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p21-activated kinase (PAK) is required for Fas-induced JNK activation in Jurkat cells
T Rudel1, F T Zenke, T H Chuang
1The Scripps Research Institute, Department of Immunology, La Jolla, CA 92037, USA.
Abstract:
The process of apoptosis is a critical component of normal immune system development and homeostasis, and in many cells this involves signaling through the c-Jun amino terminal kinase (JNK) pathway. In Jurkat T cells, Fas-induced JNK activity is dependent upon activation of the caspase cascades known to be central components of the apoptotic program. We show in Jurkat cell lines expressing a dominant negative PAK construct that PAK signaling is necessary for JNK activation in response to Fas receptor cross-linking. Inhibition of JNK activation induced by Fas does not impair cell death as assessed by DNA fragmentation. However, expression of the catalytically active C terminus of PAK2, which is generated through caspase action during Fas-mediated apoptosis, induces Jurkat cell apoptosis. We conclude that PAK activity resulting from caspase-mediated cleavage is a necessary component of JNK activation induced by Fas receptor signaling and that PAK2 can contribute to the induction of cell death.
Insights
Programmed cell death (apoptosis) involves the c-Jun amino terminal kinase (JNK) pathway. PAK signaling is essential for JNK activation during Fas-induced apoptosis in Jurkat T cells.
Area of Science:
- Immunology
- Cell Biology
- Molecular Biology
Background:
- Apoptosis is crucial for immune system development and homeostasis.
- The c-Jun amino terminal kinase (JNK) pathway is involved in apoptosis in many cell types.
- Fas-induced JNK activation in Jurkat T cells depends on caspase cascades.
Purpose of the Study:
- To investigate the role of PAK signaling in Fas-induced JNK activation and apoptosis in Jurkat T cells.
- To determine if PAK activity is necessary for JNK activation downstream of Fas receptor cross-linking.
- To explore the contribution of caspase-cleaved PAK2 to apoptosis induction.
Main Methods:
- Utilized Jurkat T cell lines expressing dominant-negative PAK constructs.
- Examined JNK activation in response to Fas receptor cross-linking.
- Assessed DNA fragmentation as a measure of cell death.
- Expressed the catalytically active C terminus of PAK2 to evaluate its apoptotic potential.
Main Results:
- PAK signaling is necessary for JNK activation following Fas receptor cross-linking in Jurkat T cells.
- Inhibition of JNK activation did not prevent Fas-induced DNA fragmentation (cell death).
- Expression of the caspase-generated active C terminus of PAK2 induced apoptosis in Jurkat T cells.
Conclusions:
- PAK activity, specifically from caspase-mediated cleavage, is a required component for JNK activation during Fas receptor signaling.
- PAK2 can directly contribute to the induction of apoptosis in T cells.