Interleukin‐2 induces tyrosine phosphorylation and nuclear translocation of stat3 in human T lymphocytes

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Abstract
An early biochemical event associated with T cell activation through the interleukin‐2 receptor (IL‐2R) is tyrosine phosphorylation of several intracellular substrates. The exact mechanism by which IL‐2 regulates transcription of different genes is presently unknown. Here, we report that stimulation through the IL‐2R induced tyrosine phosphorylation and subsequent nuclear translocation of stat3, a newly identified member of the signal transducers and activators of transcription (STAT) family of proteins. In contrast, stat1 proteins were not tyrosine phosphorylated after IL‐2 ligation, whereas tyrosine‐phosphorylated stat1 proteins (91 and 84 kDa proteins) were translocated to the nucleus following interferon‐γ treatment of HeLa cells.Apart from stat3, another cytoplasmic protein was tyrosine phosphorylated and subsequently translocated to the nucleus in response to IL‐2. This protein had an apparent molecular mass of 84 kDa and was not recognized by stat3 or stat1 mAb or antisera. Since IL‐2 induced nuclear translocation of the 84 kDa protein and stat3 followed identical kinetics, p84 is a candidate for a new, yet undefined, member of the STAT family. Taken together, we report that IL‐2 induces tyrosine phosphorylation and subsequent nuclear translocation of stat3 and an as yet undefined 84‐kDa protein in antigen‐specific human T cell lines.