Mock-, vector-, and RNAi-treated cells were solubilized in NP40 lysis buffer (10 mM Tris at pH 7.5, 150 mM NaCl, 0.5% NP40, 5 mM EDTA, 5 mg/ml aprotinine, and 3 mM pAPMSF) and then centrifuged at 12,000 rpm for 10 min at 4uC. The lysates were subjected to immunoprecipitation with an anti-STAT3 antibody (Santa Cruz Biotechnology). Then, these immunocomplexes were analyzed as described for the Western blot assay. These immunocomplexes were detected by an anti-p300 antibody (Santa-Cruz Biotechnology).