Cross-competition for binding of alpha 1-antitrypsin (alpha 1 AT)-elastase complexes to the serpin-enzyme complex receptor by other serpin-enzyme complexes and by proteolytically modified alpha 1 AT.
The serpin-enzyme complex (SEC) receptor recognizes a pentapeptide neo-domain of alpha 1-antitrypsin (alpha 1 AT)-elastase complexes and, in so doing, mediates internalization and intracellular catabolism of the macromolecular complex, mediates an increase in synthesis of alpha 1 AT, and elicits neutrophil chemotactic activity. In previous studies we have shown that this pentapeptide domain is highly conserved among members of the serpin family and that binding of a synthetic peptide corresponding to this region (125I-peptide 105Y, SIP-PEVKFNKPFVYLI, based on alpha 1 AT sequence 359-374) to HepG2 cells is blocked by several serpin-enzyme complexes. To determine whether the SEC receptor is the primary HepG2 cell surface binding site for these serpin-enzyme complexes, we examined the capacity for serpin-enzyme complexes to compete with each other for binding to the SEC receptor. The results indicate that binding of 125I-elastase-alpha 1 AT complexes is blocked by thrombin-antithrombin III (ATIII), thrombin-heparin cofactor II, and cathepsin G-alpha 1-antichymotrypsin (alpha 1 ACT) complexes. Moreover, unlabeled elastase-alpha 1 AT complexes compete for binding of 125I-thrombin-ATIII, 125I-thrombin-heparin cofactor II, and 125I-cathepsin G-alpha 1 ACT complexes. Preformed soluble tissue plasminogen activator-plasminogen activator inhibitor 1 complexes also compete for binding of elastase-alpha 1 AT complexes to the SEC receptor but do so to a less effective extent, probably because of a less favorable pentapeptide sequence for binding to the SEC receptor. Under conditions in which these serpin-enzyme complexes would be expected to bind to the SEC receptor there is an increase in synthesis of alpha 1 AT but not in synthesis of ATIII or alpha 1 ACT. Proteolytically modified alpha 1 AT also competes for binding of 125I-elastase-alpha 1 AT complexes to the SEC receptor and vice versa. The purified 51-kDa amino-terminal fragment of alpha 1 AT does not compete for binding of 125I-elastase-alpha 1 AT complexes, indicating that the pentapeptide neodomain in the 4-kDa carboxyl-terminal fragment is sufficient for binding to the SEC receptor.
Department of Pediatrics, Washington University School of Medicine, St. Louis, Missouri 63110.
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G
Joslin
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Wittwer
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Adams
D M
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Tollefsen
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A
August
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DH
Perlmutter
D000595:Amino Acid Sequence; D000990:Antithrombin III / Q000378:metabolism; D001665:Binding Sites; D001667:Binding, Competitive; D056649:Cathepsin G; D002403:Cathepsins / Q000378:metabolism; D002460:Cell Line; D015844:Heparin Cofactor II / Q000378:metabolism; D006801:Humans; D008969:Molecular Sequence Data; D010196:Pancreatic Elastase / Q000378:metabolism*; D010446:Peptide Fragments / Q000737:chemistry / Q000378:metabolism; D011956:Receptors, Cell Surface / Q000378:metabolism*; D012697:Serine Endopeptidases; D013917:Thrombin / Q000378:metabolism; D000514:alpha 1-Antichymotrypsin / Q000378:metabolism; D000515:alpha 1-Antitrypsin / Q000378:metabolism*
D010446:Peptide Fragments; D011956:Receptors, Cell Surface; D000514:alpha 1-Antichymotrypsin; D000515:alpha 1-Antitrypsin; C064184:serpin-enzyme complex receptor; D015844:Heparin Cofactor II; D000990:Antithrombin III; D002403:Cathepsins; D012697:Serine Endopeptidases; C534094:CTSG protein, human; D056649:Cathepsin G; D010196:Pancreatic Elastase; D013917:Thrombin