Purification and partial characterization of a plasminogen activator inhibitor from the human glioblastoma, U138

A plasminogen activator inhibitor was purified to apparent homogeneity from conditioned media of U138 cells. The inhibitor is a glycoprotein with a pI of 5.4 and an apparent molecular weight of 45,000. The inhibitor forms sodium dodecyl sulfate-stable complexes with plasminogen activators and trypsin but not with plasmin, thrombin, or pancreatic kallikrein. Some biochemical and immunochemical characteristics of the U138 inhibitor distinguish it from other known plasminogen activator inhibitors. The expression of this inhibitor by U138 cells could be modulated by incubation in phorbol myristate acetate, interleukin-1, tumor necrosis factor, and gamma interferon, but not in beta interferon. Thus, the expression of the plasminogen activator inhibitor can be influenced by biological response modifiers known to be active in the brain and in the neural response to inflammatory stimuli. Therefore, this inhibitor, along with protease nexin, may be involved in brain development and regulation.