Exposure to Propylparaben During Pregnancy and Lactation Induces Long-Term Alterations to the Mammary Gland in Mice

The mammary gland is a hormone sensitive organ that is susceptible to endocrine-disrupting chemicals (EDCs) during the vulnerable periods of parous reorganization (ie, pregnancy, lactation, and involution). Pregnancy is believed to have long-term protective effects against breast cancer development; however, it is unknown if EDCs can alter this effect. We examined the long-term effects of propylparaben, a common preservative used in personal care products and foods, with estrogenic properties, on the parous mouse mammary gland. Pregnant BALB/c mice were treated with 0, 20, 100, or 10 000 µg/kg/day propylparaben throughout pregnancy and lactation. Unexposed nulliparous females were also evaluated. Five weeks post-involution, mammary glands were collected and assessed for changes in histomorphology, hormone receptor expression, immune cell number, and gene expression. For several parameters of mammary gland morphology, propylparaben reduced the effects of parity. Propylparaben also increased proliferation, but not stem cell number, and induced modest alterations to expression of ERα-mediated genes. Finally, propylparaben altered the effect of parity on the number of several immune cell types in the mammary gland. These results suggest that propylparaben, at levels relevant to human exposure, can interfere with the effects of parity on the mouse mammary gland and induce long-term alterations to mammary gland structure. Future studies should address if propylparaben exposures negate the protective effects of pregnancy on mammary cancer development.

Inter-Individual Variation in Response to Estrogen in Human Breast Explants

Exposure to estrogen is strongly associated with increased breast cancer risk. While all women are exposed to estrogen, only 12% are expected to develop breast cancer during their lifetime. These women may be more sensitive to estrogen, as rodent models have demonstrated variability in estrogen sensitivity. Our objective was to determine individual variation in expression of estrogen receptor (ER) and estrogen-induced responses in the normal human breast. Human breast tissue from female donors undergoing reduction mammoplasty surgery were collected for microarray analysis of ER expression. To examine estrogen-induced responses, breast tissue from 23 female donors were cultured ex- vivo in basal or 10 nM 17β-estradiol (E2) media for 4 days. Expression of ER genes (ESR1 and ESR2) increased significantly with age. E2 induced consistent increases in global gene transcription, but expression of target genes AREG, PGR, and TGFβ2 increased significantly only in explants from nulliparous women. E2-treatment did not induce consistent changes in proliferation or radiation induced apoptosis. Responses to estrogen are highly variable among women and not associated with levels of ER expression, suggesting differences in intracellular signaling among individuals. The differences in sensitivity to E2-stimulated responses may contribute to variation in risk of breast cancer.

Effects of Benzophenone-3 and Propylparaben on Estrogen Receptor-Dependent R-Loops and DNA Damage in Breast Epithelial Cells and Mice

BACKGROUND

Endocrine-disrupting chemicals have been shown to have broad effects on development, but their mutagenic actions that can lead to cancer have been less clearly demonstrated. Physiological levels of estrogen have been shown to stimulate DNA damage in breast epithelial cells through mechanisms mediated by estrogen-receptor alpha (ERα). Benzophenone-3 (BP-3) and propylparaben (PP) are xenoestrogens found in the urine of >96% of U.S.

OBJECTIVES

We investigated the effect of BP-3 and PP on estrogen receptor-dependent transactivation and DNA damage at concentrations relevant to exposures in humans.

METHODS

In human breast epithelial cells, DNA damage following treatment with 17β-estradiol (E2), BP-3, and PP was determined by immunostaining with antibodies against γ-H2AX and 53BP1. Estrogenic responses were determined using luciferase reporter assays and gene expression. Formation of R-loops was determined with DNA: RNA hybrid-specific S9.6 antibody. Short-term exposure to the chemicals was also studied in ovariectomized mice. Immunostaining of mouse mammary epithelium was performed to quantify R-loops and DNA damage in vivo.

RESULTS

Concentrations of 1μM and 5μM BP-3 or PP increased DNA damage similar to that of E2 treatment in a ERα-dependent manner. However, BP-3 and PP had limited transactivation of target genes at 1μM and 5μM concentrations. BP-3 and PP exposure caused R-loop formation in a normal human breast epithelial cell line when ERα was introduced. R-loops and DNA damage were also detected in mammary epithelial cells of mice treated with BP-3 and PP.

CONCLUSIONS

Acute exposure to xenoestrogens (PP and BP-3) in mice induce DNA damage mediated by formation of ERα-dependent R-loops at concentrations 10-fold lower than those required for transactivation. Exposure to these xenoestrogens may cause deleterious estrogenic responses, such as DNA damage, in susceptible individuals. https://doi.org/10.1289/EHP5221.

Sterilization of Silastic Capsules Containing 17β-Estradiol for Effective Hormone Delivery in Mus musculus

Silastic capsules are frequently used to study the physiologic effects of estrogen exposure in animal models. The Officeof Laboratory Animal Welfare requires the sterilization of nonpharmaceutical-grade compounds before use. We compared 2commonly used terminal sterilization methods-ionizing radiation (IR) and ethylene oxide (EO)-for their utility in sterilizingsilastic capsules containing 0.05 or 0.1 mg 17β-estradiol (E2). E2-specific ELISA demonstrated that serum estrogen levelsdid not differ between mice implanted with 0.05-mg E2 capsules that were sterilized with IR or EO and those implanted withnonsterilized capsules. Likewise, mammary gland morphology and progesterone receptor expression and proliferation inmammary epithelium were similar among mice treated with E2 capsules, regardless of sterilization method, and pregnant day15 mice. In addition, IR-sterilized 0.1-mg E2 pellets provided high serum E2. We conclude that neither ionizing radiation norethylene oxide degraded E2 or the cellulose matrix, suggesting that these methods of sterilization are appropriate to provideeffective sterile hormone capsules for animal research.

Abstract 1807: Inter-individual variation in response to estrogen in the mammary gland

Background: Previous research has highlighted the paradoxical nature of estrogen in both contributing to and reducing the risk of breast cancer. Exposure to xenoestrogens may affect this delicate balance between the protective effects of estrogen and its contribution to breast cancer risk. The effects of xenoestrogens may differ among individual women, as genetic diversity has been shown to impact responses to chemicals and breast cancer susceptibility. We hypothesize that there are subsets of individuals uniquely sensitive to estrogen and xenoestrogens.

Methods: In order to identify high and low estrogen response groups, we utilized primary human breast tissues and primary human breast epithelial cells. Explant cultures of primary human breast tissues maintain the normal tissue architecture, while primary human breast epithelial cells are more efficiently used for mechanistic studies. Primary breast tissues were treated with 17β-estradiol (E2), an estrogen receptor alpha (ERα) specific agonist PPT, and an estrogen receptor beta (ERβ) specific agonist ERB041 in order to examine estrogen responsiveness. TUNEL assays were used to examine apoptotic responses. Because expression of estrogen receptor in primary human breast epithelial cells is lost in culture, we treat with TGFβ receptor inhibitors RepSox and SB431542 to restore estrogen receptor expression. We also take conditionally immortalized human breast epithelial cell (ciHMEC) lines and TERT immortalized normal breast epithelial cell lines and transfect in ESR1 to examine responses to E2 and xenoestrogens BP3 and PP.

Results: Our results show that, based on quantitative PCR analysis of estrogen receptor target genes, individuals vary in response to estrogen receptor agonist treatment. Our results from treatment of primary breast epithelial cells with TGFβ inhibitors show an increase in the levels of ESR1 expression by 2-3 fold compared to control. We are testing whether this is sufficient to restore estrogen-induced responses. Current results from the ciHMEC and normal TERT immortalized breast epithelial cell lines also illustrate the differences in response among individuals. Some individuals have estrogenic responses at physiological doses of BP3 and PP which are similar to responses seen from treating with pregnancy levels of E2.

Conclusions: These models demonstrate the variation in estrogenic responses between individual patient samples. Estrogenic compounds PPT, ERB041, PP, and BP3 can induce similar responses to those of E2 in certain individuals, as reflected in target gene expression and transactivation data. Responses to E2 and xenoestrogens vary among TERT immortalized lines and ciHMEC lines, just as responses to E2 and other estrogen receptor agonists varied among individual explant patient samples. The ciHMEC lines can be used to define the mechanistic differences in estrogen sensitivity among women.

Citation Format: Karen A. Dunphy, Amye L. Black, Sallie S. Schneider, D Joseph Jerry. Inter-individual variation in response to estrogen in the mammary gland [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2018; 2018 Apr 14-18; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2018;78(13 Suppl):Abstract nr 1807.

Abstract 3750: Xenoestrogens cause estrogen receptor-dependent R-loop formation and DNA damage

Background: The hormone 17β-estradiol (E2) plays an important role in breast cell proliferation and development but prolonged exposures and higher levels of E2 have been linked to genomic instability and breast cancer. Recent studies show E2 induced transactivations lead to DNA damage. A variety of environmental chemicals mimic the activities of estrogen, referred to as xenoestrogens. Thus, our hypothesis is to determine whether xenoestrogens stimulate transcriptional response and induce DNA damage similarly like E2.

Methods: The T-47D breast cancer cell line is used as a model because it expresses both estrogen receptors (ERα & ERβ) as found in normal breast tissue. Cells were exposed a physiologic range of E2 (17β-estradiol) [0.5-100nM] and the xenoestrogens, e.g., benzophenone-3 (BP-3) [0.5-50µM] and propyl paraben (PP) [0.5-10µM] with or without ER-antagonist ICI (1µM) for 24 hours. Transcriptional responses were quantified using an integrated ERE-luciferase reporter and qPCR for endogenous genes. Proliferation was monitored using the Alamar Blue assay. DNA damage was determined using γ-H2AX. R-loops were detected using the S9.6 antibody against DNA-RNA hybrids in the genome.

Results: Exposure of T-47D cells to physiologic levels of E2, PP and BP3 causes significant increase in DNA double-strand breaks (DSBs) as determined by γ-H2AX staining. We demonstrate a concomitant increase in R-loop formation with increase in γH2AX intensity. Treatment with RNaseH depletes R-loop intensity, corroborating the result. E2 and PP induce transactivation as determined by Luciferase reporter assay as well as expression of ER-response genes (PGR and AREG), whereas BP3 has modest effect on transactivation of PGR. ER transactivation as well as R-loop formation by E2, PP and BP3 were abrogated with ICI, demonstrating ER-dependency of R-loop formation. Consistent with the transcriptional response, proliferation studies determined that E2 showed highest proliferation followed by PP. However, BP3 showed no increase in proliferation.

Conclusions: Our results show that xenoestrogens have strikingly different activities in transactivation and proliferation. However, both xenoestrogens appear to stimulate R-loop accumulation that leads to DSB in an ER-dependent manner.

Citation Format: Karen A. Dunphy, Prabin Dhangada Majhi, Aman Sharma, Amy L. Roberts, Elizabeth A. Daniele, Sallie S. Schneider, D Joseph Jerry. Xenoestrogens cause estrogen receptor-dependent R-loop formation and DNA damage [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2018; 2018 Apr 14-18; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2018;78(13 Suppl):Abstract nr 3750.

Oxybenzone Alters Mammary Gland Morphology in Mice Exposed During Pregnancy and Lactation

Hormones and endocrine-disrupting chemicals are generally thought to have permanent “organizational” effects when exposures occur during development but not adulthood. Yet, an increasing number of studies have shown that pregnant females are disrupted by endocrine-disrupting chemical exposures, with some effects that are permanent. Here, we examined the long-term effects of exposure to oxybenzone, an estrogenic chemical found in sunscreen and personal care products, on the morphology of the mammary gland in mice exposed during pregnancy and lactation. Female mice were exposed to vehicle or 30, 212, or 3000 µg oxybenzone/kg/d, from pregnancy day 0 until weaning. A nulliparous group, receiving vehicle treatment, was also evaluated. Mammary glands were collected 5 weeks after involution for whole-mount, histological, immunohistochemical, and molecular analyses. Exposure to 3000 µg oxybenzone/kg/d induced permanent changes to ductal density that was significantly different from both the nulliparous and vehicle groups. The two highest doses of oxybenzone similarly induced an intermediate phenotype for expression of progesterone receptor. A monotonic, dose-dependent increase in cell proliferation was also observed in the oxybenzone-treated females, becoming statistically significant at the highest dose. Finally, oxybenzone exposure induced an intermediate phenotype for Esr1 expression in all oxybenzone-treated groups. These data suggest that oxybenzone, at doses relevant to human exposures, produces long-lasting alterations to mammary gland morphology and function. Further studies are needed to determine if exposure to this chemical during pregnancy and lactation will interfere with the known protection that pregnancy provides against breast cancer.

Genetic variation in sensitivity to estrogens and breast cancer risk

Breast cancer risk is intimately intertwined with exposure to estrogens. While more than 160 breast cancer risk loci have been identified in humans, genetic interactions with estrogen exposure remain to be established. Strains of rodents exhibit striking differences in their responses to endogenous ovarian estrogens (primarily 17β-estradiol). Similar genetic variation has been observed for synthetic estrogen agonists (ethinyl estradiol) and environmental chemicals that mimic the actions of estrogens (xenoestrogens). This review of literature highlights the extent of variation in responses to estrogens among strains of rodents and compiles the genetic loci underlying pathogenic effects of excessive estrogen signaling. Genetic linkage studies have identified a total of the 35 quantitative trait loci (QTL) affecting responses to 17β-estradiol or diethylstilbestrol in five different tissues. However, the QTL appear to act in a tissue-specific manner with 9 QTL affecting the incidence or latency of mammary tumors induced by 17β-estradiol or diethylstilbestrol. Mammary gland development during puberty is also exquisitely sensitive to the actions of endogenous estrogens. Analysis of mammary ductal growth and branching in 43 strains of inbred mice identified 20 QTL. Regions in the human genome orthologous to the mammary development QTL harbor loci associated with breast cancer risk or mammographic density. The data demonstrate extensive genetic variation in regulation of estrogen signaling in rodent mammary tissues that alters susceptibility to tumors. Genetic variants in these pathways may identify a subset of women who are especially sensitive to either endogenous estrogens or environmental xenoestrogens and render them at increased risk of breast cancer.

Cancer Cell Discrimination Using Host-Guest "Doubled" Arrays

We report a nanosensor that uses cell lysates to rapidly profile the tumorigenicity of cancer cells. This sensing platform uses host-guest interactions between cucurbit[7]uril and the cationic headgroup of a gold nanoparticle to non-covalently modify the binding of three fluorescent proteins of a multi-channel sensor in situ. This approach doubles the number of output channels to six, providing single-well identification of cell lysates with 100% accuracy. Significantly, this classification could be extended beyond the training set, determining the invasiveness of novel cell lines. The unique fingerprint of these cell lysates required minimal sample quantity (200 ng, ∼1000 cells), making the methodology compatible with microbiopsy technology.

Abstract 5047: Role of estrogen receptors alpha and beta in the balance between proliferation and surveillance

Estrogens have paradoxical effects in both promoting and preventing breast cancer. The proliferative actions of estrogens promote the expansion of both normal mammary epithelium and breast cancer. But estrogen also activates p53-mediated surveillance and apoptotic pathways to eliminate cells with potential oncogenic mutations. This is exemplified by tumor regression in response to high dose estrogen-treatment in postmenopausal breast cancer. Estrogens mediate their effects through the activation of two estrogen receptor subtypes: Estrogen Receptor alpha (ERα)and Estrogen Receptor beta (ERβ). Our objective is to examine the contribution of these receptors in mediating surveillance as opposed to proliferation by comparing selective estrogen receptor agonists with 17β-estradiol (E2) for induction of proliferation and surveillance in three model systems: (1) in vivo mouse model, (2) in vitro MCF7-tet-off-ERβ model, and (3) an ex-vivo human mammary explant model. Selective activation of ERβ with the agonist diarylpropionitrile (DPN) in vivo enhances p53-mediated apoptosis in the mouse mammary epithelium without stimulating proliferation. In addition, radiation-induced apoptosis is significantly reduced in mice lacking ERβ (βERKO). E2 or the ERα selective agonist pyrazole triol (PPT) induced the expression of estrogen response genes including progesterone receptor and amphiregulin in all three models. DPN-mediated activation of ERβ failed to induce the expression of these genes. The ERβ agonist DPN selectively induced the expression of genes that repress proliferation including TGFβ and inhibitors of canonical WNT signaling, WNT5a and AXIN2. DPN was also more potent in stimulating EGR1, a modulator of p53 activity, and CEBPd, a pro-apoptotic gene. Conclusions: The ability of DPN and ERβ to potentiate surveillance pathways while limiting proliferation suggests that ERβ agonists may provide a new approach for chemoprevention of breast cancer.

Citation Format: D. Joseph Jerry, Karen A. Dunphy, Amy L. Roberts, Margarita Brown. Role of estrogen receptors alpha and beta in the balance between proliferation and surveillance. [abstract]. In: Proceedings of the 106th Annual Meeting of the American Association for Cancer Research; 2015 Apr 18-22; Philadelphia, PA. Philadelphia (PA): AACR; Cancer Res 2015;75(15 Suppl):Abstract nr 5047. doi:10.1158/1538-7445.AM2015-5047

Pregnancy offers new insights into mechanisms of breast cancer risk and resistance

Pregnancy induces long-lasting changes in gene expression that are associated with a reduction in breast cancer risk. Although several mechanisms have been proposed to mediate the reduction in breast cancer risk among parous women, recent studies focus attention on progenitor cells as major targets. The results suggest new biomarkers that may improve risk prediction and provide endpoints for assessment of clinical responses to prophylactic therapies.

Oncogenic transformation of mammary epithelial cells by transforming growth factor beta independent of mammary stem cell regulation

Background

Transforming growth factor beta (TGFβ) is transiently increased in the mammary gland during involution and by radiation. While TGFβ normally has a tumour suppressor role, prolonged exposure to TGFβ can induce an oncogenic epithelial to mesenchymal transition (EMT) program in permissive cells and initiate the generation of cancer stem cells. Our objective is to mimic the transient exposure to TGFβ during involution to determine the persistent effects on premalignant mammary epithelium.

Method

CDβGeo cells, a transplantable mouse mammary epithelial cell line, were treated in vitro for 14 days with TGFβ (5 ng/ml). The cells were passaged for an additional 14 days in media without TGFβ and then assessed for markers of EMT and transformation.

Results

The 14-day exposure to TGFβ induced EMT and transdifferentiation in vitro that persists after withdrawal of TGFβ. TGFβ-treated cells are highly tumorigenic in vivo, producing invasive solid de-differentiated tumours (100%; latency 6.7 weeks) compared to control (43%; latency 32.7 weeks). Although the TGFβ-treated cells have initiated a persistent EMT program, the stem cell population was unchanged relative to the controls. The gene expression profiles of TGFβ-treated cells demonstrate de-differentiation with decreases in the expression of genes that define luminal, basal and stem cells. Additionally, the gene expression profiles demonstrate increases in markers of EMT, growth factor signalling, TGFβ2 and changes in extra cellular matrix.

Conclusion

This model demonstrates full oncogenic EMT without an increase in stem cells, serving to separate EMT markers from stem cell markers.

MiR203 mediates subversion of stem cell properties during mammary epithelial differentiation via repression of ΔNP63α and promotes mesenchymal-to-epithelial transition

During reproductive life, the mammary epithelium undergoes consecutive cycles of proliferation, differentiation and apoptosis. Doing so relies on the retained proliferative capacity, prolonged lifespan and developmental potency of mammary stem cells (MaSCs). ΔNp63α, the predominant TP63 isoform in mammary epithelia, is robustly expressed in MaSCs and is required for preservation of self-renewing capacity in diverse epithelial structures. However, the mechanism(s) underlying subversion of this activity during forfeiture of self-renewing capacity are poorly understood. MicroRNAs (miRNAs) govern critical cellular functions including stem cell maintenance, development, cell cycle regulation and differentiation by disrupting translation of target mRNAs. Data presented here indicate that expression of miR203, a miRNA that targets ΔNp63α and ΔNp63β is activated during luminal epithelial differentiation and that this pattern is observed in the murine mammary hierarchy. In addition, we present evidence that the transcription factor Zeb1 represses miR203 expression, thus enhancing ΔNp63α protein levels. Furthermore, ectopic miR203 suppresses ΔNp63α expression, proliferation and colony formation. The anti-clonogenic effects mediated by miR203 require suppression of ΔNp63α. In addition, ectopic miR203 promotes mesenchymal-to-epithelial transition and disrupts activities associated with epithelial stem cells. These studies support a model in which induction of miR203 mediates forfeiture of self-renewing capacity via suppression of ΔNp63α and may also have anti-tumorigenic activity through its reduction of EMT and cancer stem cell populations.

The role of activin in mammary gland development and oncogenesis

TGFβ contributes to mammary gland development and has paradoxical roles in breast cancer because it has both tumor suppressor and tumor promoter activity. Another member of the TGFβ superfamily, activin, also has roles in the developing mammary gland, but these functions, and the role of activin in breast cancer, are not well characterized. TGFβ and activin share the same intracellular signaling pathways, but divergence in their signaling pathways are suggested. The purpose of this review is to compare the spatial and temporal expression of TGFβ and activin during mammary gland development, with consideration given to their functions during each developmental period. We also review the contributions of TGFβ and activin to breast cancer resistance and susceptibility. Finally, we consider the systemic contributions of activin in regulating obesity and diabetes; and the impact this regulation has on breast cancer. Elevated levels of activin in serum during pregnancy and its influence on pregnancy associated breast cancer are also considered. We conclude that evidence demonstrates that activin has tumor suppressing potential, without definitive indication of tumor promoting activity in the mammary gland, making it a good target for development of therapeutics.

Radiation acts on the microenvironment to affect breast carcinogenesis by distinct mechanisms that decrease cancer latency and affect tumor type

Tissue microenvironment is an important determinant of carcinogenesis. We demonstrate that ionizing radiation, a known carcinogen, affects cancer frequency and characteristics by acting on the microenvironment. Using a mammary chimera model in which an irradiated host is transplanted with oncogenic Trp53 null epithelium, we show accelerated development of aggressive tumors whose molecular signatures were distinct from tumors arising in nonirradiated hosts. Molecular and genetic approaches show that TGFβ mediated tumor acceleration. Tumor molecular signatures implicated TGFβ, and genetically reducing TGFβ abrogated the effect on latency. Surprisingly, tumors from irradiated hosts were predominantly estrogen receptor negative. This effect was TGFβ independent and linked to mammary stem cell activity. Thus, the irradiated microenvironment affects latency and clinically relevant features of cancer through distinct and unexpected mechanisms.

Repression of mammary stem/progenitor cells by p53 is mediated by Notch and separable from apoptotic activity

Breast cancer is the most common tumor among women with inherited mutations in the p53 gene (Li-Fraumeni syndrome). The tumors represent the basal-like subtype, which has been suggested to originate from mammary stem/progenitor cells. In mouse mammary epithelium, mammosphere-forming potential was increased with decreased dosage of the gene encoding the p53 tumor suppressor protein (Trp53). Limiting dilution transplantation also showed a 3.3-fold increase in the frequency of long-term regenerative mammary stem cells in Trp53-/- mice. The repression of mammospheres by p53 was apparent despite the absence of apoptotic responses to radiation indicating a dissociation of these two activities of p53. The effects of p53 on progenitor cells were also observed in TM40A cells using both mammosphere-forming assays and the DsRed-let7c-sensor. The frequency of long-term label-retaining epithelial cells was decreased in Trp53-/- mammary glands indicating that asymmetric segregation of DNA is diminished and contributes to the expansion of the mammary stem cells. Treatment with an inhibitor of γ-secretase (N-[N-(3,5-difluorophenacetyl)-L-alanyl]-S-phenylglycine t-butyl ester) reduced the number of Trp53-/- mammospheres to the level found in Trp53+/+ cells. These results demonstrate that basal levels of p53 restrict mammary stem/progenitor cells through Notch and that the Notch pathway is a therapeutic target to prevent expansion of this vulnerable pool of cells.

Abstract 3380: Transient Tgfβ exposure causes persistent transdifferentiation in mouse mammary epithelial cells in vitro and in vivo

Transforming growth factor beta (Tgfβ) is transiently increased during involution in the mammary gland following a pregnancy and may promote the risk of pregnancy associated breast cancer (PABC). While tgfβ inhibits growth of normal mammary epithelium and has a functional role in restoring the pre-pregnancy architecture of the mammary gland, this cytokine also has tumor promoter function because it promotes epithelial to mesenchymal transition (EMT) and initiates metastatic behavior in tumor cells. We hypothesize that transient Tgfβ exposure, to mimic involution, selects for cells that are susceptible to EMT and increases risk for PABC. We have found that short term 14 day treatment of CDβGeo cells, a mouse mammary epithelial cell line, with Tgfβ (5ng/ml) promotes EMT. These cells are persistently transdifferentiated (pTD) even after withdrawal of Tgfβ. In contrast to the parental CDβGeo cells, the pTD cells have decreased expression of E-cadherin (3-fold, p<0.05) and increased levels of N-cadherin (4-fold, p<0.05). The pTD cells also exhibited a striking increase in motility and invasion in Matrigel (invasion index >3-fold, p<0.01), but there was no difference in proliferation rates between CDβGeo cells and pTD cells. The pTD cells also were strongly tumorigenic when transplanted into cleared mammary fat pads (80% of pTD,TE50=43 days vs <10% of CDβGeo at 80days; p<0.01). Levels of Snail mRNA were also increased in pTD (2-fold;p<0.01) and in the tumors derived from the pTD transplants (>5-fold;p<0.01). In addition, expression of Tgfb2 mRNA was also increased (2.8-fold;p<0.05) in the pTD cells. These results demonstrate that transient exposure to Tgfβ causes persistent transdifferentation with increases in Snail and Tgfb2 expression in CDβGeo cells and suggest maintenance of transdifferentiation through an autocrine positive feedback loop.

Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 102nd Annual Meeting of the American Association for Cancer Research; 2011 Apr 2-6; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2011;71(8 Suppl):Abstract nr 3380. doi:10.1158/1538-7445.AM2011-3380

Mammary epithelial transplant procedure

This article describes and compares the fat pad clearance procedure developed by DeOme KB et al. and the sparing procedure developed by Brill B et al., followed by the mammary epithelial transplant procedure. The mammary transplant procedure is widely used by mammary biologists because it takes advantage of the fact that significant development of the mammary epithelium doesn't occur until after puberty. At 3 weeks of age, growth of the mammary epithelial tree is confined to the vicinity of the nipple and the fat pad is largely devoid of mammary epithelium, but by 7 weeks of age the epithelial ductal tree extends throughout the entire fat pad. Therefore, if this small portion of the fat pad containing epithelium, the region between the nipple and the lymph node, is removed at 3 weeks of age, the endogenous epithelium will never populate the mammary fat pad and the fat pad is described as "cleared". At this time, mammary epithelium from another source can be transplanted in the cleared fat pad where it has the potential to extend mammary ductal trees through out the fat pad. This procedure has been utilized in many experimental models including the examination of tumor phenotype in transgenic mammary epithelial tissue without the confounding effects of genotype on the entire animal, in the identification of mammary stem cells by transplanting cells in limited dilution, determining if hyperplastic nodules proceed to mammary tumors, and to assess the effect of prior hormone exposure on the behavior of the mammary epithelium. Three week old host mice are anesthetized, cleaned and restrained on a surgical stage. A mid-sagittal incision is made through the skin, but not the peritoneum, extending from the pubis to the sternum. Oblique cuts are made through the skin from the mid-sagittal incision across the pelvis toward each leg. The skin is pulled away from the peritoneum to expose the 4th inguinal mammary gland. The fat pad is cleared by removing the fat pad tissue anterior to the lymph node. Epithelium fragments or epithelial cells are transplanted into the remaining cleared fat pad and the mouse is closed.

Estrogens, regulation of p53 and breast cancer risk: a balancing act

The paradoxical effects of ovarian hormones in both the promotion and prevention of breast cancer have been debated for over 30 years. Genetic studies have demonstrated that ovarian hormones act through NF-kappaB to stimulate proliferation and ductal elongation, whereas the p53 tumor suppressor protein plays a central role in rendering the mammary epithelium resistant to tumorigenesis. Transcriptional profiles now suggest that ovarian hormones stimulate a constellation of genes that interact with NF-kappaB and p53 to arbitrate the competing demands for proliferation and surveillance. Genes that participate in chromatin remodeling are among the acute transcriptional responses to estrogens and progestins. These genes are proposed to initiate epigenetic programs that influence the balance between proliferation and surveillance, and render the breast epithelium resistant to tumors.

Abstract A5: Transient TGFβ exposure reprograms mouse mammary epithelial cells in vitro and in vivo

Transforming growth factor beta (TGFβ) has been shown to inhibit growth of normal breast epithelium, but promotes aggressive behaviors in breast carcinomas. Normal breast epithelia are exposed transiently to increased levels of TGFβ during involution. During radiation therapy for breast cancer, the breast epithelium is also exposed transiently to TGFβ.While TGFβ restricts growth of most normal breast epithelia, it may have divergent effects on progenitor cells. The CDβgeo cells have been shown to be enriched for mammary progenitor cells (Deugnier et al., 2006). Treatment of CDβgeo cells with TGFβ1 resulted in modest decreases in E-cadherin levels after 14 days (TD0). However, withdrawal of TGFβ and passaging the cells over 14 days resulted in transdifferentiation (TD14). In contrast to the parental CDβgeo cells, the TD14 cells had decreased expression of E-cadherin (3-fold, p<0.05) and increased levels of N-cadherin (4-fold, p<0.05). The TD14 cells also exhibited a striking increasing in motility and invasion of Matrigel (invasion index=3.7-fold), but there was no difference in proliferation rates between the CDβgeo and TD14 cells. The TD14 also were strongly tumorigenic when transplanted into cleared mammary fat pads (TE50=43 days). To determine if Smad signaling is required, Smad4 expression was knocked down using shRNA (ΔSmad4). The ΔSmad4 cells exhibited decreased expression of E-cadherin, but were not tumorigenic when transplanted into cleared mammary fat pads. The levels of Snail mRNA in CDβgeo cells were increased 3-fold following exposure to TGFβ1 treatment (TD14 cells). Levels of Snail were also increased (3.5-fold) in tumors derived from the TD14 cells. Although E-cadherin expression was reduced in ΔSmad4 cells, the levels of Snail remained equivalent to that in CDβgeo cells even after exposure to TGFβ1. These results demonstrate that transient exposure to TGF-β1 acts through Smad4-dependent signals to cause irreversible changes in the expression of Snail resulting in tumorigenic phenotype.

Citation Information: Cancer Res 2009;69(23 Suppl):A5.

Estrogen and progesterone induce persistent increases in p53-dependent apoptosis and suppress mammary tumors in BALB/c-Trp53+/- mice

Introduction

Treatment with estrogen and progesterone (E+P) mimics the protective effect of parity on mammary tumors in rodents and depends upon the activity of p53. The following experiments tested whether exogenous E+P primes p53 to be more responsive to DNA damage and whether these pathways confer resistance to mammary tumors in a mouse model of Li-Fraumeni syndrome.

Methods

Mice that differ in p53 status (Trp53^+/+, Trp53^+/-, Trp53^-/-) were treated with E+P for 14 days and then were tested for p53-dependent responses to ionizing radiation. Responses were also examined in parous and age-matched virgins. The effects of hormonal exposures on tumor incidence were examined in BALB/c-Trp53^+/- mammary tissues.

Results

Nuclear accumulation of p53 and apoptotic responses were increased similarly in the mammary epithelium from E+P-treated and parous mice compared with placebo and age-matched virgins. This effect was sustained for at least 7 weeks after E+P treatment and did not depend on the continued presence of ovarian hormones. Hormone stimulation also enhanced apoptotic responses to ionizing radiation in BALB/c-Trp53^+/- mice but these responses were intermediate compared with Trp53^+/+ and Trp^-/- tissues, indicating haploinsufficiency. The appearance of spontaneous mammary tumors was delayed by parity in BALB/c-Trp53^+/- mice. The majority of tumors lacked estrogen receptor (ER), but ER⁺ tumors were observed in both nulliparous and parous mice. However, apoptotic responses to ionizing radiation and tumor incidence did not differ among outgrowths of epithelial transplants from E+P-treated donors and nulliparous donors.

Conclusion

Therefore, E+P and parity confer a sustained increase in p53-mediated apoptosis within the mammary epithelium and suppress mammary tumorigenesis, but this effect was not retained in epithelial outgrowths.

Estrogen and progesterone regulate radiation-induced p53 activity in mammary epithelium through TGF-beta-dependent pathways

DNA damage normally induces p53 activity, but responses to ionizing radiation in the mammary epithelium vary among developmental stages. The following studies examined the hormones and growth factors that regulate radiation-responsiveness of p53 in mouse mammary epithelium. Immunoreactive p21/WAF1 and TUNEL staining were used as indicators of p53 activity following exposure to ionizing radiation. In ovariectomized mice, radiation-induced accumulation of p21/WAF1 was minimal in the mammary epithelial cells (<1%). Systemic injections of estrogen and progesterone (E+P) for 72 h were necessary to recover maximal expression of p21/WAF1 following ionizing radiation (55%). The effects of E+P on radiation-induced p21/WAF1 were p53-dependent as responses were absent in Trp53-/- mice. Though hormonal treatments stimulated increases in the proportion of cycling cells (PCNA-positive), this was not directly correlated with p53 activity. Whole organ cultures were used to determine whether E+P act directly upon the mammary gland. Treatment with E+P was sufficient to render p53 responsive to radiation, but TGF-beta-neutralizing antibodies blocked responsiveness. In the absence of E+P, TGF-beta1 alone did not alter p53 activity. These results demonstrate that estrogen and progesterone together with TGF-beta signaling are necessary for maintenance of p53 activity in the mammary epithelium.