Involvement of activator protein 1 complexes in the epithelium-specific activation of the laminin gamma 2-chain gene promoter by hepatocyte growth factor (scatter factor)

Laminin-5 is a trimer of laminin alpha 3, beta 3 and gamma 2 chains that is found in the intestinal basement membrane. Deposition of the laminin gamma 2 chain at the basement membrane is of great interest because it undergoes a developmental shift in its cellular expression. Here we study the regula tory elements that control basal and cytokine-activated transcriptional exp ression of the LAMC2 gene, which encodes the laminin gamma 2 chain. By usin g transient transfection experiments we demonstrated the presence of consti tutive and cytokine-responsive cis-elements. Comparison of the transcriptio nal activity of the LAMC2 promoter in the epithelial HT29mtx cells with tha t in small-intestinal fibroblastic cells (C20 cells) led us to conclude tha t two regions with constitutive epithelium-specific activity are present be tween positions -1.2 and -0.12 kb. This was further validated by transfecti ons of primary foetal intestinal endoderm and mesenchyme. A 2.5 kb portion of the LAMC2 5' flanking region was equally responsive to PMA and hepatocyt e growth factor (HGF), whereas it was less responsive to transforming growt h factor beta 1. A minimal promoter limited to the initial 120 bp upstream of the transcriptional start site maintained inducibility by PMA and HGF. T his short promoter fragment contains two activator protein 1 (AP-1) element s and the 5'-most of these is a composite AP-1/Sp1 element. The 5'AP-1 elem ent is crucial to the HGF-mediated activity of the promoter; analysis of in teracting nuclear proteins demonstrated that AP-1 proteins containing JunD mediate the response to HGF.