Caveolin-1 negatively regulates SR-BI mediated selective uptake of high-density lipoprotein-derived cholesteryl ester.
The class B, type I scavenger receptor (SR-BI) mediates the selective uptake of high density lipoprotein (HDL) cholesteryl esters and the efflux of free cholesterol. SR-BI is predominantly associated with caveolae in Chinese hamster ovary cells. The caveola protein, caveolin-1, binds to cholesterol and is involved in intracellular cholesterol trafficking. We previously demonstrated a correlative increase in caveolin-1 expression and the selective uptake of HDL cholesteryl esters in phorbol ester-induced differentiated THP-1 cells. The goal of the present study was to determine if the expression of caveolin-1 is the causative factor in increasing selective cholesteryl ester uptake in macrophages. To test this, we established RAW and J-774 cell lines that stably expressed caveolin-1. Transfection with caveolin-1 cDNA did not alter the amount of 125I-labeled HDL that associated with the cells, although selective uptake of HDL [3H]cholesteryl ether was decreased by approximately 50%. The amount of [3H]cholesterol effluxed to HDL was not affected by caveolin-1. To directly address whether caveolin-1 inhibits SR-BI-dependent selective cholesteryl ester uptake, we overexpressed caveolin-1 by adenoviral vector gene transfer in Chinese hamster ovary cells stably transfected with SR-BI. Caveolin-1 inhibited the selective uptake of HDL [3H]cholesteryl ether by 50-60% of control values without altering the extent of cell associated HDL. We next used blocking antibodies to CD36 and SR-BI to demonstrate that the increase in selective [3H]cholesteryl ether uptake previously seen in differentiated THP-1 cells was independent of SR-BI. Finally, we used beta-cyclodextrin and caveolin overexpression to demonstrate that caveolae depleted of cholesterol facilitate SR-BI-dependent selective cholesteryl ester uptake and caveolae containing excess cholesterol inhibit uptake. We conclude that caveolin-1 is a novel negative regulator of SR-BI-dependent selective cholesteryl ester uptake.
Matveev
S
S
Department of Physiology, University of Kentucky Medical School, Lexington 40536, USA.
Uittenbogaard
A
A
van Der Westhuyzen
D
D
Smart
E J
EJ
D000818:Animals; D000906:Antibodies / Q000494:pharmacology; D018955:CD36 Antigens / Q000276:immunology / Q000378:metabolism*; D016466:CHO Cells; D021941:Caveolae / Q000187:drug effects / Q000378:metabolism; D051242:Caveolin 1; D022461:Caveolins / Q000235:genetics / Q000378:metabolism*; D002454:Cell Differentiation / Q000187:drug effects; D002478:Cells, Cultured; D002784:Cholesterol / Q000493:pharmacokinetics*; D006224:Cricetinae; D004952:Esters / Q000493:pharmacokinetics; D006801:Humans; D008075:Lipoproteins, HDL / Q000378:metabolism*; D008264:Macrophages / Q000166:cytology / Q000187:drug effects / Q000378:metabolism; D008565:Membrane Proteins; D051379:Mice; D011971:Receptors, Immunologic; D018110:Receptors, Lipoprotein / Q000378:metabolism; D051116:Receptors, Scavenger; D051122:Scavenger Receptors, Class B; D013755:Tetradecanoylphorbol Acetate / Q000494:pharmacology; D014162:Transfection
D000906:Antibodies; C495540:CAV1 protein, human; D018955:CD36 Antigens; C495541:Cav1 protein, mouse; D051242:Caveolin 1; D022461:Caveolins; D004952:Esters; D008075:Lipoproteins, HDL; D008565:Membrane Proteins; D011971:Receptors, Immunologic; D018110:Receptors, Lipoprotein; D051116:Receptors, Scavenger; C495124:SCARB1 protein, human; C454739:Scarb1 protein, mouse; D051122:Scavenger Receptors, Class B; D002784:Cholesterol; D013755:Tetradecanoylphorbol Acetate