Abstract
Transduction of a mitogenic signal from the cell membrane to the nucleus involves the adapter proteins SHC and Grb2, which mediate activation of the Ras/mitogen-activated protein (MAP) kinase pathway. In contrast to receptor tyrosine kinases (RTKs), the signalling steps leading to Ras/MAP kinase activation by G-protein-coupled receptors (GPCRs) are still poorly characterized but appear to include beta gamma subunits of heterotrimeric G-proteins and as-yet unidentified tyrosine kinases. We report here that the epidermal growth factor receptor (EGFR) and the neu oncoprotein become rapidly tyrosine-phosphorylated upon stimulation of Rat-1 cells with the GPCR agonists endothelin-1, lysophosphatic acid and thrombin, suggesting that there is an intracellular mechanism for transactivation. Specific inhibition of EGFR function by either the selective tyrphostin AG1478 or a dominant-negative EGFR mutant suppressed MAP kinase activation and strongly inhibited induction of fos gene expression and DNA synthesis. Our results demonstrate a role for RTKs as downstream mediators in GPCR mitogenic signalling and suggest a ligand-independent mechanism of RTK activation through intracellular signal crosstalk.
Publication types
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Research Support, Non-U.S. Gov't
MeSH terms
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Animals
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Calcium-Calmodulin-Dependent Protein Kinases / metabolism
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Cell Division / physiology
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Cell Line
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Endothelin Receptor Antagonists
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Endothelins / pharmacology
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Enzyme Activation
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ErbB Receptors / antagonists & inhibitors
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ErbB Receptors / genetics
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ErbB Receptors / metabolism*
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GTP-Binding Proteins / metabolism*
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Humans
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Lipopolysaccharides / pharmacology
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Mitogen-Activated Protein Kinase 1
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Mitogen-Activated Protein Kinase 3
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Mitogen-Activated Protein Kinases*
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Peptides, Cyclic / pharmacology
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Phosphorylation
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Proto-Oncogene Proteins c-fos / biosynthesis
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Proto-Oncogene Proteins c-fos / genetics
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Rats
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Receptor, ErbB-2 / drug effects
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Receptor, ErbB-2 / metabolism
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Recombinant Proteins / genetics
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Recombinant Proteins / metabolism
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Signal Transduction*
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Thrombin / pharmacology
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Transcriptional Activation*
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Tyrosine / metabolism
Substances
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Endothelin Receptor Antagonists
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Endothelins
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Lipopolysaccharides
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Peptides, Cyclic
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Proto-Oncogene Proteins c-fos
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Recombinant Proteins
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Tyrosine
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ErbB Receptors
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Receptor, ErbB-2
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Calcium-Calmodulin-Dependent Protein Kinases
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Mitogen-Activated Protein Kinase 1
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Mitogen-Activated Protein Kinase 3
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Mitogen-Activated Protein Kinases
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Thrombin
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GTP-Binding Proteins
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cyclo(Trp-Asp-Pro-Val-Leu)