Cooperative control via lymphoid enhancer factor 1/T cell factor 3 and estrogen receptor-alpha for uterine gene regulation by estrogen

Oestrogen Activates the MAP3K1 Cascade and β-Catenin to Promote Granulosa-like Cell Fate in a Human Testis-Derived Cell Line

Sex determination triggers the differentiation of the bi-potential gonad into either an ovary or testis. In non-mammalian vertebrates, the presence or absence of oestrogen dictates gonad differentiation, while in mammals, this mechanism has been supplanted by the testis-determining gene SRY. Exogenous oestrogen can override this genetic trigger to shift somatic cell fate in the gonad towards ovarian developmental pathways by limiting the bioavailability of the key testis factor SOX9 within somatic cells. Our previous work has implicated the MAPK pathway in mediating the rapid cellular response to oestrogen. We performed proteomic and phosphoproteomic analyses to investigate the precise mechanism through which oestrogen impacts these pathways to activate β-catenin-a factor essential for ovarian development. We show that oestrogen can activate β-catenin within 30 min, concomitant with the cytoplasmic retention of SOX9. This occurs through changes to the MAP3K1 cascade, suggesting this pathway is a mechanism through which oestrogen influences gonad somatic cell fate. We demonstrate that oestrogen can promote the shift from SOX9 pro-testis activity to β-catenin pro-ovary activity through activation of MAP3K1. Our findings define a previously unknown mechanism through which oestrogen can promote a switch in gonad somatic cell fate and provided novel insights into the impacts of exogenous oestrogen exposure on the testis.

Exogenous Oestrogen Impacts Cell Fate Decision in the Developing Gonads: A Potential Cause of Declining Human Reproductive Health

The increasing incidence of testicular dysgenesis syndrome-related conditions and overall decline in human fertility has been linked to the prevalence of oestrogenic endocrine disrupting chemicals (EDCs) in the environment. Ectopic activation of oestrogen signalling by EDCs in the gonad can impact testis and ovary function and development. Oestrogen is the critical driver of ovarian differentiation in non-mammalian vertebrates, and in its absence a testis will form. In contrast, oestrogen is not required for mammalian ovarian differentiation, but it is essential for its maintenance, illustrating it is necessary for reinforcing ovarian fate. Interestingly, exposure of the bi-potential gonad to exogenous oestrogen can cause XY sex reversal in marsupials and this is mediated by the cytoplasmic retention of the testis-determining factor SOX9 (sex-determining region Y box transcription factor 9). Oestrogen can similarly suppress SOX9 and activate ovarian genes in both humans and mice, demonstrating it plays an essential role in all mammals in mediating gonad somatic cell fate. Here, we review the molecular control of gonad differentiation and explore the mechanisms through which exogenous oestrogen can influence somatic cell fate to disrupt gonad development and function. Understanding these mechanisms is essential for defining the effects of oestrogenic EDCs on the developing gonads and ultimately their impacts on human reproductive health.

Role of Wnt signalling in early pregnancy

The integration of a complex network of signalling molecules promotes implantation of the blastocyst and development of the placenta. These processes are crucial for a successful pregnancy and fetal growth and development. The signalling network involves both cell-cell and cell-extracellular matrix communication. The family of secreted glycoprotein ligands, the Wnts, plays a major role in regulating a wide range of biological processes, including embryonic development, cell fate, proliferation, migration, stem cell maintenance, tumour suppression, oncogenesis and tissue homeostasis. Recent studies have provided evidence that Wnt signalling pathways play an important role in reproductive tissues and in early pregnancy events. The focus of this review is to summarise our present knowledge of expression, regulation and function of the Wnt signalling pathways in early pregnancy events of human and other model systems, and its association with pathological conditions. Despite our recent progress, much remains to be learned about Wnt signalling in human reproduction. The advancement of knowledge in this area has applications in the reduction of infertility and the incidence and morbidity of gestational diseases.

Estrogen receptor beta (ERβ) mediates expression of β-catenin and proliferation in prostate cancer cell line PC-3

The aim of the present study was to characterize the mechanism underlying estrogen effects on the androgen-independent prostate cancer cell line PC-3. 17β-estradiol and the ERβ-selective agonist DPN, but not the ERα-selective agonist PPT, increased the incorporation of [methyl-(3)H]thymidine and the expression of Cyclin D2, suggesting that ERβ mediates the proliferative effect of estrogen on PC-3 cells. In addition, upregulation of Cyclin D2 and incorporation of [methyl-(3)H]thymidine induced by 17β-estradiol and DPN were blocked by the ERβ-selective antagonist PHTPP in PC-3 cells. Upregulation of Cyclin D2 and incorporation of [methyl-(3)H]thymidine induced by DPN were also blocked by PKF118-310, a compound that disrupts β-catenin-TCF (T-cell-specific transcription factor) complex, suggesting the involvement of β-catenin in the estradiol effects in PC-3 cells. A diffuse immunostaining for non-phosphorylated β-catenin was detected in the cytoplasm of PC-3 cells. Low levels of non-phosphorylated β-catenin immunostaining were also detected near the plasma membrane and in nuclei. Treatment of PC-3 cells with 17β-estradiol or DPN markedly increased non-phosphorylated β-catenin expression. These effects were blocked by pretreatment with the ERβ-selective antagonist PHTPP, PI3K inhibitor Wortmannin or AKT inhibitor MK-2206, indicating that ERβ-PI3K/AKT mediates non-phosphorylated β-catenin expression. Cycloheximide blocked the DPN-induced upregulation of non-phosphorylated β-catenin, suggesting de novo synthesis of this protein. In conclusion, these results suggest that estrogen may play a role in androgen-independent prostate cancer cell proliferation through a novel pathway, involving ERβ-mediated activation of β-catenin.

Mechanisms of uterine estrogen signaling during early pregnancy in mice: an update

Adherence of an embryo to the uterus represents the most critical step of the reproductive process. Implantation is a synchronized event between the blastocyst and the uterine luminal epithelium, leading to structural and functional changes for further embryonic growth and development. The milieu comprising the complex process of implantation is mediated by estrogen through diverse but interdependent signaling pathways. Mouse models have demonstrated the relevance of the expression of estrogen-modulated paracrine factors to uterine receptivity and implantation window. More importantly, some factors seem to serve as molecular links between different estrogen pathways, promoting cell growth, acting as molecular chaperones, or amplifying estrogenic effects. Abnormal expression of these factors can lead to implantation failure and infertility. This review provides an overview of several well-characterized signaling pathways that elucidates the molecular cross talk involved in the uterus during early pregnancy.

Control of regional decidualization in implantation: Role of FoxM1 downstream of Hoxa10 and cyclin D3

Appropriate regulation of regional uterine stromal cell decidualization in implantation, at the mesometrial triangle and secondary decidual zone (SDZ) locations, is critical for successful pregnancy, although the regulatory mechanisms remain poorly understood. In this regard, the available animal models that would specifically allow mechanistic analysis of site-specific decidualization are strikingly limited. Our study found that heightened expression of FoxM1, a Forkhead box transcription factor, is regulated during decidualization, and its conditional deletion in mice reveals failure of implantation with regional decidualization defects such as a much smaller mesometrial decidua with enlarged SDZ. Analysis of cell cycle progression during decidualization both in vivo and in vitro demonstrates that the loss of FoxM1 elicits diploid cell deficiency with enhanced arrests prior to mitosis and concomitant upregulation of polyploidy. We further showed that Hoxa10 and cyclin D3, two decidual markers, control transcriptional regulation and intra-nuclear protein translocation of FoxM1 in polyploid cells, respectively. Overall, we suggest that proper regional decidualization and polyploidy development requires FoxM1 signaling downstream of Hoxa10 and cyclin D3.

Epigenetic changes through DNA methylation contribute to uterine stromal cell decidualization

Embryo-uterine interaction during early pregnancy critically depends on the coordinated expression of numerous genes at the site of implantation. The epigenetic mechanism through DNA methylation (DNM) plays a major role in the control of gene expression, although this regulatory event remains unknown in uterine implantation sites. Our analysis revealed the presence of DNA methyltransferase 1 (Dnmt1) in mouse endometrial cells on the receptive d 4 of pregnancy and early postattachment (d 5) phase, whereas Dnmt3a had lower abundant expression. Both Dnmt1 and Dnmt3a were coordinately expressed in decidual cells on d 6-8. 5-Methycytosine showed a similar expression pattern to that of Dnmt1. The preimplantation inhibition of DNM by 5-aza-2'-deoxycytodine was not antagonistic for embryonic attachment, although endometrial stromal cell proliferation at the site of implantation was down-regulated, indicating a disturbance with the postattachment decidualization event. Indeed, the peri- or postimplantation inhibition of DNM caused significant abrogation of decidualization, with concomitant loss of embryos. We next identified decidual genes undergoing alteration of DNM using methylation-sensitive restriction fingerprinting. One such gene, Chromobox homolog 4, an epigenetic regulator in the polycomb group protein family, exhibited hypomethylation in promoter DNA and increased expression with the onset of decidualization. Furthermore, inhibition of DNM resulted in enhanced expression of hypermethylated genes (Bcl3 and Slc16a3) in the decidual bed as compared with control, indicating aberration of gene expression may be associated with DNM-inhibition-induced decidual perturbation. Overall, these results suggest that uterine DNM plays a major role for successful decidualization and embryo development during early pregnancy.

Parathyroid hormone-related protein activates Wnt signaling to specify the embryonic mammary mesenchyme

Parathyroid hormone-related protein (PTHrP) regulates cell fate and specifies the mammary mesenchyme during embryonic development. Loss of PTHrP or its receptor (Pthr1) abolishes the expression of mammary mesenchyme markers and allows mammary bud cells to revert to an epidermal fate. By contrast, overexpression of PTHrP in basal keratinocytes induces inappropriate differentiation of the ventral epidermis into nipple-like skin and is accompanied by ectopic expression of Lef1, β-catenin and other markers of the mammary mesenchyme. In this study, we document that PTHrP modulates Wnt/β-catenin signaling in the mammary mesenchyme using a Wnt signaling reporter, TOPGAL-C. Reporter expression is completely abolished by loss of PTHrP signaling and ectopic reporter activity is induced by overexpression of PTHrP. We also demonstrate that loss of Lef1, a key component of the Wnt pathway, attenuates the PTHrP-induced abnormal differentiation of the ventral skin. To characterize further the contribution of canonical Wnt signaling to embryonic mammary development, we deleted β-catenin specifically in the mammary mesenchyme. Loss of mesenchymal β-catenin abolished expression of the TOPGAL-C reporter and resulted in mammary buds with reduced expression of mammary mesenchyme markers and impaired sexual dimorphism. It also prevented the ectopic, ventral expression of mammary mesenchyme markers caused by overexpression of PTHrP in basal keratinocytes. Therefore, we conclude that a mesenchymal, canonical Wnt pathway mediates the PTHrP-dependent specification of the mammary mesenchyme.

Endometrial stromal beta-catenin is required for steroid-dependent mesenchymal-epithelial cross talk and decidualization

BACKGROUND

Beta-catenin is part of a protein complex associated with adherens junctions. When allowed to accumulate to sufficient levels in its dephosphorylated form, beta-catenin serves as a transcriptional co-activator associated with a number of signaling pathways, including steroid hormone signaling pathways.

METHODS

To investigate the role of beta-catenin in progesterone (P₄) signaling and female reproductive physiology, conditional ablation of Ctnnb1 from the endometrial mesenchymal (i.e. stromal and myometrial), but not epithelial, compartment was accomplished using the Amhr2-Cre mice. Experiments were conducted to assess the ability of mutant female mice to undergo pregnancy and pseudopregnancy by or through oil-induced decidualization. The ability of uteri from mutant female mice to respond to estrogen (E₂) and P₄ was also determined.

RESULTS

Conditional deletion of Ctnnb1 from the mesenchymal compartment of the uterus resulted in infertility stemming, in part, from complete failure of the uterus to decidualize. E₂-stimulated epithelial cell mitosis and edematization were not altered in mutant uteri indicating that the mesenchyme is capable of responding to E₂. However, exposure of ovariectomized mutant female mice to a combined E₂ and P₄ hormone regimen consistent with early pregnancy revealed that mesenchymal beta-catenin is essential for indirectly opposing E₂-induced epithelial proliferation by P₄ and in some mice resulted in development of endometrial metaplasia. Lastly, beta-catenin is also required for the induced expression of genes that are known to play a fundamental role in decidualization such as Ihh, Ptch1, Gli1 and Muc1

CONCLUSIONS

Three salient points derive from these studies. First, the findings demonstrate a mechanistic linkage between the P₄ and beta-catenin signaling pathways. Second, they highlight an under appreciated role for the mesenchymal compartment in indirectly mediating P₄ signaling to the epithelium, a process that intimately involves mesenchymal beta-catenin. Third, the technical feasibility of deleting genes in the mesenchymal compartment of the uterus in an effort to understand decidualization and post-natal interactions with the overlying epithelium has been demonstrated. It is concluded that beta-catenin plays an integral role in selective P₄-directed epithelial-mesenchymal communication in both the estrous cycling and gravid uterus.

n-Butyl benzyl phthalate promotes breast cancer progression by inducing expression of lymphoid enhancer factor 1

Environmental hormones play important roles in regulating the expression of genes involved in cell proliferation, drug resistance, and breast cancer risk; however, their precise role in human breast cancer cells during cancer progression remains unclear. To elucidate the effect of the most widely used industrial phthalate, n-butyl benzyl phthalate (BBP), on cancer progression, we evaluated the results of BBP treatment using a whole human genome cDNA microarray and MetaCore software and selected candidate genes whose expression was changed by more than ten-fold by BBP compared with controls to analyze the signaling pathways in human breast cancer initiating cells (R2d). A total of 473 genes were upregulated, and 468 were downregulated. Most of these genes are involved in proliferation, epithelial-mesenchymal transition, and angiogenesis signaling. BBP induced the viability, invasion and migration, and tube formation in vitro, and Matrigel plug angiogenesis in vivo of R2d and MCF-7. Furthermore, the viability and invasion and migration of these cell lines following BBP treatment was reduced by transfection with a small interfering RNA targeting the mRNA for lymphoid enhancer-binding factor 1; notably, the altered expression of this gene consistently differentiated tumors expressing genes involved in proliferation, epithelial-mesenchymal transition, and angiogenesis. These findings contribute to our understanding of the molecular impact of the environmental hormone BBP and suggest possible strategies for preventing and treating human breast cancer.

The role of LEF1 in endometrial gland formation and carcinogenesis

Endometrial carcinoma is the most common gynecologic cancer, yet the mechanisms underlying this disease process are poorly understood. We hypothesized that Lef1 is required for endometrial gland formation within the uterus and is overexpressed in endometrial cancer. Using Lef1 knockout (KO) mice, we compared uterine gland development to wild-type (WT) controls, with respect to both morphology and expression of the Lef1 targets, cyclin D1 and MMP7. We characterized the dynamics of Lef1 protein expression during gland development and the mouse estrus cycle, by immunostaining and Western blot. Finally, we investigated the roles of cyclin D1 and MMP7 in gland and cancer formation in the mouse, and assessed the relevance of Lef1 to human cancer by comparing expression levels in cancerous and normal endometrial tissues. Lef1 upregulation in mouse endometrium correlates with the proliferative stages of the estrus cycle and gland development during the neonatal period. WT mice endometrial glands began to develop by day 5 and were easily identified by day 9, whereas Lef1 KO mice endometrial glands had not developed by day 9 although the endometrial lining was intact. We found that during gland development cyclin D1 is elevated and localized to the gland buds, and that this requires the presence of Lef1. We also noted that Lef1 protein was expressed at higher levels in endometrial cancers within mice and humans when compared to normal endometrium. Our loss-of-function data indicate that Lef1 is required for the formation of endometrial glands in the mouse uterus. Lef1 protein elevation corresponds to gland formation during development, and varies cyclically with the mouse estrus cycle, in parallel with gland regeneration. Finally, Lef1 is overexpressed in human and mouse endometrial tumors, consistent with it playing a role in gland proliferation.

Isoflavones as a smart curer for non-alcoholic fatty liver disease and pathological adiposity via ChREBP and Wnt signaling

OBJECTIVE

Non-alcoholic fatty liver disease (NAFLD) and pathological adiposity has emerged as an important modern disease. Along with this, the requirement for alternative and natural medicine for preventing NAFLD and adiposity has been increasing rapidly and considerably. In this report, we will review the biological effect and mechanisms of soy isoflavones on NAFLD and pathologic adiposity mainly through the novel pathways, de novo lipogenic carbohydrate responsive element binding protein (ChREBP) and anti-adipogenic Wnt signaling.

METHODS

This paper reviews in vitro and in vivo isoflavone studies published in 2002 to 2011 in North America and East Asia.

RESULTS

Collectively, the data support a beneficial relation of isoflavones and NAFLD and/or adiposity. Isoflavones suppress ChREBP signaling via protein kinase A (PKA) and/or 5'-AMP activated protein kinase (AMPK)-dependent phosphorylation, which prevents ChREBP from binding to the promoter regions of lipogenic enzyme. Furthermore, isoflavones directly stimulate Wnt signaling via estrogen receptors-dependent pathway, which inactivates glycogen synthase kinase-3 beta (GSK-3β), transactivate T-cell factor/lymphoid-enhancer factor (TCF/LEF), the effector of Wnt signaling, degrade adipogenic peroxisome proliferator-activated receptor γ (PPARγ), augment p300/CBP, the transcriptional co-activators of TCF/LEF.

CONCLUSIONS

Natural compound isoflavones may be useful alternative medicines in preventing NAFLD and pathological adiposity and this action may be partially associated with ChREBP and Wnt signaling.

Research resource: whole-genome estrogen receptor α binding in mouse uterine tissue revealed by ChIP-seq

To advance understanding of mechanisms leading to biological and transcriptional endpoints related to estrogen action in the mouse uterus, we have mapped ERα and RNA polymerase II (PolII) binding sites using chromatin immunoprecipitation followed by sequencing of enriched chromatin fragments. In the absence of hormone, 5184 ERα-binding sites were apparent in the vehicle-treated ovariectomized uterine chromatin, whereas 17,240 were seen 1 h after estradiol (E₂) treatment, indicating that some sites are occupied by unliganded ERα, and that ERα binding is increased by E₂. Approximately 15% of the uterine ERα-binding sites were adjacent to (<10 kb) annotated transcription start sites, and many sites are found within genes or are found more than 100 kb distal from mapped genes; however, the density (sites per base pair) of ERα-binding sites is significantly greater adjacent to promoters. An increase in quantity of sites but no significant positional differences were seen between vehicle and E₂-treated samples in the overall locations of ERα-binding sites either distal from, adjacent to, or within genes. Analysis of the PolII data revealed the presence of poised promoter-proximal PolII on some highly up-regulated genes. Additionally, corecruitment of PolII and ERα to some distal enhancer regions was observed. A de novo motif analysis of sequences in the ERα-bound chromatin confirmed that estrogen response elements were significantly enriched. Interestingly, in areas of ERα binding without predicted estrogen response element motifs, homeodomain transcription factor-binding motifs were significantly enriched. The integration of the ERα- and PolII-binding sites from our uterine sequencing of enriched chromatin fragments data with transcriptional responses revealed in our uterine microarrays has the potential to greatly enhance our understanding of mechanisms governing estrogen response in uterine and other estrogen target tissues.

Nucleolar Sik-similar protein (Sik-SP) is required for the maintenance of uterine estrogen signaling mechanism via ERα

Sik-similar protein (Sik-SP), a small nucleolar ribonucleoprotein, has been shown to be primarily involved in ribosome biogenesis. However, its role in the hormone-directed nuclear receptor signaling is largely unknown. Here, we provide novel evidence that Sik-SP is required for appropriate regulation of estrogen receptor (ER)α-mediated estradiol-17β (E2)-dependent uterine physiologic responses in mice. Studies by Western blotting using the newly developed antibodies for Sik-SP showed that this protein is up-regulated in both the ovariectomized wild-type and ERα null uteri by E2. Immunohistochemical analyses in uterine sections showed that this protein is induced in the epithelial and stromal cells. Coimmunoprecipitation studies revealed that E2 directs molecular interaction between Sik-SP and ERα. Furthermore, gel-mobility shift and chromatin immunoprecipitation analyses provided evidence that Sik-SP is recruited with ERα to estrogen-responsive uterine gene promoters. Overexpression of Sik-SP in vitro demonstrated a role for Sik-SP in cellular growth and viability. In a primary uterine epithelial-stromal coculture system, E2 exhibited early induction of Sik-SP in both the epithelial and stromal cells. Interestingly, suppression of Sik-SP in this coculture model, for the stromal but not epithelial cells, caused perturbation of E2-dependent proliferation in the epithelial cell layer. Similarly, in vivo uterine suppression of Sik-SP also caused inhibition of epithelial cell proliferation and aberrant prolongation of water imbibition in the late phase by E2. Finally, studies showed that Sik-SP is physiologically important during the onset of implantation by E2. In conclusion, Sik-SP, an early E2-responsive nucleolar protein, is necessary to induce E2-dependent ERα-mediated appropriate physiologic responses in the uterus.

Oestradiol regulates β-catenin-mediated transcription in neurones

Oestradiol acts in the brain by multiple mechanisms, including the regulation of transcriptional activity through classical oestrogen receptors, α and β, and by the activation of membrane/cytoplasm-initiated signalling cascades. In neuroblastoma cells, primary neurones in culture and in the brain in vivo, oestradiol activates the phosphoinositide 3-kinase/Akt/glycogen synthase kinase 3 signalling pathway by a mechanism involving oestrogen receptor α. Through this pathway, oestradiol regulates the stability of β-catenin, induces the translocation of β-catenin to the cell nucleus and regulates β-catenin-mediated transcription through the T cell factor/DNA complex. Genomic analyses in neuroblastoma cells have revealed that the set of genes regulated by oestradiol through β-catenin is not identical to that regulated by the Wnt signalling pathway, revealing a new mechanism for oestradiol signalling in neurones.

Mouse primary uterine cell coculture system revisited: ovarian hormones mimic the aspects of in vivo uterine cell proliferation

Previously, the uterine epithelial-stromal coculture system had limited success mimicking in vivo ovarian hormone-dependent cell-specific proliferation. Here, we established a mouse primary uterine coculture system, in which cells collected in pseudopregnancy specifically on d 4 are conducive to supporting hormone-induced cell-specific proliferation. When two cell types are placed in coculture without direct contact via cell culture inserts (nonadjacent), as opposed to with contact (adjacent), epithelial cells exhibit significant proliferation by estradiol-17β (E2), whereas progesterone in combination with E2 caused inhibition of epithelial cell proliferation and a major shift in proliferation from epithelial to stromal cells. Epithelial cell integrity, with respect to E-cadherin expression, persisted in nonadjacent, but not adjacent, conditions. In subsequent studies of nonadjacent cocultures, localization of estrogen receptor (ER)α and progesterone receptor (PR), but not ERβ, appeared to be abundant, presumably indicating that specific ER or PR coregulator expression might be responsible for this difference. Consistently, an agonist of ERα, but not ERβ, was supportive of proliferation, and antagonists of ER or PR totally eliminated cell-specific proliferation by hormones. RT-PCR analyses also revealed that hormone-responsive genes primarily exhibit appropriate regulation. Finally, suppression of immunoglobulin heavy chain binding protein, a critical regulator of ERα signaling, in epithelial and/or stromal cells caused dramatic inhibition of E2-dependent epithelial cell proliferation, suggesting that a molecular perturbation approach is applicable to mimic in vivo uterine control. In conclusion, our established coculture system may serve as a useful alternative model to explore in vivo aspects of cell proliferation via communication between the epithelial and stromal compartments under the direction of ovarian hormones.

GPR30 activation opposes estrogen-dependent uterine growth via inhibition of stromal ERK1/2 and estrogen receptor alpha (ERα) phosphorylation signals

Although estradiol-17β (E2)-regulated early and late phase uterine responses have been well defined, the molecular mechanisms linking the phases remain poorly understood. We have previously shown that E2-regulated early signals mediate cross talk with estrogen receptor (ER)-α to elicit uterine late growth responses. G protein-coupled receptor (GPR30) has been implicated in early nongenomic signaling mediated by E2, although its role in E2-dependent uterine biology is unclear. Using selective activation of GPR30 by G-1, we show here a new function of GPR30 in regulating early signaling events, including the inhibition of ERK1/2 and ERα (Ser118) phosphorylation signals and perturbation of growth regulation under the direction of E2 in the mouse uterus. We observed that GPR30 primarily localizes in the uterine epithelial cells, and its activation alters gene expression and mediates inhibition of ERK1/2 and ERα (Ser118) phosphorylation signals in the stromal compartment, suggesting a paracrine signaling is involved. Importantly, viral-driven manipulation of GPR30 or pharmacological inhibition of ERK1/2 activation effectively alters E2-dependent uterine growth responses. Overall, GPR30 is a negative regulator of ERα-dependent uterine growth in response to E2. Our work has uncovered a novel GPR30-regulated inhibitory event, which may be physiologically relevant in both normal and pathological situations to negatively balance ERα-dependent uterine growth regulatory functions induced by E2.

Estrogenic activity of bisphenol A and 2,2-bis(p-hydroxyphenyl)-1,1,1-trichloroethane (HPTE) demonstrated in mouse uterine gene profiles

BACKGROUND

Interest and concern regarding potentially estrogenic substances have resulted in development of model systems to evaluate mechanisms of such chemicals. Microarray studies have indicated that estradiol (E2)-stimulated uterine responses can be divided into early and late phases. Comparison of E2 uterine transcript profiles and those of other estrogenic chemicals of interest in vivo indicates mechanisms and activities of test compounds.

OBJECTIVES

We compared transcript responses and mechanisms of response using mouse reproductive tracts after treatment with E2, estriol (E3), bisphenol A (BPA), and 2,2-bis(p-hydroxyphenyl)-1,1,1-trichloroethane (HPTE).

METHODS

Uterine RNA from ovariectomized wild-type mice, estrogen receptor α (ERα) knockout (αERKO) mice, and mice expressing a DNA-binding-deficient ERα (KIKO) treated with E2, E3, BPA, or HPTE for 2 or 24 hr was analyzed by microarray. Resulting regulated transcripts were compared by hierarchical clustering and correlation analysis, and response patterns were verified by reverse-transcription real-time polymerase chain reaction (RT-PCR).

RESULTS

Both xenoestrogens, BPA and HPTE, showed profiles highly correlated to that of E2 in the early response phase (2 hr), but the correlation diminished in the later response phase (24 hr), similar to the known weak estrogen E3. Both xenoestrogens also mimicked E2 in samples from KIKO mice, indicating that they are able to utilize the indirect tethering mode of ERα signaling. No response was detected in ERα-null uteri, indicating that ERα mediates the responses.

CONCLUSION

Our study forms a basis on which patterns of response and molecular mechanisms of potentially estrogenic chemicals can be assessed.

Genistein and daidzein repress adipogenic differentiation of human adipose tissue-derived mesenchymal stem cells via Wnt/β-catenin signalling or lipolysis

OBJECTIVES

One aspect of the effects of isoflavones against fat deposition might be at least associated with the mechanism by which Wnt/β-catenin signalling inhibits adipocyte differentiation. However, it remains completely unknown as to whether isoflavones might influence Wnt signalling during commitment of pluripotent mesenchymal stem cells (MSCs) to adipose lineages. In the present study, we have investigated the mechanisms underlying effects of genistein and daidzein, the major soy isoflavones, on anti-adipogenic Wnt/β-catenin signalling.

MATERIALS AND METHODS

Adipose tissue-derived (AD) MSCs were exposed continuously to genistein and daidzein (0.01-100 μm) during adipogenic differentiation (21 days). An oestrogen antagonist, ICI 182,780, was used to determine whether or not the isoflavones activated Wnt signalling via oestrogen receptors (ERs).

RESULTS

Genistein and daidzein suppressed adipogenic differentiation of AD-MSCs in a dose-dependent manner and inhibited expression of adipogenic markers, PPARγ, SREBP-1c and Glut 4, from mid-phase differentiation. Microarrays showed that anti-adipogenic effects of genistein were principally attributable to activation of Wnt signalling via ERs-dependent pathway, such as Erk/JNK signalling and LEF/TCF4 co-activators. These findings were supported by evidence that the effects of genistein were offset by ICI182,780. Unlike genistein, daidzein inhibited adipogenesis through stimulation of lipolysis, with for example, PKA-mediated hormone sensitive lipase. This is consistent with the increase in glycerol released from AD-MSCs. In conclusion, understanding that different sets of mechanisms of the two isoflavones on adipogenesis will help the design of novel strategies to prevent observed current epidemic levels of obesity, using isoflavones.

Wnt signalling in implantation, decidualisation and placental differentiation--review

The family of secreted Wingless ligands plays major roles in embryonic development, stem cell maintenance, differentiation and tissue homeostasis. Accumulating evidence suggests that the canonical Wnt pathway involving nuclear recruitment of β-catenin and activation of Wnt-dependent transcription factors is also critically involved in development and differentiation of the diverse reproductive tissues. Here, we summarise our present knowledge about expression, regulation and function of Wnt ligands and their frizzled receptors in murine and human endometrial and placental cell types. In mice, Wnt signalling promotes early trophoblast lineage development, blastocyst activation, implantation and chorion-allantois fusion. Moreover, different Wnt ligands play essential roles in the development of the murine uterine tract, in cycling endometrial cells and during decidualisation. In humans, estrogen-dependent endometrial cell proliferation, decidualisation, trophoblast attachment and invasion were shown to be controlled by the particular signalling pathway. Failures in Wnt signalling are associated with infertility, endometriosis, endometrial cancer and gestational diseases such as complete mole placentae and choriocarcinomas. However, our present knowledge is still scarce due to the complexity of the Wnt network involving numerous ligands, receptors and non-canonical pathways. Hence, much remains to be learned about the role of different Wnt signalling cascades in reproductive cell types and their changes under pathological conditions.

Estrogen-mediated regulation of Igf1 transcription and uterine growth involves direct binding of estrogen receptor alpha to estrogen-responsive elements

Estrogen enables uterine proliferation, which depends on synthesis of the IGF1 growth factor. This proliferation and IGF1 synthesis requires the estrogen receptor (ER), which binds directly to target DNA sequences (estrogen-responsive elements or EREs), or interacts with other transcription factors, such as AP1, to impact transcription. We observe neither uterine growth nor an increase in Igf1 transcript in a mouse with a DNA-binding mutated ER alpha (KIKO), indicating that both Igf1 regulation and uterine proliferation require the DNA binding function of the ER. We identified several potential EREs in the Igf1 gene, and chromatin immunoprecipitation analysis revealed ER alpha binding to these EREs in wild type but not KIKO chromatin. STAT5 is also reported to regulate Igf1; uterine Stat5a transcript is increased by estradiol (E(2)), but not in KIKO or alpha ERKO uteri, indicating ER alpha- and ERE-dependent regulation. ER alpha binds to a potential Stat5a ERE. We hypothesize that E(2) increases Stat5a transcript through ERE binding; that ER alpha, either alone or together with STAT5, then acts to increase Igf1 transcription; and that the resulting lack of IGF1 impairs KIKO uterine growth. Treatment with exogenous IGF1, alone or in combination with E(2), induces proliferation in wild type but not KIKO uteri, indicating that IGF1 replacement does not rescue the KIKO proliferative response. Together, these observations suggest in contrast to previous in vitro studies of IGF-1 regulation involving AP1 motifs that direct ER alpha-DNA interaction is required to increase Igf1 transcription. Additionally, full ER alpha function is needed to mediate other cellular signals of the growth factor for uterine growth.

Selective disruption of ER{alpha} DNA-binding activity alters uterine responsiveness to estradiol

In vitro models have been used to demonstrate that estrogen receptors (ERs) can regulate estrogen-responsive genes either by directly interacting with estrogen-responsive element (ERE) DNA motifs or by interacting with other transcription factors such as AP1. In this study, we evaluated estrogen (E(2))-dependent uterine gene profiles by microarray in the KIKO mouse, an in vivo knock-in mouse model that lacks the DNA-binding function of ERalpha and is consequently restricted to non-ERE-mediated responses. The 2- or 24-h E(2)-mediated uterine gene responses were distinct in wild-type (WT), KIKO, and alphaERKO genotypes, indicating that unique sets of genes are regulated by ERE and non-ERE pathways. After 2 h E(2) treatment, 38% of the WT transcripts were also regulated in the KIKO, demonstrating that the tethered mechanism does operate in this in vivo model. Surprisingly, 1438 E(2)-regulated transcripts were unique in the KIKO mouse and were not seen in either WT or alphaERKO. Pathway analyses revealed that some canonical pathways, such as the Jak/Stat pathway, were affected in a similar manner by E(2) in WT and KIKO. In other cases, however, the WT and KIKO differed. One example is the Wnt/beta-catenin pathway; this pathway was impacted, but different members of the pathway were regulated by E(2) or were regulated in a different manner, consistent with differences in biological responses. In summary, this study provides a comprehensive analysis of uterine genes regulated by E(2) via ERE and non-ERE pathways.

Estradiol activates beta-catenin dependent transcription in neurons

Estradiol may fulfill a plethora of functions in neurons, in which much of its activity is associated with its capacity to directly bind and dimerize estrogen receptors. This hormone-protein complex can either bind directly to estrogen response elements (ERE's) in gene promoters, or it may act as a cofactor at non-ERE sites interacting with other DNA-binding elements such as AP-1 or c-Jun. Many of the neuroprotective effects described for estrogen have been associated with this mode of action. However, recent evidence suggests that in addition to these “genomic effects”, estrogen may also act as a more general “trophic factor” triggering cytoplasmic signals and extending the potential activity of this hormone. We demonstrated that estrogen receptor alpha associates with β-catenin and glycogen synthase kinase 3 in the brain and in neurons, which has since been confirmed by others. Here, we show that the action of estradiol activates β-catenin transcription in neuroblastoma cells and in primary cortical neurons. This activation is time and concentration-dependent, and it may be abolished by the estrogen receptor antagonist ICI 182780. The transcriptional activation of β-catenin is dependent on lymphoid enhancer binding factor-1 (LEF-1) and a truncated-mutant of LEF-1 almost completely blocks estradiol TCF-mediated transcription. Transcription of a TCF-reporter in a transgenic mouse model is enhanced by estradiol in a similar fashion to that produced by Wnt3a. In addition, activation of a luciferase reporter driven by the engrailed promoter with three LEF-1 repeats was mediated by estradiol. We established a cell line that constitutively expresses a dominant-negative LEF-1 and it was used in a gene expression microarray analysis. In this way, genes that respond to estradiol or Wnt3a, sensitive to LEF-1, could be identified and validated. Together, these data demonstrate the existence of a new signaling pathway controlled by estradiol in neurons. This pathway shares some elements of the insulin-like growth factor-1/Insulin and Wnt signaling pathways, however, our data strongly suggest that it is different from that of both these ligands. These findings may reveal a set of new physiological roles for estrogens, at least in the Central Nervous System (CNS).

Embryo-uterine cross-talk during implantation: the role of Wnt signaling

During mammalian pregnancy, it has been demonstrated that the quality of embryo implantation determines the quality of ongoing pregnancy and fetal development. Recent studies have provided increasing evidence that differential Wnt signaling plays diverse roles in multiple peri-implantation events. This review focuses on recent progress on various aspects of Wnt signaling in preimplantation embryo development, blastocyst activation for implantation and uterine decidualization. Future studies with conditional deletion of Wnt family members are hoped to provide deeper insight on the pathophysiological significance of Wnt proteins on early pregnancy events.