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

Rosetta Stone for Cancer Cure: Comparison of the Anticancer Capacity of Endogenous Estrogens, Synthetic Estrogens and Antiestrogens

This work presents the history of the recognition of principal regulatory capacities of estrogen hormones having been mistakenly regarded as breast cancer promoting agents for more than 120 years. Comprehensive analysis of the results of clinical, epidemiological, immunological and molecular studies justified that endogenous estrogens are the principal regulators of embryonic development, survival and reproduction via orchestrating appropriate expression and even edition of all genes in mammalians. Medical use of chemically modified synthetic estrogens caused toxic complications; thromboembolic events and increased cancer risk in female organs as they proved to be endocrine disruptors deregulating estrogen receptors (ERs) rather than their activators. Synthetic estrogen treatment exhibits ambiguous correlations with cancer risk at different sites, which may be attributed to an inhibition of the unliganded activation of estrogen receptors (ERs) coupled with compensatory liganded activation. The principle of estrogen induced breast cancer led to the introduction of antiestrogen therapies against this tumor; inhibition of the liganded activation of estrogen receptors and aromatase enzyme activity. The initial enthusiasm turned into disappointment as the majority of breast cancers proved to be primarily resistant to antiestrogens. In addition, nearly all patients showing earlier good tumor responses to endocrine therapy, later experienced secondary resistance leading to metastatic disease and fatal outcome. Studying the molecular events in tumors responsive and unresponsive to antiestrogen therapy, it was illuminated that a complete inhibition of liganded ER activation stimulates the growth of cancers, while a successful compensatory upregulation of estrogen signal may achieve DNA restoration, tumor regression and patient's survival. Recognition of the principal role of endogenous estrogens in gene expression, gene edition and DNA repair, estrogen treatment and stimulation of ER expression in patients may bring about a great turn in medical practice.

Adverse outcome pathways for ionizing radiation and breast cancer involve direct and indirect DNA damage, oxidative stress, inflammation, genomic instability, and interaction with hormonal regulation of the breast

Knowledge about established breast carcinogens can support improved and modernized toxicological testing methods by identifying key mechanistic events. Ionizing radiation (IR) increases the risk of breast cancer, especially for women and for exposure at younger ages, and evidence overall supports a linear dose-response relationship. We used the Adverse Outcome Pathway (AOP) framework to outline and evaluate the evidence linking ionizing radiation with breast cancer from molecular initiating events to the adverse outcome through intermediate key events, creating a qualitative AOP. We identified key events based on review articles, searched PubMed for recent literature on key events and IR, and identified additional papers using references. We manually curated publications and evaluated data quality. Ionizing radiation directly and indirectly causes DNA damage and increases production of reactive oxygen and nitrogen species (RONS). RONS lead to DNA damage and epigenetic changes leading to mutations and genomic instability (GI). Proliferation amplifies the effects of DNA damage and mutations leading to the AO of breast cancer. Separately, RONS and DNA damage also increase inflammation. Inflammation contributes to direct and indirect effects (effects in cells not directly reached by IR) via positive feedback to RONS and DNA damage, and separately increases proliferation and breast cancer through pro-carcinogenic effects on cells and tissue. For example, gene expression changes alter inflammatory mediators, resulting in improved survival and growth of cancer cells and a more hospitable tissue environment. All of these events overlap at multiple points with events characteristic of "background" induction of breast carcinogenesis, including hormone-responsive proliferation, oxidative activity, and DNA damage. These overlaps make the breast particularly susceptible to ionizing radiation and reinforce that these biological activities are important characteristics of carcinogens. Agents that increase these biological processes should be considered potential breast carcinogens, and predictive methods are needed to identify chemicals that increase these processes. Techniques are available to measure RONS, DNA damage and mutation, cell proliferation, and some inflammatory proteins or processes. Improved assays are needed to measure GI and chronic inflammation, as well as the interaction with hormonally driven development and proliferation. Several methods measure diverse epigenetic changes, but it is not clear which changes are relevant to breast cancer. In addition, most toxicological assays are not conducted in mammary tissue, and so it is a priority to evaluate if results from other tissues are generalizable to breast, or to conduct assays in breast tissue. Developing and applying these assays to identify exposures of concern will facilitate efforts to reduce subsequent breast cancer risk.

Good Guy or Bad Guy? The Duality of Wild-Type p53 in Hormone-Dependent Breast Cancer Origin, Treatment, and Recurrence

"Lactation is at one point perilously near becoming a cancerous process if it is at all arrested", Beatson, 1896. Most breast cancers arise from the milk-producing cells that are characterized by aberrant cellular, molecular, and epigenetic translation. By understanding the underlying molecular disruptions leading to the origin of cancer, we might be able to design novel strategies for more efficacious treatments or, ambitiously, divert the cancerous process. It is an established reality that full-term pregnancy in a young woman provides a lifetime reduction in breast cancer risk, whereas delay in full-term pregnancy increases short-term breast cancer risk and the probability of latent breast cancer development. Hormonal activation of the p53 protein (encode by the TP53 gene) in the mammary gland at a critical time in pregnancy has been identified as one of the most important determinants of whether the mammary gland develops latent breast cancer. This review discusses what is known about the protective influence of female hormones in young parous women, with a specific focus on the opportune role of wild-type p53 reprogramming in mammary cell differentiation. The importance of p53 as a protector or perpetrator in hormone-dependent breast cancer, resistance to treatment, and recurrence is also explored.

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.

Long non-coding RNAs may serve as biomarkers in breast cancer combined with primary lung cancer

Long non-coding RNAs (lncRNAs) have been shown to play important regulatory role in certain type of cancers biology, including breast and lung cancers. However, the lncRNA expression in breast cancer combined with primary lung cancer remains unknown. In this study, databases of the Cancer Genome Atlas (TCGA) and the lncRNA profiler of contained candidate 192 lncRNAs were utilized. 11 lncRNAs were differentially expressed in breast cancer, 9 candidate lncRNAs were differentially expressed in lung cancer. In order to find the aberrant expression of lncRNAs in breast cancer combined with primary lung cancer, seven samples of primary breast cancer and lung cancer were studied for the expression of selected lncRNAs. The results showed that SNHG6 and NEAT1 were reversely expressed in breast cancer combined with primary lung cancer compared with primary breast or lung cancer. In addition, a significant correlation of lncRNAs was found in the patients whose age was above 56 in breast cancer. What's more, PVT1 expression was negatively correlated with the pathological stage, and the level of ER, PR, HER2, p53 in breast cancer. Furthermore, lncRNA expression did not have significant relationship with the 5-year survival of patients with breast cancer combined with primary lung cancer. The findings revealed that PVT1, SNHG6, NEAT1 may serve as a prognostic marker for breast cancer combined with primary lung cancer. Therefore, these lncRNAs are potential molecular indicators in the diagnosis and prognosis of cancer in the future.

Primary Ewing's Sarcoma/Primitive Neuroectodermal Tumor of Kidney with Caval Involvement in a Pregnant Woman

In this article, we report the case of a woman in whom was found an abdominal mass during pregnancy and who underwent nephrectomy and extraction of the emboli after delivery. The kidney had a volume of 15 × 10 × 8 cm and pathological diagnosis was primary Ewing's sarcoma. The patient was treated with conventional chemotherapy for 1 year after surgery, at which time multiple metastases were found. From this case, we surmise that hormonal changes that occur during pregnancy may accelerate the growth of Ewing's sarcoma of the kidney, suggesting that renal tumors in pregnant women demand serious attention and that anti-cancer treatment should begin as soon as possible.

Regulation of p53 level by UBE4B in breast cancer

p53 is possibly the most important mammalian tumor suppressor and it is mutated or lost in more than half of all human cancers. The stability of p53 is primarily determined by the RING domain E3 ubiquitin ligase Hdm2, which targets p53 for proteasomal degradation, restraining the potent activity of p53 and enabling cell survival and proliferation. UBE4B has been shown to physically interact with p53 and Hdm2 and to negatively regulate p53 stability and function. However, no one has determined whether UBE4B promotes p53 degradation in breast cancer. In this study, UBE4B promoted the degradation and ubiquitination of p53 to inhibit the apoptosis of cancer cells and promote tumorigenesis. Our results indicate that UBE4B regulates p53 in breast cancer and could be a viable target for developing new therapeutic strategies for breast cancer treatment.

Estrogen and cancer

Estrogen exhibits a broad spectrum of physiological functions ranging from regulation of the menstrual cycle and reproduction to modulation of bone density, brain function, and cholesterol mobilization. Despite the beneficial actions of endogenous estrogen, sustained exposure to exogenous estrogen is a well-established risk factor for various cancers. We summarize our current understanding of the molecular mechanisms of estrogen signaling in normal and cancer cells and discuss the major challenges to existing antiestrogen therapies.

Interferon regulatory factor 4 binding protein is a novel p53 target gene and suppresses cisplatin-induced apoptosis of breast cancer cells

Background

Our previous work demonstrated that ectopic expression of interferon regulatory factor 4 binding protein (IBP) was correlated with the malignant behaviour of human breast cancer cells. The mechanisms controlling differential expression of IBP in breast cancer still remain unknown.

Results

To investigate the mechanism of IBP dysregulation in breast cancer, we identified IBP was a novel p53 target gene. IBP expression was negatively regulated by wild-type p53 and was p53 dependently suppressed by DNA damage agent cisplatin. Furthermore, high levels of IBP were found to decrease cisplatin-induced growth suppression and apoptotic cell death, which was associated with decreased p53 activity and imbalanced Bcl-2 family member expression.

Conclusions

IBP is a novel p53 target gene which suppresses cisplatin-mediated apoptosis of breast cancer cells via negative feedback regulation of the p53 signalling pathway, suggesting IBP may serve as a target for pharmacologic intervention of breast cancer resistant to cisplatin therapy.

Canine tumors: a spontaneous animal model of human carcinogenesis

The enormous biologic complexity of human cancer has stimulated the development of more appropriate experimental models that could resemble in a natural and spontaneous manner the physiopathologic aspects of cancer biology. Companion animals have many desired characteristics that fill the gap between in vitro and in vivo studies, and these characteristics have proven to be important in understanding many complex molecular aspects of human cancer. Spontaneous tumors in dogs share a wide variety of epidemiologic, biologic, and clinical features with human cancer, which makes this animal model both attractive and underused in oncology research. In this review, we summarize the importance of naturally occurring canine tumors as valuable tools for studying numerous aspects of human cancer as well as the potential use of this animal model for the development of new cancer treatments. We address specifically the use of canine mammary tumors as an increasingly powerful model to study human breast cancer.

The power of DNA double-strand break (DSB) repair testing to predict breast cancer susceptibility

Most presently known breast cancer susceptibility genes have been linked to DSB repair. To identify novel markers that may serve as indicators for breast cancer risk, we performed DSB repair analyses using a case-control design. Thus, we examined 35 women with defined familial history of breast and/or ovarian cancer (first case group), 175 patients with breast cancer (second case group), and 245 healthy women without previous cancer or family history of breast cancer (control group). We analyzed DSB repair in peripheral blood lymphocytes (PBLs) by a GFP-based test system using 3 pathway-specific substrates. We found increases of microhomology-mediated nonhomologous end joining (mmNHEJ) and nonconservative single-strand annealing (SSA) in women with familial risk vs. controls (P=0.0001-0.0022) and patients with breast cancer vs. controls (P=0.0004-0.0042). Young age (<50) at initial diagnosis of breast cancer, which could be indicative of genetic predisposition, was associated with elevated SSA using two different substrates, amounting to similar odds ratios (ORs=2.54-4.46, P=0.0059-0.0095) as for familial risk (ORs=2.61-4.05, P=0.0007-0.0045). These findings and supporting validation data underscore the great potential of detecting distinct DSB repair activities in PBLs as method to estimate breast cancer susceptibility beyond limitations of genotyping and to predict responsiveness to therapeutics targeting DSB repair-dysfunctional tumors.

Assessing estrogen signaling aberrations in breast cancer risk using genetically engineered mouse models

Aberrations in estrogen signaling increase breast cancer risk. Molecular mechanisms that impact breast cancer initiation, promotion, and progression can be investigated using genetically engineered mouse models. Increasing estrogen receptor alpha (ERα) expression levels twofold is sufficient to initiate and promote breast cancer progression. Initiation and promotion can be increased by p53 haploinsufficiency and by coexpressing the nuclear coactivators amplified in breast cancer 1 (AIB1) or the splice variant AIB1Δ3. Progression to invasive cancer is found with coexpression of these nuclear coactivators as well as following a single dose of 7,12-dimethylbenz(a)anthracene. Loss of signal transducer and activator of transcription 5a reduces the prevalence of initiation and promotion but does not protect from invasive cancer development. Cyclin D1 loss completely interrupts mammary epithelial proliferation and survival when ERα is overexpressed. Loss of breast cancer gene 1 increases estrogen signaling and cooperates with ERα overexpression in initiation, promotion, and progression of mammary cancer.

RUNX3 acts as a tumor suppressor in breast cancer by targeting estrogen receptor α

Transcription factor RUNX3 is inactivated in a number of malignancies, including breast cancer, and is suggested to function as a tumor suppressor. How RUNX3 functions as a tumor suppressor in breast cancer remains undefined. Here, we show that about 20% of female Runx3(+/-) mice spontaneously developed ductal carcinoma at an average age of 14.5 months. Additionally, RUNX3 inhibits the estrogen-dependent proliferation and transformation potential of ERα-positive MCF-7 breast cancer cells in liquid culture and in soft agar and suppresses the tumorigenicity of MCF-7 cells in severe combined immunodeficiency mice. Furthermore, RUNX3 inhibits ERα-dependent transactivation by reducing the stability of ERα. Consistent with its ability to regulate the levels of ERα, expression of RUNX3 inversely correlates with the expression of ERα in breast cancer cell lines, human breast cancer tissues and Runx3(+/-) mouse mammary tumors. By destabilizing ERα, RUNX3 acts as a novel tumor suppressor in breast cancer.

An epidemiological overview of the relationship between hormone replacement therapy and breast cancer

Large-scale randomized clinical trials and observational studies have consistently found that use of hormone replacement therapy (HRT) increases the risk of breast cancer. More recently, ecological studies have shown correlations between dramatic reductions in use of HRT in many countries, and declines in the rates of breast cancer in older women. Meta-analyses of data from the trials and observational studies show that the increase in breast cancer risk is greater for combined estrogen-progestin therapies compared with estrogen alone; that for both types of preparation, breast cancer risk increases with duration of use; and that the risks decrease relatively quickly after cessation of use. For both estrogen-only and combined therapies, the risk of breast cancer is higher if therapy is initiated close to the time of the menopause, relative to the risks in women starting HRT later. Most drug regulatory authorities currently recommend that HRT be prescribed only to fully informed women who have moderate-to-severe menopausal symptoms, for the shortest duration possible; and it is recommended that the need for therapy be reviewed at least every 6-12 months.

Map making in the 21st century: charting breast cancer susceptibility pathways in rodent models

Genetic factors play an important role in determining risk and resistance to increased breast cancer. Recent technological advances have made it possible to analyze hundreds of thousands of single nucleotide polymorphisms in large-scale association studies in humans and have resulted in identification of alleles in over 20 genes that influence breast cancer risk. Despite these advances, the challenge remains in identifying what the functional polymorphisms are that confer the increased risk, and how these genetic variants interact with each other and with environmental factors. In rodents, the incidence of mammary tumors varies among strains, such that they can provide alternate ideas for candidate pathways involved in humans. Mapping studies in animals have unearthed numerous loci for breast cancer susceptibility that have been validated in human populations. In a reciprocal manner, knockin and knockout mice have been used to validate the tumorigenicity of risk alleles found in population studies. Rodent studies also underscore the complexity of interactions among alleles. The fact that genes affecting risk and resistance to mammary tumors in rodents depend greatly upon the carcinogenic challenge emphasizes the importance of gene x environment interactions. The challenge to rodent geneticists now is to capitalize on the ability to control the genetics and environment in rodent models of tumorigenesis to better understand the biology of breast cancer development, to identify those polymorphisms most relevant to human susceptibility and to identify compensatory pathways that can be targeted for improved prevention in women at highest risk of developing breast cancer.

Steroid hormone receptors in cancer development: a target for cancer therapeutics

The steroid hormone receptors (SHRs) are ligand-dependent intracellular transcription factors that are known to influence the development and growth of many human cancers. SHRs pass signals from a steroid/hormone to the target genes by interacting with specific response element DNA sequences and various coregulatory proteins that consists of activators and/or corepressors. Disruptions in physiological functions of SHRs leads to several types of malignancies such as breast cancer, leukemia and lymphoma, prostate cancer, ovarian cancer, and lung cancer among others. Steroids/hormones/SHRs and their coregulators have opened up a unique window for novel steroid-based targeted therapies for cancer. Thus, dysregulation of SHR signaling in cancers compared with normal tissues can be exploited to target drugs that prevent and treat human cancers. In recent years, hormonal therapy has made a major contribution to the treatment of several cancers including reduced recurrence rates and longer survival rates. Development of various steroid receptor modulators and their potential therapeutic efficacies has provided us a great opportunity to effectively manage diseases like cancer in future. In this review article, we have summarized up-to-date knowledge of the role of SHRs in the development and progression of cancers, and potential endocrine-based therapeutic approaches to tackle these diseases.

Variation in genes coding for AMP-activated protein kinase (AMPK) and breast cancer risk in the European Prospective Investigation on Cancer (EPIC)

AMP-activated protein kinase (AMPK) is an energy sensing/signalling intracellular protein which is activated by an increase in the cellular AMP:ATP ratio after ATP depletion. Once activated, AMPK inhibits fatty acid synthesis and the Akt-mTOR pathway, and activates the p53-p21 axis. All these molecular mechanisms are thought to play a key role in breast carcinogenesis. We investigated the genetic variability of four genes encoding AMPK (PRKAA1, PRKAA2, PRKAB1 and PRKAB2). Using a tagging approach and selecting SNPs we covered all the common genetic variation of these genes. We tested association of tagging SNPs in our four candidate genes with breast cancer (BC) risk in a study of 1340 BC cases and 2536 controls nested into the European Prospective Investigation into Cancer and Nutrition (EPIC). Given the relevance of AMPK on fatty acid synthesis and the importance of body fatness as a BC risk factor, we tested association of SNPs and body-mass index as well. We observed no statistically significant association between the SNPs in the PRKAs genes and BC risk and BMI after correction for multiple testing.

Polymorphic variants in TSC1 and TSC2 and their association with breast cancer phenotypes

TSC1 acts coordinately with TSC2 in a complex to inhibit mTOR, an emerging therapeutic target and known promoter of cell growth and cell cycle progression. Perturbation of the mTOR pathway, through abnormal expression or function of pathway genes, could lead to tumorigenesis. TSC1 and TSC2 expression is reduced in invasive breast cancer as compared with normal mammary epithelium. Because single nucleotide polymorphisms (SNPs) in regulatory genes have been implicated in risk and age at diagnosis of breast cancers, systematic SNP association studies were performed on TSC1 and TSC2 SNPs for their associations with clinical features of breast cancer. TSC1 and TSC2 haplotypes were constructed from genotyping of multiple loci in both genes in healthy volunteers. SNPs were selected for further study using a bioinformatics approach based on SNP associations with drug response in NCI-60 cell lines and evidence of selection bias based on haplotype frequencies. Genotyping for five TSC1 and one TSC2 loci were performed on genomic DNA from 1,137 women with breast cancer. This study found that for TSC1 rs7874234, TT variant carriers had a 9-year later age at diagnosis of estrogen receptor positive (ER+), but not ER-, ductal carcinomas (P = 0.0049). No other SNP locus showed an association with age at diagnosis, nor any other breast cancer phenotype. TSC1 rs7874234 is hypothesized to be functional in ER+ breast cancer because the T allele, but not the C allele, may create an estrogen receptor element (ERE) site, resulting in increased TSC1 transcription and subsequent inhibition of mTOR.