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.

Proliferative signaling initiated in ACTH receptors

This article reviews recent results of studies aiming to elucidate modes of integrating signals initiated in ACTH receptors and FGF2 receptors, within the network system of signal transduction found in Y1 adrenocortical cells. These modes of signal integration should be central to the mechanisms underlying the regulation of the G0-->G1-->S transition in the adrenal cell cycle. FGF2 elicits a strong mitogenic response in G0/G1-arrested Y1 adrenocortical cells, that includes a) rapid and transient activation of extracellular signal-regulated kinases-mitogen-activated protein kinases (ERK-MAPK) (2 to 10 min), b) transcription activation of c-fos, c-jun and c-myc genes (10 to 30 min), c) induction of c-Fos and c-Myc proteins by 1 h and cyclin D1 protein by 5 h, and d) onset of DNA synthesis stimulation within 8 h. ACTH, itself a weak mitogen, interacts with FGF2 in a complex manner, blocking the FGF2 mitogenic response during the early and middle G1 phase, keeping ERK-MAPK activation and c-Fos and cyclin D1 induction at maximal levels, but post-transcriptionally inhibiting c-Myc expression. c-Fos and c-Jun proteins are mediators in both the strong and the weak mitogenic responses respectively triggered by FGF2 and ACTH. Induction of c-Fos and stimulation of DNA synthesis by ACTH are independent of PKA and are inhibited by the PKC inhibitor GF109203X. In addition, ACTH is a poor activator of ERK-MAPK, but c-Fos induction and DNA synthesis stimulation by ACTH are strongly inhibited by the inhibitor of MEK1 PD98059.

Sp1 and SF-1 interact and cooperate in the regulation of human steroidogenic acute regulatory protein gene expression

Steroidogenic acute regulatory (StAR) protein plays a critical role in the movement of cholesterol from the outer to the inner mitochondrial membrane. Steroidogenic factor 1 (SF-1) controls basal and cAMP-stimulated transcription of the StAR gene. The 1.3-kb StAR promoter has three SF-1 binding sites, and two consensus transcription factor Spl binding sequences near the two most distal SF-1 binding sites. Spl mediates cAMP-dependent transcription of steroidogenic P450 enzyme genes, raising the possibility of Sp1 involvement in cAMP regulation of the StAR gene. However, the mechanism of Spl-mediated, cAMP-stimulated responsiveness is not known. In this study, we elucidated the roles of Sp1 and SF-1 in the regulation of the human StAR gene promoter. We found that there was negligible promoter activity in a pGL2 StAR construct (-235 to +39) in which Spl and SF-1 binding sites were mutated in Y-1 adrenal tumor cells. An Sp1 binding site mutation (pGL2Sp1M) did not support promoter activity, suggesting that Spl cooperates with SF-1 in regulating StAR promoter function. In gel shift assays, the SF-1 binding site formed a complex with an SF-1-GST fusion protein and Spl. Coimmunoprecipitation cross-linking experiments indicated that SF-1 physically interacts with Sp1 in vitro. Finally, a mammalian two-hybrid system was employed to demonstrate that Spl and SF-1 associate in vivo. In conclusion, our data indicate that Spl and SF-1 physically interact and cooperate in the regulation of human StAR promoter activity.

In vivo observation of a nuclear channel-like system: evidence for a distinct interchromosomal domain compartment in interphase cells

We have investigated the interchromosomal domain compartment in living cells by transfecting cDNA coding for Xenopus vimentin, engineered to contain a nuclear localization signal (NLS), coupled to the green fluorescent protein. In human vimentin-free SW13 cells, this chimeric protein was deposited in body-like "dots" both at 37 degrees C, the nonpermissive temperature for assembly of the amphibian vimentin, and 28 degrees C, the optimal temperature for Xenopus vimentin assembly, indicating that the chimeric protein was assembly incompetent. However, when transfected into a subclone stably expressing Xenopus NLS-vimentin (SW13-SC), the chimeric protein incorporated, as a fluorescent tracer, into the structures formed by NLS-vimentin and allowed us to visualize the outgrowth of the vimentin fibers after a temperature shift to 28 degrees C in living cells. In particular, we followed the time-dependent outgrowth of fibers from nuclear dots, first connecting two dots each and with time three and more, eventually generating a spatially restricted fiber system consisting of few loop-like arrays traversing the nucleus. Virtually identical results were obtained when the temperature was lowered only to 30 and 32 degrees C, respectively. An engineered human NLS-vimentin, without need for temperature shift, formed seemingly identical patterns of nuclear fibrils at 37 degrees C in three additionally transfected human cell lines: MCF-7, PLC, and HeLa. When the epithelial cytokeratin pair 8 and 18 was expressed in the nucleus via an engineered NLS in the cytokeratin 18 gene, more network-like, extended filament arrays were generated. Notably, in cotransfection experiments with Xenopus NLS-vimentin, we observed that the formation of these cytokeratin networks at 37 degrees C initiated from dots that nearly entirely colocalized with the aggregated amphibian NLS-vimentin. After a shift to 28 degrees C, extending Xenopus NLS-vimentin and cytokeratin filaments frequently followed the same path through the nucleus. These data indicate that interphase cells contain a seemingly equivalent, accessible interchromosomal space.

Two cases of osteosarcoma occurring as second malignancy of childhood cancer

We report on two patients in whom osteosarcoma occurred as second malignancy of childhood cancer. One patient had a malignant teratoma and the other adrenocortical carcinoma as the primary cancer. The emergence of cancer in cured cases and long-term survival cases of childhood cancer may result in an increase in the number of osteosarcomas seen in adolescence occurring as second malignancy. Anti-cancer drugs in large does were used for the treatment of a malignant teratoma in the former. These anti-cancer drugs may be involved in the occurrence of the second malignancy. In the latter, the patient has the germ-line mutation of p53 tumor suppressor gene, so genetic factors are presumably related to the occurrence of the second malignancy.

Dax-1 as one of the target genes of Ad4BP/SF-1

The DAX-1 (also known as AHC) gene encodes an unusual member of the nuclear hormone receptor superfamily. DAX-1 plays a critical role during gonadal and adrenal differentiation since mutations of the human DAX-1 gene cause X-linked adrenal hypoplasia congenita associated with hypogonadotropic hypogonadism. In recent studies, DAX-1 was reported to function as a transcriptional suppressor of Ad4BP/SF-1, a critical transcription factor in gonadal and adrenal differentiation. With respect to implication of Ad4BP/SF-1 in the transcriptional regulation of the DAX-1 gene, inconsistent findings have been previously reported. We investigated the upstream region of the mouse Dax-1 (also known as Ahch) gene and identified a novel Ad4/SF-1 site by transient transfection and electrophoretic mobility shift assays. In addition, immunohistochemical analyses with a specific antibody to Dax-1 indicated the presence of immunoreactive cells in steroidogenic tissues, pituitary gland, and hypothalamus. Although the distributions of Dax-1 and Ad4BP/SF-1 were very similar, they were not completely identical. The expression of Dax-1 was significantly impaired in knock-out mice of the Ftz-f1 gene, which encodes Ad4BP/ SF-1. Taken together, our findings indicate that Ad4BP/SF-1 controls the transcription of the Dax-1 gene.

Cloning of a novel kinase (SIK) of the SNF1/AMPK family from high salt diet-treated rat adrenal

PCR-coupled cDNA subtraction hybridization was adapted to identify the genes expressed in the adrenocortical tissues from high salt diet-treated rat. A novel cDNA clone, termed salt-inducible kinase (SIK), encoding a polypeptide (776 amino acids) with significant similarity to protein serine/ threonine kinases in the SNF1/AMPK family was isolated. An in vitro kinase assay demonstrated that SIK protein had autophosphorylation activity. Northern blot revealed that SIK mRNA levels were markedly augmented by ACTH treatment both in rat adrenal glands and in Y1 cells. SIK may play an important role in the regulation of adrenocortical functions in response to high plasma salt and ACTH stimulation.

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.

Adrenocortical cells are the site of secretion and action of insulin-like growth factors and TNF-alpha

Insulin-like growth factors I and/or II are expressed in adrenal cells, and modulate their proliferation and steroid hormone synthesis suggesting that they may function as paracrine/autocrine factors. In some species, at least ACTH induces insulin-like growth factor synthesis. Thus, these peptide growth factors mediate at least some of the effects of ACTH on adrenocortical cell proliferation and differentiation. Human fetal adrenals express insulin-like growth factor II gene abundantly and ACTH-dependently, while in adult adrenals, the expression is low and no ACTH dependent regulation has been demonstrated. Hormonally active adrenocortical carcinomas and virilizing adenomas express insulin-like growth factor II gene abundantly. This phenomenon is associated with reduced expression of two putative tumor suppressor genes (H19 and p57KIP2) locating on the same genomically imprinted locus on human chromosome 11p15.5. Tumor necrosis factor-alpha belongs to the cytokines which modulate hypothalamic-pituitary-adrenal axis. It is a potent inducer of ACTH secretion but, at the adrenal level, it seems to mainly inhibit ACTH-induced steroidogenesis and also insulin-like growth factor II expression. It is produced in adrenocortical steroidogenic cells in addition to macrophages, which suggests that tumor necrosis factor-alpha may have some autocrine/paracrine functions in the adrenal cortex.

Unmasking a growth-promoting effect of the adrenocorticotropic hormone in Y1 mouse adrenocortical tumor cells

The adrenocorticotropic hormone (ACTH) inhibits the growth of Y1 mouse adrenocortical tumor cells as well as normal adrenocortical cells in culture but stimulates adrenocortical cell growth in vivo. In this study, we investigated this paradoxical effect of ACTH on cell proliferation in Y1 adrenal cells and have unmasked a growth-promoting effect of the hormone. Y1 cells were arrested in the G1 phase of the cell cycle by serum starvation and monitored for progression through S phase by measuring [3H]thymidine incorporation into DNA and by measuring the number of nuclei labeled with bromodeoxyuridine. Y1 cells were stimulated to progress through S phase and to divide after a brief pulse of ACTH (up to 2 h). This effect of ACTH appeared to be cAMP independent, since ACTH also induced cell cycle progression in Kin-8, a Y1 mutant with defective cAMP-dependent protein kinase activity. The growth-promoting effect of ACTH in Y1 was preceded by the rapid activation of p44 and p42 mitogen-activated protein kinases and by the accumulation of c-FOS protein. In contrast, continuous treatment with ACTH (14 h) inhibited cell cycle progression in Y1 cells by a cAMP-dependent pathway. The inhibitory effect of ACTH mapped to the midpoint of G1. Together, the results demonstrate a dual effect of ACTH on cell cycle progress, a cAMP-independent growth-promoting effect early in G1 possibly mediated by mitogen-activated protein kinase and c-FOS, and a cAMP-dependent inhibitory effect at mid-G1. It is suggested that the growth-inhibitory effect of ACTH at mid-G1 represents an ACTH-regulated check point that limits cell cycle progression.

Voltage dependent calcium and potassium currents in Y-1 adrenocortical cells are unresponsive to ACTH

In this report we use both whole cell and perforated patch clamp recording techniques to characterize calcium and potassium channels in Y-1 adrenocortical cells in order to assess their responsiveness to ACTH. Both transient and long-lasting components of an inward calcium current were identified which were similar to T and L-type Ca2+ currents. With Ba2+ as the charge carrier, the transient current activated at voltages more hyperpolarized than -50 mV with V1/2 for activation at -78.1 mV, and for steady state inactivation at -52.3 mV. The L-type current activated at -20 mV, with a V1/2 for activation at -29.9 mV and steady state inactivation at -44.2 mV. Under perforated patch conditions the response was shifted to more depolarized voltages. Both currents were responsive to agents which usually affect T- or L-type Ca2+ currents. The transient current was completely blocked by 50 microM lanthanum or 200 microM nickel and partially blocked by 300 mM amiloride. Cadmium (100 microM) and nifedipine (300 nM) completely blocked the long-lasting current while omega-conotoxin GVIA (1992 nM) inhibited the current by only 20-25%. The agonist, Bay K 8644 was stimulatory at 50 nM. Both transient and sustained outward potassium currents similar to A-type and delayed rectifier currents, respectively, were present. The transient current demonstrated fast activation at voltages more positive than -10 mV, inactivation with continued depolarization and steady state inactivation at V1/2 = -50 mV. The sustained current activated rapidly and had minimal inactivation with continued depolarization. The transient current was blocked by 5 mM 4AP and the sustained by 25 mM TEA. While Y-1 cells contain both calcium and potassium currents similar to those found in other adrenocortical cells, none of the currents were affected by ACTH or AII, secretagogues which stimulate steroidogenesis. These data, combined with the inability of both Ca2+ and K+ channel blockers to alter ACTH-induced steroidogenesis as reported earlier, suggests that neither calcium nor potassium currents are responsive to ACTH in Y-1 cells.

Genomic structure and promoter characterization of the human ACTH receptor gene

One kb of the 5'-flanking region of the human ACTH receptor gene was isolated and partially characterized. Transient transfections with hGH reporter confirmed the promoter activity in Y1 cells. Putative elements for transcription factors involved in regulation were noted in the sequence. The promoter activity of some of the constructs is responsive to a treatment by forskolin, due to the presence of several CRE-like sequences.

Molecular strategies for the dominant inhibition of protein kinase C

The regulatory (R) domain of PKC alpha fused to glutathione-S-transferase (GST-R alpha) competitively inhibited PKC activity associated with extracts of Y1 mouse adrenocortical tumor cells and the activities of several specific PKC isozymes. GST-R alpha did not inhibit the activities of cAMP-dependent protein kinase, cGMP-dependent protein kinase or calmodulin-dependent myosin light chain kinase. GST-R alpha inhibited PKC activities 20 times more potently than did a synthetic peptide corresponding to the pseudosubstrate sequence of PKC alpha. In intact yeast cells, the R domain prevented PKC beta-1-induced inhibition of growth and cytokinesis. These results indicate that the R domain of PKC alpha acts as a specific, dominant inhibitor of PKC activity, and suggest that the PKC alpha R domain may provide a useful genetic tool to assess the roles of PKC in various signal transduction processes.

Regulation of growth by ACTH in the Y-1 line of mouse adrenocortical cells

Y-1 adrenal cells were cell cycle arrested by serum starvation to characterize a G0-->G1-->S transition in these cells. Cycle arrested Y-1 cells start to enter S phase 8h after serum feeding, reaching more than 90% cells synthesizing DNA by 24h. ACTH displays a dual effect in the G0-->G1-->S transition: 2h ACTH treatment stimulates DNA synthesis initiation, but longer treatments inhibit S phase entry. This dual effect of ACTH is similar to the antagonistic actions of PMA (phorbol-12-miristate-13-acetate) on the G0-->G1-->S transition. However ACTH and PMA are likely to have different mechanisms of action. ACTH inhibitory effect requires PKA, whereas PMA inhibitory effect is not dependent on PKA. ACTH induces the proto-oncogenes c-fos and c-jun, but inhibits the expression of the c-myc proto-oncogene. PMA, on the other hand, induces equally well c-fos, c-jun and c-myc. We hypothesize that ACTH promotes G0-->G1 transition by induction of c-fos and c-jun and blocks G1-->S transition by c-myc inhibition.

Characterization of the hamster CYP11B2 gene regulatory regions

We have isolated a hamster CYP11B2 gene encoding the cytochrome P450 aldosterone synthase. In comparison with the CYP11B2 gene of other species, cis-elements named Ad1, Ad2, Ad3, and Ad4, were identified in the 5'-untranslated region of the hamster gene. Mouse adrenal tumor cells were transiently transfected with chimaeric reporter constructs, fused to the bacterial chloramphenicol acyltransferase (CAT) reporter gene, to study the regulation of expression of the hamster CYP11B2 gene. The highest basal expression was obtained with the -130 bp construct. Decreasing the length of the regulatory region of the CYP11B2 gene beyond that of -130 bp, to exclude Ad2 and Ad1 elements, resulted in successive decreases in CAT activity. Increasing the length of the regulatory region beyond that of -130 bp also resulted in a reduction of CAT activity, indicating the presence of inhibitory cis-elements in this area of the gene. Forskolin stimulated the CAT activity of all constructs, the highest of which occurred with the -130 bp construct, indicating that the gene is controlled by the PKA signalling pathway. TPA, however, had no stimulatory effects on any of these constructs. Staurosporine, an inhibitor of the PKC pathway, stimulated cells transfected with the different constructs in a similar manner as forskolin, indicating that PKC might act, at least in Y-1 cells, as a negative regulator on the hamster CYP11B2 promoter.

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.

Amplification of the transketolase gene in desensitization-resistant mutant Y1 mouse adrenocortical tumor cells

As shown previously, mutants of the Y1 mouse adrenocortical tumor cell line that resist agonist-induced desensitization of adenylyl cyclase have elevated levels of a 68-kDa protein (designated p68), suggesting a possible relationship between p68 and the regulation of adenylyl cyclase activity. In the present study, cDNA cloning and sequencing were used to identify p68 as mouse transketolase. Cells overexpressing p68 exhibited a 17.4-fold increase in transketolase enzymatic activity relative to parental Y1 cells and a 28-fold amplification of the transketolase gene as determined by Southern blot hybridization analysis. Using fluorescent in situ hybridization analysis, the transketolase gene was mapped to mouse chromosome 16B1 and to human chromosome 3p21.2. Transketolase gene amplification was associated with telomeric fusion of the chromosome 16 pair together with the appearance of multiple copies of the transketolase gene throughout a different chromosome. The relationship between overexpression of transketolase and desensitization resistance was evaluated in somatic cell hybrids formed between a desensitization-resistant adrenal cell line and a desensitization-sensitive rat glial cell line. In these hybrids, transketolase overexpression behaved dominantly, whereas desensitization resistance behaved recessively. These results dissociate the desensitization resistance phenotype from overexpression of transketolase and suggest that desensitization resistance may have resulted from disruption of an essential regulatory gene in conjunction with the amplification event.