Transforming Growth Factor-β Stimulates Interleukin-11 Transcription via Complex Activating Protein-1-dependent Pathways

Studies were undertaken to characterize the mechanism by which transforming growth factor-beta1 (TGF-beta1) stimulates epithelial cell interleukin (IL)-11 production. Nuclear run-on studies demonstrated that TGF-beta1 is a potent stimulator of IL-11 gene transcription. TGF-beta1 also stimulated the luciferase activity in cells transfected with reporter gene constructs containing nucleotides -728 to +58 of the IL-11 promoter. Studies with progressive 5' deletion constructs and site-specific mutations demonstrated that this stimulation was dependent on 2 AP-1 sites between nucleotides -100 and -82 in the IL-11 promoter. Mobility shift assays demonstrated that TGF-beta1 stimulated AP-1 protein-DNA binding to both AP-1 sites. Supershift analysis demonstrated that JunD was the major moiety contributing to AP-1-DNA binding in unstimulated cells and that c-Jun-, Fra-1-, and Fra-2-DNA binding were increased whereas JunD-DNA binding was decreased in TGF-beta1-stimulated cells. The sequence in the IL-11 promoter that contains the AP-1 sites also conferred TGF-beta1 responsiveness, in a position-independent fashion, on a heterologous minimal promoter. Thus, TGF-beta1 stimulates IL-11 gene transcription via a complex AP-1-dependent pathway that is dependent on 2 AP-1 motifs between nucleotides -100 and -82 that function as an enhancer in the IL-11 promoter.