title: Cell surface expression of C1qRP/CD93 is stabilized by O-glycosylation.
abstract: C1qRP/CD93 is a cell surface receptor predominantly expressed on monocytes, neutrophils, endothelial cells, and early stem cell precursors. In phagocytic cells, it has been characterized as contributing to the enhancement of FcR- and CR1-induced phagocytosis triggered by innate immune system defense collagens such as C1q and mannose binding lectin (MBL). Previously, we demonstrated a high level of glycosylation on C1qRP/CD93 that was predominantly O-linked. In this study, we investigate the role of glycosylation in C1qRP/CD93 stability first by inhibiting O-glycosylation by addition of benzyl 2-acetamido-2-deoxy-alpha-D-galactopyranoside (BAG) to the human histiocytic cell line U937, and secondly, by expression of C1qRP/CD93 in the CHO-derived cell line ldlD which has a reversible defect in protein glycosylation. In both U937 cells and in ldlD cells transfected to express C1qRP/CD93, glycosylation deficiency caused cell surface expression levels of C1qRP/CD93 to decrease, concomitant with the detection of C1qRP/CD93 reactivity in the culture media. Metabolic labeling studies show that when glycosylation is absent, C1qRP/CD93 is synthesized and rapidly released into the culture supernatant or degraded. These studies demonstrate that O-glycosylation is important in the stable cell surface expression of C1qRP/CD93 .
authors.affiliation: Department of Molecular Biology & Biochemistry, University of California, Irvine, California 92697-3900, USA.
authors.forename: Minha
authors.initials: M
authors.lastname: Park
authors.forename: Andrea J
authors.initials: AJ
authors.lastname: Tenner
mesh_terms: D000818:Animals; D016466:CHO Cells; D002352:Carrier Proteins; D002462:Cell Membrane / Q000378:metabolism*; D006224:Cricetinae; D005786:Gene Expression Regulation; D006031:Glycosylation; D006801:Humans; D018960:Hyaluronan Receptors; D008562:Membrane Glycoproteins; D024101:Mitochondrial Proteins; D011951:Receptors, Complement / Q000378:metabolism*; D020298:U937 Cells
chemical_list: C087299:C1QBP protein, human; D002352:Carrier Proteins; D018960:Hyaluronan Receptors; D008562:Membrane Glycoproteins; D024101:Mitochondrial Proteins; D011951:Receptors, Complement; C032402:complement 1q receptor