Role of glycosphingolipids in HIV-1 entry: requirement of globotriosylceramide (Gb3) in CD4/CXCR4-dependent fusion

We have recently shown that addition of human erythrocyte glycosphingolipids (GSL) to non-human CD4(+) or GSL-depleted human CD4+ cells rendered those cells susceptible to gp120-gp41-mediated cell fusion (Puri et al., BBRC, 1998). One GSL fraction (Fraction 3) isolated from human rlythrocyte GSL mixture exhibited the highest recovery of fusion following incorporation into CD4(+) non-human and GSL-depleted HeLa-CD4 cells (HeLaCD4/GSL(-)). Structural analysis of Fraction 3 showed that this GSL had identical head group as the known GSL, Gal(alpha 1 --> 4)Gal(beta 1 --> 4)Glc-Ceramide (Gb3) (Puri el al., PNAS, 1998). Here we report that presence of Gb3 in CD4(+)/CXCR4(+) cells but not CD4(+)/CXCR4(-) cells allows fusion with HIV-1(Lai)-envelope glycoprotein expressing cells (TF228). Therefore, Gb3 functions in conjunction with HIV-1 co-receptor, CXCR4 to promote fusion. We propose that Gb3 functions by recruiting CD4 and/or CXCR4 at the fusion site through structurally specific interactions.