The role of chaperone and co-chaperone proteins in alphaherpesvirus replication

Viruses as obligate intracellular parasites have evolved to hijack and utilize host proteins to ensure their replication and spread. Because of their limited coding potential, viral intruders heavily rely on the host metabolic machinery. In the first part of this thesis, we identified two novel cellular pathways that are required for replication of the human alphaherpesvirus Varicella Zoster Virus (VZV). We showed that pharmacological inhibition of the host chaperone protein Hsp90 prevents plaque formation and spread of VZV in tissue culture cells. Moreover, we identified the co-chaperone BAG3, as a host protein that interacts with the virus replication machinery. Importantly, genetic analysis revealed that VZV is unable to efficiently replicate and spread in cells that express reduced levels of the co-chaperone.;During these studies we demonstrated that unlike VZV, Herpes Simplex Virus (HSV), a closely related member of the alphaherpesvirus family, is not sensitive to loss of BAG3 and replicates with the same efficiency in the presence and absence of the co-chaperone. It is known that during infection, expression of potent viral activators can mask the requirement for cellular proteins and hide the function of host components that modulate virus replication. Therefore, we looked for proteins that are encoded by HSV and confer resistance to loss of BAG3. Expression of the multifunctional virus activator ICP0 was shown to be required for efficient replication in cells silenced for BAG3. Using a mutant virus deleted for ICP0 we demonstrated that BAG3 controls a novel pathway that promotes the very early stages of virus gene expression.;Although VZV encodes an ortholog of ICP0 (ORF61p) it cannot efficiently replicate without BAG3. Therefore, we hypothesized that ORF61p does not provide ICP0's function in this setting and the two proteins must possess distinct functions. In the last part of this thesis, we directly tested the role of ORF61p as a mimetic of ICP0's well-described function to disperse and degrade host proteins that are components of Nuclear Domains 10. These studies highlighted key differences in the activities of these viral activators and indicated that although HSV and VZV are closely related, they have evolved distinct ways to commandeer their hosts and ensure their efficient replication.