PLASMINOGEN-ACTIVATOR INHIBITOR TYPE-2 INHIBITS TUMOR-NECROSIS-FACTOR-ALPHA-INDUCED APOPTOSIS - EVIDENCE FOR AN ALTERNATE BIOLOGICAL FUNCTION

Plasminogen activator inhibitor type 2 (PAI-2) is a serine proteinase inhibitor or serpin that is a major product of macrophages in response to endotoxin and inflammatory cytokines. We have explored the role of PAI-2 in apoptotic cell death initiated by tumor necrosis factor alph a (TNF). HeLa cells stably transfected with PAI-2 cDNA were protected from TNF-induced apoptosis, whereas cells transfected with antisense P AI-2 cDNA, a control gene, or the plasmid vector alone remained suscep tible, The level of PAI-2 expressed by different HeLa cell clones was inversely correlated with their sensitivity to TNF. Loss of TNF sensit ivity was not a result of loss of TNF receptor binding. In contrast, P AI-2 expression did not confer protection against apoptosis induced by ultraviolet or ionizing radiation. The serine proteinase urokinase-ty pe plasminogen activator was not demonstrated to be the target of PAI- 2 action. The P-1-Arg amino acid residue of PAI-2 was determined to be required for protection, because cells expressing PAI-2 with an Ala i n this position were not protected from TNF-mediated cell death. The r esults suggest that intracellular PAI-2 might be an important factor i n regulating cell death in TNF-mediated inflammatory processes through inhibition of a proteinase involved in TNF-induced apoptosis.