IL-5, IL-3, and GM-CSF are hematopoietic cytokines that are key mediators of the allergic inflammatory response. The receptors for these three cytokines consist of a cytokine-specific α (Rα) chain and a shared common β (βc) chain. Herein, we demonstrate that agonistic ligation of these receptor subunits rapidly induces proteasomal degradation of the βc, but not the Rα, cytoplasmic domain, resulting in termination of signal transduction and yielding a truncated βc isoform ligated to the Rα subunit. Proteasomal degradation of the βc cytoplasmic domain was also a prerequisite for endocytosis and lysosomal degradation of the ligated receptor subunits. Moreover, proteasome-dependent termination of signaling induced by one βc-engaging cytokine resulted in cellular desensitization to signal transduction by subsequent stimulation with another βc-engaging cytokine. These data provide the first evidence for ligand-dependent proteasomal degradation of the βc cytoplasmic domain, and they establish a novel mechanism for heterotypic desensitization of shared cytokine receptor signaling.
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