MULTIPLE PROMOTERS OF HUMAN CHOLINE-ACETYLTRANSFERASE AND AROMATIC L-AMINO-ACID DECARBOXYLASE GENES

The promoter regions of human choline acetyltransferase (ChAT) and aro matic L-amino acid decarboxylase (AADC) genes have been analyzed by tr ansient transfection assays. AADC gene is transcribed from two alterna tive noncoding first exons, 1N and 1NN, expressed in pheochomocytoma a nd hepatoma cells, respectively. 5' flanking sequences of exon 1 N (fr om 9000 to 147 bp) display promoter activity in SK-N-BE neuroblastoma cells, but not in MC-I-XC cholinergic neuroepithelioma cells, and in A ADC-rich non-neuronal cells. On the contrary, 5' flanking sequences of exon 1 NN (from 1117 to 119 bp) display high promoter activity in hum an hepatoma cells HepG2, but not in SK-N-BE cells, suggesting high deg rees of specificity of promoters N and NN for AADC-expressing neuronal and non-neuronal cells, respectively. Preliminary evidence suggests t hat leukemia inhibitory factor suppresses the activity of the neuronal promoter in cultured sympathetic neurons. Two alternative first exons , R and M, have been localized in human ChAT gene, and the correspondi ng promoters characterized in cholinergic PC12 and NG-108-15 cells, an d in non-cholinergic neuro2A cells. Several positively or negatively a cting cis elements have been localized in the two promoters, as well a s a cAMP-inducible, enhancer-like element in the second intron. Among the various cell lines studied, there was no correlation between promo ter activities and the expression of the endogenous ChAT gene, suggest ing that the fine-tuning of ChAT gene expression is controlled by sile ncer elements which remain to be localized.