Apolipoprotein A-I stimulates the transport of intracellular cholesterol to cell-surface cholesterol-rich domains (caveolae).
We have studied the effect of lipid-free human plasma apolipoprotein A-I (apoA-I) on the transport of newly synthesized cholesterol to cell-surface cholesterol-rich domains, which in human skin fibroblasts are mainly represented by caveolae. Changes in transport of newly synthesized cholesterol were assessed after labelling cells with [(14)C]acetate at 15 degrees C and warming cells to permit the transfer of cholesterol, followed by the selective oxidation of cholesterol in cholesterol-rich domains (caveolae) in the plasma membrane before their partial purification. ApoA-I, but not BSA added in an equimolar concentration, enhanced the transport of cholesterol to the caveolae up to 5-fold in a dose- and time-dependent manner. The effect of apoA-I on cholesterol transport exceeded its effect on cholesterol efflux, resulting in an accumulation of intracellular cholesterol in caveolae. Methyl-beta-cyclodextrin, added at a concentration promoting cholesterol efflux to the same extent as apoA-I, also stimulated cholesterol trafficking, but was 3-fold less effective than apoA-I. Progesterone inhibited the transport of newly synthesized cholesterol to the caveolae. Treatment of cells with apoA-I stimulated the expression of caveolin, increasing the amount of caveolin protein and mRNA by approx. 2-fold. We conclude that apoA-I induces the transport of intracellular cholesterol to cell-surface caveolae, possibly in part through the stimulation of caveolin expression.
Sviridov
D
D
Baker Medical Research Institute, P.O. Box 6492, Melbourne, Vic. 8008, Australia. dmitri.sviridov@baker.edu.au
Fidge
N
N
Beaumier-Gallon
G
G
Fielding
C
C
D016632:Apolipoprotein A-I / Q000737:chemistry* / Q000494:pharmacology*; D001692:Biological Transport; D021941:Caveolae / Q000378:metabolism*; D002462:Cell Membrane / Q000378:metabolism*; D002478:Cells, Cultured; D002784:Cholesterol / Q000737:chemistry / Q000378:metabolism*; D003505:Cyclodextrins / Q000494:pharmacology; D004305:Dose-Response Relationship, Drug; D005347:Fibroblasts / Q000378:metabolism; D006801:Humans; D050356:Lipid Metabolism; D011374:Progesterone / Q000494:pharmacology; D012333:RNA, Messenger / Q000378:metabolism; D012867:Skin / Q000378:metabolism; D013696:Temperature; D013997:Time Factors; D047392:beta-Cyclodextrins
D016632:Apolipoprotein A-I; D003505:Cyclodextrins; D012333:RNA, Messenger; D047392:beta-Cyclodextrins; C108732:methyl-beta-cyclodextrin; D011374:Progesterone; D002784:Cholesterol