MULTIPLE CYTOKINES ACTIVATE PHOSPHATIDYLINOSITOL 3-KINASE IN HEMATOPOIETIC-CELLS - ASSOCIATION OF THE ENZYME WITH VARIOUS TYROSINE-PHOSPHORYLATED PROTEINS

Activation of phosphatidylinositol (PI) 3-kinase is a common sequel to tyrosine kinase activation and appears to be essential for tyrosine k inases to induce proliferation. Since multiple hemopoietic growth fact ors activate tyrosine kinases, we investigated whether these growth fa ctors activate PI 3-kinase. We show that interleukin-3 (IL-3), interle ukin-4 (IL-4), interleukin-5 (IL-5), granulocyte-macrophage colony sti mulating factor (GM-CSF), and steel factor (SLF) all activate PI 3-kin ase. These cytokines increased the amount of PI 3-kinase activity that could be immunoprecipitated with anti-phosphotyrosine antibodies from the MC-9 mast cell line or from the hemopoietic progenitor cell line FDC-P1, Increases in this assay frequently correlate with PI 3-kinase activation in vivo, To determine directly whether these factors activa te PI 3-kinase in vivo, we measured the levels of 3-phosphorylated ino sitol phospholipids in intact P-32-labeled MC-9 cells. IL-3, IL-4, IL- 5, GM-CSF, and SLF all caused increased synthesis of the PI 3-kinase p roducts phosphatidylinositol 3,4-bisphosphate and phosphatidylinositol 3,4,5-trisphosphate with a relative potency of SLF >> IL-3> IL-5, GM- CSF > IL-4. In contrast, IL-4 caused the largest increase in the in vi tro anti-phosphotyrosine immune complex PI 3-kinase assay. Thus, the i n vitro assay does not accurately reflect in vivo activation of PI 3-k inase. Cytokine treatment did not stimulate tyrosine phosphorylation o f either the 85-kDa regulatory subunit or the 110-kDa catalytic subuni t of PI 3-kinase and is therefore not required for activation of PI 3- kinase by these factors. Cytokine treatment did induce PI 3-kinase to associate with other tyrosine-phosphorylated proteins in a cytokine-sp ecific manner. PI 3-kinase associated with c-kit after SLF stimulation , a 170-kDa protein after IL-4 stimulation, and a 70-kDa protein after treatment with IL 3 or GM-CSF. Thus, multiple hemopoietic growth fact ors that act through different types of receptors activate PI 3-kinase in vivo and induce factor-specific interactions of PI 3-kinase with o ther tyrosine-phosphorylated proteins.