Gene/Protein Disease Symptom Drug Enzyme Compound
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Query: UNIPROT:P06889 (Mol)
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In situ hybridization and immunohistochemical localization of cytochrome P450 cholesterol side-chain cleavage (P450scc), 3 beta-hydroxysteroid dehydrogenase (3 beta HSD), cytochrome P450 17 alpha-hydroxylase (P450c17) and cytochrome P450 aromatase (P450arom) was performed in 50 morphologically normal human premenopausal ovaries, and correlated these findings with their endometrial phase. In general, mRNA expression of these enzymes examined by in situ hybridization were in good agreement with immunolocalization examined by immunohistochemistry. Expression of P450scc, 3 beta HSD and P450c17 was observed in large-sized preantral follicles, consisting of more than five layers of granulosa cells, preovulatory follicles, corpora lutea, and some degenerating corpora lutea and atretic follicles in all endometrial phases. Several follicles and/or corpora lutea positive for these enzymes were observed in the same ovary. Expression of P450arom was generally observed in only one follicle (antral or preovulatory follicle) or corpus luteum per case in mid proliferative to premenstrual phase, and was not observed in menstrual to early proliferative phase. These findings indicated that (1) expression of steroidogenic enzymes was associated with the continual human ovarian process including follicular development and atresia, and (2) especially, P450arom expression may occur only in a selected antral follicle and may have an important role in dominant follicular development.
Mol Cell Endocrinol 1993 Nov
PMID:Temporal and spatial localization of steroidogenic enzymes in premenopausal human ovaries: in situ hybridization and immunohistochemical study. 814 96

Distribution and postnatal changes of aromatase mRNA in the Wistar strain female rats brain were investigated to elucidate the mechanism of the region-specific and stage-related regulations of brain aromatase activity. Total RNAs extracted from the hypothalamus-preoptic area (HPOA), amygdala, cerebral cortex, cerebellum and anterior hypophysis were subjected to a quantitative reverse transcription-polymerase chain reaction-Southern blotting (RT-PCR-SB) assay. The levels of aromatase mRNA were as follows: amygdala > cerebral cortex not equal to HPOA >> cerebellum not equal to anterior hypophysis. These results roughly paralleled the distribution of the aromatase activity and the aromatase protein reported previously, with the exception of that of the cerebral cortex. The postnatal developmental patterns of aromatase mRNA in the HPOA and cerebral cortex were further studied. The levels of aromatase mRNA in the HPOA tended to be high around birth (day 0) and to decrease at days 4-8 followed by no remarkable change to an adult. The developmental pattern in the HPOA was essentially similar to that of aromatase activity. On the other hand, in the cerebral cortex where very low or no aromatase activity was reported throughout developmental stages, aromatase mRNA was low but detectable level around day 0, thereafter gradually increased to an adult level. From these results, it is inferred that synthesis of the aromatase protein by the level of the mRNA seems to mainly regulate the aromatase activity in a region-specific and stage-related fashion in most parts of the rat brain, except for the cerebral cortex where the posttranscriptional regulation may play an important role.
J Steroid Biochem Mol Biol 1994 Apr
PMID:Distribution and postnatal changes of aromatase mRNA in the female rat brain. 818 Jan 15

Isoflavonoid phytoestrogens and lignans in plants are known to be constituents of animal and human food and recently they have been found in human urine and other biological materials. These compounds have received increasing attention because of their interesting biological properties and possible role in human cancer and other diseases. The present study demonstrates that the main mammalian lignan enterolactone (trans-2,3-bis[(3-hydroxyphenyl)methyl]-butyrolactone) and some other diphenols are moderate or weak inhibitors of human estrogen synthetase (aromatase) and that this lignan binds to or near the substrate region of the active site of the P-450 enzyme. The inhibition is competitive with respect to testosterone and androstenedione, and the lignan affinity is 1/75-1/300 that of these natural substrates. It is suggested that the high concentration of lignans in vegetarians, by inhibiting aromatase in peripheral and/or cancer cells and lowering estrogen levels, may play a protective role as antipromotional compounds during growth of estrogen-dependent cancers.
J Steroid Biochem Mol Biol 1993 Feb
PMID:Inhibition of human aromatase by mammalian lignans and isoflavonoid phytoestrogens. 838 17

Three approaches have been taken to elucidate further the biological importance of intratumoural aromatase activity. (i) MCF7 and T47D hormone-dependent breast cancer cell lines both showed detectable aromatase activity in vitro. The up-regulation of this by TGF alpha indicates the possible existence of an autocrine growth stimulatory loop involving aromatase. (ii) Both tamoxifen and cytotoxic chemotherapy caused the suppression of aromatase activity in breast carcinomas in vivo. Aromatase activity prior to treatment did not predict for clinical response to tamoxifen. (iii) Transfection of aromatase into MCF7 cells led to their growth being stimulated by low doses of androgens and this was inhibited by the aromatase inhibitor CGS 16949A.
J Steroid Biochem Mol Biol 1993 Mar
PMID:Control of aromatase in breast cancer cells and its importance for tumor growth. 838 39

Particularly in postmenopausal women, peripheral aromatase appears to be the major source of oestrogens which may encourage the growth of hormone-dependent tumours. Studies have therefore been undertaken to determine factors which influence biosynthesis of oestrogens within breast tissues. Aromatase activity was measured in (i) breast cancers by incubating tumour homogenates with [7 alpha 3H]testosterone and characterizing the production of radioactively-labelled oestradiol and (ii) breast fat by incubation of sub-cellular fractions of fibroblast cell lines with [1 beta 3H]androstenedione and monitoring the formation of 3H2O. Evidence has been presented that (i) certain treatment regimes for cancer profoundly influence aromatase activity in breast tumours, (ii) aromatase activity is elevated in breast fat associated with malignancy and (iii) breast-derived fluids and extracts can markedly affect aromatase activity in cultured fibroblasts of breast fat.
J Steroid Biochem Mol Biol 1993 Mar
PMID:Factors influencing aromatase activity in the breast. 838 38

The cytochrome P450 aromatase gene is transcriptionally regulated by FSH and steroids in granulosa cells of developing ovarian follicles. To characterize the molecular mechanisms by which this regulation occurs, the promoter of the rat aromatase gene has been analyzed by 1) mapping the transcriptional start site, 2) constructing deletion mutant reporter genes for transfection assays, and 3) determining DNA-protein interactions by gel shift assays. Transient transfection assays indicated that promoter sequences between -176 and -31 basepairs (bp) were required for cAMP inducibility of reporter constructs in primary cultures of granulosa cells and for expression in rat R2C Leydig cells, which constitutively express high amounts of aromatase mRNA. Nuclear extract proteins from granulosa cells and R2C Leydig cells specifically bound a labeled -176/13-bp fragment and were competed by cold competitor fragment as well as by a shorter region (-90/-66 bp) containing an AGGTCA hexameric motif. Competition was inhibited by mutation of the central GGs and was affected by adjacent 5' contextual sequences. A possible candidate for the binding activity observed in granulosa cells and R2C cell nuclear extracts binds an oligonucleotide containing the aromatase AGGTCA motif and is an orphan member of the steroid/thyroid hormone superfamily. These results are the first to characterize cis-acting DNA elements in the aromatase promoter, identify a region that confers cAMP inducibility in granulosa cells and constitutive expression in R2C cells, and localize a hexameric sequence within this region that binds at least one member of the orphan receptor class of transcription factors.
Mol Endocrinol 1993 Mar
PMID:cis-acting elements of the rat aromatase promoter required for cyclic adenosine 3',5'-monophosphate induction in ovarian granulosa cells and constitutive expression in R2C Leydig cells. 838 57

NCI-H295 is a recently described human adrenocortical carcinoma cell line that makes a variety of steroid hormones. We sought to determine if steroidogenesis in these cells employs the same enzymes as those used in normal adrenal steroidogenesis, and if the genes encoding those enzymes exhibit characteristic responsiveness to activators of the protein kinase-A and -C pathways of intracellular second messengers. Northern blots show that NCI-H295 cells contain abundant mRNAs for three key steroidogenic enzymes, cytochrome P450scc, cytochrome P450c17, and cytochrome P450c21. These mRNAs accumulated in a time- and dose-dependent fashion in response to 8-bromo-cAMP (8Br-cAMP), forskolin, cholera toxin, and 3-isobutyl-1-methylxanthine, all activators of the protein kinase-A pathway. Nuclear run-on assays and actinomycin-D transcriptional inhibition experiments show that cAMP regulates the expression of all three genes primarily at the transcriptional level. Inhibition of protein synthesis with cycloheximide did not prevent the cAMP-induced accumulation of P450scc or P450c17 mRNAs, but did inhibit accumulation of P450c21 mRNA, suggesting that cAMP is acting through a mechanism dependent on protein synthesis to promote accumulation of P450c21 mRNA. Stimulation of the protein kinase-C pathway with phorbol ester decreased P450scc and P450c17 mRNAs, but stimulated the accumulation of P450c21 mRNA. RNase protection experiments, Northern blot hybridizations, and reverse transcription-polymerase chain reaction show that NCI-H295 cells express both the 11 beta-hydroxylase (P450c11 beta) encoded by the P450c11B1 gene and the aldosterone synthetase (P450c11AS) encoded by the P450c11B2 gene. 8Br-cAMP increased the abundance of both of these mRNAs with similar kinetics, with maximal accumulation of both after about 24 h. NCI-H295 cells also contain the mRNAs for aromatase and insulin-like growth factor-II. 8Br-cAMP increased the abundance of aromatase mRNA and decreased the abundance of IGF-II mRNA. These studies show that NCI-H295 cells express most of the enzymes needed for human adrenal steroidogenesis, and that the genes encoding these enzymes respond to stimulation of second messenger pathways in a manner similar to that of human adrenals. NCI-H295 cells appear to be a good model for studying the molecular regulation of human adrenal steroidogenesis.
Mol Endocrinol 1993 Mar
PMID:Regulation of steroidogenesis in NCI-H295 cells: a cellular model of the human fetal adrenal. 838 59

The synthesis of estrogens from androgens is catalyzed by a microsomal cytochrome P450 termed aromatase (P450arom). The expression of this enzyme is highly regulated in both a developmental and cell-type specific fashion. We have chosen to examine the molecular basis of aromatase gene regulation by studying two models of aromatase expression: the Sebright bantam chicken and the R2C rat Leydig tumor cell line. In the first model, affected (Sebright) chickens express aromatase in many extragonadal tissues, while normal Leghorn chickens express aromatase only in the ovary and hypothalamus. Our studies have demonstrated that in normal chickens the site of transcription initiation is located approx. 147 nucleotides upstream of the initiator methionine. While Sebright animals also express aromatase mRNA initiated at an analogous initiation site in the ovary, a distinctive species of aromatase mRNA is also detected and is present in ovary and extragonadal tissues. This mRNA contains an identical coding sequence, but contains an alternatively spliced 5' noncoding exon that is derived from a distinctive promoter. The second model, the R2C Leydig tumor cell line, provides ample contrast. This cell line expresses high basal levels of aromatase (150-200 pmol/h/mg protein) that is suppressed with administration of 8 bromo cAMP or forskolin but the activity is not altered by glucocorticoids or epidermal growth factor treatment. Despite this distinctive pattern of regulation, at least three species of aromatase mRNA are detected in Northern blots, each of which is also detected in rat ovary. Primer extension and S1 nuclease assays indicate that both granulosa cells and R2C cells utilize a promoter that is located approx. 97 nucleotides upstream of the initiator methionine. These studies suggest that the "ovarian" promoter is evolutionarily conserved in both rats and chickens. These results further imply that the genetic mechanisms controlling the diversity of aromatase expression among tissues and among different species are likely to fall into two groups: those that employ distinctive promoters and alternative splicing and those that effect different patterns of regulation through a common ("ovarian") promoter.
J Steroid Biochem Mol Biol 1993 Mar
PMID:Diverse mechanisms of control of aromatase gene expression. 847 47

Aromatase is a microsomal cytochrome P450 that converts androgens to estrogens by three sequential oxidations. The isolation of the 19-hydroxy and 19-oxo androgens suggests that the first two oxidations occur at the C19 carbon. However, the mechanism of the third oxidation, which results in C10--C19 bond cleavage, has not been determined. Two proposed mechanisms which remain viable involve either initial 1 beta-hydrogen atom abstraction or addition of the ferric peroxy anion from aromatase to the C19 aldehyde. Semiempirical molecular orbital calculations (AM1) were used to study potential reaction mechanisms initiated by initial 1 beta-hydrogen atom abstraction. Initially, the energetics of carbon--carbon bond cleavage of the keto and enol forms of C1-radicals were studied and were found to be energetically similar. A mechanism was proposed in which the 19-oxo intermediate is subject to initial nucleophilic attack by the protein. The geometry of the A-ring in the androgens is between that for the 1-radicals and estrogen, suggesting that some transition state stabilization for the homolytic cleavage reaction can occur. More recently, studies on liver microsomal cytochrome P450 mediated deformylation of xenobiotic aldehydes supports mechanisms involving an alkyl peroxy intermediate formed by addition of the ferric peroxy anion from aromatase to the C19 aldehyde. Although this intermediate could proceed through several different concerted or non-concerted pathways, one non-concerted pathway involves the heterolytic cleavage of the dioxygen bond resulting in an active oxygenating species (iron-oxene) and a diol. The diol could then undergo hydrogen atom abstraction followed by homolytic carbon--carbon bond cleavage as in the mechanisms modeled previously. When this cleavage was modeled for seven aldehydes, a good correlation with reported experimental aldehyde turnover numbers was obtained. However, when dialkoxy derivatives of the aldehydes are subject to microsomal metabolism, the rates of carbon-carbon cleavage products do not approach the rates of deformylation of the aldehyde analog.
J Steroid Biochem Mol Biol 1993 Mar
PMID:Studies on the mechanism of aromatase and other cytochrome P450 mediated deformylation reactions. 847 50

Aromatase activity in fetal rat testes and ovaries was demonstrated by the conversion of tritiated testosterone or 19-hydroxyandrostenedione into estrone and estradiol, which were identified and quantified by double isotopic dilution and recrystallization to constant specific activity. Testes formed mostly estradiol, ovaries mostly estrone. Aromatase activity was stimulated by cAMP in both the testes and ovaries as early as 17 days of fetal life. Stimulation by FSH was noted at this same stage in the testis, but not before 3-4 days after birth in the ovary. LH was without effect on aromatase activity in both kinds of gonads. Basal estrogen secretion was non-existent or undetectable in both the testes and ovaries in fetal stages. In the presence of cAMP and as early as 17 days of fetal life, the testes released estradiol, as early as 14 days the ovaries released estrone. Estrogen secretion was stimulated by LH and FSH at fetal stages in the testis and at infantile stages in the ovary. Responsiveness to gonadotrophins closely followed the appearance of the receptors.
J Steroid Biochem Mol Biol 1993 Mar
PMID:Estrogen production by fetal rat gonads. 847 60


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