-infection, c-Myc levels wane, hyper-proliferation is attenuated, and full expression of the LMPs, particularly LMP1-mediated NFκB activity, is observed (11). These cells rely on NFκB signaling for survival (12) and display a distinct mitochondrial anti-apoptotic phenotype with up-regulation of BFL-1 (5, 7).…”

“…We have previously demonstrated that latency IIb and latency III cells have unique survival requirements and apoptotic regulation (7, 17, 18). However, these studies analyzed bulk LCL populations and did not address single-cell level differences.…”

LTRs activated by Epstein-Barr virus-induced transformation of B cells alter the transcriptome

“…Transformation of primary B cells leads to genomewide transcriptional changes including a decrease of apoptotic genes and an increase of proliferative genes (Allday 2013;Price and Luftig 2014;Price et al 2017). EBV-induced transformation of primary B cells also leads to DNA hypomethylation at about two-thirds of the genome (Hernando et al 2013;Hansen et al 2014).…”