Increase in Cytosolic Calcium Upregulates the Synthesis of Type 1 Plasminogen Activator Inhibitor in the Human Histiocytic Cell Line

In the U937 histiocytic cell line, we investigated the effect of calcium-mobilizing agents with or without tumor necrosis factor-a (TNF) on the regulation of the synthesis of plasminogen activator inhibitor-type 1 (PAI-l). Cultured U937 cells were stimulated with ionophore A23187 and thapsigargin with or without TNF. The response was analyzed in terms of cytosolic calcium mobilization, PAL1 accumulation in the medium, and PAI-1 mRNA expression. The study was extended to urokinase (uPA) secretion and surface expression of its receptor (uPAR). Using Fluo-3 as a calcium-indicator dye to measure cytosolic calcium mobilization, we showed by flow cytometry that both agents mobilized calcium in a dose-dependent manner. TNF provoked a slight calcium mobilization that was also observed by digital imaging microscopy. Association of TNF with the calcium-mobilizing agents potentiated the calcium mobilization. Both calciummobilizing agents induced at 18 hours a dose-dependent accumulation of PAL1 in culture medium, whereas uPA was not affected. TNF alone induced a more marked accumulation of PAI-1 than of uPA. Association of TNF with the agents induced a PAL1 response that was more than additive of