Direct evidence that Gi-coupled receptor stimulation of mitogen-activated protein kinase is mediated by G beta gamma activation of p21ras.
Abstract
Stimulation of Gi-coupled receptors leads to the activation of mitogen-activated protein
kinases (MAP kinases). In several cell types, this appears to be dependent on the
activation of p21ras (Ras). Which G-protein subunit(s) (G alpha or the G beta gamma
complex) primarily is responsible for triggering this signaling pathway, however,
is unclear. We have demonstrated previously that the carboxyl terminus of the beta-adrenergic
receptor kinase, containing its G beta gamma-binding domain, is a cellular G beta
gamma antagonist capable of specifically distinguishing G alpha- and G beta gamma-mediated
processes. Using this G beta gamma inhibitor, we studied Ras and MAP kinase activation
through endogenous Gi-coupled receptors in Rat-1 fibroblasts and through receptors
expressed by transiently transfected COS-7 cells. We report here that both Ras and
MAP kinase activation in response to lysophosphatidic acid is markedly attenuated
in Rat-1 cells stably transfected with a plasmid encoding this G beta gamma antagonist.
Likewise in COS-7 cells transfected with plasmids encoding Gi-coupled receptors (alpha
2-adrenergic and M2 muscarinic), the activation of Ras and MAP kinase was significantly
reduced in the presence of the coexpressed G beta gamma antagonist. Ras-MAP kinase
activation mediated through a Gq-coupled receptor (alpha 1-adrenergic) or the tyrosine
kinase epidermal growth factor receptor was unaltered by this G beta gamma antagonist.
These results identify G beta gamma as the primary mediator of Ras activation and
subsequent signaling via MAP kinase in response to stimulation of Gi-coupled receptors.
Type
Journal articleSubject
AnimalsCell Line
Cercopithecus aethiops
Cyclic AMP-Dependent Protein Kinases
Enzyme Activation
GTP-Binding Proteins
Guanosine Triphosphate
In Vitro Techniques
Mitogen-Activated Protein Kinase 1
Peptide Fragments
Protein-Serine-Threonine Kinases
Protein-Tyrosine Kinases
Proto-Oncogene Proteins p21(ras)
Rats
Receptors, Adrenergic, beta
Receptors, Cell Surface
Receptors, G-Protein-Coupled
Receptors, Lysophosphatidic Acid
Signal Transduction
beta-Adrenergic Receptor Kinases
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Robert J. Lefkowitz
The Chancellor's Distinguished Professor of Medicine
Dr. Lefkowitz’s memoir, A Funny Thing Happened on the Way to Stockholm, recounts his
early career as a cardiologist and his transition to biochemistry, which led to his
Nobel Prize win.
Robert J. Lefkowitz, M.D. is Chancellor’s Distinguished Professor of Medicine and
Professor of Biochemistry and Chemistry at the Duke University Medical Center. He
has bee

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