Coinfection with multiple strains of the Epstein-Barr virus in human immunodeficiency virus-associated hairy leukoplakia

The Epstein-Barr virus EBNA-2 gene in oral hairy leukoplakia: strain variation, genetic recombination, and transcriptional expression

Oral hairy leukoplakia (HLP) lesions frequently contain defective Epstein-Barr virus (EBV) genomes with deletions in the EBNA-2 gene that abundantly replicate and persist within the lesion. To characterize these viral strains and recombinant variants, the EBNA-2 gene in EBV DNA from several different HLP biopsy specimens was analyzed. Amplification of EBNA-2 coding sequences by PCR demonstrated the presence in HLP of intact EBNA-2 genes as well as a variety of internally deleted variants of both EBNA-2A and EBNA-2B. Some of the deletion variants evolved within the HLP lesion from intact EBNA-2 genes, while other variants appeared to be transmissible strains that directly infected the lesion. Intrastrain recombination within the HLP lesion also generated variation within the EBNA-2 polyproline region. Cloning and sequencing of HLP cDNA demonstrated transcription from the internally deleted EBNA-2 open reading frame, indicating that these variant genes are expressed in HLP. Comparative analysis of the HLP EBNA-2 sequences confirmed previous findings of EBV coinfection with multiple types and strains. Sequence variation of these wild-type genes demonstrated that EBNA-2A sequences distinguish at least two separate strains and a variety of substrains of EBV type 1. Two of the HLP EBNA-2A sequences contained amino acid changes in a cytotoxic T-cell epitope within an otherwise highly conserved region of the gene. These data indicate that EBV coinfection, strain variation, and recombination within the EBNA-2 gene are common features of HLP and suggest that the expression of internally deleted EBNA-2 variants could contribute to EBV pathogenesis in permissive infection.

Epstein-Barr virus intrastrain recombination in oral hairy leukoplakia

In laboratory lymphoblastoid cell lines and in natural human infections, Epstein-Barr virus (EBV) strains have been identified by DNA restriction fragment length polymorphisms of the BamHI H fragment. Multiple, heterogeneous BamHI H fragments have been detected in oral hairy leukoplakia (HLP), raising the question of EBV coinfection with multiple strains. To investigate whether the heterogeneous BamHI H fragments represent different EBV strains or recombinant variants of the same strain, EBV DNA from HLP lesions was analyzed to characterize the viral strains and determine the source of possible recombinant variants. Clones of heterogeneous BamHI H fragments from a single HLP lesion were determined to have strain identity on the basis of sequence identity of the EBNA-2 genes. Intrastrain homologous recombination within the IR2 internal repeat region and nonhomologous recombination of other sequences accounted for the heterogeneity of the BamHI H fragments. PCR amplification from additional HLP specimens detected similar recombinant variants. A possible example of site-specific recombination joining the BamHI Y portion of the EBNA-2 gene to sequences within the BamHI S fragment was also detected in multiple HLP specimens. These data indicate that intrastrain recombination during productive replication confounds the use of restriction fragment length polymorphism analysis of the BamHI Y and H fragments to identify EBV strains in HLP. In patients with permissive epithelial EBV infections, EBV strains could be more accurately distinguished by sequence identity or divergence within known regions of genetic strain variation.

Autoantigenic proteins that bind recombinogenic sequences in Epstein-Barr virus and cellular DNA

We have identified conserved autoantigenic cellular proteins that bind to G-rich sequence motifs in recombinogenic regions of Epstein-Barr virus (EBV) DNA. This binding activity, called TRBP, recognizes the EBV terminal repeats, a locus responsible for interconversion of linear and circular EBV DNA. We found that TRBP also binds to EBV DNA sequences involved in deletion of EBNA2, a gene product required for immortalization. We show that TRBP binds sequences present in repetitive cellular DNA, such as variable-number tandem repeats (VNTR) and immunoglobulin heavy-chain class switch regions. We propose that EBV utilizes cellular DNA recombination systems to mediate several types of viral genome alterations. These findings may lead to an understanding of the mechanism of rearrangements of EBV DNA that are a central feature of the biology of the virus.

"The end of innocence" revisited: resistance of herpesviruses to antiviral drugs

In the past 4 years, interest in drug-resistant herpesviruses has evolved from the realm of academic laboratory studies to that of great clinical importance. Recurrent and persistent infections due to the herpes simplex viruses, varicella-zoster virus, and human cytomegalovirus have been an unwelcome consequence of immunosuppression in graft recipients, cancer patients, and those suffering from AIDS. Treatment of these infections with the available antiviral drugs, such as acyclovir, ganciclovir, and foscarnet, has resulted in both clinical benefit and the emergence of drug-resistant variants. In addition, the role of Epstein-Barr virus is being clarified for an array of disease syndromes, and therapeutic approaches are beginning to emerge. In the present review, the emergence and clinical importance of drug resistance among the herpesviruses have been explored. Furthermore, particular attention has been focused on our understanding of the mechanisms of drug resistance and how that understanding will guide us in the development of more effective antiviral drugs and drug usage.

Epstein-Barr virus (EBV) gene expression in EBV-positive peripheral T-cell lymphomas

Epstein-Barr virus (EBV) DNA has been detected in peripheral T-cell lymphomas. In this study, analysis of the EBV termini indicated that the infection was clonal and nonpermissive. Analysis of viral expression detected the processed, spliced mRNAs representing EBNA1, LMP1, LMP2, and BamHI A transcripts in all EBV-positive peripheral T-cell lymphomas. The LMP1 protein was detected by immunofluorescence in a single specimen. In contrast, neither the EBNA2 protein nor the spliced EBNA2 mRNA were detected. These data indicate that EBV-infected T-cell lymphomas are clonal expansions of a single EBV-infected cell with a pattern of gene expression which is distinct from that detected in Burkitt's lymphomas or posttransplant lymphomas but similar to viral expression in nasopharyngeal carcinomas.

Unconventional processing of the 3' termini of the Epstein-Barr virus DNA polymerase mRNA

Northern blot analysis of the Epstein-Barr virus DNA polymerase mRNA identified two discrete sizes of virally encoded polymerase transcripts, 5.08 kb detected in strains P3HR1, Raji, W-91, and FF-41 and 3.7 kb detected solely in the prototype B95-8 strain. 3' S1-nuclease mapping and analysis of cDNA sequence generated by RNA-based PCR demonstrated that the 3.7-kb polymerase mRNA from B95-8 terminates 484 base pairs downstream of the open reading frame in a region of the genome remarkable for its lack of an apparent polyadenylylation signal. Moreover, between the cleavage point and the poly(A) tract of the cDNAs are a series of inserted nucleotides, mostly adenosine and uridine residues of unknown origin. A similar analysis of the 3' terminus of the 5.0-kb mRNA from the other cell lines revealed that polyadenylylation occurs 1.4 kb downstream of the B95-8 terminus. This region is deleted in B95-8, which accounts for the alternate upstream terminus used in B95-8. Like the 3.7-kb terminus, the 5.0-kb terminus lacks a canonical polyadenylylation signal, but contains a rarely used UAUAAA sequence 32 bp upstream of the poly(A) tail. These results indicate that the mRNA encoded by the Epstein-Barr virus DNA polymerase gene is polyadenylylated at two different termini without the use of canonical signals, raising the possibility of involvement of a virus-encoded factor in 3' processing of this message.