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FADD is required for multiple signaling events downstream of the receptor Fas
1Department of Cell Biology, Harvard Medical School, Boston, Massachusetts 02115, USA.
Abstract:
To identify essential components of the Fas-induced apoptotic signaling pathway, Jurkat T lymphocytes were chemically mutagenized and selected for clones that were resistant to Fas-induced apoptosis. We obtained five cell lines that contain mutations in the adaptor FADD. All five cell lines did not express FADD by immunoblot analysis and were completely resistant to Fas-induced death. Complementation of the FADD mutant cell lines with wild-type FADD restored Fas-mediated apoptosis. Fas activation of caspase-2, caspase-3, caspase-7, and caspase-8 and the proteolytic cleavage of substrates such as BID, protein kinase Cdelta, and poly(ADP-ribose) polymerase were completely defective in the FADD mutant cell lines. In addition, Fas activation of the stress kinases p38 and c-Jun NH2 kinase and the generation of ceramide in response to Fas ligation were blocked in the FADD mutant cell lines. These data indicate that FADD is essential for multiple signaling events downstream of Fas.
Insights
Fas-associated death domain (FADD) is crucial for Fas-induced apoptosis. Mutants lacking FADD resist Fas-mediated cell death, highlighting FADD's essential role in this critical signaling pathway.
Area of Science:
- Cell Biology
- Molecular Biology
- Immunology
Background:
- The Fas receptor (also known as CD95 or APO-1) plays a key role in initiating apoptosis, a programmed cell death process.
- Understanding the molecular machinery downstream of Fas is critical for comprehending immune regulation and disease pathogenesis.
Purpose of the Study:
- To identify essential adaptor proteins in the Fas-induced apoptotic signaling pathway.
- To elucidate the specific functions of FADD in mediating Fas-triggered cellular responses.
Main Methods:
- Chemical mutagenesis of Jurkat T lymphocytes to generate apoptosis-resistant clones.
- Immunoblot analysis to assess FADD expression levels.
- Complementation assays using wild-type FADD to restore apoptosis.
- Analysis of caspase activation and substrate cleavage downstream of Fas.
Main Results:
- Five distinct cell lines with mutations in the Fas-associated death domain (FADD) were isolated.
- These FADD-deficient cell lines exhibited complete resistance to Fas-induced apoptosis.
- Restoration of FADD expression rescued Fas-mediated apoptosis.
- Activation of caspases (caspase-2, -3, -7, -8) and cleavage of substrates (BID, PKCdelta, PARP) were abolished in FADD mutants.
- Fas-induced activation of stress kinases (p38, JNK) and ceramide generation were also blocked.
Conclusions:
- Fas-associated death domain (FADD) is indispensable for multiple signaling events downstream of Fas receptor activation.
- FADD acts as a central adaptor protein, integrating signals required for initiating apoptosis and other cellular responses.
- Targeting FADD or its interactions may offer therapeutic strategies for modulating apoptosis in various diseases.