Specific sites for EBV association in the Namalwa Burkitt lymphoma cell line and in a lymphoblastoid line transformed in vitro with EBV

Mechanism and therapeutic implications of pomalidomide-induced immune surface marker upregulation in EBV-positive lymphomas

Epstein-Barr virus (EBV) downregulates immune surface markers to avoid immune recognition. Pomalidomide (Pom) was previously shown to increase immune surface marker expression in EBV-infected tumor cells. We explored the mechanism by which Pom leads to these effects in EBV-infected cells. Pom increased B7-2/CD86 mRNA, protein, and surface expression in EBV-infected cells but this was virtually eliminated in EBV-infected cells made resistant to Pom-induced cytostatic effects. This indicates that Pom initiates the upregulation of these markers by interacting with its target, cereblon. Interestingly, Pom increased the proinflammatory cytokines IP-10 and MIP-1∝/β in EBV infected cells, supporting a possible role for the phosphoinositide 3-kinase (PI3K)/AKT pathway in Pom's effects. Idelalisib, an inhibitor of the delta subunit of PI3 Kinase, blocked AKT-Ser phosphorylation and Pom-induced B7-2 surface expression. PU.1 is a downstream target for AKT that is expressed in EBV-infected cells. Pom treatment led to an increase in PU.1 binding to the B7-2 promoter based on ChIP analysis. Thus, our data indicates Pom acts through cereblon leading to degradation of Ikaros and activation of the PI3K/AKT/PU.1 pathway resulting in upregulation of B7-2 mRNA and protein expression. The increased immune recognition in addition to the increases in proinflammatory cytokines upon Pom treatment suggests Pom may be useful in the treatment of EBV-positive lymphomas.

Non-Random Pattern of Integration for Epstein-Barr Virus with Preference for Gene-Poor Genomic Chromosomal Regions into the Genome of Burkitt Lymphoma Cell Lines

Background: Epstein-Barr virus (EBV) is an oncogenic virus found in about 95% of endemic Burkitt lymphoma (BL) cases. In latently infected cells, EBV DNA is mostly maintained in episomal form, but it can also be integrated into the host genome, or both forms can coexist in the infected cells. Methods: In this study, we mapped the chromosomal integration sites of EBV (EBV-IS) into the genome of 21 EBV+ BL cell lines (BL-CL) using metaphase fluorescence in situ hybridization (FISH). The data were used to investigate the EBV-IS distribution pattern in BL-CL, its relation to the genome instability, and to assess its association to common fragile sites and episomes. Results: We detected a total of 459 EBV-IS integrated into multiple genome localizations with a preference for gene-poor chromosomes. We did not observe any preferential affinity of EBV to integrate into common and rare fragile sites or enrichment of EBV-IS at the chromosomal breakpoints of the BL-CL analyzed here, as other DNA viruses do. Conclusions: We identified a non-random integration pattern into 13 cytobands, of which eight overlap with the EBV-IS in EBV-transformed lymphoblastoid cell lines and with a preference for gene- and CpGs-poor G-positive cytobands. Moreover, it has been demonstrated that the episomal form of EBV interacts in a non-random manner with gene-poor and AT-rich regions in EBV+ cell lines, which may explain the observed affinity for G-positive cytobands in the EBV integration process. Our results provide new insights into the patterns of EBV integration in BL-CL at the chromosomal level, revealing an unexpected connection between the episomal and integrated forms of EBV.

Macaca arctoides gammaherpesvirus 1 (strain herpesvirus Macaca arctoides): virus sequence, phylogeny and characterisation of virus-transformed macaque and rabbit cell lines

Herpesvirus Macaca arctoides (HVMA) has the propensity to transform macaque lymphocytes to lymphoblastoid cells (MAL-1). Inoculation of rabbits with cell-free virus-containing supernatant resulted in the development of malignant lymphomas and allowed isolation of immortalised HVMA-transformed rabbit lymphocytes (HTRL). In this study, the HVMA genome sequence (approx. 167 kbp), its organisation, and novel aspects of virus latency are presented. Ninety-one open reading frames were identified, of which 86 were non-repetitive. HVMA was identified as a Lymphocryptovirus closely related to Epstein-Barr virus, suggesting the designation as 'Macaca arctoides gammaherpesvirus 1' (MarcGHV-1). In situ lysis gel and Southern blot hybridisation experiments revealed that the MAL-1 cell line contains episomal and linear DNA, whereas episomal DNA is predominantly present in HTRL. Integration of viral DNA into macaque and rabbit host cell genomes was demonstrated by fluorescence in situ hybridisation on chromosomal preparations. Analysis of next-generation sequencing data confirmed this finding. Approximately 400 read pairs represent the overlap between macaque and MarcGHV-1 DNA. Both, MAL-1 cells and HTRL show characteristics of a polyclonal tumour with B- and T-lymphocyte markers. Based on analysis of viral gene expression and immunohistochemistry, the persistence of MarcGHV-1 in MAL-1 cells resemble the latency type III, whereas the expression pattern observed in HTRL was more comparable with latency type II. There was no evidence of the presence of STLV-1 proviral DNA in MAL-1 and HTRL. Due to the similarity to EBV-mediated cell transformation, MarcGHV-1 expands the available in vitro models by simian and rabbit cell lines.

The search for a gene involved in the determination of limited duplicative capacity in human cells

On the assumption that EBV integration into the genome of human B lymphocyte might lead to the inactivation of a hypothetical gene determining the limited duplicative capacity and consequently participate to the cell immortalization, a search for the human-virus junction was done. This led to the identification of a site of integration in the central part of the heavy chain of the immunoglobulin region. The coincidence of the involvement of the site in lymphomatogenesis with the first complete characterization of an integration site led to the speculation that the heavy chain gene itself might be an important controller of cell duplication in the B lymphocyte.

Non-random integration of Epstein-Barr virus in lymphoblastoid cell lines

In order to examine the role of Epstein-Barr virus (EBV) in the immortalization of human B lymphocytes and in the pathogenesis of lymphoid malignancies, we investigated whether the EBV integration into the human genome is randomly distributed or whether the virus integrates preferentially at certain sites. Twelve in vitro immortalized human lymphoblastoid cell lines (LCLs), two in vivo infected LCLs, and one Burkitt's lymphoma cell line (EB2) were examined by non-radioactive in situ hybridization (ISH) with a biotinylated EBV probe. Recurrent hybridization sites were detected in all 15 cell lines. The chromosomes frequently carrying the EBV genome were chromosomes 1, 2, 4, and 5. In more than 70 chromosomal bands, a greater number of integration sites than expected was found (p < 0.05). Approximately half of these bands were involved in the majority of the cell lines (for example, 1p31, 1q43, 2p22, 3q28, 4q13, 5p14, 5q12, and 11p15) whereby band 5p14 was involved in all LCLs analyzed. Virtually no viral integrations were found on the sex chromosomes (X, Y). The majority of the EBV integrations was found in G-band-positive material (p < 0.0001). Thus, our findings clearly show that EBV integrates into the human genome in a non-random manner.

Epstein-Barr virus DNA recombines via latent origin of replication with the human genome in the lymphoblastoid cell line RGN1

We show here that in a lymphoblastoid cell line Epstein-Barr virus DNA recombines with the human genome. The genetic exchange involves the oriP region of the virus. A junction between viral and human DNA from this line has been cloned and sequenced. The results indicate that the integration of Epstein-Barr virus DNA involves a region of the human genome which contains internal short repetition. An 800-bp probe has been isolated from the human part of the junction. This probe has been used to show that the human region exists as a duplication in normal cells.

Different localization of Epstein-Barr virus genome in two subclones of the Burkitt lymphoma cell line Namalwa

The Epstein-Barr virus genome contained in the Burkitt lymphoma line Namalwa was previously localized to the short arm of chromosome 1. Analysis of a different subline of the same Namalwa line by means of Southern analysis carried out on genomic DNA, as well as in situ hybridization, showed a localization on the X chromosome.

Synergism between aphidicolin and adenoviruses in the induction of breaks at fragile sites on human chromosomes

Infection of human embryonic kidney cells with adenoviruses results in the induction of gaps and breaks in cell chromosomes. With adenovirus type 12, cytogenetic damage is known to occur primarily at fragile sites on chromosomes 1 and 17. We have mapped adenovirus type 5-induced breaks and have observed that, although they occur on all chromosomes, they are localized primarily on bands where fragile sites have been mapped. The susceptibility of fragile sites to adenovirus led us to investigate their expression upon combined treatments with virus and aphidicolin, a frequently used inducer of fragile sites. Under these experimental conditions, the frequency of damage at all sites was found to increase significantly, and the magnitude of such increases indicated a synergistic effect between drug and virus.