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Colony stimulating factor-1 -CSF-1- stimulates temperature dependent phosphorylation and activation of the RAF-1 proto-oncogene product

: Sabatini, D.M.; App, H.; Rapp, U.R.; Stanley, E.R.; Baccarini, M.

EMBO Journal 9 (1990), Nr.11, S.3649-3657
ISSN: 0261-4189
Fraunhofer ITA ( ITEM) ()
amino acid sequence; colony stimulating factor; CSF; macrophage; macrophage colony stimulating factor; proto-oncogene protein; receptor

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 o f the CSF-1 response.