1. Serum amyloid A is a ligand for scavenger receptor class B type I and inhibits high density lipoprotein binding and selective lipid uptake.
- Author
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Cai L, de Beer MC, de Beer FC, and van der Westhuyzen DR
- Subjects
- Adenoviridae genetics, Animals, CD36 Antigens, CHO Cells, Cell Line, Cholesterol Esters metabolism, Cricetinae, Dose-Response Relationship, Drug, Gene Transfer Techniques, Humans, Ligands, Mice, Microscopy, Confocal, Protein Binding, Protein Isoforms, Receptors, Immunologic metabolism, Receptors, Scavenger, Scavenger Receptors, Class B, Temperature, Time Factors, Lipid Metabolism, Lipoproteins, HDL metabolism, Receptors, Immunologic physiology, Serum Amyloid A Protein biosynthesis
- Abstract
Serum amyloid A is an acute phase protein that is carried in the plasma largely as an apolipoprotein of high density lipoprotein (HDL). In this study we investigated whether SAA is a ligand for the HDL receptor, scavenger receptor class B type I (SR-BI), and how SAA may influence SR-BI-mediated HDL binding and selective cholesteryl ester uptake. Studies using Chinese hamster ovary cells expressing SR-BI showed that (125)I-labeled SAA, both in lipid-free form and in reconstituted HDL particles, functions as a high affinity ligand for SR-BI. SAA also bound with high affinity to the hepatocyte cell line, HepG2. Alexa-labeled SAA was shown by fluorescence confocal microscopy to be internalized by cells in a SR-BI-dependent manner. To assess how SAA association with HDL influences HDL interaction with SR-BI, SAA-containing HDL was isolated from mice overexpressing SAA through adenoviral gene transfer. SAA presence on HDL had little effect on HDL binding to SR-BI but decreased (30-50%) selective cholesteryl ester uptake. Lipid-free SAA, unlike lipid-free apoA-I, was an effective inhibitor of both SR-BI-dependent binding and selective cholesteryl ester uptake of HDL. We have concluded that SR-BI plays a key role in SAA metabolism through its ability to interact with and internalize SAA and, further, that SAA influences HDL cholesterol metabolism through its inhibitory effects on SR-BI-mediated selective lipid uptake.
- Published
- 2005
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