Epstein-Barr virus with heterogeneous DNA disrupts latency

Abstract

By cloning the HR-1 Burkitt lymphoma line, we previously uncovered two distinct biological variants of nontransforming Epstein-Barr virus (EBV). The most commonly cloned variant has a low rate of spontaneous viral synthesis and is unable to induce early antigen in Raji cells (EAF). A rare variant spontaneously releases virus which is capable of inducing early antigen in Raji cells (EAI+). Since EAF virus lacks heterogeneous DNA (het-) and EAI+ virus contains heterogeneous DNA (het+), we suggested that spontaneous viral synthesis and induction of early antigen are biological properties which correlate with the presence of het sequences. The present experiments provide three new lines of experimental evidence in favor of this hypothesis. (i) Revertant subclones of the EAI+ het+ variant which have lost the het DNA concomitantly lost EAI ability. Thus, het DNA is not stably associated with the cells as are the episomes. (ii) het DNA was acquired by two het-subclones of the HR-1 line after superinfection with EAI+ virus. After superinfection, these clones synthesized EAI+ het+ virus. Thus, het DNA may be maintained in the HR-1 line by cell-to-cell spread. (iii) Virus with het DNA activated full expression of endogenous latent EBV of the transforming phenotype in a line of immortalized neonatal lymphocytes designated X50-7. By use of restriction endonuclease polymorphisms unique to both the superinfecting and endogenous genomes, we show that the genome of the activated virus resembles that of the virus which was endogenous to X50-7 cells. This result suggests that het sequences result in transactivation of the latent EBV. het DNA had homology with EBV sequences which are not normally contiguous on the physical map of the genome. het DNA was always accompanied by the presence of DNA of nonheterogenous HR-1. Thus, het DNA is a form of "defective" EBV DNA. However, the biological effect of this defective DNA is to enhance rather than to interfere with EBV replication. This is a novel property of defective virus.

Pathways of activation of the Epstein-Barr virus productive cycle

“…Several different conditions or stimuli can be used to induce the virus productive cycle; these include 12-0-tetradecanoylphorbol-13-acetate (TPA) (37), butyrate, iododeoxyuridine, transforming growth factor ,B (3), and cross-linking surface immunoglobulin (33) on latently infected cells. Superinfection of latently infected cells with defective variants of P3HR1 EBV (7) (such as het [28]) also activates the productive cycle. Virus production in vivo is readily observed in oral hairy leukoplakia, an epithelial lesion frequently found in patients with AIDS (16).…”

The zta transactivator involved in induction of lytic cycle gene expression in Epstein-Barr virus-infected lymphocytes binds to both AP-1 and ZRE sites in target promoter and enhancer regions

“…In the case of Epstein-Barr virus (EBV), three phosphorylated nuclear transactivator proteins have been described that either specifically or nonspecifically stimulate gene expression from lytic-cycle viral promoters in transient cotransfection assays (10,26,43,64). The lytic cycle of EBV can be reactivated from latently infected B lymphocytes in culture after various chemical manipulations, including treatment with tumor promoters (68), sodium butyrate, anti-immunoglobulin M (IgM), and calcium ionophores as well as by superinfection with rearranged defective P3HR-1 virus genomes in which all three EBV transactivators potentially come under the transcriptional control of the BamHI-W or -C latency promoters (12,45).…”

Size heterogeneity of EBV and mitochondrial DNAs in Burkitt's lymphoma lines

“…Thus, these data support the notion of a 20 kb defective species in the LY91 cell line. Recent experiments by Miller and collaborators have emphasised the dependence upon defective (or heterogeneous, bet) forms of EBV for the induction of viral early antigens and virion formation (13,21). Unlike the normal viral gename, the defective species was readily lost upon passage of cells in culture and viral producer cells concamitantly converted to latently infected cells (21).…”