Browsing by Subject "Yellow fever virus"
Now showing 1 - 3 of 3
- Results Per Page
- Sort Options
Item Characterization of Host Factors Affecting Viral Entry(2019-04-10) Rinkenberger, Nicholas Ryan; Alto, Neal; Schoggins, John W.; Pfeiffer, Julie K.; Reese, Tiffany A.Viruses are obligate, intracellular parasites. For a virus to infect a host cell, it must gain access to the interior of the host cell by some means. In animals, this often involves the exploitation of host processes such as receptor-mediated endocytosis and vesicular trafficking. Zika virus is an emerging arbovirus with global health and economic impacts. Interestingly, while Asian lineage Zika virus causes human disease and has been associated with severe neurological complications, African lineage Zika virus has only rarely been reported to cause human disease. Large strides have been made in understanding Zika virus infection. However, the mechanism used by Zika virus to enter host cells remains somewhat obscure. In chapter 2, I delineate and compare the pathway utilized by both Asian and African lineage Zika virus to enter host cells. I find that these viruses require clathrin-mediated endocytosis and Rab5a function in a conserved manner. Additionally, all Zika virus strains tested were sensitive to pH in the range of 6.5-6.1 and were reliant on endosomal acidification for infection. I found that Zika virus preferentially fuses with late endosomes. Comparing lineages, Zika virus enters cells in a highly conserved manner. Just as viruses have evolved to exploit host factors to promote their entry and replication, hosts have developed mechanisms of defense against viral infection. Recognition of viral infection by vertebrate hosts results in the expression and secretion of interferon. Interferon signaling subsequently results in the induction of hundreds of interferon-stimulated genes (ISGs) which restrict pathogen infection. Some of these ISGs specifically block viral entry. Surprisingly, a small group of ISGs was previously identified which actually promote viral infection. In chapter 3, I characterize the mechanism of action of MCOLN2, one of the ISGs found to promote viral infection. I assign a role for MCOLN2 in modulating viral entry. I show that MCOLN2 specifically promotes viral vesicular trafficking and subsequent escape from endosomal compartments. This mechanism requires channel activity, occurs independently of antiviral signaling, and broadly applies to enveloped RNA viruses that require endosomal acidification for infection, including influenza A virus, yellow fever virus, and Zika virus.Item Characterization of the Antiviral Effector IFI6(2018-11-26) Richardson, Ryan Blake; Yan, Nan; Schoggins, John W.; Levine, Beth; Pfeiffer, Julie K.The innate immune response is a critical line of host defense against invading pathogens. The production of interferon (IFN) and the subsequent expression of interferon stimulated genes (ISGs) are major contributors to the innate immune response, which establish an antiviral state in the cell. Flaviviruses such as dengue virus, Zika virus, and West Nile virus rely intimately on host pathways for completing a replication cycle, and have developed strategies to overcome the inhibitory effect of the innate immune response. To identify host factors required during an IFN response to flavivirus infection, a genome-wide CRISPR screen was carried out. Two of the top hits from the screen were IFI6, a previously identified ISG long predicted to be antiviral, and BiP, a luminal chaperone in the endoplasmic reticulum (ER). I questioned whether IFI6 was important for the antiviral response to flaviviruses and sought to investigate its role during infection. I confirmed the results from the CRISPR screen and showed that cells lacking IFI6 were insensitive to IFN, suggesting a key role in the innate immune response to flaviviruses. This was complemented by overexpression studies which showed IFI6 is potently inhibitory to flavivirus infection. I further demonstrated that BiP is required for an intact IFN response and importantly mediates expression of IFI6, which it binds in a chaperone-dependent manner. I also showed that IFI6 is localized to the ER and is an integral membrane protein. Importantly, IFI6 acts during the flavivirus life cycle to inhibit replication and formation of replication complexes, which are formed by rearrangement of ER membranes. IFI6 specifically inhibits flaviviruses, since other viruses that replicate at the ER such as hepatitis C virus (HCV) are not affected by IFI6. I hypothesize the key to this specificity lies in the orientation of the replication complexes - HCV complexes extend outwards into the cytoplasm while flaviviruses bud inwards into the lumen. Taken together, these data support a model where IFI6 is sensitive to membrane alterations specifically induced by flaviviruses but not other viruses, which provides the innate immune response with a potent and specific ISG to block viral infection.Item Neuronal Dissemination Patterns of Three Distinct Viruses and Mechanisms Regulating Viral Retrograde Axonal Transport(2015-09-29) Luethy, Lauren Nicole; D'Orso, Iván; Pfeiffer, Julie K.; Schoggins, John W.; Lin, WeichunViruses from several distinct families can infect the central nervous system (CNS), but mechanisms and host factors that influence dissemination are not completely understood. I previously identified barriers that limit poliovirus and yellow fever virus 17D (YFV-17D) dissemination following peripheral injection of mice. To investigate how different viruses disseminate from peripheral tissue to the CNS, I intramuscularly injected mice with genetically marked pools of viruses and monitored dissemination along the sciatic nerve to the spinal cord and brain. Transport efficiency of each virus was compared in immune competent and immune deficient mice in the presence or absence of muscle damage, which was previously shown to enhance retrograde axonal transport of poliovirus in the sciatic nerve. I found that immune deficiency enhanced poliovirus and YFV-17D transport to the CNS. While muscle damage dramatically enhanced poliovirus dissemination it did not enhance YFV-17D dissemination, likely because YFV-17D entered the CNS through the blood. Like poliovirus, reovirus type 3 Dearing strain is transported through peripheral nerves to the CNS. Using genetically marked reoviruses, I found that young age and immune deficiency, but not muscle damage, enhanced reovirus transport to the CNS from peripheral tissues. Overall, my data suggest that these three viruses access the CNS through different routes and with different efficiencies. Though muscle damage enhances neuronal poliovirus dissemination, the mechanisms that regulate this are unclear. I tested dissemination of the marked viruses following intramuscular injection in the presence or absence of potential regulatory factors. Several growth factors, including brain-derived neurotrophic factor, were previously shown to enhance retrograde axonal transport. In conjunction with poliovirus injection, brain-derived neurotrophic factor or other growth factors were not observed to enhance viral dissemination. Microarray analysis of muscle samples was performed to compare host gene expression in damaged and non-damaged tissue. Several host transcripts had elevated transcript levels in damaged muscles, including tissue inhibitor of metalloproteinase-1 (TIMP-1) and monocyte chemoattractant protein-1 (MCP-1). The targets of TIMP regulation, matrix metalloproteinases (MMPs), were previously shown to stimulate retrograde axonal transport following damage to peripheral tissues. MCP-1 has also been suggested to enhance viral dissemination. Altering MCP-1 or MMP levels during poliovirus infection revealed no direct impact on poliovirus dissemination. Though mechanisms regulating viral dissemination following muscle damage remain unclear, the path is open for exploration.