An auxiliary mode of apoptotic DNA fragmentation provided by phagocytes
- Dorian McIlroy1,2,
- Masato Tanaka1,2,
- Hideki Sakahira1,2,
- Hidehiro Fukuyama1,2,
- Misao Suzuki3,
- Ken-ichi Yamamura3,
- Yoshiyuki Ohsawa4,
- Yasuo Uchiyama4, and
- Shigekazu Nagata1,2,5
- 1Department of Genetics, and 4Cell Biology and Anatomy, Osaka University Medical School, and 2Core Research for Evolutional Science and Technology, Japan Science and Technology Corporation, Suita, Osaka 565-0871, Japan; 3Institute of Molecular Embryology and Genetics, Kumamoto University School of Medicine, Kumamoto 862-0976, Japan
Abstract
CAD (caspase-activated DNase) can cause DNA fragmentation in apoptotic cells. Transgenic mice that ubiquitously express a caspase-resistant form of the CAD inhibitor (ICAD) were generated. Thymocytes prepared from the mice were resistant to DNA fragmentation induced by a variety of stimuli. However, similar numbers of TUNEL-positive cells were present in adult tissues of transgenic and wild-type mice. Exposure to γ-irradiation caused a striking increase in the number of TUNEL-positive cells in the thymus of wild-type, but not transgenic, mice. TUNEL-positive nuclei in transgenic mice were confined to thymic macrophages. When apoptotic thymocytes from the transgenic mice were cocultured with macrophages, the thymocytes underwent phagocytosis and their chromosomal DNA underwent fragmentation. This DNA fragmentation was sensitive to inhibitors that block the acidification of lysosomes. Hence, we conclude that the DNA fragmentation that occurs during apoptosis not only can result cell-autonomously from CAD activity but can also be attributed to a lysosomal acid DNase(s), most likely DNase II, after the apoptotic cells are engulfed.
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Footnotes
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↵5 Corresponding author.
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E-MAIL nagata{at}genetic.med.osaka-u.ac.jp; FAX 81-6-6879-3319.
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- Received December 20, 1999.
- Accepted January 21, 2000.
- Cold Spring Harbor Laboratory Press
