Characterization of two high-density lipoprotein binding sites on porcine hepatocyte plasma membranes: contribution of scavenger receptor class B type I (SR-BI) to the low-affinity component.
Two HDL(3) high- and low-affinity binding sites are present on the human hepatoma cell line (HepG(2)). Recently, we have suggested that the high-affinity binding sites might modulate the endocytosis of HDL through the low-affinity binding sites [Guendouzi, K. (1998) Biochemistry 37, 14974-14980], highlighting the physiological importance of this family of HDL high-affinity binding sites. The present data demonstrate the presence of HDL(3) high-affinity (K(d) = 0.37 microg/mL, B(max) = 260 ng/mg of protein) and low-affinity (K(d) = 86.2 microg/mL, B(max) = 14 300 ng/mg of protein) binding sites on purified porcine hepatocyte plasma membranes. By contrast, free apoA-I was strictly specific to the high-affinity sites (K(d) = 0.2 microg/mL and B(max) = 72 ng/mg of protein). Competition experiments between (125)I-labeled HDL(3) and either LDL, oxidized LDL, or anti-SR-BI IgG as competitors show that SR-BI is mostly responsible (70% displacement) for the binding of HDL(3) to the low-affinity binding sites. By contrast, the same competition experiments using (125)I-labeled free apoA-I clearly excluded SR-BI as the high-affinity binding receptor. We conclude that the binding of HDL onto hepatocyte plasma membranes involves: (1) two low-affinity binding receptors, one being SR-BI; (2) one family of high-affinity binding sites unrelated to SR-BI.
Martinez
L O
LO
Institut Féderatif de Recherche d'immunologie moleculaire et cellulaire, IFR 30, INSERM, Unité 326, Phospholipides membranaires, Signalisation cellulaire et Lipoprotéines, Hôpital Purpan, Toulouse, France.
Georgeaud
V
V
Rolland
C
C
Collet
X
X
Tercé
F
F
Perret
B
B
Barbaras
R
R
D000595:Amino Acid Sequence; D000818:Animals; D016632:Apolipoprotein A-I / Q000378:metabolism; D001667:Binding, Competitive; D018955:CD36 Antigens / Q000378:metabolism / Q000502:physiology; D002462:Cell Membrane / Q000737:chemistry / Q000378:metabolism; D004134:Dimyristoylphosphatidylcholine / Q000378:metabolism; D006801:Humans; D007700:Kinetics; D008075:Lipoproteins, HDL / Q000737:chemistry* / Q000302:isolation & purification / Q000378:metabolism*; D008099:Liver / Q000737:chemistry* / Q000166:cytology / Q000378:metabolism*; D008565:Membrane Proteins / Q000737:chemistry* / Q000302:isolation & purification / Q000378:metabolism*; D008969:Molecular Sequence Data; D011485:Protein Binding; D011971:Receptors, Immunologic / Q000378:metabolism / Q000502:physiology*; D018110:Receptors, Lipoprotein; D051116:Receptors, Scavenger; D051122:Scavenger Receptors, Class B; D013552:Swine
D016632:Apolipoprotein A-I; D018955:CD36 Antigens; D008075:Lipoproteins, HDL; D008565:Membrane Proteins; D011971:Receptors, Immunologic; D018110:Receptors, Lipoprotein; D051116:Receptors, Scavenger; C495124:SCARB1 protein, human; C454739:Scarb1 protein, mouse; D051122:Scavenger Receptors, Class B; D004134:Dimyristoylphosphatidylcholine