Cdx2 homeoprotein inhibits non-homologous end joining in colon cancer but not in leukemia cells

Cdx2, a gene of the paraHox cluster, encodes a homeodomain transcription factor that plays numerous roles in embryonic development and in homeostasis of the adult intestine. Whereas Cdx2 exerts a tumor suppressor function in the gut, its abnormal ectopic expression in acute leukemia is associated to a pro-oncogenic function. To try to understand this duality, we have hypothesized that Cdx2 may interact with different protein partners in the two tissues and set up experiments to identify them by tandem affinity purification. We show here that Cdx2 interacts with the Ku heterodimer specifically in intestinal cells, but not in leukemia cells, via its homeodomain. Ku proteins do not affect Cdx2 transcriptional activity. However, Cdx2 inhibits in vivo and in vitro the DNA repair activity mediated by Ku proteins in intestinal cells. Whereas Cdx2 does not affect the recruitment of Ku proteins and DNA-PKcs into the DNA repair complex, it inhibits DNA-PKcs activity. Thus, we report here a new function of Cdx2, acting as an inhibitor of the DNA repair machinery, that may contribute to its tumor suppressor function specifically in the gut

The Cdx2 homeotic gene : in vivo functions and regulation in intestinal pathologies

Le gène Cdx2 exerce de nombreuses fonctions au cours du développement embryonnaire. Son expression est maintenue spécifiquement dans l’épithélium intestinal adulte. Cdx2 est diminué dans les cancers colorectaux (CCR), favorisant la migration et la dissémination des cellules tumorales. Cette diminution de Cdx2 est réversible, suggérant une dérégulation du gène. Nous avons étudié d’une part les fonctions intestinales de Cdx2 au cours du développement et surtout chez l’adulte, et d’autre part les mécanismes moléculaires associés à la dérégulation de Cdx2 dans les CCR.Une approche d’invalidation conditionnelle de Cdx2 chez la souris a été choisie. Nous montrons que Cdx2 est nécessaire pour l’établissement de l’identité intestinale au cours du développement. De plus, dans l’intestin adulte il contribue au maintien de l’identité des cellules souches et intervient dans la différenciation terminale des cellules épithéliales. Le croisement du modèle murin transgénique pCdx2-9LacZ avec le modèle de cancérogénèse colique spontanée Apc∆14/+ indique que les éléments nécessaires à la diminution d’expression de Cdx2 dans les CCR sont sur le promoteur de 9kb de Cdx2. Par ailleurs, nous montrons une corrélation d’expression entre les protéines HNF4α, régulateur transcriptionnel de Cdx2, et Cdx2 dans des échantillons de tumeurs intestinales humaines et murines. L’invalidation conditionnelle de Hnf4α dans l’intestin est associée à une réduction d’expression de Cdx2 et à une plus grande susceptibilité des animaux à la tumorigenèse colique chimio-induite. HNF4α constitue un facteur important de la dérégulation de Cdx2 dans les CCR et exerce une fonction suppresseur de tumeur dans l’intestinThe Cdx2 gene exerts many functions during embryonic development. Its expression is maintained specifically in the adult intestinal epithelium. Cdx2 expression is reduced in colorectal cancers (CRC); moreover, this reduction promotes migration and the spread of colon tumor cells. The alteration of Cdx2 in CRC is reversible, suggesting a deregulation of the gene. The objectives of my project were to study the functions of Cdx2 during intestinal development and in adults and to study the molecular mechanisms associated with the deregulation of Cdx2 in CRC. An approach of conditional invalidation of Cdx2 in mice has been used. We show that Cdx2 plays a key role in establishing the intestinal identity during development. In addition, at the adult stage Cdx2 is involved in the maintaining of the intestinal stem cells identity and in the control of terminal differentiation of intestinal epithelial cells. Crossing the transgenic mouse model pCdx2-9LacZ with spontaneous colon carcinogenesis model ApcΔ14/+ indicates that the elements necessary for the decrease of Cdx2 expression are located on the Cdx2 promoter of 9kb. Earlier team works have highlighted HNF4α as a transcriptional regulator of Cdx2 expression. In this work, we have demonstrated a correlation between HNF4α and Cdx2 protein expression in samples of human and mouse intestinal tumors. The conditional invalidation of Hnf4α in the intestine is associated with a reduction of Cdx2 expression, and a greater susceptibility for mice to chemo-induced colonic tumorigenesis. HNF4α is an important factor in the deregulation of Cdx2 in CRC and it exerts itself a tumor suppressor function in the gut

The Cdx2 homeotic gene : in vivo functions and regulation in intestinal pathologies

Le gène Cdx2 exerce de nombreuses fonctions au cours du développement embryonnaire. Son expression est maintenue spécifiquement dans l’épithélium intestinal adulte. Cdx2 est diminué dans les cancers colorectaux (CCR), favorisant la migration et la dissémination des cellules tumorales. Cette diminution de Cdx2 est réversible, suggérant une dérégulation du gène. Nous avons étudié d’une part les fonctions intestinales de Cdx2 au cours du développement et surtout chez l’adulte, et d’autre part les mécanismes moléculaires associés à la dérégulation de Cdx2 dans les CCR.Une approche d’invalidation conditionnelle de Cdx2 chez la souris a été choisie. Nous montrons que Cdx2 est nécessaire pour l’établissement de l’identité intestinale au cours du développement. De plus, dans l’intestin adulte il contribue au maintien de l’identité des cellules souches et intervient dans la différenciation terminale des cellules épithéliales. Le croisement du modèle murin transgénique pCdx2-9LacZ avec le modèle de cancérogénèse colique spontanée Apc∆14/+ indique que les éléments nécessaires à la diminution d’expression de Cdx2 dans les CCR sont sur le promoteur de 9kb de Cdx2. Par ailleurs, nous montrons une corrélation d’expression entre les protéines HNF4α, régulateur transcriptionnel de Cdx2, et Cdx2 dans des échantillons de tumeurs intestinales humaines et murines. L’invalidation conditionnelle de Hnf4α dans l’intestin est associée à une réduction d’expression de Cdx2 et à une plus grande susceptibilité des animaux à la tumorigenèse colique chimio-induite. HNF4α constitue un facteur important de la dérégulation de Cdx2 dans les CCR et exerce une fonction suppresseur de tumeur dans l’intestinThe Cdx2 gene exerts many functions during embryonic development. Its expression is maintained specifically in the adult intestinal epithelium. Cdx2 expression is reduced in colorectal cancers (CRC); moreover, this reduction promotes migration and the spread of colon tumor cells. The alteration of Cdx2 in CRC is reversible, suggesting a deregulation of the gene. The objectives of my project were to study the functions of Cdx2 during intestinal development and in adults and to study the molecular mechanisms associated with the deregulation of Cdx2 in CRC. An approach of conditional invalidation of Cdx2 in mice has been used. We show that Cdx2 plays a key role in establishing the intestinal identity during development. In addition, at the adult stage Cdx2 is involved in the maintaining of the intestinal stem cells identity and in the control of terminal differentiation of intestinal epithelial cells. Crossing the transgenic mouse model pCdx2-9LacZ with spontaneous colon carcinogenesis model ApcΔ14/+ indicates that the elements necessary for the decrease of Cdx2 expression are located on the Cdx2 promoter of 9kb. Earlier team works have highlighted HNF4α as a transcriptional regulator of Cdx2 expression. In this work, we have demonstrated a correlation between HNF4α and Cdx2 protein expression in samples of human and mouse intestinal tumors. The conditional invalidation of Hnf4α in the intestine is associated with a reduction of Cdx2 expression, and a greater susceptibility for mice to chemo-induced colonic tumorigenesis. HNF4α is an important factor in the deregulation of Cdx2 in CRC and it exerts itself a tumor suppressor function in the gut

Role of β-catenin in development of bile ducts

Beta-catenin is known to play stage- and cell-specific functions during liver development. However, its role in development of bile ducts has not yet been addressed. Here we used stage-specific in vivo gain- and loss-of-function approaches, as well as lineage tracing experiments in the mouse, to first demonstrate that β-catenin is dispensable for differentiation of liver precursor cells (hepatoblasts) to cholangiocyte precursors. Second, when β-catenin was depleted in the latter, maturation of cholangiocytes, bile duct morphogenesis and differentiation of periportal hepatocytes from cholangiocyte precursors was normal. In contrast, stabilization of β-catenin in cholangiocyte precursors perturbed duct development and cholangiocyte differentiation. We conclude that β-catenin is dispensable for biliary development but that its activity must be kept within tight limits. Our work is expected to significantly impact on in vitro differentiation of stem cells to cholangiocytes for toxicology studies and disease modeling

"OpenLAB": A 2-hour PCR-based practical for high school students.

The Strasbourg University PhD school in Life and Health Sciences launched an initiative called "OpenLAB." This project was developed in an effort to help high school teenagers understand theoretical and abstract concepts in genetics. A second objective of this program is to help students in defining their future orientation and to attract them to biology. The general idea is a 2-hour PCR-based practical that is developed around a fictitious criminal investigation. The practical is taught by PhD graduate students who bring all the required reagents and modern equipment into the classroom. Running the PCR provides free time dedicated to discussions with students about their future plans after the high school diploma. A specific website and a powerpoint presentation were developed to provide appropriate scientific information. Starting on a modest scale in Strasbourg in December 2008, "OpenLAB" was rapidly and well received all around, visiting 53 classes spread over a 200 km area in Alsace until May 2009. It permitted interactions with almost one thousand students in their last year of high school, with the prospect to visit 20% more classes this school year. Our experience, along with feedback from students and their teachers, suggests that it is possible to reach out to many students and have a strong impact with a rather limited budget.journal article2010 Sepimporte

Fine-tuning and autoregulation of the intestinal determinant and tumor suppressor homeobox gene CDX2 by alternative splicing

On the basis of phylogenetic analyses, we uncovered a variant of the CDX2 homeobox gene, a major regulator of the development and homeostasis of the gut epithelium, also involved in cancer. This variant, miniCDX2, is generated by alternative splicing coupled to alternative translation initiation, and contains the DNA-binding homeodomain but is devoid of transactivation domain. It is predominantly expressed in crypt cells, whereas the CDX2 protein is present in crypt cells but also in differentiated villous cells. Functional studies revealed a dominant-negative effect exerted by miniCDX2 on the transcriptional activity of CDX2, and conversely similar effects regarding several transcription-independent functions of CDX2. In addition, a regulatory role played by the CDX2 and miniCDX2 homeoproteins on their pre-mRNA splicing is displayed, through interactions with splicing factors. Overexpression of miniCDX2 in the duodenal Brunner glands leads to the expansion of the territory of these glands and ultimately to brunneroma. As a whole, this study characterized a new and original variant of the CDX2 homeobox gene. The production of this variant represents not only a novel level of regulation of this gene, but also a novel way to fine-tune its biological activity through the versatile functions exerted by the truncated variant compared to the full-length homeoprotein. This study highlights the relevance of generating protein diversity through alternative splicing in the gut and its diseases

Fine-tuning and autoregulation of the intestinal determinant and tumor suppressor homeobox gene CDX2 by alternative splicing

On the basis of phylogenetic analyses, we uncovered a variant of the CDX2 homeobox gene, a major regulator of the development and homeostasis of the gut epithelium, also involved in cancer. This variant, miniCDX2, is generated by alternative splicing coupled to alternative translation initiation, and contains the DNA-binding homeodomain but is devoid of transactivation domain. It is predominantly expressed in crypt cells, whereas the CDX2 protein is present in crypt cells but also in differentiated villous cells. Functional studies revealed a dominant-negative effect exerted by miniCDX2 on the transcriptional activity of CDX2, and conversely similar effects regarding several transcription-independent functions of CDX2. In addition, a regulatory role played by the CDX2 and miniCDX2 homeoproteins on their pre-mRNA splicing is displayed, through interactions with splicing factors. Overexpression of miniCDX2 in the duodenal Brunner glands leads to the expansion of the territory of these glands and ultimately to brunneroma. As a whole, this study characterized a new and original variant of the CDX2 homeobox gene. The production of this variant represents not only a novel level of regulation of this gene, but also a novel way to fine-tune its biological activity through the versatile functions exerted by the truncated variant compared to the full-length homeoprotein. This study highlights the relevance of generating protein diversity through alternative splicing in the gut and its diseases