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Journal of Lipid Research, Vol. 47, 51-58, January 2006 Reevaluation of the role of the multidrug-resistant P-glycoprotein in cellular cholesterol homeostasis
* Department of Cell Biology NC10, Cleveland Clinic Foundation, Cleveland, OH Published, JLR Papers in Press, October 7, 2005.
1 To whom correspondence should be addressed. e-mail:smithj4{at}.ccf.org The multidrug resistance P-glycoprotein (P-gp) was recently proposed to redistribute cholesterol in the plasma membrane, suggesting that P-gp could modulate cholesterol efflux to cholesterol acceptors. To address this hypothesis and to reevaluate the role of P-gp in cholesterol homeostasis, we first analyzed the role of P-gp expression on cholesterol efflux in P-gp stably transfected drug-selected LLC-MDR1 cells. Cholesterol efflux to methyl-ß-cyclodextrin (CD) was 4-fold higher in LLC-MDR1 cells compared with control LLC-PK1 cells, indicating that the accessible pool of plasma membrane cholesterol was increased by P-gp expression. However, using the P-gp-inducible cells lines HeLa MDR-Tet and 77.1 MDR-Tet, cholesterol efflux to CD, apolipoprotein A-I, or HDL was not associated with P-gp expression. In addition, we did not observe any effect of P-gp expression on cellular free and esterified cholesterol content, cholesteryl ester uptake from LDL and HDL particles, or acyl-CoA:cholesterol acyltransferase activity. Therefore, we conclude that P-gp expression does not play a major role in cholesterol homeostasis in P-gp-inducible cells and that the effects of P-gp on cholesterol homeostasis previously described in drug-selected cells might result from non-P-gp pathways that were also induced by selection for drug resistance.
Supplementary key words cholesterol efflux ABCA1 cyclodextrin apolipoprotein A-I Abbreviations: apoA-I, apolipoprotein A-I; CD, methyl-ß-cyclodextrin; CE, cholesteryl ester; COE, cholesteryl oleyl ether; DAPI, 4',6-diamidino-2-phenylindole; FC, free cholesterol; MDR, multidrug resistance; P-gp, P-glycoprotein; Rho-123, rhodamine 123
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