Certain tumors, including melanomas and neuronal tumors, as well as embryonic neural tissue, express gangliosides (GD2, GD3, and 9OAcGD3) found only in low levels, or not at all, in normal adult tissue, implying a role for them in the phenotypic properties of these cells and tissues. The experiments proposed are focused on understanding certain biological function(s) of gangliosides in normal and transformed cells. Many studies indirectly indicate that interactions between membrane proteins and gangliosides present in the same bilayer do occur, and that these interactions regulate the function of these proteins. The proposed experiments explore this concept directly in two independent but complementary systems. The first is based on the work of others indicating an association between the vitronectin receptor (VNr) found on melanoma cells and certain melanoma gangliosides. Using liposomes reconstituted from purified VNr and gangliosides, the functional and biochemical aspects of VNr-ganglioside association will be studied directly.In a parallel experimental approach, expression cloning techniques will be utilized to clone the cDNA's of key enzymes involved in ganglioside biosynthesis. These clones will then be utilized to manipulate the expression of different gangliosides on the cell's surface. The anticipated approach entails starting with a cell line which expresses only a simple ganglioside structure, and then transfection with the cDNA encoding for the glycosyltransferase (or regulatory protein(s) which control it) which attaches a sugar residue to this ganglioside, building the next ganglioside in the biosynthetic pathway. In this fashion, the ganglioside profile of a single cell line could be manipulated in a fashion heretofore not possible. Functional studies on the cell's integrin molecule(s) would then be performed and correlated with its ganglioside profile. These results would be directly comparable with the in vitro reconstituted system described above. This general approach can be adapted to the study a wide range of proteins.The three gangliosides noted above are just three of many examples of the aberrant glycosylation of glycolipids and glycoproteins found with malignant transformation. The longterm objectives of these studies is understanding the enzymatic basis, regulation, and functional consequences of these changes, with the hope of a greater understanding of the biology of both normal and malignant tissues.
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