Insulin and dexamethasone inhibit TGF-beta-induced apoptosis of hepatoma cells upstream of the caspase activation cascade.
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.
Wanke
Ines
I
Department of Toxicology, Institute of Pharmacology and Toxicology, University of Tübingen, Wilhelmstr. 56, 72074 Tübingen, Germany.
Schwarz
Michael
M
Buchmann
Albrecht
A
D000818:Animals; D017209:Apoptosis / Q000187:drug effects* / Q000502:physiology; D006528:Carcinoma, Hepatocellular / Q000201:enzymology / Q000378:metabolism / Q000473:pathology*; D061945:Caspase Inhibitors; D020169:Caspases / Q000378:metabolism; D045744:Cell Line, Tumor; D003907:Dexamethasone / Q000494:pharmacology*; D004789:Enzyme Activation / Q000187:drug effects; D004791:Enzyme Inhibitors / Q000494:pharmacology; D006801:Humans; D007328:Insulin / Q000494:pharmacology*; D008114:Liver Neoplasms, Experimental / Q000201:enzymology / Q000378:metabolism / Q000473:pathology*; D051381:Rats; D016212:Transforming Growth Factor beta / Q000037:antagonists & inhibitors* / Q000494:pharmacology
D061945:Caspase Inhibitors; D004791:Enzyme Inhibitors; D007328:Insulin; D016212:Transforming Growth Factor beta; D003907:Dexamethasone; D020169:Caspases