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Vav regulates peptide-specific apoptosis in thymocytes
Y Y Kong1, K D Fischer, M F Bachmann
1Amgen Institute, University of Toronto, Toronto, Ontario, Canada M5G 2C1.
Abstract:
The protooncogene Vav functions as a GDP/GTP exchange factor (GEF) for Rho-like small GTPases involved in cytoskeletal reorganization and cytokine production in T cells. Gene-targeted mice lacking Vav have a severe defect in positive and negative selection of T cell antigen receptor transgenic thymocytes in vivo, and vav-/- thymocytes are completely resistant to peptide-specific and anti-CD3/anti-CD28-mediated apoptosis. Vav acts upstream of mitochondrial pore opening and caspase activation. Biochemically, Vav regulates peptide-specific Ca2+ mobilization and actin polymerization. Peptide-specific cell death was blocked both by cytochalasin D inhibition of actin polymerization and by inhibition of protein kinase C (PKC). Activation of PKC with phorbol ester restored peptide-specific apoptosis in vav-/- thymocytes. Vav was found to bind constitutively to PKC-theta in thymocytes. Our results indicate that peptide-triggered thymocyte apoptosis is mediated via Vav activation, changes in the actin cytoskeleton, and subsequent activation of a PKC isoform.
Insights
The protooncogene Vav is crucial for T cell apoptosis. Its absence prevents T cell death by regulating actin cytoskeleton and protein kinase C (PKC) signaling.
Area of Science:
- Immunology
- Cell Biology
- Molecular Biology
Background:
- The protooncogene Vav acts as a GDP/GTP exchange factor (GEF) for Rho-like small GTPases.
- Vav plays a role in cytoskeletal reorganization and cytokine production in T cells.
Purpose of the Study:
- To investigate the role of Vav in T cell antigen receptor (TCR) mediated thymocyte apoptosis.
- To elucidate the molecular mechanisms by which Vav regulates TCR-induced cell death.
Main Methods:
- Utilized gene-targeted mice lacking Vav (vav-/-).
- Assessed thymocyte selection, apoptosis, calcium mobilization, and actin polymerization.
- Investigated the involvement of protein kinase C (PKC) and cytochalasin D.
Main Results:
- Vav-deficient thymocytes exhibit defects in positive and negative selection and are resistant to apoptosis.
- Vav acts upstream of mitochondrial pore opening and caspase activation.
- Vav regulates peptide-specific calcium mobilization and actin polymerization, pathways involving PKC-theta.
Conclusions:
- Peptide-triggered thymocyte apoptosis is mediated by Vav activation.
- Vav signaling involves actin cytoskeleton remodeling and subsequent activation of a PKC isoform.
- Vav is a key regulator of T cell development and apoptosis.