Characterization of two newly established EBV-containing lymphoblastoid cell lines from patients with myeloid leukemias

The V-val subtype Epstein-Barr virus nuclear antigen 1 promotes cell survival after serum withdrawal

Epstein-Barr virus (EBV) can establish latent infection and has been associated with various human cancers. Epstein-Barr nuclear antigen 1 (EBNA1) is the only viral protein that is expressed in all EBV-associated malignant tissues. The N- and C-terminal domains of EBNA1, which are connected by internal glycine/alanine-rich short repeat sequences of various sizes, show sequence divergence across EBV strains isolated from around the world. At least five subtypes have been described, according to the amino acid at residue 487: P-ala, P-thr, V-val, V-pro, and V-leu. Whether the variations of EBNA-1 contribute to the pathogenesis of EBV or simply reflect the geographical distribution of EBV remain to be investigated. Furthermore, the cell effects conferred by EBNA1 subtypes that differ from that of the B95.8 prototype, which belongs to the P-ala subtype, remain to be elucidated. In this study, PCR was amplified with the full-length V-val EBNA1 gene from the CG3 cell line, an EBV-carrying lymphoblastoid cell line derived from a Taiwanese chronic myeloid leukemia patient. Plasmids expressing His-tagged EBNA1 fusion proteins in E. coli were constructed and used to raise antibodies in rabbit. The V-val EBNA1 gene was then cloned into a eukaryotic expression vector and successfully expressed in the transfected cultured cells. Expression of V-val EBNA1 rendered 293 cells able to undergo serum‑independent cell proliferation, providing them with anti-apoptotic abilities, which are two characteristics of cancer cells. These data suggested that use of EBNA1 originally derived from tumor cells, rather than the more commonly utilized prototype, when investigating the potential role of EBNA1 in the oncogenesis of EBV-associated malignancies, is crucial.

A role for Epstein-Barr viral BALF1 in facilitating tumor formation and metastasis potential

Epstein-Barr virus (EBV) is a ubiquitous human herpesvirus that triggers transformation and tumorigenesis of latently infected B cells in vitro. BALF1, a Bcl-2-like EBV gene expressed in both latent and lytic stages, was recently characterized in EBV-infected cells; however, the role and function of BALF1 has remained elusive. Here, we demonstrate that BALF1 expression alters cellular morphology. Importantly, BALF1 promotes cellular transformation, with tumorigenicity assays showing larger and substantially greater numbers of tumors in BALF1 transfectant-injected mice compared to mice injected with pcDNA control transfectants. In addition, BALF1 expression increases cell survival under low-serum conditions, an effect that is attributable to suppression of apoptosis, not to promotion of cell-cycle progression. Furthermore, BALF1 transfectants exhibit markedly increased tumor metastasis in vitro and in vivo. Taken together, these findings suggest that BALF1 may be a new tumor marker for EBV diagnosis and provide a new direction for research on treatments of EBV-associated tumors.

Presence of activation-related m-RNA for EBV and CMV in the bone marrow of patients with myelodysplastic syndromes

The bone marrow (BM) in myelodysplastic syndromes (MDS) undergoes pathobiological changes that mimic an inflammatory process, and hence, an infectious etiology was suspected in these disorders. In the present report, we examined the bone marrow mononuclear cells (BMMNC) of 19 MDS patients and seven normal donors for the expression of one latency-related (Latency membrane protein 1 (LMP-1) and immediate early protein (IEP)) and one activation-related (BZLF and DNA-Pol) m-RNA each for two herpes viruses, Epstein-Barr virus (EBV) and cytomegalovirus (CMV), respectively. Reverse transcriptase polymerase chain reaction was used for this purpose. The latency-related transcripts (EBV-LMP-1 and CMV-IEP) were present in all the MDS and normal specimens. Intriguingly, 10/19 MDS specimens ( approximately 53%) and 2/7 normal donors ( approximately 28%) were positive for active EBV-BZLF (P=0.0067), while 2/19 MDS specimens ( approximately 11%) with 1/7 normal ( approximately 14%) showed active CMV-DNA-Pol (P=0.1588). Later, from another set of MDS patients (n=7) and normal donors (n=4), BM stromal cultures were established, which, at a 75% confluency, were overlaid with cord blood mononuclear cells (CBMNC). IEP was detectable in the CBMNC before and after co-incubation with MDS, as well as normal stroma. So, it was also present both in MDS and normal stromal cells. The other three were absent both in MDS and normal stromal layers. In CBMNC though, active EBV-BZLF and CMV-DNA-Pol m-RNA were detectable in one of seven MDS co-cultures each, albeit from different patients. None of the normal co-cultures showed active virus, either in stroma or CBMNC. Thus, the present report demonstrates, for the first time, the presence of active herpes viruses in the BMMNC of MDS patients and reveals the ability of the MDS stroma to support the viral activation.

Identification of a promoter for the latent membrane protein 1 gene of Epstein-Barr virus that is specifically activated in human epithelial cells

Latent membrane protein 1 (LMP 1) is one of two Epstein-Barr virus (EBV)-encoded proteins that expressed in nasopharyngeal carcinoma (NPC) cells. Previous studies showed that a 3.5-kb transcript of the LMP 1 gene, in addition to the 2.8-kb transcript, was detected in a B95-8-EBV-containing, nude mice-passaged NPC tumor, C15. This indicated that a transcript was initiated from a region 5' to the putative promoter, ED-L1. We have isolated an EBV variant from a NPC tissue, and this virus strain contained a more pathogenic LMP 1 gene. DNA sequence analysis of the 5'-upstream region showed distinct variations as compared to that of B95-8 strain. To test if the LMP 1 gene of the NPC strain also contained an upstream promoter, we generated a series of deletion plasmids encompassing positions -1,030 to +20 of the LMP 1 promoter and tested for their abilities to drive the expression of the reporter gene in human epithelial cell lines, C-33A and NPC-TW076. We found that the region between -643 and -496 contained a promoter activity that was approximately five-fold higher than the putative promoter, ED-L1. This region between -643 and -496 was designated as ED-L1E. C-33A cells containing the genomic clone pT7(E) or the clone that had deleted a 94-bp ED-L1 sequence (delta94) was used to determine the transcription initiation sites by RNase protection assay. Results showed that a transcription initiation site was located at nucleotide 170,099 ("A") of EBV genome. The transcript was expressed in NPC biopsies and in human primary normal epithelial cells transfected with pT7(E) and delta94, respectively, as examined by reverse transcriptase-polymerase chain reaction (RT-PCR) analysis. Furthermore, the ED-L1E was not regulated by the EBV-encoded nuclear antigen 1-mediated transcriptional enhancer family of repeats (FR) in C-33A cells. Our results suggested that the ED-L1E was specifically activated in epithelial cells. The biological significance of the selective usage of the ED-L1E promoter was discussed.

Characterization of 5'-upstream sequence of the latent membrane protein 1 (LMP-1) gene of an Epstein-Barr virus identified in nasopharyngeal carcinoma tissues

Sequence variations of the 5'-upstream region of latent membrane protein 1 (LMP-1) in two Epstein-Barr virus (EBV) strains have been reported before (Chen et al., 1992). To investigate the effect of these variations on gene expression, we constructed a series of deletion plasmids encompassing positions -950 to +20 of the LMP-1 promoter region and tested for the ability to drive chloramphenicol acetyltransferase (CAT) gene expression in C33A cells. Results showed that the promoter activities of constructs from NPC strain were 3-fold lower than the corresponding constructs from the B95-8 strain. In addition, the region between -54 and +20 contained the basic, constitutive promoter activity for both strains. Sequence analysis of this region indicated that an activating transcription factor (ATF) binding site, TGACGTAG, which is present in B95-8 strain was changed to TCTCGTAG in NPC strain. A chimeric plasmid study suggested that these sequence variations in the ATF binding site may contribute to the 3-fold increase of CAT activity observed for B95-8 strain. Furthermore, the activity of the promoter constructs was not activated by EBV-encoded nuclear antigen 2 (EBNA-2) in C33A cells. However, the promoter activities were upregulated in B-lymphocyte cells such as CG3 and CA46 cells. The biological significance of this difference in promoter activity of LMP-1 gene between two strains and the involvement of the cellular factors were discussed.

Detection of mutations in the p53 gene in human head and neck carcinomas by single strand conformation polymorphism analysis

Using the polymerase chain reaction (PCR)-based single strand conformation polymorphism (SSCP) analysis, we have examined the highly conserved regions of the p53 gene in 58 biopsy samples of head and neck tumors. Mutations were found in 13/58 (23%) tumor specimens, but not in 6 normal tissues. Ten of 13 mutations were due to single base changes and the remaining 3 were 1- or 8-base deletion mutants. These mutations were clustered in exons 5 and 7 and resulted in amino acid changes. Our results seem to indicate that mutations in the p53 gene contribute to a significant number of cases of the head and neck tumors including 20% of nasopharyngeal carcinoma biopsies. The relationship of Epstein-Barr virus or human papillomavirus and p53 gene mutations in this group of cancers was also analyzed and discussed.