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MEK kinase 1 is critically required for c-Jun N-terminal kinase activation by proinflammatory stimuli and growth
1Laboratory of Gene Regulation and Signal Transduction, Department of Pharmacology, University of California at San Diego, 9500 Gilman Drive, La Jolla, CA 92093, USA.
Abstract:
Exposure of eukaryotic cells to extracellular stimuli results in activation of mitogen-activated protein kinase (MAPK) cascades composed of MAPKs, MAPK kinases (MAP2Ks), and MAPK kinase kinases (MAP3Ks). Mammals possess a large number of MAP3Ks, many of which can activate the c-Jun N-terminal kinase (JNK) MAPK cascade when overexpressed, but whose biological function is poorly understood. We examined the function of the MAP3K MEK kinase 1 (MEKK1) in proinflammatory signaling. Using MEKK1-deficient embryonic stem cells prepared by gene targeting, we find that, in addition to its function in JNK activation by growth factors, MEKK1 is required for JNK activation by diverse proinflammatory stimuli, including tumor necrosis factor alpha, IL-1, double-stranded RNA, and lipopolysaccharide. MEKK1 is also essential for induction of embryonic stem cell migration by serum factors, but is not required for activation of other MAPKs or the IkappaB kinase signaling cascade.
Insights
MEK kinase 1 (MEKK1) is crucial for activating the c-Jun N-terminal kinase (JNK) pathway in response to inflammatory signals and growth factors. This protein is essential for cell migration but not for other key signaling cascades.
Area of Science:
- Cellular signaling pathways
- Molecular biology
- Immunology
Background:
- Mitogen-activated protein kinase (MAPK) cascades are central to cellular responses to extracellular stimuli.
- Mammalian cells have numerous MAPK kinase kinase 3 (MAP3K) proteins, but their specific biological roles, particularly in inflammatory signaling, remain largely uncharacterized.
Purpose of the Study:
- To investigate the function of MEK kinase 1 (MEKK1), a specific MAP3K, in the context of inflammatory signaling pathways.
- To determine MEKK1's role in the activation of the c-Jun N-terminal kinase (JNK) cascade by various stimuli.
Main Methods:
- Gene targeting was employed to create MEKK1-deficient embryonic stem cells.
- JNK activation was assessed in response to growth factors and diverse proinflammatory stimuli, including tumor necrosis factor alpha, IL-1, double-stranded RNA, and lipopolysaccharide.
- Embryonic stem cell migration assays were performed, and activation of other MAPKs and the IkappaB kinase cascade were examined.
Main Results:
- MEKK1 is essential for JNK activation induced by both growth factors and a range of proinflammatory signals.
- MEKK1 plays a critical role in serum-induced embryonic stem cell migration.
- MEKK1 deficiency did not affect the activation of other MAPK pathways or the IkappaB kinase signaling cascade.
Conclusions:
- MEKK1 is a key mediator of JNK activation in response to inflammatory stimuli, highlighting its importance in proinflammatory signaling.
- MEKK1's role extends to cellular processes like migration, indicating a broader function beyond JNK activation.
- MEKK1 is specifically required for JNK pathway activation, distinguishing its function from other MAPK signaling cascades.