Human immunodeficiency virus type 1 infection of SK-N-MC cells: domains of gp120 involved in entry into a CD4-negative, galactosyl ceramide/3' sulfo-galactosyl ceramide-positive cell line

Abstract

The primary receptor for human immunodeficiency virus (HIV) is the CD4 molecule; however, in vitro evidence suggests that a neutral glycolipid, galactosyl ceramide (GalCer) or a derivative molecule, 3 sulfogalactosyl ceramide (GalS), may serve as an alternative receptor for HIV type 1 (HIV-1) in cells of neural and colonic origin. Biochemical studies have demonstrated that recombinant gp120 envelope protein binds to GalCer/GalS in both solid-phase enzyme-linked immunosorbent assay and high-performance thin-layer chromatography overlays. We have used the SK-N-MC cell line, a CD4-negative, GalCer/GalS-positive cell line previously characterized as susceptible to HIV-1 infection, to identify virus isolates with either a positive infection phenotype, HIV HxB2 , or a negative infection phenotype, HIV-1 89.6. Using a solid-phase virus binding assay, we determined the level of restriction in HIV-1 89.6 infection to be at the level of virus-glycolipid binding. Furthermore, using HIV-1 HxB2-HIV-1 89.6 chimeras, we have identified a 193-amino-acid fragment from the envelope region of HIV-1 HxB2 containing the V3, V4, and V5 regions which confers a positive infection phenotype on the HIV-1 89.6 background. Recombinant viruses which separate this 193-amino-acid fragment into two distinct chimeras are each able to confer a positive infection phenotype on the background of HIV 89.6 , suggesting that a stable GalCer/GalS-envelope interaction is dependent on the conformation of the envelope protein in the context of the viral membrane. Alternatively, the GalCer/GalS-gp120 bond may involve multiple sites on the oligomeric envelope protein.

The CD4-independent tropism of human immunodeficiency virus type 2 involves several regions of the envelope protein and correlates with a reduced activation threshold for envelope-mediated fusion

“…The glycolipid galactosyl ceramide mediates CD4-independent infection of some neural cell lines by certain HIV-1 isolates (32), and the V3 loop, as well as a region encompassing V4 to V5, has been shown to confer this phenotype (33). HIV-1 variants capable of infecting in this CD4-independent manner bind to sulfogalactosyl ceramide, whereas those which are CD4 dependent do not (33). This is in contrast to the findings reported here for CD4-independent HIV-2.…”

“…For HIV-1, this has been demonstrated for cell lines of nervous system, fibroblast, and liver origin (9,11,21,31,32,73). In the case of some neural cell lines, this may be mediated by a glycolipid, galactosyl ceramide (32), and sequences in either V3 or V4/V5 determine this tropism (33). Efficient CD4-independent infection has been documented for several HIV-2 isolates (14).…”

Globotriaosyl ceramide receptor function – Where membrane structure and pathology intersect

“…The V3 loop also contains a GSL binding motif [77] to which several glycolipids, galactosyl ceramide, sulfogalactosyl ceramide, GM3, GD3 and Gb 3 adhere [78][79][80][81]. GalCer binding by gp120 has been strongly implicated as the mechanism of HIV targeting and entry into CD4 negative cells, such as mucosal epithelial cells [79,82,83].…”

Dynamic tradeoffs in the raft‐mediated entry of human immunodeficiency virus type 1 into cells

“…Consistent with this mechanism, favorable binding affinities (K d : 0.6-130 nM) between gp120 and sphingolipids have been reported (Conboy et al, 2002). Further, sphingolipids may function as receptors for HIV-1 binding to cells without involving the CD4 receptor (Harouse et al, 1995;Kensinger et al, 2004). Such effects of membrane constituents on entry may well extend beyond HIV-1.…”