IL-13 AND IL-4 SHARE SIGNAL-TRANSDUCTION ELEMENTS AS WELL AS RECEPTORCOMPONENTS IN TF-1 CELLS

IL-13 and IL-4 are growth factors for the human erythroleukemia cell l ine TF-1. In these cells both cytokines share overlapping binding site s, but the number of sites for IL-13 is half of that for IL-4. Two mon oclonal antibodies against the extracellular domain of the IL-4R alpha chain completely abolish the binding of IL-13, although IL-13 does no t bind to this chain. Following receptor triggering, IL-13 and IL-4 in duce the phosphorylation of a 170 kDa protein, probably the IL-4-induc ed phosphotyrosine substrate. In addition the phosphorylation of the 1 70 kDa protein results in its tight association with phosphatidylinosi tol-3-kinase.