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Arch Biochem Biophys. 2001 Dec 1;396(1):128-32.

Erythropoietin-stimulated Raf-1 tyrosine phosphorylation is associated with the tyrosine kinase Lyn in J2E erythroleukemic cells.

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Laboratory for Cancer Medicine, Western Australian Institute for Medical Research, Royal Perth Hospital, Department of Biochemistry, The University of Western Australia, Western Australia 6000, Australia.


The serine/threonine kinase Raf-1 is crucial for transducing intracellular signals emanating from numerous growth factors. Here we used the J2E erythroid cell line transformed by the nu-raf/nu-myc oncogenes to examine the effects of erythropoietin on endogenous Raf-1 activity. Despite the presence of constitutively active v-raf in these cells, Raf-1 exokinase activity increased after erythropoietin stimulation. This increase in enzymatic activity coincided with tyrosine phosphorylation of Raf-1 on residue Y341. Significantly, the tyrosine kinase Lyn coimmunoprecipitated with Raf-1, and Raf-1 was not tyrosine-phosphorylated in a J2E subclone lacking Lyn. Therefore, it was concluded that Lyn may be the kinase responsible for tyrosine phosphorylating Raf-1 and increasing its exokinase activity in response to erythropoietin.

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