Abstract
The serine/threonine kinase RAF-1 is phosphorylated in intact macrophages in response to CSF-1 at 37 degrees C The augmented phosphorylation of RAF-1 and a concomitant increase in RAF-1 associated serine/threonine kinase activity are kinetically later events than CSF-1 induced protein tyrosine phosphorylation. Furthermore, phosphoamino acid analysis of RAF-1 reveals the presence of phosphoserine, trace amounts of phosphothreonine but no phosphotyrosine and the phosphorylated RAF-1 does not react with anti-phosphotyrosine antibodies. In contrast to CSF-1 induced protein tyrosine phosphorylation, RAF-1 phosphorylation and activation are temperature dependent and do not occur at 4 degrees C. Furthermore, coprecipitation experiments failed to reveal any noncovalent association of RAF-1 with the CSF-1 receptor. Thus, while RAF-1 is not a direct substrate for the CSF-1 receptor tyrosine kinase in vivo, its temperature dependent phosphorylation and activation represent an intriguing aspect of the CSF-1 response.
Publication types
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Research Support, U.S. Gov't, P.H.S.
MeSH terms
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Amino Acid Sequence
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Animals
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In Vitro Techniques
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Macrophage Colony-Stimulating Factor / pharmacology*
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Macrophages / metabolism*
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Mice
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Molecular Sequence Data
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Oligopeptides / metabolism
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Phosphorylation
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Phosphoserine / metabolism
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Phosphothreonine / metabolism
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Phosphotyrosine
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Platelet-Derived Growth Factor / pharmacology
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Precipitin Tests
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Protein Kinases / metabolism
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Protein Serine-Threonine Kinases
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Proto-Oncogene Proteins / metabolism*
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Proto-Oncogene Proteins c-raf
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Receptor, Macrophage Colony-Stimulating Factor / metabolism
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Receptors, Cell Surface / metabolism
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Receptors, Platelet-Derived Growth Factor
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Temperature
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Tyrosine / analogs & derivatives
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Tyrosine / metabolism
Substances
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Oligopeptides
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Platelet-Derived Growth Factor
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Proto-Oncogene Proteins
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Receptors, Cell Surface
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Phosphothreonine
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Phosphoserine
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Phosphotyrosine
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Tyrosine
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Macrophage Colony-Stimulating Factor
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Protein Kinases
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Receptor, Macrophage Colony-Stimulating Factor
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Receptors, Platelet-Derived Growth Factor
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Protein Serine-Threonine Kinases
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Proto-Oncogene Proteins c-raf