Balance of Gata3 and Ramp2 in hepatocytes regulates hepatic vascular reconstitution in postoperative liver regeneration

BACKGROUND & AIMS

Post-hepatectomy liver failure (PHLF) leads to poor prognosis in patients undergoing hepatectomy, with hepatic vascular reconstitution playing a critical role. However, the regulators of hepatic vascular reconstitution remain unclear. In this study, we aimed to investigate the regulatory mechanisms of hepatic vascular reconstitution and identify biomarkers predicting PHLF in patients undergoing hepatectomy.

METHODS

Candidate genes that were associated with hepatic vascular reconstitution were screened using adeno-associated virus vectors in Alb-Cre-CRISPR/Cas9 mice subjected to partial hepatectomy. The biological activities of candidate genes were estimated using endothelial precursor transfusion and associating liver partition and portal vein ligation for staged hepatectomy (ALPPS) models. The level of candidates was detected in biopsies from patients undergoing ALPPS. Risk factors for PHLF were also screened using retrospective data.

RESULTS

Downregulation of Gata3 and upregulation of Ramp2 in hepatocytes promoted the proliferation of liver sinusoidal endothelial cells and hepatic revascularization. Pigment epithelium-derived factor (PEDF) and vascular endothelial growth factor A (VEGFA) played opposite roles in regulating the migration of endothelial precursors from bone marrow and the formation of new sinusoids after hepatectomy. Gata3 restricted endothelial cell function in patient-derived hepatic organoids, which was abrogated by a Gata3 inhibitor. Moreover, overexpression of Gata3 led to higher mortality in ALPPS mice, which was improved by a PEDF-neutralizing antibody. The expression of Gata3/RAMP and PEDF/VEGFA tended to have a negative correlation in patients undergoing ALPPS. A nomogram incorporating multiple factors, such as serum PEDF/VEGF index, was constructed and could efficiently predict the risk of PHLF.

CONCLUSIONS

The balance of Gata3 and Ramp2 in hepatocytes regulates the proliferation of liver sinusoidal endothelial cells and hepatic revascularization via changes in the expression of PEDF and VEGFA, revealing potential targets for the prevention and treatment of PHLF.

IMPACT AND IMPLICATIONS

In this study, we show that the balance of Gata3 and Ramp2 in hepatocytes regulates hepatic vascular reconstitution by promoting a shift from pigment epithelium-derived factor (PEDF) to vascular endothelial growth factor A (VEGFA) expression during hepatectomy- or ALLPS (associating liver partition and portal vein ligation for staged hepatectomy)-induced liver regeneration. We also identified serum PEDF/VEGFA index as a potential predictor of post-hepatectomy liver failure in patients who underwent hepatectomy. This study improves our understanding of how hepatocytes contribute to liver regeneration and provides new targets for the prevention and treatment of post-hepatectomy liver failure.

Sustained Activation of CLR/RAMP Receptors by Gel-Forming Agonists

Background: Adrenomedullin (ADM), adrenomedullin 2 (ADM2), and CGRP family peptides are important regulators of vascular vasotone and integrity, neurotransmission, and fetoplacental development. These peptides signal through CLR/RAMP1, 2, and 3 receptors, and protect against endothelial dysfunction in disease models. As such, CLR/RAMP receptor agonists are considered important therapeutic candidates for various diseases. Methods and Results: Based on the screening of a series of palmitoylated chimeric ADM/ADM2 analogs, we demonstrated a combination of lipidation and accommodating motifs at the hinge region of select peptides is important for gaining an enhanced receptor-activation activity and improved stimulatory effects on the proliferation and survival of human lymphatic endothelial cells when compared to wild-type peptides. In addition, by serendipity, we found that select palmitoylated analogs self-assemble to form liquid gels, and subcutaneous administration of an analog gel led to the sustained presence of the peptide in the circulation for >2 days. Consistently, subcutaneous injection of the analog gel significantly reduced the blood pressure in SHR rats and increased vasodilation in the hindlimbs of adult rats for days. Conclusions: Together, these data suggest gel-forming adrenomedullin analogs may represent promising candidates for the treatment of various life-threatening endothelial dysfunction-associated diseases such as treatment-resistant hypertension and preeclampsia, which are in urgent need of an effective drug.

Function of the cytoplasmic tail of human calcitonin receptor-like receptor in complex with receptor activity-modifying protein 2

Receptor activity-modifying protein 2 (RAMP2) enables calcitonin receptor-like receptor (CRLR) to form an adrenomedullin (AM)-specific receptor. Here we investigated the function of the cytoplasmic C-terminal tail (C-tail) of human (h)CRLR by co-transfecting its C-terminal mutants into HEK-293 cells stably expressing hRAMP2. Deleting the C-tail from CRLR disrupted AM-evoked cAMP production or receptor internalization, but did not affect [(125)I]AM binding. We found that CRLR residues 428-439 are required for AM-evoked cAMP production, though deleting this region had little effect on receptor internalization. Moreover, pretreatment with pertussis toxin (100ng/mL) led to significant increases in AM-induced cAMP production via wild-type CRLR/RAMP2 complexes. This effect was canceled by deleting CRLR residues 454-457, suggesting Gi couples to this region. Flow cytometric analysis revealed that CRLR truncation mutants lacking residues in the Ser/Thr-rich region extending from Ser(449) to Ser(467) were unable to undergo AM-induced receptor internalization and, in contrast to the effect on wild-type CRLR, overexpression of GPCR kinases-2, -3 and -4 failed to promote internalization of CRLR mutants lacking residues 449-467. Thus, the hCRLR C-tail is crucial for AM-evoked cAMP production and internalization of the CRLR/RAMP2, while the receptor internalization is dependent on the aforementioned GPCR kinases, but not Gs coupling.

The role of peptides and receptors of the calcitonin family in the regulation of bone metabolism

The 'calcitonin family' is a group of peptide hormones that share structural similarities with calcitonin, and includes calcitonin gene-related peptide (CGRP), amylin, adrenomedullin and adrenomedullin 2 (intermedin). These hormones are produced by different tissues, with calcitonin being produced in thyroid C cells, alphaCGRP predominantly in neural tissue, amylin in beta-islet cells of the pancreas and adrenomedullin in many tissues and cell types. Bone appears to be a common target for all the peptides of the calcitonin family, although the specific bone effects of the peptides vary. Administration of calcitonin produces rapid lowering of serum calcium levels, mainly through inhibition of bone resorption by osteoclasts. In vitro and in a number of animal experimental models, amylin and CGRP are also effective in inhibiting osteoclast activity and bone resorption. Amylin, adrenomedullin and CGRP can also affect cells of the osteoblast lineage, inducing osteoblast proliferation and promoting bone formation. Receptors for the peptides of the calcitonin family are formed by heterodimerization of the calcitonin receptor (CTR) or calcitonin receptor-like receptor (CLR) with receptor activity modifying proteins (RAMPs). Although the different combinations of these proteins create receptors with distinct ligand specificities, there is a degree of cross-reactivity and the receptors are able to bind other ligands from the family, usually with lower affinity. Analysis of the expression of the receptors for the calcitonin family in 16 samples of human osteoblasts showed high levels of CLR and RAMP1, low levels of RAMP2 and no expression of RAMP3 or CTR. Recent studies of the bone phenotype of knockout animals lacking the calcitonin, alphaCGRP or amylin gene indicated that in this experimental system the main physiological role of amylin in bone is the inhibition of bone resorption, that of CGRP is the activation of bone formation, while calcitonin, unexpectedly appears to be inhibiting bone formation without affecting bone resorption. Further investigations will be required to determine the mechanisms of action of calcitonin peptides in bone and their significance to human bone physiology.

Unaltered mRNA expression of calcitonin-like receptor and receptor activity modifying proteins in human arteries in stroke and myocardial infarction

Calcitonin-like receptor (CL-R) is a functional CGRP1-receptor when complexed with RAMP1 or an adrenomedullin-receptor or when complexed with RAMP2 or RAMP3. This study was carried out 1. to set up a method to examine the relative quantity of mRNA of CL-R, RAMP1, RAMP2 and RAMP3 in human coronary (CA), pulmonary (PA) and middle cerebral arteries (MCA), and 2. to examine the level of mRNA expression in cerebra- and cardiovascular diseases. The method was validated with respect to the use of postmortem tissue and we compared beta-actin and GAPDH as housekeeping genes. There was no time-dependent change in total RNA and level of mRNA for p-actin or GAPDH could be detected in vessels removed from 1 and 5 days post mortem. The expression of beta-actin appears lower in coronary artery than in pulmonary artery and middle cerebral artery with no significant difference for GAPDH; both worked well. There were some differences in mRNA expression for CL-R (higher) and RAMP3 (lower) in middle cerebral artery compared to coronary artery and pulmonary artery. There was no significant difference in mRNA for RAMP1 and RAMP2 in the three types of arteries. We did not observe any difference in mRNA for CL-R and RAMPs in arteries from patients with hemorrhagic stroke, arteriosclerosis and acute myocardial infarction when compared to patients without these diagnoses. Thus the mRNA expression seems to be unaltered in these disorders.

Expression of adrenomedullin in human epicardial adipose tissue: role of coronary status

Epicardial white adipose tissue (eWAT) is in close contact with coronary vessels and therefore could alter coronary homeostasis. Adrenomedullin (AM) is a potent vasodilatator and antioxidative peptide which has been shown to play a cytoprotective role in experimental models of acute myocardial infarction. We studied, using immunohistochemistry and qRT-PCR, the expression of AM and its receptors calcitonin receptor-like receptor (CRLR), and receptor activity-modifying protein (RAMP)2 and -3 in paired biopsies of subcutaneous WAT (sWAT) and eWAT obtained from patients with coronary artery disease (CAD) or without CAD (NCAD). In eWAT obtained from NCAD or CAD patients, immunoreactivity for AM, CRLR, and RAMP2 and -3 was detected in blood vessel walls and isolated stromal cells close to adipocytes. Some of the AM positive stromal cells colocalized CD68 immunoreactivity. eWAT from CAD patients showed increased AM immunoreactivity and AM gene expression. CRLR mRNA levels were comparable in sWAT of both groups and decreased by 40-50% in eWAT, irrespectively of the coronary status. RAMP2 mRNA concentrations did not change while RAMP3 mRNA levels increased in sWAT from CAD patients. There was a positive linear relationship between eWAT 11beta-hydroxysteroid dehydrogenase type 1 mRNA (11beta-HSD-1, the enzyme that converts inactive to active glucocorticoids) and AM mRNA. In conclusion, we demonstrate that AM and its receptors are expressed in eWAT. Our data suggest that eWAT AM, which could originate from macrophages, is related to 11beta-HSD-1 expression. AM synthesis, which is increased in eWAT during chronic CAD in humans, can play a cardioprotective role.

Calcitonin gene-related peptide-evoked sustained tachycardia in calcitonin receptor-like receptor transgenic mice is mediated by sympathetic activity

Calcitonin gene-related peptide (CGRP) and adrenomedullin (AM) are potent vasodilators and exert positive chronotropic and inotropic effects on the heart. Receptors for CGRP and AM are calcitonin receptor-like receptor (CLR)/receptor-activity-modifying protein (RAMP) 1 and CLR/RAMP2 heterodimers, respectively. The present study was designed to delineate distinct cardiovascular effects of CGRP and AM. Thus a V5-tagged rat CLR was expressed in transgenic mice in the vascular musculature, a recognized target of CGRP. Interestingly, basal arterial pressure and heart rate were indistinguishable in transgenic mice and in control littermates. Moreover, intravenous injection of 2 nmol/kg CGRP, unlike 2 nmol/kg AM, decreased arterial pressure equally by 18 ± 5 mmHg in transgenic and control animals. But the concomitant increase in heart rate evoked by CGRP was 3.7 times higher in transgenic mice than in control animals. The effects of CGRP in transgenic and control mice, different from a decrease in arterial pressure in response to 20 nmol/kg AM, were suppressed by 2 μmol/kg of the CGRP antagonist CGRP(8-37). Propranolol, in contrast to hexamethonium, blocked the CGRP-evoked increase in heart rate in both transgenic and control animals. This was consistent with the immunohistochemical localization of the V5-tagged CLR in the superior cervical ganglion of transgenic mice. In conclusion, hypotension evoked by CGRP in transgenic and control mice was comparable and CGRP was more potent than AM. Unexpectedly, the CLR/RAMP CGRP receptor overexpressed in postganglionic sympathetic neurons of transgenic mice enhanced the positive chronotropic action of systemic CGRP.

Rapid zygosity determination in mice by SYBR Green real-time genomic PCR of a crude DNA solution

We examined whether crude DNA extracts prepared from gene-engineered mouse tissues are suitable as a template for zygosity determination by SYBR Green real-time genomic PCR. A crude DNA solution was prepared by brief incubation with lysis buffer containing ear, tail, or fetus of ROSA26 mouse, a gene-trapped strain carrying the beta-galactosidase (beta-gal) gene. Five serially diluted crude DNA samples (original, 2-, 4-, 8-, 16-diluted) were next prepared and then subjected to three-step (95 degrees C, 60 degrees C and 72 degrees C) reactions of real-time PCR to detect the beta-gal gene and the receptor-activity-modifying protein 3 (ramp3) gene (as an internal reference gene). The slopes of standard curves obtained from the real-time PCR indicated that amplification efficiency was approximately 99%, and the efficiencies of target and reference were almost equal. With this system, we next determined the zygosity of mice derived from mating heterozygous ROSA26 females and males, and found a sharp distinction in zygosity, wild-type, heterozygous and homozygous. Assessment of crude DNA samples from other gene-engineered mice including B6ZP3Cre-Tg, B6rAM-Tg, and Ramp2-gene-targeted strains revealed that our method was effective for determination of zygosity. The present method is more convenient and rapid than formerly published methods employing purified genomic DNA as a template. Our method will be particularly useful for experiments requiring rapid and accurate genotyping of gene-modified animals/fetuses.

The effects of C-terminal truncation of receptor activity modifying proteins on the induction of amylin receptor phenotype from human CTb receptors

Receptor activity modifying proteins (RAMPs) interact with calcitonin receptors to produce novel amylin receptor phenotypes. We have recently demonstrated that the short intracellular C-terminus of RAMPs plays a key role in the function of amylin receptors derived from the CTa calcitonin receptor through the use of chimeric RAMPs and RAMPs that are truncated at the C-terminus [15, Udawela M, Christopoulos G, Morfis M, Christopoulos A, Ye S, Tilakaratne N, Sexton PM. A critical role for the short intracellular C terminus in receptor activity modifying protein function. Mol Pharmacol 2006;70:1750-60., 18, Udawela M, Christopoulos G, Tilakaratne N, Christopoulos A, Albiston A, Sexton PM. Distinct receptor activity-modifying protein domains differentially modulate interaction with calcitonin receptors. Mol Pharmacol 2006;69:1984-89.]. The calcitonin receptor in humans is expressed as two major alternatively spliced isoforms termed CTa and CTb. Relatively little is known about how alternate splicing of the receptor affects the interaction between calcitonin receptors and RAMPs. We have examined the effect of RAMP truncation, through use of mutant constructs that delete the last 8 amino acids of each of the 3 known human RAMPs, and characterised these for interaction with CTb receptors through co-expression in COS-7 cells. As seen with the CTa receptor isoform, RAMP truncation caused a marked loss in induction of AMYb receptor phenotypes as characterised by (125)I-rat amylin radioligand binding assays and cAMP accumulation assays; the latter as a marker of receptor signalling. The effect was most pronounced for RAMP1 and RAMP2 deletion mutants, but attenuated responses were also observed with co-expressed RAMP3 deletion mutants. These data support a direct role for the RAMP C-terminus in the interaction of RAMP/calcitonin receptor complexes with intracellular accessory proteins involved in signalling and/or receptor trafficking.

Frequent inactivation of RAMP2, EFEMP1 and Dutt1 in lung cancer by promoter hypermethylation

PURPOSE

The goal of this study is to identify novel genes frequently silenced by promoter hypermethylation in lung cancer.

EXPERIMENTAL DESIGNS

Bioinformatic analysis was done to identify candidate genes significantly down-regulated in lung cancer. The effects of DNA methyltransferase inhibitor 5-aza-2'-deoxycytidine on the expression of the candidate genes were determined. Methylated CpG sites in the promoters of the candidate genes were identified using bisulfite DNA sequencing. Methylation-specific PCR was developed and used to analyze DNA methylation in cell lines and clinical specimen. Pathologic and functional analyses were done to study the role of one candidate gene, receptor activity-modifying protein 2 (RAMP2), in suppressing lung cancer cell growth.

RESULTS

Among 54 candidate genes down-regulated in lung cancer, 31 were found to contain CpG islands in their promoters. Six of these 31 genes could be reactivated by 5-aza-2'-deoxycytidine in at least four of six lung cancer cell lines analyzed. Promoter hypermethylation of RAMP2, epidermal growth factor-containing fibulin-like extracellular matrix protein 1, and deleted in U Twenty Twenty cells was detected in 36% to 77% of 22 lung cancer cell lines and in 38% to 50% of 32 primary lung tumors, whereas hypermethylathion of these genes was rarely found in the matched normal samples. The methylation frequencies of these genes in lung cancer were similar to those of commonly used methylation markers, such as RAS association domain family protein 1A, p16, and methylguanine-DNA methyltransferase. Immunohistochemistry showed that RAMP2 was down-regulated in a majority of lung tumors, and RAMP2 down-regulation was correlated with high tumor grade. Ectopic expression of RAMP2 inhibited lung cancer cell growth and caused apoptotic cell death. Knockdown of RAMP2 by RNA interference stimulated cell proliferation.

CONCLUSIONS

Studying the newly identified genes may provide new insight into lung tumorigenesis. These genes might be useful as molecular markers of lung cancer.

Calcitonin receptor-like receptor and receptor activity modifying protein 1 in the rat dorsal horn: localization in glutamatergic presynaptic terminals containing opioids and adrenergic alpha2C receptors

Calcitonin gene-related peptide (CGRP) is abundant in the central terminals of primary afferents. However, the function of CGRP receptors in the spinal cord remains unclear. CGRP receptors are heterodimers of calcitonin receptor-like receptor (CRLR) and receptor activity modifying protein 1 (RAMP1). We studied the localization of CRLR and RAMP1 in the rat dorsal horn using well-characterized antibodies against them, which labeled numerous puncta in laminae I-II. In addition, RAMP1 was found in cell bodies, forming patches at the cell surface. The CRLR- and RAMP1-immunoreactive puncta were further characterized using double and triple labeling. Colocalization was quantified in confocal stacks using Imaris software. CRLR did not colocalize with primary afferent markers, indicating that these puncta were not primary afferent terminals. CRLR- and RAMP1-immunoreactive puncta contained synaptophysin and vesicular glutamate transporter-2 (VGLUT2), showing that they were glutamatergic presynaptic terminals. Electron microscopic immunohistochemistry confirmed that CRLR immunoreactivity was present in axonal boutons that were not in synaptic glomeruli. Using tyramide signal amplification for double labeling with the CRLR and RAMP1 antibodies, we found some clear instances of colocalization of CRLR with RAMP1 in puncta, but their overall colocalization was low. In particular, CRLR was absent from RAMP1-containing cells. Many of the puncta stained for CRLR and RAMP1 were labeled by anti-opioid and anti-enkephalin antibodies. CRLR and, to a lesser extent, RAMP1 also colocalized with adrenergic alpha(2C) receptors. Triple label studies demonstrated three-way colocalization of CRLR-VGLUT2-synaptophysin, CRLR-VGLUT2-opioids, and CRLR-opioids-alpha(2C) receptors. In conclusion, CRLR is located in glutamatergic presynaptic terminals in the dorsal horn that contain alpha(2C) adrenergic receptors and opioids. Some of these terminals contain RAMP1, which may form CGRP receptors with CRLR, but in others CRLR may form other receptors, possibly by dimerizing with RAMP2 or RAMP3. These findings suggest that CGRP or adrenomedullin receptors modulate opioid release in the dorsal horn.

Adrenomedullin is induced by hypoxia and enhances pancreatic cancer cell invasion

Adrenomedullin (ADM) is synthesized by different types of cells and acts by binding calcitonin receptor-like receptor (CRLR) and members of the receptor activity-modifying protein (RAMP) family. In this study, the expression and functional role of ADM and its signaling components were investigated in pancreatic adenocarcinoma (PDAC). By QRT-PCR, median mRNA levels of ADM and CRLR were 1.5- and 2.4-fold higher, respectively, in PDAC tissues compared to normal pancreatic tissues. By immunohistochemistry, ADM, CRLR, RAMP1 and RAMP2, but not RAMP3, were expressed in pancreatic cancer cells. ADM serum levels were significantly increased in PDAC patients compared to healthy controls and chronic pancreatitis (CP) patients, with an area under the ROC curve of 0.83 and 0.98, respectively. At a cut-off level of 30.6 ng/ml, the specificity of ADM to differentiate PDAC from controls and CP patients was 85.5 and 83.6%, with a sensitivity of 80 and 100%. All 5 evaluated pancreatic cancer cells lines expressed ADM, CRLR, RAMP1 and RAMP2, whereas RAMP3 was expressed in only 1/5 pancreatic cancer cell lines. ADM was strongly induced by hypoxia and significantly increased invasiveness in 3/5 human pancreatic cancer cells. Blocking of CRLR decreased invasiveness in 4/5 human pancreatic cancer cells. In addition, rADM slightly up-regulated vascular endothelial growth factor secretion in 3/5 cell lines. In conclusion, ADM is induced by hypoxia and over-expressed in PDAC and might therefore serve as a potential tumor marker. Furthermore, ADM increases invasiveness of some pancreatic cancer cells and might influence angiogenesis, suggesting that blocking this pathway might have a therapeutic potential.

Receptor Activity-modifying Proteins 2 and 3 Have Distinct Physiological Functions from Embryogenesis to Old Age

RAMPs (receptor activity modifying proteins) impart remarkable effects on G protein-coupled receptor (GPCR) signaling. First identified through an interaction with the calcitonin receptor-like receptor (CLR), these single transmembrane proteins are now known to modulate the in vitro ligand binding affinity, trafficking, and second messenger pathways of numerous GPCRs. Consequently, the receptor-RAMP interface represents an attractive pharmacological target for the treatment of disease. Although the three known mammalian RAMPs differ in their sequences and tissue expression, results from in vitro biochemical and pharmacological studies suggest that they have overlapping effects on the GPCRs with which they interact. Therefore, to determine whether RAMP2 and RAMP3 have distinct functions in vivo, we generated mice with targeted deletions of either the RAMP2 or RAMP3 gene. Strikingly, we found that, although RAMP2 is required for survival, mice that lack RAMP3 appear normal until old age, at which point they have decreased weight. In addition, mice with reduced expression of RAMP2 (but not RAMP3) display remarkable subfertility. Thus, each gene has functions in vivo that cannot be accomplished by the other. Because RAMP2, RAMP3, and CLR transduce the signaling of the two potent vasodilators adrenomedullin and calcitonin gene-related peptide, we tested the effects of our genetic modifications on blood pressure, and no effects were detected. Nevertheless, our studies reveal that RAMP2 and RAMP3 have distinct physiological functions throughout embryogenesis, adulthood, and old age, and the mice we have generated provide novel genetic tools to further explore the utility of the receptor-RAMP interface as a pharmacological target.

Hypoxic induction of receptor activity-modifying protein 2 alters regulation of pulmonary endothelin-1 by adrenomedullin: induction under normoxia versus inhibition under hypoxia

The vasodilator adrenomedullin (AM) is up-regulated in pulmonary hypertension, and inhaled AM is beneficial in patients. Therefore, we investigated the effects of AM on pulmonary endothelin-1 (ET-1). In normoxic isolated rat lungs (IRL) and rat pulmonary artery endothelial cells (RPAEC), the calcitonin gene-related peptide type-1 receptor (CGRP1R) antagonist human (h)CGRP(8-37) decreased ET-1 secretion, and the AM receptor antagonist hAM(22-52) had no effect. Exogenous AM (1 and 10 pM) increased ET-1 levels, which was abolished by hCGRP(8-37) and protein kinase A (PKA) inhibition. At 50 and 100 pM, AM decreased ET-1, an effect sensitive to hAM(22-52), NO inhibition, and protein kinase G (PKG) inhibition. In RPAEC, these results were attributed to altered ET-1 gene expression; low exogenous AM also promoted activity of endothelin-converting enzyme, and high AM increased the number of endothelin type-B (ETB) receptor sites. Hypoxia significantly elevated AM and ET-1 levels in IRL and RPAEC, and hAM(22-52), NO inhibition, or PKG inhibitors caused a further ET-1 rise. These interventions also prevented the hypoxia-related increase in ETB sites in RPAEC. In RPAEC, both high AM and hypoxia down-regulated receptor activity-modifying protein (RAMP)1, but they up-regulated RAMP2 protein and AM receptor sites, and RAMP2 silencing by small interference RNA proved its pivotal role for signal switching. In conclusion, endogenous pulmonary AM up-regulates ET-1 and endothelin-converting enzyme activity under physiological conditions, via CGRP1R and PKA. In contrast, hypoxia-induced high AM levels, via AM1 receptor and NO/PKG, down-regulate ET-1 gene expression and promote expression of ETB receptors. This hypoxia-related switch of AM signaling can be attributed to up-regulation of the RAMP2/AM1 receptor system.

Expression and effect of adrenomedullin in pheochromocytoma

This study investigates the expression of human adrenomedullin (ADM) and its receptor-receptor activity modifying protein 2/calcitonin receptor-like receptor (RAMP2/CRLR) mRNA in pheochromocytoma by reverse transcriptase polymerase chain reaction (RT-PCR) and its effect on the proliferation of pheochromocytoma cells by MTT. The mRNA expression of ADM and its receptor RAMP2/CRLR was present in normal adrenal medulla and pheochromocytoma tissues. The mRNA expression of ADM, RAMP2, and CRLR is markedly higher in pheochromocytomas than in normal medulla. ADM inhibits the proliferation of human pheochromocytoma cells and exerts a possible autocrine or paracrine effect in the adrenal.

[Alterations of intermedin and its receptor system in oleic acid-induced acute lung injury of rats]

OBJECTIVE

To investigate the changes of pulmonary IMD and its receptor system-calcitonin receptor-like receptor (CL) and receptor activity modifying proteins (RAMPs) mRNA in acute lung injury(ALI) induced by oleic acid of rats.

METHODS

Contents of IMD in plasma and lung homogenates were measured by radioimmunoassay(RIA). The lung mRNA of IMD, CL and RAMPs was determined by semi-quantitative RT-PCR.

RESULTS

Compared with control group, in ALI group, the contents of IMD1-53 in plasma and lung homogenates were decreased by 20.8% and 74.5% (all P < 0.05) , respectively. Furthermore , it was found that the levels of IMD, CL, RAMP1 and RAMP2 mRNA in lung were decreased by 30%, 38%, 26% and 37.9% (all P < 0. 05) , respectively. The levels of CL , RAMP1 or RAMP2 mRNA were positively correlated with down-regulations of IMD mRNA in ALI. However, compared with control group, the maximum binding capacity of IMD1-53 to plasma membranes was significantly increased in ALI group, and the affinity of IMD1-53 for its receptor almost had no change.

CONCLUSION

The amount of IMD 1-53 is down-regulated and IMD receptor system also down-regulated in Oliec acid induced ALI of rats. These changes suggest that IMD and its receptor system probably are involved in the development of ALI.

Gene silencing of human RAMP2 mediated by short-interfering RNA

Adrenomedullin (AM) is a regulatory peptide widely expressed, along its receptors, in cells and tissues, of which it controls many basic and specific functions acting in an autocrine-paracrine manner. However, the unequivocal demonstration of the physiological relevance of the regulatory role of AM would require the study of cells where the endogenous AM system has been suppressed. For this task we developed a technique to silence the AM gene in human umbilical vein endothelial cells (HUVECs) and the human embryonal kidney cell line (HEK-293). AM acts via two subtypes of receptor, named AM1 and AM2, which derive from the interaction of the calcitonin receptor-like receptors with two chaperones, called receptor activity modifying proteins (RAMP2 and RAMP3). Hence, we developed a protocol to suppress the human AM1 receptor by silencing the RAMP2 gene by transfection with short interfering RNAs (siRNAs). HUVECs were transfected using a new Ambion transfection reagent. RAMP2 gene silencing was determined in HUVECs by measuring RAMP2 mRNA levels in transfected and control cells by real-time polymerase chain reaction. The RAMP2 gene silencing was approximately 60% and was observed 48 h after transfection. Matrigel assay in vitro was carried out to evaluate the effects of siRNA sequences. HUVECs cells were plated on matrigel and the analysis of capillary-like tubule formation showed that the cells were viable. The knockdown of the RAMP2 gene decreased the formation of tubes in response to 10(-8) M AM. The conclusion is drawn that siRNA technology can be successfully used in the investigations on AM and AM receptor functions.

Intermedin1-53 protects the heart against isoproterenol-induced ischemic injury in rats

Intermedin is a novel member of the calcitonin/calcitonin gene-related peptide (CGRP) family peptide, which has vasodilatory and hypotensive actions identical to those of adrenomedullin and CGRP. Cleavage sites located between 2 basic amino acids at Arg93-Arg94 result in the production of prepro-intermedin95-147, namely intermedin1-53. The bioactive action of intermedin1-53 and its physiological significance are unclear. In this work, we aimed to explore the effects of intermedin1-53 on acute myocardial injury induced by isoproterenol. Myocardial ischemia injury in rats was induced by subcutaneous injection of a high dose of isoproterenol, and the therapeutic effect of intermedin1-53 was observed. Plasma lactate dehydrogenase activity, myocardial and plasma malondialdehyde content were higher in the isoproterenol group than that in controls. Isoproterenol-treated rats showed lower maximal rate of increase and decrease of left-ventricle pressure development (+/-left-ventricle dp/dtmax) and higher left-ventricle end-diastolic pressure (all P<0.01), which suggested severe heart failure and myocardial injury. Semi-quantitative RT-PCR analysis showed that the gene expression of calcitonin receptor-like receptor and receptor-activity-modifying protein (RAMP)1, RAMP2 and RAMP3 in ventricular myocardia were up-regulated by 79% (P<0.01), 48% (P<0.01), 31% (P<0.05) and 130% (P<0.01), respectively, compared with controls. In myocardial sarcolemmal membranes, the maximum binding capacity for [125I]-intermedin1-53 was increased by 118% (P<0.01) in the isoproterenol group compared with controls. Rats treated with low dosage intermedin1-53 (5 nmol/kg/day, 2 days) showed 21% (P<0.05) higher myocardial cAMP content, 18% and 31% higher+left-ventricle dp/dtmax and -left-ventricle dp/dtmax respectively, 288% lower left-ventricle end-diastolic pressure (all P<0.01), and attenuated myocardial lactate dehydrogenase leakage and malondialdehyde formation (all P<0.01). Treatment with high dosage intermedin1-53 (20 nmol/kg/day, 2 days) gave better results than that with low dosage intermedin1-53. These results suggest that the intermedin receptor system was up-regulated in isoproterenol-induced myocardial ischemic injury and intermedin1-53 might play a pivotal cardioprotective role in such injury.

Adrenomedullin increases the expression of calcitonin-like receptor and receptor activity modifying protein 2 mRNA in human microvascular endothelial cells

Adrenomedullin (AM) is a multifunctional peptide hormone, which plays a significant role in vasodilation and angiogenesis, implicating it in hypertension as well as in carcinogenesis. AM exerts its effects via the calcitonin receptor-like receptor (CRLR, now known as CL) complexed with either receptor activity modifying protein (RAMP) 2 or 3. We have investigated the effect of AM on immortalized human microvascular endothelial cells 1, since endothelial cells are a major source as well as a target of AM actions in vivo. Cells treated with AM showed elevated cAMP in a time (5-45 min)-dependent and dose (10(-6)-10(-14) M)-dependent manner. Pre-treatment with the AM receptor antagonist AM(22-52) partially suppressed the AM-induced increase in cAMP levels. An increase in extracellular signal-regulated kinase 1/2 phosphorylation was observed after 5 min of treatment with 10(-8) M AM. This phosphorylation was specific, since we were able to block the AM-induced effect with 1 microM U0126, a specific mitogen-activated protein/extracellular signal-regulated kinase kinase inhibitor. Using real-time PCR, we were able to show for the first time that AM upregulates peptide and mRNA expression of vascular endothelial growth factor (VEGF). However, AM treatment of cells did not result in increased cell proliferation. Instead, we observed that AM and VEGF induced cell migration, which could be inhibited by the AM(22-52) and anti-VEGF antibody respectively. AM also significantly elevated mRNA levels of CL (after 2 and 24 h treatment) and RAMP2 (after 1 and 24 h treatment). The upregulation of the AM receptor at two time points reflects possibly different cellular responses to short- and long-term exposure to AM.

Adrenomedullin Peptide: Gene Expression of Adrenomedullin, its Receptors and Receptor Activity Modifying Proteins, and Receptor Binding in Rat Testis—Actions on Testosterone Secretion1

Adrenomedullin (ADM) has been shown to be present in the human and rat male reproductive systems. This study demonstrates the expression of ADM in the rat testis and its effect on the secretion of testosterone. Whole testicular extracts had 5.43 +/- 0.42 fmol of immunoreactive ADM per milligram of protein and 84 +/- 8 fg of ADM mRNA per picogram of Actb (beta-actin) mRNA. Immunocytochemical studies showed positive ADM immunostaining in the Leydig cells and in the Sertoli cells. Gel filtration chromatography of testicular extracts showed two peaks, with the predominant one eluting at the position of the ADM precursor. Furthermore, the testis was shown to coexpress mRNAs encoding the calcitonin receptor-like receptor and receptor activity modifying protein 1 (Ramp1), Ramp2, and Ramp3. These account for the specific binding of ADM to the testis, which was partially inhibited by human ADM (22-52) and by human calcitonin gene-related peptide (8-37), the ADM and calcitonin gene-related peptide receptor antagonists, respectively. Administration of ADM to testicular blocks in vitro resulted in a dose-dependent inhibition of hCG-stimulated release of testosterone, which was abolished by the administration of ADM (22-52). Our results suggest a paracrine effect of ADM on testicular steroidogenesis.

The gene expression of adrenomedullin, calcitonin-receptor-like receptor and receptor activity modifying proteins (RAMPs) in CCl4-induced rat liver cirrhosis

This study was undertaken to determine AM expression in carbon tetrachloride (CCl4)-induced liver cirrhosis developed with peritoneal ascites. Sprague-Dawley rats received subcutaneous injections of CCl4 twice weekly in olive oil (1:1, 0.3 ml per kg body weight) for 6 or 12 weeks until ascites developed, or saline in olive oil as control. At 6 weeks, fibrosis developed and at 12 weeks cirrhosis developed with ascites formation. At both 6 and 12 weeks, increases in plasma renin and AM were evident, as was the gene expression of AM. At 12 weeks after CCl4 injection, the gene expression of calcitonin-like-receptor (CRLR) and receptor activity modifying proteins (RAMP1, RAMP2 and RAMP3) were all elevated when compared to the control. The results suggest that liver cirrhosis increases mRNA expressions of AM, CRLR and RAMP1, RAMP2 and RAMP3 and that the increase in AM gene expression precedes the development of cirrhosis. The increase in AM synthesis as reflected by an increase in AM gene expression, together with a lack of increase in AM peptide at both 6 and 12 weeks may suggest an elevation of AM release. Given the potent vasodilatory action of AM, the increase in the synthesis and release of AM in the cirrhotic liver may also contribute to peripheral vasodilatation in liver cirrhosis.

Effects of calcitonin on the function of human osteoclast-like cells formed from CD14-positive monocytes

Calcitonin inhibits bone-resorbing activity of osteoclasts. Expression of mRNA of calcitonin receptor (CTR) and its related proteins was examined in human osteoclasts and their progenitors. CD14-positive (CD14 + macrophages) in the monocytes prepared from human peripheral blood cells differentiated into macrophages (CD14 +) presence of macrophage colony-stimulating factor (M-CSF) or into osteoclast-like cells (OCLs) in the presence of M-CSF plus receptor activator of NFkappaB ligand. CD14 macrophages expressed mRNA of CTR-like receptor (CRLR), receptor activity modifying protein (RAMP) 1, RAMP2, and RAMP3, but not CTR. In contrast, OCLs expressed mRNA of CTR but not CRLR or RAMPs. Human OCLs cultured on dentine slices formed actin rings (corresponding to clear zones) and resorption pits on the slices. Calcitonin disrupted actin rings and inhibited the pit-forming activity of OCLs. CTR is known to couple to cAMP-dependent protein kinase (PKA) and protein kinase C (PKC). The effect of calcitonin on actin ring disruption was partially blocked by adding H-7, an inhibitor of both PKA and PKC. Both forskolin, an activator of PKA, and phorbol myristate, an activator of PKC, disrupted actin rings in OCLs. These results suggest that both PKA- and PKC-mediated signals are involved in calcitonin-induced inhibition of human OCL function.

Distinct receptor activity-modifying protein domains differentially modulate interaction with calcitonin receptors

Calcitonin receptors (CTRs) dimerize with receptor activity-modifying proteins (RAMPs) to generate high-affinity amylin (AMY) receptors; however, the relative contribution of individual RAMP domains to the formation of AMY receptors is poorly understood. We have used chimeras between RAMP1 and RAMP2 that specifically exchanged the N-terminal, transmembrane, or C-terminal domain and examined these in assays of [(125)I]amylin binding or peptide-induced cAMP signaling in COS-7 cells transiently transfected with wild-type or chimeric RAMPs and human CTRa. The specificity of peptides in competition for [(125)I]amylin binding was principally dictated by the N-terminal domain present in the chimeras; however, the maximal level of binding induced was dictated by the transmembrane domain present. This extended previous data (Zumpe et al., 2000) to provide a distinction between the transmembrane domain and the C terminus in this function. In contrast to the effects on binding, each of the RAMP domains played a role in the signaling phenotype of the receptors. In particular, the potency of calcitonin gene-related peptide (CGRP) was most influenced by the C-terminal domain present, in which the presence of the RAMP1 C-terminal domain led to increased potency over CTRa alone, whereas chimeras with the RAMP2 C-terminal domain did not induce increased CGRP potency. The data provide additional support for the importance of the N terminus in determining binding affinity but reveal a prominent role of the transmembrane domain in the strength of amylin binding and a unique role for the C terminus in signaling by peptides to stimulate cAMP production.

Potentiated response to adrenomedullin in myocardia and aortas in spontaneously hypertensive rat

Adrenomedullin (AM) is a multifunctional regulatory peptide, and endogenous AM is an important factor in regulating cardiovascular and renal homeostasis as a potent cardio-reno-protective factor. To illustrate the protective mechanism of adrenomedullin (AM) on the cardiovascular system by observing (1) the changes in mRNA and protein levels of AM and its receptor-calcitonin receptor-like receptor (CL) and receptor activity-modifying proteins (RAMPs)-in myocardia and aortas of spontaneously hypertensive rats (SHRs) and (2) the response of cardiovascular tissue to AM. The AM content and cyclic adenosine monophosphate (cAMP) production in myocardia and aortas were measured in SHRs and Wistar Kyoto (WKY) rats (11-week-old) by radioimmunoassay (RIA). The mRNA levels of brain natriuretic peptide (BNP), AM, CL, RAMP1, -2, -3 were determined by semi-quantitative RTPCR. Protein levels of CL, RAMP1, -2, -3 were assayed by Western blotting. SHRs had severe hypertension, and the tail-blood pressure was 76.7% higher, the ratio of heart weight to body weight (heart coefficient) 45.5% higher, and the BNP gene expression 4.5-fold higher than that of WKY rats (all p < 0.01). The AM-ir content in plasma, myocardia and aortas of SHRs increased by 42.5%, 68.3% and 80.4%, respectively (all p < 0.01) compared with WKY rats. Furthermore, the mRNA levels of AM, CL, RAMP1, RAMP2 and RAMP3 were elevated by 46% (p < 0.01), 62% (p < 0.05), 51.2% (p < 0.01), 41% (p < 0.01) and 54% (p < 0.01), respectively, in myocardia and by 72%, 87%, 155%, 53% and 74% (all p < 0.01), respectively, in aortas. The elevated mRNA level of CL, RAMP1 RAMP2 and RAMP3 correlated positively with that of AM mRNA in hypertrophic myocardia (r= 0.943, 0.621, 0.688 and 0.633, respectively, all p < 0.01) and aortas (r = 0.762, 0.892, 0.828 and 0.736, respectively, all p < 0.01). The protein levels of CL, RAMP1, RAMP2 and RAMP3 in myocardia and aortas of SHRs were increased compared with that of WKY rats. The response to AM was potentiated in myocardia and aortas in SHRs, and the production of cAMP was increased by 47% and 65% (both p < 0.01), respectively. AM-stimulated cAMP generation in myocardia and aortas was blocked by both AM(22-52), the specific antagonist of AM, and calcitonin gene-related peptide (CGRP)(8-37), the antagonist of the CGRP1 receptor. In myocardia and aortas of SHRs, the gene expressions and protein levels of AM, CL, RAMP1, RAMP2 and RAMP3 were increased, and the response to AM was potentiated. AM-stimulated cAMP generation in myocardia and aortas was blocked by both AM(22-52) and CGRP(8-37). The results suggest that the changes of AM and its receptors in cardiovascular tissue, and the increased response of cardiovascular tissue to AM might importantly impact the pathogenesis of hypertension.

Enhanced Vascular Responses to Adrenomedullin in Mice Overexpressing Receptor-Activity–Modifying Protein 2

Adrenomedullin (AM) levels are elevated in cardiovascular disease, but little is known of the role of specific receptor components. AM acts via the calcitonin receptor-like receptor (CLR) interacting with a receptor-activity–modifying protein (RAMP). The AM 1 receptor is composed of CLR and RAMP2, and the calcitonin gene–related peptide (CGRP) receptor of CLR and RAMP1, as determined by molecular and cell-based analysis. This study examines the relevance of RAMP2 in vivo. Transgenic (TG) mice that overexpress RAMP2 in smooth muscle were generated. The role of RAMP2 in the regulation of blood pressure and in vascular function was investigated. Basal blood pressure, acute angiotensin II–raised blood pressure, and cardiovascular properties were similar in wild-type (WT) and TG mice. However, the hypotensive effect of IV AM, unlike CGRP, was enhanced in TG mice ( P <0.05), whereas a negative inotropic action was excluded by left-ventricular pressure–volume analysis. In aorta relaxation studies, TG vessels responded in a more sensitive manner to AM (EC 50 , 8.0±1.5 nmol/L) than WT (EC 50 , 17.9±3.6 nmol/L). These responses were attenuated by the AM receptor antagonist, AM 22-52 , such that residual responses were identical in all mice. Remaining relaxations were further inhibited by CGRP receptor antagonists, although neither affected AM responses when given alone. Mesenteric and cutaneous resistance vessels were also more sensitive to AM in TG than WT mice. Thus RAMP2 plays a key role in the sensitivity and potency of AM-induced hypotensive responses via the AM 1 receptor, providing evidence that this receptor is a selective target for novel therapeutic approaches.

Functions of the cytoplasmic tails of the human receptor activity-modifying protein components of calcitonin gene-related peptide and adrenomedullin receptors

Receptor activity-modifying proteins (RAMPs) enable calcitonin receptor-like receptor (CRLR) to function as a calcitonin gene-related peptide receptor (CRLR/RAMP1) or an adrenomedullin (AM) receptor (CRLR/RAMP2 or -3). Here we investigated the functions of the cytoplasmic C-terminal tails (C-tails) of human RAMP1, -2, and -3 (hRAMP1, -2, and -3) by cotransfecting their C-terminal deletion or progressive truncation mutants into HEK-293 cells stably expressing hCRLR. Deletion of the C-tail from hRAMP1 had little effect on the surface expression, function, or intracellular trafficking of the mutant heterodimers. By contrast, deletion of the C-tail from hRAMP2 disrupted transport of hCRLR to the cell surface, resulting in significant reductions in (125)I-hAM binding and evoked cAMP accumulation. The transfection efficiency for the hRAMP2 mutant was comparable with that for wild-type hRAMP2; moreover, immunocytochemical analysis showed that the mutant hRAMP2 remained within the endoplasmic reticulum. FACS analysis revealed that deleting the C-tail from hRAMP3 markedly enhances AM-evoked internalization of the mutant heterodimers, although there was no change in agonist affinity. Truncating the C-tails by removing the six C-terminal amino acids of hRAMP2 and -3 or exchanging their C-tails with one another had no effect on surface expression, agonist affinity, or internalization of hCRLR, which suggests that the highly conserved Ser-Lys sequence within hRAMP C-tails is involved in cellular trafficking of the two AM receptors. Notably, deleting the respective C-tails from hRAMPs had no effect on lysosomal sorting of hCRLR. Thus, the respective C-tails of hRAMP2 and -3 differentially affect hCRLR surface delivery and internalization.

Differential expression of components of the cardiomyocyte adrenomedullin/intermedin receptor system following blood pressure reduction in nitric oxide-deficient hypertension

Adrenomedullin (AM) and intermedin (IMD; adrenomedulln-2) are vasodilator peptides related to calcitonin gene-related peptide (CGRP). The actions of these peptides are mediated by the calcitonin receptor-like receptor (CLR) in association with one of three receptor activity-modifying proteins. CGRP is selective for CLR/receptor activity modifying protein (RAMP)1, AM for CLR/RAMP2 and -3, and IMD acts at both CGRP and AM receptors. In a model of pressure overload induced by inhibition of nitric-oxide synthase, up-regulation of AM was observed previously in cardiomyocytes demonstrating a hypertrophic phenotype. The current objective was to examine the effects of blood pressure reduction on cardiomyocyte expression of AM and IMD and their receptor components. Nomega-nitro-L-arginine methyl ester (L-NAME) (35 mg/kg/day) was administered to rats for 8 weeks, with or without concurrent administration of hydralazine (50 mg/kg/day) and hydrochlorothiazide (7.5 mg/kg/day). In left ventricular cardiomyocytes from L-NAME-treated rats, increases (-fold) in mRNA expression were 1.6 (preproAM), 8.4 (preproIMD), 3.4 (CLR), 4.1 (RAMP1), 2.8 (RAMP2), and 4.4 (RAMP3). Hydralazine/hydrochlorothiazide normalized systolic blood pressure (BP) and abolished mRNA up-regulation of hypertrophic markers sk-alpha-actin and BNP and of preproAM, CLR, RAMP2, and RAMP3 but did not normalize cardiomyocyte width nor preproIMD or RAMP1 mRNA expression. The robust increase in IMD expression indicates an important role for this peptide in the cardiac pathology of this model but, unlike AM, IMD is not associated with pressure overload upon the myocardium. The concordance of IMD and RAMP1 up-regulation indicates a CGRP-type receptor action; considering also a lack of response to BP reduction, IMD may, like CGRP, have an anti-ischemic function.

Localization of calcitonin receptor-like receptor and receptor activity modifying protein 1 in enteric neurons, dorsal root ganglia, and the spinal cord of the rat

Calcitonin receptor-like receptor (CLR) and receptor activity modifying protein 1 (RAMP1) comprise a receptor for calcitonin gene related peptide (CGRP) and intermedin. Although CGRP is widely expressed in the nervous system, less is known about the localization of CLR and RAMP1. To localize these proteins, we raised antibodies to CLR and RAMP1. Antibodies specifically interacted with CLR and RAMP1 in HEK cells coexpressing rat CLR and RAMP1, determined by Western blotting and immunofluorescence. Fluorescent CGRP specifically bound to the surface of these cells and CGRP, CLR, and RAMP1 internalized into the same endosomes. CLR was prominently localized in nerve fibers of the myenteric and submucosal plexuses, muscularis externa and lamina propria of the gastrointestinal tract, and in the dorsal horn of the spinal cord of rats. CLR was detected at low levels in the soma of enteric, dorsal root ganglia (DRG), and spinal neurons. RAMP1 was also localized to enteric and DRG neurons and the dorsal horn. CLR and RAMP1 were detected in perivascular nerves and arterial smooth muscle. Nerve fibers containing CGRP and intermedin were closely associated with CLR fibers in the gastrointestinal tract and dorsal horn, and CGRP and CLR colocalized in DRG neurons. Thus, CLR and RAMP1 may mediate the effects of CGRP and intermedin in the nervous system. However, mRNA encoding RAMP2 and RAMP3 was also detected in the gastrointestinal tract, DRG, and dorsal horn, suggesting that CLR may associate with other RAMPs in these tissues to form a receptor for additional peptides such as adrenomedullin.

Antiapoptotic effect of calcitonin gene-related peptide on oxidative stress-induced injury in H9c2 cardiomyocytes via the RAMP1/CRLR complex

Calcitonin gene-related peptide (CGRP) plays an important role in the mediation of protective effects observed in situations such as ischemic preconditioning in rat hearts. In this study, we investigated in H9c2 rat cardiomyoblasts if the protective effect of CGRP could be linked to an inhibitory effect on the apoptotic pathway. We also determined the specificity of observed effects by treatment with adrenomedullin (ADM) in stress conditions generated by 100 microM hydrogen peroxide. Using MTT assays, we demonstrate that a pretreatment with CGRP decreases by half the loss of cell viability induced by H(2)O(2). CGRP inhibits phosphatidylserine externalization, caspase 3 activation and DNA fragmentation due to oxidative stress. Using RT-PCR, we observed an increase in Bcl-2 mRNA expression induced by CGRP treatment. Dot blotting experiments showed that, in stress conditions, Bcl-2 protein level decreases while Bax is increased. CGRP administration prior to stress prevents these effects. The three-receptor activity modifying protein (RAMP) isotypes were detected by RT-PCR in H9c2 cells and in left ventricle rat tissue, RAMP1 and RAMP3 being the most abundant in both cases. RAMP1 expression was upregulated by CGRP while RAMP3 mRNA level was decreased. Cell viability assessed by MTT indicates that, contrary to CGRP, pretreatment of stressed cells with ADM, a RAMP2 agonist, fails to protect them while treatment with CGRP(8-37) (a RAMP1 and 2 inhibitor) abolished CGRP protective effect. Taken together, these data suggest that CGRP has antiapoptotic properties through the RAMP1/CRLR complex. CGRP could be used to prevent apoptosis in an ischemia-reperfusion context.

Receptor-activity-modifying proteins are required for forward trafficking of the calcium-sensing receptor to the plasma membrane

The calcium-sensing receptor (CaSR) is a class III G-protein-coupled receptor (GPCR) that responds to changes in extracellular calcium concentration and plays a crucial role in calcium homeostasis. The mechanisms controlling CaSR trafficking and surface expression are largely unknown. Using a CaSR tagged with the pH-sensitive GFP super-ecliptic pHluorin (SEP-CaSR), we show that delivery of the GPCR to the cell surface is dependent on receptor-activity-modifying proteins (RAMPs). We demonstrate that SEP-CaSRs are retained in the endoplasmic reticulum (ER) in COS7 cells that do not contain endogenous RAMPs whereas they are delivered to the plasma membrane in HEK 293 cells that do express RAMP1. Coexpression of RAMP1 or RAMP3, but not RAMP2, in COS7 cells was sufficient to target the CaSR to the cell surface. RAMP1 and RAMP3 colocalised and coimmunoprecipitated with the CaSR suggesting that these proteins associate within the cell. Our results indicate that RAMP expression promotes the forward trafficking of the GPCR from the ER to the Golgi apparatus and results in mature CaSR glycosylation, which is not observed in RAMP-deficient cells. Finally, silencing of RAMP1 in the endogenously expressing HEK293 cells using siRNA resulted in altered CaSR traffic. Taken together, our results show that the association with RAMPs is necessary and sufficient to transfer the immature CaSR retained in the ER towards the Golgi where it becomes fully glycosylated prior to delivery to the plasma membrane and demonstrate a role for RAMPs in the trafficking of a class III GPCR.

[Expression of adrenomedullin and its receptor mRNA in the tissues of normal adrenal medulla and pheochromocytoma]

OBJECTIVE

To investigate the expression of human adrenomedullin (ADM) and its receptor-receptor activity modifying protein 2/calcitonin receptor-like receptor (RAMP2/CRLR) mRNA in the tissues of normal adrenal medulla and pheochromocytoma.

METHODS

Total RNA was extracted from normal adrenal medulla and pheochromocytomas. The expression of ADM and RAMP2/CRLR mRNA were studied by reverse transcription-polymerase chain reaction. The ratios of ADM/GAPDH, RAMP2/ GAPDH, CRLR/GAPDH were used to evaluate the expression levels of ADM, RAMP2 and CRLR mRNA.

RESULTS

Expressions of ADM and its receptor- RAMP2/CRLR mRNA were detected in normal adrenal medulla and pheochromocytoma tissues. ADM/GAPDH were 0.48+/-0.09 and 0.75+/-0.24, RAMP2/ GAPDH 0.79+/-0.12 and 1.29+/-0.30, CRLR/GAPDH 0.40+/-0.08 and 0.87+/-0.22 in normal adrenal medulla and pheochromocytomas, respectively (P < 0.05).

CONCLUSION

ADM exerts a possible autocrine or paracrine effect in the adrenal. ADM may be involved in the pathogenesis of pheochromocytoma.

Receptor Activity-modifying Protein (RAMP) Isoform-specific Regulation of Adrenomedullin Receptor Trafficking by NHERF-1

Receptor activity-modifying proteins (RAMPs 1-3) are single transmembrane accessory proteins critical to various G-protein coupled receptors for plasma membrane expression and receptor phenotype. A functional receptor for the vasodilatory ligand, adrenomedullin (AM), is comprised of RAMP2 or RAMP3 and calcitonin receptor-like receptor (CRLR). It is now known that RAMP3 protein-protein interactions regulate the recycling of the AM2 receptor. The major aim of this study was to identify other interaction partners of RAMP3 and determine their role in CRLR-RAMP3 trafficking. Trafficking of G-protein-coupled receptors has been shown to be regulated by the Na+/H+ exchanger regulatory factor-1 (NHERF-1), an adaptor protein containing two tandem PSD-95/Discs-large/ZO-1 homology (PDZ) domains. In HEK 293T cells expressing the AM2 receptor, the complex undergoes agonist-induced desensitization and internalization. However, in the presence of NHERF-1, although the AM receptor (CRLR/RAMP3) undergoes desensitization, the internalization of the receptor complex is blocked. Overlay assays and mutational analysis indicated that RAMP3 and NHERF-1 interact via a PDZ type I domain on NHERF-1. The internalization of the CRLR-RAMP complex was not affected by NHERF-1 when CRLR was co-expressed with RAMP1 or RAMP2. Mutation of the ezrin/radixin/moesin (ERM) domain on NHERF-1 indicated that NHERF-1 inhibits CRLR/RAMP3 complex internalization by tethering the complex to the actin cytoskeleton. When examined in a primary culture of human proximal tubule cells endogenously expressing the CRLR-RAMP3 complex and NHERF-1, the CRLR-RAMP complex desensitizes but is unable to internalize upon agonist stimulation. Knock-down of either RAMP3 or NHERF-1 by RNA interference technology enabled agonist-induced internalization of the CRLR-RAMP complex. These results, using both endogenous and overexpressed cellular models, indicate a novel function for NHERF-1 and RAMP3 in the internalization of the AM receptor and suggest additional regulatory mechanisms for receptor trafficking.

Novel Function for Receptor Activity-modifying Proteins (RAMPs) in Post-endocytic Receptor Trafficking

RAMPs (1-3) are single transmembrane accessory proteins crucial for plasma membrane expression, which also determine receptor phenotype of various G-protein-coupled receptors. For example, adrenomedullin receptors are comprised of RAMP2 or RAMP3 (AM1R and AM2R, respectively) and calcitonin receptor-like receptor (CRLR), while a CRLR heterodimer with RAMP1 yields a calcitonin gene-related peptide receptor. The major aim of this study was to determine the role of RAMPs in receptor trafficking. We hypothesized that a PDZ type I domain present in the C terminus of RAMP3, but not in RAMP1 or RAMP2, leads to protein-protein interactions that determine receptor trafficking. Employing adenylate cyclase assays, radioligand binding, and immunofluorescence microscopy, we observed that in HEK293 cells the CRLR-RAMP complex undergoes agonist-stimulated desensitization and internalization and fails to resensitize (i.e. degradation of the receptor complex). Co-expression of N-ethylmaleimide-sensitive factor (NSF) with the CRLR-RAMP3 complex, but not CRLR-RAMP1 or CRLR-RAMP2 complex, altered receptor trafficking to a recycling pathway. Mutational analysis of RAMP3, by deletion and point mutations, indicated that the PDZ motif of RAMP3 interacts with NSF to cause the change in trafficking. The role of RAMP3 and NSF in AM2R recycling was confirmed in rat mesangial cells, where RNA interference with RAMP3 and pharmacological inhibition of NSF both resulted in a lack of receptor resensitization/recycling after agonist-stimulated desensitization. These findings provide the first functional difference between the AM1R and AM2R at the level of post-endocytic receptor trafficking. These results indicate a novel function for RAMP3 in the post-endocytic sorting of the AM-R and suggest a broader regulatory role for RAMPs in receptor trafficking.

Osteoclast-like cells express receptor activity modifying protein 2: application of laser capture microdissection

Receptor activity modifying proteins (RAMPs) act as receptor modulators that determine the ligand specificity of receptors for the calcitonin (CT) family. The purpose of this study was to analyze the expression of RAMPs in osteoclast-like cells using the laser capture microdissection (LCM) technique. Mouse bone marrow and spleen cells were co-cultured on a film designed for LCM. After 10 days, 250 osteoclast-like cells were captured using the LCM system. Total RNA from these cells was used to synthesize cDNA and RT-PCR analysis was performed. Osteoclast-like cells expressed CT receptor (CTR), CT receptor-like receptor (CRLR) and RAMP2, but did not express RAMP1 or RAMP3. These results indicated (1) that a pure population of osteoclast-like cells can be prepared by LCM and gene expression of this population can be analyzed by RT-PCR and (2) that RT-PCR shows that osteoclast-like cells express RAMP2, CTR and CRLR, suggesting the potential for adrenomedullin binding to osteoclast-like cells. This is the first report that osteoclast-like cells express RAMP2.

Response of adrenomedullin system to cytokine in cardiac fibroblasts-role of adrenomedullin as an antifibrotic factor

OBJECTIVE

The adrenomedullin system acts as an autocrine or paracrine factor (or both) in the development of cardiac hypertrophy and in the regulation of cardiac function. However, several aspects of the local action of adrenomedullin remain unclear. We studied the effects of interleukin 1-beta (IL-1beta) on the adrenomedullin system in cardiac fibroblasts and also examined the pathophysiological significance of such effects.

METHODS

We cultured rat neonatal cardiac fibroblasts with or without IL-1beta and measured (1) two molecular forms of adrenomedullin in culture medium by specific immunoradiometric assay; (2) gene expression of adrenomedullin, calcitonin receptor like receptor (CRLR), receptor activity modifying protein2 (RAMP2), and RAMP3, components of the adrenomedullin receptor, by Northern blot analysis or RT-PCR analysis; (3) intracellular cAMP levels in response to exogenously administered adrenomedullin; and (4) (3)H-proline incorporation with and without a specific adrenomedullin antisense oligodeoxynucleotide.

RESULTS

(1) IL-1beta time-dependently increased the levels of two molecular forms of adrenomedullin, adrenomedullin-mature and adrenomedullin-glycine (P<0.01). In contrast to known levels in plasma (about 10%), adrenomedullin-mature was a major molecular form in the culture medium of cardiac fibroblasts and myocytes (65-80%). (2) IL-1beta significantly increased gene expression of adrenomedullin and its receptor components (adrenomedullin: +46%, CRLR: +460%, RAMP2: +32%, RAMP3: +350%, all P<0.01). (3) Preincubated IL-1beta elevated the intracellular cAMP response to exogenous adrenomedullin administered at a concentration of 10(-7) M (+26%, P<0.05). (4) Adrenomedullin antisense oligodeoxynucleotide treatment significantly lowered adrenomedullin-mature levels in culture medium (-50%). Adrenomedullin nonsense oligodeoxynucleotide treatment did not change (3)H-proline incorporation or mRNA levels of collagen I and III, whereas adrenomedullin antisense oligodeoxynucleotide treatment significantly increased (3)H-proline incorporation and mRNA levels of collagen I and III in IL-1beta-treated cardiac fibroblasts.

CONCLUSION

These results provide evidence that the adrenomedullin system acts as an autocrine antifibrotic factor in the regulation of collagen synthesis in cardiac fibroblasts exposed to higher cytokine levels. This may beneficially modulate the pathophysiology of certain cardiac diseases.

Concomitant expression of adrenomedullin and its receptor components in rat adipose tissues

Adrenomedullin (AM) expressed by and secreted from a variety of cells plays pluripotent roles in an autocrine/paracrine fashion. The present study was undertaken to explore the expression of AM and its receptor genes in adipose tissues, their changes during the development of obesity, and the process of preadipocyte differentiation. Both mature adipocytes and stromal vascular cells constituting adipose tissue expressed AM transcript. AM and its receptor component [calcitonin receptor-like receptor and receptor activity-modifying protein-2 (CRLR/RAMP2)] mRNAs were expressed in a variety of rat adipose tissues, including epididymal, mesenteric, retroperitoneal, and subcutaneous adipose tissue. AM mRNA levels in rat and human epididymal adipose tissue were about one-tenth of those in the kidney. Steady-state mRNA levels of AM and CRLR/RAMP2 in epididymal, mesenteric, and retroperitoneal adipose tissues in rats fed a high-fat diet for 4 wk were far greater than those in rats with normal diet accompanied by increased plasma AM levels, whereas steady-state AM mRNA levels conversely decreased in other organs, such as kidney and liver. AM mRNA expressed in a mouse preadipocyte cell line (3T3-L1) transiently decreased by day 3, returned to basal level by day 6, and then increased by day 9 during preadipocyte differentiation, which paralleled AM secretion from the cells. However, the addition of either exogenous AM or AM receptor antagonist calcitonin gene-related peptide-(8-37), to block endogenous AM did not affect lipid droplet accumulation during preadipocyte differentiation. The present study demonstrates for the first time that AM and its receptor component (CRLR/RAMP2) mRNAs were concomitantly expressed in various adipose tissues, whose tissue-specific upregulation was induced during the development of obesity. These data suggest that AM may act as a new member of adipokines, although its functional role, as well as its pathophysiological significance in obesity, remains to be determined.

RAMP2 and RAMP3 mRNA levels are increased in failing rat cardiomyocytes and associated with increased responsiveness to adrenomedullin

Adrenomedullin (AM) is a potent vasorelaxing peptide with natriuretic and diuretic actions. Recent data indicate that AM may function as an endogenous regulator of cardiac function. We investigated to what extent AM, the AM receptor subtypes, and AM receptor-associated proteins were regulated in cardiomyocytes and non-cardiomyocytes of rats with congestive heart failure (CHF), and whether such regulation was paralleled by corresponding alterations of functional responses to AM. Cardiomyocytes and non-cardiomyocytes were isolated from myocardial tissue of rats 7 days after induction of myocardial infarction or sham operation. AM immunoreactivity was found in cardiomyocytes, endothelial cells, and fibroblasts. Robust increase of AM mRNA levels was observed both in the cardiomyocytes and in the non-cardiomyocytes of CHF rats compared to that of sham-operated rats (2.7-fold and 3.7-fold, respectively, P <0.05). Fairly high mRNA levels and immunoreactivity against the AM receptor chaperone receptor activity-modifying protein-2 (RAMP2) were also detected in the cardiomyocytes and non-cardiomyocytes. However, induction of RAMP2 mRNA expression was restricted to cardiomyocytes (1.8-fold increase in cardiomyocytes from CHF rats vs. sham rats; P <0.05). In contrast, very low levels of RAMP3 mRNA were observed. RAMP3 mRNA levels, however, were elevated in both cardiomyocytes and non-cardiomyocytes from CHF rats (6.5-fold and 2.4-fold increase vs. sham rats, respectively; P <0.05). Parallel increases of specific AM receptor binding sites and of AM-stimulated adenylyl cyclase activities were observed in failing cardiomyocytes compared to cardiomyocytes from sham rats (fivefold and sixfold increase, respectively; P <0.05). Thus, this study demonstrates that AM mRNA levels, AM receptor binding sites, and AM-stimulated adenylyl cyclase activities are increased in cardiomyocytes from failing rat hearts. Furthermore, our data suggest that induction of RAMP2 and RAMP3 contributes to the increased responsiveness to AM in failing cardiomyocytes.

Adrenomedullin (AM) and receptor-activity-modifying proteins in glomeruli with Thy.1 glomerulonephritis

BACKGROUND

Adrenomedullin (AM) has antiproliferative and proapoptotic effects on mesangial cells in culture, but the regulation of AM and its receptors in glomeruli with glomerulonephritis have not been clarified.

METHODS

We examined sequential changes in the mRNA expression of AM and its receptors (receptor-activity-modifying proteins; RAMPs), and AM production in the glomeruli of Thy.1 glomerulonephritis, using quantitative reverse transcription-polymerase chain reaction (RT-PCR) and immunoradiometric assay (IRMA).

RESULTS

Both the mRNA and the protein levels of AM in glomeruli isolated from rats 7 days after injection with anti-thymocyte serum (ATS), when mesangial cell proliferation peaked, were unchanged compared with those in control rats. However, on day 14, when almost all glomeruli had appeared to return to normal, AM mRNA expression was significantly increased (day 14 vs control: 51.2 +/- 9.1 vs 28.4 +/- 7.1 (mmol/mol glyceraldehyde-3-phosphate dehydrogenase; GAPDH); P < 0.05), as was the AM concentration (12.0 +/- 0.8 vs 8.4 +/- 0.4 fmol/10(4) glomeruli; P < 0.01). Subsequently, by 28 days after ATS injection, both levels decreased to the control ones. The mRNA expression of AM and RAMP2, in the glomeruli of Thy.1 glomerulonephritis changed similarly over time. Immunohistochemical staining revealed that AM production in mesangial cells was increased predominantly on day 14.

CONCLUSIONS

AM and RAMP increased during the reso-lution phase of increased mesangial proliferation in Thy.1 glomerulonephritis, but not during the mesangial proliferative phase. Considering the antiproliferative and proapoptotic effects of AM, its action on mesangial cells may be related to the amelioration of glomerulonephritis.

Amylin receptors: molecular composition and pharmacology

Several receptors which bind the hormone AMY (amylin) with high affinity have now been identified. The minimum binding unit is composed of the CT (calcitonin) receptor at its core, plus a RAMP (receptor activity modifying protein). The receptors have been named AMY1(a), AMY2(a) and AMY3(a) in accordance with the association of the CT receptor (CT(a)) with RAMP1, RAMP2 and RAMP3 respectively. The challenge is now to determine the localization and pharmacological nature of each of these receptors. Recent attempts to achieve these aims will be briefly discussed.

Progesterone upregulates calcitonin gene-related peptide and adrenomedullin receptor components and cyclic adenosine 3'5'-monophosphate generation in Eker rat uterine smooth muscle cell line

Calcitonin gene-related peptide (CGRP) and adrenomedullin (AM), two potent smooth-muscle relaxants, have been shown to cause uterine relaxation. Both CGRP- and AM-binding sites in the uterus increase during pregnancy and decrease at labor and postpartum. These changes in binding sites appear to be related to the changes in calcitonin receptor-like receptor (CRLR), receptor activity-modified protein 1 (RAMP1), RAMP2, and RAMP3 mRNA levels. It is not clear, however, whether the changes in the receptor components occur in the myometrial cells and whether the steroid hormones can directly alter these receptor components in the muscle cells. In addition, the mechanism of CGRP and AM signaling in the rat myometrium is not well understood. Therefore, we examined the mRNA expression of CGRP- and AM-receptor components, G protein Galphas, CGRP, and AM stimulation of cAMP and cGMP, and the effects of progesterone on these parameters in the Eker rat uterine myometrial smooth-muscle cell line (ELT3). ELT3 cells expressed CGRP- and AM-receptor components CRLR, RAMP1, RAMP2, and RAMP3. Expression of CRLR and RAMP1 mRNA increased with progesterone treatment and decreased with estradiol-17beta treatment. However, RAMP2 and RAMP3 mRNA expressions were unaltered by both progesterone and estradiol. Progesterone increased (P<0.05) Galphas expression and augmented CGRP- and AM-induced increases in cAMP levels. In uterine smooth-muscle cells, the antagonist to Galphas protein NF449 decreased basal as well as CGRP- and AM-stimulated cAMP levels. None of the cell treatments affected cyclic GMP production. Our results suggest that the progesterone-stimulated increases in CGRP and AM receptors, Galphas protein levels, and cAMP generation in the myometrial cells may be responsible for increased uterine relaxation sensitivity to CGRP and AM during pregnancy.

The role of adrenomedullin and receptors in glomerular hyperfiltration in streptozotocin-induced diabetic rats

BACKGROUND

Since adrenomedullin (AM) elicits vasodilatation by binding to specific AM receptors consisted of calcitonin-receptor-like receptor (CRLR)/receptor-activity-modifying protein 2 (RAMP2) or CRLR/receptor-activity-modifying protein 3 (RAMP3) on endothelial cells and stimulating nitric oxide production, AM possibly involves in glomerular capillary dilatation in early phase of diabetic nephropathy.

METHODS

Streptozotocin (STZ)-induced diabetic Sprague-Dawley rats at 4 weeks after the injection were employed for expression studies of AM, RAPM2, and RAMP3. The measurement of AM peptide levels in kidney tissue, plasma, and urine was performed. Human aortic endothelial cells (HAEC) were used to investigate functional link between glucose-induced AM production and nitric oxide release.

RESULTS

STZ rats showed glomerular hypertrophy and increased urinary NO2- and NO3- excretion. By Northern blot analyses, AM and RAPM2 mRNAs significantly increased in the kidneys of STZ rats, while RAMP3 mRNA was not altered. In STZ rats, AM peptide was actively secreted into urine (1280 +/- 360 fmol/day vs. control 110 +/- 36 fmol/day). AM peptide was mainly detected on cortical and medullary collecting duct cells in control rat kidneys and AM peptide and mRNA were up-regulated on afferent arterioles and glomeruli of STZ rats. RAMP2 expression was detected on afferent arterioles and not in glomeruli in control rats and it was up-regulated on glomerular endothelial cells in STZ rats. In HAEC culture, d-glucose stimulated AM and nitric oxide production and they were suppressed by addition of AM antisense oligodeoxynucleotides.

CONCLUSION

Up-regulated expression of AM and RAMP2 in afferent arterioles and glomeruli may be related to selective dilatation of glomerular capillary in acute phase of type 1 diabetes.

RAMPs and CRLR expressions in osteoblastic cells after dexamethasone treatment

Adrenomedullin (ADM) is a potent stimulator of osteoblastic activity and promotes bone growth in vivo. ADM receptors are formed by heterodimerization of the CRLR and a RAMP2 or RAMP3 molecule. Since glucocorticoid responsive elements were recently identified in the human CRLR promoter and that glucocorticoids exert a major action in bones, we investigated the acute effect of dexamethasone (Dex) treatment on ADM receptor components in osteoblastic cell types: the MC3T3-E1 cells and calvaria-derived osteoblastic cells. Changes in expression of CRLR and RAMPs molecules were evaluated at mRNA levels using RT-PCR and at protein levels by Western blot analysis. We found that Dex increased expression of RAMP1 and RAMP2 mRNA in a time-dependent but dose-independent manner, while RAMP3 was unchanged. In contrast, Dex decreased the CRLR mRNA expression and these changes were reflected at protein levels. We suggest that Dex, in osteoblastic cells, altered ADM receptor by inhibition of CRLR expression and consequently could impair the ADM anabolic effect on bone. Our findings could explain in part, the detrimental side effects observed at bone level during glucocorticoid therapy.

Estrogen and phytoestrogen regulate the mRNA expression of adrenomedullin and adrenomedullin receptor components in the rat uterus

The serum estrogen surge in the uterus triggers precisely-timed physiological and biochemical responses required establishing and maintaining pregnancy. Previous reports have shown that consumption of phytoestrogen-containing plants may disrupt the precise control of pregnancy. To evaluate the effects of phytoestrogens in the uterus, we screened for estradiol (E2)-inducible genes in immature rat uteri. We identified the gene for receptor-activity-modifying protein 2 (Ramp2), known to be a component of the adrenomedullin (ADM) receptor, as responsive to both E2 and the phytoestrogen coumestrol (Cou). We further examined the expression of ADM and ADM signaling components Ramp2, Ramp3, and CRLR in the immature rat uterus and found that both E2 and Cou regulated these genes expression. In addition, treatment with ADM increased uterine weight and edema similar to that observed after Cou treatment. Our findings indicated that the phytoestrogen caused the abnormal induction of vasoactive factors in the uterus.

Regulation of adrenomedullin signaling in kidney interstitial fibroblasts

Adrenomedullin (AM), a potent vasodilatory peptide has beneficial effects in the kidney IN VIVO. The major aim of the present study was to determine the presence of AM receptor and the biological outcomes of AM on kidney interstitial fibroblasts in culture. Utilizing RT-PCR we found that NRK-49F cells express calcitonin receptor like receptor (CRLR) and receptor activity modifying protein 2 (RAMP2) but not RAMP3. Treatment of these cells with AM resulted in a concentration-dependent increase in cAMP activation. The activation of adenylate cyclase system was enhanced by over-expression of CRLR, RAMP2 and RAMP3. Furthermore, AM-stimulated adenylate cyclase activity was inhibited by AM-[22-52] the AM receptor antagonist. AM also caused a PKA-dependent increase in CRE-luciferase activity. To test the biological consequences of AM treatment and the signaling pathways mediating them, we examined the effect of AM on proliferation of NRK-49F cells and the desensitization of AM receptor. AM caused a significant decrease in proliferation that was AM-receptor mediated but was PKA independent. In addition, AM also caused desensitization of cAMP response within a few minutes of treatment. This effect of AM was also not mediated via cAMP pathway as forskolin failed to desensitize AM receptor, and a PKA-inhibitor did not inhibit the desensitization. Taken together these results demonstrate that NRK-49F cells express functional AM receptor that when activated by AM results in a significant reduction of cell proliferation. Although cAMP activation by AM, as in other systems, is also observed in NRK-49F cells, PKA-independent pathways lead to some of the biological responses observed in these cells.

Aspartate(69) of the calcitonin-like receptor is required for its functional expression together with receptor-activity-modifying proteins 1 and -2

The calcitonin-like receptor (CLR) associated with receptor-activity-modifying proteins (RAMP) 1 or -2 recognizes calcitonin gene-related peptide (CGRP) and adrenomedullin (AM), respectively. The amino acid sequence CNRTWDGWLCW corresponding to residues 64-74 in the extracellular N-terminus of the CLR is conserved. The Asp(69) (D(69)) is present in all family B1 G-protein-coupled receptors. Here the D(69) of a V5-tagged mouse CLR has been mutated to Ala (A), Glu (E), and Asn (N). The function of the intact and the mutant CLR was investigated in COS-7 cells coexpressing myc-tagged mouse RAMP1 or -2. In CLR/RAMP1 and -2 expressing cells CGRP and AM stimulated cAMP formation with an EC(50) of 0.17 and 0.50 nM, respectively. The expression of the D69A, D69E, and D69N mutants at the cell surface was comparable to that of the intact CLR. cAMP stimulation by CGRP and AM was abolished in the D69A mutant. With the D69E mutant the EC(50) of CGRP and AM were 1000-fold higher than those with the intact CLR. With the D69N mutant the EC(50) of CGRP was 0.48 nM and that of AM 0.44 nM, but the maximal cAMP formation was reduced to 24% and to 12% of cells with the intact CLR. Co-immunoprecipitation of RAMP1 with the CLR, indicating complex formation, was reduced with the D69A, D69N, and D69E mutants. RAMP2 co-precipitated with the mutant receptors indistinguishable from the intact CLR. In conclusion, mutation of D69 to N, E or A in the CLR did not affect its expression at the cell surface, but impaired or abolished the CGRP and AM receptor function in the presence of RAMP1 and -2, respectively.

[Increased atria expression of receptor activity-modifying proteins in heart failure patients]

OBJECTIVE

Receptor activity-modifying proteins (RAMPs) determine the ligand specificity of the calcitonin receptor-like receptor (CRLR); co-expression of RAMP1 and CRLR results in a calcitonin gene related peptide (CGRP) receptor, whereas the association of RAMP2 or RAMP3 with CRLR gives an adrenomedullin(ADM) receptor. As CGRP and ADM may play a beneficial role in heart failure, this study aimed at the question whether RAMPs mRNAs are changed in heart failure.

METHODS

Semi-quantitative reverse transcription-PCR (RT-PCR) was used to detect and quantify the mRNAs of RAMP1 and RAMP3 in the atria of heart failing patients.

RESULTS

It was found that the expressions of RAMP1, RAMP2 and RAMP3 mRNAs increased with the worsening of heart function, but the expressions of RAMP1 and RAMP2 mRNA decreased at level IV of heart failure.

CONCLUSION

The above results demonstrated in the atria of heart failure patients an up-regulation of CGRP receptor by an increase of RAMP1 in association with CRLR and an up-regulation of ADM receptor by an increase of RAMP2 expression in association with CRLR, thus suggesting that CGRP and ADM receptors be playing a functional role in compensating the chronic heart failure in human.

Expression of calcitonin gene-related peptide type 1 receptor mRNA and their activity-modifying proteins in the rat nucleus accumbens

The calcitonin receptor-like receptor (CRLR) and the orphan receptor RDC-1 have been proposed to be calcitonin gene-related peptide type 1 (CGRP1) receptors, and receptor activity-modifying proteins (RAMPs) determine the ligand specificity of CRLR. Coexpression of RAMP1 and CRLR resulted in functional CGRP1 receptors; the complex of RAMP2 or RAMP3 and CRLR created functional adrenomedullin receptor. Although high levels of CGRP binding sites in the nucleus accumbens have been reported, little is known about the expression of these novel CGRP receptors. In the present study, we used real-time quantitative RT-PCR to detect and quantitate the relative expression of CGRP, CRLR, RAMP1-3 and RDC-1 in the nucleus accumbens of intact rats and rats with inflammation. Our results demonstrate that CGRP, CRLR, RAMP1 and RAMP2 exist in the nucleus accumbens of intact rats, and that they were significantly upregulated in rats with inflammation. In contrast, no expression was detected for RDC-1 and RAMP3. These findings indicated a functional role for CGRP and its receptors in inflammation and pain modulation.

Differential gene expression of adrenomedullin receptors in pressure- and volume-overloaded heart--role of angiotensin II

Left ventricular (LV) adrenomedullin (AM) gene expression differs between pressure overload (POL) and volume overload (VOL) and angiotensin II could be a critical stimulator of AM gene expression in POL and VOL models. Calcitonin receptor-like receptor (CRLR) co-expressed with receptor activity modifying protein 2 (RAMP2) or RAMP3 functions as an AM receptor. Levels of CRLR, RAMP2 and RAMP3 mRNA that were significantly increased within 24 h returned to the basal level at 5 days after the imposition of POL in the present study. In contrast, mRNA levels of CRLR and RAMP2 gradually increased over 6 weeks after the imposition of VOL. Continuous infusion of angiotensin II stimulated LV AM gene and AM receptor gene expression independently of LV peak-systolic and LV end-diastolic pressure. The gene expression of LV AM receptors increased in different types of cardiac overload. The present study revealed an intimate association between the AM signaling system and angiotensin II.

Tumor necrosis factor-alpha downregulates adrenomedullin receptors in human coronary artery smooth muscle cells

We examined the effects of tumor necrosis factor (TNF)-alpha on the expression and functionality of adrenomedullin (AM) receptors in cultured human coronary artery smooth muscle cells. Analysis of real-time quantitative polymerase chain reactions showed that these cells abundantly express two AM receptors comprised of calcitonin receptor-like receptor (CRLR) and receptor activity-modifying protein 1 (RAMP1) or RAMP2. TNF-alpha induced time- and dose-dependent decreases in the expression of CRLR and RAMP1/2 mRNAs, thereby diminishing AM-evoked cAMP production. The suppression of these three mRNAs was unaffected by inhibiting NOS, protein kinase G, protein kinase A, superoxide formation or NF-kappaB activation.