title: Sialylated complex-type N-glycans enhance the signaling activity of soluble intercellular adhesion molecule-1 in mouse astrocytes.
abstract: Intercellular adhesion molecule-1 (ICAM-1) occurs as both a membrane and a soluble, secreted glycoprotein (sICAM-1). ICAM-1 on endothelial cells mediates leukocyte adhesion by binding to leukocyte function associated antigen-1 (LFA-1) and macrophage antigen-1 (Mac-1). Recombinant mouse sICAM-1 induces the production of macrophage inflammatory protein-2 (MIP-2) in mouse astrocytes by a novel LFA-1- and Mac-1-independent mechanism. Here we showed that N-glycan structures of sICAM-1 influence its ability to induce MIP-2 production. sICAM-1 expressed in Chinese hamster ovary (CHO) cells was a more potent inducer of MIP-2 production than sICAM-1 expressed in HEK 293 cells, suggesting that posttranslational modification of sICAM-1 could influence its signaling activity. To explore the roles of glycosylation in sICAM-1 activity, we expressed sICAM-1 in mutant CHO cell lines differing in glycosylation, including Lec2, Lec8, and Lec1 as well as in CHO cells cultured in the presence of the alpha-mannosidase-I inhibitor kifunensine. Signaling activity of sICAM-1 lacking sialic acid was reduced 3-fold compared with sICAM-1 from CHO cells. The activity of sICAM-1 lacking both sialic acid and galactose was reduced 12-fold, whereas the activity of sICAM-1 carrying only high mannose-type N-glycans was reduced 12-26-fold. sICAM-1 glycoforms carrying truncated glycans retained full ability to bind to LFA-1 on leukocytes. Thus, sialylated and galactosylated complex-type N-glycans strongly enhanced the ability of sICAM-1 to induce MIP-2 production in astrocytes but did not alter its binding to LFA-1 on leukocytes. Glycosylation could therefore serve as a means to regulate specifically the signaling function of sICAM-1 in vivo.
authors.affiliation: Department of Biochemistry and Molecular Biology, Oklahoma Center for Medical Glycobiology, University of Oklahoma Health Sciences Center, Oklahoma City, Oklahoma 73104, USA. vivianne.otto@pharma.ethz.ch
authors.forename: Vivianne I
authors.initials: VI
authors.lastname: Otto
authors.forename: Thomas
authors.initials: T
authors.lastname: Schürpf
authors.forename: Gerd
authors.initials: G
authors.lastname: Folkers
authors.forename: Richard D
authors.initials: RD
authors.lastname: Cummings
mesh_terms: D000818:Animals; D001253:Astrocytes / Q000378:metabolism*; D016466:CHO Cells; D002460:Cell Line; D054426:Chemokine CXCL2; D006224:Cricetinae; D005260:Female; D006031:Glycosylation; D006801:Humans; D018799:Intercellular Adhesion Molecule-1 / Q000737:chemistry / Q000378:metabolism*; D016169:Lymphocyte Function-Associated Antigen-1 / Q000378:metabolism; D051379:Mice; D015846:Monokines / Q000378:metabolism; D011134:Polysaccharides / Q000737:chemistry / Q000378:metabolism; D011499:Protein Processing, Post-Translational; D015398:Signal Transduction
chemical_list: D054426:Chemokine CXCL2; D016169:Lymphocyte Function-Associated Antigen-1; D015846:Monokines; D011134:Polysaccharides; D018799:Intercellular Adhesion Molecule-1