Micro RNAs of Epstein-Barr Virus Promote Cell Cycle Progression and Prevent Apoptosis of Primary Human B Cells

Abstract

Cellular and viral microRNAs (miRNAs) are involved in many different processes of key importance and more than 10,000 miRNAs have been identified so far. In general, relatively little is known about their biological functions in mammalian cells because their phenotypic effects are often mild and many of their targets still await identification. The recent discovery that Epstein-Barr virus (EBV) and other herpesviruses produce their own, barely conserved sets of miRNAs suggests that these viruses usurp the host RNA silencing machinery to their advantage in contrast to the antiviral roles of RNA silencing in plants and insects. We have systematically introduced mutations in EBV's precursor miRNA transcripts to prevent their subsequent processing into mature viral miRNAs. Phenotypic analyses of these mutant derivatives of EBV revealed that the viral miRNAs of the BHRF1 locus inhibit apoptosis and favor cell cycle progression and proliferation during the early phase of infected human primary B cells. Our findings also indicate that EBV's miRNAs are not needed to control the exit from latency. The phenotypes of viral miRNAs uncovered by this genetic analysis indicate that they contribute to EBV-associated cellular transformation rather than regulate viral genes of EBV's lytic phase.

Epstein–Barr virus microRNAs reduce immune surveillance by virus-specific CD8 + T cells

“…Therefore, miRNA-mediated reduction of IL-12 could lead to decreased T-cell activation and recognition at different stages of infection and malignant disease. Among TAPregulating miRNAs, miR-BHRF1-3 is predominantly expressed initially upon infection and in latency III in vitro (36), but miR-BART17 also shows expression in memory B cells and cancer cells (48), suggesting that EBV miRNA-mediated TAP regulation could likewise be important in vivo.…”

“…1A) to evaluate if EBV miRNAs counteract immune surveillance by EBV-specific CD8 + T cells. B cells (CD19 + ) isolated from peripheral blood mononuclear cells (PBMCs) from EBV-positive donors were infected with two EBV strains: the laboratory strain B95-8 (WT/B95-8), expressing 13 viral miRNAs, and its derivative ΔmiR, expressing no viral miRNAs (36). Twelve hours later, autologous CD8 + T cells were added, and the cells were cocultured for 4 wk (Fig.…”

“…EBV MiRNAs Inhibit Recognition, Killing, and Expansion of EBV-Specific CD8 + T Cells. Earlier studies had shown that B-cell survival could be compromised in cells infected with the ΔmiR EBV devoid of miRNAs, because some viral miRNAs contribute to EBVassociated cellular transformation in the early phase of infection (36)(37)(38). To evaluate a possible role of viral miRNAs in controlling immune functions of EBV-specific CD8 + T cells, we established polyclonal EBV-specific CD8 + T cells from different donors.…”

Infection of Epstein–Barr virus in a gastric carcinoma cell line induces anchorage independence and global changes in gene expression

“…The EBV B95-8 laboratory strain that readily transforms primary B lymphocytes is deleted for most of the BART miRNAs, which, in combination with the minimal expression in B-cell lines, indicates that they are not required for B-cell transformation (11,14). However, a cluster of three miRNAs that are produced from the primary EBNA2 transcript have been shown to contribute to B-cell transformation (15,16). The contribution of the BART miRNAs to the development of EBV-associated cancers of epithelial origin has only begun to be explored.…”

A Cluster of Virus-Encoded MicroRNAs Accelerates Acute Systemic Epstein-Barr Virus Infection but Does Not Significantly Enhance Virus-Induced Oncogenesis In Vivo

“…Two of the three BHRF1 miRNAs are located in the BHRF1 3= untranslated region and one is located immediately 5= to the BHRF1 lytic mRNA transcription start site (7,9). The roles of these BHRF1 miRNAs were unclear until recent in vitro studies using viral knockouts in lymphoblastoid cell lines (LCLs), a widely used cellular model of latency III EBV infection, revealed that the BHRF1 miRNAs cooperate to enhance B cell expansion, reduce levels of latent gene expression, and possibly also inhibit apoptosis (10)(11)(12). Additionally, as circumstantial evidence for the roles of these miRNAs, studies that comprehensively examined the targets of EBV miRNAs have shown that BHRF1 miRNAs bind a number of targets involved in proliferation, latent gene expression, and regulation of apoptosis (13,14).…”