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

David Holowka,Ryan M. Young,Xinmin Zheng,Barbara Baird

doi:10.1074/jbc.m408339200

Abstract

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

Highlights

Fc⑀RI, the high affinity receptor for IgE, is a member of the family of multichain immune recognition receptors including T and B cell receptors for antigen, certain NK cell receptors, and other Fc receptors on various hematopoietic cells
Reconstitution of Signaling in CHO Cells Is Dependent on the Location of PTP Activity—We showed in Fig. 1 that Lyn expressed in CHO cells is highly active, most likely because it is strongly phosphorylated at its active site
Our present findings showed that a transmembrane tyrosine phosphatase, PTP␣, plays an essential role in the regulation of Fc⑀RI phosphorylation by Lyn when this kinase and receptor are co-expressed in CHO cells

Summary

Introduction

Fc⑀RI, the high affinity receptor for IgE, is a member of the family of multichain immune recognition receptors including T and B cell receptors for antigen, certain NK cell receptors, and other Fc receptors on various hematopoietic cells. We found that co-expression of a lipid raft-excluded transmembrane tyrosine phosphatase, PTP␣, suppresses Lyn kinase activity and markedly reduces the level of spontaneous phosphorylation of Fc⑀RI, while facilitating its antigen-stimulated phosphorylation.

Results

Conclusion