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Involvement of caspase family proteases in transforming growth factor-beta-induced apoptosis
1Dr. H.L. Tsai Memorial Laboratory, Institute of Molecular Medicine, College of Medicine, Taipei, Taiwan.
Abstract:
Transforming growth factor-beta (TGF-beta) is a potent inducer of programmed cell death in liver as well as some hepatoma cell lines. To explore the mechanism by which TGF-beta induces apoptosis, we investigated the role of caspase family proteases in the apoptotic death of a human hepatoma cell line, Hep3B. We showed that TGF-beta-induced apoptosis was blocked by expression of the cowpox virus protein CrmA, a serpin-like pseudosubstrate for some of the caspase family proteases. CrmA expression, however, did not affect TGF-beta-induced regulation of promoter activities of the cyclin A and plasminogen activator inhibitor type I genes. These results indicate that CrmA inhibits a step specific for the apoptotic effect of TGF-beta. In addition to CrmA, a tripeptide caspase-protease inhibitor, z-Val-Ala-Asp-fluoromethylketone could also suppress TGF-beta-induced apoptosis in a dose-dependent manner. In TGF-beta-treated Hep3B cells, we observed a specific degradation of the catalytic subunit of DNA-dependent protein kinase, which was previously shown to be a substrate of caspase-3 but not several other members of the caspase family. This degradation was not seen in Hep3B cells transfected with CrmA nor in Hep3B cells pretreated with the tripeptide caspase inhibitor. Our study indicates a requirement of caspase family proteases in TGF-beta-induced apoptosis.
Insights
Transforming growth factor-beta (TGF-beta) triggers apoptosis in liver cells. Caspase proteases are essential for this TGF-beta-induced cell death, as shown by inhibitor studies.
Area of Science:
- Cell Biology
- Molecular Biology
- Biochemistry
Background:
- Transforming growth factor-beta (TGF-beta) induces programmed cell death (apoptosis) in liver and hepatoma cells.
- The precise molecular mechanisms underlying TGF-beta-induced apoptosis require further elucidation.
Purpose of the Study:
- To investigate the role of caspase family proteases in TGF-beta-induced apoptosis in the human hepatoma cell line Hep3B.
- To identify specific caspase-dependent events in the apoptotic pathway initiated by TGF-beta.
Main Methods:
- Utilized cowpox virus protein CrmA and a tripeptide caspase inhibitor (z-Val-Ala-Asp-fluoromethylketone) to block caspase activity.
- Assessed the impact of caspase inhibition on TGF-beta-induced apoptosis and gene promoter activity.
- Examined the degradation of DNA-dependent protein kinase catalytic subunit in response to TGF-beta treatment.
Main Results:
- TGF-beta-induced apoptosis in Hep3B cells was significantly inhibited by CrmA and the tripeptide caspase inhibitor.
- CrmA did not affect TGF-beta-induced gene promoter regulation, indicating a specific role in apoptosis.
- Specific degradation of the DNA-dependent protein kinase catalytic subunit, a caspase-3 substrate, was observed in TGF-beta-treated cells and prevented by caspase inhibitors.
Conclusions:
- Caspase family proteases are required for TGF-beta-induced apoptosis in human hepatoma cells.
- The findings highlight the critical role of caspases, particularly caspase-3, in mediating TGF-beta-driven apoptotic signaling pathways.