Identification of a serpin-enzyme complex receptor on human hepatoma cells and human monocytes.
Formation of the covalently stabilized complex of alpha 1-antitrypsin (alpha 1-AT) with neutrophil elastase, the archetype of serine proteinase inhibitor serpin-enzyme complexes, is associated with structural rearrangement of the alpha 1-AT molecule and hydrolysis of a reactive-site peptide bond. An approximately 4-kDa carboxyl-terminal cleavage fragment is generated. alpha 1-AT-elastase complexes are biologically active, possessing chemotactic activity and mediating increases in expression of the alpha 1-AT gene in human monocytes and macrophages. This suggested that structural rearrangement of the alpha 1-AT molecule, during formation of a complex with elastase, exposes a domain that is recognized by a specific cell surface receptor or receptors. To test this hypothesis, the known three-dimensional structure of alpha 1-AT and comparisons of the primary structures of the serpins were used to select a potentially exteriorly exposed and highly conserved region in the complexed form of alpha 1-AT as a candidate ligand (carboxyl-terminal fragment, amino acids 359-374). We show here that synthetic peptides based on the sequence of this region bind specifically and saturably to human hepatoma cells and human monocytes (Kd = 4.0 X 10(-8) M, 4.5 X 10(5) plasma membrane receptors per cell) and mediate increases in synthesis of alpha 1-AT. Binding of peptide 105Y (Ser-Ile-Pro-Pro-Glu-Val-Lys-Phe-Asn-Lys-Pro-Phe-Val-Tyr-Leu-Ile) is blocked by alpha 1-AT-elastase complexes, antithrombin III (AT III)-thrombin complexes, alpha 1-antichymotrypsin (alpha 1-ACT)-cathepsin G complexes, and, to a lesser extent, complement component C1 inhibitor-C1s complexes, but not by the corresponding native proteins. Binding of peptide 105Y is also blocked by peptides with sequence corresponding to carboxy-terminal fragments of the serpins AT III and alpha 1-ACT, but not by peptides having the sequence of the extreme amino terminus of alpha 1-AT. The results also show that peptide 105Y inhibits binding of 125I-labeled alpha 1-AT-elastase complexes. Thus, these studies demonstrate an abundant, relatively high-affinity cell surface receptor which recognizes serpin-enzyme complexes (SEC receptor). This receptor is capable of modulating the production of at least one of the serpins, alpha 1-AT. Since the ligand specificity is similar to that previously described for in vivo clearance of serpin-enzyme complexes, the SEC receptor may also be involved in the clearance of certain serpin-enzyme complexes.
Perlmutter
D H
DH
Department of Pediatrics, Washington University School of Medicine, Saint Louis, MO 63110.
Glover
G I
GI
Rivetna
M
M
Schasteen
C S
CS
Fallon
R J
RJ
D000595:Amino Acid Sequence; D001667:Binding, Competitive; D006528:Carcinoma, Hepatocellular; D002460:Cell Line; D002462:Cell Membrane / Q000378:metabolism; D006801:Humans; D007700:Kinetics; D019272:Leukocyte Elastase; D008113:Liver Neoplasms; D008969:Molecular Sequence Data; D009000:Monocytes / Q000378:metabolism*; D010196:Pancreatic Elastase / Q000378:metabolism*; D010455:Peptides / Q000138:chemical synthesis / Q000378:metabolism*; D011956:Receptors, Cell Surface / Q000378:metabolism*; D015843:Serpins / Q000378:metabolism*; D014407:Tumor Cells, Cultured / Q000378:metabolism*; D000515:alpha 1-Antitrypsin / Q000096:biosynthesis / Q000378:metabolism*
D010455:Peptides; D011956:Receptors, Cell Surface; D015843:Serpins; D000515:alpha 1-Antitrypsin; C037741:alpha 1-antitrypsin-leukocyte elastase complex; C064184:serpin-enzyme complex receptor; D010196:Pancreatic Elastase; D019272:Leukocyte Elastase