Regulation of the tyrosine hydroxylase and dopamine β‐hydroxylase genes by the transcription factor AP‐2

The retinoic acid‐inducible and developmentally regulated transcription factor AP‐2 plays an important role during development. In adult mammals, AP‐2 is expressed in both neural and non‐neural tissues. However, the function of AP‐2 in different neuronal phenotypes is poorly understood. In this study, transcriptional regulation of tyrosine hydroxylase (TH) and dopamine β‐hydroxylase (DBH) genes by AP‐2 was investigated. AP‐2 binding sites were identified in the upstream regions of both genes. Electrophoretic mobility shift assays (EMSA) and DNase I footprinting analyses indicate that the AP−2 interaction with these motifs is more prominent in catecholaminergic SK‐N‐BE(2)C and CATH.a than in non‐catecholaminergic HeLa and HepG2 cell lines. Exogenous expression of AP‐2 robustly transactivated TH and DBH promoter activities in non‐catecholaminergic cell lines. While AP‐2 regulates the DBH promoter activity via a single site, transactivation of the TH promoter by AP‐2 appears to require multiple sites. In support of this, mutation of multiple AP‐2 binding sites but not that of single site diminished the basal promoter activity of the TH gene in cell lines that express TH and abolished transactivation by exogenous AP‐2 expression in cell lines that do not express TH. In contrast, mutation of a single AP‐2 binding site of the DBH gene completely abolished transactivation by AP‐2. Double‐label immunohistochemistry showed that AP‐2 is coexpressed with TH in noradrenergic and adrenergic neurons in both the central and peripheral nervous systems of adult rodents. Numerous non‐catecholaminergic cell groups within the spinal cord, medulla, cerebellum, and pons also express AP‐2. The concentration of AP‐2 in dorsomedial locations along the neuraxis suggests a regionally specific role for this transcription factor in the regulation of neuronal function. Based on these findings we propose that AP‐2 may coregulate TH and DBH gene expression and thus participate in expression/maintenance of neurotransmitter phenotypes in (nor)adrenergic neurons and neuroendocrine cells.