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Khurana, Sandhya

Microbiology and Molecular Genetics

2008

PhD

The spatial and temporal regulation of viral release is critical for its dissemination. To understand the role of cellular factors in viral release, we sought to acquire a better understanding of the molecular composition of the membrane segments utilized by human immunodeficiency virus type 1 (HIV-1) for its egress, Here, we reveal the presence of tetraspanin-enriched microdomains (TEMs) containing the tetraspanins CD9, CD63, CD81 and CD82 at the plasma membrane of HeLa cells, each TEM extending from a few to a few hundred nanometers. Further, we reveal that the HIV-1 Gag protein, which directs viral assembly and release, accumulates at surface TEMs together with the HIV-1 envelope glycoprotein. TSGlOl and VPS28, components of the mammalian ESCRTl complex, critical for HIV-1 budding, are also recruited to cell surface TEMs upon virus expression, suggesting that HIV-1 egress can be gated through these microdomains. Additionally, we demonstrate that HIV-1 and influenza assembly occurs at different microsegments of the plasma membrane of HeLa cells. We find that influenza virus, unlike HIV-1, does not bud through TEMs containing CD9 and CD63. Consequently, the anti-CD9 antibody K41 which redistributes its antigen and also other tetraspanins to cell-cell adhesion sites, interferes with HIV-1 but not with influenza virus release suggesting that the bimodal egress of these two pathogenic viruses, like their entry into target cells, is guided by specific sets of host cell proteins. The targeting of HIV-1 assembly to TEMs could be instrumental in facilitating efficient transmission of HIV-1 to target cells. We hypothesize that tetraspanins promote the dissemination of this virus by preventing fusion of the producer with the target cell and maintaining integrity of the virological synapse (VS).