title: B cell antigen receptor and CD40 differentially regulate CD22 tyrosine phosphorylation.
abstract: Cell surface molecules on lymphocytes positively or negatively modulate the Ag receptor signaling, and thus regulate the fate of the cell. CD22 is a B cell-specific cell surface protein that contains multiple ITIMs in the cytoplasmic tail, and critically regulates B cell activation and survival. CD22 regulation on B cell signaling is complex because CD22 can have both positive and negative roles in various contexts. We generated phosphospecific polyclonal Abs reacting four major CD22 tyrosine motifs (Y762, Y807, Y822, and Y842) and analyzed the pattern and intensity of phosphorylation of these tyrosine residues. The tyrosine motifs, Y762, Y822, and Y842, are considered as ITIM, whereas the other, Y807, is suggested to be important for Grb2 recruitment. Approximately 10% of the four tyrosine residues were constitutively phosphorylated. Upon anti-IgM ligation, CD22 Y762 underwent most rapid phosphorylation, whereas all four tyrosine residues were eventually phosphorylated equally at approximately 35% of all CD22 molecules in the cell. By contrast, anti-CD40 stimulation specifically up-regulated anti-IgM-induced phosphorylation of tyrosines within two ITIM motifs, Y762 and Y842, which was consistent with in vivo finding of the negative role of CD22 in CD40 signaling. Thus, CD22 phosphorylation is not only quantitatively but also qualitatively regulated by different stimulations, which may determine the outcome of B cell signaling.
authors.affiliation: Department of Dermatology, Faculty of Medicine, University of Tokyo, Tokyo, Japan. fujimoto-m@umin.ac.jp
authors.forename: Manabu
authors.initials: M
authors.lastname: Fujimoto
authors.forename: Yoshihiro
authors.initials: Y
authors.lastname: Kuwano
authors.forename: Rei
authors.initials: R
authors.lastname: Watanabe
authors.forename: Nobuko
authors.initials: N
authors.lastname: Asashima
authors.forename: Hiroko
authors.initials: H
authors.lastname: Nakashima
authors.forename: Satoko
authors.initials: S
authors.lastname: Yoshitake
authors.forename: Hitoshi
authors.initials: H
authors.lastname: Okochi
authors.forename: Kunihiko
authors.initials: K
authors.lastname: Tamaki
authors.forename: Jonathan C
authors.initials: JC
authors.lastname: Poe
authors.forename: Thomas F
authors.initials: TF
authors.lastname: Tedder
authors.forename: Shinichi
authors.initials: S
authors.lastname: Sato
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D000888:Antibodies, Anti-Idiotypic / Q000494:pharmacology; D000918:Antibody Specificity; D001402:B-Lymphocytes / Q000276:immunology* / Q000378:metabolism; D019013:CD40 Antigens / Q000378:metabolism*; D002460:Cell Line; D006801:Humans; D007075:Immunoglobulin M / Q000276:immunology; D007700:Kinetics; D021962:Membrane Microdomains / Q000276:immunology / Q000378:metabolism; D051379:Mice; D008810:Mice, Inbred C57BL; D018345:Mice, Knockout; D010766:Phosphorylation; D011947:Receptors, Antigen, B-Cell / Q000378:metabolism*; D051918:Sialic Acid Binding Ig-like Lectin 2 / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D015398:Signal Transduction; D014443:Tyrosine / Q000737:chemistry
chemical_list: D000888:Antibodies, Anti-Idiotypic; D019013:CD40 Antigens; C497868:Cd22 protein, mouse; D007075:Immunoglobulin M; D011947:Receptors, Antigen, B-Cell; D051918:Sialic Acid Binding Ig-like Lectin 2; D014443:Tyrosine