Control of tyrosine hydroxylase gene expression in chromaffin and PC12 cells.

Chromaffin and PC12 cells were used to elucidate mechanisms of stimulation of gene expression of tyrosine hydroxylase (TH), the pivotal enzyme in catecholamine biosynthesis. A plethora of treatments elevate TH gene expression. Elevated cAMP triggers increased TH gene expression, primarily by an increase in mRNA transcription. Although a variety of treatments that elevate [Ca(2+)](i), increase TH transcription, there are important differences among them, indicating different calcium signalling pathways in regulating TH gene expression acting at the CRE/CaRE (cyclic AMP/calcium response element). Several complexes, such as ATF-1/jun and CREB/AT-1 heterodimers bind this element. Activation of protein kinase C by phorbol esters, NGF and EGF activate TH transcription through the AP-1 site. TH transcription is also stimulated by glucocorticoids, increased cell density, hypoxia, and several other treatments. In some instances, post-transcriptional mechanisms also contribute to the intricate fine tuning of regulation of TH gene expression.