Gyetko M R, Shollenberger S B, Sitrin R G
Department of Internal Medicine, University of Michigan Medical Center, Ann Arbor 48109-0360.
J Leukoc Biol. 1992 Mar;51(3):256-63. doi: 10.1002/jlb.51.3.256.
This study delineates the regulatory effects of inflammatory cytokines on mononuclear phagocyte plasminogen activator (PA) activity. The mechanisms by which mononuclear phagocytes modulate PA activity are described. Mononuclear phagocytes regulate net PA activity by the balanced expression of urokinase-type PA (uPA), in either secreted or membrane-associated forms, and a specific plasminogen activator inhibitor, PAI-2. Therefore, understanding how immunomodulators regulate macrophage PA activity requires that the comparative effects of uPA and PAI-2 be elucidated. We determine how recombinant interferon-gamma (IFN) and tumor necrosis factor-alpha (TNF) regulate plasminogen activation in monoblast-like U937 cells and normal human monocytes. In U937 cells, both IFN and TNF induced concurrent increases in secreted PA and PA inhibitor activities. These effects were accompanied by increased immunoreactive uPA and PAI-2 in conditioned media (enzyme-linked immunosorbent assay) and steady-state levels of cellular uPA and PAI-2 mRNA (Northern analysis). To determine the relative abilities of IFN and TNF to either promote or inhibit plasmin generation, we directly compared the effects IFN and TNF, using optimal stimulating concentrations. IFN induced PA activity to 180% of the level achieved by TNF. In contrast, IFN elicited only 78% of the PA inhibitor produced by TNF stimulation. These differences in secreted activity can be explained by the shift in balance between uPA and PAI-2 proteins. Immunoreactive uPA was induced equally by IFN and TNF, but TNF generated higher levels of PAI-2. The same overall pattern of results was seen in normal human monocytes. IFN and TNF differ greatly in the ability to augment receptor-bound PA activity in U937 cells, as IFN induced a twofold increase but TNF had no effect. We conclude that IFN and TNF modulate mononuclear phagocyte proteolytic activity through coordinate regulation of secreted and receptor-bound uPA, balanced against concurrent expression of PAI-2. These effects are cytokine specific, as IFN is superior to TNF in stimulating expression of both secreted and receptor-associated PA activities. These properties suggest mechanisms by which mononuclear phagocytes control proteolysis in cytokine-rich inflammatory foci.
本研究阐述了炎性细胞因子对单核吞噬细胞纤溶酶原激活物（PA）活性的调节作用。描述了单核吞噬细胞调节PA活性的机制。单核吞噬细胞通过尿激酶型PA（uPA）分泌或膜结合形式以及特异性纤溶酶原激活物抑制剂PAI-2的平衡表达来调节净PA活性。因此，了解免疫调节剂如何调节巨噬细胞PA活性需要阐明uPA和PAI-2的比较效应。我们确定重组干扰素-γ（IFN）和肿瘤坏死因子-α（TNF）如何调节单核细胞样U937细胞和正常人单核细胞中的纤溶酶原激活。在U937细胞中，IFN和TNF均诱导分泌型PA和PA抑制剂活性同时增加。这些效应伴随着条件培养基中免疫反应性uPA和PAI-2的增加（酶联免疫吸附测定）以及细胞uPA和PAI-2 mRNA的稳态水平（Northern分析）。为了确定IFN和TNF促进或抑制纤溶酶生成的相对能力，我们使用最佳刺激浓度直接比较了IFN和TNF的作用。IFN诱导的PA活性达到TNF所达到水平的180%。相反，IFN诱导产生的PA抑制剂仅为TNF刺激产生量的78%。分泌活性的这些差异可以通过uPA和PAI-2蛋白之间平衡的改变来解释。IFN和TNF对免疫反应性uPA的诱导程度相同，但TNF产生的PAI-2水平更高。在正常人单核细胞中也观察到相同的总体结果模式。IFN和TNF在增强U937细胞中受体结合的PA活性的能力上有很大差异，因为IFN诱导增加了两倍，而TNF没有作用。我们得出结论，IFN和TNF通过对分泌型和受体结合型uPA的协同调节来调节单核吞噬细胞的蛋白水解活性，并与PAI-2的同时表达保持平衡。这些效应具有细胞因子特异性，因为IFN在刺激分泌型和受体相关PA活性的表达方面优于TNF。这些特性提示了单核吞噬细胞在富含细胞因子的炎性病灶中控制蛋白水解的机制。
