Abstract
Mitogen-activated protein (MAP) kinases p42mapk and p44mapk are activated in cells stimulated with epidermal growth factor (EGF) and other agents. A principal pathway for MAP kinase (MAPK) activation by EGF consists of sequential activations of the guanine nucleotide exchange factor Sos, the guanosine triphosphate binding protein Ras, and the protein kinases Raf-1, MAPK kinase (MKK), and MAPK. Because adenosine 3',5'-monophosphate (cAMP) does not activate MAPK and has some opposing physiologic effects, the effect of increasing intracellular concentrations of cAMP with forskolin and 3-isobutyl-1-methylxanthine on the EGF-stimulated MAPK pathway was studied. Increased concentrations of cAMP blocked activation of Raf-1, MKK, and MAPK in Rat1hER fibroblasts, accompanied by a threefold increase in Raf-1 phosphorylation on serine 43 in the regulatory domain. Phosphorylation of Raf-1 in vitro and in vivo reduces the apparent affinity with which it binds to Ras and may contribute to the blockade by cAMP.
Publication types
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Research Support, Non-U.S. Gov't
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Research Support, U.S. Gov't, P.H.S.
MeSH terms
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1-Methyl-3-isobutylxanthine / pharmacology
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3T3 Cells
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Amino Acid Sequence
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Animals
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Cell Line
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Colforsin / pharmacology
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Cyclic AMP / metabolism*
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Cyclic AMP-Dependent Protein Kinases / metabolism
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Enzyme Activation / drug effects
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Epidermal Growth Factor / pharmacology*
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Mice
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Mitogen-Activated Protein Kinase 1
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Mitogen-Activated Protein Kinase Kinases
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Molecular Sequence Data
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Phosphorylation
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Protein Kinases / metabolism
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Protein Serine-Threonine Kinases / metabolism*
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Protein-Tyrosine Kinases / metabolism*
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Proto-Oncogene Proteins / metabolism
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Proto-Oncogene Proteins c-raf
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Proto-Oncogene Proteins p21(ras) / metabolism*
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Rats
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Signal Transduction*
Substances
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Proto-Oncogene Proteins
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Colforsin
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Epidermal Growth Factor
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Cyclic AMP
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Protein Kinases
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Protein-Tyrosine Kinases
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Protein Serine-Threonine Kinases
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Proto-Oncogene Proteins c-raf
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Cyclic AMP-Dependent Protein Kinases
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Mitogen-Activated Protein Kinase 1
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Mitogen-Activated Protein Kinase Kinases
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Proto-Oncogene Proteins p21(ras)
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1-Methyl-3-isobutylxanthine