FIG. 9.

Stat3 mediates IL-6-induced expression from the C/EBPδ promoter. (A) Stat3 but not Stat1 transactivates the C/EBPδ promoter. The (−127)-Luc construct was cotransfected into Hep3B cells with expression vectors for Stat1 or Stat3 or the parental pCDNA1 vector, together with pRSV β-gal as an internal standard, and tested for basal and IL-6-induced luciferase expression. (B) Stat3 transactivation of C/EBPδ promoter mutants. The indicated deletion and point mutants (Fig. 3 and 4) were cotransfected with the Stat3 expression vector into Hep3B cells and tested for basal and IL-6-inducible luciferase expression. (C) Stat3 transactivates a heterologous promoter containing the C/EBPδ APRE. The indicated TK promoter-luciferase reporter constructs (Fig. 8) were cotransfected with the Stat3 expression plasmid into Hep3B cells and tested for basal and IL-6-inducible expression. The cell extracts were assayed for luciferase and β-galactosidase activities as described in Fig. 3. The values represent the averages of three to six independent experiments.