Transcription of the rat tyrosine hydroxylase (TH) gene is controlled by enhancer sequences in its 5' flanking region; these enhancers include the AP1-, AP2-, dyad-, POU/Oct- binding domain, and cAMP response element (CRE) motifs. Of cis-regulatory elements, a putative E-box is located at -190 bp on the 5' flanking region of TH. In this study, we investigated whether the TH gene expression is regulated by bHLH transcription factors such as NeuroD or neurogenin 1. We used mouse neural stem cells, A3B1L6, immortalized with v-myc. In A3B1L6 cells, protein kinase A (PKA) increased TH activity. The stimulatory effect of PKA was dependent on a CRE located at -45 bp from the site of transcription initiation, suggesting that A3B1L6 provides an appropriate system for the study of TH gene expression. Importantly, coexpression of NeuroD or neurogenin 1 with a ubiquitous bHLH partner E47 could transactivate the TH promoter. The data indicate that expression of the TH gene may be regulated by bHLH transcription factors probably through the E-box at -190.

Keywords: tyrosine hydroxylase (TH), neural stem cell, NeuroD, PKA, CREB