Postlactational Involution: Molecular Mechanisms and Relevance for Breast Cancer Development

Mammary gland tissue changes appearance and functionality in different sequential steps. The tissue of virgin, pregnant, or lactating mammary glands changes controlled by finely regulated physiological processes. A fourth stage (involution), triggered upon weaning, involves remodeling, and the gland regresses to resemble a prepregnant stage. This highly complex process characterized by a high degree of epithelial cell death and tissue remodeling can be divided into phases, which can be independent of each other. The present article describes a variety of signaling pathway components, transcription factors, and mRNA stabilization proteins that play a role in the regulation of cell fate during the involution process. These molecular actors are finely related in health to trigger the delicate mechanism that govern involution after weaning, leaving the gland in a latent stage until needed again. Importantly, it has been shown that this process may contribute to cancer development in the years following childbirth, mainly because of the involvement of inflammatory and remodeling factors

Mechanical strain induces involution-associated events in mammary epithelial cells

<p>Abstract</p> <p>Background</p> <p>Shortly after weaning, a complex multi-step process that leads to massive epithelial apoptosis is triggered by tissue local factors in the mouse mammary gland. Several reports have demonstrated the relevance of mechanical stress to induce adaptive responses in different cell types. Interestingly, these signaling pathways also participate in mammary gland involution. Then, it has been suggested that cell stretching caused by milk accumulation after weaning might be the first stimulus that initiates the complete remodeling of the mammary gland. However, no previous report has demonstrated the impact of mechanical stress on mammary cell physiology. To address this issue, we have designed a new practical device that allowed us to evaluate the effects of radial stretching on mammary epithelial cells in culture.</p> <p>Results</p> <p>We have designed and built a new device to analyze the biological consequences of applying mechanical stress to cells cultured on flexible silicone membranes. Subsequently, a geometrical model that predicted the percentage of radial strain applied to the elastic substrate was developed. By microscopic image analysis, the adjustment of these calculations to the actual strain exerted on the attached cells was verified. The studies described herein were all performed in the HC11 non-tumorigenic mammary epithelial cell line, which was originated from a pregnant BALB/c mouse. In these cells, as previously observed in other tissue types, mechanical stress induced ERK1/2 phosphorylation and c-Fos mRNA and protein expression. In addition, we found that mammary cell stretching triggered involution associated cellular events as Leukemia Inhibitory Factor (LIF) expression induction, STAT3 activation and AKT phosphorylation inhibition.</p> <p>Conclusion</p> <p>Here, we show for the first time, that mechanical strain is able to induce weaning-associated events in cultured mammary epithelial cells. These results were obtained using a new practical and affordable device specifically designed for such a purpose. We believe that our results indicate the relevance of mechanical stress among the early post-lactation events that lead to mammary gland involution.</p

Discovery of BRCA Mutations: Historical Perspective of Its Scientific, Clinical and Social Impact

In the human genome, BRCA1 and BRCA2 (for BReast CAncer 1 and 2) genes encode for proteins involved in several functions that are crucial for the maintenance of genome stability and integrity. They participate in DNA damage response and repair pathways and, therefore, act as tumor suppressor genes. Mutations in these genes, which are located in chromosomes 17q21 and 13q13 respectively, are responsible for a great fraction of inherited breast and ovarian cancers, as well as other pathologies, such as Fanconi Anemia. Approximately 30 years ago, a report from a group of the School of Public Health at the University of California about a hypothetical gene that led to predisposition to early-onset breast cancer in certain families changed the history of breast cancer research, diagnosis, and prevention. Nowadays, the accessibility of genetic testing and the availability of different approaches as wide coverage screenings, prophylactic mastectomies, and risk-lowering drugs benefits BRCA1 and BRCA2 mutation carriers enormously. This chapter summarizes the unique trajectory of BRCA research and its scientific and social implications

Mammary differentiation induces expression of Tristetraprolin, a tumor suppressor AU-rich mRNA-binding protein

Tristetraprolin (TTP) is a RNA-binding protein that inhibits the expression of pro-inflammatory cytokines and invasiveness-associated genes. TTP levels are decreased in many different cancer types and it has been proposed that this protein could be used as a prognostic factor in breast cancer. Here, using publicly available DNA microarray datasets, “serial analysis of gene expression” libraries and qRT-PCR analysis, we determined that TTP mRNA is present in normal breast cells and its levels are significantly decreased in all breast cancer subtypes. In addition, by immunostaining, we found that TTP expression is higher in normal breast tissue and benign lesions than in infiltrating carcinomas. Among these, lower grade tumors showed increased TTP expression compared to higher grade cancers. Therefore, these data indicate that TTP protein levels would provide a better negative correlation with breast cancer invasiveness than TTP transcript levels. In mice, we found that TTP mRNA and protein expression is also diminished in mammary tumors. Interestingly, a strong positive association of TTP expression and mammary differentiation was identified in normal and tumor cells. In fact, TTP expression is highly increased during lactation, showing good correlation with various mammary differentiation factors. TTP expression was also induced in mammary HC11 cells treated with lactogenic hormones, mainly by prolactin, through Stat5A activation. The effect of this hormone was highly dependent on mammary differentiation status, as prolactin was unable to elicit a similar response in proliferating or neoplastic mammary cells. In summary, these studies show that TTP expression is strongly linked to the mammary differentiation program in human and mice, suggesting that this protein might play specific and relevant roles in the normal physiology of the gland.Facultad de Ciencias MédicasCentro de Investigaciones Inmunológicas Básicas y Aplicada

Liver X receptor-α activation enhances cholesterol secretion in lactating mammary epithelium

Liver X receptors (LXRs) are li-gand-dependent transcription factors activated by cholesterol metabolites. These receptors induce a suite of target genes required for de novo synthesis of triglycerides and cholesterol transport in many tissues. Two different isoforms, LXRβ and LXRβ, have been well characterized in liver, adipocytes, macrophages, and intestinal epithelium among others, but their contribution to cholesterol and fatty acid efflux in the lactating mammary epithelium is poorly understood. We hypothesize that LXR regulates lipogenesis during milk fat production in lactation. Global mRNA analysis of mouse mammary epithelial cells (MECs) revealed multiple LXR/RXR targets upregulated sharply early in lactation compared with midpregnancy. LXRβ is the primary isoform, and its protein levels increase throughout lactation in MECs. The LXR agonist GW3965 markedly induced several genes involved in cholesterol transport and lipogenesis and enhanced cytoplasmic lipid droplet accumulation in the HC11 MEC cell line. Importantly, in vivo pharmacological activation of LXR increased the milk cholesterol percentage and induced sterol regulatory element-binding protein 1c (Srebp1c) and ATP-binding cassette transporter a7 (Abca7) expression in MECs. Cumulatively, our findings identify LXRβ as an important regulator of cholesterol incorporation into the milk through key nodes of de novo lipogenesis, suggesting a potential therapeutic target in women with difficulty initiating lactation.Fil: Grinman, Diego Yair. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Fisiología, Biología Molecular y Neurociencias. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Fisiología, Biología Molecular y Neurociencias; ArgentinaFil: Careaga Quiroga, Valeria Pilar. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Departamento de Química Orgánica; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; ArgentinaFil: Wellberg, Elizabeth A.. University of Colorado; Estados UnidosFil: Dansey, Maria Virginia. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Departamento de Química Biológica; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; ArgentinaFil: Kordon, Edith Claudia. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Fisiología, Biología Molecular y Neurociencias. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Fisiología, Biología Molecular y Neurociencias; ArgentinaFil: Anderson, Steven M.. University of Colorado; Estados UnidosFil: Maier, Marta Silvia. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Departamento de Química Orgánica; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; ArgentinaFil: Burton, Gerardo. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Departamento de Química Orgánica; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; ArgentinaFil: MacLean, Paul S.. University of Colorado; Estados UnidosFil: Rudolph, Michael C.. University of Colorado; Estados UnidosFil: Pecci, Adali. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Fisiología, Biología Molecular y Neurociencias. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Fisiología, Biología Molecular y Neurociencias; Argentin

Angiotensin-(1-7) counteracts the transforming effects triggered by angiotensin II in breast cancer cells

Angiotensin (Ang) II, the main effector peptide of the renin-angiotensin system, has been implicated in multiple aspects of cancer progression such as proliferation, migration, invasion, angiogenesis and metastasis. Ang-(1-7), is a biologically active heptapeptide, generated predominantly from AngII by the enzymatic activity of angiotensin converting enzyme 2. Previous studies have shown that Ang-(1-7) counterbalances AngII actions in different pathophysiological settings. In this study, we have analysed the impact of Ang( 1-7) on AngII-induced pro-tumorigenic features on normal murine mammary epithelial cells NMuMG and breast cancer cells MDA-MB-231. AngII stimulated the activation of the survival factor AKT in NMuMG cells mainly through the AT1 receptor. This PI3K/AKT pathway activation also promoted epithelial-mesenchymal transition (EMT). Concomitant treatment of NMuMG cells with AngII and Ang-(1-7) completely abolished EMT features induced by AngII. Furthermore, Ang-(1-7) abrogated AngII induced migration and invasion of the MDA-MB-231 cells as well as pro-angiogenic events such as the stimulation of MMP-9 activity and VEGF expression. Together, these results demonstrate for the first time that Ang-(1-7) counteracts tumor aggressive signals stimulated by AngII in breast cancer cells emerging the peptide as a potential therapy to prevent breast cancer progression

Mouse mammary tumors display Stat3 activation dependent on leukemia inhibitory factor signaling

Introduction: It has been demonstrated that leukemia inhibitory factor (LIF) induces epithelium apoptosis through Stat3 activation during mouse mammary gland involution. In contrast, it has been shown that this transcription factor is commonly activated in breast cancer cells, although what causes this effect remains unknown. Here we have tested the hypothesis that locally produced LIF can be responsible for Stat3 activation in mouse mammary tumors. Methods: The studies were performed in different tumorigenic and non-tumorigenic mammary cells. The expression of LIF and LIF receptor was tested by RT-PCR analysis. In tumors, LIF and Stat3 proteins were analyzed by immunohistochemistry, whereas Stat3 and extracellular signal-regulated kinase (ERK)1/2 expression and phosphorylation were studied by Western blot analysis. A LIF-specific blocking antibody was used to determine whether this cytokine was responsible for Stat3 phosphorylation induced by conditioned medium. Specific pharmacological inhibitors (PD98059 and Stat3ip) that affect ERK1/2 and Stat3 activation were used to study their involvement in LIF-induced effects. To analyze cell survival, assays with crystal violet were performed. Results: High levels of LIF expression and activated Stat3 were found in mammary tumors growing in vivo and in their primary cultures. We found a single mouse mammary tumor cell line, LM3, that showed low levels of activated Stat3. Incidentally, these cells also showed very little expression of LIF receptor. This suggested that autocrine/paracrine LIF would be responsible for Stat3 activation in mouse mammary tumors. This hypothesis was confirmed by the ability of conditioned medium of mammary tumor primary cultures to induce Stat3 phosphorylation, activity that was prevented by pretreatment with LIF-blocking antibody. Besides, we found that LIF increased tumor cell viability. Interestingly, blocking Stat3 activation enhanced this effect in mammary tumor cells. Conclusion: LIF is overexpressed in mouse mammary tumors, where it acts as the main Stat3 activator. Interestingly, the positive LIF effect on tumor cell viability is not dependent on Stat3 activation, which inhibits tumor cell survival as it does in normal mammary epithelium. © 2007 Quaglino et al.; licensee BioMed Central Ltd.Fil:Quaglino, A. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales; Argentina.Fil:Schere-Levy, C. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales; Argentina.Fil:Romorini, L. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales; Argentina.Fil:Kordon, E.C. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales; Argentina

Selection of Early-Occurring Mutations Dictates Hormone-Independent Progression in Mouse Mammary Tumor Lines

Mice harboring three mouse mammary tumor virus (MMTV) variants develop pregnancy-dependent (PD) tumors that progress to pregnancy-independent (PI) behavior through successive passages. Herein, we identified 10 predominant insertions in PI transplants from 8 independent tumor lines. These mutations were also detected in small cell populations in the early PD passages. In addition, we identified a new viral insertion upstream of the gene Rspo3, which is overexpressed in three of the eight independent tumor lines and codes for a protein very similar to the recently described protein encoded by Int7. This study suggests that during progression towards hormone independence, clonal expansion of cells with specific mutations might be more relevant than the occurrence of new MMTV insertions

Morphological and immunohistochemical analysis of MMTV(LA)-induced HIT and LM3 mammary tumors growing

<p><b>Copyright information:</b></p><p>Taken from "Mouse mammary tumors display Stat3 activation dependent on leukemia inhibitory factor signaling"</p><p>http://breast-cancer-research.com/content/9/5/R69</p><p>Breast cancer research : BCR 2007;9(5):R69-R69.</p><p>Published online 10 Oct 2007</p><p>PMCID:PMC2242666.</p><p></p> Hematoxylin/eosin-stained tumors. Moderately differentiated hormone-independent tumors (HIT). Papillary formations into lumen of cystic ducts and less differentiated zones with small glandular structures. Original magnification ×100; inset ×400. LM3 poorly differentiated adenocarcinoma with abundant infiltrated vascular stroma. Areas with sarcomatous appearance and apoptotic images (black arrowheads). Original magnification in (a, b) ×100; inset ×400. Leukemia inhibitory factor (LIF) immunohistochemistry. HIT: heterogenous and regular distribution mainly in poorly differentiated areas with cytoplasmic and nucleic positive staining; intense cytoplasmic staining increasing peripherally indicates a secretory pattern (arrowhead). LM3 tumor: patchy LIF staining. Inset: positive cytoplasmic staining; the ill-defined cell membrane pattern with granular cytoplasmic staining indicates LIF secretion (arrowhead). Involuting (48-hour) and lactating mammary glands were used as positive and negative controls, respectively, for LIF staining. Original magnification in (c-f) 250×; inset: 400× Stat3 (signal transduction and activators of transcription 3) immunohistochemistry. HIT: stromal and predominantly epithelial positive nuclear staining in solid areas. Inset: stained nuclei were also seen in glandular regions. LM3 tumor: intense cytoplasmic positive staining in stromal and epithelial cells. The inset shows a negative gland surrounded by positive stromal cells. Original magnification in (g, h) 250×; inset: 400