Anticancer effects of bufalin on human hepatocellular carcinoma HepG2 cells: roles of apoptosis and autophagy

Int J Mol Sci. 2013 Jan 11;14(1):1370-82. doi: 10.3390/ijms14011370.

Abstract

The traditional Chinese medicine bufalin, extracted from toad's skin, has been demonstrated to exert anticancer activities in various kinds of human cancers. The mechanisms of action lie in its capacity to induce apoptosis, or termed type I programmed cell death (PCD). However, type II PCD, or autophagy, participates in cancer proliferation, progression, and relapse, as well. Recent studies on autophagy seem to be controversial because of the dual roles of autophagy in cancer survival and death. In good agreement with previous studies, we found that 100 nM bufalin induced extensive HepG2 cell apoptosis. However, we also noticed bufalin triggered autophagy and enhanced Beclin-1 expression, LC3-I to LC3-II conversion, as well as decreased p62 expression and mTOR signaling activation in HepG2 cells. Blockage of autophagy by selective inhibitor 3-MA decreased apoptotic ratio in bufalin-treated HepG2 cells, suggesting a proapoptotic role of bufalin-induced autophagy. Furthermore, we investigated the underlying mechanisms of bufalin-induced autophagy. Bufalin treatment dose-dependently promoted AMPK phosphorylation while AMPK inhibition by compound C significantly attenuated bufalin-induced autophagy. Taken together, we report for the first time that bufalin induces HepG2 cells PCD, especially for autophagy, and the mechanism of action is, at least in part, AMPK-mTOR dependent.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • AMP-Activated Protein Kinases / metabolism
  • Antineoplastic Agents / chemistry
  • Antineoplastic Agents / pharmacology*
  • Apoptosis / drug effects*
  • Apoptosis Regulatory Proteins / metabolism
  • Autophagy / drug effects*
  • Beclin-1
  • Blotting, Western
  • Bufanolides / chemistry
  • Bufanolides / pharmacology*
  • Carcinoma, Hepatocellular / metabolism
  • Carcinoma, Hepatocellular / pathology
  • Carcinoma, Hepatocellular / ultrastructure
  • Cell Proliferation / drug effects
  • Dose-Response Relationship, Drug
  • Hep G2 Cells
  • Humans
  • Liver Neoplasms / metabolism
  • Liver Neoplasms / pathology
  • Liver Neoplasms / ultrastructure
  • Membrane Proteins / metabolism
  • Microscopy, Confocal
  • Microscopy, Electron, Transmission
  • Microtubule-Associated Proteins / metabolism
  • Molecular Structure
  • Phosphorylation / drug effects
  • Signal Transduction / drug effects
  • TOR Serine-Threonine Kinases / metabolism

Substances

  • Antineoplastic Agents
  • Apoptosis Regulatory Proteins
  • BECN1 protein, human
  • Beclin-1
  • Bufanolides
  • MAP1LC3A protein, human
  • Membrane Proteins
  • Microtubule-Associated Proteins
  • MTOR protein, human
  • TOR Serine-Threonine Kinases
  • AMP-Activated Protein Kinases
  • bufalin