Promoter CpG methylation of Hox-a10 and Hox-a11 in mouse uterus not altered upon neonatal diethylstilbestrol exposure

Maternal exposure to di(2-ethylhexyl) phthalate (DEHP) causes multigenerational adverse effects on the uterus of F1 and F2 offspring rats

Phthalates are one of the ubiquitous chemicals found in day-to-day products like food packaging, children's toys, and other consumer commodities. There is rising concern that repeated exposure to phthalates during pregnancy and lactation could have long-term effects on maternal and fetal health. We hypothesize that exposure to DEHP during the developmental windows might affect the expression of molecules that regulate uterine function and that this effect would be passed on to further generations. Rat dams were treated with olive oil (vehicle) or DEHP (100 mg/kg b.wt./day) orally from gestational day 9 (GD 9) to the end of lactation (PND 21). F₀ maternal DEHP exposure resulted in multigenerational (F₁ and F₂) reproductive toxicity, as evidenced by an extended estrous cycle, decreased mating, fertility, and fecundity indices. Serum progesterone and estradiol levels were decreased and their cognate receptors (PR and ERα) in the uterus were decreased in the DEHP-exposed offspring rats. Further analysis of the expression of estrogen and progesterone regulatory genes such as Hox a11, VEGF A, Ihh, LIFR, EP4, PTCH, NR2F2, BMP2, and Wnt4 were reduced in the uteri of adult F₁ and F₂ generation rats born from DEHP-exposed F₀ dams. Decreased expression of these crucial proteins due to DEHP exposure may lead to defects in epithelial proliferation and secretion, uterine receptivity, and decidualization in the uteri of successive generations. This study showed that maternal DEHP exposure impairs the expression of molecules that regulate uterine function and this multigenerational effect is transmitted via maternal lineage.

Disruption of developmental programming with long-term consequences after exposure to a glyphosate-based herbicide in a rat model

Glyphosate-based herbicides (GBHs) have been associated with endocrine disrupting effects on reproductive organs. We examined whether postnatal exposure to GBH affects developmental programming of the uterus with long-term consequences. Female Wistar pups received vehicle (control) or GBH (2 mg of glyphosate/kg/day) from postnatal day (PND) 1 to PND7, where the developing uterus is highly sensitive to endocrine disruption. Short-, mid- and long-term effects were evaluated on PND8, PND120 and PND600, respectively. GBH induced hyperplasia and epigenetic alterations in the uterus of neonatal females (PND8). DNA hypermethylation, enrichment of H3K9me3 and reductions of H3K27me3 at regulatory regions of the morphoregulatory gene Hoxa10 resulted in gene downregulation. In young adult females (PND120), GBH increased 17β-estradiol (E2) and decreased progesterone (P4) serum levels, altering estrous cyclicity. Aged females (PND600) exposed to GBH developed leiomyoma and pre-neoplastic glandular lesions in the uterus. Vaginal rhabdomyosarcoma and intrahepatic bile duct adenoma were also observed. In conclusion, neonatal exposure to GBH altered the expression and induced hypermethylation of the Hoxa10 gene in uterine tissue at early life, and increased E2/P4 ratio serum level at middle-age. We propose that epigenetic reprogramming of Hoxa10 in association with hormonal imbalance could be among the possible mechanisms underlying the long-term adverse effects detected in GBH-exposed rats.

Homeobox genes for embryo implantation: From mouse to human

The proper development of uterus to a state of receptivity and the attainment of implantation competency for blastocyst are 2 indispensable aspects for implantation, which is considered to be a critical event for successful pregnancy. Like many developmental processes, a large number of transcription factors, such as homeobox genes, have been shown to orchestrate this complicated but highly organized physiological process during implantation. In this review, we focus on progress in studies of the role of homeobox genes, especially the Hox and Msx gene families, during implantation, together with subsequent development of post-implantation uterus and related reproductive defects in both mouse models and humans, that have led to better understanding of how implantation is precisely regulated and provide new insights into infertility.

Epigenetics and epidemiology: models of study and examples

Epidemiological studies have successfully identified several environmental causes of disease, but often these studies are limited by methodological problems (e.g. lack of sensitivity and specificity in exposure assessment; confounding). Proposed approaches to improve observational studies of environmental associations are Mendelian randomization and the meet-in-the-middle (MITM) approach. The latter uses signals from the growing field of -omics as putative intermediate biomarkers in the pathogenetic process that links exposure with disease. The first part of this approach consists in the association between exposure and disease. The next step consists in the study of the relationship between (biomarkers of) exposure and intermediate -omic biomarkers of early effect; thirdly, the relation between the disease outcome and intermediate -omic biomarkers is assessed. We propose that when an association is found in all three steps it is possible that there is a casual association. One of the associations that have been investigated extensively in the recent years but is not completely understood is that between environmental endocrine disruptors and breast cancer. Here we present an example of how the "meet-in-the-middle" approach can be used to address the role of endocrine disruptors, by reviewing the relevant literature.

Towards incorporating epigenetic mechanisms into carcinogen identification and evaluation

Remarkable progress in the field of epigenetics has turned academic, medical and public attention to the potential applications of these new advances in medicine and various fields of biomedical research. The result is a broader appreciation of epigenetic phenomena in the a etiology of common human diseases, most notably cancer. These advances also represent an exciting opportunity to incorporate epigenetics and epigenomics into carcinogen identification and safety assessment. Current epigenetic studies, including major international sequencing projects, are expected to generate information for establishing the 'normal' epigenome of tissues and cell types as well as the physiological variability of the epigenome against which carcinogen exposure can be assessed. Recently, epigenetic events have emerged as key mechanisms in cancer development, and while our search of the Monograph Volume 100 revealed that epigenetics have played a modest role in evaluating human carcinogens by the International Agency for Research on Cancer (IARC) Monographs so far, epigenetic data might play a pivotal role in the future. Here, we review (i) the current status of incorporation of epigenetics in carcinogen evaluation in the IARC Monographs Programme, (ii) potential modes of action for epigenetic carcinogens, (iii) current in vivo and in vitro technologies to detect epigenetic carcinogens, (iv) genomic regions and epigenetic modifications and their biological consequences and (v) critical technological and biological issues in assessment of epigenetic carcinogens. We also discuss the issues related to opportunities and challenges in the application of epigenetic testing in carcinogen identification and evaluation. Although the application of epigenetic assays in carcinogen evaluation is still in its infancy, important data are being generated and valuable scientific resources are being established that should catalyse future applications of epigenetic testing.

Dietary folate deficiency in pseudopregnant mice has no effect on homeobox A10 promoter methylation or expression

During the reproductive cycle, a number of genes controlling endometrial changes are regulated by DNA methylation, a common epigenetic modification. Because dietary folate affects DNA methylation, we determined whether a folate-deficient diet (FDD) alters DNA methylation in endometria of pseudopregnant mice, focusing on the homeobox A10 (Hoxa10) promoter. Mice were given an FDD or control diet for 40 to 45 days and examined on day 5 of pseudopregnancy. Compared to control mice, FDD mice had lower folate levels in liver and serum (P = .004). However, the FDD did not significantly affect DNA methylation within the cytosine-guanine dinucleotide (CpG)-rich Hoxa10 promoter, even when specific CpG sites were examined (P > .05). In endometrial tissue sections, the localization of anti-Hoxa10 staining was unchanged in FDD mice. Therefore, folate deficiency did not significantly affect promoter methylation or expression of Hoxa10.

Transgenerational neuroendocrine disruption of reproduction

Exposure to endocrine disrupting chemicals (EDCs) is associated with dysfunctions of metabolism, energy balance, thyroid function and reproduction, and an increased risk of endocrine cancers. These multifactorial disorders can be 'programmed' through molecular epigenetic changes induced by exposure to EDCs early in life, the expression of which may not manifest until adulthood. In some cases, EDCs have detrimental effects on subsequent generations, which indicates that traits for disease predisposition may be passed to future generations by nongenomic inheritance. This Review discusses current understanding of the epigenetic mechanisms that underlie sexual differentiation of reproductive neuroendocrine systems in mammals and summarizes the literature on transgenerational epigenetic effects of representative EDCs: vinclozolin, diethylstilbesterol, bisphenol A and polychlorinated biphenyls. The article differentiates between context-dependent epigenetic transgenerational changes--namely, those that require environmental exposure, either via the EDC itself or through behavioral or physiological differences in parents--and germline-dependent epigenetic mechanisms. These processes, albeit discrete, are not mutually exclusive and can involve similar molecular mechanisms including DNA methylation and histone modifications and may predispose exposed individuals to transgenerational disruption of reproductive processes. New insights stress the crucial need to develop a clear understanding of how EDCs may program the epigenome of exposed individuals and their descendants.

Epigenetic effects of endocrine-disrupting chemicals on female reproduction: an ovarian perspective

The link between in utero and neonatal exposure to environmental toxicants, such as endocrine-disrupting chemicals (EDCs) and adult female reproductive disorders is well established in both epidemiological and animal studies. Recent studies examining the epigenetic mechanisms involved in mediating the effects of EDCs on female reproduction are gathering momentum. In this review, we describe the developmental processes that are susceptible to EDC exposures in female reproductive system, with a special emphasis on the ovary. We discuss studies with select EDCs that have been shown to have physiological and correlated epigenetic effects in the ovary, neuroendocrine system, and uterus. Importantly, EDCs that can directly target the ovary can alter epigenetic mechanisms in the oocyte, leading to transgenerational epigenetic effects. The potential mechanisms involved in such effects are also discussed.

Endocrine disruptors in female reproductive tract development and carcinogenesis

Growing concerns over endocrine disrupting chemicals (EDCs) and their effects on human fetal development and adult health have promoted research into the underlying molecular mechanisms of endocrine disruption. Gene targeting technology has allowed insight into the genetic pathways governing reproductive tract development and how exposure to EDCs during a critical developmental window can alter reproductive tract development, potentially forming the basis for adult diseases. This review primarily uses diethylstilbestrol (DES) as a model agent for EDCs and discusses the recent progress elucidating how DES and other EDCs affect murine female reproductive tract development and cancer at the molecular level.

Hypermethylation of homeobox A10 by in utero diethylstilbestrol exposure: an epigenetic mechanism for altered developmental programming

Diethylstilbestrol (DES) is a nonsteroidal estrogen that induces developmental anomalies of the female reproductive tract. The homeobox gene HOXA10 controls uterine organogenesis, and its expression is altered after in utero DES exposure. We hypothesized that an epigenetic mechanism underlies DES-mediated alterations in HOXA10 expression. We analyzed the expression pattern and methylation profile of HOXA10 after DES exposure. Expression of HOXA10 is increased in human endometrial cells after DES exposure, whereas Hoxa10 expression is repressed and shifted caudally from its normal location in mice exposed in utero. Cytosine guanine dinucleotide methylation frequency in the Hoxa10 intron was higher in DES-exposed offspring compared with controls (P = 0.017). The methylation level of Hoxa10 was also higher in the caudal portion of the uterus after DES exposure at the promoter and intron (P < 0.01). These changes were accompanied by increased expression of DNA methyltransferases 1 and 3b. No changes in methylation were observed after in vitro or adult DES exposure. DES has a dual mechanism of action as an endocrine disruptor; DES functions as a classical estrogen and directly stimulates HOXA10 expression with short-term exposure, however, in utero exposure results in hypermethylation of the HOXA10 gene and long-term altered HOXA10 expression. We identify hypermethylation as a novel mechanism of DES-induced altered developmental programming.

Lifestyle, genes, and cancer

It is estimated that almost 1.5 million people in the USA are diagnosed with cancer every year. However, due to the substantial effect of modifiable lifestyle factors on the most prevalent cancers, it has been estimated that 50% of cancer is preventable. Physical activity, weight loss, and a reduction in alcohol use can strongly be recommended for the reduction of breast cancer risk. Similarly, weight loss, physical activity, and cessation of tobacco use are important behavior changes to reduce colorectal cancer risk, along with the potential benefit for the reduction of red meat consumption and the increase in folic acid intake. Smoking cessation is still the most important prevention intervention for reducing lung cancer risk, but recent evidence indicates that increasing physical activity may also be an important prevention intervention for this disease. The potential benefit of lifestyle change to reduce prostate cancer risk is growing, with recent evidence indicating the importance of a diet rich in tomato-based foods and weight loss. Also, in the cancers for which there are established lifestyle risk factors, such as physical inactivity for breast cancer and obesity for colorectal cancer, there is emerging information on the role that genetics plays in interacting with these factors, as well as the interaction of combinations of lifestyle factors. Integration of genetic information into lifestyle factors can help to clarify the causal relationships between lifestyle and genetic factors and assist in better identifying cancer risk, ultimately leading to better-informed choices about effective methods to enhance health and prevent cancer.

Persistent hypomethylation in the promoter of nucleosomal binding protein 1 (Nsbp1) correlates with overexpression of Nsbp1 in mouse uteri neonatally exposed to diethylstilbestrol or genistein

Neonatal exposure of CD-1 mice to diethylstilbestrol (DES) or genistein (GEN) induces uterine adenocarcinoma in aging animals. Uterine carcinogenesis in this model is ovarian dependent because its evolution is blocked by prepubertal ovariectomy. This study seeks to discover novel uterine genes whose expression is altered by such early endocrine disruption via an epigenetic mechanism. Neonatal mice were treated with 1 or 1000 microg/kg DES, 50 mg/kg GEN, or oil (control) on d 1-5. One group of treated mice was killed before puberty on d 19. Others were ovariectomized or left intact, and killed at 6 and 18 months of age. Methylation-sensitive restriction fingerprinting was performed to identify differentially methylated sequences associated with neonatal exposure to DES/GEN. Among 14 candidates, nucleosomal binding protein 1 (Nsbp1), the gene for a nucleosome-core-particle binding protein, was selected for further study because of its central role in chromatin remodeling. In uteri of immature control mice, Nsbp1 promoter CpG island (CGI) was minimally methylated. Once control mice reached puberty, the Nsbp1 CGI became hypermethylated, and gene expression declined further. In contrast, in neonatal DES/GEN-treated mice, the Nsbp1 CGI stayed anomalously hypomethylated, and the gene exhibited persistent overexpression throughout life. However, if neonatal DES/GEN-treated mice were ovariectomized before puberty, the CGI remained minimally to moderately methylated, and gene expression was subdued except in the group treated with 1000 microg/kg DES. Thus, the life reprogramming of uterine Nsbp1 expression by neonatal DES/GEN exposure appears to be mediated by an epigenetic mechanism that interacts with ovarian hormones in adulthood.

Developmental exposure to Bisphenol a impairs the uterine response to ovarian steroids in the adult

Morphoregulator genes like members of the Hox gene family regulate uterine development and are associated with endocrine-related processes such as endometrial proliferation and differentiation in the adult uterus. Exposure to neonatal endocrine disruptors could affect signaling events governed by Hox genes, altering the developmental trajectory of the uterus with lasting consequences. We investigated whether neonatal exposure to bisphenol A (BPA) alters Hoxa10 and Hoxa11 mRNA uterine expression shortly after treatment as well as in the adult. Moreover, we studied whether xenoestrogen exposure may affect the adult uterine response to hormonal stimuli. Newborn females received vehicle, 0.05 mg/kg.d BPA, 20 mg/kg*d BPA, or diethylstilbestrol (0.2 microg/kg*d) on postnatal d 1, 3, 5, and 7). At postnatal d 8, real time RT-PCR assays showed a decrease in Hoxa10 and Hoxa11 expression in all xenoestrogen-treated groups. To evaluate the long-term effects, we used adult ovariectomized rats with hormonal replacement. The subepithelial stroma in BPA- and diethylstilbestrol-treated animals showed an impaired proliferative response to steroid treatment associated with a silencing of Hoxa10 but not associated with changes in the methylation pattern of the Hoxa10 promoter. BPA animals showed that the Hoxa10 reduction was accompanied by an increased stromal expression of the silencing mediator for retinoic acid and thyroid hormone receptor. The spatial coexpression of steroid receptors Hoxa10 and silencing mediator for retinoic acid and thyroid hormone receptor was established using immunofluorescence. Our data indicate that postnatal BPA exposure affects the steroid hormone-responsiveness of uterine stroma in adulthood. Whether this impaired hormonal response is associated with effects on uterine receptivity and decidualization is currently under investigation.

Experimental murine endometriosis induces DNA methylation and altered gene expression in eutopic endometrium

The eutopic endometrium in women with endometriosis demonstrates diminished endometrial receptivity and altered gene expression. It is unknown if the endometrium being defective gives rise to a predisposition toward endometriosis and infertility or, alternatively, if endometriosis causes the altered endometrial receptivity. Here we created experimental endometriosis in mice and examined the expression of several markers of endometrial receptivity in the eutopic endometrium. Methylation of Hoxa10 was also evaluated as a potential mechanism responsible for altered gene expression. Expression of each gene was measured using quantitative real-time RT-PCR at 14 wk after induction of endometriosis. Expression of Hoxa10 and Hoxa11, which are necessary for endometrial receptivity, were decreased in the endometriosis group. Insulin-like growth factor binding protein-1 (Igfbp1) mRNA was decreased in the endometriosis group. However, there was no change in Integrin beta3 (Itgb3) mRNA expression. Total progesterone receptor (Pgr-AB) was increased in the endometriosis group and the ratio of Pgr-B to Pgr-AB was increased, indicating a shift from Pgr-A to Pgr-B expression. Basic transcription element-binding protein-1 (Bteb1), official symbol and name Klf9, Kruppel-like factor 9, which functionally interacts with Pgr in endometrium, was also decreased in the endometriosis group. In addition, hypermethylation of Hoxa10 in the endometriosis group was shown by methylation-specific PCR and confirmed by bisulfite sequencing. These findings demonstrate that normal endometrium, when placed in an ectopic location to create experimental endometriosis, led to characteristic changes in gene expression in eutopic endometrium. These data suggest the existence of a signal conduction pathway from endometriosis that alters endometrial gene expression through altered Pgr signaling and epigenetic programming.

Transcription factors GATA-1 and Fli-1 regulate human HOXA10 expression in megakaryocytic cells

HOXA10 is a member of the HOX family of regulatory genes that are involved in hematopoiesis. Its role in megakaryopoiesis has been suggested by its expression in immature megakaryocytes and by the proliferation of megakaryocyte-primitive blast colonies upon HOXA10 overexpression. We sought to understand the role of HOXA10 in megakaryopoiesis better, by investigating its transcriptional regulation. Analysis of the 5' untranslated region and transfection of promoter/plasmids into human tissue culture cell lines identified transcriptionally active sequences that contain GATA-1 and Ets-1 sites and a putative binding site for its neighboring gene, HOXA11. Gel shift assays confirmed protein-DNA interactions at these sites. Mutation of the GATA-1 and the Ets-1 motifs amplified the expression of HOXA10 in HEL and K562 cells, confirming the importance of these cis-acting elements in regulating HOXA10 expression in megakaryocytic cells. Chromatin immunoprecipitation (ChIP) and chloramphenicol acetyl transferase (CAT) assays confirm that HOXA11 binds to the putative binding site, resulting in repression of HOXA10 expression. These data taken together give insight into the regulation of HOXA10 expression in megakaryocytic differentiation.

Absence of uterine tumours in CD-1 mice treated neonatally with subcutaneous tamoxifen or 4-hydroxyoestradiol

The effects of subcutaneous dosing of neonatal CD-1 mice with tamoxifen on days 1-5 after birth at doses of 0, 5, 10, 25 or 50 microg/pup or with 4-hydroxyoestradiol at 2 microg/pup have been investigated. Animals were culled at 1.5, 3, 6, 12 and 18 months after dosing and changes in uterine and ovarian pathology examined. Results showed both compounds to result in uterine hypoplasia relative to controls. At 18 months after dosing in the uterus, there was a fairly marked atrophy of the muscle layer, mild to moderate glandular hyperplasia of the endometrium even though these irregularly shaped glands did not penetrate through the myometrium and no adenocarcinomas were detected. At 18 months after dosing, oviducts showed mild focal adenomatous changes characterized by penetration epithelial hyperplasia, changes similar to those previously reported as 'diverticulosis and salpingitis isthmica nodosa' following diethylstilbestrol treatment of mice. At this time, both tamoxifen and 4-hydroxyoestradiol also affected the ovaries which showed a paucity of follicles and no corpora lutea, suggesting that there had been disruption to the oestrus cycle, particularly with tamoxifen at the highest dose where the ovaries of mice contained no developing follicles. At 18 months, control mice were cycling normally. Results failed to substantiate that tamoxifen and 4-hydroxyoestradiol are uterine carcinogens in this neonatal mouse model.

Role of physical activity in modulating breast cancer risk as defined by APC and RASSF1A promoter hypermethylation in nonmalignant breast tissue

Physical activity reduces breast cancer risk. Promoter hypermethylation of the tumor suppressor genes APC and RASSF1A, which is potentially reversible, is associated with breast cancer risk. We conducted a cross-sectional study in 45 women without breast cancer to determine the association of physical activity with promoter hypermethylation of APC and RASSF1A in breast tissue. We used quantitative methylation-specific PCR to test the methylation status of APC and RASSF1A, and questionnaires to assess study covariates and physical activity (measured in metabolic equivalent hours per week). In univariate analyses, the study covariate, benign breast biopsy number, was positively associated with promoter hypermethylation of APC (P = 0.01) but not RASSF1A. Mulitvariate logistic regression indicated that, although not significant, physical activities for a lifetime [odds ratio (OR), 0.57; 95% confidence interval (95% CI), 0.22-1.45; P = 0.24], previous 5 years (OR, 0.62; 95% CI, 0.34-1.12; P = 0.11), and previous year (OR, 0.72; 95% CI, 0.43-1.22; P = 0.22) were inversely related to promoter hypermethylation of APC but not RASSF1A for all physical activity measures. Univariate logistic regression indicated that physical activities for a lifetime, previous 5 years, and previous year were inversely associated with benign breast biopsy number, and these results were approaching significance for lifetime physical activity (OR, 0.41; 95% CI, 0.16-1.01; P = 0.05) and significant for physical activity in the previous 5 years (OR, 0.57; 95% CI, 0.34-0.94; P = 0.03). The study provides indirect evidence supporting the hypothesis that physical activity is inversely associated with promoter hypermethylation of tumor suppressor genes, such as APC, in nonmalignant breast tissue.

Cancer Susceptibility: Epigenetic Manifestation of Environmental Exposures

Cancer is a disease that results from both genetic and epigenetic changes. Discordant phenotypes and varying incidences of complex diseases such as cancer in monozygotic twins as well as genetically identical laboratory animals have long been attributed to differences in environmental exposures. Accumulating evidence indicates, however, that disparities in gene expression resulting from variable modifications in DNA methylation and chromatin structure in response to the environment also play a role in differential susceptibility to disease. Despite a growing consensus on the importance of epigenetics in the etiology of chronic human diseases, the genes most prone to epigenetic dysregulation are incompletely defined. Moreover, neither the environmental agents most strongly affecting the epigenome nor the critical windows of vulnerability to environmentally induced epigenetic alterations are adequately characterized. These major deficits in knowledge markedly impair our ability to understand fully the etiology of cancer and the importance of the epigenome in diagnosing and preventing this devastating disease.

Hormonal imprinting: phylogeny, ontogeny, diseases and possible role in present-day human evolution

Hormonal (chemical) imprinting which was first observed (and named) by us in the seventies of the last century, is a general biological phenomenon which takes place when the developing receptor meets its target hormone for the first time. Under the effect of imprinting, receptors mature and reach their maximal binding capacity. It also influences the cells' hormone production and different functions depending on receptors and hormones. Hormonal imprinting is present already at the unicellular level causing the development of specific receptors and helping the easier recognition of useful or harmful surrounding molecules. The phenomenon is an important factor in the survival of the species, as the effect of imprinting is transmitted to the progeny cell generations. At the same time it possibly helps the selection of molecules which are suitable for acting as hormones in higher ranked animals. In mammals, hormonal imprinting takes place perinatally and determines the function of receptor-signal-transduction systems as well as hormone production for life. However, there are other critical imprinting periods for continuously developing cells. Excess of the target hormones or presence of foreign molecules which are able to bind to the receptors, provoke faulty imprinting in the critical periods with life-long morphological, biochemical, functional or behavioural consequences. As many receptor-bound foreign molecules are used as medical treatments and many such molecules are present around us and inside us as environmental pollutants, they--causing faulty imprinting--are able to predispose the (human) organism to cardiovascular, endocrine, metabolic and cancerous diseases. It seems likely that this effect is connected with disturbance of DNA methylation process in the critical periods of life. There are some signs of the transgenerational effect of faulty imprinting and this could be manifested in the evolution of humans by an epigenetic route.

Xenoestrogen exposure imprints expression of genes (Hoxa10) required for normal uterine development

The developing reproductive tract is sensitive to endocrine perturbation. Bisphenol A (BPA), a xenoestrogen, is a common component of food storage plastics and dental composites. We tested the ability of BPA to alter expression of HOXA10, a gene necessary for uterine development. A dose-response increase in HOXA10 mRNA expression was demonstrated in Ishikawa cells treated with 0.1 nM to 25 microM BPA. To determine whether in utero BPA exposure resulted in a lasting alteration of uterine HOXA10 expression, mice were treated with 0.5-5.0 mg/kg BPA on gestational days 9-16. A dose-responsive increase was seen in stromal cell HOXA10 expression in 2- and 6-week-old mice exposed in utero. To discern the mechanism of BPA action, the HOXA10 estrogen response element (ERE) and autoregulatory element (ARE) were tested for BPA responsiveness. BPA drove luciferase expression from HOXA10-ERE and ARE reporter constructs. HOXA10 ERE mediated induction was blocked by ER antagonist ICI, while HOXA10 ARE induction was blocked by either ICI or HOXA10 antisense. BPA affects HOXA10 expression through the HOXA10 ERE and indirectly through the ARE. BPA initially alters HOXA10 expression through the ERE, however, the response is imprinted and uncoupled from estrogen stimulation in the adult. Several xenoestrogens alter HOX gene expression, indicating that HOX genes are a common target of endocrine disruption. In utero exposure to a xenoestrogen produces reproductive tract alterations by imprinting essential developmental regulatory genes.

Fetal origins of breast cancer

Susceptibility to breast cancer might be pre-determined in utero. Alterations in the fetal hormonal environment, caused by either maternal diet or exposure to environmental factors with endocrine activities, can modify the epigenome, and these modifications are inherited in somatic daughter cells and maintained throughout life. These epigenetic modifications might lead to changes in mammary gland development, such as increased vulnerability of epithelial targets for malignant transformation. According to this hypothesis, on post-pubertal exposure to an initiating factor, such as a carcinogen, high levels of hormones and radiation, the mammary epithelial targets, perhaps stem cells, in terminal end buds/terminal ductal lobular units would be at an increased risk of malignant transformation. The increased susceptibility for cancer initiation might result from high levels of cell proliferation, reduced apoptosis and/or altered stromal regulation. Thus, maternal diet and environmental exposure might increase the risk of breast cancer by inducing permanent epigenetic changes in the fetus that alter the susceptibility to factors that can initiate breast cancer. Identifying the epigenetically altered target genes and their ligands might lead to strategies to prevent this disease in some women.

Timing of Dietary Estrogenic Exposures and Breast Cancer Risk

The same dietary component, such as fat or phytochemicals in plant foods, can have an opposite effect on breast cancer risk if exposed in utero through a pregnant mother or at puberty. Dietary exposures during pregnancy often have similar effects on breast cancer risk among mothers and their female offspring. High fat intake and obesity are illustrative examples: excessive pregnancy weight gain that increases high birth weight is associated with increased breast cancer risk among mothers and daughters. High body weight during childhood is inversely linked to later breast cancer risk. The main reason why the age when dietary exposures occur determines their effect on breast cancer risk likely reflects the extensive programming of the mammary gland during fetal life and subsequent reprogramming at puberty and pregnancy. Programming is a series of epigenetic/transcriptional modifications in gene expression that can be influenced by changes in the hormonal environment induced, for example, by diet. Because epigenetic modifications are inherited by daughter cells, they can persist throughout life if they occur in mammary stem cells or uncommitted mammary myoepithelial or luminal progenitor cells. Our results indicate that the estrogen receptor (ER), mitogen-activated protein kinase (MAPK), and the tumor suppressors BRCA1, p53, and caveolin-1 are among the genes affected by diet-induced alterations in programming/reprogramming. Consequently, mammary gland morphology may be altered in a manner that increases or reduces susceptibility to malignant transformation, including an increase/reduction in cell proliferation, differentiation, and survival, or in the number of terminal end buds (TEBs) or pregnancy-induced mammary epithelial cells (PI-MECs) that are the sites where breast cancer is initiated. Thus, dietary exposures during pregnancy and puberty may play an important role in determining later risk by inducing epigenetic changes that modify vulnerability to breast cancer.

Environmental and nutritional effects on the epigenetic regulation of genes

Major efforts have been directed towards the identification of genetic mutations, their use as biomarkers, and the understanding of their consequences on human health and well-being. There is an emerging interest, however, in the possibility that environmentally-induced changes at levels other than the genetic information could have long-lasting consequences as well. This review summarises our current knowledge of how the environment, nutrition, and ageing affect the way mammalian genes are organised and transcribed, without changes in the underlying DNA sequence. Admittedly, the link between environment and epigenetics remains largely to be explored. However, recent studies indicate that environmental factors and diet can perturb the way genes are controlled by DNA methylation and covalent histone modifications. Unexpectedly, and not unlike genetic mutations, aberrant epigenetic alterations and their phenotypic effects can sometimes be passed on to the next generation.

Endocrine-disrupting chemicals use distinct mechanisms of action to modulate endocrine system function

The term endocrine-disrupting chemicals is used to define a structurally diverse class of synthetic and natural compounds that possess the ability to alter various components of the endocrine system and potentially induce adverse health effects in exposed individuals and populations. Research on these compounds has revealed that they use a variety of both nuclear receptor-mediated and non-receptor-mediated mechanisms to modulate different components of the endocrine system. This review will describe in vitro and in vivo studies that highlight the spectrum of unique mechanisms of action and biological effects of four endocrine-disrupting chemicals--diethylstilbestrol, genistein, di(n-butyl)phthalate, and methoxyacetic acid--to illustrate the diverse and complex nature of this class of compounds.

Neonatal estrogenic exposure suppresses PTEN-related endometrial carcinogenesis in recombinant mice

Human endometrial carcinomas, as well as complex atypical hyperplasias (CAH), are estrogen related and frequently have mutations in the PTEN gene. However, the mutual contribution of estrogen and PTEN mutations to endometrial carcinogenesis in vivo is unknown. To address this issue, we investigated whether neonatal estrogenic treatments augment the incidence of CAH and carcinomas in murine PTEN (mPTEN) heterozygous (+/-) mutant mice, an animal model for endometrial carcinoma. Low doses of diethylstilbestrol (1 ng/g/day), genistein (50 microg/g/day) in phytoestrogens, estriol (E(3)) (4 microg/g/day), and vehicle (ethanol and corn oil) were administered subcutaneously daily to neonatal pups from the 1st to 5th day after birth. At 52 weeks of age, the morphological changes in the endometrium, and uterine expression of Hoxa 10 and Hoxa 11, were evaluated. These Hoxa genes are abdominal B-type homeobox genes, which normally regulate differentiation of the Müllerian duct. The incidence of CAH and adenocarcinomas of the endometrium was significantly decreased by the neonatal estrogenic treatments in the mPTEN+/- mice. Coincidentally, all treatments significantly decreased the stromal cell density, and CAH and adenocarcinomas rarely developed in the epithelium adjacent to the affected endometrial stroma. Moreover, the uterine expression of Hoxa 10 in mice with neonatal genistein and E(3) treatments, and that of Hoxa 11 in mice with all treatments, was significantly lower when compared with vehicle alone. Taken together, neonatal estrogenic exposure induced stromal atrophy and/or hyalinization accompanied by repressed expression of Hoxa 10 and Hoxa 11, and exerted an inhibitory effect on PTEN-related tumorigenesis. These findings provide new insight into the interaction between endometrial epithelium and stroma in endometrial carcinogenesis in vivo.

The mode of action of organic carcinogens on cellular structures

Most genotoxic organic carcinogens require metabolic activation to exert their detrimental effects. The present review summarizes the mechanisms of how organic carcinogens are bioactivated into DNA-reactive descendants. Beginning with the history of discovery of some important human organic carcinogens, the text guides through the development of the knowledge on their molecular mode of action that has grown over the past decades. Some of the most important molecular mechanisms in chemical carcinogenesis, the role of the enzymes involved in bioactivation, the target gene structures of some ultimate carcinogenic metabolites, and implications for human cancer risk assessment are discussed.

Hsp90 and environmental impacts on epigenetic states: a model for the trans-generational effects of diethylstibesterol on uterine development and cancer

Hsp90 is a chaperone for over 100 'client proteins' in the cell, most of which are involved in signaling pathways. For example, Hsp90 maintains several nuclear hormone receptors, such as the estrogen receptor (ER), as agonist-receptive monomers in the cytoplasm. In the presence of agonist, Hsp90 dissociates and the receptors dimerize, enter the nucleus and ultimately activate transcription of the target genes. Increasing evidence suggests that Hsp90 also has a role in modifying the chromatin conformation of many genes. For example, Hsp90 has recently been shown to increase the activity of the histone H3 lysine-4 methyltransferase SMYD3, which activates the chromatin of target genes. Further evidence for chromatin-remodeling functions is that Hsp90 acts as a capacitor for morphological evolution by masking epigenetic variation. Release of the capacitor function of Hsp90, such as by environmental stress or by drugs that inhibit the ATP-binding activity of Hsp90, exposes previously hidden morphological phenotypes in the next generation and for several generations thereafter. The chromatin-modifying phenotypes of Hsp90 have striking similarities to the trans-generational effects of the ER agonist diethylstilbesterol (DES). Prenatal and perinatal exposure to DES increases the predisposition to uterine developmental abnormalities and cancer in the daughters and granddaughters of exposed pregnant mice. In this review, we propose that trans-generational epigenetic phenomena involving Hsp90 and DES are related and that chromatin-mediated WNT signaling modifications are required. This model suggests that inhibitors of Hsp90, WNT signaling and chromatin-remodeling enzymes might function as anticancer agents by interfering with epigenetic reprogramming and canalization in cancer stem cells.

Neonatal tamoxifen treatment of mice leads to adenomyosis but not uterine cancer

Tamoxifen is contraindicated during pregnancy but many births have been reported in breast cancer patients taking this drug and numbers might be expected to increase with FDA approval of tamoxifen for risk reduction in women at high, risk of breast cancer. The neonatal mouse, exquisitely sensitive to xenobiotic estrogens, has been used to investigate the effects of short-term oral dosing with tamoxifen (1 mg/kg on days 2-5 after birth) on long-term changes in uterine pathology and gene expression. Increased adenomyosis incidence and severity was evident in the tamoxifen-treated mice with increasing age. Uterine weights in treated mice remained lower than the corresponding controls up until 9 months, after which they became greater but during life-time studies (up to 36 months), there was no development of uterine tumours. Pathological examination of uterine tissues showed there to be extensive down-growth of endometrial glands and stroma into thickened, abnormal myometrium that had disorganised fascicles of smooth muscle and increased interstitial collagen deposition. In advanced cases, the endometrial epithelium showed mild degrees of focal hyperplasia and squamous metaplasia but no atypical cytology suggestive of premalignant change. Microarray analysis of uterine RNA taken at 1.5, 3, 6, 9 and 12 months showed from 4500 ESTs, only 12 genes were continuously over-expressed by tamoxifen treatment over this time, while none was continuously down-regulated. Up-regulated genes include those for nerve growth factor (Ngfa), cathepsin B (Ctsb), transforming growth factor beta induced (Tqfbi) and collagens (Colla1, Colla2). Results provide a basis for understanding the mechanism for tamoxifen induced tissue remodelling and the development of adenomyosis.

Epigenetic alteration by the chemical substances, food and environmental factors

Epigenetic alteration is one of the most important mechanisms for gene regulation; however, it is not changes in gene function with DNA sequence changes. Recently, epigenetics were studied in the wide ranging fields of research. In the present review, we introduce recent studies on epigenetic alteration, especially DNA methylation, by chemical exposure, food intake and environmental factors. In addition, we introduced our results on alteration of DNA methylation by transient exposure of neonatal mice to diethylstilbestrol. As these data suggest that chemical exposure, food intake and environmental factors are responsible for epigenetic alteration, we insist the necessity of the new risk assessment focusing on epigenetic alteration. (Reprod Med Biol 2004; 3: 115-121).

Lessons learned from perinatal exposure to diethylstilbestrol

The synthetic estrogen diethylstilbestrol (DES) is well documented to be a perinatal carcinogen in both humans and experimental animals. Exposure to DES during critical periods of differentiation permanently alters the programming of estrogen target tissues resulting in benign and malignant abnormalities in the reproductive tract later in life. Using the perinatal DES-exposed rodent model, cellular and molecular mechanisms have been identified that play a role in these carcinogenic effects. Although DES is a potent estrogenic chemical, effects of low doses of the compound are being used to predict health risks of weaker environmental estrogens. Therefore, it is of particular interest that developmental exposure to very low doses of DES has been found to adversely affect fertility and to increase tumor incidence in murine reproductive tract tissues. These adverse effects are seen at environmentally relevant estrogen dose levels. New studies from our lab verify that DES effects are not unique; when numerous environmental chemicals with weak estrogenic activity are tested in the experimental neonatal mouse model, developmental exposure results in an increased incidence of benign and malignant tumors including uterine leiomyomas and adenocarcinomas that are similar to those shown following DES exposure. Finally, growing evidence in experimental animals suggests that some adverse effects can be passed on to subsequent generations, although the mechanisms involved in these trans-generational events remain unknown. Although the complete spectrum of risks to DES-exposed humans are uncertain at this time, the scientific community continues to learn more about cellular and molecular mechanisms by which perinatal carcinogenesis occurs. These advances in knowledge of both genetic and epigenetic mechanisms will be significant in ultimately predicting risks to other environmental estrogens and understanding more about the role of estrogens in normal and abnormal development.

Neonatal diethylstilbestrol exposure induces persistent elevation of c-fos expression and hypomethylation in its exon-4 in mouse uterus

Perinatal exposure to diethylstilbestrol (DES) induces reproductive tract cancers later in life in both humans and animals. Because there is no clear evidence that perinatal DES exposure induces gene mutation, we proposed that perinatal DES exposure causes epigenetic methylation changes that result in persistent alterations in gene expression, leading to tumorigenesis. The proto-oncogene c-fos is one of the immediately induced genes in uterine epithelium after estrogen simulation and a key player in uterine carcinogenesis. Here, we investigated c-fos expression in mice neonatally exposed to DES (2 microg/pup/day on postnatal days 1-5). The mRNA levels of c-fos in uteri of neonatal DES-treated mice were persistently 1.4-1.9-fold higher than that in the control mice from day 5 to day 60. Overall, the uterine c-fos expression level in the neonatal DES-exposed group was significantly higher than that in the control group. After examination of the methylation status of the c-fos gene, we found that the CpGs in promoter and intron-1 regions were completely unmethylated. In exon-4, from day 17 to day 60, the percentage of unmethylated CpGs was higher in neonatal DES-exposed mice uteri than that in control (42%, 51%, 47%, and 42% in DES-exposed mice vs 33%, 34%, 33%, and 21% in control mice at day 17, 21, 30, and 60, respectively). These results suggest that perinatal DES exposure may permanently alter gene expression and methylation, and the methylation modification may occur in either the promoter regions or other regulatory sites in the gene.

Environmental exposure, DNA methylation, and gene regulation: lessons from diethylstilbesterol-induced cancers

DNA methylation is an epigenetic mechanism that regulates chromosomal stability and gene expression. Abnormal DNA methylation patterns have been observed in many types of human tumors, including those of the breast, prostate, colon, thyroid, stomach, uterus, and cervix. We and others have shown that exposure to a wide variety of xenobiotics during critical periods of mammalian development can persistently alter the pattern of DNA methylation, resulting in potentially adverse biological effects such as aberrant gene expression. Thus, this epigenetic mechanism may underlie the observed increased risk in adulthood of several chronic diseases, including cancer, in response to xenobiotic exposures early in life. We present here the lessons learned from studies on the effects of perinatal diethylstilbesterol (DES) exposure on the methylation pattern of the promoters of several estrogen-responsive genes associated with the development of reproductive organs. Perinatal DES exposure, which induces epithelial tumors of the uterus in mice and is associated with several reproductive tract abnormalities and increased vaginal and cervical cancer risk in women, provides a clear example of how estrogenic xenobiotic exposure during a critical period of development can abnormally demethylate DNA sequences during organ development and possibly increase cancer risk later in life. In addition, nutritional factors and stress may also alter DNA methylation during early life and modulate the risk of cancer and other chronic diseases in adulthood. We suggest that DNA methylation status may be influenced by environmental exposures in early life, leading to increased risk of cancer in adulthood.

Gestational and lactational exposure of male mice to diethylstilbestrol causes long-term effects on the testis, sperm fertilizing ability in vitro, and testicular gene expression

The objective of the study was to determine the long-term effects of gestational and lactational exposure to diethylstilbestrol (DES; 0, 0.1, 1, and 10 microg/kg maternal body weight) on mouse testicular growth, epididymal sperm count, in vitro fertilizing ability, and testicular gene expression using cDNA microarrays and real-time PCR in mice on postnatal day (PND) 21, 105, and 315. In the high dose group there was a persistent decrease in the number of Sertoli cells, and sperm count was decreased on PND315 (P < 0.05). Sperm motion was unaffected; however, the in vitro fertilizing ability of epididymal sperm was decreased in the high dose group on both PND105 (P < 0.001) and PND315 (P < 0.05). Early and latent alterations in the expression of genes involved in estrogen signaling (estrogen receptor alpha), steroidogenesis (steroidogenic factor 1, 17alpha-hydroxylase/C17,20-lyase, P450 side chain cleavage, steroidogenic acute regulatory protein, and scavenger receptor class B1), lysosomal function (LGP85 and prosaposin), and regulation of testicular development (testicular receptor 2, inhibin/activin beta C, and Hoxa10) were confirmed by real-time PCR. The results demonstrate that early exposure to DES causes long-term adverse effects on testicular development and sperm function, and these effects are associated with changes in testicular gene expression, even long after the cessation of DES exposure.