Nurr1 Represses Tyrosine Hydroxylase Expression via SIRT1 in Human Neural Stem Cells

Abstract

Nurr1 is an orphan nuclear receptor best known for its essential role in the development and maintenance of midbrain dopaminergic (DA) neurons. During DA neurogenesis, Nurr1 directly targets human tyrosine hydroxylase (hTH). Here we investigated this targeting to identify the molecular mechanisms by which Nurr1 regulates DA neurogenesis. We previously cloned the hTH promoter and found three consensus elements for Nurr1 binding: NBRE-A, -B, and -C. In the present study, gel retardation and luciferase assays using hTH constructs showed that Nurr1 preferentially bound to NBRE-A, through which it mediated transcriptional activity. Furthermore, Nurr1 displayed dual-function transcriptional activities depending on the cell type. In DA-like SH-SY5Y cells, Nurr1 dose-dependently stimulated hTH-3174 promoter activity by 7- to 11-fold. However, in the human neural stem cell (hNSC) line HB1.F3, Nurr1 strongly repressed transcription from the same promoter. This repression was relieved by mutation of only the NBRE-A element and by nicotinamide [an inhibitor of class III histone deacetylases (HDACs), such as SIRT1], but not by trichostatin A (an inhibitor of class I and II HDACs). SIRT1 was strongly expressed in the nucleus of HB1.F3 cells, while it was localized in the cytoplasm in SH-SY5Y cells. ChIP assays of HB1.F3 cells showed that Nurr1 overexpression significantly increased the SIRT1 occupancy of the NBRE-A hTH promoter region, while low SIRT1 levels were observed in control cells. In contrast, no significant SIRT1 recruitment was observed in SH-SY5Y cells. These results indicate that differential SIRT1 localization may be involved in hTH gene regulation. Overall, our findings suggest that Nurr1 exists in dual transcriptional complexes, including co-repressor complexes that can be remodeled to become co-activators and can fine-tune hTH gene transcription during human DA neurogenesis.

Nicotinamide restricts neural precursor proliferation to enhance catecholaminergic neuronal subtype differentiation from mouse embryonic stem cells

“…A previous study in our laboratory demonstrated the benefits of applying nicotinamide as a differentiation agent to aid the conversion of stem cells to mature GABAergic neurons (18). Findings from this work and published literature (27)(28)(29) imply that this bioactive nutrient may also function as a catecholaminergic differentiation signal implicated in the development or maintenance of basal ganglia circuitry.…”

Nicotinamide restricts neural precursor proliferation to enhance catecholaminergic neuronal subtype differentiation from mouse embryonic stem cells

“…A previous study in our laboratory demonstrated the benefits of applying nicotinamide as a differentiation agent to aid the conversion of stem cells to mature GABAergic neurons [ 18 ]. Findings from this work and published literature [ 27 – 29 ] imply that this bioactive nutrient may also function as a catecholaminergic differentiation signal implicated in the development or maintenance of basal ganglia circuitry.…”

A novel synthetic activator of Nurr1 induces dopaminergic gene expression and protects against 6-hydroxydopamine neurotoxicity in vitro

“…Interestingly, transcriptional responses to Nurr1 appear to depend both on cell type and on the constitutive level of Nurr1 expression [17]. For example, Nurr1 strongly induces TH expression in rodent neural precursor and differentiated cells, but the inductive effects on TH in human neural precursor cells are more modest [18] and can even be repressive in human neural stem cells [19]. Such varying transcriptional responses to Nurr1 may depend on the constitutive level of protein expression.…”