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Genome digestion is a dispensable consequence of physiological cell death mediated by cytotoxic T lymphocytes
D S Ucker1, P S Obermiller, W Eckhart
1Division of Immunology and Membrane Biology, Salk Institute, La Jolla, California 92037.
Abstract:
We examined virally transformed murine fibroblast clones as targets for cytotoxic T lymphocyte (CTL)-triggered lysis and genome digestion. Strikingly, while all clones were essentially equivalent in the ability to be lysed, one clone, SV3T3-B2.1, failed to exhibit genome digestion associated with CTL attack. Other aspects of the physiological cell death process, including loss of adhesion and nuclear envelope breakdown (lamin phosphorylation and solubilization), were not altered in this clone. The absence of genome digestion associated with CTL-induced cell death correlated with the absence of endodeoxyribonuclease activity in the nuclei of that clone. Characterization of the activity affected identifies a calcium-dependent, DNase I-like endonuclease of approximately 40 kDa, normally present constitutively in all cell nuclei, as the enzyme responsible for genome digestion associated with CTL-mediated cell death. These observations indicate that neither genome digestion per se nor its consequences [such as activation of poly(ADP-ribose) polymerase] are essential for cell death resulting from the triggering of this cell suicide process.
Insights
Cytotoxic T lymphocyte (CTL) attack triggers cell death, but genome digestion is not essential. A specific endonuclease is responsible for this DNA fragmentation during CTL-mediated apoptosis.
Area of Science:
- Immunology
- Cell Biology
- Molecular Biology
Background:
- Cytotoxic T lymphocytes (CTLs) induce target cell death through various mechanisms.
- Genome digestion is a known feature of CTL-mediated apoptosis.
- The specific enzymes and necessity of genome digestion in this process require further elucidation.
Purpose of the Study:
- To investigate the role of genome digestion in CTL-induced cell death.
- To identify the endonuclease responsible for DNA fragmentation during CTL attack.
- To determine if genome digestion is essential for CTL-mediated apoptosis.
Main Methods:
- Utilized virally transformed murine fibroblast clones as targets for CTLs.
- Assessed target cell lysis, genome digestion, and other cell death markers (adhesion, nuclear envelope breakdown).
- Characterized nuclear endodeoxyribonuclease activity in CTL-resistant and CTL-sensitive clones.
Main Results:
- All tested fibroblast clones were equally susceptible to CTL-mediated lysis.
- One clone (SV3T3-B2.1) lacked genome digestion despite CTL attack.
- Absence of genome digestion correlated with a lack of calcium-dependent, DNase I-like endonuclease activity.
- Other cell death indicators were unaffected in the clone lacking genome digestion.
Conclusions:
- Genome digestion is mediated by a specific ~40 kDa calcium-dependent endonuclease.
- Genome digestion is not essential for CTL-induced cell death.
- Consequences of genome digestion, such as poly(ADP-ribose) polymerase activation, are also not essential for this form of cell death.