GENETIC AND BIOLOGICAL DETERMINANTS OF AVIAN TUMOR VIRUS SUSCEPTIBILITY
Location: Avian Disease and Oncology Laboratory
Title: Gene Expression Profiling in rMd5- and rMd5-delta-meq-Infected Chickens
Submitted to: Avian Diseases
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: March 27, 2011
Publication Date: September 1, 2011
Citation: Xu, M., Zhang, H., Lee, L.F., Gao, H., Sharif, S., Silva, R.F., Heidari, M. 2011. Gene expression profiling in rMd5- and rMd5-delta-meq-infected chickens. Avian Diseases. 55(3):358-367.
Interpretive Summary: Marek’s disease (MD) causes enormous economical losses to the poultry industry. Marek’s disease virus (MDV), the etiological agent of MD, is a herpesvirus that causes cancer-like disease along with suppression of immune system and evasion of immune responses in infected chickens. Cytokines are secreted proteins, which are important mediators and regulators of host immune responses. The main function of cytokines is orchestrating the functional activities of the cells of the immune system. Among the many essential MDV genes that play a critical role in the viral virulence, meq is the only MDV-encoded gene that is known to be involved in tumor development. In this study, we investigated the expression analysis of a panel of cytokines and other immune related genes in chickens infected with an intact MDV strain termed rMd5 or a mutant form of the virus lacking both copies of meq gene termed rMd5delta-meq. The data obtained from the study shows that presence of meq in the intact virus (rMd5) down regulates the expression of certain immune related genes when compared to the mutant virus (rMd5delta-meq), suggesting that meq functions as an immune suppressive protein. In addition, we also found out that meq plays an important role in intensifying the process of MDV-induced cell death in a sub-population of T cells (immune cells)in chickens. This information is important as it provides insights into the molecular mechanism of MDV virulence and its interference with the normal function of the immune system. The information also serves as the groundwork for future investigations that are aimed at enhancing the immune response to MD and consequently better control of this important disease of chickens.
Marek’s disease (MD) is a lymphoproliferative disorder of domestic chickens caused by a highly contagious and oncogenic alpha-herpesvirus, Marek’s disease virus (MDV). MD is characterized by bursal/thymic atrophy and rapid onset of T cell lymphomas that infiltrate lymphoid tissues, visceral organs, and peripheral nerves with severe clinical signs that includes transient paralysis, anemia, weight loss, and neurological disorders. Using overlapping cosmids- and BAC-cloned MDV, it has been shown that MDV-encoded vIL-8, pp38, vTR, vLIP, RLORF4, and meq are among the many essential genes that play critical roles in viral pathogenesis. Of all the genes investigated so far, only meq has been shown to be consistently expressed in all MDV-derived tumors and lymphoblastoid cell lines. Meq is a basic leucine-zipper protein that shares homology with jun/fos family of transcriptional factors. There are two copies of meq gene within MDV genome that are only present in the serotype 1 strains. It has been shown conclusively that deletion of meq results in loss of transformation of T cells in chickens with no effect on early cytolytic phase of infection in lymphoid organs, which is essential for induction of innate and adaptive immunity. The goal of this study was to investigate 1) the effect of meq oncogene on the expression pattern of select chicken immune and non-immune related genes and 2) its potential role in MDV-induced apoptosis. We used Real-Time RT-PCR to evaluate the expression profiling of a panel of chicken genes in rMd5- and rMd5delta-meq-infected chickens at 5, 14, 21, and 35 days post infection (dpi). Although the transcriptional activities of several immune-related genes including IL-6, IL-10, cMGF, GM-CSF, iNOS, IFNbeta, and INFgamma were higher in rMd5delta-meq-infected chickens at 5 dpi when compared to the rMd5-infected birds, the differences in expression levels of the tested genes between the two viral constructs were not significant. In addition, a reduction in the transcriptional activity of Bcl2 in recombinant fowlpox virus (rFPV)+meq-infected chicken embryonic fibroblasts suggested that meq alone did not impede FPV-induced apoptosis. The likely suppressive nature and anti-inflammatory function of meq oncogene and its possible role in virus-induced cell death is discussed.