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Bile acids stimulate cFLIP phosphorylation enhancing TRAIL-mediated apoptosis
Hajime Higuchi1, Jung-Hwan Yoon, Annette Grambihler
1Division of Gastroenterology and Hepatology, Mayo Medical School, Clinic, and Foundation, Rochester, Minnesota 55905, USA.
The Journal of Biological Chemistry
|October 31, 2002
Summary
Bile acids enhance TRAIL-induced apoptosis in liver cells by affecting the death-inducing signaling complex (DISC). This involves increased caspase activation and altered cFLIP protein activity, revealing mechanisms of bile acid cytotoxicity.
Area of Science:
- Hepatology
- Cell Biology
- Molecular Toxicology
Background:
- Bile acids are known to cause liver injury through apoptosis.
- Death receptor signaling pathways, such as TNF-Related Apoptosis-Inducing Ligand (TRAIL)-mediated apoptosis, are crucial in regulating cell death.
- Understanding how bile acids interact with these pathways is vital for comprehending liver disease pathogenesis.
Purpose of the Study:
- To investigate the effects of bile acids on TRAIL-mediated apoptosis in hepatocytes.
- To elucidate the molecular mechanisms by which bile acids potentiate death receptor signaling.
- To examine the role of glycochenodeoxycholate (GCDCA) in TRAIL-induced apoptosis and its impact on the death-inducing signaling complex (DISC).
Main Methods:
- Utilized HuH-7 cells stably transfected with a bile acid transporter.
- Assessed TRAIL-induced apoptosis markers, including caspase activation, bid cleavage, and cytochrome c release.
- Analyzed the composition and processing of the TRAIL DISC, including receptor expression, caspase recruitment, and cFLIP binding, using techniques like Western blotting and GST pull-down assays.
- Investigated the role of cFLIP phosphorylation and protein kinase C (PKC) in bile acid-mediated potentiation of apoptosis.
Main Results:
- Bile acids, specifically GCDCA, enhanced TRAIL-induced apoptosis in hepatocytes.
- GCDCA increased the activation of caspases 8 and 10, bid cleavage, and caspase 3 activation.
- While GCDCA did not alter the expression of key apoptosis-related proteins, it increased caspase recruitment/processing in the DISC and reduced cFLIP recruitment.
- GCDCA-induced cFLIP phosphorylation reduced its binding to FADD, an effect reversed by a PKC inhibitor, which also attenuated bile acid-potentiated apoptosis.
Conclusions:
- Bile acids potentiate TRAIL-induced apoptosis by modulating the DISC composition and function.
- GCDCA-induced cFLIP phosphorylation plays a critical role in enhancing hepatocyte apoptosis via the TRAIL pathway.
- These findings provide novel insights into the mechanisms of bile acid-induced liver injury and the regulation of death receptor signaling.