A new bile acid transporter? Wolters H, Kuipers F, Sloof Maarten JH, Vonk Roel J. ATP-dependent taurocholate transport in human liver plasma membrane. J Clin Invest 1992;90:2321–2326

Green tea catechins exhibit hypocholesterolemic effects probably via their inhibitory effects on intestinal bile acid absorption. Ileal apical sodium-dependent bile acid transporter (ASBT) is responsible for reabsorption of bile acids. The present studies were, therefore, designed to investigate the modulation of ASBT function and membrane expression by green tea catechins in human embryonic kidney HEK-293 cells stably transfected with ASBT-V5 fusion protein and intestinal Caco-2 monolayers. Our data showed that ASBT activity was significantly decreased by (−)-epigallocatechin-3-gallate (EGCG) but not other green tea catechins. Inhibition of PKC, phosphatidylinositol 3-kinase, and MAPK-dependent pathways failed to block the reduction in ASBT activity by EGCG. Kinetics studies showed a significant decrease in the Vmax of the transporter, whereas total ASBT content on the plasma membrane was unaltered by EGCG. Concomitant with the decrease in ASBT function, EGCG significantly reduced ASBT pool in the detergent-insoluble fraction, while increasing its presence in the detergent-soluble fraction of plasma membrane. Furthermore, EGCG decreased the association of ASBT with floating lipid raft fractions of cellular membrane on Optiprep density gradient. In conclusion, our data demonstrate a novel role of lipid rafts in the modulation of ASBT function by the dietary component EGCG, which may underlie the hypocholesterolemic effects of green tea.

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59 ATP-DEPENDENT TAUROCHOLATE TRANSPORT IN HUMAN LIVER PLASMA MEMBRANE VESICLES

Journal of Pediatric Gastroenterology and Nutrition ◽

10.1097/00005176-199210000-00083 ◽

1992 ◽

Vol 15 (3) ◽

pp. 350

Author(s):

H. Wolters ◽

F. Kuipers ◽

RJ. Vonk

Keyword(s):

Plasma Membrane ◽

Human Liver ◽

Membrane Vesicles ◽

Plasma Membrane Vesicles ◽

Liver Plasma Membrane ◽

Taurocholate Transport

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Modulation of ileal bile acid transporter (ASBT) activity by depletion of plasma membrane cholesterol: association with lipid rafts

AJP Gastrointestinal and Liver Physiology ◽

10.1152/ajpgi.00237.2007 ◽

2008 ◽

Vol 294 (2) ◽

pp. G489-G497 ◽

Cited By ~ 33

Author(s):

Fadi Annaba ◽

Zaheer Sarwar ◽

Pradeep Kumar ◽

Seema Saksena ◽

Jerrold R. Turner ◽

...

Keyword(s):

Plasma Membrane ◽

Bile Acid ◽

Lipid Rafts ◽

Cholesterol Content ◽

Membrane Cholesterol ◽

Hek 293 ◽

Hek 293 Cells ◽

293 Cells ◽

Bile Acid Transporter ◽

Acid Transporter

Apical sodium-dependent bile acid transporter (ASBT) represents a highly efficient conservation mechanism of bile acids via mediation of their active transport across the luminal membrane of terminal ileum. To gain insight into the cellular regulation of ASBT, we investigated the association of ASBT with cholesterol and sphingolipid-enriched specialized plasma membrane microdomains known as lipid rafts and examined the role of membrane cholesterol in maintaining ASBT function. Human embryonic kidney (HEK)-293 cells stably transfected with human ASBT, human ileal brush-border membrane vesicles, and human intestinal epithelial Caco-2 cells were utilized for these studies. Floatation experiments on Optiprep density gradients demonstrated the association of ASBT protein with lipid rafts. Disruption of lipid rafts by depletion of membrane cholesterol with methyl-β-cyclodextrin (MβCD) significantly reduced the association of ASBT with lipid rafts, which was paralleled by a decrease in ASBT activity in Caco-2 and HEK-293 cells treated with MβCD. The inhibition in ASBT activity by MβCD was blocked in the cells treated with MβCD-cholesterol complexes. Kinetic analysis revealed that MβCD treatment decreased the Vmax of the transporter, which was not associated with alteration in the plasma membrane expression of ASBT. Our study illustrates that cholesterol content of lipid rafts is essential for the optimal activity of ASBT and support the association of ASBT with lipid rafts. These findings suggest a novel mechanism by which ASBT activity may be rapidly modulated by alterations in cholesterol content of plasma membrane and thus have important implications in processes related to maintenance of bile acid and cholesterol homeostasis.

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