Fig. 6.

The sequence of events that follows the binding of STAT3 homodimers to the SOCS3 promoter. (A) CHIP assays. Quantitative ChIP assays were performed with chromatin from IL-6–treated or untreated A4 cells expressing wild-type STAT3, using antibodies against total STAT3, Y705-phosphoryl-STAT3, S727-phosphoryl-STAT3, STAT3-K140me2, SET9, and LSD1. The immunoprecipitated DNA was amplified by qPCR, using primers specific for SOCS3. Values (percent of the inputs) are the mean ± SD of triplicates performed on three separate chromatin preparations. Data were analyzed using origin75 software and compared by using the unpaired Student's t test. All of the values obtained with each antibody were corrected for background by subtracting the value for untreated cells, which was about 0.1% of the input in each case. Note that the data shown are averages, representing mixed populations of cells. We expect that each individual promoter will not be able to bind both the methyltransferase and the demethylase simultaneously. (B) A model for the sequence of events that follows the binding of STAT3 homodimers to the SOCS3 promoter. Events following the binding of LSD1 and demethylation of STAT3 are not represented because they are not well understood at present.