PTEN-deficient intestinal stem cells initiate intestinal polyposis

The architect who never sleeps: tumor-induced plasticity

Tumor cell plasticity is an event that has been observed in several malignancies. In fact, most of the solid tumors are characterized by cellular heterogeneity and undergo constant changes as the tumor develops. The increased plasticity displayed by these cells allows them to acquire additional properties, enabling epithelial-mesenchymal transitions, dedifferentiation and the acquisition of stem cell-like properties. Here we discuss the particular importance of an inflammatory microenvironment for the bidirectional control of cellular plasticity and the potential for therapeutic intervention.

Enteric bacterial protein AvrA promotes colonic tumorigenesis and activates colonic beta-catenin signaling pathway

Salmonella infections can become chronic and increase the risk of cancer. The mechanisms by which specific Salmonella organisms contribute to cancer, however, are still unknown. Live and attenuated Salmonella are used as vectors to target cancer cells, but there have been no systematic studies of the oncogenic potential of chronic Salmonella infections in cancer models. AvrA, a pathogenic product of Salmonella, is inserted into host cells during infection and influences eukaryotic cell pathways. In the current study, we colonized mice with Salmonella AvrA-sufficient or AvrA-deficient Salmonella typhimirium strains and induced inflammation-associated colon cancer by azoxymethane/dextran sulfate sodium (AOM/DSS). We confirmed Salmonella persisted in the colon for up to 45 weeks. Salmonella was identified not only in epithelial cells on the colonic luminal surface and base of the crypts but also in invading tumors. Tumor incidence in the AvrA+infected group was 100% compared with 51.4% in the AOM/DSS group without bacterial gavage and 56.3% in mice infected with the AvrA- strain. Infection with AvrA+ strain also altered tumor distribution from the distal to proximal colon that might reflect changes in the microbiome. AvrA-expressing bacteria also upregulated beta-catenin signaling as assessed by decreased beta-catenin ubiquitination, increased nuclear beta-catenin and increased phosphorylated-beta-catenin (Ser552), a marker of proliferating stem-progenitor cells. Other β-catenin targets increased by AvrA included Bmi1, a cancer stem cell marker, matrix metalloproteinase-7, and cyclin D1. In summary, AvrA-expressing Salmonella infection activates β-catenin signals and enhances colonic tumorigenesis. Our findings provide important new mechanistic insights into how a bacterial protein targets proliferating stem-progenitor cells and contributes to cancer development. Our observations also raise a note of caution regarding the use of mutant Salmonella organisms as vectors for anti-cancer therapy. Finally, these studies could suggest biomarkers (such as AvrA level in gut) to assess cancer risk in susceptible individuals and infection-related dysregulation of β-catenin signaling in cancer.

Intestinal stem cells and celiac disease

Stem cells (SCs) are the key to tissue genesis and regeneration. Given their central role in homeostasis, dysfunctions of the SC compartment play a pivotal role in the development of cancers, degenerative disorders, chronic inflammatory pathologies and organ failure. The gastrointestinal tract is constantly exposed to harsh mechanical and chemical conditions and most of the epithelial cells are replaced every 3 to 5 d. According to the so-called Unitarian hypothesis, this renewal is driven by a common intestinal stem cell (ISC) residing within the crypt base at the origin of the crypt-to-villus hierarchical migratory pattern. Celiac disease (CD) can be defined as a chronic immune-mediated disease that is triggered and maintained by dietary proteins (gluten) in genetically predisposed individuals. Many advances have been achieved over the last years in understanding of the pathogenic interactions among genetic, immunological and environmental factors in CD, with a particular emphasis on intestinal barrier and gut microbiota. Conversely, little is known about ISC modulation and deregulation in active celiac disease and upon a gluten-free diet. Nonetheless, bone marrow-derived SC transplantation has become an option for celiac patients with complicated or refractory disease. This manuscript summarizes the “state of the art” regarding CD and ISCs, their niche and potential role in the development and treatment of the disease.

Islet1 and its co-factor Ldb1 are expressed in quiescent cells of mouse intestinal epithelium

Islet1 belongs to Lim homeobox (Lhx) gene family which encodes transcription factors that have been conserved in evolution. They form complexes with other transcriptional regulators, among them obligatory co-factors encoded by Ldb genes. Isl1 (Islet1), Lhx and Ldb1 genes play a crucial role in organ patterning, cell fate determination and cell differentiation in both embryonic and adult tissues. In this study we analyzed expression pattern of Isl1 and its co-factor Ldb1 in small intestine. We also studied the biological role of Ldb1 in gut endoderm. Quantitative PCR analysis revealed a relatively high level of expression of Lhx1, Isl1, Isl2, Lmx1a, Ldb1 and Ldb2 mRNAs in the gut tissue as compared to the level of less abundant detectable Lmx1b mRNA. Immunohistochemical studies demonstrated a unique pattern of Ldb1 and Islet1 proteins in the crypt compartment. Ldb1 is produced at a low level in majority of crypt cells; but, its abundant expression was demonstrated for some single cells. Islet1 is also expressed in single cells of the crypt. Double staining experiments with Ldb1 and Isl1 antibodies showed that both genes are co-expressed in certain cells of the crypt. Further analysis revealed the Ldb1-expressing cells in the gut are both of endodermal and mesodermal origin. Proliferation studies using antibodies to phospho-histone H3 and Ki-67 antigens, as well as long-term BrdU labeling, showed that cells prominently expressing Ldb1/Islet1 are quiescent but do not belong to any known terminally differentiated cell lineages. They may represent a group of stem-like cells in the crypt. Further experiments by cell lineage tracing should be performed to better characterize this cell population. Functional studies of mice with Ldb1 gene ablated in gut endoderm revealed no specific role of Ldb1 in that tissue.

Prostaglandin E2 alters Wnt-dependent migration and proliferation in neuroectodermal stem cells: implications for autism spectrum disorders

Prostaglandin E2 (PGE₂) is a natural lipid-derived molecule that is involved in important physiological functions. Abnormal PGE₂ signalling has been associated with pathologies of the nervous system. Previous studies provide evidence for the interaction of PGE₂ and canonical Wnt signalling pathways in non-neuronal cells. Since the Wnt pathway is crucial in the development and organization of the brain, the main goal of this study is to determine whether collaboration between these pathways exists in neuronal cell types. We report that PGE₂ interacts with canonical Wnt signalling through PKA and PI-3K in neuroectodermal (NE-4C) stem cells. We used time-lapse microscopy to determine that PGE₂ increases the final distance from origin, path length travelled, and the average speed of migration in Wnt-activated cells. Furthermore, PGE₂ alters distinct cellular phenotypes that are characteristic of Wnt-induced NE-4C cells, which corresponds to the modified splitting behaviour of the cells. We also found that in Wnt-induced cells the level of β-catenin protein was increased and the expression levels of Wnt-target genes (Ctnnb1, Ptgs2, Ccnd1, Mmp9) was significantly upregulated in response to PGE₂ treatment. This confirms that PGE₂ activated the canonical Wnt signalling pathway. Furthermore, the upregulated genes have been previously associated with ASD. Our findings show, for the first time, evidence for cross-talk between PGE₂ and Wnt signalling in neuronal cells, where PKA and PI-3K might act as mediators between the two pathways. Given the importance of PGE₂ and Wnt signalling in prenatal development of the nervous system, our study provides insight into how interaction between these two pathways may influence neurodevelopment.

SPARC promotes leukemic cell growth and predicts acute myeloid leukemia outcome

Aberrant expression of the secreted protein, acidic, cysteine-rich (osteonectin) (SPARC) gene, which encodes a matricellular protein that participates in normal tissue remodeling, is associated with a variety of diseases including cancer, but the contribution of SPARC to malignant growth remains controversial. We previously reported that SPARC was among the most upregulated genes in cytogenetically normal acute myeloid leukemia (CN-AML) patients with gene-expression profiles predictive of unfavorable outcome, such as mutations in isocitrate dehydrogenase 2 (IDH2-R172) and overexpression of the oncogenes brain and acute leukemia, cytoplasmic (BAALC) and v-ets erythroblastosis virus E26 oncogene homolog (ERG). In contrast, SPARC was downregulated in CN-AML patients harboring mutations in nucleophosmin (NPM1) that are associated with favorable prognosis. Based on these observations, we hypothesized that SPARC expression is clinically relevant in AML. Here, we found that SPARC overexpression is associated with adverse outcome in CN-AML patients and promotes aggressive leukemia growth in murine models of AML. In leukemia cells, SPARC expression was mediated by the SP1/NF-κB transactivation complex. Furthermore, secreted SPARC activated the integrin-linked kinase/AKT (ILK/AKT) pathway, likely via integrin interaction, and subsequent β-catenin signaling, which is involved in leukemia cell self-renewal. Pharmacologic inhibition of the SP1/NF-κB complex resulted in SPARC downregulation and leukemia growth inhibition. Together, our data indicate that evaluation of SPARC expression has prognosticative value and SPARC is a potential therapeutic target for AML.

Inhibition of Notch signaling reduces the number of surviving Dclk1+ reserve crypt epithelial stem cells following radiation injury

We have previously reported that doublecortin-like kinase 1 (Dclk1) is a putative intestinal stem cell (ISC) marker. In this report, we evaluated the use of Dclk1 as a marker of surviving ISCs in response to treatment with high-dose total body irradiation (TBI). Both apoptotic and mitotic Dclk1(+) cells were observed 24 h post-TBI associated with a corresponding loss of intestinal crypts observed at 84 h post-TBI. Although the Notch signaling pathway plays an important role in regulating proliferation and lineage commitment within the intestine, its role in ISC function in response to severe genotoxic injury is not yet fully understood. We employed the microcolony assay to functionally assess the effects of Notch inhibition with difluorophenacetyl-l-alanyl-S-phenylglycine t-butyl ester (DAPT) on intestinal crypt stem cell survival following severe (>8 Gy) radiation injury. Following treatment with DAPT, we observed a nearly 50% reduction in the number of surviving Dclk1(+) crypt epithelial cells at 24 h after TBI and similar reduction in the number of surviving small intestinal crypts at 84 h. These data indicate that inhibition of Notch signaling decreases ISC survival following radiation injury, suggesting that the Notch signaling pathway plays an important role in ISC-mediated crypt regeneration. These results also suggest that crypt epithelial cell Dclk1 expression can be used as one potential marker to evaluate the early survival of ISCs following severe radiation injury.

Comprehensive analysis of β-catenin target genes in colorectal carcinoma cell lines with deregulated Wnt/β-catenin signaling

Background

Deregulation of Wnt/β-catenin signaling is a hallmark of the majority of sporadic forms of colorectal cancer and results in increased stability of the protein β-catenin. β-catenin is then shuttled into the nucleus where it activates the transcription of its target genes, including the proto-oncogenes MYC and CCND1 as well as the genes encoding the basic helix-loop-helix (bHLH) proteins ASCL2 and ITF-2B. To identify genes commonly regulated by β-catenin in colorectal cancer cell lines, we analyzed β-catenin target gene expression in two non-isogenic cell lines, DLD1 and SW480, using DNA microarrays and compared these genes to β-catenin target genes published in the PubMed database and DNA microarray data presented in the Gene Expression Omnibus (GEO) database.

Results

Treatment of DLD1 and SW480 cells with β-catenin siRNA resulted in differential expression of 1501 and 2389 genes, respectively. 335 of these genes were regulated in the same direction in both cell lines. Comparison of these data with published β-catenin target genes for the colon carcinoma cell line LS174T revealed 193 genes that are regulated similarly in all three cell lines. The overlapping gene set includes confirmed β-catenin target genes like AXIN2, MYC, and ASCL2. We also identified 11 Kyoto Encyclopedia of Genes and Genomes (KEGG) pathways that are regulated similarly in DLD1 and SW480 cells and one pathway – the steroid biosynthesis pathway – was regulated in all three cell lines.

Conclusions

Based on the large number of potential β-catenin target genes found to be similarly regulated in DLD1, SW480 and LS174T cells as well as the large overlap with confirmed β-catenin target genes, we conclude that DLD1 and SW480 colon carcinoma cell lines are suitable model systems to study Wnt/β-catenin signaling and associated colorectal carcinogenesis. Furthermore, the confirmed and the newly identified potential β-catenin target genes are useful starting points for further studies.

PTEN loss and KRAS activation leads to the formation of serrated adenomas and metastatic carcinoma in the mouse intestine

Mutation or loss of the genes PTEN and KRAS have been implicated in human colorectal cancer (CRC), and have been shown to co-occur despite both playing a role in the PI3' kinase (PI3'K) pathway. We investigated the role of these genes in intestinal tumour progression in vivo, using genetically engineered mouse models, with the aim of generating more representative models of human CRC. Intestinal-specific deletion of Pten and activation of an oncogenic allele of Kras was induced in wild-type (WT) mice and mice with a predisposition to adenoma development (Apc(fl/+) ). The animals were euthanized when they became symptomatic of a high tumour burden. Histopathological examination of the tissues was carried out, and immunohistochemistry used to characterize signalling pathway activation. Mutation of Pten and Kras resulted in a significant life-span reduction of mice predisposed to adenomas. Invasive adenocarcinoma was observed in these animals, with evidence of activation of the PI3'K pathway but no metastasis. However, mutation of Pten and Kras in WT animals not predisposed to adenomas led to perturbed homeostasis of the intestinal epithelium and the development of hyperplastic polyps, dysplastic sessile serrated adenomas and metastasizing adenocarcinomas with serrated features. These studies demonstrate synergism between Pten and Kras mutations in intestinal tumour progression, in an autochthonous and immunocompetent murine model, with potential application to preclinical drug testing. In particular, they show that Pten and Kras mutations alone predispose mice to the spectrum of serrated lesions that reflect the serrated pathway of CRC progression in humans.

Epithelial-specific loss of PTEN results in colorectal juvenile polyp formation and invasive cancer

Cowden syndrome (CS) is a rare autosomal dominant cancer-prone disorder caused by germ-line mutation of the phosphatase and tensin homolog mutated on chromosome 10 (PTEN) tumor-suppressor gene. Affected patients commonly develop juvenile polyps, and show an elevated risk of developing colorectal cancers. The etiology of these peculiar polyps remains unclear, although previous work has suggested somatic PTEN alterations in the stroma of juvenile polyps. After a long latency period, we find epithelial-specific PTEN deletion to cause formation of juvenile polyps in the colorectum without stromal PTEN loss. More important, we find that these lesions closely recapitulate all of the characteristic histopathological features of juvenile polyps seen in patients with CS, including stromal alterations and dysplastic transformation to colorectal carcinoma. The stromal alterations we identify after epithelial-specific PTEN loss suggest that PTEN may be involved in altered epithelial-mesenchymal cross talk, which, in turn, predisposes to colorectal neoplasia and polyposis. Our transgenic model is the first to recapitulate colorectal juvenile polyposis in patients with CS. We conclude that stromal PTEN loss is not a prerequisite for the formation of juvenile polyps, and that colorectal juvenile polyps in CS are bona fide neoplastic precursor lesions.

Adult intestinal stem cells: critical drivers of epithelial homeostasis and regeneration

Small populations of adult stem cells are responsible for the remarkable ability of the epithelial lining of the intestine to be efficiently renewed and repaired throughout life. The recent discovery of specific markers for these stem cells, together with the development of new technologies to track endogenous stem cell activity in vivo and to exploit their ability to generate new epithelia ex vivo, has greatly improved our understanding of stem cell-driven homeostasis, regeneration and cancer in the intestine. These exciting new insights into the biology of intestinal stem cells have the potential to accelerate the development of stem cell-based therapies and ameliorate cancer treatments.

Enteric bacteria and cancer stem cells

Intestinal bacteria can contribute to cell proliferation and cancer development, particularly in chronic infectious diseases in which bacteria and/or bacterial components might interfere with cell function. The number of microbial cells within the gut lumen is estimated to be 100 trillion, which is about 10-times larger than the number of eukaryotic cells in the human body. Because of the complexity of the gut flora, identifying the specific microbial agents related to human diseases remains challenging. Recent studies have demonstrated that the stemness of colon cancer cells is, in part, orchestrated by the microenvironment and is defined by high Wnt activity. In this review article, we will discuss recent progress with respect to intestinal stem cells, cancer stem cells, and the molecular mechanisms of enteric bacteria in the activation of the Wnt pathway. We will also discuss the roles of other pathways, including JAK-STAT, JNK, and Notch, in regulating stem cell niches during bacterial infections using Drosophila models. Insights gained from understanding how host-bacterial interaction during inflammation and cancer may serve as a paradigm for understanding the nature of self-renewal signals.

Macrophage migration arrest due to a winning balance of Rac2/Sp1 repression over β-catenin-induced PLD expression

Monocytes and neutrophils infiltrate into tissues during inflammation and stay for extended periods of time until the initial insult is resolved or sometimes remain even longer in the case of chronic inflammation. The mechanism as to why phagocytes become immobilized after the initial cell migration event is not understood completely. Here, we show that overexpression or hyperactivation of Rac2 decreases sustained chemotactic responses of macrophages to MCP-1/CCL2. The resulting leukocyte arrest is not caused by a diminished availability of the cytokine receptor CCR2 that remains intact during MCP-1 stimulation. We show a novel mechanism that links the Rac2-dependent arrest of chemotaxis to decreased expression of PLD2 through the transcription regulator Sp1. Prolonged Rac2 activity leads to nuclear overactivation of Sp1, which acts as a repressor for PLD2. Also, another signaling component plays a regulatory role: β-catenin. Although early times of stimulation (≈ 20 min) with MCP-1/CCL2 resulted in activation of β-catenin with a positive effect on PLD2, after ≈ 3 h of stimulation, the levels of β-catenin were reduced and not able to prevent the negative effect of Rac2 on PLD2 activity. This is a novel molecular mechanism underlying immobilization of monocyte/macrophage migration that is important for the physiological maintenance of leukocytes at the site of inflammation. If this immobilization is prolonged enough, it could lead to chronic inflammation.

NAFLD, NASH and liver cancer

NAFLD affects a large proportion of the US population and its incidence and prevalence are increasing to epidemic proportions around the world. As with other liver diseases that cause cirrhosis, NAFLD increases the risk of liver cancer, a disease with poor outcomes and limited therapeutic options. The incidences of hepatocellular carcinoma (HCC) and intrahepatic cholangiocarcinoma are also rising, and HCC is now the leading cause of obesity-related cancer deaths in middle-aged men in the USA. In this Review, we summarize the correlations between liver cancer and NAFLD-related cirrhosis, and the role of the metabolic syndrome in the development of liver cancer from diverse aetiologies, including HCV-mediated cirrhosis. Recent advances in understanding the progression of NAFLD to HCC from preclinical models will also be discussed. Targeted genetic manipulation of certain metabolic or stress-response pathways, including one-carbon metabolism, NF-κB, PTEN and microRNAs, has been valuable in elucidating the pathways that regulate carcinogenesis in NAFLD. Although tremendous advances have occurred in the identification of diagnostic and therapeutic opportunities to reduce the progression of NAFLD, considerable gaps in our knowledge remain with regard to the mechanisms by which NAFLD and its risk factors promote liver cancer.

The Musashi family of RNA binding proteins: master regulators of multiple stem cell populations

In order to maintain their unlimited capacity to divide, stem cells require controlled temporal and spatial protein expression. The Musashi family of RNA-binding proteins have been shown to exhibit this necessary translational control through both repression and activation in order to regulate multiple stem cell populations. This chapter looks in depth at the initial discovery and characterisation of Musashi in the model organism Drosophila, and its subsequent emergence as a master regulator in a number of stem cell populations. Furthermore the unique roles for mammalian Musashi-1 and Musashi-2 in different stem cell types are correlated with the perceived diagnostic power of Musashi expression in specific stem cell derived oncologies. In particular the potential role for Musashi in the identification and treatment of human cancer is considered, with a focus on the role of Musashi-2 in leukaemia. Finally, the manipulation of Musashi expression is proposed as a potential avenue towards the targeted treatment of specific aggressive stem cell cancers.

Tumor and its microenvironment: a synergistic interplay

The mutual and interdependent interaction between tumor and its microenvironment is a crucial topic in cancer research. Recently, it was reported that targeting stromal events could improve efficacies of current therapeutics and prevent metastatic spreading. Tumor microenvironment is a "complex network" of different cell types, soluble factors, signaling molecules and extracellular matrix components, which orchestrate the fate of tumor progression. As by definition, cancer stem cells (CSCs) are proposed to be the unique cell type able to maintain tumor mass and survive outside the primary tumor at metastatic sites. Being exposed to environmental stressors, including reactive oxygen species (ROS), CSCs have developed a GSH-dependent antioxidant system to improve ROS defense capability and acquire a malignant phenotype. Nevertheless, tumor progression is dependent on extracellular matrix remodeling, fibroblasts and macrophages activation in response to oxidative stress, as well as epithelial mesenchymal transition (EMT)-inducing signals and endothelial and perivascular cells recruitment. Besides providing a survival advantage by inducing de novo angiogenesis, tumor-associated vessels contribute to successful dissemination by facilitating tumor cells entry into the circulatory system and driving the formation of pre-metastatic niche. In this review, we focus on the synergistic effect of hypoxia inducible factors (HIFs) and vascular endothelial growth factors (VEGFs) in the successful outgrowth of metastasis, integrating therefore many of the emerging models and theories in the field.

Localized Fgf10 expression is not required for lung branching morphogenesis but prevents differentiation of epithelial progenitors

Localized Fgf10 expression in the distal mesenchyme adjacent to sites of lung bud formation has long been thought to drive stereotypic branching morphogenesis even though isolated lung epithelium branches in the presence of non-directional exogenous Fgf10 in Matrigel. Here, we show that lung agenesis in Fgf10 knockout mice can be rescued by ubiquitous overexpression of Fgf10, indicating that precisely localized Fgf10 expression is not required for lung branching morphogenesis in vivo. Fgf10 expression in the mesenchyme itself is regulated by Wnt signaling. Nevertheless, we found that during lung initiation simultaneous overexpression of Fgf10 is not sufficient to rescue the absence of primary lung field specification in embryos overexpressing Dkk1, a secreted inhibitor of Wnt signaling. However, after lung initiation, simultaneous overexpression of Fgf10 in lungs overexpressing Dkk1 is able to rescue defects in branching and proximal-distal differentiation. We also show that Fgf10 prevents the differentiation of distal epithelial progenitors into Sox2-expressing airway epithelial cells in part by activating epithelial β-catenin signaling, which negatively regulates Sox2 expression. As such, these findings support a model in which the main function of Fgf10 during lung development is to regulate proximal-distal differentiation. As the lung buds grow out, proximal epithelial cells become further and further displaced from the distal source of Fgf10 and differentiate into bronchial epithelial cells. Interestingly, our data presented here show that once epithelial cells are committed to the Sox2-positive airway epithelial cell fate, Fgf10 prevents ciliated cell differentiation and promotes basal cell differentiation.

Colorectal cancer defeating? Challenge accepted!

Colorectal tumours are actually considered as aberrant organs, within it is possible to notice a different stage of cell growth and differentiation. Their origin is reported to arise from a subpopulation of tumour cells endowed with, just like the healthy stem cells, self-renewal and aberrant multi-lineage differentiation capacity likely to be called colorectal cancer stem cells (CCSCs). Cancer stem cells (CSCs) fate, since their origin, reflects the influences from their microenvironment (or niche) both in the maintenance of stemness, in promoting their differentiation, and in inducing epithelial-mesenchymal transition, responsible of CSCs dissemination and subsequent formation of metastatic lesions. The tumour cells heterogeneity and their immuno-response resistance nowadays probably responsible of the failure of the conventional therapies, make this research field an open issue. Even more importantly, our increasing understanding of the cellular and molecular mechanisms that regulate CSC quiescence and cell cycle regulation, self-renewal, chemotaxis and resistance to cytotoxic agents, is expected to eventually result in tailor-made therapies with a significant impact on the morbidity and overall survival of colorectal cancer patients.

Heparan sulfate on intestinal epithelial cells plays a critical role in intestinal crypt homeostasis via Wnt/β-catenin signaling

Heparan sulfate (HS), a constituent of HS proteoglycans (HSPGs), is a linear polysaccharide present on the cell surface. HSPGs modulate functions of several growth factors and signaling molecules. We examined whether small intestinal epithelial HS plays some roles in crypt homeostasis using intestinal epithelium cell (IEC)-specific HS-deficient C57Bl/6 mice. Survival rate after total body irradiation was significantly reduced in HS-deficient mice due to profound intestinal injury. HS-deficient IECs exhibited Wnt/β-catenin pathway disruption, decreased levels of β-catenin nuclear localization, and reduced expression of Wnt target genes, including Lgr5 during crypt regeneration. Moreover, epithelial HS increased Wnt binding affinity of IECs, promoted phosphorylation of Wnt coreceptor LRP6, and enhanced Wnt/β-catenin signaling following ex vivo stimulation with Wnt3a, whereas activation of canonical Wnt signaling following direct inhibition of glycogen synthase kinase-3β by lithium chloride was similar between HS-deficient and wild-type mice. Thus HS influences the binding affinity of IECs to Wnt, thereby promoting activation of canonical Wnt signaling and facilitating regeneration of small intestinal crypts after epithelial injury.

IDO1 metabolites activate β-catenin signaling to promote cancer cell proliferation and colon tumorigenesis in mice

BACKGROUND & AIMS

Indoleamine 2,3 dioxygenase-1 (IDO1) catabolizes tryptophan along the kynurenine pathway. Although IDO1 is expressed in inflamed and neoplastic epithelial cells of the colon, its role in colon tumorigenesis is not well understood. We used genetic and pharmacologic approaches to manipulate IDO1 activity in mice with colitis-associated cancer and human colon cancer cell lines.

METHODS

C57Bl6 wild-type (control), IDO1-/-, Rag1-/-, and Rag1/IDO1 double-knockout mice were exposed to azoxymethane and dextran sodium sulfate to induce colitis and tumorigenesis. Colitis severity was assessed by measurements of disease activity, cytokine levels, and histologic analysis. In vitro experiments were conducted using HCT 116 and HT-29 human colon cancer cells. 1-methyl tryptophan and small interfering RNA were used to inhibit IDO1. Kynurenine pathway metabolites were used to simulate IDO1 activity.

RESULTS

C57Bl6 mice given pharmacologic inhibitors of IDO1 and IDO1-/- mice had lower tumor burdens and reduced proliferation in the neoplastic epithelium after administration of dextran sodium sulfate and azoxymethane than control mice. These reductions also were observed in Rag1/IDO1 double-knockout mice compared with Rag1-/- mice (which lack mature adaptive immunity). In human colon cancer cells, blockade of IDO1 activity reduced nuclear and activated β-catenin, transcription of its target genes (cyclin D1 and Axin2), and, ultimately, proliferation. Exogenous administration of IDO1 pathway metabolites kynurenine and quinolinic acid led to activation of β-catenin and proliferation of human colon cancer cells, and increased tumor growth in mice.

CONCLUSIONS

IDO1, which catabolizes tryptophan, promotes colitis-associated tumorigenesis in mice, independent of its ability to limit T-cell-mediated immune surveillance. The epithelial cell-autonomous survival advantage provided by IDO1 to colon epithelial cells indicate its potential as a therapeutic target.

Phosphatase and tensin homologue deleted on chromosome 10

Phosphatase and tensin homologue deleted on chromosome 10 (PTEN) is a tumor suppressor gene deleted or mutated in many human cancers such as glioblastoma, spinal tumors, prostate, bladder, adrenals, thyroid, breast, endometrium, and colon cancers. They result from loss of heterozygosity (LOH) for the PTEN gene on chromosome 10q23. Previous studies reported that various drugs, chemicals, and foods can up-regulate PTEN mRNA and protein expression in different cell lines, and they may be useful in the future prevention and/or treatment of these cancers. PTEN has also been observed to have prognostic significance and is gradually being accepted as an independent prognostic factor. This will help in monitoring disease progression and/or recurrence, with a view to improving treatment outcomes and reducing the associated morbidity and mortality from these cancers. Neprilysin (NEP) is a zinc-dependent metallopeptidase that cleaves and inactivates some biologically active peptides thus switching off signal transduction at the cell surface. Decreased NEP expression in many cancers has been reported. NEP can form a complex with PTEN and enhance PTEN recruitment to the plasma membrane as well as stabilize its phosphatase activity. MicroRNA-21 (miR-21) post-transcriptionally down-regulates the expression of PTEN and stimulates growth and invasion in non-small cell lung cancer (NSCLC) (lung Ca), suggesting that this may be a potential therapeutic target in the future treatment of NSCLC. PTEN is a tumor suppressor gene associated with many human cancers. This has diagnostic, therapeutic, and prognostic significance in the management of many human cancers, and may be a target for new drug development in the future.

Random chromosome segregation in mouse intestinal epithelial stem cells

The mammalian intestinal epithelium is endowed with a high cell turnover sustained by a few stem cells located in the bottoms of millions of crypts. Until recently, it was generally assumed that the extreme sensitivity to DNA damaging agents leading to cell death and the asymmetric mode of chromosome segregation of intestinal epithelial stem cells prevented the illicit survival of mutated stem cells and guarded against mistakes leading to aneuploidy and neoplastic transformation. Recent evidence points instead to a pool of mutipotent self-renewing stem cells capable of repairing DNA by homologous recombination significantly more efficiently than other crypt cells. Furthermore, the equilibrium between cell division and differentiation is achieved at the level of the cell population obeying to a random mode of chromosome segregation and a predominantly symmetric mode of cell division. This review summarizes the experimental findings on the mode of cell division adopted by intestinal epithelial stem cells.

N-cadherin regulates the proliferation and differentiation of ventral midbrain dopaminergic progenitors

Adherens junction (AJ) between dopaminergic (DA) progenitors maintains the structure of ventricular zone and polarity of radial glia cells in the ventral midbrain (vMB) during embryonic development. However, it is unclear how loss of N-cadherin might influence the integrity of the AJ and the process of DA neurogenesis. Here, we used conditional gene targeting approaches to perform the region-specific removal of N-cadherin in the neurogenic niche of DA neurons in the vMB. Removal of N-cadherin in the vMB using Shh-Cre disrupts the AJs of DA progenitors and radial glia processes in the vMB. Surprisingly, loss of N-cadherin in the vMB leads to a significant expansion of DA progenitors, including those expressing Sox2, Ngn2, and Otx2. Cell cycle analyses reveal that the cell cycle exit in the progenitor cells is decreased in the mutants from E11.5 to E12.5. In addition, the efficiency of DA progenitors in differentiating into DA neurons is decreased from E10.5 to E12.5, leading to a marked reduction in the number of DA neurons at E11.5, E12.5, and E17.5. Loss of N-cadherin leads to the diffuse distribution of β-catenin proteins, which are a critical component of AJ and Wnt signaling, from the AJ throughout the entire cytoplasm in neuroepithelial cells, suggesting that canonical Wnt signaling might be activated in the DA progenitors in vMB. Taken together, these results support the notion that N-cadherin regulates the proliferation of DA progenitors and the differentiation of DA neurons through canonical Wnt-β-catenin signaling in the vMB.

AKT activation by N-cadherin regulates beta-catenin signaling and neuronal differentiation during cortical development

BACKGROUND

During cerebral cortical development, neural precursor-precursor interactions in the ventricular zone neurogenic niche coordinate signaling pathways that regulate proliferation and differentiation. Previous studies with shRNA knockdown approaches indicated that N-cadherin adhesion between cortical precursors regulates β-catenin signaling, but the underlying mechanisms remained poorly understood.

RESULTS

Here, with conditional knockout approaches, we find further supporting evidence that N-cadherin maintains β-catenin signaling during cortical development. Using shRNA to N-cadherin and dominant negative N-cadherin overexpression in cell culture, we find that N-cadherin regulates Wnt-stimulated β-catenin signaling in a cell-autonomous fashion. Knockdown or inhibition of N-cadherin with function-blocking antibodies leads to reduced activation of the Wnt co-receptor LRP6. We also find that N-cadherin regulates β-catenin via AKT, as reduction of N-cadherin causes decreased AKT activation and reduced phosphorylation of AKT targets GSK3β and β-catenin. Inhibition of AKT signaling in neural precursors in vivo leads to reduced β-catenin-dependent transcriptional activation, increased migration from the ventricular zone, premature neuronal differentiation, and increased apoptotic cell death.

CONCLUSIONS

These results show that N-cadherin regulates β-catenin signaling through both Wnt and AKT, and suggest a previously unrecognized role for AKT in neuronal differentiation and cell survival during cortical development.

Acute WNT signalling activation perturbs differentiation within the adult stomach and rapidly leads to tumour formation

A role for WNT signalling in gastric carcinogenesis has been suggested due to two major observations. First, patients with germline mutations in adenomatous polyposis coli (APC) are susceptible to stomach polyps and second, in gastric cancer, WNT activation confers a poor prognosis. However, the functional significance of deregulated WNT signalling in gastric homoeostasis and cancer is still unclear. In this study we have addressed this by investigating the immediate effects of WNT signalling activation within the stomach epithelium. We have specifically activated the WNT signalling pathway within the mouse adult gastric epithelium via deletion of either glycogen synthase kinase 3 (GSK3) or APC or via expression of a constitutively active β-catenin protein. WNT pathway deregulation dramatically affects stomach homoeostasis at very short latencies. In the corpus, there is rapid loss of parietal cells with fundic gland polyp (FGP) formation and adenomatous change, which are similar to those observed in familial adenomatous polyposis. In the antrum, adenomas occur from 4 days post-WNT activation. Taken together, these data show a pivotal role for WNT signalling in gastric homoeostasis, FGP formation and adenomagenesis. Loss of the parietal cell population and corresponding FGP formation, an early event in gastric carcinogenesis, as well as antral adenoma formation are immediate effects of nuclear β-catenin translocation and WNT target gene expression. Furthermore, our inducible murine model will permit a better understanding of the molecular changes required to drive tumourigenesis in the stomach.

Cancer stem-like cell properties are regulated by EGFR/AKT/β-catenin signaling and preferentially inhibited by gefitinib in nasopharyngeal carcinoma

We report that the epidermal growth factor receptor (EGFR) pathway plays a critical role in regulating cancer stem-like cells (CSCs) in nasopharyngeal carcinoma (NPC), one of the most common malignant tumors in Southeast Asia. Effects of EGFR on maintaining CSCs are mainly mediated by AKT signaling, and β-catenin is responsible for governing CSC properties in response to EGFR/AKT activation. Significantly, CSCs are enriched by cisplatin and decreased by gefitinib in NPC xenograft models. Upon reimplantation in secondary mice, tumor cells derived from cisplatin-treated mice grew rapidly, whereas regrowth of tumor cells from gefitinib-treated mice was severely diminished. We further demonstrate that expression of EGFR correlates with expression of β-catenin and Nanog in primary tumor specimens from NPC patients. These findings provide mechanistic and preclinical evidence supporting the use of gefitinib alone or in combination with a chemotherapeutic agent in first-line therapy for patients with NPC. In addition, our results suggest that targeting β-catenin represents a rational clinical modality for patients whose tumors harbor activated EGFR or AKT.

APC loss-induced intestinal tumorigenesis in Drosophila: Roles of Ras in Wnt signaling activation and tumor progression

Adenomatous polyposis coli (APC) and K-ras are the two most frequently mutated genes found in human colorectal cancers. In human colorectal cancers, Wnt signaling activation after the loss of APC is hypothesized to be the key event for adenoma initiation, whereas additional mutations such as Ras activation are required for the progression from adenoma to carcinoma. However, accumulating data have led to conflicting views regarding the precise role of Ras in APC loss-induced tumorigenesis. Here, using Drosophila midgut as a model system, we show that in the absence of Ras, APC mutant epithelial cells cannot initiate hyperplasia, suggesting that Ras plays an essential role in tumor initiation. Conversely, activating Ras by expressing oncogenic Ras or Raf in APC-deficient cells led to a blockage of cell differentiation and to preinvasive tumor outgrowth, characteristics that are shared by advanced colorectal carcinoma in humans. Mechanistically, we find that Ras is not required for Wnt signaling activation after APC loss, although Ras hyperactivation is able to potentiate Wnt signaling by increasing the cytoplasmic and nuclear accumulation of Armadillo/β-catenin via mechanisms independent of JNK/Rac1 or PI3K-Akt signaling, partly owing to the downregulation of DE-cadherin. Together with the data from gene expression analyses, our results indicate that both parallel and cooperative mechanisms of Wnt and Ras signaling are responsible for the initiation and progression of intestinal tumorigenesis after APC loss.

Identifying the stem cell of the intestinal crypt: strategies and pitfalls

Decades ago, two nonoverlapping crypt stem cell populations were proposed: Leblond's Crypt Base Columnar (CBC) cell and Potten's +4 cell. The identification of CBC markers including Lgr5 has confirmed Leblond's predictions that CBC cells are anatomically distinct, long-lived stem cells that permanently cycle. While Potten originally described +4 cells as proliferative and unusually radiation-sensitive, recent efforts to identify +4 stem cells have focused on the identification of cells that are quiescent and radiation-resistant. Here, we describe commonalities and discrepancies between the individual studies and discuss challenges of marker-based lineage tracing.

Intestinal label-retaining cells are secretory precursors expressing Lgr5

The rapid cell turnover of the intestinal epithelium is achieved from small numbers of stem cells located in the base of glandular crypts. These stem cells have been variously described as rapidly cycling or quiescent. A functional arrangement of stem cells that reconciles both of these behaviours has so far been difficult to obtain. Alternative explanations for quiescent cells have been that they act as a parallel or reserve population that replace rapidly cycling stem cells periodically or after injury; their exact nature remains unknown. Here we show mouse intestinal quiescent cells to be precursors that are committed to mature into differentiated secretory cells of the Paneth and enteroendocrine lineage. However, crucially we find that after intestinal injury they are capable of extensive proliferation and can give rise to clones comprising the main epithelial cell types. Thus, quiescent cells can be recalled to the stem-cell state. These findings establish quiescent cells as an effective clonogenic reserve and provide a motivation for investigating their role in pathologies such as colorectal cancers and intestinal inflammation.

Identification of a pathway by which glucose regulates β-catenin signalling via the cAMP/protein kinase A pathway in β-cell models

Pancreatic β-cells are highly responsive to changes in glucose, but the mechanisms involved are only partially understood. There is increasing evidence that the β-catenin signalling pathway plays an important role in regulating β-cell function, but the mechanisms regulating β-catenin signalling in these cells is not well understood. In the present study we show that β-catenin levels and downstream signalling are regulated by changes in glucose levels in INS-1E and β-TC6-F7 β-cell models. We found a glucose-dependent increase in levels of β-catenin in the cytoplasm and nucleus of INS-1E cells. Expression of cyclin D1 also increased with glucose and required the presence of β-catenin. This was associated with an increase in phosphorylation of β-catenin on Ser552, which is known to stabilize the molecule and increase its transcriptional activity. In a search for possible signalling intermediates we found forskolin and cell-permeable cAMP analogues recapitulated the glucose effects, suggesting a role for cAMP and PKA (cAMP-dependent protein kinase/protein kinase A) downstream of glucose. Furthermore, glucose caused sustained increases in cAMP. Two different inhibitors of adenylate cyclase and PKA signalling blocked the effects of glucose, whereas siRNA (small interfering RNA) knockdown of PKA blocked the effects of glucose on β-catenin signalling. Finally, reducing β-catenin levels with either siRNA or pyrvinium impaired glucose- and KCl-stimulated insulin secretion. Taken together the results of the present study define a pathway by which changes in glucose levels can regulate β-catenin using a mechanism which involves cAMP production and the activation of PKA. This identifies a pathway that may be important in glucose-dependent regulation of gene expression and insulin secretion in β-cells.

Sprouty2, PTEN, and PP2A interact to regulate prostate cancer progression

Concurrent activation of RAS/ERK and PI3K/AKT pathways is implicated in prostate cancer progression. The negative regulators of these pathways, including sprouty2 (SPRY2), protein phosphatase 2A (PP2A), and phosphatase and tensin homolog (PTEN), are commonly inactivated in prostate cancer. The molecular basis of cooperation between these genetic alterations is unknown. Here, we show that SPRY2 deficiency alone triggers activation of AKT and ERK, but this is insufficient to drive tumorigenesis. In addition to AKT and ERK activation, SPRY2 loss also activates a PP2A-dependent tumor suppressor checkpoint. Mechanistically, the PP2A-mediated growth arrest depends on GSK3β and is ultimately mediated by nuclear PTEN. In murine prostate cancer models, Pten haploinsufficiency synergized with Spry2 deficiency to drive tumorigenesis, including metastasis. Together, these results show that loss of Pten cooperates with Spry2 deficiency by bypassing a novel tumor suppressor checkpoint. Furthermore, loss of SPRY2 expression correlates strongly with loss of PTEN and/or PP2A subunits in human prostate cancer. This underlines the cooperation between SPRY2 deficiency and PTEN or PP2A inactivation in promoting tumorigenesis. Overall, we propose SPRY2, PTEN, and PP2A status as an important determinant of prostate cancer progression. Characterization of this trio may facilitate patient stratification for targeted therapies and chemopreventive interventions.

Dose-dependent roles for canonical Wnt signalling in de novo crypt formation and cell cycle properties of the colonic epithelium

There is a gradient of β-catenin expression along the colonic crypt axis with the highest levels at the crypt bottom. In addition, colorectal cancers show a heterogeneous subcellular pattern of β-catenin accumulation. However, it remains unclear whether different levels of Wnt signalling exert distinct roles in the colonic epithelium. Here, we investigated the dose-dependent effect of canonical Wnt activation on colonic epithelial differentiation by controlling the expression levels of stabilised β-catenin using a doxycycline-inducible transgenic system in mice. We show that elevated levels of Wnt signalling induce the amplification of Lgr5+ cells, which is accompanied by crypt fission and a reduction in cell proliferation among progenitor cells. By contrast, lower levels of β-catenin induction enhance cell proliferation rates of epithelial progenitors without affecting crypt fission rates. Notably, slow-cycling cells produced by β-catenin activation exhibit activation of Notch signalling. Consistent with the interpretation that the combination of Notch and Wnt signalling maintains crypt cells in a low proliferative state, the treatment of β-catenin-expressing mice with a Notch inhibitor turned such slow-cycling cells into actively proliferating cells. Our results indicate that the activation of the canonical Wnt signalling pathway is sufficient for de novo crypt formation, and suggest that different levels of canonical Wnt activations, in cooperation with Notch signalling, establish a hierarchy of slower-cycling stem cells and faster-cycling progenitor cells characteristic for the colonic epithelium.

Establishment of intestinal stem cell niche during amphibian metamorphosis

In the amphibian intestine during metamorphosis, most of the larval epithelial cells undergo apoptosis, whereas a small number of them survive. These cells dedifferentiate into stem cells through interactions with the microenvironment referred to as "stem cell niche" and generate the adult epithelium analogous to the mammalian counterpart. Since all processes of the larval-to-adult intestinal remodeling can be experimentally induced by thyroid hormone (TH) both in vivo and in vitro, the amphibian intestine provides us a valuable opportunity to study how adult stem cells and their niche are formed during postembryonic development. To address this issue, a number of expression and functional analyses of TH response genes have been intensely performed in the Xenopus laevis over the past two decades, by using organ culture and transgenic techniques. We here review recent progress in this field, focusing on key signaling pathways involved in establishment of the stem cell niche and discuss their evolutionarily conserved roles in the vertebrate intestine.

Moesin is a glioma progression marker that induces proliferation and Wnt/β-catenin pathway activation via interaction with CD44

Moesin is an ERM family protein that connects the actin cytoskeleton to transmembrane receptors. With the identification of the ERM family protein NF2 as a tumor suppressor in glioblastoma, we investigated roles for other ERM proteins in this malignancy. Here, we report that overexpression of moesin occurs generally in high-grade glioblastoma in a pattern correlated with the stem cell marker CD44. Unlike NF2, moesin acts as an oncogene by increasing cell proliferation and stem cell neurosphere formation, with its ectopic overexpression sufficient to shorten survival in an orthotopic mouse model of glioblastoma. Moesin was the major ERM member activated by phosphorylation in glioblastoma cells, where it interacted and colocalized with CD44 in membrane protrusions. Increasing the levels of moesin competitively displaced NF2 from CD44, increasing CD44 expression in a positive feedback loop driven by the Wnt/β-catenin signaling pathway. Therapeutic targeting of the moesin-CD44 interaction with the small-molecule inhibitor 7-cyanoquinocarcinol (DX-52-1) or with a CD44-mimetic peptide specifically reduced the proliferation of glioblastoma cells overexpressing moesin, where the Wnt/β-catenin pathway was activated. Our findings establish moesin and CD44 as progression markers and drugable targets in glioblastoma, relating their oncogenic effects to activation of the Wnt/β-catenin pathway.

Fibroblast growth factor receptor-mediated activation of AKT-β-catenin-CBP pathway regulates survival and proliferation of murine hepatoblasts and hepatic tumor initiating stem cells

Fibroblast Growth Factor (FGF)-10 promotes the proliferation and survival of murine hepatoblasts during early stages of hepatogenesis through a Wnt-β-catenin dependent pathway. To determine the mechanism by which this occurs, we expanded primary culture of hepatoblasts enriched for progenitor markers CD133 and CD49f from embryonic day (E) 12.5 fetal liver and an established tumor initiating stem cell line from Mat1a(-/-) livers in media conditioned with recombinant (r) FGF10 or rFGF7. FGF Receptor (R) activation resulted in the downstream activation of MAPK, PI3K-AKT, and β-catenin pathways, as well as cellular proliferation. Additionally, increased levels of nuclear β-catenin phosphorylated at Serine-552 in cultured primary hepatoblasts, Mat1a(-/-) cells, and also in ex vivo embryonic liver explants indicate AKT-dependent activation of β-catenin downstream of FGFR activation; conversely, the addition of AKT inhibitor Ly294002 completely abrogated β-catenin activation. FGFR activation-induced cell proliferation and survival were also inhibited by the compound ICG-001, a small molecule inhibitor of β-catenin-CREB Binding Protein (CBP) in hepatoblasts, further indicating a CBP-dependent regulatory mechanism of β-catenin activity.

CONCLUSION

FGF signaling regulates the proliferation and survival of embryonic and transformed progenitor cells in part through AKT-mediated activation of β-catenin and downstream interaction with the transcriptional co-activator CBP.

MicroRNA-320 suppresses the stem cell-like characteristics of prostate cancer cells by downregulating the Wnt/beta-catenin signaling pathway

Prostate cancer (PCa) is a leading cause of mortality and morbidity in men worldwide, and emerging evidence suggests that the CD44(high) prostate tumor-initiating cells (TICs) are associated with its poor prognosis. Although microRNAs are frequently dysregulated in human cancers, the influence of microRNAs on PCa malignancy and whether targeting TIC-associated microRNAs inhibit PCa progression remain unclear. In this study, we found that miR-320 is significantly downregulated in PCa. Overexpression of miR-320 in PCa cells decreases PCa tumorigenesis in vitro and in vivo. Global gene expression profiling of miR-320-overexpressing PCa cells reveals that downstream target genes of Wnt/β-catenin pathway and cancer stem cell markers are significantly decreased. MicroRNA-320 inhibits β-catenin expression by targeting the 3'-untranslated region of β-catenin mRNA. The reduction of miR-320 associated with increased β-catenin was also found in CD44(high) subpopulation of prostate cancer cells and clinical PCa specimens. Interestingly, knockdown of miR-320 significantly increases the cancer stem-like properties, such as tumorsphere formation, chemoresistance and tumorigenic abilities, although enriching the population of stem-like TICs among PCa cells. Furthermore, increased miR-320 expression in prostate stem-like TICs significantly suppresses stem cell-like properties of PCa cells. These results support that miR-320 is a key negative regulator in prostate TICs, and suggest developing miR-320 as a novel therapeutic agent may offer benefits for PCa treatment.

Consistent activation of the β-catenin pathway by Salmonella type-three secretion effector protein AvrA in chronically infected intestine

Salmonella infection is a common public health problem that can become chronic and increase the risk of cancer. Live, mutated Salmonella is used to target cancer cells. However, few studies have addressed chronic Salmonella infection in vivo. AvrA is a Salmonella type-three secretion effector that is multifunctional, inhibiting intestinal inflammation and enhancing proliferation. β-catenin is a key player in intestinal renewal, inflammation, and tumorigenesis. We hypothesize that in Salmonella-infected intestine, AvrA chronically activates the β-catenin pathway and increases cell proliferation, thus deregulating the intestinal responses to bacterial infection. We followed mice with Salmonella infection for 27 wk and investigated the physiological effects and role of AvrA on β-catenin in chronically infected intestine. We found that AvrA persistently regulated β-catenin posttranslational modifications, including phosphorylation and acetylation. Moreover, the upstream regulator Akt, transcription factors, T cell factors, nuclear β-catenin, and β-catenin target genes were enhanced in mice infected with Salmonella-expressing AvrA. AvrA has a chronic functional role in promoting intestinal renewal. In summary, we have uncovered an essential role of Salmonella AvrA in chronically activating β-catenin and impacting intestinal renewal in small intestine and colon. Our study emphasizes the importance of AvrA in chronic bacterial infection.

Transcription factor Oct1 is a somatic and cancer stem cell determinant

Defining master transcription factors governing somatic and cancer stem cell identity is an important goal. Here we show that the Oct4 paralog Oct1, a transcription factor implicated in stress responses, metabolic control, and poised transcription states, regulates normal and pathologic stem cell function. Oct1^HI cells in the colon and small intestine co-express known stem cell markers. In primary malignant tissue, high Oct1 protein but not mRNA levels strongly correlate with the frequency of CD24^LOCD44^HI cancer-initiating cells. Reducing Oct1 expression via RNAi reduces the proportion of ALDH^HI and dye efflux^HI cells, and increasing Oct1 increases the proportion of ALDH^HI cells. Normal ALDH^HI cells harbor elevated Oct1 protein but not mRNA levels. Functionally, we show that Oct1 promotes tumor engraftment frequency and promotes hematopoietic stem cell engraftment potential in competitive and serial transplants. In addition to previously described Oct1 transcriptional targets, we identify four Oct1 targets associated with the stem cell phenotype. Cumulatively, the data indicate that Oct1 regulates normal and cancer stem cell function.

Understanding the mechanisms that control stem cell function is a fundamental prerequisite both for the full application of stem cells to regenerative medicine and for a full understanding of the relationship between stem cells and cancer. In this study we show that a transcription factor known as Oct1 is a central regulator of normal and cancer stem cell function. We show that high Oct1 levels are associated with stem cells in multiple normal and malignant settings. Altering Oct1 expression, up or down, correspondingly alters multiple stem cell parameters, as well as stem cell function. We highlight known and identify new target genes Oct1 binds to that are consistent with a role in stem cell function.

β-Catenin activates the HOXA10 and CDX4 genes in myeloid progenitor cells

HoxA10 is a homeodomain transcription factor that is involved in maintenance of the myeloid progenitor population and implicated in myeloid leukemogenesis. Previously, we found that FGF2 and CDX4 are direct target genes of HoxA10 and that HOXA10 is a Cdx4 target gene. We also found that increased production of fibroblast growth factor 2 (Fgf2) by HoxA10-overexpressing myeloid progenitor cells results in activation of β-catenin in an autocrine manner. In this study, we identify novel cis elements in the CDX4 and HOXA10 genes that are activated by β-catenin in myeloid progenitor cells. We determine that β-catenin interacts with these cis elements, identifying both CDX4 and HOXA10 as β-catenin target genes in this context. We demonstrate that HoxA10-induced CDX4 transcription is influenced by Fgf2-dependent β-catenin activation. Similarly, Cdx4-induced HOXA10 transcription is influenced by β-catenin in an Fgf2-dependent manner. Increased expression of a set of Hox proteins, including HoxA10, is associated with poor prognosis in acute myeloid leukemia. Cdx4 contributes to leukemogenesis in Hox-overexpressing acute myeloid leukemia, and increased β-catenin activity is also associated with poor prognosis. The current studies identify a molecular mechanisms through which increased expression of HoxA10 increases Cdx4 expression by direct CDX4 activation and by Fgf2-induced β-catenin activity. This results in Cdx4-induced HoxA10-expression, creating a positive feedback mechanism.

Inducible progenitor-derived Wingless regulates adult midgut regeneration in Drosophila

The ability to regenerate following stress is a hallmark of self-renewing tissues. However, little is known about how regeneration differs from homeostatic tissue maintenance. Here, we study the role and regulation of Wingless (Wg)/Wnt signalling during intestinal regeneration using the Drosophila adult midgut. We show that Wg is produced by the intestinal epithelial compartment upon damage or stress and it is exclusively required for intestinal stem cell (ISC) proliferation during tissue regeneration. Reducing Wg or downstream signalling components from the intestinal epithelium blocked tissue regeneration. Importantly, we demonstrate that Wg from the undifferentiated progenitor cell, the enteroblast, is required for Myc-dependent ISC proliferation during regeneration. Similar to young regenerating tissues, ageing intestines required Wg and Myc for ISC hyperproliferation. Unexpectedly, our results demonstrate that epithelial but not mesenchymal Wg is essential for ISC proliferation in response to damage, while neither source of the ligand is solely responsible for ISC maintenance and tissue self-renewal in unchallenged tissues. Therefore, fine-tuning Wnt results in optimal balance between the ability to respond to stress without negatively affecting organismal viability.

Wnt signaling in mammary glands: plastic cell fates and combinatorial signaling

The mouse mammary gland is an outstanding developmental model that exemplifies the activities of many of the effector pathways known to organize mammalian morphogenesis; furthermore, there are well-characterized methods for the specific genetic manipulation of various mammary epithelial cell components. Among these signaling pathways, Wnt signaling has been shown to generate plasticity of fate determination, expanding the genetic programs available to cells in the mammary lineage. It is responsible first for the appearance of the mammary fate in embryonic ectoderm and then for maintaining bi-potential basal stem cells in adult mammary ductal trees. Recent technical developments have led to the separate analysis of various mammary epithelial cell subpopulations, spurring the investigation of Wnt-dependent interactions. Although Wnt signaling was shown to be oncogenic for mouse mammary epithelium even before being identified as the principle oncogenic driver for gut epithelium, conclusive data implicating this pathway as a tumor driver for breast cancer lag behind, and we examine potential reasons.

Noncanonical Wnt signaling maintains hematopoietic stem cells in the niche

Wnt signaling is involved in self-renewal and maintenance of hematopoietic stem cells (HSCs); however, the particular role of noncanonical Wnt signaling in regulating HSCs in vivo is largely unknown. Here, we show Flamingo (Fmi) and Frizzled (Fz) 8, members of noncanonical Wnt signaling, both express in and functionally maintain quiescent long-term HSCs. Fmi regulates Fz8 distribution at the interface between HSCs and N-cadherin(+) osteoblasts (N-cad(+)OBs that enrich osteoprogenitors) in the niche. We further found that N-cad(+)OBs predominantly express noncanonical Wnt ligands and inhibitors of canonical Wnt signaling under homeostasis. Under stress, noncanonical Wnt signaling is attenuated and canonical Wnt signaling is enhanced in activation of HSCs. Mechanistically, noncanonical Wnt signaling mediated by Fz8 suppresses the Ca(2+)-NFAT- IFNγ pathway, directly or indirectly through the CDC42-CK1α complex and also antagonizes canonical Wnt signaling in HSCs. Taken together, our findings demonstrate that noncanonical Wnt signaling maintains quiescent long-term HSCs through Fmi and Fz8 interaction in the niche.

Cooperative interaction of MUC1 with the HGF/c-Met pathway during hepatocarcinogenesis

Background

Hepatocyte growth factor (HGF) induced c-Met activation is known as the main stimulus for hepatocyte proliferation and is essential for liver development and regeneration. Activation of HGF/c-Met signaling has been correlated with aggressive phenotype and poor prognosis in hepatocellular carcinoma (HCC). MUC1 is a transmembrane mucin, whose over-expression is reported in most cancers. Many of the oncogenic effects of MUC1 are believed to occur through the interaction of MUC1 with signaling molecules. To clarify the role of MUC1 in HGF/c-Met signaling, we determined whether MUC1 and c-Met interact cooperatively and what their role(s) is in hepatocarcinogenesis.

Results

MUC1 and c-Met over-expression levels were determined in highly motile and invasive, mesenchymal-like HCC cell lines, and in serial sections of cirrhotic and HCC tissues, and these levels were compared to those in normal liver tissues. Co-expression of both c-Met and MUC1 was found to be associated with the differentiation status of HCC. We further demonstrated an interaction between c-Met and MUC1 in HCC cells. HGF-induced c-Met phosphorylation decreased this interaction, and down-regulated MUC1 expression. Inhibition of c-Met activation restored HGF-mediated MUC1 down-regulation, and decreased the migratory and invasive abilities of HCC cells via inhibition of β-catenin activation and c-Myc expression. In contrast, siRNA silencing of MUC1 increased HGF-induced c-Met activation and HGF-induced cell motility and invasion.

Conclusions

These findings indicate that the crosstalk between MUC1 and c-Met in HCC could provide an advantage for invasion to HCC cells through the β-catenin/c-Myc pathway. Thus, MUC1 and c-Met could serve as potential therapeutic targets in HCC.

PEA-15 unphosphorylated at both serine 104 and serine 116 inhibits ovarian cancer cell tumorigenicity and progression through blocking β-catenin

Ovarian cancer is a major cause of death among women; there remains an urgent need to develop new effective therapies to target this cancer. Phosphoprotein enriched in astrocytes (PEA-15) is a 15-kDa phosphoprotein that is known to bind ERK1/2, thus blocking cell proliferation. The physiological activity of PEA-15 is dependent on the phosphorylation status of serine 104 (Ser104) and Ser116. However, little is known about the impact of PEA-15 phosphorylation on tumor progression. We have previously shown that overexpression of PEA-15 has an antitumor effect against both breast and ovarian cancer cells. Here, we report that using a human ovarian cancer tissue microarray, we found that tissues from patients with ovarian cancer were significantly more likely than adjacent normal tissues to express PEA-15 phosphorylated at both sites. Using phosphomimetic and nonphosphorylatable mutants of PEA-15, we found that mutant double-unphosphorylated PEA-15 in which Ser104 and Ser116 were substituted with alanine (PEA-15-AA) had a more potent antitumorigenic effect in ovarian cancer than did phosphomimetic PEA-15 in which Ser104 and Ser116 were substituted with aspartic acid (PEA-15-DD). Further, we observed that the antitumorigenic effect of PEA-15-AA was a result of inhibition of the migration capacity of cells and inhibition of in vivo angiogenesis. This inhibition was partially dependent on inhibition of β-catenin expression and nuclear translocalization. Taken together, our results suggest that phosphorylated PEA-15 is an important contributor to the aggressiveness of ovarian cancer and justify the development of PEA-15-AA as an effective therapeutic molecule in the treatment of ovarian cancer.

Cancer-stimulated mesenchymal stem cells create a carcinoma stem cell niche via prostaglandin E2 signaling

Mesenchymal cells of the tumor-associated stroma are critical determinants of carcinoma cell behavior. We focus here on interactions of carcinoma cells with mesenchymal stem cells (MSC), which are recruited to the tumor stroma and, once present, are able to influence the phenotype of the carcinoma cells. We find that carcinoma cell-derived interleukin-1 (IL-1) induces prostaglandin E(2) (PGE(2)) secretion by MSCs. The resulting PGE(2) operates in an autocrine manner, cooperating with ongoing paracrine IL-1 signaling, to induce expression of a group of cytokines by the MSCs. The PGE(2) and cytokines then proceed to act in a paracrine fashion on the carcinoma cells to induce activation of β-catenin signaling and formation of cancer stem cells. These observations indicate that MSCs and derived cell types create a cancer stem cell niche to enable tumor progression via release of PGE(2) and cytokines.

SIGNIFICANCE

Although PGE2 has been implicated time and again in fostering tumorigenesis, its effects on carcinoma cells that contribute specifically to tumor formation are poorly understood. Here we show that tumor cells are able to elicit a strong induction of the COX-2/microsomal prostaglandin-E synthase-1 (mPGES-1)/PGE(2) axis in MSCs recruited to the tumor-associated stroma by releasing IL-1, which in turn elicits a mesenchymal/stem cell–like phenotype in the carcinoma cells.

Wnt-RhoA signaling is involved in dental enamel development

Transgenic mice that express dominant-negative RhoA (RhoA(DN) ) in ameloblasts have hypoplastic enamel with defects in molar cusps. β-catenin and Wnt5a were up-regulated in enamel organs of RhoA(DN) transgenic mice, which indicated that both canonical and non-canonical Wnt pathways are implicated in the process of enamel defect formation. It was hypothesized that expression of RhoA(DN) in ameloblasts interfered with normal enamel development through the pathways that were induced by fluoride. The Wnt and RhoA pathways were further investigated in an ameloblast-lineage cell line (ALC) by treatment with sodium fluoride (NaF). The activities of RhoA and Rho-associated protein kinase (ROCK) II decreased significantly by 8-12 hours, similar to decreased activity in RhoA(DN) transgenic mice. Both canonical and non-canonical Wnt pathways were activated by treatment with NaF, which was verified by western blotting and the β-catenin-TCF/LEF (T cell factor lymphanoid/enhancer factor) reporter gene (TOPflash) assay. β-catenin localization to both cytoplasm and nucleus was up-regulated in NaF-treated ALC, while Gsk-3β, the negative regulator of the Wnt pathway, showed a decreased pattern of expression. The current results indicate that both Wnt and RhoA pathways are implicated in fluoride-induced signaling transductions in the ALC as well as in the development of enamel defects in RhoA(DN) transgenic mice.