Interest has increased recently in the ability of retinoids (naturally occuring metabolites and synthetic analogs of vitamin A) to modulate the growth and differentiation of normal, preneoplastic and malignant cells in culture and in experimental animals and man. The mechanism of these actions of retinoids has yet to be elucidated. Recent studies have demonstrated that retinoids can induce specific changes in the glycosylation of certain cell surface membrane glycoproteins (gps). The increasing evidence on the important role that cell surface gps play in growth control provides a firm basis for the hypothesis that retinoids might modulate tumor cell growth by altering the structure and the function of specific surface gps. The long-term objective of this study is to establish whether this hypothesis is correct. Mouse S91 melanoma cells which are very sensitive to the growth inhibitory action of retinoic acid (RA) as well as RA-resistant mutants derived from them will be employed as a model system. These cells have been chosen because RA enhances the activity of several glycosyltransferases and stimulates the glycosylation of a Mr 160,000 cell surface sialogp (gp160) in the RA-sensitive parental cells but not in RA-resistant mutants. These results suggested that RA-enhanced glycosylation of gp160 might lead to changes in the funciton of this cell surface gp160 and consequently to growth inhibition. To investigate this idea gp160 will be purified from conditioned media and from solubilized partially-purified surface membranes of cells grown in the absence and presence of RA using immunoaffinity-, lectin affinity-, and conventional-chromatography, and prereparative gel electrophoresis. The purified gp160 will be characterized with respect to the structure of the polypeptide and the oligosaccharide chains. Monoclonal antibodies (mAbs) will be prepared against gp160 and used in immunofluorescence localization of gp160 and in immunoprecipitation or immunoblotting of gp160 or of its putative complexes with different ligands. gp160 ability to bind hormones and growth factors in solution or on the cell surface will be examined. A further investigation of gp16 functions will evaluate its ability, as well as that of mAb directed against it, to modify cell growth and interfere with cell-cell and cell-extracellular matrix adhesion in culture and with the implantation of tumor cells in mouse lungs following intravenous injection in vivo.
