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MEK kinase 1, a substrate for DEVD-directed caspases, is involved in genotoxin-induced apoptosis
C Widmann1, P Gerwins, N L Johnson
1Division of Basic Sciences, National Jewish Center for Immunology and Respiratory Medicine, Denver, Colorado 80206, USA. johnsonlab@njc.org
Abstract:
MEK kinase 1 (MEKK1) is a 196-kDa protein that, in response to genotoxic agents, was found to undergo phosphorylation-dependent activation. The expression of kinase-inactive MEKK1 inhibited genotoxin-induced apoptosis. Following activation by genotoxins, MEKK1 was cleaved in a caspase-dependent manner into an active 91-kDa kinase fragment. Expression of MEKK1 stimulated DEVD-directed caspase activity and induced apoptosis. MEKK1 is itself a substrate for CPP32 (caspase-3). A mutant MEKK1 that is resistant to caspase cleavage was impaired in its ability to induce apoptosis. These findings demonstrate that MEKK1 contributes to the apoptotic response to genotoxins. The regulation of MEKK1 by genotoxins involves its activation, which may be part of survival pathways, followed by its cleavage, which generates a proapoptotic kinase fragment able to activate caspases. MEKK1 and caspases are predicted to be part of an amplification loop to increase caspase activity during apoptosis.
Insights
Genotoxic agents activate MEK kinase 1 (MEKK1), which is then cleaved by caspases to induce apoptosis. This MEKK1 cleavage generates a proapoptotic fragment, amplifying caspase activity.
Area of Science:
- Cellular biology
- Molecular mechanisms of apoptosis
- Signal transduction pathways
Background:
- MEK kinase 1 (MEKK1) is a protein involved in cellular responses.
- Genotoxic agents can trigger cell death pathways.
- Apoptosis is a critical process for cellular homeostasis.
Purpose of the Study:
- To investigate the role of MEK kinase 1 (MEKK1) in genotoxin-induced apoptosis.
- To elucidate the activation and cleavage mechanisms of MEKK1 in response to genotoxins.
- To understand the relationship between MEKK1, caspases, and apoptosis.
Main Methods:
- Expression of wild-type and kinase-inactive MEKK1.
- Analysis of genotoxin-induced apoptosis.
- Assessment of caspase activity (DEVD-directed).
- Investigation of MEKK1 cleavage by caspases, including CPP32 (caspase-3).
- Use of caspase-cleavage-resistant MEKK1 mutants.
Main Results:
- Genotoxic agents activate MEKK1 through phosphorylation.
- Kinase-inactive MEKK1 inhibits genotoxin-induced apoptosis.
- Activated MEKK1 is cleaved in a caspase-dependent manner into an active 91-kDa fragment.
- MEKK1 expression stimulates caspase activity and induces apoptosis.
- MEKK1 is a substrate for CPP32 (caspase-3).
- A mutant MEKK1 resistant to caspase cleavage showed impaired apoptosis induction.
Conclusions:
- MEK kinase 1 (MEKK1) plays a crucial role in the apoptotic response to genotoxins.
- Genotoxin-induced MEKK1 regulation involves activation and subsequent caspase-dependent cleavage.
- Cleavage of MEKK1 generates a proapoptotic fragment that activates caspases.
- MEKK1 and caspases form a positive feedback loop to enhance apoptotic signaling.