Biosynthesis and post-translational processing of lectin-like oxidized lowdensity lipoprotein receptor-1 (LOX-1) - N-linked glycosylation affects cell-surface expression and ligand binding

LOX-1 (lectin-like oxidized low density lipoprotein receptor-1) is a type I I 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, b y pulse-chase labeling and glycosidase digestion, that LOX-1 is synthesized as a 40-kDa precursor protein with N-linked high mannose carbohydrate chai ns (pre-LOX-1), which is subsequently further glycosylated and processed in to the 48-kDa mature form within 40 min, Furthermore, when treated with an N-glycosylation inhibitor, tunicamycin, both tumor necrosis factor-alpha-ac tivated 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 immu nofluorescence confocal microscopy demonstrated that the deglycosylated for m of LOX-1 is not efficiently transported to the cell surface, but is retai ned in the endoplasmic reticulum or Golgi apparatus in tumor necrosis facto r-alpha-activated bovine aortic endothelial cells, but not in BLOX-1-CHO ce lls. Radiolabeled Ox-LDL binding studies revealed that the deglycosylated f orm of LOX-1 expressed on the cell surface of BLOX-1-CHO cells has a reduce d affinity for Ox-LDL binding, Taken together, N-linked glycosylation appea rs to play key roles in the cell-surface expression and ligand binding of L OX-1.