EBV-induced miR-34a functions to stimulate transformed B cell growth

Abstract

Background Epstein-Barr virus (EBV) is a member of the gammag-herpesvirus family estimated to infect 90% of the world's population. Despite the high prevalence of infection, EBV-associated malignancies are largely kept in check by a strong cytotoxic T cell immune response. However, EBV causes lymphoproliferative disease in immune-deficient individuals and plays a role in the pathogenesis of African Burkitt lymphoma, Hodgkin's disease, and nasopharyngeal carcinoma. In vitro, EBV infection of B cells results in proliferation and outgrowth of indefinitely proliferating lymphoblastoid cell lines (LCLs). Thus, LCLs represent a viable model for the pathogenesis of EBV-associated malignancies. microRNAs are small noncoding RNAs that posttranscriptionally regulate gene expression to control a variety of processes including development, cell cycle, and immunity. Their role in EBV transformation and lymphomas is currently not well understood. Results Using a miRNA microarray, we identified a number of cellular miRNAs that were over- or under-expressed comparing resting CD19+ B cells to EBV-infected, proliferating B cells and immortalized LCLs. In particular, we focused on miR-34a, whose expression was induced by EBV. This miRNA has been previously reported to be a pro-apoptotic target of p53 implicated in the response to DNA damage. Surprisingly, contrary to its regulation in other cell types, miR-34a was not found to be p53 responsive in LCLs. In order to understand the functional role of this miRNA in EBV transformation, we constructed a miRNA sponge. miR-34a knockdown in LCLs showed that these cells depend on normal miR- 34a expression to proliferate and to aggregate. Conclusions miR-34a is important for efficient growth and survival of EBV-transformed cells, in contrast to its tumor suppressive role in carcinoma and sarcoma-derived cell lines.