Human cytomegalovirus (CMV) remains a major cause of congenital disease in children as well as a significant opportunistic pathogen in immunocompromised individuals, causing acute and chronic disease consequences despite the use of antiviral drugs. CMV modulates host cell behavior during infection in ways that affects susceptibility to intrinsic cellular defense pathways. Programmed cell death (PCD), sensor-triggered interferon activation, and signaling cascades are all affected starting at early times during infection. Importantly, these have their greatest impact at late times that coincide with viral maturation. Our work has shown that CMV-encoded cell death suppressors and protein kinases interface with cellular fate pathways late in the course of viral replication. Cell death suppression and phosphorylation changes are hypothesized to control a specific viral program, termed cmvPCD to terminate the replication cycle. This revised project will investigate the events, process and control of maturation by CMV-encoded cell death suppressors and cell cycle dysregulation.
The first aim of proposed investigations will focus primarily on the dissection of an intrinsic, stress-related serine-dependent apoptosis-like pathway we discovered to be active in CMV-infected cells, evaluating the events that occur at mitochondria and downstream of mitochondria to drive cell death. Viral functions promote cell death, and these are active during the late phase of replication when levels of the cellular serine protease HtrA2/Omi increase. We will investigate the role of cell cycle and viral protein kinase triggers of death using infected cell-based assays in order to seek a link between these pathways.
The second aim will investigate the mechanism(s) through which this serine protease-dependent pathway is controlled by a betaherpesvirus-conserved viral mitochondrial-localized inhibitor of apoptosis (vMIA), the product of the human UL37x1 gene. We will identify critical viral and cellular targets of vMIA action, integrating previous evidence that this viral cell death suppressor requires an interaction with GADD45 family proteins for activity and that the anti-apoptotic family protein Bcl-xL is an associated player. We believe that the interplay between these viral and cellular proteins sustain cell viability through HtrA2/Omi activation in infected cells, suggesting a role in pathogenesis. This important topic will be studied as aim three, through studies in mice infected with murine CMV mutants that disrupt the functionally homologous gene (m38.5) or replace the murine CMV gene with the human CMV gene. Through these efforts we will gain a complete understanding of the processes that underlie control of programmed cell death in CMV replication in cells and in an intact animal host.
Human cytomegalovirus (CMV) remains a major cause of congenital disease in children as well as a significant opportunistic pathogen in immunocompromised individuals, causing acute and chronic disease consequences despite the use of antiviral drugs. Virus-infected cells die in a proscribed way that relies on a novel host cell pathway triggered by a mitochondrial resident serine protease HtrA2/Omi and is controlled by the product of the viral UL37x1 gene, a powerful suppressor of cell death. This investigation will lead to a more complete understanding of the interplay of cellular and viral functions as determinants of cell fate.
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