Abstract
Avicins, a family of plant triterpene electrophiles, can trigger apoptosis-associated tumor cell death, and suppress chemical-induced carcinogenesis by its anti-inflammatory, anti-mutagenic, and antioxidant properties. Here, we show that tumor cells treated with benzyloxycarbonylvalyl-alanyl–aspartic acid (O-methyl)–fluoro-methylketone, an apoptosis inhibitor, and Bax−/−Bak−/− apoptosis-resistant cells can still undergo cell death in response to avicin D treatment. We demonstrate that this non-apoptotic cell death is mediated by autophagy, which can be suppressed by chloroquine, an autophagy inhibitor, and by specific knockdown of autophagy-related gene-5 (Atg5) and Atg7. Avicin D decreases cellular ATP levels, stimulates the activation of AMP-activated protein kinase (AMPK), and inhibits mammalian target of rapamycin (mTOR) and S6 kinase activity. Suppression of AMPK by compound C and dominant-negative AMPK decreases avicin D-induced autophagic cell death. Furthermore, avicin D-induced autophagic cell death can be abrogated by knockdown of tuberous sclerosis complex 2 (TSC2), a key mediator linking AMPK to mTOR inhibition, suggesting that AMPK activation is a crucial event targeted by avicin D. These findings indicate the therapeutic potential of avicins by triggering autophagic cell death.
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Abbreviations
- AMPK:
-
AMP-activated protein kinase
- Atg:
-
autophagy-related gene
- CQ:
-
chloroquine
- LC3:
-
light-chain 3
- MP:
-
methylpyruvate
- mTOR:
-
mammalian target of rapamycin
- TSC2:
-
tuberous sclerosis complex 2
- zVAD–fmk:
-
benzyloxycarbonylvalyl-alanyl–aspartic acid (O-methyl)–fluoro-methylketone
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Acknowledgements
We thank Dr. Craig B Thompson for providing Bax−/− Bak−/− cells, Dr. Kun-Liang Guan for providing AMPK-DN plasmid, Dr. Gaochao Zhou from Merck Research Laboratories for providing compound C. We thank Dr. YL Lu for her helpful discussion. We thank Mr. K Dunner, Jr. and Ms. Shuangxing Yu for the expert technical assistance. This work was supported by the Clayton Foundation for Research, the Biomedical Research Foundation (to JUG), Developmental Research Awards from National Institutes of Health SPORE (P50-CA83639) (to Z.X.X), and MD Anderson Cancer Center Core Grant CA16672 from the National Cancer Institute, which supported the core facilities.
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Xu, ZX., Liang, J., Haridas, V. et al. A plant triterpenoid, avicin D, induces autophagy by activation of AMP-activated protein kinase. Cell Death Differ 14, 1948–1957 (2007). https://doi.org/10.1038/sj.cdd.4402207
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DOI: https://doi.org/10.1038/sj.cdd.4402207
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