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Activation of Apoptosis by Cytoplasmic Microinjection of Cytochrome c
07:42

Activation of Apoptosis by Cytoplasmic Microinjection of Cytochrome c

Published on: June 29, 2011

Irradiation of mitochondria initiates apoptosis in a cell free system

N Taneja1, R Tjalkens, M A Philbert

  • 1Department of Radiation Oncology, University of Michigan, Ann Arbor, MI 48109, USA.

Oncogene
|April 21, 2001
PubMed

Insights

Ionizing radiation (IR) triggers apoptosis by directly damaging mitochondria, leading to cytochrome c release. This mitochondrial pathway, involving caspase-9, is crucial for IR-induced cell death, with Bcl-X(L) acting as a key regulator.

Area of Science:

  • Cell Biology
  • Biochemistry
  • Radiation Biology

Background:

  • Understanding the molecular mechanisms of ionizing radiation (IR)-induced apoptosis is crucial for modulating cellular sensitivity, particularly in cancer therapy.
  • The primary target and biochemical pathways initiating IR-induced apoptosis remain key areas of investigation.

Purpose of the Study:

  • To elucidate the primary target of IR that initiates apoptosis in mammalian cells.
  • To identify the key biochemical pathways involved in IR-induced apoptosis, focusing on mitochondrial involvement.

Main Methods:

  • Cell-free assays were employed to study IR-induced apoptosis.
  • Mitochondrial membrane potential, permeability transition pore (PTP) opening, and cytochrome c release were assessed.
  • The role of caspases (caspase-9 and caspase-8) and Bcl-X(L) in IR-induced apoptosis was investigated through genetic manipulation (dominant-negative mutants and overexpression).

Main Results:

  • Irradiation of isolated mitochondria was shown to be a primary event initiating apoptosis.
  • IR induced loss of mitochondrial membrane potential, PTP opening, and subsequent cytochrome c release.
  • Apaf-1 and ATP were essential for initiating apoptosis after cytochrome c release.
  • Inhibition of caspase-9 significantly blocked IR-induced apoptosis, while caspase-8 inhibition had minimal effect.
  • Overexpression of Bcl-X(L) inhibited IR-induced apoptosis by preventing mitochondrial dysfunction and cytochrome c release.

Conclusions:

  • Mitochondria are a primary target of ionizing radiation, initiating the apoptotic cascade.
  • The intrinsic apoptotic pathway, involving mitochondrial release of cytochrome c and activation of caspase-9, is critical for IR-induced apoptosis.
  • Bcl-X(L) plays a significant role in regulating IR-induced apoptosis by stabilizing mitochondrial function.

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