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

Abstract

Adrenomedullin (ADM) is a polypeptide originally discovered in a human pheochromocytoma and is also present in normal adrenal medulla. It has been proposed that ADM could be involved in the regulation of adrenal steroidogenesis via paracrine mechanisms. Our aim was to find out if ADM gene is expressed in adrenocortical tumors and how ADM gene expression is regulated in adrenal cells. ADM mRNA was detectable by Northern blotting in most normal and hyperplastic adrenals, adenomas and carcinomas. The average concentration of ADM mRNA in the hormonally active adrenocortical adenomas was about 80% and 7% of that in normal adrenal glands and separated adrenal medulla respectively. In adrenocortical carcinomas, the ADM mRNA concentration was very variable, but on average it was about six times greater than that in normal adrenal glands. In pheochromocytomas, ADM mRNA expression was about ten times greater than that in normal adrenals and three times greater than in separated adrenal medulla. In primary cultures of normal adrenal cells, a protein kinase C inhibitor, staurosporine, reduced ADM mRNA accumulation in a dose- and time-dependent fashion (P < 0.01), whereas it simultaneously increased the expression of human cholesterol side-chain cleavage enzyme (P450 scc) gene (a key gene in steroidogenesis). In cultured Cushing's adenoma cells, adrenocorticotropin, dibutyryl cAMP ((Bu)2cAMP) and staurosporine inhibited the accumulation of ADM mRNA by 40, 50 and 70% respectively (P < 0.05), whereas the protein kinase C activator, 12-O-tetradecanoyl phorbol 13-acetate (TPA), increased it by 50% (P < 0.05). In primary cultures of pheochromocytoma cells, treatment with (Bu)2cAMP for 1 and 3 days increased ADM mRNA accumulation two- to threefold (P < 0.05). Our results show that ADM mRNA is present not only in adrenal medulla and pheochromocytomas, but also in adrenocortical neoplasms. Both protein kinase A- and C-dependent mechanisms regulate ADM mRNA expression in adrenocortical and pheochromocytoma cells supporting the suggested role for ADM as an autocrine or paracrine (or both) regulator of adrenal function.

Hypoxia-Inducible Factor-1 (HIF-1) Up-Regulates Adrenomedullin Expression in Human Tumor Cell Lines during Oxygen Deprivation: A Possible Promotion Mechanism of Carcinogenesis

“…Maternal decidual cells and embryonic cells (fetal cytotrophoblast giant cells) of the ectoplacental cone, a site that mimics the invasion process of carcinogenesis, also show abundant expression of AM/AM-R (8,9). After its initial identification in a human pheochromocytoma, further studies have demonstrated increased AM expression in tumor tissue of ganglioneuroblastoma, neuroblastoma, and adrenocortical carcinomas (10,11). In addition, AM plasma levels are elevated in patients with gastrointestinal or lung cancer (12).…”

Autocrine role of adrenomedullin in the human adrenal cortex

“…Previous studies from our laboratory have demonstrated the presence of both adrenomedullin mRNA and peptide in the rat adrenal zona glomerulosa . In the human, adrenomedullin message is found in adrenocortical tumours and cultured cells (Liu et al 1997, Takahashi et al 1998. Furthermore, studies on the adrenocortical SW13 cell line have also found that immunoreactive adrenomedullin is produced and released into the culture medium (Takahashi et al 1998), in common with many other human tumour cell lines (Miller et al 1996).…”

“…In some cases, however, for example the SW13 cell line, it appears that adrenomedullin release is constitutive and not regulated by hormones which alter adrenal function (Takahashi et al 2000), in which case it is unlikely to be a significant regulator of adrenal function. In the human adrenal cortex, however, there is evidence that adrenomedullin gene expression is actively regulated (Liu et al 1997), although regulation of peptide secretion has not been investigated. One of the aims of the present study was to determine whether the H295R cell line resembles human adrenal tissue in that adrenomedullin is actively regulated.…”

Role of the Endogenous Adrenomedullin System in Regulating the Secretion and Growth of Rat Adrenal Cortex

“…AM, acting via calcitonin gene-related peptide (CGRP)8-37-and AM22-52-sensitive receptors, has been found 1) to inhibit angiotensin-II (Ang-II)-and K -stimulated aldosterone secretion, and 2) to enhance the growth of ZG cells both in vivo and in vitro. Evidence has been provided that the pAM gene is expressed in rat (8) and human ZG cells (9), as well as in several benign and malignant adrenocortical tumors (10,11) and the adrenocortical carcinoma cell lines SW13 and NCI-H295 (12)(13)(14). Moreover, low but sizeable concentrations of immunoreactive (ir)-AM have been detected in dispersed human and rat ZG and aldosteronoma cells (8,9,11), as well as in the culture medium of the SW13 cell line (13,14).…”