Cell cycle inhibitors in control of chronic gammaherpesvirus infection

Murine gammaherpesvirus 68 is biologically related to the human gammaherpesviruses, Epstein Barr Virus and Kaposi's sarcoma associated herpesvirus. Gammaherpesviruses are significant medical and veterinary pathogens that cause a wide variety of malignancies associated with chronic inflammation and reactivation from latency, and a better understanding of reactivation from latency is clearly needed. Infection with gammaherpesviruses in healthy individuals results in an acute lytic infection that is rapidly cleared, with subsequent establishment of latent infection. Previous work demonstrated that the gammaherpesvirus 68 viral cyclin is essential for efficient reactivation from latency, that is, a viral cyclin deficient virus reactivates from latency at a frequency 100-fold lower than does wild-type virus. Gammaherpesvirus viral cyclins can interact with and activate host cyclin dependent kinases. Heterodimeric cyclin dependent kinase complexes are in turn regulated by cyclin-dependent kinase inhibitors. p18INK4c and p27Kip1 are two cyclin dependent kinase inhibitors and tumor suppressors that play a critical role in lymphocytes.;In vitro, over-expression studies have been used to determine potential substrates and binding partners of the viral cyclin. These studies have provided critical insights into the capabilities of viral cyclins; however, this work has been done outside the context of viral infection. The activities and true functions of the viral cyclins are likely to be further regulated in vivo during the course of viral infection. Given the global requirement for the viral cyclin in reactivation from latency and the link between increased reactivation, the viral cyclin and chronic disease, it is important to identify host molecules that regulate this pathway. The goal of this work is to better define the mechanism of the viral cyclin in reactivation from latency in vivo. In the studies described in this dissertation, I have utilized wild type gammaHV68 and a viral cyclin deficient virus to study the establishment of latency and reactivation in mice genetically deficient for two cyclin dependent kinase inhibitors, p18 INK4c and p27Kip1. The work described in chapters IV and V of this dissertation identified two host proteins that affect the reactivation process. These two host proteins have different and unique functions in gammaherpesvirus 68 reactivation from latency. The identification of these host proteins and their role in virus infection furthers our understanding of the function of the viral cyclin during gammaHV pathogenesis, thus providing critical information for the design of new therapeutics.