TISSUE-SPECIFIC EXPRESSION OF THE NONNEURONAL PROMOTER OF THE AROMATIC L-AMINO-ACID DECARBOXYLASE GENE IS REGULATED BY HEPATOCYTE-NUCLEAR-FACTOR-1

The rat aromatic L-amino acid decarboxylase (AADC) gene contains alter native promoters which direct expression of neuronal and nonneuronal m RNAs that differ only in their 5'-untranslated regions (UTRs). We have analyzed the expression of the nonneuronal promoter of the rat AADC g ene in the kidney epithelial cell line LLC-PK1 and in cells which do n ot express the nonneuronal form of AADC by transient transfection. The se studies revealed that the first 1.1 kilobases of the nonneuronal pr omoter, including the nonneuronal-specific 5'-UTR (Exon 1), contains s ufficient information to direct tissue-specific expression. Serial del etions of this promoter localized the cis-active element to a region b etween -52 and -28 base pairs upstream of the nonneuronal transcriptio n start site. An APT-rich sequence, within this region which we have t ermed KL-1, was found to bind a kidney and liver-specific factor by DN ase footprint analysis and was capable of directing tissue-specific ex pression from a heterologous promoter. Moreover, when the KL-1 sequenc e was mutated in the context of the entire promoter sequence, all tran scriptional activity was abolished. DNA sequence comparison revealed t hat the KL-1 fragment is highly homologous to the binding site for hep atocyte nuclear factor-1 (HNF-1). Mobility shift studies utilizing an antibody to HNF-1 demonstrated binding of HNF-1 to the KL-1 fragment a nd cotransfection of HNF-1 cDNA into cells which do not express the no nneuronal form of AADC resulted in activation of transfected AADC nonn euronal promoter constructs. These results strongly suggest that the t ranscription factor which regulates the tissue-specific expression of the nonneuronal form of AADC mRNA is HNF-1.