Insulin and dexamethasone inhibit TGF-beta-induced apoptosis of hepatoma cells upstream of the caspase activation cascade

Toxicology. 2004 Nov 15;204(2-3):141-54. doi: 10.1016/j.tox.2004.06.020.


Insulin and dexamethasone are potent inhibitors of apoptosis induced by transforming growth factor-beta1 (TGF-beta) in hepatoma cells. Using FTO-2B rat hepatoma cells, we determined whether the anti-apoptotic effects of these agents result from interference within or upstream of the TGF-beta-induced caspase cascade. Activation of different initiator and effector caspases, Bax and Bcl-xL expression, mitochondrial cytochrome c release and activation of PKB/Akt were analyzed by use of synthetic caspase substrates and Western blotting, respectively. TGF-beta-induced apoptosis was characterized by release of cytochrome c from mitochondria and activation of caspases-3, -7, -8 and -9. These effects were observable as early as 8-12 h after start of treatment and increased with time of observation. Inhibition of TGF-beta-induced apoptosis by insulin and dexamethasone was paralleled by a strong reduction of caspase-3-like activity. Caspase-8 activation was almost completely suppressed by these agents, and caspase-9 activity was decreased to levels within or slightly above unstimulated control cells. In addition, cytochrome c release from mitochondria was efficiently repressed, which was associated with upregulation of Bcl-xL by dexamethasone and activation of PKB/Akt by insulin. Thus, both anti-apoptotic compounds exert their inhibitory effects through modulation of anti-apoptotic signalling pathways involved in regulation of cytochrome c release and activation of the caspase machinery.

Publication types

  • Comparative Study
  • Research Support, Non-U.S. Gov't

MeSH terms

  • Animals
  • Apoptosis / drug effects*
  • Apoptosis / physiology
  • Carcinoma, Hepatocellular / enzymology
  • Carcinoma, Hepatocellular / metabolism
  • Carcinoma, Hepatocellular / pathology*
  • Caspase Inhibitors*
  • Caspases / metabolism
  • Cell Line, Tumor
  • Dexamethasone / pharmacology*
  • Enzyme Activation / drug effects
  • Enzyme Inhibitors / pharmacology
  • Humans
  • Insulin / pharmacology*
  • Liver Neoplasms, Experimental / enzymology
  • Liver Neoplasms, Experimental / metabolism
  • Liver Neoplasms, Experimental / pathology*
  • Rats
  • Transforming Growth Factor beta / antagonists & inhibitors*
  • Transforming Growth Factor beta / pharmacology


  • Caspase Inhibitors
  • Enzyme Inhibitors
  • Insulin
  • Transforming Growth Factor beta
  • Dexamethasone
  • Caspases