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A role for Jun-N-terminal kinase in anoikis; suppression by bcl-2 and crmA
S M Frisch1, K Vuori, D Kelaita
1Burnham Institute, La Jolla Cancer Research Center, California 92037, USA. sfrisch@ljcrf.edu
Abstract:
The disruption of interactions between extracellular matrix and specific cognate integrins triggers apoptosis in epithelial cells, in a process termed "anoikis." To understand anoikis, the connections between epithelial cell integrin signaling and the apoptosis-regulatory proteins are being explored. We report herein that early after detachment from matrix, epithelial cells activate Jun-N-Terminal Kinases (JNKs; alternatively known as Stress-activated Protein Kinases), which are also activated by other apoptotic stimuli. The activity of this pathway was required for anoikis. Another early response to cell suspension was the activation of the ICE-related cysteine protease, ICE/LAP3; this activation and anoikis were suppressed by the ICE-protease inhibitor, crmA. The overexpression of bcl-2 suppressed ICE/LAP3 activation as well. Surprisingly, bcl-2 and crmA attenuated the activation of JNKs following cell suspension, suggesting that the JNK pathway is regulated directly or indirectly by proteolysis. In addition, the blockage of the JNK pathway attenuated the activation of ICE/LAP3, suggesting a positive feedback loop between the ICE and JNK systems. These results indicate the following sequence of information flow in anoikis: integrins-->bcl-2/bax-->(ICE-proteases<-->JNK)-->apopt osis. Cell-cell interactions, which were previously shown to sensitize cells to anoikis, caused bcl-2 mRNA to be downregulated, a permissive event for downstream apoptotic signaling.
Insights
Anoikis, or programmed cell death upon detachment, involves Jun-N-Terminal Kinases (JNKs) and ICE-related proteases. These pathways interact in a feedback loop, ultimately leading to apoptosis in epithelial cells.
Area of Science:
- Cell Biology
- Molecular Biology
- Apoptosis Research
Background:
- Anoikis is a form of programmed cell death in epithelial cells triggered by the loss of cell-matrix interactions.
- Understanding the molecular mechanisms linking integrin signaling to apoptosis is crucial for cell biology research.
Purpose of the Study:
- To elucidate the signaling pathways involved in anoikis.
- To investigate the roles of Jun-N-Terminal Kinases (JNKs) and ICE-related proteases in anoikis.
- To define the interplay between integrin signaling, apoptosis regulators, and cell-cell interactions in anoikis.
Main Methods:
- Investigated epithelial cell detachment-induced apoptosis (anoikis).
- Assessed the activation of Jun-N-Terminal Kinases (JNKs) and ICE-related cysteine protease (ICE/LAP3).
- Utilized ICE-protease inhibitor (crmA) and bcl-2 overexpression to study pathway regulation.
Main Results:
- Epithelial cell detachment activated JNKs and ICE/LAP3, both required for anoikis.
- Overexpression of bcl-2 and treatment with crmA suppressed ICE/LAP3 activation and also attenuated JNK activation.
- JNK pathway inhibition reduced ICE/LAP3 activation, indicating a positive feedback loop.
- Cell-cell interactions downregulated bcl-2 mRNA, facilitating anoikis.
Conclusions:
- Anoikis involves a signaling cascade: integrins → bcl-2/bax → (ICE-proteases ↔ JNK) → apoptosis.
- JNK and ICE-protease pathways are interconnected and regulate anoikis.
- bcl-2 and protease activity influence JNK activation, suggesting complex regulatory mechanisms.