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Ectopic expression of the serine protease inhibitor PI9 modulates death receptor-mediated apoptosis

J A Kummer1, O Micheau, P Schneider

  • 1Department of Biochemistry, University of Lausanne, BIL Biomedical Research Center, Chemin des Boveresses 155, CH-1066 Epalinges, Switzerland. j.a.kummer@umcutrecht.nl

Cell Death and Differentiation
|May 5, 2007
PubMed

Insights

Protease inhibitor 9 (PI9) regulates apoptosis by inhibiting key caspases. This serine protease inhibitor interacts with caspase-8 and -10, controlling programmed cell death pathways triggered by TNF superfamily ligands.

Area of Science:

  • Molecular Biology
  • Cell Biology
  • Biochemistry

Background:

  • Apoptosis, or programmed cell death, is a critical cellular process regulated by caspases.
  • Tumor necrosis factor (TNF) receptor superfamily members can initiate apoptosis by activating pro-caspase-8 and -10.
  • Inhibitors like c-FLICE-inhibitory protein modulate apoptosis by blocking caspase activation.

Purpose of the Study:

  • To investigate the role of human intracellular serine protease inhibitor 9 (PI9) in regulating apoptosis.
  • To determine if PI9 inhibits apoptosis induced by death receptor ligands.
  • To elucidate the mechanism by which PI9 affects apoptosis.

Main Methods:

  • Assessed the ability of PI9 to inhibit TNF-, TNF-related apoptosis-inducing ligand-, and Fas ligand-mediated apoptosis in TNF-sensitive cell lines.
  • Utilized a mutated PI9 (Glu --> Ala at the reactive center P1 residue) to test the requirement of its protease activity.
  • Examined the direct interaction between PI9 and the active forms of caspase-8 and -10.

Main Results:

  • PI9 significantly inhibited apoptosis induced by TNF superfamily death ligands in specific cell lines.
  • A PI9 mutant lacking reactive center P1 residue function failed to inhibit death receptor-induced cell death, indicating a protease-dependent mechanism.
  • PI9 directly interacted with intermediate active forms of caspase-8 and -10, suggesting a direct inhibition mechanism.

Conclusions:

  • Human intracellular serpin PI9 acts as a regulator of apoptosis.
  • PI9 inhibits apoptosis by directly interacting with and inhibiting apical caspases, specifically caspase-8 and -10.
  • These findings highlight PI9's role in controlling programmed cell death pathways.

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