Park Minha, Tenner Andrea J
Department of Molecular Biology & Biochemistry, University of California, Irvine, California 92697-3900, USA.
J Cell Physiol. 2003 Sep;196(3):512-22. doi: 10.1002/jcp.10332.
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 .
C1qRP/CD93是一种主要在单核细胞、中性粒细胞、内皮细胞和早期干细胞前体上表达的细胞表面受体。在吞噬细胞中，它被认为有助于增强由先天性免疫系统防御胶原蛋白（如C1q和甘露糖结合凝集素（MBL））触发的FcR和CR1诱导的吞噬作用。此前，我们证明了C1qRP/CD93上存在高水平的糖基化，且主要为O-连接糖基化。在本研究中，我们首先通过向人组织细胞系U937中添加苄基2-乙酰氨基-2-脱氧-α-D-吡喃半乳糖苷（BAG）来抑制O-糖基化，其次通过在蛋白质糖基化存在可逆缺陷的CHO衍生细胞系ldlD中表达C1qRP/CD93，来研究糖基化在C1qRP/CD93稳定性中的作用。在转染表达C1qRP/CD93的U937细胞和ldlD细胞中，糖基化缺陷均导致C1qRP/CD93的细胞表面表达水平下降，同时在培养基中检测到C1qRP/CD93的反应性。代谢标记研究表明，当不存在糖基化时，C1qRP/CD93被合成并迅速释放到培养上清液中或被降解。这些研究表明，O-糖基化对C1qRP/CD93在细胞表面的稳定表达很重要。
