Person: Lee, Jennifer
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Lee
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Jennifer
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Lee, Jennifer
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Publication Epigenetic Regulation of Lytic and Latent Herpes Simplex Virus 1 Infection(2015-05-01) Lee, Jennifer; Wang, Fred; Kuroda, Mitzi; Bachenheimer, Steven L.; DeCaprio, JamesEpigenetic regulation plays a major role in whether the herpes simplex virus 1 (HSV-1) will initiate viral gene expression and lytic infection or instead suppress its gene expression and establish a latent infection. Prior to this study, it was known that cells respond to naked DNA by assembling chromatin to silence foreign genetic material. However, during lytic infection of epithelial cells, viral proteins VP16 and ICP0 have been implicated in limiting chromatin association and promoting euchromatic histone modifications on the HSV-1 genome. We hypothesized that the viral genome would also be subject to silencing by heterochromatin modification during lytic infection. To test this we examined the association of chromatin and heterochromatic modifications during lytic infection with WT viruses and ICP0-null mutant viruses. We found that heterochromatin modifications H3K9me3 and H3K27me3 associate initially with all viruses, but were removed rapidly during infection with WT HSV-1. ICP0-null viruses were not able to remove histones or heterochromatin, indicating a role for ICP0 in reversing epigenetic silencing. In latent infection, HSV-1 undergoes epigenetic silencing as a means to suppress gene expression and persist in neurons. Surprisingly, in this study, we find that ICP0-null viruses accumulate less heterochromatin on lytic gene promoters relative to WT viruses. This suggests that ICP0 may function to promote infection of neurons, or assist in the establishment or maintenance of latent infection. Additionally, during latency the viral genome maintains active expression from the latency-associated transcript (LAT) region, and this region retains markers of euchromatin that are excluded from the lytic viral genes. The insulator protein, CTCF, binds to a site downstream of this region between the LAT and ICP0 promoters. We find that during latent infection, deletion of this site promoted accumulation of H3K27me3 at the LAT promoter and reduced reactivation competence of the virus, but surprisingly enhanced LAT expression. This suggests that CTCF balances epigenetic repression to promote latency and maintain reactivation competence. In summary, this dissertation suggests that during lytic infection HSV reverses cell-mediated epigenetic repression and promotes viral gene expression, while during latency, the virus co-opts epigenetic mechanisms to maintain a silenced but poised genome.Publication Herpesviral ICP0 Protein Promotes Two Waves of Heterochromatin Removal on an Early Viral Promoter during Lytic Infection(American Society of Microbiology, 2016) Lee, Jennifer; Raja, Priya; Knipe, DavidABSTRACT Herpesviruses must contend with host cell epigenetic silencing responses acting on their genomes upon entry into the host cell nucleus. In this study, we confirmed that unchromatinized herpes simplex virus 1 (HSV-1) genomes enter primary human foreskin fibroblasts and are rapidly subjected to assembly of nucleosomes and association with repressive heterochromatin modifications such as histone 3 (H3) lysine 9-trimethylation (H3K9me3) and lysine 27-trimethylation (H3K27me3) during the first 1 to 2 h postinfection. Kinetic analysis of the modulation of nucleosomes and heterochromatin modifications over the course of lytic infection demonstrates a progressive removal that coincided with initiation of viral gene expression. We obtained evidence for three phases of heterochromatin removal from an early gene promoter: an initial removal of histones and heterochromatin not dependent on ICP0, a second ICP0-dependent round of removal of H3K9me3 that is independent of viral DNA synthesis, and a third phase of H3K27me3 removal that is dependent on ICP0 and viral DNA synthesis. The presence of ICP0 in transfected cells is also sufficient to promote removal of histones and H3K9me3 modifications of cotransfected genes. Overall, these results show that ICP0 promotes histone removal, a reduction of H3K9me3 modifications, and a later indirect reduction of H3K27me3 modifications following viral early gene expression and DNA synthesis. Therefore, HSV ICP0 promotes the reversal of host epigenetic silencing mechanisms by several mechanisms.Publication A Herpesviral Lytic Protein Regulates the Structure of Latent Viral Chromatin(American Society for Microbiology, 2016) Raja, Priya; Lee, Jennifer; Pan, Dongli; Pesola, Jean; Coen, Donald; Knipe, DavidABSTRACT Latent infections by viruses usually involve minimizing viral protein expression so that the host immune system cannot recognize the infected cell through the viral peptides presented on its cell surface. Herpes simplex virus (HSV), for example, is thought to express noncoding RNAs such as latency-associated transcripts (LATs) and microRNAs (miRNAs) as the only abundant viral gene products during latent infection. Here we describe analysis of HSV-1 mutant viruses, providing strong genetic evidence that HSV-infected cell protein 0 (ICP0) is expressed during establishment and/or maintenance of latent infection in murine sensory neurons in vivo. Studies of an ICP0 nonsense mutant virus showed that ICP0 promotes heterochromatin and latent and lytic transcription, arguing that ICP0 is expressed and functional. We propose that ICP0 promotes transcription of LATs during establishment or maintenance of HSV latent infection, much as it promotes lytic gene transcription. This report introduces the new concept that a lytic viral protein can be expressed during latent infection and can serve dual roles to regulate viral chromatin to optimize latent infection in addition to its role in epigenetic regulation during lytic infection. An additional implication of the results is that ICP0 might serve as a target for an antiviral therapeutic acting on lytic and latent infections.