The bile acid-activated phosphatidylinositol 3-kinase pathway inhibits Fas apoptosis upstream of bid in rodent hepatocytes.
OBJECTIVE
Bile acids differentially modulate hepatocyte injury in cholestasis. Although glycochenodeoxycholate (GCDC) induces Fas-mediated hepatocyte apoptosis, taurochenodeoxycholate (TCDC) simultaneously activates a phosphatidylinositol 3-kinase (PI 3-K)-mediated survival pathway blocking Fas apoptosis. In this study, the mechanisms by which the TCDC/PI 3-K survival signal disrupts Fas signaling were examined.


METHODS
Studies were performed in primary cultures of mouse hepatocytes and the bile-salt-transporting McNtcp.24 rat hepatoma cell line.


RESULTS
GCDC, but not TCDC, resulted in cytochrome c release demonstrating that TCDC blocked apoptosis upstream of mitochondria. In contrast, both GCDC and TCDC treatment resulted in Fas aggregation and recruitment of a dominant-negative FADD green fluorescent protein (GFP) and C360S procaspase 8-GFP to the plasma membrane. Despite recruitment of procaspase 8 to the plasma membrane by both bile acids, only GCDC resulted in increases of caspase 8 activity and Bid-GFP mitochondrial translocation. However, when PI-3K was inhibited with wortmannin or dominant-negative PI 3-K, TCDC-induced Bid-GFP mitochondrial translocation and cytochrome c release.


CONCLUSIONS
The TCDC/PI 3-K survival signal blocks Fas-mediated apoptosis by preventing caspase 8 activation and Bid mitochondrial translocation. Potentiation of this survival pathway in cholestasis has the potential to attenuate liver injury.
Takikawa
Y
Y
Division of Gastroenterology and Hepatology, Mayo Clinic, Rochester, Minnesota 55905, USA.
Miyoshi
H
H
Rust
C
C
Roberts
P
P
Siegel
R
R
Mandal
P K
PK
Millikan
R E
RE
Gores
G J
GJ
D048868:Adaptor Proteins, Signal Transducing; D000818:Animals; D017209:Apoptosis; D051023:BH3 Interacting Domain Death Agonist Protein; D002352:Carrier Proteins / Q000378:metabolism* / Q000502:physiology; D053181:Caspase 8; D053453:Caspase 9; D020169:Caspases / Q000378:metabolism; D002779:Cholestasis / Q000209:etiology; D003574:Cytochrome c Group / Q000378:metabolism; D004789:Enzyme Activation; D004792:Enzyme Precursors / Q000378:metabolism; D053200:Fas-Associated Death Domain Protein; D005999:Glycochenodeoxycholic Acid / Q000494:pharmacology; D008297:Male; D051379:Mice; D008810:Mice, Inbred C57BL; D008928:Mitochondria / Q000201:enzymology; D019869:Phosphatidylinositol 3-Kinases / Q000502:physiology*; D013657:Taurodeoxycholic Acid / Q000494:pharmacology*; D019014:fas Receptor / Q000502:physiology*
D048868:Adaptor Proteins, Signal Transducing; D051023:BH3 Interacting Domain Death Agonist Protein; C494815:Bid protein, mouse; D002352:Carrier Proteins; D003574:Cytochrome c Group; D004792:Enzyme Precursors; C505534:Fadd protein, mouse; C505535:Fadd protein, rat; D053200:Fas-Associated Death Domain Protein; D019014:fas Receptor; D013657:Taurodeoxycholic Acid; D005999:Glycochenodeoxycholic Acid; D019869:Phosphatidylinositol 3-Kinases; C505526:Casp8 protein, mouse; C505528:Casp8 protein, rat; C506434:Casp9 protein, mouse; C506435:Casp9 protein, rat; D053181:Caspase 8; D053453:Caspase 9; D020169:Caspases