Cucurbitacin I induces protective autophagy in glioblastoma in vitro and in vivo

J Biol Chem. 2014 Apr 11;289(15):10607-19. doi: 10.1074/jbc.M113.528760. Epub 2014 Mar 5.


There is an urgent need for new therapeutic avenues to improve the outcome of patients with glioblastoma multiforme (GBM). Current studies have suggested that cucurbitacin I, a natural selective inhibitor of JAK2/STAT3, has a potent anticancer effect on a variety of cancer cell types. This study showed that autophagy and apoptosis were induced by cucurbitacin I. Exposure of GBM cells to cucurbitacin I resulted in pronounced apoptotic cell death through activating bcl-2 family proteins. Cells treatment with cucurbitacin I up-regulated Beclin 1 and triggered autophagosome formation and accumulation as well as conversion of LC3I to LC3II. Activation of the AMP-activated protein kinase/mammalian target of rapamycin/p70S6K pathway, but not the PI3K/AKT pathway, occurred in autophagy induced by cucurbitacin I, which was accompanied by decreased hypoxia-inducible factor 1α. Stable overexpression of hypoxia-inducible factor 1α induced by FG-4497 prevented cucurbitacin I-induced autophagy and down-regulation of bcl-2. Knockdown of beclin 1 or treatment with the autophagy inhibitor 3-methyladenine also inhibited autophagy induced by cucurbitacin I. A coimmunoprecipitation assay showed that the interaction of Bcl-2 and Beclin 1/hVps34 decreased markedly in cells treated with cucurbitacin I. Furthermore, knockdown of beclin 1 or treatment with the lysosome inhibitor chloroquine sensitized cancer cells to cucurbitacin I-induced apoptosis. Finally, a xenograft model provided additional evidence for the occurrence of cucurbitacin I-induced apoptosis and autophagy in vitro. Our findings provide new insights into the molecular mechanisms underlying cucurbitacin I-mediated GBM cell death and may provide an efficacious therapy for patients harboring GBM.

Keywords: Apoptosis; Autophagy; Chloroquine; Cucurbitacin I; Glioblastoma; Hypoxia-inducible Factor (HIF); Signal Transduction.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Animals
  • Apoptosis
  • Apoptosis Regulatory Proteins / metabolism
  • Autophagy / drug effects*
  • Beclin-1
  • Cell Line, Tumor
  • Cell Proliferation / drug effects
  • Cell Survival / drug effects
  • Chloroquine / pharmacology
  • Drug Screening Assays, Antitumor
  • Female
  • Glioblastoma / drug therapy*
  • Glioblastoma / metabolism
  • Humans
  • Hypoxia-Inducible Factor 1, alpha Subunit / metabolism
  • Mice
  • Mice, Inbred BALB C
  • Neoplasm Transplantation
  • Plant Extracts / pharmacology*
  • Proto-Oncogene Proteins c-bcl-2 / metabolism
  • RNA, Small Interfering / metabolism
  • Signal Transduction
  • Transfection
  • Triterpenes / pharmacology*
  • Triterpenes / therapeutic use


  • Apoptosis Regulatory Proteins
  • Beclin-1
  • Becn1 protein, mouse
  • HIF1A protein, human
  • Hypoxia-Inducible Factor 1, alpha Subunit
  • Plant Extracts
  • Proto-Oncogene Proteins c-bcl-2
  • RNA, Small Interfering
  • Triterpenes
  • Chloroquine
  • cucurbitacin I