Cross-inhibition of SR-BI- and ABCA1-mediated cholesterol transport by the small molecules BLT-4 and glyburide.
Scavenger receptor class B type I (SR-BI) and ABCA1 are structurally dissimilar cell surface proteins that play key roles in HDL metabolism. SR-BI is a receptor that binds HDL with high affinity and mediates both the selective lipid uptake of cholesteryl esters from lipid-rich HDL to cells and the efflux of unesterified cholesterol from cells to HDL. ABCA1 mediates the efflux of unesterified cholesterol and phospholipids from cells to lipid-poor apolipoprotein A-I (apoA-I). The activities of ABCA1 and other ATP binding cassette superfamily members are inhibited by the drug glyburide, and SR-BI-mediated lipid transport is blocked by small molecule inhibitors called BLTs. Here, we show that one BLT, [1-(2-methoxy-phenyl)-3-naphthalen-2-yl-urea] (BLT-4), blocked ABCA1-mediated cholesterol efflux to lipid-poor apoA-I at a potency similar to that for its inhibition of SR-BI (IC(50) approximately 55-60 microM). Reciprocally, glyburide blocked SR-BI-mediated selective lipid uptake and efflux at a potency similar to that for its inhibition of ABCA1 (IC(50) approximately 275-300 microM). As is the case with BLTs, glyburide increased the apparent affinity of HDL binding to SR-BI. The reciprocal inhibition of SR-BI and ABCA1 by BLT-4 and glyburide raises the possibility that these proteins may share similar or common steps in their mechanisms of lipid transport.
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CHEMICAL CHEMICAL CHEMICAL CHEMICAL CHEMICAL CHEMICAL CHEMICAL CHEMICAL CHEMICAL CHEMICAL CHEMICAL CHEMICAL CHEMICAL CHEMICAL GENE-Y GENE-Y GENE-N GENE-Y GENE-Y GENE-Y GENE-N GENE-Y GENE-N GENE-N GENE-N GENE-Y GENE-Y GENE-Y GENE-N GENE-Y GENE-Y GENE-N GENE-Y GENE-Y GENE-Y GENE-Y GENE-Y GENE-Y GENE-Y
glyburide glyburide cholesteryl esters cholesterol cholesterol ATP glyburide BLT 1-(2-methoxy-phenyl)-3-naphthalen-2-yl-urea BLT-4 cholesterol glyburide glyburide cholesterol Scavenger receptor class B type I ABCA1 HDL SR-BI SR-BI ABCA1 HDL SR-BI HDL HDL HDL ABCA1 SR-BI apolipoprotein A-I ABCA1 apoA-I ABCA1 ATP binding cassette superfamily SR-BI ABCA1 apoA-I SR-BI SR-BI SR-BI ABCA1