Interaction of CD82 Tetraspanin Proteins with HTLV-1 Envelope Glycoproteins Inhibits Cell-to-Cell Fusion and Virus Transmission

Abstract The entry of retroviruses into their target cell involves interactions between the virus envelope glycoproteins and their cellular receptors, as well as accessory ligand–receptor interactions involving adhesion molecules that can also participate in fusion. We have studied the contribution of CD82 proteins to the transmission of the human T-cell leukemia virus type 1 (HTLV-1), which is greatly dependent on cell-to-cell contacts. CD82 proteins belong to a class of cell surface molecules, the tetraspanins, that can act as molecular facilitators in cellular adhesion processes. The coexpression of CD82 proteins with HTLV-1 envelope glycoproteins resulted in marked inhibition of syncytium formation, whereas CD82 proteins had no effect on syncytium formation induced by human immunodeficiency virus type 1 (HIV-1) envelope proteins. The presence of CD82 proteins also inhibited cell-to-cell transmission of HTLV-1. Coimmunoprecipitation and cocapping experiments showed that CD82 associates with HTLV-1 envelope glycoproteins, both within the cell and at the cell surface. Finally, whereas the intracellular maturation of HTLV-1 glycoproteins was not modified by the presence of CD82 proteins, HTLV-1 protein coproduction delayed the intracellular maturation of CD82 proteins. There thus seems to be a reciprocal interaction between virus and cell proteins, and the cellular proteins involved in adhesion modulate retrovirus transmission both positively, as shown in other systems, and negatively, as shown here.