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

GPA33 expression in colorectal cancer can be induced by WNT inhibition and targeted by cellular therapy

GPA33 is a promising surface antigen for targeted therapy in colorectal cancer (CRC). It is expressed almost exclusively in CRC and intestinal epithelia. However, previous clinical studies have not achieved expected response rates. We investigated GPA33 expression and regulation in CRC and developed a GPA33-targeted cellular therapy. We examined GPA33 expression in CRC cohorts using immunohistochemistry and immunofluorescence. We analyzed GPA33 regulation by interference with oncogenic signaling in vitro and in vivo using inhibitors and conditional inducible regulators. Furthermore, we engineered anti-GPA33-CAR T cells and assessed their activity in vitro and in vivo. GPA33 expression showed consistent intratumoral heterogeneity in CRC with antigen loss at the infiltrative tumor edge. This pattern was preserved at metastatic sites. GPA33-positive cells had a differentiated phenotype and low WNT activity. Low GPA33 expression levels were linked to tumor progression in patients with CRC. Downregulation of WNT activity induced GPA33 expression in vitro and in GPA33-negative tumor cell subpopulations in xenografts. GPA33-CAR T cells were activated in response to GPA33 and reduced xenograft growth in mice after intratumoral application. GPA33-targeted therapy may be improved by simultaneous WNT inhibition to enhance GPA33 expression. Furthermore, GPA33 is a promising target for cellular immunotherapy in CRC.

Lipid Raft Facilitated Receptor Organization and Signaling: A Functional Rheostat in Embryonic Development, Stem Cell Biology and Cancer

Molecular views of plasma membrane organization and dynamics are gradually changing over the past fifty years. Dynamics of plasma membrane instigate several signaling nexuses in eukaryotic cells. The striking feature of plasma membrane dynamics is that, it is internally transfigured into various subdomains of clustered macromolecules. Lipid rafts are nanoscale subdomains, enriched with cholesterol and sphingolipids, reside as floating entity mostly on the exoplasmic leaflet of the lipid bilayer. In terms of functionality, lipid rafts are unique among other membrane subdomains. Herein, advances on the roles of lipid rafts in cellular physiology and homeostasis are discussed, precisely, on how rafts dynamically harbor signaling proteins, including GPCRs, catalytic receptors, and ionotropic receptors within it and orchestrate multiple signaling pathways. In the developmental proceedings signaling are designed for patterning of overall organism and they differ from the somatic cell physiology and signaling of fully developed organisms. Some of the developmental signals are characteristic in maintenance of stemness and activated during several types of tumor development and cancer progression. The harmony between extracellular signaling and lineage specific transcriptional programs are extremely important for embryonic development. The roles of plasma membrane lipid rafts mediated signaling in lineage specificity, early embryonic development, stem cell maintenance are emerging. In view of this, we have highlighted and analyzed the roles of lipid rafts in receptor organization, cell signaling, and gene expression during embryonic development; from pre-implantation through the post-implantation phase, in stem cell and cancer biology.

Mechanisms of mucosal healing: treating inflammatory bowel disease without immunosuppression?

Almost all currently available treatments for inflammatory bowel disease (IBD) act by inhibiting inflammation, often blocking specific inflammatory molecules. However, given the infectious and neoplastic disease burden associated with chronic immunosuppressive therapy, the goal of attaining mucosal healing without immunosuppression is attractive. The absence of treatments that directly promote mucosal healing and regeneration in IBD could be linked to the lack of understanding of the underlying pathways. The range of potential strategies to achieve mucosal healing is diverse. However, the targeting of regenerative mechanisms has not yet been achieved for IBD. Stem cells provide hope as a regenerative treatment and are used in limited clinical situations. Growth factors are available for the treatment of short bowel syndrome but have not yet been applied in IBD. The therapeutic application of organoid culture and stem cell therapy to generate new intestinal tissue could provide a novel mechanism to restore barrier function in IBD. Furthermore, blocking key effectors of barrier dysfunction (such as MLCK or damage-associated molecular pattern molecules) has shown promise in experimental IBD. Here, we review the diversity of molecular targets available to directly promote mucosal healing, experimental models to identify new potential pathways and some of the anticipated potential therapies for IBD.

Mechanisms of mucosal healing: treating inflammatory bowel disease without immunosuppression?

Almost all currently available treatments for inflammatory bowel disease (IBD) act by inhibiting inflammation, often blocking specific inflammatory molecules. However, given the infectious and neoplastic disease burden associated with chronic immunosuppressive therapy, the goal of attaining mucosal healing without immunosuppression is attractive. The absence of treatments that directly promote mucosal healing and regeneration in IBD could be linked to the lack of understanding of the underlying pathways. The range of potential strategies to achieve mucosal healing is diverse. However, the targeting of regenerative mechanisms has not yet been achieved for IBD. Stem cells provide hope as a regenerative treatment and are used in limited clinical situations. Growth factors are available for the treatment of short bowel syndrome but have not yet been applied in IBD. The therapeutic application of organoid culture and stem cell therapy to generate new intestinal tissue could provide a novel mechanism to restore barrier function in IBD. Furthermore, blocking key effectors of barrier dysfunction (such as MLCK or damage-associated molecular pattern molecules) has shown promise in experimental IBD. Here, we review the diversity of molecular targets available to directly promote mucosal healing, experimental models to identify new potential pathways and some of the anticipated potential therapies for IBD.

Infection with a hypervirulent strain of Helicobacter pylori primes gastric cells toward intestinal transdifferentiation

BACKGROUND

Intestinal metaplasia, gastric-to-intestinal transdifferentiation, occurs as a result of the misexpression of certain regulatory factors, leading to genetic reprogramming. Here, we have evaluated the H. pylori-induced expression patterns of these candidate genes.

METHODS

The expression levels of 1) tissue-specific transcription factors (RUNX3, KLF5, SOX2, SALL4, CDX1 and CDX2), 2) stemness factors (TNFRSF19, LGR5, VIL1) and 3) tissue-specific mucins (MUC5AC, MUC2) were evaluated by quantitative real-time PCR in gastric primary cells (GPCs), in parallel with two gastric cancer (MKN45 and AGS) cell lines, up to 96h following H. pylori infection.

RESULTS

Following H. pylori infection of GPCs, RUNX3 declined at 24h post infection (-6.2 ± 0.3) and remained downregulated for up to 96h. Subsequently, overexpression of self-renewal and pluripotency transcription factors, KLF5 (3.6 ± 0.2), SOX2 (7.6 ± 0.5) and SALL4 (4.3 ± 0.2) occurred. The expression of TNFRSF19 and LGR5, demonstrated opposing trends, with an early rise of the former (4.5 ± 0.3) at 8h, and a simultaneous fall of the latter (-1.8 ± 0.5). This trend was reversed at 96h, with the decline in TNFRSF19 (-5.5 ± 0.2), and escalation of LGR5 (2.6 ± 0.2) and VIL1 (1.8 ± 0.3). Ultimately, CDX1 and CDX2 were upregulated by 1.9 and 4.7-fold, respectively. The above scenario was, variably observed in MKN45 and AGS cells.

CONCLUSION

Our data suggests an interdependent gene regulatory network, induced by H. pylori infection. This interaction begins with the downregulation of RUNX3, upregulation of self-renewal and pluripotency transcription factors, KLF5, SOX2 and SALL4, leading to the downregulation of TNFRSF19, upregulation of LGR5 and aberrant expression of intestine-specific transcription factors, potentially facilitating the process of gastric-to-intestinal transdifferentiation.

Emerging role of nutritional short-chain fatty acids (SCFAs) against cancer via modulation of hematopoiesis

The understanding of gut microbiota has emerged as a significant frontier in development of strategies to maintain normal human body's homeostasis and preventing the disease development over the last decade. The composition of the gut microbiota influences the clinical benefit of immune checkpoints in patients with advanced cancer, but the mechanisms underlying this relationship are unclear. Cancer is among the leading causes of mortality worldwide. So far, there is no universal treatment for cancer and despite significant advances, a lot of improvement on cancer therapy is required. Owing to its role in preserving the host's health and maintaining cellular integrity, the human gut microbiome has recently drawn a lot of interest as a target for cancer treatment. Dietary fiber is fermented by the gut microbiota to generate short-chain fatty acids (SCFAs), such as acetate, butyrate, and propionate, which are physiologically active metabolites. SCFAs can modulate the pathophysiology of the tumor environment through various critical signaling pathways. In addition, SCFAs can bind to carcinogens and other toxic chemicals, thus facilitating their biotransformation and elimination through different excretory mechanisms. This review discusses the mechanisms of action of short-chain fatty acids in modulating hematopoiesis of various immune system cells and the resultant beneficial anti-cancer effects. It also provides future perspectives on cancer therapy.

Clinicopathological significance of the EMT-related proteins and their interrelationships in prostate cancer. An immunohistochemical study

The chronic inflammation influences a microenvironment, where as a result of losing control over tissue homeostatic mechanisms, the carcinogenesis process may be induced. Inflammatory response cells can secrete a number of factors that support both initiation and progression of cancer and also they may consequently induct an epithelial-mesenchymal transition (EMT), the process responsible for development of distant metastasis. Macrophage migration inhibitory factor (MIF) acts as a pro-inflammatory cytokine that is considered as a link between chronic inflammation and tumor development. MIF can function as a modulator of important cancer-related genes expression, as well as an activator of signaling pathways that promotes the development of prostate cancer. The study was performed on FFPE tissues resected from patients who underwent radical prostatectomy. To investigate the relationship of studied proteins with involvement in tumor progression and initiation of epithelial-to-mesenchymal transition (EMT) process, we selected clinicopathological parameters related to tumor progression. Immunohistochemical analyses of MIF, SOX-4, β-catenin and E-cadherin were performed on TMA slides. We found a statistically significant correlation of overall β-catenin expression with the both lymph node metastasis (p<0.001) and presence of angioinvasion (p = 0.012). Membrane β-catenin expression was associated with distant metastasis (p = 0.021). In turn, nuclear MIF was correlated with lymph node metastasis (p = 0.003). The positive protein-protein correlations have been shown between the total β-catenin protein expression level with level of nuclear SOX-4 protein expression (r = 0.27; p<0.05) as well as negative correlation of β-catenin expression with level of nuclear MIF protein expression (r = -0.23; p<0.05). Our results seem promising and strongly highlight the potential role of MIF in development of nodal metastases as well as may confirm an involvement of β-catenin in disease spread in case of prostate cancer.

Small subset of Wnt-activated cells is an initiator of regrowth in colorectal cancer organoids after irradiation

Most colorectal cancers (CRCs) are differentiated adenocarcinomas, which maintain expression of both stemness and differentiation markers. This observation suggests that CRC cells could retain a regeneration system of normal cells upon injury. However, the role of stemness in cancer cell regeneration after irradiation is poorly understood. Here, we examined the effect of radiation on growth, stemness, and differentiation in organoids derived from differentiated adenocarcinomas. Following a sublethal dose of irradiation, proliferation and stemness markers, including Wnt target genes, were drastically reduced, but differentiation markers remained. After a static growth phase after high dose of radiation, regrowth foci appeared; these consisted of highly proliferating cells that expressed stem cell markers. Radiosensitivity and the ability to form foci differed among the cancer tissue‐originated spheroid (CTOS) lines examined and showed good correlation with in vivo radiation sensitivity. Pre‐treating organoids with histone deacetylase inhibitors increased radiation sensitivity; this increase was accompanied by the suppression of Wnt signal‐related gene expression. Accordingly, Wnt inhibitors increased organoid radiosensitivity. These results suggested that only a small subset of, but not all, cancer cells with high Wnt activity at the time of irradiation could give rise to foci formation. In conclusion, we established a radiation sensitivity assay using CRC organoids that could provide a novel platform for evaluating the effects of radiosensitizers on differentiated adenocarcinomas in CRC.

Relationship between apical junction proteins, gene expression and cancer

The apical junctional complex (AJC) is a cell-cell adhesion system present at the upper portion of the lateral membrane of epithelial cells integrated by the tight junction (TJ) and the adherens junction (AJ). This complex is crucial to initiate and stabilize cell-cell adhesion, to regulate the paracellular transit of ions and molecules and to maintain cell polarity. Moreover, we now consider the AJC as a hub of signal transduction that regulates cell-cell adhesion, gene transcription and cell proliferation and differentiation. The molecular components of the AJC are multiple and diverse and depending on the cellular context some of the proteins in this complex act as tumor suppressors or as promoters of cell transformation, migration and metastasis outgrowth. Here, we describe these new roles played by TJ and AJ proteins and their potential use in cancer diagnostics and as targets for therapeutic intervention.

Generation of functional human hepatocytes in vitro: current status and future prospects

Liver and hepatocyte transplantation are the only effective therapies for late-stage liver diseases, in which the liver loses its regenerative capacity. However, there is a shortage of donors. As a potential alternative approach, functional hepatocytes were recently generated from various cell sources. Analysis of drug metabolism in the human liver is important for drug development. Consequently, cells that metabolize drugs similar to human primary hepatocytes are required. This review discusses the current challenges and future perspectives concerning hepatocytes and hepatic progenitor cells that have been reprogrammed from various cell types, focusing on their functions in transplantation models and their ability to metabolize drugs.

Tight Junction Proteins and Signaling Pathways in Cancer and Inflammation: A Functional Crosstalk

The ability of epithelial cells to organize through cell–cell adhesion into a functioning epithelium serves the purpose of a tight epithelial protective barrier. Contacts between adjacent cells are made up of tight junctions (TJ), adherens junctions (AJ), and desmosomes with unique cellular functions and a complex molecular composition. These proteins mediate firm mechanical stability, serves as a gatekeeper for the paracellular pathway, and helps in preserving tissue homeostasis. TJ proteins are involved in maintaining cell polarity, in establishing organ-specific apical domains and also in recruiting signaling proteins involved in the regulation of various important cellular functions including proliferation, differentiation, and migration. As a vital component of the epithelial barrier, TJs are under a constant threat from proinflammatory mediators, pathogenic viruses and bacteria, aiding inflammation and the development of disease. Inflammatory bowel disease (IBD) patients reveal loss of TJ barrier function, increased levels of proinflammatory cytokines, and immune dysregulation; yet, the relationship between these events is partly understood. Although TJ barrier defects are inadequate to cause experimental IBD, mucosal immune activation is changed in response to augmented epithelial permeability. Thus, the current studies suggest that altered barrier function may predispose or increase disease progression and therapies targeted to specifically restore the barrier function may provide a substitute or supplement to immunologic-based therapies. This review provides a brief introduction about the TJs, AJs, structure and function of TJ proteins. The link between TJ proteins and key signaling pathways in cell proliferation, transformation, and metastasis is discussed thoroughly. We also discuss the compromised intestinal TJ integrity under inflammatory conditions, and the signaling mechanisms involved that bridge inflammation and cancer.

Wnt/β-catenin signalling is necessary for gut differentiation in a marine annelid, Platynereis dumerilii

Background

Wnt/β-catenin (or canonical) signalling pathway activity is necessary and used independently several times for specification of vegetal fate and endoderm, gut differentiation, maintenance of epithelium in adult intestine and the development of gut-derived organs in various vertebrate and non-vertebrate organisms. However, its conservation in later stages of digestive tract development still remains questionable due to the lack of detailed data, mainly from Spiralia.

Results

Here we characterize the Pdu-Tcf gene, a Tcf/LEF orthologue and a component of Wnt/β-catenin pathway from Platynereis dumerilii, a spiralian, marine annelid worm. Pdu-Tcf undergoes extensive alternative splicing in the C-terminal region of the gene generating as many as eight mRNA isoforms some of which differ in the presence or absence of a C-clamp domain which suggests a distinct DNA binding activity of individual protein variants. Pdu-Tcf is broadly expressed throughout development which is indicative of many functions. One of the most prominent domains that exhibits rather strong Pdu-Tcf expression is in the putative precursors of endodermal gut cells which are detected after 72 h post-fertilization (hpf). At day 5 post-fertilization (dpf), Pdu-Tcf is expressed in the hindgut and pharynx (foregut), whereas at 7 dpf stage, it is strongly transcribed in the now-cellularized midgut for the first time. In order to gain insight into the role of Wnt/β-catenin signalling, we disrupted its activity using pharmacological inhibitors between day 5 and 7 of development. The inhibition of Wnt/β-catenin signalling led to the loss of midgut marker genes Subtilisin-1, Subtilisin-2, α-Amylase and Otx along with a drop in β-catenin protein levels, Axin expression in the gut and nearly the complete loss of proliferative activity throughout the body of larva. At the same time, a hindgut marker gene Legumain was expanded to the midgut compartment under the same conditions.

Conclusions

Our findings suggest that high Wnt/β-catenin signalling in the midgut might be necessary for proper differentiation of the endoderm to an epithelium capable of secreting digestive enzymes. Together, our data provide evidence for the role of Wnt/β-catenin signalling in gut differentiation in Platynereis.

Genome-wide analysis of PDX1 target genes in human pancreatic progenitors

Objective

Homozygous loss-of-function mutations in the gene coding for the homeobox transcription factor (TF) PDX1 leads to pancreatic agenesis, whereas heterozygous mutations can cause Maturity-Onset Diabetes of the Young 4 (MODY4). Although the function of Pdx1 is well studied in pre-clinical models during insulin-producing β-cell development and homeostasis, it remains elusive how this TF controls human pancreas development by regulating a downstream transcriptional program. Also, comparative studies of PDX1 binding patterns in pancreatic progenitors and adult β-cells have not been conducted so far. Furthermore, many studies reported the association between single nucleotide polymorphisms (SNPs) and T2DM, and it has been shown that islet enhancers are enriched in T2DM-associated SNPs. Whether regions, harboring T2DM-associated SNPs are PDX1 bound and active at the pancreatic progenitor stage has not been reported so far.

Methods

In this study, we have generated a novel induced pluripotent stem cell (iPSC) line that efficiently differentiates into human pancreatic progenitors (PPs). Furthermore, PDX1 and H3K27ac chromatin immunoprecipitation sequencing (ChIP-seq) was used to identify PDX1 transcriptional targets and active enhancer and promoter regions. To address potential differences in the function of PDX1 during development and adulthood, we compared PDX1 binding profiles from PPs and adult islets. Moreover, combining ChIP-seq and GWAS meta-analysis data we identified T2DM-associated SNPs in PDX1 binding sites and active chromatin regions.

Results

ChIP-seq for PDX1 revealed a total of 8088 PDX1-bound regions that map to 5664 genes in iPSC-derived PPs. The PDX1 target regions include important pancreatic TFs, such as PDX1 itself, RFX6, HNF1B, and MEIS1, which were activated during the differentiation process as revealed by the active chromatin mark H3K27ac and mRNA expression profiling, suggesting that auto-regulatory feedback regulation maintains PDX1 expression and initiates a pancreatic TF program. Remarkably, we identified several PDX1 target genes that have not been reported in the literature in human so far, including RFX3, required for ciliogenesis and endocrine differentiation in mouse, and the ligand of the Notch receptor DLL1, which is important for endocrine induction and tip-trunk patterning. The comparison of PDX1 profiles from PPs and adult human islets identified sets of stage-specific target genes, associated with early pancreas development and adult β-cell function, respectively. Furthermore, we found an enrichment of T2DM-associated SNPs in active chromatin regions from iPSC-derived PPs. Two of these SNPs fall into PDX1 occupied sites that are located in the intronic regions of TCF7L2 and HNF1B. Both of these genes are key transcriptional regulators of endocrine induction and mutations in cis-regulatory regions predispose to diabetes.

Conclusions

Our data provide stage-specific target genes of PDX1 during in vitro differentiation of stem cells into pancreatic progenitors that could be useful to identify pathways and molecular targets that predispose for diabetes. In addition, we show that T2DM-associated SNPs are enriched in active chromatin regions at the pancreatic progenitor stage, suggesting that the susceptibility to T2DM might originate from imperfect execution of a β-cell developmental program.

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PDX1 ChIP-seq analysis revealed 5664 target genes in human pancreatic progenitors, including unreported target genes.

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Comparison of PDX1 profiles from PPs and adult human islets identified stage-specific PDX1 target gene sets.

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T2DM-associated SNPs are enriched in active chromatin regions from iPSC-derived PPs.

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Three SNPs fall into PDX1 occupied sites, located in intronic regions of the developmental regulatory TFs TCF7L2 and HNF1B.

The Roles of the Wnt-Antagonists Axin and Lrp4 during Embryogenesis of the Red Flour Beetle Tribolium castaneum

In both vertebrates and invertebrates, the Wnt-signaling pathway is essential for numerous processes in embryogenesis and during adult life. Wnt activity is fine-tuned at various levels by the interplay of a number of Wnt-agonists (Wnt ligands, Frizzled-receptors, Lrp5/6 coreceptors) and Wnt-antagonists (among them Axin, Secreted frizzled and Lrp4) to define anterior–posterior polarity of the early embryo and specify cell fate in organogenesis. So far, the functional analysis of Wnt-pathway components in insects has concentrated on the roles of Wnt-agonists and on the Wnt-antagonist Axin. We depict here additional features of the Wnt-antagonist Axin in the flour beetle Tribolium castaneum. We show that Tc-axin is dynamically expressed throughout embryogenesis and confirm its essential role in head development. In addition, we describe an as yet undetected, more extreme Tc-axin RNAi-phenotype, the ectopic formation of posterior abdominal segments in reverse polarity and a second hindgut at the anterior. For the first time, we describe here that an lrp4 ortholog is involved in axis formation in an insect. The Tribolium Lrp4 ortholog is ubiquitously expressed throughout embryogenesis. Its downregulation via maternal RNAi results in the reduction of head structures but not in axis polarity reversal. Furthermore, segmentation is impaired and larvae develop with a severe gap-phenotype. We conclude that, as in vertebrates, Tc-lrp4 functions as a Wnt-inhibitor in Tribolium during various stages of embryogenesis. We discuss the role of both components as negative modulators of Wnt signaling in respect to axis formation and segmentation in Tribolium.

In vitro patterning of pluripotent stem cell-derived intestine recapitulates in vivo human development

The intestine plays a central role in digestion, nutrient absorption and metabolism, with individual regions of the intestine having distinct functional roles. Many examples of region-specific gene expression in the adult intestine are known, but how intestinal regional identity is established during development is a largely unresolved issue. Here, we have identified several genes that are expressed in a region-specific manner in the developing human intestine. Using human embryonic stem cell-derived intestinal organoids, we demonstrate that the duration of exposure to active FGF and WNT signaling controls regional identity. Short-term exposure to FGF4 and CHIR99021 (a GSK3β inhibitor that stabilizes β-catenin) resulted in organoids with gene expression patterns similar to developing human duodenum, whereas longer exposure resulted in organoids similar to ileum. When region-specific organoids were transplanted into immunocompromised mice, duodenum-like organoids and ileum-like organoids retained their regional identity, demonstrating that regional identity of organoids is stable after initial patterning occurs. This work provides insights into the mechanisms that control regional specification of the developing human intestine and provides new tools for basic and translational research.

Summary: Human embryonic stem cell-derived intestinal organoids can be patterned into duodenum-like or ileum-like tissue, recapitulating in vivo human development.

The Colonic Crypt Protects Stem Cells from Microbiota-Derived Metabolites

In the mammalian intestine, crypts of Leiberkühn house intestinal epithelial stem/progenitor cells at their base. The mammalian intestine also harbors a diverse array of microbial metabolite compounds that potentially modulate stem/progenitor cell activity. Unbiased screening identified butyrate, a prominent bacterial metabolite, as a potent inhibitor of intestinal stem/progenitor proliferation at physiologic concentrations. During homeostasis, differentiated colonocytes metabolized butyrate likely preventing it from reaching proliferating epithelial stem/progenitor cells within the crypt. Exposure of stem/progenitor cells in vivo to butyrate through either mucosal injury or application to a naturally crypt-less host organism led to inhibition of proliferation and delayed wound repair. The mechanism of butyrate action depended on the transcription factor Foxo3. Our findings indicate that mammalian crypt architecture protects stem/progenitor cell proliferation in part through a metabolic barrier formed by differentiated colonocytes that consume butyrate and stimulate future studies on the interplay of host anatomy and microbiome metabolism.

Wnt/β-Catenin Signaling Activation beyond Robust Nuclear β-Catenin Accumulation in Nondysplastic Barrett's Esophagus: Regulation via Dickkopf-1

INTRODUCTION: Wnt/β-catenin signaling activation has been reported only during the late steps of Barrett’s esophagus (BE) neoplastic progression, but not in BE metaplasia, based on the absence of nuclear β-catenin. However, β-catenin transcriptional activity has been recorded in absence of robust nuclear accumulation. Thus, we aimed to investigate the Wnt/β-catenin signaling in nondysplastic BE. METHODS: Esophageal tissues from healthy and BE patients without dysplasia were analyzed for Wnt target gene expression by quantitative reverse transcription polymerase chain reaction (qRT-PCR) and immunohistochemistry. Esophageal squamous (EPC1-& EPC2-hTERT), BE metaplastic (CP-A), and adenocarcinoma (OE33) cell lines were characterized for Wnt activation by qRT-PCR, Western blot, and luciferase assay. Wnt activity regulation was examined by using recombinant Wnt3a and Dickkopf-1 (Dkk1) as well as Dkk1 short interfering RNA. RESULTS: Wnt target genes (AXIN2, c-MYC, Cyclin D1, Dkk1) and Wnt3a were significantly upregulated in nondysplastic BE compared with squamous mucosa. Elevated levels of dephosphorylated β-catenin were detected in nondysplastic BE. Nuclear active β-catenin and TOPflash activity were increased in CP-A and OE33 cells compared with squamous cells. Wnt3a-mediated β-catenin signaling activation was abolished by Dkk1 in CP-A cells. TOPFlash activity was elevated following Dkk1 silencing in CP-A but not in OE33 cells. Dysplastic and esophageal adenocarcinoma tissues demonstrated further Dkk1 and AXIN2 overexpression. CONCLUSIONS: Despite the absence of robust nuclear accumulation, β-catenin is transcriptionally active in nondysplastic BE. Dkk1 overexpression regulates β-catenin signaling in BE metaplastic but not in adenocarcinoma cells, suggesting that early perturbation of Dkk1-mediated signaling suppression may contribute to BE malignant transformation.

A direct role for murine Cdx proteins in the trunk neural crest gene regulatory network

Numerous studies in chordates and arthropods currently indicate that Cdx proteins have a major ancestral role in the organization of post-head tissues. In urochordate embryos, Cdx loss-of-function has been shown to impair axial elongation, neural tube (NT) closure and pigment cell development. Intriguingly, in contrast to axial elongation and NT closure, a Cdx role in neural crest (NC)-derived melanocyte/pigment cell development has not been reported in any other chordate species. To address this, we generated a new conditional pan-Cdx functional knockdown mouse model that circumvents Cdx functional redundancy as well as the early embryonic lethality of Cdx mutants. Through directed inhibition in the neuroectoderm, we provide in vivo evidence that murine Cdx proteins impact melanocyte and enteric nervous system development by, at least in part, directly controlling the expression of the key early regulators of NC ontogenesis Pax3,Msx1 and Foxd3 Our work thus reveals a novel role for Cdx proteins at the top of the trunk NC gene regulatory network in the mouse, which appears to have been inherited from their ancestral ortholog.

TCF/Lef regulates the Gsx ParaHox gene in central nervous system development in chordates

BACKGROUND

The ParaHox genes play an integral role in the anterior-posterior (A-P) patterning of the nervous system and gut of most animals. The ParaHox cluster is an ideal system in which to study the evolution and regulation of developmental genes and gene clusters, as it displays similar regulatory phenomena to its sister cluster, the Hox cluster, but offers a much simpler system with only three genes.

RESULTS

Using Ciona intestinalis transgenics, we isolated a regulatory element upstream of Branchiostoma floridae Gsx that drives expression within the central nervous system of Ciona embryos. The minimal amphioxus enhancer region required to drive CNS expression has been identified, along with surrounding sequence that increases the efficiency of reporter expression throughout the Ciona CNS. TCF/Lef binding sites were identified and mutagenized and found to be required to drive the CNS expression. Also, individual contributions of TCF/Lef sites varied across the regulatory region, revealing a partial division of function across the Bf-Gsx-Up regulatory element. Finally, when all TCF/Lef binding sites are mutated CNS expression is not only abolished, but a latent repressive function is also unmasked.

CONCLUSIONS

We have identified a B. floridae Gsx upstream regulatory element that drives CNS expression within transgenic Ciona intestinalis, and have shown that this CNS expression is dependent upon TCF/Lef binding sites. We examine the evolutionary and developmental implications of these results, and discuss the possibility of TCF/Lef not only as a regulator of chordate Gsx, but as a deeply conserved regulatory factor controlling all three ParaHox genes across the Metazoa.

Tales of Tails (and Trunks): Forming the Posterior Body in Vertebrate Embryos

A major question in developmental biology is how the early embryonic axes are established. Recent studies using different model organisms and mammalian in vitro systems have revealed the surprising result that most of the early posterior embryonic body forms from a Wnt-regulated bipotential neuromesodermal progenitor population that escapes early germ layer patterning. Part of the regulatory network that drives the maintenance and differentiation of these progenitors has recently been determined, but much remains to be discovered. This review discusses some of the common features present in all vertebrates, as well as unique aspects that different species utilize to establish their anterior-posterior (A-P) axis.

Genetic and nongenetic etiology of nonsyndromic anorectal malformations: a systematic review

Congenital anorectal malformations (ARMs) are one of the most frequently observed birth defects of the digestive system. However, their etiology remains elusive. Therefore, we aim to summarize and critically appraise all existing literature on the genetic and nongenetic etiology of nonsyndromic ARM and to conclude with unifying hypotheses and directions for future research. A structured literature search on English language human studies was conducted in PubMed and Embase up to October 1, 2013, resulting in 112 included articles. Research on the identification of genes underlying nonsyndromic ARM is remarkably scarce. Most studies were focused on screening of candidate genes for mutations or single-nucleotide polymorphisms, which did not yield any substantial evidence. Nongenetic factors fairly consistently found to be associated with ARM are assisted reproductive techniques, multiple pregnancy, preterm delivery, low birth weight, maternal overweight or obesity, and preexisting diabetes. This review provides indications for the involvement of both genes and nongenetic risk factors in the etiology of ARM. In future studies, large cohorts of patients with ARM from national and international collaborations are needed to acquire new hypotheses and knowledge through hypothesis-generating approaches. Challenges for future studies may also lie in the investigation of gene-gene and gene-environment interactions.

Helicobacter pylori-Induced Signaling Pathways Contribute to Intestinal Metaplasia and Gastric Carcinogenesis

Helicobacter pylori (H. pylori) induces chronic gastric inflammation, atrophic gastritis, intestinal metaplasia, and cancer. Although the risk of gastric cancer increases exponentially with the extent of atrophic gastritis, the precise mechanisms of gastric carcinogenesis have not been fully elucidated. H. pylori induces genetic and epigenetic changes in gastric epithelial cells through activating intracellular signaling pathways in a cagPAI-dependent manner. H. pylori eventually induces gastric cancer with chromosomal instability (CIN) or microsatellite instability (MSI), which are classified as two major subtypes of gastric cancer. Elucidation of the precise mechanisms of gastric carcinogenesis will also be important for cancer therapy.

Wnt/catenin signaling in adult stem cell physiology and disease

Wnt signaling plays an important role in development and disease. In this review we focus on the role of the canonical Wnt signaling pathway in somatic stem cell biology and its critical role in tissue homeostasis. We present current knowledge how Wnt/β-catenin signaling affects tissue stem cell behavior in various organ systems, including the gut, mammary gland, the hematopoietic and nervous system. We discuss evidence that canonical Wnt signaling can both maintain potency and an undifferentiated state as well as cause differentiation in somatic stem cells, depending on the cellular and environmental context. Based on studies by our lab and others, we will attempt to explain the dichotomous behavior of this signaling pathway in determining cell fate decisions and put special emphasis on the interaction of β-catenin with two highly homologous co-activator proteins, CBP and p300, to shed light on the their differential role in the outcome of Wnt/β-catenin signaling. Furthermore, we review current knowledge regarding the aberrant regulation of Wnt/β-catenin signaling in cancer biology, particularly its pivotal role in the context of cancer stem cells. Finally, we discuss data demonstrating that small molecule modulators of the β-catenin/co-activator interaction can be used to shift the balance between undifferentiated proliferation and differentiation, which potentially presents a promising therapeutic approach to stem cell based disease mechanisms.

Akt regulates β-catenin in a rat model of focal cerebral ischemia-reperfusion injury

The present study aimed to investigate the effects of the phosphoinositide 3‑kinase (PI3K)/Akt signaling pathway on the Wnt/β‑catenin signaling pathway in rats with focal cerebral ischemia‑reperfusion injury. A total of 96 rat focal cerebral ischemia‑reperfusion models, established according to a modified version of Longa's method, were randomly divided into four groups: Sham‑operated (S), cerebral ischemia‑reperfusion injury (I), cerebral ischemia‑reperfusion + basic fibroblast growth factor (bFGF) post‑processing and, finally, cerebral ischemia‑reperfusion + bFGF post‑processing + PI3K inhibitor LY294002 (LY). Each group consisted of 24 rats and each group was divided into four subgroups according to the indicated reperfusion times of 12, 24, 48 and 72 h. The morphological changes of the cortical tissue and the cellular apoptosis were determined using hematoxylin and eosin staining and the terminal deoxynucleotidyl transferase dUTP nick end labeling method, respectively. The expression levels of phosphorylated (p‑)Akt, glycogen synthase kinase‑3β (GSK‑3β) mRNA and β‑catenin in the cortical tissue were detected at different time‑points. The number of apoptotic cells and the expression levels of p‑Akt, GSK‑3β mRNA and β‑catenin in the I and LY groups were significantly higher compared with those in the S group (P<0.05). In the bFGF group, the number of apoptotic cells and the mRNA expression levels of GSK‑3β were significantly decreased, whereas the expression levels of p‑Akt and β‑catenin were significantly increased compared with those in the I and LY groups (P<0.05). In cerebral ischemia‑reperfusion injury, the PI3K/Akt signaling pathway regulated β‑catenin, the main member of the Wnt signaling pathway, via GSK‑3β, providing information to assist in further investigation of the mechanism of β‑catenin in ischemia‑reperfusion injury.

SOX1 down-regulates β-catenin and reverses malignant phenotype in nasopharyngeal carcinoma

Background

Aberrant activation of the Wnt/β-catenin signaling pathway is an important factor in the development of nasopharyngeal carcinoma (NPC). Previous studies have demonstrated that the developmental gene sex-determining region Y (SRY)-box 1 (SOX1) inhibits cervical and liver tumorigenesis by interfering with the Wnt/β-catenin signaling pathway. However, the role of SOX1 in NPC remains unclear. This study investigates the function of SOX1 in NPC pathogenesis.

Results

Down-regulation of SOX1 was detected in NPC cell lines and tissues. Besides, quantitative methylation-specific polymerase chain reaction revealed that SOX1 promoter was hypermethylated in NPC cell lines. Ectopic expression of SOX1 in NPC cells suppressed colony formation, proliferation and migration in vitro and impaired tumor growth in nude mice. Restoration of SOX1 expression significantly reduced epithelial-mesenchymal transition, enhanced cell differentiation and induced cellular senescence. Conversely, transient knockdown of SOX1 by siRNA in these cells partially restored cell proliferation and colony formation. Notably, SOX1 was found to physically interact with β-catenin and reduce its expression independent of proteasomal activity, leading to inhibition of Wnt/β-catenin signaling and decreased expression of downstream target genes.

Conclusions

SOX1 decreases the expression of β-catenin in a proteasome-independent manner and reverses the malignant phenotype in NPC cells.

Electronic supplementary material

The online version of this article (doi:10.1186/1476-4598-13-257) contains supplementary material, which is available to authorized users.

β-catenin enhances odontoblastic differentiation of dental pulp cells through activation of Runx2

An intense stimulus can cause death of odontoblasts and initiate odontoblastic differentiation of stem/progenitor cell populations of dental pulp cells (DPCs), which is followed by reparative dentin formation. However, the mechanism of odontoblastic differentiation during reparative dentin formation remains unclear. This study was to determine the role of β-catenin, a key player in tooth development, in reparative dentin formation, especially in odontoblastic differentiation. We found that β-catenin was expressed in odontoblast-like cells and DPCs beneath the perforation site during reparative dentin formation after direct pulp capping. The expression of β-catenin was also significantly upregulated during odontoblastic differentiation of in vitro cultured DPCs. The expression pattern of runt-related transcription factor 2 (Runx2) was similar to that of β-catenin. Immunofluorescence staining indicated that Runx2 was also expressed in β-catenin–positive odontoblast-like cells and DPCs during reparative dentin formation. Knockdown of β-catenin disrupted odontoblastic differentiation, which was accompanied by a reduction in β-catenin binding to the Runx2 promoter and diminished expression of Runx2. In contrast, lithium chloride (LiCl) induced accumulation of β-catenin produced the opposite effect to that caused by β-catenin knockdown. In conclusion, it was reported in this study for the first time that β-catenin can enhance the odontoblastic differentiation of DPCs through activation of Runx2, which might be the mechanism involved in odontoblastic differentiation during reparative dentin formation.

β-catenin regulates Pax3 and Cdx2 for caudal neural tube closure and elongation

Non-canonical Wnt/planar cell polarity (PCP) signaling plays a primary role in the convergent extension that drives neural tube closure and body axis elongation. PCP signaling gene mutations cause severe neural tube defects (NTDs). However, the role of canonical Wnt/β-catenin signaling in neural tube closure and NTDs remains poorly understood. This study shows that conditional gene targeting of β-catenin in the dorsal neural folds of mouse embryos represses the expression of the homeobox-containing genes Pax3 and Cdx2 at the dorsal posterior neuropore (PNP), and subsequently diminishes the expression of the Wnt/β-catenin signaling target genes T, Tbx6 and Fgf8 at the tail bud, leading to spina bifida aperta, caudal axis bending and tail truncation. We demonstrate that Pax3 and Cdx2 are novel downstream targets of Wnt/β-catenin signaling. Transgenic activation of Pax3 cDNA can rescue the closure defect in the β-catenin mutants, suggesting that Pax3 is a key downstream effector of β-catenin signaling in the PNP closure process. Cdx2 is known to be crucial in posterior axis elongation and in neural tube closure. We found that Cdx2 expression is also repressed in the dorsal PNPs of Pax3-null embryos. However, the ectopically activated Pax3 in the β-catenin mutants cannot restore Cdx2 mRNA in the dorsal PNP, suggesting that the presence of both β-catenin and Pax3 is required for regional Cdx2 expression. Thus, β-catenin signaling is required for caudal neural tube closure and elongation, acting through the transcriptional regulation of key target genes in the PNP.

Wnt/β-catenin signalling regulates Sox17 expression and is essential for organizer and endoderm formation in the mouse

Several signalling cascades are implicated in the formation and patterning of the three principal germ layers, but their precise temporal-spatial mode of action in progenitor populations remains undefined. We have used conditional gene deletion of mouse β-catenin in Sox17-positive embryonic and extra-embryonic endoderm as well as vascular endothelial progenitors to address the function of canonical Wnt signalling in cell lineage formation and patterning. Conditional mutants fail to form anterior brain structures and exhibit posterior body axis truncations, whereas initial blood vessel formation appears normal. Tetraploid rescue experiments reveal that lack of β-catenin in the anterior visceral endoderm results in defects in head organizer formation. Sox17 lineage tracing in the definitive endoderm (DE) shows a cell-autonomous requirement for β-catenin in midgut and hindgut formation. Surprisingly, wild-type posterior visceral endoderm (PVE) in midgut- and hindgut-deficient tetraploid chimera rescues the posterior body axis truncation, indicating that the PVE is important for tail organizer formation. Upon loss of β-catenin in the visceral endoderm and DE lineages, but not in the vascular endothelial lineage, Sox17 expression is not maintained, suggesting downstream regulation by canonical Wnt signalling. Strikingly, Tcf4/β-catenin transactivation complexes accumulated on Sox17 cis-regulatory elements specifically upon endoderm induction in an embryonic stem cell differentiation system. Together, these results indicate that the Wnt/β-catenin signalling pathway regulates Sox17 expression for visceral endoderm pattering and DE formation and provide the first functional evidence that the PVE is necessary for gastrula organizer gene induction and posterior axis development.

Acetylation of human TCF4 (TCF7L2) proteins attenuates inhibition by the HBP1 repressor and induces a conformational change in the TCF4::DNA complex

The members of the TCF/LEF family of DNA-binding proteins are components of diverse gene regulatory networks. As nuclear effectors of Wnt/β-catenin signaling they act as assembly platforms for multimeric transcription complexes that either repress or activate gene expression. Previously, it was shown that several aspects of TCF/LEF protein function are regulated by post-translational modification. The association of TCF/LEF family members with acetyltransferases and deacetylases prompted us to investigate whether vertebrate TCF/LEF proteins are subject to acetylation. Through co-expression with p300 and CBP and subsequent analyses using mass spectrometry and immunodetection with anti-acetyl-lysine antibodies we show that TCF4 can be acetylated at lysine K₁₅₀ by CBP. K₁₅₀ acetylation is restricted to TCF4E splice variants and requires the simultaneous presence of β-catenin and the unique TCF4E C-terminus. To examine the functional consequences of K₁₅₀ acetylation we substituted K₁₅₀ with amino acids representing the non-acetylated and acetylated states. Reporter gene assays based on Wnt/β-catenin-responsive promoter regions did not indicate a general role of K₁₅₀ acetylation in transactivation by TCF4E. However, in the presence of CBP, non-acetylatable TCF4E with a K₁₅₀R substitution was more susceptible to inhibition by the HBP-1 repressor protein compared to wild-type TCF4E. Acetylation of K₁₅₀ using a bacterial expression system or amino acid substitutions at K₁₅₀ alter the electrophoretic properties of TCF4E::DNA complexes. This result suggests that K₁₅₀ acetylation leads to a conformational change that may also represent the mechanism whereby acetylated TCF4E acquires resistance against HBP1. In summary, TCF4 not only recruits acetyltransferases but is also a substrate for these enzymes. The fact that acetylation affects only a subset of TCF4 splice variants and is mediated preferentially by CBP suggests that the conditional acetylation of TCF4E is a novel regulatory mechanism that diversifies the transcriptional output of Wnt/β-catenin signaling in response to changing intracellular signaling milieus.

Engraftment potential of spheroid-forming hepatic endoderm derived from human embryonic stem cells

Transplantation and drug discovery programs for liver diseases are hampered by the shortage of donor tissue. While recent studies have shown that hepatic cells can be derived from human embryonic stem cells (hESCs), few cases have shown selective enrichment of hESC-derived hepatocytes and their integration into host liver tissues. Here we demonstrate that the dissociation and reaggregation procedure after an endodermal differentiation of hESC produces spheroids mainly consisted of cells showing hepatic phenotypes in vitro and in vivo. A combined treatment with Wnt3a and bone morphogenic protein 4 efficiently differentiated hESCs into definitive endoderm in an adherent culture. Dissociation followed by reaggregation of these cells in a nonadherent condition lead to the isolation of spheroid-forming cells that preferentially expressed early hepatic markers from the adherent cell population. Further differentiation of these spheroid cells in the presence of the hepatocyte growth factor, oncostatin M, and dexamethasone produced a highly enriched population of cells exhibiting characteristics of early hepatocytes, including glycogen storage, indocyanine green uptake, and synthesis of urea and albumin. Furthermore, we show that grafted spheroid cells express hepatic features and attenuate the serum aspartate aminotransferase level in a model of acute liver injury. These data suggest that hepatic progenitor cells can be enriched by the spheroid formation of differentiating hESCs and that these cells have engraftment potential to replace damaged liver tissues.

Cdx1 and Cdx2 exhibit transcriptional specificity in the intestine

The caudal-related homeodomain transcription factors Cdx1 and Cdx2 are expressed in the developing endoderm with expression persisting into adulthood. Cdx1^−/− mutants are viable and fertile and display no overt intestinal phenotype. Cdx2 null mutants are peri-implantation lethal; however, conditional mutation approaches have revealed that Cdx2 is required for patterning the intestinal epithelium and specification of the colon. Cdx2 is also necessary for homeostasis of the intestinal tract in the adult, where Cdx1 and Cdx2 appear to functionally overlap in the distal colon, but not during intestinal development. Cdx1 and Cdx2 exhibit complete overlap of expression in the intestine, although they differ in their relative levels, with Cdx1 maximal in the distal colon and Cdx2 peaking in the proximal cecum. Moreover, Cdx1 protein is graded along the crypt-villus axis, being abundant in the crypts and diminishing towards the villi. Cdx2 is expressed uniformly along this axis, but is differentially phosphorylated; the functional relevance of these expression domains and phosphorylation is currently unknown. Cdx1 and Cdx2 have been suggested to exhibit functional specificity in the intestinal tract. In the present study, using cell-based models, we found that relative to Cdx1, Cdx2 was significantly less potent at effecting a transcriptional response from the Cdx1 promoter, a known Cdx target gene. We subsequently assessed this relationship in vivo using a “gene swap” approach and found that Cdx2 cannot substitute for Cdx1 in this autoregulatory loop. This is in marked contrast with the ability of Cdx2 to support Cdx1 expression and function in paraxial mesoderm and vertebral patterning, thus providing novel in vivo evidence of context-dependent transcriptional specificity between these transcription factors.

Cripto-1 enhances the canonical Wnt/β-catenin signaling pathway by binding to LRP5 and LRP6 co-receptors

Cripto-1 is implicated in multiple cellular events, including cell proliferation, motility and angiogenesis, through the activation of an intricate network of signaling pathways. A crosstalk between Cripto-1 and the canonical Wnt/β-catenin signaling pathway has been previously described. In fact, Cripto-1 is a downstream target gene of the canonical Wnt/β-catenin signaling pathway in the embryo and in colon cancer cells and T-cell factor (Tcf)/lymphoid enhancer factor binding sites have been identified in the promoter and the first intronic region of the mouse and human Cripto-1 genes. We now demonstrate that Cripto-1 modulates signaling through the canonical Wnt/β-catenin/Tcf pathway by binding to the Wnt co-receptors low-density lipoprotein receptor-related protein (LRP) 5 and LRP6, which facilitates Wnt3a binding to LRP5 and LRP6. Cripto-1 functionally enhances Wnt3a signaling through cytoplasmic stabilization of β-catenin and elevated β-catenin/Tcf transcriptional activation. Conversely, Wnt3a further increases Cripto-1 stimulation of migration, invasion and colony formation in soft agar of HC11 mouse mammary epithelial cells, indicating that Cripto-1 and the canonical Wnt/β-catenin signaling co-operate in regulating motility and in vitro transformation of mammary epithelial cells.

Wnt signaling in lung organogenesis

Reporter transgene, knockout, and misexpression studies support the notion that Wnt/beta-catenin signaling regulates aspects of branching morphogenesis, regional specialization of the epithelium and mesenchyme, and establishment of progenitor cell pools. As demonstrated for other foregut endoderm-derived organs, beta-catenin and the Wnt/beta-catenin signaling pathway contribute to control of cellular proliferation, differentiation and migration. However, the contribution of Wnt/beta-catenin signaling to these processes is shaped by other signals impinging on target tissues. In this review, we will concentrate on roles for Wnt/beta-catenin in respiratory system development, including segregation of the conducting airway and alveolar compartments, specialization of the mesenchyme, and establishment of tracheal asymmetries and tracheal glands.

A WNT/p21 circuit directed by the C-clamp, a sequence-specific DNA binding domain in TCFs

The lymphoid enhancer factor 1/T cell factor (LEF/TCF) family of transcription factors are downstream effectors of the WNT signaling pathway, which drives colon tumorigenesis. LEF/TCFs have a DNA sequence-specific high-mobility group (HMG) box that binds Wnt response elements (WREs). The "E tail" isoforms of TCFs are alternatively spliced to include a second DNA binding domain called the C-clamp. We show that induction of a dominant negative C-clamp version of TCF1 (dnTCF1E) induces p21 expression and a stall in the growth of DLD1 colon cancer cells. Induction of a C-clamp mutant did not efficiently induce p21, nor did it stall cell growth. Microarray analysis revealed that induction of p21 by wild-type dnTCF1E (dnTCF1E(WT)) correlated with a decrease in expression of multiple p21 suppressors that act at multiple levels from transcription (SP5, YAP1, and RUNX1), RNA stability (MSI2), and protein stability (CUL4A). We show that the C-clamp is a sequence-specific DNA binding domain that can make contacts with 5'-RCCG-3' elements upstream or downstream of WREs. The C-clamp-RCCG interaction was critical for TCF1E-mediated transcriptional control of p21-connected target gene promoters. Our results indicate that a rapid-response WNT/p21 circuit is driven by C-clamp target gene selection.

Methylation-dependent activation of CDX1 through NF-κB: a link from inflammation to intestinal metaplasia in the human stomach

The caudal homeobox factor 1 (CDX1) is an essential transcription factor for intestinal differentiation. Its aberrant expression in intestinal metaplasia of the upper gastrointestinal tract is a hallmark within the gastritis-metaplasia-carcinoma sequence. CDX1 expression is influenced by certain pathways, such as Wnt, Ras, or NF-κB signaling; however, these pathways alone cannot explain the transient expression of CDX1 in intestinal metaplasia or the molecular inactivation mechanism of its loss in cases of advanced gastric cancer. In this study, we investigated the epigenetic inactivation of CDX1 by promoter methylation, as well as the functional link of CDX1 promoter methylation to the inflammatory NF-κB signaling pathway. We identified methylation-dependent NF-κB binding to the CDX1 promoter and quantified it using competitive electrophoretic mobility shift assays and chromatin immunoprecipitation. A methylated CDX1 promoter was associated with closed chromatin structure, reduced NF-κB binding, and transcriptional silencing. Along the gastritis-metaplasia-carcinoma sequence, we observed a biphasic pattern of tumor necrosis factor-α (TNF-α) protein expression and an inverse biphasic pattern of CDX1 promoter methylation; both are highly consistent with CDX1 protein expression. The stages of hyper-, hypo-, and hyper-methylation patterns of the CDX1 promoter were inversely correlated with the NF-κB signaling activity along this sequence. In conclusion, these functionally interacting events drive CDX1 expression and contribute to intestinal metaplasia, epithelial dedifferentiation, and carcinogenesis in the human stomach.

Caudal homeobox protein Cdx-2 cooperates with Wnt pathway to regulate claudin-1 expression in colon cancer cells

Dysregulation of tight junctions (TJs) is often associated with human diseases including carcinogenesis and recent studies support role of TJ integral proteins in the regulation of Epithelial-to-Mesenchymal Transition (EMT). In this regard, expression of claudin-1, a key constituent of TJs, is highly increased in colon cancer and is causally associated with the tumor growth and progression. However, mechanism/s underlying regulation of claudin-1 expression in intestinal epithelial cells remains poorly understood. In our studies, we have identified putative binding sites for intestinal transcription factors Cdx1, -2 and GATA4 in the 5'-flanking region of the claudin-1 gene. Our further studies using full length and/or deletion mutant constructs in two different human colon cancer cell lines, SW480 and HCT116, showed key role of Cdx1, Cdx2 and GATA4 in the regulation of claudin-1 mRNA expression. However, overexpression of Cdx2 had the most potent effect upon claudin-1 mRNA expression and promoter activity. Also, in colon cancer patient samples, we observed a significant and parallel correlation between claudin-1 and Cdx2 expressions. Chromatin immunoprecipitation (ChIP) assay confirmed the Cdx2 binding with claudin-1 promoter in vivo. Using Cdx2 deletion mutant constructs, we further mapped the Cdx2 C-terminus domain to be important in the regulation of claudin-1 promoter activity. Interestingly, co-expression of activated β-catenin further induced the Cdx2-dependent upregulation of claudin-1 promoter activity while expression of the dominant negative (dn)-TCF-4 abrogated this activation. Taken together, we conclude that homeodomain transcription factors Cdx1, Cdx2 and GATA4 regulate claudin-1 gene expression in human colon cancer cells. Moreover, a functional crosstalk between Wnt-signaling and transcriptional activation related to caudal-related homeobox (Cdx) proteins and GATA-proteins is demonstrated in the regulation of claudin-1 promoter-activation.

Caudal-related homeobox (Cdx) protein-dependent integration of canonical Wnt signaling on paired-box 3 (Pax3) neural crest enhancer

One of the earliest events in neural crest development takes place at the neural plate border and consists in the induction of Pax3 expression by posteriorizing Wnt·β-catenin signaling. The molecular mechanism of this regulation is not well understood, but several observations suggest a role for posteriorizing Cdx transcription factors (Cdx1/2/4) in this process. Cdx genes are known as integrators of posteriorizing signals from Wnt, retinoic acid, and FGF pathways. In this work, we report that Wnt-mediated regulation of murine Pax3 expression is indirect and involves Cdx proteins as intermediates. We show that Pax3 transcripts co-localize with Cdx proteins in the posterior neurectoderm and that neural Pax3 expression is reduced in Cdx1-null embryos. Using Wnt3a-treated P19 cells and neural crest-derived Neuro2a cells, we demonstrate that Pax3 expression is induced by the Wnt-Cdx pathway. Co-transfection analyses, electrophoretic mobility shift assays, chromatin immunoprecipitation, and transgenic studies further indicate that Cdx proteins operate via direct binding to an evolutionarily conserved neural crest enhancer of the Pax3 proximal promoter. Taken together, these results suggest a novel neural function for Cdx proteins within the gene regulatory network controlling neural crest development.

Direct and indirect contribution of human embryonic stem cell-derived hepatocyte-like cells to liver repair in mice

BACKGROUND & AIMS

Many studies of embryonic stem cells have investigated direct cell replacement of damaged tissues, but little is known about how donor cell-derived signals affect host tissue regeneration. We investigated the direct and indirect roles of human embryonic stem cell-derived cells in liver repair in mice.

METHODS

To promote the initial differentiation of human embryonic stem cells into mesendoderm, we activated the β-catenin signaling pathway with lithium; cells were then further differentiated into hepatocyte-like cells. The differentiated cells were purified by indocyanine green staining and laser microdissection and characterized by immunostaining, polymerase chain reaction, biochemical function, electron microscopy, and transplantation analyses. To investigate indirect effects of these cells, secreted proteins (secretomes) were analyzed by a label-free quantitative mass spectrometry. Carbon tetrachloride was used to induce acute liver injury in mice; cells or secreted proteins were administered by intrasplenic or intraperitoneal injection, respectively.

RESULTS

The differentiated hepatocyte-like cells had multiple features of normal hepatocytes, engrafted efficiently into mice, and continued to have hepatic features; they promoted proliferation of host hepatocytes and revascularization of injured host liver tissues. Proteomic analysis identified proteins secreted from these cells that might promote host tissue repair. Injection of the secreted proteins into injured livers of mice promoted significant amounts of tissue regeneration without cell grafts.

CONCLUSIONS

Hepatocyte-like cells derived from human embryonic stem cells contribute to recovery of injured liver tissues in mice, not only by cell replacement but also by delivering trophic factors that support endogenous liver regeneration.

How do they do Wnt they do?: regulation of transcription by the Wnt/β-catenin pathway

Wnt/β-catenin signalling is known to play many roles in metazoan development and tissue homeostasis. Misregulation of the pathway has also been linked to many human diseases. In this review, specific aspects of the pathway's involvement in these processes are discussed, with an emphasis on how Wnt/β-catenin signalling regulates gene expression in a cell and temporally specific manner. The T-cell factor (TCF) family of transcription factors, which mediate a large portion of Wnt/β-catenin signalling, will be discussed in detail. Invertebrates contain a single TCF gene that contains two DNA-binding domains, the high mobility group (HMG) domain and the C-clamp, which increases the specificity of DNA binding. In vertebrates, the situation is more complex, with four TCF genes producing many isoforms that contain the HMG domain, but only some of which possess a C-clamp. Vertebrate TCFs have been reported to act in concert with many other transcription factors, which may explain how they obtain sufficient specificity for specific DNA sequences, as well as how they achieve a wide diversity of transcriptional outputs in different cells.

Molecular mechanisms of Barrett's esophagus

Barrett's esophagus (BE) is defined as the metaplastic conversion of esophageal squamous epithelium to intestinalized columnar epithelium. As a premalignant lesion of esophageal adenocarcinoma (EAC), BE develops as a result of chronic gastroesophageal reflux disease (GERD). Many studies have been conducted to understand the molecular mechanisms of this disease. This review summarizes recent results involving squamous and intestinal transcription factors, signaling pathways, stromal factors, microRNAs, and other factors in the development of BE. A conceptual framework is proposed to guide future studies. We expect elucidation of the molecular mechanisms of BE to help in the development of improved management of GERD, BE, and EAC.

Negative cross-talk between calcium-sensing receptor and β-catenin signaling systems in colonic epithelium

Here, we examined the role of the extracellular Ca(2+)-sensing receptor (CaSR) in the control of colonic epithelial cell proliferation in vivo and changes in β-catenin triggered by CaSR stimulation in human colonic epithelial cells in vitro. The in vivo studies, using a novel Casr intestinal-specific knock-out mouse, indicate that the genetic ablation of the Casr leads to hyperproliferation of colonic epithelial cells, expansion of the proliferative zone, changes in crypt structure, and enhanced β-catenin nuclear localization. The in vitro results indicate that stimulation of the CaSR, by Ca(2+) or by the calcimimetic R-568, produced a striking and time-dependent decrease in the phosphorylation of β-catenin at Ser-552 and Ser-675, two amino acid residues that promote β-catenin transcriptional activity. The reduced phosphorylation of β-catenin coincided with a decline in its nuclear localization and a marked redistribution to the plasma membrane. Furthermore, CaSR stimulation promoted a down-regulation of β-catenin-mediated transcriptional activation. These studies demonstrate that signaling pathways emanating from the CaSR control colonic epithelial cell proliferation in vivo and suggest that the mechanism involves regulation of β-catenin phosphorylation.

Krüppel-like factor 5 is important for maintenance of crypt architecture and barrier function in mouse intestine

BACKGROUND & AIMS

Krüppel-like factor 5 (KLF5) is transcription factor that is expressed by dividing epithelial cells of the intestinal epithelium. KLF5 promotes proliferation in vitro and in vivo and is induced by mitogens and various stress stimuli. To study the role of KLF5 in intestinal epithelial homeostasis, we examined the phenotype of mice with conditional deletion of Klf5 in the gut.

METHODS

Mice were generated with intestinal-specific deletion of Klf5 (Vil-Cre;Klf5fl/fl). Morphologic changes in the small intestine and colon were examined by immunohistochemistry, immunoblotting, and real-time polymerase chain reaction.

RESULTS

Klf5 mutant mice were born at a normal Mendelian ratio but had high mortality compared with controls. Complete deletion of Klf5 from the intestinal mucosa resulted in neonatal lethality that corresponded with an absence of epithelial proliferation. Variegated intestinal-specific deletion of Klf5 in adult mice resulted in morphologic changes that included a regenerative phenotype, impaired barrier function, and inflammation. Adult mutant mice exhibited defects in epithelial differentiation and migration. These changes were associated with reduced expression of Caudal type homeobox (Cdx) 1, Cdx2, and Eph and ephrin signaling proteins. Concomitantly, Wnt signaling to β-catenin was reduced. Proliferation in regenerative crypts was associated with increased expression of the progenitor cell marker Sox9.

CONCLUSIONS

Deletion of Klf5 in the gut epithelium of mice demonstrated that KLF5 maintains epithelial proliferation, differentiation, and cell positioning along the crypt radial axis. Morphologic changes that occur with deletion of Klf5 are associated with disruption of canonical Wnt signaling and increased expression of Sox9.

Wnt signaling specifies and patterns intestinal endoderm

Wnt signaling has been implicated in many developmental processes, but its role in early endoderm development is not well understood. Wnt signaling is active in posterior endoderm as early as E7.5. Genetic and chemical activation show that the Wnt pathway acts directly on endoderm to induce the intestinal master regulator Cdx2, shifting global gene away from anterior endoderm and toward a posterior, intestinal program. In a mouse embryonic stem cell differentiation platform that yields pure populations of definitive endoderm, Wnt signaling induces intestinal gene expression in all cells. We have identified a set of genes specific to the anterior small intestine, posterior small intestine, and large intestine during early development, and show that Wnt, through Cdx2, activates large intestinal gene expression at high doses and small intestinal gene expression at lower doses. These findings shed light on the mechanism of embryonic intestinal induction and provide a method to manipulate intestinal development from embryonic stem cells.

Cloning and characterization of β-catenin gene in early embryonic developmental stage of Artemia sinica

β-Catenin plays a crucial role in embryonic development and responds to the activation of several signal transduction pathways. In this paper, in order to understand the functions of β-catenin gene in early embryonic development of Artemia sinica, the complete cDNA sequence was cloned for the first time using RACE technology, then the sequence was analyzed by some bioinformatic methods. The expression of the β-catenin gene was investigated at various stages during the embryonic development using quantitative real-time PCR and immunohistochemistry assay. Through the investigation, the result of real-time PCR illustrated that β-catenin gene might relate to the response of A. sinica's immune system and osmotic pressure system in early embryonic developmental stage. Meanwhile, Immunohistochemistry assay demonstrated that during embryonic development, β-catenin was mainly expressed in the cephalothorax. Besides, we discovered that β-catenin might not be a maternal gene in A. sinica, and this new phenomenon may explain a constitutive and regional expression during the early embryonic development of A. sinica.

Regulation of self-renewal and differentiation by the intestinal stem cell niche

The gastrointestinal epithelium is a highly organised tissue that is constantly being renewed. In order to maintain homeostasis, the balance between intestinal stem cell (ISC) self-renewal and differentiation must be carefully regulated. In this review, we describe how the intestinal stem cell niche provides a unique environment to regulate self-renewal and differentiation of ISCs. It has traditionally been believed that the mesenchymal myofibroblasts play an important role in the crosstalk between ISCs and the niche. However, recent evidence in Drosophila and in vertebrates suggests that epithelial cells also contribute to the niche. We discuss the multiple signalling pathways that are utilised to regulate stemness within the niche, including members of the Wnt, BMP and Hedgehog pathways, and how aberrations in these signals lead to disruption of the normal crypt-villus axis. Finally, we also discuss how CDX1 and inhibition of the Notch pathway are important in specifying enterocyte and goblet cell differentiation respectively.

Stem cells in gastrointestinal cancers: a matter of choice in cell fate determination

Cancerous stem cells share the same properties of self-renewal and differentiation as normal stem cells, and have a similar phenotype to adult stem cells isolated from the same tissue. Some believe that cancer stem cells are derived from mutation of normal stem cells, whereas others suspect them to have different origins. Although complicated and controversial, the stem cell as the progenitor of cancer has found support in leukemia research, and subsequently in some solid tumors. It was first accepted that both stem and progenitor cells could acquire genetic abnormalities that would lead to uncontrolled replication and dysregulated differentiation, causing them to transform into cancerous stem cells that might then initiate and maintain a tumor. In this article, we discuss recent progress in the studies of stomach and intestinal cancer stem cells, while focusing on the complex molecular pathways underlying stem cell transformation and gastrointestinal tumorigenesis. This understanding provides a basis for promising new therapies that may specifically target gastrointestinal cancer stem cells.

Biology of Barrett's esophagus and esophageal adenocarcinoma

The past few years have brought new advances in our understanding of the molecular mechanisms underlying the development of Barrett's esophagus and esophageal adenocarcinoma. Although knowledge of the genetic basis for these conditions has not yet translated into clinically useful biomarkers, the current pace of biomedical discovery holds endless possibilities for molecular medicine to improve the diagnosis and management of patients with these conditions. This article provides a useful conceptual basis for understanding the molecular events involved in the making of Barrett metaplasia and in its neoplastic progression, and provides a rationale for evaluating studies on the application of molecular medicine to the diagnosis and management of patients with Barrett's esophagus and esophageal adenocarcinoma.