Stimulation of pp60c-src kinase activity in FDC-P1 cells by polyoma middle-T antigen and hematopoietic growth factors

Either of two hematopoietic growth factors, GM-CSF or IL-3, are required for the growth of the bone marrow-derived FDC-P1 cell line. These factors induce cellular tyrosine-specific protein kinases when added to resting cells. The receptors for these factors have not been unambiguously shown to contain a kinase domain. To determine whether src-related kinases, in particular pp60-c-src, are regulated by GM-CSF or IL-3, FDC-P1 cells were transfected with plasmids carrying polyoma middle-T antigen, a potent activator of pp60c-src. Middle-T-expressing cells showed a reduced requirement for GM-CSF and IL-3 and selected clones grew in the absence of these factors. Middle-T formed a complex with pp60c-src and stimulated its in vitro kinase activity 20-50 fold. pp60c-src kinase activity was further increased if middle-T-expressing, factor-independent cells were treated with GM-CSF or IL-3.