Human breast cancer stem cell markers CD44 and CD24: enriching for cells with functional properties in mice or in man?

Identification of breast cancer stem cells as the cells within breast tumors that have the ability to give rise to cells that make up the bulk of the tumor mass has shifted the focus of cancer research. However, there is still much debate concerning the unique nature of the markers that distinguish cancer stem cells in the breast. As such, understanding whether CD44+/CD24- breast cancer cells are merely more successful in overcoming an engraftment incompatibility that exists when injecting human cells into the mouse adipose tissue or are indeed bona fide cancer stem cells is of great importance

Differential Mammary Gland Development in FVB and C57Bl/6 Mice: Implications for Breast Cancer Research

A growing body of research suggests a linkage between pubertal mammary gland development and environmental factors such as diet as modifiers of long term breast cancer risk. Much of this research is dependent upon mouse models, which may vary between studies. However, effects may be strain dependent and further modified by diet, which has not been previously examined. Therefore, the objective of the present study was to determine whether mammary gland development differs between FVB and C57Bl/6 strains on diets containing either n-6 or n-3 polyunsaturated fats. Developmental measures related to onset of puberty and mammary gland development differed between strains. Mice fed the n-3 polyunsaturated fatty acids (PUFA) diet were shown to have lower numbers of terminal end buds, a marker of mammary gland development. This study helps to further clarify differences in development and dietary response between FVB and C57Bl/6 mice in order to more appropriately relate mammary gland research to human populations

The Hippo Transducer TAZ Interacts with the SWI/SNF Complex to Regulate Breast Epithelial Lineage Commitment

Lineage-committed cells of many tissues exhibit substantial plasticity in contexts such as wound healing and tumorigenesis, but the regulation of this process is not well understood. We identified the Hippo transducer WWTR1/TAZ in a screen of transcription factors that are able to prompt lineage switching of mammary epithelial cells. Forced expression of TAZ in luminal cells induces them to adopt basal characteristics, and depletion of TAZ in basal and/or myoepithelial cells leads to luminal differentiation. In human and mouse tissues, TAZ is active only in basal cells and is critical for basal cell maintenance during homeostasis. Accordingly, loss of TAZ affects mammary gland development, leading to an imbalance of luminal and basal populations as well as branching defects. Mechanistically, TAZ interacts with components of the SWI/SNF complex to modulate lineage-specific gene expression. Collectively, these findings uncover a new role for Hippo signaling in the determination of lineage identity through recruitment of chromatin-remodeling complexes

NOX4-dependent ROS production by stromal mammary cells modulates epithelial MCF-7 cell migration

BACKGROUND: The influence of the stromal microenvironment on the progression of epithelial cancers has been demonstrated. Unravelling the mechanisms by which stromal cells affect epithelial behaviour will contribute in understanding cellular malignancy. It has been proposed that redox environment has a role in the acquisition of malignancy. In this work, we studied the influence of epithelial cells on the stromal redox status and the consequence of this phenomenon on MCF-7 cell motility. METHODS: We analysed in a co-culture system, the effect of RMF-EG mammary stromal cells on the migratory capacity of MCF-7 cell line. To test whether the NOX-dependent stromal redox environment influences the epithelial migratory behaviour, we knocked down the expression of NOX4 using siRNA strategy. The effect of TGF-b1 on NOX4 expression and activity was analysed by qPCR, and intracellular ROS production was measured by a fluorescent method. RESULTS: Migration of MCF-7 breast epithelial cells was stimulated when co-cultured with RMF-EG cells. This effect depends on stromal NOX4 expression that, in turn, is enhanced by epithelial soluble factors. Pre-treatment of stromal cells with TGF-b1 enhanced this migratory stimulus by elevating NOX4 expression and intracellular ROS production. TGF-b1 seems to be a major component of the epithelial soluble factors that stimulate NOX4 expression. CONCLUSIONS: Our results have identified that an increased stromal oxidative status, mainly provided by an elevated NOX4 expression, is a permissive element in the acquisition of epithelial migratory properties. The capacity of stromal cells to modify their intracellular ROS production, and accordingly, to increase epithelial motility, seems to depend on epithelial soluble factors among which TGF-b1 have a decisive role.This work was supported by the grant (1080196 to JM) from the Fondo Nacional de Ciencia y Tecnologı´a (FONDECYT) of Chile

Hormonal control of p53 and chemoprevention

Improvements in the detection and treatment of breast cancer have dramatically altered its clinical course and outcome. However, prevention of breast cancer remains an elusive goal. Parity, age of menarche, and age at menopause are major risk factors drawing attention to the important role of the endocrine system in determining the risk of breast cancer, while heritable breast cancer susceptibility syndromes have implicated tumor suppressor genes as important targets. Recent work demonstrating hormonal modulation of the p53 tumor suppressor pathway draws together these established determinants of risk to provide a model of developmental susceptibility to breast cancer. In this model, the mammary epithelium is rendered susceptible due to impaired p53 activity during specific periods of mammary gland development, but specific endocrine stimuli serve to activate p53 function and to mitigate this risk. The results focus attention on p53 as a molecular target for therapies to reduce the risk of breast cancer

Knockout and transgenic mice of Trp53: what have we learned about p53 in breast cancer?

The human p53 tumor suppressor gene TP53 is mutated at a high frequency in sporadic breast cancer, and Li-Fraumeni syndrome patients who carry germline mutations in one TP53 allele have a high incidence of breast cancer. In the 10 years since the first knockout of the mouse p53 tumor suppressor gene (designated Trp53) was published, much has been learned about the contribution of p53 to biology and tumor suppression in the breast through the use of p53 transgenic and knockout mice. The original mice deficient in p53 showed no mammary gland phenotype. However, studies using BALB/c-Trp53-deficient mice have demonstrated a delayed involution phenotype and a mammary tumor phenotype. Together with other studies of mutant p53 transgenes and p53 bitransgenics, a greater understanding has been gained of the role of p53 in involution, of the regulation of p53 activity by hormones, of the effect of mouse strain and modifier genes on tumor phenotype, and of the cooperation between p53 and other oncogenic pathways, chemical carcinogens and hormonal stimulation in mammary tumorigenesis. Both p53 transgenic and knockout mice are important in vivo tools for understanding breast cancer, and are yet to be exploited for developing therapeutic strategies in breast cancer

Cell-state transitions regulated by SLUG are critical for tissue regeneration and tumor initiation

Perturbations in stem cell activity and differentiation can lead to developmental defects and cancer. We use an approach involving a quantitative model of cell-state transitions in vitro to gain insights into how SLUG/SNAI2, a key developmental transcription factor, modulates mammary epithelial stem cell activity and differentiation in vivo. In the absence of SLUG, stem cells fail to transition into basal progenitor cells, while existing basal progenitor cells undergo luminal differentiation; together, these changes result in abnormal mammary architecture and defects in tissue function. Furthermore, we show that in the absence of SLUG, mammary stem cell activity necessary for tissue regeneration and cancer initiation is lost. Mechanistically, SLUG regulates differentiation and cellular plasticity by recruiting the chromatin modifier lysine-specific demethylase 1 (LSD1) to promoters of lineage-specific genes to repress transcription. Together, these results demonstrate that SLUG plays a dual role in repressing luminal epithelial differentiation while unlocking stem cell transitions necessary for tumorigenesis

Clonogenic growth of human breast cancer cells co-cultured in direct contact with serum-activated fibroblasts

INTRODUCTION: Accumulating evidence suggests that fibroblasts play a pivotal role in promoting the growth of breast cancer cells. The objective of the present study was to characterize and validate an in vitro model of the interaction between small numbers of human breast cancer cells and human fibroblasts. METHODS: We measured the clonogenic growth of small numbers of human breast cancer cells co-cultured in direct contact with serum-activated, normal human fibroblasts. Using DNA microarrays, we also characterized the gene expression profile of the serum-activated fibroblasts. In order to validate the in vivo relevance of our experiments, we then analyzed clinical samples of metastatic breast cancer for the presence of myofibroblasts expressing α-smooth muscle actin. RESULTS: Clonogenic growth of human breast cancer cells obtained directly from in situ and invasive tumors was dramatically and consistently enhanced when the tumor cells were co-cultured in direct contact with serum-activated fibroblasts. This effect was abolished when the cells were co-cultured in transwells separated by permeable inserts. The fibroblasts in our experimental model exhibited a gene expression signature characteristic of 'serum response' (i.e. myofibroblasts). Immunostaining of human samples of metastatic breast cancer tissue confirmed that myofibroblasts are in direct contact with breast cancer cells. CONCLUSION: Serum-activated fibroblasts promote the clonogenic growth of human breast cancer cells in vitro through a mechanism that involves direct physical contact between the cells. This model shares many important molecular and phenotypic similarities with the fibroblasts that are naturally found in breast cancers