| Abstract: | Cell-cell adhesion is a multi-step process which may be initiated by binding of cell surface carbohydrates to complementary carbohydrate receptors on apposing cell surfaces. We have modeled such interactions using polyacrylamide gels covalently derivatized with glycosides, to which intact cells specifically adhere; chicken hepatocytes adhere to gels derivatized with N-acetylglucosamine (GlcNAc). Initially adhesion is blocked (or reversed) by soluble GlcNAc, but becomes sugar-resistant rapidly at 37 degrees C, perhaps due to cellular modification of the carbohydrate-derivatized surface (Guarnaccia, S. P., Kuhlenschmidt, M. S., Slife, C. W., and Schnaar, R. L. (1982) J. Biol. Chem. 257, 14293-14299). We report here that, subsequent to recognition and adhesion, intact chicken hepatocytes transfer phosphate covalently to GlcNAc-derivatized gels. Metabolically radiolabeled cells (32Pi) were incubated on polyacrylamide gels derivatized with various aminohexyl glycosides. Noncovalently bound material was then removed from the gels by extensive washing in detergents and salt solutions. Subsequent radiochemical analysis revealed that phosphate was transferred selectively to GlcNAc-derivatized gels (up to 20-fold more than to glucose-, galactose-, or mannose-derivatized gels). Soluble GlcNAc (but not other sugars) or low temperature inhibited phosphate transfer. The phosphorylation was mediated by intact cells; cell lysate was itself incapable of specific phosphate transfer and attenuated specific transfer when added to intact cells. When GlcNAc was immobilized using a cleavable (disulfide-containing) linker arm the transferred phosphate radiolabel could be solubilized by disulfide reduction and recovered for further analysis. The released phosphorylated product migrated as a single low molecular weight species upon gel permeation chromatography, paper electrophoresis, and cellulose thin layer chromatography. Acid hydrolysis of the phosphorylated product generated a compound with the mobility of GlcNAc-6-P in five different separation systems. Treatment with alkaline phosphatase converted the radiolabel to a compound with the properties of inorganic phosphate. These data indicate that; subsequent to carbohydrate recognition and adhesion, intact hepatocytes generate phosphomonoesters of recognized carbohydrates outside of their plasma membranes. |
