P300/CBP is required for transcriptional induction by interleukin-4 and interacts with Stat6

Interleukin-4 (IL-4) induces tyrosine phosphorylation of the latent transcr iption factor Stat6, which mediates the transcriptional responses of IL-4, The transactivation domain of Stat6 has recently been mapped to the C-termi nal region of Stat6, We have investigated the mechanism by which Stat6, thr ough its transactivation domain, induces transcription. Previous studies ha ve shown that diverse regulated transcription factors interact with coactiv ators such as p300 and CBP, We report that Stat6 used the interaction with p300/CBP to exert its stimulatory effects. Overexpression of p300/CBP incre ased IL-4-induced transcription of Stat6 activated reporter genes, The requ irement of p300/CBP for Stat6-mediated transactivation is shown by coexpres sion of the adenovirus E1A protein. E1A repressed the IL-4-induced reporter gene activity, while mutants of E1A, which do not interact with p300/CBP, failed to block the IL-4-induced response. In addition, we found that the m inimal transactivation domain of Stat6, when fused to the GAL4 DNA-binding domain, was repressed by E1A, whereas the fusion protein p300-VP16 increase d the transcriptional activity. in two-hybrid protein interaction assays in mammalian cells, we mapped the interaction domain of CBP to a C-terminal r egion between amino acids 1850 and 2176, a region distinct from the interac tion domain of CBP with Stat1, Stat2 or Stat5. Finally, we show that antibo dies raised against p300 coimmunoprecipitated Stat6 and p300 from transfect ed COS7 cells and antibodies against Stat6 coimmunprecipitated endogenous S tat6 and CBP from Ba/F3 cells. Our data suggest that the transactivation do main of Stat6 makes contact with the basal transcription machinery by bindi ng to p300/CBP.