Neuropeptides in the amphibian brain.
Explore the source record for details and available documents.
Amino Acid Sequence↗
SEARCH · Search PubMed
Results for “Pro-Opiomelanocortin”
Search indexed PubMed citations on genomics, clinical trials, systematic reviews and public health. Explore titles, authors and supplied subject terms, then open the PubMed record.
Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.
Routing and release of input and output messengers of peptidergic systems.
Explore the source record for details and available documents.
Animals↗
Evidence for orphan nuclear receptor TR4 in the etiology of Cushing disease.
Cushing disease (CD) is a life-threatening disorder attributed to excess pituitary tumor-derived adrenocorticotrophic hormone (ACTH) and adrenal steroid secretion caused by pituitary tumors. Whereas CD was first described in 1932, the underlying genetic basis driving tumor growth and ACTH secretion remains unsolved. Here, we show that testicular orphan nuclear receptor 4 (TR4, nuclear receptor subfamily 2, group C, member 2) is overexpressed in human corticotroph tumors as well as in human and mouse corticotroph tumor cell lines. Forced overexpression of TR4 in both human and murine tumor cells increased proopiomelanocortin transcription, ACTH secretion, cellular proliferation, and tumor invasion rates in vitro. Conversely, knockdown of TR4 expression reversed all phenotypes. Mechanistically, we show that TR4 transcriptionally activates proopiomelanocortin through binding of a direct repeat 1 response element in the promoter, and that this is enhanced by MAPK-mediated TR4 phosphorylation. In vivo, TR4 overexpression promotes murine corticotroph tumor growth as well as enhances ACTH and corticosterone production, whereas TR4 knockdown decreases circulating ACTH and corticosterone levels in mice harboring ACTH-secreting tumors. Our findings directly link TR4 to the etiology of corticotroph tumors, hormone secretion, and cell growth as well as identify it as a potential target in the treatment of CD.
ACTH-Secreting Pituitary Adenoma↗
A mammalian tripartite enhancer cluster controls hypothalamic Pomc expression, food intake, and body weight.
Food intake and energy balance are tightly regulated by a group of hypothalamic arcuate neurons expressing the proopiomelanocortin (POMC) gene. In mammals, arcuate-specific POMC expression is driven by two cis-acting transcriptional enhancers known as nPE1 and nPE2. Because mutant mice lacking these two enhancers still showed hypothalamic Pomc mRNA, we searched for additional elements contributing to arcuate Pomc expression. By combining molecular evolution with reporter gene expression in transgenic zebrafish and mice, here, we identified a mammalian arcuate-specific Pomc enhancer that we named nPE3, carrying several binding sites also present in nPE1 and nPE2 for transcription factors known to activate neuronal Pomc expression, such as ISL1, NKX2.1, and ERα. We found that nPE3 originated in the lineage leading to placental mammals and remained under purifying selection in all mammalian orders, although it was lost in Simiiformes (monkeys, apes, and humans) following a unique segmental deletion event. Interestingly, ablation of nPE3 from the mouse genome led to a drastic reduction (>70%) in hypothalamic Pomc mRNA during development and only moderate (<33%) in adult mice. Comparison between double (nPE1 and nPE2) and triple (nPE1, nPE2, and nPE3) enhancer mutants revealed the relative contribution of nPE3 to hypothalamic Pomc expression and its importance in the control of food intake and adiposity in male and female mice. Altogether, these results demonstrate that nPE3 integrates a tripartite cluster of partially redundant enhancers that originated upon a triple convergent evolutionary process in mammals and that is critical for hypothalamic Pomc expression and body weight homeostasis.
Animals↗
Proopiomelanocortin in the helminth Schistosoma mansoni. Synthesis of beta-endorphin, ACTH, and alpha-MSH. Existence of POMC-related sequences.
Explore the source record for details and available documents.
Adrenocorticotropic Hormone↗
Cerebrospinal fluid and plasma concentrations of POMC-related peptides in multiple sclerosis.
Explore the source record for details and available documents.
Adult↗
Diurnal corticotropin-releasing hormone mRNA variation in the hypothalamus exhibits a rhythm distinct from that of plasma corticosterone.
The hypothalamopituitary-adrenal axis exhibits a diurnal rhythm as witnessed by the daily excursion of corticosterone in plasma. The rhythm appears to be mediated largely by the stimulation of CRH neurons in the paraventricular nucleus (PVN) of the hypothalamus. In the present study, we investigated the effects of circadian influence on CRH mRNA levels in the paraventricular hypothalamus. Animals were sacrificed through a 24-hour period to establish a detailed time course of CRH mRNA fluctuations. Levels of both type I and type II corticosterone receptor mRNAs were also measured in this area to see whether changes correlate with that of CRH mRNA. Plasma levels of ACTH were quantified as an index for CRH peptide secretion. The results indicate that changes in ACTH closely paralleled alterations in corticosterone levels with an increasing trend starting at 1 PM, suggesting that the diurnal secretory drive commences around this time. The CRH mRNA rhythm as determined by RNase protection assays appeared to change in an anticipatory fashion to these endocrine fluctuations, increasing during the light phase and reaching maximal levels just prior to dark (5-6 PM). An abrupt decrease of 30% in the CRH mRNA content was detected in the hypothalamus within 2 h after dark (8 PM) and coincided with the peak of plasma corticosterone levels. However, other periodic variations in the CRH mRNA content were not accompanied by changes in plasma corticosterone. Neither types of corticosterone receptor mRNAs showed any diurnal change suggesting that the expression of steroid receptors in the hypothalamus is not regulated by circadian influences. We conclude that CRH mRNA levels fluctuate diurnally but are inversely related to corticosterone levels only in the early evening.
Adrenocorticotropic Hormone↗
Intrahippocampal colchicine alters hypothalamic corticotropin-releasing hormone and hippocampal steroid receptor mRNA in rat brain.
The hippocampus appears to be an important modulator of the negative feedback effects of glucocorticoids on the hypothalamic-pituitary-adrenal axis. It is not known if hippocampal subfields CA1-4 or the dentate gyrus differentially alter gene expression of corticotropin-releasing hormone (CRH) in the paraventricular nucleus (PVN) of the hypothalamus. We, therefore, examined the effects of selective destruction of dentate gyrus granule cells, which send excitatory glutaminergic inputs to subfields CA4, CA3 and CA2, on CRH expression in the PVN. To determine the possible involvement of steroid receptors in the regulation of CRH expression, we examined the effects of intrahippocampal colchicine on gene expression of the mineralocorticoid (MR; type I) and glucocorticoid (GR; type II) receptors in hippocampal CA fields and dentate gyrus. Colchicine produced a selective loss of dentate gyrus granule cells without affecting pyramidal cells in CA1-4 as early as 1 day after injection; granule cells were completely destroyed after 3 days. CRH mRNA levels were reduced by 38-48% in the PVN 2-14 days after colchicine. MR mRNA levels were decreased in dorsal and ventral CA fields 1-7 days after colchicine. GR mRNA levels were relatively unchanged, showing a slight decrease only in dorsal CA fields on days 2-7. Unexpectedly, CRH was transiently expressed in dorsal and ventral CA fields 1-3 days after colchicine. In the same time period, mRNA levels of inositol 1,4,5-trisphosphate kinase were decreased, suggesting that increases in neural metabolic activity, indicated by this marker, are not responsible for the transient CRH effect. The results suggest that the dentate gyrus is important for maintenance of steroid hormone receptor mRNA levels in the hippocampus and CRH expression in the hypothalamic PVN, and that CRH gene expression is differentially regulated in the hypothalamus and hippocampus.
Adrenocorticotropic Hormone↗
In vitro regulation of pituitary ACTH secretion in inflammatory disease susceptible Lewis (LEW/N) and inflammatory disease resistant Fischer (F344/N) rats.
We have previously shown that susceptibility to inflammatory disease in Lewis (LEW/N) rats is related to their limited hypothalamic-pituitary-adrenal (HPA) axis responses to a variety of inflammatory stimuli, while the relative resistance to inflammatory disease in Fischer (F344/N) rats is related to their potent HPA axis responses to these same stimuli. In vivo studies also showed that LEW/N pituitary ACTH responses to exogenous corticotropin-releasing hormone (CRH) were blunted compared to F344/N. To determine if there is a fundamental difference in pituitary corticotroph function between the two strains, independent of other factors influencing the HPA axis, we compared ACTH responses to a variety of stimuli in LEW/N and F344/N primary pituitary cell cultures. Here we show that in vitro basal ACTH secretion and peak ACTH response to CRH, forskolin and 8-bromo-cAMP are 50% lower in LEW/N than F344/N rats. However, these findings can be explained by other observations: diminished basal ACTH content, POMC mRNA, and a decreased number of corticotrophs, in pituitary cell cultures from LEW/N compared to F344/N rats. In addition, LEW/N corticotrophs were more sensitive to dexamethasone and to corticosterone suppression of CRH-stimulated ACTH secretion compared to F344/N. The data support the possibility of an HPA axis defect in LEW/N rats at the pituitary level which could be secondary to prolonged understimulation by hypothalamic CRH, or could also be partially related to enhanced glucocorticoid feedback inhibition.
8-Bromo Cyclic Adenosine Monophosphate↗
Survey of neuropeptide gene expression in tumor cell lines.
The presence of 3 different neuropeptide mRNAs with a strict cell-specific expression in vivo was investigated in 13 tumor cell lines from neuroendocrine and in 23 tumor cell lines from non-neuroendocrine origin. Northern blots showed no expression of mRNA for vasopressin (VP) in the 36 tested cell lines. Very low oxytocin (OT) mRNA hybridization signals were detected in the rat pituitary tumor cell line GH4C2 and the rat pancreas tumor cell line RIN5. Both the rat pituitary tumor cell line AtT-20 and the human myeloid leukemia cell line K562, contained proopiomelanocortin (POMC) mRNA. The low incidence of VP, OT and POMC gene expression in the tested tumor cell lines was not influenced by treatments inducing differentiation. In contrast, the cholecystokinin (CCK) gene which is widely present in nervous and endocrine systems was abundantly expressed in the human primitive neuroepithelioma cell line SK-N-MC and its clonal derivative SK-N-MC-IX-C. The results indicate that the expression of neuropeptide genes is very rare in tumor cell lines. The lack of expression in undifferentiated cells agrees with the appearance of expression after day 13 of the embryogenesis when maturation of neurons begins.
Animals↗
The effect of insulin-induced hypoglycemia on gene expression in the hypothalamic-pituitary-adrenal axis of the rat.
This study has examined the effects of insulin-induced hypoglycemia on expression of the CRH, arginine vasopressin, and POMC genes and corresponding peptides in freely moving, unanesthetized, male Sprague-Dawley rats. Animals were infused with 150 mM NaCl for 3 days before the experimental day and were then administered insulin (4 U/kg) or saline iv. In one experiment animals were killed 0, 30, 60, or 90 min after insulin or saline, and RNA was isolated from anterior pituitary, cerebral cortex, and punches of the hypothalamic paraventricular and supraoptic nuclei. In a second experiment, animals were killed 90 min after insulin or saline treatment, and RNA was isolated from whole hypothalami. RNA was analyzed by Northern blot. Plasma glucose fell from 106 +/- 5 to 38 +/- 2 mg/dl after insulin administration and remained low for the duration of the experiment. Plasma levels of ACTH, corticosterone, and vasopressin were 10-, 6-, and 4-fold higher, respectively, in the insulin-treated vs. control animals (by analysis of variance, P less than 0.0001 in all cases), while plasma CRH was unchanged. During hypoglycemia POMC mRNA levels were 1.8-fold higher in the insulin-treated group (by analysis of variance, P less than 0.025). In contrast, paraventricular nucleus, whole hypothalamic, and parietal cortex CRH mRNA and vasopressin mRNA were unchanged. These data support previous studies which indicated that POMC gene expression is increased by hypoglycemia. However, we found no evidence for an increase in paraventricular nucleus or cerebral cortex CRH mRNA expression during hypoglycemia-associated stimulation of the hypothalamic-pituitary-adrenal axis, suggesting that another factor(s) may mediate the observed increase in POMC gene expression.
Adrenocorticotropic Hormone↗
Beta-endorphin inhibits hypoglycemia-induced gene expression of corticotropin-releasing factor in the rat hypothalamus.
Endogenous opioid peptides have a role in the regulation of the hypothalamic-pituitary-adrenal axis. Recently, beta-endorphin (EP) has been thought to inhibit CRF release in vivo and in vitro. In the present study we examined the effects of central administration of EP on ACTH secretion and gene expression of both CRF in the hypothalamus and POMC in the anterior pituitary gland (AP) during basal and insulin-induced hypoglycemia in pentobarbital-anesthetized rats. Administration of EP in the lateral ventricle decreased basal CRF levels in the median eminence and inhibited basal and hypoglycemia-induced ACTH secretion in a dose-dependent manner. Hypoglycemia-induced POMC mRNA levels in the AP and CRF mRNA levels in the hypothalamus were also dose-dependently inhibited by the administration of EP. The inhibitory effect of EP was reversed by naloxone. These results suggest that 1) central administration of EP acts through the opioid receptor to inhibit hypoglycemia-induced CRF gene expression in the hypothalamus and CRF release, which results in a decrease in ACTH secretion and POMC mRNA levels in the AP; and 2) the active site of EP is the CRF neuron in the paraventricular nucleus.
Adrenocorticotropic Hormone↗
Ectopic corticotropin-releasing hormone produced by a transfected cell line chronically activates the pituitary-adrenal axis in transkaryotic rats.
Hypothalamic CRH is the primary positive regulatory factor of the pituitary-adrenal axis. The purpose of our study was to analyze the chronic effects of CRH on the production and secretion of POMC peptides from both the anterior lobe (AL) and neurointermediate lobe (NIL) of the pituitary by mimicking the syndrome of ectopic CRH secretion from neuroendocrine tumors. We first generated stably transfected W2 medullary thyroid carcinoma cell lines with a rat CRH expression vector under the transcriptional control of a cytomegalovirus gene promoter. These cell lines constitutively expressed the foreign gene, accurately processed the encoded prepro-CRH, and secreted biologically active CRH with an estimated potency equivalent to that of synthetic CRH-(1-41)NH2. The cell line designated W2CRH-7 was implanted sc in the syngeneic rat strain WAG/Rij and produced tumors that abundantly secreted CRH into the peripheral circulation. Four weeks postimplantation, W2CRH-7, but not wild-type W2, cells caused significant increases in the AL content of beta-endorphin-like immunoreactivity comparable to that caused by adrenalectomy (ADX). Plasma ACTH and serum beta-endorphin-like immunoreactivity were increased to a greater extent by ADX than by W2CRH-7 cell implantation. The NIL of both male and female rats showed either no change or a tendency to decreased beta-endorphin concentrations with no change in the acetylation or carboxy-shortening profiles judged by cation exchange chromatography in response to the ectopic CRH treatment. Rats of both sexes maintained a profound activation of the pituitary adrenal axis up to 16 weeks postimplantation, with normalized adrenal gland weights 5 times that of controls. The chronic secretion of CRH by W2CRH-7 cells resulted in a complete cessation of body growth in all rats up to the maximum time tested of 16 weeks. The lack of growth was partly ameliorated by concomitant ADX, suggesting an important role for adrenal glucocorticoids in these effects. We conclude that 1) the transplantable W2CRH-7 cell line provides a highly effective and reproducible means of sustained CRH treatment that mimics the syndrome of ectopic CRH expression by neuroendocrine tumors; 2) AL corticotrophs respond to chronic CRH by a sustained production and secretion of POMC peptides, leading to a marked adrenal cortical hyperplasia, with no evidence of biologically significant desensitization; 3) chronic CRH tends to decrease the NIL content of beta-endorphin,with remarkably little effect on posttranslational processing; and 4) the syndrome of chronic ectopic CRH in WAG/Rij rats includes a cessation of body growth at least partly due to products of the adrenal glands.
Adrenalectomy↗
Lymphocyte-derived adrenocorticotropin is insufficient to stimulate adrenal steroidogenesis in hypophysectomized rats.
Cells of the immune system can produce and respond to peptide hormones associated with the endocrine system. However, the physiological significance of these endocrine-immune interactions is not known. It has been postulated that cells of the immune system, when stimulated with viruses that induce interferon-alpha, produce sufficient levels of ACTH to stimulate adrenal steroidogenesis and, thus, function as an auxiliary source of ACTH that may have a role in the response to stress. However, we have confirmed that levels of ACTH-related peptides produced by immunocompetent cells are far lower than those produced by the pituitary, raising questions about the ability of lymphocyte-derived ACTH to stimulate adrenal function. Furthermore, we have rigorously examined this issue using intact and hypophysectomized rats treated with Newcastle disease virus. Although high levels of interferon-alpha were produced by both intact and hypophysectomized rats, and the plasma corticosterone concentration increased dramatically in intact animals, corticosterone remained undetectable in hypophysectomized rats. The lack of a corticosterone response in these animals was not due to adrenal insensitivity to ACTH, as shown by a normal rise in corticosterone following Cosyntropin injection 8 h after hypophysectomy. The findings demonstrate that levels of ACTH produced by nonpituitary sources in response to viral infection are not sufficient to stimulate adrenal steroidogenesis.
Adrenal Cortex Hormones↗
A certain step of proteolytic processing of proopiomelanocortin occurs during the transition between two distinct stages of secretory granule maturation in rat anterior pituitary corticotrophs.
To obtain antibodies specific for precursor POMC and its cleaved peptides, we prepared synthetic peptides corresponding to the cleavage site (ST-1) between ACTH and beta-lipotropic hormone moieties of POMC and to amidated joining peptide (JP; ST-3) and generated their polyclonal antibodies in rabbits. The anti-ST-1 serum immunoprecipitated only POMC in the extract of AtT-20 cells. In addition to a similar immunoprecipitation examination, an immunoabsorption test showed that anti-ST-3 serum recognizes cleaved peptides, 16K amino-terminal peptide, and JP, but not POMC precursor. Double immunolabeling with gold particles of different sizes for the precursor POMC and its cleaved peptides revealed that the former was localized in electron-dense secretory granules, whereas the latter was found in the electron-lucent secretory granules in the same ultrathin cryosections. Colocalization of POMC and its cleaved peptides in the same secretory granules was rarely observed. Only POMC immunolabeling was detected in the Golgi cisternae. These results suggest that a certain step of proteolytic processing of POMC occurs in the secretory granules during the transition between the two distinct stages of secretory granule maturation in the rat anterior pituitary corticotroph.
Adrenocorticotropic Hormone↗
Presence and regulation of a truncated proopiomelanocortin gene transcript in rat pancreatic islets.
The demonstration of proopiomelanocortin-(POMC-) derived peptides in the endocrine pancreas suggests a local biosynthesis of these peptides. Using Northern blot analysis we demonstrated a 800 nucleotide POMC-like mRNA species. The POMC-like mRNA was demonstrable in a part of the pancreatic islets by the in situ hybridization technique. A small number of single cells within the exocrine pancreas were also found to give positive hybridization signals. Isolated islets were incubated under normoglycemic conditions with dibutyryl-cAMP (3mM) or dexamethasone (0.1mM) for 4 h. Dibutyryl-cAMP significantly (p < 0.01) increased the POMC-like mRNA content to 177 +/- 39.1% of the control whereas dexamethasone decreased it to 66.9 +/- 11.4% of the control. In vivo treatment of adult rats with 80 micrograms dexamethasone over 3 days showed also a reduction of the POMC-like mRNA level in the islets. In conclusions, the POMC gene is expressed in adult rat islets and can be regulated by dexamethasone and dibutyryl-cAMP. Whether the truncated POMC-like mRNA reported here is the source of the biosynthetic POMC-like products detected in the islets is not yet known.
Animals↗
Acute unilateral nephrectomy elicits a specific increase in plasma of peptides derived from the N-terminal region of proopiomelanocortin.
Acute unilateral nephrectomy (AUN) causes natriuresis from the contralateral kidney through neurohumoral reflex pathways that involve an increase in the plasma of peptides derived from the N-terminal region of the adrenocorticotropic hormone (ACTH)/beta-endorphin precursor proopiomelanocortin (POMC). To determine the specificity of these humoral changes, the concentrations in plasma of ACTH and two peptides arising from the N-terminal fragment (NTF) of POMC, NTF32-49 and gamma-melanocyte-stimulating hormone (gamma-MSH), and of another natriuretic peptide, atrial natriuretic peptide (ANP), were measured by RIA with highly specific antisera to these epitopes. Group I experiments followed the course of sodium excretion (UNaV) for 120 min after AUN or sham nephrectomy. UNaV more than doubled within 60 min of AUN, and this natriuresis was maintained for the remainder of the experiment, whereas UNaV in sham rats did not change. There was no difference in plasma immunoreactive (ir) ACTH or ir-ANP concentrations between sham and AUN rats 120 min after the procedure, but plasma ir-NTF concentration was double in AUN rats compared with sham (P < 0.03). In Group II experiments, animals were killed 30, 60, 90, or 120 min after AUN and the urinary response related to peptide concentrations in plasma. UNaV rose rapidly after AUN, reaching a maximum value within 45 min that again was double the control value and remained stable for the duration of the experiment, up to 120 min after AUN. There was no significant change in ir-ACTH or ir-ANP at any point after AUN compared with values in sham AUN rats. However, plasma concentrations of both ir-NTF and ir-gamma-MSH were elevated 30 min after AUN and reached values at 120 min that were again double the values in sham rats (P < 0.05 for both).(ABSTRACT TRUNCATED AT 250 WORDS)
Acute Kidney Injury↗
Analysis of gastrinomas by immunohistochemistry and in situ hybridization histochemistry.
Gastrinomas from 25 patients were examined by immunohistochemistry (IHC) and in situ hybridization histochemistry (ISH). Most patients (84%) presented with the Zollinger-Ellison syndrome. Six had multiple endocrine neoplasia type I (MEN-I). Twelve patients (48%) had duodenal primaries and 11 of 12 of these had metastases to regional lymph nodes and/or liver in spite of the small sizes of the primary tumors (mean size of 0.9 cm). Five patients had pancreatic gastrinomas and eight patients had metastatic tumor in regional lymph nodes or liver at surgery but a primary was not found. IHC and ISH analyses showed that all cases were positive for gastrin protein and 24 of 25 (96%) expressed gastrin mRNA that was easily detected in formalin-fixed, paraffin-embedded tissue sections. Both benign and malignant tumors expressed alpha subunit of human chorionic gonadotropin protein (alpha-HCG). However, only malignant gastrinomas (29%) expressed adrenocorticotropic hormone protein or proopiomelanocortin (POMC) mRNA. ISH and Northern hybridization analysis revealed that chromogranin A mRNA was the most common member of the chromogranin/secretogranin (Cg/Sg) family which was expressed in both benign and malignant gastrinomas. These results indicate that duodenal gastrinomas are common in both sporadic and MEN-1-associated cases, and small duodenal primaries may be associated with extensive regional lymph node and liver metastases. Expression of ACTH/POMC protein and mRNA was consistently associated only with malignant gastrinomas while gastrin protein, gastrin mRNA and Cgs/Sgs mRNAs were readily detected in both benign and malignant gastrinomas.
Adrenocorticotropic Hormone↗