title: Modulation of urokinase-type plasminogen activator and plasminogen activator inhibitor-2 expression by U-937 mononuclear phagocytes. Effects of 1 alpha, 25-dihydroxyvitamin D3 and phorbol ester.
abstract: Mononuclear phagocytes are known to produce both urokinase-type plasminogen activator (u-PA) and a specific PA inhibitor, PAI-2. In this study we have investigated the effects of calcitriol and PMA-induced differentiation on the comparative expression of PA and PAI in monoblast-like U937 cells. Cells were incubated for 96 h in the presence or absence of 50 nM calcitriol. After transfer into serum-free medium, the cells were cultured for 48 h with PMA (0 to 50 ng/ml). PA and PAI activities of conditioned media and cell lysates were measured with a plasminogen dependent colorimetric assay. Control cells uniformly secreted PAI activity (70.3 +/- 24.9 PAI U/ml), while calcitriol pretreatment induced the cells to secrete PA activity (52.6 +/- 47.2 milli-Ploug unit/ml). PMA induced secretion of PAI activity in calcitriol-pretreated cells to levels 4.6- to 8.3-fold greater than controls (p less than 0.05). Parallel effects on PA and PAI activities were seen in cell lysates. To determine how changes in the expression of u-PA and PAI-2 might account for these effects, mRNA for u-PA and PAI-2 were assessed by Northern blot analysis. Calcitriol induced an increase in u-PA mRNA with a marked reduction in PAI-2 mRNA. PMA alone induced modest increases in both mRNA species. In calcitriol pre-treated cells, PMA induced a moderate increase in u-PA mRNA and a marked increase in PAI-2 mRNA. We conclude that agonist-specific differentiation of U937 cells modulates the expression of PA and PAI activities by altering the proportionate biosynthesis of u-PA and PAI-2 proteins. The ability of mononuclear phagocytes to control plasminogen activation at inflammatory foci may therefore be contingent on the independent regulation of u-PA and PAI-2 gene expression.
mesh_terms: D015152:Blotting, Northern; D002117:Calcitriol / Q000494:pharmacology*; D002460:Cell Line; D006023:Glycoproteins / Q000302:isolation & purification / Q000378:metabolism*; D006801:Humans; D009000:Monocytes / Q000201:enzymology* / Q000378:metabolism; D010960:Plasminogen Activators / Q000037:antagonists & inhibitors / Q000302:isolation & purification / Q000378:metabolism*; D015849:Plasminogen Inactivators; D013755:Tetradecanoylphorbol Acetate / Q000494:pharmacology*; D014568:Urokinase-Type Plasminogen Activator / Q000302:isolation & purification / Q000378:metabolism*
chemical_list: D006023:Glycoproteins; D015849:Plasminogen Inactivators; D010960:Plasminogen Activators; D014568:Urokinase-Type Plasminogen Activator; D002117:Calcitriol; D013755:Tetradecanoylphorbol Acetate