The differential, tissue-specific regulation of oxytocin (OT) binding sites allows the neurohypophysial nonapeptide OT to fulfill a dual role: to induce uterine contractions at parturition and to mediate milk ejection during lactation. Whereas uterine OT binding sites are up-regulated prior to parturition and are rapidly down-regulated thereafter, mammary gland OT binding sites gradually increase throughout gestation and remain up-regulated during the ensuing lactation period. Here, we structurally characterized OT receptor (OTR) mRNA in mammary gland and analyzed its expression during gestation and lactation and in response to steroid treatment. In mammary gland tissues, we found a 6.7 and a 5.4 kb OTR mRNA species, and both species were further analyzed by RACE (rapid amplification of cDNA ends). The 6.7 kb mRNA was found to be common to mammary gland and uterus and to extend 618 nucleotides beyond the published sequence of the rat OTR gene. The 5.4 kb mRNA species is unique to the mammary gland and terminates at a mammary gland-specific polyadenylation site that is not preceded by a classical polyadenylation signal. RT-PCR analysis did not provide any evidence for differences in the coding regions, suggesting that both uterine and mammary gland OTR mRNAs encode the same receptor protein. Furthermore, primer extension experiments showed that no differences exist in the specific transcriptional initiation sites of the OTR gene in the two tissues. During pregnancy, OTR mRNA per mammary gland increased approximately 150-fold and remained high during lactation, consistent with the previously identified regulation of OT binding sites and the role of OT during lactation. Whereas estrogen administration strongly induced the uterine OTR mRNA levels (>5-fold), mammary gland remained unaffected by steroid treatment. Moreover, tamoxifen had no effect on the mammary gland OTR mRNA level. In summary, our data demonstrate a differential control of OTR expression in uterus versus mammary gland and a mammary gland-specific OTR mRNA polyadenylation site. However, this differential control apparently does not involve the expression of different receptor genes nor the utilization of tissue-specific transcriptional initiation sites.
C Breton, D Di Scala-Guenot and HH Zingg
F. F. Bolander and M. E. Blackstone
The envelope protein, gp52, of the mouse mammary tumour virus (MMTV) binds to a cell-surface receptor as a first step in infection. A protein with characteristics of this receptor was measured on freshly isolated cells using, as ligand, 125I-labelled gp52 purified from C3H/HeN mice. The gp52-binding protein was found in all mouse tissues examined, but was present at highest concentrations in the mammary gland and spleen where it reached 4.2±0.3 (s.e.m.) pmol/mg protein; the dissociation constant was 30±7 pm. Binding to mammary epithelium could be displaced by either the RIII or 34I-R strains of MMTV, and binding was blocked by antibodies to gp52. Levels in the liver and adrenal glands were only 25% of those in the mammary gland, while the concentrations in the ovary and salivary gland were intermediate. Scatchard analyses of the binding data suggested that there was only a single set of high-affinity binding sites. During late pregnancy and lactation, receptor levels in mammary epithelium rose threefold, while those in the liver and salivary gland were unchanged. This induction would result in the mammary gland having 12 times the gp52-binding protein than other tissues and may result in the preferential reinfection of this tissue during lactation, with subsequent tumour formation.
GD Jahnke, MJ Miller, A Martinez, L Montuenga and F Cuttitta
Adrenomedullin (AM) is a recently identified amidated peptide produced by a variety of tissue types. We have investigated the involvement of AM and its receptor (AM-R) in developing mouse mammary glands and have examined what influence ovarian hormones have on AM and AM-R expression in this system. Tissues from ductal morphogenesis, virgin adult, pregnancy, and lactation stages were assessed for AM and AM-R by molecular, biochemical and immunohistochemical techniques. Results from these studies indicated that messenger RNA for AM and AM-R and immunoreactivity for AM were expressed in the luminal epithelium of small and large ducts and in terminal end buds. Immunoreactive AM was identified as a cytoplasm component of ductal cells, with some cells also having nuclear staining. Western blot analysis of mammary gland tissues yielded two molecular mass species (M(r) 14,000 and 18,500) of AM immunoreactivity in the mammary gland for the above developmental stages, consistent with processed intermediate and prohormone forms respectively. Ovariectomy alone or followed by hormonal treatments did not alter the expression pattern for these two proteins. By Western blot, the fully processed AM form (M(r) 6000) was identified in milk extracts from lactating glands. These data suggest a potential role for AM and its receptor in the maintenance of mammary gland homeostasis and suggests a potential role for AM in development of the newborn.
P.F. Whitelaw, C.D. Smyth, C.M. Howles and S.G. Hillier
Current understanding of the endocrine and paracrine regulation of follicular oestrogen synthesis predicts that aromatase cytochrome P450 (P450arom) mRNA is inducible by FSH in granulosa cells. LH receptor mRNA is constitutively expressed in thecal/interstital cells, and is also thought to be induced in granulosa cells in response to joint stimulation by FSH and oestrogen. This study provides direct evidence that FSH induces the ovarian P450arom gene selectively, perhaps exclusively, in the granulosa cells of Graafian follicles. FSH-induction of LH receptor mRNA occurs simultaneously but is independent of oestrogen synthesis per se.
Ilaria Cimmino, Francesco Oriente, Vittoria D’Esposito, Domenico Liguoro, Pasquale Liguoro, Maria Rosaria Ambrosio, Serena Cabaro, Francesco D’Andrea, Francesco Beguinot, Pietro Formisano and Rossella Valentino
The dramatic rise in obesity and metabolic syndrome can be related, at least in part, to environmental chemical factors such as Bisphenol-A (BPA). In this study, we aimed to understand the effects of low-dose Bisphenol-A on the human mature adipocytes and stromal vascular fraction (SVF) cells, obtained from subcutaneous mammary adipose tissue of overweight female patients, undergoing surgical mammary reduction. 24 and/or 48-h exposure to BPA 0.1 nM elicited significant increase of the inflammatory molecules interleukin-6 (IL-6), interleukin-8 (IL-8), monocyte chemo-attractant protein 1α (MCP1α) and induced G protein-coupled estrogen receptor 30 (GPR30) levels more than two-fold both in mature adipocytes and SVF cells. These effects were similar to that obtained in the presence of GPR30-specific agonist G1 (100 nM) and were reverted by G15 (1 µM), a GPR30-selective antagonist. As a result of BPA-GPR30 signaling activation, fatty acid synthase (FAS) and leptin mRNA levels were significantly higher upon BPA exposure (P < 0.05) in mature adipocytes, with an opposite effect on adiponectin (ADIPOQ). In addition, an increase in SVF cell proliferation and ERK1/2 phosphorylation, was observed, compared to untreated cells. G15 reverted all of these effects. Interestingly, the action of BPA on SVF cell growth was mimicked by IL-8 treatment and was reverted by incubation with anti-IL8 antibodies. All these data suggest that BPA at 0.1 nM, a ten times lower concentration than environmental exposure, increases the expression of pro-inflammatory cytokines via GPR30 both in mature mammary adipocytes and in SVF cells with a possible involvement of IL-8.
MA Hattori, N Nishida, K Takesue, Y Kato and N Fujihara
The present study was designed to evaluate the regulation of nitric oxide (NO) synthesis in porcine oocytes during follicular development. Cumulus-oocyte complexes were obtained by aspirating the small follicles of immature porcine ovaries and cultured at 39 degrees C for 24-72 h with FSH in a serum-free medium. The oocyte-surrounding cumulus cells markedly proliferated and expressed LH receptor mRNA in response to FSH. The endothelial type of NO synthase (eNOS) (130 kDa) was detected in the oocyte, but not in the proliferated cumulus cells, by immunoblotting. The amount of oocyte eNOS did not significantly alter during culture, but measurement of nitrite and nitrate revealed FSH suppression of NO synthesis by approximately 50%. NO-releasing agents were added to the cultures to examine the effect of NO on the growth of cumulus cells. NO-releasing agents showed inhibitory effects on proliferation of the cumulus cells and expression of LH receptor mRNA. Thus, synthesis of eNOS-derived NO is suppressed in the porcine oocyte during development with no change in the enzyme amount, and it is suggested that it has an inhibitory function in the growth of cumulus cells.
L Bjornstrom, E Kilic, M Norman, MG Parker and M Sjoberg
Both 17beta-estradiol and prolactin play important roles in the mammary gland, raising the possibility of functional cross-talk between the two signaling pathways. Here, we demonstrate that estrogen receptor-alpha (ERalpha) and -beta (ERbeta) are both able to potentiate transcription from a Stat5-responsive promoter when activated by prolactin. Potentiation was observed not only in the presence of 17beta-estradiol, but also in the presence of anti-estrogens such as tamoxifen and ICI 182,780. The magnitude of the response was dependent on cell-type: in the HC11 mouse mammary epithelial cell line ERbeta potentiates transcription efficiently whereas ERalpha showed low activity. Conversely, in COS-7 cells, both estrogen receptors were active. We show that activation domains in the N-terminus (AF-1) and the C-terminus (AF-2) of the ERs are dispensable for potentiation. The effects are dependent on the presence of an intact DNA-binding/hinge domain, which we show is capable of interacting with Stat5b in vitro and in HC11 cell extracts. We conclude that ERalpha and ERbeta act as coactivators for Stat5b through a mechanism which is independent of AF-1 and AF-2.
D Marcantonio, LE Chalifour, MA Alaoui-Jamali And H T Huynh, MA Alaoui-Jamali, MA Alaoui-Jamali, HT Huynh and HT Huynh
Steroid-sensitive gene-1 (SSG1) is a novel gene we cloned, found regulated by 17beta-estradiol in the rat uterus and mammary gland, and over-expressed in 7,12-dimethylbenz(a)anthracene-induced rat mammary tumors. We show here that SSG1 mRNA and protein expression are regulated by androgens in the rat ventral prostate. Increases in SSG1 mRNA levels were detected by Northern blotting after 24 h and reached a 27-fold peak 96 h following castration, relative to SSG1 mRNA expression in sham-operated rats. Dihydrotestosterone or testosterone supplementation of castrated rats prevented this rise in SSG1 mRNA. In contrast with SSG1 mRNA expression, SSG1 protein was decreased 16-fold 2 weeks following castration but was at control levels in the prostates of castrated rats receiving dihydrotestosterone or testosterone. Although SSG1 is regulated by androgens in vivo, treatment of LnCap cells with dihydrotestosterone, cyproterone acetate or flutamide did not result in the regulation of SSG1 protein levels in vitro. Immunofluorescence studies show that SSG1 is mainly expressed in prostatic smooth muscle cells. These results indicate that SSG1 is an androgen-regulated gene that is expressed in the smooth muscle component of the rat ventral prostate in vivo.
Amelia J Brennan, Julie A Sharp, Christophe M Lefèvre and Kevin R Nicholas
Mammary explants can be hormonally stimulated to mimic the biochemical changes that occur during lactogenesis. Previous studies using mammary explants concluded that the addition of exogenous macromolecules were required for mammary epithelial cells to remain viable in culture. The present study examines the survival of mammary explants from the dairy cow using milk protein gene expression as a functional marker of lactation and cell viability. Mammary explants cultured from late pregnant cows mimicked lactogenesis and showed significantly elevated milk protein gene expression after 3 days of culture with lactogenic hormones. The subsequent removal of exogenous hormones from the media for 10 days resulted in the down-regulation of milk protein genes. During this time, the mammary explants remained hormone responsive, the alveolar architecture was maintained and the expression of milk protein genes was re-induced after a second challenge with lactogenic hormones. We report that a population of bovine mammary epithelial cells have an intrinsic capacity to remain viable and hormone responsive for extended periods in chemically defined media without any exogenous macromolecules. In addition, we found mammary explant viability was dependent on de novo protein and RNA synthesis. Global functional microarray analysis showed that differential expression of genes involved in energy production, immune responses, oxidative stress and apoptosis signalling might contribute to cell survival. As the decline in milk production in dairy cattle after peak lactation results in considerable economic loss, the identification of novel survival genes may be used as genetic markers for breeding programmes to improve lactational persistency in dairy cows.
D J Tisdall, K Watanabe, N L Hudson, P Smith and K P McNatty
A key question in elucidating the role of FSH in ovarian function is to determine when during follicular growth the FSH receptor first appears. The aim of this study was to examine the site and time of FSH receptor gene expression during early follicular growth. This study was carried out on ovaries of adult sheep during the luteal and prostaglandin-induced follicular phase of the oestrous cycle and also on ovaries of fetal sheep at 90, 100, 120 and 135 days of gestation (term=day 147).
Using reverse transcription-PCR and a set of PCR primers spanning exons 8/9/10, two partial FSH receptor cDNAs (500 and 310 bp) were isolated from adult sheep ovary. It was shown by sequencing that exon 8 was deleted in the 310 bp cDNA, implying that this was part of an alternatively spliced FSH receptor transcript. Using RNA in situ hybridisation on ovaries of adult sheep, FSH receptor mRNA was observed in granulosa cells of early preantral follicles with one to two cell layers and it was seen that gene expression continued throughout folliculogenesis into advanced stages of atresia. Moreover, in the fetus, FSH receptor gene expression was detected in follicles with two or more layers of granulosa cells in ovaries taken at 100, 120 and 135 days of gestation.
These results suggest that the FSH receptor gene is expressed after the granulosa cells of a folllicle have begun to divide but not during the earliest stages of follicle growth, namely the transformation of a primordial follicle to a primary follicle.