Abstract
G protein-coupled receptors (GPCRs) have been shown to stimulate extracellular regulated kinases (ERKs) through a number of linear pathways that are initiated by G(q/11) or G(i) proteins. We studied signaling to the ERK cascade by receptors that simultaneously activate both G protein subfamilies. In HEK293T cells, bradykinin B(2) receptor (B(2)R)-induced stimulation of ERK2 and transcriptional activity of Elk1 are dependent on Galpha(q)-mediated protein kinase C (PKC) and on Galpha(i)-induced Ras activation, while they are independent of Gbetagamma subunits, phosphatidylinositol 3-kinase, and tyrosine kinases. Similar results were obtained with m(1) and m(3) muscarinic receptors in HEK293T cells and with the B(2)R in human and mouse fibroblasts, indicating a general mechanism in signaling toward the ERK cascade. Furthermore, the bradykinin-induced activation of ERK is strongly reduced in Galpha(q/11)-deficient fibroblasts. In addition, we found that constitutively active mutants of Galpha(q/11) or Galpha(i) proteins alone poorly stimulate ERK2, whereas a combination of both led to synergistic effects. We conclude that dually coupled GPCRs require a cooperation of Galpha(i)- and G(q/11)-mediated pathways for efficient stimulation of the ERK cascade. Cooperative signaling by multiple G proteins thus might represent a novel concept implicated in the regulation of cellular responses by GPCRs.
Publication types
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Research Support, Non-U.S. Gov't
MeSH terms
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Animals
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Cell Line
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Cell Line, Transformed
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Cyclic AMP-Dependent Protein Kinases / metabolism
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DNA-Binding Proteins*
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Enzyme Activation
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GTP-Binding Protein alpha Subunits, Gi-Go / genetics
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GTP-Binding Protein alpha Subunits, Gi-Go / metabolism*
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GTP-Binding Protein alpha Subunits, Gq-G11
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GTP-Binding Protein beta Subunits*
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GTP-Binding Protein gamma Subunits*
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GTP-Binding Proteins / genetics
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GTP-Binding Proteins / metabolism*
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Heterotrimeric GTP-Binding Proteins*
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Humans
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MAP Kinase Signaling System*
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Mice
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Mitogen-Activated Protein Kinase 1 / genetics
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Mitogen-Activated Protein Kinase 1 / metabolism
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Mitogen-Activated Protein Kinases / genetics
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Mitogen-Activated Protein Kinases / metabolism*
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Phosphatidylinositol 3-Kinases / metabolism
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Potassium Channels / genetics
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Protein Kinase C / metabolism
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Proto-Oncogene Proteins c-raf / metabolism
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Proto-Oncogene Proteins*
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Receptor, Bradykinin B2
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Receptor, Muscarinic M1
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Receptor, Muscarinic M3
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Receptors, Bradykinin / metabolism
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Receptors, Cell Surface / metabolism
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Receptors, Muscarinic / metabolism
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Transcription Factors*
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Transcriptional Activation
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Virulence Factors, Bordetella / pharmacology
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beta-Adrenergic Receptor Kinases
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ets-Domain Protein Elk-1
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ras Proteins / metabolism
Substances
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DNA-Binding Proteins
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ELK1 protein, human
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Elk1 protein, mouse
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G-protein Beta gamma
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GTP-Binding Protein beta Subunits
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GTP-Binding Protein gamma Subunits
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Potassium Channels
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Proto-Oncogene Proteins
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Receptor, Bradykinin B2
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Receptor, Muscarinic M1
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Receptor, Muscarinic M3
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Receptors, Bradykinin
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Receptors, Cell Surface
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Receptors, Muscarinic
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Transcription Factors
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Virulence Factors, Bordetella
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ets-Domain Protein Elk-1
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Phosphatidylinositol 3-Kinases
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Proto-Oncogene Proteins c-raf
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Cyclic AMP-Dependent Protein Kinases
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Protein Kinase C
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beta-Adrenergic Receptor Kinases
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Mitogen-Activated Protein Kinase 1
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Mitogen-Activated Protein Kinases
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GTP-Binding Proteins
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GTP-Binding Protein alpha Subunits, Gi-Go
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GTP-Binding Protein alpha Subunits, Gq-G11
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Heterotrimeric GTP-Binding Proteins
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ras Proteins