Ligand-induced association of surface immunoglobulin with the detergent-insoluble cytoskeletal matrix of the B lymphocyte.

Ligand binding is believed to induce surface immunoglobulin (Ig) to form a physical association with the underlying cell cytoskeleton. We investigated this interaction by use of nonionic detergents, which are known to dissolve membrane proteins but preserve a detergent-insoluble cytoskeletal residue. In the absence of ligand treatment, surface Ig in the B cell plasma membrane was fully dissolved by nonionic detergent; however, interaction with a ligand converted the receptor to a novel, detergent-insoluble state. The conversion of surface Ig to a detergent-insoluble form required receptor cross-linking but occurred independently of capping. Several types of experiments demonstrated that this form of Ig was not due to the size insolubility of immune complexes and involved a stable, noncovalent association of the receptor with the detergent-insoluble, cytoskeletal residue. Incubation of ligand-bound cells at 37 degrees C promoted the degradation of surface Ig and the appearance of new, lower m.w. species, including a major soluble protein (50,000 daltons) that was antigenically related to surface Ig. These events corresponded to receptor endocytosis by several criteria (time course, temperature sensitivity, and energy dependence). Taken together, these results were consistent with the ligand-induced transmembrane attachment of receptors to the underlying cytoskeletal matrix followed by receptor internalization and catabolism.