The ligand-binding domain of CD22 is needed for inhibition of the B cell receptor signal, as demonstrated by a novel human CD22-specific inhibitor compound.
CD22 is a B cell-specific transmembrane protein of the Siglec family. It binds specifically to alpha2,6-linked sialic acid (Sia) residues, which are also present on glycoproteins on the B cell surface. CD22 acts as a negative regulator in B cell receptor-mediated signaling by recruitment of Src homology 2 domain-containing tyrosine phosphatase (SHP)-1 to its intracellular tail. To analyze how ligand-binding of CD22 influences its intracellular signaling domain, we designed synthetic sialosides as inhibitors for the lectin domain of CD22. One of these compounds inhibited binding of human CD22-Fc to target cells over 200-fold better than Sia and was highly selective for human CD22. When Daudi cells or primary B cells were stimulated with anti-immunoglobulin (Ig)M in presence of this sialoside inhibitor, a higher Ca(2+) response was observed, similar to CD22-deficient B cells. Accordingly, a lower tyrosine-phosphorylation of CD22 and SHP-1 recruitment was demonstrated in presence of the sialoside. Thus, by interfering with ligand binding of CD22 on the B cell surface, we have shown for the first time that the lectin domain of CD22 has a direct, positive influence on its intracellular inhibitory domain. Also, we have developed a novel low molecular weight compound which can enhance the response of human B cells.
Kelm
Soerge
S
Centre for Biomolecular Interactions Bremen, University Bremen, Department for Biology and Chemistry, 28334 Bremen, Germany.
Gerlach
Judith
J
Brossmer
Reinhard
R
Danzer
Claus-Peter
CP
Nitschke
Lars
L
D000818:Animals; D015703:Antigens, CD / Q000737:chemistry / Q000276:immunology*; D000944:Antigens, Differentiation, B-Lymphocyte / Q000737:chemistry / Q000276:immunology*; D001665:Binding Sites; D015815:Cell Adhesion Molecules; D002460:Cell Line; D006801:Humans; D007141:Immunoglobulin Fc Fragments; D007700:Kinetics; D037102:Lectins; D008024:Ligands; D051379:Mice; D017027:Protein Tyrosine Phosphatases / Q000378:metabolism; D011947:Receptors, Antigen, B-Cell / Q000276:immunology*; D011993:Recombinant Fusion Proteins / Q000494:pharmacology; D051918:Sialic Acid Binding Ig-like Lectin 2; D014407:Tumor Cells, Cultured; D018909:src Homology Domains
D015703:Antigens, CD; D000944:Antigens, Differentiation, B-Lymphocyte; C497867:CD22 protein, human; C497868:Cd22 protein, mouse; D015815:Cell Adhesion Molecules; D007141:Immunoglobulin Fc Fragments; D037102:Lectins; D008024:Ligands; D011947:Receptors, Antigen, B-Cell; D011993:Recombinant Fusion Proteins; D051918:Sialic Acid Binding Ig-like Lectin 2; D017027:Protein Tyrosine Phosphatases