Epstein-Barr virus, the TCL-1 oncogene and Burkitt's lymphoma

Seroprevalence of Epstein-Barr virus and cytomegalovirus infections in Presidente Figueiredo, Amazonas, Brazil

Epstein-Barr virus (EBV) and cytomegalovirus (CMV) infections affect around 95% of the world's population. In Brazil, there are few epidemiological reports related to EBV and CMV infection, especially in the western Amazon region. This study aimed to estimate the seroprevalence of EBV and CMV infection in individuals residents in Presidente Figueiredo, Amazonas, Brazil. Blood samples of 443 individuals were tested for the presence of anti-EBV and anti-CMV IgG antibodies through an enzyme-linked immunosorbent assay. EBV (95.9%; 95% CI: 0.94;0.98), CMV (96.8%; 95% CI: 0.95;0.98) and CMV/EBV (93%;95% CI: 0.91-0.95) coinfection were highly prevalent in the study population. Children (1 to 5 years) not attending school were less susceptible to EBV (OR 0.15; 95% CI: 0.05-0.52; p = 0.017) and CMV infections (OR 0.05; 95% CI: 0.02 - 0.17; p < 0.0001). Teenagers at high school showed increased susceptibility to CMV infection (OR 4.65; 95%CI: 1.43-15.08; p = .013) and EBV/CMV co-infection (OR 3.04; 95%CI: 1.44-6.45; p = 0.005). The seroprevalence of CMV and EBV infections were preeminent and tend to increase with age in the study population. Either attendance to a daycare facility or primary school before the age of 5 years may increase the susceptibility to EBV or CMV infection.

The Modes of Dysregulation of the Proto-Oncogene T-Cell Leukemia/Lymphoma 1A

Simple Summary

T-cell leukemia/lymphoma 1A (TCL1A) is a proto-oncogene that is mainly expressed in embryonic and fetal tissues, as well as in some lymphatic cells. It is frequently overexpressed in a variety of T- and B-cell lymphomas and in some solid tumors. In chronic lymphocytic leukemia and in T-prolymphocytic leukemia, TCL1A has been implicated in the pathogenesis of these conditions, and high-level TCL1A expression correlates with more aggressive disease characteristics and poorer patient survival. Despite the modes of TCL1A (dys)regulation still being incompletely understood, there are recent advances in understanding its (post)transcriptional regulation. This review summarizes the current concepts of TCL1A’s multi-faceted modes of regulation. Understanding how TCL1A is deregulated and how this can lead to tumor initiation and sustenance can help in future approaches to interfere in its oncogenic actions.

Abstract

Incomplete biological concepts in lymphoid neoplasms still dictate to a large extent the limited availability of efficient targeted treatments, which entertains the mostly unsatisfactory clinical outcomes. Aberrant expression of the embryonal and lymphatic TCL1 family of oncogenes, i.e., the paradigmatic TCL1A, but also TML1 or MTCP1, is causally implicated in T- and B-lymphocyte transformation. TCL1A also carries prognostic information in these particular T-cell and B-cell tumors. More recently, the TCL1A oncogene has been observed also in epithelial tumors as part of oncofetal stemness signatures. Although the concepts on the modes of TCL1A dysregulation in lymphatic neoplasms and solid tumors are still incomplete, there are recent advances in defining the mechanisms of its (de)regulation. This review presents a comprehensive overview of TCL1A expression in tumors and the current understanding of its (dys)regulation via genomic aberrations, epigenetic modifications, or deregulation of TCL1A-targeting micro RNAs. We also summarize triggers that act through such transcriptional and translational regulation, i.e., altered signals by the tumor microenvironment. A refined mechanistic understanding of these modes of dysregulations together with improved concepts of TCL1A-associated malignant transformation can benefit future approaches to specifically interfere in TCL1A-initiated or -driven tumorigenesis.

Analysis of global methylation using a Zta-expressing nasopharyngeal carcinoma cell line

EBV infects more than 90% of the human population and persists in most individuals as a latent infection where the viral genome is silenced by host-driven methylation. The lytic cycle is initiated when the viral protein Zta binds to methylated BRLF1 and BRRF1 promoters. Although studies reveal the role of Zta and methylation changes in the viral genome upon EBV infection to reactivation, whether Zta plays any role in alteration of methylation in the host genome remains unknown. Using an inducible model, we demonstrate that global DNA methylation, based on whole-genome 5-methylcytosine content, and regional DNA methylation in repetitive elements, imprinting genes and the X chromosome, remains unchanged in response to Zta expression. Expression of DNA methyltransferases was also unaffected by ectopically expressed Zta. Our data imply that alteration of host gene expression following EBV reactivation may reflect methylation-independent Zta-mediated gene activation and not epigenetic modification of the host genome.

T-cell leukemia 1 expression in nodal Epstein-Barr virus-negative diffuse large B-cell lymphoma and primary mediastinal B-cell lymphoma

The physiologic expression of the product of the proto-oncogene TCL1 (T-cell leukemia 1) is primarily restricted to early embryonic cells. In nonneoplastic B cells, the expression of TCL1 is determined by the differentiation step with silencing at the germinal center stage. TCL1 protein is overexpressed in a wide variety of human diseases. It has been shown that TCL1 is a powerful B-cell oncogene, which has been implicated in the pathogenesis of various types of mature B-cell lymphomas. There is no comparative information in the literature addressing the expression of TCL1 in pediatric and adult nodal diffuse large B-cell lymphoma or primary mediastinal large B-cell lymphoma. We studied 55 cases of adult and pediatric diffuse large B-cell lymphoma and primary mediastinal large B-cell lymphoma to analyze the phenotypic profile of these lymphomas, including TCL1 expression, and its relationship with clinical outcome in different age groups. The cases were analyzed by immunohistochemistry for the expression of TCL1, CD10, BCL-2, BCL-6, and MUM1. We also evaluated c-MYC translocation by fluorescence in situ hybridization. TCL1 was observed in 11 cases, 5 pediatric and 6 adult cases, all but one diffuse large B-cell lymphoma. Pediatric cases showed a significant association between TCL1 expression, high proliferative index, and presence of c-MYC translocation. TCL1 positivity was predominantly found in germinal center phenotype diffuse large B-cell lymphoma. Overall survival was worse in adult TCL1-positive cases than pediatric ones. Primary mediastinal large B-cell lymphomas infrequently expressed TCL1 in both age groups.

The TCL1 family of oncoproteins: co-activators of transformation

The T-cell leukaemia/lymphoma 1 (TCL1)-family oncoproteins augment AKT signal transduction and enhance cell proliferation and survival. Chromosome rearrangements, faulty developmental silencing and Epstein-Barr virus infection appear to dysregulate the expression of TCL1-family genes, provoking several important types of lymphocyte cancer. A key role for TCL1 proteins in cell transformation has been established in studies of transgenic mouse models, which develop a unique spectrum of T- and B-cell malignancies. How TCL1 proteins are regulated and dysregulated, how they promote transformation and the potential for therapies modelled on TCL1 interactions have important implications for understanding and treating lymphocyte cancers.

Epstein-Barr virus in hepatocellular carcinogenesis

AIM: In recent years, studies have suggested that Epstein-Barr virus (EBV) is associated with HCC. The present study was to determine the prevalence of EBV in HCC patients, and whether EBV acted synergistically with hepatitis viruses in HCC carcinogenesis.

METHODS: Liver tissue 115 HCC patients and 26 non-carcinoma patients were studied. Polymerase chain reaction (PCR) was performed to detect EBV BamHI W DNA, EBV LMP1 DNA, HBV X DNA, and HBV S DNA. Reverse transcription PCR (RT-PCR) was performed to detect HCV RNA and HDV RNA. Immunohistochemistry was performed to detect LMP1, HBsAg, HBcAg and HCV. The positive ratios were compared between HCC group and control group by χ² test.

RESULTS: Totally, 78 HCC samples whose β -globulin DNA was positively detected by amplified PCR were selected. PCR was performed in all cases for EBV DNA and HBV DNA. RT-PCR was performed in 18 cases for HCV RNA and HDV RNA. EBV BamHI W and EBV LMP1 were positive in 18 and 6 cases, respectively. HBV X gene and HBV S gene were positive in 42 and 27 cases respectively. HCV was positive in one of the 18 cases, and none was positive for HDV. The positive rates were 28.2% (22 of 78) for EBV DNA (BamHI W and/or LMP1) and 56.4% (44 of 78) for HBV DNA (X gene and/or S gene) respectively. In addition, 12 cases were positive for both EBV DNA and HBV DNA. Among the 26 cases in the control group, 2 cases were positive for EBV BamHI W, 4 positive for HBV X gene and 3 positive for HBV S gene. The positive rates were 8.0% (2 of 26) and 23.1% (6 of 26), respectively, for EBV DNA and HBV DNA. The result of DNA sequencing of BamHI W was 100% homologous with the corresponding sequence of B95-8. There was significant difference in EBV infection rate between HCC patients and controls (χ² = 4.622, P < 0.05). The difference in HBV infection rate was also significant (χ² = 8.681, P < 0.05). However, there was no obvious correlation between HBV and EBV in HCC patients (χ² = 0.835, P > 0.05). LMP1, HBV (HBsAg, HBcAg) and HCV were detected positively in 25, 45 and 6 of 78 cases of HCC tissues respectively. In the 26 control cases, the corresponding positive cases were 2, 4 and 0. The difference in EBV infection rate between HCC patients and control cases was statistically significant (χ² = 6.02, P < 0.05). The difference in HBV infection rate was also statistically significant (χ² = 10.03, P < 0.05). In the 25 cases with positive LMP1 expression, 6 were in the nuclei of tumor cells, 9 in the cytoplasm of tumor cells and 10 in mesenchymal lymphocyte cytoplasm.

CONCLUSION: The existence of EBV infection in HCC tissues suggests that EBV may be involved in the hepatocellular carcinogenesis in China. HBV infection may be a major cause of HCC. There is no correlation between EBV and HBV in the development of HCC. The prevalence of HCV infection is low in our area, and HDV appears not to play a direct role in hepatocellular carcinogenesis.

The LCR of EBV makes Burkitt's lymphoma endemic

The spectacular ability of Epstein-Barr virus (EBV) to immortalize and morphologically transform human B cells in vitro to lymphoblastoid cell lines (LCLs) is central to most molecular models of viral oncogenesis. However, binding of transcription factor and oncoprotein c-Myc to the major locus control region (LCR) of the viral genome directs us to an alternative model for the origin of Burkitt's lymphoma (BL). In this model, improved nuclear maintenance of the viral genome and the continuous expression of anti-apoptotic functions in B cells exhibiting class I EBV latency contribute to the generation of BL, without any detour through EBV nuclear antigen (EBNA) 2-driven B-cell immortalization (also called class III latency).