OSBP-related protein 8 (ORP8) suppresses ABCA1 expression and cholesterol efflux from macrophages.
ORP8 is a previously unexplored member of the family of oxysterol-binding protein-related proteins (ORP). We now report the expression pattern, the subcellular distribution, and data on the ligand binding properties and the physiological function of ORP8. ORP8 is localized in the endoplasmic reticulum (ER) via its C-terminal transmembrane span and binds 25-hydroxycholesterol, identifying it as a new ER oxysterol-binding protein. ORP8 is expressed at highest levels in macrophages, liver, spleen, kidney, and brain. Immunohistochemical analysis revealed ORP8 in the shoulder regions of human coronary atherosclerotic lesions, where it is present in CD68(+) macrophages. In advanced lesions the ORP8 mRNA was up-regulated 2.7-fold as compared with healthy coronary artery wall. Silencing of ORP8 by RNA interference in THP-1 macrophages increased the expression of ATP binding cassette transporter A1 (ABCA1) and concomitantly cholesterol efflux to lipid-free apolipoprotein A-I but had no significant effect on ABCG1 expression or cholesterol efflux to spherical high density lipoprotein HDL(2). Experiments employing an ABCA1 promoter-luciferase reporter confirmed that ORP8 silencing enhances ABCA1 transcription. The silencing effect was partially attenuated by mutation of the DR4 element in the ABCA1 promoter and synergized with that of the liver X receptor agonist T0901317. Furthermore, inactivation of the E-box in the promoter synergized with ORP8 silencing, suggesting that the suppressive effect of ORP8 involves both the liver X receptor and the E-box functions. Our data identify ORP8 as a negative regulator of ABCA1 expression and macrophage cholesterol efflux. ORP8 may, thus, modulate the development of atherosclerosis.
Yan
Daoguang
D
Department of Molecular Medicine, National Public Health Institute, Biomedicum, FI-00251 Helsinki, Finland.
Mäyränpää
Mikko I
MI
Wihuri Research Institute, FI-00140 Helsinki, Finland; Department of Forensic Medicine, University of Helsinki, FI-00014 Helsinki, Finland.
Wong
Jenny
J
School of Biotechnology and Biomolecular Sciences, The University of New South Wales, Sydney 2052, Australia.
Perttilä
Julia
J
Department of Molecular Medicine, National Public Health Institute, Biomedicum, FI-00251 Helsinki, Finland.
Lehto
Markku
M
Department of Molecular Medicine, National Public Health Institute, Biomedicum, FI-00251 Helsinki, Finland.
Jauhiainen
Matti
M
Department of Molecular Medicine, National Public Health Institute, Biomedicum, FI-00251 Helsinki, Finland.
Kovanen
Petri T
PT
Wihuri Research Institute, FI-00140 Helsinki, Finland.
Ehnholm
Christian
C
Department of Molecular Medicine, National Public Health Institute, Biomedicum, FI-00251 Helsinki, Finland.
Brown
Andrew J
AJ
School of Biotechnology and Biomolecular Sciences, The University of New South Wales, Sydney 2052, Australia.
Olkkonen
Vesa M
VM
Department of Molecular Medicine, National Public Health Institute, Biomedicum, FI-00251 Helsinki, Finland. Electronic address: vesa.olkkonen@ktl.fi.
D064286:ATP Binding Cassette Transporter 1; D018528:ATP-Binding Cassette Transporters / Q000235:genetics / Q000378:metabolism*; D015703:Antigens, CD / Q000378:metabolism; D015214:Antigens, Differentiation, Myelomonocytic / Q000378:metabolism; D015153:Blotting, Western; D002352:Carrier Proteins / Q000235:genetics / Q000378:metabolism*; D002460:Cell Line; D002784:Cholesterol / Q000378:metabolism*; D003331:Coronary Vessels / Q000737:chemistry / Q000378:metabolism; D004268:DNA-Binding Proteins / Q000037:antagonists & inhibitors; D006801:Humans; D006845:Hydrocarbons, Fluorinated; D007150:Immunohistochemistry; D000071518:Liver X Receptors; D008156:Luciferases / Q000235:genetics / Q000378:metabolism; D008264:Macrophages / Q000166:cytology / Q000187:drug effects / Q000378:metabolism*; D008856:Microscopy, Fluorescence; D008957:Models, Genetic; D057093:Orphan Nuclear Receptors; D011401:Promoter Regions, Genetic / Q000235:genetics; D034622:RNA Interference; D012333:RNA, Messenger / Q000235:genetics / Q000378:metabolism; D018160:Receptors, Cytoplasmic and Nuclear / Q000037:antagonists & inhibitors; D011987:Receptors, Steroid / Q000235:genetics / Q000378:metabolism*; D011993:Recombinant Fusion Proteins / Q000235:genetics / Q000378:metabolism; D013449:Sulfonamides / Q000494:pharmacology; D014158:Transcription, Genetic / Q000187:drug effects; D014162:Transfection; D000098825:Oxysterol Binding Proteins; D000097382:CD68 Molecule; D005466:Fluorocarbons; D000096926:Benzenesulfonamides
D064286:ATP Binding Cassette Transporter 1; D018528:ATP-Binding Cassette Transporters; D015703:Antigens, CD; D015214:Antigens, Differentiation, Myelomonocytic; D002352:Carrier Proteins; D002784:Cholesterol; D004268:DNA-Binding Proteins; D006845:Hydrocarbons, Fluorinated; D000071518:Liver X Receptors; D008156:Luciferases; D057093:Orphan Nuclear Receptors; D012333:RNA, Messenger; D018160:Receptors, Cytoplasmic and Nuclear; D011987:Receptors, Steroid; D011993:Recombinant Fusion Proteins; D013449:Sulfonamides; D000098825:Oxysterol Binding Proteins; C577836:ABCA1 protein, human; C067980:CD68 antigen, human; D000097382:CD68 Molecule; C423915:T0901317; D005466:Fluorocarbons; D000096926:Benzenesulfonamides