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

Piper sarmentosum Roxb. Inhibits Angiotensin-Converting Enzyme Activity in Phorbol 12-Myristate-13-Acetate-Induced Endothelial Cells

Angiotensin-converting enzyme (ACE) plays a crucial role in the pathogenesis of hypertension. Piper sarmentosum Roxb., an herb known for its antihypertensive effect, lacks a comprehensive understanding of the mechanism underlying its antihypertensive action. This study aimed to elucidate the antihypertensive mechanism of aqueous extract of P. sarmentosum leaves (AEPS) via its modulation of the ACE pathway in phorbol 12-myristate-13-acetate (PMA)-induced human umbilical vein endothelial cells (HUVECs). HUVECs were divided into five groups: control, treatment with 200 µg/mL AEPS, induction 200 nM PMA, concomitant treatment with 200 nM PMA and 200 µg/mL AEPS, and treatment with 200 nM PMA and 0.06 μM captopril. Subsequently, ACE mRNA expression, protein level and activity, angiotensin II (Ang II) levels, and angiotensin II type 1 receptor (AT1R) and angiotensin II type 2 receptor (AT2R) mRNA expression in HUVECs were determined. AEPS successfully inhibited ACE mRNA expression, protein and activity, and angiotensin II levels in PMA-induced HUVECs. Additionally, AT1R expression was downregulated, whereas AT2R expression was upregulated. In conclusion, AEPS reduces the levels of ACE mRNA, protein and activity, Ang II, and AT1R expression in PMA-induced HUVECs. Thus, AEPS has the potential to be developed as an ACE inhibitor in the future.

Triadimefon suppresses fetal adrenal gland development after in utero exposure

Triadimefon is a broad-spectrum antifungal agent, which is widely used in agriculture to control mold and fungal infections. It is considered an endocrine disruptor. Whether triadimefon exposure can inhibit the development of fetal adrenal glands and the underlying mechanism remain unclear. Thirty-two pregnant female Sprague-Dawley rats were randomly divided into four groups. Dams were gavaged triadimefon (0, 25, 50, and 100 mg/kg/day) daily for 10 days from gestational day (GD) 12 to GD 21. Triadimefon significantly reduced the thickness of the zona fasciculata of male fetuses at 100 mg/kg, although it did not change the thickness of the zona glomerulosa. It significantly reduced the serum aldosterone levels of male fetuses at a dose of 100 mg/kg, and significantly reduced serum corticosterone and adrenocorticotropic hormone levels at doses of 50 and 100 mg/kg. Triadimefon significantly down-regulated the expression of Agtr1, Mc2r, Star, Cyp11b1, Cyp11b2, Igf1, Nr5a1, Sod2, Gpx1, and Cat, but did not affect the mRNA levels of Scarb1, Cyp11a1, Cyp21, Hsd3b1, and Hsd11b2. Triadimefon markedly reduced AT1R, CYP11B2, IGF1, NR5A1, and MC2R protein levels. Triadimefon significantly reduced the phosphorylation of AKT1 and ERK1/2 at 100 mg/kg without affecting the phosphorylation of AKT2. In contrast, it significantly increased AMPK phosphorylation at 100 mg/kg. In conclusion, exposure to triadimefon during gestation inhibits the development of fetal adrenal cortex in male fetuses. This inhibition is possibly due to the reduction of several proteins required for the synthesis of steroid hormones, and may be involved in changes in antioxidant contents and the phosphorylation of AKT1, ERK1/2, and AMPK.

Signaling Interactions in the Adrenal Cortex

The major physiological stimuli of aldosterone secretion are angiotensin II (AII) and extracellular K(+), whereas cortisol production is primarily regulated by corticotropin (ACTH) in fasciculata cells. AII triggers Ca(2+) release from internal stores that is followed by store-operated and voltage-dependent Ca(2+) entry, whereas K(+)-evoked depolarization activates voltage-dependent Ca(2+) channels. ACTH acts primarily through the formation of cAMP and subsequent protein phosphorylation by protein kinase A. Both Ca(2+) and cAMP facilitate the transfer of cholesterol to mitochondrial inner membrane. The cytosolic Ca(2+) signal is transferred into the mitochondrial matrix and enhances pyridine nucleotide reduction. Increased formation of NADH results in increased ATP production, whereas that of NADPH supports steroid production. In reality, the control of adrenocortical function is a lot more sophisticated with second messengers crosstalking and mutually modifying each other's pathways. Cytosolic Ca(2+) and cGMP are both capable of modifying cAMP metabolism, while cAMP may enhance Ca(2+) release and voltage-activated Ca(2+) channel activity. Besides, mitochondrial Ca(2+) signal brings about cAMP formation within the organelle and this further enhances aldosterone production. Maintained aldosterone and cortisol secretion are optimized by the concurrent actions of Ca(2+) and cAMP, as exemplified by the apparent synergism of Ca(2+) influx (inducing cAMP formation) and Ca(2+) release during response to AII. Thus, cross-actions of parallel signal transducing pathways are not mere intracellular curiosities but rather substantial phenomena, which fine-tune the biological response. Our review focuses on these functionally relevant interactions between the Ca(2+) and the cyclic nucleotide signal transducing pathways hitherto described in the adrenal cortex.

PCP4: a regulator of aldosterone synthesis in human adrenocortical tissues

Purkinje cell protein 4 (PCP4) is a calmodulin (CaM)-binding protein that accelerates calcium association and dissociation with CaM. It has been previously detected in aldosterone-producing adenomas (APA), but details on its expression and function in adrenocortical tissues have remained unknown. Therefore, we performed the immunohistochemical analysis of PCP4 in the following tissues: normal adrenal (NA; n=15), APA (n=15), cortisol-producing adenomas (n=15), and idiopathic hyperaldosteronism cases (IHA; n=5). APA samples (n=45) were also submitted to quantitative RT-PCR of PCP4, CYP11B1, and CYP11B2, as well as DNA sequencing for KCNJ5 mutations. Transient transfection analysis using PCP4 siRNA was also performed in H295R adrenocortical carcinoma cells, following ELISA analysis, and CYP11B2 luciferase assays were also performed after PCP4 vector transfection in order to study the regulation of PCP4 protein expression. In our findings, PCP4 immunoreactivity was predominantly detected in APA and in the zona glomerulosa of NA and IHA. In APA, the mRNA levels of PCP4 were significantly correlated with those of CYP11B2 (P<0.0001) and were significantly higher in cases with KCNJ5 mutation than WT (P=0.005). Following PCP4 vector transfection, CYP11B2 luciferase reporter activity was significantly higher than controls in the presence of angiotensin-II. Knockdown of PCP4 resulted in a significant decrease in CYP11B2 mRNA levels (P=0.012) and aldosterone production (P=0.011). Our results indicate that PCP4 is a regulator of aldosterone production in normal, hyperplastic, and neoplastic human adrenocortical cells.

Glutamate receptors and the regulation of steroidogenesis in the human adrenal gland: the metabotropic pathway

BACKGROUND

l-glutamate is a major excitatory neurotransmitter in the mammalian brain. Glutamate receptors have been reported in the rat adrenal cortex and in human aldosterone-producing adenomas (APA). However, details regarding the expression levels and functions of these receptors in human adrenocortical tissues remain unknown.

METHODS

The mRNA levels of glutamate receptors were evaluated by qPCR in: 12 normal adrenal cortex (NAC), 11 APA, and 12 cortisol-producing adenoma (CPA) tissues. Protein localization was evaluated by immunohistochemistry for 15 NAC, 5 idiopathic hyperaldosteronism cases, 15 APA and 15 CPA. H295R cells were treated with angiotensin-II or forskolin alone or combined with the GRM2/3 agonist LY354740.

RESULTS

The level of GRM3 mRNA was higher in APA than in CPA (P=0.0086) or NAC (P=0.0022). GRM1, IGLUR2, and IGLUR3 were also detected in adrenocortical tissues. When added to angiotensin-II/forskolin treatments, LY354740 decreased aldosterone and cortisol production in H295R cells.

CONCLUSIONS

GRM3 is considered to regulate steroidogenesis in adrenocortical tissues.

NCI-H295R, a human adrenal cortex-derived cell line, expresses purinergic receptors linked to Ca²⁺-mobilization/influx and cortisol secretion

Purinergic receptor expression and involvement in steroidogenesis were examined in NCI-H295R (H295R), a human adrenal cortex cell line which expresses all the key enzymes necessary for steroidogenesis. mRNA/protein for multiple P1 (A_2A and A_2B), P2X (P2X₅ and P2X₇), and P2Y (P2Y₁, P2Y₂, P2Y₆, P2Y₁₂, P2Y₁₃, and P2Y₁₄) purinergic receptors were detected in H295R. 2MeS-ATP (10–1000 µM), a P2Y₁ agonist, induced glucocorticoid (GC) secretion in a dose-dependent manner, while other extracellular purine/pyrimidine agonists (1–1000 µM) had no distinct effect on GC secretion. Extracellular purines, even non-steroidogenic ones, induced Ca²⁺-mobilization in the cells, independently of the extracellular Ca²⁺ concentration. Increases in intracellular Ca²⁺ concentration induced by extracellular purine agonists were transient, except when induced by ATP or 2MeS-ATP. Angiotensin II (AngII: 100 nM) and dibutyryl-cyclic AMP (db-cAMP: 500 µM) induced both GC secretion and Ca²⁺-mobilization in the presence of extracellular Ca²⁺ (1.2 mM). GC secretion by AngII was reduced by nifedipine (10–100 µM); whereas the Ca²⁺ channel blocker did not inhibit GC secretion by 2MeS-ATP. Thapsigargin followed by extracellular Ca²⁺ exposure induced Ca²⁺-influx in H295R, and the cells expressed mRNA/protein of the component molecules for store-operated calcium entry (SOCE): transient receptor C (TRPC) channels, calcium release-activated calcium channel protein 1 (Orai-1), and the stromal interaction molecule 1 (STIM1). In P2Y₁-knockdown, 2MeS-ATP-induced GC secretion was significantly inhibited. These results suggest that H295R expresses a functional P2Y₁ purinergic receptor for intracellular Ca²⁺-mobilization, and that P2Y₁ is linked to SOCE-activation, leading to Ca²⁺-influx which might be necessary for glucocorticoid secretion.

Estrogen-related receptor α in normal adrenal cortex and adrenocortical tumors: involvement in development and oncogenesis

AIMS

The nuclear hormone receptor estrogen-related receptor α (ERRα) regulates the activation of mitochondrial genes in various human tissues, but its role in the adrenal gland and its disorders has not been defined. Therefore, we examined ERRα expression in both normal adrenal cortex (NAC) and adrenocortical tumor (ACT) in order to study the possible correlation of ERRα with adrenal development and tumor development.

METHODS

Human adrenal specimens (non-pathological fetal n=7; non-pathological post-birth n=40; aldosterone producing adenoma (APA) n=11; cortisol producing adenoma (CPA) n=11; adrenocortical carcinoma (ACC) n=8) were immunohistochemically examined in this study. NAC (n=13) and ACT (n=28) frozen tissue specimens were also available for studying ERRα mRNA levels.

KEY FINDINGS

In fetal NAC tissues, ERRα labeling index (LI) in fetal zone (FZ) was significantly higher that that in neocortex (NC), and the differences among age groups for overall mean LI was statistically significant when analyzed according to individual cortical layers. ERRα LI was also significantly higher in ACC than in other types of ACT. ERRα mRNA was detected in NAC and all types of ACT.

SIGNIFICANCE

Results of our present study suggest a possible role of ERRα in adrenal development and ACC.

Human adrenocortical carcinoma cell lines

The human adrenal cortex secretes mineralocorticoids, glucocorticoids and adrenal androgens. These steroids are produced from unique cell types located within the three distinct zones of the adrenal cortex. Disruption of adrenal steroid production results in a variety of diseases that can lead to hypertension, metabolic syndrome, infertility and androgen excess. The adrenal cortex is also a common site for the development of adenomas, and rarely the site for the development of carcinomas. The adenomas can lead to diseases associated with adrenal steroid excess, while the carcinomas are particularly aggressive and have a poor prognosis. In vitro cell culture models provide important tools to examine molecular and cellular mechanisms controlling both the normal and pathologic function of the adrenal cortex. Herein, we discuss currently available human adrenocortical carcinoma cell lines and their use as model systems for adrenal studies.

Acute and chronic regulation of aldosterone production

Aldosterone is the major mineralocorticoid synthesized by the adrenal and plays an important role in the regulation of systemic blood pressure through the absorption of sodium and water. Aldosterone production is regulated tightly by selective expression of aldosterone synthase (CYP11B2) in the adrenal outermost zone, the zona glomerulosa. Angiotensin II (Ang II), potassium (K(+)) and adrenocorticotropin (ACTH) are the main physiological agonists which regulate aldosterone secretion. Aldosterone production is regulated within minutes of stimulation (acutely) through increased expression and phosphorylation of the steroidogenic acute regulatory (StAR) protein and over hours to days (chronically) by increased expression of the enzymes involved in the synthesis of aldosterone, particularly CYP11B2. Imbalance in any of these processes may lead to several disorders of aldosterone excess. In this review we attempt to summarize the key molecular events involved in the acute and chronic phases of aldosterone secretion.

Comparison of aldosterone production among human adrenocortical cell lines

Several human adrenocortical cell lines have been used as model systems for aldosterone production. However, these cell lines have not been directly compared with each other. Human adrenal cell lines SW13, CAR47, the NCI-H295 and its sub-strains and sub-clones were compared with regard to aldosterone production and aldosterone synthase (CYP11B2) expression. Culture media was collected 48 h after incubation, aldosterone secretion was measured and the data were normalized to the amount of cell protein. RNA was isolated for microarray analysis and quantitative RT-PCR (qPCR). The cell lines with the highest aldosterone production were further tested with regard to angiotensin II (Ang II) stimulation. Neither aldosterone nor CYP11B2 transcript were detected in SW13 or CAR47 cells. The aldosterone production by the NCI-H295, H295A, H295R-S1, H295R-S2, H295R-S3, HAC13, HAC15 and HAC50 were 119, 1, 6, 826, 18, 139, 412, and 1 334 (pmol/mg protein/48 h), respectively. H295A and H295R-S1 expressed less CYP11B2 than the commonly used H295R-S3 cells; while NCI-H295, H295R-S2, HAC13, HAC15 and HAC50 expressed 24-, 14-, 3-, 10-, and 35-fold higher CYP11B2 compared with the H295R-S3 cells. When treated with Ang II, NCI-H295, H295R-S2, HAC13, HAC15 and HAC50 showed significantly higher aldosterone production than the basal level (p<0.05). A comparison of the available human adrenal cell lines indicates that the H295R-S2 and the clonal cell lines, HAC13, HAC15 and HAC50 produced the highest levels of aldosterone and responded well to Ang II.

Regulation of adrenal aldosterone production by serine protease prostasin

A serine protease prostasin has been demonstrated to have a pivotal role in the activation of the epithelial sodium channel. Systemic administration of adenovirus carrying human prostasin gene in rats resulted in an increase in plasma prostasin and aldosterone levels. However, the mechanism by which the elevation of prostasin levels in the systemic circulation stimulated the plasma aldosterone levels remains unknown. Therefore, we examined if prostasin increases the aldosterone synthesis in a human adrenocortical cell line (H295R cells). Luciferase assay using CYP11B2 promoter revealed that prostasin significantly increased the transcriptional activity of CYP11B2. Prostasin significantly increased both CYP11B2 mRNA expression and aldosterone production in a dose-dependent manner. Surprisingly, treatment with camostat mesilate, a potent prostasin inhibitor, had no effect on the aldosterone synthesis by prostasin and also a protease-dead mutant of prostasin significantly stimulated the aldosterone production. A T-type/L-type calcium channel blocker and a protein kinase C (PKC) inhibitor significantly reduced the aldosterone synthesis by prostasin. Our findings suggest a stimulatory effect of prostasin on the aldosterone synthesis by adrenal gland through the nonproteolytic action and indicate a new role of prostasin in the systemic circulation.

Angiotensin II regulation of adrenocortical gene transcription

Angiotensin II (Ang II) is the key peptide hormone in the renin-angiotensin-aldosterone system (RAAS). Its ability to regulate levels of circulating aldosterone relies on actions on adrenal glomerulosa cells. Many of the Ang II effects on glomerulosa cells involve a precisely coordinated regulation of signaling cascades and gene expression. The development of genome-wide gene arrays has allowed the definition of transcriptome-wide effects of Ang II in adrenocortical cells. Analysis of the Ang II gene targets reveals broad effects on cellular gene expression, particularly the rapid induction of numerous transcription factors that may regulate long-term steroid metabolism and cell growth/proliferation. Herein we discuss the Ang II-induced genes in adrenocortical cells and review the progress in defining the role of these genes in zona glomerulosa function.

Angiotensin II regulation of ovine fetoplacental artery endothelial functions: interactions with nitric oxide

During normal pregnancy, elevated angiotensin II (Ang II) concentrations in the maternal and fetal circulations are associated with dramatic increases in placental angiogenesis and blood flow. Much is known about a local renin-angiotensin system within the uteroplacental vasculature. However, the roles of Ang II in regulating fetoplacental vascular functions are less well defined. In the fetal placenta, the overall in vivo vasoconstrictor responses of the blood vessels to Ang II infusion is thought to be less than that in its maternal counterpart, even though infused Ang II induces vasoconstriction. Recent data from our laboratories suggest that Ang II stimulates cell proliferation and increases endothelial nitric oxide synthase (eNOS) and production of nitric oxide (NO) in ovine fetoplacental artery endothelial cells. These data imply that elevations of the known vasoconstrictor Ang II in the fetal circulation may indeed play a role in the marked increases in fetoplacental angiogenesis and that Ang II-elevated endothelial NO production may partly attenuate Ang II-induced vasoconstriction on vascular smooth muscle. Together with both of these processes, the high levels of Ang II in the fetal circulation may serve to modulate overall fetoplacental vascular resistance. In this article, we review currently available data on the expression of Ang II receptors in the ovine fetal placenta with particular emphasis on the effects of Ang II on ovine fetoplacental endothelium. The potential cellular mechanisms underlying the regulation of Ang II on endothelial growth and vasodilator production are discussed.

Translation of the human angiotensin II type 1 receptor mRNA is mediated by a highly efficient internal ribosome entry site

Activation of the angiotensin II type 1 receptor (AT1R) is closely involved in the pathogenesis of cardiovascular disease. The human AT1R (hAT1R) mRNA splice variants have long 5'-untranslated regions (5'-UTRs) ranging from 272 to 414 bp that have the potential to form stable secondary structures. In this study, we show that the 5'-UTR of hAT(1)R mRNAs contains an internal ribosome entry site (IRES) located within the first 40 bp of the proximal end of exon 1. Experiments utilizing the hAT1R 5'-UTR as a molecular decoy demonstrate a reduction in IRES activity of approximately 50%. This inhibition is most efficient for the hAT1R IRES suggesting that a defined set of trans-factors are required to initiate translation through this cis-element. Translation initiation from the hAT1R IRES appears to be physiologically relevant since IRES activity was maintained during serum starvation, a cellular stress known to inhibit cap-dependent translation. These results suggest that cap-independent translation initiation by internal ribosome entry may represent an important mechanism for the regulation of hAT1R expression.

Isolation of a full length ovine angiotensin II type-1 receptor (AT1-R) cDNA

A full-length ovine AT1-R cDNA (2358 bases: Genebank AF254119) was isolated from ovine adrenal cortex using 3'-RACE. While homology of the 5'-untranslated region to human sequence was low (34.2%), the beginning of both human exon 1 and human exon 5 (encoding the end of the 5'-untranslated sequence/complete protein coding region/3'-untranslated sequence) were exceptionally conserved and in context. The intervening untranslated sequence showed lower homology to human sequence, but still contained four additional ATG sequences close to corresponding "in frame" TGA Stop codons shown in human to impair AT1-R translation in vitro. The putative protein coding sequence was >99% identical to the previous reported ovine genomic sequence. The predicted amino acid sequence in turn encoded a protein with the properties of a seven alpha-helix transmembrane receptor sharing closest homology (99.1%) to the bovine receptor and lowest to the rat Type la (90.5%). The 3'-untranslated region showed relatively high homology to the porcine and bovine receptor cDNA, but did not share the additional 643 bases found only in the bovine 3'-untranslated region. The ovine 3'-sequence included a polyadenylation signal as well as three AUUUA destabilization sequences observed in most other species including human. Thus ovine AT1-R mRNA stability may be short lived, and control of degradation may be an additional mechanism for regulation of ovine AT1-R expression.

Expression of endothelial and inducible nitric oxide synthases and nitric oxide production in ovine placental and uterine tissues during late pregnancy

We evaluated the expression of endothelial (eNOS) and inducible (iNOS) nitric oxide (NO) synthases, NO production, and the role of angiotensin II (ANG II) in regulating NO production during late ovine pregnancy (day 110-142). Samples of the following tissues were obtained: fetal [cotyledonary (COT)] and maternal [caruncular (CAR)] portions of the placentoma, intercotyledonary fetal chorioallantoic membrane (ICOT) and intercaruncular maternal endometrium (ICAR). Using immunohistochemistry, eNOS positive staining was detected in all four tissues, primarily in the endothelium, chorioallantoic membrane, and luminal and glandular epithelium. For iNOS, the positive staining was observed primarily in stromal cells in ICOT and ICAR. Expression of eNOS and iNOS proteins was confirmed in COT using Western immunoblot. eNOS protein levels increased (P< 0.05) approximately 3.5-fold from day 110 to 130 and then declined at term, whereas no change in iNOS protein levels was observed throughout the days studied. The tissue explants of COT, CAR, ICOT and ICAR were cultured in media in the absence or presence of ANG II (10(-9)or 10(-7) m) for 24 h. Total NO (nitrate and nitrite) levels in the explant-conditioned media were determined by chemiluminesence. In fetal COT, total NO levels increased (P< 0.05) 3.5-fold from day 110 to 130 and then declined (P< 0.05) at term. In ICOT, total NO levels exhibited a gradually increasing trend (r(2)=0.96, P< 0.01) from day 110 to days 130 and 142. In maternal CAR, total NO levels were higher (P< 0.05) on day 130 than those on days 120 and 142, whereas no change in total NO levels was observed in ICAR. ANG II at 10(-7) m treatment decreased (P< 0.05) total NO levels in COT on day 130. Thus, during late ovine pregnancy: (1) eNOS is expressed in COT, CAR, ICOT and ICAR while iNOS is primarily seen in stromal cells of ICOT and ICAR; (2) NO production by COT exhibits a biphasic pattern and parallels the changes in eNOS, but not iNOS protein levels, suggesting that eNOS is a predominant NOS isoform for the NO production; and (3) ANG II may contribute partially to decreases in NO production by COT at term.

Ontogeny and regulation of the AT1 and AT2 receptors in the ovine fetal adrenal gland

The expression and regulation of the receptors for angiotensin II (both AT1 and AT2) were examined in the ovine fetal adrenal gland by RNase protection assay (RPA), in situ hybridisation histochemistry, immunohistochemistry and Western blotting. Both mRNA and protein for the AT1 receptor were present in the zona glomerulosa and zona fasciculata of the cortex, but not in the medulla, from as early as these zonas were distinguishable (60 days of gestation; term is 145-150 days), and even present in the steroidogenic cells of the unzoned gland at 40 days. The mRNA for the AT2 receptor was present in the same locations (but never in the medulla) from 40-130 days, and declined to extremely low levels after 140 days. The infusion of ang II, 1 microg/h, for 3 days, at mid-gestation (76 +/- 2 days) caused a significant decrease in mRNA for AT1 but no change in AT2 levels. Thus, the biologically active receptor (in terms of aldosterone stimulation) is present in the ovine fetal adrenal from very early in development, and can be down-regulated by mid-gestation.

Local renin-angiotensin system is involved in K+-induced aldosterone secretion from human adrenocortical NCI-H295 cells

NCI-H295, a human adrenocarcinoma cell line, has been proposed as a model system to define the role of the renin-angiotensin system in the regulation of aldosterone production in humans. Because the precise cellular localization of the components of the renin-angiotensin system in human adrenal cortical cells remains unclear, we investigated their localization in this defined cell system. NCI-H295 cells expressed both angiotensinogen and renin as shown by reverse transcriptase polymerase chain reaction and immunohistochemistry. Human angiotensin-converting enzyme (ACE) was not detectable by immunocytochemistry, ACE binding, or reverse transcriptase polymerase chain reaction. However, 3.5 mmol/L K+ stimulated the formation of both angiotensin I and angiotensin II 1. 9- and 2.5-fold, respectively, and increased aldosterone release 3. 0-fold. The K+-induced stimulation of aldosterone release was decreased by captopril and enalaprilat (24% and 26%, respectively) and by the angiotensin type 1 (AT1)-receptor antagonist losartan (28%). Angiotensin II-induced stimulation of aldosterone release was abolished by losartan treatment. Specific [125I]Sar1-angiotensin II binding was detected by receptor autoradiography. The binding of [125I]Sar1-angiotensin II was completely displaced by the AT1 antagonist losartan but not by the AT2 receptor ligand PD 123319, confirming the expression of angiotensin II AT1 receptors in NCI-H295 cells. Our results demonstrate that NCI-H295 cells express most of the components of the renin-angiotensin system. Our failure to detect ACE, however, suggests that the production of angiotensin II in NCI-H295 cells may be ACE independent. NCI-H295 cells are able to produce angiotensin II, and K+ increases aldosterone secretion in part through an angiotensin-mediated pathway. The production of angiotensin II in NCI-H295 cells demonstrates that this human cell line can be useful to characterize the role of locally produced angiotensin II in the regulation of aldosterone release.

Specific pregnancy-induced angiotensin II type-1 receptor expression in ovine uterine artery does not involve formation of alternate splice variants or alternate promoter usage

Recently we reported that pregnancy is associated with a dramatic increase in angiotensin II type-1 receptor (AT1-R; both protein and mRNA) in ovine uterine artery endothelial cells (UAEC), which far exceeds that seen in omental (systemic) arteries. Recent reports also suggest that alternate splicing of AT1-R mRNA may play a role in regulation of AT1-R expression in humans. Herein, we have investigated the possibility of alternate transcript splicing/promoter usage in UAEC from pregnant ewes by 5'-RACE (rapid amplification of cDNA 5'-ends). To provide our control "reference" sequences, we first performed 5'-RACE analysis of AT1-R mRNA transcripts in liver, kidney, and adrenal cortex. Analysis of 17 resultant clones showed exceptional homology, indicating that a single identically spliced mRNA product is observed in all three ovine tissues. Homology of the 5'-untranslated region to that of the human was low (34.2%), but four in-context start/stop codons and the beginning of human exons 1 and 5 were highly conserved. Subsequently we isolated 30 individual clones using UAEC RNA from three pregnant ewes and found no evidence of any sequence formed through unique splicing or promoter usage. We conclude that the pregnancy-induced increase in AT1-R expression unique to UAEC during pregnancy is not mediated by splicing of a unique transcript or unique promoter usage.

Isolation of an ovine genomic sequence containing the full-length angiotensin II type-1 receptor

We have isolated from a genomic library using PCR amplification an 1171 base sequence containing a putative ovine AT1-R protein coding sequence of 1080 bases. As expected the protein coding sequence is of greater than 99% homology to the partial protein coding sequence reported by Robillard et al, with only one base difference. Relative to other species, highest homology at the level of the cDNA protein coding sequence is to bovine (97.6%) and lowest homology to rat Type 1a (83.3%). The predicted protein amino acid sequence in turn encodes a protein with the properties of a seven alpha-helix transmembrane receptor (by TMPred) sharing closest homology (98.6%) to the bovine receptor and lowest to the rat Type 1a (90.2%). As expected from such a high degree of interspecies homology, amino acids identified by site-directed mutagenesis of the human or rat AT1A-R as involved in binding and action of AII are very highly conserved in the ovine sequence. In addition, both bovine and ovine AT1-R are known to exhibit lower affinity for DuP753 than human AT1-R, and in bovine AT1-R this has been suggested to coincide with the amino acid substitutions Ala->Thr (163) and Leu->Met (262) relative to the human sequence. Our ovine AT1-R cDNA sequence shares these same bovine substitutions.

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.

Multiple signal transduction systems regulate angiotensin II type 1 (AT1) receptor mRNA expression in bovine adrenocortical cells

Regulation of AT1 receptor mRNA expression is an important determinant of angiotensin II-induced steroidogenesis. We have PCR-amplified the bovine adrenal AT1 receptor coding region using primers designed from the published bovine AT1 receptor sequence. This has been used as a probe on Northern blots to detect changes in the levels of AT1 receptor mRNA in primary cultures of bovine zona fasciculata cells in response to activation of several different signal transduction mechanisms in addition to two major adrenal steroid products, cortisol and aldosterone. AT1 receptor mRNA decreased in response to 6hr AII (10 nM) treatment, but returned to basal levels following 48h AII treatment. This effect was mimicked by the phorbol ester PMA (1 microM) and the calcium ionophore A23187 (1 microM), both singly and in combination. Activation of the cAMP pathway by ACTH (1 nM) and 8-bromo-cAMP (0.1 microM) also decreased AT1 receptor mRNA levels. In contrast, both IGF-1 (10 ng/ml) and potassium ions (12 mM) increased the levels of AT1 receptor mRNA. Finally, cortisol (10 microM) but not aldosterone (100 nM) decreased AT1 receptor mRNA. We conclude that the regulation of AT1 receptor mRNA in bovine zona fasciculata cells could involve several different signal transduction systems in addition to adrenocortical steroids themselves.