Total body exposure to ultraviolet radiation does not influence plasma levels of immunoreactive beta-endorphin in man

BACKGROUND/AIMS

A growing number of reports support evidence of proopiomelanocortin (POMC)-derived peptides in human skin cells, although not consistently. Also the effect of ultraviolet radiation (UVR) on cutaneous and plasma levels of these POMC peptides has not been established unequivocally. We hypothesized that production of beta-endorphin (betaE) may explain the sense of well-being many people experience when sun-bathing. The aim of the present study was to investigate whether exposure of the skin to UVR elevates plasma betaE.

METHOD

Healthy volunteers (n=26) received a single, weighted dose of 15 J/cm2 of UVA. Several times during the hour following irradiation, plasma betaE- immunoreactivity (betaE-IR) was determined by radioimmunoassay. The effect of repeated exposure was assessed in 35 patients treated with UVB, UVA, or UVA-1. Plasma ACTH-IR was monitored in parallel.

RESULTS

Overall, plasma levels of betaE-IR and ACTH-IR showed no significant changes during the experiment, indicating that these peptides are not influenced by single or repeated exposures to UVR of different wavelengths.

CONCLUSION

On the basis of these results, the skin does not appear to contribute significantly to the levels of circulating betaE or ACTH. These data offer no support for the hypothesis that exposure to UVR leads to an increased concentration of circulating betaE, which could contribute to the feeling of well-being that often accompanies sun-bathing.

Familial neurohypophysial diabetes insipidus in a large Dutch kindred: effect of the onset of diabetes on growth in children and cell biological defects of the mutant vasopressin prohormone

Familial neurohypophysial diabetes insipidus (FNDI) is an autosomal dominant trait in which expression of a mutant vasopressin prohormone reduces vasopressin production. We investigated the NP85 Cys-->Gly mutant vasopressin prohormone in a large kindred in The Netherlands. We demonstrate that growth retardation is an important early sign in two children from this kindred, which recuperates by substitution therapy with 1-desamino-8-D-arginine vasopressin. To obtain clues about the basis for the dominant inheritance of FNDI, we analyzed the trafficking and processing of the mutant vasopressin prohormone in cell lines by metabolic labeling and immunoprecipitation. The mutant vasopressin prohormone was retained in the endoplasmic reticulum and thus was not processed to vasopressin. This defect was not caused by dimerization of the vasopressin prohormone via its unpaired cysteine residue. High level expression of the mutant vasopressin prohormone in cell lines resulted in strong accumulation in the endoplasmic reticulum and an altered morphology of this organelle. We hypothesize that disturbance of the endoplasmic reticulum results in dysfunction and ultimately cell death of the cells expressing the mutant prohormone. Our data support the hypothesis that FNDI is a progressive neurodegenerative disease with delayed onset of symptoms. Its treatment requires early detection of symptoms for which growth parameters are useful.

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.

Long-term impairment of social memory in the rat after social defeat is not restored by desglycinamide-vasopressin

Repeated social defeat followed by individual housing caused a long-term impairment of social memory in male rats. Social memory, as assessed in the social discrimination test using an intertrial interval of 3 min, was impaired for at least 8 weeks after the social defeat experience. Since social memory of male rodents depends on proper functioning of the sexually dimorphic vasopressin system, it was investigated whether a centrally active vasopressin fragment could restore the impaired social memory. Subcutaneous administration of 6 microg/kg of the vasopressin fragment desglycinamide-vasopressin (VP1-8) 40 days after social defeat slightly improved social memory in both control and socially defeated rats. It is concluded that social defeat followed by individual housing caused a long-term impairment of social memory, which was not restored by treatment with VP1-8.

Delayed effect of the vasopressin metabolite VP4-8 on the social memory of sexually naive male rats

RATIONALE

Endogenous vasopressin is involved in the social memory of the male rat and administration of exogenous vasopressin improves social memory. These findings are mainly based on studies using sexually experienced males that were tested in the social recognition test.

OBJECTIVE

The present study was aimed to establish whether the modulation of social memory by vasopressin fragments depends on the sexual experience of the male rat. For this purpose, the social discrimination test was used, since this test is more suitable than the social recognition test for measuring social memory in sexually naive males.

METHODS

Male rats were tested in the social discrimination test and treated subcutaneously with the vasopressin metabolite [pGlu4,Cyt6]vasopressin-(4-8) (VP4-8). VP4-8 shares with vasopressin the effects on memory processes but lacks the peripheral effects of vasopressin.

RESULTS

VP4-8 (1 microgram/kg) acutely improved the social memory of sexually experienced male rats, confirming previous reports. However, in sexually naive males VP4-8 failed to improve social memory in doses ranging from 0.1 microgram/kg to 1 microgram/kg. Instead, 1 microgram/kg VP4-8 or 6 micrograms/kg desglycinamide-vasopressin were found to exert a delayed effect in sexually naive rats. This delayed effect resulted in an improved social memory 2 days after administration.

CONCLUSIONS

Vasopressin sensitisation is discussed as a possible underlying mechanism of the observed delayed effect of vasopressin fragments. It is concluded that in male rats sexual experience can influence the modulation of social memory by vasopressin.

Immunohistochemical localization of the vasopressin V1b receptor in the rat brain and pituitary gland: anatomical support for its involvement in the central effects of vasopressin

Biological effects of vasopressin (VP) are mediated by four different receptors, two of which (the V1a and the oxytocin receptors) have been well characterized in the rodent brain, suggesting that these are the main receptors responsible for the central effects of VP. However, transcripts of the V1b VP receptor (V1bR) have been detected throughout the rat brain by RT-PCR and in situ hybridization, indicating that the V1bR adds to the population of central VP receptors. Because there are no specific ligands for the V1bR, the receptor protein itself has been difficult to visualize. In the present study, the distribution of the V1bR protein was investigated in the rat forebrain, midbrain, hindbrain, and cerebellum by immunohistochemistry using an antiserum raised against a synthetic fragment of the carboxylterminal of the rat V1bR protein. Immunohistochemistry revealed the presence of the V1bR in pituitary corticotrophs as expected. In naive, untreated rats, fiber networks containing V1bR-immunoreactivity were mainly concentrated in the hypothalamus, amygdala, cerebellum, and particularly in those areas with a leaky blood brain barrier or close to the circumventricular organs (medial habenula, subfornical organ, organum vasculosum laminae terminalis, median eminence, and nuclei lining to the third and fourth ventricles). A strikingly dense network was present in the external zone of the median eminence. Colchicine treatment was required to reveal the localization of V1bR-immunoreactive cell bodies. V1bR-containing cell bodies and associated protrusions were mainly located in the hippocampus, caudate putamen, cortex, thalamus, olfactory bulb, and cerebellum. These results demonstrate the widespread distribution of the V1bR protein in the rat brain over multiple, functionally distinct neuronal systems. These data suggest that the V1bR mediates different physiological functions of VP in the brain.

Differential responses of phosphorylated mitogen-activated protein kinase and phosphorylated cyclic-AMP response element-binding protein immunoreactivity in the rat brain to sub-convulsive pentylenetetrazol

The possible advantage of using multiple phospho-specific antibodies to study changes in brain activity was assessed. For this purpose, rats were injected intraperitoneally with either a control treatment or 15 mg/kg pentylenetetrazol. The sub-convulsive dose of pentylenetetrazol did not induce marked behavioural effects. Ten minutes after treatment, the rats were perfused and the brains were dissected. Adjacent brain sections were immunohistochemically stained for phosphorylated cyclic-AMP response element-binding protein and phosphorylated mitogen-activated protein kinase. Opposite effects of pentylenetetrazol treatment were observed on the immunoreactivity of these two antibodies within the hypothalamic paraventricular nucleus, the supraoptic nucleus and the arcuate nucleus. In these regions, pentylenetetrazol treatment increased phosphorylated mitogen-activated protein kinase immunoreactivity, but decreased phosphorylated cyclic-AMP response element-binding protein immunoreactivity. These findings show that changes in the activity of a brain nucleus can be accompanied by differential changes in the activity of two signal transduction pathways, which can be detected immunohistochemically. Therefore, the use of multiple phospho-specific antibodies may enhance our potential to monitor changes in brain activity.

Social memory in the rat: circadian variation and effect of circadian rhythm disruption

Disruption of circadian rhythm can impair long-term passive avoidance memory of rats and mice. The present study investigated whether disruption of circadian rhythm can also impair social memory of male rats. Social memory was assessed using the social discrimination test, in which a short-term olfactory memory is formed by social interaction with a juvenile rat during a learning trial. After an intertrial interval, a retrieval trial is performed, in which social memory is expressed as a decreased attention paid to the same juvenile as compared to a new juvenile. First, the social memory at four different time points across the light-dark cycle was measured with an intertrial interval of 10 or 25 min. There was no significant circadian variation of social memory across the light-dark cycle. Subsequently, the effect of a -6 or 12-h phase shift on social memory was studied. These phase shifts were previously found to impair long-term passive avoidance memory. However, no effect of either phase shift was observed in the social discrimination test. It is concluded that the disruption of circadian rhythm had no effect on the social memory of rats. Differences between short-term social memory and long-term passive avoidance memory are discussed in relation to their apparent differential susceptibility to the effects of circadian rhythm disruption.

Common requirements for melanocortin-4 receptor selectivity of structurally unrelated melanocortin agonist and endogenous antagonist, Agouti protein

The activity of melanocortin receptors (MCR) is regulated by melanocortin peptide agonists and by the endogenous antagonists, Agouti protein and AgRP (Agouti-related protein). To understand how the selectivity for these structurally unrelated agonists and antagonist is achieved, chimeric and mutants MC3R and MC4R were expressed in cell lines and pharmacologically analyzed. A region containing the third extracellular loop, EC3, of MC4R was essential for selective Agouti protein antagonism. In addition, this part of MC4R, when introduced in MC3R, conferred Agouti protein antagonism. Further mutational analysis of this region of MC4R demonstrated that Tyr(268) was required for the selective interaction with Agouti protein, because a profound loss of the ability of Agouti protein to inhibit (125)I-labeled [Nle(4),d-Phe(7)]alpha-melanocyte-stimulating hormone (MSH) binding was observed by the single mutation of Tyr(268) to Ile. This same residue conferred selectivity for the MC4R selective agonist, [d-Tyr(4)]MT-II, whereas it inhibited interaction with the MC3R-selective agonist, [Nle(4)]Lys-gamma(2)-MSH. Conversely, mutation of Ile(265) in MC3 (the corresponding residue of Tyr(268)) to Tyr displayed a gain of affinity for [d-Tyr(4)]MT-II, but not for Agouti protein, and a loss of affinity for [Nle(4)]Lys-gamma(2)-MSH as compared with wild-type MC3R. This single amino acid mutation thus confers the selectivity of MC3R toward a pharmacological profile like that observed for MC4R agonists but not for the antagonist, Agouti protein. Thus, selectivity for structurally unrelated ligands with opposite activities is achieved in a similar manner for MC4R but not for MC3R.

Analysis of three Ptx2 splice variants on transcriptional activity and differential expression pattern in the brain

Three different transcripts of the homeodomain gene termed pituitary homeobox (Ptx) 2 (Pitx2/Brx/Rieg/Solurshin/Arp) were cloned from different species encoding proteins belonging to the paired-like family of homeodomain proteins. Ptx2a (324 amino acids), Ptx2b (271 amino acids), and Ptx2c (318 amino acids) share the C terminus, including the homeodomain, and have different N termini. Here we report the comparative analysis of all three different Ptx2 splice variants for their transcriptional activity and their expression pattern in the adult rat brain. Ptx2 is able to trans-activate via different model promoters in different cell lines. A mild difference in trans-activating potential is observed among the splice variants, but the underlying mechanism is at present unknown. It is surprising that all Ptx2 transcripts displayed an identical expression pattern in the brain. This markedly restricted pattern is limited to the following brain areas: the anterior and intermediate lobes of the pituitary gland, the subthalamic nucleus, the posterior hypothalamic nucleus, the mammillary bodies, the red nucleus, and the deep gray layer of the superior colliculus. The data presented suggest that all variants of Ptx2 are involved in the development and regulation of distinct neuronal cell groups and the pituitary gland.

Genetic pathways in the developmental specification of hypothalamic neuropeptide and midbrain catecholamine systems

The neuropeptide concept concerns the diverse and broad physiological functions of neuropeptides in behavioral adaptation. Neuropeptides like vasopressin and corticotropin-releasing hormone can coordinate multiple brain functions due to the anatomical organization of the neurons producing them. The cell bodies are focally positioned in the hypothalamus and send long-reaching efferents to limbic and brainstem areas. Likewise, midbrain dopamine systems coordinate emotional behaviors and movement control by specific connectivity of neurons in the midbrain to limbic and striatal centers, respectively. The fundament of the functions of these signalling molecules is laid out during development when transmitter identity and connectivity are specified. This is a highly controlled process involving multiple transcription factors and growth factors acting together in genetic pathways. Here, the genetic pathways enrolling in developing vasopressin, corticotropin-releasing hormone, and midbrain dopamine neurons are discussed.

A diabetes insipidus vasopressin prohormone altered outside the central core of neurophysin accumulates in the endoplasmic reticulum

Over 20 mutations affecting the neurophysin moiety of the vasopressin prohormone, have been identified in families suffering from familial neurohypophysial diabetes insipidus (FNDI). Only one of these, NP87E-->stop, is located outside the central conserved domain implicated in sorting of the vasopressin prohormone. To obtain clues about the mechanism of induction of FNDI by this atypical mutant we stably expressed wild type and NP87E-->stop vasopressin prohormones in (neuro)endocrine cell lines. Metabolic labeling and immunoprecipitation demonstrated reduced processing of the mutant prohormone to neurophysin. In addition, evoked secretion of neurophysin and vasopressin was diminished, suggesting that part of the mutant is retained in another intracellular compartment than the secretory granules. Indeed, immunofluorescence demonstrated accumulation of the truncated vasopressin prohormone in the endoplasmic reticulum. We conclude that the presence of the vasopressin moiety and the central conserved core of the neurophysin domain suffices for sorting and processing, but not for efficient endoplasmic reticulum exit of the vasopressin-neurophysin molecule.

Molecular misreading in non-neuronal cells

+1 Frame-shifted proteins such as amyloid precursor protein(+1) and ubiquitin-B(+1) have been identified in the neuropathological hallmarks of Alzheimer's disease. These frameshifts are caused by dinucleotide deletions in GAGAG motifs of messenger RNA encoded by genes that have maintained the unchanged wild-type DNA sequence. This process is termed 'molecular misreading'. A key question is whether this process is confined to neurons or whether it could also occur in non-neuronal cells. A transgenic mouse line (MV-B) carrying multiple copies of a rat vasopressin minigene as a reporter driven by the MMTV-LTR promotor was used to screen non-neuronal tissues for molecular misreading by means of detection of the rat vasopressin(+1) protein and mutated mRNA. Molecular misreading was demonstrated to occur in several organs (e.g., epididymis and the parotid gland) where transgenic vasopressin expression is abundant, but its penetrance is variable both between and within tissues. This implies that non-neural tissues too, could be affected by cellular derangements caused by molecular misreading.

Processing of frameshifted vasopressin precursors

Biosynthesis of the vasopressin (VP) prohormone in magnocellular neurones of the hypothalamo-neurohypophysial system comprises endoplasmic reticulum (ER) transit, sorting into the regulated secretory pathway and subsequent processing in the individual proteins VP, neurophysin and a glycoprotein. These processes are severely disrupted in the homozygous diabetes insipidus (di/di) Brattleboro rat, which expresses a mutant VP precursor due to a single nucleotide deletion in the neurophysin region of the VP gene resulting in VP deficiency. Previous studies have shown the presence of additional frameshift mutations in VP transcripts, in solitary magnocellular neurones of the di/di rat due to a GA dinucleotide deletion resulting in two different mutant VP precursors with partly restored reading frame. Frameshifted VP precursors are also expressed in several magnocellular neurones in wild-type rats. In this study, we determined if the +1 frameshifted precursors from di/di and wild-type rats can lead to biosynthesis of the hormone VP. Therefore, eukaryotic expression plasmids containing the frameshifted VP cDNAs were transiently expressed in peptidergic tumour cell lines, and cells were analysed by reversed phase high-performance liquid chromatography and specific radioimmunoassays, and by immunofluoresence. Neuro2A neuroblastoma cells expressing the +1 frameshifted precursors of di/di rats retained products in the cell body. Only precursor or insignificant quantities of neurophysin-immunoreactive products were detected. In contrast, in AtT20 cells, frameshifted VP precursors were at least partly processed to yield the VP peptide, indicating that they have access to the regulated secretory pathway. Comparison between the two cell lines showed a very slow ER transit of the wild-type prohormone combined with inefficient processing in Neuro2A cells. The results show that mutant precursors can reach the regulated secretory pathway if ER transport is sufficiently rapid as in the case of AtT20 cells. This suggests that the di/di rat may regain the capacity to biosynthesize authentic VP through these +1 frameshifted precursors in magnocellular neurones.

Condition-dependent presence of beta-lipotropin-like peptide in human keratinocytes

This study aimed to characterize the beta-endorphin-immunoreactive material (betaE-IR) detectable in normal human keratinocytes (NHK). The effects of different culturing conditions and UV-irradiation on production of betaE-IR by NHK were assessed by radioimmunoassay and HPLC. All culture systems contained low levels of betaE-IR that was increased in conditioned media after UV-irradiation under certain conditions. NHK grown in nutrient-poor medium contained highest levels of betaE-IR that exhibited beta-lipotropin-like properties after HPLC analysis. The other culturing conditions displayed no authentic betaE-related peptides. Our results indicate that under certain culturing conditions NHK can produce POMC peptides like beta-lipotropin, which can be induced by UV-radiation.

A response element for the homeodomain transcription factor Ptx3 in the tyrosine hydroxylase gene promoter

Tyrosine hydroxylase (TH) is the rate-limiting enzyme in the biosynthesis of catecholamines, which takes place in different types of neuronal systems and nonneuronal tissues. The transcriptional regulation of the TH gene, which is complex and highly variable among different tissues, reflects this heterogeneity. We recently isolated a homeodomain transcription factor, named Ptx3, that is uniquely expressed in the dopaminergic neurons of the substantia nigra pars compacta and ventral tegmental area, which together form the mesencephalic dopaminergic system. This strict localization and its coinciding induction of expression with the TH gene during development suggested a possible role for this transcription factor in the control of the TH gene. We report here the presence of a responsive element for Ptx3 located at position -50 to -45 of the rat TH promoter. Transient transfections using TH promoter constructs and electrophoretic mobility shift assays using Ptx3-containing nuclear extracts demonstrated that this region binds Ptx3 protein and confers a transcriptional effect on the TH gene. Depending on the cell type, the effect of Ptx3 was an eight- to 12-fold enhancement of TH promoter activity in Neuro2A neuroblastoma cells, or a 60-80% repression in nonneuronal human embryonic kidney 293 cells. Despite the close association of the Ptx3-binding site and the major cyclic AMP-response element in the TH gene, no interplay was found between Ptx3 and cyclic AMP-modulating agents. In combination with the orphan nuclear receptor Nurr1, which is required for the induction of the TH gene in mesencephalic dopaminergic neurons, the TH promoter activity to Ptx3 was enhanced in Neuro2A cells. Nurr1 alone displayed only very weak activity on the TH promoter in this cell type. The results demonstrate that the homeodomain protein Ptx3 has the potential to act on the promoter of the TH gene in a markedly cell type-dependent fashion. This suggests that Ptx3 contributes to the regulation of TH expression in mesencephalic dopaminergic neurons.

Expression of the orphan receptor TR4 during brain development of the rat

The orphan receptor TR4, member of the nuclear hormone receptor family, is related to the orphan receptors TR2, COUP-TFI and ARP-1, and was originally cloned from the adult rat brain. The latter two orphan receptors have been implicated in central nervous system (CNS) development. To investigate a possible role for TR4 in brain development, expression of TR4 was studied in rat embryos. At embryonic days 14.5 and 19.5, high expression of TR4 was found in the CNS, while low expression was detected throughout the embryo. In postnatal rats, TR4 was mainly expressed in the hippocampus and cerebellum, resembling the expression pattern found in adult brain. These data show that like COUP-TFI and ARP-1, expression of TR4 becomes restricted to distinct areas. In adult brain, TR4 is predominantly expressed in granule cells of both hippocampus and cerebellum. The data suggest a possible role for TR4 during proliferation and maturation of brain structures.

A second independent pathway for development of mesencephalic dopaminergic neurons requires Lmx1b

We identified the LIM homeodomain transcription factor Lmx1b in the mesencephalic dopamine (mesDA) systems of embryos and adults. Analysis of spatiotemporal expression in Lmx1b null mutants and wild-type mice implicated a cascade involving Lmx1b in the early development of mesDA neurons. Although disruption of this cascade did not block induction of tyrosine hydroxylase (TH), a key enzyme in DA synthesis, or Nurr1, a nuclear hormone receptor, Lmx1b knockout mice failed to induce the mesDA-specific homeodomain gene Ptx3 in TH-positive neurons. Eventually, this small set of TH-positive neurons was lost during embryonic maturation. The data suggest that at least two molecular cascades operate during the specification of the mesDA system, one specifying neurotransmitter phenotype and another essential for other aspects of mesDA neuron differentiation.

Different spatiotemporal expression of DOC2 genes in the developing rat brain argues for an additional, nonsynaptic role of DOC2B in early development

DOC2A and DOC2B are two homologous genes implicated in synaptic vesicle exocytosis. Their complementary, nonoverlapping expression patterns in adult rat brain suggest that they exert similar functions in different neurons. We have analysed the expression pattern of the two genes in the developing rat brain by in situ hybridization. Unexpectedly, we found no parallel expression of the two genes during development. DOC2B mRNA was highly expressed as early as embryonic day 12 (E12) throughout the neuroepithelium, long before synaptic transmission is functional, and the expression remained abundant from E12 onwards. In contrast, faint expression of DOC2A transcripts was first detected at E17 in ventral brain areas, and it extended gradually to other brain structures in the sequence of their ontology, i.e. structures that had formed first also expressed DOC2A first. At postnatal day 3, both genes were highly expressed throughout the brain. This overlapping expression diverged to the complementary distribution of the adult brain. The temporal and spatial differences in expression point to a functional divergence between these homologous genes during brain development: the pattern of DOC2A is consistent with its proposed synaptic function, whereas that of DOC2B suggests an additional, nonsynaptic role in proliferating cells.

Mutations in the vasopressin prohormone involved in diabetes insipidus impair endoplasmic reticulum export but not sorting

Familial neurohypophysial diabetes insipidus is characterized by vasopressin deficiency caused by heterozygous expression of a mutated vasopressin prohormone gene. To elucidate the mechanism of this disease, we stably expressed five vasopressin prohormones with a mutation in the neurophysin moiety (NP14G-->R, NP47E-->G, NP47DeltaE, NP57G-->S, and NP65G-->V) in the neuroendocrine cell lines Neuro-2A and PC12/PC2. Metabolic labeling demonstrated that processing and secretion of all five mutants was impaired, albeit to different extents (NP65G-->V >/= NP14G-->R > NP47DeltaE >/= NP47E-->G > NP57G-->S). Persisting endoglycosidase H sensitivity revealed these defects to be due to retention of mutant prohormone in the endoplasmic reticulum. Mutant prohormones that partially passed the endoplasmic reticulum were normally targeted to the regulated secretory pathway. Surprisingly, this also included mutants with mutations in residues involved in binding of vasopressin to neurophysin, a process implicated in targeting of the prohormone. To mimick the high expression in vasopressin-producing neurons, mutant vasopressin prohormones were transiently expressed in Neuro-2A cells. Immunofluorescence displayed formation of large accumulations of mutant prohormone in the endoplasmic reticulum, accompanied by redistribution of an endoplasmic reticulum marker. Our data suggest that prolonged perturbation of the endoplasmic reticulum eventually leads to degeneration of neurons expressing mutant vasopressin prohormones, explaining the dominant nature of the disease.

Conformation of the core sequence in melanocortin peptides directs selectivity for the melanocortin MC3 and MC4 receptors

Melanocortin peptides regulate a variety of physiological processes. Five melanocortin receptors (MC-R) have been cloned and the MC3R and MC4R are the main brain MC receptors. The aim of this study was to identify structural requirements in both ligand and receptor that determine gamma-melanocyte-stimulating hormone (MSH) selectivity for the MC3R versus the MC4R. Substitution of Asp10 in [Nle4]Lys-gamma2-MSH for Gly10 from [Nle4]alpha-MSH, increased both activity and affinity for the MC4R while the MC3R remained unaffected. Analysis of chimeric MC3R/MC4Rs and mutant MC4Rs showed that Tyr268 of the MC4R mainly determined the low affinity for [Nle4]Lys-gamma2-MSH. The data demonstrate that Asp10 determines selectivity for the MC3R, however, not through direct side chain interactions, but probably by influencing how the melanocortin core sequence is presented to the receptor-binding pocket. This is supported by mutagenesis of Tyr268 to Ile in the MC4R which increased affinity and activity for [Nle4]Lys-gamma2-MSH, but decreased affinity for two peptides with constrained cyclic structure of the melanocortin core sequence, MT-II and [D-Tyr4]MT-II, that also displayed lower affinity for the MC3R. This study provides a general concept for peptide receptor selectivity, in which the major determinant for a selective receptor interaction is the conformational presentation of the core sequence in related peptides to the receptor-binding pocket.

Biosynthesis of the vacuolar H+-ATPase accessory subunit Ac45 in Xenopus pituitary

Vacuolar H+-ATPases (V-ATPases) mediate the acidification of multiple intracellular compartments, including secretory granules in which an acidic milieu is necessary for prohormone processing. A search for genes coordinately expressed with the prohormone proopiomelanocortin (POMC) in the melanotrope cells of Xenopus intermediate pituitary led to the isolation of a cDNA encoding the complete amino-acid sequence of the type I transmembrane V-ATPase accessory subunit Ac45 (predicted size 48 kDa). Comparison of Xenopus and mammalian Ac45 sequences revealed conserved regions in the protein that may be of functional importance. Western blot analysis showed that immunoreactive Ac45 represents a approximately 40-kDa product that is expressed predominantly in neuroendocrine tissues; deglycosylation resulted in a approximately 27-kDa immunoreactive Ac45 product which is smaller than predicted for the intact protein. Biosynthetic studies revealed that newly synthesized Xenopus Ac45 is an N-glycosylated protein of approximately 60 kDa; the nonglycosylated, newly synthesized form is approximately 46 kDa which is similar to the predicted size. Immunocytochemical analysis showed that in Xenopus pituitary, Ac45 is highly expressed in the biosynthetically active melanotrope cells. We conclude that the regionally conserved Xenopus Ac45 protein is synthesized as an N-glycosylated approximately 60-kDa precursor that is intracellularly cleaved to an approximately 40-kDa product and speculate that it may assist in the V-ATPase-mediated acidification of neuroendocrine secretory granules.

The magnocellular neurons of the hypothalamo-neurohypophyseal system display remarkable neuropeptidergic phenotypes leading to novel insights in neuronal cell biology

For decades the magnocellular neurons of the hypothalamo-neurophypophyseal system (HNS), in which either vasopressin or oxytocin are produced and released into the bloodstream, have been playing a pivotal role in fundamental discoveries in the nervous system. The primary structure of vasopressin and oxytocin was the first of all neuropeptides to be published, i.e., in the 1950s by the Nobel prize laureate Du Vigneaud. Moreover, many trend-setting discoveries have their origin in the HNS, which abundantly expresses vasopressin and oxytocin, clearly displays its function and is relatively easily to manipulate. Examples are the phenomenon of coexpression of neuropeptides, patch-clamping of nerve endings, axonal transport of RNA, neuroglia interactions and the behavioral effects. An extraordinarily intriguing example is the homozygous Brattleboro rat, which lacks vasopressin by a germ-line mutation, and has disclosed many of the fundamental characteristics of peptidergic neurons, and neurons in general. In this chapter we will discuss a few of them, in particular the recent data on mutations in vasopressin RNA. It is to be expected that the HNS will retain its informative role in the next decades.

Biochemistry of vasopressin fragments

Vasopressin (VP) undergoes a step-wise aminopeptidase conversion process in the brain, leading to accumulation of several metabolites. Some of these metabolites, in particular [pGlu4,Cyt6]VP 4-9 and 4-8, show behavioral effects comparable to VP, but are more potent and selective than VP. Most data favor the existence of a separate receptor for the VP metabolites distinct of the classical VP and oxytocin receptors, although its identity has remained obscure thus far. The characterization of this receptor is a major challenge to understand how the brain VP system generates and regulates divers central functions.

Vasopressin metabolites: a link between vasopressin and memory?

The effects of endogenous metabolites of the neuropeptide vasopressin (VP) in behavioural tests led to the hypothesis that VP metabolites have a more selective function than VP. In contrast to VP, no peripheral effects have been found thus far with VP metabolites and their function seems to be associated with memory-related behaviour. VP metabolites can improve both consolidation and retrieval of memory. Effects on autonomic and electrophysiological parameters and interactions with other neurotransmitter systems have provided some information about the processes that could underlie the effects of VP metabolites on memory-related behaviour. There is evidence that the effects of VP metabolites could be mediated by a VP metabolite receptor, which is different from the known VP receptors. The VP metabolite receptor could be a link between the neuropeptide VP and memory-related behaviour.

Hypothalamic transcription factors and the regulation of the hypothalamo-neurohypophysial system

The transcription factors that confer high level expression and regulate the genes encoding neurohypophysial hormones are largely unknown. A number of different approaches have been taken to identify these factors and to elucidate molecular mechanisms of physiological gene regulation. In this chapter two transcription factor families are considered: homeodomain proteins and nuclear receptors. Their identification in the hypothalamus and actions on the OT gene are addressed here.

Expression of melanocortin receptors and pro-opiomelanocortin in the rat spinal cord in relation to neurotrophic effects of melanocortins

Although neurotrophic effects of alpha-melanocyte-stimulating hormone (alpha-MSH) are well established, the mechanism underlying these effects is unknown. To identify candidate components of the signaling system that may mediate these effects, in the present study rat spinal cord, dorsal root ganglia, sciatic nerve and soleus muscle were analysed for the expression of the neural MC3, MC4 and MC5 receptors and for the expression of the melanocortin precursor pro-opiomelanocortin (POMC). In rat lumbar spinal cord, the MC4 receptor was the only MC receptor subtype for which mRNA was detectable using RNAse protection assays. In situ binding studies using 125I-NDP-MSH, a synthetic alpha-MSH analogue, demonstrated MC receptor protein in the rat spinal cord, predominantly localised in substantia gelatinosa and area X, surrounding the central canal. Furthermore, POMC mRNA was demonstrated in rat spinal cord and dorsal root ganglia. These findings suggest a functional melanocortin system in the rat spinal cord, that might be involved in peripheral nerve repair. Regulation of POMC or MC receptor transcripts does not appear to be involved in the response to peripheral nerve crush in rats, since no change in mRNA expression patterns was detected after sciatic nerve crush, using quantitative RNAse protection assays. Nevertheless, subtle changes in melanocortin receptor binding did occur postsurgically in several regions of the spinal cord in both sham-operated and sciatic nerve-lesioned rats. The robust expression of MC receptor protein in spinal cord regions that are generally associated with nociception suggests a potentially broader involvement of endogenous melanocortins in spinal pathways which mediate the responses to peripheral injury, in addition to any direct melanocortin effects on sprouting and neurite outgrowth.

Intracellular trafficking of the vacuolar H+-ATPase accessory subunit Ac45

Ac45 is a type I transmembrane protein associated with vacuolar H+-ATPase, a proton pump mediating the acidification of multiple intracellular organelles. In this study, we examined the intracellular routing of Ac45 in transfected CV-1 fibroblasts. Steady state immunolabeling showed that Ac45 is located on the plasma membrane and in a vacuolar compartment in the juxtanuclear region. Antibody internalization experiments revealed that Ac45 is rapidly retrieved from the cell surface and is targeted to the vacuolar structures. The 26-residue cytoplasmic tail of Ac45 was intrinsically capable of mediating endocytosis of the cell surface protein Tac, indicating that the tail contains an autonomous internalization signal. Immunolocalization studies on cells expressing carboxy-terminally truncated Ac45 mutants showed the presence of essential routing information in the membrane-distal region of the cytoplasmic tail. Further mutational analysis of this region, which lacks the recognized tyrosine- or di-leucine-based sorting motifs, suggested that multiple sites rather than a short linear sequence are responsible for the internalization. Collectively, our results indicate that the cytoplasmic tail of Ac45 contains autonomous targeting information distinct from previously described routing determinants.

Mutations in RNA: a first example of molecular misreading in Alzheimer's disease

In the past decade, considerable progress has been made in the understanding of the neurodegenerative changes that occur in Alzheimer's disease (AD). Knowledge about this disease is based mainly on studies of inherited forms of AD, although most cases of AD are of the non-familial type. Recently, a novel type of mutation in 'vulnerable' dinucleotide repeats in messenger RNA was discovered in AD patients: in this type of mutation a mutated transcript is produced from a correct DNA sequence, a process that we call 'molecular misreading'. The resulting mutated '+1 proteins' are prominent neuropathological hallmarks of AD and they are present in most elderly non-demented people also. This suggests that the dinucleotide deletions in transcripts could be one of the earliest events in the neuropathogenesis of AD and an important factor in normal aging.

Asp10 in Lys-gamma2-MSH determines selective activation of the melanocortin MC3 receptor

The melanocortin MC3 and MC4 receptors are the main melanocortin receptors expressed in brain. Of the endogenous melanocortins, gamma2-melanocortin stimulating hormone (MSH) selectively activates the melanocortin MC3 receptor, whereas alpha- and beta-MSH activate all melanocortin receptors. The aim was to gain an insight into the contribution of amino acids in positions 5 and 10 of melanocortins to the selectivity of [Nle4]Lys-gamma2-MSH for the melanocortin MC3 receptor versus the melanocortin MC4 receptor. Introduction of Asp10 into [Nle4]alpha-MSH as in [Nle4,Gly5,Asp10]alpha-MSH selectively increased the EC50 value for the melanocortin MC4 receptor. Conversely, removal of Asp10, as in [Nle4,Gly10]Lys-gamma2-MSH, selectively decreased the EC50 value for the melanocortin MC4 receptor. Thus, Asp10 in Lys-gamma2-MSH determined selectivity for the melanocortin MC3 receptor versus the melanocortin MC4 receptor.

Negative feedback control of the retinoid-retinoic acid/retinoid X receptor pathway by the human TR4 orphan receptor, a member of the steroid receptor superfamily

Amino acid sequence analysis indicates that the human TR4 orphan receptor (TR4) is a member of the estrogen/thyroid receptor subfamily of the steroid/thyroid receptor superfamily and recognizes the AGGTCA direct repeat (DR) of the hormone response element. Here we demonstrate using the electrophoretic mobility shift assay that TR4 binds specifically to DR with a spacing of 1 and 5 base pairs (DR1 and DR5), which are the response elements for retinoic acid receptor (RAR) and retinoid X receptor (RXR), respectively. A reporter gene assay using chloramphenicol acetyltransferase demonstrated that TR4 repressed RA-induced transactivation in a TR4 dose-dependent manner. Inhibition of the retinoid signal pathway also occurs through natural response elements found in CRBPII and RARbeta genes. Our data suggest that the mechanism of repression may not involve the formation of functionally inactive heterodimers between TR4 and RAR or RXR. Instead, we show that TR4 may compete for hormone response elements with RAR and RXR due to its higher binding affinity. Furthermore, treatment of F9 murine teratocarcinoma (F9) cells with 10(-6) M all-trans-retinoic acid increased TR4 mRNA levels, and this change was accompanied by an increased amount of endogenous TR4 protein that can bind to RXRE in electrophoretic mobility shift assay. Our data therefore strongly suggest that the retinoid signal pathway can be regulated by TR4 in a negative feedback control mechanism, which may restrict retinoic acid signaling to certain elements in a cell-specific fashion.

Expression of melanocortin-5 receptor in secretory epithelia supports a functional role in exocrine and endocrine glands

Melanocortins (alphaMSH and ACTH-related peptides) influence the physiological functions of certain peripheral organs, including exocrine and endocrine glands. This study was designed to determine the identity and anatomical localization of the melanocortin receptors (MC-R) expressed in these organs in the rat. MC5-R messenger RNA was found in exocrine glands, including lacrimal, Harderian, preputial, and prostate glands and pancreas, as well as in adrenal gland, esophagus, and thymus, as demonstrated by ribonuclease protection assays. In exocrine glands, MC5-R messenger RNA expression was restricted to secretory epithelia. MC-R protein was likewise present in secretory epithelia of exocrine glands, as determined by 125I-labeled [Nle4,D-Phe7]alphaMSH ([125I]NDP-MSH) binding and autoradiography in tissue sections. Specific [125I]NDP-MSH binding was also observed in adrenal cortex, thymus, spleen, and esophageal and trachealis muscle. MC receptors in these sites are accessible to circulating MC-R agonists in vivo, as specific binding of [125I]NDP-MSH was observed in exocrine and adrenal glands after systemic injection in vivo. Taken together, these findings show that the MC5 receptor is commonly and selectively expressed in exocrine glands and other peripheral organs. Based on these findings and compelling evidence from other studies, a functional coherence is suggested between central and peripheral actions of melanocortins and melanocortin receptors in physiological functions, including thermoregulation, immunomodulation, and sexual behavior.

TR4 orphan receptor crosstalks to chicken ovalbumin upstream protein-transcription factor and thyroid hormone receptor to induce the transcriptional activity of the human immunodeficiency virus type 1 long-terminal repeat

Here we investigate the roles of human testicular orphan receptors, TR2 and TR4, on the gene regulation of the long-terminal repeat of the human immunodeficiency virus type 1 (HIV-LTR). In gel-retardation assays, a palindromic element at the 5'-end of HIV-LTR,5'-AGGGGTCAGATATCCACTGACCTTT-3',showed high affinity to TR2 and TR4 with an equilibrium dissociation constant (Kd) of 1.11 +/- 0.48 (n = 3) and 0.52 +/- 0.12 nM (n = 3), respectively. Interestingly, each half-site of the palindromic element is sufficient to compete with the binding of the labeled palindromic element to TR2 or TR4 with an equilibrium inhibition constant (ki) around 10 nM. However, the transiently expressed TR2 or TR4 in Chinese hamster ovary (CHO) cells or Japanese quail muscle myoblasts (QM7) cells showed no activity in regulating the transcriptional activity of the chloramphenicol acetyltransferase (CAT) reporter gene inserted downstream of the HIV-LTR promoter. Although both TR2 and TR4 showed no effect on CAT activity by itself, our data showed only the TR4 could crosstalk to the chicken ovalbumin upstream protein-transcription factor (COUP-TF1) and thyroid hormone receptor (TR alpha 1), and potentiated the transcriptional activity of HIV-LTR on the CAT reporter gene regulated by COUP-TF1 and TR alpha 1. These results indicate that TR4, but not TR2, may couple to other nuclear receptors in the upregulation of the HIV replication.

Structure-function relationships of the vasopressin prohormone domains

1. In this review the structure-function relationships of the different vasopressin prohormone domains are dated and discussed, with special reference to the neurophysin and glycopeptide domains. 2. The primary structures of the currently known neurophysins and glycopeptide sequences are compared and discussed. 3. The hormone-binding and aggregational properties of neurophysin are reviewed and related to a possible function within the regulated secretory pathway. 4. It is proposed, based on the properties reviewed here as well as our own data shown here, that the sorting of the vasopressin prohormone is initiated by hormone binding, which triggers aggregation of the prohormone into the characteristic dense cores of the regulated secretory pathway. 5. This may suggest that prohormone sorting into the regulated secretory pathway is, in general, determined by noncovalent, intramolecular interactions that promote aggregation.

Transgenic and transcriptional studies on neurosecretory cell gene expression

1. Studies of the regulation of neurosecretory cell gene expression suffer from the lack of suitable cell lines. Two approaches have been used to overcome this deficit: transfection of neuropeptide genes into heterologous cell lines and generation of transgenic animals. 2. Studies with heterologous cell lines have revealed the potential involvement of nuclear hormone receptors, POU proteins, and fos/jun/ATF family members in the regulation of the vasopressin and oxytocin genes. Although limited in their scope, these studies have contributed greatly to the dissection of basic properties of elements in the vasopressin and oxytocin gene promoters. 3. Transgenic mice, and more recently rats, have been used to elucidate genomic regions governing cell specificity and physiological regulation of neurosecretory gene expression. The genes encoding the neuropeptides vasopressin and oxytocin have been used in many transgenic studies, due to the well-defined expression patterns and physiology of the endogenous neuropeptides. Cell-specific and physiologically regulated expression of these transgenes has been achieved, demonstrating the action of putative repressor elements and regulation of the expression of one gene by sequences present in the other gene. 4. Appropriate expression and translation of transgenes have resulted in the production of several useful systems. Expression of oncogene sequences in gonadotropin-releasing hormone neurons has allowed the development of cell lines from the resulting tumors, overproduction of corticotropin-releasing factor has produced animal models of anxiety and obesity, and directed ectopic expression of growth hormone has generated a potentially useful rat model of dwarfism. These and other animal models of human disease will provide important avenues for the development of therapeutic strategies.

Nurr1 is essential for the induction of the dopaminergic phenotype and the survival of ventral mesencephalic late dopaminergic precursor neurons

Nurr1 is a member of the nuclear receptor superfamily of transcription factors that is expressed predominantly in the central nervous system, including developing and mature dopaminergic neurons. Recent studies have demonstrated that Nurr1 is essential for the induction of phenotypic markers of ventral mid-brain dopaminergic neurons whose generation is specified by the floor plate-derived morphogenic signal sonic hedgehog (SHH), but the precise role of Nurr1 in this differentiative pathway has not been established. To provide further insights into the role of Nurr1 in the final differentiation pathway, we have examined the fate of dopamine cell precursors in Nurr1 null mutant mice. Here we demonstrate that Nurr1 functions at the later stages of dopamine cell development to drive differentiation of ventral mesencephalic late dopaminergic precursor neurons. In the absence of Nurr1, neuroepithelial cells that give rise to dopaminergic neurons adopt a normal ventral localization and neuronal phenotype characterized by expression of the homeodomain transcription factor and mesencephalic marker, Ptx-3, at embryonic day 11.5. However, these late precursors fail to induce a dopaminergic phenotype, indicating that Nurr1 is essential for specifying commitment of mesencephalic precursors to the full dopaminergic phenotype. Further, as development progresses, these mid-brain dopamine precursor cells degenerate in the absence of Nurr1, resulting in loss of Ptx-3 expression and a concomitant increase in apoptosis of ventral midbrain neurons in newborn null mutant mice. Taken together, these data indicate that Nurr1 is essential for both survival and final differentiation of ventral mesencephalic late dopaminergic precursor neurons into a complete dopaminergic phenotype.

A homeodomain gene Ptx3 has highly restricted brain expression in mesencephalic dopaminergic neurons

The mesencephalic dopaminergic (mesDA) system regulates behavior and movement control and has been implicated in psychiatric and affective disorders. We have identified a bicoid-related homeobox gene, Ptx3, a member of the Ptx-subfamily, that is uniquely expressed in these neurons. Its expression starting at E11.5 in the developing mouse midbrain correlates with the appearance of mesDA neurons. The number of Ptx3-expressing neurons is reduced in Parkinson patients, and these neurons are absent from 6-hydroxydopamine-lesioned rats, an animal model for this disease. Thus, Ptx3 is a unique transcription factor marking the mesDA neurons at the exclusion of other dopaminergic neurons, and it may be involved in developmental determination of this neuronal lineage.

Homeobox gene Prx3 expression in rodent brain and extraneural tissues

Different cDNA clones encoding a rat homeobox gene and the mouse homologue OG-12 were cloned from adult rat brain and mouse embryo mRNA, respectively. The predicted amino acid sequences of the proteins belong to the paired-related subfamily of homeodomain proteins (Prx homeodomains). Hence, the gene was named Prx3 and the mouse and rat genes are indicated as mPrx3 and rPrx3, respectively. In the mouse as well as in the rat, the predicted Prx3 proteins share the homeodomain but have three different N termini, a 12-aa residue variation in the C terminus, and contain a 14-aa residue motif common to a subset of homeodomain proteins, termed the "aristaless domain." Genetic mapping of Prx3 in the mouse placed this gene on chromosome 3. In situ hybridization on whole mount 12.5-day-old mouse embryos and sections of rat embryos at 14.5 and 16.5 days postcoitum revealed marked neural expression in discrete regions in the lateral and medial geniculate complex, superior and inferior colliculus, the superficial gray layer of the superior colliculus, pontine reticular formation, and inferior olive. In rat and mouse embryos, nonneuronal structures around the oral cavity and in hip and shoulder regions also expressed the Prx3 gene. In the adult rat brain, Prx3 gene expression was restricted to thalamic, tectal, and brainstem structures that include relay nuclei of the visual and auditory systems as well as other ascending systems conveying somatosensory information. Prx3 may have a role in specifying neural systems involved in processing somatosensory information, as well as in face and body structure formation.

Pattern changes of pituitary peptides in rat after salt-loading as detected by means of direct, semiquantitative mass spectrometric profiling

We have established a differential peptide display method, based on a mass spectrometric technique, to detect peptides that show semiquantitative changes in the neurointermediate lobe (NIL) of individual rats subjected to salt-loading. We employed matrix-assisted laser desorption/ionization mass spectrometry, using a single-reference peptide in combination with careful scanning of the whole crystal rim of the matrix-analyte preparation, to detect in a semiquantitative manner the molecular ions present in the unfractionated NIL homogenate. Comparison of the mass spectra generated from NIL homogenates of salt-loaded and control rats revealed a selective and significant decrease in the intensities of several molecular ion species of the NIL homogenates from salt-loaded rats. These ion species, which have masses that correspond to the masses of oxytocin, vasopressin, neurophysins, and an unidentified putative peptide, were subsequently chemically characterized. We confirmed that the decreased molecular ion species are peptides derived exclusively from propressophysin and prooxyphysin (i.e., oxytocin, vasopressin, and various neurophysins). The putative peptide is carboxyl-terminal glycopeptide. The carbohydrate moiety of the latter peptide was determined by electrospray tandem MS as bisected biantennary Hex3HexNAc5Fuc. This posttranslational modification accounts for the mass difference between the predicted mass of the peptide based on cDNA studies and the measured mass of the mature peptide.

The rat galanin-gene promoter: response to members of the nuclear hormone receptor family, phorbol ester and forskolin

We have cloned a rat genomic DNA fragment of approximately 12.5 kb. Nine kb of the cloned fragment lie in the 5'-flanking region of the gene and contain the promoter elements, while the remaining 3.5 kb contain the first four complete exons, the first three introns, and part of the fourth intron of the rat galanin gene. We have partially analysed some of the elements within the proximal sequence of this promoter which may influence the transcriptional regulation of the rat galanin gene. The rat galanin-gene promoter contains many regions which share homology with both the human and the bovine galanin genes and certain cis-elements appear to be conserved among the three species. In an attempt to test whether some of these elements are functional in the rat gene, transient transfection studies were carried out in selected cell lines. Estrogen, thyroid hormone and retinoic acid all showed a minimal degree of promoter stimulation when the rat galanin-gene promoter was co-transfected with the appropriate hormone receptors in Neuro 2A cells, while co-transfection of the nuclear orphan receptor ELP1 was able to stimulate transcription of a galanin promoter-driven reporter-gene construct (-374 bp) by 35-fold. The galanin promoter mediated a 3-4-fold induction in response to forskolin or TPA. Deletion of a 5-bp element at -50 bp from the start of transcription was able to greatly reduce the forskolin response but not the TPA response. These results point to several elements that may be targets of transcription factors linked to extracellular stimuli.

Identification of direct repeat 4 as a positive regulatory element for the human TR4 orphan receptor. A modulator for the thyroid hormone target genes

While the TR4 orphan receptor (TR4) is able to repress the expression of its target genes via its interaction with the direct repeat 1-hormone response element (DR1-HRE) and DR2-HRE, we now report that TR4 can also induce the transcriptional activity of the reporter gene containing a DR4-HRE via chloramphenicol acetyltransferase assay. Electrophoretic mobility shift assay and Scatchard analysis reveal a strong binding affinity (dissociation constant = 2 nM) between TR4 and DR4-HRE. The induction mediated by TR4 was detected not only in the synthetic DR4-HRE but also in some genes, such as rat alpha-myosin heavy-chain and S14 genes, containing the DR4 or DR4-like motif, which have been suggested to be the response elements for a thyroid hormone receptor. Our data also demonstrate this TR4-mediated gene induction is TR4 dose- and DR4 sequence-dependent. Together, our data suggest that DR4-HRE can be a positive regulatory element for TR4, which may be able to induce the transcriptional activity of the genes containing such positive HREs.

DOC2 proteins in rat brain: complementary distribution and proposed function as vesicular adapter proteins in early stages of secretion

DOC2 proteins constitute a novel protein family that may function in secretion and contain a double C2 domain. We have cloned and characterized two DOC2 isoforms in rat brain and studied their interactions with other proteins implicated in secretion. DOC2A was virtually brain specific, DOC2B ubiquitous. Within brain, the isoforms were expressed nonuniformly and complementary within neurons, not astroglia, and copurified with synaptic vesicles. Affinity purification, yeast two-hybrid analysis, and coimmunoprecipitation revealed that DOC2 binds munc18, a protein also implicated in secretion. The first DOC2 C2 domain and most of munc18 are involved in direct interactions. Munc18 may regulate formation of 'core complexes' during vesicle docking, by interacting with syntaxin. We show that DOC2 and syntaxin compete for munc18. Other core complex components shifted the equilibrium between syntaxin-munc18 versus DOC2-munc18. These data suggest that DOC2 proteins are vesicular adapter proteins regulating munc18-syntaxin complexes and herewith synaptic vesicle docking.

Molecular pharmacology of neural melanocortin receptors

The cloning of melanocortin receptors opened new avenues to identify selective ligands for this receptor family. gamma-MSH was characterized as a melanocortin-3 receptor selective agonist, [D-Arg8]ACTH-(4-10) and [Pro8,10, Gly9]ACTH-(4-10) were characterized as melanocortin-4 receptor antagonists. The application of these ligands in vivo revealed that melanocortin-4 receptors mediate melanocortin-induced grooming behaviour in the rat. Since we still lack potent and selective melanocortin receptor ligands, we performed homology modelling and site directed mutagenesis of the melanocortin-4 receptor, in order to understand how melanocortins bind melanocortin receptors. A histidine at position 260 in the melanocortin-4 receptor is important for normal receptor function. However this residue is not forming a salt bridge with a glutamate at position 92 to keep the receptor in an inactive conformation, nor with the glutamate in the melanocortin peptides as had been suggested before.

Effects of estrogen on oxytocin receptor messenger ribonucleic acid expression in the uterus, pituitary, and forebrain of the female rat

Oxytocin receptors are regulated during parturition and lactation. Gonadal steroids are thought to be key players in this regulation. It is not well documented how oxytocin receptor gene expression is regulated in the CNS. In this study we analyzed potential estrogen effects on the oxytocin receptor mRNA levels in some areas integral to the limbic-hypothalamic system, namely the ventromedial nucleus of the hypothalamus (VMH), posterior medial nucleus of amygdala (MeAmyg), and arcuate nucleus (ARC), as well as the caudate putamen (CPu), CA1 region of the hippocampus, anterior pituitary, and uterine tissue of ovariectomized (OVX) female rats. By in situ hybridization we observed a 4.4-fold increase in oxytocin receptor mRNA levels in the VMH after 48 h of estrogen treatment when compared to OVX rats. Smaller increases were observed in the MeAmyg, hippocampus, and anterior pituitary (3.18, 1.76, and 2.55, respectively). No changes in oxytocin receptor mRNA levels were observed in the CPu or ARC after estrogen treatment. A similar finding resulted from slot-blot analysis of total mRNA extracts. In uterine tissue, 48 h of estrogen treatment increased oxytocin receptor mRNA level in the myometrium (3.13-fold). No changes in oxytocin receptor mRNA levels were observed after 12 and 24 h of estrogen treatment. These findings suggest that the estrogenic regulation of oxytocin receptor binding in both CNS and uterine tissues may in part be mediated by de novo synthesis of oxytocin receptor mRNA or by alterations in the stability of oxytocin receptor gene transcripts.

Immunocytochemical evidence for the presence of vasopressin in intermediate sized neurosecretory granules of solitary neurohypophyseal terminals in the homozygous Brattleboro rat

A single base deletion (delta G) in the vasopressin gene is the cause of diabetes insipidus in the homozygous Brattleboro rat (di/di). The resulting frameshift leads to the expression of an aberrant vasopressin precursor which is unable to enter the secretory pathway, thereby preventing vasopressin biosynthesis. In a small number of solitary magnocellular hypothalamic neurons within the supraoptic and paraventricular nuclei, the reading frame is restored by a dinucleotide (delta GA) frameshift mutation, at two separate GAGAG motifs downstream of the original G-deletion. This results in two + 1 di-vasopressin precursors that are still partially mutated within the neurophysin region. The present study provides immunocytochemical evidence which demonstrates that, within magnocellular solitary neurons of the supraoptic and paraventricular nuclei of the di/di rat, the + 1 di-vasopressin precursors can enter the secretory pathway followed by their enzymatic processing into vasopressin during axonal transport to the neural lobe. However, the cellular characteristics of biosynthesis are different from those of wild-type rats. Immunoelectron microscopical localization of vasopressin gene products in the neural lobe of did/di rats revealed their presence in neurosecretory granules, the diameter of which is intermediate (116 nm) between those of the neurosecretory granules in the di/di (80-100 nm) and wild-type (160 nm) rats.

Proopiomelanocortin gene product regulation in keratinocytes

Proopiomelanocortin (POMC) is the precursor for adrenocorticotropic hormone, melanocyte-stimulating hormones, beta-lipotropic hormone (beta LPH), and beta endorphin. These peptides can function as neurotransmitters, modulate immune responses, and affect melanogenesis. We investigated POMC expression and protein processing in normal human keratinocytes. On Northern blot analysis, the baseline expression of the 1.2-kb POMC transcript was upregulated by ultraviolet radiation (UVR) or by stimulation with interleukin-1 alpha (IL-1 alpha) or phorbol 12-tetradecanoate 13-acetate (TPA). On Western blot analysis, POMC, beta LPH, and beta-endorphin were detected in cell extracts under baseline conditions. beta LPH level increased substantially after UVR, IL-1 alpha, or TPA. Within 36 h after TPA stimulation, beta-endorphin became undetectable in cell extracts, coinciding with an increase of beta-endorphin-immunoreactive protein in the culture medium. Our data establish that keratinocytes synthesize POMC protein as well as its derivatives beta LPH and beta-endorphin, and that this process is modulated by TPA, IL-1A, and UVR. beta LPH and beta-endorphin of keratinocyte origin may thus be involved in melanogenesis and/or immunomodulation in the skin after sun exposure, and their release into the circulation may also have systemic effects.

Mutant vasopressin precursors in the human hypothalamus: evidence for neuronal somatic mutations in man

We report here the expression of mutant proteins displaying the +1 reading frame of the vasopressin and oxytocin precursors in magnocellular neurons of the human hypothalamus. Our data demonstrate a high frequency of frameshift mutations in these neurons and thus provide the first evidence of somatic mutations in neurons of the human brain. The results imply that other neuronal populations and specific genes may also undergo similar mutational events with possible consequences for neuronal functioning and pathology.