Restriction of RD114 virus growth is due to altered processing of the env glycoprotein during a single cycle of infection in non-permissive cells. This novel mechanism of viral restriction was the result of a phenotypic alteration of the virus's ability to reinfect non-permissive cells and undergo multiple rounds of virus replication. Further analysis of the modified SU viral membrane protein indicates that non-permissive cells overglycosylate the protein, leading to an increase in apparent molecular weight, and an inability to infect FeF cells. This block appears to function at the cell surface, since treatment of the non-permissive cells for 24 hours with glycosylation inhibitors renders them about 100-fold more susceptible to infection by virus containing the higher molecular weight form of SU protein. This restriction may involve developmentally- regulated genes, since of eight cell lines tested, only two, both derived from fetal tissue, were permissive for RD114 containing the high molecular weight form of SU. It was previously shown that at least one strain of feline immunodeficiency virus (FIV) is able to infect HeLa cells, is transiently expressed and induces cell fusion. The fusion of HeLa by FIV can be blocked by neutralizing anti-FIV antibody and by a soluble form of the FIV SU protein. These results suggest that FIV infection of HeLa involves virus-receptor interactions similar to what is observed in permissive feline cells, and this may serve as a model for lentivirus infection and fusion of human cells.
