title: ORP2, a homolog of oxysterol binding protein, regulates cellular cholesterol metabolism.
abstract: Oxysterol binding protein (OSBP) related proteins (ORPs) constitute a family that has at least 12 members in humans. In the present study we characterize one of the novel OSBP homologs, ORP2, which we show to be expressed ubiquitously in mammalian tissues. The ORP2 cDNA encodes a deduced 55 kDa protein that lacks a pleckstrin homology (PH) domain, a feature found in the other family members. Sucrose gradient centrifugation analysis of Chinese hamster ovary (CHO) cell post-nuclear supernatant demonstrated that ORP2 is distributed in soluble and membrane-bound fractions. Immunofluorescence microscopy of the endogenous and overexpressed ORP2 in CHO cells suggested that the membrane-bound fraction of the protein localizes to the Golgi apparatus. Stably transfected CHO cells that overexpress ORP2 showed an increase in [14C]cholesterol efflux to serum, apolipoprotein A-I (apoA-I), and phosphatidyl choline vesicles. The proportion of cellular [14C]cholesterol that is esterified and the ACAT activity measured as [14C]oleyl-CoA conversion into cholesteryl [14C]oleate by the cellular membranes, were markedly decreased in the ORP2 expressing cells. Transient high level overexpression of ORP2 interfered with the clearance of a secretory pathway protein marker from the Golgi complex. The results implicate ORP2 as a novel regulator of cellular sterol homeostasis and intracellular membrane trafficking.
authors.affiliation: Department of Molecular Medicine, National Public Health Institute, Biomedicum, P.O. Box 104, FIN-00251 Helsinki, Finland.
authors.forename: Saara
authors.initials: S
authors.lastname: Laitinen
authors.forename: Markku
authors.initials: M
authors.lastname: Lehto
authors.forename: Sanna
authors.initials: S
authors.lastname: Lehtonen
authors.forename: Kati
authors.initials: K
authors.lastname: Hyvärinen
authors.forename: Sanna
authors.initials: S
authors.lastname: Heino
authors.forename: Eero
authors.initials: E
authors.lastname: Lehtonen
authors.forename: Christian
authors.initials: C
authors.lastname: Ehnholm
authors.forename: Elina
authors.initials: E
authors.lastname: Ikonen
authors.forename: Vesa M
authors.initials: VM
authors.lastname: Olkkonen
mesh_terms: D016632:Apolipoprotein A-I / Q000378:metabolism; D002460:Cell Line; D002784:Cholesterol / Q000378:metabolism*; D006056:Golgi Apparatus / Q000378:metabolism; D006801:Humans; D010713:Phosphatidylcholines / Q000378:metabolism*; D012333:RNA, Messenger / Q000096:biosynthesis; D011987:Receptors, Steroid / Q000235:genetics / Q000378:metabolism*; D014018:Tissue Distribution; D000098825:Oxysterol Binding Proteins
chemical_list: D016632:Apolipoprotein A-I; C461064:OSBPL2 protein, human; D010713:Phosphatidylcholines; D012333:RNA, Messenger; D011987:Receptors, Steroid; D000098825:Oxysterol Binding Proteins; D002784:Cholesterol