Faculty
 |
Akira Ono |
HIV-1 Replication and Host Cellular Membranes
My laboratory studies the interactions between cellular structures and enveloped viruses. I am particularly interested in the roles played by cellular membranes during replication of retroviruses including HIV-1. Two major areas of research in this laboratory are: i) the role of membrane microdomain structures in virus replication and ii) molecular mechanisms that determine the sites of virus assembly.
1. The role of lipid rafts in HIV-1 replication
Advances in cell biology revealed that the plasma membrane is not a homogenous sea of lipid, but consists of various types of microdomains with specific sets of protein and lipid components. One such microdomain is the cholesterol-rich lipid raft. Rafts facilitate various cellular functions, such as signal transduction and protein trafficking, often by providing concentration platforms for promoting protein-protein interactions. A top priority of my research is to fully understand the roles that rafts play throughout the replication cycle of HIV-1 and other retroviruses.
HIV-1 Gag, the major building block of virus particles, has been identified as a raft-associated protein. Moreover, raft disruption severely impairs HIV-1 virus particle production and infectivity of released progeny virions. These findings suggest that rafts play important role(s) in both virus assembly and particle infectivity. We are currently identifying the steps in the assembly/release pathway at which rafts are involved. Future studies will be aimed at determining the molecular mechanisms by which rafts promote virus assembly as well as the nature of the raft subsets involved in infectious virus particle production.
Virus transmission at the interface between two cells 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 infected individuals. However, the mechanism of cell-to-cell transmission has not been well studied. Interestingly, we observed that, when a producer cell contacts a target cell, lipid rafts and Gag colocalize at the cell-cell contact interface. These results suggest that lipid rafts play a key role in cell-to-cell HIV-1 transmission. The laboratory will further characterize raft-rich contact structures and examine their role(s) in virus spread.
2. The targeting of virus assembly
Targeting of Gag to the location at which virus particle formation occurs, usually the plasma membrane, is a major aspect of retrovirus particle production. Various cellular proteins are targeted to the plasma membrane through the interaction between their basic domains (e.g., pleckstrin homology domain) and the plasma membrane-enriched lipid, phosphatidylinositol-(4,5)-bisphosphate (PIP2). Intriguingly, we found that PIP2 perturbation severely reduced virus particle production by mistargeting Gag to late endosomes. These results suggest that PIP2 plays an active role in Gag targeting. Ongoing studies are focused on understanding the mechanisms by which PIP2 directs Gag to the plasma membrane.
In macrophages, HIV-1 particle assembly occurs normally at late endosomes, unlike in other cell types. HIV particles formed in late endosomes are thought to be released from macrophages through a poorly characterized exosome pathway. Such late endosomes may serve as viral reservoirs and may release their contents upon contact with T cells. We are investigating the determinants of Gag targeting to late endosomes and attempting to identify the regulators of virus particle release from this organelle.
Selected Publications:
Ono, A., J.M. Orenstein, and E.O. Freed. 2000. Role of the Gag matrix domain in targeting human immunodeficiency virus type 1 assembly. J. Virol. 74:2855-2866.
Ono, A., D. Demirov, and E.O. Freed. 2000. Relationship between human immunodeficiency virus type 1 Gag multimerization and membrane binding. J. Virol. 74:5142-5150.
Ono, A., and E.O. Freed. 2001. Plasma membrane rafts play a critical role in HIV-1 assembly and release. Proc. Natl. Acad. Sci. USA. 98:13925-13930.
Demirov, D.G., A. Ono, J.M. Orenstein, and E.O. Freed. 2002. Overexpression of the N-terminal domain of TSG101 inhibits HIV-1 budding by blocking late domain function. Proc. Natl. Acad. Sci. USA. 99:955-960.
Ono, A.*, and E.O. Freed. 2004. Cell-type-dependent targeting of human immunodeficiency virus type 1 assembly to the plasma membrane and the multivesicular body. J Virol. 78:1552-1563.
Ono, A.*, S.D. Ablan, S. J. Lockett, K. Nagashima and E.O. Freed. 2004. Phosphatidylinositol (4,5) bisphosphate regulates HIV-1 Gag targeting to the plasma membrane. Proc. Natl. Acad. Sci. USA. 41:14889-14894.
Ono, A.*, and E.O. Freed. 2005. The role of lipid rafts in virus replication. Adv. Virus Res. 64:311-358 (review).
Ono, A.* , A.A. Waheed, and E.O. Freed. 2005. Association of human immunodeficiency virus type 1 Gag with membrane does not require highly basic sequences in the nucleocapsid: Use of a novel Gag multimerization assay. In revision for J. Virol. 79:14131-14140.
* corresponding author
