Oligosaccharide-related epitope specific for a brain-specific glycoprotein, 1D4 antigen

Coordinated regulation of circadian rhythms and homeostasis by the suprachiasmatic nucleus

We have demonstrated that in rats activities of various enzymes related to gluconeogenesis and amino acid metabolism show circadian rhythms. Based on these results, we have explored the molecular mechanisms underlying circadian oscillation and phase response to light of the master clock located in the dorsomedial subdivision of the suprachiasmatic nucleus (SCN) and found various proteins closely related to phase response such as BIT/SHPS-1 and those of circadian oscillation, some of which are involved in protein-tyrosine phosphorylation.On the other hand, we have presented several lines of evidence that the ventrolateral subdivision of the SCN includes not only the control center of energy supply to the brain, but also that of homeostasis such as blood glucose, blood pressure, water balance, and body temperature. We have also shown that besides these functions, the latter subdivision is involved in the regulations of hormone secretions such as insulin, glucagon, corticosterone and vasopressin. It has been also shown by electrophysiological means that light exposure to rat eye enhances sympathetic nerve activity, whereas it depresses parasympathetic nerve activity. Thus, environmental light is implicated not only in the phase-shift through the retinohypthalamic tract (RHT), but also control of autonomic nerve activities through the RHT, It is also discussed in this review how the two divisions are interconnected and how environmental light is involved in this interconnection.

Differential galactosylation of neuronal and haematopoietic signal regulatory protein-(α) determines its cellular binding-specificity

Signal regulatory protein-(α) (SIRP(α)) is a member of the Ig superfamily selectively expressed by neuronal and myeloid cells. The molecule mediates functional interactions with CD47/integrin-associated protein. Here we provide evidence for the tissue-specific glycosylation of neuronal and haematopoietic SIRP(α). We demonstrate a major difference in the galactosylation of N-linked glycans isolated from neuronal (i.e. brain-derived) SIRP(α) as compared to myeloid (i.e. spleen-derived) SIRP(α), with neuronal SIRP(α) almost completely lacking galactose. (β)4-galactosyltransferase assays demonstrated that this is most likely due to a low galactosylation capacity of the brain. In order to investigate the role of galactosylation of SIRP(α) in cellular interactions, soluble recombinant SIRP(α) glycoforms containing galactose (SIRP(α)-Fc) or lacking galactose (SIRP(α)((Δ)Gal)-Fc) were produced. Binding studies demonstrated superior binding of SIRP(α)((Δ)Gal)-Fc to cerebellar neurons and isolated lymphocytes. In contrast, SIRP(α)-Fc bound relatively strong to macrophages. These data show that the galactosylation of SIRP(α) determines its cellular binding specificity.

Human Signal-Regulatory Protein Is Expressed on Normal, But Not on Subsets of Leukemic Myeloid Cells and Mediates Cellular Adhesion Involving Its Counterreceptor CD47

Signal-regulatory proteins (SIRPs) comprise a novel transmembrane glycoprotein family involved in the negative regulation of receptor tyrosine kinase-coupled signaling pathways. To analyze the expression and function of SIRPs, we prepared soluble recombinant fusion proteins of the extracellular regions of SIRP1 and SIRP2, as well as a variety of monoclonal antibodies (MoAbs) against these domains. The antibodies reacted predominantly with monocytes, granulocytes, dendritic cells, and their precursors, as well as with bone marrow CD34+, AC133+, CD90+hematopoietic stem/progenitor cells. In contrast, SIRP expression was absent or significantly reduced on the majority of myeloid blasts from patients with acute myeloid leukemia (AML) or chronic myeloid leukemia (CML). Functional studies showed that the extracellular domains of SIRP1 and SIRP2 support adhesion of a number of primary hematopoietic cells and cell lines. This interaction could be blocked by 4 of 7 SIRP1-reactive MoAbs. In addition, SIRP1 and SIRP2 competed for the same cell binding site, suggesting a common widely expressed SIRP ligand. In an approach to identify this molecule, MoAbs were generated against the SIRP-binding cell line CCRF-CEM, and MoAb CC2C6 was selected because of its capacity to inhibit cell binding to SIRP1. Further analysis showed that this antibody recognized CD47, a ubiquitously expressed plasma membrane protein previously implicated in integrin function, host defense action, and neutrophil migration. In this study, we identify CD47 as the extracellular ligand for human SIRP and show that these two counterreceptors are involved in cellular adhesion.

Human Signal-Regulatory Protein Is Expressed on Normal, But Not on Subsets of Leukemic Myeloid Cells and Mediates Cellular Adhesion Involving Its Counterreceptor CD47

Signal-regulatory proteins (SIRPs) comprise a novel transmembrane glycoprotein family involved in the negative regulation of receptor tyrosine kinase-coupled signaling pathways. To analyze the expression and function of SIRPs, we prepared soluble recombinant fusion proteins of the extracellular regions of SIRP1 and SIRP2, as well as a variety of monoclonal antibodies (MoAbs) against these domains. The antibodies reacted predominantly with monocytes, granulocytes, dendritic cells, and their precursors, as well as with bone marrow CD34+, AC133+, CD90+hematopoietic stem/progenitor cells. In contrast, SIRP expression was absent or significantly reduced on the majority of myeloid blasts from patients with acute myeloid leukemia (AML) or chronic myeloid leukemia (CML). Functional studies showed that the extracellular domains of SIRP1 and SIRP2 support adhesion of a number of primary hematopoietic cells and cell lines. This interaction could be blocked by 4 of 7 SIRP1-reactive MoAbs. In addition, SIRP1 and SIRP2 competed for the same cell binding site, suggesting a common widely expressed SIRP ligand. In an approach to identify this molecule, MoAbs were generated against the SIRP-binding cell line CCRF-CEM, and MoAb CC2C6 was selected because of its capacity to inhibit cell binding to SIRP1. Further analysis showed that this antibody recognized CD47, a ubiquitously expressed plasma membrane protein previously implicated in integrin function, host defense action, and neutrophil migration. In this study, we identify CD47 as the extracellular ligand for human SIRP and show that these two counterreceptors are involved in cellular adhesion.

Prominent 85-kDa oligomannosidic glycoproteins of rat brain are signal regulatory proteins and include the SHP substrate-1 for tyrosine phosphatases

The glycoprotein component in rat brain reacting most strongly with Galanthus nivalis agglutinin (GNA) on western blots migrates as an 85-kDa band. GNA identifies mannose-rich oligosaccharides because it is highly specific for terminal alpha-mannose residues. After purification of this 85-kDa glycoprotein band by chromatography on GNA-agarose and preparative gel electrophoresis, binding of other lectins demonstrated the presence of fucose and a trace of galactose, but no sialic acid. Treatment with N-Glycanase or endoglycosidase H produced a 65-kDa band, indicating that it consisted of about one-fourth N-linked oligomannosidic carbohydrate moieties. High-performance anion-exchange chromatography and fluorescence-assisted carbohydrate electrophoresis indicated that the major carbohydrate moiety is a heptasaccharide with the structure Manalpha1-6(Manalpha1-3)Manalpha1-6(Manalpha1-3) Manbeta1-4Glc-NAcbeta1-4GlcNAc (Man5GlcNAc2). Determination of amino acid sequences of peptides produced by endoproteinase digestion demonstrated that this 85-kDa mannose-rich glycoprotein component contained the SHP substrate-1 for phosphotyrosine phosphatases and at least one other member of the signal-regulatory protein (SIRP) family. The unusually high content of oligomannosidic carbohydrate moieties on these receptor-like members of the immunoglobulin superfamily in neural tissue could be of functional significance for intercellular adhesion or signaling.

BIT, an immune antigen receptor-like molecule in the brain

We previously found a brain-specific glycoprotein in the rat brain. It postnatally increases and is rich in the mature brain. We cloned cDNA of this protein. It is composed of a signal peptide, a V-type immunoglobulin domain, two C1-type immunoglobulin domains, a transmembrane segment and a cytoplasmic region containing two tyrosine-based activation motifs (TAM) that are variants of the antigen receptor signaling motifs. The overall structure is similar to those of immune antigen receptors. This molecule, BIT (brain immunoglobulin-like molecule with TAMs), is a major endogenous substrates of brain tyrosine kinases in vitro. Cerebral cortical neurons could extend their neurites on BIT-coated substrate and anti-BIT monoclonal antibody specifically inhibited the effect. These findings and our recent study concerning BIT signal transduction mechanism suggest that BIT, an immune antigen receptor-like molecule of the brain, functions as a membrane signaling molecule that may participate in cell-cell interaction.

Activation of protein-tyrosine phosphatase SH-PTP2 by a tyrosine-based activation motif of a novel brain molecule

BIT (a brain immunoglobulin-like molecule with tyrosine-based activation motifs) is a brain-specific membrane protein which has two cytoplasmic TAMs (tyrosine-based activation motifs). Using the Far Western blotting technique, we detected association of a 70-kDa protein with the tyrosine-phosphorylated TAMs of BIT. A mouse brain cDNA library in lambdagt11 was screened for this association, and two positive clones encoding tyrosine phosphatase SH-PTP2 were isolated. SH-PTP2 has two SH2 domains and is believed to function as a positive mediator in receptor tyrosine kinase signaling. SH-PTP2 and BIT were coimmunoprecipitated from phosphorylated rat brain lysate, and BIT was a major tyrosine-phosphorylated protein associated with SH-PTP2 in this lysate. This interaction was also observed in Jurkat T cells transfected with BIT cDNA depending on tyrosine phosphorylation of BIT. Bisphosphotyrosyl peptides corresponding to BIT-TAMs stimulated SH-PTP2 activity 33-35-fold in vitro, indicating that two SH2 domains of SH-PTP2 simultaneously interact with two phosphotyrosines of BIT-TAM. Our findings suggest that the tyrosine phosphorylation of BIT results in stimulation of the signal transduction pathway promoted by SH-PTP2 and that BIT is probably a major receptor molecule in the brain located just upstream of SH-PTP2.

Different subsets of CNS neurons express different glycosaminoglycan epitopes on large perineuronal proteoglycans

Proteoglycans are known to occur in the central nervous tissue, but their function is not well understood. We made a biochemical study of four perineuronal antigens on different subsets of rat brain neurons and found that three antigens recognized by antibodies against glycosaminoglycan epitopes were large proteoglycans. Molecular masses estimated by immunoblotting were 700 kDa for 473, 376 and 1B5 antigens and 600 kDa for the 374 antigen. Reactivities of the antigens on immunoblots to monoclonal antibodies (MAbs) 473 and 376 were lost, and that to MAb 1B5 uncovered, after chondroitinase ABC treatment as in the brain sections. The elution profiles from ion-exchange and gel-filtration column chromatography of 473, 376 and 1B5 antigens were quite similar, but those of 374 antigen were slightly different. The immunoaffinity-purified 473 antigen migrated at 700 kDa on sodium dodecylsulfate gel electrophoresis, and chondroitinase ABC treatment decreased the molecular mass to 600 kDa. The 473 antigen was recognized by MAbs 376 and 1B5 although these MAbs also reacted with 473-negative 700 kDa molecules. These results suggest that neuronal subset-specific glycosylation may occur on the 700 kDa proteoglycans, and that the glycosaminoglycan structures may be involved in the pericellular diversity of CNS neurons.