Biosynthesis and Post-translational Processing of Lectin-like Oxidized Low Density Lipoprotein Receptor-1 (LOX-1)

LOX-1 (lectin-likeoxidized low density lipoprotein receptor-1) is a type II membrane protein belonging to the C-type lectin family that can act as a cell-surface receptor for atherogenic oxidized low density lipoprotein (Ox-LDL) and may play crucial roles in atherogenesis. In this study, we show, by pulse-chase labeling and glycosidase digestion, that LOX-1 is synthesized as a 40-kDa precursor protein withN-linked high mannose carbohydrate chains (pre-LOX-1), which is subsequently further glycosylated and processed into the 48-kDa mature form within 40 min. Furthermore, when treated with anN-glycosylation inhibitor, tunicamycin, both tumor necrosis factor-α-activated bovine aortic endothelial cells and CHO-K1 cells stably expressing bovine LOX-1 (BLOX-1-CHO) exclusively produced a 32-kDa deglycosylated form of LOX-1. Cell enzyme-linked immunosorbent assay, flow cytometry, and immunofluorescence confocal microscopy demonstrated that the deglycosylated form of LOX-1 is not efficiently transported to the cell surface, but is retained in the endoplasmic reticulum or Golgi apparatus in tumor necrosis factor-α-activated bovine aortic endothelial cells, but not in BLOX-1-CHO cells. Radiolabeled Ox-LDL binding studies revealed that the deglycosylated form of LOX-1 expressed on the cell surface of BLOX-1-CHO cells has a reduced affinity for Ox-LDL binding. Taken together,N-linked glycosylation appears to play key roles in the cell-surface expression and ligand binding of LOX-1.

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