Cytokines induce urokinase-dependent adhesion of human myeloid cells. A regulatory role for plasminogen activator inhibitors.

Abstract

Differentiation of monocytic precursors often results in adhesive properties thought to be important in migration. In this study, the influence of cytokines, known to induce macrophage differentiation, on the adhesiveness of the monocytic cell line U937 was examined in vitro. Despite development of a macrophage morphology, < 5% of cytokine-stimulated U937 cells were adherent at 24 h. Addition of 1-10 nM urokinase-type plasminogen activator (uPA) induced adherence in the presence of transforming growth factor type beta-l, 1,25-(OH)2 vitamin D3, granulocyte macrophage colony-stimulating factor, or tumor necrosis factor alpha. uPA-dependent adhesiveness was reversible after 24 h of stimulation with cytokines and uPA as adherence was prevented by the subsequent addition of anti-uPA antibodies. Adherence induced by diisopropylfluorophosphate-inactivated uPA was severalfold greater than that seen with active uPA. This difference was largely due to cellsurface turnover of active uPA complexed with plasminogen activator inhibitor (PAI). These data indicate that cytokines prime monocyte progenitors for uPA receptor-mediated signals leading to adherence, continued uPA receptor occupancy is required for adherence, and PAI decreases adherence by promoting clearance of uPA / PAI complexes. Thus the interaction of uPA and PAI at the cell surface, known to affect extracellular matrix proteolysis and hence myeloid cell migration, also regulates adhesion. The coordinated regulation of these two uPA functions by PAI may enhance the migratory potential of monocytic cells. (J. Clin. Invest. 1993. 91:1541-1552

Urokinase Induces Expression of Its Own Receptor in Beas2B Lung Epithelial Cells

“…It has also been reported previously that the specific binding capacity for uPA and cell surface uPAR expression is increased by PMA, epidermal growth factor, LPS, TGF-␤, and tumor necrosis factor-␣ in various cell lines (28,41). To extend our understanding of the regulation of uPAR by epithelial cells, we analyzed the effect of uPA on uPAR and uPAR mRNA expression.…”

“…We also measured binding of 125 I-uPA by the method of Waltz et al (28) with modifications. Beas2B cells grown to confluence in 24-well plates were treated with or without uPA for 24 h in serum-free media containing 0.5% BSA.…”

Conformational Regulation of Urokinase Receptor Function

“…Importantly, the acquisition of the adherent phenotype is allegedly dependent on up-regulation of both uPA and uPAR, leading to increased surface densities of the corresponding uPA-uPAR complexes (44,45). Accordingly, we chose to stimulate these three monocytic cell lines with 100 nM PMA before plating them on vitronectin-coated coverslips in the presence or absence of 10 nM pro-uPA S356A and 100 nM anti-uPAR mAbs representing the various epitope bins.…”

The cell biology of leukocyte-mediated proteolysis

“…Macrophages also synthesize and secrete uPA. In addition, uPA is bound to uPAR on the cell surface of activated macrophages [65,66], and the proteinase-receptor complex is thought to play important roles in cell adherence and locomotion that are independent of their roles in pericellular proteolysis [65,67].…”