IMMOBILIZATION OF FC-EPSILON-RECEPTORS BY WHEAT-GERM-AGGLUTININ - RECEPTOR DYNAMICS IN IGE-MEDIATED SIGNAL-TRANSDUCTION

Transmembrane signaling initiated by the receptor with high affinity f or Fc stem of IgE(FcepsilonRI) requires the diffusion-dependent cross- linkage and persistent aggregation of the FcepsilonRI. Disruption or p revention of receptor cross-links at any time during the secretory res ponse quickly terminates secretion. We found that in the rat basophili c leukemia mast cell line, addition of wheat germ agglutinin, a lectin that binds to the FcepsilonRI alpha subunit, caused a precipitous dec line in the lateral diffusional and electrokinetic mobilities of the F cepsilonRI. Both the unoccupied FcepsilonRI and IgE-FcepsilonRI comple xes became immobilized, as determined from in situ electromigration an d postelectric field relaxation. Immobilization of the FcepsilonERI by wheat germ agglutinin was accompanied by a ligand-reversible associat ion of I-125-IgE-FcepsilonRI complexes with the Triton X-100-insoluble cytoskeletal fraction . Wheat germ agglutinin rapidly inhibited Fceps ilonRI-mediated signal transduction and secretion, whether cross-linka ge was initiated by multivalent antigen, covalent IgE oligomers, anti- IgE, or anti-FcepsilonRI antibody. Inhibition of signaling and secreti on occurred on simultaneous addition of wheat germ agglutinin and anti gen, and also when wheat germ agglutinin was added at increasing times after induction of FcepsilonRI cross-linkage. Wheat germ agglutinin n either reduced the affinity of anti-DNP IgE for haptenic DNP-lysine no r reversed the binding of IgE to the FcepsilonRI. Although wheat germ agglutinin caused internalization of the FcepsilonRI, the onset of inh ibition preceded and its extent exceeded that of internalization. Whea t germ agglutinin did not interfere with the secretory apparatus, as i ndicated by its lack of inhibition of secretion elicited by calcium io nophores. These findings suggest that inhibition of signal transductio n is secondary to an initial event linked to immobilization of the Fce psilonRI. Implications of these results are discussed with respect to the dynamics of FcepsilonRI aggregation on rat basophilic leukemia cel ls.