Specific inhibition of interleukin-4-dependent Stat6 activation by an intracellularly delivered peptide.

The transcription factor Stat6 (signal transducer and activator of transcription 6) is activated following stimulation with interleukin (IL)-4 or IL-13. Stat6 binds via a single SH2 domain first to tyrosine-phosphorylated motifs in the IL-4Ralpha chain, and then to another Stat6 molecule, which results in the formation of active dimers. We show here that a peptide derived from the Stat6-binding region of IL-4Ralpha (Stat6BP) is an effective inhibitor when it is delivered into cells by coupling with a membrane-permeable peptide. Stat6BP completely inhibited IL-4 dependent phosphorylation of Stat6, as well as basal and IL-4 stimulated transcription from a reporter gene construct with a Stat6-dependent promoter, while IL-3 and IL-4 dependent phosphorylation of Stat5 was not affected. The inhibitory effect of Stat6BP was transient, but could be prolonged by treating the cells with the phosphatase inhibitor pervanadate.