Angiotensin II inhibits luteinizing hormone-stimulated cholesterol side chain cleavage expression and stimulates basic fibroblast growth factor expression in bovine luteal cells in primary culture

Angiotensin II has been identified immunohistochemically in the ovaries of both rats and humans. Here we present evidence that angiotensin II (an extremely vasoactive agent in a wide range of tissues) may be involved in the regulation of the major steroidogenic enzyme in the ovary, cholesterol side chain cleavage cytochrome P-450 (P-450scc), as well as of basic fibroblast growth factor (bFGF), which has been implicated as an angiogenic factor in the bovine corpus luteum. We have used primary cultures of bovine luteal cells to examine the effect of angiotensin II and its receptor antagonist, saralasin, on expression of mRNA encoding bFGF as well as on progesterone production and the expression of mRNA encoding cholesterol side chain cleavage cytochrome P-450 (P-450scc). Neither angiotensin II nor saralasin when added alone to the culture medium had any effect on basal progesterone production. Luteinizing hormone (LH) caused a 15-fold increase in progesterone accumulation after 24 h of exposure which was reduced to 5-fold in the presence of angiotensin II. This appeared to be receptor-mediated in that although saralasin alone had no effect on LH-stimulated progesterone accumulation, it significantly reversed the inhibition by angiotensin II. This pattern was mirrored by the levels of mRNA encoding P-450scc, i.c., LH induced the highest levels of expression of this message, these levels were reduced by angiotensin II, and saralasin partially overcame this reduction. Levels of mRNA encoding bFGF were elevated by both LH and angiotensin II. Treatment with saralasin, however, resulted in complete inhibition of bFGF mRNA expression in the presence of both LH and angiotensin II. These results suggest a role for angiotensin II to mediate the action of LH as a regulator of bFGF expression and hence, potentially, angiogenesis. Local production of angiotensin II might also contribute to the refractoriness of luteal progesterone secretion to LH at the time of luteal regression.

Use of molecular probes to study regulation of aromatase cytochrome P-450

Aromatase, an enzyme complex localized in the endoplasmic reticulum of estrogen-producing cells, is composed of NADPH-cytochrome P-450 reductase, and aromatase cytochrome P-450 (cytochrome P-450AROM). To define the molecular mechanisms involved in the multifactorial regulation of cytochrome P-450AROM in estrogen-producing cells, we have isolated a cDNA specific for human cytochrome P-450AROM and have used this cDNA to isolate the human cytochrome P-450AROM gene. The cDNA sequence encodes a polypeptide of 503 amino acids and contains--near the carboxy-terminus, a region of high homology with the putative heme-binding regions of other P-450 cytochromes. COS1 cells transfected with an expression plasmid containing the cytochrome P-450AROM cDNA had the capacity to aromatize testosterone, androstenedione and 16 alpha-hydroxyandrostenedione, suggesting that a single polypeptide catalyzes all steps of the aromatization reaction using either of the three major C19-substrates. The human cytochrome P-450AROM gene is greater than 52 kb in size and consists of 10 exons and 9 introns. Hormonally induced changes in aromatase activity of human ovarian granulosa and adipose stromal cells are associated with comparable changes in cytochrome P-450AROM gene expression and synthesis, whereas the reductase component is only modestly affected. Studies are in progress to define the molecular mechanisms involved in the regulation of cytochrome P-450AROM gene expression in estrogen-producing cells.

Structural analysis of the gene encoding human aromatase cytochrome P-450, the enzyme responsible for estrogen biosynthesis

The structural gene encoding aromatase cytochrome P-450 (P-450AROM) was isolated from human genomic DNA. The gene spans at least 52 kilobases and is composed of 10 exons, the first of which is untranslated. Analysis of the transcription initiation site of human P-450AROM mRNA reveals the differential use of 1 of 3 consecutive G residues at the cap site. DNA sequence analysis indicates that the gene has a putative TATA (ATAAAA) sequence at -23 base pairs (bp) and putative CAAT binding sequences beginning at -41, -67, and -83 bp. The 5'-flanking region contains sequences similar to consensus sequences of cis-acting elements defined as regulators of aromatase gene expression. These putative sequences include a cAMP regulatory element at -211 bp, an AP1 (protein kinase C) site at -54 bp, and glucocorticoid regulatory elements at -352 bp and within the first intron at +346 bp. There appears to be only one gene encoding P-450AROM in the human genome. Two major species of human P-450AROM mRNA (3.4 and 2.9 kilobases) are derived from the use of two polyadenylation signals.

Brenner tumor of the ovary: immunoanalysis of steroidogenic enzymes in 23 cases

Immunohistochemical analysis of cytochromes P-450 aromatase and P-450 17 alpha-hydroxylase, which catalyze the production of estrogens and androgens, respectively, was performed for 23 cases of ovarian Brenner tumor. Immunoreactivity for P-450 aromatase was observed in the epithelial cells of the tumor distinctly in two cases and faintly in four cases, while immunoreactivity for P-450 17 alpha-hydroxylase was seen in two cases. No immunoreactivity was observed in the stromal cells of the tumors, nor were luteinized cells observed in the cases examined. No correlation was observed between the immunoreactivity of cytochromes P-450 in the epithelial cells of the tumor and endometrial abnormalities. These findings, together with a review of the literature, suggest that the usual Brenner tumor is not associated with specific steroidogenesis. Rare massive Brenner tumors may, however, be capable of androgenic or estrogenic activity.

Complexity of steroid hydroxylase gent expression in the adrenal cortex A microcosm of regulated transcription

Regulation of the expression of steroid hydroxylase genes in the adrenal cortex involves mechanisms required for maintenance of optimal steroidogenesis, tissue specificity, and ontogeny of the steroidogenic pathway. Evaluation of the molecular basis of this complexity promises to unfold new aspects of regulated eukaryotic gene expression.

Deletion of a phenylalanine in the N-terminal region of human cytochrome P-450(17 alpha) results in partial combined 17 alpha-hydroxylase/17,20-lyase deficiency

Steroid 17 alpha-hydroxylase and 17,20-lyase activities reside within the same polypeptide chain (cytochrome P-450(17 alpha)), and consequently human 17 alpha-hydroxylase deficiencies are characterized by defects in either or both of these activities. Human mutants having these deficiencies represent an excellent source of material for investigation of P-450(17 alpha) structure-function relationships. The CYP17 gene from an individual having partial combined 17 alpha-hydroxylase/17,20-lyase deficiency has been characterized structurally and the homozygous mutation found to be the deletion of the phenylalanine codon (TTC) at either amino acid position 53 or 54 in exon 1. Reconstruction of this mutation into a human P-450(17 alpha) cDNA followed by expression in COS 1 cells led to production of the same amount of immunodetectable P-450(17 alpha) protein as found with expression of the normal human P-450(17 alpha) cDNA. However, 17 alpha-hydroxylase activity of this mutant protein measured in intact cells was less than 37% of that observed upon expression of the wild-type enzyme, whereas 17,20-lyase activity of the mutant was less than 8% of that observed with the normal enzyme. When estimated in intact cells, the Km for 17 alpha-hydroxylation of progesterone was increased by a factor of 2 in the mutant enzyme, whereas the Vmax was reduced by a factor of 3. In order to estimate the kinetic parameters for the 17,20-lyase reaction, microsomes were isolated from transfected COS 1 cells to enrich for this activity. Surprisingly, the specific activity of the mutant 17 alpha-hydroxylase in microsomes was 3-fold less than that observed in intact cells, indicating that the structure of mutant P-450(17 alpha) was dramatically altered upon disruption of COS 1 cells. Apparently the deletion of a single phenylalanine in the N-terminal region of P-450(17 alpha) alters its folding in such a way that both enzymatic activities are dramatically decreased, leading to the partial combined deficiency observed in this individual.

Regulation of cholesterol side-chain cleavage and 17 alpha-hydroxylase/lyase activities in proliferating human theca interna cells in long term monolayer culture

In this report we describe the development and characterization of a long term culture system to study regulation of the expression of 17 alpha-hydroxylase, cholesterol side-chain cleavage, and 3 beta-hydroxysteroid dehydrogenase in human theca interna cells. Conditions have been established for the dispersal, growth, freezing, and storage of functional human theca interna cells isolated from preovulatory follicles of women undergoing laparoscopy for gamete intrafallopian tube transfer and in vitro fertilization procedures. Theca interna cells grown under these conditions have a doubling rate of 28-32 h and are morphologically distinct from human granulosa cells grown under the same conditions. Theca interna cells were grown, passed for successive passages, and transferred into serum-free medium containing forskolin, hCG, LH, or cAMP analogs. There was a time- and dose-dependent increase in 17 alpha-hydroxylase activity and progesterone synthesis from endogenous precursors. Added pregnenolone was converted to 17 alpha-hydroxypregnenolone, which was further converted primarily to dehydroepiandrosterone and, to a much lesser extent, androstenedione. Progesterone was converted to 17 alpha-hydroxyprogesterone and 16 alpha-hydroxyprogesterone. In studies using 17 alpha-hydroxyprogesterone as substrate, no metabolism to androstenedione or any other product was detectable. Similarly, 4-pregnen-20 alpha-ol-one (20 alpha-dihydroprogesterone) was not metabolized to any detectable products. Northern analysis performed on total RNA obtained from forskolin-stimulated theca interna cultures verified that the increase in 17 alpha-hydroxylase activity was associated with a corresponding increase in levels of mRNA specific for 17 alpha-hydroxylase cytochrome P-450. Message levels for cholesterol side-chain cleavage P-450 were similarly increased in cells treated with forskolin. No detectable mRNA encoding aromatase cytochrome P-450 was discerned. This procedure for the preparation and study of proliferating human theca internal cells provides an opportunity to study regulation of the expression of steroidogenic enzymes and other cellular processes unique to human ovarian cells.

Identification of a common molecular basis for combined 17 alpha-hydroxylase/17,20-lyase deficiency in two Mennonite families

During the course of studies to characterize mutations of the CYP17 gene that cause the 17 alpha-hydroxylase-deficient form of congenital adrenal hyperplasia we have discovered two ostensibly unrelated Mennonite families in which affected individuals are homozygous for the same mutation. The defect is a four-base duplication in exon 8 of the CYP17 gene, which alters the reading frame encoding the C-terminal 26 amino acids of cytochrome P450(17 alpha).

Structural characterization of the bovine CYP17 (17 alpha-hydroxylase) gene

The complete exonic and partial intronic sequence of the bovine CYP17 (P45017 alpha) gene has been determined. The gene contains eight exons with exon/intron boundaries which are identical to those determined previously for the human CYP17 gene. The site of initiation of transcription of this gene is located within a 6-base sequence 52 bp from the initiation of translation. Considerable sequence homology (58.7%) is found when approximately 500 bp of the 5'-flanking sequences of the bovine and human CYP17 genes are compared. A computer-based search of this region of bovine CYP17 for consensus sequences associated with binding of transcription factors (i.e., GR, PR, CREB/ATF, AP1, AP2, AP3, AP4, AP5, OTF, CTF/NF1, SP1) shows only the consensus CREB/ATF sequence TGACGT which is also found to be at approximately the same position in the human CYP17 gene. In bovine adrenal cortex, transcription of the CYP17 gene is regulated by the peptide hormone adrenocorticotropin via cAMP. Whether the consensus CREB/ATF sequence is associated with the cAMP-mediated transcription of the CYP17 gene remains to be elucidated.

Effect of ACTH on the stability of mRNAs encoding bovine adrenocortical P-450scc, P-45011 beta, P-45017 alpha, P-450C21 and adrenodoxin

ACTH treatment of bovine adrenocortical cells in primary culture causes increased accumulation of mRNAs encoding cytochromes P-450SCC, P-450(11)beta, P-450(17) alpha, P-450C21 and adrenodoxin as well as increased transcriptional activity of their respective genes. In this study we have shown that ACTH does not greatly affect the half-life of mRNAs encoding P-450(11)beta, P-450(17)alpha, P-450C21 and adrenodoxin. However, in the case of P-450SCC mRNA, ACTH causes a five-fold increase in the half-life leading to a significant stabilization of P-450SCC mRNA. Thus it appears that the levels of mRNAs encoding P-450(11)beta, P-450(17)alpha, P-450C21 and adrenodoxin are regulated by ACTH primarily at the transcriptional level, while that for P-450SCC is regulated at both the transcriptional and post-transcriptional levels.

Immunohistochemical studies of steroidogenic enzymes (aromatase, 17 alpha-hydroxylase and cholesterol side-chain cleavage cytochromes P-450) in sex cord-stromal tumors of the ovary

Aromatase, 17 alpha-hydroxylase, and cholesterol side-chain cleavage P-450 cytochromes (P-450AROM, P-450(17 alpha,) and P-450SCC, respectively) were immunohistochemically localized in nine granulosa cell tumors, 15 thecomas, ten Sertoli-Leydig cell tumors, two steroid cell tumors, five fibromas, and five sclerosing stromal tumors. In the thecomas, P-450SCC and P-450(17 alpha) were positive in luteinized theca cells and in cells with vacuolated cytoplasm, while P-450AROM was not observed. In the steroid cell tumors, all the P-450 cytochromes were intensely stained. P-450SCC and P-450(17 alpha) were present in cells with vacuolated cytoplasm in two cases of sclerosing stromal tumor. P-450AROM was weakly demonstrated in one of the granulosa cell tumors. P-450(17 alpha,) P-450SCC, and P-450AROM were all faintly stained in the Sertoli-Leydig cell tumors. No P-450 cytochrome immunoreactivity was observed in any fibroma.

Ultrasound determination of the relationship of radioactive plaques to the base of choroidal melanomas

There is an assumption that radioactive plaques placed at surgery are, and will remain, in proper relationship to the base of the tumor. The plaque dose is calculated based on this assumption. In fact, factors such as loose sutures, improper diameter estimations, pressure from adjacent rectus muscles, and intervening tissue (oblique muscles) can compromise this relationship. Ultrasound provides a practical method of imaging the tumor and plaque simultaneously. The authors have used postoperative ultrasound to monitor the accuracy of iodine-125 plaque placement in nine cases. Detection of eccentrically placed and malpositioned plaques provides valuable insight which can be used to refine surgical technique. Detection of plaque tilting by oblique muscles can serve as a basis for recalculating dosage. The relationship of plaque margins to vital ocular structures such as the optic nerve can also be determined by ultrasound.

Glucocorticoid regulation of the rat cytochrome P450c (P450IA1) gene: receptor binding within intron I

The actions of polycyclic aromatic hydrocarbons and glucocorticoids to regulate the expression of cytochrome P450c were investigated using cultured fetal rat hepatocytes. Cytochrome P450c mRNA content, determined by Northern blot analysis, was induced in cells treated with 1,2-benzanthracene from levels undetectable in untreated cells. When dexamethasone was included in the culture medium together with 1,2-benzanthracene there was a further 2-fold increase in the induction of cytochrome P450c mRNA. The concentration of dexamethasone required for a half-maximal increase in cytochrome P450c mRNA content was approximately 10(-9) M. By nuclear run-on transcription assays, treatment with 1,2-benzanthracene induced cytochrome P450c transcription 5.3-fold over untreated cells. In the presence of dexamethasone and 1,2-benzanthracene, there was a further 2-fold increase in cytochrome P450c transcription. Southwestern blotting and exonuclease footprinting methods have identified binding interactions of a purified glucocorticoid receptor fraction with portions of the cytochrome P450c gene within the first intron. Using a chimeric plasmid containing the first intron, the first exon, and 824 bp of 5'-flanking region of the cytochrome P450c gene, chloramphenicol acetyltransferase activity was induced in transfected HepG2 hepatoma cells by the addition of 1,2-benzanthracene. The addition of dexamethasone induced a further 2.2-fold increase in activity. Deletion of the first intron within the chimeric plasmid abolished responsiveness to dexamethasone. It is concluded that glucocorticoids act together with polycyclic aromatic hydrocarbons to increase the levels of cytochrome P450c expressed in the fetal rat hepatocyte, and that this action is mediated by the glucocorticoid receptor. A glucocorticoid responsive element, which binds the glucocorticoid receptor, has been identified within the first intron of the cytochrome P450c gene. These results suggest that glucocorticoids play a significant role in the response of the hepatic cytochrome P450c gene to xenobiotics.

Developmental regulation of P-45017 alpha gene expression in fetal bovine adrenal

Among the multifactorial aspects of regulation of steroid hydroxylase gene expression, it is the developmental process which leads to imprinting of expression of particular steroid hydroxylases in specific cell types. We have begun to investigate the ontogeny of steroidogenesis in fetal bovine tissues. Expression of most steroid hydroxylases and related enzymes is detectable in adrenals of the smallest fetuses studied and continues throughout fetal life. Like the other steroid hydroxylases, P-450(17)alpha is detectable in the earliest fetal adrenals studied. However, following an increase in expression, P-450(17)alpha disappears from the fetal adrenal by 100 days gestational age and remains absent until about 230 days gestational age. The absence of P-450(17)alpha is correlated with the absence of cortisol in the fetal adrenal and the absence of ACTH in fetal plasma. Thus expression of P-450(17)alpha in bovine fetal adrenal appears to be strictly dependent on cAMP while expression of other steroid hydroxylases appears to involve both cAMP-dependent and cAMP-independent mechanisms. Furthermore, P-450(17)alpha is expressed in fetal testis at gestational times when it is absent in fetal adrenal. We have begun to examine binding of nuclear proteins from adrenals of various gestational ages to the 5'-flanking region of the bovine P-450(17)alpha gene. Preliminary evidence indicates the presence of a protein in nuclei of fetal adrenals not expressing P-450(17)alpha that is not present in fetal adrenals of other gestational ages.