FIGURE 7.

STAT3 is recruited to the Eme1 promoter when phosphorylated only on its serine 727 residue. Growing HT29 cells were treated or not with sn38 as indicated above and soluble chromatin was prepared and immunoprecipitated with antibodies directed against STAT3 (IP:STAT3) or its serine or tyrosine phosphorylated forms (IP:S727 or IP:Y705). In parallel, cells were serum-starved and stimulated or not with IL-6 (10 ng/ml) for 30 min, and the chromatin was immunoprecipitated under the same conditions. DNA was amplified using pair of primers that covers the STAT3 proximal binding sites of the cyclin D1 (panel C), Myc (panel D), and Eme1, (panel A and B) promoters as indicated. ChIP assays were then quantified by real-time PCR as compared with the signals obtained on each genes with a control IgG (n = 3). Note that sn38 (−) in the legend means growing cells, whereas IL6 (0) means serum-starved cells.