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Plasminogen activator inhibitor type 2 inhibits tumor necrosis factor alpha-induced apoptosis. Evidence for an
J L Dickinson1, E J Bates, A Ferrante
1Queensland Cancer Fund Experimental Oncology Unit, Queensland Institute of Medical Research, Brisbane, Australia.
Abstract:
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 alpha (TNF). HeLa cells stably transfected with PAI-2 cDNA were protected from TNF-induced apoptosis, whereas cells transfected with antisense PAI-2 cDNA, a control gene, or the plasmid vector alone remained susceptible. The level of PAI-2 expressed by different HeLa cell clones was inversely correlated with their sensitivity to TNF. Loss of TNF sensitivity was not a result of loss of TNF receptor binding. In contrast, PAI-2 expression did not confer protection against apoptosis induced by ultraviolet or ionizing radiation. The serine proteinase urokinase-type plasminogen activator was not demonstrated to be the target of PAI-2 action. The P1-Arg amino acid residue of PAI-2 was determined to be required for protection, because cells expressing PAI-2 with an Ala in this position were not protected from TNF-mediated cell death. The results suggest that intracellular PAI-2 might be an important factor in regulating cell death in TNF-mediated inflammatory processes through inhibition of a proteinase involved in TNF-induced apoptosis.
Insights
Plasminogen activator inhibitor type 2 (PAI-2) protects cells from tumor necrosis factor alpha (TNF)-induced apoptosis. This protective role of PAI-2 in inflammatory processes is crucial for regulating cell death.
Area of Science:
- Cell Biology
- Molecular Biology
- Immunology
Background:
- Plasminogen activator inhibitor type 2 (PAI-2) is a serpin produced by macrophages in response to inflammatory stimuli.
- Tumor necrosis factor alpha (TNF) is a key cytokine involved in inflammatory processes and apoptosis.
Purpose of the Study:
- To investigate the role of PAI-2 in TNF-induced apoptotic cell death.
- To determine the mechanism by which PAI-2 affects TNF sensitivity.
Main Methods:
- HeLa cells were stably transfected with PAI-2 cDNA or antisense PAI-2 cDNA.
- Cells were treated with TNF, ultraviolet, or ionizing radiation to induce apoptosis.
- TNF receptor binding and PAI-2's P1-Arg residue were analyzed.
Main Results:
- PAI-2 expression protected HeLa cells from TNF-induced apoptosis, inversely correlating with sensitivity.
- Protection was specific to TNF and not observed with radiation-induced apoptosis.
- The P1-Arg residue of PAI-2 was essential for its protective function.
Conclusions:
- Intracellular PAI-2 plays a significant role in regulating cell death during TNF-mediated inflammatory responses.
- PAI-2 likely inhibits a specific proteinase involved in the TNF apoptotic pathway.
- PAI-2's function is distinct from its role in regulating urokinase-type plasminogen activator.