Common Molecular Mechanisms of Mammary Gland Development and Breast Cancer

The mammary gland undergoes major developmental changes during puberty and pregnancy. It is thought that stem cells drive mammary gland development during puberty and are responsible for tissue maintenance as well as the major growth and remodelling that occurs with every pregnancy. The use of sophisticated cell separation procedures has facilitated the prospective isolation of mammary epithelial stem and differentiated cell subpopulations from the mouse mammary gland, while studies of primary human breast cancers have described sub-populations of tumourigenic cells capable of initiating tumour growth in immuno-compromised mice. These potential tumour 'stem cells' constitute an important therapeutic target population with respect to cancer therapy, as these are likely to be the cells which maintain tumour growth. Understanding the origin of these cells, their relationship to breast cancer subtypes, and how and why they differ from normal breast stem cells will lead to a revolution in tumour understanding, treatment and prevention. (Part of a Multi-author Review).     

In vitro neurogenesis: development and functional implications of iPSC technology

Neurogenesis is the developmental process regulating cell proliferation of neural stem cells, determining their differentiation into glial and neuronal cells, and orchestrating their organization into finely regulated functional networks. Can this complex process be recapitulated in vitro using induced pluripotent stem cell (iPSC) technology? Can neurodevelopmental and neurodegenerative diseases be modeled using iPSCs? What is the potential of iPSC technology in neurobiology? What are the recent advances in the field of neurological diseases? Since the applications of iPSCs in neurobiology are based on the capacity to regulate in vitro differentiation of human iPSCs into different neuronal subtypes and glial cells, and the possibility of obtaining iPSC-derived neurons and glial cells is based on and hindered by our poor understanding of human embryonic development, we reviewed current knowledge on in vitro neural differentiation from a developmental and cellular biology perspective. We highlight the importance to further advance our understanding on the mechanisms controlling in vivo neurogenesis in order to efficiently guide neurogenesis in vitro for cell modeling and therapeutical applications of iPSCs technology.     

Chromosome integrity checkpoints in stem and progenitor cells: transitions upon differentiation,pathogenesis, and aging

Loss of chromosome integrity is a major contributor to cancer. Checkpoints within the cell division cycle that facilitate the accuracy and outcome of chromosome segregation are thus critical pathways for preserving chromosome integrity and preventing chromosomal instability. The spindle assembly checkpoint, the decatenation checkpoint and the post-mitotic tetraploidy checkpoint ensure the appropriate establishment of the spindle apparatus, block mitotic entry upon entanglement of chromosomes or prevent further progression of post-mitotic cells that display massive spindle defects. Most of our knowledge on these mechanisms originates from studies conducted in yeast, cancer cell lines and differentiated cells. Considering that in many instances cancer derives from transformed stem and progenitor cells, our knowledge on these checkpoints in these cells just started to emerge. With this review, we provide a general overview of the current knowledge of these checkpoints in embryonic as well as in adult stem and progenitor cells with a focus on the hematopoietic system and outline common mis-regulations of their function associated with cancer and leukemia. Most cancers are aging-associated diseases. We will thus also discuss changes in the function and outcome of these checkpoints upon aging of stem and progenitor cells.     

Cardiovascular development: towards biomedical applicability

Investigating the signalling pathways that regulate heart development is essential if stem cells are to become an effective source of cardiomyocytes that can be used for studying cardiac physiology and pharmacology and eventually developing cell-based therapies for heart repair. Here, we briefly describe current understanding of heart development in vertebrates and review the signalling pathways thought to be involved in cardiomyogenesis in multiple species. We discuss how this might be applied to stem cells currently thought to have cardiomyogenic potential by considering the factors relevant for each differentiation step from the undifferentiated cell to nascent mesoderm, cardiac progenitors and finally a fully determined cardiomyocyte. We focus particularly on how this is being applied to human embryonic stem cells and provide recent examples from both our own work and that of others.     

Loss of CD24 expression promotes ductal branching in the murine mammary gland

CD24 is expressed on mammary stem cells and is used as a marker for their isolation, yet its function in the mammary gland still needs to be examined. Here we show that CD24 is expressed throughout the luminal epithelial cell layer, but only weakly in myoepithelial cells. During lactation, CD24 expression was suppressed within alveoli, but upregulated post-lactation, returning to a pre-pregnant spatial distribution. CD24-deficient mice exhibited an accelerated mammary gland ductal extension during puberty and an enhanced branching morphogenesis, resulting in increased furcation in the ductal structure. CD24−/− mammary epithelial cells were able to completely repopulate cleared mammary fat pads and to give rise to fully functional mammary glands. Together, these data suggest that while CD24 is expressed in mammary epithelium compartments thought to contain stem cells, CD24 is not a major regulator of mammary stem/progenitor cell function, but rather plays a role in governing branching morphogenesis.     

Tightrope act: autophagy in stem cell renewal, differentiation, proliferation, and aging

Autophagy is a constitutive lysosomal catabolic pathway that degrades damaged organelles and protein aggregates. Stem cells are characterized by self-renewal, pluripotency, and quiescence; their long life span, limited capacity to dilute cellular waste and spent organelles due to quiescence, along with their requirement for remodeling in order to differentiate, all suggest that they require autophagy more than other cell types. Here, we review the current literature on the role of autophagy in embryonic and adult stem cells, including hematopoietic, mesenchymal, and neuronal stem cells, highlighting the diverse and contrasting roles autophagy plays in their biology. Furthermore, we review the few studies on stem cells, lysosomal activity, and autophagy. Novel techniques to detect autophagy in primary cells are required to study autophagy in different stem cell types. These will help to elucidate the importance of autophagy in stem cells during transplantation, a promising therapeutic approach for many diseases.     

Role of the microenvironment in myeloid malignancies

The bone marrow microenvironment (BMM) regulates the fate of hematopoietic stem cells (HSCs) in homeostatic and pathologic conditions. In myeloid malignancies, new insights into the role of the BMM and its cellular and molecular actors in the progression of the diseases have started to emerge. In this review, we will focus on describing the major players of the HSC niche and the role of the altered niche function in myeloid malignancies, more specifically focusing on the mesenchymal stroma cell compartment.     

Impact of T cell selection methods in the success of clinical adoptive immunotherapy

Chemotherapy and/or radiotherapy regular regimens used for conditioning of recipients of hematopoietic stem cell transplantation (SCT) induce a period of transient profound immunosuppression. The onset of a competent immunological response, such as the appearance of viral-specific T cells, is associated with a lower incidence of viral infections after haematopoietic transplantation. The rapid development of immunodominant peptide virus screening together with advances in the design of genetic and non-genetic viral- and tumoural-specific cellular selection strategies have opened new strategies for cellular immunotherapy in oncologic recipients who are highly sensitive to viral infections. However, the rapid development of cellular immunotherapy in SCT has disclosed the role of the T cell selection method in the modulation of functional cell activity and of in vivo secondary effects triggered following immunotherapy.     

HIV/AIDS: modified stem cells in the spotlight

Since HIV/AIDS was first recognized in 1981, an urgent need has existed for the development of novel therapeutic strategies to treat the disease. Due to the current antiretroviral therapy not being curative, human stem cell-based therapeutic intervention has emerged as an approach for its treatment. Genetically modified hematopoietic stem cells (HSCs) possess the potential to self-renew, reconstitute the immune system with HIV-resistant cells, and thus control, or even eliminate, viral replication. However, HSCs may be difficult to isolate in sufficient number from HIV-infected individuals for transplantation and/or re-infusion of autologous HSCs preparations would also include some contaminating HIV-infected cells. Furthermore, since genetic modification of HSCs is not completely efficient, the risk of providing unprotected immune cells to become new targets for HIV to infect could contribute to continued immune system failure. Therefore, induced pluripotent stem cells (iPSCs) should be considered a new potential source of cells to be engineered for HIV resistance and subsequently differentiated into clonal anti-HIV HSCs or hematopoietic progeny for transplant. In this article, we provide an overview of the current possible cellular therapies for treating HIV/AIDS.     

Metabolic circuits in neural stem cells

Metabolic activity indicative of cellular demand is emerging as a key player in cell fate decision. Numerous studies have demonstrated that diverse metabolic pathways have a critical role in the control of the proliferation, differentiation and quiescence of stem cells. The identification of neural stem/progenitor cells (NSPCs) and the characterization of their development and fate decision process have provided insight into the regenerative potential of the adult brain. As a result, the potential of NSPCs in cell replacement therapies for neurological diseases is rapidly growing. The aim of this review is to discuss the recent findings on the crosstalk among key regulators of NSPC development and the metabolic regulation crucial for the function and cell fate decisions of NSPCs. Fundamental understanding of the metabolic circuits in NSPCs may help to provide novel approaches for reactivating neurogenesis to treat degenerative brain conditions and cognitive decline.     

Signal transduction via the stem cell factor receptor/c-Kit

Together with its ligand, stem cell factor, the receptor tyrosine kinase c-Kit is a key controlling receptor for a number of cell types, including hematopoietic stem cells, mast cells, melanocytes and germ cells. Gain-of-function mutations in c-Kit have been described in a number of human cancers, including testicular germinomas, acute myeloid leukemia and gastrointestinal stromal tumors.Stimulation of c-Kit by its ligand leads to dimerization of receptors, activation of its intrinsic tyrosine kinase activity and phosphorylation of key tyrosine residues within the receptor. These phosphorylated tyrosine residues serve as docking sites for a number of signal transduction molecules containing Src homology 2 domains, which will thereby be recruited to the receptor and activated many times through phosphorylation by the receptor. This review discusses our current knowledge of signal transduction molecules and signal transduction pathways activated by c-Kit and how their activation can be connected to the physiological outcome of c-Kit signaling.     

Extensive characterization of sphere models established from colorectal cancer cell lines

Links between cancer and stem cells have been proposed for many years. As the cancer stem cell (CSC) theory became widely studied, new methods were developed to culture and expand cancer cells with conserved determinants of “stemness”. These cells show increased ability to grow in suspension as spheres in serum-free medium supplemented with growth factors and chemicals. The physiological relevance of this phenomenon in established cancer cell lines remains unclear. Cell lines have traditionally been used to explore tumor biology and serve as preclinical models for the screening of potential therapeutic agents. Here, we grew cell-forming spheres (CFS) from 25 established colorectal cancer cell lines. The molecular and cellular characteristics of CFS were compared to the bulk of tumor cells. CFS could be isolated from 72 % of the cell lines. Both CFS and their parental CRC cell lines were highly tumorigenic. Compared to their parental cells, they showed similar expression of putative CSC markers. The ability of CRC cells to grow as CFS was greatly enhanced by prior treatment with 5-fluorouracil. At the molecular level, CFS and parental CRC cells showed identical gene mutations and very similar genomic profiles, although microarray analysis revealed changes in CFS gene expression that were independent of DNA copy-number. We identified a CFS gene expression signature common to CFS from all CRC cell lines, which was predictive of disease relapse in CRC patients. In conclusion, CFS models derived from CRC cell lines possess interesting phenotypic features that may have clinical relevance for drug resistance and disease relapse.     

Migration inhibition of mammary epithelial cells by Syk is blocked in the presence of DDR1 receptors

The non-receptor tyrosine kinase Syk is a well-characterized hematopoietic signal transducer, which is also expressed in non-hematopoietic cells. In epithelial cells, the function of Syk is not wholly known. It interacts with the receptor tyrosine kinase DDR1 and is frequently lost from metastatic mammary tumors. Here, using genetic tracing, we demonstrate Syk expression in murine mammary epithelium, myoepithelium and skin epithelium, but not in intestinal or lung epithelia. Investigating possible functions of Syk, we found a substantial suppression of cell mobility that depended on Syk kinase activity in trans-well migration and wounding assays. Co-expression of DDR1 resulted in constitutive interaction and strong activation of Syk kinase. Most importantly, Syk-mediated migration inhibition was blocked in the presence of DDR1, while conversely DDR1 knockdown restored migration inhibition. Our study identifies Syk as a potent inhibitor of epithelial migration and describes a first functional consequence of the interaction with the collagen receptor DDR1.     

Mononuclear phagocyte-mediated antifungal immunity: the role of chemotactic receptors and ligands

Over the past two decades, fungal infections have emerged as significant causes of morbidity and mortality in patients with hematological malignancies, hematopoietic stem cell or solid organ transplantation and acquired immunodeficiency syndrome. Besides neutrophils and CD4⁺ T lymphocytes, which have long been known to play an indispensable role in promoting protective antifungal immunity, mononuclear phagocytes are now being increasingly recognized as critical mediators of host defense against fungi. Thus, a recent surge of research studies has focused on understanding the mechanisms by which resident and recruited monocytes, macrophages and dendritic cells accumulate and become activated at the sites of fungal infection. Herein, we critically review how a variety of G-protein coupled chemoattractant receptors and their ligands mediate mononuclear phagocyte recruitment and effector function during infection by the most common human fungal pathogens.