Cell Death Pathways in Cytomegalovirus Pathogenesis and Control Cytomegalovirus (CMV) is a major cause of disease in newborns and immunocompromised hosts. Contributing to medical significance, this virus encodes an arsenal of immunomodulatory gene products that assure efficient systemic infection as well as long-term persistence and latency. This project focuses on host defense at the portal of entry in the first cells that become infected. We address the interplay of host programmed cell death (PCD) pathways and the CMV-encoded suppressors that inhibit cell death in sculpting pathogenesis. Importantly, PCD pathways interface with CMV-encoded suppressors in an evolutionarily conserved fashion such that there are mechanistic similarity in murine and human CMV. Extrinsic apoptosis mediated through caspase 8 and necrosis mediated by receptor interacting protein 3 (RIP3) kinase play out within infected cells by interfacing with two interlocked classes of CMV cell death suppressors, one that is betaherpesvirus- conserved and suppresses caspase 8 activation (vICA) and the other, recently discovered, that blocks necrotic cell death (vIRA) unleashed by vICA inhibition of caspase 8. The necrotic PCD pathway and the relationship between vICA and vIRA were brought to light through our incisive studies employing murine CMV and mutant strains of mice. Here, we will investigate the interplay of these virus-encoded PCD suppressors and the cognate PCD pathways they inhibit, identifying key mechanism(s) that likely have broad significance in pathogen-host interactions. Relevance to human CMV will be established by identifying the RIP3-dependent necrotic death suppressor(s) encoded by this virus and studying mechanism. We will determine the role of apoptosis and necrosis in the earliest stages of infection of monocyte-derived macrophage. In this manner, we gain knowledge and understanding relevant to conserved aspects of apoptotic and necrotic PCD in host defense, which is the only immune mechanism currently able to completely stop virus and prevent infection:
Specific Aim 1 will identify the human CMV-encoded inhibitor of RIP3-dependent necrosis and investigate the interplay of inhibitors of extrinsic apoptosis (caspase 8) and necrosis (RIP3) on cell fate outcomes, focusing on changes in protein-protein interactions and cell signaling machinery that trigger cell death.
Specific Aim will evaluate the contribution of caspase 8- and RIP3-regulated cell death pathways to cell fate outcome by investigating the mechanism of Casp8 inhibition by vICA, as well as changes in protein-protein interactions that contribute to RIP3 RHIM- and kinase-dependent necrosis in cells and mice.
This proposal focuses on the cytomegalovirus (CMV) control of cell death pathways that impact first line host defense at the portal of entry. The project will make fundamental contributions to CMV pathogenesis as well as to host defense by linking experimental animal model to authentic settings with human CMV. A newly recognized arm of the immune system is able to prevent CMV infection by inducing a form of programmed cell death called programmed ecrosis. CMV deflects this pathway to undermine clearance and assure persistence. This virus suppresses apoptosis as well as a programmed necrosis tusing a set of evolutionarily conserved viral cell death suppressors conserved from rodents to humans. Apoptosis and necrosis pathways evolved to fight off viruses and counteract virus-encoded cell death suppressors.