Reconstitution of Regulated Phosphorylation of FcϵRI by a Lipid Raft-excluded Protein-tyrosine Phosphatase

Abstract

To examine the exquisite regulation of IgE-FcϵRI tyrosine phosphorylation by Lyn kinase that is stimulated by antigen-mediated cross-linking, we utilized co-expression of FcϵRI and Lyn in Chinese hamster ovary cells, which results in high basal levels of Lyn kinase activity and spontaneous phosphorylation of FcϵRI. We found that co-expression of a lipid raft-excluded transmembrane tyrosine phosphatase, PTPα, suppresses Lyn kinase activity and markedly reduces the level of spontaneous phosphorylation of FcϵRI, while facilitating its antigen-stimulated phosphorylation. Other tyrosine phosphatases, including SHP-1, CD45, and a lipid raft-preferring chimeric version of PTPα fail to reconstitute antigen-dependent FcϵRI phosphorylation. We concluded that both substrate specificity and submembrane location are critical to phosphatase-mediated regulation of Lyn kinase activity that supports activation of FcϵRI.