Experiments from our laboratory have demonstrated that galactosyl ceramide (GalCer or galactocerebroside), or a closely related molecule plays a significant role in the entry of HIV-1 into cell lines derived from the human nervous system. In these studies we demonstrated that antibodies against GalCer inhibited or decreased infection of two cell lines, U373-MG, derived from glioblastoma, and SK-N-MC, derived from a peripheral neuroblastoma. Furthermore, in accompanying experiments there was specific binding between recombinant gp120, the HIV receptor binding protein, and GalCer immobilized on an HPTLC plate. This binding was saturable, and was partially mapped to the polar head of the GalCer molecule, as expected if this interaction were to occur in vivo. Since GalCer is an important nervous system glycolipid, comprising around 14 percent of the dry weight of brain white matter, and is a critical surface molecule in myelinating cells, these results are potentially important in explaining some of the nervous system abnormalities noted in HIV infected individuals. To extend these findings, we will define the region(s) of gp120 responsible for this interaction using several complementary approaches: (i) inhibition of binding by monospecific or monoclonal anti-gp120 antibodies, (ii) competition for gp120-GalCer binding with peptides, and (iii) generation of gp120 mutants. We will explore the possibility that gp120-GalCer binding is due to a carbohydrate-carbohydrate interaction by using lectins, antibodies against carbohydrates and by expressing recombinant gp120 in cell lines with glycosylation defects. The findings using in vitro binding assays will be related to virus infection in SK-N-MC cells. These results will give us a better understanding of the interaction of this viral protein, a key determinant of HIV pathogenicity, and a common nervous system glycolipid.
