You will be presented with the abstract, introduction, and discussion section from a biomedical research article. Your task is to create a summary that a layperson can understand, capturing the essence of the research article. Keep essential scientific terms, but ensure that the language remains clear and the concepts are explained in an uncomplicated manner.

Title: Epstein-Barr virus ensures B cell survival by uniquely modulating apoptosis at early and late times after infection}
Article:
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.
Introduction:
An estimated 15% of cancers worldwide are caused by infectious agents like viruses. Of these, Epstein-Barr virus( EBV) was the first human tumor virus discovered and is associated with malignancies of both B lymphocyte and epithelial cell origin. Normally, T cells prevent the development of EBV-associated malignancies and the virus persists quiescently in latently-infected memory B cells. As a result, nearly all adults in the world are latently infected( Longnecker et al., 2013), making EBV a particularly widespread and successful pathogen. However, in the absence of a healthy immune system, such as following organ transplant or HIV infection, EBV can transform B cells leading to markedly increased rates of lymphoma in these populations. Primary human B cell infection in vitro by EBV leads to their growth transformation and serves as a model for oncogenesis in EBV-associated lymphomas. This process requires the expression of six viral latent genes: Epstein-Barr Nuclear Antigen 1( EBNA1), EBNA2, EBNA-LP, EBNA3A, EBNA3C and Latent Membrane Protein 1( LMP1)( Longnecker et al., 2013). EBNA2, the major viral transcriptional activator and the first to be expressed upon infection, upregulates expression of the other viral EBNA genes as well as host genes( Wang et al., 2000; Zimber-Strobl and Strobl, 2001). EBNA2 also activates the expression of the viral oncoprotein LMP1, which drives the immortalization of the infected B cell into a lymphoblastoid cell line, or LCL, that proliferates indefinitely in culture. Together, the EBV latent oncoproteins mimic key aspects of normal B cell biology, promote proliferation, and inhibit the host innate tumor suppressor response to uncontrolled proliferation( Allday, 2013; Price and Luftig, 2014). It is well-established that the LMP1 oncoprotein is necessary for continued LCL growth and survival( Kaye et al., 1993; Zimber-Strobl et al., 1996). LMP1 mimics a pro-survival TNF receptor that signals constitutively through the NFκB pathway to promote proliferation and suppress apoptosis in transformed cells( Cahir-McFarland et al., 2000; Okan et al., 1995; Pratt et al., 2012). In fact, inhibition of the NFκB pathway activated downstream of LMP1 leads to apoptosis in LCLs. However, recent work from our laboratory has demonstrated that, early after infection, B cells rapidly proliferate despite low levels of LMP1 expression and NFκB activation( Nikitin et al., 2010; Price et al., 2012). Surprisingly, these early-infected cells also show no overt signs of apoptosis despite strong activation of the cellular DNA damage response( Nikitin et al., 2014). This suggests that in early-infected cells, there is a viral-mediated mechanism independent of LMP1 signaling that promotes survival. Several LMP1-independent mechanisms to subvert apoptosis have been described. For example, the viral BCL-2 homologue BHRF1 confers chemoresistance in a mouse model of Burkitt lymphoma( BL)( Kvansakul et al., 2010). Similarly, the viral BHRF1 and BALF1 proteins exert non-redundant roles in protecting initially infected cells from apoptosis( Altmann and Hammerschmidt, 2005). In addition, expression of the EBNA3 proteins induces resistance to apoptosis in BL cells and primary B cells by downregulating Bim expression( Paschos et al., 2009; Skalska et al., 2013), thereby making infected cells less ‘primed’ for apoptosis. The EBNA3 family is also known to epigenetically downregulate additional human genes involved in cell cycle regulation and apoptosis( Allday, 2013; Harth-Hertle et al., 2013; Hertle et al., 2009; Paschos et al., 2012; Skalska et al., 2013). It has been shown that the EBNA3 proteins mediate these epigenetic effects, in part, via interacting with additional proteins in such a way that chromatin architecture can be dramatically altered( Bazot et al., 2015; McClellan et al., 2013). While thought to be generally repressive in nature, recent work has shown that in some instances EBNA3 proteins can activate gene transcription( Bazot et al., 2015). In sum, viral proteins confer several survival advantages to infected cells, which often results in EBV-positive lymphomas that are more difficult to treat than their EBV-negative counterparts( Kelly et al., 2006). The intrinsic apoptosis pathway is controlled by complex protein—protein interactions at the surface of mitochondria that regulate the release of cytochrome c( Youle and Strasser, 2008). These functional interactions can be interrogated with an established approach called ‘BH3 profiling’, which uses peptides derived from BH3-only pro-apoptotic proteins to identify the anti-apoptotic BCL-2 family members important for preventing apoptosis in a particular cell( Del Gaizo Moore and Letai, 2013; Deng et al., 2007). Furthermore, molecular characterization of the interface between BH3 domains of these proteins has allowed for the creation of a new class of small molecule inhibitors that promote apoptosis directly in sensitive cell types( Billard, 2013; Oltersdorf et al., 2005). These so-called ‘BH3 mimetics’ are highly specific and show great promise in clinical trials( Letai, 2008). In this study, we characterized the BH3 profile of uninfected and EBV-infected primary human B cells from early proliferation through long-term outgrowth. We validated these profiles using BH3 mimetics and, importantly, identified a novel virus-specific transition in survival mechanisms between early and late stages of latent infection with implications for therapy of EBV-associated malignancies.
Discussion:
Suppression of apoptosis by EBV is essential for establishment of latent infection in the immune-competent host and promotes tumorigenesis in the immune suppressed host. While EBV encodes two putative BCL-2 homologues, these proteins are not required for survival after the first 24 hr following B cell infection( Altmann and Hammerschmidt, 2005). Rather, constitutive NFκB signaling from the viral oncoprotein LMP1, a TNFR homologue, is thought to be responsible for apoptotic suppression in latently infected, proliferating cells( Cahir-McFarland et al., 2000; Pratt et al., 2012). However, the initial burst of B cell proliferation induced by EBV is driven by expression of the viral EBNA transcription factors( EBNA1, 2, 3A, 3B, 3C, and LP) in the absence of appreciable LMP1 or NFκB activity( Price et al., 2012). Furthermore, this early period of hyper-proliferation activates a growth-suppressive DNA damage response, which would be expected to promote apoptosis( Nikitin et al., 2010). We, therefore, sought to identify the mechanism of survival during early infection by using BH3 profiling to query mitochondrial control of apoptosis prior to and through latent EBV infection and outgrowth of primary human B cells into LCLs. While BH3 profiling has been previously performed on virus-infected cells( Cojohari et al., 2015), this study focused on HCMV and was limited to a single EBV-positive Burkitt lymphoma cell line, Akata, which expresses only the viral EBNA1 protein. In our BH3 profiling study, we found that mature human peripheral blood B cells depend solely on BCL-2 for survival while EBV latent infection further suppressed apoptotic priming during outgrowth by initially upregulating MCL-1, followed by BFL-1. Mechanistically, we identified a new and unique role for the viral latent protein EBNA3A in apoptosis resistance during both early and late EBV-induced B cell proliferation. The importance of EBNA3A in B cell transformation and survival was previously recognized, but our studies now define the molecular basis for the inhibition of apoptosis. While both EBNA3A and EBNA3C suppress the pro-apoptotic protein Bim( Paschos et al., 2009), only EBNA3A was required to mitigate resistance to a BCL2 antagonist through outgrowth. EBNA3A regulated the BH3 profile of EBV-infected cells and suppressed apoptosis by promoting MCL-1 mitochondrial localization and increasing BFL-1 mRNA transcription. Transcription of BFL-1 was previously shown to be regulated by the EBV transcription factor EBNA2( Pegman et al., 2006) as well as LMP1-induced NFκB( Pratt et al., 2012). Our work now indicates that EBNA3A coordinates a chromatin architecture through an EBV super enhancer that facilitates NFκB-mediated activation of BFL-1 transcription. Therefore, our studies highlight a new cooperative role among EBNA3A, EBNA2, and LMP1 in transcriptional activation important for EBV-immortalized cell survival. The importance of MCL-1 in early EBV-infected human B cells coupled with the critical role of MCL-1 in germinal center( GC) formation and memory B cell survival in the mouse( Vikstrom et al., 2010) is consistent with the GC model of EBV infection. The GC model posits that EBV infection of naïve B cells promotes B cell maturation mimicking the GC reaction to access the long-lived memory B cell compartment and thus persisting for the lifetime of the host( Burns et al., 2015; Roughan and Thorley-Lawson, 2009). Our data support this model in that early infection of B cells by EBV promotes MCL-1 as a critical apoptotic regulator similar that observed for GC B cells in the mouse( Vikstrom et al., 2010). Furthermore, MCL-1 copy number gains and mutations are often found in B cell lymphomas( Wenzel et al., 2013). Therefore, the mechanism by which EBNA3A enhances MCL-1 function at the mitochondria may provide broad insight into apoptotic regulation during B-cell maturation and lymphomagenesis. The early phase of EBV infection where EBNAs are expressed with little or no expression of LMPs is known as latency IIb( Price and Luftig, 2015). The latency IIb expression pattern has also been observed by immuno-histochemical analysis in EBV-positive HIV-associated lymphomas, post-transplant lymphomas, in acute infectious mononucleosis, and in tumors of humanized mouse models of EBV infection( Price and Luftig, 2015). Indeed, a recent study found that an EBV recombinant lacking LMP1 was capable of forming B cell tumors in a humanized mouse model( Ma et al., 2015). The survival of these cells as well as those in other latency IIb expressing tissues likely depends on EBNA3A and MCL-1, while latency III cells expressing LMP proteins and high level NFκB signaling are likely to be less primed and to rely on BFL-1. As BH3 profiling has been a powerful predictive tool for chemotherapeutic responses in leukemias( Montero et al., 2015), our new findings suggest that such an approach could allow for better treatment decisions for EBV-associated malignancies.
Over 90% of adults around the world are infected with the Epstein-Barr virus . Like other closely related viruses , such as those that cause chicken pox and cold sores , an infection lasts for the rest of the person’s life , although the virus generally remains in a latent or dormant state . However , under certain conditions the latent viruses can cause cancers to develop; in fact , it is estimated that such infections are responsible for nearly 2% of all cancer deaths worldwide . One way that healthy human cells prevent cancer is by triggering their own death in a process called apoptosis . The Epstein-Barr virus can block apoptosis , therefore making the cells more likely to become cancerous . Previous research identified one protein in the Epstein-Barr virus that promotes cancer by preventing infected cells from dying as normal . However , even in the absence of this protein , Epstein-Barr virus-infected cells remain resistant to apoptosis . This suggests that the virus has another way of blocking cell death . Price et al . have now used a technique that stresses living cells in a way that reveals which proteins prevent apoptosis to study human cells infected with the Epstein-Barr virus . This revealed that soon after infection , the virus could force the human cell to produce MCL-1 , a protein that prevents cell death . Later , the Epstein-Barr virus enlisted a second human protein called BFL-1 , which makes the infected cell further resistant to apoptosis . Price et al . discovered that a protein in the Epstein-Barr virus called EBNA3A controls the production of the MCL-1 and BFL-1 proteins . In the future , developing therapies that target these proteins may lead to new treatments for cancers caused by the Epstein-Barr virus . Such treatments would be likely to have fewer side effects for patients than traditional chemotherapies .