UPTON LAB
RESEARCH
Viral control of programmed cell death
Necroptosis is a programmed cell death pathway triggered and subsequently inhibited by MCMV infection.  We and others have shown that cells infected with MCMV lacking the viral inhibitor of necroptosis as well as cells infected with Influenza A Virus (IAV) sense infection via a host pattern recognition receptor known as DAI.  Once infection is recognized, DAI interacts with RIPK3, the central mediator of necroptosis thus setting the cell death program into motion.  Our goal is to elucidate how DAI senses viral infection as well as determine the mechanism by which DAI transduces downstream signaling.  Our collaboration with the Balachandran lab at Fox Chase Cancer Center resulted in the identification of  viral RNAs produced by IAV infection as interacting with DAI, resulting in necroptosis (Thapa 2016). This led us to determine the events of viral infection necessary for the induction of necroptosis directing our attention to transcription mediated by the major transactivator of MCMV, IE3 (Sridharan 2017).  Additionally, we are investigating the minimal requirements for a critical domain present in all proteins involved in the necroptotic cascade known as the RHIM.
Beta Herpesvirus Deubiquitinases
All viruses have to combat with the cellular ubiquitin (Ub) system en route to successful infection.  Ubiquitin is a versatile posttranslational modification controlling many diverse cellular processes, from protein quality control, trafficking and degradation to signal transduction pathways. Ubiquitin (Ub) is a versatile posttranslational modification controlling many diverse cellular processes, from intracellular trafficking and protein degradation to innate immune signaling.  Activation of sequential E1-E2-E3 Ub-ligase cascades result in covalent attachment of one or more Ub molecules to lysine residues in substrate proteins.   Arrays of different Ub-Ub linkages, in large part, dictate the regulatory role of Ub modification on the stability, localization, or function of target proteins.  Conversely, Ub can be removed from modified proteins to reverse its effects through the activities of numerous deubiquitinating enzymes (DUBs). All herpesviruses encode DUBs that are implicated in facilitating the viral life cycle; however a thorough understanding of the activity, specificity and biology of these viral DUBs during a natural infection remains incomplete.  We have recently shown that conserved DUB activities encoded by the murine cytomegalovirus (MCMV) DUB control inflammation and viral pathogenesis during infection in a natural host by modulating the expression and secretion of a critical virally encoded chemokine. Building on these observations, preliminary data implicates MCMV DUB activity targets the ER-associated degradation (ERAD) machinery and other critical host pathways during infection.
Beta Herpesvirus dUTPases
dUTPases are a family of genes involved in nucleotide metabolism in our cells. They convert dUTP to dUMP and in turn provide precursor nucleotides to the host cell. Based on sequence
similarity, MCMV has a designated dUTPase sequence, M72. This viral dUTPase is a Herpesvirus core gene (it belongs to a list of about 45 genes conserved across the family of Herpesviruses). However, we do not know anything about the role of M72 gene in viral pathogenesis. We are examining the contribution of MCMV M72 to viral infection, identifying its cellular binding partners, and investigating their role in infection.
