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Defective TNF-alpha-induced apoptosis in STAT1-null cells due to low constitutive levels of caspases

A Kumar1, M Commane, T W Flickinger

  • 1Department of Molecular Biology, Lerner Research Institute, The Cleveland Clinic Foundation, Cleveland, OH 44195, USA.

Science (New York, N.Y.)
|December 31, 1997
PubMed

Insights

Signal transducers and activators of transcription (STATs) regulate gene expression. STAT1 is crucial for apoptosis by tumor necrosis factor alpha (TNF-alpha) and caspase expression, independent of its role in induced gene transcription.

Area of Science:

  • Molecular Biology
  • Cellular Biology
  • Immunology

Background:

  • Signal transducers and activators of transcription (STATs) are key mediators of cytokine and growth factor signaling.
  • STAT1 plays a role in the constitutive expression of caspases (Ice, Cpp32, Ich-1) in human fibroblasts.
  • STAT1-deficient cells exhibit resistance to tumor necrosis factor alpha (TNF-alpha)-induced apoptosis.

Purpose of the Study:

  • To investigate the role of STAT1 in TNF-alpha-induced apoptosis.
  • To determine the relationship between STAT1's function in apoptosis and its role in gene transcription.
  • To elucidate the specific domains of STAT1 required for mediating apoptosis.

Main Methods:

  • Comparison of apoptosis sensitivity in STAT1-null and wild-type human fibroblasts.
  • Analysis of caspase expression (Ice, Cpp32, Ich-1) in STAT1-deficient cells.
  • Assessment of apoptosis and protease expression in cells reconstituted with wild-type or mutant STAT1alpha.

Main Results:

  • STAT1-null cells are resistant to TNF-alpha-induced apoptosis.
  • Reintroduction of STAT1alpha restores TNF-alpha sensitivity and caspase expression.
  • STAT1 variants with mutations in dimerization domains restore apoptosis sensitivity, suggesting a distinct mechanism from STAT1-mediated gene induction.

Conclusions:

  • STAT1 is essential for TNF-alpha-induced apoptosis in human fibroblasts.
  • STAT1 regulates the expression of key apoptotic proteases (caspases).
  • The apoptotic functions of STAT1 are separable from its transcriptional activation functions, particularly regarding STAT dimerization.

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