The low density lipoprotein receptor-related protein mediates the cellular degradation of tissue factor pathway inhibitor.
The low density lipoprotein receptor-related protein/alpha 2-macroglobulin receptor (LRP) is a cell-surface glycoprotein of 4525 amino acids that functions as a hepatic endocytosis receptor for several plasma proteins. These include alpha 2-macroglobulin-protease complexes, free plasminogen activators as well as plasminogen activators complexed with their inhibitors, and beta-migrating very low density lipoproteins complexed with either apolipoprotein E or lipoprotein lipase. In the current study we used human and rat hepatoma cell lines to demonstrate that LRP can mediate the degradation of tissue factor pathway inhibitor (TFPI), a Kunitz-type plasma serine protease inhibitor that regulates tissue factor-induced blood coagulation. The cellular degradation of 125I-labeled TFPI (125I-TFPI) was inhibited more than 80% both by antibodies directed against LRP and by the LRP-associated 39-kDa protein, a protein that inhibits the binding and/or cell-mediated degradation of all ligands by LRP. Using rat hepatoma cells, we report that at 4 degrees C, 125I-TFPI binds to approximately 2 x 10(6) sites per cell with an equilibrium dissociation constant of approximately 30 nM. 125I-TFPI binding to the cell surface is not inhibited by the 39-kDa protein. Taken together, our results suggest that TFPI binds to an as-yet-unidentified cell surface molecule. After binding, LRP mediates the cellular degradation of TFPI.
Warshawsky
I
I
Edward Mallinckrodt Department of Pediatrics, Jewish Hospital at Washington University School of Medicine, St. Louis, MO 63110.
Broze
G J
GJ
Schwartz
A L
AL
D000818:Animals; D006528:Carcinoma, Hepatocellular; D002460:Cell Line; D004591:Electrophoresis, Polyacrylamide Gel; D006801:Humans; D007074:Immunoglobulin G / Q000494:pharmacology; D007700:Kinetics; D008074:Lipoproteins / Q000096:biosynthesis / Q000302:isolation & purification / Q000378:metabolism*; D008113:Liver Neoplasms; D008114:Liver Neoplasms, Experimental; D026503:Low Density Lipoprotein Receptor-Related Protein-1; D008970:Molecular Weight; D051381:Rats; D011971:Receptors, Immunologic / Q000096:biosynthesis / Q000302:isolation & purification / Q000378:metabolism*; D011993:Recombinant Fusion Proteins / Q000096:biosynthesis / Q000302:isolation & purification / Q000378:metabolism; D015842:Serine Proteinase Inhibitors / Q000378:metabolism*; D013997:Time Factors; D014407:Tumor Cells, Cultured; D000511:alpha-Macroglobulins / Q000378:metabolism
D007074:Immunoglobulin G; D008074:Lipoproteins; D026503:Low Density Lipoprotein Receptor-Related Protein-1; D011971:Receptors, Immunologic; D011993:Recombinant Fusion Proteins; D015842:Serine Proteinase Inhibitors; D000511:alpha-Macroglobulins; C051928:lipoprotein-associated coagulation inhibitor