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A role for caspase 2 and PIDD in the process of p53-mediated apoptosis

Nicole Baptiste-Okoh1, Anthony M Barsotti, Carol Prives

  • 1Department of Biological Sciences, Columbia University, New York, NY 10027, USA.

Proceedings of the National Academy of Sciences of the United States of America
|February 2, 2008
PubMed

Insights

DNA-damaging agents trigger apoptosis via p53, involving PIDD and caspase 2. This pathway is crucial for cytochrome c release and cell death, even with a defective p53 transactivation domain.

Area of Science:

  • Molecular Biology
  • Cell Biology
  • Cancer Research

Background:

  • The tumor suppressor protein p53 plays a critical role in cellular responses to DNA damage.
  • p53's transactivation domain is essential for regulating target gene expression and mediating apoptosis.
  • Mutant p53 variants can retain or gain functions, impacting cancer progression and treatment response.

Purpose of the Study:

  • To investigate the role of a p53 mutant with an inactive transactivation domain (p53(Q22/S23)) in DNA damage-induced apoptosis.
  • To elucidate the specific molecular mechanisms and key mediators involved in p53-dependent apoptosis, particularly concerning caspase activation and target gene induction.
  • To determine whether p53's transcriptional activity is fully required for initiating apoptosis or for downstream events.

Main Methods:

  • Utilized human tumor-derived H1299 cells expressing inducible wild-type or mutant p53(Q22/S23).
  • Applied DNA-damaging agents to induce apoptosis.
  • Assessed apoptosis through cytochrome c release, nuclear fragmentation, and DNA content analysis.
  • Investigated caspase activation, specifically caspase 2.
  • Examined the expression of proapoptotic target genes like PIDD and AIP1.
  • Employed RNA interference (RNAi) to silence PIDD and assess its impact on apoptosis.

Main Results:

  • p53(Q22/S23) induced apoptosis, characterized by cytochrome c release, nuclear fragmentation, and sub-G1 DNA content, although at a slower rate than wild-type p53.
  • Key downstream effector caspases were not activated, but caspase 2 activation was essential for cytochrome c release and cell death.
  • Despite a defective transactivation domain, p53(Q22/S23) induced proapoptotic targets PIDD and AIP1 similarly to wild-type p53.
  • Silencing PIDD using RNAi suppressed apoptosis induced by both wild-type p53 and p53(Q22/S23).

Conclusions:

  • The initial phase of DNA damage-induced, p53-mediated apoptosis relies on a mechanism involving PIDD and caspase 2.
  • Caspase 2 activation is a critical early event required for cytochrome c release and subsequent cell death.
  • Full transcriptional regulatory functions of p53 may not be necessary for the initiation of apoptosis but rather for events occurring downstream of cytochrome c release.

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