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Papers In Press, published online ahead of print October 1, 2007
J. Lipid Res., doi:10.1194/jlr.M700102-JLR200

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Journal of Lipid Research, Vol. 48, 2193-2211, October 2007
Copyright © 2007 by American Society for Biochemistry and Molecular Biology

SCP-2/SCP-x gene ablation alters lipid raft domains in primary cultured mouse hepatocytes

Barbara P. Atshaves^*, Avery L. McIntosh^*, H. Ross Payne, Adalberto M. Gallegos, Kerstin Landrock^*, Nobuyo Maeda, Ann B. Kier and Friedhelm Schroeder^1,*

^* Department of Physiology and Pharmacology, Texas A&M University, Texas Veterinary Medical Center, College Station, TX 77843-4466
Department of Pathobiology, Texas A&M University, TVMC, College Station, TX 77843-4467
Department of Pathology, University of North Carolina at Chapel Hill, Chapel Hill, NC 27599-7525

The online version of this article (available at http://www.jlr.org) contains supplementary data in the form of one figure and five tables.

Published, JLR Papers in Press, July 3, 2007.

¹ To whom correspondence should be addressed. e-mail: fschroeder{at}cvm.tamu.edu

Although reverse cholesterol transport from peripheral cell types is mediated through plasma membrane microdomains termed lipid rafts, almost nothing is known regarding the existence, protein/lipid composition, or structure of these putative domains in liver hepatocytes, cells responsible for the net removal of cholesterol from the body. Lipid rafts purified from hepatocyte plasma membranes by a nondetergent affinity chromatography method were: i) present at 33 ± 3% of total plasma membrane protein; ii) enriched in key proteins of the reverse cholesterol pathway [scavenger receptor class B type I (SR-B1), ABCA1, P-glycoprotein (P-gp), sterol carrier protein-2 (SCP-2)]; iii) devoid of caveolin-1; iv) enriched in cholesterol, sphingomyelin, GM1, and phospholipids low in polyunsaturated fatty acid and double bond index; and v) exhibited an intermediate liquid-ordered lipid phase with significant transbilayer fluidity gradient. Ablation of the gene encoding SCP-2 significantly altered lipid rafts to: i) increase the proportion of lipid rafts present, thereby increasing raft total content of ABCA1, P-gp, and SR-B1; ii) increase total phospholipids while decreasing GM1 in lipid rafts; iii) decrease the fluidity of lipid rafts, consistent with the increased intermediate liquid-ordered phase; and iv) abolish the lipid raft transbilayer fluidity gradient. Thus, despite the absence of caveolin-1 in liver hepatocytes, lipid rafts represented nearly one-third of the mouse hepatocyte plasma membrane proteins and displayed unique protein, lipid, and biophysical properties that were differentially regulated by SCP-2 expression.

Supplementary key words sterol carrier protein • SR-B1 • reverse cholesterol transport • ABCA1

Abbreviations: apoA-I, apolipoprotein A-I; cis-parinaric acid, 9Z,11E,13E,15Z-octatetradecanoic acid; ConA, concanavalin A; DBI, double bond index; DHE, dehydroergosterol; DPH, 1,6-diphenyl-1,3,5-hexatriene; DPH-Pro, 3(1,6-diphenyl-1,3,5-hexatrienyl)-propionic acid; DPH-TMA, 1,6-diphyenyl-1,3,5-hexatrienyl-trimethylammonium; eNOS, endothelial nitic oxide synthase; L-FABP, liver fatty acid binding protein; NBD-stearic acid, 12-(N-methyl)-N-[(7-nitrobenz-2-oxa-1,3-diazol-4-yl)amino]-octadecanoic acid; PA, phosphatidic acid; PC, choline glycerophospholipid; PE, ethanolamine glycerophospholipid; P-gp, P-glycoprotein; PI, phosphatidylinositol; PS, phosphatidylserine; RCT, reverse cholesterol transport; SCP-2, sterol carrier protein-2; SM, sphingomyelin; SR-B1, scavenger receptor class B type I

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