Neu5Gc-mediated high-affinity interaction is dispensable for CD22 cis-ligands to regulate B cell signaling.

CD22 (also known as Siglec-2) is an inhibitory receptor expressed in B cells. CD22 specifically recognizes α2,6 sialic acid and interacts with α2,6 sialylated membrane proteins expressed on the same cell (cis-ligands) and those derived from outside of the cell (trans-ligands). Previously, CD22 cis-ligands were shown to regulate the activity of CD22, thereby regulating both BCR ligation-induced signaling and low-level "tonic" signaling in the absence of BCR ligation that regulates the survival and differentiation of B cells.

CD72 is an inhibitory pattern recognition receptor that recognizes ribosomes and suppresses production of anti-ribosome autoantibody.

B cell responses to nucleic acid-containing self-antigens that involve intracellular nucleic acid sensors play a crucial role in autoantibody production in SLE. CD72 is an inhibitory B cell co-receptor that down-regulates BCR signaling, and prevents the development of SLE. We previously showed that CD72 recognizes the RNA-containing self-antigen Sm/RNP, a target of SLE-specific autoantibodies, and induces B cell tolerance to Sm/RNP by specifically inhibiting B cell response to this self-antigen.

LAPTM5 mediates immature B cell apoptosis and B cell tolerance by regulating the WWP2-PTEN-AKT pathway.

Elimination of autoreactive developing B cells is an important mechanism to prevent autoantibody production. However, how B cell receptor (BCR) signaling triggers apoptosis of immature B cells remains poorly understood. We show that BCR stimulation up-regulates the expression of the lysosomal-associated transmembrane protein 5 (LAPTM5), which in turn triggers apoptosis of immature B cells through two pathways.

The inhibitory coreceptor CD22 restores B cell signaling by developmentally regulating immunodeficient B cells.

The protein tyrosine phosphatase CD45 plays a crucial role in B cell antigen receptor (BCR) signaling by activating Src family kinases. mice show altered B cell development and a phenotype likely due to reduced steady-state signaling; however, B cells show relatively normal BCR ligation-induced signaling. In our investigation of how BCR signaling was restored in cells, we found that the coreceptor CD22 switched from an inhibitory to a stimulatory function in these cells.

The Protein Tyrosine Phosphatase SHP-1 (PTPN6) but Not CD45 (PTPRC) Is Essential for the Ligand-Mediated Regulation of CD22 in BCR-Ligated B Cells.

CD22 is an inhibitory B cell coreceptor that regulates B cell development and activation by downregulating BCR signaling through activation of SH2-containing protein tyrosine phosphatase-1 (SHP-1). CD22 recognizes α2,6 sialic acid as a specific ligand and interacts with α2,6 sialic acid-containing membrane molecules, such as CD45, IgM, and CD22, expressed on the same cell. Functional regulation of CD22 by these endogenous ligands enhances BCR ligation-induced signaling and is essential for normal B cell responses to Ags.

Identification of Siglec Cis-Ligands by Proximity Labeling.

Siglecs are known to be bound and regulated by membrane molecules that display specific sialic acid-containing ligands and are present on the same cell (cis-ligands). Because of the low-affinity binding of Siglecs to the glycan ligands, conventional methods such as immunoprecipitation are not suitable for identification of Siglec cis-ligands. Here we describe efficient and specific labeling of cis-ligands of CD22 (also known as Siglec-2) on B lymphocytes by proximity labeling using tyramide.

Differential Regulation of Thermodynamic Binding Forces of Levocetirizine and ()-Cetirizine by Lys191 in Human Histamine H₁ Receptors.

Cetirizine is a zwitterionic second-generation antihistamine containing - and -enantiomers, levocetirizine, and ()-cetirizine. Levocetirizine is known to have a higher affinity for the histamine H₁ receptors than ()-cetirizine; ligand-receptor docking simulations have suggested the importance of the formation of a salt bridge (electrostatic interaction) between the carboxylic group of levocetirizine and the Lys191 residue at the fifth transmembrane domain of human histamine H₁ receptors. In this study, we evaluated the roles of Lys191 in the regulation of the thermodynamic binding forces of levocetirizine in comparison with ()-cetirizine.

CD22-Binding Synthetic Sialosides Regulate B Lymphocyte Proliferation Through CD22 Ligand-Dependent and Independent Pathways, and Enhance Antibody Production in Mice.

Sialic acid-binding immunoglobulin-like lectins (Siglecs) are expressed in various immune cells and most of them carry signaling functions. High-affinity synthetic sialoside ligands have been developed for various Siglecs. Therapeutic potentials of the nanoparticles and compounds that contain multiple numbers of these sialosides and other reagents such as toxins and antigens have been demonstrated.

Proximity labeling of cis-ligands of CD22/Siglec-2 reveals stepwise α2,6 sialic acid-dependent and -independent interactions.

Lectins expressed on the cell surface are often bound and regulated by the membrane molecules containing the glycan ligands on the same cell (cis-ligands). However, molecular nature and function of cis-ligands are generally poorly understood partly because of weak interaction between lectins and glycan ligands. Cis-ligands are most extensively studied in CD22 (also known as Siglec-2), an inhibitory B lymphocyte receptor specifically recognizing α2,6 sialic acids.

Asp73-dependent and -independent regulation of the affinity of ligands for human histamine H receptors by Na.

The affinity of ligands for G-protein-coupled receptors (GPCRs) is allosterically regulated by Na via a highly conserved aspartate residue (Asp) in the second transmembrane domain of GPCRs. In the present study, we examined the Na-mediated regulation of the affinity of ligands for G-protein-coupled human histamine H receptors in Chinese hamster ovary cells. The affinities of 3 agonists and 20 antihistamines were evaluated by their displacement curves against the binding of [H]-mepyramine to membrane preparations in the presence or absence of 100mM NaCl.

CD72 negatively regulates B lymphocyte responses to the lupus-related endogenous toll-like receptor 7 ligand Sm/RNP.

Toll-like receptor 7 (TLR7) plays an essential role in development of systemic lupus erythematosus by co-stimulating B cells reactive to the endogenous TLR7 ligand Sm/ribonucleoprotein (RNP), a crucial lupus self-antigen. However, how the TLR7-mediated autoimmune response is regulated is not yet known. In this study, we demonstrate that CD72, an inhibitory B cell co-receptor known to prevent development of lupus, recognizes Sm/RNP at the extracellular C-type lectin-like domain (CTLD) and specifically inhibits B cell response to Sm/RNP.

C-terminal of human histamine H receptors regulates their agonist-induced clathrin-mediated internalization and G-protein signaling.

It has been suggested that the agonist-induced internalization of G-protein-coupled receptors from the cell surface into intracellular compartments regulates cellular responsiveness. We previously reported that G -protein-coupled human histamine H receptors internalized via clathrin-dependent mechanisms upon stimulation with histamine. However, the molecular determinants of H receptors responsible for agonist-induced internalization remain unclear.

The affinity of histamine for Gq protein-coupled histamine H(1)-receptors is predominantly regulated by their internalization in human astrocytoma cells.

We examined the regulatory mechanisms of the affinity of Gq protein-coupled histamine H(1)-receptors for histamine after histamine pretreatment in intact human U373 MG astrocytoma cells. In control cells, the displacement curves for histamine against the binding of 5 nM [(3)H]mepyramine, a radioligand for H(1)-receptors, showed the presence of two binding sites for histamine, that is, high and low affinity sites. Pretreatment with 0.

Dermatan sulfate epimerase 2 is the predominant isozyme in the formation of the chondroitin sulfate/dermatan sulfate hybrid structure in postnatal developing mouse brain.

Chondroitin sulfate (CS) and dermatan sulfate (DS) are expressed in significant amounts in the brain and play important roles in the development of the central nervous system in mammals. CS and DS structures are often found in a single CS/DS hybrid chain. The l-iduronic acid (IdoA)-containing domain, which defines a DS-type domain, appears key to the biological functions of the CS/DS hybrid chain.

Development of a mouse monoclonal antibody against the chondroitin sulfate-protein linkage region derived from shark cartilage.

Glycosaminoglycans (GAGs) like chondroitin sulfate (CS) and heparan sulfate (HS) are synthesized on the tetrasaccharide linkage region, GlcAbeta1-3Galbeta1-3Galbeta1-4Xylbeta1-O-Ser, of proteoglycans. The Xyl can be modified by 2-O-phosphate in both CS and HS, whereas the Gal residues can be sulfated at C-4 and/or C-6 in CS but not in HS. To study the roles of these modifications, monoclonal antibodies were developed against linkage glycopeptides of shark cartilage CS proteoglycans, and one was characterized in detail.