Regulation of Plasminogen Receptor Expression on Monocytoid Cells by β1-Integrin-dependent Cellular Adherence to Extracellular Matrix Proteins

Sun-Ok Kim,Edward F Plow,Lindsey A Miles

doi:10.1074/jbc.271.39.23761

Sun-Ok Kim, Edward F Plow + Show 1 more

Open Access

https://doi.org/10.1074/jbc.271.39.23761

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Abstract

Plasminogen binding sites function to arm cell surfaces with the proteolytic activity of plasmin, critical for degradation of extracellular matrices. We have assessed the effects of adhesion of the representative monocytoid cell lines, THP-1 and U937, to purified extracellular matrix proteins on their expression of plasminogen receptors. After adhesion to immobilized fibronectin, adherent and nonadherent subpopulations of cells were separated. Plasminogen binding to the nonadherent population of cells increased 3-fold, whereas binding to the adherent population decreased by 60%. These changes were due to differences in the plasminogen binding capacities of the cells, while the affinities of the cells for plasminogen were unchanged. The up-regulation of receptor expression in the nonadherent cell population was: 1) induced rapidly and reversibly, 2) independent of new protein synthesis, 3) required an interaction between adherent and nonadherent cell populations, and 4) associated with an enhanced ability of the cells to promote plasminogen activation and to degrade fibronectin. Other immobilized adhesive proteins, laminin and vitronectin, also supported up-regulation of plasminogen receptors in the nonadherent cells. Carboxypeptidase B treatment eliminated the increment in the plasminogen binding capacity of the nonadherent cells, suggesting that the increase in binding was due to exposure of new carboxyl-terminal lysyl residues on the cell surfaces. Furthermore, both the adherence of the cells and up-regulation of plasminogen binding sites was abolished by beta1-integrin monoclonal antibodies. These results suggest that proteins found in extracellular matrices have the capacity to modulate the expression of plasminogen binding sites, thus regulating local proteolysis and cell migration.

Highlights

The expression of cell surface binding sites for plasminogen is widespread among cells of both prokaryotic and eukaryotic organisms
In view of the close interrelationship between cell adhesion and proteolysis, we have examined the effect of adherence of monocytoid cells to purified extracellular matrix proteins on plasminogen receptor expression
Role of Cell Adhesion in Modulation of Plasminogen Receptor Expression—We tested whether adhesion of THP-1 monocytoid cells to isolated extracellular matrix proteins could modulate plasminogen receptor expression

Summary

EXPERIMENTAL PROCEDURES

Proteins—Glu-plasminogen was purified from fresh human blood collected into 3 mM benzamidine, 3 mM EDTA, 100 units/ml Trasylol (FBA Pharmaceuticals, New York, NY), 100 ␮g/ml soybean trypsin inhibitor (Sigma). Vitronectin (Vn) was purified as described previously [31], and its concentration was determined using an extinction coefficient of 13.8 [31]. Cells—The human monocytoid cell line, THP-1 [35] was cultured in RPMI 1640 (Whittaker/MA Bioproducts, Walkersville, MD) containing penicillin G (100 units/ml), streptomycin (100 ␮g/ml), 1 mM sodium pyruvate, 0.05 M HEPES, pH 7.35, 5 ϫ 10Ϫ4% ␤-mercaptoethanol, and 5% fetal calf serum (Irvine Scientific, Irvine, CA). U937 cells were cultured in RPMI 1640 containing 100 units/ml penicillin G, 100 ␮g/ml streptomycin, and 5% fetal calf serum. Nonspecific binding was defined as counts bound to the cells in the presence of 200 mM ⑀-aminocaproic acid. For scu-PA, nonspecific binding was determined as counts bound in the presence of 100 nM unlabeled scu-PA.

The abbreviations used are

RESULTS

DISCUSSION