AP-1, CREB and CBP transcription factors differentially regulate the tyrosine hydroxylase gene

The tyrosine hydroxylase (TH) gene encodes the rate-limiting enzyme in the biosynthesis of catecholamines. We have investigated the roles of two elements of the TH promoter, the TH-'Fat Specific Element' (TH-FSE) which binds the Fos-Jun complex, and the cAMP Response Element (CRE), which binds CREB and the co-activator protein, CREB Binding Protein (CBP) in regulating TH gene transcription. In PC12 cells, the TH-FSE was required for induction by NGF while the CRE was required for induction by cAMP. We show that both elements can function independently and contribute strongly to TH promoter basal activity in PC12 cells. We employed transient expression in the F9 teratocarcinoma cell line to vary experimentally the levels of the nuclear regulators implicated in TH control by the PC12 studies. In F9 cells, the TH promoter was strongly activated by Fos and Jun, and by PKA-stimulated CREB protein. In F9 and NIH3T3 cells, CBP, a co-activator which targets Fos-Jun and PKA-stimulated CREB, also induced the TH promoter. Immunohistochemical studies in rat brain regions enriched in dopaminergic neurons, including the midbrain and olfactory bulb (OB), suggest that Fos-Jun and CREB make differential contributions to TH gene activity in different tissues. Whereas changes in Fos protein levels parallel decreases in TH protein upon olfactory deprivation, CBP levels remain unchanged. This suggests that CRE-associated factors, including CBP, are not major regulators in the OB. In contrast, the presence of CREB and the absence of Fos immunoreactivity in midbrain dopaminergic cells suggests that the CRE is the primary regulator in this region.