Distinctive tyrosine phosphorylation pattern of CD19 during BCR and CD40 signaling

Abstract

CD19 regulates constitutive and B cell antigen receptor (BCR)‐induced signaling through its cytoplasmic domain that contains nine conserved tyrosine residues. Of nine tyrosine residues, studies have clarified that three tyrosines, CD19‐Y513, CD19‐Y482, and CD19‐Y391, have central roles. Herein, we demonstrate distinctive patterns of tyrosine phophorylation of CD19 following various stimulations using antibodies reactive with each phosphorylated tyrosine residue. BCR ligation caused tyrosine phophorylation of Y513, followed by Y391 phosphorylation that preceded Y482 phosphorylation. IgG‐BCR induced more rapid phosphorylation of Y513 and more intense phosphorylation of Y482 and Y391 when compared with IgM‐BCR. Furthermore, simultaneous CD40 stimulation with BCR ligation resulted in much enhanced and prolonged phosphorylation of the three tyrosine residues. Phosphorylated tyrosine residues of CD19 also exhibited unique distribution: majority of phosphorylated Y513 located within the lipid rafts, while Y482 and Y391 were phosphorylated mainly out of the lipid rafts following the BCR ligation. Collectively, these observations contribute to better understanding of CD19 functions.