Cucurbitacin E Induces Autophagy via Downregulating mTORC1 Signaling and Upregulating AMPK Activity.

Abstract

Cucurbitacins, the natural triterpenoids possessing many biological activities, have been reported to suppress the mTORC1/p70S6K pathway and to induce autophagy. However, the correlation between such activities is largely unknown. In this study, we addressed this issue in human cancer cells in response to cucurbitacin E (CuE) treatment. Our results showed that CuE induced autophagy as evidenced by the formation of LC3-II and colocalization of punctate LC3 with the lysosomal marker LAMP2 in HeLa and MCF7 cells. However, CuE induced much lower levels of autophagy in ATG5-knocked down cells and failed to induce autophagy in DU145 cells lacking functional ATG5 expression, suggesting the dependence of CuE-induced autophagy on ATG5. Consistent with autophagy induction, mTORC1 activity (as reflected by p70S6K and ULK1S758 phosphorylation) was inhibited by CuE treatment. The suppression of mTORC1 activity was further confirmed by reduced recruitment of mTOR to the lysosome, which is the activation site of mTORC1. In contrast, CuE rapidly activated AMPK leading to increased phosphorylation of its substrates. AMPK activation contributed to CuE-induced suppression of mTORC1/p70S6K signaling and autophagy induction, since AMPK knockdown diminished these effects. Collectively, our data suggested that CuE induced autophagy in human cancer cells at least partly via downregulation of mTORC1 signaling and upregulation of AMPK activity.

• Authors: Qing-Bing Zha, Xiao-Yu Zhang, Qiu-Ru Lin, Li-Hui Xu, Gao-Xiang Zhao, Hao Pan, Dan Zhou, Dong-Yun Ouyang, Ze-Huan Liu, Xian-Hui He
• Journal: PloS one (PLoS One) Vol. 10 Issue 5 Pg. e0124355 ( 2015) ISSN: 1932-6203 [Electronic] United States
• PMID: 25970614 (Publication Type: Journal Article, Research Support, Non-U.S. Gov't)

Chemical References

• ATG5 protein, human
• Antineoplastic Agents, Phytogenic
• Autophagy-Related Protein 5
• Intracellular Signaling Peptides and Proteins
• LAMP2 protein, human
• Lysosomal-Associated Membrane Protein 2
• MAP1LC3A protein, human
• Microtubule-Associated Proteins
• Multiprotein Complexes
• RNA, Small Interfering
• Triterpenes
• Autophagy-Related Protein-1 Homolog
• Mechanistic Target of Rapamycin Complex 1
• Protein Serine-Threonine Kinases
• Ribosomal Protein S6 Kinases, 70-kDa
• TOR Serine-Threonine Kinases
• ULK1 protein, human
• AMP-Activated Protein Kinases
• cucurbitacin E

Topics

• AMP-Activated Protein Kinases (genetics, metabolism)
• Antineoplastic Agents, Phytogenic (pharmacology)
• Autophagy (drug effects)
• Autophagy-Related Protein 5
• Autophagy-Related Protein-1 Homolog
• Cell Line, Tumor
• Cell Survival (drug effects)
• Gene Expression Regulation, Neoplastic
• HeLa Cells
• Humans
• Intracellular Signaling Peptides and Proteins (genetics, metabolism)
• Lysosomal-Associated Membrane Protein 2 (genetics, metabolism)
• Lysosomes (drug effects, metabolism)
• MCF-7 Cells
• Mechanistic Target of Rapamycin Complex 1
• Microtubule-Associated Proteins (antagonists & inhibitors, genetics, metabolism)
• Multiprotein Complexes (antagonists & inhibitors, genetics, metabolism)
• Phosphorylation (drug effects)
• Protein Serine-Threonine Kinases (genetics, metabolism)
• RNA, Small Interfering (genetics, metabolism)
• Ribosomal Protein S6 Kinases, 70-kDa (antagonists & inhibitors, genetics, metabolism)
• Signal Transduction
• TOR Serine-Threonine Kinases (antagonists & inhibitors, genetics, metabolism)
• Triterpenes (pharmacology)