Mechanism of concanavalin A-induced anchorage of the major cell surface glycoproteins to the submembrane cytoskeleton in 13762 ascites mammary adenocarcinoma cells.

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Abstract
Concanavalin A (Con A)-induced anchorage of the major cell surface sialoglycoprotein component complex (ASGP-1/ASGP-2) was studied in 13762 rat mammry adenocarcinoma sublines with mobile (MAT-B1 subline) and immobile (MAT-C1 subline) cell surface Con A receptors. Treatment of cells, isolated microvilli or microvillar membranes with Con A resulted in marked retention of ASGP-1 and ASGP-2, a Con A-binding protein, in cytoskeletal residues of both sublines obtained by extraction with Triton X-100 in PBS. When Con A-treated microvillar membranes were extracted with a buffer containing Triton X-100, the sialoglycoprotein complex was found associated in the residues with a transmembrane complex composed of actin, a 58,000-dalton polypeptide, and a cytoskeleton-associated glycoprotein (CAG), also a Con A-binding protein, in MAT-C1 membranes, and of actin and CAG in MAT-B1 membranes. Untreated membrane Triton residues retained very little ASGP-1/ASGP-2 complex. Association of the sialoglycomembrane complex and the transmembrane complex was also demonstrated in Con A-treated, but not untreated, microvilli by their comigration on CsCl gradients. Association of both complexes with the cytoskeleton of microvilli was shown by sucrose density gradient centrifugation. A fraction of the polymerized actin comigrated with the transmembrane complex alone in the absence of Con A and with both the transmembrane complex and the sialoglycoprotein complex in the presence of Con A. Anchorage of the sialoglycoprotein complex to the cytoskeleton on Con A treatment apparently occurs by cross-linking ASGP-2, the major cell surface Con A-binding component, to CAG of the transmembrane complex, which is natively linked to the cytoskeleton via its actin component. Since Con A-induced anchorage occurs in sublines with mobile and immobile receptors, the anchorage process cannot be responsible for the differences in receptor mobility between the sublines.