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

Area of Science:

• Biochemistry
• Cell Biology
• Molecular Oncology

Background:

• Cucurbitacins are natural triterpenoids with diverse biological activities.
• Previous studies suggest cucurbitacins suppress the mTORC1/p70S6K pathway and induce autophagy.
• The precise relationship between these effects remains largely unexplored.

Purpose of the Study:

• To investigate the correlation between cucurbitacin E (CuE)-induced autophagy and mTORC1/p70S6K pathway suppression in human cancer cells.
• To elucidate the role of ATG5 and AMPK in CuE-mediated cellular responses.

Main Methods:

• Treatment of human cancer cell lines (HeLa, MCF7, DU145) with cucurbitacin E (CuE).
• Assessment of autophagy induction via LC3-II formation and LC3/LAMP2 colocalization.
• Evaluation of ATG5 dependence for CuE-induced autophagy.
• Analysis of mTORC1 activity through p70S6K and ULK1 phosphorylation.
• Investigation of AMPK activation and its role in CuE's effects.
• Utilized ATG5 knockdown and AMPK knockdown experiments.

Main Results:

• CuE treatment induced autophagy in HeLa and MCF7 cells, dependent on ATG5.
• CuE inhibited mTORC1 activity, evidenced by reduced p70S6K and ULK1 phosphorylation and decreased mTOR recruitment to lysosomes.
• CuE rapidly activated AMPK, leading to increased phosphorylation of its substrates.
• AMPK activation was crucial for CuE-induced mTORC1 suppression and autophagy induction, as demonstrated by knockdown experiments.

Conclusions:

• CuE induces autophagy in human cancer cells, at least partially through the downregulation of mTORC1 signaling.
• CuE-induced autophagy is mediated by the upregulation of AMPK activity.
• The findings clarify the molecular mechanisms underlying cucurbitacin E's biological activities in cancer cells.