Human cytomegalovirus (HCMV) is a medically significant pathogen associated with severe clinical disease in immune deficient people. In recent years, medical researchers have gained appreciation that HCMV infection is also associated with a number of proliferative diseases such as cardiovascular disease, chronic bowel inflammatory disease and gastro-intestinal cancer. At the core of these manifestations is a virally programmed highjacking of cellular machinery. HCMV directly modulates signal transduction pathways, promotes changes in cellular processes, globally alters gene expression and induces disease mediators such as inflammatory cytokines. Interactions of HCMV envelope proteins with cellular receptors are the initiators of many of these changes. HCMV envelope glycoprotein B (gB) plays several fundamental roles in infection including receptor binding, membrane fusion, and activation of signal transductionpathways. Correspondingly, gB is under intense host surveillance. gB is recognized by pathogen sensors known as Toll-like receptors and serves as a trigger of host innate immunity, a discovery made by our laboratory in the previous funding period. Both branches of the adaptive immune system also recognize gB. It elicits potent neutralizing antibodies and has multiple epitopes recognized by cytotoxic T cell responses. The goal of these studies is to define the molecular underpinnings of the interactions of gB with cellular molecules. We also seek to characterize the consequences and cellular responses to these interactions in hopes that this knowledge will yield valuable insights into HCMV pathogenesis. In the previous funding period, we discovered that HCMV engages cellular integrins as entry mediators and signaling molecules. We also detected a novel disintegrin-like domain in the amino terminus of gB that had homology to cellular integrin binding proteins. Strikingly, this domain is very highly conserved in all beta and many gamma herpesviruses suggesting that integrins may serve as co-receptors for this medically significant group of pathogens. Studies proposed herein will test the hypothesis that the gB disintegrin-like domain directly mediates engagement of cellular integrins and that the consequence of this interaction is to prime downstream events such as membrane fusion, capsid-tegument translocation and/or gene expression. We also discovered that heptad repeat regions predictive of alpha helical coil-coils are present in gB and are important in the penetration stage of infection. Both the disintegrin-like domain and heptad repeat region will be subject to genetic analysis. In collaborative studies with Dr. Sam Gellman, a pioneer in beta-peptide technology, we will synthesize and characterize beta-peptide mimics of the gB coiled-coil domain. These data will be used to develop rational design of anti-fusogenic mimics that may ultimately be useful in treatment of HCMV disease.
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