title: Inhibition of alpha-glucosidases I and II increases the cell surface expression of functional class A macrophage scavenger receptor (SR-A) by extending its half-life.
abstract: The class A scavenger receptor (SR-A) is a multifunctional trimeric membrane glycoprotein involved in atherogenesis. The mature receptor can mediate the binding and internalization of a number of specific ligands, including modified low-density lipoprotein. We have investigated the effects of inhibiting N-glycan processing on SR-A expression, distribution, and activity in the murine macrophage cell line RAW264.7. We have found that SR-A normally interacts with calnexin in the endoplasmic reticulum and in its mature form carries complex N-glycans. The imino sugar, N-butyldeoxynojirimycin (NB-DNJ) is an inhibitor of the N-glycan processing enzymes alpha-glucosidases I and II. Following NB-DNJ treatment SR-A became Endo H-sensitive, consistent with inhibition of N-glycan processing. A dose-dependent increase in cell surface expression of SR-A was observed in response to NB-DNJ treatment. The receptor on inhibitor-treated cells was still functional because the increased surface expression resulted in a proportional enhancement in the endocytosis of the ligand, acetylated low-density lipoprotein. The expression of SR-A on NB-DNJ cultured cells was further enhanced by co-treatment with interferon-gamma. Quantitative reverse transcriptase-PCR analysis did not show a significant difference in the amount of SR-A mRNA in NB-DNJ-treated RAW264.7 cells. However, the half-life of SR-A protein was significantly increased. These data indicate the retention of glucosylated N-glycans does not result in gross misfolding and degradation of this receptor or prevent its transport to the cell surface. SR-A interacts with calnexin and when the association is prevented changes in the recycling kinetics and rate of turnover of the receptor result, leading to enhanced cell surface expression.
authors.affiliation: Department of Cardiology, First Hospital, Xi'an Jiaotong University, Jiankang Road, Xi'an 710061, China.
authors.forename: Gang
authors.initials: G
authors.lastname: Tian
authors.forename: David
authors.initials: D
authors.lastname: Wilcockson
authors.forename: V Hugh
authors.initials: VH
authors.lastname: Perry
authors.forename: Pauline M
authors.initials: PM
authors.lastname: Rudd
authors.forename: Raymond A
authors.initials: RA
authors.lastname: Dwek
authors.forename: Frances M
authors.initials: FM
authors.lastname: Platt
authors.forename: Nick
authors.initials: N
authors.lastname: Platt
mesh_terms: D017485:1-Deoxynojirimycin / Q000031:analogs & derivatives* / Q000494:pharmacology; D000818:Animals; D000970:Antineoplastic Agents / Q000494:pharmacology; D037281:Calnexin / Q000378:metabolism; D002232:Carbocyanines / Q000493:pharmacokinetics; D004357:Drug Synergism; D024202:Electrophoretic Mobility Shift Assay; D004705:Endocytosis / Q000187:drug effects / Q000502:physiology; D004791:Enzyme Inhibitors / Q000494:pharmacology; D065089:Glycoside Hydrolase Inhibitors; D006031:Glycosylation; D007371:Interferon-gamma / Q000494:pharmacology; D008077:Lipoproteins, LDL / Q000493:pharmacokinetics; D008264:Macrophages / Q000166:cytology / Q000378:metabolism*; D051379:Mice; D021381:Protein Transport / Q000187:drug effects / Q000502:physiology; D012333:RNA, Messenger / Q000032:analysis; D011956:Receptors, Cell Surface / Q000378:metabolism; D011971:Receptors, Immunologic / Q000235:genetics / Q000378:metabolism*; D051116:Receptors, Scavenger; D020133:Reverse Transcriptase Polymerase Chain Reaction; D051117:Scavenger Receptors, Class A; D000520:alpha-Glucosidases / Q000378:metabolism
chemical_list: D000970:Antineoplastic Agents; D002232:Carbocyanines; D004791:Enzyme Inhibitors; D065089:Glycoside Hydrolase Inhibitors; D008077:Lipoproteins, LDL; C495140:Msr1 protein, mouse; D012333:RNA, Messenger; D011956:Receptors, Cell Surface; D011971:Receptors, Immunologic; D051116:Receptors, Scavenger; D051117:Scavenger Receptors, Class A; C032629:acetyl-LDL; C097511:didodecylindocarbocyanine; D037281:Calnexin; D017485:1-Deoxynojirimycin; D007371:Interferon-gamma; C059896:miglustat; C034251:4-nitrophenyl-alpha-glucosidase; C042059:glucosidase I; D000520:alpha-Glucosidases