The identification of a cis-acting element involved in cyclic 3‘,5‘-adenosine monophosphate regulation of bovine vasopressin gene expression

Circadian rhythms of sorting nexin 25 in the mouse suprachiasmatic nucleus

Entrainment of mammalian circadian rhythms requires receptor-mediated signaling in the hypothalamic suprachiasmatic nucleus (SCN), the site of the master circadian pacemaker. Receptor-mediated signaling is regulated by endocytosis, indicating that endocytosis-related proteins contribute to SCN pacemaking. Sorting nexin 25 (SNX25) belongs to the sorting nexin superfamily, whose members are responsible for membrane attachment to organelles of the endocytic system. In this study, we showed that Snx25 mRNA and SNX25 protein are highly expressed and exhibit remarkable circadian rhythms in the SCN of adult mice. Expression was maximal at about zeitgeber time (ZT) 16 in the subjective night and minimal at ZT8 in the subjective day. Prominent SNX25 immunoreactivity was found in the arginine vasopressin-positive neurons of the SCN. These findings suggest that SNX25 is a new actor in endocytic signaling, perhaps contributing to the circadian pacemaking system.

The Phosphorylation of CREB at Serine 133 Is a Key Event for Circadian Clock Timing and Entrainment in the Suprachiasmatic Nucleus

Within the suprachiasmatic nucleus (SCN)-the locus of the master circadian clock- transcriptional regulation via the CREB/CRE pathway is implicated in the functioning of the molecular clock timing process, and is a key conduit through which photic input entrains the oscillator. One event driving CRE-mediated transcription is the phosphorylation of CREB at serine 133 (Ser¹³³). Indeed, numerous reporter gene assays have shown that an alanine point mutation in Ser¹³³ reduces CREB-mediated transcription. Here, we sought to examine the contribution of Ser¹³³ phosphorylation to the functional role of CREB in SCN clock physiology in vivo. To this end, we used a CREB knock-in mouse strain, in which Ser¹³³ was mutated to alanine (S/A CREB). Under a standard 12 h light-dark cycle, S/A CREB mice exhibited a marked alteration in clock-regulated wheel running activity. Relative to WT mice, S/A CREB mice had highly fragmented bouts of locomotor activity during the night phase, elevated daytime activity, and a delayed phase angle of entrainment. Further, under free-running conditions, S/A CREB mice had a significantly longer tau than WT mice and reduced activity amplitude. In S/A CREB mice, light-evoked clock entrainment, using both Aschoff type 1 and 6 h "jet lag" paradigms, was markedly reduced relative to WT mice. S/A CREB mice exhibited attenuated transcriptional drive, as assessed by examining both clock-gated and light-evoked gene expression. Finally, SCN slice culture imaging detected a marked disruption in cellular clock phase synchrony following a phase-resetting stimulus in S/A CREB mice. Together, these data indicate that signaling through CREB phosphorylation at Ser¹³³ is critical for the functional fidelity of both SCN timing and entrainment.

Astroglial Modulation of Hydromineral Balance and Cerebral Edema

Maintenance of hydromineral balance (HB) is an essential condition for life activity at cellular, tissue, organ and system levels. This activity has been considered as a function of the osmotic regulatory system that focuses on hypothalamic vasopressin (VP) neurons, which can reflexively release VP into the brain and blood to meet the demand of HB. Recently, astrocytes have emerged as an essential component of the osmotic regulatory system in addition to functioning as a regulator of the HB at cellular and tissue levels. Astrocytes express all the components of osmoreceptors, including aquaporins, molecules of the extracellular matrix, integrins and transient receptor potential channels, with an operational dynamic range allowing them to detect and respond to osmotic changes, perhaps more efficiently than neurons. The resultant responses, i.e., astroglial morphological and functional plasticity in the supraoptic and paraventricular nuclei, can be conveyed, physically and chemically, to adjacent VP neurons, thereby influencing HB at the system level. In addition, astrocytes, particularly those in the circumventricular organs, are involved not only in VP-mediated osmotic regulation, but also in regulation of other osmolality-modulating hormones, including natriuretic peptides and angiotensin. Thus, astrocytes play a role in local/brain and systemic HB. The adaptive astrocytic reactions to osmotic challenges are associated with signaling events related to the expression of glial fibrillary acidic protein and aquaporin 4 to promote cell survival and repair. However, prolonged osmotic stress can initiate inflammatory and apoptotic signaling processes, leading to glial dysfunction and a variety of brain diseases. Among many diseases of brain injury and hydromineral disorders, cytotoxic and osmotic cerebral edemas are the most common pathological manifestation. Hyponatremia is the most common cause of osmotic cerebral edema. Overly fast correction of hyponatremia could lead to central pontine myelinolysis. Ischemic stroke exemplifies cytotoxic cerebral edema. In this review, we summarize and analyze the osmosensory functions of astrocytes and their implications in cerebral edema.

Structural and functional diversity of nonapeptide hormones from an evolutionary perspective: A review

The article presents an overview of the comparative distribution, structure and functions of the nonapeptide hormones in chordates and non chordates. The review begins with a historical preview of the advent of the concept of neurosecretion and birth of neuroendocrine science, pioneered by the works of E. Scharrer and W. Bargmann. The sections which follow discuss different vertebrate nonapeptides, their distribution, comparison, precursor gene structures and processing, highlighting the major differences in these aspects amidst the conserved features across vertebrates. The vast literature on the anatomical characteristics of the nonapeptide secreting nuclei in the brain and their projections was briefly reviewed in a comparative framework. Recent knowledge on the nonapeptide hormone receptors and their intracellular signaling pathways is discussed and few grey areas which require deeper studies are identified. The sections on the functions and regulation of nonapeptides summarize the huge and ever increasing literature that is available in these areas. The nonapeptides emerge as key homeostatic molecules with complex regulation and several synergistic partners. Lastly, an update of the nonapeptides in non chordates with respect to distribution, site of synthesis, functions and receptors, dealt separately for each phylum, is presented. The non chordate nonapeptides share many similarities with their counterparts in vertebrates, pointing the system to have an ancient origin and to be an important substrate for changes during adaptive evolution. The article concludes projecting the nonapeptides as one of the very first common molecules of the primitive nervous and endocrine systems, which have been retained to maintain homeostatic functions in metazoans; some of which are conserved across the animal kingdom and some are specialized in a group/lineage-specific manner.

Hypothalamic-Pituitary--Adrenal Axis-Feedback Control

The hypothalamo-pituitary-adrenal axis (HPA) is responsible for stimulation of adrenal corticosteroids in response to stress. Negative feedback control by corticosteroids limits pituitary secretion of corticotropin, ACTH, and hypothalamic secretion of corticotropin-releasing hormone, CRH, and vasopressin, AVP, resulting in regulation of both basal and stress-induced ACTH secretion. The negative feedback effect of corticosteroids occurs by action of corticosteroids at mineralocorticoid receptors (MR) and/or glucocorticoid receptors (GRs) located in multiple sites in the brain and in the pituitary. The mechanisms of negative feedback vary according to the receptor type and location within the brain-hypothalmo-pituitary axis. A very rapid nongenomic action has been demonstrated for GR action on CRH neurons in the hypothalamus, and somewhat slower nongenomic effects are observed in the pituitary or other brain sites mediated by GR and/or MR. Corticosteroids also have genomic actions, including repression of the pro-opiomelanocortin (POMC) gene in the pituitary and CRH and AVP genes in the hypothalamus. The rapid effect inhibits stimulated secretion, but requires a rapidly rising corticosteroid concentration. The more delayed inhibitory effect on stimulated secretion is dependent on the intensity of the stimulus and the magnitude of the corticosteroid feedback signal, but also the neuroanatomical pathways responsible for activating the HPA. The pathways for activation of some stressors may partially bypass hypothalamic feedback sites at the CRH neuron, whereas others may not involve forebrain sites; therefore, some physiological stressors may override or bypass negative feedback, and other psychological stressors may facilitate responses to subsequent stress.

Transcription factor CREB3L1 mediates cAMP and glucocorticoid regulation of arginine vasopressin gene transcription in the rat hypothalamus

BACKGROUND

Arginine vasopressin (AVP), a neuropeptide hormone that functions in the regulation of water homeostasis by controlling water re-absorption at kidneys, is synthesised in supraoptic nucleus and paraventricular nucleus of the hypothalamus. An increase in plasma osmolality stimulates secretion of AVP to blood circulation and induces AVP synthesis in these nuclei. Although studies on mechanism of AVP transcriptional regulation in hypothalamus proposed that cAMP and glucocorticoids positively and negatively regulate Avp expression, respectively, the molecular mechanisms have remained elusive. Recently, we identified CREB3L1 (cAMP-responsive element binding protein 3 like 1) as a putative transcription factor of Avp transcription in the rat hypothalamus. However the mechanism of how CREB3L1 is regulated in response of hyperosmotic stress in the neurons of hypothalamus has never been reported. This study aims to investigate effect of previously reported regulators (cAMP and glucocorticoid) of Avp transcription on transcription factor CREB3L1 in order to establish a molecular explanation for cAMP and glucocorticoids effect on AVP expression.

RESULTS

The effect of cAMP and glucocorticoid treatment on Creb3l1 was investigated in both AtT20 cells and hypothalamic organotypic cultures. The expression of Creb3l1 was increased in both mRNA and protein level by treatment with forskolin, which raises intracellular cAMP levels. Activation of cAMP by forskolin also increased Avp promoter activity in AtT20 cells and this effect was blunted by shRNA mediated silencing of Creb3l1. The forskolin induced increase in Creb3l1 expression was diminished by combined treatment with dexamethasone, and, in vivo, intraperitoneal dexamethasone injection blunted the increase in Creb3l1 and Avp expression induced by hyperosmotic stress.

CONCLUSION

Here we shows that cAMP and glucocorticoid positively and negatively regulate Creb3l1 expression in the rat hypothalamus, respectively, and regulation of cAMP on AVP expression is mediated through CREB3L1. This data provides the connection between CREB3L1, a newly identified transcription factor of AVP expression, with the previously proposed mechanism of Avp transcription which extends our understanding in transcription regulation of Avp in the hypothalamus.

The use of protein-DNA, chromatin immunoprecipitation, and transcriptome arrays to describe transcriptional circuits in the dehydrated male rat hypothalamus

The supraoptic nucleus (SON) of the hypothalamus is responsible for maintaining osmotic stability in mammals through its elaboration of the antidiuretic hormone arginine vasopressin. Upon dehydration, the SON undergoes a function-related plasticity, which includes remodeling of morphology, electrical properties, and biosynthetic activity. This process occurs alongside alterations in steady state transcript levels, which might be mediated by changes in the activity of transcription factors. In order to identify which transcription factors might be involved in changing patterns of gene expression, an Affymetrix protein-DNA array analysis was carried out. Nuclear extracts of SON from dehydrated and control male rats were analyzed for binding to the 345 consensus DNA transcription factor binding sequences of the array. Statistical analysis revealed significant changes in binding to 26 consensus elements, of which EMSA confirmed increased binding to signal transducer and activator of transcription (Stat) 1/Stat3, cellular Myelocytomatosis virus-like cellular proto-oncogene (c-Myc)-Myc-associated factor X (Max), and pre-B cell leukemia transcription factor 1 sequences after dehydration. Focusing on c-Myc and Max, we used quantitative PCR to confirm previous transcriptomic analysis that had suggested an increase in c-Myc, but not Max, mRNA levels in the SON after dehydration, and we demonstrated c-Myc- and Max-like immunoreactivities in SON arginine vasopressin-expressing cells. Finally, by comparing new data obtained from Roche-NimbleGen chromatin immunoprecipitation arrays with previously published transcriptomic data, we have identified putative c-Myc target genes whose expression changes in the SON after dehydration. These include known c-Myc targets, such as the Slc7a5 gene, which encodes the L-type amino acid transporter 1, ribosomal protein L24, histone deactylase 2, and the Rat sarcoma proto-oncogene (Ras)-related nuclear GTPase.

Cell-type specific expression of the vasopressin gene analyzed by AAV mediated gene delivery of promoter deletion constructs into the rat SON in vivo

The magnocellular neurons (MCNs) in the supraoptic nucleus (SON) of the hypothalamus selectively express either oxytocin (Oxt) or vasopressin (Avp) neuropeptide genes. In this paper we examine the cis-regulatory domains in the Avp gene promoter that are responsible for its cell-type specific expression. AAV vectors that contain various Avp gene promoter deletion constructs using EGFP as the reporter were stereotaxically injected into the rat SON. Two weeks following the injection immunohistochemical assays of EGFP expression from these constructs were done to determine whether the expressed EGFP reporter co-localizes with either the Oxt- or Avp-immunoreactivity in the MCNs. The results identify three major enhancer domains located at −2.0 to −1.5 kbp, −1.5 to −950 bp, and −950 to −543 bp in the Avp gene promoter that regulate the expression in Avp MCNs. The results also show that cell–type specific expression in Avp MCNs is maintained in constructs containing at least 288 bp of the promoter region upstream of the transcription start site, but this specificity is lost at 116 bp and below. Based on these data, we hypothesize that the −288 bp to −116 bp domain contains an Avp MCN specific activator and a possible repressor that inhibits expression in Oxt-MCNs, thereby leading to the cell-type specific expression of the Avp gene only in the Avp-MCNs.

CREB influences timing and entrainment of the SCN circadian clock

The transcriptional feedback circuit, which is at the core of the suprachiasmatic nucleus (SCN) circadian (i.e., 24 h) clock, is tightly coupled to both external entrainment cues, such as light, as well as rhythmic cues that arise on a system-wide level within the SCN. One potential signaling pathway by which these cues are conveyed to the molecular clock is the CREB/CRE transcriptional cascade. In this study, we employed a tetracycline-inducible CREB repressor mouse strain, in which approximately 60% of the SCN neurons express the transgene, to test CREB functionality in the clock and its effects on overt rhythmicity. We show that attenuated CREB signaling in the SCN led to a significant reduction in light-evoked clock entrainment. An examination of circadian timing revealed that CREB repressor mice exhibited normal free-running rhythms in the absence of external lighting cues. However, under conditions of constant light, which typically leads to a lengthening of the circadian period, CREB repressor mice exhibited a dramatic arrhythmic phenotype, which could be reversed with doxycycline. At a cellular level, the repression of CREB led to a significant reduction in both the expression of the circadian clock proteins PERIOD1 and PERIOD2 and the clock output hormones AVP and VIP. Together, these data support the idea that the CRE transcriptional pathway orchestrates transcriptional events that are essential for both the maintenance of SCN timing and light entrainment of the circadian clock.

Fos proteins are not prerequisite for osmotic induction of vasopressin transcription in supraoptic nucleus of rats

While it is well known that osmotic stimulation induces the expression of Fos family members in the supraoptic nucleus (SON), it is unclear whether the induced protein products are involved in the regulation of the gene transcription of arginine vasopressin (AVP). In the present study, we examined the in vivo correlation between changes in AVP gene transcription and expression of the various Fos family members in the SON after acute osmotic stimuli. The data demonstrated that the peak of AVP transcription (measured by intronic in situ hybridization) observed 15min after an injection of hypertonic saline preceded the expression of Fos proteins, which became detectable at 30min and peaked at 120min. Electrophoretic mobility shift assay showed that the expressed Fos proteins bound to the composite AP-1/CRE-like site in the AVP promoter. These data suggest that Fos proteins in the SON induced by acute osmotic stimuli could affect AVP gene transcription by binding to the AVP promoter, but they are not prerequisite for the induction of AVP gene transcription.

Gene regulation system of vasopressin and corticotropin-releasing hormone

The neurohypophyseal hormones, arginine vasopressin and corticotropin-releasing hormone (CRH), play a crucial role in the physiological and behavioral response to various kinds of stresses. Both neuropeptides activate the hypophysial-pituitary-adrenal (HPA) axis, which is a central mediator of the stress response in the body. Conversely, they receive the negative regulation by glucocorticoid, which is an end product of the HPA axis. Vasopressin and CRH are closely linked to immune response; they also interact with pro-inflammatory cytokines. Moreover, as for vasopressin, it has another important role, which is the regulation of water balance through its potent antidiuretic effect. Hence, it is conceivable that vasopressin and CRH mediate the homeostatic responses for survival and protect organisms from the external world.

A tight and elaborate regulation system of the vasopressin and CRH gene is required for the rapid and flexible response to the alteration of the surrounding environments. Several important regulatory elements have been identified in the proximal promoter region in the vasopressin and CRH gene. Many transcription factors and intracellular signaling cascades are involved in the complicated gene regulation system. This review focuses on the current status of the basic research of vasopressin and CRH. In addition to the numerous known facts about their divergent physiological roles, the recent topics of promoter analyses will be discussed.

Structure of neurohypophysial hormone genes and changes in the levels of expression during spawning season in grass puffer (Takifugu niphobles)

Vasotocin (VT) has been shown to influence various aspects of social and sexual behaviors in a broad range of vertebrate species, but less is known about the mechanisms through which this peptide modulates behavior. Additionally, much less is known about roles of isotocin (IT) in regulation of behavior. Grass puffer, Takifugu niphobles, has unique spawning behavior; spawning occurs on beach only for several days around the spring tide and is conducted by a group of 10-60 individuals, of which one is female. As a first step toward investigating the roles of VT and IT in this species' spawning behavior, we determined the structures of the VT and IT genes from grass puffer using the genome resources of the closely related tiger puffer and green puffer. We then used these sequences to develop real-time PCR assays and examined changes in expression of the VT and IT genes over the spawning season. The structures of VT and IT genes are well conserved among three puffer species. Particularly, the sequence similarities between grass and tiger puffers were very high not only in the coding region (85-99%), but also in the non-coding regions (92-98%) that include the 5'-upstream regions. The levels of expression of VT gene increased in the brain of pre-spawning females. The levels of VT mRNA in the spawning females tended to be higher than that in the spawning males. In contrast, the levels of IT mRNA did not show such variation. The present results suggest that VT gene expression augments in the brain of females during the spawning period. The unique spawning behavior of grass puffer provides a useful model for studying the molecular mechanism of sexual behavior utilizing the genome resources of tiger puffer.

The effects of osmotic stimulation and water availability on c-Fos and FosB staining in the supraoptic and paraventricular nuclei of the hypothalamus

We studied the effects of osmotic stimulation on the expression of FosB and c-Fos in the supraoptic nucleus (SON) and paraventricular nucleus (PVN). Adult male rats were divided into two groups that were injected with lidocaine (0.1-0.2 ml sc) followed by either 0.9% or 6% NaCl (1 ml/100 g bw sc). After the NaCl injections, the rats were anesthetized and perfused 2, 6, or 8 h after the injections. Their brains were prepared for immunocytochemistry and stained with FosB and c-Fos antibodies. The number of c-Fos-positive cells was significantly increased only at 2 h in the SON and PVN. In contrast, the number of FosB-positive cells was significantly increased at 6, and 8 h in both the SON and PVN. In a second experiment, the effect of water availability on FosB staining 8 h after injections of 6% NaCl was tested in 3 groups of rats: water ad libitum, rats that had no access to water, and rats that were given water 2 h prior to perfusion. FosB staining was significantly reduced in both the SON and the PVN of rats that had ad libitum water compared to the two water-restricted groups. In the third experiment, rats were injected with either 0.9% NaCl or 6% NaCl and were either given ad libitum access to water or water restricted for 6 h after the injections and perfused 24 h after the saline injections. FosB staining was not increased when water was available ad libitum. FosB staining was significantly increased at 24 h in the rats injected with 6% NaCl when water was restricted. Thus, FosB may continue to influence protein expression in the SON and PVN for at least 24 h following acute osmotic stimulation.

Identification of a novel receptor for an invertebrate oxytocin/vasopressin superfamily peptide: molecular and functional evolution of the oxytocin/vasopressin superfamily

Annetocin is structurally related to an OT (oxytocin)/VP (vasopressin) family peptide, which has been isolated from the earthworm Eisenia foetida and has been shown to induce OT-like egg-laying behaviour. We now report the identification of an endogenous AnR (annetocin receptor). The deduced AnR precursor displays high sequence similarity with OT/VP receptors. Genomic analysis of the AnR gene revealed that the intron-inserted position is conserved between the AnR gene and the mammalian OT/VP receptor genes. These results indicate that AnR and mammalian OT/VP receptors share a common ancestor gene. Administration of annetocin to the AnR expressed in Xenopus oocytes induced a calcium-dependent signal transduction. Reverse transcriptase-PCR analysis and in situ hybridization showed that the AnR gene is expressed specifically in the nephridia located in the clitellum region, although the nephridia are distributed throughout the worm body. This result suggests that annetocin induces egg-laying behaviour through its action on the nephridia. This is the first description concerning the functional correlation between an invertebrate OT/VP-related peptide and egg-laying behaviour.

MAP kinases and the adaptive response to hypertonicity: functional preservation from yeast to mammals

The adaptation to hypertonicity in mammalian cells is driven by multiple signaling pathways that include p38 kinase, Fyn, the catalytic subunit of PKA, ATM, and JNK2. In addition to the well-characterized tonicity enhancer (TonE)-TonE binding protein interaction, other transcription factors (and their respective cis elements) can potentially respond to hypertonicity. This review summarizes the current knowledge about the signaling pathways that regulate the adaptive response to osmotic stress and discusses new insights from yeast that could be relevant to the osmostress response in mammals.

Deciphering the mechanisms of homeostatic plasticity in the hypothalamo-neurohypophyseal system—genomic and gene transfer strategies

The hypothalamo-neurohypophyseal system (HNS) is the specialised brain neurosecretory apparatus responsible for the production of a peptide hormone, vasopressin, that maintains water balance by promoting water conservation at the level of the kidney. Dehydration evokes a massive increase in the regulated release of hormone from the HNS, and this is accompanied by a plethora of changes in morphology, electrical properties and biosynthetic and secretory activity, all of which are thought to facilitate hormone production and delivery, and hence the survival of the organism. We have adopted a functional genomic strategy to understand the activity dependent plasticity of the HNS in terms of the co-ordinated action of cellular and genetic networks. Firstly, using microarray gene-profiling technologies, we are elucidating which genes are expressed in the HNS, and how the pattern of expression changes following physiological challenge. The next step is to use transgenic rats to probe the functions of these genes in the context of the physiological integrity of the whole organism.

cAMP-dependent protein kinase A mediation of vasopressin gene expression in the hypothalamus of the osmotically challenged rat

We have tested the hypothesis that 3', 5'-cyclic adenosine monophosphate (cAMP)-dependent protein kinase A (PKA) is involved in the regulation of the vasopressin (VP) gene in the magnocellular neurons of the paraventricular nucleus (PVN) of the osmotically challenged rat. An adenoviral vector expressing a potent peptide inhibitor of PKA, Ad.CMV.PKIalpha, was demonstrated to be highly efficient in vitro. Ad.CMV.PKIalpha was then introduced into the PVN of rats bearing a VP reporter transgene (3-VCAT-3) consisting of the VP structural gene containing an epitope reporter in exon III, flanked by 3 kb of upstream and 3 kb of downstream sequence Robust transgene expression is seen in VP neurons of the PVN, and this increases following 72 h of dehydration. Ad.CMV.PKIalpha significantly blunted 3-VCAT-3 expression in the osmotically stimulated PVN. Our evidence suggests that PKA mediates changes in VP gene expression in response to dehydration through sequences contained within the 3-VCAT-3 transgene.

Neurone-specific expression and regulation of the pufferfish isotocin and vasotocin genes in transgenic mice

We used comparative genetics to investigate the location, structure and evolution of the oxytocin and vasopressin gene regulatory regions. The pufferfish, Fugu rubripes, is an attractive vertebrate model for comparison because of its maximal evolutionary distance from mammals and short intergenic regions. To determine whether regulatory DNA is conserved between oxytocin and vasopressin, and their Fugu homologs, isotocin and vasotocin, we generated transgenic mice bearing overlapping Fugu cosmids that contained the isotocin and/or vasotocin genes as well as short isotocin (5 kb) and vasotocin (9 kb) constructs. Our study shows that the Fugu isotocin and vasotocin genes express specifically in the mouse oxytocinergic and vasopressinergic neurones, respectively, and that the cis-regulatory elements which mediate neurone-specific expression are located within the short transgene constructs tested. Thus, the neurone-specific expression of the oxytocin and vasopressin gene families, and the mechanisms mediating the cell-specificity, evolved before the divergence of the fish and mammalian lineages. Salt-loading of transgenic mice induced an increase in abundance of isotocin, but not vasotocin mRNA in the cognate neurones. It appears that either the vasotocin gene does not respond to osmotic perturbations or the vasotocin transgene construct tested lacks osmotic response elements. Comparisons of homologous flanking sequences of the Fugu and mouse genes identified several short matching sequences, which are candidate regulatory elements.

Cyclic adenosine 3',5'-monophosphate regulation of corticotropin-releasing hormone promoter activity in AtT-20 cells and in a transformed hypothalamic cell line

The regulation of CRH promoter activity by cAMP was studied in two cell lines, the pituitary corticotroph cell line AtT-20 and the immortalized hypothalamic cell line 4B, which expresses CRH and vasopressin. In 4B cells transfected with a CRH promoter-luciferase construct, the adenylyl cyclase stimulator, forskolin, increased luciferase activity in parallel with increases in intracellular cAMP. In 4B cells, however, the phosphodiesterase inhibitor, isobutylmethylxanthine, potentiated forskolin-stimulated cAMP without affecting further increases in luciferase activity. In AtT-20 cells, forskolin plus isobutylmethylxanthine elevated cAMP only slightly, but increased luciferase activity to levels similar to those observed in 4B cells. AtT-20 cells were also unresponsive to 8-bromo-cAMP, due in part to higher phosphodiesterase (PDE) activities. Although both cells contained PDE1, -3, and -4, inhibition of either PDE4 or PDE1 potentiated luciferase activity stimulated by submaximal forskolin concentrations in 4B cells, while only simultaneous inhibition of PDE3 and PDE4 was effective in AtT-20 cells. The data show that minor elevations in intracellular cAMP are sufficient for full stimulation of CRH promoter activity regardless of the cell line. Furthermore, poor CRH promoter activation in AtT-20 cells appears to result from deficient cAMP production and rapid cAMP degradation by PDE.

Regulation of gene promoters of hypothalamic peptides

In order to fulfill their roles in neuroendocrine regulation, specific hypothalamic neurons are devoted to produce and deliver biologically active peptides to the pituitary gland. The biosynthesis and release of peptides are strictly controlled by afferents to these hypothalamic neurons. Cell-specific expression and biosynthetic regulation largely relies on transcription from the gene promoter for which the 5(')-flanking regions of the peptidergic genes contain essential elements. Cell-specific transcription factors employ these regulatory elements to exert their control over the expression of the peptidergic gene. This article explores the properties of regulatory elements of the major hypothalamic peptides, somatostatin, growth hormone-releasing hormone, gonadotropin-releasing hormone, thyrotropin-releasing hormone, corticotropin-releasing hormone, vasopressin and oxytocin, and the transcription factors acting on them. These transcription factors are often endpoints of signal transduction pathways that can be activated by neurotransmitters or steroid hormones. Others are essential to provide cell-specific expression of the peptidergic gene during development and mature regulation.

The vasopressin gene non-canonical Hogness box: effect on protein binding and promoter function

Comparison of the promoter sequences of the genes encoding the neuropeptide hormone vasopressin from a number of organisms has revealed that they do not contain a classical Hogness box. In all vertebrate species examined, the canonical TATA box is replaced with a CATA sequence. We hypothesised that this conserved modified sequence may play a role in the regulation of vasopressin promoter activity. We used electrophoretic mobility shift assays to show that TATA and CATA sequences generate different complexes with SON nuclear proteins. Further, the transfection of wild-type (CATA) and mutated (TATA) VP promoter-reporter constructs into a heterologous cell line demonstrated a sequence-specific effect on transcriptional activity. The CATA sequence contributes to weaker promoter activity than a TATA box, but is able to interact with the upstream elements to increase the efficacy of an enhancer. The CATA box may thus be involved in the cell-specific and physiological regulation of the VP gene.

Gene regulation in the magnocellular hypothalamo-neurohypophysial system

The hypothalamo-neurohypophysial system (HNS) is the major peptidergic neurosecretory system through which the brain controls peripheral physiology. The hormones vasopressin and oxytocin released from the HNS at the neurohypophysis serve homeostatic functions of water balance and reproduction. From a physiological viewpoint, the core question on the HNS has always been, "How is the rate of hormone production controlled?" Despite a clear description of the physiology, anatomy, cell biology, and biochemistry of the HNS gained over the last 100 years, this question has remained largely unanswered. However, recently, significant progress has been made through studies of gene identity and gene expression in the magnocellular neurons (MCNs) that constitute the HNS. These are keys to mechanisms and events that exist in the HNS. This review is an inventory of what we know about genes expressed in the HNS, about the regulation of their expression in response to physiological stimuli, and about their function. Genes relevant to the central question include receptors and signal transduction components that receive and process the message that the organism is in demand of a neurohypophysial hormone. The key players in gene regulatory events, the transcription factors, deserve special attention. They do not only control rates of hormone production at the level of the gene, but also determine the molecular make-up of the cell essential for appropriate development and physiological functioning. Finally, the HNS neurons are equipped with a machinery to produce and secrete hormones in a regulated manner. With the availability of several gene transfer approaches applicable to the HNS, it is anticipated that new insights will be obtained on how the HNS is able to respond to the physiological demands for its hormones.

The central effects of orexin-A in the hypothalamic-pituitary-adrenal axis in vivo and in vitro in male rats

Orexin-A is synthesized in the posterolateral hypothalamus and immunoreactive fibres project to many central nervous system structures, including the paraventricular nucleus, which is rich in corticotropin releasing factor (CRF) neurones and neuropeptide Y (NPY) innervation. We investigated the central effects of orexin-A on the hypothalamic-pituitary-adrenal (HPA) axis by measuring plasma concentrations of corticosterone and adrenocorticotropic hormone (ACTH) in vivo. We explored the potential neuropeptide pathways involved by investigating the effects of orexin-A on CRF, NPY, arginine vasopressin (AVP) and noradrenaline release from hypothalamic explants in vitro. Intracerebroventricular (i.c.v.) injection of orexin-A (3 nmol) in male rats stimulated increases in plasma concentrations of corticosterone between 10 and 40 min after injection, and of plasma ACTH at 20 and 90 min after injection. Orexin-A significantly stimulated CRF and NPY release from hypothalamic explants in vitro. Orexin-A did not stimulate CRF release in the presence of the selective NPY Y1 receptor antagonist, BIBP3226. BIBP3226 alone did not alter CRF release from hypothalamic explants. Orexin-A had no effect in vitro on the release of other neuropeptides, AVP and noradrenaline, involved in the central regulation of the HPA axis. These results suggest that orexin-A is involved in activation of the HPA axis, and that these effects could be mediated via the release of NPY.

Transcriptional regulation of the thyrotropin-releasing hormone gene by leptin and melanocortin signaling

Starvation causes a rapid reduction in thyroid hormone levels in rodents. This adaptive response is caused by a reduction in thyrotropin-releasing hormone (TRH) expression that can be reversed by the administration of leptin. Here we examined hypothalamic signaling pathways engaged by leptin to upregulate TRH gene expression. As assessed by leptin-induced expression of suppressor of cytokine signaling-3 (SOCS-3) in fasted rats, TRH neurons in the paraventricular nucleus are activated directly by leptin. To a greater degree, they also contain melanocortin-4 receptors (MC4Rs), implying that leptin can act directly or indirectly by increasing the production of the MC4R ligand, alpha-melanocyte stimulating hormone (alpha-MSH), to regulate TRH expression. We further demonstrate that both pathways converge on the TRH promoter. The melanocortin system activates the TRH promoter through the phosphorylation and DNA binding of the cAMP response element binding protein (CREB), and leptin signaling directly regulates the TRH promoter through the phosphorylation of signal transducer and activator of transcription 3 (Stat3). Indeed, a novel Stat-response element in the TRH promoter is necessary for leptin's effect. Thus, the TRH promoter is an ideal target for further characterizing the integration of transcriptional pathways through which leptin acts.

Distribution of dopamine D1 receptors in the nucleus paraventricularis of the hypothalamus in rats: an immunohistochemical study

The present study investigated the distribution of dopamine D1 receptor protein in the nucleus paraventricularis of the hypothalamus. It was found that the nucleus paraventricularis of the hypothalamus contains a relatively large number of cells which are positive for presence of dopamine D1 receptor protein. The vast majority of dopamine D1 receptor-positive neurons was found in the magnocellular part, but they were also present in considerable quantity in the parvocellular part of this subregion of the hypothalamus. When measured by the Western blot technique, the quantity of D1 receptor protein found in the paraventricular nucleus of the hypothalamus was at the level found in the prefrontal cortex. It was also found that dopamine D1 receptor protein was present in neurons constitutively displaying phosphorylated CREB protein, i.e. neurons which are, as might be speculated, under the tonic influence of neurotransmitters whose receptors operate via cAMP and pCREB as second or third messengers. The presence of dopamine D1 receptors in the nucleus paraventricularis of the hypothalamus may suggest, at an anatomical level, that these receptors are involved in controlling the release of hormones, as well as their synthesis at the level of transcription, which is regulated by phosphorylation of CREB protein. Finally, the present immunocytochemical findings offer an anatomical substrate for the role of dopamine and its receptors of D1 subtype in the regulation of the activity of paraventricular neurons seen in the functional studies.

Transgenic studies in rats and mice on the osmotic regulation of vasopressin gene expression

Over the past 10-15 years, profoundly important transgenic techniques have been developed that enable new genes to be introduced into whole mammalian organisms. This review describes the ways in which transgenic animals, both rats and mice, have been used to study the mechanisms by which the expression of the vasopressin gene is confined to specific neurones in the hypothalamus, and how the pattern of that expression is altered following an osmotic challenge to the organism.

Stimulatory and inhibitory regulators of the hypothalamo-pituitary-adrenocortical axis

Short- and long-term metabolic effects of stress are mediated through the hypothalamo-pituitary-adrenocortical (HPA) axis and the sympathetic nervous system. While efficient functioning of these systems is essential for life processes, dysfunction can lead to hypercortisolaemia and inappropriately elevated catecholamines, resulting in immunosuppression and associated pathologies. This review will concentrate on the central mechanisms involved in the control of HPA axis activity, particularly neuronal, neuropeptide and transcriptional input to CRF and AVP expression in the hypothalamus. The emphasis of the article will be on our increased understanding of selective and specific responses of the HPA axis to different types of stressors. Elucidating the biochemical mechanisms underlying stress may permit the development of pharmacological strategies to treat chronic stress which exacts such a major toll on our quality of life today.

Tumour-specific arginine vasopressin promoter activation in small-cell lung cancer

Small-cell lung cancer (SCLC) can produce numerous mitogenic neuropeptides, which are not found in normal respiratory epithelium. Arginine vasopressin is detected in up to two-thirds of SCLC tumours whereas normal physiological expression is essentially restricted to the hypothalamus. This presents the opportunity to identify elements of the gene promoter which could be exploited for SCLC-specific targeting. A series of human vasopressin 5' promoter fragments (1048 bp, 468 bp and 199 bp) were isolated and cloned upstream of a reporter gene. These were transfected into a panel of ten cell lines, including SCLC with high or low endogenous vasopressin transcription, non-SCLC and bronchial epithelium. All these fragments directed reporter gene expression in the five SCLC cell lines, but had negligible activity in the control lines. The level of reporter gene expression reflected the level of endogenous vasopressin production, with up to 4.9-fold (s.d. 0.34) higher activity than an SV40 promoter. The elements required for this strong, restricted, SCLC-specific promoter activity are contained within the 199-bp fragment. Further analysis of this region indicated involvement of E-box transcription factor binding sites, although tumour-specificity was retained by a 65-bp minimal promoter fragment. These data show that a short region of the vasopressin promoter will drive strong expression in SCLC in vitro and raise the possibility of targeting gene therapy to these tumours.

Circadian regulation of cAMP response element-mediated gene expression in the suprachiasmatic nuclei

A program of stringently-regulated gene expression is thought to be a fundamental component of the circadian clock. Although recent work has implicated a role for E-box-dependent transcription in circadian rhythmicity, the contribution of other enhancer elements has yet to be assessed. Here, we report that cells of the suprachiasmatic nuclei (SCN) exhibit a prominent circadian oscillation in cAMP response element (CRE)-mediated gene expression. Maximal reporter gene expression occurred from late-subjective night to mid-subjective day. Cycling of CRE-dependent transcription was not observed in other brain regions, including the supraoptic nucleus and piriform cortex. Levels of the phospho-active form of the transcription factor CREB (P-CREB) varied as a function of circadian time. Peak P-CREB levels occurred during the mid- to late-subjective night. Furthermore, photic stimulation during the subjective night, but not during the subjective day, triggered a marked increase in CRE-mediated gene expression in the SCN. Reporter gene experiments showed that activation of the p44/42 mitogen-activated protein kinase signaling cascade is required for Ca2+-dependent stimulation of CRE-mediated transcription in the SCN. These findings reveal the CREB/CRE transcriptional pathway to be circadian-regulated within the SCN, and raise the possibility that this pathway provides signaling information essential for normal clock function.

Functional neuroanatomy of the parvocellular vasopressinergic system: transcriptional responses to stress and glucocorticoid feedback

This chapter summarizes the regulation of vasopressin (VP) transcription within the parvocellular neurosecretory cells of the hypothalamic paraventricular nucleus in vivo, with special reference to stress-response and glucocorticoid feedback. VP is commonly held as the first and the most potent among the co-secretagogues that act synergistically with corticotropin-releasing factor (CRF-41) to induce adrenocorticotropin (ACTH) from the anterior pituitary in response to various internal and external stimuli. Cellular levels of the primary transcripts of VP and CRF genes, revealed by in situ hybridization histochemistry using probes complementary to intronic sequences, are increased after acute challenges with different time courses. In contrast to the rapid stress-induced upregulation of CRF gene expression, VP transcription shows a delayed increase suggesting different regulatory mechanisms governing the two main ACTH releasing neuropeptides in the parvocellular neurosecretory neurons. With respect of transcription factors that may mediate these effects, besides rapid phosphorylation of the cAMP-response element-binding protein (CREB), VP activation in the parvocellular neurons requires additional newly synthesized factors such as those encoded by immediate-early genes, like c-fos. In addition, it has recently been revealed that glucocorticoid negative feedback during stress, selectively targets vasopressin transcription in the parvocellular neurons that is likely mediated by interaction of glucocorticoid receptors and immediate-early gene products. These data speak for the emerging consensus that VP is the principal factor that imparts situation-specific drive and represents the regulated variable governing hypothalamo-pituitary-adrenocortical axis during stress.

Evidence for conservation of the vasopressin/oxytocin superfamily in Annelida

Annetocin is a structurally and functionally oxytocin-related peptide isolated from the earthworm Eisenia foetida. We present the characterization of the annetocin cDNA. Sequence analyses of the deduced precursor polypeptide revealed that the annetocin precursor is composed of three segments: a signal peptide, an annetocin sequence flanked by a Gly C-terminal amidation signal and a Lys-Arg dibasic processing site, and a neurophysin domain, similar to other oxytocin family precursors. The proannetocin showed 37.4-45.8% amino acid homology to other prohormones. In the neurophysin domain, 14 cysteines and amino acid residues essential for association of a neurophysin with a vasopressin/oxytocin superfamily peptide were conserved, suggesting that the Eisenia neurophysin can bind to annetocin. Furthermore, in situ hybridization experiments demonstrated that the annetocin gene is expressed exclusively in neurons of the central nervous system predicted to be involved in regulation of reproductive behavior. These findings confirm that annetocin is a member of the vasopressin/oxytocin superfamily. This is the first identification of the cDNA encoding the precursor of an invertebrate oxytocin-related peptide and also the first report of the identification of an annelid vasopressin/oxytocin-related precursor.

Something fishy in the rat brain: molecular genetics of the hypothalamo-neurohypophysial system

The brain peptides vasopressin and oxytocin play crucial roles in the regulation of salt and water balance. The genes encoding these neurohormones are regulated by cell-specific and physiological cues, but the molecular mechanisms remain obscure. New strategies, involving the introduction of rat transgenes into rats, are being used to address these issues, but the complexity of the rat genome has hampered progress. By contrast, the pufferfish, Fugu rubripes, has a "junk-free" genome. The oxytocin homologue from Fugu, isotocin, has been introduced into rats and is expressed in oxytocin neurons, where it is upregulated by physiological perturbations that upregulate the oxytocin gene. The Fugu and rat lineages separated 400 million years ago, yet the mechanisms that regulate the isotocin and oxytocin genes have been conserved. Fugu genome analysis and transgenesis in the physiologically tractable rat host are a powerful combination that will enable the identification of fundamental components of the neural systems that control homeostasis.

Protein synthesis blockade differentially affects the stress-induced transcriptional activation of neuropeptide genes in parvocellular neurosecretory neurons

Corticotropin-releasing factor (CRF) and arginine vasopressin (AVP) are synergistically interacting ACTH secretagogues that are co-expressed by parvocellular neurosecretory neurons of the hypothalamic paraventricular nucleus (PVH). To shed light on the mechanisms that mediate the stress-induced transcriptional activation of these neuropeptide genes, quantitative hybridization histochemical methods were used to assess the effects of systemic treatment with the protein synthesis inhibitor, cycloheximide, on the ether stress-induced upregulation of primary CRF and AVP transcripts, in vivo. Pretreatment with cycloheximide prevented the induction of FOS, but not CREB phosphorylation, normally seen in response to acute ether exposure, and significantly attenuated the stress-induced rise in AVP, but not CRF, heteronuclear RNA expression in the parvocellular division of the PVH. These results support the view that distinct molecular mechanisms govern the expression of the two principal corticotropin-releasing factors, in vivo.

Patterns of neuronal activation during development of sodium sensitive hypertension in SHR

The effects of regular (RNa) or high (HNa) sodium diet for 3, 7, and 14 days on Fra-like immunoreactivity (Fra-LI) in the brains of Wistar-Kyoto rats (WKY) and spontaneously hypertensive rats (SHR) were examined using an antibody that recognizes all known members of the Fos family (Fos, Fos-B, Fra-1, and Fra-2). Two weeks of HNa significantly exacerbated hypertension in SHR but had no effects in WKY. On RNa, compared with WKY, SHR showed higher Fra-LI in the median preoptic nucleus, supraoptic nucleus, both parts of the paraventricular nucleus, nucleus of the solitary tract, and central gray. Fra-LI in the subfornical organ did not differ between the two strains. On RNa, Fra-LI in the anterior hypothalamic area could be detected only in WKY. In osmoregulatory areas, HNa diet increased Fra-LI in both SHR and WKY to comparable extents, but in the median preoptic nucleus, Fra-LI was increased to a greater extent in SHR. HNa produced smaller increases in the subfornical organ of SHR compared with WKY. In both the parvocellular and magnocellular paraventricular nuclei, increases in Fra-LI by HNa were more pronounced in SHR than in WKY. In the anterior hypothalamic area, Fra-LI could no longer be detected in WKY on HNa, whereas it appeared in SHR. HNa increased Fra-LI in the NTS and central gray to similar levels in WKY and SHR. These results indicate that WKY and SHR differ in the pattern of neuronal activation accompanying maturation on RNa. HNa activates neurons in a number of brain areas, and the pattern of these changes also differs between WKY and SHR.

Positive and negative regulation of the rat vasopressin gene promoter

To study the transcriptional regulation of the vasopressin gene in vitro, 3 kb of the 5' regulatory region of the rat vasopressin gene was isolated and subcloned, along with a series of various deletion mutants, into vectors containing the luciferase reporter gene. After transfecting these genes transiently into the human choriocarcinoma cell line JEG-3 along with a glucocorticoid receptor (GR) expression vector, transcriptional activity was quantitated using the luciferase assay. Forskolin, 8-bromo-cAMP, and protein kinase A catalytic subunit expression all markedly increased transcription from the 3-kb promoter. Analyses with deletion mutants of the promoter showed that two cAMP-responsive element (CRE)-like sequences (-227 to -220 bp and -123 to -116 bp) contribute to this positive regulation. Expression of KCREB, a dominant negative mutant of the cAMP-responsive element binding protein (CREB), suggested the involvement of CREB. Transfection of the activator protein 2 (AP2) DNA consensus sequence partially blocked transcription. Dexamethasone suppressed forskolin-stimulated expression. The negative effect of glucocorticoid was GR dependent and may be mediated by a mechanism not involving GR binding to DNA because it was independent of the putative glucocorticoid-responsive element previously reported in the vasopressin promoter (-622 to -608 bp) and was preserved in the shorter promoter constructs in which no glucocorticoid-responsive element-like sequence was found. Our data suggest that several trans-acting factors including CREB, AP2, and GR are likely to be involved in vasopressin gene transcription and that the positive and negative regulation of vasopressin gene transcription is complex.

Transcription of the vasoactive intestinal peptide gene in response to glucocorticoids: differential regulation of alternative transcripts is modulated by a labile protein in rat anterior pituitary

Expression of the vasoactive intestinal peptide (VIP) gene is controlled by glucocorticoids in a tissue- and endocrine status-specific manner. We have investigated the molecular mechanisms that determine glucocorticoid regulation of VIP gene expression in the rat pituitary. In initial experiments, using explant cultures of rat pituitary glands, we have demonstrated that treatment with the glucocorticoid agonist dexamethasone leads to a marked increase in VIP mRNA levels. This effect was found to be selective for the larger of two alternatively polyadenylated VIP transcripts, and in addition, protein synthesis inhibitors markedly enhanced the magnitude of this response indicating that a labile pituitary protein acts to attenuate the transcript-selective response to glucocorticoids. Nuclear run-on analysis of transcription demonstrated that the effects of dexamethasone in vitro are mediated largely, if not completely, at the level of transcription. In order to investigate the role of VIP promoter sequence in the glucocorticoid response, we then demonstrated that the activity of rat VIP gene promoter/reporter constructs in GH3 pituitary cells are up-regulated by dexamethasone. This up-regulation is virtually abolished following removal of promoter sequence between -162 and -89 of the start of transcription. Using an in vitro electrophoretic mobility shift assay, we have also demonstrated that this region of the promoter binds recombinant glucocorticoid receptor protein. The results of our study therefore indicate a direct mechanism of action for the modulation of VIP gene expression by glucocorticoids, and furthermore provide evidence of a mechanism that permits selective glucocorticoid regulation of alternative VIP transcripts.

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.

Circadian rhythms and autoregulatory transcription loops--going round in circles?

Recent advances in the molecular analysis of biological timing have appeared to bring us closer to an answer to the 'big question', namely, 'What is the timing mechanism that enables an organism to measure the circadian (around 24 h) period?'. In this minireview, we consider the validity of the fashionable concept that autoregulatory feedback loops, centered on transcription, form the basis of the clock, and we offer a fresh view of recent progress as it relates to mammalian systems.

Expression of inducible cAMP early repressor (ICER) in hypothalamic magnocellular neurons

Cyclic AMP-responsive genes are regulated both positively and negatively by a number of constitutively expressed nuclear proteins. These proteins bind to cAMP-responsive DNA elements in their target genes and they are activated by protein kinase A-mediated phosphorylation. The cAMP response element modulator gene encodes for several constitutively expressed products. However, a second intronic promoter within the gene is inducible and produces another negatively acting transcription factor, inducible cAMP early repressor (ICER). ICER shows a diurnal pattern of expression in the pineal gland, but to date it has not been noted elsewhere in the brain. Here we show expression of ICER mRNA in hypothalamic magnocellular neurons following osmotic stimulation over a time course consistent with a modulatory effect on the expression of other immediate-early genes, such as c-fos. However, since ICER was not present in magnocellular neurons during parturition, its presence is not a prerequisite for the transient expression of c-fos.

Enhanced transcription of the human alpha 2A-adrenergic receptor gene by cAMP: evidence for multiple cAMP responsive sequences in the promoter region of this gene

Expression of the human alpha 2A-adrenergic receptor gene is induced by cAMP. The present studies were designed to define potential cAMP-responsive enhancer elements (CREs) in the promoter region of this gene. Regions from the 5'-flanking sequences of the gene were placed in a promoterless vector with a chloramphenicol acetyltransferase (CAT) reporter gene, and cAMP-stimulated CAT activity was assayed in transfected JEG-3 placental carcinoma cells. Enhancer activity responsive to cAMP was located in DNA sequences both upstream and downstream from the endogenous promoter region. Within the upstream sequences there is a putative "core sequence" homologous to the eight base CRE consensus palindrome, but this region did not function independently as a CRE enhancer; additional upstream sequences were required to provide significant enhancer activity in response to cAMP. Regulation of expression of the alpha 2A-adrenergic gene by cAMP is complex and involves multiple and likely novel DNA sequences.