1. Cryptic chemotactic activity of fibronectin for human monocytes resides in the 120-kDa fibroblastic cell-binding fragment
R A Clark, N E Wikner, D E Doherty, D A Norris J Biol Chem. 1988 Aug 25;263(24):12115-23.
Monocytes and lymphocytes form a second wave of infiltrating blood leukocytes in areas of tissue injury. The mechanisms for monocyte accumulation at these sites are not completely understood. Recently, however, fragments from extracellular matrix proteins including collagen, elastin, and fibronectin have been shown to induce monocyte chemotaxis. In this report we demonstrate that chemotactic activity for human monocytes is expressed when a 120-kDa fragment containing the RGDS cell-binding peptide is released from intact fibronectin or from larger fibronectin fragments. Monocytes, either from mononuclear cell Ficoll-Hypaque preparations (10-20% monocytes, 89-90% lymphocytes) or from elutriation preparations (95% monocytes, 5% lymphocytes), but not lymphocytes, migrated toward 120-kDa fragment preparations (10(-7) M) in blind-end chambers when the cells were separated from the chemoattractant by a 5-micron pore polycarbonate filter either alone or overlying a 0.45-micron pore nitrocellulose filter. Neutrophils migrated toward zymosan-activated serum but not toward 10(-5)-10(-8) M concentrations of the 120-kDa fragment. Intact fibronectin had no chemotactic activity for human monocytes. Fibronectin was isolated from citrated human plasma by sequential gelatin-Sepharose affinity and DEAE ion-exchange chromatography in the presence of buffers containing 1 mM phenylmethylsulfonyl fluoride to prevent fragmentation. Controlled enzymatic digestion with thermolysin cleaved fibronectin into 30 kDa fibrin, 45 kDa collagen, and 150/160-kDa cell and heparin domains. Upon prolonged digestion, purified 150/160-kDa fragments were cleaved into 120-kDa cell and 30/40-kDa heparin-binding fragments. Even though the intact fibronectin molecule, the 150/160-kDa fragments, and the 120-kDa fragment, have cell binding activity for Chinese hamster ovary fibroblasts, only the 120-kDa fragment expressed chemotactic activity for human monocytes. Thus, the 120-kDa fibroblastic cell-binding fragment contains a cryptic site for monocyte chemotaxis which is expressed upon enzymatic cleavage of fibronectin.
2. Characterization of biologically active domains on elastin: identification of a monoclonal antibody to a cell recognition site
D S Wrenn, G L Griffin, R M Senior, R P Mecham Biochemistry. 1986 Sep 9;25(18):5172-6. doi: 10.1021/bi00366a028.
Monoclonal antibodies to bovine alpha-elastin were characterized with solid-phase ELISA, Western blot, immunoprecipitation, and immunoaffinity chromatography. One monoclonal antibody, BA-4, bound to insoluble elastin, alpha-elastin, and tropoelastin and to peptide fragments generated by proteolytic digestion of insoluble elastin. Immunoaffinity chromatography of elastin fragments released from insoluble elastin with pancreatic elastase demonstrated that BA-4 was specific for a chemotactically active epitope composed of valine, glycine, alanine, and proline in a molar ratio of approximately 2:2:1:1. This composition matches the Val-Gly-Val-Ala-Pro-Gly repeating sequence in elastin that has been shown to be a chemoattractant for fibroblasts and monocytes. Specific ablation of the chemotactic activity of synthetic Val-Gly-Val-Ala-Pro-Gly by BA-4 IgG confirmed the identity of the epitope recognized by the monoclonal antibody and suggests that, despite its hydrophobic nature, this cell recognition domain is accessible on the surface of elastin and is strongly immunogenic. BA-4 should prove useful for investigating cell surface receptors for elastin.
3. Characterization of monocyte chemotactic protein-1 binding to human monocytes
A J Valente, M M Rozek, C J Schwartz, D T Graves Biochem Biophys Res Commun. 1991 Apr 15;176(1):309-14. doi: 10.1016/0006-291x(91)90925-w.
Monocyte chemotactic protein-1 (MCP-1) stimulates chemotaxis of peripheral blood monocytes. In order to understand the biologic basis of this specific activity, binding studies of 125I-MCP-1 were undertaken. MCP-1 showed saturable binding to monocytes. Scatchard analysis of the monocyte binding data indicate that there are approximately 1,600 high affinity binding sites per monocyte with a Kd = 1.1 nM. Studies with synthetic peptides constructed according to the MCP-1 amino acid sequence indicate that a synthetic peptide, MCP-1[13-35], stimulates monocyte migration and competes with native MCP-1 for binding sites. Inhibition of MCP-1 binding was tested with chemotactic connective tissue proteins. No inhibition of MCP-1 binding was observed with either collagen, elastin-derived peptides or fibronectin. These results identify a single class of unique high affinity MCP-1 binding sites that are likely to recognize a peptide domain on MCP-1 which include the amino acids within the region, 13-35.
