The recent cloning of the ACTH receptor (ACTH-R) gene allows investigation of the tissue localization and relative abundance of ACTH-R mRNA in normal and neoplastic adrenal cortex. Using in situ hybridization (ISH) we studied the expression of ACTH-R mRNA in four adult adrenals of brain-dead patients, two cortisol-producing adenomas (CPA), three aldosterone-producing adenomas (APA), one non-functional adenoma (NFA), and three carcinomas. The results were compared with the mRNA expression of key steroidogenic enzymes and of the glucocorticoid receptor (GR) mRNA using Northern blotting. In adult adrenals, messenger RNA encoding ACTH-R was localized in all three zones of the adrenal cortex, in accordance with the stimulatory role of ACTH on mineralocorticoid, glucocorticoid and adrenal androgen secretion. In comparison, expression of side-chain cleavage enzyme (P450scc) showed a similar tissue distribution with mRNA abundance in all three zones, whereas 17-hydroxylase/17-20 lyase (P450c17) mRNA expression was only detected in the zona fasciculata and zona reticularis. All CPAs and APAs expressed significant levels of ACTH-R mRNA whereas an NFA showed low expression of ACTH-R mRNA. Two of three adrenocortical carcinomas expressed ACTH-R mRNA. Northern analysis using dot blot was employed to quantify ACTH-R and GR mRNA expression and confirmed the ISH data: ACTH-R mRNA expression was high in CPAs (275 and 195% vs 100 +/- 25% in adult adrenals), APAs (127, 200 and 221%) and two carcinomas (99 and 132%), but low in the NFA (7%) and in an androgen secreting carcinoma (16%). GR mRNA expression was high in the NFA (195%) and in two of three carcinomas (93, 188, 227%). We conclude that ACTH-R mRNA is upregulated in functional adenomas by yet unidentified mechanisms. The tissue distribution of ACTH-R and P450 enzyme mRNA expression is highly variable in neoplastic adrenals and does not allow a clear differentiation between benign and malignant tumors.
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M Reincke, F Beuschlein, G Menig, G Hofmockel, W Arlt, R Lehmann, M Karl, and B Allolio
M Fassnacht, F Beuschlein, S Vay, P Mora, B Allolio, and M Reincke
The adrenostatic compound aminoglutethimide (AG), a potent inhibitor of the P450 side chain cleavage enzyme, is used in the treatment of ACTH-dependent or adrenal Cushing's syndrome. Recently, AG has been shown to inhibit ACTH receptor (ACTH-R) mRNA expression in ovine adrenocortical cells in a time-dependent fashion. To investigate whether ACTH-R down-regulation will also be induced in tumor cells, we studied the effect of AG on ACTH-R expression in the human NCI-h295 adrenocortical carcinoma cell line, which expresses functional ACTH receptors and produces steroids of the glucocorticoid, mineralocorticoid and androgen pathway. The cells were incubated in triplicate with increasing doses of AG (3, 30, 300 microM) which suppressed steroid secretion dose-dependently. After 48 h, cells were harvested, and total RNA was extracted, electrophoresed, blotted and hybridized with a human ACTH-R cDNA probe. In parallel experiments, after preincubation with AG the cells were stimulated with ACTH (10 nM) for 10 min and the intracellular cAMP accumulation was determined by RIA. AG significantly suppressed the baseline ACTH-R mRNA expression in a dose-dependent fashion (300 microM AG, 5+/-1%; 30 microM AG, 64+/-1%; 3 microM AG, 108+/-19% compared with control cells, 100+/-11%). The reduced ACTH-R mRNA expression was paralleled by low ACTH-induced cAMP accumulation indicating reduced expression of the ACTH-R protein. The adrenostatic compound metyrapone, an inhibitor of 11beta-hydroxylase activity, also suppressed ACTH-R mRNA expression in a similar fashion. Stimulation of the protein kinase A pathway by simultaneous incubation of ACTH (10 nM) or forskolin (10 microM) together with AG was not able to overcome the steroid biosynthesis blockade, but reversed the inhibitory effects of AG on the ACTH-R mRNA expression. Also, cortisol (12 microM) reversed the AG-induced ACTH-R mRNA expression. We conclude that AG induces profound ACTH-R down-regulation in the NCI-h295 cell line either by affecting the gene expression or by decreasing transcript accumulation via an effect on RNA stability. This novel action of AG can be reversed by stimulation of the cAMP pathway and of the glucocorticoid-mediated signal transduction cascade. As the down-regulation occurs in vitro at concentrations which are reached during treatment with AG in humans it may contribute to its therapeutic activity in adrenal disease.
IA Hansen, O Jakob, S Wortmann, T Arzberger, B Allolio, and E Blind
The polypeptide TIP39 (tuberoinfundibular peptide of 39 residues) is a potent activator of the parathyroid hormone (PTH)-2 receptor (P2R) and an antagonist of the PTH-1 receptor (P1R). To clarify its possible physiological function(s), we studied its interaction with the human P1R and P2R and examined the expression of TIP39 in man and mouse. To find out possible sites of this ligand interaction in the organism, we identified the genes encoding the TIP39 protein precursors of Homo sapiens and Mus musculus in the databases of the human and mouse genome projects respectively. We then obtained the full-length cDNAs of both species by RACE-PCR. The deduced TIP39 preprohormones consist of an N-terminal 30 amino acid (aa) signal peptide followed by a 29 aa TIP39 precursor-related peptide, an Arg-Arg processing site, and the actual 39 aa TIP39 sequence. The first 23 aa of the actual TIP39 sequence, thought to contain the P2R receptor activation site, are identical in man and mouse and thus phylogenetically conserved. By contrast, the 16 aa C-terminal portion showed a higher degree of diversity (75% aa identity). By using RT-PCR, TIP39 was found to be highly expressed in human central nervous system tissues, trachea, fetal liver, and, to a lesser degree, in human heart and kidney. Using in situ hybridization, TIP39 mRNA expression was revealed in various areas of the mouse brain. In a homologous human cell model using human embryonic kidney 293 cells stably transfected with human P1R and P2R, human TIP39 did bind to P1R with moderate affinity (IC(50) approximately 10(-7)-10(-6 )M), but showed higher affinity binding to P2R (IC(50) approximately 10(-8)M), comparable to the affinity of human N-terminal PTH (hPTH(1-34)) to this receptor. In P2R-transfected cells, the cAMP pathway was activated more efficiently ( approximately 10-fold) by TIP39 as a ligand compared to hPTH(1-34). In P1R-transfected cells, only hPTH(1-34) but not TIP39 was able to elicit a cAMP response, but TIP39 was able to directly antagonize the cAMP-stimulating effect of hPTH(1-34) on this receptor. In conclusion, we could show a possible function of TIP39 for the human organism as a potent activator of P2R (e.g. in brain) as well as an antagonist of the action of PTH and/or PTH-related protein on P1R (e.g. in bone and kidney). The physiological role of TIP39 in calcium metabolism with regard to these actions remains to be determined. The tools developed in this work will allow us to investigate the possible role of TIP39 as a locally or systemically secreted ligand modulating the function of the PTH receptor family.
M Fassnacht, A Franke, A Dettling, S Hahner, M Zink, S Wudy, and B Allolio
Bisphosphonates (BPs), specific inhibitors of osteoclasts, are well established in the management of skeletal metastases in breast cancer. Recent studies have suggested that these compounds may also directly influence tumor cell proliferation. As adrenocortical cancer frequently leads to bone metastases, we investigated the effects of clodronate (CLO) in the human adrenocortical cancer cell line NCI-H295 and in primary cultures of bovine adrenocortical cells. Both the non-amino BP CLO and the amino BP pamidronate (PAM) exhibited a dose-dependent antiproliferative effect in both cell types (cell viability in NCI-H295 cells: 100 microM CLO: 98+/-8%; 500 microM CLO 76+/-6%; 1000 microM CLO 53+/-2; 10 microM PAM 96+/-3%; 50 microM PAM 46+/-6%; 100 microM PAM 11+/-1% vs untreated control cells: 100+/-10%; P<0.01). FACS analysis in NCI-H295 cells treated with either CLO or PAM demonstrated both apoptotic and necrotic cell death. However, while during PAM treatment cell number and hormone secretion decreased in parallel, we observed specific impairment of steroidogenesis in the presence of CLO with a dose-dependent increase in the 17-OH-progesterone/cortisol ratio (100 microM CLO 134+/-30%; 500 microM CLO 284+/-10%; 1000 microM CLO 545+/-130% vs 100+/-20% in control cells; P<0.01). Further analysis in ACTH-stimulated bovine adrenal cells using stable isotope dilution/gas chromatography-mass spectrometry demonstrated CLO-induced inhibition of adrenal 21-hydroxylase (P450c21) activity leading to a dose-dependent increase in the 17-OH-progesterone/11-deoxycortisol ratio. In conclusion, we demonstrate a dose-dependent antiproliferative effect of CLO and PAM in adrenocortical cells. In addition, for the first time, we describe a suppressive effect of CLO on steroidogenesis via inhibition of adrenal 21-hydroxylase (P450c21) activity.