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

Chinese hamster ovary fibroblasts previously transfected with the high affi nity receptor for IgE (Fc epsilon RI) were further transfected with the cu 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 cy toplasmic domain of either the beta subunit or the gamma subunit of Fc epsi lon RI. Whereas native Tac failed to affect the aggregation-induced phospho rylation of Fc epsilon RI, both chimeric constructs substantially inhibited this reaction. Alternatively, the Fc epsilon RI-bearing fibroblasts were t ransfected with two chimeric constructs in which the cytoplasmic domain of Tac was replaced with a modified short form of Lyn kinase. The Lyn in both of the chimeric constructs had been mutated to remove the sites that are no rmally myristoylated and palmitoylated, respectively; one of the constructs had in addition been altered to be catalytically inactive. The catalytical ly active construct enhanced, and the inactive construct inhibited, aggrega tion-induced phosphorylation of the receptors. All of the chimeric construc ts were largely distributed outside the detergent resistant microdomains, a nd whereas aggregation caused them to move to the domains in part, their ag gregation was neither necessary nor enhanced their effects. These results a nd others indicate that the receptor and Lyn interact through protein-prote in interactions that neither are dependent upon either the posttranslationa l modification of the kinase with lipid moieties nor result exclusively fro m their co-localization in specialized membrane domains.