Immobilization of Fc epsilon receptors by wheat germ agglutinin. Receptor dynamics in IgE-mediated signal transduction.

Abstract

Transmembrane signaling initiated by the receptor with high affinity for Fc stem of IgE(Fc epsilon RI) requires the diffusion-dependent cross-linkage and persistent aggregation of the Fc epsilon RI. Disruption or prevention of receptor cross-links at any time during the secretory response quickly terminates secretion. We found that in the rat basophilic leukemia mast cell line, addition of wheat germ agglutinin, a lectin that binds to the Fc epsilon RI alpha subunit, caused a precipitous decline in the lateral diffusional and electrokinetic mobilities of the Fc epsilon RI. Both the unoccupied Fc epsilon RI and IgE-Fc epsilon RI complexes became immobilized, as determined from in situ electromigration and postelectric field relaxation. Immobilization of the Fc epsilon RI by wheat germ agglutinin was accompanied by a ligand-reversible association of 125I-IgE-Fc epsilon RI complexes with the Triton X-100-insoluble cytoskeletal fraction. Wheat germ agglutinin rapidly inhibited Fc epsilon RI-mediated signal transduction and secretion, whether cross-linkage was initiated by multivalent antigen, covalent IgE oligomers, anti-IgE, or anti-Fc epsilon RI antibody. Inhibition of signaling and secretion occurred on simultaneous addition of wheat germ agglutinin and antigen, and also when wheat germ agglutinin was added at increasing times after induction of Fc epsilon RI cross-linkage. Wheat germ agglutinin neither reduced the affinity of anti-DNP IgE for haptenic DNP-lysine nor reversed the binding of IgE to the Fc epsilon RI. Although wheat germ agglutinin caused internalization of the Fc epsilon RI, the onset of inhibition preceded and its extent exceeded that of internalization. Wheat germ agglutinin did not interfere with the secretory apparatus, as indicated by its lack of inhibition of secretion elicited by calcium ionophores. These findings suggest that inhibition of signal transduction is secondary to an initial event linked to immobilization of the Fc epsilon RI. Implications of these results are discussed with respect to the dynamics of Fc epsilon RI aggregation on rat basophilic leukemia cells.