Perspectives on Strengthening Cancer Research and Control in Latin America Through Partnerships and Diplomacy: Experience of the National Cancer Institute's Center for Global Health

According to the Pan American Health Organization, noncommunicable diseases, including cancer, are the leading causes of preventable and premature death in the Americas. Governments and health care systems in Latin America face numerous challenges as a result of increasing morbidity and mortality from cancer. Multiple international organizations have recognized the need for collaborative action on and technical support for cancer research and control in Latin America. The Center for Global Health at the US National Cancer Institute (NCI-CGH) is one entity among many that are working in the region and has sought to develop a strategy for working in Latin America that draws on and expands the collaborative potential of engaged, skilled, and diverse partners. NCI-CGH has worked toward developing and implementing initiatives in collaboration with global partners that share the common objectives of building a global cancer research community and translating research results into evidence-informed policy and practice. Both objectives are complementary and synergistic and are additionally supported by an overarching strategic framework that is focused on partnerships and science diplomacy. This work highlights the overall strategy for NCI-CGH engagement in Latin America through partnerships and diplomacy, and highlights selected collaborative efforts that are aimed at improving cancer outcomes in the region.

Prevention of childhood obesity and food policies in Latin America: from research to practice

BACKGROUND

Addressing childhood obesity in Latin America requires a package of multisectoral, evidence-based policies that enable environments conducive to healthy lifestyles.

OBJECTIVE

Identify and examine key elements to translating research into effective obesity policies in Latin America.

METHODS

We examined obesity prevention policies through case studies developed with an expert in the specific policy. Policies were selected based on their level of implementation, visibility and potential impact to reduce childhood obesity. They include: (i) excise taxes on sugar sweetened beverages and energy-dense foods; (ii) front-of-package food label legislation; (iii) trans fatty acids removal from processed foods; and (iv) Ciclovías recreativas or 'open streets'. Case studies were coded to identify components that explained successful implementation and sustainability using the Complex Adaptive Health Systems framework.

RESULTS

The analysis identified key elements for effective and sustainable policy, including evidence justifying policy; evidence-based advocacy by civil society; political will; and legislation and skillful negotiations across government, academia, the private sector and civil society. Scientific evidence and evaluation played an important role in achieving tipping points for policies' launch and sustain effective implementation.

CONCLUSIONS

Well-coordinated, intersectoral partnerships are needed to successfully implement evidence-based anti-obesity policies. Prospective policy research may be useful for advancing knowledge translation.

Tackling NCD in LMIC: Achievements and Lessons Learned From the NHLBI-UnitedHealth Global Health Centers of Excellence Program

Effectively tackling the growing noncommunicable disease (NCD) burden in low- and middle-income countries (LMIC) is a major challenge. To address research needs in this setting for NCDs, in 2009, National Heart, Lung, and Blood Institute (NHLBI) and UnitedHealth Group (UHG) engaged in a public-private partnership that supported a network of 11 LMIC-based research centers and created the NHLBI-UnitedHealth Global Health Centers of Excellence (COE) Program. The Program's overall goal was to contribute to reducing the cardiovascular and lung disease burdens by catalyzing in-country research institutions to develop a global network of biomedical research centers. Key elements of the Program included team science and collaborative approaches, developing research and training platforms for future investigators, and creating a data commons. This Program embraced a strategic approach for tackling NCDs in LMICs and will provide capacity for locally driven research efforts that can identify and address priority health issues in specific countries' settings.

Grand challenges: Integrating mental health care into the non-communicable disease agenda

In the third article of a five-part series providing a global perspective on integrating mental health, Victoria Ngo and colleagues discuss the benefits and requirements of collaborative care models, where non-communicable disease and mental health care are integrated and provided in the primary care setting. Please see later in the article for the Editors' Summary

Inhibition of vasopressin V1b receptor translation by upstream open reading frames in the 5'-untranslated region

The 5'-UTR of the vasopressin V1b receptor (V1bR) mRNA contains small open reading frames (ORF) located upstream (u) of the main ORF encoding the V1bR. The ability of the three proximal uORFs to be translated into peptides and their influence on V1bR translation was examined using fusion constructs of uORFs and V5 epitope, or ATG/ATA uORF mutations in the V1bR cDNA. In vitro translation and western blot analysis after transfection of uORF1-V5 or uORF2-V5 into cells revealed that uORF1 can be translated. As predicted by computer analysis, in vitro translation using a rabbit reticulocyte/canine microsome system, immunohistochemistry and western blot in membranes of transfected cells with uORF1-V5 revealed translocation of the uORF1 peptide into membrane fractions. In vitro translation of V1bR cDNA with mutations of the two uORFs proximal to the initiating methionine, uORFs 1 and 2 (Mut 1-2), or uORF2 (Mut 2) showed significantly increased translation of a 46 kDa band corresponding to the V1bR, compared with wild-type (WT) V1bR, an effect that was attenuated by cotranslation of uORF1-V5. Consistently, VP-induced inositol phosphate formation was higher in Chinese hamster ovay cells transfected with Mut 1-2 than with WT V1bR. Immunohistochemical and western blot analysis, using an antibody against uORF1, revealed peptide immunoreactivity in rat pituitary but not in liver. Pituitary uORF immunoreactivity increased following glucocorticoid administration. The present study shows that uORFs in the 5'-UTR of the V1bR mRNA inhibit V1bR translation, and suggests that translation of a 38-amino acid membrane peptide encoded by uORF1 exerts tonic inhibition of V1bR translation.

Vasopressinergic regulation of the hypothalamic pituitary adrenal axis and stress adaptation

Vasopressin (VP) stimulates pituitary ACTH secretion through interaction with receptors of the V1b subtype (V1bR, V3R), located in the plasma membrane of the pituitary corticotroph, mainly by potentiating the stimulatory effects of corticotropin releasing hormone (CRH). Chronic stress paradigms associated with corticotroph hyperresponsiveness lead to preferential expression of hypothalamic VP over CRH and upregulation of pituitary V1bR, suggesting an important role for VP during adaptation of the hypothalamic-pituitary-adrenal (HPA) axis to stress. Vasopressinergic regulation of ACTH secretion depends on the number of V1bRs as well as coupling of the receptor to phospholipase C (PLC) in the pituitary. Regulation of V1bR gene transcription may involve a number of regulatory elements in the promoter region, of which a GAGA box was shown to be essential. Although V1bR gene transcription is necessary to maintain V1bR mRNA levels, the lack of correlation between VP binding and V1bR mRNA suggests that regulation of mRNA translation is a major regulatory step of the number of V1bRs. V1bR translation appears to be under tonic inhibition by upstream minicistrons and positive regulation through protein kinase C (PKC) activation of an internal ribosome entry site (IRES) in the 5' untranslated region (5'UTR) of the mRNA. The data provide mechanisms by which regulation of hypothalamic VP and pituitary V1bR content contribute to controlling HPA axis activity during chronic stress.

Translational regulation of the vasopressin v1b receptor involves an internal ribosome entry site

Posttranscriptional mechanisms play an important role regulating pituitary levels of vasopressin V1b receptors (V1bR) during adaptation to stress. This study investigates the involvement of an internal ribosome entry site (IRES) in the 5'untranslated region (5'UTR) on V1bR translation. Transfection of bicistronic luciferase constructs into MCF-7 cells showed marked increases in translation of the second cistron after insertion of a 499-bp fragment of the V1bR 5'UTR in the intercistronic region, independently of cap-mediated translation, indicating the presence of IRES activity. IRES-mediated translation was potentiated by the protein kinase C activators, 12-O-tetradecanoylphorbol 13-acetate (PMA) and bryostatin 1, and appears to involve phosphorylation of amino terminus of eIF4G. In Chinese hamster ovary cells transfected with pV1bR-green fluorescent protein (pV1bR-GFP), PMA increased V1bR-GFP protein levels when cap-mediated translation was inhibited by rapamycin. The effect of PMA was due to increased translation because it persisted under transcriptional blockade by actinomycin D, and it was completely abolished by cycloheximide. In addition, PMA stimulated [35S]methionine incorporation into V1bR-GFP but not beta-actin in the absence of mRNA changes. The data show that regulation of IRES activity in the 5'UTR of the V1bR mRNA probably through phosphorylation of eIF4G may serve as a mechanism for rapid changes in V1bR translation to meet physiological demands.

Transcriptional and post-transcriptional mechanisms regulating the rat pituitary vasopressin V1b receptor gene

The number of V1b vasopressin receptors (V1bR) in the anterior pituitary plays an important role during adaptation of the hypothalamic-pituitary-adrenal axis to stress in rats. Regulation of V1bR expression involves transcriptional and translational mechanisms. One of the elements mediating transcriptional activation of the rat V1bR gene is a long stretch of GAGA repeats (GAGA box) in the promoter located near the transcription start point capable of binding a protein complex of 127 kDa present in pituitary nuclear extracts. There is a lack of correlation between changes in V1bR mRNA and the number of VP binding sites, suggesting that V1bR expression depends on the efficiency of V1b R mRNA translation into protein. Two mechanisms by which the 5' untranslated region (5'-UTR) of the rat V1bR mRNA can mediate either inhibition or activation of V1bR mRNA translation have been identified. First, upstream open reading frames (ORF) present in the 5'-UTR repress translation of the major ORF encoding the V1b receptor, and secondly, an internal ribosome entry site (IRES) activates V1bR translation. Stimulation of IRES activity through protein kinase C-mediated pathways results in V1bR mRNA translation increasing V1bR protein levels. The existence of multiple loci of regulation for the V1bR at transcriptional and translational levels provides a mechanism to facilitate plasticity of regulation of the number of pituitary vasopressin receptors according to physiological demand.

Transcriptional regulation of the pituitary vasopressin V1b receptor involves a GAGA-binding protein

The role of CT repeats (inverted GAGA box) in the rat vasopressin V1b receptor (V1bR) promoter in the transcriptional regulation of this gene was studied in H32 hypothalamic cells, which express endogenous V1bR. Transfection of a 2.5-kb V1bR fragment (2161 bp upstream and 377 bp downstream of the proximal transcriptional start point) into a luciferase vector (V1bRp2.5-Luc) results in promoter activity in these cells. The 670-bp proximal promoter fragment containing the GAGA box showed maximal promoter activity, whereas deletion of the GAGA box abolished transcription. Drosophila GAGA-binding protein increased V1bR promoter activity by 11-fold when cotransfected with V1bRp2.5-Luc and increased endogenous V1bR expression. Electrophoretic mobility shift assay showed specific binding of pituitary nuclear extracts to radiolabeled GAGA oligonucleotides, which increased following restraint stress in rats, a condition associated with V1bR up-regulation. DNA-binding activity involved a protein complex because it was abolished by deoxycholate. Size-exclusion column chromatography showed a complex of 127 kDa, which dissociated into approximately 70-kDa components after deoxycholate/Nonidet P-40 treatment. This study demonstrates that interactions of GAGA-binding proteins with the GAGA box of the V1bR promoter activate V1bR gene expression and provides a potential mechanism for physiological regulation of V1bR transcription.

Regulation of pituitary corticotropin releasing hormone receptors

Corticotropin releasing hormone (CRH) stimulates pituitary ACTH secretion through type-1 CRH (CRH1) receptors. Stimulation of the hypothalamic pituitary adrenal (HPA) axis as well as increased corticotroph responsiveness during stress and adrenalectomy are associated with marked pituitary CRH binding downregulation. The presence of CRH1 receptors in the pituitary are essential to maintain ACTH secretion. Downregulation of CRH binding is associated with normal or elevated levels of CRH1 receptor mRNA and this may contribute to the maintainence of permissive levels of CRH1 receptors in the pituitary. Injection of either CRH or glucocorticoids in rats in vivo induces CRH binding and CRH1 receptor mRNA downregulation, whereas their simultaneous administration causes only transient CRH1 receptor mRNA loss. Vasopressin increases CRH1 receptor mRNA levels. This suggest that interactions between CRH, vasopressin and glucocorticoids accounts for CRH1 receptor mRNA upregulation during stress. The lack of correlation between CRH binding and CRH1 receptor mRNA indicates that the major sites for pituitary CRH1 receptor regulation are at the post-transcriptional level.

Inhibition of corticotropin releasing hormone type-1 receptor translation by an upstream AUG triplet in the 5' untranslated region

The influence of an upstream open reading frame (ORF) in the 5'-untranslated region (UTR) of the mRNA on corticotropin-releasing hormone receptor type 1 (CRHR1) translation was studied in constructs containing the 5'-UTR of CRHR1, with or without an ATG-to-ATA mutation in the upstream ORF, and the main ORF of luciferase or CRHR1. Upstream mutation in luciferase constructs increased luciferase activity when transfected into COS-7 or AtT20 cells compared with the native 5'-UTR. Transfection of CRHR1 constructs containing the upstream mutation into AtT20 or LVIP2.0zc reporter cells, resulted in higher (125)I-Tyr-oCRH binding and corticotropin-releasing hormone-stimulated cAMP production, without changes in CRHR1 mRNA levels (measured by RNase protection assay). In vitro translation of luciferase or CRHR constructs with or without mutation of the upstream ATG, and Western blot analysis with anti-luciferase and anti-CRHR1 antibodies confirmed that mutation of the upstream ATG increases translation of the main ORF. The mechanism by which the upstream ORF inhibits translation may involve translation of the upstream peptide, because in vitro translation, or transfection into LVIP2.0zc cells of a fusion construct of the upstream ORF and green fluorescent protein (GFP) yielded a band consistent with the molecular size of GFP protein. The study shows that the upstream AUG in 5'-UTR of CRHR1 mRNA inhibits receptor expression by inhibiting mRNA translation and suggests the short open reading frame in the 5'-UTR plays a role in regulating translation of the CRH receptor.

Vasopressinergic regulation of the hypothalamic-pituitary-adrenal axis: implications for stress adaptation

In addition to its role on water conservation, vasopressin (VP) regulates pituitary ACTH secretion by potentiating the stimulatory effects of corticotropin releasing hormone (CRH). The pituitary actions of VP are mediated by plasma membrane receptors of the V1b subtype, coupled to calcium-phospholipid signaling systems. VP is critical for adaptation of the hypothalamic-pituitary-adrenal (HPA) axis to stress as indicated by preferential expression of VP over CRH in parvocellular neurons of the hypothalamic paraventricular nucleus, and the upregulation of pituitary VP receptors during stress paradigms associated with corticotroph hyperresponsiveness. V1b receptor mRNA levels and coupling of the receptor to phospolipase C are stimulated by glucocorticoids, effects which may contribute to the refractoriness of VP-stimulated ACTH secretion to glucocorticoid feedback. The data suggest that vasopressinergic regulation of the HPA axis is critical for sustaining corticotroph responsiveness in the presence of high circulating glucocorticoid levels during chronic stress.

Isolation and characterization of the promoter region of the rat vasopressin V1b receptor gene

Regulation of pituitary vasopressin V1b receptors plays a critical role in regulating pituitary adrenocorticotropic hormone (ACTH) secretion during adaptation to stress. The objective of this study was to isolate the promoter regulatory region of the V1b receptor gene to better understand the molecular mechanisms involved in V1b receptor regulation. Screening of a rat genomic library using probes directed to the coding region and to the 5'UTR of the rat V1b receptor resulted in the isolation of several clones containing the 5'upstream regions of the V1b receptor cDNA. Sequencing of an 11.2 Kb fragment revealed 8.2 Kb upsteam of the reported cDNA sequence, which contains a putative promoter regulatory region. The 3' end of the clone contained 1472 base pairs corresponding to the recognized cDNA sequence, followed by 1506 bp of unknown sequence located at the end of the sixth transmembrane domain, probably corresponding to an intron, characteristic of these family of receptors. An additional 161 bp intron was found in the 5'UTR, similar to that described in the rat oxytocin receptor gene. 5'RACE and RNase protection analysis mapped two major putative transcription start points at -830 and -861 bp from the starting methionine. Analysis of the putative promoter region showed no indication of a proximal TATA box, but the presence of a CACA box, a GAGA box, several AP-1 and AP-2 sites and a cluster of Sp1 sites upstream of the AP-2 sites. A luciferase construct containing a 2.1-kb of putative promoter, and part of the 5'UTR including the first intron, showed promoter activity when transfected into COS-7, CHO and PC12 cell lines but not in AtT-20 cells. A similar construct without the intron and distal 5'UTR sequence has no promoter activity in the same cell lines. In summary, the V1b receptor gene contains at least 3 exons and 2 introns. The 5'flanking sequence contains several potential sites for transcriptional regulation, and induced luciferace activity only in constructs containing intron 1, suggesting that the latter is important for receptor gene activation. The data provide bases for future analysis of the regulatory elements controlling V1b receptor transcription.

Regulation of vasopressin V1b receptors in the anterior pituitary gland of the rat

Vasopressin secreted by parvocellular neurones of the hypothalamic paraventricular nucleus modulates pituitary adrenocorticotrophic hormone (ACTH) secretion by acting upon vasopressin V1b type receptors in the pituitary corticotroph coupled to phospholipase C. Regulation of V1b receptors contributes to the adaptation of the hypothalamic-pituitary-adrenal (HPA) axis to stress, as evidenced by the correlation between vasopressin receptor number and pituitary ACTH responsiveness. V1b receptor upregulation during chronic stress is associated with elevated circulating glucocorticoids and vasopressin expression in parvocellular neurones, suggesting that these factors control V1b receptor expression. Removal of circulating glucocorticoids by adrenalectomy causes sustained vasopressin receptor downregulation, but reduces V1b receptor mRNA only transiently. The latter effect is not mediated by increased corticotrophin-releasing hormone (CRH) and vasopressin release, since it is not prevented by lesions of the hypothalamic paraventricular nucleus. Adrenalectomy causes sustained V1b receptor loss in Brattleboro rats, which lack hypothalamic vasopressin, suggesting that vasopressin mediates V1b receptor mRNA recovery. Exogenous glucocorticoid administration downregulates pituitary vasopressin binding but increases V1b receptor mRNA and facilitates coupling of the receptor to phospholipase C, effects which may contribute to the refractoriness of vasopressin actions to glucocorticoid feedback. The lack of parallelism between changes in pituitary vasopressin binding and V1b receptor mRNA levels during manipulation of the HPA axis indicates that V1b receptor content depends on post-transcriptional mechanisms rather than steady-state V1b receptor mRNA levels. These studies suggest that interaction between glucocorticoids and vasopressin plays an important role in regulating V1b receptor mRNA expression during alterations of the HPA axis. In addition, the recent characterization of a major part of the V1b receptor gene provides a basis for studying the molecular mechanisms regulating the V1b receptor.

Glucocorticoids increase vasopressin V1b receptor coupling to phospholipase C

Vasopressin (VP) stimulates pituitary ACTH secretion after binding to V1b VP receptors (V1b-R) coupled to phospholipase C (PLC). This effect of VP on ACTH secretion, unlike that of CRH, is resistant to glucocorticoid feedback. To determine whether changes in V1b-R expression or signaling mediate the refractoriness to glucocorticoids, the effects of glucocorticoids on pituitary VP binding, V1b-R messenger RNA (mRNA) and VP-stimulated inositol phosphate (IP) formation were studied in vivo and in vitro in the rat. Dexamethasone injection for 7 days decreased VP binding but increased V1b-R mRNA, indicating that mRNA levels do not reflect receptor number. In spite of the binding loss, VP-stimulated IP formation was enhanced in dexamethasone-treated rats, suggesting that glucocorticoids increase the coupling efficiency of the V1b receptor to phospholipase C. Pretreatment of pituitary cells in vitro with dexamethasone or corticosterone, also potentiated IP formation by low and high doses of VP, indicating that glucocorticoids act directly in the pituitary and not through changes in hypothalamic factors. The effect is mediated by glucocorticoid receptors because it was blocked by glucocorticoid but not mineralocorticoid antagonists. Dexamethasone potentiated the stimulation of IP by other PLC-dependent ligands (GnRH, TRH) but not that by the calcium ionophore, ionomycin, suggesting a site of action between the receptor and PLC. After treatment with dexamethasone, in vivo or in vitro, Western blot analysis revealed marked increases in the GTP binding protein, Galpha(q), which may account for the potentiating effect of glucocorticoid on ligand-stimulated IP. The data demonstrate that glucocorticoids increase coupling of the V1b-R with PLC thereby providing a mechanism by which VP facilitates corticotroph responsiveness in spite of elevated levels of plasma glucocorticoids during stress.

Reduced activity of hypothalamic corticotropin-releasing hormone neurons in transgenic mice with impaired glucocorticoid receptor function

Loss of central glucocorticoid receptor (GR) function is thought to be involved in the development of neuroendocrine and psychiatric disorders associated with corticotropin-releasing hormone (CRH) hyperactivity. The possible causal relationship between defective GR function and altered activity of CRH neurons was studied in transgenic mice (TG) expressing antisense RNA against GR. Immunocytochemical studies showed significant reductions in CRH immunoreactive neurons in the paraventricular nucleus (PVN) and in CRH and vasopressin (AVP) stores in the external zone of the median eminence. Concomitantly, stimulus-evoked CRH secretion from mediobasal hypothalami of TG mice in vitro was reduced significantly. However, CRH mRNA levels in the PVN of TG mice were marginally lower than those in wild-type (WT) mice. 125I-CRH binding autoradiography revealed no differences between WT and TG animals in any of the brain regions that were studied. Basal plasma corticosterone (cort) levels and 125I-CRH binding, CRH-R1 mRNA, POMC mRNA, and POMC hnRNA levels in the anterior pituitary gland were similar in WT and TG mice. Intraperitoneal injection of interleukin-1beta (IL-1beta) increased plasma cort levels, CRH mRNA in the PVN, and anterior pituitary POMC hnRNA similarly in WT and TG mice. The injection of saline significantly reduced anterior pituitary CRH-R1 mRNA levels in WT mice, but not in TG mice, whereas IL-1beta produced a decrease in these mRNA levels in both strains. The data show that long-term GR dysfunction can be associated with reduced activity of CRH neurons in the PVN and decreased sensitivity of pituitary CRH-R1 mRNA to stimulus-induced downregulation. Moreover, the hypothalamic changes observed in this model suggest that impaired GR function, at least if present since early embryonic life, does not necessarily result in CRH hyperexpression characteristics of disorders such as major depression.

Interaction between glucocorticoids and corticotropin releasing hormone (CRH) in the regulation of the pituitary CRH receptor in vivo in the rat

Acute stress causes biphasic changes in corticotropin releasing hormone (CRH) receptor mRNA expression with an early decrease followed by an increase. However, in the absence of glucocorticoids in adrenalectomized rats, stress results in prolonged CRH receptor (CRH-R) mRNA loss, suggesting that interactions between glucocorticoids and hypothalamic factors are critical for regulation of CRH receptor mRNA. To address this question, CRH binding, type-1 CRH-R mRNA, POMC mRNA and POMC hnRNA expression were measured by binding autoradiography and in situ hybridization in pituitaries from intact and adrenalectomized rats. CRH-R mRNA decreased by 59% 5 h after injection of corticosterone (10 mg s.c.) and returned to basal levels by 18 h, a time when plasma corticosterone concentrations were still elevated, and CRH binding and POMC hnRNA were significantly reduced. Elevations in plasma corticosterone in the range of acute stress by injection of 2 mg s.c. caused CRH-R mRNA expression to return to near basal values by 6 h, after a 52% and 39% decrease at 2 h and 4 h. More transient changes were seen after a single injection of CRH (1 microg), with a 44% decrease in CRH-R mRNA and a 175% increase in POMC hnRNA by 2 h, returning to basal values by 4 h. The transient effect of CRH was not due to clearance of CRH from the circulation or receptor desensitization since CRH receptor mRNA expression also recovered after injection of a higher dose (10 microg) or repeated injections of CRH which caused sustained increases in plasma CRH and pituitary POMC hnRNA levels. CRH injection in adrenalectomized rats decreased CRH-R mRNA for up to 6 h, suggesting that glucocorticoids are permissive for the recovery of CRH-R mRNA. Supporting this hypothesis, simultaneous injection of corticosterone and CRH restored CRH-R mRNA expression by 4 h, and increased CRH binding 4 h and 6 h after injection. The data show that interaction between CRH and glucocorticoids counteracts individual inhibitory effects of these regulators alone, and that such effects are likely to contribute to the regulatory pattern of pituitary CRH receptors during acute stress.

Regulation of pituitary V1b vasopressin receptor messenger ribonucleic acid by adrenalectomy and glucocorticoid administration

Regulation of the number of pituitary vasopressin (VP) receptors plays an important role in controlling pituitary responsiveness during alterations of the hypothalamic pituitary adrenal axis. The mechanisms regulating these VP receptors were studied by analysis of the effects of adrenalectomy and glucocorticoid administration on V1b receptor (V1b-R) messenger RNA (mRNA) by Northern blot and by in situ hybridization in the rat. Adrenalectomy transiently decreased V1b-R mRNA levels by 18 h (77% and 62% for the 3.7-kb and 3.2-kb bands in the Northern blots, and 50% by in situ hybridization), returning to basal levels after 6 days. The decrease in V1b-R mRNA after 18 h adrenalectomy was fully prevented by dexamethasone (100 microg s.c.) but not by elimination of hypothalamic CRH and VP by paraventricular nucleus lesions or median eminence deafferentation. In sham-operated rats, dexamethasone increased receptor mRNA by 50% after 6 days. In contrast to Sprague-Dawley rats, in Brattleboro rats (di/di), which lack hypothalamic VP, adrenalectomy caused a sustained decrease in V1b-R mRNA levels (<50% of controls by 6 days). The data show that pituitary V1b-R mRNA is positively regulated by glucocorticoids and that the recovery of V1b-R mRNA levels after prolonged adrenalectomy is probably mediated by VP. In addition, the data suggest that the down-regulation of VP binding after long-term adrenalectomy is due to posttranscriptional events rather than to changes in V1b-R mRNA.

Regulation of pituitary corticotropin releasing hormone (CRH) receptor mRNA and CRH binding during adrenalectomy: role of glucocorticoids and hypothalamic factors

The role of glucocorticoids and hypothalamic factors on CRH receptor expression in the pituitary were studied by analysis of the effects of adrenalectomy and suppression of CRH and VP secretion by hypothalamic lesions in the rat. Consistent with previous in situ hybridization studies, Northern blots showed that pituitary CRH receptor mRNA decreased only transiently after adrenalectomy, falling to 51% of the control levels after 18 h, and returning to control values after 6 days (112%). The early decrease was prevented by dexamethasone injection, 100 micrograms, s.c. The role of increased levels of CRH and VP in the pituitary portal circulation on the transient decrease in CRH receptor mRNA levels after adrenalectomy were studied by in situ hybridization in rats subjected in PVN lesions or median eminence deafferentation by hypothalamic anterolateral cuts (ALC). PVN lesion (12 days) or ALC (8 days) resulted in undetectable irCRH and VP in the external zone of the median eminence and had no effect on basal levels of pituitary POMC mRNA, CRH binding and CRH receptor mRNA. In sham lesioned rats, adrenalectomy for 18 h or 4 days caused the expected increases in pituitary POMC hnRNA and mRNA, and decreases in CRH binding. CRH-R mRNA levels decreased by about 50% after 18 h adrenalectomy but returned to basal by 4 days. PVN lesion or ALC fully prevented the fall in CRH binding after 18 h or 4 days adrenalectomy and the increase in POMC mRNA after 4 days adrenalectomy, whereas only attenuated the decrease in CRH receptor mRNA and increase in POMC mRNA levels after 18 h adrenalectomy. Administration of a CRH antagonist did not affect CRH receptor mRNA and POMC hnRNA and mRNA indicating that residual CRH in the median eminence after hypothalamic surgery is not responsible for the effect of adrenalectomy. These studies confirm previous in situ hybridization studies showing that adrenalectomy causes transient decreases in pituitary CRH receptor mRNA levels. The data indicate that while increases in hypothalamic CRH secretion following glucocorticoid withdrawal mediate pituitary CRH receptor binding loss and the increase in POMC expression after long-term adrenalectomy, CRH only partially accounts for the early changes in CRH receptor mRNA and POMC mRNA.

Regulation of messenger ribonucleic acid for corticotropin releasing hormone receptor in the pituitary during stress

The mechanism regulating pituitary CRH receptors during stress was studied by analysis of the changes in CRH receptor messenger RNA (mRNA) and CRH binding after acute and repeated stress and CRH and vasopressin (VP) administration in intact and adrenalectomized rats. Acute stress caused time- and stress type-dependent changes in pituitary CRH receptor expression. In situ hybridization studies showed biphasic changes in CRH receptor mRNA after immobilization stress for 1 h and decreases by 2 h (P < 0.01). Increases (P < 0.01) were seen 4 and 8 h after the initiation of the stress, and a return to near basal levels by 12 and 18 h. A different pattern, with a decrease by 4 h (P < 0.01) and levels similar to controls after 12 and 18 h, was observed after a single ip injection of hypertonic saline (1.5 M NaCl). Binding autoradiography showed significant increases in pituitary CRH binding 4, 10, and 12 h after immobilization stress, but significant decreases 4, 12, and 18 h after ip hypertonic saline. In contrast, repeated immobilization or ip hypertonic saline for 8 or 14 days increased pituitary CRH receptor mRNA, and CRH binding was decreased. To determine the role of hypothalamic CRH and VP on these stress-induced changes, rats were injected for 14 days with CRH, VP, or their combination at doses mimicking stress levels in pituitary portal circulation (1 microgram/day sc). Repeated injection of CRH or VP increased CRH receptor mRNA and CRH binding (P < 0.05). CRH receptor mRNA levels further increased after combined administration of CRH and VP (P < 0.01), but CRH binding showed a tendency to decrease. The role of glucocorticoids on CRH receptor regulation was studied by analysis of the effects of stress on CRH receptor mRNA and CRH binding in adrenalectomized (ADX) rats with and without corticosterone replacement in the drinking water. Although in 6-day ADX rats pituitary CRH receptor mRNA levels were markedly reduced after acute immobilization, glucocorticoid replacement restored the stimulatory effect of stress to levels observed in intact rats. Similarly, a single sc injection of CRH (1 microgram) decreased CRH receptor mRNA in ADX rats but not in glucocorticoid-replaced ADX rats. CRH binding showed the expected decrease after ADX and was unchanged after stress or CRH injection. The increased pituitary CRH receptor mRNA after stress suggests that stress-induced CRH receptor down-regulation is due to increased receptor occupancy and internalization rather than to a decrease in receptor synthesis. The data suggest that increased hypothalamic secretion of CRH and VP mediates the delayed up-regulatory effect of stress on CRH receptor mRNA, and that resting levels of glucocorticoids are required for this effect. In addition, increased VP levels are permissive for the down-regulation of CRH binding induced by chronic pituitary exposure to stress levels of CRH.

Regulation of pituitary vasopressin V1b receptor mRNA during stress in the rat

Previous studies have shown a parallel relationship between pituitary vasopressin (VP) receptor content and responsiveness of the corticotroph during chronic stress. The regulation of pituitary VP receptors was further studied by analysis of V1b VP receptor mRNA levels in pituitaries of rats subjected to chronic immobilization, i.p. hypertonic saline injection (physical stress paradigms associated with increased pituitary responsiveness), and water deprivation, or to 2% saline in the drinking water (osmotic stress paradigms associated with decreased pituitary responsiveness). Northern blot hybridization with a 363 bp 32P-labelled fragment of the rV1b receptor cDNA coding sequence revealed two bands of about 3.7 and 3.2 Kb, whereas a probe directed to the 5' untranslated region recognized only the 3.7 Kb band. Repeated i.p. hypertonic saline injection, 3 times in 24 h at 8 h intervals, or daily for 8 days, increased the intensity of the 3.7 Kb band by 155 +/- 17.5% (P < 0.01) and 118 +/- 14.6% (P < 0.01), respectively, while the 3.2 Kb band increased by 122 +/- 39.3% (P < 0.01) only after 3 times injection. Smaller increases of 39 +/- 11 and 33 +/- 9% (P < 0.05) in the 3.7 Kb band were found after repeated immobilization 3 times in 24 h and 2 h for 8 days respectively. In situ hybridization studies confirmed significant increases (P < 0.05) in V1b receptor mRNA levels after 8 and 14 days repeated immobilization (63 +/- 19% and 83 +/- 10%) or i.p. hypertonic saline injection (110 +/- 13% and 73 +/- 20%). In response to acute stress, V1b receptor mRNA increased by 77 +/- 5% (3.7 Kb band) after 4 h immobilization for 1 h, whereas both bands were reduced by 49 +/- 5% and 45 +/- 5%, 4 h after a single i.p. hypertonic saline injection. The decrease in V1b receptor mRNA following a single i.p. hypertonic saline injection was prevented by pretreatment with a V1 receptor antagonist, suggesting that increased VP secretion may account for this effect. In spite of the decrease in V1b receptor mRNA following i.p. hypertonic saline injection, VP binding in pituitary membrane rich fractions, and VP-stimulated inositol phosphate formation in quartered hemipituitaries were increased by 24 and 39%, respectively. V1b receptor mRNA levels were unchanged or decreased following prolonged osmotic stimulation. These studies suggest that increased V1b receptor mRNA levels contribute to the VP receptor upregulation observed during repeated immobilization and i.p. hypertonic saline injection, whereas the lack of parallelism between V1b receptor mRNA and VP binding indicates that regulation of steady-state levels of V1b receptor mRNA is not a primary determinant in the control of pituitary VP receptor concentration during stress.

Regulation of hypothalamic and pituitary corticotropin-releasing hormone receptor messenger ribonucleic acid by adrenalectomy and glucocorticoids

The effects of adrenalectomy and glucocorticoids on the regulation of corticotropin-releasing hormone (CRH) receptor expression in the hypothalamic paraventricular nucleus (PVN) and pituitary were studied by in situ hybridization in the rat using a complementary RNA probe directed toward the coding region of the type 1 CRH receptor. Eighteen hours after adrenalectomy, CRH receptor messenger RNA (mRNA) expression in the PVN was significantly increased, whereas longer term adrenalectomy (4 and 6 days) had no effect. This transient effect of adrenalectomy was prevented by glucocorticoid replacement. In intact rats, 4 h after immobilization for 1 h or a single ip hypertonic saline injection, CRH receptor mRNA in the PVN markedly increased (P < 0.01), an effect that was unchanged by adrenalectomy (4 or 6 days) or dexamethasone injection (100 micrograms at -14 and 50 micrograms at -1 h) before stress. In the pituitary, CRH receptor mRNA levels decreased transiently after adrenalectomy (-62% after 18 h), returning to basal levels 4 or 6 days after adrenalectomy. The early decrease was prevented by glucocorticoid replacement. In intact rats, dexamethasone (100 micrograms, sc) caused a significant decrease in pituitary CRH receptor mRNA levels 2-10 h after injection, returning to basal levels after 15 h. On the other hand, dexamethasone (5-300 micrograms, sc) had no effect on pituitary CRH receptor mRNA levels 18 h after injection. The data show that although stress stimulation of CRH mRNA in the PVN is glucocorticoid independent, basal levels are likely to be under dual, transcriptional and posttranscriptional, control by glucocorticoids. In the pituitary, changes in hypothalamic CRFs probably play a major role in the control of CRH receptor mRNA levels during manipulations of circulating glucocorticoids levels. In addition, the inability of long term adrenalectomy and glucocorticoid administration to modify pituitary CRH receptor mRNA levels suggests that CRH receptor down-regulation observed under these experimental conditions depends mainly on translational and post-translational events rather than receptor mRNA levels.

A connexin-32 mutation associated with Charcot-Marie-Tooth disease does not affect channel formation in oocytes

Members of the connexin family differ most in their carboxy-termini, both with respect to sequence and length. In order to assess the contribution of this region to channel function, a series of carboxy-terminal deletion mutants were tested in the paired-oocyte expression system. Connexin-32 can be truncated by 64 amino acids without detectable loss of its known channel properties. Removal of additional amino acids results in a progressive loss of function over a stretch of 4 amino acids. In addition to this effect of length the charge of the carboxy-terminus appears to be another determinant of channel function. One of the fully functional deletion mutants, carrying a stop codon after amino acid-219, had been reported to be associated with Charcot-Marie-Tooth disease. The implications of this finding are discussed.

Regulation of pituitary vasopressin receptors during chronic stress: relationship to corticotroph responsiveness

The relationship between vasopressin (VP) receptor levels in the anterior pituitary and VP-stimulated ACTH release in vitro was studied in rats subjected to various chronic stress paradigms. The stress models used were water deprivation for 60 h and administration of 2% NaCl in the drinking water (both of which are associated with decreased pituitary ACTH responsiveness), and repeated i.p. hypertonic saline injections or repeated daily immobilization for 14 days (associated with increased ACTH responsiveness to novel stimuli). VP receptors were measured by binding of [3H]arginine-VP to anterior pituitary membrane-rich fractions, and ACTH responses to VP in collagenase dispersed anterior pituitary cells. In control rats, binding of [3H]AVP was saturable and high affinity, with a Kd of 0.45 +/- 0.05 nM and a Bmax of 138.8 +/- 8.1 fmol/mg. In pituitary membranes from stressed rats, binding affinity was unchanged, but Bmax changed according to the type of stress. While VP binding was markedly reduced after water deprivation and 2% saline (25% and 49%, respectively), it was significantly increased after repeated i.p. hypertonic saline injections and repeated immobilization (126% and 154% of controls, respectively). The changes in VP binding were associated to parallel changes in maximum VP-stimulated ACTH production in vitro, with a 34% decrease in water deprived rats and a 25% increase in hypertonic saline injected rats. The potentiating effect of VP on corticotropin releasing hormone-stimulated ACTH was also reduced in cells from water-restricted rats, and increased in cells from rats given repeated injections of hypertonic saline. The data show a direct relationship between changes in corticotroph responsiveness and changes in pituitary VP receptors during chronic stress, suggesting that pituitary VP receptor regulation is involved in the adaptation of the HPA axis during chronic stress.

Mutational analysis of gap junction formation

The paired oocyte cell-cell channel assay was used to investigate the mechanisms involved in the process of formation of gap junction channels. Single oocytes, injected with connexin-specific mRNAs, accumulate a pool of precursors from which cell-cell channels can form rapidly upon pairing. Several lines of evidence, including immunohistochemistry and surface labeling, indicate that part of this precursor pool is located in the cell membrane, probably in the form of closed hemichannels. The homophilic binding of hemichannels to each other can be mimicked by synthetic peptides representing the extracellular loop sequences of connexin32. The peptides specifically suppress channel formation. A crucial role is established for the six cysteines in the extracellular domains that are conserved in all vertebrate gap junction proteins. Change of any of these cysteines into serines results in absolute loss of function of the mutant connexin. The effects of thiol-specific reagents on channel formation suggest that docking and/or opening of channels involves disulfide exchange. Several of the variable amino acids in the extracellular loop sequences were found to determine specificity of connexin-connexin interactions.

Cell/cell channel formation involves disulfide exchange

The oocyte cell/cell-channel assay was used to identify amino acids involved in the process of cell/cell-channel formation. The expression of the rat liver gap-junction protein, connexin 32, in single oocytes, results in the accumulation of a pool of channel precursors. Upon pairing of such oocytes, cell/cell channels form rapidly from this pool. The rate of formation is affected by thiol-specific reagents and the pH. This suggests the involvement of extracellular cysteine residues in the channel formation process. Two connexin-32 mutants were generated by site-directed mutagenesis in which cysteine residues were replaced by serine. Both mutant connexins were unable to form cell/cell channels. Thus, the cysteine residues appear to play an important role in the channel formation process.

Gating properties of connexin32 cell-cell channels and their mutants expressed in Xenopus oocytes

Carboxyl-terminal deletion mutants of the gap junction protein connexin32 were tested in the oocyte cell-cell channel assay. Oocytes expressing a mutant lacking 58 carboxyl terminal amino acids were found to exhibit junctional conductances of the same magnitude as oocytes expressing wild-type connexin32. The gating properties of the channels formed by this mutant of connexin32 with respect to transjunctional voltage and cytoplasmic acidification are indistinguishable from those found with wild-type connexin32 channels. This includes a novel pH-dependent voltage gate. In another mutant, two carboxyl terminal serine residues, Ser233 and Ser240, were replaced by Asn residues. This double mutant has properties indistinguishable from wild-type connexin32, suggesting that phosphorylation of either of these serines is not required for channel opening.

Formation of hybrid cell-cell channels

The oocyte cell-cell channel assay was used to demonstrate that connexin-43 is a cell-cell channel-forming protein as previously shown for connexin-32. Expression of connexin-32 in one and connexin-43 in the other oocyte of a pair results in the formation of junctional conductances at rates similar to those observed when only one or the other connexin is expressed in both oocytes of a pair. This suggests that hybrid cell-cell channels form in the oocyte system. Hybrid channels also form when a connexin-43 mRNA-injected oocyte is paired with a noninjected oocyte expressing endogenous connexin. The latter hybrids have properties apparently contributed by both types of hemichannels. Pure connexin-43 channels are not voltage gated, whereas pure oocyte channels are voltage dependent; hybrids of these channels rectify.