Gary Whittaker, PhD
Department of Microbiology and Immunology
Dr. Whittaker is an Associate Professor in the Department of Microbiology and Immunology and has been associated with the department since 1996. He received a bachelor's degree in Biochemistry, and his Ph.D. in Microbiology from Leeds University U.K - studying the molecular biology and biochemistry of equine herpesvirus. He obtained postdoctoral training at Yale University in the laboratory of Dr. Ari Helenius, studying the cell biology of influenza virus replication. Dr Whittaker's laboratory is focussed on the entry of influenza and coronaviruses into host cells and is funded by research grants from the American Lung Association and the National Institutes of Health.
Research Interests
The primary research interests of the Whittaker laboratory are in defining the cellular events required for successful infection of host cells by influenza virus and coronaviruses. The principal goals are to study the entry mechanism of enveloped viruses into their host cells, in order to gain information on the pathogenic properties of the virus, and to determine the general endocytic trafficking events that viruses use during cell infection. The laboratory has been examining the entry pathways of influenza virus for many years, and has recently expanded their work to examine infectious bronchitis virus (IBV), as a model for coronaviruses such as SARS-CoV.
Influenza virus entry: A general theme of the research on influenza virus is to use molecular tools to define the endocytosis pathways leading to infection, combining such tools (e.g. dominant-negative mutants of cellular proteins) with more conventional morphological and pharmacological approaches. To address the role of clathrin during influenza virus internalization, the Whittaker laboratory has analyzed influenza virus entry in cells expressing dominant-negative forms of dynamin and Eps15, and have shown that entry is not restricted to clathrin-mediated endocytosis, but can also occur through alternative, non-clathrin, routes of entry. They are currently investigating the molecular basis of these novel routes of entry. Other analyses of the later steps in endocytosis include the use of dominant-negative forms of Rab proteins needed for formation and trafficking of early and late endosomes (Rab5 and Rab7 respectively). These data suggest that influenza (unlike other viruses) requires a specific intracellular trafficking that routes the virus to the late endosome, as part of the lysosome-targeted pathway of endocytosis. Recently they have also shown that influenza virus requires the ubiqutin-vps sorting machinery for entry. This requirement is unprecedented during virus entry, but has been shown for other viruses (e.g. retroviruses, paramyxoviruses) during assembly and budding. Overall, these data imply that influenza may have a specific receptor or co-receptor (in addition to the well-established sialic acid receptor) for functional infection in vivo. One current focus is to determine possible co-receptors or co-factors necessary for influenza virus internalization and/or endosomal trafficking.
Another area of interest is to use the same molecular tools to examine filamentous forms of influenza virus. Such morphological forms are implicated in the natural infection of clinical isolates of influenza. They are very large particles (routinely 2-3 µm in length), in contrast to the small spherical particles obtained from tissue culture and studied to date. The filamentous forms of the virus may have severe constraints for entry by the “traditional” clathrin-mediated route of internalization. Indeed the preliminary data suggest that filamentous viruses enter viruses with the same kinetics whether or not our dominant-negative dynamin is being expressed—giving credence to the idea that other internalization routes can be used. They are currently studying what these alternative routes might be.
Coronavirus entry: In contrast to the wealth of information on influenza virus entry, little is known about coronaviruses entry cells. The Whittaker laboratory is examining the entry pathway of the avian coronavirus infectious bronchitis virus (IBV), seeking to develop molecular inhibition assays to determine the possible role of endosomes in infection, and has recently developed a virus-cell fusion assay for coronaviruses. In this work, IBV offers several advantages as a model coronavirus, including the ability to generate large amount of virus in embryonated eggs, and the availability of well-characterized antibodies to the S and M proteins. We are currently using cell-cell fusion assays and MLV/luciferase-pseudoyped virions to study S protein proteolytic priming and low pH-dependent fusion activation for both IBV and SARS-CoV with the goal of identifyting key fusion domains for the coronavirus spike protein.