AN AP-1 ENHANCER MEDIATES TPA-INDUCED TRANSCRIPTIONAL ACTIVATION OF THE CHICKEN INSULIN-LIKE GROWTH FACTOR-I GENE

As a step to elucidate a role of protein kinase C(PKC) pathways in the regulation of insulin-like growth factor I(IGF-I) gene, we sought to determine whether the IGF-I gene promoter of chicken can be a target of regulation by PKC. An initial gene transfer study showed that, in a human cell line HepG2, the IGF-I gene promoter directs accurate transcription of IGF-I-luciferase fusion gene and enhances luciferase activity. Treatment of transfected cells with 12-o-tetradecanoylphorbol 13-acetate(TPA) increased promoter activity of 2100 and 600bp 5′-flanking sequence 4.9-and 3.6-fold, respectively. Site-directed mutagenesis in the AP-l-like sequence located within the 600bp resulted in 91% loss of its TPA-induced promoter activity, and a gel mobility-shift analysis revealed that TPA-stimulation of HepG2 cells caused a dramatic increase in specific protein-binding to the AP-1-like sequence, suggesting that the sequence functions as an AP-l enhancer. These observations support a direct role for PKC pathways in activating the IGF-I gene promoter in chicken. © 1993 Academic Press. Inc.