Three Lysine Residues in the Common β Chain of the Interleukin-5 Receptor Are Required for Janus Kinase (JAK)-dependent Receptor Ubiquitination, Endocytosis, and Signaling

Eosinophils are multifunctional leukocytes implicated in the pathogenesis of numerous inflammatory diseases including allergic asthma and hypereosinophilic syndrome. Eosinophil physiology is critically dependent on IL-5 and the IL-5 receptor (IL-5R), composed of a ligand binding alpha chain (IL-5R alpha), and a common beta chain, beta c. Previously, we demonstrated that the beta c cytoplasmic tail is ubiquitinated and degraded by proteasomes following IL-5 stimulation. However, a complete understanding of the role of beta c ubiquitination in IL-5R biology is currently lacking. By using a well established, stably transduced HEK293 cell model system, we show here that in the absence of ubiquitination, beta c subcellular localization, IL-5-induced endocytosis, turnover, and IL-5R signaling were significantly impaired. Whereas ubiquitinated IL-5Rs internalized into trafficking endosomes for their degradation, ubiquitination-deficient IL-5Rs accumulated on the cell surface and displayed blunted signaling even after IL-5 stimulation. Importantly, we identified a cluster of three membrane-proximal beta c lysine residues (Lys(457), Lys(461), and Lys(467)) whose presence was required for both JAK1/2 binding to beta c and receptor ubiquitination. These findings establish that JAK kinase binding to beta c requires the presence of three critical beta c lysine residues, and this binding event is essential for receptor ubiquitination, endocytosis, and signaling.