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Galpha12 and Galpha13 regulate extracellular signal-regulated kinase and c-Jun kinase pathways by different
T A Voyno-Yasenetskaya1, M P Faure, N G Ahn
1Department of Cellular and Molecular Pharmacology and Medicine, University of California, San Francisco, 94143, USA.
Abstract:
Many growth factors and agonists for G protein-coupled receptors activate mitogen-activated protein (MAP) kinase pathways, including the extracellular signal-regulated kinase (ERK) pathway and the c-Jun kinase (JNK) pathway. Transient transfection of dominant negative and constitutively active pathway components in COS-7 cells shows that two G protein subunits, Galpha12 and Galpha13, inhibit the ERK pathway and stimulate the JNK pathway. Constitutively active (GTPase-deficient) Galpha12 and Galpha13 both inhibit ERK pathway activation by epidermal growth factor. A Galpha13/alphaz chimera, which responds to stimulation by Gi-coupled receptors, mediates inhibition of ERK via such a receptor, the dopamine-2 receptor. In addition, expression of a dominant negative mutant of the GTPase, Cdc42, blocks activation of the JNK pathway by Galpha12 and Galpha13 but does not alter inhibition of ERK activation by the same Galpha proteins; conversely, mutationally activated Cdc42 stimulates the JNK pathway but has no effect on the ERK pathway. Our results show that different mechanisms mediate two effects of Galpha12 and Galpha13: the ERK pathway inhibition is mediated at the level of MAP kinase kinase in a Ras- and Raf-independent fashion, whereas the JNK pathway stimulation is mediated by Cdc42.
Insights
G protein subunits Galpha12 and Galpha13 differentially regulate mitogen-activated protein (MAP) kinase pathways. They inhibit the extracellular signal-regulated kinase (ERK) pathway and stimulate the c-Jun kinase (JNK) pathway via Cdc42.
Area of Science:
- Cellular signaling
- Molecular biology
- Signal transduction
Background:
- Growth factors and G protein-coupled receptors activate MAP kinase pathways, including ERK and JNK.
- G protein subunits play crucial roles in cellular signaling cascades.
Purpose of the Study:
- To investigate the roles of G protein subunits Galpha12 and Galpha13 in regulating ERK and JNK pathways.
- To elucidate the mechanisms by which Galpha12 and Galpha13 modulate these MAP kinase pathways.
Main Methods:
- Transient transfection of dominant-negative and constitutively active pathway components in COS-7 cells.
- Utilizing Galpha13/alphaz chimeras and dominant-negative Cdc42 mutants.
- Assessing ERK and JNK pathway activation in response to G protein subunit expression.
Main Results:
- Galpha12 and Galpha13 were found to inhibit ERK pathway activation, independent of Ras and Raf.
- These G protein subunits stimulate the JNK pathway.
- Cdc42 mediates the Galpha12/Galpha13-induced JNK pathway stimulation.
- ERK pathway inhibition by Galpha12/Galpha13 occurs at the MAP kinase kinase level.
Conclusions:
- Galpha12 and Galpha13 exhibit distinct regulatory mechanisms for ERK and JNK pathways.
- ERK pathway inhibition is mediated upstream of MAP kinase kinase, while JNK pathway stimulation involves Cdc42.