Herpesviruses are a significant cause of morbidity and mortality in humans and animals worldwide. Herpes simplex virus (HSV) remains a major global pathogen causing oral and genital infections, blindness, encephalitis, and neonatal infections. The long-term goal of my laboratory is to understand the molecular processes that herpesviruses use to gain entry into host cells. HSV causes lifelong, latent infection for which there is no cure. A better understanding of how HSV interacts with the cell during the initial stages of infection will identify novel intervention strategies and antiviral drug targets. We utilize a combination of cellular, molecular, biochemical, and microscopic approaches to delineate the step-by-step itinerary of the incoming virus.
The long-held dogma that herpesviruses enter cells by fusion with the plasma membrane in a pH-independent manner was overturned when we identified a pH-dependent endocytic entry pathway for HSV into epithelial cells. It is now appreciated that herpesviruses utilize acid-dependent pathways in a cell-specific manner. Our current research focuses on the virus-cell interactions needed for two sequential steps in the initiation of infection: penetration of the genome-containing capsid into the cytoplasm and transport of the capsid to the nucleus, the site of herpesviral DNA replication. My lab has shown that to accomplish these steps, HSV engages the two distinct machineries of intracellular degradation: the low pH endosomal-lysosomal pathway and the 26S proteasome system.
Model of the role of the cellular degradation machinery in the initiation of HSV infection. For illustration, nonendocytic (A) and endocytic (B) pathways are shown in a single cell. In neurons (A), the capsid penetrates directly at the plasma membrane. In mucosal epithelial cells (B), HSV is taken up by a lysosome-terminal endosomal pathway. The normal, low pH environment of an endosome serves as a cue for HSV to escape prior to lysosomal degradation. The mildly acidic pH of ~ 5.8 triggers conformational change in envelope glycoprotein B (gB), which is needed for membrane fusion and penetration of the capsid into the cytosol. Regardless of pathway (A, B), the penetrated capsid requires active proteasomes for transport to the nuclear envelope. The virion protein ICP0, which is present in the tegument layer, regulates the proteasome-dependent delivery of capsids.