Viral Genome Methylation Differentially Affects the Ability of BZLF1 versus BRLF1 To Activate Epstein-Barr Virus Lytic Gene Expression and Viral Replication

Self Cite

Epstein-Barr virus (EBV) maintains a lifelong latent infection within a subset of its host IMPORTANCEThis study is the first one to show that the cellular transcription factor BLIMP1, a key player in both epithelial and B-cell differentiation, induces reactivation of the oncogenic herpesvirus Epstein-Barr virus (EBV) out of latency into lytic replication in a variety of cancerous epithelial cell types as well as in some, but not all, B-cell types that contain this virus in a dormant state. The mechanism by which BLIMP1 does so involves strongly turning on expression of both of the immediate early genes of the virus, probably by directly acting upon the promoters as part of protein complexes or indirectly by altering the expression or activities of some cellular transcription factors and signaling pathways. The fact that EBV ؉ cancers usually contain mostly undifferentiated cells may be due in part to these cells dying from lytic EBV infection when they differentiate and express wild-type BLIMP1.

Section: Methodsmentioning

confidence: 99%

Section: Importancementioning

confidence: 99%

Cellular Differentiation Regulator BLIMP1 Induces Epstein-Barr Virus Lytic Reactivation in Epithelial and B Cells by Activating Transcription from both the R and Z Promoters

Reusch

Nawandar

Wright

et al. 2015

Self Cite

“…Cell lines containing pCEP4 episomal vectors were maintained in 200 g of hygromycin (Roche)/ml to select for retention of the vector. Normal oral keratinocyte (NOK) and NOK-Akata cells (a gift from Shannon Kenney, University of Wisconsin) have been previously described (19) and were maintained in keratinocyte-SFM (Life Technologies, Inc.) supplemented with epidermal growth factor, bovine pituitary extract, and antibiotic/antimycotic.…”

Section: Methodsmentioning

confidence: 99%

Host Gene Expression Is Regulated by Two Types of Noncoding RNAs Transcribed from the Epstein-Barr Virus BamHI A Rightward Transcript Region

Marquitz

Mathur

Edwards

et al. 2015

In Epstein-Barr virus-infected epithelial cancers, the alternatively spliced BamHI A rightward transcripts (BARTs) are the most abundant viral polyadenylated RNA. The BART introns form the template for the production of 44 microRNAs (miRNAs), and the spliced and polyadenylated exons form nuclear non-protein-coding RNAs. Analysis of host cell transcription by RNA-seq during latency in AGS cells identified a large number of reproducibly changed genes. Genes that were downregulated were enriched for BART miRNA targets. Bioinformatics analysis predicted activation of the myc pathway and downregulation of XBP1 as likely mediators of the host transcriptional changes. Effects on XBP1 activity were not detected in these cells; however, myc activation was confirmed through use of a myc-responsive luciferase reporter. To identify potential regulatory properties of the spliced, polyadenylated BART RNAs, a full-length cDNA clone of one of the BART isoforms was obtained and expressed in the Epstein-Barr virus (EBV)-negative AGS cells. The BART cDNA transcript remained primarily nuclear yet induced considerable and consistent changes in cellular transcription, as profiled by RNA-seq. These transcriptional changes significantly overlapped the transcriptional changes induced during latent EBV infection of these same cells, where the BARTs are exclusively nuclear and do not encode proteins. These data suggest that the nuclear BART RNAs are functional long noncoding RNAs (lncRNAs). The abundant expression of multiple forms of noncoding RNAs that contribute to growth regulation without expression of immunogenic proteins would be an important mechanism for viral oncogenesis in the presence of a functional immune system. IMPORTANCEInfection with Epstein-Barr virus (EBV) is nearly ubiquitous in the human population; however, it does contribute to the formation of multiple types of cancer. In immunocompromised patients, EBV causes multiple types of lymphomas by expressing viral oncogenes that promote growth and survival of infected B lymphocytes. EBV-positive gastric carcinoma does not require immune suppression, and the viral oncoproteins that are frequent targets for an immunological response are not expressed. This study demonstrates using transcriptional analysis that the expression of various classes of viral non-protein-coding RNAs likely contribute to the considerable changes in the host transcriptional profile in the AGS gastric cancer cell line. This is the first report to show that the highly expressed polyadenylated BamHI A rightward transcripts (BART) viral transcript in gastric carcinoma is in fact a functional viral long noncoding RNA. These studies provide new insight into how EBV can promote transformation in the absence of viral protein expression. L atent infection with Epstein-Barr virus (EBV), a nearly ubiquitous human herpesvirus, is responsible for multiple malignancies in the two types of cells that it infects: B lymphocytes and epithelial cells (1). The mechanism by which EBV leads to transformation dep...

“…In B cells, the viral lytic cascade is induced by the two immediate early genes BZLF1 and BRLF1, which cooperate to induce expression of all downstream lytic genes (20). BRLF1, whose expression depends on cellular transcription factors that differ from those required by BZLF1, is uniquely required in at least some epithelial cells (21). Expression of BRLF1 is enhanced by B lymphocyte-induced maturation protein 1 (BLIMP1) and KLF4, both of which are expressed in epithelial cells in a differentiation-dependent manner.…”

Section: Now and The Futurementioning

confidence: 99%

The Long and Complicated Relationship between Epstein-Barr Virus and Epithelial Cells

Hutt-Fletcher

2017

The roles of epithelial cells in infection and persistence of the EpsteinBarr virus (EBV) have long been difficult to resolve. However, recent developments have reinforced the conclusion that these cells are a major site of virus replication and raised the possibility that, like papillomaviruses, EBV has evolved to take advantage of epithelial differentiation to ensure survival, persistence, and spread.KEYWORDS Epstein-Barr virus, epithelial cells, tropism E pstein-Barr virus (EBV) is well known as a human lymphotropic herpesvirus that was isolated from a Burkitt's lymphoma in the early 1960s (1). It is a well-described causal agent of infectious mononucleosis and an important player in the development of lymphoid tumors. It is well used as a tool for immortalizing human B cells. Soon after its discovery, an association between EBV and epithelial malignancies was revealed (2) and the presence of the virus was confirmed within epithelial cells of nasopharyngeal carcinoma (3). Yet, as late as 2005, a distinguished speaker at an international herpesvirus meeting declared that epithelial cells were not relevant to the general biology of EBV. How was that possible, and where are we today? EARLY WORKEarly works described EBV DNA and RNA in squamous epithelial cells shed in the oral cavity during acute infectious mononucleosis (4, 5). Thus, the model with B cells as the reservoir of latent EBV and epithelial cells as the site of productive lytic replication in vivo was developed. However, additional support for the routine involvement of epithelial cells in primary and persistent infections was, for many years, quite elusive. In the absence of any obvious lesions, such as those seen in herpes simplex infections, the finding of an infected cell in the oral cavity was much like looking for the proverbial needle in the haystack. Compounding the problem was the difficulty in infecting epithelial cells in vitro. With the advent of the AIDS epidemic, oral hairy leukoplakia appeared, which was the first and remains the only disease caused entirely by productive replication of EBV. Oral hairy leukoplakia, which is an epithelial hyperplasia typically found on the lateral tongue (6), is full of and driven by EBV lytic replication (7,8). This bolstered the case for epithelial cells in the oral cavity being responsible for the production of cell-free virus in saliva, but still, normal epithelial cells were readily found to contain virus only in individuals coinfected with the human immunodeficiency virus (9). For a while, the model of persistence pivoted toward the idea that in the absence of malignancy or other underlying disease, B cells alone are involved in infection (10).Three sets of observations subsequently helped spur a return to the yin-and-yang description of epithelial and B cell infection. Despite the uncertainty about the role of epithelial cells in EBV biology, its presence in epithelial cells of patients with nasopharyngeal carcinoma and gastric cancer indicates that EBV remains important for understanding...