Induction of Epstein - Barr virus Lytic Replication
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Epstein-Barr virus (EBV) is a member of the herpesvirus family and is one of the most common human viruses. In the United States, 95% of adults between 35 and 40 years of age have been infected with EBV. EBV is the etiological agent of infectious mononucleosis and is associated with a number of diverse lymphomas and epithelial cancers, including African Burkitt's lymphoma, nasopharyngeal carcinoma and gastric malignancies. Though EBV primarily infects B lymphocytes and epithelial cells, the sequence of infection is not well understood. In infected B cells, EBV establishes persistent latent infections. The latent state of the virus in a cell is characterized by the expression of a small subset of viral genes and the latent membrane proteins, which are essential for induction and maintenance of host cell proliferation and viral latency. Despite the fact that latency is a predominant state of the life cycle in B cells and in virus-associated malignancies, the virus must replicate lytically in order to be passed from cell to cell and between individuals. Lytic reactivation of EBV from its latent state leads to expression of the majority of viral genes and the release of viral progeny that are capable of infecting new cells. The latent-to-lytic cycle switch has been extensively investigated because of its obvious implications for EBV-associated malignant diseases and for future therapy for EBV-positive cancers. Previous studies have investigated EBV induction only in B cells and epithelial cells, which are cell line types that are naturally infected by the virus. Currently, there is no good model that can efficiently trigger the switch from latency to lytic cycle and initiate significant viral production. This lack of a good model particularly limits our ability to study the virus and design effective therapies for EBV-induced malignancies. In the present study, I propose novel methods for EBV lytic induction in the virus infected erythroleukemic cell line, K562. K562 is a highly undifferentiated multipotent leukemia cell line that can be induced to differentiate into erythroid, myeloid or megakaryocytic lineages. It has been previously shown that hydroxyurea, a ribonucleoside diphosphate reductase inhibitor, induced K562 cell differentiation through activation of p38 kinase, one of a group of MAP kinases. Here, I hypothesize that induced differentiation of K562 EBV-infected cells with hydroxyurea will stimulate the switch from latent-to-lytic cycle and lead to more efficient viral replication and production. Thus far there has been no complete viral production induced by differentiation of K562 EBV-infected cell lines with hydroxyurea, but the initiation of abortive viral replication has not been ruled out. More attempts have been made to induce EBV lytic replication: several projects were launched that included expression of the EBV immediate-early lytic gene BZLF1 and cellular transcription factor Oct-1, as well as the knockout of the cellular interferon-induced transmembrane proteins (ifitm). In the future, these stimulations of the EBV lytic cycle can be used separately or combined in order to boost a high rate of viral production, which is important to facilitate studies of EBV biology through facile development and exploration of mutant viruses, and to develop effective therapeutic options for EBV-positive diseases.