title: Overexpression of OSBP-related protein 2 (ORP2) induces changes in cellular cholesterol metabolism and enhances endocytosis.
abstract: ORP2 [OSBP (oxysterol-binding protein)-related protein 2] belongs to the 12-member mammalian ORP gene/protein family. We characterize in the present study the effects of inducible ORP2 overexpression on cellular cholesterol metabolism in HeLa cells and compare the results with those obtained for CHO cells (Chinese-hamster ovary cells) that express ORP2 constitutively. In both cell systems, the prominent phenotype is enhancement of [14C]cholesterol efflux to all extracellular acceptors, which results in a reduction of cellular free cholesterol. No change was observed in the plasma membrane cholesterol content or distribution between raft and non-raft domains upon ORP2 expression. However, elevated HMG-CoA (3-hydroxy-3-methylglutaryl-CoA) reductase activity and LDL (low-density lipoprotein) receptor expression, as well as enhanced transport of newly synthesized cholesterol to a cyclodextrin-accessible pool, suggest that the ORP2 expression stimulates transport of cholesterol out of the endoplasmic reticulum. In contrast with ORP2/CHO cells, the inducible ORP2/HeLa cells do not show down-regulation of cholesterol esterification, suggesting that this effect represents an adaptive response to long-term cholesterol depletion in the CHO cell model. Finally, we provide evidence that ORP2 binds PtdIns(3,4,5)P(3) and enhances endocytosis, phenomena that are probably interconnected. Our results suggest a function of ORP2 in both cholesterol trafficking and control of endocytic membrane transport.
authors.affiliation: Department of Molecular Medicine, National Public Health Institute, Biomedicum, P.O. Box 104, Helsinki FI-00251, Finland.
authors.forename: Riikka
authors.initials: R
authors.lastname: Hynynen
authors.forename: Saara
authors.initials: S
authors.lastname: Laitinen
authors.forename: Reijo
authors.initials: R
authors.lastname: Käkelä
authors.forename: Kimmo
authors.initials: K
authors.lastname: Tanhuanpää
authors.forename: Sari
authors.initials: S
authors.lastname: Lusa
authors.forename: Christian
authors.initials: C
authors.lastname: Ehnholm
authors.forename: Pentti
authors.initials: P
authors.lastname: Somerharju
authors.forename: Elina
authors.initials: E
authors.lastname: Ikonen
authors.forename: Vesa M
authors.initials: VM
authors.lastname: Olkkonen
mesh_terms: D000818:Animals; D001693:Biological Transport, Active; D016466:CHO Cells; D002784:Cholesterol / Q000378:metabolism*; D006224:Cricetinae; D004705:Endocytosis / Q000502:physiology*; D004951:Esterification; D005786:Gene Expression Regulation / Q000502:physiology; D006367:HeLa Cells; D006801:Humans; D021962:Membrane Microdomains / Q000502:physiology; D011973:Receptors, LDL / Q000096:biosynthesis; D011987:Receptors, Steroid / Q000096:biosynthesis*; D000098825:Oxysterol Binding Proteins
chemical_list: D002784:Cholesterol; D011973:Receptors, LDL; D011987:Receptors, Steroid; C461064:OSBPL2 protein, human; D000098825:Oxysterol Binding Proteins