Expression Pattern of Epstein-Barr Virus Latent Genes in Cell Lines Derived from Oral Squamous Cell Carcinoma

Abstract

IntroductionEBV is a ubiquitous human herpes virus which establishes life-long persistent infection of B-cells in over 90% of the adult population of the world (1). Upon primary infection, EBV occasionally causes infectious mononucleosis. After primary infection, irrespective of whether it is clinically overt or silent, EBV establishes a life-long carrier state. EBV is associated with Burkitt's lymphoma (BL), undifferentiated nasopharyngeal carcinoma (NPC) and opportunistic lymphomas in immunocompromised hosts. EBV is also implicated in Hodgkin's disease (HD), certain T-cell lymphomas and gastric carcinoma (2, 3).Several EBV genes are potentially expressed in latently infected cells: EBNA-1, -2, -3A, -3B, -3C and leader protein (LP); LMP-1, -2A, -2B; untranslated EBER 1 and 2; and a transcript containing the BARF0 (2). Depending on the latent gene expression pattern, three main types of EBV latency have been described so far. In type I latency, EBNA-1, EBER 1, 2 and BARF0 transcripts are expressed (e.g., in vivo BL cells and several BL cell lines like Akata cell line) (4, 5). In type II latency, in addition to the genes expressed in type I, LMP genes are expressed (e.g., NPC and HD) (6). All of the latent genes are expressed in type III latency (e.g., in vitro EBV-immortalized B lymphoblastoid cell lines (LCL) and some B lymphoproliferative disorders of immunosuppressed patients) (7,8). Activity of the BamHI-C, -W or Q promoter (Cp, Wp or Qp accordingly) determines which of the EBNA transcripts will be expressed. In type I and II latency, Qp mediates selective expression of EBNA-1 transcript. However in type III latency, active Cp or Wp results in expression of all of the six EBNA mRNAs (2).EBV replication was detected within the epithelial cells of AIDS-associated oral hairy leukoplakia (10). Sev- LMP-1 is an integral membrane protein and it aggregates in patches on the plasma membrane (16). LMP-1 is suggested to be essential for B-lymphocyte growth transformation (17) and transforms rodent fibroblast cell line, Rat-1 (18). The Rat-1 cells expressing LMP-1 are tumorigenic in nude mice. In B-lymphocytes, LMP-1 is able to upregulate a number of cellular genes, including the apoptosis inhibiting bcl-2 gene (19). LMP-1 is frequently expressed in NPC biopsies (20,21). Expression of LMP-1 was detected in 20% cases of oral leukoplakia (22). In our previous report, 6 of 7 (85.7%) cases of OSCC were LMP1 positive (14). Therefore, LMP-1 might be an important component of transformation in epithelial tumors.Although there are some reports concerning association of EBV with OSCC in vivo, there is contradiction among the researchers about transcription of EBV genes in oral epithelium, specially the latent genes. So far, there have been no reports about in vitro expression pattern of EBV in OSCC cell lines. We, therefore, introduced EBV into the OSCC cell lines and successfully isolated EBVpositive OSCC cell lines. We investigated the expression pattern of EBV latent genes in isolated OSCC cells. Materials and Methods Cell l...