A novel basal promoter element is required for expression of the rat tyrosine hydroxylase gene

Nucleotide sequence conservation of novel and established cis-regulatory sites within the tyrosine hydroxylase gene promoter

Tyrosine hydroxylase (TH) is the rate-limiting enzyme in catecholamine biosynthesis and its gene proximal promoter ( < 1 kb upstream from the transcription start site) is essential for regulating transcription in both the developing and adult nervous systems. Several putative regulatory elements within the TH proximal promoter have been reported, but evolutionary conservation of these elements has not been thoroughly investigated. Since many vertebrate species are used to model development, function and disorders of human catecholaminergic neurons, identifying evolutionarily conserved transcription regulatory mechanisms is a high priority. In this study, we align TH proximal promoter nucleotide sequences from several vertebrate species to identify evolutionarily conserved motifs. This analysis identified three elements (a TATA box, cyclic AMP response element (CRE) and a 5'-GGTGG-3' site) that constitute the core of an ancient vertebrate TH promoter. Focusing on only eutherian mammals, two regions of high conservation within the proximal promoter were identified: a ∼250 bp region adjacent to the transcription start site and a ∼85 bp region located approximately 350 bp further upstream. Within both regions, conservation of previously reported cis-regulatory motifs and human single nucleotide variants was evaluated. Transcription reporter assays in a TH -expressing cell line demonstrated the functionality of highly conserved motifs in the proximal promoter regions and electromobility shift assays showed that brain-region specific complexes assemble on these motifs. These studies also identified a non-canonical CRE binding (CREB) protein recognition element in the proximal promoter. Together, these studies provide a detailed analysis of evolutionary conservation within the TH promoter and identify potential cis-regulatory motifs that underlie a core set of regulatory mechanisms in mammals.

Complex molecular regulation of tyrosine hydroxylase

Tyrosine hydroxylase, the rate-limiting enzyme in catecholamine biosynthesis, is strictly controlled by several interrelated regulatory mechanisms. Enzyme synthesis is controlled by epigenetic factors, transcription factors, and mRNA levels. Enzyme activity is regulated by end-product feedback inhibition. Phosphorylation of the enzyme is catalyzed by several protein kinases and dephosphorylation is mediated by two protein phosphatases that establish a sensitive process for regulating enzyme activity on a minute-to-minute basis. Interactions between tyrosine hydroxylase and other proteins introduce additional layers to the already tightly controlled production of catecholamines. Tyrosine hydroxylase degradation by the ubiquitin-proteasome coupled pathway represents yet another mechanism of regulation. Here, we revisit the myriad mechanisms that regulate tyrosine hydroxylase expression and activity and highlight their physiological importance in the control of catecholamine biosynthesis.

Genetically engineered murine models--contribution to our understanding of the genetics, molecular pathology and therapeutic targeting of neuroblastoma

Genetically engineered mouse models (GEMM) have made major contributions to a molecular understanding of several adult cancers and these results are increasingly being translated into the pre-clinical setting where GEMM will very likely make a major impact on the development of targeted therapeutics in the near future. The relationship of pediatric cancers to altered developmental programs, and their genetic simplicity relative to adult cancers provides unique opportunities for the application of new advances in GEMM technology. In neuroblastoma the well-characterized TH-MYCN GEMM is increasingly used for a variety of molecular-genetic, developmental and pre-clinical therapeutics applications. We discuss: the present and historical application of GEMM to neuroblastoma research, future opportunities, and relevant targets suitable for new GEMM strategies in neuroblastoma. We review the potential of these models to contribute both to an understanding of the developmental nature of neuroblastoma and to improved therapy for this disease.

Epigenetic, transcriptional and posttranscriptional regulation of the tyrosine hydroxylase gene

The activity of tyrosine hydroxylase (TH, EC 1.14.16.2) gene and protein determines the catecholamine level, which, in turn, is crucial for the organism homeostasis. The TH gene expression is regulated by near all possible regulatory mechanisms on epigenetic, transcriptional and posttranscriptional levels. Ongoing molecular characteristic of the TH gene reveals some of the cis and trans elements necessary for its proper expression but most of them especially these responsible for tissue specific expression remain still obscure. This review will focus on some aspects of TH regulation including spatial chromatin organization of the TH locus and TH gene, regulatory elements mediating basal, induced and cell-specific activity, transcriptional elongation, alternative TH RNA processing, and the regulation of TH RNA stability in the cell.

Fasudil attenuates sympathetic nervous activity in the adrenal medulla of spontaneously hypertensive rats

We investigated the effects of fasudil, a Rho kinase inhibitor, on hypertension in spontaneously hypertensive rats and on the catecholamine synthetic pathway. Ten-week-old male SHR and Wistar-Kyoto rats were administered fasudil (10 mg/kg/day s.c.) for 4 days. Systolic blood pressure was measured using the tail-cuff method. Catecholamine levels were measured with high-performance liquid chromatography-ECD methods. Tyrosine hydroxylase protein levels were measured in Western blot analysis. The tyrosine hydroxylase mRNA level was measured using real-time PCR methods. Fasudil significantly decreased systolic blood pressure in spontaneously hypertensive rats, but not in Wistar-Kyoto rats. Fasudil also significantly decreased catecholamine, tyrosine hydroxylase protein, and tyrosine hydroxylase mRNA levels in the adrenal medulla of spontaneously hypertensive rats. These results suggest that the depressor effects of fasudil on hypertension in spontaneously hypertensive rats may be related to inhibition of the catecholamine synthetic pathway.

A tyrosine hydroxylase-yellow fluorescent protein knock-in reporter system labeling dopaminergic neurons reveals potential regulatory role for the first intron of the rodent tyrosine hydroxylase gene

Degeneration of the dopaminergic neurons of the substantia nigra is a hallmark of Parkinson's disease. To facilitate the study of the differentiation and maintenance of this population of dopaminergic neurons both in vivo and in vitro, we generated a knock-in reporter line in which the yellow fluorescent protein (YFP) replaced the first exon and the first intron of the tyrosine hydroxylase (TH) gene in one allele by homologous recombination. Expression of YFP under the direct control of the entire endogenous 5' upstream region of the TH gene was predicted to closely match expression of TH from the wild type allele, thus marking functional dopaminergic neurons. We found that YFP was expressed in dopaminergic neurons differentiated in vitro from the knock-in mouse embryonic stem cell line and in dopaminergic brain regions in knock-in mice. Surprisingly, however, YFP expression did not overlap completely with TH expression, and the degree of overlap varied in different TH-expressing brain regions. Thus, the reporter gene did not identify functional TH-expressing cells with complete accuracy. A DNaseI hypersensitivity assay revealed a cluster of hypersensitivity sites in the first intron of the TH gene, which was deleted by insertion of the reporter gene, suggesting that this region may contain cis-acting regulatory sequences. Our results suggest that the first intron of the rodent TH gene may be important for accurate expression of TH.

Tyrosine hydroxylase transcription depends primarily on cAMP response element activity, regardless of the type of inducing stimulus

In neurons and neuroendocrine cells, tyrosine hydroxylase (TH) gene expression is induced by stimuli that elevate cAMP, by depolarization, and by hypoxia. Using these stimuli, we examined TH promoter mutants, cAMP response element binding protein (CREB) phosphorylation site mutants, and transcriptional interference with dominant negative transcription factors to assess the relative contributions of CREB/AP-1 family members to the regulation of basal and inducible TH transcription in PC12 cells. We found that basal transcription depends on transcription factor activity at the partial dyad (-17 bp), CRE (-45 bp), and AP1 (-205 bp) elements. Induced transcription is regulated primarily by activity at the CRE, with only small contributions from the AP1 or hypoxia response element 1 (HRE1; -225 bp) elements, regardless of inducing stimulus. CREB, ATF-1, and CREMtau all mediate CRE-dependent transcription, with CREB and CREMtau being more effective than ATF-1. Phosphorylation of CREB on Ser133, but not on Ser142 or Ser143, is required for induced transcription, regardless of inducing stimulus.

Orphan nuclear receptor Nurr1 directly transactivates the promoter activity of the tyrosine hydroxylase gene in a cell-specific manner

Tyrosine hydroxylase (TH) catalyzes the first and rate-limiting step of catecholamine synthesis and its expression is necessary for neurotransmitter specification of all catecholaminergic neurons, while dopamine beta-hydroxylase (DBH) is essential for the noradrenergic phenotype. In the present study, we show that Nurr1, an orphan nuclear receptor critical for dopaminergic (DA) neuron development, directly transactivates the promoter activity of the TH gene in a cell type-dependent manner, while it does not regulate the DBH promoter. Consistent with these results, only the TH promoter contains multiple sequence motifs homologous to the known Nurr1-binding motif, NBRE. TH promoter deletional analysis indicates that < 1.0 kb upstream sequences, encompassing three NBRE-like motifs (i.e. NL1, NL2 and NL3) are mostly responsible for the effects of Nurr1. Among these potential motifs, site-directed mutational analysis showed that NL1, residing from - 35 to - 28 bp, was most critical for mediating the transactivation by Nurr1. Strikingly, however, both DNase I footprinting and electrophoretic mobility shift assays showed that NL3, but not NL1 or NL2, has high binding affinity to Nurr1. To determine whether the proximity of these motifs may be important for transactivation by Nurr1 in the transient transfection assay, we generated reporter gene constructs in which NL3 is immediately proximal to the TATA box. Indeed, NL3 was more efficient in this position than NL1 or NL2 for mediating the transactivation by Nurr1. Our results suggest that Nurr1 may play a direct role for specification of DA neurotransmitter identity by activating TH gene transcription in a cell context-dependent manner.

Heparin facilitates glial cell line-derived neurotrophic factor signal transduction

Glial cell-line neurotrophic factor (GDNF), a neurotrophic factor with heparin binding affinity, promotes the survival and differentiation of a variety of neuronal cells including dopaminergic neuron. The effect of heparin on GDNF signaling was investigated based on the expression of the tyrosine hydroxyrase (TH) gene in neurobalstoma cells. Up-regulation of TH gene mRNA by GDNF was enhanced by co-administration of heparin. This facilitation by heparin was particularly evident at suboptimal levels of GDNF, which was consistent with the luciferase assay using TH gene promoter. Pretreatment with heparitinase decreased TH promoter activity in the absence of heparin. Phosphorylation of extracellular regulated kinase was increased in the presence of heparin, although tyrosine phosphorylation of Ret receptor tyrosine kinase was not affected by heparin. Expression of early response genes such as c-fos or Egr1 increased and sustained in the presence of heparin more than that without heparin. These results indicate that interaction with glycosaminoglycans such as heparin affects GDNF signal transduction positively.

In vitro regulated expression of tyrosine hydroxylase in ventral midbrain neurons from Nurr1-null mouse pups

The transcription factor Nurr1, an orphan member of the steroid-thyroid hormone nuclear receptor superfamily, is essential for the proper terminal differentiation of ventral midbrain dopaminergic neurons. Disruption of the Nurr1 gene in mice by homologous recombination abolishes synthesis of dopamine (DA) and expression of DA biosynthetic enzymes, including tyrosine hydroxylase (TH), in the ventral midbrain without affecting the synthesis of DA in other areas of the brain. At birth, however, dopaminergic neuron precursors in Nurr1 null (-/-) pups remain as shown by continued expression of residual, untranslated Nurr1 mRNA not altered by homologous recombination. Since Nurr1 disruption is lethal shortly after birth, to further investigate the developmental properties of these neurons, dissociated ventral midbrain neurons from newborn pups were grown for 5 days on an astrocyte feeder layer, subjected to various treatments and then evaluated for expression of TH by fluorescent immunocytochemistry. Initially, a small percentage of neurons (0.26% +/- 0.07%) from the ventral midbrain of Nurr1 -/- pups were TH-immunoreactive (TH-IR). No change in TH expression was observed in the presence of glial cell line-derived neurotrophic factor (GDNF), brain-derived neurotrophic factor (BDNF), or DA alone or in combination. Treatment with forskolin (Fsk), however, significantly increased the percentage of TH-IR neurons (1.36% +/- 0.15%). Combination of Fsk, BNDF, and DA further increased the percentage of TH-IR neurons (2.58% +/- 0.50%). Therefore, these data suggest that dopaminergic neuron precursors, which develop in vivo without Nurr1, remain in an undifferentiated condition that is permissive to the induction of TH in vitro. J. Neurosci. Res. 64:322-330, 2001. Published 2001 Wiley-Liss, Inc.

The cAMP responsive element and CREB partially mediate the response of the tyrosine hydroxylase gene to phorbol ester

Tyrosine hydroxylase (TH) gene promoter activity is increased in PC12 cells that are treated with the phorbol ester, 12-O-tetradecanoylphorbol 13-acetate (TPA). Mutagenesis of either the cAMP responsive element (CRE) or the activator protein-1 element (AP1) within the TH gene proximal promoter leads to a dramatic inhibition of the TPA response. The TH CRE and TH AP1 sites are also independently responsive to TPA in minimal promoter constructs. TPA treatment results in phosphorylation of cAMP responsive element binding protein (CREB) and activation of cAMP-dependent protein kinase (PKA) in PC12 cells; hence, we tested whether CREB and/or PKA are essential for the TPA response. In CREB-deficient cells, the response of the full TH gene proximal promoter or the independent response of the TH CRE by itself to TPA is inhibited. The TPA-inducibility of TH mRNA is also blocked in CREB-deficient cells. Expression of the PKA inhibitor protein, PKI, also inhibits the independent response of the TH CRE to TPA. Our results support the hypothesis that TPA stimulates the TH gene promoter via signaling pathways that activate either the TH AP1 or TH CRE sites. Both signaling pathways are dependent on CREB and the TH CRE-mediated pathway is dependent on PKA.

4.5 kb of the rat tyrosine hydroxylase 5' flanking sequence directs tissue specific expression during development and contains consensus sites for multiple transcription factors

To delineate DNA sequences responsible for developmentally correct expression of the rat tyrosine hydroxylase (TH) gene, we analyzed a line of transgenic mice expressing high levels of human placental alkaline phosphatase (AP) under control of 4.5 kb of 5' flanking DNA from the rat TH gene in embryos and adults. Several regions, such as the accessory olfactory bulb, which were not thought to synthesize TH protein or do so only transiently, were shown to express TH protein using an improved method of antigen retrieval for TH immunohistochemistry. Many of these regions had been shown to express TH-driven reporter genes in transgenic mice. In the central nervous system, AP was detected in essentially all TH-expressing cell groups throughout development and in adults. In the peripheral nervous system, transgene expression paralleled endogenous TH expression in the developing adrenal medulla and sympathetic ganglia but not in transiently TH-positive cells in dorsal root ganglia. Peripheral expression in the adult adrenal medulla was very weak and absent in sympathetic ganglia. The specificity with which the 4.5 kb region directs transgene expression in embryos is comparable to that observed with longer 5' flanking promoter regions, implying that this region contains the control elements for appropriate expression during development. Sequence analysis of the region demonstrates a GT dinucleotide repeat, an element that resembles the neural restrictive silencer element (NRSE), which restricts transcription of neuronal genes in non-neuronal cells, and consensus sites for three families of transcription factors, Ptx1/3, Nurr1 and Gli1/2, which are required for the early differentiation of mesencephalic neurons.

CREB mediates the cAMP-responsiveness of the tyrosine hydroxylase gene: use of an antisense RNA strategy to produce CREB-deficient PC12 cell lines

cAMP initiates the PKA signaling cascade in rat pheochromocytoma PC12 cells, resulting in transcriptional activation of the tyrosine hydroxylase (TH) gene. This effect is mediated primarily through the cAMP responsive element (CRE), located at position -45 to -38 within the TH gene promoter. In this study, we applied an antisense RNA strategy to evaluate the role of the cAMP responsive element binding protein (CREB) in regulating TH gene expression. CREB antisense RNA expression vectors were stably introduced into PC12 cells to generate cell lines deficient in CREB. CREB protein and mRNA levels were diminished up to 90% in the stably transfected cell lines. Promoter analysis experiments demonstrated that cAMP-mediated inducibility of either TH gene proximal promoter activity or the activity of the TH CRE by itself fused upstream of a basal promoter was diminished in CREB-deficient cell lines. PKA activity in the CREB-deficient cell lines was comparable to the activity in control cell lines. In addition, neither ATF1, nor CREM proteins were significantly down-regulated in the CREB-deficient cells. Most significantly, the cAMP-inducibility of endogenous TH mRNA was completely blocked in the CREB-deficient cells, indicating that the response of the endogenous gene to cAMP was dependent on CREB. These results support the hypothesis that CREB (not other CRE-binding proteins) is the key transcription factor that is required for regulating TH gene expression in response to cAMP. Furthermore, our studies indicate that these CREB-deficient PC12 cells are excellent tools to study the participation of CREB in gene regulation.

Genetic regulatory elements introduced into neural stem and progenitor cell populations

The genetic manipulation of neural cells has advantage in both basic biology and medicine. Its utility has provided a clearer understanding of how the survival, connectivity, and chemical phenotype of neurones is regulated during, and after, embryogenesis. Much of this achievement has come from the recent generation by genetic means of reproducible and representative supplies of precursor cells which can then be analyzed in a variety of paradigms. Furthermore, advances made in the clinical use of transplantation for neurodegenerative disease have created a demand for an abundant, efficacious and safe supply of neural cells for grafting. This review describes how genetic methods, in juxtaposition to epigenetic means, have been used advantageously to achieve this goal. In particular, we detail how gene transfer techniques have been developed to enable cell immortalization, manipulation of cell differentiation and commitment, and the controlled selection of cells for purification or safety purposes. In addition, it is now also possible to genetically modify antigen presentation on cell surfaces. Finally, there is detailed the transfer of therapeutic products to discrete parts of the central nervous system (CNS), using neural cells as elegant and sophisticated delivery vehicles. In conclusion, once the epigenetic and genetic controls over neural cell production, differentiation and death have been more fully determined, providing a mixture of hard-wired elements and more flexibly expressed characteristics becomes feasible. Optimization of the contributions and interactions of these two controlling systems should lead to improved cell supplies for neurotransplantation.

Cell type-specific regulatory sequences control expression of the Drosophila FMRF-NH2 neuropeptide gene

The FMRFamide (dFMRFa) neuropeptide gene is expressed in about 17 diverse cell types in the Drosophila central nervous system. This expression pattern is generated by transcriptional control elements that are distributed over 8 kilobases of dFMRFa DNA. Previous studies identified one enhancer within the dFMRFa 5' region that is both necessary and sufficient to drive reporter transgene expression in one of the 17 dFMRFa cell types, the OL2 neurons. We now report the presence of two additional, non-overlapping enhancers within the gene: One drives expression by the six Tv neuroendocrine cells, and another in the four X and X2 interneurons. We also show that the Tv neuron-specific enhancer itself has complex organization, with several positively and negatively acting cis elements. Together, these results describe the organization of what is likely to be a prototypic neuronal gene promoter: an assemblage of multiple, independent, cell type-specific enhancers, each consisting of multiple quantitative elements.

Transcriptional regulation of the GluR2 gene: neural-specific expression, multiple promoters, and regulatory elements

To understand how neurons control the expression of the AMPA receptor subunit GluR2, we cloned the 5' proximal region of the rat gene and investigated GluR2 promoter activity by transient transfection. RNase protection and primer extension of rat brain mRNA revealed multiple transcription initiation sites from -340 to -481 bases upstream of the GluR2 AUG codon. The relative use of 5' start sites was different in cortex and cerebellum, indicating complexity of GluR2 transcript expression among different sets of neurons. When GluR2 promoter activity was investigated by plasmid transfection into cultured cortical neurons, cortical glia, and C6 glioma cells, the promoter construct with the strongest activity, per transfected cell, was 29.4-fold (+/- 3.7) more active in neurons than in non-neural cells. Immunostaining of cortical cultures showed that >97% of the luciferase-positive cells also expressed the neuronal marker MAP-2. Evaluation of internal deletion and substitution mutations identified a functional repressor element I RE1-like silencer and functional Sp1 and nuclear respiratory factor-1 (NRF-1) elements within a GC-rich proximal GluR2 promoter region. The GluR2 silencer reduced promoter activity in glia and non-neuronal cell lines by two- to threefold, was without effect in cortical neurons, and could bind the RE1-silencing transcription factor (REST) because cotransfection of REST into neurons reduced GluR2 promoter activity in a silencer-dependent manner. Substitution of the GluR2 silencer by the homologous NaII RE1 silencer further reduced GluR2 promoter activity in non-neuronal cells by 30-47%. Maximal positive GluR2 promoter activity required both Sp1 and NRF-1 cis elements and an interelement nucleotide bridge sequence. These results indicate that GluR2 transcription initiates from multiple sites, is highly neuronal selective, and is regulated by three regulatory elements in the 5' proximal promoter region.

CRE and TRE sequences of the rat tyrosine hydroxylase promoter are required for TH basal expression in adult mice but not in the embryo

Tyrosine hydroxylase (TH), the rate-limiting enzyme in the biosynthesis of catecholamine neurotransmitters, is expressed in a restricted number of areas, and subject to numerous regulations during development and in adulthood. Two transcription factor binding sites present in the proximal region of the TH gene, the TPA-responsive element (TRE) and the c-AMP responsive element (CRE), have been shown to play important roles in TH gene regulation in vitro. In order to elucidate in vivo the role of these two sites, we produced transgenic mice bearing a 5.3-kb fragment from the 5' flanking sequence of the TH gene with mutations in either the CRE-or TRE-sites. Using the intact 5.3-kb fragment fused to two different reporter genes (HSV1-tk and lacZ), we show that this promoter fragment is able to specifically direct expression in catecholaminergic tissues both in adult mice and embryos. Interestingly, the CRE- and TRE-mutated transgenes were not expressed in adult mice, contrary to the situation in embryos where they were specifically expressed in catecholaminergic regions. These results demonstrate that the CRE and TRE play an essential role in basal TH expression in adult tissues in vivo. Moreover, they suggest that distinct transcription factors are involved in TH regulation in developing and adult tissues. In support of this, gel mobility shift experiments revealed a complex present only in embryonic tissues. Taken together, these data highlight the diversity of the mechanisms underlying the establishment and maintenance of the catecholaminergic phenotype.