EGF controls the in vivo developmental potential of a mammary epithelial cell line possessing progenitor properties

The bilayered mammary epithelium comprises a luminal layer of secretory cells and a basal layer of myoepithelial cells. Numerous data suggest the existence of self-renewing, pluripotent mammary stem cells; however, their molecular characteristics and differentiation pathways are largely unknown. BC44 mammary epithelial cells in culture, display phenotypic characteristics of basal epithelium, i.e., express basal cytokeratins 5 and 14 and P-cadherin, but no smooth muscle markers. In vivo, after injection into the cleared mammary fat pad, these cells gave rise to bilayered, hollow, alveolus-like structures comprising basal cells expressing cytokeratin 5 and luminal cells positive for cytokeratin 8 and secreting β-casein in a polarized manner into the lumen. The persistent stimulation of EGF receptor signaling pathway in BC44 cells in culture resulted in the loss of the in vivo morphogenetic potential and led to the induction of active MMP2, thereby triggering cell scattering and motility on laminin 5. These data (a) suggest that BC44 cells are capable of asymmetric division for self-renewal and the generation of a differentiated progeny restricted to the luminal lineage; (b) clarify the function of EGF in the control of the BC44 cell phenotypic plasticity; and (c) suggest a role for this phenomenon in the mammary gland development

Enrichment and characterization of thymus-repopulating cells in stroma-dependent cultures of rat bone marrow

The bone marrow precursor cells seeding the thymus have been difficult to investigate using fresh bone marrow and in vivo thymus reconstitution assays. We have therefore designed a short-term bone marrow culture system allowing the study of thymus-repopulating cells in the marrow microenvironment. Low-density rat bone marrow cells were grown on pre-established mouse bone marrow stromal cell layers. Cocultured cells were maintained either under steroid-free conditions (Whitlock/Witte-type culture) or in the presence of 10(-7) M hydrocortisone (Dexter-type culture). After 3 days in vitro, the unanchored cell fractions were tested for their ability to colonize and repopulate fetal mouse thymic lobes in vitro. Both fresh low-density cells and Whitlock/Witte-type cultures, but not Dexter-type cultures, gave rise intrathymically to significant numbers of rat donor-type Thy-1.1high CD2+ CD5low CD43+ cells accounting for 50% to 90% of the organ-cultured cells at day 14. Repopulation of fetal mouse thymic lobes by rat Thy-1.1high cells could be used as a readout assay for initiation of thymopoiesis from bone marrow precursor cells, since 90% of the cells were CD3-/low and TCRalphabeta-/low and 15% of the cells co-expressed CD4 and CD8. Dose-response analysis showed that thymus repopulating cells were at least maintained, if not amplified during the 3-day culture period, leading to at least a 10-fold enrichment as compared to unfractionated bone marrow. Unlike fresh low-density cells before culture, short-term Whitlock/Witte-type cultures were depleted in myeloid-restricted precursor cells. In culture, the thymus-repopulating activity was predominantly associated with a 10% lymphoid cell subset which did not express the B-lineage-associated antigens revealed by HIS24 (the rat B220 equivalent) and HIS50 mAbs. We propose that unanchored thymus-repopulating cells enriched in Whitlock/Witte-type cultures may represent lymphoid-restricted, T-cell precursors of the bone marrow capable of emigrating and colonizing the thymus

Mammary stem cells have myoepithelial cell properties.

Contractile myoepithelial cells dominate the basal layer of the mammary epithelium and are considered to be differentiated cells. However, we observe that up to 54% of single basal cells can form colonies when seeded into adherent culture in the presence of agents that disrupt actin-myosin interactions, and on average, 65% of the single-cell-derived basal colonies can repopulate a mammary gland when transplanted in vivo. This indicates that a high proportion of basal myoepithelial cells can give rise to a mammary repopulating unit (MRU). We demonstrate that myoepithelial cells, flow-sorted using two independent myoepithelial-specific reporter strategies, have MRU capacity. Using an inducible lineage-tracing approach we follow the progeny of myoepithelial cells that express α-smooth muscle actin and show that they function as long-lived lineage-restricted stem cells in the virgin state and during pregnancy.This work was funded by Cancer Research UK, Breast Cancer Campaign, the University of Cambridge, Hutchison Whampoa Limited, La Ligue Nationale Contre le Cancer (Equipe Labelisée 2013) and a grant from Agence Nationale de la Recherche ANR- 08-BLAN-0078-01 to M.A.G.This is the author accepted manuscript. The final version is available from Nature at http://www.nature.com/ncb/journal/vaop/ncurrent/full/ncb3025.html

Vers la caractérisation des cellules souches de la glande mammaire murine adulte

L’épithélium mammaire est une bicouche composée d’une part de cellules myoépithéliales basales et d’autre part de cellules luminales. Les propriétés si particulières de la morphogenèse post-natale de la glande mammaire, notamment la mise en place du réseau canalaire durant la puberté, et la formation d’alvéoles à chaque grossesse, suggèrent que des cellules souches résident dans l’épithélium mammaire adulte. Différentes stratégies incluant notamment l’analyse de la rétention de marqueurs de l’ADN, l’étude du potentiel de développement in vivo de sous-populations cellulaires et des approches transgéniques, sont utilisées depuis quelques années pour isoler et caractériser les cellules souches et progénitrices de l’épithélium mammaire murin. Les caractéristiques moléculaires de ces cellules restent à définir de façon précise mais des progrès notables ont déjà été réalisés pour leur enrichissement et leur identification

Growth defects induced by perturbation of β1-integrin function in the mammary gland epithelium result from a lack of MAPK activation via the Shc and Akt pathways

Adhesion to extracellular matrix (ECM) induces intracellular signals that modulate cell proliferation, survival and differentiation. To study signalling events triggered by cell–ECM interactions in vivo we used transgenic mice exhibiting reduced mammary epithelial cell proliferation and increased apoptosis rates during the growth phase in pregnancy and lactation due to expression of a β1-integrin dominant-negative mutant in the mammary gland epithelium. Here we show that ERK and JNK MAPKs were markedly less activated in lactating transgenic glands thereby accounting for the growth defects. The FAK pathway was not affected suggesting a mechanism of activation additional to the ECM signal. On the contrary, the significant decrease of Shc phosphorylation, Grb2 recruitment and the reduced phosphorylation level of Akt Thr308 and Akt substrates FKHR and Bad detected in transgenic glands show that activation of the Shc and the Akt pathways require intact cell–ECM interactions. These results provide an insight into the mechanisms of growth control by integrin-mediated adhesion that operate in vivo

Podoplanin regulates mammary stem cell function and tumorigenesis by potentiating Wnt/β-catenin signaling

Stem cells (SCs) drive mammary development, giving rise postnatally to an epithelial bilayer composed of luminal and basal myoepithelial cells. Dysregulation of SCs is thought to be at the origin of certain breast cancers; however, the molecular identity of SCs and the factors regulating their function remain poorly defined. We identified the transmembrane protein podoplanin (Pdpn) as a specific marker of the basal compartment, including multipotent SCs, and found Pdpn localized at the basal-luminal interface. Embryonic deletion of Pdpn targeted to basal cells diminished basal and luminal SC activity and affected the expression of several Wnt/β-catenin signaling components in basal cells. Moreover, Pdpn loss attenuated mammary tumor formation in a mouse model of β-catenin-induced breast cancer, limiting tumor-initiating cell expansion and promoting molecular features associated with mesenchymal-to-epithelial cell transition. In line with the loss-of-function data, we demonstrated that mechanistically Pdpn enhances Wnt/β-catenin signaling in mammary basal cells. Overall, this study uncovers a role for Pdpn in mammary SC function and, importantly, identifies Pdpn as a new regulator of Wnt/β-catenin signaling, a key pathway in mammary development and tumorigenesis.The work was supported by grants from Agence Nationale de la Recherche (ANR-13-BSV2-0001), Ligue Contre le Cancer (Equipe Labelisée 2013), Cancéropôle Île-de-France (2014-1-SEIN-01-ICR-1) and Labex Celtisphybio (ANR-10-LABX-0038) part of the Idex PSL. L.B. received funding from the Ministère de l'Enseignement Supérieur et de la Recherche and from the Fondation pour la Recherche Médicale.Peer reviewe

Myc is required for beta-catenin-mediated mammary stem cell amplification and tumorigenesis.

International audienceBACKGROUND: Basal-like breast cancer is a heterogeneous disease characterized by the expression of basal cell markers, no estrogen or progesterone receptor expression and a lack of HER2 overexpression. Recent studies have linked activation of the Wnt/beta-catenin pathway, and its downstream target, Myc, to basal-like breast cancer. Transgenic mice K5DeltaNbetacat previously generated by our team present a constitutive activation of Wnt/beta-catenin signaling in the basal myoepithelial cell layer, resulting in focal mammary hyperplasias that progress to invasive carcinomas. Mammary lesions developed by K5DeltaNbetacat mice consist essentially of basal epithelial cells that, in contrast to mammary myoepithelium, do not express smooth muscle markers. METHODS: Microarray analysis was used to compare K5DeltaNbetacat mouse tumors to human breast tumors, mammary cancer cell lines and the tumors developed in other mouse models. Cre-Lox approach was employed to delete Myc from the mammary basal cell layer of K5DeltaNbetacat mice. Stem cell amplification in K5DeltaNbetacat mouse mammary epithelium was assessed with 3D-culture and transplantation assays. RESULTS: Histological and microarray analyses of the mammary lesions of K5DeltaNbetacat females revealed their high similarity to a subset of basal-like human breast tumors with squamous differentiation. As in human basal-like carcinomas, the Myc pathway appeared to be activated in the mammary lesions of K5DeltaNbetacat mice. We found that a basal cell population with stem/progenitor characteristics was amplified in K5DeltaNbetacat mouse preneoplastic glands. Finally, the deletion of Myc from the mammary basal layer of K5DeltaNbetacat mice not only abolished the regenerative capacity of basal epithelial cells, but, in addition, completely prevented the tumorigenesis. CONCLUSIONS: These results strongly indicate that beta-catenin-induced stem cell amplification and tumorigenesis rely ultimately on the Myc pathway activation and reinforce the hypothesis that basal stem/progenitor cells may be at the origin of a subset of basal-like breast tumors