Serine phosphorylation of Stat6 negatively controls its DNA-binding function.

In response to interleukin-4 (IL-4) or IL-13 stimulation of cells, Stat6 becomes phosphorylated on Tyr(641) and forms homodimers that migrate to the nucleus, bind to cognate DNA elements, and drive the transcription of target genes. Here, we show that phosphorylation of multiple serine residues ablates its DNA-binding activity in IL-4 stimulated cells. The phosphorylation sites are mapped to the transactivation domain (TAD) of Stat6. Importantly, serine phosphorylation of Stat6 TAD does not affect the phosphorylation of Tyr(641), nor does it affect the dimer formation or the ability of translocating to the nucleus in IL-4-stimulated cells. Collectively, these data suggest that phosphorylation of multiple serine residues in the TAD possibly induces conformational changes in Stat6 dimers that cause the loss of DNA binding and, thus, negatively control the expression of IL-4-responsive genes.