Distinction in the mode of receptor-mediated endocytosis between high density lipoprotein and acetylated high density lipoprotein: evidence for high density lipoprotein receptor-mediated cholesterol transfer.
The interactions of high density lipoprotein (HDL) and acetylated high density lipoprotein (acetyl-HDL) with isolated rat sinusoidal liver cells have been investigated. Cellular binding of 125I-acetyl-HDL at 0 degrees C demonstrated the presence of a specific, saturable membrane-associated receptor. This receptor was affected neither by formaldehyde-treated albumin nor by low density lipoprotein modified either by acetylation or malondialdehyde, ligands known to undergo receptor-mediated endocytosis by the cells, indicating that the receptor for acetyl-HDL constitutes a distinct class among the scavenger receptors for chemically modified proteins. Parallel binding experiments using 125I-HDL also revealed the presence on these cells of a receptor for unmodified HDL. The ligand specificities of these two receptors were similar to each other except that the acetyl-HDL receptor was sensitive to polyanions such as dextran sulfate and fucoidin. Interaction of HDL with the cells at 37 degrees C was totally different from that of acetyl-HDL. Cellular binding of HDL was not accompanied by subsequent intracellular degradation of its apoprotein moiety, whereas its cholesterol moiety was significantly transferred to the cells. In contrast, acetyl-HDL was endocytosed and underwent lysosomal degradation as a holoparticle. This shift in receptor-recognition from the HDL receptor to the acetyl-HDL receptor was accomplished by acetylation of approximately 8% of the total lysine residues of HDL apoprotein. This unique difference in endocytic behavior between HDL and acetyl-HDL suggests a potential link of the HDL receptor to HDL-mediated cholesterol transfer in sinusoidal liver cells.
D000107:Acetylation; D000818:Animals; D001053:Apolipoproteins / Q000378:metabolism; D002352:Carrier Proteins; D002784:Cholesterol / Q000378:metabolism*; D003080:Cold Temperature; D004705:Endocytosis; D008075:Lipoproteins, HDL / Q000378:metabolism*; D008099:Liver / Q000378:metabolism; D008297:Male; D016601:RNA-Binding Proteins; D051381:Rats; D011919:Rats, Inbred Strains; D011956:Receptors, Cell Surface / Q000378:metabolism*; D018110:Receptors, Lipoprotein
D001053:Apolipoproteins; D002352:Carrier Proteins; D008075:Lipoproteins, HDL; D016601:RNA-Binding Proteins; D011956:Receptors, Cell Surface; D018110:Receptors, Lipoprotein; C031616:high density lipoprotein receptors; C075197:high density lipoprotein binding protein; D002784:Cholesterol