Processing and routage of HIV glycoproteins by furin to the cell surface

Proteolytic activation of HIV-I and HIV-2 envelope glycoprotein precursors (gp160 and gp140, respectively) occurs at the carboxyl side of a consensus motif consisting of the highly basic amino acid sequence. We have shown pre viously (Hallenberger et al., 1997) and confirmed in this report: that furi n and PC7 can be considered as the putative physiological enzymes involved in the proteolytic activation of the HIV-1 and HIV-2 envelope precursors. I n this study, we show by cell surface biotinylation and immunoprecipitation of the cell surface associated viral glycoproteins with antibodies that th e mature viral envelope glycoproteins are correctly transported to the cell membrane. Furthermore, we show that the uncleaved forms of the glycoprotei ns (gp160(HIV-1) and gp140(HIV-2)) are also highly represented at the cell surface. First, transient expression of gp160 and gp140 into CV1, a cell li ne known to be inefficient in the proteolytic processing of the ena gene, r esults in the expression of gp160 and gp140 at the cell surface. Moreover, HIV-1 infection of T cells also showed that gp160 is directed to the cell s urface. In addition, we show that the precursor is not incorporated in the virus particle following the budding from the cell surface. Furthermore, a gp160 mutant (deficient for three carbohydrate sites on the gp41), shown to be poorly processed with the coexpressed endoproteases, is found to be tra nsported as an uncleaved precursor to the cell surface. In contrast to HIV envelope glycoproteins? the influenza hemagglutinin precursor (HA0), that i s thought to be matured by the furin-like enzymes as well, is found to be r etained within the cell and is not able to reach the cell surface. Taken to gether, these results show that the proteolytic maturation of the viral env elope precursors of human immunodeficiency viruses type 1 and type 2 is not a prerequisite for cell surface targeting of the HIV glycoproteins. Implic ations of these results for antiviral immune response are discussed. (C) 19 99 Elsevier Science B.V. All rights reserved.