Abstract
The lipolysis-stimulated receptor (LSR) is a lipoprotein receptor primarily expressed in the liver and activated by free fatty acids. Antibodies inhibiting LSR functions showed that the receptor is a heterotrimer or tetramer consisting of 68-kDa (alpha) and 56-kDa (beta) subunits associated through disulfide bridges. Screening of expression libraries with these antibodies led to identification of mRNAs derived by alternate splicing from a single gene and coding for proteins with molecular masses matching that of LSR alpha and beta. Antibodies directed against a synthetic peptide of LSR alpha and beta putative ligand binding domains inhibited LSR activity. Western blotting identified two liver proteins with the same apparent molecular mass as that of LSR alpha and beta. Transient transfections of LSR alpha alone in Chinese hamster ovary cells increased oleate-induced binding and uptake of lipoproteins, while cotransfection of both LSR alpha and beta increased oleate-induced proteolytic degradation of the particles. The ligand specificity of LSR expressed in cotransfected Chinese hamster ovary cells closely matched that previously described using fibroblasts from subjects lacking the low density lipoprotein receptor. LSR affinity is highest for the triglyceride-rich lipoproteins, chylomicrons, and very low density lipoprotein. We speculate that LSR is a rate-limiting step for the clearance of dietary triglycerides and plays a role in determining their partitioning between the liver and peripheral tissues.
Highlights
Chylomicrons transport, in plasma, dietary triglycerides (TG)1 and liposoluble vitamins absorbed by the intestine after a meal [1]
The lipolysis-stimulated receptor (LSR) is a lipoprotein receptor primarily expressed in the liver and activated by free fatty acids
Screening of expression libraries with these antibodies led to identification of mRNAs derived by alternate splicing from a single gene and coding for proteins with molecular masses matching that of LSR ␣ and 
Summary
Chylomicrons transport, in plasma, dietary triglycerides (TG) and liposoluble vitamins absorbed by the intestine after a meal [1]. The residues of chylomicrons are released from the endothelium and taken up by the liver Both the low density lipoprotein (LDL) receptor and the LDL receptor-related protein (LRP) contribute to this process [2, 3]. We have reported the characterization of a lipoprotein receptor that is inhibited by receptor-associated protein at concentrations similar to those achieved in the receptor-associated protein overexpression study [9] This receptor was originally identified by its binding of LDL in the presence of FFA and is hereafter referred to as the lipolysis-stimulated receptor (LSR). We propose that LSR represents a rate-limiting step for the clearance of dietary TG from the circulation
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