Gene/Protein Disease Symptom Drug Enzyme Compound
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Query: UNIPROT:P06889 (Mol)
 630,302 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Aromatase P450 (P450arom) is the enzyme responsible for estrogen biosynthesis. Studies of the relationship of the function of this enzyme to its structure have been hampered by lack of a suitable preparation. In the present report we describe the expression of a recombinant derivative of P450arom in insect cells by means of the baculovirus vector system. This protein, which lacks the first 41 amino acids from the N-terminus, and hence the membrane-spanning region, has spectral properties and activity similar to that of the wildtype protein. Moreover, the presence of a hexameric histidine tag at the C-terminus permits its facile purification by means of nickel-agarose affinity chromatography. This system permits the synthesis of quantities of a biologically active derivative of P450arom suitable for studies designed to explore the relationship of function to structure.
Mol Cell Endocrinol 1995 Apr 01
PMID:Expression of a recombinant derivative of human aromatase P450 in insect cells utilizing the baculovirus vector system. 766 73

The cytochrome P450 aromatase (P450arom) enzyme is required for bioconversion of androgen to oestrogen. In this study ovarian P450arom mRNA and enzyme activity have been measured during development in normal mice and hypogondal (hpg) mice which lack circulating gonadotrophins. A semi-quantitative reverse transcription-PCR (RT-PCR) technique was used to measure cytochrome P450arom mRNA levels and aromatase enzyme activity was measured directly. Using RT-PCR, P450arom mRNA was detectable in the adult mouse ovary and also in the uterus, kidney, brain and skeletal muscle but not in cardiac smooth muscle. In the normal mouse, P450arom mRNA was detectable in the ovary on the day of birth (day 1) and levels increased significantly up to day 15 with the most marked changes seen between days 1 and 5. Aromatase activity was also detectable at all ages in the ovary and increased significantly between days 1 and 7. In ovaries from hpg mice, normal levels of P450arom mRNA were present on day 1 but there was no significant change in P450arom mRNA at later ages up to day 15. These results show that in the newborn mouse ovary, which contains only primordial follicles, there is a basal expression of P450arom mRNA which is not gonadotrophin-dependent. After 1 day, however, gonadotrophins are required for normal expression of ovarian P450arom and this coincides with development of primary and secondary follicles.
J Mol Endocrinol 1995 Jun
PMID:Development of cytochrome P450 aromatase mRNA levels and enzyme activity in ovaries of normal and hypogonadal (hpg) mice. 766 21

A variety of data suggesting a relationship between estrogens and the immune system prompted a study of aromatase activity in blood lymphocytes. A tritiated water aromatase assay detected activity of 1.9 to 25.1 pmol/g protein/h in 14 samples of human lymphocytes. To confirm these results, additional tritiated water and product isolation assays were performed on a large pool of lymphocytes obtained from 4 U of blood. An assay using [1 beta-3H]androstenedione generated high apparent aromatase activity, 943 pmol/g protein/h, but this activity could not be blocked by the aromatase inhibitor, CGS 16949A. More direct methods of evaluation yielded the following results: (1) PCR demonstrated no aromatase mRNA production in lymphocytes; (2) direct product isolation using [1,2,6,7-3H]androstenedione yielded insignificant production of estrone and estradiol; (3) immunostaining of fixed lymphocyte smears with a polyclonal antibody to aromatase yielded equivocal results. These data suggest the presence of pseudoaromatase in blood lymphocytes. Since circulating lymphocyte pseudoaromatase levels can be correlated with various factors in patients, such as age, menopausal status, and glucose ingestion, further studies of this activity are warranted.
J Steroid Biochem Mol Biol 1993 Mar
PMID:Pseudoaromatase in circulating lymphocytes. 768 40

Aromatase activity was measured in explant cultures from the newborn mouse and rat brain and in homogenates of regions of the rat brain sampled between birth and 51 days of age. Conversion of 19-[3H]hydroxy-androstenedione to estradiol and estrone was detected in explant cultures from the mouse preoptic/septal region, anterior cingulate cortex, and midbrain, as well as from the rat preoptic area, septum, hippocampus, anterior cingulate cortex, and midbrain central grey. No detectable estrogen biosynthesis was observed in explants from the cerebellum and spinal cord of either species. Measurements of aromatase in tissue homogenates using 1 beta[3H]androstenedione as substrate revealed detectable enzyme activity in the hypothalamus + preoptic area, amygdala, hippocampus, anterior cingulate cortex, and midbrain, from birth onward. Aromatase activity per milligram of tissue protein was highest in the hypothalamus-preoptic area and amygdala, followed by the hippocampus, midbrain, and cingulate cortex. In all brain regions, aromatase activity was markedly higher at Postnatal Days 1 and 7 than later in life. In both the cingulate cortex and the hippocampus, aromatase was barely detectable above the assay blank in adult (51 day) animals. These results demonstrate that regions of the developing rodent neo- and archicortex have the capacity to convert androgen to estrogen, consistent with a role for local estrogen biosynthesis in the sexual differentiation of higher brain functions.
Mol Cell Neurosci 1994 Dec
PMID:Aromatase in the cerebral cortex, hippocampus, and mid-brain: ontogeny and developmental implications. 770 44

The conversion of testosterone to estradiol is catalyzed by cytochrome P450 aromatase. In situ aromatization is required for the full expression of the effects of testosterone in the brain. This study examined the subcellular distribution and reaction kinetics of aromatase in the adult rat brain. Preoptic area, hypothalamus and amygdala were homogenized in isotonic sucrose buffered with potassium phosphate. Tissue homogenates were fractionated by ultracentrifugation. Aromatase activity was measured using a previously validated 3H2O assay. Marker enzymes were measured to identify organelles in the different subcellular fractions. Aromatase activity in all 3 tissues was enriched 10-fold in microsomes, but not in other subcellular fractions. The addition of either a NADPH-generating system or 1 mM NADPH to the reaction mixture stimulated aromatase activity in all subcellular fractions, whereas NADH was only minimally effective. In general, substrate affinity constants were equivalent in all brain areas and subcellular fractions (approximately 10 nM) suggesting that one predominant catalytic form of the enzyme is present in the rat brain. One week after castration, aromatase activity was significantly reduced in all subcellular fractions of preoptic area and in the whole homogenate and microsomal fraction of the hypothalamus. Castration did not significantly alter aromatase activity in any subcellular compartment of amygdala. To more critically evaluate its subcellular localization, aromatase activity was measured in purified synaptosomes. Aromatase activity was not enriched in these preparations suggesting that it is not substantially associated with nerve terminals in rat brain.
J Steroid Biochem Mol Biol 1995 May
PMID:Subcellular localization and kinetic properties of aromatase activity in rat brain. 774 12

Aromatase activity may be detected in most, but not all, breast cancers, and in certain tumours there appears to be decreased sensitivity to the aromatase inhibitor 4-hydroxyandrostenedione (4-OHA). The aims of the present study were to measure aromatase activity, and its sensitivity to 4-OHA, in breast tumours, and to examine the CYP19 gene encoding the aromatase cytochrome P450 (P450arom) for the presence of mutations. In vitro aromatase activity and sensitivity to 4-OHA were measured by determining the conversion of tritiated testosterone to tritiated oestradiol in breast tumour tissue in the absence and presence of 4-OHA (10 nM). Genomic DNA was extracted from five tumours: one showing no detectable aromatase activity and four displaying evidence of aromatase activity (two sensitive and two insensitive to 4-OHA). Subsequent PCR-single-strand conformation polymorphism analysis revealed a variation in the mobility of single-stranded DNA for exons III, VII and X, corresponding, as shown by direct sequencing of PCR products, to common polymorphism of the aromatase gene. This study does not provide evidence for mutation in the coding exons of the P450arom gene which would account for either the absence of aromatase activity or its changed sensitivity to 4-OHA in breast cancers.
J Mol Endocrinol 1994 Dec
PMID:Analysis of the aromatase cytochrome P450 gene in human breast cancers. 789 51

The expression of aromatase mRNA in cultured mouse brain cells was measured by a quantitative reverse transcription-PCR method using an internal standard. Aromatase mRNA was expressed in the cultured neurons prepared from diencephalon at 0.037 +/- 0.005 attomol/microgram total RNA. However, the mRNA was detected in neither the neurons from cerebral cortex nor astrocytes. These results demonstrate that expression of aromatase mRNA is regulated in cell type- and region-specific manners in cultured brain cells. The aromatase mRNA levels in neurons obtained from diencephalon were not affected by administration of testosterone, estradiol, dexamethasone, forskolin, or 12-O-tetradecanoyl 13-acetate. The results are in apparent disagreement with previous reports concerning regulation by androgens of brain aromatase activity in vivo and may suggest that aromatase expression in brain neurons is not directly induced by androgens. Androgen induction of brain aromatase may be mediated by several steps including cell-cell (neuron-neuron and/or neuron-glia) interaction.
Brain Res Mol Brain Res 1994 Jul
PMID:Cell type- and region-specific expression of aromatase mRNA in cultured brain cells. 796 52

The brain regions controlling song are much larger in male than in female zebra finches. This sex difference is thought to arise developmentally when the male's brain is exposed to higher levels of estrogen. The synthesis of estrogen from androgen is catalyzed by aromatase, a key enzyme implicated in song development in the zebra finch. To study the role of estrogen synthesis in the organization of brain regions responsible for song, a cDNA encoding aromatase was isolated from a zebra finch ovarian cDNA library. The 3188 bp cDNA contains a 1527 bp open reading frame with 5' and 3' untranslated regions of 116 bp and 1545 bp, respectively. The deduced polypeptide is 509 amino acids in length, and is highly homologous to aromatases reported for chicken (92%), human (72%), mouse (70%), rat (69%) and trout (53%). Northern blot analysis revealed 5.4 kb, 4.8 kb and 3.2 kb aromatase mRNAs in brain and ovary. In situ hybridization histochemistry revealed the expression of aromatase mRNA in ovarian thecal cells of some, but not all, follicles, suggesting that aromatase gene expression is regulated during follicular maturation. In the adult brain, the distribution of aromatase mRNA was surprisingly widespread, and included the preoptic area, hypothalamus, hippocampus and neostriatum. By contrast, little aromatase mRNA expression was noted in the song nuclei (HVC, RA, area X). This study, the first description of aromatase mRNA expression by in situ hybridization in the brain of any species, identifies a surprisingly large number of cells that express aromatase mRNA in the zebra finch telencephalon. This pattern may be a unique feature of all songbirds.
Brain Res Mol Brain Res 1994 Jul
PMID:Isolation and characterization of a zebra finch aromatase cDNA: in situ hybridization reveals high aromatase expression in brain. 796 62

Steroid sex hormones have an organizational role in gender-specific brain development. Aromatase, converting testosterone (T) to oestradiol-17 beta (E2), is a key enzyme in the brain and the regulation of this enzyme is likely to determine availability of E2 effective for neural differentiation. In rodents, oestrogens are formed very actively during male perinatal brain development. This paper reviews work on the sexual differentiation of the brain aromatase system in vitro. Embryonic day 15 mouse hypothalamic culture aromatase activity (AA: mean Vmax = 0.9 pmol/h/mg protein) is several times greater than in the adult, whereas apparent Km is similar for both (approximately 30-40 nM). Using microdissected brain areas and cultured cells of the mouse, sex differences in hypothalamic AA during both early embryonic and later perinatal development can be demonstrated, with higher E2 formation in the male than in the female. The sex differences are brain region-specific, since no differences between male and female are detectable in cultured cortical cells. AA quantitation and immunoreactive staining with an aromatase polyclonal antibody both identify neuronal rather than astroglial localizations of the enzyme. Kainic acid eliminates the gender difference in hypothalamic oestrogen formation indicating, furthermore, that this sex dimorphism is neuronal. Gender-specific aromatase regulation is regional in the brain. Oestrogen formation is specifically induced in cultured hypothalamic neurones of either sex by T, since androgen has no effect on cortical cells. Androgen is clearly involved in the growth of hypothalamic neurones containing aromatase. It appears that differentiation of the brain involves maturation of a gender-specific network of oestrogen-forming neurones.
J Steroid Biochem Mol Biol 1994 Jun
PMID:Brain formation of oestrogen in the mouse: sex dimorphism in aromatase development. 804 7

The insulin-like growth factors (IGFs-I and -II) are mediators of cellular growth and differentiation. The expression of these growth factor genes is temporally and hormonally regulated in the uterus during pregnancy, suggesting potentially important roles in embryonic development, implantation, and successful progression of pregnancy. A known regulator of uterine IGF-I secretion is estrogen, which is produced by pre-implantation mammalian embryos of several species and whose amounts may be influenced by growth factors via their effects on the transcriptional activities of steroidogenic enzyme genes. We have previously proposed that within the uterine microenvironment, a positive feedback loop may link uterine secretion of IGFs with embryonic production of estrogens to maintain and coordinate the timing of biological signals essential for embryo development. The present study examined the temporal relationships between the levels of conceptus cytochrome P450 aromatase mRNA and protein and concentrations of IGF-I and -II in uterine luminal fluids of pigs. A DNA fragment encoding a highly conserved region among mammalian aromatase P450 proteins was isolated by hybridization screening of a porcine genomic DNA library with a human aromatase P450 cDNA fragment as probe. A synthetic oligopeptide DDVIDGYPVKKGTNI within this highly conserved region was used to generate an antiserum in sheep that recognized a protein of M(r) 49,000 in Western blot analysis of porcine ovarian, placental, endometrial, and conceptus extracts. A radioimmunoassay (RIA) for aromatase P450 was established and validated using this antiserum. RIA demonstrated highest levels of aromatase P450 protein in extracts of days 10, 11, and 12 porcine conceptuses with significantly diminished levels in elongated conceptuses at days 15 and 18. In the conceptus, aromatase P450 was localized to the inner cell layer (hypoblast) of the trophectoderm. A major mRNA transcript of approximately 3 kb in length was demonstrated by Northern blot analysis of conceptus RNA with a porcine aromatase P450 antisense RNA probe. The relative levels of aromatase P450 mRNA were higher in conceptuses at day 12 than at days 15 and 18, in parallel with the levels of aromatase P450 protein. RIA of uterine luminal fluids demonstrated maximal concentrations of IGF-I at day 12, which were significantly decreased by day 15, and increased concentrations of IGF-II by day 12, which were maintained until day 18 of pregnancy. These results demonstrate that the transient expression of conceptus aromatase P450 mRNA and protein in elongating pig blastocysts is coincident with their capacity to secrete estrogens and with the rapidly changing concentrations of IGFs within the uterine microenvironment.(ABSTRACT TRUNCATED AT 400 WORDS)
Mol Reprod Dev 1994 Jan
PMID:Transient expression of the cytochrome P450 aromatase gene in elongating porcine blastocysts is correlated with uterine insulin-like growth factor levels during peri-implantation development. 812 25


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