Protection from tumor necrosis factor-mediated cytolysis by overexpression of plasminogen activator inhibitor type-2.

Pretreatment of HT-1080 fibrosarcoma cells with tumor necrosis factor (TNF) induced resistance to the cytolytic activity of this cytokine in combination with cycloheximide. This resistance correlated with the synthesis of plasminogen activator inhibitor type-2 (PAI-2). HT-1080 cells were transfected with a PAI-2 expression vector in both sense and antisense orientation. The resistance to TNF-mediated cytolysis of transfected cell clones was correlated with the level of PAI-2 expression. Cells expressing antisense PAI-2 RNA showed reduced expression of PAI-2 and increased sensitivity to TNF-mediated cytolysis. Cells expressing constitutively PAI-2 were treated with TNF and cycloheximide to select cells with increased resistance to cytolysis and enhanced PAI-2 expression. PAI-2 gradually disappeared during a treatment with TNF and cycloheximide. This finding suggested that PAI-2 formed a complex with a target proteinase, which could be involved in mediating the cytolytic activity of TNF.