Irradiation of mitochondria initiates apoptosis in a cell free system

Document Type

Article

Abstract

The ability to modulate the sensitivity of mammalian cells to ionizing radiation (IR) (e.g. using chemotherapeutics) is dependent on our understanding of the primary target and biochemical pathway that leads to IR-induced apoptosis. We demonstrate using a cell free assay that irradiation of mitochondria is a primary event that initiates IR-induced apoptosis. IR results in loss of mitochondrial membrane potential, opening of the permeability transition pore (PTP) and the release of cytochrome c (cyto c). Apaf-1 and ATP were required to initiate apoptosis upon release of cyto c from mitochondria. The importance of mitochondrial events in the initiation of IR-induced apoptosis was also supported by the observation that inhibition of caspase-9 by the over-expression of dominant negative mutants resulted in the inhibition of IR-induced apoptosis. In contrast, inhibition of caspase-8 had only a minor impact on IR-induced apoptosis. Over-expression of Bcl-X(L) inhibited the initiation of IR-induced apoptosis due to its ability to prevent the loss of mitochondrial membrane potential, PTP opening and cytochrome c release. In a cell free assay for apoptosis, mitochondria as well as cytosol derived from Bcl-X(L) over-expressing cells were less efficient at supporting apoptosis in response to IR suggesting multiple roles for Bcl-X(L) in the regulation of apoptosis.

Medical Subject Headings

Adenosine Triphosphate (metabolism); Amino Acid Chloromethyl Ketones (pharmacology); Apoptosis (drug effects, physiology, radiation effects); Apoptotic Protease-Activating Factor 1; Biological Transport; Caspase 8; Caspase 9; Caspase Inhibitors; Caspases (genetics, metabolism); Cell Extracts (pharmacology); Cell Membrane (radiation effects); Cell Nucleus (drug effects, radiation effects); Cell-Free System; Cyclosporine (pharmacology); Cysteine Proteinase Inhibitors (pharmacology); Cytochrome c Group (metabolism); Cytosol (radiation effects); Electrons; Humans; Jurkat Cells (drug effects); Mitochondria (radiation effects); Proteins (metabolism); Proto-Oncogene Proteins c-bcl-2 (genetics, metabolism, radiation effects); Reactive Oxygen Species (metabolism); bcl-X Protein

Publication Date

1-11-2001

Publication Title

Oncogene

ISSN

0950-9232

Volume

20

Issue

2

First Page

167

Last Page

77

PubMed ID

11313941

Digital Object Identifier (DOI)

10.1038/sj.onc.1204054

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