Slit2N Inhibits Transmission Of HIV-1 From Dendritic Cells To T-Cells By Modulating Novel Cytoskeletal Elements

During sexual contact, HIV-1 can enter the mucous membranes of the vagina, throat, or rectum. There, the virus encounters potential target cells, including antigen-presenting cells such as dermal dendritic cells (DC), Langerhans cells, and plasmacytoid DCs, which play pivotal roles in both innate and adaptive immunity. All DC subsets are susceptible to HIV-1 infection or internalization of intact virus, and appear to facilitate cell-mediated transmission of HIV-1 in the mucosa and lymphatic tissues.

Once internalized, HIV-1 can be transmitted from DCs to T-cells at a specialized junction termed the infectious synapse (IS). Recent studies reveal that several actin-rich DC membrane extensions, including actin filopodia, membrane sheets, cytonemes, and nanotubes, establish direct contact between cells at the IS and facilitate HIV-1 transmission. Although the virus can infect T-cells directly (cis-infection), transmission of HIV-1 from DCs to T-cells at IS (trans-infection and de novo trans-infection) appears to be some 10 to 100 times more efficient than direct infection; therefore, cell-to-cell transmission is an attractive target for novel HIV therapeutics.

We evaluated the effects of Slit2N, a ligand for the Roundabout (Robo) receptors, on the transmission of HIV-1 from DCs to T-cells. Slit2N inhibits HIV-1 transmission to T-cells and its replication. Binding of HIV-1 to DC-SIGN on the surface of DCs initiates signaling through cellular-Src (c-Src) and cell division control protein 42 (Cdc42), which modulates actin polymerization and filopodia formation via the actin-related protein 2/3 (Arp2/3) complex and mammalian Diaphanous 2 (mDia2). Slit2N inhibited HIV-1-induced signaling through both Arp2/3 and mDia2, decreased filopodial extensions on virus-infected DCs, and inhibited cell-to-cell transmission of HIV-1 at the IS in a Robo1-dependent manner. Of particular note, we identified Flightless-1 (Fli1) as a novel, Robo1-interacting protein, and demonstrated that it is required for efficient cell-to-cell transmission of HIV-1.

These results suggest that targeting the Slit/Robo pathway involves the modulation of previously unrecognized cytoskeletal elements in HIV-1 transmission, and thus, offers an innovative strategy to limit viral infection in the host.