Emily E Marshall

Publications of Emily E Marshall

• Multifaceted Evasion of the Interferon Response by Cytomegalovirus.

  Authors: Emily E Marshall, Adam P Geballe

  Journal of interferon & cytokine research : the official journal of the International Society for Interferon and Cytokine Research. 09/2009;

  Human cytomegalovirus (HCMV), which infects the majority of the population worldwide, causes few, if any, symptoms in otherwise healthy people but is responsible for considerable morbidity andHuman cytomegalovirus (HCMV), which infects the majority of the population worldwide, causes few, if any, symptoms in otherwise healthy people but is responsible for considerable morbidity and mortality in immunocompromised patients and in congenitally infected newborns. The evolutionary success of HCMV depends in part on its ability to evade host defense systems. Here we review recent progress in elucidating the remarkable assortment of mechanisms employed by HCMV and the related beta-herpesviruses, murine cytomegaloviruses (MCMV) and rhesus cytomegaloviruses (RhCMV), for counteracting the host interferon (IFN) response. Very early after infection, cellular membrane sensors such as the lymphotoxin beta receptor initiate the production of antiviral cytokines including type I IFNs. However, virion factors, such as pp65 (ppUL83) and viral proteins made soon after infection including the immediate early gene 2 protein (pUL122), repress this response by interfering with steps in the activation of IFN regulatory factor 3 and NF-kappaB. CMVs then exert a multi-pronged attack on downstream IFN signaling. HCMV infection results in decreased accumulation and phosphorylation of the IFN signaling kinases Jak1 and Stat2, and the MCMV protein pM27 mediates Stat2 down-regulation, blocking both type I and type II IFN signaling. The HCMV immediate early gene 1 protein (pUL123) interacts with Stat2 and inhibits transcriptional activation of IFN-regulated genes. Infection also causes reduction in the abundance of p48/IRF9, a component of the ISGF3 transcription factor complex. Furthermore, CMVs have multiple genes involved in blocking the function of IFN-induced effectors. For example, viral double-stranded RNA-binding proteins are required to prevent the shutoff of protein synthesis by protein kinase R, further demonstrating the vital importance of evading the IFN response at multiple levels during infection.

• Essential role for either TRS1 or IRS1 in human cytomegalovirus replication.

  Authors: Emily E Marshall, Craig J Bierle, Wolfram Brune, Adam P Geballe

  Journal of virology. 03/2009;

  Viral infections often produce double-stranded RNA (dsRNA), which in turn triggers potent antiviral responses including the global repression of protein synthesis mediated by protein kinase R (PKR)Viral infections often produce double-stranded RNA (dsRNA), which in turn triggers potent antiviral responses including the global repression of protein synthesis mediated by protein kinase R (PKR) and 2'-5' oligoadenylate synthetase (OAS). As a consequence, many viruses have evolved genes, such as those encoding dsRNA-binding proteins, which counteract these pathways. Human cytomegalovirus (HCMV) encodes two related proteins, pTRS1 and pIRS1, which bind dsRNA and can prevent activation of the PKR and OAS pathways. HCMV mutants lacking either IRS1 or TRS1 replicate at least moderately well in cell culture. However, as we demonstrate in the present study, an HCMV mutant lacking both IRS1 and TRS1 (HCMV[DeltaI/DeltaT]) has a severe replication defect. Infection with HCMV[DeltaI/DeltaT] results in a profound inhibition of overall and viral protein synthesis, as well as increased phosphorylation of eukaryotic initiation factor 2alpha. The vaccinia virus E3L gene can substitute for IRS1 or TRS1, enabling HCMV replication. Despite the accumulation of dsRNA in HCMV infected cells, the OAS pathway remains inactive, even in HCMV[DeltaI/DeltaT]-infected cells. These results suggest that PKR-mediated phosphorylation of eIF2alpha is the dominant dsRNA-activated pathway responsible for inhibition of protein synthesis and HCMV replication in the absence of both IRS1 and TRS1, and that the requirement for evasion of the PKR pathway likely explains the necessity of IRS1 or TRS1 for productive infection.

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• Binding and nuclear relocalization of protein kinase R by human cytomegalovirus TRS1.

  Authors: Morgan Hakki, Emily E Marshall, Katherine L De Niro, Adam P Geballe

  Journal of virology. 01/2007; 80(23):11817-26.

  The human cytomegalovirus (HCMV) TRS1 and IRS1 genes block the phosphorylation of the alpha subunit of eukaryotic initiation factor 2 (eIF2alpha) and the consequent shutoff of cellular proteinThe human cytomegalovirus (HCMV) TRS1 and IRS1 genes block the phosphorylation of the alpha subunit of eukaryotic initiation factor 2 (eIF2alpha) and the consequent shutoff of cellular protein synthesis that occur during infection with vaccinia virus (VV) deleted of the double-stranded RNA binding protein gene E3L (VVDeltaE3L). To further define the underlying mechanism, we first evaluated the effect of pTRS1 on protein kinase R (PKR), the double-stranded RNA (dsRNA)-dependent eIF2alpha kinase. Immunoblot analyses revealed that pTRS1 expression in the context of a VVDeltaE3L recombinant decreased levels of PKR in the cytoplasm and increased its levels in the nucleus of infected cells, an effect not seen with wild-type VV or a VVDeltaE3L recombinant virus expressing E3L. This effect of pTRS1 was confirmed by visualizing the nuclear relocalization of PKR-EGFP expressed by transient transfection. PKR present in both the nuclear and cytoplasmic fractions was nonphosphorylated, indicating that it was unactivated when TRS1 was present. PKR also accumulated in the nucleus during HCMV infection as determined by indirect immunofluorescence and immunoblot analysis. Binding assays revealed that pTRS1 interacted with PKR in mammalian cells and in vitro. This interaction required the same carboxy-terminal region of pTRS1 that is necessary to rescue VVDeltaE3L replication in HeLa cells. The carboxy terminus of pIRS1 was also required for rescue of VVDeltaE3L and for mediating an interaction of pIRS1 with PKR. These results suggest that these HCMV genes directly interact with PKR and inhibit its activation by sequestering it in the nucleus, away from both its activator, cytoplasmic dsRNA, and its substrate, eIF2alpha.