Inter-retroviral Fusion Mediated by Human Immunodeficiency Virus or Murine Leukemia Virus Glycoproteins: Independence of Cellular Membranes and Membrane Vesicles

AbstractWe have recently demonstrated for the first time that inter-retroviral membrane fusion, i.e., membrane fusion between individual retroviral particle populations with incorporated HIV-1 Env and cellular receptors, respectively, can occur (Sparacio et al. 2000, Virology 271: 248–252). We have extended these analyses here and confirmed that fusion between particles can occur in the extracellular medium independent of any cellular membranes and that luciferase transduction, mediated by the fused structures, is independent of significant potential contribution by contaminating membrane vesicles. We have additionally analyzed whether membrane fusion between HIV-like particles can be mediated by amphotropic murine leukemia virus (MuLV) glycoprotein and its respective cellular receptor, PiT-2. We demonstrate that PiT-2 can be incorporated into HIV-like particles and can fuse with MuLV-Env-carrying particles. This occurs only in the situation in which the incorporated MuLV-Env protein has been activated to fusion activity by HIV protease-mediated removal of the C-terminal R-peptide and is completely inhibited when the respective particles are generated in the presence of the HIV protease inhibitor, Saquinavir