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Apoptosis-inducing membrane vesicles. A novel agent with unique properties
1Department of Medicine, the Arthritis Center, Boston University School of Medicine, 715 Albany Street, Boston, MA 02118, USA.
Abstract:
The CD95 ligand (FasL) transmembrane protein is found on activated T cells and cells outside the immune system. A well-known turnover process of membrane FasL is mediated by matrix metalloproteinase, which generates soluble FasL (sFasL). Here, we demonstrate that membrane FasL turnover occurs effectively through the release of membrane vesicles. Quantitative analysis indicates that this process is as effective as sFasL release for FasL-3T3 cells but somewhat less effective for FasL-expressing T cells. The apoptosis-inducing membrane vesicles display unique properties not found in FasL-expressing cells and sFasL. Unlike sFasL, vesicle-associated FasL remained bioactive, killing the same panel of targets that are susceptible to FasL-expressing cells. In contrast to FasL-expressing T cells, FasL-mediated killing by vesicles do not involve LFA-1/ICAM interaction and do not depend on de novo protein synthesis. These observations indicate that the release of FasL-bearing vesicles contributes to the turnover of cell-associated FasL, but the impact of the bioactive FasL-expressing vesicles on the function of cell-associated FasL is different from that of sFasL.
Insights
Membrane-bound CD95 ligand (FasL) can be released via vesicles, offering a new pathway for FasL turnover. These FasL-bearing vesicles are bioactive and mediate killing differently than soluble FasL.
Area of Science:
- Immunology
- Cell Biology
- Molecular Biology
Background:
- CD95 ligand (FasL) is a transmembrane protein crucial for immune cell function and apoptosis.
- Matrix metalloproteinase-mediated shedding generates soluble FasL (sFasL), a known mechanism for FasL turnover.
- The role of alternative FasL turnover pathways, such as vesicle release, remains less understood.
Purpose of the Study:
- To investigate the role of membrane vesicle release in the turnover of membrane-bound FasL.
- To characterize the properties and bioactivity of FasL released via membrane vesicles.
- To compare the mechanisms of FasL-mediated killing by vesicles versus sFasL and cell-associated FasL.
Main Methods:
- Quantitative analysis of FasL release from FasL-expressing cells (FasL-3T3 cells and T cells).
- Characterization of apoptosis-inducing properties of released membrane vesicles.
- Assessment of vesicle-associated FasL bioactivity and comparison with sFasL and cell-associated FasL.
- Investigation of the involvement of LFA-1/ICAM interaction and protein synthesis in vesicle-mediated killing.
Main Results:
- Membrane FasL turnover occurs effectively through the release of membrane vesicles, comparable to sFasL release in some cell types.
- FasL-bearing vesicles exhibit unique properties and retain bioactivity, effectively killing target cells.
- Vesicle-mediated FasL killing does not rely on LFA-1/ICAM interaction or de novo protein synthesis, unlike T cell-mediated killing.
- The functional impact of vesicle-associated FasL differs from that of sFasL.
Conclusions:
- Membrane vesicle release is a significant pathway for CD95 ligand (FasL) turnover.
- FasL-bearing vesicles represent a distinct functional entity with unique mechanisms of action in cell-mediated cytotoxicity.
- Understanding vesicle-mediated FasL release provides new insights into immune regulation and apoptosis.