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Chan, Ying Kai

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Chan

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Ying Kai

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Chan, Ying Kai
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    Interplay of Dengue Virus and the Human Immune Response
    (2015-05-07) Chan, Ying Kai; Gehrke, Lee; Cepko, Constance; Rabkin, Samuel; Muhlberger, Elke
    RIG-I is a key cytosolic sensor of many RNA viruses, including dengue virus (DV), the most significant arboviral pathogen. Upon viral RNA binding, RIG-I signals via the adaptor protein MAVS, located at mitochondria, to induce the expression of interferons (IFNs), proinflammatory cytokines and interferon-stimulated genes (ISGs), thereby establishing an antiviral state. Among the ISGs, the IFITM proteins are critical for antiviral restriction of numerous pathogenic viruses including DV by inhibiting viral entry. Here, we uncover how DV escapes RIG-I-mediated immunity. The NS3 protein of DV binds directly to 14-3-3ε, a mitochondrial-targeting protein that is essential for translocation of RIG-I from the cytosol to mitochondria. Specifically, NS3 blocks 14-3-3ε from forming a “translocon” complex with RIG-I and its upstream activator, TRIM25, thereby inhibiting RIG-I translocation to mitochondria for MAVS interaction and antiviral signaling. Furthermore, RIG-I that fails to translocate to mitochondria is degraded in a lysosome-dependent manner in DV- infected cells. Intriguingly, NS3 binds to 14-3-3ε using a phosphomimetic motif that resembles a canonical phospho-serine/threonine motif found in cellular 14-3-3-interaction partners. We engineer a recombinant DV encoding a mutant NS3 protein deficient in 14-3-3ε binding (DV2KIKP) and find that this mutant virus is attenuated in replication compared to the parental virus. Strikingly, DV2KIKP fails to antagonize RIG-I and elicits high levels of IFNs, proinflammatory cytokines and ISGs in human hepatocytes and monocytes. Taken together, our data reveal a novel phosphomimetic-based mechanism for viral antagonism of innate immunity and provide a foundation for DV vaccine development. DV can infect cells directly, or complex with non-neutralizing antibodies to infect Fc- receptor-bearing cells in a secondary infection, which is associated with severe disease. While it has been shown that IFITMs restrict DV direct infection, it is unknown if the latter process, commonly termed antibody-dependent enhancement (ADE), might bypass IFITM-mediated restriction. Comparison of direct and ADE-mediated DV infection shows that IFITM proteins restrict both infection modes equally, suggesting that upregulation of IFITMs may be a therapeutic strategy. In summary, our work elucidates several molecular aspects of the interplay of DV with the human immune response, which may guide the rational design of vaccines and antivirals.
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    TIM-family Proteins Promote Infection of Multiple Enveloped Viruses through Virion-associated Phosphatidylserine
    (Public Library of Science, 2013) Jemielity, Stephanie; Wang, Jinyize J.; Chan, Ying Kai; Ahmed, Asim; Li, Wenhui; Monahan, Sheena; Bu, Xia; Farzan, Michael; Freeman, Gordon; Umetsu, Dale; DeKruyff, Rosemarie H.; Choe, Hyeryun
    Human T-cell Immunoglobulin and Mucin-domain containing proteins (TIM1, 3, and 4) specifically bind phosphatidylserine (PS). TIM1 has been proposed to serve as a cellular receptor for hepatitis A virus and Ebola virus and as an entry factor for dengue virus. Here we show that TIM1 promotes infection of retroviruses and virus-like particles (VLPs) pseudotyped with a range of viral entry proteins, in particular those from the filovirus, flavivirus, New World arenavirus and alphavirus families. TIM1 also robustly enhanced the infection of replication-competent viruses from the same families, including dengue, Tacaribe, Sindbis and Ross River viruses. All interactions between TIM1 and pseudoviruses or VLPs were PS-mediated, as demonstrated with liposome blocking and TIM1 mutagenesis experiments. In addition, other PS-binding proteins, such as Axl and TIM4, promoted infection similarly to TIM1. Finally, the blocking of PS receptors on macrophages inhibited the entry of Ebola VLPs, suggesting that PS receptors can contribute to infection in physiologically relevant cells. Notably, infection mediated by the entry proteins of Lassa fever virus, influenza A virus and SARS coronavirus was largely unaffected by TIM1 expression. Taken together our data show that TIM1 and related PS-binding proteins promote infection of diverse families of enveloped viruses, and may therefore be useful targets for broad-spectrum antiviral therapies.
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    IFITM Proteins Restrict Antibody-Dependent Enhancement of Dengue Virus Infection
    (Public Library of Science, 2012) Chan, Ying Kai; Huang, I-Chueh; Farzan, Michael
    Interferon-inducible transmembrane (IFITM) proteins restrict the entry processes of several pathogenic viruses, including the flaviviruses West Nile virus and dengue virus (DENV). DENV infects cells directly or via antibody-dependent enhancement (ADE) in Fc-receptor-bearing cells, a process thought to contribute to severe disease in a secondary infection. Here we investigated whether ADE-mediated DENV infection bypasses IFITM-mediated restriction or whether IFITM proteins can be protective in a secondary infection. We observed that IFITM proteins restricted ADE-mediated and direct infection with comparable efficiencies in a myelogenous leukemia cell line. Our data suggest that IFITM proteins can contribute to control of secondary DENV infections.