Phosphorylation of a Fes-related protein in response to granulocyte-macrophage colony stimulating factor.

Previous work has suggested that a 97-kDa protein (p97) is involved in the signal transduction pathway of granulocyte-macrophage colony stimulating factor (GM-CSF) as well as interleukin 3, erythropoietin, and interleukin 2. We have examined the relationship of p97 to the protein tyrosine kinase Fes in the GM-CSF signal transduction pathway in erythroid and myeloid cell lines. GM-CSF stimulation of three different cell lines induced tyrosine phosphorylation of p97 as well as a number of other phosphotyrosylproteins. Although each cell line expressed the proto-oncogene product Fes, antisera specific for Fes did not recognize p97 in immunoblotting experiments. Furthermore, immunodepletion of Fes did not reduce the amount of p97 in GM-CSF-treated cells. Two-dimensional gel electrophoresis demonstrated that p97 and Fes have similar charge to mass ratios, and limited proteolytic mapping of p97 and Fes suggested that these proteins may be related but are not identical. Our studies demonstrate that p97 is not Fes but is probably a Fes-related protein.