Epstein-Barr virus infection phenocopies apoptosis regulation in germinal center B cells

Abstract

The Epstein-Barr virus (EBV) is a ubiquitous human pathogen that infects more than >95% of the global adult population. In immunocompetent individuals, EBV infection is asymptomatic and takes place in the oral cavity, where EBV establishes a life-long latent infection in memory B cells by temporally regulating viral gene expression to mimic B cell maturation. In immunocompromised individuals, however, EBV infection can give rise to infectious mononucleosis, epithelial carcinomas, and lymphomas. To model EBV-mediated lymphomagenesis, infection of EBV in vitro generates growth-transformed and immortalized lymphoblastoid cell lines (LCLs), which allows for the characterization of dynamic viral and host gene expression. Our lab has found that the early phase after infection is transcriptionally distinct from the late phase when infected B cells are fully growth-transformed. We also found that apoptosis regulation in each phase of infection is uniquely regulated by a single viral nuclear protein that regulates host gene expression through epigenetic mechanisms. To determine if apoptosis regulation in EBV-infected B cells is virus-specific, I have characterized apoptosis regulation in uninfected maturing B cells and mitogen-stimulated B cells. For the upregulation of one anti-apoptotic protein, EBV infection promotes a chromatin structure resembling that in germinal center light zone B cells, indicating that EBV phenocopies germinal center chromatin regulation to promote apoptosis resistance. In addition to apoptosis regulation, EBV infection phenocopies various aspects of GC B cells and plasmablasts, where the inhibition of plasma cell differentiation increases the efficiency of immortalization and growth-transformation of B cells infected in vitro. The work outlined in this dissertation demonstrate that viral and host genes cooperate in mediating apoptosis regulation, differentiation, and ultimately fate-determination of EBV-infected B cells.