Epstein-Barr virus: detection of genome in somatic cell hybrids of Burkitt lymphoblastoid cells

Epstein-Barr virus and nasopharyngeal carcinoma

The Epstein-Barr virus (EBV) has been studied for over 25 years as a probable cause of certain human cancers, including nasopharyngeal carcinoma (NPC). This is a low-incidence head and neck cancer in Western countries (including the USA), but is the third-leading cancer in males in Southeast Asia. Evidence supporting an etiologic relation between this virus and NPC includes the fact that there is a 100% infection rate in patients with this cancer and that EBV DNA and antigens have been demonstrated in all biopsies examined to date. The determination that EBV is at least a major co-factor in the etiology of NPC has led to the development of new diagnostic and prognostic tests for this disease using anti-viral markers. Of particular importance to the diagnosis of NPC were the findings, initially reported by the Henles [Int J Cancer 17:1-7, 1976], that the serum of patients with NPC contain IgA antibodies to EBV at a high frequency. In general, 80-90% of patients with this disease contain serum IgA antibodies to EBV as opposed to 10-30% of the normal population. This finding has resulted in the development and successful employment of tests measuring this antibody as adjuncts to pathology in the diagnosis of NPC including the occult form. In addition, this finding has resulted in the development of tests for the early detection of this disease. The IgA test for antibodies to EBV is currently employed in large screening programs in Southeast Asia designed to identify those individuals at risk for the development of NPC.(ABSTRACT TRUNCATED AT 250 WORDS)

Transfection of a rearranged viral DNA fragment, WZhet, stably converts latent Epstein-Barr viral infection to productive infection in lymphoid cells

An Epstein-Barr viral gene (ZEBRA) is identified that, in human lymphoblastoid cells, activates a switch causing the virus to shift from the latent to the replicative phase of its life cycle. We have shown that a 2.7-kilobase-pair rearranged Epstein-Barr virus DNA fragment of this gene (BamHI fragment WZhet) induced transient expression of viral replicative antigens and polypeptides when it was transfected into a somatic cell hybrid, which was derived from the fusion of an epithelial line cell with a Burkitt lymphoma cell. We now show that this rearranged WZhet fragment, when introduced stably into lymphoblastoid cells, will activate expression of the complete viral replicative cycle in 1-10% of the lymphoblastoid cells, leading to production of biologically active virions that can immortalize primary lymphocytes. The transfected plasmid appears to be regulated in a manner analogous to the complete Epstein-Barr virus genome.

A cis-acting element from the Epstein-Barr viral genome that permits stable replication of recombinant plasmids in latently infected cells

The Epstein-Barr viral (EBV) genome of approximately equal to 170 kilobase pairs (kbp) is maintained as a plasmid in human B lymphoblasts transformed by the virus. We have identified a cis-acting element within 1.8 kbp of the viral genome that allows recombinant plasmids carrying it to be selected at high frequency and maintained as plasmids in cells latently infected by EBV. This functional element(s) requires a segment of DNA at least 800 bp and at most 1800 bp long, which contains a family of 30-bp tandem repeats at one end. Since this region confers efficient stable replication only to plasmids transfected into cells containing EBV genomes, its function probably requires trans-acting products encoded elsewhere in the viral genome.

Identification of a region of the Epstein-Barr virus (B95-8) genome required for transformation

In a previous study the identification of a region(s) of the Epstein-Barr virus (EBV) genome, which is associated with transformation, was attempted by marker rescue. A transforming EBV was rescued from D98/HR-1 hybrid cells, which contain the non-transforming HR-1 EBV genome, after transfection with specific BamHI and Charon 4A fragments (J. Stoerker and R. Glaser, Proc. Nat. Acad. Sci. USA 80, 1726-1729, 1983). In this study, characterization of the EBV DNA in four human lymphoblastoid cell lines (LCL) transformed with rescued virus was performed. It was found that recombination between the transfected fragments, BamHI H,F,X and the Charon 4A fragment (EB-26-36) which is equivalent to the BamHI H,F,X region, and the endogenous HR-1 EBV genome in the D98/HR-1 cells took place. This recombination resulted in the formation of transforming EBV. The EBV DNA in the four LCLs are similar to each other and to HR-1 EBV DNA. However, the EBV DNA in all four LCLs also contain the U2 region plus additional sequences of B95-8 DNA. The U2 region is deleted in HR-1 EBV DNA which is associated with HR-1 cells and the D98/HR-1 hybrid cells. Thus, transforming activity of the HR-1-like viruses rescued from D98/HR-1 cells was concomitant with the recombination of the 0.26-0.36 region of the EBV genome, suggesting that this region is necessary for at least the initiation of transformation.

Rescue of transforming Epstein-Barr virus (EBV) from EBV-genome-positive epithelial hybrid cells transfected with subgenomic fragments of EBV DNA

Transfection experiments using subgenomic fragments of the B95-8 strain of Epstein-Barr virus (EBV) DNA and EBV genome (HR-1)-positive epithelial/Burkitt hybrid cells (D98/HR-1) were carried out to determine whether an interaction between the transfecting virus fragment(s) and the endogenous HR-1 EBV genome could take place. Expression of EBV-specific antigens, including early antigen and virus capsid antigen, was examined in transfected cells by immunofluorescence. Attempts were also made to recover biologically active EBV from the D98/HR-1 cells after transfection with cloned fragments of B95-8 DNA. We found that D98/HR-1 cells transfected with the BamHI H or H, F, and X fragments were positive for early antigen 3 days after transfection. Spent media from transfected D98/HR-1 cells maintained for 20-30 days in culture were pooled, filtered, concentrated, and used as a potential source of virus to inoculate human umbilical cord blood lymphocytes. No evidence of transformation was observed with such preparations. However, if spent medium from D98/HR-1 cell cultures was first treated with iododeoxyuridine (to induce EBV DNA synthesis and replicative cycle) and then transfected with the BamHI H, F, and X fragments of B95-8 DNA and used to infect cord blood lymphocytes, transformation was obtained. A lymphoblastoid cell line derived in this manner, designated HI-HFX, is an EBV nuclear antigen-positive nonproducer cell line. Similar results were obtained with preparations from iododeoxyuridine-treated D98/HR-1 cells transfected with the EB 26-36 fragment of B95-8 DNA cloned in a Charon 4A vector. The EB 26-36 fragment contains the BamHI H, F, and X regions.

Changes in the expression of two Epstein-Barr virus-associated antigens, EBNA and RANA, during the cell cycle of transformed human B lymphoblasts

Two methods of cell sychronization, density-dependent arrest and double thymidine block, were used to assign two Epstein-Barr virus-associated antigens to different parts of the growth cycle of the human B lymphblastoid cell lines, WI-L2 and Raji. The Epstein-Barr nuclear antigen (EBNA), as detected by anti-complement immunofluorescence, was maximally expressed during early S phase, decreased during the G2 and M phases, and was absent in early G1. In contrast, the rheumatoid arthritis nuclear antigen (RANA), as detected by anti-immunoglobulin immunofluorescence with a prototype serum form a patient with rheumatoid arthritis, was maximally expressed during early G1 phase, progressively decreased during S and early G2, and reappeared during late G2/M.

Epstein-Barr virus in somatic cell hybrids between mouse cells and human nasopharyngeal carcinoma cells

Somatic cell hybrids between mouse cells and cells derived directly from NPC biopsies were produced in order to study the association of the Epstein-Barr virus (EBV) genome and the expression of Epstein-Barr nuclear antigen (EBNA) with the human chromosome(s). All attempts to correlate the presence of EBV-DNA and the expression of EBNA with the presence of a particular human chromosome(s) showed that the segregation of EBV-DNA or of EBNA and human chromosomes was dysconcordant. The data, therefore, suggest that in the hybrids studied the presence of EBA-DNA is not determined by the presence of a specific human chromosome.

Effect of dibutyryl cyclic AMP on the induction of Epstein-Barr virus in hybrid cells

Treatment of Epstein-Barr virus (EBV) negative somatic cell hybrids with 5'-iododeoxyuridine (IUdR) induced synthesis of EBV antigens and virus particles. When dibutyryl cAMP (Bt(2)-cAMP) was present in medium after exposure of cultures to IUdR, the incidence of cells synthesizing EBV early and virus capsid antigens was increased. The time necessary for appearance of EBV particles after induction by IUdR was significantly reduced in the presence of Bt(2)-cAMP. This enhancement was evident to a lesser degree with 3':5' cAMP than with Bt(2)-cAMP and did not occur with any other of the related compounds tested. The response observed was dose dependent. Untreated (no IUdR) EBV negative hybrid cells exposed to Bt(2)-cAMP also synthesized EBV antigens. The concentration of intracellular cAMP may act as one of the control mechanisms selecting for gene expression in this system.