Gastrulation leads to the formation of the embryonic germ layers, ectoderm, mesoderm and endoderm, and is the first key morphogenetic process that occurs in development. Gastrulation provides a unique developmental assay system in which to study cellular movements and rearrangements in vivo. The different cell movements occurring during gastrulation take place in a highly coordinated spatial and temporal manner, indicating that they must be controlled by a complex interplay of morphogenetic and inductive events. Generally, cell movement constitutes a highly integrated program of different cellular behaviors including sensing, polarization, cytoskeletal reorganization, and changes in adhesion and cell shape. During migration, these different behaviors require a continuous regulation and feedback control to direct and coordinate them. In this work, we analyze the cellular and molecular mechanisms underlying the different types of cell behaviors during gastrulation in zebrafish. Specifically, we focus on the role of the adhesive and mechanical properties of germ layer progenitors in the regulation of gastrulation movements. In the first part of the project, we investigated the role of the adhesive and mechanical properties of the different germ layer progenitor cell types for germ layer separation and stratification. In the second part of this study, we applied the same methodology to determine the function of germ layer progenitor cell adhesion in collective cell migration. Tissue organization is thought to depend on the adhesive and mechanical properties of the constituent cells. However, it has been difficult to determine the precise contribution of these different properties due to the lack of tools to measure them. Here we use atomic force microscopy (AFM) to quantify the adhesive and mechanical properties of the different germ layer progenitor cell types. Applying this methodology, we demonstrate that mesoderm and endoderm progenitors are more adhesive than ectoderm cells and that E-cadherin is the main adhesion molecule regulating this differential adhesion. In contrast, ectoderm progenitors exhibit a higher actomyosin-dependent cell cortex tension than mesoderm and endoderm progenitors. Combining these data with tissue self-assembly in vitro and in vivo, we provide evidence that the combinatorial activities of cell adhesion and cell cortex tension direct germ layer separation and stratification. It has been hypothesized that the directionality of cell movement during collective migration results from a collective property. Using a single cell transplantation assay, we show that individual progenitor cells are capable of normal directed migration when moving as single cells, but require cell-cell adhesion to participate in coordinated and directed migration when moving collectively. These findings contribute to the understanding of the gastrulation process. Cell-cell adhesion is required for collective germ layer progenitor cell migration, and cell cortex tension is critical for germ layer separation and stratification. However, many questions still have to be solved. Future studies will have to explore the interaction between the adhesive and mechanical progenitor cell properties, as well as the role of these properties for cell protrusion formation, cell polarization, interaction with extracellular matrix, and their regulation by different signaling pathways.

<p>Juvenile nucleus pulposus (NP) cells of the intervertebral disc (IVD) are large, vacuolated cells that form cell clusters with numerous cell-cell interactions. With maturation and aging, NP cells lose their ability to form these cell clusters, with associated changes in NP cell phenotype, morphology and proteoglycan synthesis that may contribute to IVD degeneration. Studies demonstrate healthy, juvenile NP cells exhibit potential for preservation of multi-cell clusters and NP cell phenotype when cultured upon soft, laminin-containing substrates; however, the mechanisms that regulate metabolism and phenotype of these NP cells are not understood. N-cadherin is a cell adhesion molecule that is present in juvenile NP cells, but disappears with age. The goal of this dissertation was to reveal the role of N-cadherin for NP cells in multi-cell clusters that contribute to the maintenance of the juvenile NP cell morphology and phenotype in vitro, and to evaluate the potential for laminin- functionalized poly(ethylene glycol) (PEG-LM) hydrogels to promote human NP cells towards a juvenile NP cell phenotype. </p><p>In this dissertation, juvenile porcine IVD cells were promoted to form cell clusters in vitro, and analyzed for preservation of the juvenile NP phenotype on soft, laminin-rich hydrogels. In the first part of this dissertation, preservation of the porcine juvenile NP cell phenotype and presence of N-cadherin was analyzed by culturing porcine NP cells on soft, laminin-rich or PEG-LM hydrogels. Secondly, cadherin-blocking experiments were performed to prevent cluster formation in order to study the importance of cluster formation in NP cell signaling. Finally, human IVD cells were cultured on PEG-LM hydrogels to investigate the potential to revert degenerate, human NP cells toward a juvenile NP cell phenotype and morphology. </p><p>Findings reveal soft (<500 Pa), laminin-rich substrates promote NP cell clustering, a key feature of the juvenile NP cell that is associated with N-cadherin positive expression. Additionally, N-cadherin-mediated cell-clustering regulates NP cell matrix production and gene expression of NP-specific and NP-matrix related markers. Inhibition of N-cadherin-mediated contacts resulted in decreased expression of juvenile NP cell features. Finally, juvenile human NP cells are also able to form N-cadherin positive cell clusters on soft, PEG-LM hydrogels with higher expression of juvenile NP cell features compared to culturing on stiff PEG-LM hydrogels. Some degenerate, human NP cells are also able to form N-cadherin positive cell clusters with some features of the juvenile NP cell. </p><p>The studies presented in this dissertation support the proposed hypothesis and establish the importance of soft, laminin-rich substrates in promoting NP cell clustering behaviors with associated features of a juvenile cell phenotype and morphology. Additionally, these studies establish a regulatory role for N-cadherin in juvenile NP cells and suggest that preservation of N-cadherin-mediated cell-cell contacts is important for preserving the juvenile NP cell phenotype and morphology. Furthermore, findings from this dissertation reveal the ability to promote degenerate, mature human NP cells towards a juvenile NP cell phenotype, demonstrating the potential to use PEG-LM hydrogels as a means for autologous cell delivery for the restoration of healthy IVD.</p> / Dissertation

La croissance tumorale et le processus de métastatisation dépendent de la néoformation de vaisseaux sanguins ou néoangiogenèse. Parmi les molécules intervenant dans ce processus, l'adrenomédul1ine (AM) est un peptide, dont l'expression est corrélée à l'agressivité de certaines tumeurs, et qui représente un maillon «clé» dans les interactions entre les cellules tumorales et les cellules du microenvironnement. Les résultats spectaculaires qu'offre le traitement des xénogreffes de cellules issues de glioblastomes (GBM) humains par les anticorps dirigés contre l'AM ou son récepteur sont très encourageants, puisque la tumeur traitée régresse en quelques semaines, la vascularisation tumorale s'en trouve touchée de manière spécifique. C'est dans ce contexte, que nous avons choisi de poursuivre notre travail sur les mécanismes d'action de l'AM dans la néoangiogenèse. Grâce à des études in vitro et in vivo, nous avons pu montrer que l'AM est impliquée dans plusieurs étapes de la néoangiogenèse tumorale : migration des cellules endothéliales, stabilisation des contacts endothéliaux et endothélio-péricytaires, recrutement des cellules mésenchymateuses. Nos résultats démontrent que nous sommes en présence d'une molécule d'AM qui agit sur diverses cibles moléculaires et cellulaires, régulant la stabilité du complexe d”adhésion intercellulaire VE-cadhérine/-caténine, nécessaire à la protection des interactions homotypiques et hétérotypiques de l°endothélium nouvellement formé. Ainsi, l'étude des mécanismes d'action de l'AM réalisée pennettra d'établir ue stratégie thérapeutique autour de l'AM. / Tumoral growth and process of metastatization depend on the formation of new blood vessels or angiogenesis. Among the molecules implicated in this process, adrenomedullin (AM) is a peptide, which expression is correlated with the aggressiveness of tumors, and which represents a "key" link in the interactions between tumoral cells and the microenvironment cells. The spectacular results offered by the treatment of human glioblastoma (GBM) xenograft by antibodies directed against the AM or its receptor are very encouraging, as the treated tumor declines in some weeks, and the tumoral vascularization is also touched in a specific way. In this context, we chose to pursue our work on the mechanisms of action of AM in angiogenesis. In vitro and in vivo studies showed that AM is involved in several stages of tumoral angiogenesis : migration of endothelial cells, stabilization of endothelial contacts, stabilization of the pericyte coverage, recruitment of multipotent cells. Our results demonstrate that we are in presence of a molecule of AM which acts on diverse molecular and cellular targets, regulating the stability of the VE-cadherin/β-catenin complex, required for the protection of the homotypics and heterotypics interactions of the newly formed endothelium. The study of the mechanisms of action of AM realized will allow us to establish a therapeutic strategy around AM.

Background: Oral Tongue Squamous Cell Carcinoma (OTSCC) is the most frequent and aggressive carcinoma in the head and neck region. Its incidence has increased during the last decades, especially in young patients (≤40 years) mainly female. These young patients have either not been exposed to the traditional risk factors for this disease, or have a much reduced duration of exposure than the typical OTSCC patient. The reasons behind this increasing incidence remain unknown. The aims of this thesis were to analyse the presence and possible role of human papillomavirus (HPV) in oral tongue cancer in correlation with its surrogate marker p16 and its receptor syndecan-1. Other aims were to evaluate expression of EMT (epithelial to mesenchymal transition) - related markers, such as E-cadherin, β-catenin, CK5 and CK19, and to address the potential predictive role of podoplanin in the loco-regional metastatic process. Clinical parameters including age, sex, geographical distribution, relapse, tumour staging and grading were also investigated for a possible correlation with biomarker expression and prediction of survival rate and therapeutic strategy. Materials and methods: More than one hundred samples of OTSCC coming from two University Hospitals of two different countries (Sweden and Italy) were analysed. HPV presence was evaluated by in situ hybridisation for detection of the high-risk HPV 16 and indirectly by immunohistochemistry (IHC) of its surrogate marker p16. Expression of the HPV receptor syndecan-1 and the EMT biomarkers E-cadherin, β-catenin, CK5, CK19 were also evaluated by immunohistochemistry. Samples were scored using a quick score (QS), taking both number and intensity of cells stained into account. Podoplanin expression was investigated at both protein and RNA level. Results: Tumour size and lymph node metastasis correlated to both overall and disease-free survival. Despite variable expression of the syndecan-1 receptor, HPV 16 was not detected in any sample analysed, excluding a possible association with p16, which was expressed in 33% of the cases. All EMT-related markers were commonly expressed in tongue cancer. Data showed E-cadherin to be an independent prognostic factor with higher expression associated with poor overall survival. Notably, E-cadherin, β-catenin and CK5 directly correlated to each other. Multivariate analysis of clinical data demonstrated that age of the patient is an independent prognostic factor with younger patients showing a worse survival rate. Patients younger than 40 years also showed significantly higher expression of podoplanin. Data for geographic distribution revealed a difference in expression of E-cadherin between Swedish and Italian patients. Conclusions: In contrast to SCC of the base of the tongue and the tonsil, HPV is not present in OTSCC, excluding HPV infection as a risk factor. Higher levels of E-cadherin and young age is associated with poor survival in OTSCC patients. The different frequency of EMT markers seen between Swedish and Italian patients suggests an important role for the environment and the geographical area in the onset of different molecular patterns of OTSCC.

E-cadherin (Cdh1), is a major component of epithelial adherens junctions, binds the Wnt pathway effector &beta;-catenin and is lost at the invasive edge of colon cancers. Crypt stem cells give rise to 4 cell lineages that, with the exception of Paneth cells, travel along the crypt-villus axis over 3 days and are shed by anoikis. Gain of function of the Wnt pathway by a mutation in Adenomatous Polyposis Coli (Apc) disrupts enterocyte turnover to result in adenoma formation. Homozygote null Cdh1 is embryonic lethal, and heterozygote Cdh1 can promote Apc^1638N induced adenoma formation, but we lack models that assess additional functions of Cdh1 in the adenoma to carcinoma transition. The aim of this thesis was to evaluate the effect of Cdh1 loss of function in the murine intestine, including in the setting of Wnt pathway activation. To do this, germline and intestinal specific conditional Cdh1 loss of function models were generated. Conditional homozygous deletion of Cdh1 resulted in embryonic lethality using Villin-Cre. In adults, homozygous Cdh1 loss using the tamoxifen inducible Villin-CreER^T2 led to intestinal inflammation, bacteraemia and disrupted crypt-villus architecture. Combined conditional homozygous deletion of Cdh1 and Apc resulted in Wnt pathway upregulation assessed by &beta;-catenin immunolabelling. Strain dependent effects of Cdh1 heterozygosity were apparent on the Apc heterozygote background: Apc^Min/&plus; Cdh1^&plus;/- (C57BL/6J) had no effect on survival or adenoma phenotype compared to littermate Apc^Min/&plus;; Cdh1^+/fl increased adenoma burden in Apc^&plus;/fl Vil-Cre animals (B6D2/C57BL/6J). Low frequency recombination of Apc^fl/fl using Lgr5-EGFP-IRES-CreER^T2 bypasses the loss of heterozygosity event relied on in heterozygous Apc tumour models achieving a large adenoma burden within 4 weeks. Cdh1 loss did not alter survival or adenoma phenotype in this model, including the development of large caecal tumours. Immunolabelling of tumours from Apc^fl/fl Cdh1^fl/fl animals showed persistent E-cadherin protein expression, suggesting incomplete recombination or that double homozygote enterocytes failed to survive. In vitro adenoma culture was used to test whether E-cadherin loss was incompatible with enterocyte survival in the setting of Wnt activation. Apc^fl/fl Cdh1^{&plus;/&plus;} and Apc^fl/fl Cdh1^fl/fl adenoma were cultured in matrigel and treated with an adenovirus expressing Cre recombinase under a CMV promoter (Ad-Cre). Ad-Cre had no effect on Apc^fl/fl Cdh1^+/+ adenoma growth. Ad-Cre treated Apc^fl/fl Cdh1^fl/fl adenoma organoids showed cells where E‑cadherin loss resulted in Wnt pathway upregulation as assessed by nuclear &beta;-catenin and Axin2 expression, and epithelial mesenchymal transition shown by upregulation of fibronectin, twist and vimentin. This work supports a role for E-cadherin in modulation of the Wnt pathway. Further investigation is required to define the cell adhesion versus Wnt regulatory functions of E-cadherin.

Many signaling pathways have been shown to be involved in the formation of the vascular system. Among them are the endothelial specific receptor families such as VEGF, Ang/Tie, as well as other signaling pathways such as semaphorins, which are also involved, in axonal guidance. It is known that the interaction between receptor tyrosine kinase, Tie2, VE-Cadherin, and VE-PTP mediate endothelial cell quiescence and adhesion. However, the structural basis of these interactions is not well understood. The aim of our study is to characterize the binding interactions between these players. Another important part of our study is describing the cross-talk between vasculature and nervous system by characterizing the Neuropilin/Plexin/Semaphorin system. VE-Cadherin along with neuropilins plays an essential role by directing VEGF signals to the appropriate location and coordinating the activation of downstream molecules. We characterize the interaction between Tie2, VE-PTP and VE-Cadherin by (FRET)-based proximity assay, fluorescence lifetime imaging, and co-immunoprecipitation assays. Our data showed a consistent localization of the protein and FRET signal for Tie2 and VE-PTP prior to ligand recognition. We showed the association between Tie2 and VE-Cadherin complex by co-immunoprecipatation. However, our FRET data was not consistent. The examination of VE-PTP and VE-Cadherin for association and localization of the protein showed a very unique, mutually exclusive localization of the protein. Our study of Neuropilin/Plexin/Semaphorin system showed changes in the protein localization, FRET signal and morphology upon stimulation of HEK293 cells expressing Nrp/plexin with Sema3D. In this system VE-Cadherin along with neuropilins plays an essential role by directing VEGF signals to the appropriate location and coordinating the activation of downstream molecules. The characterization of extracellular binding between Tie2, VE-PTP, and VE-Cadherin, will help to better understand the molecular mechanisms of normal and tumor angiogenesis to develop new anti-angiogeneic therapies.

Genomic instability and acquisition of invasiveness through the basement membrane extracellular matrix (ECM) are two major processes for epithelial cell malignancy in breast cancer. DNA double-strand break repair (DSBR) is one of the processes that get misregulated during breast cancer progression. In addition, radiation induced breaks such as those induced during radiation therapy to treat breast cancer patients are repaired by DSBR, rendering this pathway relevant for therapy as well. DSBR can occur either by homologous recombination (HR) or non-homologous end-joining (NHEJ). HR is accepted as the more error-free pathway. HR is regulated by the cell cycle status such that an increase is observed in G2/M, whereas NHEJ is observed throughout the cell cycle. Previous data show that ECM signaling regulates HR, as well as the kinetics of ionizing radiation (IR) induced complex formation at break sites, or foci kinetics. Both human breast epithelial cell lines and primary mouse mammary epithelial cells were used to show that the ECM receptor β1-integrin is necessary and sufficient in down regulating HR, as well as IR induced foci formation kinetics for the DSBR proteins RAD51, MRE11, and γ-H2AX in single mammary epithelial cells. RAD51 is required for most HR, whereas MRE11 and γ-H2AX function in HR as well as DNA damage signaling. Interestingly, ECM signaling up-regulates HR in cells that have “correct” in vivo-like cell-cell junctions. Based on the observation that single cells and junctioned cells respond to ECM in exact opposite manner, I hypothesized that ECM signaling may interact with cell-cell junction signaling pathways in regulating DNA repair. To test this hypothesis, I asked whether the main breast epithelial adherens junction cadherin, E-cadherin, is involved. I blocked E-cadherin function using a monoclonal antibody MB2. The function blocking was demonstrated by the loss of cell-cell junction interactions and observation of increased cell scattering using phase microscopy. I then asked whether blocking E-cadherin altered the expression and localization of proteins related to DNA repair. Indirect immuno-fluorescence showed that in the E-cadherin blocked non-tumorigenic breast epithelial cell line HMT-3522 S1 there is an up-regulation of nuclear γ-H2AX and RAD51, as well as an increase in the proliferation marker Ki67. In non-proliferative MB2 blocked cells there is an upregulation of γ-H2AX and reduced Ki67. Furthermore, in these proliferative and non-proliferative blocked cells we were able to see lower levels of β-catenin near the cell membrane and an increase in its levels inside the cell especially in the nucleus. The latter has been confirmed also by western blot technique comparing the nuclear and cytoplasmic fraction expression. In addition, western blots showed that total RAD51 level was down-regulated by E-cadherin blocking and γ-H2AX levels were found to be higher in proliferative and non-proliferative MB2 treated cells. MB2 treated cells have a higher frequency of HR in the absence of ECM and in the presence of ECM, MB2 blocking abolishes the ECM effect on HR. Furthermore, in the absence of ECM, RAD51 siRNA treated cells down-regulated HR but the absence of RAD51 did not down regulate HR in the presence of ECM. I was not able to see any difference in the phosphorylated forms of β-catenin such as Tyr-142, Ser-45 and Tyr-86 that has the ability to enter into the nucleus. Therefore, E-cadherin was found to block nuclear β-catenin, RAD51 and γ-H2AX in a proliferation-independent manner. E-cadherin also was necessary for ECM to up-regulate HR. The up-regulation of HR by ECM was only slightly dependent on RAD51 suggesting a novel E-cadherin-dependent and RAD51-independent HR component in breast epithelial cells in contact with ECM as they are in vivo in the normal breast tissue. These experiments will help us to understand the role of E-cadherin and β-catenin in DNA double-stand break repair directly, as well as in combination with ECM signaling. Both alterations in integrin mediated signaling and cell-cell junction integrity contribute to breast cancer progression by rendering breast epithelial cells more invasive. My project will shed light on whether these invasive processes also alter DNA repair and contribute to genome stability. Understanding of the interrelationships among integrin signaling, cell-cell junctions, and genome stability will contribute to understanding normal breast cell processes and open up investigations on how these may go awry in cancer progression.

Cell proliferation and contact inhibition play a major role in maintaining epithelial cell homeostasis. A hallmark of epithelial cells is strong cell-cell junctions. These junctions include E-Cadherin, a type of adherens junction that is critical for both barrier function and contact inhibition. Prior experiments by other groups have shown that adherens junctions are subject to mechanical tension. Externally applied forces (e.g. stretch) results in changes in E-Cadherin forces that coordinate proliferation. My current work tests the hypothesis that E-Cadherin forces mediate the spatial regulation of cell proliferation even in the absence of externally applied forces.

Les patients atteints de MICI (maladie de Crohn et recto-colite hémorragique) présentent souvent des lésions des cellules de l'épithélium intestinal. La rémission de ces maladies nécessite à la fois un arrêt de l'inflammation et une migration des entérocytes pour réparer les dommages épithéliaux. Cette migration cellulaire appelée restitution intestinale requiert des adhérences cellule-MEC et cellule-cellule réalisées par les complexes protéiques associés aux intégrines et cadhérines. Le but de cette thèse a été d'étudier l'impact deSaccharomyces boulardii (Sb) sur la réparation de l'épithélium intestinal lésé. Nous avons montré que le surnageant de Sb contenait des facteurs modulant la restitution de l'épithélium intestinal in vivo et in vitro sans affecter la prolifération des cellules épithéliales. Ces effets motogéniques du surnageant de Sb s'exercent via la modulation des molécules d'adhérence. En effet, le surnageant de Sb augmente l'affinité de l'intégrine α2β1 pour son ligand le collagène de type I mais entre en compétition avec les intégrine αvβ5, pour inhiber l'adhérence des entérocytes sur la vitronectine. Ces modifications de l'adhérence avec la matrice extracellulaire entraînent une régulation des voies de signalisation émanant des intégrines et une réorganisation des plaquesd'adhérence. Ces évènements vont accroître la migration des entérocytes. De plus, nos résultats préliminaires portant sur Sb et l'adhérence cellule-cellule durant la restitution intestinale ont montré une implication de la E-cadhérine dans la migration induite par Sb. / Intestinal epithelial cell damage is frequently seen in IBD patients with ulcerative colitis or Crohn's disease. The remission of these diseases requires both the cessation of inflammation and the migration of enterocytes torepair the damaged epithelium. Adhesions with the ECM and the adjacent cells using complex of proteins associated with integrins and cadherins are necessary for this cell migration called intestinal restitution. Theaim of this thesis was to study the effect of S.boulardii on the resealing of a wound in intestinal epithelia. First of all, we demonstrated that the supernatant of S.boulardii contains factors that modulate intestinal epithelial cell restitution both in vitro and in vivo without affecting cell proliferation. We showed that the motogenic factors of S.boulardii act by modulating adhesion molecules. Indeed, the supernatant of S.boulardii increase the the affinity between 21 and it ligand the collagen type I, but also compete with integrin v5 to block theadhesion of enterocytes on vitronectin. These modifications of adhesion on extracellular matrix lead to aregulation of signaling pathway mediated by integrins, and a reorganization of focal adhesions. These eventscontribute to an increase of the migration of enterocytes. Add to this, our preliminaries results on S.boulardiiand cell-cell adhesion during intestinal restitution show an involvement of E-cadherin in the migrationS.boulardii-induced. With this work, we have demonstrated that heat-sensitive motogenic factors secreted by S.boulardii can enhance intestinal restitution with a dynamic regulation of adhesion between integrin and the ECM.

Au cours de ma thèse, j’ai étudié la contribution de miR-205 dans le développement du cancer du sein. MiR-205 a été choisi suite à l'analyse comparative de l'expression du miRome entre la lignée « normale » MCF10A et une lignée cancéreuse dérivée MCF10A-CA1a. J’ai démontré que l’expression de miR-205 augmente durant la tumorigenèse tandis que miR-205 est non détectable dans la lignée cellulaire ayant un potentiel métastatique. De plus, j’ai montré que les cellules souches du cancer du sein expriment miR-205, contrairement à la population non souche. En utilisant des cultures de cellules épithéliales 3D, j’ai corrélé la fonction tumorigène de miR-205 à la répression de l'apoptose et non à une prolifération accrue. De plus, le niveau d'expression de la E-Cadhérine dépend de la quantité de miR-205 dans les différentes lignées cellulaires de MCF10A. Les études de perte de fonction suggèrent que la E-Cadhérine est impliquée dans le phénotype acini miR-205-Dépendant, en corrélation avec la transformation de cellules épithéliales du sein. L’ensemble de ces résultats met en lumière la complexité et la duplicité des miRNA durant le processus de cancérisation. Ce type d’étude ouvre des perspectives d’utilisation des miRNA dans le cadre des diagnostics et/ou thérapeutiques. / During the time I was working on my thesis, I aimed to understand the role of miR-205 in breast cancer development. MiR-205 was chosen from the comparative analysis of total micro-RNAs expression in non-Transformed and tumorigenic cell lines of the MCF10A breast epithelial cell model. I demonstrated the complexity of miR-205 functions during breast epithelial cell transformation by showing miR-205 overexpression in transformed non-Invasive cell lines and miR-205 down-Regulation in cell line with metastatic potential. Moreover, we demonstrated increased level of miR-205 expression in breast cancer stem cells in comparison with non-Stem cells. Using 3D cultures of breast epithelial cells, I succeeded to correlate the tumorigenic function of miR-205 with its role in modulation of acinar size, and to attribute it to the apoptosis repression but not increased proliferation. Further, I was able to show that miR-205 exercises its oncogenic functions via targeting ZEB1, an inhibitor of E-Cadherin. Indeed, E-Cadherin expression level depends on the amount of miR-205 in different MCF10A cell lines. Downregulating E-Cadherin restored normal acinar morphology in miR-205 expressing cells, consistent with E-Cadherin being involved in the miR-205-Dependent acini phenotype that correlates with tumorigenic breast epithelial cell transformation.