Regulation of tyrosine hydroxylase gene expression in depolarized non-transformed bovine adrenal medullary cells: second messenger systems and promoter mechanisms

Mutual Enhancement of Opioid and Adrenergic Receptors by Combinations of Opioids and Adrenergic Ligands Is Reflected in Molecular Complementarity of Ligands: Drug Development Possibilities

Crosstalk between opioid and adrenergic receptors is well characterized and due to interactions between second messenger systems, formation of receptor heterodimers, and extracellular allosteric binding regions. Both classes of receptors bind both sets of ligands. We propose here that receptor crosstalk may be mirrored in ligand complementarity. We demonstrate that opioids bind to adrenergic compounds with micromolar affinities. Additionally, adrenergic compounds bind with micromolar affinities to extracellular loops of opioid receptors while opioids bind to extracellular loops of adrenergic receptors. Thus, each compound type can bind to the complementary receptor, enhancing the activity of the other compound type through an allosteric mechanism. Screening for ligand complementarity may permit the identification of other mutually-enhancing sets of compounds as well as the design of novel combination drugs or tethered compounds with improved duration and specificity of action.

A Novel Animal Model of Parkinson's Disease Using Optogenetics: Representation of Various Disease Stages by Modulating the Illumination Parameter

BACKGROUND

The classic animal model of Parkinson's disease (PD) using neurotoxin can only simulate fixed stages of the disease by causing irreversible damage to the nigrostriatal system.

OBJECTIVES

To develop an optogenetic PD model that can modulate the severity of disease by optical stimulation by introducing the halorhodopsin (NpHR) gene into the substantia nigra compacta.

METHODS

Fifteen rats received injections of engineered AAV with NpHR-YFP gene into the substantia nigra. They were then subjected to illumination of 590-nm light wavelengths with 3 optical stimulation conditions, i.e., frequency-width: 5 Hz-10 ms (n = 5), 5 Hz-100 ms (n = 5), and 50 Hz-10 ms (n = 5). Eleven rats received 6-hydroxydopamine injections to establish the conventional PD model.

RESULTS

The optogenetic models showed characteristic PD manifestations, similar to those of the conventional models; the severity of forelimb akinesia correlated with the total illumination value (frequency × width). The group with a low illumination value (5 Hz-10 ms) was comparable to the conventional partial model whereas the groups with high illumination values (5 Hz-100 ms and 50 Hz-10 ms) were similar to the conventional complete model.

CONCLUSIONS

An optogenetic PD model has the advantage of more appropriately representing various PD stages by controlling illumination parameters.

Adrenergic Agonists Bind to Adrenergic-Receptor-Like Regions of the Mu Opioid Receptor, Enhancing Morphine and Methionine-Enkephalin Binding: A New Approach to "Biased Opioids"?

Extensive evidence demonstrates functional interactions between the adrenergic and opioid systems in a diversity of tissues and organs. While some effects are due to receptor and second messenger cross-talk, recent research has revealed an extracellular, allosteric opioid binding site on adrenergic receptors that enhances adrenergic activity and its duration. The present research addresses whether opioid receptors may have an equivalent extracellular, allosteric adrenergic binding site that has similar enhancing effects on opioid binding. Comparison of adrenergic and opioid receptor sequences revealed that these receptors share very significant regions of similarity, particularly in some of the extracellular and transmembrane regions associated with adrenergic binding in the adrenergic receptors. Five of these shared regions from the mu opioid receptor (muOPR) were synthesized as peptides and tested for binding to adrenergic, opioid and control compounds using ultraviolet spectroscopy. Adrenergic compounds bound to several of these muOPR peptides with low micromolar affinity while acetylcholine, histamine and various adrenergic antagonists did not. Similar studies were then conducted with purified, intact muOPR with similar results. Combinations of epinephrine with methionine enkephalin or morphine increased the binding of both by about half a log unit. These results suggest that muOPR may be allosterically enhanced by adrenergic agonists.

Fetal endocrine and metabolic adaptations to hypoxia: the role of the hypothalamic-pituitary-adrenal axis

In utero, hypoxia is a significant yet common stress that perturbs homeostasis and can occur due to preeclampsia, preterm labor, maternal smoking, heart or lung disease, obesity, and high altitude. The fetus has the extraordinary capacity to respond to stress during development. This is mediated in part by the hypothalamic-pituitary-adrenal (HPA) axis and more recently explored changes in perirenal adipose tissue (PAT) in response to hypoxia. Obvious ethical considerations limit studies of the human fetus, and fetal studies in the rodent model are limited due to size considerations and major differences in developmental landmarks. The sheep is a common model that has been used extensively to study the effects of both acute and chronic hypoxia on fetal development. In response to high-altitude-induced, moderate long-term hypoxia (LTH), both the HPA axis and PAT adapt to preserve normal fetal growth and development while allowing for responses to acute stress. Although these adaptations appear beneficial during fetal development, they may become deleterious postnatally and into adulthood. The goal of this review is to examine the role of the HPA axis in the convergence of endocrine and metabolic adaptive responses to hypoxia in the fetus.

Neuronal activity regulates expression of tyrosine hydroxylase in adult mouse substantia nigra pars compacta neurons

Striatal delivery of dopamine (DA) by midbrain substantia nigra pars compacta (SNc) neurons is vital for motor control and its depletion causes the motor symptoms of Parkinson's disease. While membrane potential changes or neuronal activity regulates tyrosine hydroxylase (TH, the rate limiting enzyme in catecholamine synthesis) expression in other catecholaminergic cells, it is not known whether the same occurs in adult SNc neurons. We administered drugs known to alter neuronal activity to mouse SNc DAergic neurons in various experimental preparations and measured changes in their TH expression. In cultured midbrain neurons, blockade of action potentials with 1 μM tetrodotoxin decreased TH expression beginning around 20 h later (as measured in real time by green fluorescent protein (GFP) expression driven off TH promoter activity). By contrast, partial blockade of small-conductance, Ca(2+) -activated potassium channels with 300 nM apamin increased TH mRNA and protein between 12 and 24 h later in slices of adult midbrain. Two-week infusions of 300 nM apamin directly to the adult mouse midbrain in vivo also increased TH expression in SNc neurons, measured immunohistochemically. Paradoxically, the number of TH immunoreactive (TH+) SNc neurons decreased in these animals. Similar in vivo infusions of drugs affecting other ion-channels and receptors (L-type voltage-activated Ca(2+) channels, GABA(A) receptors, high K(+) , DA receptors) also increased or decreased cellular TH immunoreactivity but decreased or increased, respectively, the number of TH+ cells in SNc. We conclude that in adult SNc neurons: (i) TH expression is activity-dependent and begins to change ∼20 h following sustained changes in neuronal activity; (ii) ion-channels and receptors mediating cell-autonomous activity or synaptic input are equally potent in altering TH expression; and (iii) activity-dependent changes in TH expression are balanced by opposing changes in the number of TH+ SNc cells.

Stress-induced activity in the locus coeruleus is not sensitive to stressor controllability

An important factor in determining the adverse consequences of a stress experience is the degree to which an individual can exert control over the stressor. Stressor controllability is known to influence brain norepinephrine levels, but its impact on activity in noradrenergic cell bodies is unknown. In the present study we investigated whether noradrenergic neurons within the locus coeruleus (LC), the major source of forebrain norepinephrine, are sensitive to stressor controllability. We exposed adult male Sprague-Dawley rats to escapable or yoked inescapable tailshock and assessed LC activity by measuring changes in the immediate early gene c-fos and the enzyme tyrosine hydroxylase (TH). We used in situ hybridization to measure levels of c-fos mRNA, TH mRNA, and TH primary transcript in the LC. In all three cases stress exposure increased expression relative to an unstressed homecage control group, but expression did not differ between controllable and uncontrollable stress. To further examine whether stressor controllability influences the number of stress-responsive LC neurons we performed double-label immunohistochemistry for TH and Fos. Again we detected an overall effect of stress, which did not differ between controllable and uncontrollable stress. We conclude that exposure to stress robustly increases expression of TH and c-fos in the LC, but this effect is not influenced by stressor controllability. To the extent that the expression of these genes reflects degree of neuronal activation, our results suggest that stress-induced activity of noradrenergic cell bodies in the LC is not sensitive to stressor controllability.

Long-term hypoxia modulates expression of key genes regulating adrenomedullary function in the late gestation ovine fetus

We previously communicated that long-term hypoxia (LTH) resulted in a selective reduction in plasma epinephrine following acute stress in fetal sheep. The present study tested the hypothesis that LTH selectively reduces adrenomedullary expression of phenylethanolamine-N-methyltransferase (PNMT), the rate-limiting enzyme for epinephrine synthesis. We also examined the effect of LTH on adrenomedullary nicotinic, muscarinic, and glucocorticoid receptor (GR) expression. Ewes were maintained at high altitude (3,820 m) from 30 to 138 days gestation (dGA); adrenomedullary tissue was collected from LTH and age-matched, normoxic control fetuses at 139-141 dGA. Contrary to our hypothesis, in addition to PNMT, adrenomedullary expression (mRNA, protein) of tyrosine hydroxylase (TH) and dopamine beta-hydroxylase (DBH) were reduced in the LTH fetus. Immunocytochemistry indicated that TH and DBH expression was lower throughout the medulla, while PNMT appeared to reflect a reduction in PNMT-expressing cells. Nicotinic receptor alpha 1, 2, 3, 5, 6, 7, beta 1, 2, and 4 subunits were expressed in the medulla of LTH and control fetuses. Messenger RNA for alpha 1 and 7 and beta 1 and 2 subunits was lower in LTH fetuses. Muscarinic receptors M1, M2, and M3 as well as the GR were also expressed, and no differences were noted between groups. In summary, LTH in fetal sheep has a profound effect on expression of key enzymes mediating adrenomedullary catecholamine synthesis. Further, LTH impacts nicotinic receptor subunit expression potentially altering cholinergic neurotransmission within the medulla. These findings have important implications regarding fetal cardiovascular and metabolic responses to stress in the LTH fetus.

Factors controlling fibroblast growth factor receptor-1's cytoplasmic trafficking and its regulation as revealed by FRAP analysis

Biochemical and microscopic studies have indicated that FGFR1 is a transmembrane and soluble protein present in the cytosol and nucleus. How FGFR1 enters the cytosol and subsequently the nucleus to control cell development and associated gene activities has become a compelling question. Analyses of protein synthesis, cytoplasmic subcompartmental distribution and movement of FGFR1-EGFP and FGFR1 mutants showed that FGFR1 exists as three separate populations (a) a newly synthesized, highly mobile, nonglycosylated, cytosolic receptor that is depleted by brefeldin A and resides outside the ER-Golgi lumen, (b) a slowly diffusing membrane receptor population, and (c) an immobile membrane pool increased by brefeldin A. RSK1 increases the highly mobile cytosolic FGFR1 population and its overall diffusion rate leading to increased FGFR1 nuclear accumulation, which coaccumulates with RSK1. A model is proposed in which newly synthesized FGFR1 can enter the (a) "nuclear pathway," where the nonglycosylated receptor is extruded from the pre-Golgi producing highly mobile cytosolic receptor molecules that rapidly accumulate in the nucleus or (b) "membrane pathway," in which FGFR1 is processed through the Golgi, where its movement is spatially restricted to trans-Golgi membranes with limited lateral mobility. Entrance into the nuclear pathway is favored by FGFR1's interaction with kinase active RSK1.

Integrative nuclear FGFR1 signaling (INFS) as a part of a universal ?feed-forward-and-gate? signaling module that controls cell growth and differentiation

A novel signaling mechanism is described through which extracellular signals and intracellular signaling pathways regulate proliferation, growth, differentiation, and other functions of cells in the nervous system. Upon cell stimulation, fibroblast growth factor receptor-1 (FGFR1), a typically plasma membrane-associated protein, is released from ER membranes into the cytosol and translocates to the cell nucleus by an importin-beta-mediated transport pathway along with its ligand, FGF-2. The nuclear accumulation of FGFR1 is activated by changes in cell contacts and by stimulation of cells with growth factors, neurotransmitters and hormones as well as by a variety of different second messengers and thus was named integrative nuclear FGFR1 signaling (INFS). In the nucleus, FGFR1 localizes specifically within nuclear matrix-attached speckle-domains, which are known to be sites for RNA Pol II-mediated transcription and co-transcriptional pre-mRNA processing. In these domains, nuclear FGFR1 colocalizes with RNA transcription sites, splicing factors, modified histones, phosphorylated RNA Pol II, and signaling kinases. Within the nucleus, FGFR1 serves as a general transcriptional regulator, as indicated by its association with the majority of active nuclear centers of RNA synthesis and processing, by the ability of nuclear FGFR1 to activate structurally distinct genes located on different chromosomes and by its stimulation of multi-gene programs for cell growth and differentiation. We propose that FGFR1 is part of a universal "feed-forward-and-gate" signaling module in which classical signaling cascades initiated by specific membrane receptors transmit signals to sequence specific transcription factors (ssTFs), while INFS elicited by the same stimuli feeds the signal forward to the common coactivator, CREB-binding protein (CBP). Activation of CBP by INFS, along with the activation of ssTFs by classical signaling cascades brings about coordinated responses from structurally different genes located at different genomic loci.

Augmentation of the noradrenergic system in alpha-2 adrenergic receptor deficient mice: anatomical changes associated with enhanced fear memory

We have investigated sensitivity to the conditioned fear procedure of mice is influenced by the genetic deletion of alpha2A adrenoceptors (ARs). We observed a heightened freezing response in the discrete cue memory test in alpha2A AR knockout (alpha2A AR KO) mice and in D79N mice, a transgenic mouse strain with functionally impaired alpha2A ARs. No significant differences in contextual memory were observed between control and alpha2A AR KO or D79N mice suggesting a minimal role for the noradrenergic system in contextual memory. We speculated that the increased freezing response of the alpha2A AR KO and D79N mice in the discrete cue setting was due to increased release of norepinephrine evoked by the unconditioned footshock stimulus. In alpha2A AR KO mice we measured a doubling in the number of noradrenergic neurons in the locus coeruleus (LC) and a large increase in the cell volume of tyrosine hydroxylase positive neurons, likely due to selective preservation of large, multipolar neurons in the subcoeruleus. Hyperplasia of the noradrenergic neurons in the nucleus tractus solitarius, A5 and A7, was also observed. Alpha2A AR KO mice exhibit greater c-Fos expression in the LC compared to wild type mice suggesting that the LC neurons in the alpha2A AR KO mice were spontaneously more active. This study suggests that alpha2A ARs are involved in the development of the central noradrenergic system and raises the possibility that alterations in alpha2A AR expression may contribute to variations in fear and stress responses.

Protein kinase A and protein kinase C signaling pathway interaction in phenylethanolamine N-methyltransferase gene regulation

The protein kinase A (PKA) and protein kinase C (PKC) signaling pathways appear to interact in regulating phenylethanolamine N-methyltransferase (PNMT) promoter-driven gene transcription in PC12 cells. Forskolin treatment of cells transfected with the rat PNMT promoter-luciferase reporter gene construct pGL3RP893 increased promoter activity approximately two-fold whereas phorbol-12-myristate-13 acetate (PMA) treatment had no effect. However, simultaneous forskolin and PMA treatment synergistically activated the PNMT promoter approximately four-fold, suggesting that PKC stimulation requires prior induction of the PKA pathway. Consistent with this possibility the adenylate cyclase inhibitor MDL12,330A, and the PKA inhibitor H-89 prevented PNMT promoter stimulation by the combination of forskolin and PMA. PKA and PKC regulation seems to be mediated in part by Egr-1 and Sp1 through their consensus elements in the PNMT promoter. Forskolin and PMA treatment of PC12 cells increased Egr-1 protein and phosphorylated Egr-1/DNA-binding complex formation to the same extent but only increased phosphorylated Sp1/DNA binding complex formation without altering Sp1 protein levels. Mutation of the - 165 bp Egr-1 and - 48 bp Sp1 sites, respectively, attenuated and abolished combined forskolin and PMA-mediated promoter activation. PNMT promoter analysis further showed that synergistic stimulation by PKA and PKC involves DNA sequences between - 442 and - 392 bp, and potentially a GCM binding element lying within this region.

Upregulation of catecholamine biosynthetic enzymes by nitric oxide

Nitric oxide (NO) is recognized as an essential intercellular messenger in central and peripheral nervous systems. In the present study, whether NO exerts effects on catecholamine (CA) biosynthetic enzymes was determined in primary cultured bovine chromaffin cells. The NO generators sodium nitroprusside (SNP) and S-nitroso-N-acetyl-D,L-penicillamine, in a dose-dependent manner, upregulated transcript levels of tyrosine hydroxylase, dopamine beta-hydroxylase, and phenylethanolamine N-methyltransferase, accompanied by long-term increases in their enzyme activities and the intracellular CA levels. The SNP effect was diminished by co-treatment with LY83583, an inhibitor of soluble guanylate cyclase, or H-8, a cyclic GMP (cGMP)-dependent protein kinase inhibitor. Co-treatment with 8-Br-cGMP did not increase further the expression of these enzyme genes induced by SNP. Taken together, the data suggest that NO leads to long-term upregulation of the CA system via induction of the genes involved and that this is mediated by cGMP-dependent signaling pathway.

Presence of cellular renin-angiotensin system in chromaffin cells of bovine adrenal medulla

The presence of a local renin-angiotensin system has been established in organs that serve as angiotensin targets. In this study, the expression of angiotensinogen mRNA and subcellular localization of renin, angiotensin-converting enzyme, and angiotensin II were investigated in bovine adrenal medullary cells in primary culture. By light microscopy, expression of angiotensinogen mRNA, immunoreactive renin, angiotensin-converting enzyme, and angiotensin II were readily detectable only in the chromaffin cells. The density distribution of renin and angiotensin II in sucrose gradients suggested a concentration in chromaffin granules, a localization directly confirmed by immunoelectron microscopy. Reverse transcriptase-polymerase chain reaction and sequencing confirmed the expression of angiotensinogen in bovine chromaffin cells and the adrenal medulla. In addition, in vitro autoradiography indicated that both angiotensin-converting enzyme and angiotensin type 1 receptors were present in the adrenal medulla. These results provide the first direct evidence that chromaffin cells in the adrenal medulla are not only the target for angiotensin but should also be considered as potential local angiotensin-generating and -storing cells.

Integrative nuclear FGFR1 signaling (INFS) pathway mediates activation of the tyrosine hydroxylase gene by angiotensin II, depolarization and protein kinase C

The integrative nuclear FGFR1 signaling (INFS) pathway functions in association with cellular growth, differentiation, and regulation of gene expression, and is activated by diverse extracellular signals. Here we show that stimulation of angiotensin II (AII) receptors, depolarization, or activation protein kinase C (PKC) or adenylate cyclase all lead to nuclear accumulation of fibroblast growth factor 2 (FGF-2) and FGFR1, association of FGFR1 with splicing factor-rich domains, and activation of the tyrosine hydroxylase (TH) gene promoter in bovine adrenal medullary cells (BAMC). The up-regulation of endogenous TH protein or a transfected TH promoter-luciferase construct by AII, veratridine, or PMA (but not by forskolin) is abolished by transfection with a dominant negative FGFR1TK-mutant which localizes to the nucleus and plasma membrane, but not by extracellularly acting FGFR1 antagonists suramin and inositolhexakisphosphate (IP6). Mechanism of TH gene activation by FGF-2 and FGFR1 was further investigated in BAMC and human TE671 cultures. TH promoter was activated by co-transfected HMW FGF-2 (which is exclusively nuclear) but not by cytoplasmic FGF-1 or extracellular FGFs. Promoter transactivation by HMWFGF-2 was accompanied by an up-regulation of FGFR1 specifically in the cell nucleus and was prevented FGFR1(TK-) but not by IP6 or suramin. The TH promoter was also transactivated by co-transfected wild-type FGFR1, which localizes to both to the nucleus and the plasma membrane, and by an exclusively nuclear, soluble FGFR1(SP-/NLS) mutant with an inserted nuclear localization signal. Activation of the TH promoter by nuclear FGFR1 and FGF-2 was mediated through the cAMP-responsive element (CRE) and was associated with induction of CREB- and CBP/P-300-containing CRE complexes. We propose a new model for gene regulation in which nuclear FGFR1 acts as a mediator of CRE transactivation by AII, cell depolarization, and PKC.

Paradoxical increase of tyrosine hydroxylase-immunoreactive retinopetal fibers in the weaver mouse

Weaver mice undergo apoptosis of the granule cell precursors of the cerebellum and nonapoptotic death of mesencephalic dopaminergic cells during post-natal development. In contrast, the number of retinal dopaminergic cells was transiently increased in weaver compared to control mice [C. Savy, E. Martin-Martinelli, A. Simon, C. Duyckaerts, C. Verney, C. Adelbrecht, R. Raisman-Vozari, J. Nguyen-Legros, Altered development of dopaminergic cells in the retina of weaver mice, J. Comp. Neurol. 1999;412:656-668]. While re-examining the retinas, we observed, in the nerve fiber layer, retinopetal tyrosine hydroxylase-immunoreactive fibers, which were dramatically increased in number throughout development and adulthood in the weaver compared to control mice.

Angiotensin II type 1 receptor-modulated signaling pathways in neurons

Mammalian brain contains high densities of angiotensin II (Ang II) type 1 (AT1) receptors, localized mainly to specific nuclei within the hypothalamus and brainstem regions. Neuronal AT1 receptors within these areas mediate the stimulatory actions of central Ang II on blood pressure, water and sodium intake, and vasopressin secretion, effects that involve the modulation of brain noradrenergic pathways. This review focuses on the intracellular events that mediate the functional effects of Ang II in neurons, via AT1 receptors. The signaling pathways involved in short-term changes in neuronal activity, membrane ionic currents, norepinephrine (NE) release, and longer-term neuromodulatory actions of Ang II are discussed. It will be apparent from this discussion that the signaling pathways involved in these events are often distinct.

Tyrosine hydroxylase expression in primary cultures of olfactory bulb: role of L-type calcium channels

Sensory activity mediates regulation of tyrosine hydroxylase (TH), the first enzyme in the dopamine biosynthetic pathway, in the rodent olfactory bulb. The current studies established for the first time primary cultures of neonatal mouse olfactory bulb expressing TH and tested whether L-type calcium channels mediate the activity-dependent regulation of the dopamine phenotype. After 1 d in vitro (DIV), a small population of TH-immunostained neurons that lacked extensive processes could be demonstrated. After an additional 2 DIV in serum-free medium, the number of TH neurons had doubled, and they exhibited long interdigitating processes. Membrane depolarization for 48 hr with 50 mM KCl produced a further 2.4-fold increase in the number of TH-immunoreactive neurons compared with control cultures. Increased TH neuron number required at least 36 hr of exposure to KCl. Forskolin, which increases intracellular cAMP levels, induced a 1.5- to 1.6-fold increase in the number of TH-immunostained neurons. Combined treatment with KCl and forskolin was not additive. Nifedipine, an L-type calcium channel blocker, completely prevented the depolarization-mediated increase in TH expression but did not block the response to forskolin. Treatment with Bay K8644, an L-type calcium channel agonist, also significantly increased the number of TH-expressing neurons. Depolarization also induced alterations in neuritic outgrowth, resulting in a stellate versus an elongate morphology that, in contrast, was not prevented by nifedipine. These results are the first demonstration that in vitro, as in vivo, depolarization increases TH expression in olfactory bulb and that L-type calcium channels mediate this activity-dependent regulation of the dopamine phenotype.

Tyrosine hydroxylase and Parkinson's disease

A consistent neurochemical abnormality in Parkinson's disease (PD) is degeneration of dopaminergic neurons in substantia nigra, leading to a reduction of striatal dopamine (DA) levels. As tyrosine hydroxylase (TH) catalyses the formation of L-DOPA, the rate-limiting step in the biosynthesis of DA, the disease can be considered as a TH-deficiency syndrome of the striatum. Similarly, some patients with hereditary L-DOPA-responsive dystonia, a neurological disorder with clinical similarities to PD, have mutations in the TH gene and decreased TH activity and/or stability. Thus, a logical and efficient treatment strategy for PD is based on correcting or bypassing the enzyme deficiency by treatment with L-DOPA, DA agonists, inhibitors of DA metabolism, or brain grafts with cells expressing TH. A direct pathogenetic role of TH has also been suggested, as the enzyme is a source of reactive oxygen species (ROS) in vitro and a target for radical-mediated oxidative injury. Recently, it has been demonstrated that L-DOPA is effectively oxidized by mammalian TH in vitro, possibly contributing to the cytotoxic effects of DOPA. This enzyme may therefore be involved in the pathogenesis of PD at several different levels, in addition to being a promising candidate for developing new treatments of this disease.

Increased tyrosine phosphorylation and novel cis-acting element mediate activation of the fibroblast growth factor-2 (FGF-2) gene by nicotinic acetylcholine receptor. New mechanism for trans-synaptic regulation of cellular development and plasticity

FGF-2, a mitogenic/neurotrophic protein, controls the development and plasticity of many types of neural cells. In neural crest-derived adrenal pheochromatocytes, induction of FGF-2 coincides with the establishment of functional innervation and is reproduced in vitro by stimulating acetylcholine receptors (AChR). The mechanisms by which AChR activate the FGF-2 gene were examined in cultured bovine adrenal medullary chromaffin (BAMC) cells in which AChR induce expression and nuclear accumulation of growth-promoting FGF-2 and FGF-2 receptors. Carbachol or nicotine increased expression of transfected FGF-2 gene promoter-luciferase constructs and were more potent than the muscarinic agonist ABMCB. Deletion analysis has identified a unique -555/-512 bp element that confers AChR stimulation and basal activity to the downstream FGF-2 promoter, and a separate protein kinase C/cAMP-responsive sequence (-625/-555 bp). Stimulation of AChR increased in vitro formation of protein complexes with the AChR-responsive element which were not displaced by target oligonucleotides for common trans-activators. Southwestern analysis identified 50-55, 125, 140 and 170 kDa proteins that interact with the AChR-responsive element in a manner stimulated by AChR. Nicotine increased tyrosine phosphorylation of cytoplasmic and nuclear proteins, including 50-55 kDa promoter-binding factors. Activation of the FGF-2 promoter was reduced by genistein. Thus, nicotinic AChR activate the FGF-2 gene via a new signaling mechanism separate from the cAMP/PKC pathways. It utilizes tyrosine phosphorylation and interaction of trans-activating factors with a novel cis-acting element. It offers a new pathway through which trans-synaptic signals may control neural development and plasticity.

Cruciform-extruding regulatory element controls cell-specific activity of the tyrosine hydroxylase gene promoter

Tyrosine hydroxylase (TH) is expressed specifically in catecholaminergic cells. We have identified a novel regulatory sequence in the upstream region of the bovine TH gene promoter formed by a dyad symmetry element (DSE1;-352/-307 bp). DSE1 supports TH promoter activity in TH-expressing bovine adrenal medulla chromaffin (BAMC) cells and inhibits promoter activity in non-expressing TE671 cells. DNase I footprinting of relaxed TH promoter DNA showed weak binding of nuclear BAMC cell proteins to a short sequence in the right DSE1 arm. In BAMC cells, deletion of the right arm markedly reduced the expression of luciferase from the TH promoter. However, deletion of the left DSE1 arm or its reversed orientation (RevL) also inactivated the TH promoter. In supercoiled TH promoter, DSE1 assumes a cruciform-like conformation i.e., it binds cruciform-specific 2D3 antibody, and S1 nuclease-cleavage and OsO4-modification assays have identified an imperfect cruciform extruded by the DSE1. DNase I footprinting of supercoiled plasmid showed that cruciformed DSE1 is targeted by nuclear proteins more efficiently than the linear duplex isomer and that the protected site encompasses the left arm and center of DSE1. Our results suggest that the disruption of intrastrand base-pairing preventing cruciform formation and protein binding to DSE1 is responsible for its inactivation in DSE1 mutants. DSE1 cruciform may act as a target site for activator (BAMC cells) and repressor (TE671) proteins. Its extrusion emerges as a novel mechanism that controls cell-specific promoter activity.

Pituitary adenylate cyclase activating polypeptide (PACAP) regulates expression of catecholamine biosynthetic enzyme genes in bovine adrenal chromaffin cells

Pituitary adenylate cyclase activating polypeptide (PACAP) elevates levels of the mRNAs encoding the catecholamine synthesizing enzymes tyrosine hydroxylase (TH), dopamine beta-hydroxylase (DBH), and phenylethanolamine N-methyltransferase (PNMT) in primary cultures of bovine adrenal chromaffin cells. PACAP potently (in nanomolar concentrations) increases the amount of mRNA for each of the three catecholamine biosynthetic enzymes. At 10 nM PACAP, TH and DBH mRNA levels increase approx 10-fold; 1 nM PACAP produces an approx 2.5-fold elevation of PNMT mRNA. In contrast to depolarizing or cholinergic stimuli, PACAP does not enhance expression of 5' upstream regions of the PNMT gene transiently transfected into chromaffin cells. Nor does PACAP stimulate the rate of PNMT gene transcription, thereby indicating that the effects of this neuropeptide do not involve enhanced transcription of this gene. However, after 16 h in the presence of transcriptional inhibitors, more PNMT mRNA is present in cultures treated with PACAP relative to control cultures, whereas amounts of TH and DBH mRNAs are not changed. PACAP likely elevates PNMT mRNA levels posttranscriptionally, possibly by stabilizing this message against degradation. Thus, although PACAP is an effective regulator for expression of all three catecholamine enzyme genes, its mechanism of action on PNMT mRNA appears to be distinctive from its effects on TH and DBH gene transcription.

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

Transcription of the rat tyrosine hydroxylase (TH) gene is controlled by enhancer sequences in its 5' flanking region; these enhancers include the AP1, dyad, and cAMP response element (CRE) motifs. We show that a novel basal promoter element (-17 GCCTGCCTGGCGA -5) positioned between the TATA box and +1 works in conjunction with the upstream AP1-dyad and CRE enhancers but cannot support transcription by itself. A mutation of this element, termed partial dyad, reduces basal expression of a reporter gene in TH-positive cell lines and TH-negative lines but has no effect on cAMP- or KCl-induced expression. A double mutant at positions -17 and -11 of the partial dyad reduces transcriptional activation by 80%. Conversely, insertion of this element into a heterologous promoter restores basal expression to levels mediated by the native TH promoter. The partial dyad is a novel activational element that is required for full expression of the TH gene and may assist in the function of the AP1, dyad, and CRE motifs and also other enhancers further upstream. Hence, the rat TH gene is unusual in that its enhancers will not function with a heterologous promoter but require a specific TH promoter sequence for full activation.

Tyrosine hydroxylase gene promoter activity is regulated by both cyclic AMP-responsive element and AP1 sites following calcium influx. Evidence for cyclic amp-responsive element binding protein-independent regulation

Membrane depolarization of PC12 cells using 50 mM KCl leads to induction of tyrosine hydroxylase (TH) mRNA. This induction of TH mRNA is apparently due to increased TH gene promoter activity mediated by the influx of Ca2+. In PC12 cells transiently transfected with a chimeric gene expressing chloramphenicol acetyltransferase (CAT) driven by the proximal TH gene 5'-flanking region, 50 mM KCl increases TH gene promoter activity 3-4-fold. Promoter analysis utilizing TH-CAT constructs containing mutagenized sequences indicates that this response to the depolarization-mediated influx of Ca2+ is primarily dependent on both the TH cAMP-responsive element (CRE) and TH activating protein-1 (AP1) site. Minimal promoter constructs that contain a single copy of either the TH CRE or TH AP1 site fused upstream of the TH gene basal promoter are only modestly responsive or nonresponsive, respectively, to depolarization. However, both these constructs are strongly responsive to the calcium ionophore, A23187. Gel shift assays indicate that TH AP1 complex formation is dramatically increased after treatment with either 50 mM KCl or A23187. Using antibodies to transcription factors of the Fos and Jun families, we show that the nuclear proteins comprising the inducible TH AP1 complex include c-Fos, c-Jun, JunB, and JunD. In cAMP-responsive element binding protein (CREB)-deficient cell lines that express antisense RNA complementary to CREB mRNA, the response of the TH gene promoter to cyclic AMP is dramatically inhibited, but the response to A23187 remains robust. This result indicates that transcription factors other than CREB can participate in the Ca2+-mediated regulation of the TH gene. In summary, our results support the hypothesis that regulation of the TH gene by Ca2+ is mediated by mechanisms involving both the TH CRE and TH AP1 sites and that transcription factors other than or in addition to CREB participate in this response.

Pituitary adenylate cyclase-activating polypeptide induces gene expression of the catecholamine synthesizing enzymes, tyrosine hydroxylase and dopamine beta hydroxylase, through 3',5'-cyclic adenosine monophosphate- and protein kinase C-dependent mechanisms in cultured porcine adrenal medullary chromaffin cells

Pituitary adenylate cyclase-activating polypeptide (PACAP)i a potent stimulant of catecholamine secretion, increased catecholamine production in cultured porcine adrenal medullary chromaffin cells. PACAP induced dose-and time-dependent increases in mRNAs for the catecholamine synthesizing enzymes, tyrosine hydroxylase (TH) and dopamine beta-hydroxylase (DBH), with maximal 6- and 4-fold increases occurring at 8-16 h, respectively. The half-maximally and maximally effective PACAP concentrations for stimulation of TH and DBH gene expression were 0.5 and 3 nM, respectively. The TH protein level also showed an increase over the unstimulated basal level at 16-24 h in PACAP-stimulate cells. We previously demonstrated that PACAP activates both phospholipase C and adenylate cyclase in adrenal medullary cells. Addition of forskolin alone induced increases in mRNA expression of both TH and DBH. The phosphodiesterase inhibitor 3- isobutyl-1-methylxanthine potentiated the induction of TH and DBH mRNAs by PACAP. Addition of the protein kinase C activator phorbol 12-myristate 13-acetate (PMA) also caused increases in TH and DBH mRNA levels. In protein kinase C-downregulated cells pretreated with PMA for 24 h, the stimulatory effect of PACAP on TH and DBH gene expression was diminished. These results suggest that cAMP and protein kinase C mediate the PACAP-induced TH and DBH gene expression. Removal of extracellular Ca2+ with EGTA enhanced the PACAP-induced increases in both cellular cAMP and mRNA levels of TH and DBH, suggesting that Ca2+ has an inhibitory effect on the induction of TH and DBH mRNAs. In conclusion, the present study indicates that PACAP coordinately upregulates the gene expression of both TH and DBH by activating the cAMP and protein kinase C signaling pathways, leading to simulation of cate-cholamine synthesis, while Ca2+ negatively regulates TH and DBH gene expression in porcine adrenal medullary cells.

Promoter elements and second messenger pathways involved in transcriptional activation of tyrosine hydroxylase by ionomycin

Membrane depolarization, or agents which increase intracellular calcium, elicit transcriptional activation of tyrosine hydroxylase (TH). In this study we analyze the factors involved in the regulation of the TH promoter by a calcium ionophore. PC12 cells were transiently transfected with plasmids containing wild type or mutated 5' flanking sequences of the rat TH gene, fused to bacterial chloramphenicol acetyl transferase (CAT). Point mutations introduced into the consensus cAMP-regulatory element (CRE) abolished the induction of CAT by ionomycin indicating that it is essential for mediating the calcium response. An intact and functional AP1 site did not confer calcium inducibility when the CRE/CaRE sequence was mutated. The extent and kinetics of the increase in intracellular calcium as well as the induction of CAT activity under the control of TH promoter by ionomycin were similar in PC12 cells and in the A123.7, protein kinase A (PKA) deficient cell line. In both cell lines addition of ionomycin rapidly increased the phosphorylation of transcription factor CREB at Ser-133. These results suggest that the activation of TH transcription by ionomycin does not require PKA. However, KN62 an inhibitor of Ca2+/calmodulin dependent (CaM) kinases prevented the induction indicating possible involvement of CAM kinases in the calcium response.

Regulation of bFGF gene expression and subcellular distribution of bFGF protein in adrenal medullary cells

Basic fibroblast growth factor (bFGF), a potent mitogenic/neurotrophic factor, controls the development and plasticity of many types of neural cells. In adrenal chromaffin cells, the appearance of bFGF protein coincided with the establishment of functional innervation, suggesting induction by trans-synaptic signals. In cultured bovine adrenal medullary cells Western blot analysis revealed 18-, 23-, and 24-kD bFGF isoforms in the cytosolic and nuclear fractions. Stimulation of acetylcholine nicotinic receptors or hormonal angiotensin II receptors or the direct stimulation of adenylate cyclase with forskolin or protein kinase C (PKC) with PMA increased the content of all bFGF isoforms. Increases in the levels of intracellular bFGF did not result in detectable presence of bFGF proteins in culture medium. Instead, bFGF proteins accumulated in the cytoplasm or the nucleus depending on whether PKC or cAMP pathways were activated. The long-term nuclear forskolin-induced accumulation of bFGF was prevented by cycloheximide or by antisense bFGF oligonucleotide and was also accompanied by an increase in bFGF mRNA. We used luciferase reporter plasmids containing the human bFGF promoter to show that the induction of bFGF resulted from transcriptional activation of the bFGF gene and was mediated by regulatory sequences located upstream from its transcription start site. Stimulation of bFGF gene expression by forskolin and PMA was synergistic and was mediated through different promoter regions. The results suggest that stimulation by cAMP and PKC is mediated through novel cis elements. The regulation of bFGF protein content also involves posttranscriptional mechanisms since changes in the levels of individual bFGF isoforms were different depending on whether cells were treated with carbachol or angiotensin II, forskolin, or PMA. The present study indicates that bFGF is an intracrine cytoplasmic-nuclear factor, whose expression is regulated by trans-synaptic and hormonal stimuli and which may act as a direct mediator of genomic responses to afferent stimulation.