Anchorage of HIV on Permissive Cells Leads to Coaggregation of Viral Particles with Surface Nucleolin at Membrane Raft Microdomains

The cross-linking of HIV on permissive cells results aggregation of HIV particles with surface nucleolin, CD4, and CXCR4, but without affecting the organization of CD45. In addition, HIV particles and nucleolin coaggregate with glycolipid-enriched membrane microdomains (GEMs) containing ganglioside, and glycosylphosphatidylinositol-linked proteins CD90 and CD59, pointing out that HIV anchorage induces lateral assemblies of specific membrane components into lipid rafts in which surface nucleolin is also incorporated. Consequently, equilibrium density fractionation of extracts from infected cells revealed that HIV proteins and nucleolin copurify with Triton X-100-resistant GEM-associated proteins. After HIV entry, nucleolin is recovered also in fractions containing HIV DNA, viral matrix, and reverse transcriptase, thus suggesting that it could accompany viral entry. We show that surface nucleolin is markedly down-regulated a few hours following HIV entry into permissive cells; an effect that appears to be the consequence of its translocation into the cytoplasm. Our findings demonstrate that anchorage of HIV particles on permissive cells induces aggegation of surface nucleolin and its association with detergent-insoluble lipid raft components. Moreover, they support the suggestion that surface nucleolin and lipid rafts are implicated in early events in the HIV entry process.