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A Fas-associated protein factor, FAF1, potentiates Fas-mediated apoptosis
1Department of Medicine, University of California, San Francisco 94143, USA.
Abstract:
Fas, a member of the tumor necrosis factor receptor family, can induce apoptosis when activated by Fas ligand binding or anti-Fas antibody crosslinking. Genetic studies have shown that a defect in Fas-mediated apoptosis resulted in abnormal development and function of the immune system in mice. A point mutation in the cytoplasmic domain of Fas (a single base change from T to A at base 786), replacing isoleucine with asparagine, abolishes the signal transducing property of Fas. Mice homozygous for this mutant allele (lprcg/lprcg mice) develop lymphadenopathy and a lupus-like autoimmune disease. Little is known about the mechanism of signal transduction in Fas-mediated apoptosis. In this study, we used the two-hybrid screen in yeast to isolate a Fas-associated protein factor, FAF1, which specifically interacts with the cytoplasmic domain of wild-type Fas but not the lprcg-mutated Fas protein. This interaction occurs not only in yeast but also in mammalian cells. When transiently expressed in L cells, FAF1 potentiated Fas-induced apoptosis. A search of available DNA and protein sequence data banks did not reveal significant homology between FAF1 and known proteins. Therefore, FAF1 is an unusual protein that binds to the wild type but not the inactive point mutant of Fas. FAF1 potentiates Fas-induced cell killing and is a candidate signal transducing molecule in the regulation of apoptosis.
Insights
Researchers identified Fas-Associated Factor 1 (FAF1), a novel protein that binds to wild-type Fas and enhances Fas-mediated apoptosis. This discovery sheds light on the molecular mechanisms regulating programmed cell death.
Area of Science:
- Molecular Biology
- Immunology
- Cell Biology
Background:
- Fas receptor activation triggers apoptosis, crucial for immune system regulation.
- Mutations in Fas impair immune function, leading to autoimmune diseases like lupus.
- The precise signal transduction pathway for Fas-mediated apoptosis remains largely unknown.
Purpose of the Study:
- To identify novel proteins interacting with the Fas receptor's cytoplasmic domain.
- To investigate the role of these interacting proteins in Fas-mediated apoptosis.
- To elucidate the molecular mechanisms underlying Fas signal transduction.
Main Methods:
- Yeast two-hybrid screening was employed to identify Fas-interacting proteins.
- Interaction studies were validated in mammalian cells.
- Functional assays assessed the impact of identified proteins on Fas-induced apoptosis.
Main Results:
- A novel protein, Fas-Associated Factor 1 (FAF1), was isolated.
- FAF1 specifically binds to wild-type Fas but not a functionally inactive mutant (lprcg).
- FAF1 expression potentiates Fas-induced apoptosis in mammalian cells.
Conclusions:
- FAF1 is a novel protein that interacts with Fas and enhances apoptosis.
- FAF1 is a potential signal-transducing molecule in the Fas pathway.
- This finding provides new insights into the regulation of programmed cell death.