Identification of the molecular target of small molecule inhibitors of HDL receptor SR-BI activity.
Scavenger receptor, class B, type I (SR-BI), controls high-density lipoprotein (HDL) metabolism by mediating cellular selective uptake of lipids from HDL without the concomitant degradation of the lipoprotein particle. We previously identified in a high-throughput chemical screen of intact cells five compounds (BLT-1-5) that inhibit SR-BI-dependent lipid transport from HDL, but do not block HDL binding to SR-BI on the cell surface. Although these BLTs are widely used to examine the diverse functions of SR-BI, their direct target(s), SR-BI itself or some other component of the SR-BI pathway, has not been identified. Here we show that SR-BI in the context of a membrane lipid environment is the target of BLT-1, -3, -4, and -5. The analysis using intact cells and an in vitro system of purified SR-BI reconstituted into liposomes was aided by information derived from structure-activity relationship (SAR) analysis of the most potent of these BLTs, the thiosemicarbazone BLT-1. We found that the sulfur atom of BLT-1 was crucially important for its inhibitory activity, because changing it to an oxygen atom resulted in the isostructural, but essentially inactive, semicarbazone derivative BLT-1sc. SAR analysis also established the importance of BLT-1's hydrophobic tail. BLTs and their corresponding inactive compounds can be used to explore the mechanism and function of SR-BI-mediated selective lipid uptake in diverse mammalian experimental models. Consequently, BLTs may help determine the therapeutic potential of SR-BI-targeted pharmaceutical drugs.
Nieland
Thomas J F
TJ
Department of Biology, Massachusetts Institute of Technology, Room 68-483, 77 Massachusetts Avenue, Cambridge, Massachusetts 02139, USA.
Shaw
Jared T
JT
Jaipuri
Firoz A
FA
Duffner
Jay L
JL
Koehler
Angela N
AN
Banakos
Sotirios
S
Zannis
Vassilis I
VI
Kirchhausen
Tomas
T
Krieger
Monty
M
D000588:Amines / Q000737:chemistry / Q000494:pharmacology; D001692:Biological Transport / Q000187:drug effects; D018955:CD36 Antigens / Q000378:metabolism*; D002460:Cell Line; D003517:Cyclopentanes / Q000737:chemistry / Q000494:pharmacology; D006801:Humans; D050356:Lipid Metabolism / Q000187:drug effects; D008075:Lipoproteins, HDL / Q000037:antagonists & inhibitors / Q000378:metabolism*; D008081:Liposomes / Q000378:metabolism; D015394:Molecular Structure; D011485:Protein Binding / Q000187:drug effects; D018110:Receptors, Lipoprotein / Q000037:antagonists & inhibitors / Q000378:metabolism*; D013329:Structure-Activity Relationship; D020349:Surface Plasmon Resonance; D013882:Thiosemicarbazones / Q000138:chemical synthesis / Q000737:chemistry / Q000494:pharmacology*
D000588:Amines; D018955:CD36 Antigens; D003517:Cyclopentanes; D008075:Lipoproteins, HDL; D008081:Liposomes; D018110:Receptors, Lipoprotein; D013882:Thiosemicarbazones; C031616:high density lipoprotein receptors