Activation of Phosphatidylinositol 3-Kinase in Cells Expressing abl Oncogene Variants

A phosphoinositide kinase specific for the D-3 position of the inositol ring, phosphatidylinositol (PI) 3-kinase, associates with activated receptors for platelet-derived growth factor, insulin, and colony-stimulating factor 1, with products of the oncogenes src, fms, yes, crk, and with polyomavirus middle T antigen. Efficient fibroblast transformation by proteins of the abl and src oncogene families requires activation of their protein-tyrosine kinase activity and membrane association via an amino-terminal myristoylation. We have demonstrated that the PI 3-kinase directly associates with autophosphorylated, activated protein-tyrosine kinase variants of the abl protein. In vivo, this association leads to accumulation of the highly phosphorylated products of PI 3-kinase, PI-3,4-bisphosphate and PI-3,4,5-trisphosphate, only in myristoylated, transforming abl protein variants. Myristoylation thus appears to be required to recruit PI 3-kinase activity to the plasma membrane for in vivo activation and correlates with the mitogenicity of the abl protein variants.