Qualitative and quantitative analyses of cell surface sialylglycoproteins and glycosphingolipids of in vivo selected mouse melanoma variant lines that show either a high (F10) or low (F1) degree of lung implantation have been made in culture and in in vivo-grown tumors. The following observations have been made concerning the cell surface characteristics of the two cell lines: (a) although the total, protein-bound, and lipid-bound sialic acid is significantly decreased (20 to 35%), the cell surface-exposed sialylglycoproteins and gangliosides showed a moderate increase in F10 cells as compared to F1 cells; (b) surface glycoproteins of melanoma cells were studied with different labeling techniques followed by polyacrylamide gel electrophoresis and fluorography. The majority of surface glycoproteins were shown to be sialylfucosylgalactosyl and/or galactosaminyl glycoproteins; (c) the high-lung-implanting F10 cells reveal certain sialylglycoproteins with molecular weights of 66,000 (in culture) and 97,000, 84,000, 74,000, and 66,000 (in vivo), as detected by the galactose oxidase method, that are absent or weakly labeled in F1 cells; (d) metabolic labeling with glucosamine followed by neuraminidase hydrolysis reveals that F10 cells contain 80% more neuraminidase-accessible total cell surface sialic acid, the majority of which was contributed by AcNeu-α-(2→3)-Gal-β-(1→4)-GlcCer as compared to F1 cells; (e) F10 cells showed an enrichment of the quantity of ceramide dihexoside and a 5- to 6-fold higher cell surface exposure compared to F1 cells; (b) dramatic differences in ganglioside profile were seen between the in vivo and in vitro growth of F1 and F10 cells. The relationship of altered cell surface architecture of sialic acid-containing components to lung-specific implantation in experimental metastases is discussed.
This work was done with the support of NIH Core Grant CA 14195-03 and NIH Research Grant 1 Rol CA 19312-01.