Erythropoietin-stimulated Raf-1 tyrosine phosphorylation is associated with the tyrosine kinase Lyn in J2E erythroleukemic cells.
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.
Tilbrook
P A
PA
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.
Colley
S M
SM
McCarthy
D J
DJ
Marais
R
R
Klinken
S P
SP
D002461:Cell Line, Transformed; D004921:Erythropoietin / Q000494:pharmacology*; D004915:Leukemia, Erythroblastic, Acute; D019950:Mitogen-Activated Protein Kinase 1 / Q000187:drug effects; D027384:Oncogene Proteins v-raf / Q000187:drug effects; D010766:Phosphorylation; D011233:Precipitin Tests; D011485:Protein Binding; D017346:Protein Serine-Threonine Kinases / Q000187:drug effects / Q000378:metabolism*; D019908:Proto-Oncogene Proteins c-raf / Q000187:drug effects / Q000378:metabolism*; D014407:Tumor Cells, Cultured; D019061:src-Family Kinases / Q000378:metabolism*
D004921:Erythropoietin; C060902:lyn protein-tyrosine kinase; D019061:src-Family Kinases; D027384:Oncogene Proteins v-raf; D017346:Protein Serine-Threonine Kinases; D019908:Proto-Oncogene Proteins c-raf; D019950:Mitogen-Activated Protein Kinase 1