Suppression of STAT3-mediated transactivation by siRNA treatment for MgcRacGAP. (A) Luciferase activities were examined in the lysates of unstimulated or IL-6– and sIL-6R–stimulated 293T cells with pretreatment with siRNA for MgcRacGAP (right columns) or a control siRNA (left columns). At 24 hours after the siRNA treatment, the cells were transfected with the STAT3 reporter and internal control with Lipofectamine plus reagents. Another 24 hours after the transfection, cells were stimulated with IL-6 (20 ng/mL) and sIL-6R (20 ng/mL) for 12 hours before the cell lysates were prepared. The lysates were then subjected to a dual luciferase assay system, as described in “Materials and methods.” The error bars show the standard deviations of triplicates. The results shown are a representative result of 3 independent experiments. (B) Expression of MgcRacGAP (upper panel) and β-tubulin (lower panel) were examined in unstimulated (lanes 1 and 3) or IL-6/sIL-6R–stimulated (lanes 2 and 4) 293T cells pretreated with a control siRNA (lanes 1 and 2) or siRNA for MgcRacGAP (lanes 3 and 4) were examined.