As obligatory parasites, viruses in general utilize a large number of host cell factors at various stages of their life cycle. We are particularly interested in the roles played by cellular structures such as the plasma membrane during replication of retroviruses including HIV-1. Three major areas of research in this laboratory are:
i) Molecular mechanisms that determine the sites of virus assembly: The interaction between HIV-1 structural protein Gag and PI(4,5)P2, a plasma-membrane-specific acidic phospholipid, is crucial for Gag binding to the plasma membrane and hence efficient HIV-1 assembly. Notably, the matrix (MA) domain of Gag, which binds PI(4,5)P2, can also binds RNA. We found that this MA-RNA binding inhibits Gag interactions with prevalent acidic phospholipids but not with PI(4,5)P2. These studies support a model in which the MA-RNA interaction ensures the specific binding of Gag to the PI(4,5)P2-containing plasma membrane. They also suggest a potentially broadly-applicable paradigm in which RNA regulates targeting of proteins to membranes by directly modulating protein-lipid interactions.
ii) Relationships between virus assembly and organization of plasma membrane microdomains: Oligomerization of membrane-bound proteins could induce reorganization of membrane microdomains such as lipid rafts and tetraspanin-enriched microdomains (TEM). Indeed, we showed that during virus assembly driven by multimerization of membrane-bound Gag, coalescence of lipid rafts and TEMs, which are otherwise distinct microdomains, occurs at assembly sites. The mechanisms by which virus assembly affects distribution of plasma membrane microdomains and their components represent one of our major interests.
iii) Roles played by cell polarity in cell-to-cell virus transmission: Virus transmission at cell contacts is a markedly more efficient mechanism of virus spread than cell-free transmission and likely represents the major mode of transmission for HIV-1 in lymphoid organs of infected individuals. We observed that in a motile, polarized T cells, Gag accumulates to a rear-end protrusion known as the uropod in a Gag-multimerization- and actin-myosin-dependent manner and that the Gag-laden uropod mediates frequent contacts with other T cells in tissue cultures. We are seeking to determine the mechanism of polarized Gag localization and to examine its role in cell-to-cell transmission in the presence of lymphoid organ constituents.
Chukkapalli, V., S.J. Oh and A. Ono. 2010. Opposing mechanisms involving RNA and lipids regulate HIV-1 Gag membrane binding through the highly basic region of the matrix domain. Proc. Natl. Acad. Sci. USA. 107, 1600-1605.
Llewellyn, G.N., I.B. Hogue, J.R. Grover, and A. Ono. 2010. Nucleocapsid promotes localization of HIV-1 Gag to uropods that participate in virological synapses between T cells. PLoS Pathogens 6: e1001167.
Monde, K., V. Chukkapalli, and A. Ono. 2011. Assembly and Replication of HIV-1 in T Cells with Low Levels of Phosphatidylinositol-(4,5)-Bisphosphate. J Virol. 85, 3584-3595.
Inlora, J., V. Chukkapalli, D. Derse, and A. Ono. 2011. Gag Localization and Virus-Like Particle Release Mediated by the Matrix Domain of Human T-Lymphotropic Virus Type 1 Gag Are Less Dependent on Phosphatidylinositol-(4,5)-Bisphosphate than Those Mediated by the Matrix Domain of HIV-1 Gag. J Virol. 85, 3584-3595.
Hogue, I.B., J.R. Grover, F. Soheilian, K. Nagashima, and A. Ono. 2011. Gag Induces the Coalescence of Clustered Lipid Rafts and Tetraspanin-Enriched Microdomains at HIV-1 Assembly Sites on the Plasma Membrane. J Virol. 85: 9749-9766.