THE NEUTRAL GLYCOSPHINGOLIPID GLOBOTRIAOSYLCERAMIDE PROMOTES FUSION MEDIATED BY A CD4-DEPENDENT CXCR4-UTILIZING HIV TYPE-1 ENVELOPE GLYCOPROTEIN

Previously, we showed that the addition of human erythrocyte glycosphi ngolipids (GSLs) to nonhuman CD4(+) or GSL-depleted human CD4(+) cells rendered those cells susceptible to HIV-1 envelope glycoprotein-media ted cell fusion. Individual components in the GSL mixture were isolate d by fractionation on a silica-gel column and incorporated into the me mbranes of CD4(+) cells. GSL-supplemented target cells were then exami ned for their ability to fuse with TF228 cells expressing HIV-1(LAI) e nvelope glycoprotein, We found that one GSL fraction, fraction 3, exhi bited the highest recovery of fusion after incorporation into CD4(+) n onhuman and GSL-depleted HeLa-CD4 cells and that fraction 3 contained a single GSL fraction. Fraction 3 was characterized by MS, NMR spectro scopy, enzymatic analysis, and immunostaining with an antiglobotriaosy lceramide (Gb3) antibody and was found to be Gal(alpha 1-->4)Gal(beta 1-->4) Glc-Cer (Gb3), The addition of fraction 3 or Gb3 to GSL-deplete d HeLa-CD4 cells recovered fusion, but the addition of galactosylceram ide, glucosylceramide, the monosialoganglioside, GM3, lactosylceramide , globoside, the disialoganglioside, GD3, or alpha-galactosidase A-dig ested fraction 3 had no effect. Our findings show that the neutral GSL , Gb3, is required for CD4/CXCR4-dependent HIV-1 fusion.