FIGURE 3.

STAT3 transcriptional activity is required in vivo for steap4 mRNA induction by IL-6. A, schematic representation of competition between STAT3α and STAT3β at a STAT3 target promoter. STAT3β lacks the transactivation domain, functions as a dominant negative form of STAT3, and blocks transactivation by STAT3α. B, qPCR analysis of steap4 mRNA expression in mouse livers infected with either Ad-GFP or Ad-GFP-STAT3β and treated with IL-6 (n = 8–11). C, ChIP assays demonstrating binding of STAT3α and STAT3β to the socs3 and steap4 promoters in GFP- or STAT3β-overexpressing livers. The C-20 STAT3 antibody (Ab) recognizes only STAT3α, whereas the K-15 antibody recognizes both STAT3α and STAT3β. A control PCR for the β-globin locus is also shown. Band intensities were measured and graphed (D).