Human monocyte-derived macrophages express an approximately 120-kD Ox-LDL binding protein with strong identity to CD68.
A protein that specifically binds oxidized LDL (Ox-LDL) has recently been characterized in mouse peritoneal macrophages and identified as macrosialin, a protein with a molecular weight of 95 kD. First, the present work shows that human monocyte-derived macrophages express a membrane protein with a molecular weight of approximately 120 kD that selectively binds Ox-LDL. Second, we tested whether this approximately 120-kD Ox-LDL binding protein had any relation to CD68, the human homologue of macrosialin. The following evidence was obtained to support the role of CD68 as an Ox-LDL binding protein: (1) Ligand blots with Ox-LDL and Western blots with Ki-M6, an anti-human CD68 monoclonal antibody, revealed a single band with a molecular weight of approximately 120 kD under reducing and nonreducing condition. (2) The expression patterns of the approximately 120-kD Ox-LDL binding membrane protein and of CD68 paralleled each other during monocyte/macrophage differentiation. (3) Digestion with N-glycosidase F demonstrated that both CD68 and the Ox-LDL binding protein are glycoproteins; both showed a similar shift of approximately 18 kD in apparent molecular weight. (4) CD68, probed with monoclonal antibody Ki-M6, and the approximately 120-kD Ox-LDL binding protein were coprecipitated with EMB11, another anti-CD68 antibody. About 5000 molecules of CD68 are expressed on the cell surface of human macrophages. Ligation of 125I-Ki-M6 to cells leads to its internalization and degradation. This capacity would be sufficient to allow for the specific uptake and degradation of Ox-LDL. Taken together, these data support a role for CD68 as a specific Ox-LDL binding protein in human monocyte-derived macrophages.
van der Kooij
M A
MA
Pharma Division, Hoffmann-La Roche Ltd, Basel, Switzerland.
von der Mark
E M
EM
Kruijt
J K
JK
van Velzen
A
A
van Berkel
T J
TJ
Morand
O H
OH
D000581:Amidohydrolases / Q000494:pharmacology; D000818:Animals; D000911:Antibodies, Monoclonal / Q000276:immunology; D000918:Antibody Specificity; D015703:Antigens, CD / Q000276:immunology / Q000378:metabolism*; D015214:Antigens, Differentiation, Myelomonocytic / Q000276:immunology / Q000378:metabolism*; D015153:Blotting, Western; D002454:Cell Differentiation; D002478:Cells, Cultured; D006031:Glycosylation; D006801:Humans; D008077:Lipoproteins, LDL / Q000378:metabolism*; D008264:Macrophages / Q000378:metabolism*; D008562:Membrane Glycoproteins / Q000737:chemistry; D051379:Mice; D008970:Molecular Weight; D009000:Monocytes / Q000166:cytology; D010084:Oxidation-Reduction; D043524:Peptide-N4-(N-acetyl-beta-glucosaminyl) Asparagine Amidase; D011233:Precipitin Tests; D011499:Protein Processing, Post-Translational; D013045:Species Specificity; D000097382:CD68 Molecule
D000581:Amidohydrolases; D000911:Antibodies, Monoclonal; D015703:Antigens, CD; D015214:Antigens, Differentiation, Myelomonocytic; D008077:Lipoproteins, LDL; D008562:Membrane Glycoproteins; D043524:Peptide-N4-(N-acetyl-beta-glucosaminyl) Asparagine Amidase; C067980:CD68 antigen, human; D000097382:CD68 Molecule; C081026:CD68 protein, mouse; C099252:oxidized low density lipoprotein