T， B， and natural killer cells are required for normal immune response and are regulated by cytokines such as IL-2. These cell signals are propagated following receptor-ligand engagement， controlling recruitment and activation of effector proteins. The IL-2 receptor β subunit (IL-2Rβ) serves in this capacity and is known to be phosphorylated. Tyrosine phosphorylation of the β chain has been studied extensively. However， the identification and putative regulatory roles for serine and threonine phosphorylation sites have yet to be fully characterized. Using LC-MS/MS and phosphospecific antibodies， a novel IL-2/IL-15 inducible IL-2Rβ phosphorylation site (Thr-450) was identified. IL-2 phosphokinetic ... More
T， B， and natural killer cells are required for normal immune response and are regulated by cytokines such as IL-2. These cell signals are propagated following receptor-ligand engagement， controlling recruitment and activation of effector proteins. The IL-2 receptor β subunit (IL-2Rβ) serves in this capacity and is known to be phosphorylated. Tyrosine phosphorylation of the β chain has been studied extensively. However， the identification and putative regulatory roles for serine and threonine phosphorylation sites have yet to be fully characterized. Using LC-MS/MS and phosphospecific antibodies， a novel IL-2/IL-15 inducible IL-2Rβ phosphorylation site (Thr-450) was identified. IL-2 phosphokinetic analysis revealed that phosphorylation of IL-2Rβ Thr-450 is rapid (2.5 min)， transient (peaks at 15 min)， and protracted compared with receptor tyrosine phosphorylation and occurs in multiple cell types， including primary human lymphocytes. Pharmacological and siRNA-mediated inhibition of various serine/threonine kinases revealed ERK1/2 as a positive regulator， whereas purified protein phosphatase 1 (PP1)， dephosphorylated Thr-450 in vitro. Reconstitution assays demonstrated that Thr-450 is important for regulating IL-2R complex formation， recruitment of JAK3， and activation of AKT and ERK1/2 and a transcriptionally active STAT5. These results provide the first evidence of the identification and functional characterization for threonine phosphorylation of an interleukin receptor.
