Evidence for a signaling role for the alpha chains of granulocyte- macrophage colony-stimulating factor (GM-CSF), interleukin-3 (IL-3), and IL-5 receptors: divergent signaling pathways between GM-CSF/IL-3 and IL-5

In the present study, we have used a human erythroleukemia cell line, TF-1, that proliferates in response to granulocyte macrophage colony stimulating factor (GM-CSF), interleukin-3 (IL-3), and interleukin-5 (IL-5) to investigate the role of receptors for these cytokines in signal transduction mechanisms involved in proliferative responses. The receptors for GM-CSF, IL-3, and IL-5 each possess a cytokine specific alpha subunit, but all three share a common beta chain. Using an immunoblotting system designed to detect phosphotyrosine containing proteins and a permeabilized cell system to detect rapid changes in phosphate turnover on proteins, we show that while GM-CSF and IL-3 use tyrosine phosphorylation to mediate mitogenic signal transduction, IL-5 uses tyrosine dephosphorylation in its signaling pathway. The use of different signaling pathways by these cytokines can be confirmed in a biologic system whereby the proliferation induced in culture by GM-CSF and IL-3 is inhibited by tyrosine kinase inhibitors, but that induced by IL-5 is enhanced. Conversely, GM-CSF- and IL-3-induced proliferation is stimulated by a tyrosine phosphatase inhibitor, yet IL-5-induced proliferation is inhibited. Inhibitors of protein kinase C inhibit IL-3- and GM-CSF-, but not IL-5-induced proliferation. We suggest that, because all these cytokines share the identical beta chain of their receptors, the cytokine specific alpha chain mediates the linkage of each receptor to the individual biochemical signal transduction pathways responsible for the different biologic activities of these cytokines.