Epstein-Barr virus small nuclear RNAs are not expressed in permissively infected cells in AIDS-associated leukoplakia.

Abstract

Epstein-Barr virus (EBV) DNA structure and gene expression were analyzed in tissue specimens from oral hairy leukoplakia (HLP), a mucocutaneous lesion that develops in patients infected with human immunodeficiency virus (HIV). The structure of the terminal restriction enzyme fragments of EBV revealed that HLP is a permissive infection without a predominant, detectable population of EBV episomal DNA. In RNA preparations from this uniquely permissive infection, EBV replicative mRNAs could be identified by Northern analysis; however, the virally encoded small nuclear RNAs, the EBERs, were not detected in most HLP RNA preparations. In situ hybridization detected EBER expression in very rare cells. These data indicate that unlike other viral small nuclear RNAs, the EBERs are not expressed during viral replication and must participate in the complex maintenance of latent EBV infection.Oral hairy leukoplakia (HLP) is a newly recognized lesion, most often located on the tongue, that occurs almost exclusively in patients with human immunodeficiency virus (HIV) infection (1). Epstein-Barr virus (EBV), usually thought of as a lymphotrophic herpesvirus, is the etiologic agent of this mucocutaneous epithelial cell disorder. HLP is the only EBV-associated disease in which acyclovir, an antiviral drug that inhibits the replication of EBV, induces clinical remission (2). This response and the detection of masses of viral particles in the infected cells make these lesions unique in EBV biology and indicate that the virus is actively replicating (1,2).Replication is relatively unusual in EBV-infected cells. Although the virus replicates in oropharyngeal epithelial cells, the transforming infection of B lymphocytes, which is the hallmark of EBV infection, is largely nonpermissive (3-6). In the latently infected B-cell lines, the viral DNA is maintained as an episome (7,8). Permissive infection develops in a small subset of cells with the expression of multiple replicative RNAs and the generation of the linear, virion form of DNA. The structure of the EBV termini permits discrimination between the linear and episomal DNA forms and therefore between permissive and latent states (9, 10).In EBV-infected cells, the most abundantly expressed viral transcripts are the nonpolyadenylylated polymerase III transcripts, EBER1 and EBER2 (EBV-encoded small nuclear RNA), which are found in ribonucleoprotein particles (RNP) (11,12). Despite their abundance, the function ofthese RNAs is unknown. The EBERs can partially substitute for the similarly sized polymerase III virus-associated (VA) transcripts encoded by adenovirus that function during viral replication (13,14). This complementation suggested that perhaps, like the VA RNAs, the EBERs also function during lytic replication. This observation was supported by studies that revealed that the EBERs are more abundant in the partially permissive virus-producer cell line B95-8 than in a latently infected lymphoid line, IB4, established by infection with B95-8 virus (15, 16). However, in co...

Epstein-Barr Virus Infection in Oral Hairy Leukoplakia: Virus Replication in the Absence of a Detectable Latent Phase

“…3). The lack of detectable EBER RNAs is consistent with recent results from Northern blotting analysis of HL biopsies (Gilligan et al, 1990), whereas the lack of detectable LMP mRNA is consistent with the absence of anti-LMP MAb staining in the same cell layers (see Fig. 4d).…”

“…Thus, the small non-polyadenylated EBERs are the most abundant viral RNAs in LCLs (Sample & Kieff, 1990) and are also strongly expressed in three EBV-associated tumours, BL (Rowe et al, 1987a), Hodgkin's disease (Pallesen et al, 1991;Wu et al, 1990) and NPC (Gilligan et al, 1990;G. Niedobitek et al, unpublished results).…”

“…However, 0001-0342 © 1991 SGM G. Niedobitek and others the expression of latent viral antigens in these lesions is restricted to EBNA 1 in BL (Rowe et al, 1987a) and to EBNA 1 usually accompanied by LMP in NPCs (Young et al, 1988;Fahraeus et al 1988). In addition, the EBERs are transcribed in both BL and NPC, apparently to similar levels as in LCLs (Howe & Steitz, 1986;Rowe et al, 1987a;Gilligan et al, 1990). Thus, the EBERs appear to be consistent markers of latent EBV infection irrespective of the precise form of latency adopted.…”

Molecular Diagnosis of Epstein-Barr Virus-Related Diseases

“…The only EBV-related lesion that lacks EBER is oral hairy leukoplakia, a purely lytic infection of oral epithelial cells. 12 EBER actually represents two RNA species, EBER1 and EBER2, encoded from two separate but homologous viral genes. EBER transcripts are expressed in latently infected cells at levels approaching a million copies per cell.…”

BHRF1, a viral homologue of the Bcl-2 oncogene, is conserved at both the sequence and functional level in different Epstein-Barr virus isolates.

“…These studies suggest that whilst BHRF1 is not consistently expressed in F. Khanim and others F. Khanim and others EBV-associated tumours, it is possible that expression of this protein at an early stage in the oncogenic process may influence the development of these malignancies. To date, the only in vivo lesion where BHRF1 is abundantly expressed is oral ' hairy ' leukoplakia (HL), a benign lesion of oral tongue mucosa which represents a focus of chronic EBV replication with absence of detectable latent gene expression (Greenspan et al, 1985 ;Gilligan et al, 1990 ;Niedobitek et al, 1991 ;Young et al, 1991). Our recent data demonstrating that BHRF1 can delay the terminal differentiation of epithelial cells through the prevention of apoptosis suggests that this protein may be responsible for HL pathology but may normally function to delay cell death during EBV replication so that full virus maturation can occur (Dawson et al, 1995).…”