Interaction between the unphosphorylated receptor with high affinity for IgE and Lyn kinase

Abstract

Chinese hamster ovary fibroblasts previously transfected with the high affinity receptor for IgE (FcεRI) were further transfected with the α subunit of the receptor for interleukin 2 (Tac) or with chimeric constructs in which the cytoplasmic domain of Tac was replaced with the C-terminal cytoplasmic domain of either the β subunit or the γ subunit of FcεRI. Whereas native Tac failed to affect the aggregation-induced phosphorylation of FcεRI, both chimeric constructs substantially inhibited this reaction. Alternatively, the FcεRI-bearing fibroblasts were transfected with two chimeric constructs in which the cytoplasmic domain of Tac was replaced with a modifed short form of Lyn kinase. The Lyn in both of the chimeric constructs had been mutated to remove the sites that are normally myristoylated and palmitoylated, respectively; one of the constructs had in addition been altered to be catalytically inactive. The catalytically active construct enhanced, and the inactive construct inhibited, aggregation-induced phosphorylation of the receptors. All of the chimeric constructs were largely distributed outside the detergent resistant microdomains, and whereas aggregation caused them to move to the domains in part, their aggregation was neither necessary nor enhanced their effects. These results and others indicate that the receptor and Lyn interact through protein-protein interactions that neither are dependent upon either the post-translational modification of the kinase with lipid moieties nor result exclusively from their co-localization in specialized membrane domains.