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Alternative Pathways of Cancer Cell Death by Rottlerin: Apoptosis versus Autophagy.

ABSTRACT: Since the ability of cancer cells to evade apoptosis often limits the efficacy of radiotherapy and chemotherapy, autophagy is emerging as an alternative target to promote cell death. Therefore, we wondered whether Rottlerin, a natural polyphenolic compound with antiproliferative effects in several cell types, can induce cell death in MCF-7 breast cancer cells. The MCF-7 cell line is a good model of chemo/radio resistance, being both apoptosis and autophagy resistant, due to deletion of caspase 3 gene, high expression of the antiapoptotic protein Bcl-2, and low expression of the autophagic Beclin-1 protein. The contribution of autophagy and apoptosis to the cytotoxic effects of Rottlerin was examined by light, fluorescence, and electron microscopic examination and by western blotting analysis of apoptotic and autophagic markers. By comparing caspases-3-deficient (MCF-7(3def)) and caspases-3-transfected MCF-7 cells (MCF-7(3trans)), we found that Rottlerin induced a noncanonical, Bcl-2-, Beclin 1-, Akt-, and ERK-independent autophagic death in the former- and the caspases-mediated apoptosis in the latter, in not starved conditions and in the absence of any other treatment. These findings suggest that Rottlerin could be cytotoxic for different cancer cell types, both apoptosis competent and apoptosis resistant.

SUBMITTER: Torricelli C

PROVIDER: S-EPMC3541534 | biostudies-literature | 2012

REPOSITORIES: biostudies-literature

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Alternative Pathways of Cancer Cell Death by Rottlerin: Apoptosis versus Autophagy.

Torricelli Claudia C Salvadori Sara S Valacchi Giuseppe G Souček Karel K Slabáková Eva E Muscettola Michela M Volpi Nila N Maioli Emanuela E

Evidence-based complementary and alternative medicine : eCAM 20121220

Since the ability of cancer cells to evade apoptosis often limits the efficacy of radiotherapy and chemotherapy, autophagy is emerging as an alternative target to promote cell death. Therefore, we wondered whether Rottlerin, a natural polyphenolic compound with antiproliferative effects in several cell types, can induce cell death in MCF-7 breast cancer cells. The MCF-7 cell line is a good model of chemo/radio resistance, being both apoptosis and autophagy resistant, due to deletion of caspase 3 ...[more]

PMID: 23320042

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Project description:BACKGROUND: Autophagy is an indispensable lysosomal self-digestion process involved in the degradation of aggregated proteins and damaged organelles. Autophagy is associated with the several pathological processes, including cancer. Cancer stem cells (CSCs) play significant roles in cancer initiation, progression and drug resistance. Recent studies have demonstrated the antitumor activities of plant-derived chemopreventive agent rottlerin (Rott). However, the molecular mechanism by which Rott induces autophagy in breast CSCs has not been investigated. RESULTS: The objectives of this study were to examine the molecular mechanism by which Rott induces autophagy which leads to apoptosis in breast CSCs. Treatment of breast CSCs with Rott for 24 h resulted in a concentration dependent induction of autophagy, followed by apoptosis as measured by flow cytometry. Electron microscopy confirmed the presence of autophagosomes in Rott treated breast CSCs. Western blot analysis showed that Rott treatment increased the expression of LC3, Beclin-1 and Atg12 that are accumulated during autophagy. Prolonged exposure of breast CSCs to Rott caused apoptosis which was associated with the suppression of phosphorylated Akt and mTOR, upregulation of phosphorylated AMPK, and downregulation of anti-apoptosis Bcl-2, Bcl-X(L), XIAP and cIAP-1. Knock-down of Atg7 or Beclin-1 by shRNA inhibited Rott-induced autophagy at 24 h. Our study also demonstrates that pre-treatment of breast CSCs with autophagosome inhibitors 3-methyladenine and Bafilomycin, as well as protein synthesis inhibitor cycloheximide inhibited Rott-induced autophagy and apoptosis. Rott induces autophagy via extensive cytoplasmic vacuolization in breast CSCs. Molecular docking results between C2-domain of protein kinase C-delta and Rott indicated that both hydrogen bonding and hydrophobic interactions contributed significantly for ligand binding with minimum binding affinity of ? 7.5 Kcal/mol. Although, autophagy inhibitors suppress the formation of cytoplasmic vacuolization and autophagy in breast CSCs, the potency of Rott to induce autophagy and apoptosis might be based on its capability to activate several pathways such as AMPK and proteasome inhibition. CONCLUSIONS: A better understanding of the relationship between autophagy and apoptosis would eventually allow us to discover novel drugs for the treatment of breast cancer by eliminating CSCs.

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Alternative Pathways of Cancer Cell Death by Rottlerin: Apoptosis versus Autophagy.

Publications

Alternative Pathways of Cancer Cell Death by Rottlerin: Apoptosis versus Autophagy.

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