The NCI-H295 cell line: a pluripotent model for human adrenocortical studies

Polychlorinated biphenyl 126 stimulates basal and inducible aldosterone biosynthesis of human adrenocortical H295R cells

To understand the effects of polychlorinated biphenyls (PCBs) on adrenal aldosterone biosynthesis, we have performed a systematical study to characterize the corresponding steroidogenic response of human adrenocortical cell line H295R to PCB126 exposure. We found that PCB126 at high concentrations stimulated basal and inducible aldosterone production. The aldosterone induction occurred concomitantly with activation of the CYP11B2 gene. Despite the fact that PCB126 acted in synergy with both potassium and angiotensin II (Ang II) in activation of aldosterone synthesis, PCB126 only modestly increased CYP11B2 mRNA expression in the presence of Ang II contrary to the synergistic transcriptional induction elicited by PCB126 and potassium. This implicated that PCB126 had differential interactions with the potassium and Ang II signaling systems in the regulation of aldosterone biosynthesis. In addition, high concentrations of PCB126 elevated transcriptional expression of the type I Ang II receptor (AT(1)) and might thus sensitize the cellular Ang II responsiveness in both basal and inducible aldosterone biosynthesis. SF-1 was not involved in the PCB126-induced transcriptional regulation despite its importance in steroidogenic gene activation.

Human adipocytes secrete mineralocorticoid-releasing factors

Obesity has become an epidemic problem in western societies, contributing to metabolic diseases, hypertension, and cardiovascular disease. Overweight and obesity are frequently associated with increased plasma levels of aldosterone. Recent evidence suggests that human fat is a highly active endocrine tissue. Therefore, we tested the hypothesis that adipocyte secretory products directly stimulate adrenocortical aldosterone secretion. Secretory products from isolated human adipocytes strongly stimulated steroidogenesis in human adrenocortical cells (NCI-H295R) with a predominant effect on mineralocorticoid secretion. Aldosterone secretion increased 7-fold during 24 h of incubation. This stimulation was comparable to maximal stimulation of these cells with forskolin (2 x 10(-5) M). On the molecular level, there was a 10-fold increase in the expression of steroid acute regulatory peptide mRNA. This effect was independent of adipose angiotensin II as revealed by the stimulatory effect of fat cell-conditioned medium even in the presence of the angiotensin type 1 receptor antagonist, valsartan. None of the recently defined adipocytokines accounted for the effect. Mineralocorticoid-stimulating activity was heat sensitive and could be blunted by heating fat cell-conditioned medium to 99 degrees C. Centrifugal filtration based on molecular mass revealed at least two releasing factors: a heat sensitive fraction (molecular mass >50 kDa) representing 60% of total activity, and an inactive fraction (molecular mass <50 kDa). However, the recovery rate increased to 92% when combining these two fractions, indicating the interaction of at least two factors. In conclusion, human adipocytes secrete potent mineralocorticoid-releasing factors, suggesting a direct link between obesity and hypertension.

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.

Interferon-inducible genes in the rat adrenal gland and vascular smooth muscle cells

Chronic stimulation of the renin-angiotensin system results in increased zona glomerulosa cells and in cells expressing the final enzyme in the synthesis of aldosterone, the cytochrome P-450 aldosterone synthase. The genes activated during adrenal remodeling are not well defined. We have reported that the expression of interferon-inducible genes, 9-27, 1-8D and 1-8U in H295R cells is stimulated by A-II. The 9-27 gene is expressed mainly in leukocytes and is associated with cell proliferation. In this study, we searched for similar genes in a rat zona glomerulosa cDNA library, and examined the regulation of the expression of these genes. We found the Rat8 gene, which has been reported to be similar to human interferon-inducible genes, as well as two similar genes, No. 10 (1096 bp), and No. 16 (630 bp). Rat8 gene and No. 16 were mainly expressed in zona glomerulosa. The product of No. 10 is thought to be a secreted protein, unlike those of 8 and 16, and its expression in the adrenal was weak in comparison. The control of the expression of rat8 or No. 16 genes differs depending on the tissue. Expression in A10 cells (derived from rat embryo thoracic aorta) was not stimulated by A-II, nor was it influenced by salt intake in the adrenal gland, but it was reduced in vascular smooth muscle cells (VSMC) of rats on a low sodium diet. These results show that genes similar to the human 1-8 gene family are expressed in rat adrenal glomerulosa cells and VSMC, but their expression is not regulated by A-II. The function of these genes in VSMC and adrenal is unknown.

Tumour-derived human adrenocortical cells express beta-adrenergic receptors: steroidogenic effects of beta-adrenergic input

It is well established that catecholamines have potent actions on adrenocortical function and steroidogenesis in different species. The effect of these substances on steroid production of the human adrenal cell line H295R is the subject of this study. H295R cells were cultured in the presence of the synthetic catecholamine, isoproterenol for four hours. Aldosterone, cortisol, and DHEA secretion was measured using direct radioimmunoassays. Administration of 10(-11)-10(-7) mol/L isoproterenol produced a dose-dependent increase in secretion of aldosterone, cortisol, and DHEA by H295R cells resulting in 3-fold, 2.5-fold, and 2-fold stimulation respectively, relative to basal values. Analysis of mRNA using nested PCR revealed the presence of all three types of beta-adrenergic receptors namely beta1, beta2, and beta3 in H295R cells. Isoproterenol had no effect on the proliferation rate of H295R cells as determined by 3H-incorporation assay and the colorimetric WST-1 cell proliferation assay.

Expression of glutathione transferase isoenzymes in the human H295R adrenal cell line and the effect of forskolin

In previous studies in our laboratory (L. Mankowitz, L. Staffas, M. Bakke, and J. Lund, Biochem J, 1995, 305, 111-118; L. Staffas, L. Mankowitz, M. Söderström, A. Blanck, I. Porsch-Hällström, C. Sundberg, B. Mannervik, B. Olin, J. Rydström, and J.W. DePierre, Biochem J, 1992, 286, 65-72) isoenzymes of GST, primarily of the mu class, have been shown to be downregulated by adrenocorticotropic hormone (ACTH) in rat and mouse adrenal cells. In the present investigation the human adrenal H295R cell line (W.E. Rainey, I.M. Bird, and J.I. Mason, Mol Cell Endocrinol, 1994, 100, 45-50) was examined in a similar manner. Analysis by reverse-phase HPLC revealed that these cells express four isoenzymes of GST, i.e., A1, A2, P1, and M4, as well as another unidentified protein that was retained by our affinity column (elution time of 32 min) and, thus, presumably binds glutathione. Among these forms, A1 was present at the highest level. Upon addition of forskolin (an activator of adenylate cyclase which has been shown previously to mimic the effect of ACTH on adrenal cells) to the culture medium, the level of A1 decreased approximately 70% by forskolin, whereas the levels of the other isoenzymes were slightly increased, and that of the unknown form doubled. Thus, the influence of ACTH on expression of GST isoenzymes in this human adrenal cell line differs from that in rat and mouse adrenal cells.

Expression of activin/inhibin receptor and binding protein genes and regulation of activin/inhibin peptide secretion in human adrenocortical cells

Activins and inhibins are glycoprotein hormones produced mainly in gonads but also in other organs. They are believed to be important para/autocrine regulators of various cell functions. We investigated activin/inhibin receptor and binding protein gene expression and the regulation of activin/inhibin secretion in human adrenal cells. RT-PCR revealed inhibin/activin alpha-, betaA/B-subunit, follistatin, activin type I/II receptor, and inhibin receptor (betaglycan and inhibin-binding protein) mRNA expression in fetal and adult adrenals and cultured adrenocortical cells. Cultured cells secreted activin A and inhibin A/B as determined by specific ELISAs. ACTH stimulated inhibin A/B secretion in fetal (1.8- and 1.8-fold of control, respectively) and in adult cells (3.4- and 1.7-fold of control, respectively) without significant effect on activin A. 8-bromoadenosine cAMP (protein kinase A activator) increased activin A and inhibin A/B secretion in the human adrenocortical NCI-H295R cell line (32-, 17-, and 3-fold of control, respectively). 12-O-tetradecanoyl phorbol-13-acetate (protein kinase C activator) stimulated both activin A and inhibin A secretion (764- and 32-fold of control, respectively), and activin treatment increased inhibin B secretion in these cells (25-fold of control). In conclusion, human adrenocortical cells produce dimeric activins and inhibins. ACTH stimulates inhibin secretion and decreases activin/inhibin secretion ratio, probably via the protein kinase A signal transduction pathway. This, together with the adrenocortical activin/ inhibin receptor and binding protein expression, suggests a physiological role for activins and inhibins in the human adrenal gland.

Genetic network identification by high density, multiplexed reversed transcriptional (HD-MRT) analysis in steroidogenic axis model cell lines

Transcriptional network analysis in steroidogenic axis cell lines requires an understanding of cellular network composition and complexity. Previous studies have shown that absence of transcriptional network components in a cell line compromises that cell line's functional capacity for transcriptional regulation. Our goal was to analyze qualitatively steroidogenic axis-derived cell lines' expression of a putative transcriptional network involved in human and mouse development. To pursue this analysis we used Northern blots and a high density-multiplexed reverse transcription-polymerase chain reaction (HD-MRT-PCR) approach. Our results revealed that, while some members of this putative network were universally expressed, only a minority of the non-constitutive targeted transcripts were present in any single line. Based on our data and previously published results for contextual expression of these transcription factors, a model was constructed possessing the topology suggestive of a scale-free network: certain network members were highly connected nodes and would represent critical sites of vulnerability. The importance of these highly connected nodes for network function is supported by the severe phenotypes exhibited by human patients and animal models when these genes are mutated. We conclude that knowledge of network composition in specific cell lines is essential for their use as models to investigate functional interactions within selected subnetworks.

Nitric oxide potently inhibits the rate-limiting enzymatic step in steroidogenesis

This study tested the hypothesis that nitric oxide (NO) inhibits the rate-limiting catalytic step in steroidogenesis, cytochrome P450 cholesterol side-chain cleaving enzyme (CYP11A1), independent of soluble guanylyl cyclase (GC-S) stimulation. To assess CYP11A1 activity, pregnenolone levels were quantified in murine adrenocortical Y1 cells in the presence of the 3beta-hydroxy-Delta(5)-steroid dehydrogenase inhibitor, 2alpha-cyano-17beta-hydroxy-4,4',17alpha-trimethylandrost-5-ene-3-one. The NO donor, (Z)-1-[2-(2-aminoethyl-N-(2-ammonioethyl)amino]diazen-1-ium-1,2-diolate(deta nonoate), inhibited vasoactive intestinal peptide-, forskolin- and 22alpha-hydroxycholesterol (22HC)-facilitated pregnenolonogenesis in the absence of GC-S activation and in the presence of a GC-S inhibitor, 1H-[1,2,4]oxadiazolo[4,3-a]quinoxalin-1-one (ODQ). CYP11A1 was also heterologously expressed in monkey COS7 cells. Deta nonoate inhibited 22HC-facilitated activity of the over-expressed enzyme in the absence of GC-S activation and in the presence of ODQ. The NO-independent, GC-S agonist, 1-benzyl-3-(5'-hydroxymethyl-2'-furyl)indazole did not inhibit steroidogenesis. The IC(50) for effects of free NO on CYP11A1 was potent and in the 0.4-2 microM range. These results support the hypothesis that NO inhibits the rate-limiting enzyme in steroidogenesis independent of GC-S activation.

Induction and inhibition of aromatase (CYP19) activity by various classes of pesticides in H295R human adrenocortical carcinoma cells

Various pesticides known or suspected to interfere with steroid hormone function were screened in H295R cells for effects on catalytic activity and mRNA expression of aromatase. Dibutyl-, tributyl-, and triphenyltin chloride decreased aromatase and ethoxyresorufin O-deethylase activities concentration dependently (1-300 nM; 24-h exposure). However, these decreases occurred only at cytotoxic concentrations, indicated by decreases in mitochondrial MTT reduction and intracellular neutral red uptake. The organotins did not cause direct inhibition during the catalytic assay (1-1000 nM; 1.5-h exposure). The same was true for p,p'-DDT, and o,p-DDT, and o,p-DDE, which decreased aromatase activity only at cytotoxic concentrations (> or =10 microM; 24-h exposure). p,p'-DDE had no effect on aromatase activity or cell viability at 1 and 10 microM. Various imidazole-like fungicides were aromatase inhibitors. Imazalil and prochloraz were potent mixed inhibitors (K(i)/K(i)(') = 0.04/0.3 and 0.02/0.3 microM, respectively), whereas propiconazole, difenoconazole, and penconazole were less potent competitive inhibitors (K(i) = 1.9, 4.5, and 4.7 microM, respectively). Fenarimol, tebuconazole, and hexaconazole decreased aromatase activity close to cytotoxic concentrations. Vinclozolin, as was shown previously for atrazine, induced aromatase activity and CYP19 mRNA levels about 2.5- and 1.5-fold, respectively. To investigate the mechanism of aromatase induction in H295R cells, the ability of the pesticides to increase intracellular cAMP levels was examined. Vinclozolin (100 microM) and atrazine (30 microM) increased cAMP levels about 1.5-fold above control. Forskolin and isobutyl methylxanthine (IBMX) increased cAMP levels 3 and 1.8-fold, respectively. Time-response curves for cAMP induction and concentration-response curves for aromatase induction by vinclozolin, atrazine, and IBMX were similar, suggesting that the mechanism of aromatase induction by these pesticides is mediated through inhibition of phosphodiesterase activity.

Role of the PKA-regulated transcription factor CREB in development and tumorigenesis of endocrine tissues

The cAMP pathway plays a major role in the development of endocrine tissues and various molecular defects of key components of this pathway (G protein, receptors, PKA, etc.) have been observed in endocrine tumors. The ubiquitous transcription factor CREB (cAMP-response element binding protein) binds to the cAMP response element (CRE) and stimulates transcription after phosphorylation on Ser(133) by PKA. The CREB family of transcription factors contains three members: CREB, CREM, and ATF-1. Targeted expression of dominant-negative mutants of CREB in transgenic mice leads to somatotrophs or thyroid hypoplasia. GH-secreting adenomas are benign secreting tumors expressing an activated mutant G alpha s protein (Gsp) in about 40% of cases. In GH-secreting adenomas CREB is always expressed and often highly phosphorylated. The CREM isoform ICER is stimulated by cAMP, and its expression is increased in Gsp-harboring tumors. After transfection in pituitary somatotroph cells, activating mutations of Gs protein (Gsp) and overexpression of wild-type G alpha S stimulate transcription of various CRE-containing promoters via CREB in a Ser(133)-specific-dependent manner. Activation of the cAMP pathway by ACTH is required for adrenal cortex (AdCx) maintenance and steroidogenesis. CREB is expressed in normal AdCx. Alterations of CRE binding proteins with loss of CREB expression and compensatory overexpression of CREMtau is observed in the human adrenocortical cancer cell line H295R. Similar alterations are found at the protein level in human malignant adrenocortical tumors. In conclusion, the CREB family of transcription factors plays an important role in the development, differentiation, and proliferation of endocrine tissues. Various alterations of the CREB family of transcription factors can be observed in endocrine tumors.

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.

Effects of 3-MeSO2-DDE and some CYP inhibitors on glucocorticoid steroidogenesis in the H295R human adrenocortical carcinoma cell line

The formation of steroids in the H295R human adrenocortical carcinoma cell line was analysed by HPLC or RIA, and based on these data the apparent catalytic activities of CYP11A, CYP17, CYP21 and CYP11B1 in this cell line were calculated. The environmental pollutant 3-methylsulfonyl-DDE (3-MeSO2-DDE) and the cytochrome P450 (CYP) inhibitors ketoconazole, metyrapone and aminoglutethimide were studied for their effects on the steroid formation. Metyrapone (IC50) of 1 microM) and 3-MeSO2-DDE (10 microM: 66 +/- 10% of control) were found to inhibit the apparent CYP11B1 activity. Ketoconazole inhibited all enzymes examined with the greatest effects on CYP11B1 (IC50) of 2.5 microM). Aminoglutethimide was examined only for effects on CYP11A activity and was shown to inhibit pregnenolone formation (20 microM: 61 +/- 4% of control). The possibility of studying all CYP enzymes in the corticosteroidogenesis makes this cell line a valuable test system to examine effects of chemicals, such as suspected endocrine disruptors, on the human glucocorticoid hormone synthesis. The inhibition of cortisol formation by 3-MeSO2-DDE supports an interaction with the active site of CYP11B1, as previously reported in mouse adrenocortical Y1 cells. In mice, this interaction led to metabolic activation and a high adrenotoxicity of 3-MeSO2-DDE. Therefore studies on the adrenotoxicity of 3-MeSO2-DDE in humans are needed.

Effects of flavonoid phytochemicals on cortisol production and on activities of steroidogenic enzymes in human adrenocortical H295R cells

Inhibitory effects of flavonoid phytochemicals, flavones, flavonols and isoflavones on cortisol production were examined in human adrenal H295R cells stimulated with di-buthylyl cAMP. In addition, the inhibitory effects of these chemicals on the activity of P450scc, 3beta-HSD type II (3beta-HSD II), P450c17, P450c21 and P45011beta, steroidogenic enzymes involved in cortisol biosynthesis, were examined in the same cells. Exposure to 12.5 microM of the flavonoids 6-hydroxyflavone, 4'-hydroxyflavone, apigenin, daidzein, genistein and formononetin significantly decreased cortisol production (by 6.3, 69.6, 47.5, 26.6, 13.8 and 11.3%, respectively), and biochanin A significantly decreased cortisol production (by 47.3%) at a concentration of 25 microM without any significant cytotoxic effects or changes in cell number. Daidzin, the 7-glucoside of daidzein, did not alter cortisol production by H295R cells at concentrations over 10 microg/ml (24 microM). Daidzein-induced reduction of cortisol production by H295R cells was not inhibited by the estrogen receptor antagonist ICI 182,780. The flavonoids 6-hydroxyflavone, daidzein, genistein, biochanin A and formononetin strongly and significantly inhibited microsomal 3beta-HSD II activity at concentrations from 1 to 25 microM, and I(50) values were estimated to be 1.3, 2, 1, 0.5 and 2.7 microM, respectively. In addition, these flavonoids significantly inhibited microsomal P450c21 activity at 12.5 and/or 25 microM. In addition, 6-hydroxyflavone inhibited activity of microsomal P450c17 and mitochondrial P45011beta at 12.5 and/or 25 microM. Results of Lineweaver-Burk's plot analysis indicate that daidzein is a competitive inhibitor of the activity of 3beta-HSD II and P450c21. K(m) and V(max) values of 3beta-HSD II for DHEA were estimated to be 6.6 microM and 328pmol/minmg protein, respectively. K(m) and V(max) values of P450c21 for progesterone were estimated to be 2.8 microM and 16pmol/minmg protein, respectively. K(i) values of 3beta-HSD II and P450c21 for daidzein were estimated to be 2.9 and 33.3 microM, respectively.

Activation of cAMP-dependent protein kinase increases the protein level of steroidogenic factor-1

The orphan nuclear receptor steroidogenic factor 1 (SF-1) is an essential regulator of endocrine organogenesis, sexual differentiation, and steroidogenesis. SF-1 is a transcriptional regulator of cAMP responsive genes, but the exact mechanisms by which cAMP-dependent PKA modulates SF-1 dependent transcription leading to increased steroidogenic output have not been determined. In this report the effects of PKA activation on SF-1 in living cells have been examined by the use of full-length SF-1 cDNA fused to the cDNA encoding green fluorescent protein (GFP). The GFP-SF-1 fusion protein localized to the nucleus of both steroidogenic Y1 cells and nonsteroidogenic COS-1 cells, and the functional properties of wild-type SF-1 were conserved. When the catalytic subunit of PKA was coexpressed with GFP-SF-1, we observed that the fluorescence emission was markedly elevated. These findings were confirmed by Western blot analysis, showing that stimulation of PKA increased SF-1 protein levels. The PKA- induced expression of SF-1 protein was not accompanied by an increase in SF-1 mRNA levels. However, pulse-chase studies showed a decrease in SF-1 degradation rate in response to activation of PKA, indicating that PKA elevates the level of SF-1 by increasing the stability of SF-1 protein.

Conditionally immortalized adrenocortical cell lines at undifferentiated states exhibit inducible expression of glucocorticoid-synthesizing genes

To facilitate studies on differentiation of adrenocortical cells and regulation of steroidogenic genes, we established cell lines from adrenals of adult transgenic mice harboring a temperature-sensitive large T-antigen gene of simian virus 40. Adrenal glands of the mice exhibited normal cortical zonation including a functionally undifferentiated cell-layer between the aldosterone-synthesizing zona glomerulosa cells and the corticosterone-synthesizing zona fasciculata cells. At a permissive temperature (33 degrees C), established cell lines AcA201, AcE60 and AcA101 expressed steroidogenic genes encoding steroidogenic factor-1, cholesterol side-chain cleavage P450scc, and steroidogenic acute regulatory protein, which are expressed throughout adrenal cortices and gonads. Genes encoding 3 beta-hydroxysteroid dehydrogenase and steroid 21-hydroxylase P450c21, which catalyze the intermediate steps for syntheses of both aldosterone and corticosterone, were inducible in the three cell lines in temperature- and/or dibutyryl cAMP-dependent manners. Notably, these cell lines displayed distinct expression patterns of the steroid 11 beta-hydroxylase P45011 beta gene responsible for the zone-specific synthesis of corticosterone. AcA201 cells expressed the P45011 beta gene at 33 degrees C, showing the property of the zona fasciculata cells, while AcE60 cells expressed it upon a shift to a nonpermissive temperature (39 degrees C). On the other hand, AcA101 expressed the P45011 beta gene at 39 degrees C synergistically with exposure to dibutyryl cAMP. None of these clones express the zona glomerulosa-specific aldosterone synthase P450aldo gene under the conditions we tested. These results show that AcE60 and AcA101 cells display a pattern of the steroidogenic gene expression similar to that of the undifferentiated cell-layer and are capable of differentiating into the zona fasciculata-like cells in vitro.

Effect of phthalate esters and alkylphenols on steroidogenesis in human adrenocortical H295R cells

We investigated the inhibitory effects of phthalate esters and alkylphenols on steroidogenesis by human adrenocortical H259R cells, a model of human steroidogenic cells. Dicyclohexyl phthalate (DCHP) at a concentration of 30 μM produced a significant decrease in the dibutyryl cAMP-stimulated cortisol secretion (76% reduction). 4-t-Pentylphenol (4-t-PP), 4-t-octylphenol (4-t-OP) and 4-nonylphenol (4-NP) also produced significant decreases in the dibutyryl cAMP-stimulated cortisol secretion by 58, 34 and 40%, respectively at 50 μM. Reductions in cortisol secretion by these chemicals were dose-dependent. To elucidate the inhibitory effects of DCHP, 4-t-PP, 4-t-OP and 4-NP on cortisol secretion from H295R cells, the effects of these chemicals on various steroidogenic enzymes, such as C(20,22)-lyase (CYP11A), 3β-hydroxysteroid dehydrogenase type II (3β-HSDII), 17α-hyroxylase/C(17,20)-lyase (CYP17), 21-hydroxylase (CYP21B) and 11β-hydroxylase (CYP11B1), were investigated. DCHP significantly inhibited CYP21B activity at 25 μM. 4-t-OP strongly inhibited CYP11A activity at 12.5 and 25 μM, and inhibited CYP17 and CYP21B at 25 μM. Similarly, 4-NP inhibited CYP11A at 25 μM and strongly inhibited CYP17 and CYP21B at 12.5 and 25 μM. Neither DCHP nor any of the alkylphenols tested altered 3β-HSDII activity.

Angiotensin stimulates the expression of interferon-inducible genes in H295R cells

Angiotensin-II (A-II) induces proliferation of zona glomerulosa cells and stimulates expression of cytochrome P-450 aldosterone synthase. The genes activated during this adrenal remodeling are not well defined. To clarify this mechanism, we sought to identify the genes whose expression is stimulated by A-II in the H295R cell line. Using a subtractive hybridization technique, we identified one clone whose expression was stimulated by A-II. The sequence of this gene was homologous to the human interferon-inducible genes, 9-27, 1-8D and 1-8U. The 5' portion of the gene was identical to the 1-8D gene product and the 3' was identical to the 9-27 gene product, but the existence of a transcript was not demonstrated by RT-PCR. The expression of these three genes was stimulated by A-II, with the 9-27 gene being most abundant. Potassium and forskolin also stimulated the expression of the 9-27 gene in the H295R cells, but not as effectively as did A-II or interferon-gamma.

Lack of toxic effects of F 12511, a novel potent inhibitor of acyl-coenzyme A: cholesterol O-acyltransferase, on human adrenocortical cells in culture

Inhibition of acyl-coenzyme A: cholesterol O-acyltransferase (EC 2.3.1.26; ACAT) reduces intracellular cholesteryl esters that are substrates for steroidogenesis in adrenal cells. The adrenal side effects of ACAT inhibitors remain a key point for their development as antiatherosclerotic agents. The aim of this study was to characterize the effects of a novel and powerful ACAT inhibitor, F 12511 (S)-2',3',5'-trimethyl-4'-hydroxy-alpha-dodecylthio-phenylacetanilide, on the NCI-H295R cell line, which has functional properties comparable to those of normal human adrenal cells. F 12511 incubated with cultured cells for 4-72 hr strongly inhibited cholesteryl oleate formation. The concentrations required to produce 50% inhibition (IC50) values) ranged from 20 to 50 nM; in the presence of low-density lipoproteins (LDL), this effect was paralleled by a decrease in cholesteryl ester mass and an increase in intracellular free cholesterol. At concentrations 100-fold larger than the IC(50) value for up to 48 hr, F 12511 reduced neither the basal release of cortisol and aldosterone nor the production of cortisol stimulated by forskolin. F 12511 did not modify the mRNA levels of the steroidogenic enzyme genes cytochrome P450 cholesterol side-chain cleavage (P450scc), cytochrome P450 17alpha-hydroxylase (P450c17), or cytochrome P450 21-hydroxylase (P450c21) or those of the LDL receptor and high-density lipoprotein scavenger receptor class B, type I (SR-BI) genes, either in the presence or absence of adenosine 3',5'-cyclic monophosphate stimulation for 24 hr. Exposure to F 12511 at up to 3 microM for 24 or 48 hr did not result in significant change in morphological and ultrastructural characteristics; the cytoplasm contained large numbers of mitochondria with intact crystae, and the same typical features of secretory activity were observed in NCI-H295R control cells. Exposure to 3 microM of F 12511 for 96 hr also did not affect cell viability. These data demonstrate that reduction of the substrate for steroidogenesis by the ACAT inhibitor F 12511 impairs neither steroid production nor transcription of genes involved in steroidogenesis and lipoprotein uptake in the pluripotent human adrenal cell line NCI-H295R.

Characterization of a proximal element in the rat preadipocyte factor-1 (Pref-1) gene promoter

Preadipocyte factor-1 (Pref-1) was shown to negatively regulate adipocyte differentiation. We recently reported that ZOG, a rat homolog of Pref-1, was specifically expressed in the adrenal zona glomerulosa. Results of the investigation of Pref-1 expression in preadipocyte and in undifferentiated adrenal cortex suggested that down-regulation of Pref-1 gene was closely correlated with the differentiation process. In this study we demonstrate that an upstream region (from -76 to -47) of the rat Pref-1 gene was essential for its expression in adrenocortical carcinoma-derived H295R cells. A nucleotide sequence found in this region, GCGTGGGCGTGGGCGGGGG (Egr/GC-box), seemed to contain three elements, two early growth response (Egr) elements and one GC-box, overlapping each other. Mutations of four or five nucleotides in a 7-nucleotides-stretch in the midst of the Egr/GC-box eliminated the binding of Sp1/3, abolished the activation by Egr-factor(s) and diminished the Pref-1 promoter activity. When mutations were introduced into the outside of the middle portion, the binding of Sp1/3 to the Egr/GC-box was abolished similarly. However, the decrease in the promoter activity was less than that found with the construct mutated at the middle. These results indicated that an element present at the 7-nucleotides-stretch in the midst of the Egr/GC-box might be important for the Pref-1 promoter activity, and this proximal element was possibly activated by a still-unidentified nuclear factor(s). This element would function as the promoter of the Pref-1 gene in H295R cells, but not in HeLa cells.

Pharmacological profile of F 12511, (S)-2',3', 5'-trimethyl-4'-hydroxy-alpha-dodecylthioacetanilide a powerful and systemic acylcoenzyme A: cholesterol acyltransferase inhibitor

The pharmacological profile of F 12511 (S)-2',3', 5'-trimethyl-4'-hydroxy-alpha-dodecylthio-phenylacetanilide, a new inhibitor of acyl-CoA: cholesterol acyltransferase (EC 2.3.1.26; ACAT), was evaluated by using different in vitro and in vivo models. In vitro, F 12511 was shown to be a highly potent inhibitor of ACAT activity in microsomal preparations from various animal species as well as of cholesterol esterification in relevant human cell lines in culture. The concentrations of F 12511 required to produce 50% inhibition of ACAT activity (IC(50) values) in microsomal preparations ranged from 41nM for hypercholesterolemic rabbit intestine to 223 nM for normocholesterolemic hamster liver. In whole cell assays using hepatic (Hep G2), intestinal (CaCo-2) and macrophagic (THP-1) cell lines, F 12511 inhibited ACAT activity with IC(50) values of 3, 7, and 71 nM, respectively. In vivo, orally administered F 12511 displayed high potency and efficacy as an antihypercholesterolemic compound in different cholesterol-fed animals (rat, guinea-pig, rabbit). For instance, in guinea-pigs the dose required to reduce plasma cholesterol levels by 30% (ED(30) value) was 0.008 mg.kg(-1.) In rabbits, an animal species prone to atherosclerosis, the hypocholesterolemic effect was accompanied by a dose-related reduction in the incidence of aortic fatty streaks that reached asymptote at 2.5 mg.kg(-1) and by an improvement of the impaired endothelial function. When given orally to chow-fed hamsters, F 12511 elicited a dose-related decrease in plasma cholesterol from 9% at 0.63 mg.kg(-1) up to 31% at 40 mg.kg(-1) associated with a preferential reduction in atherogenic lipoproteins, very low density lipoproteins (VLDL) and low density lipoproteins (LDL). Moreover, in the same dose range, F 12511 decreased hepatic cholesteryl ester concentrations and reduced liver ex vivo ACAT activity. By using a bioassay, ACAT inhibitory activity was present in plasma of treated hamsters 1 hr after oral administration of F 12511. Hence, the results in chow-fed hamsters are consistent with systemic and direct hepatic effects of F 12511. In guinea-pigs, an adreno-sensitive species, F 12511 did not impair the adrenal function (adrenocorticotrophic hormone challenge) at doses up to 2.5 mg.kg(-1,) far higher than those eliciting hypocholesterolemic effects in the same species. In conclusion, the results suggest that F 12511, a powerful and systemic ACAT inhibitor, constitutes an appropriate tool to determine whether the inhibition of ACAT constitutes an effective therapy for the treatment of hypercholesterolemia and of atherosclerosis in man.

New mechanisms of adrenostatic compounds in a human adrenocortical cancer cell line

BACKGROUND

Adrenostatic compounds are frequently used in the treatment of patients with Cushing's syndrome and act via direct inhibition of steroidogenic enzymes. However, additional mechanisms may be involved in the blockade of adrenal steroid secretion. We therefore investigated the effects of aminoglutethimide (AG), metyrapone (MTP) and etomidate (ETO) in the human NCI-h295 adrenocortical carcinoma cell line.

MATERIALS AND METHODS

Cells were incubated with increasing doses of the adrenostatic compounds. Steroid hormone secretion (cortisol, 17-OH-progesterone, DHEA-S) and cAMP synthesis were determined and Northern blot analysis and cell proliferation experiments were performed.

RESULTS

ETO was the most potent adrenostatic compound inhibiting P450c11 hydroxylase at low concentrations (IC50 15 nM), and also blocking P450 side-chain cleavage (scc) enzyme (IC50 400 nM) at higher concentrations. The pattern of enzyme inhibition was similar for MTP with an IC50 of 3-5 microM for P450c11 and 17 microM for P450scc, while AG blocked P450scc with an IC50 of 10 microM. 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%) but increased glucocorticoid receptor mRNA. The reduced ACTH-R mRNA was paralleled by low ACTH-induced cAMP accumulation indicating reduced expression of ACTH-R protein. The simultaneous incubation of hydrocortisone together with AG reversed the inhibitory effect of AG on the ACTH-R expression. AG and ETO inhibited cell proliferation in the NCI-h295 cells, but ETO was much more potent and showed antiproliferative effects at concentrations of 6 microM. The growth inhibition was not reversed by administration of hydrocortisone.

CONCLUSIONS

Our data demonstrate that adrenostatic compounds not only act by suppression of steroidogenic enzymes but can also influence both ACTH-R expression and cell proliferation in adrenal cells. As these effects occur in vitro at concentrations that are reached during treatment with these drugs in patients, they are probably also of clinical relevance. Particularly the antiproliferative activity of ETO may be useful in Cushing's syndrome due to adrenocortical cancer. The interaction of steroidogenesis, ACTH-R and glucocorticoid receptor expression as well as cell proliferation provides a new concept of the intra-adrenal response to stress in humans.

Transcriptional regulation of human 11beta-hydroxylase (hCYP11B1)

Steroid 11beta-hydroxylase is a mitochondrial enzyme that catalyzes the conversion of deoxycortisol to cortisol. The gene encoding human 11beta-hydroxylase (hCYP11B1) is expressed in the adrenal cortex under the control of circulating levels of ACTH. The current study was undertaken to define the cis-regulatory elements and transacting factors that regulate hCYP11B1 transcription. The hCYP11B1 5'-flanking DNA was studied using transient transfection of luciferase reporter constructs in NCI-H295R human adrenocortical cells. A cAMP analogue ((Bu)2cAMP) increased expression of a construct containing -1102 bp of hCYP11B1 5'-flanking DNA (pB1-1102). An element at position -71/-64 (TGACGTGA, previously termed Ad1) resembling a consensus cAMP response element (CRE) was required for maximal induction by cAMP. The Ad1 element bound several transcriptional factors in electrophoretic mobility shift assays, including CRE-binding protein, activating transcription factor-1 (ATF-1), and ATF-2, but only the ATF-2 complex migrated similarly to a complex seen using H295R nuclear extract. In addition, Western analysis of H295R and adrenal lysates demonstrated expression of high levels of ATF-2 and ATF-1. CRE-binding protein levels varied among the strains of H295R cells tested. Transcription of CYP11B1 also appeared to be regulated by steroidogenic factor-1 (SF-1). Luciferase reporter gene activity was increased after cotransfection with expression vectors containing SF-1. An element in hCYP11B1 at positions 242/-234 (CCAAGGCTC), previously termed Ad4, was required for maximal induction by SF-1 and was found to bind SF-1 in electrophoretic mobility shift assays. The key role for SF-1 in hCYP11B1 transcription is in contrast to its lack of an effect on expression of the hCYP11B2 (aldosterone synthase) isozyme. The differential effects of SF-1 on transcription of hCYP11B1 and hCYP11B2 may be one of the mechanisms controlling differential expression of these isozymes within the zonae fasciculata and glomerulosa of the human adrenal cortex.

Establishment and characterization of a human adrenocortical carcinoma xenograft model

Adrenocortical carcinomas are rare malignant tumors. They have a poor prognosis, as they are often diagnosed late and are usually resistant to chemotherapy. The lack of a suitable animal model for these tumors has been a major obstacle to the evaluation of new therapeutic agents. The aim of this study was to establish and characterize xenografts of the human adrenocortical carcinoma NCI H295R cell line as a model of adrenocortical carcinoma for future therapeutic trials. This cell line was sc injected (6 x 10(6) cells) into nude mice (n = 20). Solid tumors were locally measurable after 45 days at 90% of the inoculation sites. The xenografts were similar histologically to the original adrenocortical carcinoma from which the cell line was derived. The xenografts precisely reproduced the dysregulation of the insulin-like growth factor (IGF) system [overexpression of the IGF-II and IGF-binding protein-2 (IGFBP-2) genes] typical of adrenocortical carcinoma. Similarly to adrenocortical carcinomas, human IGFBP-2 (but not IGF-II) was secreted in mouse plasma. We analyzed steroid production (cortisol, 17-hydroxypregnenolone, 17-hydroxyprogesterone, dehydroepiandrosterone, delta4-androstenedione, 11-deoxycortisol, corticosterone, and testosterone). Xenografts produced all three class of steroids, with the preferential production of androgens of the delta4 pathway. The H295R xenograft model is a good model of human adrenocortical carcinoma, as it mimics dysregulation of the IGF system usually found in these tumors. It also produces IGFBP-2 and steroids that can be used as tumor markers. This model may therefore be useful for evaluating therapeutic agents.

Regulation by adrenocorticotropin (ACTH), angiotensin II, transforming growth factor-beta, and insulin-like growth factor I of bovine adrenal cell steroidogenic capacity and expression of ACTH receptor, steroidogenic acute regulatory protein, cytochrome P450c17, and 3beta-hydroxysteroid dehydrogenase

The purpose of this study was to evaluate the time-course effect of a 36-h treatment with ACTH (10(-8) M), transforming growth factor-beta1 (TGFbeta1; 10(-10) M), angiotensin II (AngII; 10 (-7) M), and insulin-like growth factor I (IGF-I; 10(-8) M) on the steroidogenic capacity of bovine adrenocortical cells (BAC) and on messenger RNA (mRNA) levels of ACTH receptor, cytochrome P450c17, 3beta-hydroxysteroid dehydrogenase (3betaHSD), steroidogenic acute regulatory protein (StAR), and StAR protein. ACTH and IGF-I enhanced, in a time-dependent manner, the acute 2-h ACTH-induced cortisol production, whereas TGFbeta 1 and AngII markedly reduced it. ACTH, IGF-I, and AngII increased ACTH receptor mRNA, but the opposite was observed after TGFbeta1 treatment. ACTH and IGF-I increased P450c17 and 3betaHSD mRNAs, whereas AngII and TGFbeta1 had the opposite effects. However, the effects of the four peptides on ACTH-induced cortisol production appeared before any significant alterations of the mRNA levels occurred. The most marked and rapid effect of the four peptides was on StAR mRNA. The stimulatory effect of ACTH was seen within 1.5 h, peaked at 4-6 h, and declined thereafter, but at the end of the 36-h pretreatment, the levels of StAR mRNA and protein were higher than those in control cells. IGF-I also enhanced StAR mRNA levels within 1.5 h, and these levels remained fairly constant. The effects of AngII on StAR mRNA expression were biphasic, with a peak within 1.5-3 h, followed by a rapid decline to almost undetectable levels of both mRNA and protein. TGFbeta1 had no significant effect during the first 3 h, but thereafter StAR mRNA declined, and at the end of the experiment the StAR mRNA and protein were almost undetectable. Similar results were observed when cells were treated with ACTH plus TGFbeta1. A 2-h acute ACTH stimulation at the end of the 36-h pretreatment caused a higher increase in StAR mRNA and protein in ACTH- or IGF-I-pretreated cells than in control cells, which, in turn, had higher levels than cells pretreated with TGFbeta1, ACTH plus TGFbeta1, or AngII. These results and the fact that the stimulatory (IGF-I) or inhibitory (AngII and TGFbeta1) effects on ACTH-induced cortisol production were more pronounced than those on the ability of cells to transform pregnenolone into cortisol strongly suggest that regulation of StAR expression is one of the main factors, but not the only one, involved in the positive (IGF-I) or negative (TGFbeta1 and AngII) regulation of BAC for ACTH steroidogenic responsiveness. A high correlation between steady state mRNA level and acute ACTH-induced cortisol production favors this conclusion.

Nitric oxide inhibits human aldosteronogenesis without guanylyl cyclase stimulation

Deta nonoate (deta-NO), a zwitterion nitric oxide (NO) donor, potently inhibited forskolin- and angiotensin II-stimulated aldosterone production in human adrenocortical H295R cells in a concentration-dependent manner (0.1-1000 microM). The half-maximal and maximal inhibition of forskolin-evoked aldosteronogenesis occurred at 0.6 and 100 microM deta-NO, respectively. The respective half-maximal and maximal deta-NO-mediated inhibition of angiotensin II-stimulated aldosterone generation occurred at 150 microM and 1 mM. In H295R cells, deta-NO and sodium nitroprusside did not stimulate cGMP production, and the soluble guanylyl cyclase inhibitor oxadiazoloquinoxalinone (10 microM) did not block deta-NO-mediated attenuation of aldosteronogenesis. 25-Hydroxycholesterol (10 microM)-facilitated aldosterone synthesis was also diminished with half-maximal and maximal inhibition occurring at 120 microM and 1 mM deta-NO, respectively. Taken together, these results demonstrate that NO inhibits human aldosteronogenesis without stimulating guanylyl cyclase in H295R cells.

Smad3 is involved in the intracellular signaling pathways that mediate the inhibitory effects of transforming growth factor-beta on StAR expression

Transforming growth factor betas (TGFbetas) constitute a family of dimeric proteins that regulate growth and differentiation of many cell types. TGFbeta1 is also a potent autocrine regulator of adrenocortical steroidogenesis. We have recently shown that in primary cultures of bovine fasciculo-reticularis cells, the main target of TGFbeta is the steroidogenic acute relay protein (StAR), a key protein necessary for intramitochondrial cholesterol transport. Here, we show that StAR expression is also inhibited by TGFbeta1 in the human adrenocortical carcinoma cell line NCI-H295R. This inhibitory effect is mediated by Smad proteins. Indeed, we found that overexpression of wild-type Smad3 inhibited endogenous StAR mRNA expression while overexpression of a dominant negative Smad3 protein reversed the inhibitory effect of TGFbeta1 on StAR mRNA expression. Taken together, these results demonstrate that the Smad3 protein is involved in TGFbeta-dependent regulation of steroidogenesis.

Functionally active catalytic domain is essential for guanylyl cyclase-linked receptor mediated inhibition of human aldosterone synthesis

An aspartate-to-alanine point mutation in the catalytic domain (D853A) of guanylyl cyclase-C (GC-C), the heat-stable enterotoxin (STa) receptor, rendered the enzyme catalytically inactive. Mn2+/Triton X-100-stimulated guanylyl cyclase activity was detected in membranes from COS7 cells overexpressing GC-C but not GC-CD853A. STa treatment of paired cells resulted in cGMP production in those transiently expressing GC-C but not GC-CD853A. GC-C and GC-CD853A showed similar Bmax and Kd values for [125I]STa binding in these cells, indicating that the lack of catalytic activity in the latter was not due to differing expression levels or reduced binding affinity. The involvement of the catalytic domain in aldosteronogenesis was studied in human adrenocortical H295R cells. COS7 and H295R cells infected with vaccinia virus-expressing GC-C and GC-CD853A (VVGC-CD853A) had [125I]STa-binding characteristics akin to those in transfected cells. Immunoblot confirmed that both GC-C and GC-CD853A formed similar higher order oligomers in infected cells. Virus-mediated expression of GC-C in H295R cells revealed concentration-dependent STa-stimulated cGMP formation that was undetectable in VVGC-CD853A-infected cells. STa decreased angiotensin II-stimulated human aldosterone generation in a concentration-dependent manner in vaccinia virus-expressing GC-C-infected cells but not in those infected with VVGC-CD853A. These results demonstrate that a catalytically active guanylyl cyclase is required for the inhibition of aldosteronogenesis.

The acute and chronic effects of adrenocorticotropin on the levels of messenger ribonucleic acid and protein of steroidogenic enzymes in rat adrenal in vivo

The purpose of this study was to evaluate the effects of acute (a single injection) and chronic stimulation (twice daily injection for 9 days) by ACTH on changes occurring in the temporal expression of steroidogenic enzymes in the rat adrenal in vivo. Under acute ACTH stimulation, the level of steroidogenic acute regulatory protein (StAR) messenger RNA (mRNA) was increased within 0.5 h in both zona glomerulosa (ZG) and zona fasciculata-reticularis (ZFR), with maximal increases of 220-370% and 300-350% in the ZG and ZFR, respectively. Increases in the levels of StAR protein in homogenates were also found in the ZG (700%) and the ZFR (300%), but were delayed compared with those of their mRNA. Furthermore, the increase in mitochondrial StAR protein was concomitant with that in the homogenate, indicating that the entry of StAR into mitochondria might not be necessary to increase steroidogenesis during the early stimulatory phase. The levels of c-jun, c-fos, junB, and fosB mRNA in ZG and ZFR were also rapidly maximally elevated within 0.5-1 h after ACTH administration and fell to near control levels 5 h posttreatment. The levels of c-jun protein were already increased in both zones at 1 h, reached 200% at 3 h, and remained elevated 5 h post-ACTH treatment. The levels of c-Fos protein were maximally increased by 240% in both zones after 1 h and decreased thereafter to control values at 5 h. Few changes were observed in the adrenal protein contents of cholesterol side-chain cleavage cytochrome P450 (P450scc), cytochrome P450 11beta-hydroxylase (P450C11), cytochrome P450 21-hydroxylase (P450C21), and 3beta-hydroxysteroid dehydrogenase (3betaHSD). Under chronic stimulation by ACTH, we observed elevations in the levels of plasma corticosteroids and changes in the mRNA and protein levels of many adrenal steroidogenic enzymes in both zones. In the ZG, administration of ACTH for 9 days provoked an increase in the level of StAR mRNA (210-270%) and a decrease in the levels of 3betaHSD, cytochrome P450 aldosterone synthase (P450aldo), and AT1 receptor mRNA (by 40%, 70%, and 90%, respectively), whereas the levels of P450scc and P450C21 mRNA did not differ significantly from the control values. Western blotting analysis showed that the adrenal ZG protein levels of StAR and P450scc were increased (150%), 3betaHSD was not changed, and P450C21 was decreased by 70%. In the ZFR, the levels of P450scc and StAR mRNAs were increased (260% and 570-870%, respectively). The levels of 3betaHSD, P450C21, and P450C11 mRNA did not differ from control values in that zone. Western blotting analysis showed that the ZFR protein level of 3betaHSD was not changed, P450scc and P450C21 were decreased by 40% and 60%, respectively, and StAR was increased by 160%. Although c-fos and fosB mRNAs were undetectable after 9 days of chronic ACTH treatment, c-jun mRNA and its protein were still detectable, suggesting a basic role for this protooncogene in maintaining the integrity and function of the adrenal cortex. When dexamethasone was administered to rats for 5 days to inhibit their ACTH secretion, the mRNA levels of many steroidogenic enzymes were decreased, with the exception of StAR, 3betaHSD, and P450aldo. These results confirm the importance of physiological concentrations of ACTH in maintaining normal levels of adrenocortical enzymes and also indicate that in addition to ACTH, other factors are involved in controlling the expression of StAR, 3betaHSD, and P450aldo. In conclusion, we showed that ACTH acutely increases StAR mRNA followed, after a delay, by an increase in the level of StAR protein; this suggests that posttranslational modifications of the StAR precursor occurred during the early stimulatory phase and before the apparent translation of the newly formed mRNA. The rapid induction of protooncogenes suggests their participation in the action of ACTH to stimulate steroidogenesis. (ABSTRACT TRUNCATED)

The role of calcium channels in hamster CYP11B2 gene expression

Previous studies have shown that the hamster CYP11B2 gene promoter is under the influence of angiotensin II (AII), cAMP and potassium (K+). However, very little is known about the mechanisms by which these compounds regulate the transcription of the CYP11B2 gene. Therefore we analysed the 5'-flanking region of the hamster CYP11B2 gene using a transient transfection expression system in NCI-H295 adrenocortical cells, which are known to respond to K+, cAMP and AII. The first 486 bp before the transcription initiation site were introduced upstream of the chloramphenicol acetyl transferase gene. NCI-H295 cells transfected with this -486 construct showed increased CAT activity upon treatment by K+, AII, forskolin and cAMP. The calcium channel antagonist nifedipine partially blocked the enhancing effects of AII, forskolin and cAMP by 35%, 30% and 30% respectively, whereas it completely blocked the stimulatory effects of KCl (1). These results thus show the involvement of calcium channels in the regulation of CYP11B2 gene transcription by K+, and their partial involvement in the regulation of this gene by AII, forskolin and cAMP in NCI-H295 cells.

Battle of the kinases: integration of adrenal responses to cAMP, DG and Ca2+ at the level of steroidogenic cytochromes P450 and 3betaHSD expression in H295R cells

While ACTH receptors (activating the protein kinase A pathway) are expressed throughout the human/bovine/ovine zona glomerulosa (zg) and zona fasciculata (zf), there are clear zonal differences in AII Type-1 receptor levels (activating protein kinase C/Ca2+), as well as resting membrane potential. Thus zg is most responsive to AII and K+ (Ca2+ signalling), while zf is less responsive to AII with no K+ response. Zonal function in turn requires differential expression of CYP17/3betaHSD and CYP11B2/CYP11B1. We have used the H295R cell to study how differential activation of kinase A, kinase C and Ca2+/calmodulin (CaM) kinases may alter the relative expression of the steroidogenic P450s and 3betaHSDII. While CYP11A, CYP17, 3betaHSDII, CYP21, and CYP11B1 are all induced by increases in cAMP, studies with TPA alone or in combination with forskolin reveal subsets of steroidogenic enzymes regulated either positively (CYP21, 3betaHSDII) or negatively (CYP17, CYP11A) by protein kinase C. Thus adrenal 3betaHSDII and CYP21 expression is high in zg and zf, but CYP17 is not expressed in the zg where AII activation of kinase C is highest. In turn both K+ and AII-induced elevation of Ca2+ strongly induces CYP11B2 but not CYP11B1, consistent with preferential expression of CYP11B2 in the zg. We conclude that differential signaling through kinase C and CaM kinases in addition to kinase A underlies zonal differences in both the early and late pathways involved in steroid hormone production within the adrenocortical zones.

Paclitaxel is an effective antiproliferative agent on the human NCI-H295 adrenocortical carcinoma cell line

In view of a potential clinical use, we assessed the antiproliferative effect of paclitaxel on the human steroid-secreting NCI-H295 adrenocarcinoma cell line. By MTT, paclitaxel induced a dose-dependent inhibition of cell proliferation, with IC50 lower than blood levels of the drug achieved in patients treated for other malignancies. Cell exposure to paclitaxel for 24 h at the different IC50S produced a dose-responsive increase in DNA fragmentation, morphologically confirmed by electron microscopy. A time-dependent decrease in aldosterone, cortisol and testosterone was observed. Paclitaxel is an effective antiproliferative agent in this human adrenocortical carcinoma cell line. Apoptosis induced by the drug in involved in neoplastic cell death. A potential role of the drug in the treatment of patients with adrenocortical cancer could be considered.

Regulation of the human P450scc gene by steroidogenic factor 1 is mediated by CBP/p300

Regulation of the human CYP11A gene encoding cytochrome P450scc, which catalyzes the first step of steroid synthesis, is regulated by many trans-acting transcription factors including steroidogenic factor 1 (SF-1). Transfection experiments in human adrenal NCI-H295 cells demonstrate regulation of the P450scc gene promoter region that contains several putative SF-1 binding sites. Cotransfection of SF-1 with a luciferase reporter construct containing the P450scc gene 5'-flanking region from nucleotides -1676 to +49 increased promoter activity, and deletion of the nucleotide sequence from position -1676 to -1620, which removes a putative cAMP response element (CRE), did not affect the stimulatory response to SF-1. As well, further deletion of the promoter region to nucleotide -110, which contains only one SF-1 binding site, still retained the ability to respond to exogenous SF-1. However, mutation of the remaining site which abolished SF-1 protein/DNA interaction also abrogated any functional response to the factor. All the P450scc reporter constructs which responded to SF-1 were further stimulated by exogenous p300 and CREB-binding protein (CBP), suggesting interaction between SF-1 and p300/CBP. As well, mutation of the binding site that abrogated the response to SF-1 also abolished the response to p300 and CBP. Cotransfection of the adenovirus E1A oncoprotein, which has been shown to interact with p300/CBP and interfere with its function, decreased the stimulatory effect of SF-1 and p300/CBP. Cotransfection of a mutated E1A protein, RG2, which does not interact with p300/CBP, did not alter the stimulatory effect of SF-1 and p300/CBP on the P450scc promoter. Deletion of the region from amino acid residues 2-67 in E1A, which has been postulated to interact with p300/CBP, also abolished the inhibitory effect of E1A, whereas deletion of the region from residues 120 to 140 had no effect. Two regions of CBP from amino acids 1 to 451 and from 1460 to 1891 were demonstrated to interact with SF-1 in vitro. Coexpression of fragments of the p300 protein fused to the VP16 protein in the presence of SF-1 and the -110 P450scc reporter construct indicated in vivo the interaction of two regions of p300 with SF-1, thus confirming the in vitro results. Taken together these results indicate that regulation of the human P450scc gene by SF-1 is mediated by p300/CBP. Due to the many putative roles of SF-1 to regulate many genes, its interaction with p300/CBP is potentially a key component effecting important physiological processes.

Human adrenocortical NCI-H295 cells express VIP receptors. Steroidogenic effect of vasoactive intestinal peptide (VIP)

VIP receptors are frequently overexpressed by various endocrine tumors. In this study the expression of VIP receptors in the human adrenocortical carcinoma cell line NCI-H295 and their involvement in the regulation of steroidogenesis was investigated. NCI-H295 cells express VIP1 and VIP2 receptors as demonstrated by RT-PCR, whereas they do not express VIP itself. The receptors are functionally coupled to steroidogenesis since VIP (10(-9) M to 10(-6) M) exerted a dose-dependent stimulatory effect on the release of aldosterone, cortisol, and DHEA. VIP increased ACTH-stimulated releases of aldosterone and cortisol. The proliferation rate of NCI-H295 cells was not affected by VIP. These data show that NCI-H295 cells express both forms of the VIP receptor and that VIP is involved in an ACTH-independent regulation of steroidogenesis in the adrenal tumor cells.

Direct stimulation of cortisol secretion from the human NCI H295 adrenocortical cell line by vasoactive intestinal polypeptide

OBJECTIVE

To investigate a possible direct action of vasoactive intestinal polypeptide (VIP) on adrenal cortisol secretion and to define its mechanism of action.

DESIGN

The human adrenocortical carcinoma cell line NCI H295, which is not contaminated by medullary chromaffin cells, was used to aid distinction between a direct action of VIP on adrenocortical cells and an indirect mechanism involving VIP-stimulated release of catecholamines.

METHODS

NCI H295 cells were challenged with 10(-11)-10(-7) mol/l VIP for 4 h, with or without prior exposure for 72 h to 10 micromol/l forskolin. Cortisol and cyclic AMP contents of the overlying media were measured using in-house radioimmunoassays. Cells were treated with 10(-8)-10(-6) mol/l adrenaline or 3.3 x 10(-8) mol/l VIP with and without 10(-8)-10(-6) mol/l propranolol to exclude the possibility that an indirect mechanism of action involving beta-adrenoceptors was operating.

RESULTS

VIP treatment produced an increase in cortisol secretion without pre-incubation, but this was markedly enhanced by prior exposure of cells to forskolin. VIP was potent, with a threshold of 10(-11) mol/l (n = 4), reaching a maximum 3.9+/-0.9-fold increase in effect on cells pre-exposed to forskolin (n = 4) by 3.3 x 10(-8) mol/l. This increase matched the 4 h response to 10 micromol/l forskolin. Cortisol secretion was accompanied by a parallel, dose-dependent increase in accumulation of cAMP.

CONCLUSIONS

VIP potently and directly stimulates secretion of cortisol from these adrenocortical cells of human origin via an adenylate cyclase-coupled VIP receptor. These findings raise the possibility of a significant and direct effect of VIP in the control of steroid secretion from the adrenal cortex in humans.

Synergistic activation of the human type II 3beta-hydroxysteroid dehydrogenase/delta5-delta4 isomerase promoter by the transcription factor steroidogenic factor-1/adrenal 4-binding protein and phorbol ester

Steroidogenic factor-1/adrenal 4-binding protein (SF-1/Ad4BP) is an orphan nuclear receptor/transcription factor known to regulate the P450 steroid hydroxylases; however, mechanisms that regulate the activity of SF-1/Ad4BP are not well defined. In addition, little is known about the mechanisms that regulate the human steroidogenic enzyme, type II 3beta-hydroxysteroid dehydrogenase (3beta-HSD II), the major gonadal and adrenal isoform. Regulation of the 3beta-HSD II promoter was examined using human adrenal cortical (H295R; steroidogenic) and cervical (HeLa; non-steroidogenic) carcinoma cells. H295R cells were transfected with a series of 5' deletions of 1251 base pairs (bp) of the 3beta-HSD II 5'-flanking region fused to a chloramphenicol acetyltransferase (CAT) reporter gene followed by treatment with or without phorbol ester (phorbol 12-myristate 13-acetate; PMA). CAT assay data indicated that the region from -101 to -52 bp of the promoter was required for PMA-induced expression. A putative SF-1/Ad4BP regulatory element, TCAAGGTAA, was identified by sequence homology at -64 to -56 bp of the promoter. Cotransfection of HeLa cells with the -101 3beta-HSD-CAT construct and an expression vector for SF-1/Ad4BP increased CAT activity 49-fold. Subsequent treatment with PMA induced an unexpected synergistic increase in transcriptional activity 540-fold over basal. Mutation of the putative response element (TCAAGGTAA to TCAATTTAA) abolished SF-1-induced CAT activity and the synergistic response to PMA. Gel mobility shift assays confirmed that SF-1/Ad4BP interacts with the putative element and transcripts for SF-1/Ad4BP were detected in H295R cells by Northern analysis. These data are the first to demonstrate 1) regulation of a non-cytochrome P450 steroidogenic enzyme promoter by SF-1/Ad4BP, 2) a powerful synergistic effect of PMA on SF-1/Ad4BP-induced transcription, and 3) the importance of the SF-1/Ad4BP regulatory element in the regulation of the 3beta-HSD II promoter.

The regulation of 3 beta-hydroxysteroid dehydrogenase expression

3 beta-Hydroxysteroid dehydrogenasel delta 5-->4-isomerase (3 beta-HSD) catalyzes the formation of delta 4-3-ketosteroids from delta 5-3 beta-hydroxysteroids, an obligate step in the biosynthesis not only of androgens and estrogens but also of mineralocorticoids and glucocorticoids. The enzyme is expressed in the adrenal cortex and in steroidogenic cells of the gonads, consistent with this role. However, 3 beta-HSD is also expressed in many other tissues, such as the liver and kidney, where its function is not entirely clear. It is established that a family of closely related genes encode for 3 beta-HSD. The various 3 beta-HSD isoforms are expressed in a tissue-specific manner involving separate mechanisms of regulation. The human type I 3 beta-HSD is expressed at high levels in syncytial trophoblast and in sebaceous glands, and the type II isoform is almost exclusively expressed in the adrenal cortex and gonads. An important feature in liver and kidney (at least of hamster, mouse, rabbit, and rat) is the sexual dimorphic nature of 3 beta-HSD expression. We briefly review studies on the regulation of the human 3 beta-HSD I and II genes in human trophoblast and adrenal cortex and extend this to discuss the rat 3 beta-HSD I gene expressed in adrenals and gonads. The complexity of 3 beta-HSD expression through multiple signaling pathways acting on a multigene family of enzymes may contribute importantly to the diverse patterns and locations of steroid hormone biosynthesis.

Steroidogenic acute regulatory protein (StAR) retains activity in the absence of its mitochondrial import sequence: implications for the mechanism of StAR action

Steroidogenic acute regulatory protein (StAR) plays a critical role in steroid hormone biosynthesis, presumably by facilitating the delivery of cholesterol to P450scc in the inner mitochondrial membranes. StAR is synthesized as a 37-kDa preprotein that is processed to a 30-kDa mature form by cleavage of an N-terminal mitochondrial import sequence. To identify structural features required for StAR biological activity, we mutated the human StAR cDNA, including the deletion of N- and C-terminal sequences, and examined the ability of the mutants to promote steroidogenesis and enter the mitochondria of transfected COS-1 cells. Deletion of up to 62 residues from the N terminus (N-62) did not significantly affect steroidogenesis-enhancing activity. The N-terminal deletion mutants were associated with mitochondria-enriched fractions, but import and processing were progressively impaired with increasing length of the deletion. Immunogold electron microscopy and in vitro import assays showed that the active N-62 mutant was not imported into the mitochondria. Removal of the 28 C-terminal amino acids (C-28) inactivated StAR. Deletion of the C-terminal 10 amino acids (C-10) reduced steroidogenic activity by 53%, while truncation of the last 4 amino acids had no effect. The C-28 mutant StAR was not efficiently imported into mitochondria or processed, whereas some of the C-10 mutant was processed, indicating that import had occurred. We conclude that in the COS-1 cell system used, StAR does not need to enter into mitochondria to stimulate steroidogenesis and that residues in the C terminus are essential for steroidogenesis-enhancing activity. These findings imply that StAR acts via C-terminal domains on the outside of the mitochondria.

Calcium regulates human CYP11B2 transcription

The CYP11B2 gene encodes aldosterone synthase, a cytochrome P450 (P450aldo) expressed in high levels in the adrenal zona glomerulosa. While the primary physiologic regulators of aldosterone production are circulating angiotensin II (Ang II) and potassium (K+) the action of these agents on CYP11B2 gene transcription have not been examined. Because these factors increase intracellular calcium we have hypothesized that calcium signaling pathways are one mechanism controlling CYP11B2 transcription. Previously we demonstrated that increases in intracellular calcium increase P450aldo mRNA. Herein, we analyzed the role of calcium in the expression of the human CYP11B2 gene using transient transfection of a luciferase reporter construct containing 2017 bp of human CYP11B2 5'flanking DNA in mouse Y-1 and human H295R adrenocortical cell lines. When transfected into Y-1 cells, reporter gene expression was increased following treatment with ACTH or forskolin, but not with Ang II, the L-type calcium channel agonist BAYK8644, or ionomycin. In H295R cells, however, reporter gene expression was increased following treatment with Ang II, K+, BAYK8644 ionomycin or dibutyryl cAMP (Bu2cAMP). Activation of protein kinase C with TPA did not alter reporter gene expression in either cell line. These data demonstrate that both calcium and cAMP signaling pathways regulate human CYP11B2 gene expression. In addition, the H295R adrenal cell line appears to be an appropriate model to study regulation of CYP11B2 by calcium.

Forskolin treatment directs steroid production towards the androgen pathway in the NCI-H295R adrenocortical tumour cell line

The human adrenocortical tumour cell line, NCI-H295, secretes steroids on the mineralocorticoid, glucocorticoid and adrenal androgen pathways. We have investigated the effects of 96 h treatment of cells in monolayer culture with either forskolin (10 microM) (a direct activator of adenylate cyclase), angiotensin II (10 nM) or no agonist ('control') on the steroidogenic phenotype of this cell line. Androstenedione, cortisol and corticosterone secreted into the medium in response to a subsequent 4 hour treatment with angiotensin II (10nM) indicated that the steroidogenic phenotype of NCI-H295 cells changes away from 17-deoxysteroid biosynthesis towards adrenal androgen production in response to forskolin. The NCI-H295R cell line therefore serves as a useful model for investigation of the differential regulation of the steroidogenic pathways in the human adrenal cortex.

Characterization of the upstream sequence of the human CYP11A1 gene for cell type-specific expression

The CYP11A1 gene encodes the cholesterol side-chain cleavage enzyme P450scc, which catalyzes the synthesis of steroids from cholesterol. This gene is expressed only in steroidogenic organs such as the adrenal, gonad, placenta, and brain. We have characterized an upstream regulatory element of the human CYP11A1 gene, termed AdE, which contributed to its cell type-specific expression. The AdE sequence contains two protein binding regions, AdE1 and AdE2, which bind many proteins including NF1- and Sp1-like proteins as shown by electrophoretic mobility shift assay, footprinting, competition, antibody supershift, and mutagenesis of the binding sites. When cloned in front of the CYP11A1 promoter or the heterologous thymidine kinase promoter, AdE sequences enhanced expression of the reporter gene in steroidogenic cell lines of the adrenal, gonad, and placental origin but not in nonsteroidogenic cell lines such as COS-1 and Rat-1. The function of AdE1 and AdE2 was lower when present individually than together. The combined action of multiple transcription factors binding to the AdE sequence brings about the final activation of the CYP11A1 gene in a tissue-specific manner.

Differential regulation of 11 beta-hydroxylase and aldosterone synthase in human adrenocortical H295R cells

In humans the last steps in the synthesis of aldosterone and cortisol rely on the activity of two cytochrome P450 genes termed CYP11B2 (aldosterone synthase; P450aldo) and CYP11B1 (11 beta hydroxylase; P450cl1). The mechanisms which lead to differential expression of these two genes within the adrenal cortex are not well-defined. The human adrenocortical cell line. H295R, was utilized in this study to examine the intracellular second messenger pathways regulating expression of P450aldo and P450c11. using specific ribonuclease protection assays. Treatment of H295R cells with angiotensin II or potassium (K+) caused a time-dependent induction in the level of P450aldo transcripts. While K+ treatment was more specific for the induction of P450aldo mRNA, treatment with angiotensin II increased levels of both P450aldo and P450c11 transcripts. To define the second messenger systems which influence transcript levels for these enzymes, the effects of agonists of the protein kinase A, protein kinase C, and calcium pathways were tested on the expression of P450aldo and P450c11. Activation of the protein kinase A pathway by the agonists, dibutyryl cAMP or forskolin, preferentially increased the P450c11 transcript to a greater degree than P450aldo. Interestingly, activation of the protein kinase C pathway by tetradecanoylphorbol acetate (TPA) did not alter transcripts for either P450aldo or P450c11. The calcium channel agonist BAYK 8644 mimicked the effects of K+ by increasing the transcript for P450aldo. However, the calcium channel blocker nifedipine attenuated the stimulatory effects of angiotensin II and K+ on the levels of P450aldo. However, the calcium channel blocker nifedipine attenuated the stimulatory effects of angiotensin II and K+ on the levels of P450aldo transcripts without affecting the stimulatory effect of dbcAMP. This study demonstrates that the protein kinase A pathway preferentially induces P450c11 mRNA over that of P450aldo. In addition, pharmacologic agents that affect calcium levels provide evidence for an additional regulatory mechanism in modulating the expression of P450aldo. This is of importance since the major physiologic regulators of aldosterone secretion, angiotensin II and K+ are able to increase intracellular calcium but have little effect on intracellular cAMP levels.

Role of calmodulin-dependent protein kinase II in the acute stimulation of aldosterone production

Acute aldosterone production in adrenocortical cells is highly dependent on calcium (Ca2+) and calmodulin (CaM) activation. To determine the role of calmodulin-dependent protein kinase II (CaM kinase II) in human adrenal aldosterone production, the action of KN93 (a specific CaM kinase II inhibitor) on human adrenocortical H295R cells was examined. The stimulation of aldosterone, production by angiotensin II (Ang II) and potassium (K+) were inhibited by KN93 in a concentration-dependent manner with an IC50 of approximately 0.9 and approximately 0.5 microM, respectively. Aldosterone production was also stimulated by treatment with the calcium channel activator Bay K 8644 (Bay K) (1 microM). This production was inhibited in a concentration-dependent manner by KN93 with an IC50 of between 1 and 3 microM. No inhibition by KN93 (0.3-3 microM) or by the calmodulin inhibitor calmidazolium (0.03-0.3 microM) was observed for 22R-hydroxycholesterol (22R-OHChol) stimulation of aldosterone production. Because 22R-OHChol is a substrate for the cytochrome P450 cholesterol side-chain cleavage enzyme (P450scc) and does not require active transport to the mitochondria, these results indicate that KN93 does not directly inhibit P450scc or later steps leading to aldosterone synthesis. To investigate the site of KN93 action further we examined its effect on agonists induction of steroidogenic acute regulatory (StAR) protein, which was recently shown to regulate the movement of cholesterol from the outer to the inner mitochondrial membranes. Induction of StAR protein in H295R cells by Ang II, or Bay K was not affected by co-treatment with KN93 at concentration which blocked steroidogenesis by 60-80%. These results indicate a direct role of CaM kinase II in Ang II and K+ simulation of aldosterone production and support the hypothesis that CaM kinase II may be involved in the process of cholesterol mobilization to the mitochondria.

The H295R human adrenocortical cell line contains functional atrial natriuretic peptide receptors that inhibit aldosterone biosynthesis

The inhibitory effect of atrial natriuretic peptide (ANP) on angiotensin II (AII)-stimulated aldosterone secretion has been previously studied in rat and bovine adrenal zona glomerulosa cells in primary culture. However the understanding of the mode of action of ANP at the molecular level has been hampered by limitations of those primary cell culture systems and by the lack of cell lines from human adrenal cortex. Here we demonstrate the presence of fully functional ANP receptors in the recently characterized AII-responsive adrenocortical carcinoma cell line H295R. Specific saturable binding of 125I-rANP to H295R cell membrane preparations revealed a single class of high affinity binding sites with a density of 20 fmol/mg of protein. The pharmacological profile of this ANP receptor was documented by competitive binding of 125I-rANP with naturally occurring natriuretic peptides. rANP was the most potent with a Kd of 42 pM. pBNP32 was less potent with a Kd of 174 pM. 125I-rANP binding was not competed by pCNP (NPRB-specific ligand) nor by C-ANF (NPRC-specific ligand). Photoaffinity labeling of membrane preparations with 125I-BPA-ANP revealed a single specific protein of molecular weight around 130 kDa. This protein was further identified by immunodetection with a specific antibody directed to the human ANP-specific receptor NPRA. Natriuretic peptides stimulated cGMP production by the receptor-coupled guanylate cyclase with the same specificity. Aldosterone production by AII-stimulated H295R cells was dose-dependently inhibited by rANP with an ED50 of 1.5 nM. In addition, we used this model to test two chimeric analogs of ANP and BNP. pBNP1 and pBNP3 were, respectively, 4- and 2-fold more potent than rANP in competing for 125I-rANP binding with Kd of 10 and 20 pM. pBNP1 was 24-fold more potent in inhibiting AII-stimulated aldosterone production with ED50 of 63 pM. pBNP1 is therefore the most potent natriuretic peptide analog tested. In summary, the human H295R cell line contains NPRA receptors positively coupled to the particulate guanylate cyclase and that antagonize angiotensin II stimulation of aldosterone secretion.

The steroidogenic acute regulatory protein is induced by angiotensin II and K+ in H295R adrenocortical cells

Adrenal steroid hormone biosynthesis can be activated by the protein kinase A pathway by ACTH, the protein kinase C pathway by angiotensin II (AII), or by increasing intracellular Ca2+ levels by AII or K+. Although their mechanisms of action are not known, each of these pathways is dependent upon the de novo synthesis of a protein that is required for the acute production of steroids. We have recently proposed the steroidogenic acute regulatory (StAR) protein as this required protein, therefore, we examined the effect of different agonists on StAR's expression in H295R human adrenocortical carcinoma cells. (Bu)2cAMP, AII, K+, BAYK8644 (a calcium channel agonist) and TPA are all shown to induce StAR. Aldosterone synthesis was stimulated by all the agonists with the exception of TPA, indicating that AII-stimulated steroid production is mediated by increases in intracellular calcium. Thus, these data suggest that regulation of StAR expression may represent a common mechanism for divergent pathways to acutely control adrenal steroidogenesis.

Adrenal androgen biosynthesis with special attention to P450c17

In vitro studies of human adrenal androgen synthesis are limited because of the difficulties in obtaining adrenals. We describe the use of the human adrenocortical tumor H295 cell line as a model to evaluate mechanisms controlling C19-steroid production. The cells were characterized with regard to responsiveness to a variety of agents as measured by steroid secretion and induction of 17 alpha-hydroxylase cytochrome P450 (P450c17) expression, a key enzyme in C19-steroid production. Forskolin and dibutyryl cAMP, which were more effective than ACTH, enhanced the production of DHEA and androstenedione over a 48-hour treatment period. Agents that act by increasing intracellular calcium (angiotensin II and K+ ions) as well as protein kinase A pathway activators (ACTH, forskolin, and dibutyryl cAMP) individually increased the mRNA levels and activity of P450c17. In addition, angiotensin II but not K+ ions attenuated the increased expression promoted by the kinase A agonists. Thus, the complexity of human adrenal P450c17 expression through multiple signaling pathways may contribute importantly to the diverse patterns of human adrenocortical steroidogenesis.

Potassium negatively regulates angiotensin II type 1 receptor expression in human adrenocortical H295R cells

We have previously shown that the human adrenocortical H295R cell line expresses the type 1 angiotensin II receptor (AT1-R) and that expression of this receptor is downregulated at the level of mRNA by forskolin or dibutyryl-cAMP as well as by angiotensin II (Ang II). In this study we examine the effects of K+ on both AT1-R mRNA and receptors, as monitored through 125I-Ang II binding in the presence of PD 123319. After treatment with a maximal stimulatory steroidogenic dose of K+ (14 mmol/L), H295R cells showed an increase in cytosolic free Ca2+ from 113 to 212 nmol/L. Unlike the effects of Ang II, this increase could be abolished by pretreatment with the Ca2+ channel antagonist nifedipine (1 mumol/L). AT1-R mRNA levels also fell in response to elevated extracellular K+ in a dose-dependent (Kd, 9 mmol/L; maximal fall in message at 12 mmol/L) and time-dependent (maximum 50% at 12 hours) manner. The change in AT1-R mRNA level was less rapid than that in response to activation of phosphoinositidase C by Ang II or adenylyl cyclase by forskolin or by dibutyryl-cAMP. Unlike the action of Ang II but similar to the action of forskolin or dibutyryl-cAMP, the action of K+ was sustained. Changes in mRNA level in response to treatment with K+, Ang II, or dibutyryl-cAMP were also paralleled by changes in 125I-Ang II binding in each case.(ABSTRACT TRUNCATED AT 250 WORDS)

Hormonal regulation of angiotensin II type 1 receptor expression and AT1-R mRNA levels in human adrenocortical cells

Human adrenocortical H295R cells express AII receptors which are predominantly of the AT1 but not AT2 subclass. These receptors are functionally coupled to phosphoinositidase C in a manner similar to that seen in fetal human, sheep and bovine adrenocortical cells. Treatment of H295R cells with forskolin or dbcAMP to activate the protein kinase A pathway caused a rapid (maximal by 3 h) and sustained decrease in AT1-R mRNA levels which in turn preceded a time-dependent (maximal by 12 h) and dose-dependent loss of [125I]AII binding and phosphoinositidase C activation on subsequent AII challenge. Thus, both decreased AT1-R mRNA levels and functional receptor expression appear to parallel each other in response to activation of protein kinase A. Activation of the Ca2+/protein kinase C pathways by treatment with AII also caused a rapid (maximal by 3 h) and dose-dependent loss in AT1-R mRNA, but mRNA levels subsequently rose again, approaching control levels by 36 h. Treatment with AII for 48 h had little effect on either [125I]AII binding or the subsequent phosphoinositidase C response. The effect of AII, but not forskolin, was blocked by the presence of cycloheximide. The action of AII on AT1-R mRNA was probably mediated through both protein kinase C and Ca(2+)-sensitive protein kinases as the effect at 4 h was not completely reproduced by phorbol ester alone, but was fully reproduced by a combination of phorbol ester and Ca2+ ionophore. However, increased Ca2+ influx alone, due to treatment with BAYK8644 or elevated extracellular K+, also resulted in a decrease in AT1-R mRNA levels. Thus in the H295R cell, control of AT1-R expression appears to be complex, being achieved at least in part through control of the level of AT1-R mRNA by multiple independent signaling pathways including protein kinase A, protein kinase C and Ca2+.

Adrenal-specific transgene expression and derivation of conditionally immortal rat adrenocortical cell lines

Conditional immortalisation of cells is a powerful tool for establishing in vitro models maintaining a differentiated phenotype. We are utilising this approach to derive cell lines that maintain the characteristics of glomerulosa and fasciculata cells of the adrenal cortex. Such cell lines should provide a system in which to study aspects of adrenocortical function that are relevant to hypertension, such as the effects of the renin-angiotensin system on steroidogenesis.