A short region containing an AP-1 binding site is essential for transforming growth factor-β-induced c-jun gene expression in osteoblastic cells

Abstract

Transforming growth factor-β (TGF-β) is a multifunctional regulatory peptide that elicits different responses in different cell types. Much remains unknown about the pathway of intracellular TGF-β signal transduction, but TGF-β is known to induce expression of several genes by way of the transcription factor AP-1. We studied the mechanism that mediates TGF-β-induced gene expression of c-jun, a component of AP-1, in MC3T3-E1 osteoblastic cells. To map in detail the corresponding responsive elements in the rat c-jun promoter, we generated a series of 5' deletion promoter/luciferase reporter gene constructs. Transient cell transfection assays identified the region located between positions -79 and -59 as being critical for the TGF-β response and for the basal activity of the promoter. Gel mobility shift assays indicated specific binding of nuclear proteins to this 21-bp region of the c-jun promoter containing an AP-1 binding site. These results show that the AP-1-dependent mechanism is involved in TGF-β- induced increase of c-jun induction, suggesting positive autoregulation of AP-1.