Adrenomedullin gene expression and its different regulation in human adrenocortical and medullary tumors

Adrenomedullin and tumour microenvironment

Adrenomedullin (AM) is a regulatory peptide whose involvement in tumour progression is becoming more relevant with recent studies. AM is produced and secreted by the tumour cells but also by numerous stromal cells including macrophages, mast cells, endothelial cells, and vascular smooth muscle cells. Most cancer patients present high levels of circulating AM and in some cases these higher levels correlate with a worst prognosis. In some cases it has been shown that the high AM levels return to normal following surgical removal of the tumour, thus indicating the tumour as the source of this excessive production of AM. Expression of this peptide is a good investment for the tumour cell since AM acts as an autocrine/paracrine growth factor, prevents apoptosis-mediated cell death, increases tumour cell motility and metastasis, induces angiogenesis, and blocks immunosurveillance by inhibiting the immune system. In addition, AM expression gets rapidly activated by hypoxia through a HIF-1α mediated mechanism, thus characterizing AM as a major survival factor for tumour cells. Accordingly, a number of studies have shown that inhibition of this peptide or its receptors results in a significant reduction in tumour progression. In conclusion, AM is a great target for drug development and new drugs interfering with this system are being developed.

Expression of adrenomedullin in human ovaries, ovarian sex cord-stromal tumors and cultured granulosa-luteal cells

The aim of the present study was to characterise the expression pattern of the multifunctional vasoactive peptide adrenomedullin (ADM) in human ovarian tumors, and to find hormonal regulators of ADM expression in human ovaries. The expression of ADM messenger RNA (mRNA) was higher in granulosa cell tumors than in fibrothecomas and normal ovaries, as analysed by Northern blots. In normal ovaries, ADM immunoreactivity was localised in both granulosa and thecal cells. Eight of the 90 granulosa cell tumors (9%) showed moderate and 53 (59%) weak ADM immunoreactivity, whereas 27% (11/41) of the fibrothecomas displayed weak ADM staining. FSH, protein kinase A activator (Bu)(2)cAMP, prostaglandin E(2) (PGE(2)), activin A and the broad protein kinase regulator staurosporine decreased ADM mRNA accumulation in cultured granulosa-luteal cells time- and dose-dependently. FSH, (Bu)(2)cAMP and PGE(2) increased progesterone secretion and the accumulation of the steroidogenic acute regulatory protein mRNA in these cells. In conclusion, ADM is expressed in normal human ovaries and sex cord-stromal tumors, particularly in those of granulosa cell origin. FSH, PGE(2,) (Bu)(2)cAMP and activin A suppress ADM gene expression in granulosa-luteal cells. Expression of ADM in human ovaries and its hormonal regulation in granulosa cells suggests a paracrine role for ADM in ovarian function.

Clinical and biochemical characteristics of normotensive patients with primary aldosteronism: a comparison with hypertensive cases

OBJECTIVE

It is unknown why some patients with biochemical evidence of primary aldosteronism (PA) do not develop hypertension. We aimed to compare clinical and biochemical characteristics of normotensive and hypertensive patients with PA.

DESIGN AND PATIENTS

Retrospective comparison of 10 normotensive and 168 hypertensive patients with PA for office or ambulatory blood pressure, serum potassium, plasma aldosterone and renin concentrations; the aldosterone:renin ratio, and tumour size. Comparison of initial hormonal pattern and drop in blood pressure following adrenalectomy in five normotensive and nine hypertensive patients matched for age, sex and body mass index.

RESULTS

The 10 normotensive patients were women and presented with hypokalemia or an adrenal mass. Age, plasma aldosterone and renin concentrations were similar in normotensive and hypertensive cases, but kalemia and body mass index were significantly lower in the normotensive patients. Mean tumour diameter was larger in the normotensive patients than in the hypertensive matched patients with an adenoma (P < 0.01). In normotensive patients, diastolic blood pressure and upright aldosterone correlated negatively with kalemia. Blood pressure was lowered similarly after adrenalectomy in five normotensive PA patients and in their matched hypertensive counterparts. Aldosterone synthase expression was detected in four out of five adrenal tumours.

CONCLUSIONS

Blood pressure may be normal in patients with well-documented PA. The occurrence of hypokalemia, despite a normal blood pressure profile, suggests that protective mechanisms against hypertension are present in normotensive patients.

Adrenomedullin expression does not correlate with survival in lung cancer

It is suggested that adrenomedullin (AM) plays a role in lung carcinogenesis although, to confirm this suggestion, further clinical studies are needed to determine its relationship with prognosis in lung cancer. Archived 50 paraffin-embedded tumor samples of the lung were retrospectively evaluated for AM expression by immunohistochemistry and analyzed for a possible correlation with patient characteristics and survival. Quantitation of immunoreactivity was accomplished using an immunohistochemical scoring system. The pulmonary resection specimens contained 22 squamous cell carcinomas, 15 adenocarcinomas, and 13 small cell carcinomas. Non-small cell carcinomas of the lung were more likely to express AM than small cell carcinomas of the lung. Ninety-one percent of squamous cell carcinomas and 87% of adenocarcinomas expressed AM at a moderate to strong level and grade2-4 (30-100%), which were significantly higher from the non-neo-plastic lung tissue. Twenty-three percent of small cell carcinomas of lung expressed AM. Interestingly, AM immunoreactivity was essentially weak and grade 1 (<%30) in this group. AM expression is upregulated in non-small cell carcinomas of the lung, whereas it is downregulated in small cell carcinomas and non-neo-plastic lung tissues. AM expression did not show any correlation with the differentiation of the tumor, the stage of cancer, and the overall survival of patients. These results did not support the role of adrenomedullin as an independent survival factor for lung cancer. However, AM inhibition in conjunction with other anti-angiogenic agents may be useful in the prevention and treatment of malignancies.

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.

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.

Cell and molecular biology of the multifunctional peptide, adrenomedullin

Adrenomedullin (AM) is a recently discovered regulatory peptide involved in many functions including vasodilatation, electrolyte balance, neurotransmission, growth, and hormone secretion regulation, among others. This 52-amino acid peptide is expressed by specific cell types in many organs throughout the body. A complex receptor system has been described for AM; it requires at least the presence of a seven-transmembrane-domain G-protein-coupled receptor, a single-transmembrane-domain receptor activity modifying protein, and a receptor component protein needed to establish the connection with the downstream signal transduction pathway, which usually involves cyclicAMP. In addition, a serum-binding protein regulates the biological actions of AM, frequently by increasing AM functional attributes. Changes in levels of circulating AM correlate with several critical diseases, including cardiovascular and renal disorders, sepsis, cancer, and diabetes. Whether AM is a causal agent, a protective reaction, or just a marker for these diseases is currently under investigation. New technologies seeking to elevate and/or reduce AM levels are being investigated as potential therapeutic avenues.

Paracrine effects of PAMP and adrenomedullin on the human adrenal H295R cell line: PAMP but not adrenomedullin stimulates DHEA secretion

It has previously been shown, by this laboratory and others, that adrenal cells actively secrete adrenomedullin. Here it is demonstrated that human adrenal cells also secrete the related peptide, proadrenomedullin N-terminal 20 peptide (PAMP). The actions of adrenomedullin and PAMP on adrenal steroid secretion were determined by measuring the aldosterone, cortisol and dehydroepiandrosterone (DHEA) content of cell culture medium after exposure of the human adrenal H295R cells to either PAMP or adrenomedullin. While PAMP was found to cause a dose-dependent increase in release of all the steroids into the medium, adrenomedullin only increased aldosterone and cortisol and had no effect on DHEA. These data suggest that both adrenomedullin and PAMP may be autocrine regulators of adrenal steroid secretion.

Adrenomedullin and cancer

Adrenomedullin (AM) is a pluripotent hormone with structural similarities to calcitonin gene-related peptide (CGRP), which is expressed by many tissues in the body and shows a remarkable range of effects mediated by paracrine/autocrine and possibly endocrine mechanisms. AM has been implicated as a mediator of several pathologies such as cardiovascular and renal disorders, sepsis, inflammation, diabetes and cancer, among others. AM is expressed in a variety of tumors where it aggravates several of the molecular and physiological features of malignant cells. AM has been shown to be a mitogenic factor stimulating growth in several cancer types and to encourage a more aggressive tumor phenotype. In addition, AM is an apoptosis survival factor for cancer cells and an indirect suppressor of the immune response through its binding protein, complement factor H, and regulation in expression of cytokines. AM plays an important role in environments subjected to low oxygen tensions, which is a typical feature in the proximity of solid tumors. Under these conditions, AM is upregulated through a hypoxia-inducible factor 1 (HIF-1)-dependent pathway and acts as a potent angiogenic factor promoting neovascularization. The collective findings brought together over the last years place AM as a major regulator of carcinogenesis-tumor progression and identifies its autocrine loop as a putative target for developing new strategies against human cancers.

Endogenous adrenomedullin system regulates the growth of rat adrenocortical cells cultured in vitro

The expression of adrenomedullin (AM) system (AM and its receptors), as mRNA and protein, has been detected in the mammalian adrenal zona glomerulosa (ZG) cells. Evidence has been also provided that exogenous AM is able to enhance in vivo and in vitro the proliferative activity of ZG cells. However, the possibility that endogenous AM system may act as a physiological ZG growth regulator has not yet been demonstrated. Hence, we investigated whether the prolonged (48-72 h) suppression of AM gene transcription by a specific antisense oligonucleotide or the long-lasting (24-96 h) blockade of AM receptors by the selective antagonist AM(22-52) are able to affect the growth of rat ZG cells cultured in vitro. Freshly dispersed cells were incubated for 3 h with an AM antisense or a scrambled oligonucleotide, then they were cultured for 48 or 72 h, and proAM mRNA expression and AM content was checked by reverse transcription-polymerase chain reaction and radioimmune assay, respectively. Other ZG cells were cultured in the presence of AM and/or AM(22-52). Growth assay showed that AM (10(-8) M) decreased and AM(22-52) (10(-6) M) increased the duplication time of cultured cells. AM (10(-8) M) raised proliferation index and decreased apoptotic index of cultured cells, and AM(22-52) reversed these effects. AM(22-52) (from 10(-7) to 10(-6) M) and pAM gene suppression by the antisense oligonucleotide significantly lowered proliferation index and increased apoptotic index of cultured cells, both these effects being abrogated by AM (10(-8) M). It is concluded that endogenous AM system plays a relevant role in the autocrine-paracrine regulation of cultured rat ZG-cell growth.

Role of the endogenous adrenomedullin system in regulating the secretion and growth of rat adrenal cortex

The expression of components of the adrenomedullin (AM) system (AM and its receptors) has been detected in mammalian adrenal zona glomerulosa (ZG) cells, and evidence has been provided that AM is able to inhibit agonist-stimulated aldosterone secretion from and to enhance the proliferative activity of ZG cells. However, there has been no evidence that the endogenous AM system acts as a physiological regulator of ZG function. Hence, we investigated whether the suppression of AM gene transcription by a specific antisense oligodeoxynucleotide (ODN) is able to alter the secretion and growth of rat ZG cells cultured in vitro. ZG cell cultures were examined 0, 2, 4, 6 and 8 days after treatment with scrambled sense (S)-ODN (control cultures) and AM antisense (A)-ODN. Control cultures, as well as freshly dispersed ZG cells and ODN-untreated cultures, expressed AM as mRNA and protein. A-ODN treatment suppressed AM expression within 4 days and the suppression lasted until day 6. Confluent control cultures displayed basal and angiotensin-II (Ang-II), K(+)- and adrenocorticotropic hormone (ACTH)-stimulated aldosterone secretions similar to those of ODN-untreated cultures. A-ODN treatment magnified the aldosterone response to Ang-II and K+ at days 4 and 6 (but not at day 8), without affecting the basal or ACTH-stimulated secretion. As compared to ODN-untreated and control cultures, non-confluent A-ODN-treated ones showed a 40% elongation in the duplication time, a significant decrease in the proliferation index, and a marked rise in apoptotic index from day 4 to day 8. In conclusion, our study validates the use of A-ODN to block the endogenous AM system, showing that suppression of AM-synthesis requires at least 2 days to become appreciable and persists for at least 6 days. Moreover, it provides the first evidence that endogenous AM plays a physiological role in cultured rat ZG cells, by exerting a buffering action on their acute secretory response to Ang-II and K+ and by maintaining normal basal proliferative and apoptotic activities.

Involvement of adrenomedullin induced by hypoxia in angiogenesis in human renal cell carcinoma

BACKGROUND

Adrenomedullin (AM) has pluripotent activities and is involved in the regulation of vasomotor tone, cell differentiation and embryogenesis. However, the expression and pathophysiological role of AM has not been determined in human renal cell carcinoma (RCC).

METHODS

Twenty-six RCC specimens and three cultured human RCC cell lines (A498, SN12C and KPK-13) were analyzed. Expression of AM was determined by immunohistochemistry and reverse transcription-polymerase chain reaction (RT-PCR) analysis. The correlation between AM expression and microvessel count (MVC) in RCC specimens was examined to determine if AM plays a role in tumor angiogenesis. The correlation between the expression of AM and vascular endothelial growth factor (VEGF) was also investigated. Lastly, the effect of hypoxia upon the mRNA expression of AM, VEGF and hypoxia inducible factor-1 (HIF-1) by RCC cell lines was determined.

RESULTS

Immunohistochemistry indicated that AM and VEGF were primarily localized in the cytosol of RCC cells. AM and VEGF mRNA were detected in all RCC specimens and cultured RCC cell lines analyzed by RT-PCR. There was a positive correlation between AM mRNA expression and MVC (r = 0.516, P = 0.0062), and between VEGF mRNA expression and MVC (r = 0.485, P = 0.0111). We also observed a positive correlation between AM mRNA expression and VEGF mRNA expression (r = 0.552, P = 0.0029). Hypoxia significantly induced AM and VEGF mRNA expression, although the increase of the AM mRNA level (10.6-26.7 fold) was markedly greater than that of the VEGF mRNA level (1.5-1.9 fold).

CONCLUSION

These results suggest that hypoxia-induced AM plays a part in tumor angiogenesis in conjunction with VEGF and facilitates human RCC growth under hypoxic conditions.

Adrenomedullin in the adrenal

Adrenomedullin (AM) was originally characterized in extracts of an adrenal medullary tumor. Since this original finding the peptide and its mRNA have also been found in the adrenal cortex, specifically, in the cells of the aldosterone-secreting zona glomerulosa. It is clear that the synthesis of AM is actively regulated in both cortex and medulla. Much research effort has been focused on identifying a role for AM in the adrenal gland. To date, no consistent effect on medullary catecholamine biosynthesis has been demonstrated. In the cortex the actions of AM are controversial and appear to depend on both the tissue preparation used and on the specific receptor population expressed in the individual gland. The results of further studies on the long-term actions of AM on adrenal growth and differentiation are awaited with interest.

Regulation of adrenomedullin expression and release

Adrenomedullin (AM) was originally identified in the extracts of human pheochromocytoma tissue, but this peptide is now known to be synthesized and secreted from many kinds of cells in the body, including vascular smooth muscle cells, endothelial cells, fibroblasts, cardiac myocytes, epithelial cells, and cancer cells. In this review, we summarize AM-secreting and AM gene-expressing cells in addition to the regulation of secretion and gene expression of AM. Although the data are still limited to deduce the general features of AM gene expression, synthesis, and secretion, AM is assumed to be classified into the new class of biologically active peptides, which is mainly expressed and secreted from non-endocrine type cells by the stimulation with inflammation-related substances. It is also interesting that serious physiological conditions such as inflammation or hypoxia potently stimulate AM expression and release, suggesting its unique physiological function distinct from other known biologically active peptides.

Multiple roles of adrenomedullin revealed by animal models

The newly identified adrenomedullin (AM) gene codes for a potent, highly conserved vasodilator that is expressed in many tissues. Many biological functions have been ascribed to AM based on its broad expression pattern and numerous in vitro studies, and it is currently viewed as a multifunctional peptide hormone. Recent advances in gene manipulation have permitted the development of experimental animal systems to help distinguish between gene causes and effects in the context of otherwise normal physiology, and so the normal biological function of the AM gene can be studied within the intact physiological milieu of a whole animal. In this review article, we summarize the recent findings from three different types of genetic experiments involving the AM gene.

Proadrenomedullin-derived peptides in the paracrine control of the hypothalamo-pituitary-adrenal axis

Adrenomedullin (ADM) and proadrenomedullin N-terminal 20 peptide (PAMP) are widely distributed in various body tissues and organs, including the hypothalamo-pituitary-adrenal (HPA) axis. ADM and PAMP inhibit in vitro release of ACTH from pituitary corticotropes, and findings suggest that this effect may become relevant when an exceedingly high ACTH secretion must be counteracted. ADM directly supresses angiotensin-II- and K+-stimulated aldosterone secretion from ZG cells, acting through calcitonin gene-related peptide (CGRP) type 1 ADM(22-52)-sensitive receptors, the activation of which is likely to impair Ca2+ influx. In contrast, ADM stimulates medullary chromaffin cells to release catecholamines, which in turn enhance aldosterone secretion acting in a paracrine manner. Also this effect of ADM occurs via CGRP1 receptors, which are coupled with the adenylate cyclase-dependent cascade. There is indication that in vivo these two opposite effects of ADM on ZG may interact with each other when normal aldosterone secretion has to be restored. ADM exerts a mitogenic effect on rat ZG, acting via CGRP1 receptors that activate the tyrosine kinase-dependent mitogen-activated protein kinase cascade. These findings, along with the demonstration of a high level of ADM gene expression in adrenocortical adenomas and carcinomas, may suggest a role for ADM as adrenocortical growth stimulator and tumor promoter. PAMP, like ADM, suppresses aldosterone response of ZG cells to Ca2+-dependent agonists, but, in contrast with ADM, it inhibits catecholamine release by adrenal medulla. Both effects of PAMP are mediated by PAMP(12-20)-sensitive receptors, whose signaling mechanism is likely to involve the blockade of voltage-gated Ca2+ channels. The concentrations attained by ADM and PAMP in the blood rule out the possibility that they act as true circulating hormones. Conversely, their content in the hypothalamo-pituitary complex and adrenal gland is consistent with a paracrine mechanism of action, which may play an important role in pathophysiological conditions where the function of the HPA axis has to be reset.

Adrenomedullin and calcitonin gene-related peptide receptors in the rat adrenal cortex

The actions of calcitonin gene-related peptide (CGRP) and adrenomedullin on steroid hormone secretion from the rat zona glomerulosa are controversial, with reports in the literature of both stimulatory and inhibitory effects. It appears that these results previously obtained may depend on the nature of the receptors expressed by zona glomerulosa cells. The present study was designed to characterize CGRP and adrenomedullin binding in the rat adrenal zona glomerulosa. Specific binding for both peptides was observed, with two CGRP receptor sites found, and a single population of adrenomedullin receptors, but approximately twice the number of adrenomedullin binding sites. Messenger RNA analysis of the candidate genes for CGRP and adrenomedullin receptors revealed an abundance of both CRLR and RAMP1 mRNA, suggesting that these genes encode one of the CGRP receptors in this tissue. Much less RAMP2 expression was observed, however, which suggests that another gene product may account for adrenomedullin binding. There were very low levels of RAMP3 expression, but abundant L1 mRNA present, which may suggest that this rather controversial receptor has a role in the adrenal. The finding of distinct and specific adrenomedullin and CGRP binding in this tissue may account for the different effects these peptides appear to exert on adrenal function.

Cancer and diabetes: two pathological conditions in which adrenomedullin may be involved

Adrenomedullin (AM) is a regulatory peptide involved in several physiological processes. Among them, AM has been implicated in the regulation of growth, both with mitogenic and antiproliferative activities on normal cells. AM is widely expressed during embryogenesis and may have a significant role in the proliferation and differentiation processes associated with development. AM is also expressed by cancer cell lines and tumors and has been implicated in the growth of malignant cells. Some additional activities associated with AM (antiapoptotic capabilities, angiogenic potential, and upregulation in hypoxic conditions), together with its wide distribution in cancer, suggest that AM may be an important factor in carcinogenesis. Besides its implication in growth, embryogenesis and tumor biology, AM is also involved in pancreatic regulation and diabetes. AM regulates insulin secretion and is overexpressed in the plasma of diabetic patients. Several findings indicate that AM may participate in the pathogenesis and/or clinical complications of this disease.

Transcriptional control of adrenomedullin induction by phorbol ester in human monocytic leukemia cells

Adrenomedullin is a potent vasodilator peptide that was originally identified from human pheochromocytoma. In this study, we investigated the induction of adrenomedullin gene expression in THP-1 acute monocytic leukemia cells during differentiation into macrophage-like cells by 12-O-tetradecanoylphorbol-13-acetate (TPA), and identified a cis-regulatory region of the human adrenomedullin gene responsible for TPA-induced adrenomedullin expression. Upon treatment with TPA (100 ng x mL(-1)) for 24 h, immunoreactive adrenomedullin concentrations in the culture medium and adrenomedullin mRNA levels were increased more than 10-fold, concomitant with the differentiation of THP-1 cells into macrophage-like cells. Actinomycin D abolished the TPA-induced adrenomedullin expression, indicating that the induction of ADM gene expression by TPA was regulated at the transcriptional level. Transient transfection assay revealed that a cis-acting region (positions -70 to -30) of human adrenomedullin gene was necessary for TPA-induced reporter gene expression. This region contains multiple copies of activator protein 2 (AP-2) binding sites, which are bound by purified AP-2 protein, as judged by electrophoretic mobility shift assay. The binding activity to this region was undetectable in nuclear extracts prepared from untreated THP-1 cells, but was increased in extracts prepared from TPA-treated cells. The protein binding was abolished by unlabeled oligonucleotides containing the AP-2 consensus sequence. These results indicate that the region (-70 to -30) of the human ADM gene containing multiple AP-2 binding sites is responsible for TPA-induced adrenomedullin expression in THP-1 cells.

Hypoxia-inducible factor-1 (HIF-1) up-regulates adrenomedullin expression in human tumor cell lines during oxygen deprivation: a possible promotion mechanism of carcinogenesis

Little is known about the molecular mechanisms that control adrenomedullin (AM) production in human cancers. We demonstrate here that the expression of AM mRNA in a variety of human tumor cell lines is highly induced in a time-dependent manner by reduced oxygen tension (1% O2) or exposure to hypoxia mimetics such as desferrioxamine mesylate (DFX) or CoCl2. This AM expression seems to be under hypoxia-inducible factor-1 (HIF-1) transcriptional regulation, since HIF-1alpha and HIF-1beta knockout mouse cell lines had an ablated or greatly reduced hypoxia AM mRNA induction. Similarly, inhibition or enhancement of HIF-1 activity in human tumor cells showed an analogous modulation of AM mRNA. Under hypoxic conditions, immunohistochemical analysis of tumor cell lines revealed elevated levels of AM and HIF-1alpha as compared with normoxia, and we also found an increase of immunoreactive AM in the conditioned medium of tumor cells analyzed by RIA. AM mRNA stabilization was shown to be partially responsible for the hypoxic up-regulated expression of AM. In addition, we have identified several putative hypoxia response elements (HREs) in the human AM gene, and reporter studies with selected HREs were capable of enhancing luciferase expression after exposure to DFX. Furthermore, transient coexpression of HIF-1alpha resulted in an augmented transactivation of the reporter gene after DFX treatment. Given that most solid human tumors have focal hypoxic areas and that AM functions as a mitogen, angiogenic factor, and apoptosis-survival factor, our findings implicate the HIF-1/AM link as a possible promotion mechanism of carcinogenesis.

Adrenomedullin, a multifunctional regulatory peptide

Since the discovery of adrenomedullin in 1993 several hundred papers have been published regarding the regulation of its secretion and the multiplicity of its actions. It has been shown to be an almost ubiquitous peptide, with the number of tissues and cell types synthesizing adrenomedullin far exceeding those that do not. In Section II of this paper we give a comprehensive review both of tissues and cell lines secreting adrenomedullin and of the mechanisms regulating gene expression. The data on circulating adrenomedullin, obtained with the various assays available, are also reviewed, and the disease states in which plasma adrenomedullin is elevated are listed. In Section III the pharmacology and biochemistry of adrenomedullin binding sites, both specific sites and calcitonin gene-related peptide (CGRP) receptors, are discussed. In particular, the putative adrenomedullin receptor clones and signal transduction pathways are described. In Section IV the various actions of adrenomedullin are discussed: its actions on cellular growth, the cardiovascular system, the central nervous system, and the endocrine system are all considered. Finally, in Section V, we consider some unresolved issues and propose future areas for research.

Production and secretion of two vasoactive peptides, adrenomedullin and endothelin-1, by cultured human adrenocortical carcinoma cells

The production and secretion of peptides by adrenocortical tumors have not been well studied. We therefore studied the production and secretion of two vasoactive peptides, adrenomedullin and endothelin-1 in SW-13 human adrenocortical carcinoma cells by radioimmunoassay and Northern blot analysis. Both immunoreactive-adrenomedullin and immunoreactive-endothelin were detected in the culture medium of SW-13 cells (27.7 +/- 1.6 fmol/10 (5) cells/24 h and 11.0 +/- 0.8 fmol/10 (5) cells/24 h, respectively, mean +/- SEM, n = 6). Northern blot analysis showed the expression of adrenomedullin mRNA and endothelin-1 mRNA in SW-13 cells. On the other hand, no significant amount of calcitonin gene-related peptide, corticotropin-releasing hormone, neuropeptide Y, or urocortin was secreted by SW-13 cells. Treatment with ACTH (10(-9)-10(-7) mol/l), angiotensin II (10(-9)-10(-7) mol/l), or dexamethasone (10(-8)-10(-6) mol/l) for 24 h had no significant effects on immunoreactive-adrenomedullin levels and immunoreactive-endothelin levels in the culture medium of SW-13. Treatment with tumor necrosis factor (TNF)-alpha (20 ng/ml) increased significantly both immunoreactive-adrenomedullin levels and immunoreactive-endothelin levels in the culture medium. Interferon-gamma (100 U/ml) increased the immunoreactive-endothelin levels, but not immunoreactive-adrenomedullin levels, whereas interleukin-1 (IL-1)beta (10 ng/ml) increased immunoreactive-adrenomedullin levels, but not immunoreactive-endothelin levels. These findings indicate that SW-13 human adrenocortical carcinoma cells produce and secrete two vasoactive peptides, adrenomedullin, and endothelin-1 and that the secretion of these two peptides is modulated differently by cytokines.

Expression of adrenomedullin mRNA in adrenocortical tumors and secretion of adrenomedullin by cultured adrenocortical carcinoma cells

Immunoreactive-adrenomedullin concentrations and the expression of adrenomedullin mRNA were studied in the tumor tissues of adrenocortical tumors. Northern blot analysis showed the expression of adrenomedullin mRNA in tumor tissues of adrenocortical tumors, including aldosterone-producing adenomas, cortisol-producing adenomas, a non-functioning adenoma and adrenocortical carcinomas, as well as normal parts of adrenal glands and pheochromocytomas. On the other hand, immunoreactive-adrenomedullin was not detected in about 90% cases of adrenocortical tumors (<0.12 pmol/g wet weight (ww)). Immunoreactive-adrenomedullin concentrations ranged from 0.44 to 198.2 pmol/g ww in tumor tissues of pheochromocytomas and were 9.2 +/- 1.2 pmol/g ww (mean +/- SD, n = 4) in normal parts of adrenal glands. Adrenomedullin mRNA was expressed in an adrenocortical adenocarcinoma cell line, SW-13 and immunoreactive-adrenomedullin was detected in the culture medium of SW-13 (48.9 +/- 1.8 fmol/10(5) cells/24h, mean +/- SEM, n = 4). On the other hand, immunoreactive-adrenomedullin was not detectable in the extract of SW-13 cells (<0.09 fmol/10(5) cells), suggesting that adrenomedullin was actively secreted from SW-13 cells without long-term storage. These findings indicate that adrenomedullin is produced and secreted, not only by pheochromocytomas, but also by adrenocortical tumors. Undetectable or low levels of immunoreactive-adrenomedullin in the tumor tissues of adrenocortical tumors may be due to very rapid secretion of this peptide soon after the translation from these tumors.