Gammaherpesviruses are pervasive pathogens that establish lifelong infection in their hosts. The human gammaherpesviruses Epstein-Barr Virus (EBV) and Kaposi's Sarcoma Associated Herpesvirus (KSHV) are associated with diverse diseases, including several cancers. The murine gammaherpesvirus named mouse gammaherpesvirus 68 (MHV68) serves as a model system and provides for the use of powerful mouse genetics to understand the virus-host relationship. All gammaherpesviruses encode a viral protein kinase that phosphorylates and interacts with a multitude of substrates, though the physiological relevance of many of these substrate interactions remains to be verified. As nuclear DNA viruses, herpesviruses interact with cellular histone proteins that enwrap DNA in the nucleus to form chromatin. Histone acetylation is a common post-translational modification that promotes enhanced gene expression. Histone deacetylases (HDACs) catalyze the removal of acetyl moieties from histones and are classically considered to repress transcription. Due to their repressive nature, HDACs are frequently characterized as antiviral, and several viruses have evolved mechanisms to inactivate, disrupt, relocalize, or modify HDACs to facilitate infection. For example, herpes simplex virus-1 (HSV-1) has evolved mechanisms to antagonize HDACs through two distinct viral proteins: ICP02 and the Us3 kinase3;4. We have discovered that orf36, the MHV68 kinase, interacts with and modulates HDACs during infection. We hypothesize that this modulation facilitates viral infection at several stages, including viral gen expression, DNA replication, and infectious virion production. To test this hypothesis, we will use cells and mice with conditional HDAC alleles. After excision of HDACs in cells in vitro, we will measure viral gene expression and DNA replication via qRT-PCR and infectious virion production via plaque assay. After HDAC excision in vivo, we will measure peak viral titers via plaque assay and parameters of viral latency with limiting dilution assays. The combination of in vitro and in vivo techniques will encompass a directed, yet extensive, characterization of the role of HDACs in MHV68 infection. Herpesviral kinases are critical regulators of infection and represent a tractable target for therapeutics. Additionally, histone deacetylases have emerged as important therapeutic targets in cancer treatments. Thus, understanding the interactions between herpesviral kinases, chromatin, and chromatin-modifying enzymes is critical to the development of rational therapeutics. Several orf36 functions are conserved in other gammaherpesviral kinases;thus, the results of our studies are expected to translate to human pathogens.
Nearly all humans are infected with at least one gammaherpesvirus, and gammaherpesviruses are associated with several diseases, including cancers. This project addresses the role of a specific virus component and how it is used by the virus to manipulate the infected cell and aid in the establishment of infection. Understanding the functions of virus components and how they impact infected cells is critical to the development of antiviral therapeutics and in disease treatment.
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