Related Experiment Videos
Tumor necrosis factor induces apoptosis in hepatoma cells by increasing Ca(2+) release from the endoplasmic reticulum
Byung-Chul Kim1, Heung-Tae Kim, Mizuko Mamura
1Laboratory of Cell Regulation and Carcinogenesis, National Cancer Institute, National Institutes of Health, Bethesda, Maryland 20892, USA.
Abstract:
Tumor necrosis factor (TNF) plays an import role in the control of apoptosis. The most well known apoptotic pathway regulated by TNF involves the TNFR1-associated death domain protein, Fas-associated death domain protein, and caspase-8. This study examines the mechanism of TNF-induced apoptosis in FaO rat hepatoma cells. TNF treatment significantly increased the percentage of apoptotic cells. TNF did not activate caspase-8 but activated caspase-3, -10, and -12. The effect of TNF on the expression of different members of the Bcl-2 family in these cells was studied. We observed no detectable changes in the steady-state levels of Bcl-X(L), Bax, and Bid, although TNF suppresses Bcl-2 expression. Dantrolene suppressed the inhibitory effect of TNF on Bcl-2 expression. TNF induced release of Ca(2+) from the endoplasmic reticulum (ER) that was blocked by dantrolene. Importantly, the expression of Bcl-2 blocked TNF-induced apoptosis and decreased TNF-induced Ca(2+) release. These results suggest that TNF induces apoptosis by a mechanism that involves increasing Ca(2+) release from the ER and suppression of Bcl-2 expression.
Insights
Tumor necrosis factor (TNF) triggers apoptosis in liver cells by releasing calcium from the ER and reducing Bcl-2. Dantrolene and Bcl-2 expression block this TNF-induced cell death.
Area of Science:
- Molecular Biology
- Cell Biology
- Biochemistry
Background:
- Tumor necrosis factor (TNF) is a key regulator of apoptosis.
- The canonical TNF-induced apoptotic pathway involves TNFR1, FADD, and caspase-8.
- The precise mechanisms of TNF-induced apoptosis in specific cell types require further elucidation.
Purpose of the Study:
- To investigate the mechanism of TNF-induced apoptosis in FaO rat hepatoma cells.
- To identify the specific caspases activated by TNF in this cellular model.
- To examine the role of Bcl-2 family proteins and calcium signaling in TNF-induced apoptosis.
Main Methods:
- FaO rat hepatoma cells were treated with TNF.
- Apoptosis levels were quantified.
- Caspase activation (caspase-3, -8, -10, -12), Bcl-2 family protein expression, and intracellular calcium (Ca2+) release from the endoplasmic reticulum (ER) were assessed.
- The effects of dantrolene and Bcl-2 overexpression were evaluated.
Main Results:
- TNF treatment significantly increased apoptosis in FaO cells.
- TNF activated caspase-3, -10, and -12, but not caspase-8.
- TNF suppressed Bcl-2 expression and induced Ca2+ release from the ER.
- Dantrolene inhibited TNF's effect on Bcl-2 and Ca2+ release.
- Bcl-2 expression blocked TNF-induced apoptosis and Ca2+ release.
Conclusions:
- TNF induces apoptosis in FaO rat hepatoma cells via a non-canonical pathway.
- This mechanism involves Ca2+ release from the ER and suppression of Bcl-2 expression.
- Bcl-2 plays a critical role in protecting cells against TNF-induced apoptosis.