Bivalent IAP antagonists, but not monovalent IAP antagonists, inhibit TNF-mediated NF-κB signaling by degrading TRAF2-associated cIAP1 in cancer cells.

The inhibitor of apoptosis (IAP) proteins have pivotal roles in cell proliferation and differentiation, and antagonizing IAPs in certain cancer cell lines results in induction of cell death. A variety of IAP antagonist compounds targeting the baculovirus IAP protein repeat 3 (BIR3) domain of cIAP1have advanced into clinical trials. Here we sought to compare and contrast the biochemical activities of selected monovalent and bivalent IAP antagonists with the intent of identifying functional differences between these two classes of IAP antagonist drug candidates. The anti-cellular IAP1 (cIAP1) and pro-apoptotic activities of monovalent IAP antagonists were increased by using a single covalent bond to combine the monovalent moieties at the P4 position. In addition, regardless of drug concentration, treatment with monovalent compounds resulted in consistently higher levels of residual cIAP1 compared with that seen following bivalent compound treatment. We found that the remaining residual cIAP1 following monovalent compound treatment was predominantly tumor necrosis factor (TNF) receptor-associated factor 2 (TRAF2)-associated cIAP1. As a consequence, bivalent compounds were more effective at inhibiting TNF-induced activation of p65/NF-κB compared with monovalent compounds. Moreover, extension of the linker chain at the P4 position of bivalent compounds resulted in a decreased ability to degrade TRAF2-associated cIAP1 in a manner similar to monovalent compounds. This result implied that specific bivalent IAP antagonists but not monovalent compounds were capable of inducing formation of a cIAP1 E3 ubiquitin ligase complex with the capacity to effectively degrade TRAF2-associated cIAP1. These results further suggested that only certain bivalent IAP antagonists are preferred for the targeting of TNF-dependent signaling for the treatment of cancer or infectious diseases.

Adenoviral modification of mouse brain derived endothelial cells, bEnd3, to induce apoptosis by vascular endothelial growth factor.

A second generation genetically-engineered cell-based drug delivery system, referred to as apoptotic-induced drug delivery (AIDD), was developed using endothelial cells (ECs) that undergo apoptosis upon binding of vascular endothelial growth factor (VEGF) to a Flk-1:Fas fusion protein (FF). This new AIDD was redesigned using mouse brain derived ECs, bEnd3 cells, and an adenovirus vector in order to enhance and control the expression of FF. The FF was tagged with a HA epitope (FFHA) and designed to be coexpressed with green fluorescence protein (GFP) by the regulation of cytomegalovirus promoters in the adenovirus vector. bEnd3 cells showed favorable coexpression of FFHA and GFP consistent with the multiplicity of infection of the adenovirus. Immunofluorescence analysis demonstrated that FFHA was localized at the plasma membrane, whereas GFP was predominantly located in the cytoplasm of ECs. Cell death was induced by VEGF, but not by platelet derived growth factor or fibroblast growth factor in a dose-dependent manner (range 2-20 ng/ml), and revealed caspase-dependent apoptotic profiles. The FFHA expressing bEnd3 cells underwent apoptosis when cocultured with a glioma cell (SF188V+) line able to overexpress VEGF. The combined data indicated that the FFHA adenovirus system can induce apoptotic signaling in ECs in response to VEGF, and thus, is an instrumental modification to the development of AIDD.

Activation of Akt2 Inhibits anoikis and apoptosis induced by myogenic differentiation.

Akt2, a homolog of Akt1, encodes a serine/threonine protein kinase that is amplified in ovarian and pancreatic cancers. The antiapoptotic activities of the Akt1 proto-oncogene product have been well documented, but the role of Akt2 in cellular survival is poorly understood. Here, we demonstrate that Akt2 mRNA, protein and kinase activity are upregulated during serum deprivation-induced C2C12 cell myogenic differentiation, a process that is associated with the acquisition of an apoptosis-resistant phenotype. Transient transfection of plasmids encoding wild-type and constitutively-active Akt2 conferred resistance against apoptosis in differentiating C2C12 cells, while a kinase-negative Akt2 construct did not. Adenovirus-mediated transfer of the constitutively-active Akt2 cDNA also suppressed apoptosis during serum deprivation-induced myogenic differentiation and it protected cells from apoptosis induced by cell detachment. These data indicate that Akt2 functions as an anti-apoptotic gene during cellular differentiation, a property that may contribute to its oncogenicity.

AKT activation up-regulates insulin-like growth factor I receptor expression and promotes invasiveness of human pancreatic cancer cells.

Insulin-like growth factor I receptor (IGF-IR) is frequently overexpressed in several types of human malignancy and is associated with invasion and metastasis of tumor cells. Recently, IGF-IR expression was reported to be up-regulated in the human pancreatic cancer cell line PANC-1 when cells were stably transfected with active Src. The downstream targets of Src that lead to the up-regulation of IGF-IR expression were previously unknown. We demonstrate here that AKT regulates IGF-IR expression in PANC-1 and AsPC-1 cells. Cells transfected with active Src exhibited significantly more IGF-IR protein compared with vector-transfected cells. Overexpression of wild-type or constitutively active AKT (i.e., AKT1 or AKT2) also resulted in elevated IGF-IR expression. IGF-IR protein levels were higher in cells transfected with constitutively active AKT than in cells transfected with active Src. In vitro kinase assays showed that AKT kinases are activated by active Src and inhibited by dominant negative Src or the tumor suppressor PTEN. Furthermore, AKT-induced IGF-IR expression was down-regulated by dominant-negative Src or PTEN. In addition, cells transfected with activated AKT in the presence of IGF-I were shown to have enhanced invasiveness compared with control cells. These data provide evidence for a link between AKT signaling and the regulation of IGF-IR expression and demonstrate that active AKT promotes the invasiveness of pancreatic cancer cells through the up-regulation of IGF-IR expression.

Anti-apoptotic signaling by hepatocyte growth factor/Met via the phosphatidylinositol 3-kinase/Akt and mitogen-activated protein kinase pathways.

Hepatocyte growth factor (HGF) is a ligand of the receptor tyrosine kinase encoded by the c-Met protooncogene. HGF/Met signaling has multifunctional effects on various cell types. We sought to determine the role of HGF/Met in apoptosis and identify signal transducers involved in this process. In experiments with human SK-LMS-1 leiomyosarcoma cells, we show that the Akt kinase is activated by HGF in a time- and dose-dependent manner by phosphatidylinositol 3-kinase (PI3-kinase). Akt is also activated by active tumorigenic forms of Met, i.e., ligand-independent Tpr-Met, a truncated and constitutively dimerized form of Met, and a mutationally activated version of Met corresponding to that found in human hereditary papillary renal carcinoma. In NIH 3T3 cells transfected with wild-type Met, HGF inhibits apoptosis induced by serum starvation and UV irradiation. HGF-induced survival correlates with Akt activity and is inhibited by the specific PI3-kinase inhibitor LY294002, indicating that HGF inhibits cell death through the PI3-kinase/Akt signal transduction pathway. Furthermore, transiently transfected Tpr-Met activates Akt (both Akt1 and Akt2) and protects cells from apoptosis. Mitogen-activated protein kinase (MAPK) also is activated by HGF and rescues cells from apoptosis, although the cytoprotective effect is less marked than for PI3-kinase/Akt. Blocking MAPK with the specific MAPK kinase inhibitor PD098059 impairs the ability of HGF to promote cell survival. Similar results were obtained with NIH 3T3 cells expressing the fusion protein Trk-Met and stimulated with nerve growth factor, the Trk ligand. These results demonstrate that HGF/Met is capable of protecting cells from apoptosis by using both PI3-kinase/Akt and, to a lesser extent, MAPK pathways.

The phosphatidylinositol 3-kinase/AKT signal transduction pathway plays a critical role in the expression of p21WAF1/CIP1/SDI1 induced by cisplatin and paclitaxel.

The cyclin-dependent kinase inhibitor p21WAF1/CIP1/SD11 (p21) plays a crucial role in DNA repair, cell differentiation, and apoptosis through regulation of the cell cycle. A2780 human ovarian carcinoma cells, which are sensitive to cisplatin and paclitaxel, express wild-type p53 and exhibit a p53-mediated increase in p21 in response to the chemotherapeutic agents. Here, we demonstrate that phosphatidylinositol 3-kinase (PI3K) and its downstream targets serine/threonine kinases AKT1 and AKT2 (AKT), are required for the full induction of p21 in A2780 cells treated with cisplatin or paclitaxel. Inactivation of the PI3K/AKT signal transduction pathway either by its specific inhibitor LY294002 or by expression of dominant negative AKT inhibited p21 expression but had no inhibitory effect on the expression of the proapoptotic protein BAX by cisplatin and paclitaxel treatment. In addition, overexpression of wild-type or constitutively active AKT in A2780 cells sustained the regulation of p21 induction or increased the level of p21 expression, respectively. Experiments with additional ovarian carcinoma cell lines revealed that PI3K is involved in the expression of p21 induced by cisplatin or paclitaxel in OVCAR-10 cells, which have wild-type p53, but not in OVCAR-5 cells, which lack functional p53. These data indicate that the PI3K/AKT signal transduction pathway mediates p21 expression and suggest that this pathway contributes to cell cycle regulation promoted by p53 in response to drug-induced stress. However, inactivation of PI3K/AKT signaling did not result in significant alteration of the drug sensitivity of A2780 cells, suggesting that the cell death induced by cisplatin or paclitaxel proceeds independently of cell protective effects of PI3K and AKT.

Identification of a chromosome 3p14.3-21.1 gene, APPL, encoding an adaptor molecule that interacts with the oncoprotein-serine/threonine kinase AKT2.

AKT2 is a serine/threonine kinase implicated in human ovarian and pancreatic cancers. AKT2 is activated by a variety of growth factors and insulin via phosphatidylinositol 3-kinase (PI3K). However, its normal cellular role is not well understood. To gain insight into the function of AKT2, we performed yeast two-hybrid system to screen for interacting proteins. Using this technique, we identified a novel interactor, designated APPL, which contains a pleckstrin homology (PH) domain, a phosphotyrosine binding (PTB) domain and a leucine zipper, classes of motifs defined in signaling molecules as functional interaction domains with specific targets. The PH domain of APPL shows similarity to those found in GTPase-activating proteins such as oligophrenin-1 and Graf, whereas its PTB domain exhibits homology with CED-6, an adaptor protein that promotes engulfment of apoptotic cells, and IB1, a transactivator of the GLUT2 gene. APPL is highly expressed in skeletal muscle, heart, ovary and pancreas, tissues in which AKT2 mRNA is abundant. APPL interacts with the inactive form of AKT2; moreover, APPL binds to the PI3K catalytic subunit, p110alpha. These data suggest that APPL is an adaptor that may tether inactive AKT2 to p110alpha in the cytoplasm and thereby may expedite recruitment of AKT2 and p110alpha to the cell membrane upon mitogenic stimulation. Furthermore, the APPL gene was mapped to human chromosome 3p14.3-p21.1, where deletions and other rearrangements have often been reported in a variety of tumor types. The identification of APPL may facilitate further analysis of the physiological and oncogenic activities of AKT2.

Cell cycle withdrawal promotes myogenic induction of Akt, a positive modulator of myocyte survival.

During myogenesis, proliferating myoblasts withdraw from the cell cycle, acquire an apoptosis-resistant phenotype, and differentiate into myotubes. Previous studies indicate that myogenic induction of the cyclin-dependent kinase inhibitor p21 results in an inhibition of apoptotic cell death in addition to its role as a negative cell cycle regulator. Here we demonstrate that the protein encoded by the Akt proto-oncogene is induced in C2C12 cells during myogenic differentiation with a corresponding increase in kinase activity. In differentiating cultures, expression of dominant-negative forms of Akt increase the frequency of cell death whereas expression of wild-type Akt protects against death, indicating that Akt is a positive modulator of myocyte survival. Antisense oligonucleotides against p21 block cell cycle withdrawal, inhibit Akt induction, and enhance cell death in differentiating myocyte cultures. Adenovirus-mediated transfer of wild-type or constitutively active Akt constructs confer partial resistance to cell death under conditions where cell cycle exit is blocked by the antisense oligonucleotides. Collectively, these data indicate that cell cycle withdrawal facilitates the induction of Akt during myogenesis, promoting myocyte survival.

Translocation and activation of AKT2 in response to stimulation by insulin.

The AKT2 oncogene encodes a protein-serine/threonine kinase that was recently shown to be activated by a variety of growth factors. In addition, we previously showed that AKT2 is abundant in brown fat and skeletal muscle, tissues that are highly insulin responsive and that play a role in glucose metabolism. In this study, we demonstrate that AKT2 is activated in response to stimulation by insulin in a dose- and time-dependent manner in human ovarian carcinoma cells and that activation of AKT2 is abolished in cells pretreated with wortmannin, an inhibitor of phosphatidylinositol 3-kinase (PI 3-kinase). Activation of AKT2 is manifested by changes in its phosphorylation state. Immunofluorescence experiments demonstrate that AKT2 is translocated to the plasma membrane after insulin stimulation, and this translocation is abolished by wortmannin. Both wild-type AKT2 activated by insulin and constitutively active AKT2, which has been targeted to the membrane by the addition of a myristoylation signal, were found to inactivate glycogen synthase kinase-3 (GSK-3) in vitro. GSK-3 was not inactivated by a catalytically inactive AKT2 mutant. Collectively, these data indicate that activation of AKT2 by insulin is mediated by PI 3-kinase and that GSK-3 is a downstream target of AKT2, suggesting a potentially important role of AKT2 in glycogen synthesis and other GSK-3 signaling pathways.

Akt2 mRNA is highly expressed in embryonic brown fat and the AKT2 kinase is activated by insulin.

Akt2 encodes a protein-serine/threonine kinase containing a pleckstrin homology domain characteristic of many signaling molecules. Although there has been extensive interest in the mechanism by which the closely-related Akt kinase participates in phosphatidylinositol 3-kinase-mediated signaling, comparatively little is known regarding the expression and function of Akt2. This manuscript is the first to describe Akt2 mRNA expression in the developing mouse and the activation of AKT2 by insulin. These studies demonstrate that Akt2 is especially abundant in brown fat and, to a lesser extent, skeletal muscle and liver, tissues which are highly insulin-responsive and play a role in glucose metabolism. Endogenous Akt2 expression also is upregulated in fully-differentiated C2C12 myotubes and 3T3-L1 adipocytes, suggesting that these murine cell lines represent useful in vitro models for studies of Akt2 function. We show that HA-tagged AKT2 is activated in response to insulin stimulation in vitro and that activation of AKT2 is not induced in cells pretreated with wortmannin, an inhibitor of phosphatidylinositol 3-kinase. These data suggest that Akt2 expression is fundamental to the differentiated state of fat and muscle cells and that activation of AKT2 kinase by insulin is mediated through the phosphatidylinositol 3-kinase signaling pathway.

Inborn errors of aldosterone biosynthesis in humans.

Corticosterone methyl oxidase (CMO) type I and type II deficiencies are inborn errors at the penultimate and ultimate steps in the biosynthesis of aldosterone in humans. Recently, steroid 18-hydroxylase (P450C18), or aldosterone synthase (P450aldo), was shown to be a multifunctional enzyme catalyzing these two steps of aldosterone biosynthesis, i.e., the conversion of corticosterone to 18-hydroxycorticosterone and the subsequent conversion of 18-hydroxycorticosterone to aldosterone. This observation suggests that CMO I and CMO II deficiencies are derived from two different mutations in the P450C18 gene (CYP11B2). To elucidate whether or not this is the case, we performed molecular genetic studies on CYP11B2 of both types of patients. Nucleotide sequence analysis has indicated that the gene of CMO I deficient patients is completely inactivated by a frameshift to form a stop codon due to a 5-bp nucleotide deletion in exon 1. Sequence analysis of CYP11B2 of CMO II deficient patients has revealed two point mutations, CGG-->TGG (Arg181-->Trp) in exon 3 and GTG-->GCG (Val386-->Ala) in exon 7. CYP11B1, the gene for steroid 11 beta-hydroxylase (P45011 beta) which was previously postulated to be the target for CMO II deficiency, is not impaired in these two types of patients. Expression studies using the corresponding mutant cDNAs have shown that CMO I deficient patients are null mutants with a complete lack of P450C18 whereas CMO II deficient patients are leaky mutants with an altered P450C18 activity.(ABSTRACT TRUNCATED AT 250 WORDS)

A nonsense mutation (TGG [Trp116]-->TAG [Stop]) in CYP11B1 causes steroid 11 beta-hydroxylase deficiency.

Steroid 11 beta-hydroxylase deficiency (11 beta OHD), an autosomal recessive hereditary disease, accounts for 5-8% of cases of congenital adrenal hyperplasia. In this study, we carried out a molecular genetic analysis of CYP11B1 encoding steroid 11 beta-hydroxylase (P450c11) from a Japanese patient affected with this disease. Nucleotide sequence analysis of polymerase chain reaction-amplified products of the patient's genome revealed the occurrence of a stop codon in exon 2 due to a point mutation, TGG-->TAG (Trp116-->Stop). To further analyze the role of CYP11B2 encoding steroid 18-hydroxylase (P450c18) in the 11 beta OHD patient, CYP11B2 of the patient was also amplified and sequenced. In contrast to CYP11B1, there was no mutation in CYP11B2. Restriction fragment length polymorphism analysis indicated that the 11 beta OHD patient is homozygous and his unaffected parents are heterozygous for the mutation. When a cDNA corresponding to CYP11B1 of the 11 beta OHD patient was transfected into COS-7 cells, steroid 11 beta-hydroxylase activity was not detectable in mitochondria of the cells. These results demonstrate that intact P450c11 was not produced at all due to the nonsense mutation in CYP11B1 of the patient without any mutation in CYP11B2.

Congenitally defective aldosterone biosynthesis in humans: inactivation of the P-450C18 gene (CYP11B2) due to nucleotide deletion in CMO I deficient patients.

CYP11B2, the gene coding for steroid 18-hydroxylase (P-450C18), has been recently shown to be the same gene as that for corticosterone methyl oxidase type I and type II (CMO I & II) which were previously postulated to catalyze the final two steps in the biosynthesis of aldosterone in humans. Molecular genetic analysis of CYP11B2 of three patients affected with CMO I deficiency has revealed that deletion of 5 nucleotides occurs exclusively in exon 1, resulting in a frameshift to form a stop codon in the same exon. Thus, P-450C18 is not produced at all due to the mutation, causing a complete lack of aldosterone biosynthesis in the patients. Restriction fragment length polymorphism analysis has demonstrated that the patients are homozygous and the unaffected parent is heterozygous as for the mutation, indicating that CMO I deficiency is inherited in an autosomal recessive manner. These results provide the molecular genetic basis for the characteristic biochemical phenotype of CMO I deficient patients.

The chimeric gene linked to glucocorticoid-suppressible hyperaldosteronism encodes a fused P-450 protein possessing aldosterone synthase activity.

Glucocorticoid-suppressible hyperaldosteronism (GSH) is one variety of primary aldosteronism with hypertension and is inherited in an autosomal dominant mode. A recent report has indicated that GSH is caused by a gene duplication arising from unequal crossing over between the two genes, CYP11B1 and CYP11B2, encoding P-450(11 beta) and P-450C18, respectively (Lifton et al. Nature (1992) 355, 262-265). The nucleotide sequence analysis in the present study has demonstrated that unequal crossing over in the chimeric gene formed by the gene duplication occurs within the region from the 3'-portion of exon 4 through the 5'-portion of intron 4 in Australian GSH patients. Namely, the chimeric gene encodes a fused P-450 protein consisting of the amino-terminal side of P-450(11 beta) (encoded by exons 1-4 of CYP11B1) and the carboxyl-terminal side of P-450C18 (encoded by exons 5-9 of CYP11B2). When a cDNA corresponding to the chimeric gene is transfected into COS-7 cells, the fused P-450 protein expressed in the mitochondria exhibits steroid 18-hydroxylase or aldosterone synthase activity. These results provide the molecular genetic basis for the characteristic biochemical phenotype of GSH patients.

Role of steroid 11 beta-hydroxylase and steroid 18-hydroxylase in the biosynthesis of glucocorticoids and mineralocorticoids in humans.

A gene encoding steroid 18-hydroxylase (P-450C18) was isolated from a human genomic DNA library. It was identified as CYP11B2, which was previously postulated to be a pseudogene or a less active gene closely related to CYP11B1, the gene encoding steroid 11 beta-hydroxylase (P-45011 beta) [Mornet, E., Dupont, J., Vitek, A. & White, P. C. (1989) J. Biol. Chem. 264, 20961-20967]. The nucleotide sequence of the promoter region of the P-450C18 gene is strikingly different from that of the P-45011 beta gene, although the sequences of their exons are 93% identical. The transient expression in Y-1 adrenal tumor cells of CAT constructs with a series of deletion mutants of promoter regions of both genes indicated that the two genes are regulated differently. P-450C18 as expressed in COS-7 cells exhibits steroid 18-hydroxylase activity to catalyze the synthesis of aldosterone and 18-oxocortisol and exhibits steroid 11 beta-hydroxylase activity as well. In contrast, P-45011 beta as expressed in the cultured cells exhibits steroid 11 beta-hydroxylase activity exclusively but fails to catalyze the synthesis of aldosterone and 18-oxocortisol. These results indicate that P-45011 beta and P-450C18 are products of two different genes and that the former participates in the synthesis of glucocorticoids whereas the latter participates in the synthesis of mineralocorticoids in humans.

Congenitally defective aldosterone biosynthesis in humans: the involvement of point mutations of the P-450C18 gene (CYP11B2) in CMO II deficient patients.

The gene for steroid 18-hydroxylase (P-450C18) has been recently assigned to encode corticosterone methyl oxidases Type I and Type II which were previously postulated to catalyze the final two steps in the biosynthesis of aldosterone in humans. Molecular genetic analysis of the P-450C18 gene is three patients from three different families affected with CMO II deficiency has indicated that a point mutation of CGG----TGG (181Arg----Trp) in exon 3 and one of GTG----GCG (386Val----Ala) in exon 7 occur exclusively in the gene of the patients. Analysis of PCR products by restriction enzymes (HapII and HphI) has indicated that the patients are homozygous and the unaffected parent is heterozygous for both mutations, in accordance with the established concept that CMO II deficiency is inherited in an autosomal recessive manner. These data clearly provide the molecular genetic basis for the characteristic biochemical phenotype of CMO II clinical variants.

Molecular genetic studies on the biosynthesis of aldosterone in humans.

Corticosterone methyl oxidase Type I (CMO I) and II (CMO II) have been postulated to be the enzymes involved in the final two steps of aldosterone biosynthesis in humans. We have isolated human cDNAs for P450c11 and P450c18 as well as the corresponding genes, CYP11B1 and CYP11B2. Both protein products of these two genes as expressed in COS-7 cells exhibit steroid 11ß-hydroxylase activity, but only P450c18, a product of CYP11B2, carried steroid 18-hydroxylase activity to form aldosterone. These results indicate that CYP11B2 encodes CMO, the actual catalytic function of which is retained by P450c18, a multifunctional enzyme. This conclusion is further supported by the finding that the P450c18 gene, CYP11B2, is mutated at several different loci in patients deficient in CMO I or II.

Human poly(ADP-ribose) polymerase gene. Cloning of the promoter region.

The promoter region of the poly(ADP-ribose) polymerase gene has been isolated using a Sau3AI genomic library derived from human leukocyte. It lacks typical transcriptional regulatory elements such as TATA and CAAT boxes, but it contains two potential Sp1 binding sites and three putative AP-2 binding elements. The region up to nucleotide position-99 in relation to the predominant transcriptional initiation site exhibits promoter activity as judged by chloramphenicol acetyltransferase assay and the activity is enhanced both by cAMP and by phorbol ester. Northern blot and Western blot analyses have revealed that expression of the polymerase gene is also stimulated by both of these compounds in cultured HeLa cells. Southern blot hybridization of genomic DNA separately digested with various endonucleases gives a discrete single band in each case when the 5'-untranslated region of the polymerase cDNA is used as a probe. These results indicate that poly(ADP-ribose) polymerase is encoded by a unique gene whose expression is regulable by cAMP and by phorbol ester.

Cloning and expression of a cDNA for human cytochrome P-450aldo as related to primary aldosteronism.

A cDNA clone encoding human aldosterone synthase cytochrome P-450 (P-450aldo) has been isolated from a cDNA library derived from human adrenal tumor of a patient suffering from primary aldosteronism. The insert of the clone contains an open reading frame encoding a protein of 503 amino acid residues together with a 3 bp 5'-untranslated region and a 1424 bp 3'-untranslated region to which a poly(A) tract is attached. The nucleotide sequence of P-450aldo cDNA is 93% identical to that of P-450(11) beta cDNA. Catalytic functions of these two P-450s expressed in COS-7 cells are very similar in that both enzymes catalyze the formation of corticosterone and 18-hydroxy-11-deoxycorticosterone using 11-deoxycorticosterone as a substrate. However, they are distinctly different from each other in that P-450aldo preferentially catalyzes the conversion of 11-deoxycorticosterone to aldosterone via corticosterone and 18-hydroxycorticosterone while P-450(11)beta substantially fails to catalyze the reaction to form aldosterone. These results suggest that P-450aldo is a variant of P-450(11)beta, but this enzyme is a different gene product possibly playing a major role in the synthesis of aldosterone at least in a patient suffering from primary aldosteronism.

Structural and functional characterization of human aromatase P-450 gene.

The gene encoding aromatase P-450 (CYP XIX) has been isolated from two types of human genomic DNA libraries. It spans at least 70 kb and consists of 10 exons. The translational initiation site and the termination site are located in exon 2 and exon 10, respectively. The promoter region of the gene contains a TATA box, a CAAT box and two putative AP-1 binding sites beginning at -28, -83, -55 and -68 bp, respectively, from the transcriptional initiation site. In addition, a palindromic nucleotide sequence is observed between -209 and -196 and two types of repetitious hexanucleotide (consensus: AATGAA and CCATAAGG) are also present within the regions between -485 and -433 and between -358 and -331. Transient expression studies of chloramphenicol acetyltransferase constructs bearing various lengths of 5'-flanking region of the gene show that the region between -500 and -243 contains negative cis-acting element(s), whereas the region between -242 and -183 is required for efficient transcriptional activity. Northern blot analysis demonstrates that the expression of aromatose P-450 gene is remarkably stimulated by treatment of cells with 12-O-tetradecanoyl-phorbol 13-acetate. By chloramphenicol acetyltransferase assay the region up to nucleotide position -242 relative to the transcriptional initiation site is shown to participate in the transcriptional responsiveness to this phorbol ester.