Cytochrome P450arom Research Articles

Porcine aromatases: studies on tissue-specific, functionally distinct isozymes from a single gene?

Aromatase cytochrome P450 (P450arom) is expressed in a variety of tissues. Pigs express P450arom as bilaminar blastocysts in utero, and thereafter in the gonads, adrenal glands and placenta. Our studies also demonstrate the existence of porcine isozymes of P450arom which differ substantially in their amino acid composition and function. The placental isoform, most similar to P450arom in other mammals, consists of 503 amino acids. The ovarian isoform, expressed in both theca and granulosa cells, is a 501 amino acid protein exhibiting less than 20% of the activity of the placental isozyme. Furthermore, it is inhibited not only by CGS16949A but also by etomidate which does not inhibit the placental P450arom. Partial sequences generated by the rapid amplification of the cDNA ends (RACE) procedure indicate that the expression of a third isoform in the blastocyst is switched to the placental isozyme during differentiation of the fetal membranes. In addition, these transcripts, and others from the theca, granulosa, testes, adrenal glands and placenta demonstrate differences in the 5′-untranslated region (putative exon I) suggestive of tissue-specific alternative splicing. An identical 5′-untranslated sequence was obtained from transcripts expressed in the theca and granulosa. Testes and adrenal transcripts also have identical 5′ ends, which differ substantially from the ovarian sequence. Blastocyst and placenta 5′-untranslated sequences differ from each other and from those expressed in the gonads and adrenals. Several tissue-specific transcripts thus encode porcine P450arom. Interestingly, distinct 5′ sequences exist for ovarian and testes P450arom mRNAs, suggesting different promoters and therefore regulation in the male and female gonads. The molecular origins of the functional isoforms and the tissue-specific transcripts are uncertain, however partial genomic sequence and other genetic analyses suggest the existence of multiple genes. However, sequence alignment of the placental and ovarian isoforms indicates complete conservation of putative exon III, so that complex splicing remains a possibility. Clearly, the regulation of P450arom expression is more complex in the pig than in other vertebrates investigated to date.

Seasonal changes in the immunolocalization of steroidogenic enzymes in the testes of the Japanese black bear (Ursus thibetanus japonicus).

Seasonal changes in sites of immunostaining of steroidogenic enzymes were examined in testes of the Japanese black bear, Ursus thibetanus japonicus. In addition, serum concentrations of testosterone and estradiol-17beta were investigated by radioimmunoassay, and the seasonal changes were compared with the results of immunostaining. On the basis of morphological observations of spermatogenic activity, the reproductive cycle was divided into five periods: an active period in May and June; a degenerative period in November; a resting period in January; an early-resumptive period in March; and a late-resumptive period in April. Serum concentrations of testosterone differed with season accompanied by differences in spermatogenic activity, with baseline levels in November and January, increasing levels in March and April, and high levels in May, and April and June of the next year. Immunoreactivities specific for cholesterol side-chain cleaving cytochrome P450, 17alpha-hydroxylase cytochrome P450 and 30-hydroxysteroid dehydrogenase (3beta HSD) were observed in Leydig cells throughout the year. Only the percentages of Leydig cells immunopositive for 3beta HSD exhibited seasonal differences that correlated with serum concentrations of testosterone. Aromatase cytochrome P450 (P450arom) was immunolocalized in Leydig and Sertoli cells throughout the year, in spermatids in May, and April and June of the next year and in myoid cells in January and March. The percentages of Leydig cells immunopositive for this enzyme increased in May, and January, March and June of the next year. On the other hand, no pattern of seasonal change in serum estradiol-17beta concentration was observed. These results suggest that 3beta HSD is a key enzyme in the regulation of the testosterone production in Leydig cells. Furthermore, estrogen derived from Leydig and myoid cells seems to play a role in the regulation of Leydig cells by negative feedback as a paracrine and/or autocrine mediator.

Expression of androgen receptors and steroidogenic enzymes in relation to follicular growth and atresia following ovulation in pigs.

Among the new antral follicles that develop after ovulation in pigs, the incidence of atresia, based on granulosa cell apoptosis, increases between Days 5 and 7 of the estrous cycle. The purpose of this study was to determine how follicular growth and atresia affected the expression of some key enzymes regulating follicular steroidogenesis and androgen receptor on Days 3, 5, and 7 after the onset of estrus. Ovaries were frozen in liquid propane for subsequent sectioning and immunohistochemical analysis. Ninety-six follicles were classified according to size as small (< 3 mm), medium (3-5 mm), or large (> 5 mm). Follicles in the active stages of the cell cycle were identified by the presence of the cell proliferation-associated nuclear antigen Ki-67 in granulosa cells. Follicles with apoptotic cells were identified by in situ 3'-end labeling of DNA. Staining intensity of antigens on sections was assigned a numeric value (0-3). Follicles assigned a value > 1 for 3'-end labeling in their granulosa cells were classified atretic. The percentage of atretic follicles increased (p < or = 0.05) from 5% on Days 3 and 5 to 41% on Day 7. Expression of Ki-67 in granulosa cells was more strongly (p < or = 0.05) associated with nonatretic follicles (98% expressing) than with atretic follicles (41% expressing). Aromatase cytochrome P450 (P450arom) was localized predominantly in granulosa cells of nonatretic follicles and was undetectable in atretic follicles. Androgen receptor in granulosa cells and expression of P450 17 alpha-hydroxylase/C17-20 lyase (P450c17) in theca interna were lower (p < or = 0.001) in atretic follicles than in nonatretic follicles. The expression of 3 beta-hydroxysteroid dehydrogenase (3 beta HSD) was localized to the theca interna and was unaffected by follicle atresia. In nonatretic small follicles, the expression of P450arom and P450c17 decreased (p < 0.01) between Days 3 and 7 while expression of Ki-67 was unchanged. In nonatretic follicles, increased follicle size was associated with a decrease (p < 0.01) in androgen receptor expression and increases (p < 0.01) in P450arom, P450c17, and 3 beta HSD expression. In conclusion, increased expression of steroidogenic enzymes was associated with follicular growth. Loss of P450arom expression in vivo is an early event in atresia and is followed by decreased cell proliferation, and decreased expression of androgen receptor and P450c17.

Aromatase activity and CYP19 gene expression in breast cancers.

The aromatase enzyme complex is responsible for the conversion of C19 androgens to oestrogens. Aromatase expression in oestrogen-responsive breast cancers may be an important mechanism of autocrine regulation in tumour growth. To evaluate whether aromatase cytochrome P450 (P450arom) transcript levels within breast tumours were correlated to the enzyme activity, a specific competitive reverse transcription-polymerase chain reaction (RT-PCR) was developed. In this reaction, a 32 base-deleted complementary RNA was used as internal standard. In vitro aromatase activity was measured by either the tritium release assay or characterization of oestrogen fractions. Results indicate that there is a positive correlation between P450arom transcript levels and enzyme activity, but the relationship does not reach statistical significance. Therefore, whereas aromatase mRNA quantification may be an option by which to monitor the potential of tumour to synthesize oestrogens, it will not accurately reflect enzyme activity in a minority of tumours. Preliminary evidence was obtained in a tumour with low enzyme activity and a high P450arom transcript level for the presence of an endogenous aromatase inhibitor. This study highlights the necessity to characterize factors involved in the regulation of aromatase activity in such tumours.

Detection of aromatase cytochrome P450, 17α-hydroxylase cytochrome P450 and NADPH:P450 reductase on the surface of cells in which they are expressed

Using the membrane impermeant probe NHS-LC-biotin, we show in this report that a fraction of aromatase P450 (P450arom), the enzyme that catalyzes estrogen biosynthesis, is present at the surface of cells in which it is expressed, either endogenously or as a consequence of transfection. The same findings were obtained for a truncated form of P450arom lacking the putative membrane-spanning region, thus suggesting the presence of other membrane-spanning region(s) within its structure. P450arom is not unique in this regard as we find that a fraction of 17α-hydroxylase P450 as well as NADPH:P450 reductase also are present at the cell surface. It is therefore possible that a number of microsomal P450s are expressed at the cell surface in this fashion.

1,25-Dihydroxyvitamin D3 enhances the enzymatic activity and expression of the messenger ribonucleic acid for aromatase cytochrome P450 synergistically with dexamethasone depending on the vitamin D receptor level in cultured human osteoblasts.

Not every postmenopausal woman with a low level of estrogen suffers from osteoporosis, and no correlation of bone density with serum estrogen level, but a significant correlation with adrenal androgens is often noted. Vitamin D3 has been reported to be osteoclastic in vitro, whereas the effectiveness of vitamin D3 for the treatment of osteoporosis is clinically relevant. To study the roles of these factors in the development of osteoporosis, we characterized aromatase activity converting androgens to estrogens in human osteoblasts, because postmenopausal women maintain considerable levels of adrenal androgens. Glucocorticoids at 10(-9)-10(-7) M transiently induced the expression and enzymatic activity of aromatase cytochrome P450 (P450AROM) in primary cultured osteoblasts, and the Km value for androstenedione (4.7 +/- 2.9 nM) was lower than that in adipose tissue and skin. Human osteoblasts showed a promoter specificity different from that found in other tissues. 1,25-Dihydroxyvitamin D3 [1,25-(OH)2D3] alone did not induce aromatase activity, but enhanced and maintained glucocorticoid-induced P450AROM gene expression. This synergistic effect was not observed by other sex steroids or retinoic acids. The enhancement of P450AROM activity by 1,25-(OH)2D3 varied from 0.94-fold (no enhancement) to 2.40-fold (maximal enhancement) among the individual human osteoblasts examined, but the magnitude of the enhancement was significantly correlated with the level of vitamin D receptor messenger RNA (P < 0.05). Cycloheximide did not abolish the synergistic effect of 1,25-(OH)2D3, suggesting that de novo protein synthesis is not required for the synergism with 1,25-(OH)2D3. These results suggest that bone tissue can synthesize estrogen from adrenal androgens by a unique aromatase activity depending on the level of vitamin D receptor expressed.

Mouse epididymal sperm contain active P450 aromatase which decreases as sperm traverse the epididymis.

Recently we reported that mouse germ cells in the testis contain active P450 aromatase (P450arom), the enzyme that converts androgens to estrogens. This finding suggested that germ cells have the ability to produce estrogen. Further studies have shown that germ cells in the testis of several species contain P450arom. The goal of this study was to determine if epididymal sperm contain P450arom and if P450arom activity in sperm changes during traversion of the epididymis in the adult mouse. P450arom was localized in sperm present in the efferent ductules and epididymis by immunocytochemistry using an antiserum generated against purified human placental cytochrome P450arom. P450arom immunostaining in sperm was most prominent in sperm located in the proximal caput epididymis, decreased as sperm traversed the corpus epididymis, and was only slightly apparent in sperm in the cauda epididymis. The immunolocalization of P450arom in epididymal sperm was supported by the measurement of P450arom activity in sperm by the 3H2O assay. We found that P450arom activity in sperm significantly decreases as sperm traverse the epididymis. Based upon these observations, we conclude that sperm can synthesize estrogen and that the synthesis of estrogen by sperm present in the efferent ductules and caput epididymis could be important in the process of sperm maturation.

Functional aromatase expression in porcine adrenal gland and testis.

The expression of aromatase cytochrome P450 (P450arom) in the adrenal glands, testes, and placentas of fetal and newborn pigs was investigated. Western immunoblot analysis detected a single 48-50-kDa protein band in these tissues as well as in other porcine tissues known to express P450arom including Day 12 tubular conceptuses, theca interna, and granulosa. Slight differences in migration suggested that the P450arom protein expressed in the testis was larger than that in the adrenal gland, which was, in turn, larger than that in placenta, theca, and granulosa. Consistent with P450arom expression in these tissues, a cDNA encoding porcine P450arom hybridized to a 2.3-kb transcripts in Northern analyses of porcine blastocysts, placentas, and fetal and newborn adrenal glands and testes, as well as in theca and granulosa tissues from preovulatory follicles. No differences in transcript size were detectable among tissues. The identity of P450arom transcripts was confirmed by sequence analysis of partial cDNA clones amplified from porcine fetal adrenal glands, testes, and placentas according to the RACE procedure. The sequences of the adrenal and testis clones were identical but differed from the placental sequence, which represented the first 85 amino acids of porcine P450arom. Specifically, the adrenal and testis clones expressed transcripts that resembled the ovarian isoform of porcine P450arom, rather than the porcine placental isoform, predicting a two-amino acid deletion and 12 predicted amino acid substitutions. P450arom activity was examined to further define expression in these tissues. Activity in adrenal, testis, and placental homogenates was inhibited by 4-hydroxyandrostenedione (4OH-A4) whereas inhibition by etomidate was demonstrated in the adrenal and testis homogenates but not in the placental homogenates. The sensitivity of activity in the newborn porcine adrenal glands and testes to inhibition by etomidate was similar to that of ovarian P450arom activity. The level of P450arom activity was highest in the placenta and lowest in the adrenal gland, and no effect of fetal sex was noted in either tissue. Immunocytochemical studies localized the expression of P450arom in the adrenal gland of newborns to cells at the corticomedullary junction and, with greater intensity, to cells around the developing medullary lobules. The same cells expressed cytochrome P450 17 alpha-hydroxylase, the expression of which also extended throughout the zona fasciculata. The interstitial cells were the site of P450arom expression in the testis, but no expression could be detected in any cells with the spermatic tubules. These data demonstrate that fetal and newborn porcine adrenal glands and testes express an active P450arom that resembles the isoform expressed in the ovary. The localization of adrenal expression suggests a possible role in medullary maturation and function in the fetal and newborn pig.

Intraovarian immunolocalization of steroidogenic enzymes in a Hokkaido brown bear, Ursus arctos yesoensis during the mating season.

Immunolocalization for four steroidogenic enzymes was performed on an ovary taken from a Hokkaido brown bear during the mating season. This specimen is considered to be in the follicular phase because of the presence of large follicles. In large follicles, cholesterol side-chain cleavage (P450scc) and 3 beta-hydroxysteroid dehydrogenase (3 beta HSD) were immunolocalized in theca interna cells and granulosa cells. 17 alpha-hydroxylase/C17-C20 lyase cytochrome P450 (P450c 17) was immunolocalized in theca interna cells but not in granulosa cells. Aromatase cytochrome P450 (P450arom) was immunolocalized only in granulosa cells. In medium follicles, however, P450scc and 3 beta HSD were immunolocalized only in theca interna cells, and the immunoreactivity of P450arom was detected in neither theca interna cells nor granulosa cells. Immunoreactivities of P450scc, 3 beta HSD and P450c 17 but not P450arom were detected in interstitial cells. This study suggests that estrogen biosynthesis takes place through interrelation between theca cells and granulosa cells and is explained by the so-called two-cell mechanism. Furthermore, the granulosa cells in large follicles have the capability for pregnenolone and progesterone biosynthesis, and the interstitial cell in the bear ovary is also a steroidogenic site.

Rooster Testicular Germ Cells and Epididymal Sperm Contain P450 Aromatase1

We recently found that cytochrome P450 aromatase (P450arom) is present in germ cells of the mammalian testis and is capable of converting androgens to estrogens in the male reproductive tract. The objective of the present study was to determine whether testicular germ cells and epididymal sperm of an avian species are also capable of synthesizing estrogen. P450arom was localized in the rooster testis and epididymal region by immunocytochemistry, using an antiserum generated against purified human placental cytochrome P450arom. Immunostaining was present in pachytene spermatocytes, round spermatids, elongated spermatids, flagella of late spermatids, and sperm in the epididymal region. A positive reaction was also found in nonciliated cells of the epididymal region. However, the absence of mRNA for P450arom in the epididymal region indicated that the immunoreactive protein present in the epididymal region is not synthesized in this region. The immunoreactive P450arom found in epididymal sperm was shown to be active through use of a 3H2O assay. On the basis of these data, we conclude that rooster testicular germ cells and epididymal sperm are sites for the synthesis of estrogen, a potential regulator or modulator of germinal epithelium in the testis and the epithelium of the epididymal region of the avian species.

Regulation of Placenta-specific Expression of the Aromatase Cytochrome P-450 Gene: INVOLVEMENT OF THE TROPHOBLAST-SPECIFIC ELEMENT BINDING PROTEIN

The aromatase (cytochrome P-450AROM) gene contains multiple untranslated exons I that are differentially transcribed in a tissue-specific manner. DNA sequences within the initial -301 upstream of placenta-specific exon I (exon Ia) are sufficient for placenta-specific expression of aromatase. In gel mobility shift assay, three separate domains in this region form specific binding complexes with proteins extracted from choriocarcinoma JEG-3 nuclei. A fragment containing these domains activates transcription driven by a heterologous promoter in a cell type-specific manner. Two of the binding domains that form major complexes in gel shift assay compete with each other and with a DNA fragment containing the trophoblast-specific element (TSE), which is derived from the enhancer region of the human chorionic gonadotropin alpha-subunit gene and is believed to confer placenta-specific expression of the gene. The core sequence RNCCTNNRG is sufficient for recognition of the TSE-binding protein, which is detected only in nuclear extracts prepared from placenta and choriocarcinoma. A mutation introduced in the distal TSE core in aromatase promoter resulted in marked reduction of transcriptional activity, although TSE region by itself did not show enhancer activity as that in human chorionic gonadotropin alpha-subunit gene.

Development of cytochrome P450 aromatase mRNA levels and enzyme activity in ovaries of normal and hypogonadal (hpg) mice

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.

Gonadal tumorigenesis in transgenic mice bearing the mouse inhibin alpha-subunit promoter/simian virus T-antigen fusion gene: characterization of ovarian tumors and establishment of gonadotropin-responsive granulosa cell lines.

To establish in vivo gonadal tumor models and permanent lines of gonadal somatic cells we produced transgenic (TG) mice expressing the Simian virus (SV) 40 T-antigens (T-ag), driven by 6 or 2.1 kilobase fragments of the mouse inhibin alpha-subunit promoter. Hitherto, altogether 44 TG mice, one of which carried the shorter transgene, have produced gonadal tumors. Two founder females expressing the longer transgene, KK1 and KK3, and three established TG mouse lines were studied in detail. Penetrance of the phenotype in IT6-M and IT6-F mouse lines was 100% (tumors/TG: IT6-M 22/22, IT6-F 14/14). The T-ag mRNA was strongly expressed in the gonads, adrenal glands, pituitary, and brain. The KK-1 and KK-3 ovarian tumor cells immunostained with anti-SV40 large-T antibody. The KK-1 cells possessed high-affinity LH receptors [equilibrium association constant (Ka = 7.8 x 10(10) liters/mol] and responded to human CG by elevated cAMP and progesterone production. Also FSH slightly stimulated their cAMP and estradiol production (P < 0.01). These cells expressed cytochrome P450arom and inhibin alpha mRNA, but not cytochrome P450c17 alpha. In conclusion, the KK-1 cells are immortalized luteinizing granulosa cells expressing endogenous gonadotropin receptors, steroidogenic enzymes, and inhibin alpha. These cells will be useful in studies on the molecular aspects of granulosa cell function. The present study indicates that the 6-kilobase fragment of the inhibin alpha promoter described in this article contains the elements directing tissue-specific expression in vivo and is useful for targeted expression of other genes in the gonads.

Immunocytochemical localization of cytochromes P450 17 alpha-hydroxylase and aromatase in embryonic cell layers of elongating porcine blastocysts.

Localized expression of cytochromes P450 17 alpha-hydroxylase (P450c17) and aromatase (P450arom) was investigated in embryonic cell layers of elongating porcine blastocysts by immunocytochemistry. Blastocysts were flushed from the uterus on day 12 of pregnancy, fixed in paraformaldehyde, embedded in paraffin, sectioned, and stained using immunogold- and peroxidase-based techniques. Staining for both P450c17 and P450arom was intense in spherical 7- to 10-mm blastocysts, but was absent in earlier stage 2- to 4-mm blastocysts and less intense or absent in later stage 20-mm and filamentous embryos. Cytochrome P450c17 was limited to the trophoblast of all blastocysts expressing the enzyme, and in spherical 7- to 10-mm blastocysts, essentially all cells of the trophoblast layer stained positively for P450c17. However, as elongation became apparent in 10-mm blastocysts, the cells of the trophoblast became flattened, and the expression of P450c17 declined particularly in those trophoblast cells adjacent to the embryonic disc where mesoderm outgrowth was occurring. In fact, two distinct populations of trophoblast cells became obvious: one that maintained P450c17 expression, and one that did not. Moreover, those trophoblast cells expressing P450c17 were less flattened than neighboring cells in which P450c17 expression was absent. These two morphologically and functionally distinct trophoblastic cell populations were most obvious in areas furthest from the embryonic disc. Cytochrome P450arom was expressed in the trophoblast as well as the hypoblast under the embryonic disc. Neither P450c17 nor P450arom appeared to be expressed in the embryonic disc or the mesoderm of the expanding blastocyst. These functional and structural changes in the embryonic cell layers of the elongating conceptus may be associated with the transient synthesis and secretion of estrogen that occur at the time of maternal recognition of pregnancy in the pig.

Immunocytochemical localization of cytochromes P450 17 alpha- hydroxylase and aromatase in embryonic cell layers of elongating porcine blastocysts [corrected and republished with original paging, article originally printed in Endocrinology 1994 Nov;135(5):2248-54

Localized expression of cytochromes P450 17 alpha-hydroxylase (P450c17) and aromatase (P450arom) was investigated in embryonic cell layers of elongating porcine blastocysts by immunocytochemistry. Blastocysts were flushed from the uterus on day 12 of pregnancy, fixed in paraformaldehyde, embedded in paraffin, sectioned, and stained using immunogold- and peroxidase-based techniques. Staining for both P450c17 and P450arom was intense in spherical 7- to 10-mm blastocysts, but was absent in earlier stage 2- to 4-mm blastocysts and less intense or absent in later stage 20-mm and filamentous embryos. Cytochrome P450c17 was limited to the trophoblast of all blastocysts expressing the enzyme, and in spherical 7- to 10-mm blastocysts, essentially all cells of the trophoblast layer stained positively for P450c17. However, as elongation became apparent in 10-mm blastocysts, the cells of the trophoblast became flattened, and the expression of P450c17 declined particularly in those trophoblast cells adjacent to the embryonic disc where mesoderm outgrowth was occurring. In fact, two distinct populations of trophoblast cells became obvious: one that maintained P450c17 expression, and one that did not. Moreover, those trophoblast cells expressing P450c17 were less flattened than neighboring cells in which P450c17 expression was absent. These two morphologically and functionally distinct trophoblastic cell populations were most obvious in areas furthest from the embryonic disc. Cytochrome P450arom was expressed in the trophoblast as well as the hypoblast under the embryonic disc. Neither P450c17 nor P450arom appeared to be expressed in the embryonic disc or the mesoderm of the expanding blastocyst. These functional and structural changes in the embryonic cell layers of the elongating conceptus may be associated with the transient synthesis and secretion of estrogen that occur at the time of maternal recognition of pregnancy in the pig.

Analysis of the aromatase cytochrome P450 gene in human breast cancers

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.

Immunocytochemical localization of cytochromes P450 17 alpha-hydroxylase and aromatase in embryonic cell layers of elongating porcine blastocysts.

Localized expression of cytochromes P450 17 alpha-hydroxylase (P450c17) and aromatase (P450arom) was investigated in embryonic cell layers of elongating porcine blastocysts by immunocytochemistry. Blastocysts were flushed from the uterus on day 12 of pregnancy, fixed in paraformaldehyde, embedded in paraffin, sectioned, and stained using immunogold- and peroxidase-based techniques. Staining for both P450c17 and P450arom was intense in spherical 7- to 10-mm blastocysts, but was absent in earlier stage 2- to 4-mm blastocysts and less intense or absent in later stage 20-mm and filamentous embryos. Cytochrome P450c17 was limited to the trophoblast of all blastocysts expressing the enzyme, and in spherical 7- to 10-mm blastocysts, essentially all cells of the trophoblast layer stained positively for P450c17. However, as elongation became apparent in 10-mm blastocysts, the cells of the trophoblast became flattened, and the expression of P450c17 declined particularly in those trophoblast cells adjacent to the embryonic disc where mesoderm outgrowth was occurring. In fact, two distinct populations of trophoblast cells became obvious: one that maintained P450c17 expression, and one that did not. Moreover, those trophoblast cells expressing P450c17 were less flattened than neighboring cells in which P450c17 expression was absent. These two morphologically and functionally distinct trophoblastic cell populations were most obvious in areas furthest from the embryonic disc. Cytochrome P450arom was expressed in the trophoblast as well as the hypoblast under the embryonic disc. Neither P450c17 nor P450arom appeared to be expressed in the embryonic disc or the mesoderm of the expanding blastocyst. These functional and structural changes in the embryonic cell layers of the elongating conceptus may be associated with the transient synthesis and secretion of estrogen that occur at the time of maternal recognition of pregnancy in the pig.

Immunocytochemical localization of cytochromes P450 17 alpha- hydroxylase and aromatase in embryonic cell layers of elongating porcine blastocysts [corrected and republished in Endocrinology 1994 Dec;135(6):2248-54

Localized expression of cytochromes P450 17 alpha-hydroxylase (P450c17) and aromatase (P450arom) was investigated in embryonic cell layers of elongating porcine blastocysts by immunocytochemistry. Blastocysts were flushed from the uterus on day 12 of pregnancy, fixed in paraformaldehyde, embedded in paraffin, sectioned, and stained using immunogold- and peroxidase-based techniques. Staining for both P450c17 and P450arom was intense in spherical 7- to 10-mm blastocysts, but was absent in earlier stage 2- to 4-mm blastocysts and less intense or absent in later stage 20-mm and filamentous embryos. Cytochrome P450c17 was limited to the trophoblast of all blastocysts expressing the enzyme, and in spherical 7- to 10-mm blastocysts, essentially all cells of the trophoblast layer stained positively for P450c17. However, as elongation became apparent in 10-mm blastocysts, the cells of the trophoblast became flattened, and the expression of P450c17 declined particularly in those trophoblast cells adjacent to the embryonic disc where mesoderm outgrowth was occurring. In fact, two distinct populations of trophoblast cells became obvious: one that maintained P450c17 expression, and one that did not. Moreover, those trophoblast cells expressing P450c17 were less flattened than neighboring cells in which P450c17 expression was absent. These two morphologically and functionally distinct trophoblastic cell populations were most obvious in areas furthest from the embryonic disc. Cytochrome P450arom was expressed in the trophoblast as well as the hypoblast under the embryonic disc. Neither P450c17 nor P450arom appeared to be expressed in the embryonic disc or the mesoderm of the expanding blastocyst. These functional and structural changes in the embryonic cell layers of the elongating conceptus may be associated with the transient synthesis and secretion of estrogen that occur at the time of maternal recognition of pregnancy in the pig.

Current perspectives on aromatase inhibitors in breast cancer.

One way to deprive hormone-dependent breast cancer of estrogen is to prevent its synthesis. This is achievable by inhibiting the aromatase cytochrome P-450 (P-450arom) enzyme complex responsible for the ultimate step in estrogen production. A new generation of specific and selective aromatase inhibitors is currently under investigation. The purpose of this review is to outline the preclinical test systems for screening these inhibitors, to summarize the preclinical and clinical data published to date, and to discuss the future application of these inhibitors in the management of breast cancer. Disadvantages to the use of earlier inhibitors are described. In vitro and in vivo experiments that reflect the potency and selectivity of new inhibitors are highlighted. From preliminary clinical trials, these inhibitors appear to have excellent pharmacokinetic profiles and produce few side effects when administered orally. Activity against postmenopausal metastatic breast cancer has been demonstrated for the agents reviewed. They are all now in phase III testing to determine their relative efficacy in this setting. Their application in combination with both hormone therapy and chemotherapy, in premenopausal metastatic disease, and in the adjuvant setting in both premenopausal and postmenopausal women remains to be defined.

Steroidogenic cytochrome P450 enzyme messenger ribonucleic acids and follicular fluid steroids in individual follicles during preovulatory maturation in the pig.

Changes in follicular concentrations of steroidogenic cytochrome P450 enzyme mRNAs were determined during preovulatory maturation. RNA was isolated from 59 individual follicles dissected from 18 pigs during altrenogest-synchronized preovulatory follicular maturation: at Day 1 (pre-follicular phase), Day 3 (early follicular phase), Day 5 (mid-follicular phase), and Day 7 (late follicular phase, 24-36 h after the onset of the LH surge). Follicular fluid was aspirated for steroid RIA. RNA was also isolated from pooled granulosa cells, theca tissue, and luteal tissue. RNA was analyzed by Northern and slot-blot procedures using cDNA probes to human aromatase cytochrome P450 (P450arom), porcine 17 alpha-hydroxylase cytochrome P450 (P450(17) alpha), and porcine cholesterol side-chain cleavage cytochrome P450 (P450scc). P450arom mRNA was expressed in both granulosa and theca interna cells but was not detectable in luteal tissue from Day 13 of the estrous cycle. Follicular P450arom mRNA concentration tended to increase between Days 1 and 5 and decreased (p < or = 0.05) by 92% between Days 5 and 7. Follicular fluid estradiol-17 beta concentration increased 17-fold between Days 1 and 5 and then decreased (p < or = 0.05) by 96% between Days 5 and 7. P450(17) alpha mRNA was present in theca interna but was not detected in granulosa cells or luteal tissue. Follicular P450(17) alpha mRNA concentrations did not differ significantly among days, but the content per follicle increased (p < 0.05) between Days 1 and 5 and decreased (p < 0.05) between Days 5 and 7.(ABSTRACT TRUNCATED AT 250 WORDS)