Interleukin 3 stimulation of tyrosine kinase activity in FDC-P1 cells

Interleukin 3 stimulates the proliferation of FDC-P1, a murine myeloid cell line, however the biochemical events subsequent to binding of IL3 have only recently begun to be investigated. We have previously described the activation of protein kinase C (PK-C) and serine/threonine phosphorylation of a 68 kd protein following IL3 treatment of FDC-P1 cells. Here we have used an anti-phosphotyrosine antibody to purify proteins containing phosphotyrosine following IL3 administration to FDC-P1 cells. We find that tyrosine phosphorylation of two proteins of 50 (pp50) and 70 (pp70) kilodaltons occurs rapidly following IL3 treatment. In addition to phosphotyrosine both proteins also contained phosphoserine. Together with previous evidence these results suggest that coactivation of serine/threonine and tyrosine kinase activities which target unique proteins may be an important element in IL3 signal transduction.