A Cell-Specific Enhancer of the Mouse α1-Antitrypsin Gene Has Multiple Functional Regions and Corresponding Protein-Binding Sites

Abstract

We have previously described the isolation and characterization of genomic clones corresponding to the mouse α1-antitrypsin gene (Krauter et al., DNA 5:29-36, 1986). In this report, we have analyzed the DNA sequences upstream of the RNA start site that direct hepatoma cell-specific expression of this gene when incorporated into recombinant plasmids. The 160 nucleotides 5′ to the cap site direct low-level expression in hepatoma cells, and sequences between -520 and -160 bp upstream of the RNA start site functioned as a cell-specific enhancer of expression both with the α1-antitrypsin promoter and when combined with a functional β-globin promoter. Within the enhancer region, three binding sites for proteins present in hepatoma nuclear extracts were identified. The location of each site was positioned, using both methylation protection and methylation interference experiments. Each protein-binding site correlated with a functionally important region necessary for full enhancer activity. These experiments demonstrated a complex arrangement of regulatory elements comprising the α1-antitrypsin enhancer. Significant qualitative differences exist between the findings presented here and the cis-acting elements operative in regulating expression of the human α1-antitrypsin gene (Ciliberto et al., Cell 41:531-540, 1985; De Simone et al., EMBO J. 6:2759-2766, 1987).