CD32 captures committed haemogenic endothelial cells during human embryonic development

During embryonic development, blood cells emerge from specialized endothelial cells, named haemogenic endothelial cells (HECs). As HECs are rare and only transiently found in early developing embryos, it remains difficult to distinguish them from endothelial cells. Here we performed transcriptomic analysis of 28- to 32-day human embryos and observed that the expression of Fc receptor CD32 (FCGR2B) is highly enriched in the endothelial cell population that contains HECs. Functional analyses using human embryonic and human pluripotent stem cell-derived endothelial cells revealed that robust multilineage haematopoietic potential is harboured within CD32+ endothelial cells and showed that 90% of CD32+ endothelial cells are bona fide HECs. Remarkably, these analyses indicated that HECs progress through different states, culminating in FCGR2B expression, at which point cells are irreversibly committed to a haematopoietic fate. These findings provide a precise method for isolating HECs from human embryos and human pluripotent stem cell cultures, thus allowing the efficient generation of haematopoietic cells in vitro.

MAGT1 Deficiency Dysregulates Platelet Cation Homeostasis and Accelerates Arterial Thrombosis and Ischemic Stroke in Mice

BACKGROUND

MAGT1 (magnesium transporter 1) is a subunit of the oligosaccharide protein complex with thiol-disulfide oxidoreductase activity, supporting the process of N-glycosylation. MAGT1 deficiency was detected in human patients with X-linked immunodeficiency with magnesium defect syndrome and congenital disorders of glycosylation, resulting in decreased cation responses in lymphocytes, thereby inhibiting the immune response against viral infections. Curative hematopoietic stem cell transplantation of patients with X-linked immunodeficiency with magnesium defect causes fatal bleeding and thrombotic complications.

METHODS

We studied the role of MAGT1 deficiency in platelet function in relation to arterial thrombosis and hemostasis using several in vitro experimental settings and in vivo models of arterial thrombosis and transient middle cerebral artery occlusion model of ischemic stroke.

RESULTS

MAGT1-deficient mice (Magt1^-/y) displayed accelerated occlusive arterial thrombus formation in vivo, a shortened bleeding time, and profound brain damage upon focal cerebral ischemia. These defects resulted in increased calcium influx and enhanced second wave mediator release, which further reinforced platelet reactivity and aggregation responses. Supplementation of MgCl₂ or pharmacological blockade of TRPC6 (transient receptor potential cation channel, subfamily C, member 6) channels, but not inhibition of store-operated calcium entry, normalized the aggregation responses of Magt1^-/y platelets to the control level. GP (glycoprotein) VI activation of Magt1^-/y platelets resulted in hyperphosphorylation of Syk (spleen tyrosine kinase), LAT (linker for activation of T cells), and PLC (phospholipase C) γ2, whereas the inhibitory loop regulated by PKC (protein kinase C) was impaired. A hyperaggregation response to the GP VI agonist was confirmed in human platelets isolated from a MAGT1-deficient (X-linked immunodeficiency with magnesium defect) patient. Haploinsufficiency of TRPC6 in Magt1^-/y mice could normalize GP VI signaling, platelet aggregation, and thrombus formation in vivo.

CONCLUSIONS

These results suggest that MAGT1 and TRPC6 are functionally linked. Therefore, deficiency or impaired functionality of MAGT1 could be a potential risk factor for arterial thrombosis and stroke.

The Appendix Orchestrates T-Cell Mediated Immunosurveillance in Colitis-Associated Cancer

BACKGROUND & AIMS

Although appendectomy may reduce colorectal inflammation in patients with ulcerative colitis (UC), this surgical procedure has been suggested to be associated with an increased risk of colitis-associated cancer (CAC). Our aim was to explore the mechanism underlying the appendectomy-associated increased risk of CAC.

METHODS

Five-week-old male BALB/c mice underwent appendectomy, appendicitis induction, or sham laparotomy. They were then exposed to azoxymethane/dextran sodium sulfate (AOM/DSS) to induce CAC. Mice were killed 12 weeks later, and colons were taken for pathological analysis and immunohistochemistry (CD3 and CD8 staining). Human colonic tumors from 21 patients with UC who underwent surgical resection for CAC were immunophenotyped and stratified according to appendectomy status.

RESULTS

Whereas appendectomy significantly reduced colitis severity and increased CAC number, appendicitis induction without appendectomy led to opposite results. Intratumor CD3+ and CD8+ T-cell densities were lower after appendectomy and higher after appendicitis induction compared with the sham laparotomy group. Blocking lymphocyte trafficking to the colon with the anti-α4β7 integrin antibody or a sphingosine-1-phosphate receptor agonist suppressed the inducing effect of the appendectomy on tumors' number and on CD3+/CD8+ intratumoral density. CD8+ or CD3+ T cells isolated from inflammatory neo-appendix and intravenously injected into AOM/DSS-treated recipient mice increased CD3+/CD8+ T-cell tumor infiltration and decreased tumor number. In UC patients with a history of appendectomy, intratumor CD3+ and CD8+ T-cell densities were decreased compared with UC patients without history of appendectomy.

CONCLUSIONS

In UC, appendectomy could suppress a major site of T-cell priming, resulting in a less efficient CAC immunosurveillance.

A Core Response to the CDX2 Homeoprotein During Development and in Pathologies

Whether a gene involved in distinct tissue or cell functions exerts a core of common molecular activities is a relevant topic in evolutionary, developmental, and pathological perspectives. Here, we addressed this question by focusing on the transcription factor and regulator of chromatin accessibility encoded by the Cdx2 homeobox gene that plays important functions during embryonic development and in adult diseases. By integrating RNAseq data in mouse embryogenesis, we unveiled a core set of common genes whose expression is responsive to the CDX2 homeoprotein during trophectoderm formation, posterior body elongation and intestinal specification. ChIPseq data analysis also identified a set of common chromosomal regions targeted by CDX2 at these three developmental steps. The transcriptional core set of genes was then validated with transgenic mouse models of loss or gain of function of Cdx2. Finally, based on human cancer data, we highlight the relevance of these results by displaying a significant number of human orthologous genes to the core set of mouse CDX2-responsive genes exhibiting an altered expression along with CDX2 in human malignancies.

CDX2 inducible microRNAs sustain colon cancer by targeting multiple DNA damage response pathway factors

Meta-analysis of transcripts in colon adenocarcinoma patient tissues led to the identification of a DNA damage responsive miR signature called DNA damage sensitive miRs (DDSMs). DDSMs were experimentally validated in the cancerous colon tissues obtained from an independent cohort of colon cancer patients and in multiple cellular systems with high levels of endogenous DNA damage. All the tested DDSMs were transcriptionally upregulated by a common intestine-specific transcription factor, CDX2. Reciprocally, DDSMs were repressed via the recruitment of HDAC1/2-containing complexes onto the CDX2 promoter. These miRs downregulated multiple key targets in the DNA damage response (DDR) pathway, namely BRCA1, ATM, Chk1 (also known as CHEK1) and RNF8. CDX2 directly regulated the DDSMs, which led to increased tumor volume and metastasis in multiple preclinical models. In colon cancer patient tissues, the DDSMs negatively correlated with BRCA1 levels, were associated with decreased probability of survival and thereby could be used as a prognostic biomarker. This article has an associated First Person interview with the first author of the paper.

CDX2 expression in the hematopoietic lineage promotes leukemogenesis via TGFβ inhibition

The intestine-specific caudal-related homeobox gene-2 (CDX2) homeobox gene, while being a tumor suppressor in the gut, is ectopically expressed in a large proportion of acute leukemia and is associated with poor prognosis. Here, we report that turning on human CDX2 expression in the hematopoietic lineage of mice induces acute monoblastic leukemia, characterized by the decrease in erythroid and lymphoid cells at the benefit of immature monocytic and granulocytic cells. One of the highly stimulated genes in leukemic bone marrow cells was BMP and activin membrane-bound inhibitor (Bambi), an inhibitor of transforming growth factor-β (TGF-β) signaling. The CDX2 protein was shown to bind to and activate the transcription of the human BAMBI promoter. Moreover, in a leukemic cell line established from CDX2-expressing mice, reducing the levels of CDX2 or Bambi stimulated the TGF-β-dependent expression of Cd11b, a marker of monocyte maturation. Taken together, this work demonstrates the strong oncogenic potential of the homeobox gene CDX2 in the hematopoietic lineage, in contrast with its physiological tumor suppressor activity exerted in the gut. It also reveals, through BAMBI and TGF-β signaling, the involvement of CDX2 in the perturbation of the interactions between leukemia cells and their microenvironment.

Renin-angiotensin system is involved in embryonic emergence of hematopoietic stem/progenitor cells

Angiotensin-converting enzyme (ACE), a key element of the renin-angiotensin system (RAS), has recently been identified as a new marker of both adult and embryonic human hematopoietic stem/progenitor cells (HSPCs). However, whether a full renin-angiotensin pathway is locally present during the hematopoietic emergence is still an open question. In the present study, we show that this enzyme is expressed by hematopoietic progenitors in the developing mouse embryo. Furthermore, ACE and the other elements of RAS-namely angiotensinogen, renin, and angiotensin II type 1 (AT1) and type 2 (AT2) receptors-are expressed in the paraaortic splanchnopleura (P-Sp) and in its derivative, the aorta-gonad-mesonephros region, both in human and mouse embryos. Their localization is compatible with the existence of a local autocrine and/or paracrine RAS in these hemogenic sites. in vitro perturbation of the RAS by administration of a specific AT1 receptor antagonist inhibits almost totally the generation of blood CD45-positive cells from dissected P-Sp, implying that angiotensin II signaling is necessary for the emergence of hematopoietic cells. Conversely, addition of exogenous angiotensin II peptide stimulates hematopoiesis in culture, with an increase in the number of immature c-Kit⁺ CD41⁺ CD31⁺ CD45⁺ hematopoietic progenitors, compared to the control. These results highlight a novel role of local-RAS during embryogenesis, suggesting that angiotensin II, via activation of AT1 receptor, promotes the emergence of undifferentiated hematopoietic progenitors.

Histone hypoacetylation contributes to CXCL12 downregulation in colon cancer: impact on tumor growth and cell migration

CXCL12 has been shown to be involved in colon cancer metastasis, but its expression level and molecular mechanisms regulating its expression remain controversial. We thus evaluated CXCL12 expression in a large cohort of colon adenomas and carcinomas, investigated for an epigenetic mechanism controlling its expression and evaluated the impact of CXCL12 levels on cell migration and tumor growth. CXCL12 expression was measured in human colon adenomas and carcinomas with transcriptome array and RT-qPCR. The promoter methylation was analyzed with whole-genome DNA methylation chips and protein expression by immunohistochemistry. We confirm a reduced expression of CXCL12 in 75% of MSS carcinomas and show that the decrease is an early event as already present in adenomas. The methylome analysis shows that the CXCL12 promoter is methylated in only 30% of microsatellite-stable tumors. In vitro, treatments with HDAC inhibitors, butyrate and valproate restored CXCL12 expression in three colon cell lines, increased acetylation of histone H3 within the CXCL12 promoter and inhibited cell migration. In vivo, valproate diminished (65%) the number of intestinal tumors in APC mutant mice, slowed down xenograft tumor growth concomitant to restored CXCL12 expression. Finally we identified loss of PCAF expression in tumor samples and showed that forced expression of PCAF in colon cancer cell lines restored CXCL12 expression. Thus, reduced PCAF expression may participate to CXCL12 promoter hypoacetylation and its subsequent loss of expression. Our study is of potential clinical interest because agents that promote or maintain histone acetylation through HDAC inhibition and/or HAT stimulation, may help to lower colon adenoma/carcinoma incidence, especially in high-risk families, or could be included in therapeutic protocols to treat advanced colon cancer.

The Cdx2 homeobox gene suppresses intestinal tumorigenesis through non-cell-autonomous mechanisms

Balbinot et al. show that intestinal epithelial cells depleted in the homeobox gene Cdx2 acquire an imperfect gastric-type metaplastic phenotype that, through changes in the microenvironment, induces the tumorigenic evolution of adjacent Cdx2-intact cells without themselves becoming cancerous.

Developmental genes contribute to cancer, as reported for the homeobox gene Cdx2 playing a tumor suppressor role in the gut. In this study, we show that human colon cancers exhibiting the highest reduction in CDX2 expression belong to the serrated subtype with the worst evolution. In mice, mosaic knockout of Cdx2 in the adult intestinal epithelium induces the formation of imperfect gastric-type metaplastic lesions. The metaplastic knockout cells do not spontaneously become tumorigenic. However, they induce profound modifications of the microenvironment that facilitate the tumorigenic evolution of adjacent Cdx2-intact tumor-prone cells at the surface of the lesions through NF-κB activation, induction of inducible nitric oxide synthase, and stochastic loss of function of Apc. This study presents a novel paradigm in that metaplastic cells, generally considered as precancerous, can induce tumorigenesis from neighboring nonmetaplastic cells without themselves becoming cancerous. It unveils the novel property of non–cell-autonomous tumor suppressor gene for the Cdx2 gene in the gut.

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.

Estimation of subject coregistration errors during multimodal preclinical imaging using separate instruments: origins and avoidance of artifacts

We use high-resolution [Formula: see text] data in multiple experiments to estimate the sources of error during coregistration of images acquired on separate preclinical instruments. In combination with experiments with phantoms, we completed in vivo imaging on mice, aimed at identifying the possible sources of registration errors, caused either by transport of the animal, movement of the animal itself, or methods of coregistration. The same imaging cell was used as a holder for phantoms and animals. For all procedures, rigid coregistration was carried out using a common landmark coregistration system, placed inside the imaging cell. We used the fiducial registration error and the target registration error to analyze the coregistration accuracy. We found that moving an imaging cell between two preclinical devices during a multimodal procedure gives an error of about [Formula: see text] at most. Therefore, it could not be considered a source of coregistration errors. Errors linked to spontaneous movements of the animal increased with time, to nearly 1 mm at most, excepted for body parts that were properly restrained. This work highlights the importance of animal intrinsic movements during a multiacquisition procedure and demonstrates a simple method to identify and quantify the sources of error during coregistration.

Enhanced Ghrelin Levels and Hypothalamic Orexigenic AgRP and NPY Neuropeptide Expression in Models of Jejuno-Colonic Short Bowel Syndrome

Short bowel syndrome (SBS) patients developing hyperphagia have a better outcome. Gastrointestinal endocrine adaptations help to improve intestinal functions and food behaviour. We investigated neuroendocrine adaptations in SBS patients and rat models with jejuno-ileal (IR-JI) or jejuno-colonic (IR-JC) anastomosis with and without parenteral nutrition. Circulating levels of ghrelin, PYY, GLP-1, and GLP-2 were determined in SBS rat models and patients. Levels of mRNA for proglucagon, PYY and for hypothalamic neuropeptides were quantified by qRT-PCR in SBS rat models. Histology and immunostaining for Ki67, GLP-1 and PYY were performed in SBS rats. IR-JC rats, but not IR-JI, exhibited significantly higher crypt depths and number of Ki67-positive cells than sham. Fasting and/or postprandial plasma ghrelin and PYY concentrations were higher, or tend to be higher, in IR-JC rats and SBS-JC patients than in controls. Proglucagon and Pyy mRNA levels were significantly enhanced in IR-JC rats. Levels of mRNA coding hypothalamic orexigenic NPY and AgRP peptides were significantly higher in IR-JC than in sham rats. We demonstrate an increase of plasma ghrelin concentrations, major changes in hypothalamic neuropeptides levels and greater induction of PYY in SBS-JC rats and patients suggesting that jejuno-colonic continuity creates a peculiar environment promoting further gut-brain adaptations.

Distinct mechanisms for opposite functions of homeoproteins Cdx2 and HoxB7 in double-strand break DNA repair in colon cancer cells

Homeobox genes, involved in embryonic development and tissues homeostasis in adults, are often deregulated in cancer, but their relevance in pathology is far from being fully elucidated. In colon cancers, we report that the homeoproteins HoxB7 and Cdx2 exhibit different heterogeneous patterns, Cdx2 being localized in moderately altered neoplasic glands in contrast to HoxB7 which predominates in poorly-differentiated areas; they are coexpressed in few cancer cells. In human colon cancer cells, both homeoproteins interact with the DNA repair factor KU70/80, but functional studies reveal opposite effects: HoxB7 stimulates DNA repair and cell survival upon etoposide treatment, whereas Cdx2 inhibits both processes. The stimulatory effect of HoxB7 on DNA repair requires the transactivation domain linked to the homeodomain involved in the interaction with KU70/80, whereas the transactivation domain of Cdx2 is dispensable for its inhibitory function, which instead needs the homeodomain to interact with KU70/80 and the C-terminal domain. Thus, HoxB7 and Cdx2 respectively use transcription-dependent and -independent mechanisms to stimulate and inhibit DNA repair. In addition, in cells co-expressing both homeoproteins, Cdx2 lessens DNA repair activity through a novel mechanism of inhibition of the transcriptional function of HoxB7, whereby Cdx2 forms a molecular complex with HoxB7 and prevents it to recognize its target in the chromatin. These results point out the complex interplay between the DSB DNA repair activity and the homeoproteins HoxB7 and Cdx2 in colon cancer cells, making the balance between these factors a determinant and a potential indicator of the efficacy of genotoxic drugs.

Understanding epithelial homeostasis in the intestine: An old battlefield of ideas, recent breakthroughs and remaining controversies

The intestinal epithelium constitutes the barrier between the gut lumen and the rest of the body and a very actively renewing cell population. The crypt/villus and crypt/cuff units of the mouse small intestine and colon are its basic functional units. The field is confronted with competing concepts with regard to the nature of the cells that are responsible for all the day-to day cell replacement and those that act to regenerate the tissue upon injury and with two diametrically opposed models for lineage specification. The review revisits groundbreaking pioneering studies to provide non expert readers and crypt watchers with a factual analysis of the origins of the current models deduced from the latest spectacular advances. It also discusses recent progress made by addressing these issues in the crypts of the colon, which need to be better understood, since they are the preferred sites of major pathologies.

CDX2 regulation by the RNA-binding protein MEX3A: impact on intestinal differentiation and stemness

The homeobox transcription factor CDX2 plays a crucial role in intestinal cell fate specification, both during normal development and in tumorigenic processes involving intestinal reprogramming. The CDX2 regulatory network is intricate, but it has not yet been fully uncovered. Through genome-wide screening of a 3D culture system, the RNA-binding protein MEX3A was identified as putatively involved in CDX2 regulation; therefore, its biological relevance was addressed by setting up cell-based assays together with expression studies in murine intestine. We demonstrate here that MEX3A has a repressive function by controlling CDX2 levels in gastric and colorectal cellular models. This is dependent on the interaction with a specific binding determinant present in CDX2 mRNA 3'untranslated region. We have further determined that MEX3A impairs intestinal differentiation and cellular polarization, affects cell cycle progression and promotes increased expression of intestinal stem cell markers, namely LGR5, BMI1 and MSI1. Finally, we show that MEX3A is expressed in mouse intestine, supporting an in vivo context for interaction with CDX2 and modulation of stem cell properties. Therefore, we describe a novel CDX2 post-transcriptional regulatory mechanism, through the RNA-binding protein MEX3A, with a major impact in intestinal differentiation, polarity and stemness, likely contributing to intestinal homeostasis and carcinogenesis.

Gastric intestinal metaplasia revisited: function and regulation of CDX2

Intestinal metaplasia of the stomach is a preneoplastic lesion that appears following Helicobacter pylori infection and confers increased risk for gastric cancer development. However, the molecular networks connecting infection to lesion formation and the cellular origin of this lesion remain largely unknown. A more comprehensive understanding of how intestinal metaplasia arises and is maintained will be a major breakthrough towards developing novel therapeutic interventions. Furthermore, after ascertaining the pivotal role of CDX2 in establishing and maintaining intestinal metaplasia, it becomes important to decipher the upstream molecular pathways leading to its ectopic expression. Here, we review the pathophysiology of intestinal metaplasia in the context of the molecular network involved in its establishment and maintenance, with emphasis on CDX2 function and regulation.

The tumor suppressor Apc controls planar cell polarities central to gut homeostasis

Asymmetric stem cell divisions controlled by Apc in the intestinal crypt result in regulated, anisotropic movement of daughter cells away from the niche.

The stem cells (SCs) at the bottom of intestinal crypts tightly contact niche-supporting cells and fuel the extraordinary tissue renewal of intestinal epithelia. Their fate is regulated stochastically by populational asymmetry, yet whether asymmetrical fate as a mode of SC division is relevant and whether the SC niche contains committed progenitors of the specialized cell types are under debate. We demonstrate spindle alignments and planar cell polarities, which form a novel functional unit that, in SCs, can yield daughter cell anisotropic movement away from niche-supporting cells. We propose that this contributes to SC homeostasis. Importantly, we demonstrate that some SC divisions are asymmetric with respect to cell fate and provide data suggesting that, in some SCs, mNumb displays asymmetric segregation. Some of these processes were altered in apparently normal crypts and microadenomas of mice carrying germline Apc mutations, shedding new light on the first stages of progression toward colorectal cancer.

Enteropathogenic e.coli sustains iodoacetamide-induced ulcerative colitis-like colitis in rats: modulation of IL-1β, IL-6, TNF-α, COX-2, and apoptosisi

Pathogenic or non-pathogenic bacteria from flora may play a key role in inflammatory bowel disease (IBD) pathogenesis. However, a specific infectious agent causing IBD has not been identified. This study assessed the impact of enteropathogenic E. coli (EPEC) on the modulation of IL-1beta, IL-6, TNF- alpha, COX-2, BAX and Bcl-2 expression, in sustaining inflammation of a rat colitis model. Two hundred male Sprague-Dawley rats (4 groups) were inoculated weekly or bi-weekly for 70 days, with 1 percent methylcellulose (MC), (b) 6 percent iodoacetamide (IA) in 1 percent MC, (c) 4x108 CFU of EPEC, and (d) IA+EPEC. After a month, treatment was stopped in half of the animals in each group. IL-1beta, IL-6, TNF-alpha, COX-2, BAX and Bcl-2 expression were measured in colonic mucosa scrapings. IL-1beta, IL-6, TNF-alpha, and COX-2 were significantly increased in colonic mucosa of the IA+EPEC group and to a lesser but significant level in the IA group compared to controls, or EPEC alone, both in continued and discontinued treatment groups. Additionally, the BAX/Bcl-2 ratio decreased, indicating less apoptosis in the IA+EPEC group which exhibited more necrosis. These effects increased with experiment duration. This work provides new arguments favouring the role of bacteria in IBD pathogenesis.

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.

Immunohistochemical expression of CDX2, β-catenin, and TP53 in inflammatory bowel disease-associated colorectal cancer

BACKGROUND

Inflammatory bowel disease (IBD) exposes patients to an increased risk of colorectal cancer (i-CRC) and differences between i-CRC and sporadic colorectal cancer (s-CRC) pathogenesis were reported. In s-CRC, studies indicate abnormalities in the tumor-suppressor gene Cdx2. This study compared CDX2, β-catenin, and TP53 expression in i-CRC, s-CRC, noncancer IBD, and normal control colonic mucosa.

METHODS

Expression was investigated by immunohistochemistry in 10 normal, 20 s-CRC, 11 noncancer colonic IBD and 30 i-CRC samples, and in four samples of Crohn's disease (CD)-associated small bowel adenocarcinoma (i-SBA).

RESULTS

In normal and noncancer IBD samples, CDX2 was confined to the colonocytes nuclei. CDX2 expression was normal in 90% of i-CRC, regardless of tumor differentiation or inflammation intensity. By contrast, CDX2 expression was altered in 45% s-CRC, particularly at the front of invasion in undifferentiated tumors. β-Catenin was restricted to cell membrane in all controls, in 91% noncancer IBD, and in 84% i-CRC samples, whereas 35% s-CRC showed cytoplasmic redistribution and exclusive nuclear staining at the front of invasion. TP53 was strongly and homogeneously expressed in i-CRC nuclei compared to normal control or s-CRC, and increases with inflammation intensity. Nested or diffuse TP53 was found in 81.8% of noncancer IBD samples with a higher proportion of TP53-expressing cells in the most inflamed samples. CDX2, β-catenin, and TP53 expression in CD-associated SBA appears similar to that of i-CRC. Neither Cdx2 nor β-catenin alterations are prominent features of i-CRC.

CONCLUSIONS

In i-CRC and CD-associated SBA, carcinogenesis is associated early with p53 mutations and to inflammation intensity.

CDX2 in congenital gut gastric-type heteroplasia and intestinal-type Meckel diverticula

The mechanisms that determine organ identity along the digestive tract in humans are poorly understood. Here we describe the rare case of a young patient who presented with congenital gastric-type heteroplasia in the midjejunum. The lesions, located along the antimesenteric midline of the gut, were made of histologically and functionally normal gastric epithelium without inflammation or in situ/invasive carcinoma. They resembled the anatomy of the lesions developing in the mouse gut as a result of haploinsufficiency of the Cdx2 homeobox gene. The lesions were devoid of CDX2 but without mutation in the coding sequence or in a cis-regulatory element required for intestine-specific expression. Combining these data with the CDX2 expression pattern established from human embryos and cases of Meckel diverticula, we propose a scenario for this patient's presentation, in which CDX2 was missing at the site of ventral closure during gut morphogenesis, with subsequent default differentiation into gastric instead of intestinal tissue. Altogether, these observations argue in favor of a pivotal role played by CDX2 in determining intestinal identity during human embryonic development, as previously shown experimentally in mice.

Multiple regulatory regions control the complex expression pattern of the mouse Cdx2 homeobox gene

BACKGROUND & AIMS

The Cdx2 homeobox gene exerts multiple functions including trophectoderm specification, antero-posterior patterning, and determination of intestinal identity. The aim of this study was to map genomic regions that regulate the transcription of Cdx2, with a particular interest in the gut.

METHODS

Genomic fragments covering 13 kilobase (kb) of the mouse Cdx2 locus were analyzed in transgenic mice and in cell assays.

RESULTS

No fragment was active in the trophectoderm. Fragments containing the first intron and extending up to -5-kb upstream of the transcription start site became active posteriorly at gastrulation and then inactive at midgestation in every tissue including the endoderm. Specific persistence of activity in the intestinal endoderm/epithelium beyond midgestation requires extending the genomic fragment up to -9 kb. We identified a 250-base pair segment around -8.5-kb binding and responding to endodermal factors, with a stimulatory effect exerted synergistically by HNF4alpha, GATA6, Tcf4, and beta-catenin. These factors were able to activate endogenous expression of Cdx2 in nonintestinal Hela cells.

CONCLUSIONS

Multiple regulatory regions control the complex developmental pattern of Cdx2, including far upstream sequences required for the persistence of gene expression specifically in the gut epithelium throughout life. Cooperation between HNF4alpha, GATA6, beta-catenin, and Tcf4 contributes to the intestine-specific expression of Cdx2.

Differential regulation of CDX1 and CDX2 gene expression by deficiency in methyl group donors

The CDX2 and CDX1 homeobox genes have respectively a tumour suppressor and proliferative role in the intestinal epithelium. We analyzed DNA methylation and histones modifications associated with CDX2 and CDX1 promoters in two human colon cancer cell lines expressing differentially these genes, Caco2/TC7 [CDX2 positive-CDX1 negative] and HT29 [CDX2 negative-CDX1 negative] cells. Chromatin immunoprecipitation experiments indicated that CDX2 and CDX1 gene expression correlated with a histone modifications pattern characterizing active chromatin (H3K4 trimethylated and H3 acetylated). Bisulfite DNA sequencing and methylation-specific PCR showed that CDX2 and CDX1 promoters display no methylation in HT29 cells even though both genes are not expressed. In contrast, the CDX1 promoter is methylated in Caco2/TC7. DNA demethylation by 5aza-dC or the combination of 5aza-dC plus SAHA, an inhibitor of histone deacetylases, restored CDX1 expression in Caco2/TC7 cells but these treatments were inefficient on both CDX2 and CDX1 in HT29 cells. Thus, in colon cancer cells the changes in chromatin conformation are heterogeneous and repression of CDX2 and CDX1 in HT29 cells is not due to epigenetic mechanisms. In vivo, dietary deprivation of methyl groups in rats upregulated CDX1 mRNA and downregulated to a lesser extent CDX2 mRNA expression. Moreover, methyl group deprivation downregulated CDX2 protein by changing its phosphorylation pattern. The changes in CDX2 and CDX1 expression determined by methyl group deprivation may constitute one of the mechanisms sustaining the protective role attributed to folate in colon cancer.

The human mucin MUC4 is transcriptionally regulated by caudal-related homeobox, hepatocyte nuclear factors, forkhead box A, and GATA endodermal transcription factors in epithelial cancer cells

The human gene MUC4 encodes a large transmembrane mucin that is developmentally regulated and expressed along the undifferentiated pseudostratified epithelium, as early as 6.5 weeks during fetal development. Immunohistochemical analysis of Muc4 expression in developing mouse lung and gastrointestinal tract showed a different spatio-temporal pattern of expression before and after cytodifferentiation. The molecular mechanisms governing MUC4 expression during development are, however, unknown. Hepatocyte nuclear factors (HNF), forkhead box A (FOXA), GATA, and caudal-related homeobox transcription factors (TFs) are known to control cell differentiation of gut endoderm derived-tissues during embryonic development. They also control the expression of cell- and tissue-specific genes and may thus control MUC4 expression. To test this hypothesis, we studied and deciphered the molecular mechanisms responsible for MUC4 transcriptional regulation by these TFs. Experiments using small interfering RNA, cell co-transfection, and site-directed mutagenesis indicated that MUC4 is regulated at the transcriptional level by CDX-1 and -2, HNF-1 alpha and -1 beta, FOXA1/A2, HNF-4 alpha and -4 gamma, and GATA-4, -5, and -6 factors in a cell-specific manner. Binding of TFs was assessed by chromatin immunoprecipitation, and gel-shift assays. Altogether, these results demonstrate that MUC4 is a target gene of endodermal TFs and thus point out an important role for these TFs in regulating MUC4 expression during epithelial differentiation during development, cancer, and repair.

Precancerous lesions upon sporadic activation of beta-catenin in mice

BACKGROUND & AIMS

Inappropriate activation of beta-catenin in adult tissues is associated with a wide variety of cancers, especially in the digestive tract. Classic transgenic and knockout murine models in which beta-catenin is activated in large fields of cells have provided experimental support in favor of a role for this molecule in tumorigenesis. However, these models do not reproduce the sporadic nature of the majority of human cancers, beginning with the activation of an oncogene at random in a single cell.

METHODS

We used the "hit and run" strategy to generate a mouse model in which the expression of an activated form of beta-catenin occurs sporadically in vivo.

RESULTS

Sporadic, multifocal lesions were observed in the stomach of 3% of mice aged 8 months and older. These lesions were associated with loss of Sonic hedgehog (Shh), and a causal relationship between beta-catenin activation and Shh inhibition was established in gastric cells in vitro. No lesion was detected in the intestine or in the liver. In addition, one third of female mutant mice developed benign perimammary papillomas. Mutant mice were also hypersensitive to chemically induced premalignant skin lesions.

CONCLUSIONS

These results challenge the view that activation of beta-catenin induces malignant cancerogenesis, because they show in mice that sporadically activated beta-catenin is sufficient for tumor initiation, yet without further malignant progression, and that it sensitizes cells to environmental hits. This model represents a powerful tool to investigate the interplay between genetic and environmental factors in tumor progression.

The microenvironment controls CDX2 homeobox gene expression in colorectal cancer cells

The homeobox gene CDX2 plays a major role in development, especially in the gut, and it also acts as a tumor suppressor in the adult colon. Using orthotopic and heterotopic xenografts of human primary colorectal tumor cells and cell lines in nude mice, we addressed the effect of the microenvironment on CDX2 expression. In cells expressing CDX2 at a high level in culture, this level was maintained in subcutaneous grafts but was reduced when implanted into the cecum wall. Reciprocally, in cells with low CDX2 expression in culture, the level remained low in grafts into the cecum wall but was stimulated subcutaneously. In vitro co-cultures showed that CDX2 expression was activated in cells grown on layers of skin fibroblasts but not on intestinal fibroblasts. The stimulation was transcriptional, as assessed by transfection experiments with reporter plasmids containing the murine Cdx2 promoter. Together, these data demonstrate experimentally that CDX2 expression is adaptable and strongly dependent on the microenvironment surrounding the tumor cells. We exclude a role of the Notch pathway in this regulation. The regulation of CDX2 by the microenvironment might be relevant during the process of metastatic dissemination when the gene is transiently turned down in invasive cells.

Identification and characterization of human Mex-3 proteins, a novel family of evolutionarily conserved RNA-binding proteins differentially localized to processing bodies

In Caenorhabditis elegans, the Mex-3 protein is a translational regulator that specifies the posterior blastomere identity in the early embryo and contributes to the maintenance of the germline totipotency. We have now identified a family of four homologous human Mex-3 genes, called hMex-3A to -3D that encode proteins containing two heterogeneous nuclear ribonucleoprotein K homology (KH) domains and one carboxy-terminal RING finger module. The hMex-3 are phosphoproteins that bind RNA through their KH domains and shuttle between the nucleus and the cytoplasm via the CRM1-dependent export pathway. Our analysis further revealed that hMex-3A and hMex-3B, but not hMex-3C, colocalize with both the hDcp1a decapping factor and Argonaute (Ago) proteins in processing bodies (P bodies), recently characterized as centers of mRNA turnover. Taken together, these findings indicate that hMex-3 proteins constitute a novel family of evolutionarily conserved RNA-binding proteins, differentially recruited to P bodies and potentially involved in post-transcriptional regulatory mechanisms.

Functional interaction between the homeoprotein CDX1 and the transcriptional machinery containing the TATA-binding protein

We have previously reported that the CDX1 homeoprotein interacts with the TATA-box binding protein (TBP) on the promoter of the glucose-6-phosphatase (G6Pase) gene. We show here that CDX1 interacts with TBP via the homeodomain and that the transcriptional activity additionally requires the N-terminal domain upstream of the homeodomain. CDX1 interacting with TBP is connected to members of the TFIID and Mediator complexes, two major elements of the general transcriptional machinery. Transcription luciferase assays performed using an altered-specificity mutant of TBP provide evidence for the functionality of the interaction between CDX1 and TBP. Unlike CDX1, CDX2 does not interact with TBP nor does it transactivate the G6Pase promoter. Swapping experiments between the domains of CDX1 and CDX2 indicate that, despite opposite functional effects of the homeoproteins on the G6Pase promoter, the N-terminal domains and homeodomains of both CDX1 and CDX2 have the intrinsic ability to activate transcription and to interact with TBP. However, the carboxy domains define the specificity of CDX1 and CDX2. Thus, intra-molecular interactions control the activity and partner recruitment of CDX1 and CDX2, leading to different molecular functions.

Frequent rearrangements and amplification of the CDX2 homeobox gene in human sporadic colorectal cancers with chromosomal instability

The expression of the CDX2 gene, a crucial regulator of gut homeostasis, is altered in human colorectal cancers in parallel with de-differentiation. Here, we have investigated the chromosomal status of CDX2 in human sporadic colorectal cancers with the phenotype of chromosomal instability. Allelic imbalance determination showed frequent rearrangements at the CDX2 locus. The rearrangements correlated with CDX2 gene amplification, as assessed by quantitative PCR analysis. However, they were not predictive of the Cdx2 protein pattern. These data suggest that mechanisms other than structural alterations at the CDX2 locus account for the change of expression in colorectal cancers.

Phosphorylation of the homeotic tumor suppressor Cdx2 mediates its ubiquitin-dependent proteasome degradation

The Caudal-related homeodomain transcription factor Cdx2 plays a key role in intestinal cell fate determination. Reduction of Cdx2 expression is a feature of many human colon carcinomas and inactivation of one cdx2 allele facilitates the development of invasive adenocarcinoma in the murine colon. Here, we investigated the post-translational regulation of Cdx2. We showed that various forms of Cdx2 coexist in the intestine and colon cancer cell lines, some of them being phosphorylated forms. We found that cyclin-dependent kinase 2 phosphorylated Cdx2 in vitro and in vivo. Using site-specific mutagenesis, we identified serine 281 as a new key residue for Cdx2 phosphorylation. Intriguingly, serine 281 belongs to a conserved motif of four evenly spaced serines (the 4S motif) similar to the one controlling beta-catenin degradation by the proteasome pathway. A nonphosphorylated mutant Cdx2 lacking the 4S motif (4S>A) exhibited reduced polyubiquitination upon proteasome inhibition and increased stability compared to wild-type Cdx2. In addition, we found that this mutant was less efficient to suppress colony formation than wild-type Cdx2. Thus, our data highlight a novel post-translational mechanism controlling Cdx2 degradation via phosphorylation and polyubiquitination, which may be of importance for intestinal development and cancer.

Laminin isoforms: biological roles and effects on the intracellular distribution of nuclear proteins in intestinal epithelial cells

Laminins are structurally and functionally major components of the extracellular matrix. Four isoforms of laminins (laminin-1, -2, -5 and -10) are expressed in a specific pattern along the crypt-villus axis of the intestine. Previous works indicated that expression of these isoforms is developmentally regulated and that laminins could modulate the behaviour of intestinal cells, but the exact role of each isoform remained unclear. Here, we report the first systematic analysis of the cellular functions of the four isoforms using the human colon adenocarcinoma Caco2/TC7 cell line as a model. We compared the respective abilities of each isoform to modulate adhesion, proliferation and differentiation of intestinal epithelial cells. We found that the isoforms were functionally distinct, with laminin-10 being the most adhesive substratum, laminin-2, laminin-5 and laminin-10 enhancing cellular proliferation and at the opposite, laminin-1 stimulating intestinal cell differentiation. To begin to characterise the molecular events induced by the different isoforms, we examined by immunofluorescence the intracellular distribution of several nuclear proteins, recently highlighted by a nuclear proteomic approach. We observed clear nucleocytoplasmic redistribution of these proteins, which depended on the laminin isoform. These results provide evidence for a distinct functional role of laminins in intestinal cell functions characterised by specific localisation of nuclear proteins.

SOX9 is an intestine crypt transcription factor, is regulated by the Wnt pathway, and represses the CDX2 and MUC2 genes

TCF and SOX proteins belong to the high mobility group box transcription factor family. Whereas TCFs, the transcriptional effectors of the Wnt pathway, have been widely implicated in the development, homeostasis and disease of the intestine epithelium, little is known about the function of the SOX proteins in this tissue. Here, we identified SOX9 in a SOX expression screening in the mouse fetal intestine. We report that the SOX9 protein is expressed in the intestinal epithelium in a pattern characteristic of Wnt targets. We provide in vitro and in vivo evidence that a bipartite β-catenin/TCF4 transcription factor, the effector of the Wnt signaling pathway, is required for SOX9 expression in epithelial cells. Finally, in colon epithelium-derived cells, SOX9 transcriptionally represses the CDX2 and MUC2 genes, normally expressed in the mature villus cells of the intestinal epithelium, and may therefore contribute to the Wnt-dependent maintenance of a progenitor cell phenotype.

Klotho is a novel beta-glucuronidase capable of hydrolyzing steroid beta-glucuronides

klotho mutant mice provide a unique model to analyze mechanisms of aging because their phenotypes resemble those of human aging-associated disorders. The klotho gene encodes Klotho, a type I membrane protein that shares sequence similarity with members of the glycosidase family 1. Because Klotho lacks the glutamic acid residues that have been shown to be involved in the catalytic activity of this family of enzymes, the function of this protein was unknown. Here, we have studied the biochemical characteristics of recombinant Klotho. The purified chimeric Klotho-human IgG1 Fc protein (KLFc) was assayed with a series of 4-methylumbelliferyl (4Mu) beta-glycosides as potential substrates. An enzymatic activity of Klotho was observed only with 4-methylumbelliferyl beta-D-glucuronide in contrast to bovine liver beta-glucuronidase, which exhibits a rather wide substrate specificity. Furthermore, the enzymatic activity of KLFc was reduced by the addition of specific inhibitors of beta-glucuronidase. A number of natural beta-glucuronides were screened by competitive inhibition for KLFc beta-glucuronidase. We found that steroid beta-glucuronides such as beta-estradiol 3-beta-D-glucuronide, estrone 3-beta-D-glucuronide, and estriol 3beta-D-glucuronide were hydrolyzed by KLFc. The artificial fluorescent substrate and the steroid conjugates share a common phenolic structure. Collectively, these data suggest that Klotho functions as a novel beta-glucuronidase and that steroid beta-glucuronides are potential candidates for the natural substrate(s) of Klotho.

Differential regulation of the glucose-6-phosphatase TATA box by intestine-specific homeodomain proteins CDX1 and CDX2

Glucose-6-phosphatase (Glc6Pase), the last enzyme of gluconeogenesis, is only expressed in the liver, kidney and small intestine. The expression of the Glc6Pase gene exhibits marked specificities in the three tissues in various situations, but the molecular basis of the tissue specificity is not known. The presence of a consensus binding site of CDX proteins in the minimal Glc6Pase gene promoter has led us to consider the hypothesis that these intestine-specific CDX factors could be involved in the Glc6Pase-specific expression in the small intestine. We first show that the Glc6Pase promoter is active in both hepatic HepG2 and intestinal CaCo2 cells. Using gel shift mobility assay, mutagenesis and competition experiments, we show that both CDX1 and CDX2 can bind the minimal promoter, but only CDX1 can transactivate it. Consistently, intestinal IEC6 cells stably overexpressing CDX1 exhibit induced expression of the Glc6Pase protein. We demonstrate that a TATAAAA sequence, located in position -31/-25 relating to the transcription start site, exhibits separable functions in the preinitiation of transcription and the transactivation by CDX1. Disruption of this site dramatically suppresses both basal transcription and the CDX1 effect. The latter may be restored by inserting a couple of CDX- binding sites in opposite orientation similar to that found in the sucrase-isomaltase promoter. We also report that the specific stimulatory effect of CDX1 on the Glc6Pase TATA-box, compared to CDX2, is related to the fact that CDX1, but not CDX2, can interact with the TATA-binding protein. Together, these data strongly suggest that CDX proteins could play a crucial role in the specific expression of the Glc6Pase gene in the small intestine. They also suggest that CDX transactivation might be essential for intestine gene expression, irrespective of the presence of a functional TATA box.

Cdx1 homeobox gene during human colon cancer progression

The Cdx1 homeobox gene encodes an intestine-specific transcription factor with a pro-oncogenic function in vitro. Here we have analysed the pattern of Cdx1 in human colon cancer progression. Cdx1 expression remains at a high level in the majority of the polyps and it is even overexpressed in more than one-third of the specimens, consistent with the fact that the gene is an intestine-specific target of oncogenic pathways. However, Cdx1 decreases in one-fifth of the polyps, which is reminiscent of the loss of expression previously reported in the majority of carcinomas. Allelic imbalance analysis demonstrates that the Cdx1 locus located on chromosome 5q is a major site of genomic rearrangement in colorectal cancers, and that the frequency of the rearrangements increases during polyps to carcinoma progression. Allelic imbalance at the Cdx1 locus occurs in relation to, although not invariably in association with, the rearrangements at the APC locus on the same chromosomal arm. Xenografts of primary human colon carcinomas indicate that the level of Cdx1 mRNA correlates with the intensity of allelic imbalance. Together, these data show that Cdx1 exhibits a complex pattern during colorectal cancer progression. Given that Cdx1 has a pro-oncogenic function in vitro, the maintenance of a high level of expression in polyps, and even its overexpression in one-third of the specimens, suggest that this homeobox gene may be an important factor in the process toward malignant transformation during the first steps of tumorigenesis.

Endoderm- and mesenchyme-dependent commitment of the differentiated epithelial cell types in the developing intestine of rat

During organogenesis, the intestinal tract progressively acquires a functional regionalization along the antero-posterior axis. Positional information needed for enterocytes has been studied, but the mechanisms that control Paneth and endocrine cell differentiation are poorly understood. We have used a model of endoderm/mesenchyme cross-associations to evaluate the respective roles of endoderm and mesenchyme in the cytodifferentiation of these epithelial cells. Heterotopic cross-associations comprising endoderm and mesenchyme from the presumptive proximal jejunum and colon were developed as xenografts in nude mice. Our results show that endoderm from the presumptive proximal jejunum when associated with colonic mesenchyme generate small intestinal enterocytes. Interestingly, no lysozyme-producing cells were generated. On the other hand, associations comprising colon endoderm and jejunal mesenchyme showed heterodifferentiation with typical small intestinal morphology with sucrase-isomaltase expression and Paneth cell differentiation. Heterotopic associations developed enteroendocrine cell patterns according to the normal fate of the endodermal moiety. As enteroendocrine cell commitment seems to occur before the other intestinal cell types, we cannot exclude a role of instructive signals from the mesenchyme on endocrine cell differentiation earlier in the development. These results identified a complex pattern of cell commitment, dependent of the differentiation type of the epithelial cell, on the regional origin of the endoderm and the associated mesenchyme.

Stimulation of Cdx1 by oncogenic beta-catenin/Tcf4 in colon cancer cells; opposite effect of the CDX2 homeoprotein

The homeobox gene Cdx1 is a regulator of intestinal epithelial cell proliferation and differentiation. Using a transfection approach, we showed here that the oncogenic activation of the beta-catenin pathway stimulates the endogenous expression of the Cdx1 mRNA as well as the activity of the Cdx1 promoter in cancer cells of the human colon. Reciprocally, the paralogue homeobox gene Cdx2 exerts an inhibitory effect on the basal and on the beta-catenin-stimulated activity of the Cdx1 promoter. The inhibitory effect of CDX2 requires the intact homeodomain. It is not dependent on canonical CDX binding sites in the Cdx1 promoter nor on the cis-elements specifically targeted by the beta-catenin/Tcf complex. We conclude that the oncogenically activated beta-catenin and CDX2 have opposite and independent effects on the Cdx1 homeobox gene.

Functional interference between thyroid hormone receptor alpha (TRalpha) and natural truncated TRDeltaalpha isoforms in the control of intestine development

Thyroid hormone is known to participate in the control of intestine maturation at weaning. Its action is mediated by the thyroid hormone nuclear receptors, encoded by the TRalpha and TRbeta genes. Since previous studies have shown that TRbeta plays a minor role in the gut, we focused here our analysis on the TRalpha gene. The TRalpha locus generates the TRalpha1 receptor together with the splicing variant TRalpha2 and the truncated products TRDeltaalpha1 and TRDeltaalpha2, which all lack an intact ligand binding domain. The TRDeltaalpha isoforms are transcribed from an internal promoter located in intron 7, and their distribution is restricted to a few tissues including those of the intestine. In order to define the functions of the different isoforms encoded by the TRalpha locus in the intestinal mucosa, we produced mice either lacking all known TRalpha products or harboring a mutation which inactivates the intronic promoter. We performed a detailed analysis of the intestinal phenotypes in these mice and compared it to that of the previously described TRalpha(-/-) mice, in which TRalpha isoforms are abolished but the TRDeltaalpha isoforms remain. This comparative analysis leads us to the following conclusions: (i) the TRalpha1 receptor mediates the T3-dependent functions in the intestine at weaning time and (ii) the TRDeltaalpha products negatively control the responsiveness of the epithelial cells to T3. Moreover, we show that TRDeltaalpha proteins can interfere with the transcription of the intestine-specific homeobox genes cdx1 and cdx2 and that their activity is regulated by TRalpha1. Altogether these data demonstrate that cooperation of TRalpha and TRDeltaalpha products is essential to ensure the normal postnatal development of the intestine and that mutations in the TRalpha locus can generate different phenotypes caused by the disruption of the equilibrium between these products.

Differentially expressed endoderm and mesenchyme genes along the fetal rat intestine

Developmental studies have shown that morphological and functional regionalization occurring along the mammalian intestine is defined at early fetal stages and that some aspects of this patterning are dependent on epithelial-mesenchymal cell interactions. The molecular basis of these processes are largely unknown. In this study, a differential display approach was used to identify genes differentially expressed along the longitudinal axis in the intestinal endoderm and mesenchyme moieties of 14-day-old rat fetuses at a stage prior to morpho-functional differentiation of the gut. Fifty-eight genes were identified, 36 being identical or similar to known genes and 13 corresponding to ESTs or genome sequences with unknown function. Nine cDNAs could not be assigned to any previously described nucleotide sequence. The selected genes are involved in several aspects of cell physiology, including metabolic pathways, cytoskeleton organization, signal transduction, protein biosynthesis, and regulation of gene transcription.

Wnt/(beta)-catenin signaling regulates the expression of the homeobox gene Cdx1 in embryonic intestine

During mammalian development, the Cdx1 homeobox gene exhibits an early period of expression when the embryonic body axis is established, and a later period where expression is restricted to the embryonic intestinal endoderm. Cdx1 expression is maintained throughout adulthood in the proliferative cell compartment of the continuously renewed intestinal epithelium, the crypts. In this study, we provide evidence in vitro and in vivo that Cdx1 is a direct transcriptional target of the Wnt/(beta)-catenin signaling pathway. Upon Wnt stimulation, expression of Cdx1 can be induced in mouse embryonic stem (ES) cells as well as in undifferentiated rat embryonic endoderm. Tcf4-deficient mouse embryos show abrogation of Cdx1 protein in the small intestinal epithelium, making Tcf4 the likely candidate to transduce Wnt signal in this part of gut. The promoter region of the Cdx1 gene contains several Tcf-binding motifs, and these bind Tcf/Lef1/(beta)-catenin complexes and mediate (beta)-catenin-dependent transactivation. The transcriptional regulation of the homeobox gene Cdx1 in the intestinal epithelium by Wnt/(beta)-catenin signaling underlines the importance of this signaling pathway in mammalian endoderm development.

The Cdx-1 and Cdx-2 homeobox genes in the intestine

The past years have witnessed an increasing number of reports relative to homeobox genes in endoderm-derived tissues. In this review, we focus on the caudal-related Cdx-1 and Cdx-2 homeobox genes to give an overview of the in vivo, in vitro, and ex vivo approaches that emphasize their primary role in intestinal development and in the control of intestinal cell proliferation, differentiation, and identity. The participation of these genes in colon tumorigenesis and their identification as important actors of the oncogenic process are also discussed.

The Cdx-1 and Cdx-2 homeobox genes in the intestine

The past years have witnessed an increasing number of reports relative to homeobox genes in endoderm-derived tissues. In this review, we focus on the caudal-related Cdx-1 and Cdx-2 homeobox genes to give an overview of the in vivo, in vitro, and ex vivo approaches that emphasize their primary role in intestinal development and in the control of intestinal cell proliferation, differentiation, and identity. The participation of these genes in colon tumorigenesis and their identification as important actors of the oncogenic process are also discussed.

Involvement of T3Ralpha- and beta-receptor subtypes in mediation of T3 functions during postnatal murine intestinal development

BACKGROUND & AIMS

Thyroid hormones are implicated in intestinal development. Their effects are mediated by nuclear receptors, which are transcriptional regulators activated upon binding of triiodothyronine. The aim of this study was to define the involvement of the receptor subtypes during intestinal development.

METHODS

We used strains of knockout mice lacking T3Ralpha, T3Rbeta, or both receptors, encoded by T3Ralpha and T3Rbeta genes.

RESULTS

Morphological features and expression of digestive enzymes and of two intestinal regulators, Cdx-1 and Cdx-2, were compared in wild-type and T3Ralpha, T3Rbeta, and T3Ralphabeta knockout animals. T3Ralpha-/- mice had abnormal intestinal morphology, assessed by a decrease in the number of epithelial cells along the crypt-villus axis and a decrease in proliferating crypt cells. Expression of Cdx-1 and Cdx-2, and of the digestive enzymes, was down-regulated. These parameters can be partially reversed by T3 injection. A similar (jejunum) or more severe (ileum) phenotype was found in T3Ralphabeta double mutants. In contrast, no changes occurred in T3Rbeta mice.

CONCLUSIONS

These data describe for the first time a direct effect of TH through the T3Ralpha-receptor subtypes on postnatal intestinal mucosa maturation. They also suggest that T3Rbeta receptors are dispensable but can partially substitute for T3Ralpha.

Promotion of intestinal carcinogenesis by dietary methionine

The metabolism of the polyamines spermidine and spermine is known to be enhanced in rapidly proliferating cells. Methionine is a precursor of the aminopropyl moieties of these amines. Therefore, it was of interest to study the effects of a methionine supplemented diet on polyamine metabolism and preneoplastic changes occurring in the intestinal tract of rats treated with the chemical carcinogen azoxymethane (AOM). Adult Wistar rats received 15 mg AOM/kg body wt (i.p.) once each week for 2 weeks. Thereafter, the rats were randomly divided into two groups and received controlled isoenergetic diets containing the same amount of folate, choline and vitamin B12 during 12 weeks: one group was kept on a standard diet; the other was fed the same diet, except that 1% L-methionine was added at the expense of carbohydrates. After 12 weeks, the administration of the methionine-supplemented diet stimulated the turnover rate of ileal epithelial cells, indicating enhanced crypt cell proliferation. Furthermore, in this group, a 2-fold increase in the number of aberrant hyperproliferative crypts and the appearance of tumors was observed in the colon. These effects were accompanied by the increased formation of spermidine and spermine due to the enhancement of S-adenosylmethionine decarboxylase activity and by the upregulation of Cdx-1, a homeobox gene with oncogenic potentials. The experimental data do not support the view of a chemopreventive effect of dietary methionine supplementation on intestinal carcinogenesis in rats, even at an early phase of preneoplastic development, but rather suggest that methionine promotes intestinal carcinogenesis.

Production of low-lactose milk by ectopic expression of intestinal lactase in the mouse mammary gland

We have investigated, in mice, an in vivo method for producing low-lactose milk, based on the creation of transgenic animals carrying a hybrid gene in which the intestinal lactase-phlorizin hydrolase cDNA was placed under the control of the mammary-specific alpha-lactalbumin promoter. Transgenic females expressed lactase protein and activity during lactation at the apical side of mammary alveolar cells. Active lactase was also secreted into milk, anchored in the outer membrane of fat globules. Lactase synthesis in the mammary gland caused a significant decrease in milk lactose (50-85%) without obvious changes in fat and protein concentrations. Sucklings nourished with low-lactose milk developed normally. Hence, these data validate the use of transgenic animals expressing lactase in the mammary gland to produce low-lactose milk in vivo, and they demonstrate that the secretion of an intestinal digestive enzyme into milk can selectively modify its composition.

Downregulation of the colon tumour-suppressor homeobox gene Cdx-2 by oncogenic ras

Downregulation of the colon tumour-suppressor homeobox gene Cdx-2 by oncogenic ras Constitutive activation of the ras proto-oncogene is a frequent and early event in colon cancers, but the downstream nuclear targets are not fully understood. The Cdx-1 and Cdx-2 homeobox genes play crucial roles in intestinal cell proliferation and differentiation. In addition, Cdx-2 is a colonic tumour-suppressor gene, whereas Cdx-1 has oncogenic potential. Here, we show that constitutive activation of ras alters Cdx-1 and Cdx-2 expression in human colonic Caco-2 and HT-29 cells that harbour a normal ras proto-oncogene. Oncogenic ras downregulates Cdx-2 through activation of the PKC pathway and a decline in activity of the Cdx-2 promoter AP-1 site. This decline results from a PKC-dependent decrease in the relative expression of c-Jun, an activator of Cdx-2 transcription, compared to c-Fos, an inhibitor of Cdx-2. Unlike Cdx-2, Cdx-1 is upregulated by oncogenic ras and this effect is mediated by activation of the MEK1 pathway. These results indicate that oncogenic ras activation has opposite effects on Cdx-1 and Cdx-2 expression through distinct signalling pathways and they provide the first evidence for a functional link between ras activation and the downregulation of the Cdx-2 tumour-suppressor gene in colon cancer cells.