UVM Theses and Dissertations
Format:
Print
Author:
Roy, Nathan
Dept./Program:
Cell and Molecular Biology Program
Year:
2014
Degree:
Ph. D.
Abstract:
Human immunodeficiency virus type 1 (HIV-1) currently infects an estimated 35 million people worldwide and is an enormous global health burden. Although there are many approved anti-viral treatments, their lack of availability and the rapid emergence of resistant viral strains calls for the continued development of new therapeutic avenues. To fulfill this need, a greater understanding of the basic mechanisms of the viral life cycle is crucial in order to design and test novel treatments.
HIV-1 mainly infects cells of the hematopoietic lineage and quickly spreads systemically, causing chronic CD4-T cell death resulting in acquired immunodeficiency syndrome (AIDS). Surprisingly, very little is known about how HIV-l disseminates through an infected individual. It is now thought that HIV-1 infected cells, which may be actively producing virus, will promote infection far more efficiently if they come in direct contact with neighboring cells, a process called cell-to-cell transmission. Cell-to-cell transmission is likely the predominate mode of viral transmission in cell dense areas, and is even proposed to account for the massive CD4⁺ cell death seen during infection. Because of the importance of HIV-1 cell-to-cell transmission, we chose to investigate both viral and cellular factors that could contribute to this process.
During cell-to-cell transmission, the fusogenic Env protein is expressed on the surface of the infected cell and interacts with its receptor and co-receptor on the target cell. When Env is in the context of a virion, this interaction normally triggers membrane fusion, yet during cell-to-cell transmission only a small number of cells fuse and form multinucleated syncytia. To investigate how the fusogenicity of Env is controlled while Env is still situated in the infected cell, we evaluated the nanoscale distribution and mobility of Env in the plasma membrane of infected cells. We found that an interaction between the cytoplasmic tail of Env and the viral Gag protein reorganizes Env on the nanoscale level and restricts the mobility of Env within the membrane, both of which correlate with a reduced ability of Env to facilitate fusion. We conclude that Env membrane mobility is important for its fusion function, and that Gag controls Env mobility in order to regulate its ability to fuse membranes.
In parallel, our studies aimed at investigating the role of the cellular ezrinradixin-moesin (ERM) proteins during HIV-1 cell-to-cell transmission also led us to membrane fusion and syncytia formation. The ERM protein ezrin specifically localizes to the cell-cell interface during cell-to-cell transmission and inhibits Env induced cell-cell fusion, possibly by controlling cortical actin levels. Ezrin has also been implicated in other membrane fusion events, thus Env induced fusion could serve as a model to dissect how ezrin restricts the fusion process. These data, along with the data above, suggest multiple mechanisms that control cell-cell fusion during HIV-1 transmission, possibly having implications in the efficiency of viral spread, and ultimately, disease progression.
HIV-1 mainly infects cells of the hematopoietic lineage and quickly spreads systemically, causing chronic CD4-T cell death resulting in acquired immunodeficiency syndrome (AIDS). Surprisingly, very little is known about how HIV-l disseminates through an infected individual. It is now thought that HIV-1 infected cells, which may be actively producing virus, will promote infection far more efficiently if they come in direct contact with neighboring cells, a process called cell-to-cell transmission. Cell-to-cell transmission is likely the predominate mode of viral transmission in cell dense areas, and is even proposed to account for the massive CD4⁺ cell death seen during infection. Because of the importance of HIV-1 cell-to-cell transmission, we chose to investigate both viral and cellular factors that could contribute to this process.
During cell-to-cell transmission, the fusogenic Env protein is expressed on the surface of the infected cell and interacts with its receptor and co-receptor on the target cell. When Env is in the context of a virion, this interaction normally triggers membrane fusion, yet during cell-to-cell transmission only a small number of cells fuse and form multinucleated syncytia. To investigate how the fusogenicity of Env is controlled while Env is still situated in the infected cell, we evaluated the nanoscale distribution and mobility of Env in the plasma membrane of infected cells. We found that an interaction between the cytoplasmic tail of Env and the viral Gag protein reorganizes Env on the nanoscale level and restricts the mobility of Env within the membrane, both of which correlate with a reduced ability of Env to facilitate fusion. We conclude that Env membrane mobility is important for its fusion function, and that Gag controls Env mobility in order to regulate its ability to fuse membranes.
In parallel, our studies aimed at investigating the role of the cellular ezrinradixin-moesin (ERM) proteins during HIV-1 cell-to-cell transmission also led us to membrane fusion and syncytia formation. The ERM protein ezrin specifically localizes to the cell-cell interface during cell-to-cell transmission and inhibits Env induced cell-cell fusion, possibly by controlling cortical actin levels. Ezrin has also been implicated in other membrane fusion events, thus Env induced fusion could serve as a model to dissect how ezrin restricts the fusion process. These data, along with the data above, suggest multiple mechanisms that control cell-cell fusion during HIV-1 transmission, possibly having implications in the efficiency of viral spread, and ultimately, disease progression.