Breast cancer metastasis is one of the reasons why this type of cancer is destructive even after treatment as it tends to move from one organ to another increasing the risk factor for an individual. In the metastatic cascade, the tumour undergoes many different types of stress, including extracellular (ECM) stiffness. Key proteins that have been linked to the change in stiffness of the ECM are YAP and β-catenin. Both functions similarly in the manner that they need to translocate to the nucleus and bind to their respective transcription factors in order to activate their downstream genes. In parallel this seems to be on a stiffness dependent manner. Therefore, the hypothesis is that β-catenin is able to compensate for YAP function when YAP is downregulated in a stiffness dependent manner. In this work, results show a significant increase of YAP and β-catenin translocation to the nucleus of MDA-MB-231 cells when they are subject to the stiffer substrate in comparison to the softer substrate indicating increase gene expression of their respective pathways. The effect of the stiffness was then analyzed by doing single knockdown experiments with siRNA. To investigate the response of β-catenin, knocking down YAP was done, and it was shown that β-catenin translocation significantly increased on the softer matrix, while stiffer matrix showed no significant difference. Downstream gene expression also confirmed this idea with CTGF being downregulated with β-catenin knockdown and AXIN2 being downregulated with YAP knockdown. In the cell behavioural aspect, only when the double knockdown of YAP and β-catenin was done, the migration and proliferation rate had significant lowered. This echoes the idea further of the compensating effects of β-catenin to YAP. In addition, the exploration of the cytoskeleton network was investigated, as this is a key component in protein pathways, by treating the cells using LatA and Blebbistatin, affecting F-actin and myosin-II respectively. Knowing the critical role of cytoskeletal proteins in mechanotransduction, the hypothesis is that actin filaments and myosin-II mediate the YAP & β-catenin nuclear translocation activation. Findings show the direct relationship between F-actin and YAP as actin polymerization state significantly decreased when YAP was knockdown in a similar manner to when LatA was added. When myosin-II was added, both YAP and β-catenin nuclear translocation were affected, indicating its potential role in mechanotransduction. Furthermore, it was found that cell confluency and PIEZO1 activation had significant effects in YAP & β-catenin translocation. By seeding the cells with different densities, the β-catenin signalling could be visualized with IF staining, with the conclusion that at high confluency, the β-catenin translocation was alleviated. For the PIEZO1 studies, results indicate that PIEZO1 is an upstream regulator of YAP by doing single knockdown experiments and subsequently analysing YAP signalling. The findings underscore the potential significance of β-catenin as a modulator of mechanotransduction in the absence of YAP, showcasing the complexity of the protein signalling network orchestrating cellular response due to mechanical cues. Unravelling these protein interplay could offer novel insights into therapeutic targets for breast cancer mechanotransduction. Ultimately, this research adds to the understanding of the intricate protein signalling that governs mechanotransduction in breast cancer cells. The discovery of stiffness dependent YAP & β-catenin signalling, the interplay between YAP and β-catenin pathway mechanotransduction implicated by cell density, the regulation of YAP- β-catenin interplay in mechanotransduction by PIEZO1, the importance of F-actin & myosin-II in YAP & β-catenin translocation, and the YAP & β-catenin effects on cell behaviour, all help lay the groundwork for devising targeted interventions to impede cancer progression. / Thesis / Master of Applied Science (MASc) / Breast cancer is the most prominent type of cancer that exists in women and like other cancers, it can spread to other organs such as the bone, liver, and brain even though the microenvironments are different. With different proteins like yes-associated protein (YAP) regulating this microenvironmental change in the primary and secondary sites, it can flourish and become more aggressive which leads to death for the host. The interactions of these proteins and their pathways which affects the aggressiveness of the cancers are still not well understood. This project investigates the interaction between YAP and β-catenin in response to surface stiffness to understand the mechanical regulation of breast cancer metastasis. Alongside the protein signalling, cytoskeletal components, downstream gene expression, cell confluency, and membrane proteins are explored. Our results show that an increase in stiffness allow for higher nuclear translocation for YAP and β-catenin, enhancing downstream gene expression relating to migration and proliferation. Furthermore, in lower stiffness the crosstalk between YAP and β-catenin results in an inverse relationship. These findings suggest β-catenin compensates YAP function when YAP is inhibited. In terms of the cytoskeletal protein, an integral part of the cell, the intervention saw a significant alteration in the YAP & β-catenin signalling. Additionally, cell confluency played a large role in β-catenin nuclear translocation implicating the role of cell-to-cell contact in mechanotransduction. To see if mechanosensitive membrane proteins fit into the pathway, PIEZO1 studies were done and results show that it is an upstream effector of YAP, and consequently an indirect connection with β-catenin. All in all, this thesis provides insightful information in the role of stiffness matrix, cell confluency, membrane proteins and how that regulate YAP & β-catenin. This research provides the mechanism for the synergistic therapies targeting multiple proteins to prevent cancer growth and metastasis.

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.

Thèse numérisée par la Division de la gestion de documents et des archives de l'Université de Montréal.

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.

The paralogous C-terminal binding proteins (CtBP) 1 and 2 are evolutionarily conserved transcriptional coregulators that target and disrupt the expression of several genes essential for multiple cellular processes critical to regulating tumor formation. CtBP’s ability to govern the transcription of genes necessary for apoptosis, tumor suppression, invasion/migration and EMT gives rise to its oncogenic activities. Both isoforms of CtBP are found to be overexpressed in cancers including colorectal, pancreatic, ovarian, and breast, with higher levels correlating to lower overall median survival. Although multiple lines of evidence suggest CtBP plays a role in tumorigenesis, it has never been formally characterized as an oncogene. For this reason, the goal of this dissertation was to design a set of experiments to determine the transforming ability of CtBP2 in vitro using both murine and human fibroblast and in vivo using the Apcmin/+ mouse model of cancer. Specifically, we demonstrate that overexpression of CtBP2 alone can drive transformation of NIH3T3 cells leading to loss of contact inhibition, increased x invasion/migration, and anchorage independent growth. In addition, CtBP2 was found to cooperate with the large T-antigen (LT) component of the simian virus 40 (SV40) to lead to transformation of murine embryonic fibroblasts (MEFs) and with both LT and small T-antigen (ST) to induce migration/invasion and anchorage-independent growth in BJ human foreskin fibroblasts. To confirm the role of Ctbp2 in a mouse tumor model with Ctbp overexpression, we bred Apcmin/+ mice to Ctbp2 heterozygous (Ctbp2+/-) mice, which otherwise live normal lifespans. CtBP is a known target of the APC tumor suppressor and is thus stabilized in APC mutated human colon cancers and is found in high levels in Apcmin/+ polyps. Remarkably, removing an allele of Ctbp2 doubled the median survival of Apcmin/+ mice (P <0.001) and reduced polyp formation to near undetectable levels. These data suggest the importance of CtBP2 in driving cellular transformation and identify it as a potential target for prevention or therapy in APC mutant backgrounds.

The diploma thesis was focused on evidence of selected somatic mutations in genes ALK (Anaplastic lymphoma receptor tyrosine kinase), BRAF (v-Raf murine sarcoma viral oncogene homolog B1) and β-catenin (CTNNB1) through molecular - genetic methods in the target group of neuroectodermal tumors (neuroblastoma, medulloblastoma, brain tumors, paraganglioma and pheochromocytoma). Some of them are already considered as prognostic indicators which help to identify the subtype of various tumors and on the basis of this molecular - biological classification choosing the appropriate treatment. The genetic material of 133 patients was used for the analysis divided by the type of cancer. The presence of the mutation was detected in seven cases, of which two of them beloged to the gene BRAF, one to the gene ALK and four to the gene β-catenin. The subject of research in the cases of this genes were hotspot mutation sites. The purpose was to confirm the presence of the mutation in the hotspots and contribute to the studies which are aimed at the introduction of more suitable treatment through the inhibitors of mutated genes. Keywords: ALK, BRAF, β-catenin (CTNNB1), neuroectodermal tumors, sequencing, MLPA

Student Number : 9906751K - MSc dissertation - School of Molecular and Cell Biology - Faculty of Science / In addition to its crucial role in cell adhesion, β-catenin is also known to augment gene expression by forming a complex with lymphoid enhancer factor/T-cell factor in the nucleus. Unregulated β-catenin expression and/or its increased nuclear presence can lead to abnormal cell proliferation, tumour invasion and metastasis. Pertinent is the fact that the actin cytoskeleton is central to the translocation of several nuclear proteins. This study investigated whether the actin cytoskeleton influences the nuclear translocation of β-catenin in human oesophageal squamous cell carcinoma (HOSCC), a metastatic disease of common occurrence in South Africa. Disruption of the actin cytoskeleton of five moderately differentiated HOSCC cell lines, with cytochalasin D (cytoD), showed that the nuclear β-catenin level was unaltered in SNO, WHCO1 and WHCO5, but decreased in WHCO3 and WHCO6. CytoD treatment did not affect the cytoplasmic/membrane β-catenin level in these cell lines. Further examination of the possible association between the actin cytoskeleton and nuclear β-catenin translocation, required the design and stable transfection, of a vector containing full-length human β-catenin cDNA into one of the HOSCC lines. Stimulation of exogenous β-catenin expression in transfected WHCO1 cells did not increase cellular β-catenin level, nor did the stimulation of endogenous β-catenin expression with DMSO. In most cases (SNO, WHCO1 and WHCO5) the nuclear distribution of β-catenin in HOSCC is independent of a functional actin cytoskeleton, nonetheless there are some exceptions (WHCO3 and WHCO6). The observed variation within the HOSCC lines is possibly due to specific underlying event/s particular to the cell line. The stable level of β-catenin expression could be a consequence of regulatory pathways in WHCO1 compensating for the induced imbalance of β-catenin expression.

O ameloblastoma é definido como um tumor odontogênico epitelial de crescimento lento e localmente invasivo, que acomete os maxilares com alta taxa de recorrência quando não removido adequadamente. Este trabalho tem por objetivo estudar as expressões imuno-histoquímicas das proteínas -catenina, p-Akt, CD44 e vimentina em ameloblastomas. Para este estudo foram selecionados 40 casos de ameloblastoma, pertencentes aos arquivos do Serviço de Patologia da Disciplina de Patologia Bucal da FOUSP. Para a realização das reações imuno-histoquímicas foi utilizada a técnica da estreptavidina-biotina e os cortes submetidos aos anticorpos anti--catenina, anti-pAkt, anti-CD44 e anti-vimentina separadamente. O padrão de marcação celular da -catenina nos ameloblastomas foi: marcação citoplasmática, nuclear e de membrana em 33 (82,5%) casos, marcação citoplasmática e de membrana em 7 (17,5%) casos; quanto à sua localização, em 21 (52,5%) casos marcações central e periférica, em 15 (37,5%) casos observou-se marcação central, em, 4 (10%) marcação periférica. Com relação à proteína p-AKT em 36 (90%) casos o padrão de marcação celular foi citoplasmático, sendo em 4 (10%) casos evidenciado o padrão citoplasmático e nuclear. De todos os casos analisados quanto a localização da marcação do p-AKT, 23 (57,5%) casos com marcação nas áreas central e periférica e 17 (42,5%) apresentaram marcação periférica. Nenhuma das lâminas estudadas apresentou marcação exclusiva em áreas centrais da lesão. Para a proteína CD44, 27 (67,5%) casos dos ameloblastomas estudados apresentou marcações citoplasmática e de membrana, enquanto 13 (32,5%) casos mostraram apenas marcações citoplasmáticas. No que diz respeito a localização, 28 (70%) casos apresentaram marcações centrais e periféricas concomitantes, 11 (27 %) casos marcações centrais, e 1 (2,5%) caso marcação periférica. 37 (92,5%) dos casos incluídos nesta pesquisa apresentou marcação citoplasmática para vimentina, sendo 3 (7,5%) casos negativos para a proteína. Dentre os casos com positividade, 22 (55%) referiram-se à região central 14 (7,5%) para as regiões central e periférica , e 1 (2,5%) caso para a região periférica. De acordo com os resultados obtidos, acredita-se que as áreas central e periféricas do tumor possuem células responsáveis pela proliferação e invasividade do tumor, assim como a presença de células tronco responsáveis pela invasividade do tumor, também estão presentes nessas áreas. / The ameloblastoma is defined as an epithelial odontogenic tumor of slow growth, and locally invasive, affecting the jaws with a high rate of recurrence if not removed properly. This study aims to study the immunohistochemical expression of the protein -catenin, p-Akt, CD44 and vimentin in ameloblastomas. For this study we selected 40 cases of ameloblastoma, from the archives of the Pathology of Oral Pathology FOUSP. To carry out the reactions immunohistochemical technique was used streptavidin-biotin and cuts subjected to anti--catenin, anti-pAkt, anti-CD44 and antivimentin separately. The pattern of cell labeling of -catenin in ameloblastomas was: cytoplasmic, nuclear and membrane in 33 (82.5%) cases, cytoplasmic membrane in 7 (17.5%) cases, as regards its location in 21 (52.5%) cases markings central and peripheral in 15 (37.5%) cases observed central marking in, 4 (10%) peripheral marking. With respect to the p-AKT protein in 36 (90%) cases, the staining pattern was cytoplasmic cell, and 4 (10%) patients demonstrated the nuclear and cytoplasmic pattern. In all cases analyzed as marking the location of the p-AKT, 23 (57.5%) cases with marking the central and peripheral areas and 17 (42.5%) had peripheral marking. None of the studied thin sections show labeling exclusively in the central areas of the lesion. For protein CD44, 27 (67.5%) cases of ameloblastomas studied showed markings and cytoplasmic membrane, while 13 (32.5%) cases showed only cytoplasmic markings. Regarding localization, 28 (70%) presented concomitant central and peripheral markings, 11 (27%) patients central markings, and 1 (2.5%), peripheral marking case. 37 (92.5%) of the cases included in this study showed cytoplasmic staining for vimentin, and 3 (7.5%) cases negative for protein. Among the positive cases, 22 (55%) referred to the central 14 (7.5%) for the central and peripheral, and 1 (2.5%) case for the peripheral region. According to the obtained results, it is believed that central and peripheral areas of the tumor cells have responsible for the proliferation and invasiveness of the tumor, as well as the presence of stem cells responsible for tumor invasiveness, are also present in these areas.

Les mélanocytes, cellules responsables de la pigmentation de la peau et des poils, protègent les cellules des stress environnementaux, en particulier des rayonnements ultra-violets (UV) présents à la surface de la Terre. Les UV induisent des dommages moléculaires et régulent de nombreuses voies de signalisation en aval de MC1R, MAPK, PI3K, ou PKC. A court terme, les UV peuvent induire la mélanogenèse et à long terme participent à la mélanomagenèse. Dicer, protéine clef de la maturation des microARN, est régulée par différents stress. La protéine multifonctionnelle β-caténine est impliquée dans le développement des mélanocytes. Ces deux protéines participent à la régulation fine de l'expression génique. L'objectif de cette thèse est de mettre en évidence le rôle et la régulation de Dicer dans le lignage mélanocytaire dans des conditions normales et de stress (UVB). Dans une première partie, nous nous sommes intéressés au rôle de Dicer dans la pigmentation et sa régulation dans le lignage mélanocytaire. Nous avons montré, in vivo dans un modèle murin, que Dicer est nécessaire à la fois à la mise en place du lignage mélanocytaire et au fonctionnement de ce lignage chez l'adulte. L'absence de Dicer dans le lignage mélanocytaire affecte la localisation des mélanocytes de la papille dermique du follicule pileux et empêche la pigmentation du poil. In vitro, la transcription de Dicer est régulée par différentes voies, en particulier par les protéines PI3K, RSK, GSK3β et β-caténine. L'activité répressive de β-caténine sur la transcription de Dicer est dépendante de sites LEF/TCF. Dans une deuxième partie, nous nous sommes intéressés à l'implication de Dicer, en relation avec β-caténine, dans la réponse aux UVB. Nous avons mis en évidence in vivo et in vitro la relocalisation nucléaire et l'activation transcriptionnelle de β-caténine induites par les UV. Tout comme β-caténine, les UVB répriment la migration des mélanocytes in vitro. Nous avons montré in vitro que les UVB répriment l'expression de Dicer et que cette répression est dépendante de sites de fixation de facteurs de transcription, dont LEF/TCF, présents dans la région promotrice de Dicer. Une diminution de Dicer participe à la protection des mélanocytes contre les UVB. Ce travail de thèse a donc permis de montrer le rôle de Dicer dans la pigmentation adulte et de mettre en évidence des voies de régulation de l'expression de Dicer dans les mélanocytes non stressés et dans les mélanocytes soumis à un stress UVB. / Melanocytes, cells responsible for pigmentation of the skin and hair, protect cells from environmental stress, especially ultra-violet radiations (UV) present on Earth floor. UV induce molecular damages and regulate many signaling pathways downstream of MC1R, MAPK, PI3K, or PKC. In the short term, UV can increase melanogenesis and in the long term, participate in melanomagenesis. Dicer, a key protein involved in microRNA maturation, is regulated by different types of stress. The multifunctional protein β-catenin is implicated in melanocyte development. These two proteins participate in fine regulation of gene expression. The goal of this thesis is to highlight the role and regulation of Dicer in the melanocyte lineage in normal and UVB stress conditions. In the first part, we focused on the role of Dicer in pigmentation and its regulation in the melanocyte lineage. We showed that, in a mouse model in vivo, Dicer is necessary for both establishment of melanocyte lineage and proper function of this lineage in adults. The lack of Dicer in the melanocyte lineage affects localization of melanocytes in the dermal papilla of hair follicles, preventing hair pigmentation. In vitro, Dicer transcription is regulated by different pathways, including PI3K, RSK, GSK3β and β-catenin. LEF/TCF sites mediate the repressive activity of β-catenin on Dicer transcription. In the second part, we focused on the implication of Dicer, in connection with β-catenin, in the response to UVB by melanocytes. We showed the nuclear relocalization and transcriptional activation of β-catenin induced by UV both in vivo and in vitro. Like β-catenin, UVB represses melanocyte migration in vitro. We showed in vitro that UVB represses Dicer expression and that this repression is dependent on transcription factors binding sites in the Dicer promoter region including LEF/TCF. Decreased level of Dicer participates in protection of melanocytes against UVB. This thesis work allowed us to show the role of Dicer in adult pigmentation and to highlight signaling pathways implicated in Dicer expression regulation in non-stressed melanocytes and in UVB-stressed melanocytes.

Plus de 80% des cancers colorectaux sont initiés par la perte de fonction du gène Apc. Afin d’identifier de nouvelles cibles thérapeutiques, nous avons utilisé des modèles murins présentant des mutations du gène Apc et recherché par des analyses de puces à ADN de nouveaux événements moléculaires impliqués au cours de la carcinogenèse intestinale.Cette approche nous a permis d’identifier une activation de la signalisation Notch tout au long du processus tumoral. Toutefois, cette activation n’est pas un élément clé de la progression tumorale puisque son inhibition n’empêche pas le phénotype tumoral induit par la perte du gène Apc. En parallèle, nos travaux ont permis d’identifier une induction de l’autophagie tout au long de la carcinogenèse intestinale. L’activation de ce processus biologique ouvre, quant à lui, de nouvelles perspectives thérapeutiques dans le traitement du CCR. / Over 80% of colorectal cancers are linked to an Apc mutation. To identify new therapeutic targets, we used mouse models with Apc mutations and performed microarray experiments to identify key molecular events involved in intestinal carcinogenesis. This approach allowed usto identify an activation of the Notch signaling all along tumor progression. However, this induction is dispensable for tumor development since its inhibition did not prevent the Apc phenotype. In addition, we have identified an induction of autophagy throughout intestinal carcinogenesis which appears to be an attractive therapeutic target in the treatment of CRC patients.