Les lymphomes à grandes cellules B primitifs du médiastin (PMBL) partagent des caractéristiques pathologiques avec les lymphomes diffus à grandes cellules B (DLBCL), et des caractéristiques moléculaires communes aux lymphomes de Hodgkin classiques (cHL). Le cluster oncogénique miR-17-92, localisé au niveau du chromosome 13q31, est un gène amplifié dans les DLBCL. Dans notre étude, nous avons comparé le niveau d’expression de chaque membre du clustermiR-17-92 dans une série de prélèvements de patients de 40 PMBL, 20 DLBCL et 20 cHL, et étudié les gènes cibles liés aux microARN dérégulés dans les PMBL. Nous avons montré un niveau plus élevé de miR-92a dans les PMBL que dans les DLBCL, mais pas dans les cHL. La combinaison d’une analyse in silico prédictive des cibles de miR-92a et d’une analyse transcriptomique nous a permis d’identifier FOXP1 comme la cible principale de miR-92a dans les PMBL, un résultats qui n’avait jusqu’alors pas été établi. Cette observation a été confirmée par le test 3’UTR, le niveau d’expression ARN et protéique dans les lignées cellulaires transduites. Les études in vivo sur les souris à partir des cellules transduites nous a permis de démontrer l’effet tumeur suppresseur de de miR-92a et l’effet oncogénique de FOXP1. L’expression plus élevée de miR-92a et la sous-expression de FOXP1 au niveau ARN et protéique a également été retrouvé dans les prélèvements humains de PMBL, alors que le niveau d’expression de miR-92a était bas et FOXP1 était haut dans les DLBCL. Nous en avons conclu à une régulation post-transcriptionnelle de FOXP1 par miR-92a dans les PMBL, avec une relevance clinico-pathologique pour mieux caractériser les PMBL. / Primary mediastinal large B-cell lymphoma (PMBL) shares pathological features with diffuselarge B-cell lymphoma (DLBCL), and molecular features with classical Hodgkin lymphoma (cHL). The miR-17-92 oncogenic cluster, located at chromosome 13q31, is a region that is amplified in DLBCL. Here we compared the expression of each member of the miR-17-92 oncogenic cluster insamples from 40 PMBL patients versus 20 DLBCL and 20 cHL patients, and studied the target genes linked to deregulated miRNA in PMBL. We found a higher level of miR-92a in PMBL than in DLBCL, but not in cHL. Acombination of in silico prediction and transcriptomic analyses enabled us to identify FOXP1 as a main miR-92a target gene in PMBL, a result so far not established. This was confirmed by 3’UTR, and RNA and protein expressions in transduced cell lines. In vivo studies using the transduced cell lines in mice enabled us to demonstrate a tumor suppressor effect of miR-92aand an oncogenic effect of FOXP1. The higher expression of miR-92a and the down regulation of FOXP1 mRNA and proteinwere also found in human samples of PMBL, while miR-92a expression was low and FOXP1was high in DLBCL. We concluded to a post-transcriptional regulation by miR-92a through FOXP1 targeting in PMBL, with a clinico-pathological relevance for better characterisation of PMBL.

For cancer cells to initiate cell migration and progress to metastasize, epithelial genes must be silenced and the expression of mesenchymal genes must be upregulated. During prostate carcinogenesis, E-cadherin expression is downregulated through multiple mechanisms, the majority of which combine to silence E-cadherin expression through transcriptional regulation at the level of the E-cadherin promoter. Recently it has been discovered that there is transcriptional upregulation of the mesenchymal cadherin, N-cadherin during prostate cancer metastasis. Although N-cadherin expression can be detected in human prostate cancer and in prostate carcinoma cell lines, the mechanisms controlling the transcriptional regulation of N-cadherin in cancer are uncharacterized. This body of work offers the first evidence for the mechanisms controlling the transcriptional upregulation of N-cadherin expression in prostate carcinoma. We utilized anchorage independent culture to induce downregulation of N-cadherin expression, and then analyzed the necessary events for N-cadherin upregulation when cells attached to Fibronetin (FN). In order to determine the functional regions of the N-cadherin proximal promoter that were involved in the upregulation of N-cadherin expression, we cloned regions of the human N-cadherin 5’ proximal promoter, and regions of the first intron of the N-cadherin gene into a luciferase reporter vector. It was determined that the bHLH transcription factor Twist1 controlled the upregulation of N-cadherin transcription in PC-3 cells, through β1 integrin dependent nuclear localization of Twist1. A cis-element located in the first intron of the N-cadherin gene was shown to be necessary for Twist1 mediated effects on the N-cadherin promoter. We then determined the requirements for cell-type specific expression of the N-cadherin promoter. It was determined that an additional cis-element located in the first intron of the N-cadherin gene was necessary to repress N-cadherin promoter activity in cells lacking N-cadherin. Through deletion analysis of the N-cadherin promoter luciferase construct, a DNA binding site for the transcription factor FoxP1 was discovered. FoxP1 binds to the repressive cis-element in vitro, and mutation of the FoxP1 DNA binding site eliminated cell-type specific activity of the N-cadherin promoter. Therefore, we have documented that the aberrant expression of N-cadherin in prostate carcinoma involves alterations in both positive and negative transcriptional regulators.

Les protéines de liaison à l’ARN PUMILIO 1 et 2 (PUM1/2) exercent un rôle central dans le maintien des cellules souches chez les Invertébrés en se fixant, en association avec des partenaires protéiques, sur la région 3’ UTR de certains ARNm, régulant ainsi leur devenir. A ce jour, le rôle de PUM1/2 dans les cellules souches/progénitrices hématopoïétiques (CSPHs) a été peu étudié. La perte de la coordination entre auto-renouvellement et différenciation des CSPHs peut aboutir à des hémopathies chez l'Homme, d’où la nécessité de comprendre les mécanismes sous-jacents. Notre équipe a mis en évidence, par une approche de shARN, que l’invalidation des protéines PUM1/2 dans les CSHs humaines et murines conduit à une réduction de leur expansion, associée à une apoptose accrue et un arrêt du cycle cellulaire en phase G0/G1, et aussi à une perte du potentiel clonogénique in vitro et du potentiel de reconstitution in vivo. L’objectif de notre travail a consisté à : a/ évaluer les effets de la surexpression de PUM1/2 dans les CSPHs, b/ déterminer l’implication de PUM1/2 dans les processus leucémiques, c/ étudier les mécanismes moléculaires responsables de l’activité de PUM1/2 en identifiant les cibles et les partenaires protéiques par une approche de protéomique globale. Nos résultats suggèrent qu’une surexpression modérée de PUM1 (2/3 fois) dans les cellules CD34+ limite la perte du potentiel clonogénique alors qu’une expression plus élevée (5/10 fois et plus) est toxique. L’analyse de l’expression de PUM1/2 par RT-qPCR dans les échantillons de Leucémies Aigue Myeloïdes (LAM) (GOELAMSthèque) montre une augmentation significative dans les échantillons les plus immatures (LAM0-2) comparés aux contrôles sains. La perte de PUM1/2 par shARN dans les cellules primaires de leucémies ainsi que dans des lignées issues de différents processus leucémiques réduit fortement leur survie. La recherche des partenaires associés à PUM par spectrométrie de masse a permis de découvrir Argonaute2 et MOV10 (tous les 2 impliqués dans la machinerie des miRNA), ainsi que des protéines de liaison aux ARNs, ELAV1 déjà connue pour son implication dans le maintien des CSH murines et IMP3, impliqué dans de nombreux cancers et dans la régulation du cycle cellulaire. L’invalidation de IMP3 ou ELAV1 dans les CSPHs conduisent, in vitro, aux mêmes effets observés avec la perte du PUM 1/2, une diminution de l’expansion avec une augmentation de l’apoptose, et la perte du potentiel clonogénique. Enfin, nous avons identifié FoxP1 (Forkhead box P1) comme nouvelle cible directe de PUM1/2, dont le rôle est encore très peu décrit dans l’hématopoïèse. L’étude fonctionnelle de FoxP1 sur les CSPHs par shARN mime les effets observés avec les facteurs PUM1/2. De plus, la surexpression de FoxP1 restaure partiellement les activités antiprolifératives et pro-apoptotiques générées par les shPUM1/2. Enfin, le profil d’expression de FoxP1 dans les LAM corrèle avec le profil d’expression de PUM1/2. Nos résultats confirment le rôle majeur joué par les protéines PUM1/2 en partie via la régulation positive de FoxP1 qui contribue au maintien les CSPHs normales et pathologiques. / Pumilio 1 and 2 (PUM1/2) RNA-binding proteins exert a central role in stem cell maintenance among Invertebrates by binding the 3'UTR of mRNA targets in association with protein partners, thus regulating mRNA stability/translation. Nothing is known regarding normal and pathologic hematopoietic stem and progenitor cells (HSPCs). Loss of coordination between self-renewal and differentiation of HSPCs can lead to leukemia in humans, hence the need to understand the mechanisms. Our team has highlighted the fundamental role played by the post-transcriptional regulators Pumilio (PUM) 1/2 on normal HSPC properties. By a shRNA approach, PUM 1/2 knockdown in human and murine HSPCs leads to: a/ a reduced expansion associated with an increased apoptosis and a cell cycle arrest in G0/G1 phase, b/ the loss of their clonogenic capacity and their in vivo reconstitution potential. The objective of our work is to: a/ evaluate the effects of PUM 1/2 overexpression in HSPC, b/ determine PUM1/2 involvement in leukemic processes; c/ investigate the molecular mechanisms responsible of PUM activity in HSPC by identifying protein targets and partners. Our results showed that a moderate overexpression of PUM1 (2 to 3 fold) in normal CD34+ HSPCs limits the loss of their clonogenic potential, while a higher expression (5 to 10 fold or more) is toxic. The expression analysis of PUM1/2 transcripts in Acute Myeloid Leukemia (AML) (GOELAMSthèque) showed a significant increase in the most immature samples (AML0-2) as compared to healthy controls. PUM1/2 knockdown by shRNA in AML cells significantly reduced their survival. The same effect was observed in cell lines from several leukemic processes. We identified various PUM-associated partners by mass spectrometry, Argonaute2 and MOV10 (involved in the miRNA machinery), and the RNA-binding proteins IMP3 (involved in several cancer and in cell cycle regulation) and HuR/ELAV1 (already known to be involved in murine HSPCs maintenance). IMP3 or ELAV1 knockdown in HSPCs in vitro lead to the same effect of a PUM1/2 invalidation, a decreased expansion with an increased apoptosis and the loss of clonogenic potential. Finally, we identify the forkhead box P1 (FOXP1) transcription factor as a new direct target up-regulated by PUM1 and PUM2. Functional study of FoxP1 knockdown by shRNA in HSPCs mimic PUM1/2 activities. Moreover, FOXP1 overexpression partially rescued shPUM antiproliferative and pro-apoptotic effects. Also, the PUM1/2 and FOXP1 expression levels in leukemic primary cells were measured by RT-qPCR and revealed a positive correlation. Our results reveal that PUM1/2 are direct positive regulators of FOXP1 which contributes to the maintenance of normal and leukemic HSPCs.

Breast cancer (BC) was not initially considered an immunogenic tumor; however, recent data show that immune-related factors are associated with patient prognosis and the response to treatment. Several large adjuvant clinical trials have shown that tumor infiltrating lymphocytes (TIL) are significantly associated with a better prognosis and can also predict responsiveness to pre-operative chemotherapy, particularly in the triple negative (TN) & HER2+ BC subtypes (Carsten Denkert et al. 2010; Loi et al. 2013a). Recently, the presence of ectopic lymph node-like structures characterized by distinct T and B cell zones, called tertiary lymphoid structures (TLS), were identified adjacent to the tumor (Gu-Trantien et al. 2013) in 60% of BC (Buisseret et al. 2017b) and linked with a good prognosis (Gu-Trantien et al. 2013). The mechanisms involved in TLS formation and activities and their impact on tumor immunity is relatively unknown. TIL infiltration and TLS formation are likely regulated, in part, by transcription factors (TF) that control cytokine/chemokine production within the tumor microenvironment (TME) (Pimenta and Barnes, 2014). One such TF, the forkhead box protein 1 (FOXP1) is abnormally expressed in various human tumors and has a known role in regulating immune cell functions. Contradictory data on FOXP1 expression together with a lack of information on its immune regulation led us to explore its role in this tumor type. The first part of this thesis research focused on FOXP1-mediated regulation in BC. Gene/protein analysis was examined in the four BC molecular subtypes, revealing its enriched expression in estrogen receptor positive (ER+) tumors (Luminal A/B). Luminal BC is generally less infiltrated compared with frequently high TIL infiltration in ER negative (ER-) tumors (i.e. HER2+ and TN) [reviewed in (Solinas et al. 2017a) and (Loi et al. 2014)]. We found that high FOXP1 expression in a cohort of untreated primary BC was significantly associated with a lower TIL and fewer TLS compared to FOXP1 low (FOXP1lo) tumors. This observation led us to investigate the effect of FOXP1 on cytokines and chemokines potentially involved in TIL recruitment and/or TLS formation. BC cancer cell lines were used to silence [MCF7; FOXP1hi] or overexpress [MDA-MB-231; FOXP1lo] FOXP1 expression. FOXP1 repression upregulated a number of cytokines and chemokines involved in T and B cell migration and function, while FOXP1 overexpression repressed a majority of the same factors. Expression analysis of the major T and B cell cytokine and chemokine genes was performed for FOXP1lo and FOXP1hi primary BC. These data reveal that FOXP1hi BCs have significant decreases in CXCL9, CXCL10, CXCL11, CXCL13, CX3CL1, CCL20, IL2, IL21, granzyme B and IFNγ and high levels of the immunosuppressive cytokines, IL10 and TGFβ. We next performed a lymphocyte migration assay using primary tumor supernatants prepared from FOXP1lo and FOXP1hi BC finding significantly decreased migration of total CD45+ lymphocytes, B cells, helper (CD4+) and cytotoxic (CD8+) T cells using FOXP1hi compared to FOXP1lo SN. Overall, our data suggest that FOXP1 plays an important role in repressing anti-tumor immune responses by negatively regulating TIL migration directed by specific cytokines and chemokines.The second part of this thesis research focused on the role FOXP1 plays in BC TLS. FOXP1 expression in T and B cell TIL and TLS was evaluated using RT-qPCR, multicolor flow cytometry, immunofluorescence (IF) and immunohistochemistry (IHC) and fresh, fixed and frozen breast tissues. Based on the FOXP1 expression two types of TLS were identified in BC: 1) TLS containing a germinal center (GC-TLS) and 2) TLS lacking a GC (non-GC-TLS). Examination of proteins specifically associated with active humoral immune responses allowed us to identify GC-TLS but not non-GC-TLS as functional. Gene expression analysis of micro-dissected tissues revealed distinct immune profiles that characterize B cell follicles in tonsils and spleen as well as aggregates, non-GC-TLS and GC-TLS in BC. This analysis further demonstrates that ongoing cell-mediated immune responses are associated with GC-TLS. The findings from this thesis research add important information to our understanding of how immune responses are initiated and maintained in BC and provide further insight into the identification and organization of functional immune responses at the tumor site. / Doctorat en Sciences biomédicales et pharmaceutiques (Médecine) / info:eu-repo/semantics/nonPublished

<p>Epigenetic mechanisms, including DNA methylation, play an important role in regulation of stem cell fate and tumorigenesis. The Ten-Eleven-Translocation 2 (TET2) is a core enzyme for DNA demethylation by catalyzing the conversion of 5-methylcytosine (5mC) to 5-hydromethylcytosine (5hmC). It has been shown that TET2 is the main regulator of hematopoietic stem cell homeostasis and loss of TET2 is highly associated with hematopoietic malignancies. Our previous work has also shown that loss of TET2 expression is linked to promotion of an epithelial-mesenchymal-transition phenotype and expansion of a breast cancer stem cell-like population with skewed asymmetric cell division in vitro; however, the in vivo role that TET2 plays in regulation of mammary stem cell (MaSC) fate and development of mammary pathology has yet to be determined. Here, using our newly established mammary-specific Tet2-knockout mouse model, the data reveals for the first time that TET2 plays a pivotal role in mammary gland development via directing MaSC to luminal lineage commitment in vivo. Furthermore, we find that TET2 coordinates with FOXP1 to target and demethylate FOXA1, GATA3, and ESR1, key transcription factors that orchestrate mammary luminal lineage specification and endocrine response and are often silenced by DNA methylation in aggressive human breast cancers. Finally, loss of TET2 expression leads to promotion of mammary tumor development with defective luminal cell differentiation and tamoxifen resistance in a PyMT;Tet2 deletion breast cancer mouse model. As a result, this study provides a previously unidentified role for TET2 in governing luminal lineage specification and endocrine response that underlies resistance to anti-estrogen treatments.</p>

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