Winged helix hepatocyte nuclear factor 3 and POU-domain protein Brn-2/N-Oct-3 bind overlapping sites on the neuronal promoter of human aromatic l-amino acid decarboxylase gene

The neuronal promoter of human aromatic l-amino acid decarboxylase gene has been analysed to elucidate the mechanisms of neuron type-specific expression. The (−560/+92) promoter segment was sufficient to direct luciferase expression at a higher level in SK-N-BE neuroblastoma cells, than in CHP126 neuroepithelia, HepG2 hepatoma or SK-Hep1 epithelioma cells. Deletions experiments showed that this segment contained a neuronal-specific (element T1) and a SK-N-BE-specific (element N1) cis-activating sequences. Element T1 (−72/−36) bound Sp1 and NF-Y proteins, and unidentified neuronal-specific factors. Element N1 (−102/−72) bound cell-specific factors, identified as HNF-3, N-Oct-3/Brn-2 and N-Oct-2. HNF-3 proteins recognized the sequence TCAGTAAATA that matches the consensus motif. Oct-1, N-Oct-2 and N-Oct-3 bound the AAATAATGC sequence that overlaps the HNF-3 binding site. In addition, we show that the HNF-3 binding sites from aldolase C and HNF-3β gene promoters also bind N-Oct-2 and N-Oct-3 proteins. These data suggest a functional interplay of winged helix/forkhead and POU-domain transcription factors on a variety of neuronal gene promoters.