Molecular pathways involved in pregnancy-induced prevention against breast cancer

Dual role of pregnancy in breast cancer risk

Reproductive history is one of the strongest risk factors for breast cancer in women. Pregnancy can promote short-term breast cancer risk, but also reduce a woman's lifetime risk of breast cancer. Changes in hormone levels before and after pregnancy are one of the key factors in breast cancer risk. This article summarizes the changes in hormone levels before and after pregnancy, and the roles of hormones in mammary gland development and breast cancer progression. Other factors, such as changes in breast morphology and mammary gland differentiation, changes in the proportion of mammary stem cells (MaSCs), changes in the immune and inflammatory environment, and changes in lactation before and after pregnancy, also play key roles in the occurrence and development of breast cancer. This review discusses the dual effects and the potential mechanisms of pregnancy on breast cancer risk from the above aspects, which is helpful to understand the complexity of female breast cancer occurrence.

Breast Carcinogenesis during Pregnancy: Molecular Mechanisms, Maternal and Fetal Adverse Outcomes

Breast cancer is a common type of cancer diagnosed during pregnancy, with increasing incidence over the last years, as more women choose to delay childbearing. Compared to breast cancer in general population, pregnancy-associated breast cancer (PABC) is significantly different in its terms of epidemiology, diagnostic and therapeutic management, while it exhibits particularly aggressive behavior, deriving from its unique molecular and biological profile. Although not fully elucidated, the pathophysiological basis of PABC can be traced back to a combination of hormonal and immune changes during pregnancy, breast involution and altered gene expression. There is considerable controversy in the existing literature about the influence of PABC on pregnancy outcomes, regarding both short- and long-term effects on maternal and fetal/neonatal health. The majority of PABC patients have advanced-stage disease at initial diagnosis and face a significantly poorer prognosis, with decreased survival rates. The most commonly reported adverse obstetrical–fetal events are preterm delivery and prematurity-associated neonatal morbidity, while other neonatal treatment-associated complications might also occur, even when safe therapeutic options are applied during pregnancy. The objective of the present comprehensive review was to summarize current knowledge and up-to-date evidence about the pathophysiological, molecular and biological basis of PABC, as well as its association with adverse maternal, obstetrical, fetal and neonatal outcomes.

Molecular epigenetic dynamics in breast carcinogenesis

Breast cancer has become one of the most common dreadful diseases that target women across the globe. The most obvious reasons we associate with it are either genetic mutations or dysregulation of pathways. However, there is yet another domain that has a significant role in influencing the genetic mutations and pathways. Epigenetic mechanisms influence these pathways either independently or in association with genetic mutations, thereby expediting the process of breast carcinogenesis. Breast cancer is governed by various transduction pathways such as PI3K/AKT/mTOR, NOTCH, β Catenin, NF-kB, Hedgehog, etc. There are many proteins as well that serve to be tumor suppressors but somehow lose their ability to function. This may be because of either genetic mutation or a process that represses their function. Apart from these, there are a lot of individual factors like puberty, breastfeeding, abortion, parity, circadian rhythm, alcohol consumption, pollutants, and obesity that drive these mutations and hence alter the pathways. Epigenetic mechanisms like DNA methylation, histone modifications, and lncRNAs directly or indirectly bring alterations in the proteins that are involved in the pathways. They do this by either promoting the transcription of genes or by repressing it at the ground genetic level that advances breast carcinogenesis. Epigenetics precedes genetic mutation in driving carcinogenesis and so, it needs to be explored further to diversify the possibilities of target specific treatments. In this review, the general role of DNA methylation, histone modification, and lncRNAs in breast cancer and their role in influencing the oncogenic signaling pathways along with the various factors governing them have been discussed for a better understanding of the role of epigenetics in breast carcinogenesis.

The role of gene to gene interaction in the breast's genomic signature of pregnancy

Full-term pregnancy at an early age confers long-term protection against breast cancer. Published data shows a specific transcriptomic profile controlling chromatin remodeling that could play a relevant role in the pregnancy-induced protection. This process of chromatin remodeling, induced by the breast differentiation caused by the first full-term pregnancy, has mainly been measured by the expression level of genes individually considered. However, genes equally expressed during the process of chromatin remodeling may behave differently in their interaction with other genes. These changes at the gene cluster level could constitute an additional dimension of chromatin remodeling and therefore of the pregnancy-induced protection. In this research, we apply Information and Graph Theories, Differential Co-expression Network Analysis, and Multiple Regression Analysis, specially designed to examine structural and informational aspects of data sets, to analyze this question. Our findings demonstrate that, independently of the changes in the gene expression at the individual level, there are significant changes in gene-gene interactions and gene cluster behaviors. These changes indicate that the parous breast, through the process of early full-term pregnancy, generates more modules in the networks, with higher density, and a genomic structure performing additional and more complex functions than those found in the nulliparous breast.

Relationships between Breast Feeding and Breast Cancer Subtypes: Lessons Learned from Studies in Humans and in Mice

There are differential risk relationships between parity and breast cancer according to estrogen receptor (ER) status, with an increased risk of ER^- disease reduced by breastfeeding. This may be particularly relevant for understanding the higher incidence of ER^- tumors in Black women, who are more likely to be parous and less likely to breastfeed than other U.S. groups. Potential mechanisms for these relationships may include effects of disordered breast involution on inflammatory milieu in the breast as well as epigenetic reprogramming in the mammary gland, which can affect cell fate decisions in progenitor cell pools. In normal breast tissue, parity has been associated with hypermethylation of FOXA1, a pioneer transcription factor that promotes the luminal phenotype in luminal progenitors, while repressing the basal phenotype. In breast tumors, relationships between FOXA1 methylation and parity were strongest among women who did not breastfeed. Here, we summarize the epidemiologic literature regarding parity, breastfeeding, and breast cancer subtypes, and review potential mechanisms whereby these factors may influence breast carcinogenesis, with a focus on effects on progenitor cell pools in the mammary gland.

BC200 overexpression contributes to luminal and triple negative breast cancer pathogenesis

Background

Long non coding RNAs (lncRNAs) are RNA molecules longer than 200 nucleotides that are not translated into proteins, but regulate the transcription of genes involved in different cellular processes, including cancer. Epidemiological analyses have demonstrated that parous women have a decreased risk of developing breast cancer in postmenopausal years if they went through a full term pregnancy in their early twenties. We here provide evidence of the role of BC200 in breast cancer and, potentially, in pregnancy’s preventive effect in reducing the lifetime risk of developing breast cancer.

Methods

Transcriptome analysis of normal breast of parous and nulliparous postmenopausal women revealed that several lncRNAs are differentially expressed in the parous breast. RNA sequencing of healthy postmenopausal breast tissue biopsies from eight parous and eight nulliparous women showed that there are 42 novel lncRNAs differentially expressed between these two groups. Screening of several of these 42 lncRNAs by RT-qPCR in different breast cancer cell lines, provided evidence that one in particular, lncEPCAM (more commonly known as BC200), was a strong candidate involved in cancer progression. Proliferation, migration, invasion and xerograph studies confirmed this hypothesis.

Results

The poorly studied oncogenic BC200 was selected to be tested in vitro and in vivo to determine its relevance in breast cancer and also to provide us with an understanding of its role in the increased susceptibility of the nulliparous women to cancer. Our results show that BC200 is upregulated in nulliparous women, and breast cancer cells and tissue. The role of BC200 is not completely understood in any of the breast cancer subtypes. We here provide evidence that BC200 has a role in luminal breast cancer as well as in the triple negative breast cancer subtype.

Conclusion

When overexpressed in luminal and triple negative breast cancer cell lines, BC200 shows increased proliferation, migration, and invasion in vitro. In vivo, overexpression of BC200 increased tumor size. Although treatment for cancer using lncRNAs as targets is in its infancy, the advancement in knowledge and technology to study their relevance in disease could lead to the development of novel treatment and preventive strategies for breast cancer.

HNRNPA2/B1 is upregulated in endocrine-resistant LCC9 breast cancer cells and alters the miRNA transcriptome when overexpressed in MCF-7 cells

MicroRNAs are dysregulated in breast cancer. Heterogeneous Nuclear Ribonucleoprotein A2/B1 (HNRNPA2/B1) is a reader of the N(6)-methyladenosine (m6A) mark in primary-miRNAs (pri-miRNAs) and promotes DROSHA processing to precursor-miRNAs (pre-miRNAs). We examined the expression of writers, readers, and erasers of m6A and report that HNRNPA2/B1 expression is higher in tamoxifen-resistant LCC9 breast cancer cells as compared to parental, tamoxifen-sensitive MCF-7 cells. To examine how increased expression of HNRNPA2/B1 affects miRNA expression, HNRNPA2/B1 was transiently overexpressed (~5.4-fold) in MCF-7 cells for whole genome miRNA profiling (miRNA-seq). 148 and 88 miRNAs were up- and down-regulated, respectively, 48 h after transfection and 177 and 172 up- and down-regulated, respectively, 72 h after transfection. MetaCore Enrichment analysis identified progesterone receptor action and transforming growth factor β (TGFβ) signaling via miRNA in breast cancer as pathways downstream of the upregulated miRNAs and TGFβ signaling via SMADs and Notch signaling as pathways of the downregulated miRNAs. GO biological processes for mRNA targets of HNRNPA2/B1-regulated miRNAs included response to estradiol and cell-substrate adhesion. qPCR confirmed HNRNPA2B1 downregulation of miR-29a-3p, miR-29b-3p, and miR-222 and upregulation of miR-1266-5p, miR-1268a, miR-671-3p. Transient overexpression of HNRNPA2/B1 reduced MCF-7 sensitivity to 4-hydroxytamoxifen and fulvestrant, suggesting a role for HNRNPA2/B1 in endocrine-resistance.

Breast cancer, placenta and pregnancy

BACKGROUND

Breast cancer is one of the most frequently diagnosed malignancies during pregnancy. Tumours often present characteristics of high malignancy and are hormone receptor negative/HER2 positive or triple negative. In general, pregnancy, including the postpartum period, is associated with a transiently increased risk of developing breast cancer but followed by a long-lasting protective period. Placental metastases are very rare and, thus far, breast cancer metastases in the foetal compartment have not been described. To discuss these apparently contradictory observations, this narrative review resumes immunological and hormonal alterations during pregnancy potentially affecting breast cancer risk as well as tumour growth and behaviour.

OBSERVATIONS

Upregulation of breast cancer-associated genes involved in immunological and reproductive processes has been observed in parous women and is potentially responsible for a transiently increased risk in pregnancy. In contrast, maternal immunisation and immunoglobulin production against antigens expressed on trophoblast cells, such as specific glycosylation patterns of mucin-1 or RCAS1-associated truncated glycans, seem to prevent breast cancer development in later years. Animal and human studies indicate that T cells are involved in these processes. Several placenta-derived factors, especially kisspeptin, have direct anti-tumour effects. The pregnancy-related increase of estrogen, progesterone, and other hormones influence growth and characteristics of breast cancer while the role of further placenta-secreted factors is still controversially discussed.

CONCLUSION

Several factors and cells are involved in altered breast cancer risk during and after pregnancy and have potential for developing novel treatment strategies in future.

Early Parity Epigenetic Footprint of FOXA1 Gene Body in Normal Breast Tissue of Iranian Women

BACKGROUND

Young age at first full-term pregnancy (FFTP) is an important factor in breast cancer risk reduction. It is postulated that this protective effect is the result of stable molecular signatures imprinted by physiological process of pregnancy, but the molecular mechanism of this protective role is unclear. The aim of the current study was to identify the effect of early FFTP on methylation status of FOXA1 gene body. FOXA1 is an essential transcription factor for mammary gland development and estrogen responsiveness of breast tissue.

METHODS

Fresh frozen normal breast tissues (n = 51) were collected from Iranian women who underwent cosmetic mammoplasty (27 nulliparous women and 24 parous women who have experienced first pregnancy before the age of 25). DNA was extracted and then methylated DNA immunoprecipitation (MeDIP) real-time PCR was used to assess FOXA1 gene body methylation.

RESULTS

Our results revealed that FOXA1 methylation level is significantly higher in early parous compared with nulliparous group (p = 0.041).

CONCLUSION

Our study provides new hint about the association between early FFTP and epigenetic modifications within gene body of FOXA1 in normal breast tissue. More investigation is required for clarifying molecular mechanisms underlying this association in order to develop breast cancer prevention strategies.

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.

Age at first full-term birth and breast cancer risk in BRCA1 and BRCA2 mutation carriers

PURPOSE

In the general population, an early age at first full-term birth confers protection against the risk of developing breast cancer. The relationship between age at first birth and breast cancer risk is not clear for women with a mutation in the BRCA1 or BRCA2 gene. Thus, we undertook a case-control study of women with a BRCA1 or BRCA2 mutation to study the effects of age at first full-term birth matched for other reproductive factors.

METHODS

Information about reproductive factors, including age at first birth as well as medical history, was collected from a routinely administered research questionnaire. There were 2,295 matched pairs of women with a BRCA1 or BRCA2 mutation included in the final analysis.

RESULTS

There was no significant difference in the mean age at first full-term birth among the BRCA1 (24.9 vs. 25.2; P = 0.10) or BRCA2 mutation carriers (26.5 vs. 26.6 years; P = 0.80). Findings were similar in the analysis limited to cases who were diagnosed with breast cancer prior to age 45.

CONCLUSION

This matched analysis of a large number of BRCA mutation carriers suggests that age at first birth has little influence on BRCA1 or BRCA2 breast cancer risk.

The potential contribution of dietary factors to breast cancer prevention

Breast cancer (BC), the leading cancer in women, is increasing in prevalence worldwide, concurrent with western metabolic epidemics, that is, obesity, metabolic syndrome, and diabetes, and shares major risk factors with these diseases. The corresponding potential for nutritional contributions toward BC prevention is reviewed and related to critical stages in the life cycle and their implications for carcinogenic and pathometabolic trajectories. BC initiation potentially involves diet-related pro-oxidative, inflammatory, and procarcinogenic processes, that interact through combined lipid/fatty acid peroxidation, estrogen metabolism, and related DNA-adduct/depurination/mutation formation. The pathometabolic trajectory is affected by high estrogen, insulin, and growth factor cascades and resultant accelerated proliferation/progression. Anthropometric risk factors - high birth weight, adult tallness, adiposity/BMI, and weight gain - are often reflective of these trends. A sex-based nutritional approach targets women's specific risk in western obesogenic environments, associated with increasing fatness, estrogen metabolism, n-6 : n-3 polyunsaturated fatty acid ratio, and n-6 polyunsaturated fatty acid conversion to proinflammatory/carcinogenic eicosanoids, and effects of timing of life events, for example, ages at menarche, full-term pregnancy, and menopause. Recent large-scale studies have confirmed the effectiveness of the evidence-based recommendations against BC risk, emphasizing low-energy density diets, highly nutritious plant-based regimes, physical activity, and body/abdominal adiposity management. Better understanding of dietary inter-relationships with BC, as applied to food intake, selection, combination, and processing/preparation, and recommended patterns, for example, Mediterranean, DASH, plant-based, low energy density, and low glycemic load, with high nutrient/phytonutrient density, would increase public motivation and authoritative support for early/timely prevention, optimally merging with other dietary/health goals, for lifelong BC prevention.

Functional IGF1R variant predicts breast cancer risk in women with preeclampsia in California Teachers Study

Purpose

Hypertension in pregnancy has been associated with decreased future risk of breast cancer in many but not all studies. In the Marin Women’s Study, pregnancy-induced hypertension was shown to interact with the T allele of a functional IGF1R gene variant, rs2016347, to result in lower breast density, as well as decreased breast cancer risk. Our objective was to explore these findings in a larger sample of women from the California Teachers Study (CTS).

Methods

The CTS cohort consists of over 130,000 female educators. DNA was available from a nested case–control study, which included 2,030 non-Hispanic white women who developed breast cancer and 1,552 controls. The current study included all participants from the case–control group with a self-reported history of preeclampsia (80 cases/57 controls).

Results

Comparing TT to GG genotypes revealed adjusted odds ratios of 0.38 (CI 0.13, 1.14) for all invasive breast cancers, 0.26 (CI 0.07, 0.89) for hormone receptor-positive (HR+) breast cancers, 0.15 (CI 0.04, 0.56) for those with age at first birth (AFB) < 30, and 0.10 (CI 0.02, 0.49) for those with AFB < 30 and HR+ breast cancers. Trend analysis yielded p values of 0.09, 0.03, 0.005, and 0.004 respectively, suggesting a biological effect for each T allele.

Conclusion

Study findings indicate that the T allele of IGF1R variant rs2016347 is associated with a significant reduction in breast cancer risk in women with a history of preeclampsia, most marked for HR+ breast cancer and in women with AFB < 30.

Targeted DNA Methylation Screen in the Mouse Mammary Genome Reveals a Parity-Induced Hypermethylation of Igf1r That Persists Long after Parturition

The most effective natural prevention against breast cancer is an early first full-term pregnancy. Understanding how the protective effect is elicited will inform the development of new prevention strategies. To better understand the role of epigenetics in long-term protection, we investigated parity-induced DNA methylation in the mammary gland. FVB mice were bred or remained nulliparous and mammary glands harvested immediately after involution (early) or 6.5 months following involution (late), allowing identification of both transient and persistent changes. Targeted DNA methylation (109 Mb of Ensemble regulatory features) analysis was performed using the SureSelectXT Mouse Methyl-seq assay and massively parallel sequencing. Two hundred sixty-nine genes were hypermethylated and 128 hypomethylated persistently at both the early and late time points. Pathway analysis of the persistently differentially methylated genes revealed Igf1r to be central to one of the top identified signaling networks, and Igf1r itself was one of the most significantly hypermethylated genes. Hypermethylation of Igf1r in the parous mammary gland was associated with a reduction of Igf1r mRNA expression. These data suggest that the IGF pathway is regulated at multiple levels during pregnancy and that its modification might be critical in the protective role of pregnancy. This supports the approach of lowering IGF action for prevention of breast cancer, a concept that is currently being tested clinically.