During herpes simplex virus 1 (HSV-1) infection, chromatin is dynamic and multiple opposing factors affect the quantity and state of histones on viral genomes. Although it is widely accepted that chromatin suppresses viral gene expression during latency, it is unclear to what extent histones participate in the temporal expression of viral genes during productive infection. Furthermore, the role chromatin remodeling complexes play in the regulation of viral genes is poorly understood. Although nucleosomes are not abundant on viral genomes during productive infection, several lines of evidence suggest that histones and chromatin remodeling factors contribute to the precise timing of the ordered expression of viral genes. During initial infection, the viral tegument protein VP16 interacts with factors to convert repressive histone modifications to active marks and remove histones from the promoters of immediate early genes. The immediate protein ICP0 is an E3 ubiquitin ligase that plays a role in the removal of repressive chromatin from incoming and quiescent genomes to promote viral gene expression. Immediate early protein ICP4, which is a transcriptional activator of early and late genes and repressor of immediate early genes, interacts with members of the SWI/SNF, NuRD, and INO80 chromatin remodeling complexes, suggesting a role for these factors in the regulation of viral genes. Specific chromatin remodeling complexes were found to associate with viral genomes during early and late stages of productive infection by iPOND (isolation of proteins on nascent DNA), including members of the FACT, SWI/SNF, NuRD, and INO80 complexes, as well as several other chromatin associated and modifying proteins. Furthermore, the INO80 and NuRD complexes were found to selectively associate with viral replication forks, suggesting involvement in the regulation of replication or replication-coupled events such as late viral gene expression. Therefore, the hypothesis to be tested in the proposed experiments is that cellular chromatin remodeling factors modulate histone interactons with viral genomes to precisely control the temporal expression of viral genes during productive infection. The overall goals of this proposal are to map the genome-wide histone landscape on viral genes at various stages of productive infection, as well as to dissect where, when, and how select chromatin remodeling complexes function during productive infection.
The aims outlined in this exploratory project are to 1) map and quantify interactions between histones and chromatin remodeling proteins with HSV-1 genomes a defined stages of productive infection and 2) determine the effects of knockdown of select cellular chromatin remodeling factors on histone and RNA polymerase II occupancy on viral genomes, viral gene expression, and virus multiplication. Results from these studies will reveal epigenetic mechanisms that control viral gene expression during productive HSV-1 infection and will be used in the future to propose more developed hypotheses and in depth studies.

Public Health Relevance

The overall goal of this study is to determine how chromatin remodeling factors and histones interact with HSV- 1 genomes during productive infection to control the ordered expression of viral genes. Understanding epigenetic mechanisms that control the temporal transcription of viral genes may allow for strategies to block transcription and hence virus multiplication. Furthermore, the proposed studies will shed light on mechanisms by which herpesviruses utilize host mechanisms for the regulation of viral processes, as well as how virus host interactions determine the outcome of infection. !

National Institute of Health (NIH)
National Institute of Allergy and Infectious Diseases (NIAID)
Exploratory/Developmental Grants (R21)
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Virology - A Study Section (VIRA)
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Natarajan, Ramya
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University of Pittsburgh
Schools of Medicine
United States
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