title: Niemann-pick type C1 (NPC1) overexpression alters cellular cholesterol homeostasis.
abstract: The Niemann-Pick type C1 (NPC1) protein is a key participant in intracellular trafficking of low density lipoprotein cholesterol, but its role in regulation of sterol homeostasis is not well understood. To characterize further the function of NPC1, we generated stable Chinese hamster ovary (CHO) cell lines overexpressing the human NPC1 protein (CHO/NPC1). NPC1 overexpression increases the rate of trafficking of low density lipoprotein cholesterol to the endoplasmic reticulum and the rate of delivery of endosomal cholesterol to the plasma membrane (PM). CHO/NPC1 cells exhibit a 1.5-fold increase in total cellular cholesterol and up to a 2.9-fold increase in PM cholesterol. This increase in PM cholesterol is closely paralleled by a 3-fold increase in de novo cholesterol synthesis. Inhibition of cholesterol synthesis results in marked redistribution of PM cholesterol to intracellular sites, suggesting an unsuspected role for NPC1 in internalization of PM cholesterol. Despite elevated total cellular cholesterol, CHO/NPC1 cells exhibit increased cholesterol synthesis, which may be attributable to both resistance to oxysterol suppression of sterol-regulated gene expression and to reduced endoplasmic reticulum cholesterol levels under basal conditions. Taken together, these studies provide important new insights into the role of NPC1 in the determination of the levels and distribution of cellular cholesterol.
authors.affiliation: Center for Cardiovascular Research, Department of Internal Medicine and the Department of Molecular Biology and Pharmacology, Washington University School of Medicine, St. Louis, Missouri 63110-1010, USA.
authors.forename: E E
authors.initials: EE
authors.lastname: Millard
authors.forename: K
authors.initials: K
authors.lastname: Srivastava
authors.forename: L M
authors.initials: LM
authors.lastname: Traub
authors.forename: J E
authors.initials: JE
authors.lastname: Schaffer
authors.forename: D S
authors.initials: DS
authors.lastname: Ory
mesh_terms: D000818:Animals; D016466:CHO Cells; D002352:Carrier Proteins; D002462:Cell Membrane / Q000378:metabolism; D002784:Cholesterol / Q000378:metabolism*; D002788:Cholesterol Esters / Q000378:metabolism; D006224:Cricetinae; D004721:Endoplasmic Reticulum / Q000378:metabolism; D011992:Endosomes / Q000378:metabolism; D006706:Homeostasis; D006801:Humans; D047908:Intracellular Signaling Peptides and Proteins; D008074:Lipoproteins / Q000378:metabolism; D008077:Lipoproteins, LDL / Q000378:metabolism; D008562:Membrane Glycoproteins; D000077296:Niemann-Pick C1 Protein; D009542:Niemann-Pick Diseases / Q000235:genetics; D011506:Proteins / Q000235:genetics / Q000378:metabolism*; D011994:Recombinant Proteins / Q000378:metabolism; D014162:Transfection
chemical_list: D002352:Carrier Proteins; D002788:Cholesterol Esters; D047908:Intracellular Signaling Peptides and Proteins; D008074:Lipoproteins; D008077:Lipoproteins, LDL; D008562:Membrane Glycoproteins; C106881:NPC1 protein, human; D000077296:Niemann-Pick C1 Protein; D011506:Proteins; D011994:Recombinant Proteins; C021976:cholesteryl linoleate; D002784:Cholesterol