Steroidogenic factor-1 expression is transiently repressed and c-myc expression and deoxyribonucleic acid synthesis are induced in rat granulosa cells during the periovulatory period

The expression of steroidogenic factor 1 (SF-1), cytochrome P450 aromatase (P450arom), and cytochrome P450 cholesterol side-chain cleavage (P450scc) was examined during the periovulatory period. Immature rats were injected with eCG to induce development of ovarian follicles to the preovulatory stage. At 48 h after the eCG injection, the LH surge was simulated by an injection of an ovulatory dose of hCG, and RNA was isolated at 0, 2, 4, 6, 8, and 24 h after hCG injection. The mRNA levels for SF-1, P450arom, and P450scc were relatively high in total ovarian RNA samples from eCG-treated rats. Levels of SF-1 and P450arom mRNA decreased within 2 h after injection of hCG. The SF-1 mRNA levels gradually increased from 4 to 24 h. Aromatase levels remained undetectable until 24 h after hCG. P450scc mRNA levels increased throughout the 24-h period after hCG. Levels of SF-1 and P450arom, but not P450scc, mRNA were also reduced in RNA samples from isolated granulosa cells at 4 h after hCG treatment relative to those from eCG-treated rats. In situ hybridization analysis also revealed that hCG uniformly suppressed SF-1 mRNA levels an all granulosa cells compared to those of eCG-treated controls. The relationship of SF-1 expression to immediate/early gene expression and cell cycle traverse was also examined. C-myc mRNA levels were induced by up to 10-fold at 4 h after hCG injection. Similarly, DNA synthesis, as measured by the percentage of granulosa cells that incorporated 5'-bromodeoxyuridine, was increased from 16 +/- 4% in eCG-treated rats to 61 +/- 7% at 4 h after hCG treatment (p < 0.05). This study provides the novel finding that SF-1 expression is transiently repressed to very low levels in response to the LH surge. Further, these studies suggest that granulosa cells traverse the cell cycle before becoming terminally differentiated luteal cells.     

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.     

Expression of steroidogenic enzyme and gonadotropin receptor genes in bovine follicles during ovarian follicular waves: a review

Ovarian follicular development in cattle is characterized by waves of growth during the prepubertal and postpartum periods and during estrous cycles. Each wave of follicular growth is characterized by recruitment of a cohort of follicles 4 to 5 mm in diameter. From the cohort, one follicle is selected for continued growth and becomes dominant. If luteolysis occurs during the growth phase of dominant follicles, final maturation and ovulation occurs. If luteolysis does not occur during the growing and maintenance phase of follicles, the fate is atresia. Changes in mRNA expression for the gonadotropin receptors (FSHr and LHr), key steroidogenic enzymes (cytochrome P450 side chain cleavage [P450scc], cytochrome P450 17alpha-hydroxylase-[P450c17], cytochrome P450 aromatase [P450arom], and 3beta-hydroxysteroid dehydrogenase [3beta-HSD]), and growth factors (IGF-I and -II) and their binding proteins (IGFBP) have been associated with different stages of follicular growth and atresia. In general, expression of mRNA for the gonadotropin receptors, steroidogenic enzymes, and steroidogenic acute regulatory protein (StAR) increase with progressive follicular development and is highest when dominant follicles approach maximum size. Expression of mRNA declines rapidly and becomes low or undetectable in atretic follicles. The IGF-I (granulosal cells) and IGF-II (thecal cells) are increased, whereas IGFBP-2 (granulosal cells) is reduced, in dominant follicles. Recruitment of a cohort of follicles is associated with initiation of expression of mRNA for P450scc and P450arom in granulosal cells. Selection of dominant follicles is associated with expression of mRNA for LHr and 3beta-HSD in granulosal cells. Thus, changes in gene expression likely are important to recruitment, selection, dominance, and atresia in ovarian follicles.     

Rooster testicular germ cells and epididymal sperm contain P450 aromatase

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.     

Quantitation of P450 aromatase immunoreactivity in human ovary during the menstrual cycle: relationship between the enzyme activity and immunointensity

To understand changes associated with the menstrual cycle in the human ovary, it is very important to examine chronological changes in P450 aromatase (P450arom) enzymatic activity in the normal cycling ovary. Therefore, we initially examined the correlation between intensity of P450arom immunoreactivity and its biochemical enzymatic activity in five estrogen-producing human cancer cell lines (HHUA, Ishikawa, HEC-59, OMC-2, and MCF-7). P450arom immunointensity per cell was evaluated by the CAS 200 computed image analysis system, and its catalytic activity per 10(6) culture cells was analyzed by the tritiated water method. A significant correlation (r = 0.959) was demonstrated between P450arom immunoreactivity and enzymatic activity under optimal conditions of tissue fixation and immunohistochemical procedures. We then investigated P450arom immunointensity in 31 specimens of normal cycling human ovaries to examine chronological changes in P450arom activity per cell throughout the menstrual cycle. In the follicular phase, P450arom was observed in the granulosa cells of one selected antral follicle per case during the mid- to late proliferative period, and its immunointensity per granulosa cell in the follicle was not significantly different between mid- and late proliferative periods, although serum estradiol level was markedly elevated in the late proliferative period. In the luteal phase, both P450arom immunointensity per luteinized granulosa cell in a corpus luteum and serum estradiol level reached a peak in the mid-secretory period. These findings indicate that different factors may influence ovarian P450arom activity during the follicular and luteal phases, i.e., an increased number of granulosa cells in the selected follicle during the follicular phase but changes in P450arom activity per luteinized granulosa cell in the corpus luteum during the luteal phase.     

The novel untranslated first exon "exon 0N" of the rat estrogen receptor gene

The 5'-untranslated region (UTR) of the estrogen receptor (ER) mRNA in the rat liver was analyzed by the use of the 5'-rapid amplification of the cDNA ends (5'-RACE) method. The nucleotide sequence of one of the positive RACE clones (clone 9) revealed that the existence of the novel untranslated first exon (termed "exon N") being spliced onto the exon 1 of the rat ER mRNA. We further analyzed the distribution of the ER mRNA containing the "exon 0N" (ER mRNA (0N-1)) and the ER mRNA containing the previously reported exon 0 (ER mRNA (0-1)) in the rat brain and peripheral tissues. In contrast to the wide distribution of the ER mRNA (0-1), the distribution of the ER mRNA (0N-1) was almost limited in the peripheral tissues. These results indicate that the "exon 0N" is the novel untranslated first exon of the rat ER gene, and the tissue specific expression of the ER is regulated, at least in part, by differential promoter usage in the rat.     

Lamin-binding fragment of LAP2 inhibits increase in nuclear volume during the cell cycle and progression into S phase

It is hypothesized that the two-cell model for estrogen production by the ovarian follicle is preserved in the primate corpus luteum, but there is little direct evidence to support this theory. To determine the sites of androgen and estrogen synthesis within the primate corpus luteum and to ascertain whether changes in steroid hormone levels are related to steroidogenic enzyme expression, the enzymes converting progesterone to androgen (cytochrome P450 17alpha-hydroxylase/17,20 lyase; P450(c17)) and then to estrogen (aromatase; P450(arom)), as well as P450 side-chain cleavage (P450(scc)) and 3beta-hydroxysteroid dehydrogenase (3beta HSD), were detected by immunohistochemistry in macaque luteal tissue throughout the menstrual cycle and simulated early pregnancy. Corpora lutea were collected from rhesus monkeys in the early (Days 2-4 post-LH surge), mid (Days 6-8), mid-late (Days 10-12), and late (Days 14-15) luteal phase and after 1, 3, 6, or 9 days of hCG treatment that began on Day 9 of the luteal phase. Specific cytoplasmic staining for P450(c17), P450(arom), P450(scc), and 3beta HSD was present in luteal cells, but not in the microvasculature, within all luteal tissues examined. P450(c17)-stained luteal cells were located along the vascular tracts and around the periphery of the corpus luteum. Intensely stained luteal cells were associated with blood vessels entering from the outer surface of the corpus luteum, but not with blood vessels returning from the connective tissue centrum. In contrast, P450(arom)-stained luteal cells were distributed throughout the luteal parenchyma. P450(c17) staining intensity was similar at all stages of the luteal phase; however, the number and intensity of P450(arom)-stained cells decreased by late luteal phase. In simulated early pregnancy, cells stained for P450(c17) were present near blood vessels, with some positive cells scattered throughout the corpus luteum. P450(arom) immunostaining was heterogeneous within the corpus luteum; many intensely stained cells were interspersed among others that were only lightly stained. Overall, cellular staining for P450(c17) and P450(arom) remained intense through 9 days of simulated early pregnancy. In contrast, P450(scc) and 3beta HSD immunoreactivity were not located in distinct luteal compartments. These results are consistent with a two-cell model for steroid hormone production in the primate corpus luteum, whereby paraluteal (theca-luteal) cells produce androgen substrate that is converted to estrogens by true (granulosa-) luteal cells. The divergence in enzyme detection as the luteal phase progresses, with P450(c17) labeling high and P450(arom) staining having decreased, suggests a shift in the function of the corpus luteum as it ages. Enzyme localization during chorionic gonadotropin exposure simulating early pregnancy demonstrates the continued capacity of the primate corpus luteum to produce steroid hormones.     

A syndrome of female pseudohermaphrodism, hypergonadotropic hypogonadism, and multicystic ovaries associated with missense mutations in the gene encoding aromatase (P450arom)

We report the features of a new syndrome of aromatase deficiency due to molecular defects in the CYP19 (P450arom) gene in a 46,XX female. At birth, the patient presented with a nonadrenal form of female pseudohermaphrodism. At 17 months of age, laparotomy revealed normal female internal genital structures; the histological appearance of the ovaries was normal. FSH concentrations were markedly elevated at 9.4 ng/mL LER 869, and estrone and estradiol levels were undetectable (< 37 pmol/L). By 14 yr of age, she had failed to exhibit breast development. The clitoris had enlarged to 4 x 2 cm, and pubic hair was Tanner stage IV. The plasma concentration of testosterone was elevated at 3294 pmol/L, as was androstenedione at 9951 pmol/L. Plasma estradiol levels were below 37 pmol/L. ACTH and dexamethasone tests indicated a nonadrenal source of testosterone and androstenedione. Plasma gonadotropin levels were in the castrate range. Pelvic sonography and magnetic resonance imaging showed multiple 4- to 6-cm ovarian cysts bilaterally. Despite increased circulating androgens and clitoral growth, the bone age was 10 yr at chronologic age 14 2/12 yr. Estrogen replacement therapy resulted in a growth spurt, breast development, menarche, suppression of gonadotropin levels, and resolution of the cysts. The clinical findings suggested the diagnosis of P450arom deficiency. Analyses of genomic DNA from ovarian fibroblasts demonstrated two single base changes in the coding region of the P450arom gene, one at 1303 basepairs (C-T), R435C, and the other at 1310 basepairs (G-A), C437Y, in exon 10. The molecular genetic studies indicate that the patient is a compound heterozygote for these mutations. Expression of these mutations showed that the R435C mutation had 1.1% the activity of the wild-type P450arom enzyme, whereas the C437Y mutation demonstrated no activity. The cardinal features of this syndrome are a consequence of P450arom deficiency: 1) the fetal masculinization in this syndrome can be ascribed to defective placental conversion of C19 steroids to estrogens, leading to exposure of the female fetus to excessive amounts of testosterone; 2) the pubertal failure, mild virilization, multicystic ovaries, and hyperstimulation of the ovaries by FSH and LH are the result of the inability of the ovary to aromatize testosterone and androstenedione to estrogens; and 3) the striking delay in bone age at 14 2/12 yr supports the notion that estrogens, in contrast to androgens, are the major sex steroid driving skeletal maturation during puberty. Familial P450arom deficiency, although rare, may be more common than previously suspected.(ABSTRACT TRUNCATED AT 400 WORDS)     

Tetrahydronaphthalenes: influence of heterocyclic substituents on inhibition of steroid enzymes P450 arom and P450 17

In search of new leads for selective inhibition of estrogen and androgen biosynthesis, respectively, heterocyclic substituted 2-(arylmethylene)-1-tetralones (1-4, 9-17), 2-(aryl-hydroxymethyl)-1-tetralones (5-8), exo-1a,2,3,7b-tetrahydro-1H-cyclopropa[alpha] naphthalenes (18-24), and 3-alkyl substituted 4,5-dihydronaphtho[1,2-c]pyrazoles (25-27) were synthesized and tested for inhibitory activity toward four steroidogenic enzymes (P450 arom, P450 17, P450 18, and P450 scc, as well as another P450 enzyme, thromboxane A(2) (TXA(2)) synthase. The test compounds inhibited human placental P450 arom, showing a wide range of inhibitory potencies. (Z)-4-Imidazolyl compound 17 was the most potent inhibitor, with a relative potency (rp) of 110 [rp of aminoglutethimide (AG) = 1), rp of fadrozole = 359]. A competitive type of inhibition was shown by the (E)-4-imidazolyl compound 16(rp = 71). On the other hand some of these compounds inhibited rat testicular P450 17. Maximum activity was shown by the 3-pyridyl compound 20 (rp = 10, ro of ketoconazole = 1). 20 was the only compound which exhibited a marked inhibition of TXA(2) synthase (IC(50) = 14.5 microM; IC(50) of dazoxiben = 1.1 microM). Regarding selectivity toward the steroidogenic enzymes, compound 16 was relatively selective toward P450 arom, whereas compound 20 was relatively selective toward P450 17. (P450 arom: K(m) testosterone = 42 nM, K(i)16 = 33 nM, K(i)20 = 3 microM. P450 17: K(m)progesterone = 7 microM, K(i)16 = 9 microM, K(i)20 = 80 nM). 17 and 24 were not selective since they showed strong inhibition of P450 arom (K(i)17 = 26 nM, K(i)24 = 0.12 microM) and P450 17 (K(i) 17 = 0.7 microM, K(i)24 = 0.11 microM).     

Characterization of mice deficient in aromatase (ArKO) because of targeted disruption of the cyp19 gene

The formation of estrogens from C19 steroids is catalyzed by aromatase cytochrome P450 (P450arom), the product of the cyp19 gene. The actions of estrogen include dimorphic anatomical, functional, and behavioral effects on the development of both males and females, considerations that prompted us to examine the consequences of deficiency of aromatase activity in mice. Mice lacking a functional aromatase enzyme (ArKO) were generated by targeted disruption of the cyp19 gene. Male and female ArKO mice were born with the expected Mendelian frequency from F1 parents and grew to adulthood. Female ArKO mice at 9 weeks of age displayed underdeveloped external genitalia and uteri. Ovaries contained numerous follicles with abundant granulosa cells and evidence of antrum formation that appeared arrested before ovulation. No corpora lutea were present. Additionally the stroma were hyperplastic with structures that appeared to be atretic follicles. Development of the mammary glands approximated that of a prepubertal female. Examination of male ArKO mice of the same age revealed essentially normal internal anatomy but with enlargement of the male accessory sex glands because of increased content of secreted material. The testes appeared normal. Male ArKO mice are capable of breeding and produce litters of approximately average size. Whereas serum estradiol levels were at the limit of detection, testosterone levels were elevated, as were the levels of follicle-stimulating hormone and luteinizing hormone. The phenotype of these animals differs markedly from that of the previously reported ERKO mice, in which the estrogen receptor alpha is deleted by targeted disruption.     

Identification of novel drug resistance-associated proteins by a panel of rat monoclonal antibodies

It is well established that the rabbit corpus luteum (CL) function depends upon endogenous oestradiol, the major source of which in the rabbit ovary is considered to be the ovarian follicles. The absence of oestradiol formation by the rabbit CL has been previously reported. In a hyperstimulated pseudopregnant rabbit model used in our laboratory which developed a large number of corpora lutea in response to chorionic gonadotrophin (eCG)/hCG, we observed the survival of corpora lutea in vivo, and normal levels of plasma progesterone throughout pseudopregnancy (PP), despite the scarcity or the absence of follicles as a source of the luteotrophic hormone. Measurement of oestradiol in the plasma indicated that it was at high levels and correlated with the number of corpora lutea. This led us to investigate the luteal origin of oestradiol in this model. PP was induced in rabbits by i.m. injection of 200 IU eCG daily for 2 days followed on day 4 by i.m. injection of 200 IU hCG (day 0 of PP). Luteal tissue obtained at days 5, 9 and 12 of PP and cultured for 24 h synthesized oestradiol and testosterone in addition to progesterone. However, under the same conditions, follicles had limited capacity to secrete oestradiol. The presence of an aromatase activity in luteal tissue was confirmed when exogenous testosterone was added to the culture medium. P450aromatase (P450arom) mRNA was found in luteal tissue at days 5, 9 and 12 of PP. Small or large luteal cells, obtained by enzymatic digestion of the tissue followed by centrifugation in a Percoll density gradient, were cultured during several days with or without gonadotrophin or dibutyryl cAMP (dbcAMP). Both types of cells secreted oestradiol. In small cells and luteal tissue, aromatase activity was stimulated (1.5-2-fold) by hCG and dbcAMP. Large cells exhibited a greater capacity to aromatize testosterone than small cells, but aromatase activity was not modified by hCG or by dbcAMP. FSH had no effect on aromatase activity of either luteal cell type. This intrinsic luteal tissue aromatase capacity and the absence of premature regression of corpora lutea despite the limited support of follicular oestrogen, suggest an autocrine and luteotrophic role for this luteal oestrogen.