Proteasome inhibition interferes with Gag polyprotein processing, release,and maturation of HIV-1 and HIV-2

Retrovirus assembly and maturation involve folding and transport of viral p roteins to the virus assembly site followed by subsequent proteolytic cleav age of the Gag polyprotein within the nascent virion. We report that inhibi ting proteasomes severely decreases the budding, maturation, and infectivit y of HIV. Although processing of the Env glycoproteins is not changed, prot easome inhibitors inhibit processing of tag polyprotein by the viral protea se without affecting the activity of the HIV-1 viral protease itself, as de monstrated by in vitro processing of HIV-1 tag polyprotein Pr55. Furthermor e, this effect occurs independently of the virus release function of the HI V-1 accessory protein Vpu and is not limited to HIV-1, as proteasome inhibi tors also reduce virus release and tag processing of HIV-2. Electron micros copy analysis revealed ultrastructural changes in budding virions similar t o mutants in the late assembly domain of p6(gag), a C-terminal domain of Pr 55 required for efficient virus maturation and release. Proteasome inhibiti on reduced the level of free ubiquitin in HIV-1-infected cells and prevente d monoubiquitination of p6(gag). Consistent with this, viruses with mutatio ns in PR or p6(gag) were resistant to detrimental effects mediated by prote asome inhibitors. These results indicate the requirement for an active prot easome/ubiquitin system in release and maturation of infectious HIV particl es and provide a potential pharmaceutical strategy for interfering with ret rovirus replication.