Interleukin-2 receptor {beta} T450 phosphorylation is a positive regulator for receptor complex stability and activation of signaling molecules [Immunology]
July 7th, 2015 by Ruiz-Medina, B. E., Ross, J. A., Kirken, R. A.
T, B, and natural killer (NK) cells are required for normal immune response and regulated by cytokines such as interleukin (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 extensively studied, however, identification and putative regulatory roles for serine and threonine phosphorylation sites have yet to be fully characterized. Using LC-MS/MS and phospho-specific antibodies, a novel IL-2/IL-15 inducible IL-2Rβ phosphorylation site (T450) was identified. IL-2 phospho-kinetic analysis revealed that phosphorylation of IL-2Rβ T450 is rapid (2.5 min), transient (peaks at 15 min), protracted as compared to 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 while purified protein phosphatase 1 (PP1), dephosphorylated T450 in vitro. Reconstitution assays demonstrated that T450 was important for regulating IL-2R complex formation, recruitment of JAK3, activation of AKT and ERK1/2 and a transcriptionally active STAT5. These results provide the first evidence for the identification and functional characterization for threonine phosphorylation of an interleukin receptor.