Initiation of the Host Response Against Murine Gammaherpesvirus Infection in Immunocompetent Mice

Exacerbated metastatic disease in a mouse mammary tumor model following latent gammaherpesvirus infection

Background

Controversy exists as to the ability of human gammaherpesviruses to cause or exacerbate breast cancer disease in patients. The difficulty in conducting definitive human studies can be overcome by investigating developing breast cancer in a mouse model. In this study, we utilized mice latently infected with murine gammaherpesvirus 68 (HV-68) to question whether such a viral burden could exacerbate metastatic breast cancer disease using a mouse mammary tumor model.

Results

Mice latently infected with HV-68 had a similar primary tumor burden, but much greater metastatic disease, when compared to mock treated mice given the transplantable tumor, 4 T1. This was true for lung lesions, as well as secondary tumor masses. Increased expression of pan-cytokeratin and VEGF-A in tumors from HV-68 infected mice was consistent with increased metastatic disease in these animals. Surprisingly, no viral particles could be cultured from tumor tissues, and the presence of viral DNA or RNA transcripts could not be detected in primary or secondary tumor tissues.

Conclusions

Latent HV-68 infection had no significant effect on the size of primary 4 T1 mammary tumors, but exacerbated the number of metastatic lung lesions and secondary tumors when compared to mock treated mice. Increased expression of the tumor marker, pan-cytokeratin, and VEGF-A in tumors of mice harboring latent virus was consistent with an exacerbated metastatic disease. Mechanisms responsible for this exacerbation are indirect, since no virus could be detected in cancerous tissues.

Murine gammaherpesvirus-68 expands, but does not activate, CD11b+ gr-1+ splenocytes in vivo

Background

Murine gammaherpesvirus 68 (HV-68) is an efficient pathogen, capable of infecting and establishing lifelong latency in rodents. While many studies have demonstrated the ability of this viral infection to modulate immune responses, a unifying mechanism for HV-68-induced subversion of a protective host response remains elusive. We questioned whether infection with HV-68 could expand a population of myeloid derived suppressor cells (MDSC) as one mechanism for altering protective immunity.

Methods

Mice were infected with HV-68, with viral latency being established in these animals. At varying times post-infection, cells were isolated for detection of viral genomes, phenotyping of myeloid cell populations, and ex vivo analysis of suppressor activity of myeloid cells.

Results

CD11b + Gr-1+ myeloid cells accumulated in the spleens, but not the bone marrow, of HV-68 infected mice. These cells were predominantly Gr-1+ Ly-6 G+, and could be found to contain viral genomes. Increased levels of serum S100A8/A9 produced during viral infection were consistent with the expansion of these CD11b + Gr-1+ myeloid cells. Despite their expansion, these cells exhibited no increased arginase 1 or iNOS activity, and did not have the ability to suppress anti-CD3 antibody activated T lymphocyte responses.

Conclusions

We concluded that HV-68 infection was capable of expanding a population of myeloid cells which were phenotypically similar to MDSC. However these cells were not sufficiently activated during the establishment of viral latency to actively suppress T cell responses.

Ecstasy (3,4-methylenedioxymethamphetamine) limits murine gammaherpesvirus-68 induced monokine expression

While Ecstasy (3,4-methylenedioxymethamphetamine, MDMA) has been shown to modulate immune responses, no studies have addressed drug-induced alterations to viral infection. In this study, bone marrow-derived macrophages were exposed to MDMA, then infected with murine gammaherpesvirus-68, and the expression of monokines assessed. MDMA-induced reductions in virus-stimulated monokine mRNA expression were observed in a dose-dependent manner. In particular, IL-6 mRNA expression and secretion was significantly decreased in gammaherpesvirus-infected macrophages exposed to MDMA. Concentrations of MDMA capable of reducing monokine production did not induce significant cell death and allowed normal viral gene expression. These studies represent the first to demonstrate the ability of this drug of abuse to alter a viral-induced macrophage response.

Role of the ubiquitin system and tumor viruses in AIDS-related cancer

Tumor viruses are linked to approximately 20% of human malignancies worldwide. This review focuses on examples of human oncogenic viruses that manipulate the ubiquitin system in a subset of viral malignancies; those associated with AIDS. The viruses include Kaposi's sarcoma herpesvirus, Epstein-Barr virus and human papilloma virus, which are causally linked to Kaposi's sarcoma, certain B-cell lymphomas and cervical cancer, respectively. We discuss the molecular mechanisms by which these viruses subvert the ubiquitin system and potential viral targets for anti-cancer therapy from the perspective of this system.

Publication history: Republished from Current BioData's Targeted Proteins database (TPdb; ).

Evidence for CDK-dependent and CDK-independent functions of the murine gammaherpesvirus 68 v-cyclin

Gamma-2 herpesviruses encode homologues of mammalian D-type cyclins (v-cyclins), which likely function to manipulate the cell cycle, thereby providing a cellular environment conducive to virus replication and/or reactivation from latency. We have previously shown that the v-cyclin of murine gammaherpesvirus 68 is an oncogene that binds and activates cellular cyclin-dependent kinases (CDKs) and is required for efficient reactivation from latency. To determine the contribution of v-cyclin-mediated cell cycle regulation to the viral life cycle, recombinant viruses in which specific point mutations (E133V or K104E) were introduced into the v-cyclin open reading frame were generated, resulting in the disruption of CDK binding and activation. While in vitro growth of these mutant viruses was unaffected, lytic replication in the lungs following low-dose intranasal inoculation was attenuated for both mutants deficient in CDK binding as well as virus in which the entire v-cyclin open reading frame was disrupted by the insertion of a translation termination codon. This replication defect was not apparent in spleens of mice following intraperitoneal inoculation, suggesting a cell type- and/or route-specific dependence on v-cyclin-CDK interactions during the acute phase of virus infection. Notably, although a v-cyclin-null virus was highly attenuated for reactivation from latency, the E133V v-cyclin CDK-binding mutant exhibited only a modest defect in virus reactivation from splenocytes, and neither the E133V nor K104E v-cyclin mutants were compromised in reactivation from peritoneal exudate cells. Taken together, these data suggest that lytic replication and reactivation in vivo are differentially regulated by CDK-dependent and CDK-independent functions of v-cyclin, respectively.

Murine γ-Herpesvirus 68 Limits Naturally Occurring CD4+CD25+T Regulatory Cell Activity following Infection

During microbial infections, naturally occurring CD4+CD25+ T regulatory cells can suppress protective host responses or they can limit pathogen-induced inflammatory responses. The particular role played by these cells seems to depend upon the infectious agent being investigated. Gamma-herpesviruses are efficacious pathogens which are well-known for their ability to induce lymphoproliferative disease and to establish latency in the host. However, no studies have investigated the importance of naturally occurring CD4+CD25+ T regulatory cells during infection with these viruses. Using the murine model of gamma-herpesvirus infection, murine gamma-herpesvirus 68 (gammaHV-68), we were surprised to find that levels of the CD4+CD25+ T regulatory cell transcript, FoxP3, continued to decrease as viral latency increased and as the leukocytosis phase of the disease progressed. Consistent with these results, the decrease in FoxP3 protein expression followed similar kinetics. Along with the reduced expression of this regulatory T cell marker, we also observed diminished CD4+CD25+ T regulatory cell activity in these cells isolated from gammaHV-68-infected animals. Dendritic cells infected in vitro with gammaHV-68 did not alter the ability of normal CD4+CD25+ regulatory T cells to limit the proliferation of CD4+ Th cells following stimulation. Taken together, these studies demonstrate a decreased presence and activity of CD4+CD25+ T regulatory cells during the mononucleosis-like phase of this viral infection. These alterations in naturally occurring T regulatory cell function may help to explain the dysregulation of the host's immune response which allows the uncontrolled expansion of leukocytes as viral latency is established.

Limited IL-6 production following infection with murine gammaherpesvirus 68

Murine gammaherpesvirus 68 (gammaHV-68) was found to induce IL-6 secretion following in vitro infection of macrophages, but not cultured dendritic or epithelial cells. A detectable, but very limited IL-6 response was observed in the lungs and mediastinal lymph nodes following intranasal infection. Surprisingly, no detectable in vivo IL-6 production was observed in the spleen or sera of infected mice despite observable systemic leukocytosis. These studies demonstrate that endogenous IL-6 production contributes little to the host response, or to the viral-induced mononucleosis-like disease, due to the fact that limiting amounts of this cytokine are produced in vivo during gammaHV-68 infection.