Reciprocal targeting of Hath1 and beta-catenin by Wnt glycogen synthase kinase 3beta in human colon cancer

Effects of dopamine receptor antagonists and radiation on mouse neural stem/progenitor cells

BACKGROUND

Dopamine receptor antagonists have recently been identified as potential anti-cancer agents in combination with radiation, and a first drug of this class is in clinical trials against pediatric glioma. Radiotherapy causes cognitive impairment primarily by eliminating neural stem/progenitor cells and subsequent loss of neurogenesis, along with inducing inflammation, vascular damage, and synaptic alterations. Here, we tested the combined effects of dopamine receptor antagonists and radiation on neural stem/progenitor cells.

METHODS

Using transgenic mice that report the presence of neural stem/progenitor cells through Nestin promoter-driven expression of EGFP, the effects of dopamine receptor antagonists alone or in combination with radiation on neural stem/progenitor cells were assessed in sphere-formation assays, extreme limiting dilution assays, flow cytometry and real-time PCR in vitro and in vivo in both sexes.

RESULTS

We report that hydroxyzine and trifluoperazine exhibited sex-dependent effects on murine newborn neural stem/progenitor cells in vitro. In contrast, amisulpride, nemonapride, and quetiapine, when combined with radiation, significantly increased the number of neural stem/progenitor cells in both sexes. In vivo, trifluoperazine showed sex-dependent effects on adult neural stem/progenitor cells, while amisulpride demonstrated significant effects in both sexes. Further, amisulpride increased sphere forming capacity and stem cell frequency in both sexes when compared to controls.

CONCLUSION

We conclude that a therapeutic window for dopamine receptor antagonists in combination with radiation potentially exists, making it a novel combination therapy against glioblastoma. Normal tissue toxicity following this treatment scheme likely differs depending on age and sex and should be taken into consideration when designing clinical trials.

Effects of Dopamine Receptor Antagonists and Radiation on Mouse Neural Stem/Progenitor Cells

Background

Dopamine receptor antagonists are psychotropic drugs that have been originally developed against psychiatric disorders. We recently identified dopamine receptor antagonists as potential anti-cancer agents and some have entered clinical trials against glioblastoma. Radiotherapy is known to cause cognitive impairment in patients receiving cranial irradiation through the elimination of neural stem/progenitor cells and subsequent loss of neurogenesis.

Methods

Using transgenic mice that report the presence of neural stem/progenitor cells through Nestin promoter-driven expression of enhanced green fluorescent protein, the effects of dopamine receptor antagonists alone or in combination with radiation on murine neural stem/progenitor cells were assessed in sphere-formation assays, flow cytometry and immunofluorescence in vitro and in vivo .

Results

We report that several dopamine receptor antagonists show sex-dependent effects on neural stem/progenitor cells both in vitro and in vivo . Hydroxyzine, trifluoperazine, amisulpride, nemonapride or quetiapine alone or in combination with radiation significantly increased the number of neural stem/progenitor cells in female neurospheres but not in male mice. Dopamine receptor antagonists either protected neural stem/progenitor cells from radiation or expanded the stem cell pool, thus indicating that this combination therapy against glioblastoma will not increase radiation-induced cognitive decline through increasing elimination of neural stem/progenitor cells and subsequent loss of neurogenesis.

Conclusions

We conclude that a therapeutic window for dopamine receptor antagonists in combination with radiation potentially exist, making it a novel combination therapy against glioblastoma. Normal tissue toxicity of this combination potentially differs depending on age and sex and should be taken into consideration when designing clinical trials.

Key Points

- Neural stem/progenitor cells show sex-dependent sensitivity to dopamine receptor antagonists- Dopamine receptor antagonists active against GBM increase Neural stem/progenitor cells counts.

Importance of the Study

Combination therapy of dopamine receptor antagonists with radiation have entered clinical trials against glioblastoma but the normal tissue toxicity of this combination has not been fully explored yet. Here we present evidence that some dopamine receptor antagonists show sex-dependent effects on neural stem/progenitor cells either by protecting neural stem/progenitor cells from radiation or inducing an expansion of the stem cell pool, suggesting that this combination therapy against glioblastoma will not increase radiation-induced cognitive decline through increasing elimination of neural stem/progenitor cells and subsequent loss of neurogenesis. Normal tissue toxicity of this combination potentially differs depending on age and sex and should be further explored in clinical trials.

The role of intestinal stem cell within gut homeostasis: Focusing on its interplay with gut microbiota and the regulating pathways

Intestinal stem cells (ISCs) play an important role in maintaining intestinal homeostasis via promoting a healthy gut barrier. Within the stem cell niche, gut microbiota linking the crosstalk of dietary influence and host response has been identified as a key regulator of ISCs. Emerging insights from recent research reveal that ISC and gut microbiota interplay regulates epithelial self-renewal. This article reviews the recent knowledge on the key role of ISC in their local environment (stem cell niche) associating with gut microbiota and their metabolites as well as the signaling pathways. The current progress of intestinal organoid culture is further summarized. Subsequently, the key challenges and future directions are discussed.

RNF6 promotes colorectal cancer invasion and migration via the Wnt/β-catenin pathway by inhibiting GSK3β activity

BACKGROUND

The purpose of this study was to explore the molecular mechanism underlying the interaction between ring finger protein 6 (RNF6) and glycogen synthase kinase 3β (GSK3β) in colorectal cancer (CRC).

METHODS

In this study, cell models of overexpressed or silenced RNF6 were established by liposome transfection, and IM-12 was used as the inhibitor of GSK3β. Real-time quantitative PCR and western blots were used to detect the expression of RNF6, p-GSK3β, GSK3β, and β-catenin, and MTT assays were used to quantify cell proliferation. The tumorigenicity of cells was observed by plate clonal formation assay; the invasiveness of cells was examined in Transwell Boyden chambers, and the migratory capacity of cells was tested by scratch wound assays. The rat CRC model was induced by AOM/DSS, in which we verified activity in the Wnt/β-catenin pathway by examining GSK3β phosphorylation.

RESULTS

RNF6 was upregulated in CRC samples and cell lines. Silencing or overexpressing RNF6 in colorectal cancer cells inhibited or promoted, respectively, the proliferation, tumorigenicity, invasion and migration of CRC cells, as well as expression of p-GSK3β, GSK3β and β-catenin. IM-12 reversed the Wnt/β-catenin-activated state change induced by RNF6 silencing and the inhibition of cell proliferation, tumorigenicity, invasion and migration. The same results were observed in vivo in the rat CRC model.

CONCLUSIONS

Overexpression of RNF6 in CRC increased the GSK3β phosphorylation level, which led to activation of the Wnt/β-catenin pathway and promoted the invasion and migration of CRC cells, suggesting that RNF6 may be a novel target for the treatment of CRC.

Cyclin D1 controls development of cerebellar granule cell progenitors through phosphorylation and stabilization of ATOH1

During development, neural progenitors are in proliferative and immature states; however, the molecular machinery that cooperatively controls both states remains elusive. Here, we report that cyclin D1 (CCND1) directly regulates both proliferative and immature states of cerebellar granule cell progenitors (GCPs). CCND1 not only accelerates cell cycle but also upregulates ATOH1 protein, an essential transcription factor that maintains GCPs in an immature state. In cooperation with CDK4, CCND1 directly phosphorylates S309 of ATOH1, which inhibits additional phosphorylation at S328 and consequently prevents S328 phosphorylation-dependent ATOH1 degradation. Additionally, PROX1 downregulates Ccnd1 expression by histone deacetylation of Ccnd1 promoter in GCPs, leading to cell cycle exit and differentiation. Moreover, WNT signaling upregulates PROX1 expression in GCPs. These findings suggest that WNT-PROX1-CCND1-ATOH1 signaling cascade cooperatively controls proliferative and immature states of GCPs. We revealed that the expression and phosphorylation levels of these molecules dynamically change during cerebellar development, which are suggested to determine appropriate differentiation rates from GCPs to GCs at distinct developmental stages. This study contributes to understanding the regulatory mechanism of GCPs as well as neural progenitors.

GSK3β, a Master Kinase in the Regulation of Adult Stem Cell Behavior

In adult stem cells, Glycogen Synthase Kinase 3β (GSK3β) is at the crossroad of signaling pathways controlling survival, proliferation, adhesion and differentiation. The microenvironment plays a key role in the regulation of these cell functions and we have demonstrated that the GSK3β activity is strongly dependent on the engagement of integrins and protease-activated receptors (PARs). Downstream of the integrin α₅β₁ or PAR₂ activation, a molecular complex is organized around the scaffolding proteins RACK1 and β-arrestin-2 respectively, containing the phosphatase PP2A responsible for GSK3β activation. As a consequence, a quiescent stem cell phenotype is established with high capacities to face apoptotic and metabolic stresses. A protective role of GSK3β has been found for hematopoietic and intestinal stem cells. Latters survived to de-adhesion through PAR₂ activation, whereas formers were protected from cytotoxicity through α₅β₁ engagement. However, a prolonged activation of GSK3β promoted a defect in epithelial regeneration and a resistance to chemotherapy of leukemic cells, paving the way to chronic inflammatory diseases and to cancer resurgence, respectively. In both cases, a sexual dimorphism was measured in GSK3β-dependent cellular functions. GSK3β activity is a key marker for inflammatory and cancer diseases allowing adjusted therapy to sex, age and metabolic status of patients.

Intestinal phenotype is maintained by Atoh1 in the cancer region of intraductal papillary mucinous neoplasm

Intraductal papillary mucinous neoplasm (IPMN) is a precancerous lesion of pancreatic cancer. Although there are 4 types of IPMN, among which intestinal-type IPMN is likely to progress into invasive cancer known as colloid carcinoma, no information regarding the involvement of the intestinal phenotype in the carcinogenesis of IPMN exists. The present study was conducted to explore how the intestinal differentiation system is maintained during the tumor progression of intestinal-type IPMN using surgical resection specimens. Results showed that Atoh1, a critical transcriptional factor for intestinal differentiation toward the secretory lineages of intestinal epithelial cells, was expressed in an invasive-grade IPMN. To determine the function of Atoh1 in pancreatic cancer, we generated a pancreatic ductal adenocarcinoma (PDAC) cell line overexpressing Atoh1. In a xenograft model, we successfully induced an IPMN phenotype in PDAC cells via Atoh1 induction. Finally, for the first time, we discovered that GPA33 is expressed in intestinal-type IPMN, thereby suggesting a novel target for cancer therapy. In conclusion, the intestinal differentiation system might be maintained during tumor progression of intestinal-type IPMN. Further analysis of the function of Atoh1 in IPMN might be useful for understanding the molecular mechanism underlying the malignant potential during the tumor progression of IPMN.

The Joubert Syndrome Gene arl13b is Critical for Early Cerebellar Development in Zebrafish

Joubert syndrome is characterized by unique malformation of the cerebellar vermis. More than thirty Joubert syndrome genes have been identified, including ARL13B. However, its role in cerebellar development remains unexplored. We found that knockdown or knockout of arl13b impaired balance and locomotion in zebrafish larvae. Granule cells were selectively reduced in the corpus cerebelli, a structure homologous to the mammalian vermis. Purkinje cell progenitors were also selectively disturbed dorsomedially. The expression of atoh1 and ptf1, proneural genes of granule and Purkinje cells, respectively, were selectively down-regulated along the dorsal midline of the cerebellum. Moreover, wnt1, which is transiently expressed early in cerebellar development, was selectively reduced. Intriguingly, activating Wnt signaling partially rescued the granule cell defects in arl13b mutants. These findings suggested that Arl13b is necessary for the early development of cerebellar granule and Purkinje cells. The arl13b-deficient zebrafish can serve as a model organism for studying Joubert syndrome.

Atonal bHLH transcription factor 1 is an important factor for maintaining the balance of cell proliferation and differentiation in tumorigenesis

Establishing the link between cellular processes and oncogenesis may aid the elucidation of targeted and effective therapies against tumor cell proliferation and metastasis. Previous studies have investigated the mechanisms involved in maintaining the balance between cell proliferation, differentiation and migration. There is increased interest in determining the conditions that allow cancer stem cells to differentiate as well as the identification of molecules that may serve as novel drug targets. Furthermore, the study of various genes, including transcription factors, which serve a crucial role in cellular processes, may present a promising direction for future therapy. The present review described the role of the transcription factor atonal bHLH transcription factor 1 (ATOH1) in signaling pathways in tumorigenesis, particularly in cerebellar tumor medulloblastoma and colorectal cancer, where ATOH1 serves as an oncogene or tumor suppressor, respectively. Additionally, the present review summarized the associated therapeutic interventions for these two types of tumors and discussed novel clinical targets and approaches.

Large intestine embryogenesis: Molecular pathways and related disorders (Review)

The large intestine, part of the gastrointestinal tract (GI), is composed of all three germ layers, namely the endoderm, the mesoderm and the ectoderm, forming the epithelium, the smooth muscle layers and the enteric nervous system, respectively. Since gastrulation, these layers develop simultaneously during embryogenesis, signaling to each other continuously until adult age. Two invaginations, the anterior intestinal portal (AIP) and the caudal/posterior intestinal portal (CIP), elongate and fuse, creating the primitive gut tube, which is then patterned along the antero‑posterior (AP) axis and the radial (RAD) axis in the context of left‑right (LR) asymmetry. These events lead to the formation of three distinct regions, the foregut, midgut and hindgut. All the above‑mentioned phenomena are under strict control from various molecular pathways, which are critical for the normal intestinal development and function. Specifically, the intestinal epithelium constitutes a constantly developing tissue, deriving from the progenitor stem cells at the bottom of the intestinal crypt. Epithelial differentiation strongly depends on the crosstalk with the adjacent mesoderm. Major molecular pathways that are implicated in the embryogenesis of the large intestine include the canonical and non‑canonical wingless‑related integration site (Wnt), bone morphogenetic protein (BMP), Notch and hedgehog systems. The aberrant regulation of these pathways inevitably leads to several intestinal malformation syndromes, such as atresia, stenosis, or agangliosis. Novel theories, involving the regulation and homeostasis of intestinal stem cells, suggest an embryological basis for the pathogenesis of colorectal cancer (CRC). Thus, the present review article summarizes the diverse roles of these molecular factors in intestinal embryogenesis and related disorders.

Cellular Composition and Differentiation Signaling in Chicken Small Intestinal Epithelium

The small intestine plays an important role for animals to digest and absorb nutrients. The epithelial lining of the intestine develops from the embryonic endoderm of the embryo. The mature intestinal epithelium is composed of different types of functional epithelial cells that are derived from stem cells, which are located in the crypts. Chickens have been widely used as an animal model for researching vertebrate embryonic development. However, little is known about the molecular basis of development and differentiation within the chicken small intestinal epithelium. This review introduces processes of development and growth in the chicken gut, and compares the cellular characteristics and signaling pathways between chicken and mammals, including Notch and Wnt signaling that control the differentiation in the small intestinal epithelium. There is evidence that the chicken intestinal epithelium has a distinct cellular architecture and proliferation zone compared to mammals. The establishment of an in vitro cell culture model for chickens will provide a novel tool to explore molecular regulation of the chicken intestinal development and differentiation.

Establishment of a system to evaluate the therapeutic effect and the dynamics of an investigational drug on ulcerative colitis using human colonic organoids

BACKGROUND

Ulcerative colitis (UC) is a chronic inflammatory disease of the colon with an intractable, recurrent course. The goal of UC therapy is to target mucosal healing because immune-suppressive therapy for UC frequently results in relapse. However, few drugs directly target mucosal healing. We, therefore, aim to evaluate the therapeutic effect of an investigational drug on intestinal epithelial cells in an in vitro UC model using human colonic organoids.

METHODS

Colonic organoids were isolated from human colon and cultured. A mixture of cytokines and bacterial components were used to mimic UC in humans. The effect of the investigational drug on colonic organoid was evaluated by microarray analysis and 3D immunofluorescence. The enrichment of stem cells was assessed with a colony formation assay.

RESULTS

Inflammatory stimulation resulted in a significant induction of inflammatory-related genes in colonic organoids whereas cell differentiation was suppressed. Treatment with the investigational drug KAG-308 showed reciprocal dynamics of gene expression to inflammatory stimulation, which resulted in not only the suppression of immune response but also the promotion of cellular differentiation towards secretory lineages. Moreover, SPDEF and Reg4 were identified as novel targets for the enrichment of intestinal epithelial stem cells and mucosal healing.

CONCLUSIONS

The establishment of in vitro UC model using human colonic organoid could reveal the effects and targets of investigational drugs in intestinal epithelial cells under inflammation conditions. Further maturation of this system might be more efficient to predict the effect on UC, as compared with the use of animal model, for the development of new drugs.

SCF/c-KIT Signaling Increased Mucin2 Production by Maintaining Atoh1 Expression in Mucinous Colorectal Adenocarcinoma

Mucinous colorectal adenocarcinoma (MCA) patients often a show high risk of malignant potential and a poorer survival rate. Given that the pathological feature and oncobiological characteristics of MCA are correlated with its abundant extracellular mucin2 (MUC2), we paid interest toward investigating the key factor that promotes MUC2 production exposure to highly-activated stem cell factor (SCF)/c-KIT signaling, which we believed to contribute to MCA formation. Long-term azoxymethane and dextran sodium sulfate treatment successfully induced MCA only in wild-type (WT) mice at week 37 and 43, while all c-kit loss-of-function mutant mice (Wads^m/m) developed non-MCA. Significantly, MUC2 and its key transcriptional factor Atonal homologue 1 (Atoh1) were remarkably expressed in MCA mice compared with non-MCA mice. Atoh1 was significantly elevated in colorectal cancer (CRC) cells stimulated by exogenous SCF or overexpressing c-KIT in vitro, while decreased by the blockage of SCF/c-KIT signaling with Imatinib. Furthermore, the maintained Atoh1 protein level was due to the inactive glycogen synthase kinase 3β (p-GSK3β) by virtue of the activated SCF/c-KIT-Protein Kinase B (AKT) signaling. Similar results were obtained from the ONCOMINE database and CRC patients. In conclusion, we suggested that SCF/c-KIT signaling promoted MUC2 production and MCA tumorigenesis by maintaining Atoh1 expression. Therefore, targeting the related key molecules might be beneficial for treating MCA patients.

Anti-inflammatory and anticancer effects of flavonol glycosides from Diplotaxis harra through GSK3β regulation in intestinal cells

CONTEXT AND OBJECTIVE

Diplotaxis harra (Forssk.) Boiss. (Brassicaceae) is traditionally used as an antidiabetic, anti-inflammatory or anticancer agent. In these pathologies, the glycogen synthase kinase 3 β (GSK3β) is overactivated and represents an interesting therapeutic target. Several flavonoids can inhibit GSK3β and the purpose of this study was to search for the compounds in Diplotaxis harra which are able to modulate GSK3β.

MATERIALS AND METHODS

Methanol extracts from D. harra flowers were prepared and the bio-guided fractionation of their active compounds was performed using inflammatory [protease-activated receptor 2 (PAR₂)-stimulated IEC6 cells] and cancer (human Caco-2 cell line) intestinal cells. 50-100 μg/mL of fractions or compounds purified by HPLC were incubated with cells whose inhibited form of GSK3β (Pser9 GSK3β) and survival were analyzed by Western blot at 1 h and colorimetric assay at 24 h, respectively. LC-UV-MS profiles and MS-MS spectra were used for the characterization of extracts and flavonoids-enriched fractions, and the identification of pure flavonoids was achieved by MS and NMR analysis.

RESULTS

The methanol extract from D. harra flowers and its flavonoid-enriched fraction inhibit GSK3β in PAR₂-stimulated IEC6 cells. GSK3β inhibition by the flavonoid-enriched D. harra fraction was dependent on PKC activation. The flavonoid-enriched D. harra fraction and its purified compound isorhamnetin-3,7-di-O-glucoside induced a 20% decrease of PAR₂-stimulated IEC6 and Caco-2 cell survival. Importantly, normal cells (non-stimulated IEC6 cells) were spared by these treatments.

CONCLUSION

This work indicates that flavonoids from D. harra display cytotoxic activity against inflammatory and cancer intestinal cells which could depend on GSK3β inhibition.

Role of ADAM10 in intestinal crypt homeostasis and tumorigenesis

A disintegrin and metalloproteinases (ADAMs) are a family of mSultidomain, membrane-anchored proteases that regulate diverse cellular functions, including cell adhesion, migration, proteolysis and other cell signaling events. Catalytically-active ADAMs act as ectodomain sheddases that proteolytically cleave type I and type II transmembrane proteins and some GPI-anchored proteins from the cellular surface. ADAMs can also modulate other cellular signaling events through a process known as regulated intramembrane proteolysis (RIP). Through their proteolytic activity, ADAMs can rapidly modulate key cell signaling pathways in response to changes in the extracellular environment (e.g. inflammation) and play a central role in coordinating intercellular communication. Dysregulation of these processes through aberrant expression, or sustained ADAM activity, is linked to chronic inflammation, inflammation-associated cancer and tumorigenesis. ADAM10 was the first disintegrin-metalloproteinase demonstrated to have proteolytic activity and is the prototypic ADAM associated with RIP activity (e.g. sequential Notch receptor processing). ADAM10 is abundantly expressed throughout the gastrointestinal tract and during normal intestinal homeostasis ADAM10 regulates many cellular processes associated with intestinal development, cell fate specification and maintenance of intestinal stem cell/progenitor populations. In addition, several signaling pathways that undergo ectodomain shedding by ADAM10 (e.g. Notch, EGFR/ErbB, IL-6/sIL-6R) help control intestinal injury/regenerative responses and may drive intestinal inflammation and colon cancer initiation and progression. Here, I review some of the proposed functions of ADAM10 associated with intestinal crypt homeostasis and tumorigenesis within the gastrointestinal tract in vivo. This article is part of a Special Issue entitled: Proteolysis as a Regulatory Event in Pathophysiology edited by Stefan Rose-John.

An Atoh1-S193A Phospho-Mutant Allele Causes Hearing Deficits and Motor Impairment

Atonal homolog 1 (Atoh1) is a basic helix-loop-helix (bHLH) transcription factor that is essential for the genesis, survival, and maturation of a variety of neuronal and non-neuronal cell populations, including those involved in proprioception, interoception, balance, respiration, and hearing. Such diverse functions require fine regulation at the transcriptional and protein levels. Here, we show that serine 193 (S193) is phosphorylated in Atoh1's bHLH domain in vivo Knock-in mice of both sexes bearing a GFP-tagged phospho-dead S193A allele on a null background (Atoh1^S193A/lacZ) exhibit mild cerebellar foliation defects, motor impairments, partial pontine nucleus migration defects, cochlear hair cell degeneration, and profound hearing loss. We also found that Atoh1 heterozygous mice of both sexes (Atoh1^lacZ/+) have adult-onset deafness. These data indicate that different cell types have different degrees of vulnerability to loss of Atoh1 function and that hypomorphic Atoh1 alleles should be considered in human hearing loss.SIGNIFICANCE STATEMENT The discovery that Atonal homolog 1 (Atoh1) governs the development of the sensory hair cells in the inner ear led to therapeutic efforts to restore these cells in cases of human deafness. Because prior studies of Atoh1-heterozygous mice did not examine or report on hearing loss in mature animals, it has not been clinical practice to sequence ATOH1 in people with deafness. Here, in seeking to understand how phosphorylation of Atoh1 modulates its effects in vivo, we discovered that inner ear hair cells are much more vulnerable to loss of Atoh1 function than other Atoh1-positive cell types and that heterozygous mice actually develop hearing loss late in life. This opens up the possibility that missense mutations in ATOH1 could increase human vulnerability to loss of hair cells because of aging or trauma.

Atoh1 regulation in the cochlea: more than just transcription

More than 80% of all cases of deafness are related to the death or degeneration of cochlear hair cells and the associated spiral ganglion neurons, and a lack of regeneration of these cells leads to permanent hearing loss. Therefore, the regeneration of lost hair cells is an important goal for the treatment of deafness. Atoh1 is a basic helix-loop-helix (bHLH) transcription factor that is critical in both the development and regeneration of cochlear hair cells. Atoh1 is transcriptionally regulated by several signaling pathways, including Notch and Wnt signalings. At the post-translational level, it is regulated through the ubiquitin-proteasome pathway. In vitro and in vivo studies have revealed that manipulation of these signaling pathways not only controls development, but also leads to the regeneration of cochlear hair cells after damage. Recent progress toward understanding the signaling networks involved in hair cell development and regeneration has led to the development of new strategies to replace lost hair cells. This review focuses on our current understanding of the signaling pathways that regulate Atoh1 in the cochlea.

SPDEF Induces Quiescence of Colorectal Cancer Cells by Changing the Transcriptional Targets of β-catenin

BACKGROUND & AIMS

The canonical Wnt signaling pathway activates the transcriptional activity of β-catenin. This pathway is often activated in colorectal cancer cells, but strategies to block it in tumors have not been effective. The SAM pointed domain containing ETS transcription factor (SPDEF) suppresses formation of colon tumors by unclear mechanisms. We investigated these mechanisms and the effects of SPDEF on β-catenin activity in mouse models of colorectal cancer (CRC), CRC cell lines, and mouse and human normal and cancer colonoids.

METHODS

We performed studies of Lgr5^CreERT2; β-catenin^exon3; Rosa26^{LSL-rtta-ires-EGFP}; TRE-Spdef mice, which express an oncogenic form of β-catenin in Lgr5-positive ISCs upon administration of tamoxifen and SPDEF upon administration of tetracycline. CRC lines (HCT116 and SW480) were engineered to express inducible tagged SPDEF or vector (control) and subcutaneously injected into immunodeficient NSG mice. We generated SPDEF-inducible human colonoids, including a line derived from normal rectal mucosa (control) and an adenocarcinoma line derived from a patient with germline MUTYH mutation. Full-length and truncated forms of SPDEF were expressed in CRC cells; cells were assayed for β-catenin activity and studied in immunoprecipitation and chromatin immunoprecipitation assays.

RESULTS

Expression of SPDEF was sufficient to inhibit intestinal tumorigenesis by activated β-catenin, block tumor cell proliferation, and restrict growth of established tumors. In tumor cells with activated β -catenin, expression of SPDEF induced a quiescent state, which was reversed when SPDEF expression was stopped. In mouse and human normal and tumor-derived enteroids/colonoids, those that expressed SPDEF for 3 days were significantly smaller. SPDEF inhibited the transcriptional activity of β-catenin via a protein-protein interaction, independent of SPDEF DNA binding capacity. SPDEF disrupted β-catenin binding to TCF1 and TCF3, displacing β-catenin from enhancer regions of genes that regulate the cell cycle but not genes that regulate stem cell activities.

CONCLUSIONS

In studies of mice and human CRC, we found that SPDEF induces a quiescent state in CRC cells by disrupting binding of β-catenin to TCF1 and TCF3 and regulation of genes that control the cell cycle. In this model, β-catenin activity determines the proliferation or quiescence of CRC cells based on the absence or presence of SPDEF.

HBx protein-mediated ATOH1 downregulation suppresses ARID2 expression and promotes hepatocellular carcinoma

Hepatitis B virus X protein plays a crucial role in the pathogenesis of hepatocellular carcinoma. We previously showed that the tumor suppressor ARID2 inhibits hepatoma cell cycle progression and tumor growth. Here, we evaluated whether hepatitis B virus X protein was involved in the modulation of ARID2 expression and hepatocarcinogenesis associated with hepatitis B virus infection. ARID2 expression was downregulated in HBV‐replicative hepatoma cells, HBV transgenic mice, and HBV‐related clinical HCC tissues. The expression levels of HBx were negatively associated with those of ARID2 in hepatocellular carcinoma tissues. Furthermore, HBx suppressed ARID2 at transcriptional level. Mechanistically, the promoter region of ARID2 gene inhibited by HBx was located at nt‐1040/nt‐601 and contained potential ATOH1 binding elements. In addition, ectopic expression of ATOH1 or mutation of ATOH1 binding sites within ARID2 promoter partially abolished HBx‐triggered ARID2 transcriptional repression. Functionally, ARID2 abrogated HBx‐enhanced migration and proliferation of hepatoma cells, whereas depletion of ATOH1 enhanced tumorigenecity of HCC cells. Therefore, our findings suggested that deregulation of ARID2 by HBx through ATOH1 may be involved in HBV‐related hepatocellular carcinoma development.

Caudal type homeobox 2 expression induced by leukocytapheresis might be associated with mucosal healing in ulcerative colitis

BACKGROUND AND AIM

Ulcerative colitis (UC) is a chronic inflammatory disease of the colon with an intractable, recurrent course. Although the goal of UC therapy has recently been to target mucosal healing, the molecular mechanism of mucosal healing remains unknown. In this study, we aimed to elucidate the molecular dynamics related to the proliferation and differentiation of intestinal epithelial cells during cytapheresis therapy in a short duration.

METHODS

Endoscopy was performed in 26 patients with UC in multicentre hospitals, and biopsy specimens were collected from the rectum before and within two weeks after leukocytapheresis (LCAP). The expression of representative proteins in intestinal epithelial cells and pathological findings was compared before and after LCAP.

RESULTS

The expression of caudal type homeobox 2 (CDX2) and a hes family bHLH transcription factor 1(HES1) markedly increased after LCAP. Patients with endoscopic improvement after LCAP showed the expression of CDX2 before LCAP. Moreover, the number of goblet cells significantly increased after LCAP. Patients without endoscopic improvement after LCAP did not show the expression of CDX2 before LCAP. However, the expression of CDX2 markedly increased after LCAP.

CONCLUSION

This study suggests that cytapheresis might induce CDX2 expression without affecting the cell proliferation, thus resulting in mucosal healing with goblet cell restoration.

β-Catenin-Independent Roles of Wnt/LRP6 Signaling

Wnt/LRP6 signaling is best known for the β-catenin-dependent regulation of target genes. However, pathway branches have recently emerged, including Wnt/STOP signaling, which act independently of β-catenin and transcription. We review here the molecular mechanisms underlying β-catenin-independent Wnt/LRP6 signaling cascades and their implications for cell biology, development, and physiology.

MUC4 is negatively regulated through the Wnt/β-catenin pathway via the Notch effector Hath1 in colorectal cancer

MUC4 is a transmembrane mucin lining the normal colonic epithelium. The aberrant/de novo over-expression of MUC4 is well documented in malignancies of the pancreas, ovary and breast. However, studies have reported the loss of MUC4 expression in the majority of colorectal cancers (CRCs). A MUC4 promoter analysis showed the presence of three putative TCF/LEF sites, implying a possible regulation by the Wnt/β-catenin pathway, which has been shown to drive CRC progression. Thus, the objective of our study was to determine whether MUC4 is regulated by β-catenin in CRC. We first knocked down (KD) β-catenin in three CRC cell lines; LS180, HCT-8 and HCT116, which resulted in increased MUC4 transcript and MUC4 protein. Additionally, the overexpression of stabilized mutant β-catenin in LS180 and HCT-8 resulted in a decrease in MUC4 expression. Immunohistochemistry (IHC) of mouse colon tissue harboring tubular adenomas and high grade dysplasia showed dramatically reduced Muc4 in lesions relative to adjacent normal tissue, with increased cytosolic/nuclear β-catenin. Luciferase assays with the complete MUC4 promoter construct p3778 showed increased MUC4 promoter luciferase activity in the absence of β-catenin (KD). Mutation of all three putative TCF/LEF sites showed that MUC4 promoter luciferase activity was increased relative to the un-mutated promoter. Interestingly, it was observed that MUC4 expressing CRC cell lines also expressed high levels of Hath1, a transcription factor repressed by both active Wnt/β-catenin and Notch signaling. The KD of β-catenin and/or treatment with a Notch γ-secretase inhibitor, Dibenzazepine (DBZ) resulted in increased Hath1 and MUC4 in LS180, HCT-8 and HCT116. Furthermore, overexpression of Hath1 in HCT-8 and LS180 caused increased MUC4 transcript and MUC4 protein. Taken together, our results indicate that the Wnt/β-catenin pathway suppresses the Notch pathway effector Hath1, resulting in reduced MUC4 in CRC.

Destabilization of Atoh1 by E3 Ubiquitin Ligase Huwe1 and Casein Kinase 1 Is Essential for Normal Sensory Hair Cell Development

Proneural basic helix-loop-helix transcription factor, Atoh1, plays a key role in the development of sensory hair cells. We show here that the level of Atoh1 must be accurately controlled by degradation of the protein in addition to the regulation of Atoh1 gene expression to achieve normal cellular patterning during development of the cochlear sensory epithelium. The stability of Atoh1 was regulated by the ubiquitin proteasome system through the action of Huwe1, a HECT-domain, E3 ubiquitin ligase. An interaction between Huwe1 and Atoh1 could be visualized by a proximity ligation assay and was confirmed by co-immunoprecipitation and mass spectrometry. Transfer of a lysine 48-linked polyubiquitin chain to Atoh1 by Huwe1 could be demonstrated both in intact cells and in a cell-free system, and proteasome inhibition or Huwe1 silencing increased Atoh1 levels. The interaction with Huwe1 and polyubiquitylation were blocked by disruption of casein kinase 1 (CK1) activity, and mass spectrometry and mutational analysis identified serine 334 as an important phosphorylation site for Atoh1 ubiquitylation and subsequent degradation. Phosphorylation by CK1 thus targeted the protein for degradation. Development of an extra row of inner hair cells in the cochlea and an approximate doubling in the number of afferent synapses was observed after embryonic or early postnatal deletion of Huwe1 in cochlear-supporting cells, and hair cells died in the early postnatal period when Huwe1 was knocked out in the developing cochlea. These data indicate that the regulation of Atoh1 by the ubiquitin proteasome pathway is necessary for hair cell fate determination and survival.

C-kit signaling promotes proliferation and invasion of colorectal mucinous adenocarcinoma in a murine model

It was reported that the receptor tyrosine kinase (RTK) family often highly expressed in several mucinous carcinomas. In the present study, we established a murine model of colorectal mucinous adenocardinoma (CRMAC) by treating C57 mice [both wild type (WT) and loss-of-function c-kit mutant type (Wads-/-)] with AOM+DSS for 37 weeks and found that c-kit, a member of RTK family, clearly enhanced the tumor cell proliferation by decreasing p53 and increasing cyclin D1 through AKT pathway. Significantly, c-kit strongly promoted tumor cell invasiveness by increasing ETV4, which induced MMP7 expression and epithelial-mesenchymal transition (EMT) via ERK pathway. In vitro up- or down-regulating c-kit activation in human colorectal cancer HCT-116 cells further consolidated these results. In conclusion, our data suggested that the c-kit signaling obviously promoted proliferation and invasion of CRMAC. Therefore, targeting the c-kit signaling and its downstream molecules might provide the potential strategies for treatment of patients suffering from CRMAC in the future.

PAR2-dependent activation of GSK3β regulates the survival of colon stem/progenitor cells

Protease-activated receptors PAR1 and PAR2 play an important role in the control of epithelial cell proliferation and migration. However, the survival of normal and tumor intestinal stem/progenitor cells promoted by proinflammatory mediators may be critical in oncogenesis. The glycogen synthase kinase-3β (GSK3β) pathway is overactivated in colon cancer cells and promotes their survival and drug resistance. We thus aimed to determine PAR1 and PAR2 effects on normal and tumor intestinal stem/progenitor cells and whether they involved GSK3β. First, PAR1 and PAR2 were identified in colon stem/progenitor cells by immunofluorescence. In three-dimensional cultures of murine crypt units or single tumor Caco-2 cells, PAR2 activation decreased numbers and size of normal or cancerous spheroids, and PAR2-deficient spheroids showed increased proliferation, indicating that PAR2 represses proliferation. PAR2-stimulated normal cells were more resistant to stress (serum starvation or spheroid passaging), suggesting prosurvival effects of PAR2 Accordingly, active caspase-3 was strongly increased in PAR2-deficient normal spheroids. PAR2 but not PAR1 triggered GSK3β activation through serine-9 dephosphorylation in normal and tumor cells. The PAR2-triggered GSK3β activation implicates an arrestin/PP2A/GSK3β complex that is dependent on the Rho kinase activity. Loss of PAR2 was associated with high levels of GSK3β nonactive form, strengthening the role of PAR2 in GSK3β activation. GSK3 pharmacological inhibition impaired the survival of PAR2-stimulated spheroids and serum-starved cells. Altogether our data identify PAR2/GSK3β as a novel pathway that plays a critical role in the regulation of stem/progenitor cell survival and proliferation in normal colon crypts and colon cancer.

Where hearing starts: the development of the mammalian cochlea

The mammalian cochlea is a remarkable sensory organ, capable of perceiving sound over a range of 10(12) in pressure, and discriminating both infrasonic and ultrasonic frequencies in different species. The sensory hair cells of the mammalian cochlea are exquisitely sensitive, responding to atomic-level deflections at speeds on the order of tens of microseconds. The number and placement of hair cells are precisely determined during inner ear development, and a large number of developmental processes sculpt the shape, size and morphology of these cells along the length of the cochlear duct to make them optimally responsive to different sound frequencies. In this review, we briefly discuss the evolutionary origins of the mammalian cochlea, and then describe the successive developmental processes that lead to its induction, cell cycle exit, cellular patterning and the establishment of topologically distinct frequency responses along its length.

Mucins and Wnt/β-catenin signaling in gastrointestinal cancers: an unholy nexus

The Wnt/β-catenin signaling pathway is indispensable for embryonic development, maintenance of adult tissue homeostasis and repair of epithelial injury. Unsurprisingly, aberrations in this pathway occur frequently in many cancers and often result in increased nuclear β-catenin. While mutations in key pathway members, such as β-catenin and adenomatous polyposis coli, are early and frequent occurrences in most colorectal cancers (CRC), mutations in canonical pathway members are rare in pancreatic ductal adenocarcinoma (PDAC). Instead, in the majority of PDACs, indirect mechanisms such as promoter methylation, increased ligand secretion and decreased pathway inhibitor secretion work in concert to promote aberrant cytosolic/nuclear localization of β-catenin. Concomitant with alterations in β-catenin localization, changes in mucin expression and localization have been documented in multiple malignancies. Indeed, numerous studies over the years suggest an intricate and mutually regulatory relationship between mucins (MUCs) and β-catenin. In the current review, we summarize several studies that describe the relationship between mucins and β-catenin in gastrointestinal malignancies, with particular emphasis upon colorectal and pancreatic cancer.

Atonal homolog 1 protein stabilized by tumor necrosis factor α induces high malignant potential in colon cancer cell line

Patients with inflammatory bowel disease (IBD) have an increased risk of developing colitis-associated colorectal cancer (CAC). CAC cells often develop chemoresistance, resulting in a poorer prognosis than that of sporadic colorectal cancer (CRC). The mechanism by which CAC enhances malignant potential remains unknown. We have previously reported that the proteasomal degradation of the transcription factor Atonal homolog 1 (Atoh1) protein results in the non-mucinous form of CRC. It also remains unknown whether Atoh1 protein is expressed in CAC. Therefore, in the present study, we investigated whether Atoh1 protein stabilizes in CAC. Consequently, the treatment with TNF-α stabilized Atoh1 protein through the inactivation of GSK-3β via Akt, resulting in the mucinous form of CRC cell lines. Atoh1 protein also enriched cancer stem cells with upregulated Lgr5 expression and cells in G0/G1 cell cycle phase, resulting in both the chemoresistance to 5-fluorouracil and oxaliplatin and the promotion of cell migration. Immunofluorescence of the human mucinous CAC specimens showed the accumulation of NF-κB p65 at nuclei with the expression of Atoh1 in mucinous cancer. In conclusion, the inflammation associated with carcinogenesis may preserve the differentiation system of intestinal epithelial cell (IEC), resulting in the acquisition of both the mucinous phenotype and high malignant potential associated with the enrichment of cancer stem cell.

Tetramethylpyrazine inhibits the proliferation of acute lymphocytic leukemia cell lines via decrease in GSK-3β

Tetramethylpyrazine (TMP) has been proven to be an anticancer agent in many studies. However, its effectiveness in acute lymphoblastic leukemia (ALL) and its molecular mechanisms are still unclear. The present study aimed to evaluate the effect of TMP against Jurkat and SUP-B15 ALL cell lines and to investigate the possible detailed mechanism of action of TMP. A Cell Counting Kit-8 (CCK-8) assay was employed to examine the proliferation of Jurkat and SUP-B15 cells. Flow cytometric analysis was conducted to detect the cell cycle distribution and apoptotic rate. The expression of total glycogen synthase kinase-3β (GSK-3β), cox-2, survivin, bcl-2 and p27 RNA and protein levels was detected by quantitative real-time PCR and western blot assay, respectively. Additionally, western blot analysis was used to determine the whole-cell and nuclear protein levels of GSK-3β downstream transcription factors, NF-κB (p65) and c-myc. TMP inhibited the proliferation of Jurkat and SUP-B15 cells in a dose- and time-dependent manner, with IC₅₀ values of 120 and 200 µg/ml, respectively at 48 h. TMP induced the apoptosis of Jurkat and SUP-B15 cells and synergistically blocked cell cycle progression at the G0/G1 phase. Cells treated with TMP exhibited significantly attenuated GSK-3β, NF-κB (p65) and c-myc expression, followed by downregulation of bcl-2, cox-2 and survivin and an upregulation of p27. The results showed that TMP induced apoptosis and caused cell cycle arrest in Jurkat and SUP-B15 cells through the downregulation of GSK-3β, which may have further prevented the induced translocation of NF-κB and c-myc from the cytoplasm to the nucleus.

Control of hair cell development by molecular pathways involving Atoh1, Hes1 and Hes5

Atoh1, Hes1 and Hes5 are crucial for normal inner ear hair cell development. They regulate the expression of each other in a complex network, while they also interact with many other genes and pathways, such as Notch, FGF, SHH, WNT, BMP and RA. This paper summarized molecular pathways that involve Atoh1, Hes1, and Hes5. Some of the pathways and gene regulation mechanisms discussed here were studied in other tissues, yet they might inspire studies in inner ear hair cell development. Thereby, we presented a complex regulatory network involving these three genes, which might be crucial for proliferation and differentiation of inner ear hair cells.

Lineage selection and plasticity in the intestinal crypt

We know more about the repertoire of cellular behaviours that define the stem and progenitor cells maintaining the intestinal epithelium than any other renewing tissue. Highly dynamic and stochastic processes define cell renewal. Historically the commitment step in differentiation is viewed as a ratchet, irreversibly promoting a given fate and corresponding to a programme imposed at the point of cell division. However, the emerging view of intestinal self-renewal is one of plasticity in which a stem cell state is easily reacquired. The pathway mediators of lineage selection are largely known but how they interface within highly dynamic populations to promote different lineages and yet permit plasticity is not. Advances in understanding gene regulation in the nervous system suggest possible mechanisms.

The Role of Atonal Factors in Mechanosensory Cell Specification and Function

Atonal genes are basic helix-loop-helix transcription factors that were first identified as regulating the formation of mechanoreceptors and photoreceptors in Drosophila. Isolation of vertebrate homologs of atonal genes has shown these transcription factors to play diverse roles in the development of neurons and their progenitors, gut epithelial cells, and mechanosensory cells in the inner ear and skin. In this article, we review the molecular function and regulation of atonal genes and their targets, with particular emphasis on the function of Atoh1 in the development, survival, and function of hair cells of the inner ear. We discuss cell-extrinsic signals that induce Atoh1 expression and the transcriptional networks that regulate its expression during development. Finally, we discuss recent work showing how identification of Atoh1 target genes in the cerebellum, spinal cord, and gut can be used to propose candidate Atoh1 targets in tissues such as the inner ear where cell numbers and biochemical material are limiting.

Lineage-specific expression of bestrophin-2 and bestrophin-4 in human intestinal epithelial cells

Intestinal epithelial cells (IECs) regulate the absorption and secretion of anions, such as HCO3^- or Cl^-. Bestrophin genes represent a newly identified group of calcium-activated Cl^- channels (CaCCs). Studies have suggested that, among the four human bestrophin-family genes, bestrophin-2 (BEST2) and bestrophin-4 (BEST4) might be expressed within the intestinal tissue. Consistently, a study showed that BEST2 is expressed by human colonic goblet cells. However, their precise expression pattern along the gastrointestinal tract, or the lineage specificity of the cells expressing these genes, remains largely unknown. Here, we show that BEST2 and BEST4 are expressed in vivo, each in a distinct, lineage-specific manner, in human IECs. While BEST2 was expressed exclusively in colonic goblet cells, BEST4 was expressed in the absorptive cells of both the small intestine and the colon. In addition, we found that BEST2 expression is significantly down-regulated in the active lesions of ulcerative colitis, where goblet cells were depleted, suggesting that BEST2 expression is restricted to goblet cells under both normal and pathologic conditions. Consistently, the induction of goblet cell differentiation by a Notch inhibitor, LY411575, significantly up-regulated the expression of not BEST4 but BEST2 in MUC2-positive HT-29 cells. Conversely, the induction of absorptive cell differentiation up-regulated the expression of BEST4 in villin-positive Caco-2 cells. In addition, we found that the up- or down-regulation of Notch activity leads to the preferential expression of either BEST4 or BEST2, respectively, in LS174T cells. These results collectively confirmed that BEST2 and BEST4 could be added to the lineage-specific genes of humans IECs due to their abilities to clearly identify goblet cells of colonic origin and a distinct subset of absorptive cells, respectively.

SPDEF functions as a colorectal tumor suppressor by inhibiting β-catenin activity

BACKGROUND & AIMS

Expression of the SAM pointed domain containing ETS transcription factor (SPDEF or prostate-derived ETS factor) is regulated by Atoh1 and is required for the differentiation of goblet and Paneth cells. SPDEF has been reported to suppress the development of breast, prostate, and colon tumors. We analyzed levels of SPDEF in colorectal tumor samples from patients and its tumor-suppressive functions in mouse models of colorectal cancer (CRC).

METHODS

We analyzed levels of SPDEF messenger RNA and protein in more than 500 human CRC samples and more than 80 nontumor controls. Spdef(-/-)and wild-type mice (controls) were either bred with Apc(Min/+) mice, or given azoxymethane (AOM) and dextran sodium sulfate (DSS), or 1,2-dimethylhydrazine and DSS, to induce colorectal tumors. Expression of Spdef also was induced transiently by administration of tetracycline to Spdef(dox-intestine) mice with established tumors, induced by the combination of AOM and DSS or by breeding with Apc(Min/+) mice. Colon tissues were collected and analyzed for tumor number, size, grade, and for cell proliferation and apoptosis. We also analyzed the effects of SPDEF expression in HCT116 and SW480 human CRC cells.

RESULTS

In colorectal tumors from patients, loss of SPDEF was observed in approximately 85% of tumors and correlated with progression from normal tissue, to adenoma, to adenocarcinoma. Spdef(-/-); Apc(Min/+) mice developed approximately 3-fold more colon tumors than Spdef(+/+); Apc(Min/+) mice. Likewise, Spdef(-/-) mice developed approximately 3-fold more colon tumors than Spdef(+/+) mice after administration of AOM and DSS. After administration of 1,2-dimethylhydrazine and DSS, invasive carcinomas were observed exclusively in Spdef(-/-) mice. Conversely, expression of SPDEF was sufficient to promote cell-cycle exit in cells of established adenomas from Spdef(dox-intestine); Apc(Min/+) mice and in Spdef(dox-intestine) mice after administration of AOM + DSS. SPDEF inhibited the expression of β-catenin-target genes in mouse colon tumors, and interacted with β-catenin to block its transcriptional activity in CRC cell lines, resulting in lower levels of cyclin D1 and c-MYC.

CONCLUSIONS

SPDEF is a colon tumor suppressor and a candidate therapeutic target for colon adenomas and adenocarcinoma.

The Atoh1-lineage gives rise to hair cells and supporting cells within the mammalian cochlea

The organ of Corti, located within the mammalian cochlea, contains a precise mosaic of hair cells (HC) and supporting cells (SC), the patterning of which is critical for auditory function. Progenitors of HCs and SCs are found in the same post-mitotic region of the cochlear duct during early stages of cochlear development, and both HCs and SCs are absent in mice lacking the transcription factor Atoh1. Based on existing data, Atoh1 is thought to be the earliest determinant of HC fate, and to have a cell-autonomous role in HC differentiation, but the lineage of Atoh1-positive cells within the cochlear duct remains unclear. To address this issue, we used an inducible Atoh1(Cre⁎PR) allele to permanently mark Atoh1-expressing cells at different developmental time points. We found that up to 30% of cells from the Atoh1-lineage develop as SCs, and that the number of Atoh1-positive SCs decreases both spatially and temporally in a pattern consistent with ongoing commitment. Modulation of Notch signaling, necessary for formation of the HC-SC mosaic, changes the percentage of cells from the Atoh1-lineage that develop as either HCs or SCs. The HC-SC ratio is also affected by morphogenesis of the cochlea, as inhibiting the outgrowth of the cochlear duct increases the number of Atoh1-lineage cells that develop as SCs. Our results demonstrate that the Atoh1-lineage is established early in cochlear development, but also show that expression of Atoh1 does not absolutely result in commitment to a HC fate.

The acquisition of malignant potential in colon cancer is regulated by the stabilization of Atonal homolog 1 protein

The transcription factor Atonal homolog 1 (Atoh1) plays crucial roles in the differentiation of intestinal epithelium cells. Although we have reported that the Atoh1 protein was degraded in colon cancer by aberrant Wnt signaling, a recent study has indicated that the Atoh1 protein is expressed in mucinous colon cancer (MC) and signet ring cell carcinoma (SRCC). However, the roles of the Atoh1 protein in MC are unknown. To mimic MC, a mutated Atoh1 protein was stably expressed in undifferentiated colon cancer cells. Microarray analysis revealed the acquisition of not only the differentiated cell form, but also malignant potential by Atoh1 protein stabilization. In particular, Atoh1 enhanced Wnt signaling, resulting in the induction of Lgr5 as a representative stem cell marker with the enrichment of cancer stem cells. Moreover, the fluorescent ubiquitination-based cell cycle indicator system with time-lapse live imaging demonstrated cell cycle arrest in the G0/G1 phase by Atoh1 protein stabilization. In conclusion, the Atoh1 protein regulates malignant potential rather than the differentiation phenotype of MC, suggesting the mechanism by which MC and SRCC are more malignant than non-mucinous adenocarcinoma.

Epigenetic silencing of Notch signaling in gastrointestinal cancers

The Notch signaling pathway drives proliferation, differentiation, apoptosis, cell fate choices and maintenance of stem cells during embryogenesis and in self-renewing tissues of the adult. In addition, aberrant Notch signaling has been implicated in several tumors, where Notch can function both as an oncogene or a tumor-suppressor gene, depending on the context.   This Extra View aims to review what is currently known about Notch signaling, in particular in gastrointestinal tumors, providing a summary of our data on Notch1 signaling in gastric cancer with results obtained in colorectal cancer (CRC). We have already reported that the epigenetic regulation of the Notch ligand DLL1 controls Notch1 signaling activation in gastric cancer, and that Notch1 inhibition is associated with the diffuse type of gastric cancer. Here, we describe additional data showing that in CRC cell lines, unlike gastric cancer, DLL1 expression is not regulated by promoter methylation. Moreover, in CRC, Notch1 receptor is not affected by any mutation. These data suggest a different regulation of Notch1 signaling between gastric cancer and CRC.

Atonal homolog 1 expression in lung cancer correlates with inhibitors of the Wnt pathway as well as the differentiation and primary tumor stage

Atonal homolog 1 (Atoh1) is crucial to the differentiation of many cell types and participates in tumorigenesis and progression. This study investigated the role of Atoh1 in lung cancer development and its correlation with key members of the Wnt pathway. We used immunohistochemistry to examine the expressions of Atoh1, β-catenin, Axin, chibby, and Disabled-2 (Dab2) in 118 samples of lung cancer. We also detected the cytoplasmic and nuclear expression of Atoh1 in lung cancer tissues using western blot. Atoh1 nuclear expression was negatively correlated with differentiation level (p = 0.004) and primary tumor stage (p = 0.044) of lung cancer. Nuclear Atoh1 expression was positively correlated with nuclear expression of chibby (p < 0.001) and Dab2 (p < 0.001). Cytoplasmic Atoh1 expression was positively correlated with the cytoplasmic expression of Axin (p = 0.028), chibby (p < 0.001), and Dab2 (p < 0.001). We conclude that the nuclear expression of Atoh1 was inversely correlated with the differentiation and primary tumor stage of lung cancers. The expression and localization of Atoh1 correlated with Axin, chibby, or Dab2. Atoh1 may be a potential therapeutic target for the inhibition of growth and progression of lung cancers.

Implications of protein post-translational modifications in IBD

In recent years our understanding of the pathogenesis of inflammatory bowel disease (IBD) has greatly increased. Hallmarks of IBD include loss of intestinal barrier function, increased cytokine production, and failed resolution of tissue damage. Lasting treatments are still lacking and, therefore, a better understanding of the underlying molecular mechanisms is necessary to design novel therapeutic approaches. Apart from transcriptional and posttranscriptional regulation of relevant genes, mammals have evolved a complex and efficient series of mechanisms to rapidly modify newly made proteins for the purposes of signaling and adaptation. These posttranslational protein modifications include, among others, phosphorylation, hydroxylation, neddylation, and cytokine cleavage by the inflammasome. This review focuses on our current understanding of posttranslational protein modifications with a particular focus on their relevance to IBD pathogenesis.

Epigenetic regulation of Delta-Like1 controls Notch1 activation in gastric cancer

The Notch signaling pathway drives proliferation, differentiation, apoptosis, cell fate, and maintenance of stem cells in several tissues. Aberrant activation of Notch signaling has been described in several tumours and in gastric cancer (GC), activated Notch1 has been associated with de-differentiation of lineage-committed stomach cells into stem progenitors and GC progression. However, the specific role of the Notch1 ligand (DLL1) in GC has not yet been elucidated. To assess the role of DLL1 in GC cancer, the expression of Notch1 and its ligands DLL1 and Jagged1, was analyzed in 8 gastric cancer cell lines (KATOIII, SNU601, SNU719, AGS, SNU16, MKN1, MKN45, TMK1). DLL1 expression was absent in KATOIII, SNU601, SNU719 and AGS. The lack of DLL1 expression in these cells was associated with promoter hypermethylation and 5-aza-2’deoxycitidine caused up-regulation of DLL1. The increase in DLL1 expression was associated with activation of Notch1 signalling, with an increase in cleaved Notch1 intracellular domain (NICD) and Hes1, and down-regulation in Hath1. Concordantly, Notch1 signalling was activated with the overexpression of DLL1. Moreover, Notch1 signalling together with DLL1 methylation were evaluated in samples from 52 GC patients and 21 healthy control as well as in INS-GAS mice infected with H. pylori and randomly treated with eradication therapy. In GC patients, we found a correlation between DLL1 and Hes1 expression, while DLL1 methylation and Hath1 expression were associated with the diffuse and mixed type of gastric cancer. Finally, none of the samples from INS-GAS mice infected with H. pylori, a model of intestinal-type gastric tumorigenesis, showed promoter methylation of DLL1. This study shows that Notch1 activity in gastric cancer is controlled by the epigenetic silencing of the ligand DLL1, and that Notch1 inhibition is associated with the diffuse type of gastric cancer.

GSK-3 promotes cell survival, growth, and PAX3 levels in human melanoma cells

GSK-3 is a serine/threonine kinase involved in a diverse range of cellular processes. GSK-3 exists in two isoforms, GSK-3α and GSK-3β, which possess some functional redundancy but also play distinct roles depending on developmental and cellular context. In this article, we found that GSK-3 actively promoted cell growth and survival in melanoma cells, and blocking this activity with small-molecule inhibitor SB216763 or gene-specific siRNA decreased proliferation, increased apoptosis, and altered cellular morphology. These alterations coincided with loss of PAX3, a transcription factor implicated in proliferation, survival, and migration of developing melanoblasts. We further found that PAX3 directly interacted with and was phosphorylated in vitro on a number of residues by GSK-3β. In melanoma cells, direct inhibition of PAX3 lead to cellular changes that paralleled the response to GSK-3 inhibition. Maintenance of PAX3 expression protected melanoma cells from the anti-tumor effects of SB216763. These data support a model wherein GSK-3 regulates proliferation and morphology of melanoma through phosphorylation and increased levels of PAX3.

Notch signaling and intestinal cancer

In recent years, a substantial body of evidence has accumulated to support the notion that signaling pathways known to be important during embryonic development play important roles in regulating self-renewing tissues and tumorigenesis. In this context, Notch signaling is now recognized as essential for maintaining progenitor/ stem cell population as well as for regulating cell lineage differentiation in the normal intestinal mucosa. Many studies have also showed that Notch signaling is constitutively activated in colorectal cancer and its inhibition is able to suppress the cell growth and sensitize cancer cells to treatment-induced apoptosis. Therefore, discovery of the role of γ-secretase in the Notch signaling activation has prompted intensive research on the potential use of γ-secretase inhibitors in the treatment of colon cancer. This chapter reviews the current understanding and research findings of the role of Notch signaling in intestinal homeostasis and colorectal cancer and discusses the possible Notch targeting approaches as novel molecular therapy for intestinal cancer.

Suppression of hath1 gene expression directly regulated by hes1 via notch signaling is associated with goblet cell depletion in ulcerative colitis

BACKGROUND

The transcription factor Atoh1/Hath1 plays crucial roles in the differentiation program of human intestinal epithelium cells (IECs). Although previous studies have indicated that the Notch signal suppresses the differentiation program of IEC, the mechanism by which it does so remains unknown. This study shows that the undifferentiated state is maintained by the suppression of the Hath1 gene in human intestine.

METHODS

To assess the effect of Notch signaling, doxycycline-induced expression of Notch intracellular domain (NICD) and Hes1 cells were generated in LS174T. Hath1 gene expression was analyzed by quantitative reverse-transcription polymerase chain reaction (RT-PCR). Hath1 promoter region targeted by HES1 was determined by both reporter analysis and ChIP assay. Expression of Hath1 protein in ulcerative colitis (UC) was examined by immunohistochemistry.

RESULTS

Hath1 mRNA expression was increased by Notch signal inhibition. However, Hath1 expression was suppressed by ectopic HES1 expression alone even under Notch signal inhibition. Suppression of the Hath1 gene by Hes1, which binds to the 5' promoter region of Hath1, resulted in suppression of the phenotypic gene expression for goblet cells. In UC, the cooperation of aberrant expression of HES1 and the disappearance of caudal type homeobox 2 (CDX2) caused Hath1 suppression, resulting in goblet cell depletion.

CONCLUSIONS

The present study suggests that Hes1 is essential for Hath1 gene suppression via Notch signaling. Moreover, the suppression of Hath1 is associated with goblet cell depletion in UC. Understanding the regulation of goblet cell depletion may lead to the development of new therapy for UC.

Attenuation of the beta-catenin/TCF4 complex in colorectal cancer cells induces several growth-suppressive microRNAs that target cancer promoting genes

Aberrant activation of the Wnt signaling pathway is causally involved in the formation of most colorectal cancers (CRCs). Although detailed knowledge exists regarding Wnt-regulated protein-coding genes, much less is known about the possible involvement of non-coding RNAs. Here we used TaqMan Array MicroRNA Cards, capable of detecting 664 unique human microRNAs (miRNAs), to describe changes of the miRNA transcriptome following disruption of beta-catenin/TCF4 activity in DLD1 CRC cells. Most miRNAs appeared to respond independent of host gene regulation and proximal TCF4 chromatin occupancy as inferred from expression microarray and ChIP-chip data. A module of miRNAs induced by abrogated Wnt signaling in vitro was downregulated in two independent series of human primary CRCs (n=76) relative to normal adjacent mucosa (n=34). Several of these miRNAs (miR-145, miR-126, miR-30e-3p and miR-139-5p) markedly inhibited CRC cell growth in vitro when ectopically expressed. By using an integrative approach of proteomics and expression microarrays, we found numerous mRNAs and proteins to be affected by ectopic miR-30e-3p levels. This included HELZ and PIK3C2A that were directly repressed by several miRNA binding sites as confirmed by luciferase reporter assays in combination with mutational analyses. Finally, small interfering RNA-mediated downregulation of PIK3C2A, but not HELZ, was sufficient on its own to restrict CRC cell growth. Collectively, our study demonstrates that multiple miRNAs are upregulated as a consequence of forced attenuation of Wnt signaling in CRC cells, and some of these miRNAs inhibit cell growth with concomitant suppression of several growth-stimulatory cancer-related genes.

Intestinal development and differentiation

In this review, we present an overview of intestinal development and cellular differentiation of the intestinal epithelium. The review is separated into two sections: Section one summarizes organogenesis of the small and large intestines, including endoderm and gut tube formation in early embryogenesis, villus morphogenesis, and crypt formation. Section two reviews cell fate specification and differentiation of each cell type within the intestinal epithelium. Growth factor and transcriptional networks that regulate these developmental processes are summarized.

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.

NOTCH Signaling and ATOH1 in Colorectal Cancers

The Notch receptor signaling pathway regulates expression of the basic helix-loop-helix transcription factor ATOH1 (Math1/Hath1) to determine cell fate in the intestine. In differentiating intestinal stem cells, high levels of Notch activity specify absorptive enterocyte/colonocyte differentiation, whereas high ATOH1 activity specifies secretory (goblet, enteroendocrine, and Paneth) cell differentiation. In colorectal cancer, ATOH1 is a tumor suppressor that is silenced in most tumors, while Notch is oncogenic and often highly active in human tumors. In other gastrointestinal malignancies with features of intestinal metaplasia, such as esophageal and gastric cancers, the Notch-ATOH1 pathway becomes activated. In cancers and preneoplastic tissues that retain the ability to activate ATOH1, therapeutic targeting of this pathway can be achieved by inhibiting Notch activity (with Notch-targeting antibodies or small-molecule inhibitors of γ-secretase). Thus, targeting the Notch-ATOH1 pathway represents a novel approach to differentiation therapy in gastrointestinal cancers.

Longitudinal cell formation in the entire human small intestine is correlated with the localization of Hath1 and Klf4

BACKGROUND

Double balloon endoscopy (DBE) enables the observation and collection of viable specimens from the entire intestine, thereby allowing more detailed investigation of how the structure and function of the human small intestine are regulated. The present study aimed to elucidate the regulation of cell formation in the human small intestine using biopsy specimens collected from an entire individual small intestine by DBE.

METHODS

The expression and the localization of representative genes for the differentiation program were analyzed in the entire small intestine of 10 patients. The functional correlation between Hath1 and Klf4 was analyzed in an intestinal cell line by using a Tet-On system.

RESULTS

In longitudinal cell formation in the small intestine, it was shown that goblet cells, but not Paneth cells, increased toward the ileum in each individual small intestine. Immunohistochemistry showed that Hath1-expressing cells migrated from the base of the crypt to the top of the villi in the terminal ileum, while Klf4-expressing cells migrated from the top of the villus, resulting in the colocalization of Hath1 and Klf4 in the terminal ileum. Coexpression of Hath1 and Klf4 upregulated the expression of phenotypic genes for goblet cells following the downregulation of those for Paneth cells.

CONCLUSIONS

Using mapping biopsy by DBE, we have demonstrated, for the first time, the molecular basis of the villus structure in the entire human small intestine in vivo. The present study showed that longitudinal cell formation was regulated by the colocalization of Hath1 and Klf4 that converted Paneth cell differentiation into goblet cell differentiation.

Vertebrate intestinal endoderm development

The endoderm gives rise to the lining of the esophagus, stomach and intestines, as well as associated organs. To generate a functional intestine, a series of highly orchestrated developmental processes must occur. In this review, we attempt to cover major events during intestinal development from gastrulation to birth, including endoderm formation, gut tube growth and patterning, intestinal morphogenesis, epithelial reorganization, villus emergence, as well as proliferation and cytodifferentiation. Our discussion includes morphological and anatomical changes during intestinal development as well as molecular mechanisms regulating these processes.