title: Functional characterization of newly-discovered mutations in human SR-BI.
abstract: In rodents, SR-BI has been firmly established as a physiologically relevant HDL receptor that mediates removal of HDL-cholesteryl esters (CE). However, its role in human lipoprotein metabolism is less defined. Recently, two unique point mutations in human SR-BI - S112F or T175A - were identified in subjects with high HDL-cholesterol (HDL-C) levels. We hypothesized that mutation of these conserved residues would compromise the cholesterol-transport functions of SR-BI. To test this hypothesis, S112F- and T175A-SR-BI were generated by site-directed mutagenesis. Cell surface expression was confirmed for both mutant receptors in COS-7 cells upon transient transfection, albeit at lower levels for T175A-SR-BI. Both mutant receptors displayed defective HDL binding, selective uptake of HDL-CE and release of free cholesterol (FC) from cells to HDL. Mutant receptors were also unable to re-organize plasma membrane pools of FC. While these impaired functions were independent of receptor oligomerization, inability of T175A-SR-BI to mediate cholesterol-transport functions could be related to altered N-linked glycosylation status. In conclusion, high HDL-C levels observed in carriers of S112F- or T175A-SR-BI mutant receptors are consistent with the inability of these SR-BI receptors to mediate efficient selective uptake of HDL-CE, and suggest that increased plasma HDL concentrations in these settings may not be associated with lower risk of cardiovascular disease.
authors.affiliation: Department of Pharmacology and Toxicology, Medical College of Wisconsin, Milwaukee, WI, USA.
authors.forename: Alexandra C
authors.initials: AC
authors.lastname: Chadwick
authors.forename: Daisy
authors.initials: D
authors.lastname: Sahoo
mesh_terms: D000818:Animals; D018955:CD36 Antigens / Q000235:genetics / Q000502:physiology*; D019556:COS Cells; D002522:Chlorocebus aethiops; D006031:Glycosylation; D006801:Humans; D016297:Mutagenesis, Site-Directed; D009154:Mutation
chemical_list: D018955:CD36 Antigens