HIV type 1 Gag and nucleocapsid proteins: Cytoskeletal localization and effects on cell motility

Cell motility is likely to play a pivotal role in HIV infection by promotin g the dissemination of infected cells. On the basis of observations indicat ing an interaction between HIV-1 Gag and target cell filamentous actin, we hypothesized that these interactions would promote cell motility of HIV-inf ected cells. Indeed, we have found that HIV-1 infection enhances the chemot actic response of macrophages. To specifically investigate the significance of the interactions between Gag and cellular actin, we transfected NIH 3T3 fibroblasts and HeLa cells with a construct that permits the expression of HIV-1 Gag in the absence of any other viral protein. Fractionation experim ents showed that Gag was present in cytoskeletal fraction containing long a ctin filaments and in a high-speed postcytoskeletal fraction with short act in filaments. We have also localized HIV-1 Gag to the lamellipodia of chemo attractant-stimulated cells. Significantly, the motility of Gag-expressing cells was enhanced in chemotaxis assays. In vitro mutagenesis experiments s howed that HIV-1 Gag binds filamentous actin through the nucleocapsid domai n (NC). An NC-green fluorescent protein fusion had the same cellular distri bution as the complete protein, and its expression increased cell motility. These data suggest that interactions between HIV-1 Gag and actin in infect ed cells enhance cell motility. Ultimately this enhanced motility of infect ed cells could promote the dissemination of virus into the brain and other tissues.