title: Murine gammaherpesvirus M2 protein induction of IRF4 via the NFAT pathway leads to IL-10 expression in B cells.
abstract: Reactivation of the gammaherpesviruses Epstein-Barr virus (EBV), Kaposi's sarcoma-associated herpesvirus (KSHV) and murine gammaherpesvirus 68 (MHV68) from latently infected B cells has been linked to plasma cell differentiation. We have previously shown that the MHV68 M2 protein is important for virus reactivation from B cells and, when expressed alone in primary murine B cells, can drive B cell differentiation towards a pre-plasma cell phenotype. In addition, expression of M2 in primary murine B cells leads to secretion of high levels of IL-10 along with enhanced proliferation and survival. Furthermore, the absence of M2 in vivo leads to a defect in the appearance of MHV68 infected plasma cells in the spleen at the peak of MHV68 latency. Here, employing an inducible B cell expression system, we have determined that M2 activates the NFAT pathway in a Src kinase-dependent manner--leading to induction of the plasma cell-associated transcription factor, Interferon Regulatory Factor-4 (IRF4). Furthermore, we show that expression of IRF4 alone in a B cell line up-regulates IL-10 expression in culture supernatants, revealing a novel role for IRF4 in B cell induced IL-10. Consistent with the latter observation, we show that IRF4 can regulate the IL-10 promoter in B cells. In primary murine B cells, addition of cyclosporine (CsA) resulted in a significant decrease in M2-induced IL-10 levels as well as IRF4 expression, emphasizing the importance of the NFAT pathway in M2- -mediated induction of IL-10. Together, these studies argue in favor of a model wherein M2 activation of the NFAT pathway initiates events leading to increased levels of IRF4--a key player in plasma cell differentiation--which in turn triggers IL-10 expression. In the context of previous findings, the data presented here provides insights into how M2 facilitates plasma cell differentiation and subsequent virus reactivation.
authors.affiliation: Microbiology and Molecular Genetics Graduate Program, Emory University School of Medicine, Atlanta, Georgia, United States of America ; Department of Microbiology & Immunology, Emory University School of Medicine, Atlanta, Georgia, United States of America.
authors.forename: Udaya S
authors.initials: US
authors.lastname: Rangaswamy
authors.affiliation: Department of Microbiology & Immunology, Emory University School of Medicine, Atlanta, Georgia, United States of America ; Emory Vaccine Center, Emory University School of Medicine, Atlanta, Georgia, United States of America.
authors.forename: Samuel H
authors.initials: SH
authors.lastname: Speck
mesh_terms: D000818:Animals; D001402:B-Lymphocytes / Q000276:immunology* / Q000473:pathology; D045744:Cell Line, Tumor; D049109:Cell Proliferation / Q000235:genetics; D005786:Gene Expression Regulation / Q000276:immunology*; D006566:Herpesviridae Infections / Q000235:genetics / Q000276:immunology / Q000473:pathology; D050835:Interferon Regulatory Factors / Q000235:genetics / Q000276:immunology*; D016753:Interleukin-10 / Q000235:genetics / Q000276:immunology*; D008213:Lymphocyte Activation; D051379:Mice; D008817:Mice, Mutant Strains; D018448:Models, Immunological; D050778:NFATC Transcription Factors / Q000235:genetics / Q000276:immunology*; D018144:Rhadinovirus / Q000502:physiology*; D014764:Viral Proteins / Q000235:genetics / Q000276:immunology*; D017735:Virus Latency / Q000235:genetics / Q000276:immunology; D000099218:Interferon Regulatory Factor-4
chemical_list: D050835:Interferon Regulatory Factors; D016753:Interleukin-10; D050778:NFATC Transcription Factors; D014764:Viral Proteins; D000099218:Interferon Regulatory Factor-4; C556062:IL10 protein, mouse; C577263:M2 protein, murine gammaherpesvirus 68