Among the subfamilies of herpesvirus, the gammaherpesviruses are important human pathogens because they cause a variety of diseases in humans, such as infectious mononucleosis, nasopharyngeal carcinoma, Burkitt’s lymphoma, and Kaposi’s sarcoma (30, 34). However, for numerous reasons, primate studies are not always feasible. Examination of the gene expression patterns of C-RTA/MHV-68 over a time course led to the finding that the M3 promoter is RTA responsive in the absence of other viral factors. In lymphocytes latently infected with KSHV or EBV, the level of NF-kappaB activity is high, and treatment of these cells with an NF-kappaB inhibitor leads to lytic protein synthesis consistent with virus reactivation. In defense, host-cell sensing of microbial infection may trigger signaling cascades aimed at hindering pathogen replication and alerting neighboring cells to the present danger . DOI 10.1371/journal.ppat.1002150 Alternate Journal PLoS Pathog. Examination of the gene expression patterns of C-RTA/MHV-68 over a time course led to the finding that the M3 promoter is RTA responsive in the absence of other viral factors.
Growth of the BAC-derived virus in cell culture was indistinguishable from that of wild-type MHV-68. Emerging infectious diseases (EID), a significant financial burden and public health threat, are on the rise (1). In contrast to the results obtained following intranasal inoculation, infection of mice with gammaHV68-IkappaBalphaM by the intraperitoneal route had only a modest impact on splenic latency, suggesting that route of inoculation may alter requirements for establishment of virus latency in B cells. These studies represent a potentially new in vitro model of EBV- and KSHV-associated neuronal disease development and pathogenesis. GHVs infect a wide range of cell types, including epithelial cells (Sixbey et al., 1983, 1984), endothelial cells (Boshoff et al., 1995), monocytes (Weck et al., 1999b), and lymphocytes (Alfieri et al., 1991; Sunil-Chandra et al., 1992a) (Table 1). These data indicate that the MHV68 miRNAs may facilitate virus-driven maturation of infected B cells and implicate the miRNAs as a critical determinant of gammaherpesvirus-associated disease. ORF M1 has striking homology to poxvirus serpins, while ORF M11 encodes a potential homolog of Bcl-2-like molecules encoded by other gammaherpesviruses (gene 16 of HVS and KSHV and the BHRF1 gene of EBV).
In lymphocytes latently infected with KSHV or EBV, the level of NF-κB activity is high, and treatment of these cells with an NF-κB inhibitor leads to lytic protein synthesis consistent with virus reactivation. Growth of the BAC-derived virus in cell culture was indistinguishable from that of wild-type MHV-68. Epstein-Barr virus (EBV) and Kaposi’s sarcoma-associated herpesvirus (KSHV) are human gammaherpesviruses that have been associated with the development of cancers, especially in immunocompromised patients. Murine gammaherpesvirus 68 (MHV68) is genetically related to EBV and KSHV and causes lymphoma and lymphoproliferative disease in mice, providing a useful small-animal model for mechanistic in vivo studies of the virus-host relationship. Interestingly, this impairment occurred at the proIL-1β transcript level and was independent of the RTA, the viral lytic replication and transcription activator. Furthermore, the γHV68-Cre virus also replicated normally during the acute phase of infection in the lungs of Dnmt1 conditional mice. The phylogram was constructed using the viral DNA polymerase gene by parsimony analysis with the neighbor-joining method.
The close parallels between normal, antigen-driven B cell responses and virus-infected B cell proliferation argue that in vivo, γHVs mostly induce infected B cells into normal GC reactions rather than generating large numbers of autonomously proliferating blasts. These data indicate that the MHV68 miRNAs may facilitate virus-driven maturation of infected B cells and implicate the miRNAs as a critical determinant of gammaherpesvirus-associated disease. The genome regions containing candidate γHV68 latency-associated genes shown by filled arrowheads scored strongly positive in the RT-PCR analysis of latently infected cells (Table 2). Wild-type (WT) γHV68 clone WUMS and viral cyclin-deficient (cyclin knockout [cycKO]), viral bcl-2-deficient (M11 KO), and M1-deficient (M1 KO) γHV68 mutants were passaged and grown, and titers were determined as described previously (23). Importantly, our data showed that MHV-68 has different kinetics of gene expression at different sites of infection. Furthermore, Rd1 and Rd2 were able to function as dominant-negative mutants, inhibiting trans-activation of wild-type Rta. One ORF (K3) was identified in gammaHV68 as homologous to both ORFs K3 and K5 of KSHV and contains a domain found in a bovine herpesvirus 4 major immediate-early protein.
These studies demonstrate that IFN-gamma is essential for control of chronic vascular pathology induced by gammaHV68 and suggest gamma-herpesviruses as candidate etiologic agents for human vasculitis. Real-time monitoring of M3FL infection revealed novel sites of viral replication, such as salivary glands, as well as acute replication in the nose and the lung and progression to the spleen. Clearly, this virus has evolved mechanisms to limit a protective host response capable of clearing acute or latent virus. Understanding of the mechanisms of gammaherpesvirus lymphomagenesis during chronic infection in a natural host has been limited by the exquisite species specificity of human gammaherpesviruses and the expense of primates.