Cell-specific glucocorticoid repression of calcitonin/calcitonin gene-related peptide transcription. Localization to an 18-base pair basal enhancer element

CGRP physiology, pharmacology, and therapeutic targets: migraine and beyond

Calcitonin gene-related peptide (CGRP) is a neuropeptide with diverse physiological functions. Its two isoforms (α and β) are widely expressed throughout the body in sensory neurons as well as in other cell types, such as motor neurons and neuroendocrine cells. CGRP acts via at least two G protein-coupled receptors that form unusual complexes with receptor activity-modifying proteins. These are the CGRP receptor and the AMY1 receptor; in rodents, additional receptors come into play. Although CGRP is known to produce many effects, the precise molecular identity of the receptor(s) that mediates CGRP effects is seldom clear. Despite the many enigmas still in CGRP biology, therapeutics that target the CGRP axis to treat or prevent migraine are a bench-to-bedside success story. This review provides a contextual background on the regulation and sites of CGRP expression and CGRP receptor pharmacology. The physiological actions of CGRP in the nervous system are discussed, along with updates on CGRP actions in the cardiovascular, pulmonary, gastrointestinal, immune, hematopoietic, and reproductive systems and metabolic effects of CGRP in muscle and adipose tissues. We cover how CGRP in these systems is associated with disease states, most notably migraine. In this context, we discuss how CGRP actions in both the peripheral and central nervous systems provide a basis for therapeutic targeting of CGRP in migraine. Finally, we highlight potentially fertile ground for the development of additional therapeutics and combinatorial strategies that could be designed to modulate CGRP signaling for migraine and other diseases.

The Distribution of Innervation and Immune Cell Infiltration Is Different in Genital and Extragenital Variants of Lichen Sclerosus

Lichen sclerosus (LS) is a progressive skin disease that is characterized by chronic inflammation of either genital or extragenital skin, and it disproportionately affects women. We analyzed the distribution of nerve fibers, vanilloid receptors, cell proliferation, mast cells and macrophages in genital and extragenital LS samples, as well as in healthy skin, by using immunohistochemistry. The total amount of intraepidermal nerve fibers was lower in LS samples compared to healthy controls, while the total amount of subepidermal nerve fibers and calcitonin gene-related peptide (CGRP) positive fibers was higher in genital LS samples compared to both extragenital LS and healthy controls. Cell proliferation, macrophage and mast cell density were increased in LS samples compared to healthy controls. Genital LS had a higher macrophage density compared to the extragenital variant. Mast cell distribution significantly differed between genital and extragenital LS samples, even though their total mast cell densities were similar. These findings could explain the differences between pruritic symptoms of genital and extragenital LS and provide targets for the research of novel therapeutic strategies for LS management.

Immunomodulatory Role of Neuropeptides in the Cornea

The transparency of the cornea along with its dense sensory innervation and resident leukocyte populations make it an ideal tissue to study interactions between the nervous and immune systems. The cornea is the most densely innervated tissue of the body and possesses both immune and vascular privilege, in part due to its unique repertoire of resident immune cells. Corneal nerves produce various neuropeptides that have a wide range of functions on immune cells. As research in this area expands, further insights are made into the role of neuropeptides and their immunomodulatory functions in the healthy and diseased cornea. Much remains to be known regarding the details of neuropeptide signaling and how it contributes to pathophysiology, which is likely due to complex interactions among neuropeptides, receptor isoform-specific signaling events, and the inflammatory microenvironment in disease. However, progress in this area has led to an increase in studies that have begun modulating neuropeptide activity for the treatment of corneal diseases with promising results, necessitating the need for a comprehensive review of the literature. This review focuses on the role of neuropeptides in maintaining the homeostasis of the ocular surface, alterations in disease settings, and the possible therapeutic potential of targeting these systems.

Histone Deacetylase Inhibitors Counteract CGRP Signaling and Pronociceptive Sensitization in a Rat Model of Medication Overuse Headache

Chronic triptan exposurein rodents recapitulates medication overuse headache (MOH), causing cephalic pain sensitization and trigeminal ganglion overexpression of pronociceptive proteins including CGRP. Because of these transcriptional derangements, as well as the emerging role of epigenetics in chronic pain, in the present study, we evaluated the effects of the histone deacetylase inhibitors (HDACis) panobinostat and givinostat, in rats chronically exposed to eletriptan for one month. Both panobinostat and givinostat counteracted overexpression of genes coding for CGRP and its receptor subunit RAMP1, having no effects on CLR and RCP receptor subunits in the trigeminal ganglion (TG) of eletriptan-exposed rats. Within the trigeminal nucleus caudalis (TNc), transcripts for these genes were neither upregulated by eletriptan nor altered by concomitant treatment with panobinostat or givinostat. HDACis counteracted hypersensitivity to capsaicin-induced vasodilatation in the trigeminal territory, as well as photophobic behavior and cephalic allodyniain eletriptan-exposed rats. Eletriptan did not affect CGRP, CLR, and RAMP1 expression in cultured trigeminal ganglia, whereas both inhibitors reduced transcripts for CLR and RAMP-1. The drugs, however, increased luciferase expression driven by CGRP promoter in cultured cells. Our findings provide evidence for a key role of HDACs and epigenetics in MOH pathogenesis, highlighting the therapeutic potential of HDAC inhibition in the prevention of migraine chronification.

Functional analysis of Nkx2.1 and Pax9 for calcitonin gene transcription

Nkx2.1 (TTF-1), a homeodomain-containing transcription factor essential for specific gene expression in thyroid follicular cells, exists also in the thyroidal C cells that secrete calcitonin (CT). In this report, we examined the effect of Nkx2.1 on the CT gene transcription. Luciferase reporter assay using the 2kbp promoter sequence of rat CT/CGRP gene revealed that Nkx2.1 induced a significant increase in the promoter transcription. Furthermore, we detected Pax1 and/or Pax9 gene expression in mammalian medullary thyroid carcinoma cell lines, rat rMTC and human TT cells, and in mammalian thyroid glands by RT-PCR. The Pax9 mRNA, expressed in the TT cells and rat thyroid, was then isolated by cDNA cloning. Sequence analysis showed that both rat and human Pax9 proteins contained characteristic domains: i.e. the paired domain and octapeptide motif. Alternative transcripts encoding Pax9 isoforms were not identified in the rat thyroid or TT cells. Dual luciferase assay indicated that Pax9 did not increase transcription from the CT/CGRP promoter. Pax9 also showed no cooperative effects when it was co-transfected with Nkx2.1. The results suggest that CT gene expression could be directly activated by Nkx2.1, whereas Pax9 is not involved in transcription from the 2kbp CT promoter.

Antiproliferative and antiviral mechanisms of ursolic acid and dexamethasone in cervical carcinoma cell lines

The chemical structure of ursolic acid is very similar to that of dexamethasone, a synthetic glucocorticoid. Herein, we investigated the antiproliferative and antiviral effects of ursolic acid and dexamethasone in human papillomavirus (HPV)-associated cervical cancer cells. We performed 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazonium bromide assay to measure antiproliferative activity, and also characterized apoptosis by DNA fragmentation, 4'-6-diamidino-2-phenylindole (DAPI) staining, and flow cytometry (FACS) analysis. We investigated apoptosis-related proteins using western blots. After in vitro treatment, we used reverse transcription-polymerase chain reaction for the expression of the HPV E6/E7 gene to observe the antiviral effects. Ursolic acid suppressed the growth of HPV-positive cervical carcinoma cells (HeLa, CaSki, and SiHa) in a dose- and time-dependent manner, but not the HPV-negative cervical cancer cell line (C33A). Ursolic acid-treated HeLa cells showed typical apoptosis characteristics in DNA fragmentation, DAPI staining, and FACS analysis. The expression of Fas protein was induced, and caspase-8, caspase-3, and poly ADP-ribose polymerase (PARP) proteins were cleaved after ursolic acid treatment. HPV-18 E6/E7 gene expression decreased after ursolic acid treatment in HeLa cells, but the levels of p53 and Rb proteins did not change. In contrast, dexamethasone, which has a similar structure, did not inhibit proliferation. Our findings may offer new insight into the mechanism of antiproliferative and antiviral effect of ursolic acid. Also, these results suggest that ursolic acid might be a useful anticancer drug in treatment of HPV-associated cervical neoplasia.

Type II glucocorticoid receptor immunoreactivity in the mossy cells of the rat and the mouse hippocampus

Hippocampal principal neurons, granule and pyramidal cells, are known to express type II glucocorticoid receptors (GR) and it is believed that glucocorticoids (GC) mediate at least some of their effects through GR. Under conditions of severe stress and trauma, these principal cells are vulnerable to damage and this mechanism may be exacerbated by GR. The mossy cell, an excitatory dentate gyrus neuron, is also damaged following trauma, with over 50% reported loss in rats after kainate-induced seizures. However, it has not been determined if GC play any role in protecting or exacerbating damage to this important hippocampal cell type. In the present study, we have undertaken an evaluation of the presence of GR in mossy cells of the rat and mouse utilizing an immunocytochemical double-labeling technique. To identify mossy cells in the rat, we utilized an antibody to the glutamate receptor subunit 2/3 (GluR2/3). In addition to GluR2/3 antibodies, in the mouse, an antibody to the calcium-binding protein, calretinin (CR), to identify mossy cells was also employed. Our results show that GR immunoreactivity (IR) was colocalized with GluR2/3-IR in approximately 90% of the rat and the mouse mossy cells. In addition, GR-IR was identified in the CR-IR mossy cells in the mouse hippocampus, whereas the CR-IR interneurons of rat and mouse were negative for GR-IR. The presence of GR on mossy cells may indicate the ability of GC to mediate cellular activity of these cells.

New insights into the molecular actions of serotonergic antimigraine drugs

Migraine is a painful and debilitating neurological disorder that affects approximately 10% of the adult population in Western countries. Sensitization and activation of the trigeminal ganglia nerves that innervate the meningeal blood vessels is believed to play an important role in the initiation and maintenance of migraine pain. In this capacity, release of the neuropeptide calcitonin gene-related peptide (CGRP) and the resultant neurogenic inflammation is thought to underlie the pathophysiology of migraine. Largely due to the success of the serotonin Type 1 migraine drugs such as sumatriptan, migraine pathology and therapy has become a focus of intensive clinical and physiological research during the past decade. The effectiveness of these drugs is thought to be due to their ability to block the stimulated secretion of neuropeptides from trigeminal nerves to break the vicious nociceptive cycle of migraine. A component of this nociceptive cycle involves activation of mitogen-activated protein kinase signaling pathways. Indeed, activation of mitogen-activated protein kinase pathways can increase CGRP neuropeptide synthesis and secretion. Recently, the serotonin Type 1 agonists have been shown to cause a prolonged increase in intracellular Ca(2+) in trigeminal ganglia neurons and an increased phosphatase activity that can repress stimulated CGRP secretion and transcription. Identification of molecular signaling events in migraine pathology and therapy has provided new insight into the pharmacology and signaling mechanisms of sumatriptan and related drugs, and may provide the foundation for development of novel treatments for migraine.

Responses to stable ectopic estrogen receptor-beta expression in a rat fibroblast cell line

To examine activity of estrogen receptor-beta (ERbeta) independently of estrogen receptor-alpha (ERalpha), retrovirus-mediated gene transfer was used to insert rat ERbeta into a rat fibroblast cell line (rat-1) that does not ordinarily express ER. Stable expression of ERbeta in rat-1 cells was validated and then characterized by reverse-transcription polymerase chain-reaction (RT-PCR) analysis to examine the effects of estradiol (E2) treatment on expression of specific target mRNAs. Results were compared with rat-1 cells and a previously constructed rat-1 + ERalpha cell line. Progesterone receptor mRNA was not detected in rat-1 cells and was induced by E2 in both rat-1 + ERalpha and rat-1 + ERbeta cells. Treatment with E2 resulted in an increased rate of cell proliferation (P < 0.05) in rat-1 + ERalpha cells, but not in rat-1 or rat-1 + ERbeta cells. Data confirm studies using transient ER expression demonstrating that ERalpha and ERbeta have both discrete and overlapping activity within the same cell type in the presence of the same ligand.

Calcitonin gene-related peptide gene expression in collagen-induced arthritis is differentially regulated in primary afferents and motoneurons: influence of glucocorticoids

Calcitonin gene-related peptide is involved in peripheral and spinal mechanisms of inflammatory pain. In this paper, we used collagen II-induced arthritis in the rat as a model to investigate the influence of chronic arthritic pain on calcitonin gene-related peptide gene expression in sensory and motor pathways. Additionally, we examined the effect of the glucocorticoid drug budesonide on arthritis-induced changes of calcitonin gene-related peptide expression and constitutive calcitonin gene-related peptide expression. Thirteen days after the immunization with native rat collagen type II rats developed a progressive and chronic polyarthritis which was scored with respect to the degree of swelling and/or redness of the paw and ankle joints. Budesonide significantly attenuated the extent of arthritis. Changes in calcitonin gene-related peptide expression were evaluated by semiquantitative in situ hybridization and immunocytochemistry on day 21 post-immunization. In sensory neurons of dorsal root ganglia of arthritic rats, a significant increase in calcitonin gene-related peptide messenger RNA and protein levels was seen. These increases were completely blocked by budesonide. Also in dorsal root ganglia of non-arthritic rats, budesonide had an effect, with reduced calcitonin gene-related peptide messenger RNA levels below constitutive concentrations. Image analysis of calcitonin gene-related peptide immunoreactivity revealed that changes in calcitonin gene-related peptide expression were due to alterations in calcitonin gene-related peptide expression levels rather than to de novo synthesis or changes in the numbers of calcitonin gene-related peptide expressing neurons. In spinal motoneurons of arthritic rats, marked decreases in calcitonin gene-related peptide messenger RNA and protein levels were measured. These reductions were attenuated by budesonide. The changes in calcitonin gene-related peptide expression in motoneurons correlated with the severity of arthritis in the ipsilateral hind paw. Budesonide had no effects on calcitonin gene-related peptide messenger RNA levels in motoneurons of non-arthritic rats. The opposite regulation of calcitonin gene-related peptide gene expression in primary sensory and spinal somatomotor pathways in collagen-induced arthritis suggests that calcitonin gene-related peptide plays a specific role in both chronic inflammatory pain and arthritis-induced motor dysfunction. The sensitivity of constitutive and inflammation-induced sensory calcitonin gene-related peptide expression to budesonide treatment may indicate that the beneficial effects of steroid treatment in inflammation is partly mediated by down-regulation of calcitonin gene-related peptide in sensory neurons involved in neurogenic inflammation.

Serotonergic repression of mitogen-activated protein kinase control of the calcitonin gene-related peptide enhancer

We have investigated the mechanisms underlying regulation of the calcitonin gene-related peptide (CGRP) cell-specific enhancer. Recently, we reported that this enhancer is inhibited by serotonin type-1 (5-HT1) agonists, similar to currently used antimigraine drugs. We have now tested whether this repression involves a mitogen-activated protein (MAP) kinase pathway. We first demonstrate that the CGRP enhancer is strongly (10-fold) activated by a constitutively active MAP kinase kinase (MEK1), yielding reporter activities 100-fold above the enhancerless control. The involvement of a MAP kinase pathway was confirmed by down-regulation of reporter activity upon cotransfection of a dominant negative Ras. Activation of the enhancer by MEK1 was blocked in a dose-dependent manner by the 5-HT1 receptor agonist CGS 12066A (CGS). Since it is not known whether the CGRP enhancer factors are immediate targets of MAP kinases, we then used EIk-1- and c-Jun-dependent reporter genes that are directly activated by the ERK (extracellular signal-regulated kinases) and JNK (c-Jun N-terminal kinase) MAP kinases. CGS treatment repressed the activation of both of these reporters, suggesting that at least two MAP kinases are the immediate targets of CGS-mediated repression. We further demonstrate that 5-HT1 agonists inactivate ERK by dephosphorylation, even in the presence of constitutively activated MEK1. This inactivation appears to be due to a marked increase in the level of MAP kinase phosphatase-1. These results have defined a novel and general mechanism by which 5-HT1 receptor agonists can repress MAP kinase activation of target genes, such as CGRP.

Neuroanatomical localization, pharmacological characterization and functions of CGRP, related peptides and their receptors

Calcitonin generelated peptide (CGRP) is a neuropeptide discovered by a molecular approach over 10 years ago. More recently, islet amyloid polypeptide or amylin, and adrenomedullin were isolated from human insulinoma and pheochromocytoma respectively, and revealed between 25 and 50% sequence homology with CGRP. This review discusses findings on the anatomical distributions of CGRP mRNA, CGRP-like immunoreactivity and receptors in the central nervous system, as well as the potential physiological roles for CGRP. The anatomical distribution and biological activities of amylin and adrenomedullin are also presented. Based upon the differential biological activity of various CGRP analogs, the CGRP receptors have been classified in two major classes, namely the CGRP1 and CGRP2 subtypes. A third subtype has also been proposed (e.g. in the nucleus accumbens) as it does not share the pharmacological properties of the other two classes. The anatomical distribution and the pharmacological characteristics of amylin binding sites in the rat brain are different from those reported for CGRP but share several similarities with the salmon calcitonin receptors. The receptors identified thus far for CGRP and related peptides belong to the G protein-coupled receptor superfamily. Indeed, modulation of adenylate cyclase activity following receptor activation has been reported for CGRP, amylin and adrenomedullin. Furthermore, the binding affinity of CGRP and related peptides is modulated by nucleotides such as GTP. The cloning of various calcitonin and most recently of CGRP1 and adrenomedullin receptors was reported and revealed structural similarities but also significant differences to other members of the G protein-coupled receptors. They may thus form a new subfamily. The cloning of the amylin receptor(s) as well as of the other putative CGRP receptor subtype(s) are still awaited. Finally, a broad variety of biological activities has been described for CGRP-like peptides. These include vasodilation, nociception, glucose uptake and the stimulation of glycolysis in skeletal muscles. These effects may thus suggest their potential role and therapeutic applications in migraine, subarachnoid haemorrhage, diabetes and pain-related mechanisms, among other disorders.

Binding of upstream stimulatory factor and a cell-specific activator to the calcitonin/calcitonin gene-related peptide enhancer

The calcitonin/calcitonin gene-related peptide (CT/CGRP) gene is selectively transcribed in thyroid C cells and neurons. We have previously shown that the rat CT/CGRP cell-specific enhancer is synergistically regulated by a helix-loop-helix (HLH) protein and the OB2 octamer-binding protein. In this report, we show that the HLH-OB2 enhancer is required for full promoter activity, even in the context of other HLH elements. Since this enhancer appears to be a major controlling element, we have characterized the HLH and OB2 DNA binding proteins. We have identified the major HLH complex as a heterodimer of the ubiquitous upstream stimulatory factor (USF)-1 and USF-2 proteins. USF bound the enhancer with a reasonably high affinity (KD 1.6 nM), comparable to other genes. Characterization of a series of mutations revealed that a portion of the HLH motif is also recognized by OB2 and confirmed that HLH activity requires OB2. We have shown that OB2 is a single DNA binding protein based on UV cross-linking studies. The 68-kDa protein-DNA complex was detected only in C cell lines, including a human C cell line that has robust HLH-OB2 enhancer activity. These results suggest that the calcitonin/CGRP gene is controlled by the combinatorial activity of a ubiquitous USF HLH heterodimer and an associated cell-specific activator.

Repression of vasopressin gene expression by glucocorticoids in transgenic mice: evidence of a direct mechanism mediated by proximal 5' flanking sequence

Glucocorticoids are known to exert multiple effects upon neuronal systems and neuronal gene expression but the molecular mechanisms through which these effects are mediated are largely undefined. In this study, a transgenic mouse model that expresses a bovine vasopressin transgene was used to investigate the mechanisms by which this neuropeptide gene is repressed by glucocorticoids. Using both northern analysis and a reverse transcriptase polymerase chain reaction assay, depletion of glucocorticoids with the 11,beta-hydroxylase inhibitor metyrapone was shown to result in a dexamethasone-reversed increase in ectopic adrenal transgene messenger RNA levels. This result shows that sequences within the confines of the 3.5 kb transgene are sufficient to mediate repression by glucocorticoids, and indicates the involvement of a type II glucocorticoid receptor mechanism which is independent of cellular context. Evidence for the involvement of cis-acting repressive elements in the proximal 5' flanking sequence was obtained in further studies in which bovine transgene constructs were shown to be negatively regulated by dexamethasone in 293 cells. The further demonstration that recombinant glucocorticoid receptor binds to a vasopressin promoter fragment in an in vitro electrophoretic mobility shift assay provided additional evidence of a direct mechanism of repression. Both in vitro studies were consistent with the presence of a glucocorticoid regulatory element within the region -300 to 155 of the transcription start site. The use of an in vivo transgenic system combined with in vitro analyses of gene promoter fragments enabled the characterization of the molecular mechanisms which effect physiological changes in vasopressin gene expression, and provided evidence of a direct mechanism of repression mediated by sequences within the vasopressin gene promoter.

Novel perspectives on pituitary and brain angiotensinogen

All the angiotensin peptides originate from angiotensinogen, a glycoprotein synthesized by several tissues, including the brain and the anterior pituitary. In the rat, immunohistochemistry has been used to localize angiotensinogen in gonadotropes and in uncharacterized cells surrounding sinusoids. Both cell types are capable of secreting angiotensinogen in cell culture; only the gonadotropes contain angiotensin II (AngII) and are capable of secreting it in culture. It has been asserted that the perisinusoidal cells are the only source of angiotensinogen for the generation of AngII by gonadotropes. Our current data favor the existence of a complete intracellular renin-angiotensin system (RAS) in gonadotropes and a separate extracellular system which utilizes the high concentration of angiotensinogen from perisinusoidal cells. Furthermore, we postulate that gonadotrope AngII serves mainly reproductive functions, while the proximity of angiotensinogen-secreting cells to folliculostellate cells, and their access to the intercellular sinusoidal and follicular spaces, places the extracellular RAS in a strategic position to affect pituitary growth and the mediation of acute-phase immune responses. In the rat brain, angiotensinogen is expressed by the 16-18th day of fetal life and by areas generally concerned with vasopressor, electrolyte, and fluid homeostasis. Antisense deoxyoligonucleotides to angiotensinogen mRNA lower blood pressure in hypertensive rats and inhibit in vitro growth of neuroblastoma cells, indicating a significant role for angiotensinogen in mitogenic and homeostatic functions. It is commonly agreed that astrocytes express angiotensinogen. Neuronal angiotensinogen has also been demonstrated by immunohistochemistry, as a secretion from neuronal cell cultures, and by reverse-transcriptase polymerase chain reaction. The fate of secreted astrocytic and neuronal angiotensinogen remains obscure. Angiotensinogen is regulated in a tissue-specific manner with smaller or absent responses observed for brain tissue. By using astrocyte and neuronal cultures the actions on angiotensinogen production of growth hormone, IGF-1, inflammatory lipopolysaccharide, and phorbol ester have been examined. Recent observations show that angiotensinogen is regulated positively or negatively by glucocorticoids and that a positive synergism between cAMP and glucocorticoids exists. On the basis of analogous systems for other proteins, a scheme involving glucocorticoid receptors, CREB, and AP-1 transcription factors is formulated to explain glucocorticoid-cAMP interactions. These transcriptional interactions may form a significant functional link between the RAS and adrenergic mechanisms.

Expression of the calcitonin gene family in medullary thyroid carcinoma

The regulatory peptide calcitonin was discovered in 1962. During the last decade it has been demonstrated to be part of a gene family. Calcitonin is synthesized in the parafollicular cells (C cells) of the thyroid gland. These cells give rise to an endocrine tumor, medullary thyroid carcinoma (MTC), which is found in a sporadic and an inherited form. Calcitonin is used as a tumor marker for MTC. The calcitonin gene was demonstrated in 1981 to give rise to an alternative peptide product, alpha-CGRP, and a second gene encoding a very similar peptide, beta-CGRP, has also been identified. A third CGRP-like peptide, amylin, was identified in 1986. This article summarizes the present knowledge about gene structure, regulation of gene expression, and expression of the calcitonin gene family in MTC and in MTC-derived cell lines. The methods employed for detection of gene expression and for measurement and characterized of peptide products are described, and finally the relevance of biochemical tumor markers is discussed in relation to the new diagnostic methods for inherited MTC based on molecular biological techniques.

Regulation of VIP and other neuropeptides by c-Jun in sensory neurons: implications for the neuropeptide response to axotomy

Peripheral axotomy of adult rat sensory neurons causes induction of the transcription factor c-Jun and increased expression of the neuropeptides vasoactive intestinal polypeptide (VIP), galanin and neuropeptide Y. To determine whether VIP induction is dependent on transcriptional regulation by c-Jun, we exploited the fact that c-Jun and VIP are also induced in cultured sensory neurons. We blocked c-Jun synthesis by microinjecting antisense oligonucleotides and found that VIP expression, determined by quantitative immunofluorescence, was specifically reduced. Blockade of c-June expression also resulted in reduced neuropeptide Y expression but left galanin, substance P and calcitonin gene-related peptide unaffected. Since in vitro electrophoretic mobility shift assays showed that a nominal cyclic AMP responsive element (CRE) associated with the rat VIP gene could bind c-Jun-containing transcription factor complexes, we next investigated whether VIP expression in sensory neurons might depend on transcription factor binding to the CRE. When a DNA plasmid containing multiple copies of the CRE was injected into newly cultured sensory neurons to sequester transcription factors binding the endogenous CRE, there was a selective reduction in VIP expression. VIP induction in sensory neurons therefore probably results from transcriptional activation by c-Jun acting in combination with other factor(s), possibly acting through the CRE. These results show that c-Jun can regulate transcription of other genes affected by axotomy and imply that it could be a key regulator of the neuronal axotomy response.

Thyroid parafollicular cells. An accessible model for the study of serotonergic neurons

Serotonergic neurons play key roles in modulating a wide variety of behavioral and homeostatic processes. However, there is a paucity of good model systems to study these neurons at a molecular level. In this review we will present evidence that cell lines derived from an unexpected source, thyroid parafollicular cells (PF) (also called C cells), fit the criteria for use as models for the study of serotonergic neurons. A strength of PF cell lines over other cell lines is that the parental PF cells have serotonergic properties and a neuronal potential that is consistent with their neural crest origin. Furthermore, PF cells and PF cell lines are capable of expressing the fundamental properties of serotonergic neurons, including: (1) serotonin (5-HT) biosynthesis by tryptophan hydroxylase (TPH), (2) vesicular 5-HT storage and regulated release, (3) expression of a 5-HT autoreceptor, and (4) expression of the 5-HT transporter. In this review, we will focus primarily on the serotonergic and neuronal properties of the rat CA77 PF cell line and the parental rat PF cells. The applicability of CA77 cells for molecular analyses will be described. First, their use for studies on the glucocorticoid regulation of the TPH gene will be discussed. Second, control of the calcitonin/calcitonin gene-related peptide (CT/CGRP) gene will be discussed, with particular emphasis on the application of serotonergic drugs in treating migraine headaches. These examples highlight the versatility of thyroid PF cell lines as a system for studying the control of both serotonin biosynthesis and physiological actions.

Chronic dexamethasone treatment and its effects on sensory neuropeptides, pulpal injury reactions and reparative dentin

Initial sensory nerve reactions to dental injuries include terminal sprouting and intensified immunoreactivity for calcitonin gene-related peptide (CGRP) and substance P (SP); those reactions are reduced at 4 days after injury when rats are treated daily with dexamethasone (DEX) [17]. Here we have analyzed long-term effects of DEX (daily, 0.2 mg/kg) on wound healing, sensory nerve sprouting, and CGRP/SP intensity at 7-14 days after cavity preparation. All DEX treated rats had loss of appetite and stopped growing during the postoperative periods while controls had normal postoperative growth. After 7-14 days, CGRP immunoreactivity (IR) was decreased to one-third of normal (P < 0.05) compared to vehicle in both the intact and injured molar pulp, and SP also decreased, but the neuropeptide intensity in adjacent periodontal innervation was not changed. Pulpal injury and inflammation were reduced by DEX treatment, but reparative dentin was formed just as well in the DEX rats as in the vehicle group. When the injured teeth formed fibrous dentin, there was sprouting of nerves towards that matrix, and DEX did not inhibit that reaction. The sprouts could contain intense neuropeptide immunoreactivity in DEX rats even though the CGRP/SP intensity in uninjured pulp was reduced. We conclude that (1) chronic DEX treatment causes a generalized decrease in CGRP and SP neuropeptides in pulpal nerves but not in periodontal ligament; (2) it reduces abscess formation in injured teeth; (3) it does not block reparative dentin formation; and (4) it does not block sprouting of pulpal nerves towards fibrous dentin. The selective loss of pulpal neuropeptides CGRP and SP during dexamethasone treatment may be caused by reduced dental function since there was substantial loss of appetite and chronic weight loss during the 1-2 week treatment periods.

Glucocorticosteroid receptor dimerization investigated by analysis of receptor binding to glucocorticosteroid responsive elements using a monomer-dimer equilibrium model

The aim of this study was to analyze the role of regions of the glucocorticosteroid receptor (GR) outside the DNA binding domain (DBD) in GR binding and homodimerization efficiencies by using a model according to which GR monomers and dimers are in equilibrium and able to bind to each half-palindromic motif of a GRE. We studied wild-type human GR (hGR), an N-terminal domain deleted mutant (lacking amino acids 1-417), a C-terminal deleted mutant (lacking amino acids 550-777, the main part of the ligand binding domain), and two rat GR derivatives limited to the DNA binding domain and proximal sequences. Specific GR monomer and dimer complexes with 33P-labeled palindromic or half-palindromic GREs were identified by gel-shift and methylation interference experiments. The different complexes were quantified, and the multiple equilibrium constants for their formation were determined. The affinity of the monomer for the GRE was not affected by the deletions of regions outside the DBD. However, the affinity of the dimer for the GRE was clearly increased by the presence of the N-terminal domain and, to a lesser extent, by that of the main part of the C-terminal domain. By using this model, we also obtained a GR dimerization constant in the absence of specific binding to GRE. Dimerization of the DBD was not increased by the presence of only one of the GR terminal domains, but an increase in dimerization efficiency was observed when both domains were present, suggesting a structural synergy between the N- and C-terminal domains in GR homodimerization.

Dexamethasone and activators of the protein kinase A and C signal transduction pathways regulate neuronal calcitonin gene-related peptide expression and release

Primary cultures of adult rat dorsal root ganglia (DRG) neurons were used to determine if activation of either the protein kinase A or C signal transduction pathways or treatment with the synthetic glucocorticoid dexamethasone modulate neuronal calcitonin gene-related peptide (CGRP) synthesis and release. DRG are the sites of neuronal cell bodies known to produce abundant CGRP levels, and to send axons peripherally to blood vessels and centrally to the spinal cord. Using immunocytochemical techniques, we confirmed that synthesis of immunoreactive CGRP (iCGRP) is restricted to a subpopulation of DRG neurons. Subsequently, we determined that treatment (24 h) of the neurons with either dibutyryl cAMP (1 mM) or phorbol 12-myristate 13-acetate (2 microM) increased CGRP mRNA content 2.2 +/- 0.4 (n = 6, p < 0.03) and 3.0 +/- 0.6-fold (n = 6, P < 0.02) respectively, while secreted iCGRP levels were increased 1.8 +/- 0.2 (n = 14, P < 0.005) and 4.5 +/- 1.0 (n = 14, P < 0.001)-fold over control levels. Treatment of the neurons with dexamethasone alone had no effect on CGRP expression; however, this agent was able to significantly attenuate the stimulatory effects of NGF on both CGRP mRNA accumulation and release of iCGRP. Time course studies demonstrated that in the phorbol ester treated neurons CGRP mRNA levels continued to increase at 48 h, while maximal induction with dibutyryl cAMP occurred at approximately 12 h. These results indicate that local and/or circulating factors which act through the protein kinase A and C signal transduction pathways upregulate both CGRP expression and release, while glucocorticoids attenuate the stimulatory effects of NGF.

A minimal CGRP gene promoter is inducible by nerve growth factor in adult rat dorsal root ganglion neurons but not in PC12 phaeochromocytoma cells

The calcitonin/CGRP gene is transcribed in thyroid C cells and some neuronal cells but not in other cell types. Although the promoter sequences mediating gene activity in thyroid C cells have been extensively studied, the elements responsible for promoter activity in neuronal cells and its stimulation by nerve growth factor (NGF) have not previously been defined. We report the first use of the calcium phosphate procedure to successfully transfect adult rat dorsal root ganglion neurons, which naturally express the calcitonin/calcitonin gene-related peptide (CGRP) in an NGF-inducible manner. This method was used to characterize the elements in the calcitonin/CGRP promoter which are responsible for its basal activity and NGF inducibility in DRG neurons and in PC12 cells, a neuronally derived cell line which does not naturally express the calcitonin/CGRP gene. Although the sequences required for basal activity are similar in each cell type, we show that a minimal calcitonin/CGRP promoter is NGF-responsive in dorsal root ganglion cells, but that upstream sequences are required for such inducibility in PC12 cells.

Small cell lung carcinoma cell lines express mRNA for calcitonin and alpha- and beta-calcitonin gene related peptides

Calcitonin (CT) and calcitonin gene related peptide (CGRP) are derived from preprohormones encoded by three mRNAs (CT, alpha-CGRP and beta-CGRP) from two genes (CALC1 and CALC2) on chromosome 11. Among 16 small cell lung cancer cell lines examined by RNase protection assay, 9 (56%) had detectable CT mRNA, 8 (50%) had alpha-CGRP mRNA, and 13 (81%) had beta-CGRP mRNA. At least one CALC1 transcript (CT or alpha-CGRP) was found in 11 (69%) cell lines with three having only CT mRNA, two having only alpha-CGRP mRNA, and six having both. beta-CGRP mRNA was detected in all of these 11 cell lines expressing a CALC1 transcript. Immunoreactive CT was detected by radioimmunoassay in eight of nine SCLC cell lines expressing CT mRNA, and immunoreactive CGRP was detected in 12 of 13 cell lines expressing a CGRP mRNA. The variety of expression of these three peptides in different cell lines of the same cell type should provide a useful system for further study of the control of expression of these peptides.

A novel inhibitory role for glucocorticoids in the secretion of angiotensinogen by C6 glioma cells

Astrocytes have been identified as the primary source of brain angiotensinogen (Ao), but the regulation of the secretion of this protein from astrocytes is poorly defined. In this study, the rat C6 glioma cell line was used as an astrocyte model to investigate the regulation of Ao secretion. C6 cultures secreted Ao at a rate of 4.05 +/- 1.52 (mean +/- SD) ng of Ao/10(6) cells/24 h as determined by a direct radioimmunoassay. This rate was not significantly altered by the hormones thyroxine, estradiol, angiotensin II, growth hormone, and prostaglandins or by increased levels of intracellular cyclic AMP. Treatment with the synthetic glucocorticoid dexamethasone (DEX; 10(-6) M) reduced the rate of Ao secretion to 1.82 +/- 0.28 ng of Ao/10(6) cells/24 h. By comparison, the basal secretion rate for rat H4 hepatoma cells was 142.4 +/- 10.0 ng of Ao/10(6) cells/24 h, and this increased fourfold (572.4 +/- 173.1 ng/10(6) cells/24 h) in the presence of 10(-6) M DEX. Both these inhibitory (C6) and stimulatory (H4) actions of DEX were dose related. The inhibition observed in C6 cells was mimicked by RU28362, a pure glucocorticoid agonist, and reversed by the antagonist RU486, demonstrating that DEX was functioning as a true glucocorticoid. The action of DEX was also antagonized by the cyclic AMP analogue N6,2'-O-dibutyryladenosine 3':5'-cyclic monophosphate (dBcAMP) (control, DEX, and DEX + dBcAMP, 3.58 +/- 0.73, 1.69 +/- 0.82, and 4.93 +/- 1.88 ng of Ao/10(6) cells/24 h, respectively, and by the beta-adrenergic agonist isoprenaline, which stimulates cyclic AMP production.(ABSTRACT TRUNCATED AT 250 WORDS)

Regulation of adrenocorticosteroid receptor mRNA expression in the central nervous system

1. The adrenocorticosteroid receptors are hormone-activated transcription factors that have the potential to influence gene expression in a wide variety of CNS neurons. This review summarizes the present state of knowledge regarding the localization and regulation of glucocorticoid (or type II corticosteroid) receptor and mineralocorticoid (or type I corticosteroid) receptor mRNAs in brain, from the perspective of their potential influence on a wide variety of hormone-responsive genes. 2. Corticosteroid receptors are widely but not uniformly localized in the CNS and exhibit very complex regulation by glucocorticoids, gonadal steroids, neurotransmitter systems, and endogenous circadian drive. Both receptor species are present during development, implying an ability for these transcription factors to interact with neuronal differentiation, growth, and viability, and both receptors appear to regulate with age, suggesting relationships between adrenocorticosteroid receptor populations and brain aging. Regulation of adrenocorticosteroid receptor mRNA expression at the level of polyadenylation and splicing indicates that GR and MR biosynthesis is a dynamic process susceptible to numerous classes of information. 3. Further study of GR and MR biosynthesis at the gene, mRNA, and protein level is required to determine the true meaning of the regulatory complexities seen in defined neuronal circuits.