SIGNALING THROUGH THE INTERLEUKIN-2 RECEPTOR-BETA CHAIN ACTIVATES A STAT-5-LIKE DNA-BINDING ACTIVITY

To explore the possible involvement of STAT factors (''signal transduc ers and activators of transcription'') in the interleukin 2 receptor ( IL-2R) signaling cascade, murine HT-2 cells expressing chimeric recept ors composed of the extracellular domain of the erythropoietin recepto r fused to the cytoplasmic domains of the IL-2R beta or -gamma(c) chai ns were prepared. Erythropoietin or IL-2 activation of these cells res ulted in rapid nuclear expression of a DNA-binding activity that react ed with select STAT response elements. Based on reactivity with specif ic anti-STAT antibodies, this DNA-binding activity was identified as a murine homologue of STAT-5. Induction of nuclear expression of this S TAT-5-like factor was blocked by the addition of herbimycin A, a tyros ine kinase inhibitor, but not by rapamycin, an immunophilin-binding an tagonist of IL-2-induced proliferation. The IL-2R beta chain appeared critical for IL-2-induced activation of STAT-S, since a mutant beta ch ain lacking all cytoplasmic tyrosine residues was incapable of inducin g this DNA binding. In contrast, a gamma(c) mutant lacking all of its cytoplasmic tyrosine residues proved fully competent for the induction of STAT-5, Physical binding of STAT-5 to functionally important tyros ine residues within IL-2R beta was supported by the finding that phosp horylated, but not nonphosphorylated, peptides corresponding to sequen ces spanning Y392 and Y510 of the IL-2R beta tail specifically inhibit ed STAT-5 DNA binding.