Homeobox gene Cdx1 regulates Ras, Rho and PI3 kinase pathways leading to transformation and tumorigenesis of intestinal epithelial cells

The homeobox family gene signature predicts the prognosis of osteosarcoma and correlates with immune invasion

Osteosarcoma (OS) is a prevalent invasive bone cancer, with numerous homeobox family genes implicated in tumor progression. This study aimed to develop a prognostic model using HOX family genes to assess osteosarcoma patient outcomes. Data from osteosarcoma patients in The Cancer Genome Atlas (TCGA) and Gene Expression Omnibus (GEO) cohorts were collected. LASSO regression and multivariate COX regression analyses were employed to create and validate a risk-prognosis model in a validation cohort. Four genes (HOXA1, HOXA5, HOXA6, HOXA13) were identified to construct the risk-prognosis model. Patients were categorized into high-risk and low-risk groups, with significantly better prognosis observed in the low-risk group. A nomogram was developed to predict patients' overall survival. Variances in gene function were primarily concentrated in immune-related pathways. ssGSEA indicated that immune cell content and function were relatively deficient in the high-risk group. Notably, HOXA1 overexpression suppressed osteosarcoma cell proliferation, migration, invasion, and tumor growth. The model exhibited high accuracy and versatility, enhancing early diagnosis rates and aiding clinicians in decision-making and personalized treatment.

Characterizing therapeutic signatures of transcription factors in cancer by incorporating profiles in compound treated cells

MOTIVATION

Cancers are promoted by abnormal alterations in biological processes, such as cell cycle and apoptosis. An immediate reason for those aberrant processes is the deregulation of their involved transcription factors (TFs). Thus, the deregulated TFs in cancer have been experimented as successful therapeutic targets, such as RARA and RUNX1. This therapeutic strategy can be accelerated by characterizing new potential TF targets.

RESULTS

Two kinds of therapeutic signatures of TFs in A375 (skin) and HT29 (colon) cancer cells were characterized by analyzing TF activities under effective and ineffective compounds to cancer. First, the therapeutic TFs (TTs) were identified as the TFs that are significantly activated or repressed under effective compared to ineffective compounds. Second, the therapeutically correlated TF pairs (TCPs) were determined as the TF pairs whose activity correlations show substantial discrepancy between the effective and ineffective compounds. It was facilitated by incorporating (i)compound-induced gene expressions (LINCS), (ii) compound-induced cell viabilities (GDSC) and (iii) TF-target interactions (TRUST2). As a result, among 627 TFs, the 35 TTs (such as MYCN and TP53) and the 214 TCPs (such as FOXO3 and POU2F2 pair) were identified. The TTs and the proteins on the paths between TCPs were compared with the known therapeutic targets, tumor suppressors, oncogenes and CRISPR-Cas9 knockout screening, which yielded significant consequences. We expect that the results provide good candidates for therapeutic TF targets in cancer.

AVAILABILITY AND IMPLEMENTATION

The data and Python implementations are available at https://github.com/jmjung83/TT_and_TCP.

SUPPLEMENTARY INFORMATION

Supplementary data are available at Bioinformatics online.

Caudal-dependent cell positioning directs morphogenesis of the C. elegans ventral epidermis

Strikingly, epithelial morphogenesis remains incomplete at the end of C. elegans embryonic development; newly hatched larvae undergo extensive remodelling of their ventral epidermis during the first larval stage (L1), when newly-born epidermal cells move ventrally to complete the epidermal syncytium. Prior to this remodelling, undivided lateral seam cells produce anterior adherens junction processes that are inherited by the anterior daughter cells following an asymmetric division during L1. These adherens junction processes provide the ventral migratory route for these anterior daughters. Here, we show that these processes are perturbed in pal-1/caudal mutant animals, resulting in their inheritance by posterior, seam-fated daughters. This causes aberrant migration of seam daughter cells, disrupting the ventral epidermis. Using 4D-lineaging, we demonstrate that this larval epidermal morphogenesis defect in pal-1 mutants can be traced directly back to an initial cell positioning defect in the embryo. pal-1 expression, driven by a single intronic enhancer, is required to correctly position the seam cells in embryos such that the appropriate cell junctions support the correct migratory paths of seam daughters later in development, irrespective of their fate. Thus, during ventral epithelial remodelling in C. elegans, we show that the position of migrating cells, specified by pal-1/caudal, appears to be more important than their fate in driving morphogenesis.

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caudal/pal-1 is required to form the correct cell junctions during embryogenesis.

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Correctly placed cell junctions direct larval ventral epithelial cell migration.

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larval epithelial cell migration occurs independently of cell fate.

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Embryonic epidermal expression of pal-1 is dependent on a single intronic enhancer.

Sphingadienes show therapeutic efficacy in neuroblastoma in vitro and in vivo by targeting the AKT signaling pathway

Neuroblastoma is a childhood malignancy that accounts for approximately 15% of childhood cancer deaths. Only 20-35% of children with metastatic neuroblastoma survive with standard therapy. Identification of more effective therapies is essential to improving the outcome of children with high-stage disease. Sphingadienes (SD) are growth-inhibitory sphingolipids found in natural sources including soy. They exhibit chemopreventive activity in mouse models of colon cancer, where they mediate cytotoxicity by inhibiting key pro-carcinogenic signaling pathways. In this study, the effect of SD on neuroblastoma was analyzed. Low micromolar concentrations of SD were cytotoxic to transformed and primary neuroblastoma cells independently of N-Myc amplification status. SD induced both caspase-dependent apoptosis and autophagy in neuroblastoma cells. However, only inhibition of caspase-dependent apoptosis protected neuroblastoma cells from SD-mediated cytotoxicity. SD also inhibited AKT activation in neuroblastoma cells as shown by reduced phosphorylated AKT levels. Pre-treatment with insulin attenuated SD-mediated cytotoxicity in vitro. SD-loaded nanoparticles (NP) administered parenterally to immunodeficient mice carrying neuroblastoma xenografts resulted in cytotoxic levels of SD in the circulation and significantly reduced tumor growth compared to vehicle-treated controls. Analysis of tumor extracts demonstrated reduced AKT activation in tumors of mice treated with SD-NP compared to controls treated with empty NP. Our findings indicate SD are novel potential chemotherapeutic agents that promote neuroblastoma cell death and reduce tumorigenicity in vivo.

HOXB13 expression and promoter methylation as a candidate biomarker in gastric cancer

Homeobox b13 (HOXB13) is considered to be a tumor suppressor gene in multiple types of human cancer. The present study aimed to identify the difference in expression of HOXB13 mRNA between gastric cancer (GC) tissues and corresponding non-malignant gastric tissues. The clinical significance of HOXB13 mRNA expression was also assessed in GC and a potential association between HOXB13 mRNA expression and DNA promoter methylation was observed. The expression of HOXB13 mRNA was assessed by reverse transcription-quantitative polymerase chain reaction (RT-qPCR) and HOXB13 methylation status was assessed by methylation-specific PCR (MSP) in 5 GC cell lines and 85 paired GC and normal gastric tissues. Kaplan-Meier survival curves were used to assess the survival of patients with GC. HOXB13 mRNA expression was significantly lower in primary GC tissues than in corresponding nonmalignant gastric tissues, and decreased HOXB13 expression was associated with poorer differentiation, lymph node metastasis, invasion depth and Tumor-Node-Metastasis (TNM) stage. Kaplan-Meier survival analysis demonstrated that HOXB13 mRNA expression was a significant prognostic indicator of GC patient survival. Furthermore, MSP revealed that the proportion of GC samples with hypermethylated HOXB13 (60.0%, 51/85) was increased compared with the corresponding nonmalignant gastric tissues (11.8%, 10/85). Decreased HOXB13 mRNA expression was due to DNA hypermethylation as following treatment with the DNA methyltransferase inhibitor 5-Aza-dC, HOXB13 expression in the GC MKN-45 cell line was upregulated. The results of the present study indicate that decreased expression of HOXB13 mRNA was associated with tumor differentiation, depth of invasion, lymph node metastases and TNM stage in GC, and it was a significant poor prognostic factor for patients with GC. Aberrant DNA promoter methylation was a crucial reason for the downregulation of HOXB13 mRNA expression.

Genome-wide profiling of DNA methylation and gene expression in esophageal squamous cell carcinoma

Esophageal squamous cell carcinoma (ESCC) is the leading cause of cancer-related death worldwide. Previous studies have suggested that DNA methylation involved in the development of ESCC. However, the precise mechanisms underlying the regulation and maintenance of the methylome as well as their relationship with ESCC remain poorly understood. Herein, we used methylated DNA immunoprecipitation sequencing (MeDIP-Seq) and RNA-Seq to investigate whole-genome DNA methylation patterns and the genome expression profiles in ESCC samples. The results of MeDIP-Seq analyses identified differentially methylated regions (DMRs) covering almost the entire genome with sufficient depth and high resolution. The gene ontology (GO) analysis showed that the DMRs related genes belonged to several different ontological domains, such as cell cycle, adhesion, proliferation and apoptosis. The RNA-Seq analysis identified a total of 6150 differentially expressed genes (3423 up-regulated and 2727 down-regulated). The significant GO terms showed that these genes belonged to several molecular functions and biological pathways. Moreover, the bisulfite-sequencing of genes MLH1, CDH5, TWIST1 and CDX1 confirmed the methylation status identified by MeDIP-Seq. And the mRNA expression levels of MLH1, TWIST1 and CDX1 were consistent with their DNA methylation profiles. The DMR region of MLH1 was found to correlate with survival. The identification of whole-genome DNA methylation patterns and gene expression profiles in ESCC provides new insight into the carcinogenesis of ESCC and represents a promising avenue through which to investigate novel therapeutic targets.

Sphingosine-1-phosphate lyase downregulation promotes colon carcinogenesis through STAT3-activated microRNAs

Growing evidence supports a link between inflammation and cancer; however, mediators of the transition between inflammation and carcinogenesis remain incompletely understood. Sphingosine-1-phosphate (S1P) lyase (SPL) irreversibly degrades the bioactive sphingolipid S1P and is highly expressed in enterocytes but downregulated in colon cancer. Here, we investigated the role of SPL in colitis-associated cancer (CAC). We generated mice with intestinal epithelium-specific Sgpl1 deletion and chemically induced colitis and tumor formation in these animals. Compared with control animals, mice lacking intestinal SPL exhibited greater disease activity, colon shortening, cytokine levels, S1P accumulation, tumors, STAT3 activation, STAT3-activated microRNAs (miRNAs), and suppression of miR-targeted anti-oncogene products. This phenotype was attenuated by STAT3 inhibition. In fibroblasts, silencing SPL promoted tumorigenic transformation through a pathway involving extracellular transport of S1P through S1P transporter spinster homolog 2 (SPNS2), S1P receptor activation, JAK2/STAT3-dependent miR-181b-1 induction, and silencing of miR-181b-1 target cylindromatosis (CYLD). Colon biopsies from patients with inflammatory bowel disease revealed enhanced S1P and STAT3 signaling. In mice with chemical-induced CAC, oral administration of plant-type sphingolipids called sphingadienes increased colonic SPL levels and reduced S1P levels, STAT3 signaling, cytokine levels, and tumorigenesis, indicating that SPL prevents transformation and carcinogenesis. Together, our results suggest that dietary sphingolipids can augment or prevent colon cancer, depending upon whether they are metabolized to S1P or promote S1P metabolism through the actions of SPL.

TLR4 activates the β-catenin pathway to cause intestinal neoplasia

Colonic bacteria have been implicated in the development of colon cancer. We have previously demonstrated that toll-like receptor 4 (TLR4), the receptor for bacterial lipopolysaccharide (LPS), is over-expressed in humans with colitis-associated cancer. Genetic epidemiologic data support a role for TLR4 in sporadic colorectal cancer (CRC) as well, with over-expression favoring more aggressive disease. The goal of our study was to determine whether TLR4 played a role as a tumor promoter in sporadic colon cancer. Using immunofluorescence directed to TLR4, we found that a third of sporadic human colorectal cancers over-express this marker. To mechanistically investigate this observation, we used a mouse model that over-expresses TLR4 in the intestinal epithelium (villin-TLR4 mice). We found that these transgenic mice had increased epithelial proliferation as measured by BrdU labeling, longer colonic crypts and an expansion of Lgr5+ crypt cells at baseline. In addition, villin-TLR4 mice developed spontaneous duodenal dysplasia with age, a feature that is not seen in any wild-type (WT) mice. To model human sporadic CRC, we administered the genotoxic agent azoxymethane (AOM) to villin-TLR4 and WT mice. We found that villin-TLR4 mice showed an increased number of colonic tumors compared to WT mice as well as increased β-catenin activation in non-dysplastic areas. Biochemical studies in colonic epithelial cell lines revealed that TLR4 activates β-catenin in a PI3K-dependent manner, increasing phosphorylation of β-catenin(Ser552), a phenomenon associated with activation of the canonical Wnt pathway. Our results suggest that TLR4 can trigger a neoplastic program through activation of the Wnt/β-catenin pathway. Our studies highlight a previously unexplored link between innate immune signaling and activation of oncogenic pathways, which may be targeted to prevent or treat CRC.

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.

CDX1 confers intestinal phenotype on gastric epithelial cells via induction of stemness-associated reprogramming factors SALL4 and KLF5

Intestinal metaplasia of the stomach, a mucosal change characterized by the conversion of gastric epithelium into an intestinal phenotype, is a precancerous lesion from which intestinal-type gastric adenocarcinoma arises. Chronic infection with Helicobacter pylori is a major cause of gastric intestinal metaplasia, and aberrant induction by H. pylori of the intestine-specific caudal-related homeobox (CDX) transcription factors, CDX1 and CDX2, plays a key role in this metaplastic change. As such, a critical issue arises as to how these factors govern the cell- and tissue-type switching. In this study, we explored genes directly activated by CDX1 in gastric epithelial cells and identified stemness-associated reprogramming factors SALL4 and KLF5. Indeed, SALL4 and KLF5 were aberrantly expressed in the CDX1(+) intestinal metaplasia of the stomach in both humans and mice. In cultured gastric epithelial cells, sustained expression of CDX1 gave rise to the induction of early intestinal-stemness markers, followed by the expression of intestinal-differentiation markers. Furthermore, the induction of these markers was suppressed by inhibiting either SALL4 or KLF5 expression, indicating that CDX1-induced SALL4 and KLF5 converted gastric epithelial cells into tissue stem-like progenitor cells, which then transdifferentiated into intestinal epithelial cells. Our study places the stemness-related reprogramming factors as critical components of CDX1-directed transcriptional circuitries that promote intestinal metaplasia. Requirement of a transit through dedifferentiated stem/progenitor-like cells, which share properties in common with cancer stem cells, may underlie predisposition of intestinal metaplasia to neoplastic transformation.

The six family of homeobox genes in development and cancer

The homeobox gene superfamily encodes transcription factors that act as master regulators of development through their ability to activate or repress a diverse range of downstream target genes. Numerous families exist within the homeobox gene superfamily, and are classified on the basis of conservation of their homeodomains as well as additional motifs that contribute to DNA binding and to interactions with other proteins. Members of one such family, the Six family, form a transcriptional complex with Eya and Dach proteins, and together these proteins make up part of the retinal determination network first identified in Drosophila. This network is highly conserved in both invertebrate and vertebrate species, where it influences the development of numerous organs in addition to the eye, primarily through regulation of cell proliferation, survival, migration, and invasion. Mutations in Six, Eya, and Dach genes have been identified in a variety of human genetic disorders, demonstrating their critical role in human development. In addition, aberrant expression of Six, Eya, and Dach occurs in numerous human tumors, and Six1, in particular, plays a causal role both in tumor initiation and in metastasis. Emerging evidence for the importance of Six family members and their cofactors in numerous human tumors suggests that targeting of this complex may be a novel and powerful means to inhibit both tumor growth and progression.

Thyroid hormone regulation of stem cell development during intestinal remodeling

During amphibian metamorphosis the small intestine is remodeled from larval to adult form, analogous to the mammalian intestine. The larval epithelium mostly undergoes apoptosis, while a small number of stem cells appear, actively proliferate, and differentiate into the adult epithelium possessing a cell-renewal system. Because amphibian intestinal remodeling is completely controlled by thyroid hormone (T3) through T3 receptors (TRs), it serves as an excellent model for studying the molecular mechanism of the mammalian intestinal development. TRs bind T3 response elements in target genes and have dual functions by interacting with coactivators or corepressors in a T3-dependent manner. A number of T3 response genes have been isolated from the Xenopus laevis intestine. They include signaling molecules, matrix metalloproteinases, and transcription factors. Functional studies have been carried out on many such genes in vitro and in vivo by using transgenic and culture technologies. Here we will review recent findings from such studies with a special emphasis on the adult intestinal stem cells, and discuss the evolutionarily conserved roles of T3 in the epithelial cell-renewal in the vertebrate intestine.

Six1 overexpression in mammary cells induces genomic instability and is sufficient for malignant transformation

Homeoproteins are transcription factors that act as master regulators of development and are frequently dysregulated in cancers. During embryogenesis, the Six1 homeoprotein is essential for the expansion of precursor cell populations that give rise to muscle and kidney, among other organs. Six1 overexpression is observed in numerous cancers, resulting in increased proliferation, survival, and metastasis. Here, we investigate whether Six1 can play a causal role in mammary tumor initiation. We show that Six1 overexpression in MCF12A mammary epithelial cells promotes multiple properties associated with malignant transformation, including increased proliferation, genomic instability, and anchorage-independent growth. We further show that this transformation is dependent on up-regulation of its transcriptional target, cyclin A1, which is normally expressed in the embryonic mammary gland but dramatically reduced in the adult gland. Six1-transformed MCF12A cells are tumorigenic in nude mice, forming aggressive tumors that are locally invasive and exhibit peritumoral lymphovascular invasion. In human breast carcinomas, expression of Six1 and cyclin A1 mRNA correlate strongly with each other (P < 0.0001), and expression of Six1 and cyclin A1 each correlate with Ki67, a marker of proliferation (P < 0.0001 and P = 0.014, respectively). Together, our data indicate that Six1 overexpression is sufficient for malignant transformation of immortalized, nontumorigenic mammary epithelial cells, and suggest that the mechanism of this transformation involves inappropriate reexpression of cyclin A1 in the adult mammary gland.

The homeodomain transcription factor Cdx1 does not behave as an oncogene in normal mouse intestine

The Caudal-related homeobox genes Cdx1 and Cdx2 are intestine-specific transcription factors that regulate differentiation of intestinal cell types. Previously, we have shown Cdx1 to be antiproliferative and to promote cell differentiation. However, other studies have suggested that Cdx1 may be an oncogene. To test for oncogenic behavior, we used the murine villin promoter to ectopically express Cdx1 in the small intestinal villi and colonic surface epithelium. No changes in intestinal architecture, cell differentiation, or lineage selection were observed with expression of the transgene. Classic oncogenes enhance proliferation and induce tumors when ectopically expressed. However, the Cdx1 transgene neither altered intestinal proliferation nor induced spontaneous intestinal tumors. In a murine model for colitis-associated cancer, the Cdx1 transgene decreased, rather than increased, the number of adenomas that developed. In the polyps, the expression of the endogenous and the transgenic Cdx1 proteins was largely absent, whereas endogenous Villin expression was retained. This suggests that transgene silencing was specific and not due to a general Villin inactivation. In conclusion, neither the ectopic expression of Cdx1 was associated with changes in intestinal cell proliferation or differentiation nor was there increased intestinal cancer susceptibility. Our results therefore suggest that Cdx1 is not an oncogene in normal intestinal epithelium.

Regeneration of the amphibian intestinal epithelium under the control of stem cell niche

The epithelium of the mammalian digestive tract originates from stem cells and undergoes rapid cell-renewal throughout adulthood. It has been proposed that the microenvironment around the stem cells, called 'niche', plays an important role in epithelial cell-renewal through cell-cell and cell-extracellular matrix interactions. The amphibian intestine, which establishes epithelial cell-renewal during metamorphosis, serves as a unique and good model for studying molecular mechanisms of the stem cell niche. By using the organ culture of the Xenopus laevis intestine, we have previously shown that larval-to-adult epithelial remodeling can be organ-autonomously induced by thyroid hormone (TH) and needs interactions with the surrounding connective tissue. Thus, in this animal model, the functional analysis of TH response genes is useful for clarifying the epithelial-connective tissue interactions essential for intestinal remodeling at the molecular level. Recent progress in culture and transgenic technology now enables us to investigate functions of such TH response genes in the X. laevis intestine and sheds light on molecular aspects of the stem cell niche that are common to the mammalian intestine.

Lineage dependency and lineage-survival oncogenes in human cancer

Although cell-lineage and differentiation models dominate tumour classification and treatment, the recognition that cancer is also a genomic disease has prompted a reconfiguration of cancer taxonomies according to molecular criteria. Recent evidence indicates that a synthesis of lineage-based and genetic paradigms might offer new insights into crucial and therapeutically pliable tumour dependencies. For example, MITF (microphthalmia-associated transcription factor), which is a master regulator of the melanocyte lineage, might become a melanoma oncogene when deregulated in certain genetic contexts. MITF and other lineage-survival genes therefore implicate lineage dependency (or lineage addiction) as a newly recognized mechanism that is affected by tumour genetic alterations.

The related retinoblastoma (pRb) and p130 proteins cooperate to regulate homeostasis in the intestinal epithelium

pRb, p107, and p130 are related proteins that play a central role in the regulation of cell cycle progression and terminal differentiation in mammalian cells. Nevertheless, it is still largely unclear how these proteins achieve this regulation in vivo. The intestinal epithelium is an ideal in vivo system in which to study the molecular pathways that regulate proliferation and differentiation because it exists in a constant state of development throughout an animal's lifetime. We studied the phenotypic effects on the intestinal epithelium of mutating Rb and p107 or p130. Although mutating these genes singly had little or no effect, loss of pRb and p107 or p130 together produced chronic hyperplasia and dysplasia of the small intestinal and colonic epithelium. In Rb/p130 double mutants this hyperplasia was associated with defects in terminal differentiation of specific cell types and was dependent on the increased proliferation seen in the epithelium of mutant animals. At the molecular level, dysregulation of the Rb pathway led to an increase in the expression of Math1, Cdx1, Cdx2, transcription factors that regulate proliferation and differentiation in the intestinal epithelium. The absence of Cdx1 function in Rb/p130 double mutant mice partially reverted the histologic phenotype by suppressing ectopic mitosis in the epithelium. These studies implicate the Rb pathway as a regulator of epithelial homeostasis in the intestine.

Differential regulation of intestinal alkaline phosphatase gene expression by Cdx1 and Cdx2

We have examined the role that the caudal-related homeobox transcription factors Cdx1 and Cdx2 play in activating the enterocyte differentiation marker gene intestinal alkaline phosphatase (IAP). Human colon cancer Caco-2 cells were transiently transfected with Cdx1 and/or Cdx2, and semiquantitative RT-PCR was used to study the effects on IAP mRNA expression. Transfections with a variety of IAP-luciferase reporter constructs were used to identify a Cdx response element located within the human IAP gene promoter. Protein-DNA interactions were examined by EMSA. Results showed that Cdx1 markedly induced IAP mRNA expression, whereas Cdx2 did not, and, in fact, inhibited the Cdx1 effects. Functional analysis revealed that Cdx1 transactivates (fourfold, P < 0.05) the IAP promoter through a novel Cdx response element (GTTTAGA) located between -2369 and -2375 upstream of the translational start site. EMSA showed that both Cdx1 and Cdx2 could bind to the cis element, but in cotransfection experiments, Cdx2 inhibited the Cdx1 effects by approximately 50%. Thus we have identified a previously unrecognized interaction between two important gut transcription factors, Cdx1 and Cdx2, in the context of IAP gene regulation. Cdx1 activates the IAP gene via a novel cis element, whereas Cdx2 inhibits the Cdx1 effects.

Twists and turns in the development and maintenance of the mammalian small intestine epithelium

Experimental studies during the last decade have revealed a number of signaling pathways that are critical for the development and maintenance of the intestinal epithelium and that demonstrate the molecular basis for a variety of diseases. The Notch-Delta, Wnt, Hedge Hog, TGF-beta, and other signaling pathways have been shown to form and steadily maintain the crypt-villus system, generating the proper quantities of highly-specialized cells, and ultimately defining the architectural shape of the system. Based on the characterized phenotypes and functional defects of mice resulting from various targeted knockouts, and overexpression and misexpressions of genes, a picture is emerging of the sequence of gene expression events from within the epithelium, and in the underlying mesenchyme that contribute to the regulation of cell differentiation and proliferation. This review focuses on the contributions of multiple signaling pathways to intestinal epithelial proliferation, differentiation, and structural organization, as well as the possible opportunities for cross-talk between pathways. The Notch pathway's potential ability to maintain and regulate the intestinal epithelial stem cell is discussed, in addition to its role as the primary mediator of lineage specification. Recent research that has shed light on the function of Wnt signaling and epithelial-mesenchymal cross-talk during embryonic and postnatal development is examined, along with data on the interplay of heparan sulfate proteoglycans in the signaling process.

Morphological and transcriptional responses of untransformed intestinal epithelial cells to an oncogenic β-catenin protein

Aberrant transactivation of a certain set of target genes by the beta-catenin and T-cell factor/lymphoid enhancer factor (TCF/LEF) transcription factor complexes has been implicated in the process of intestinal epithelial cells entering early colorectal carcinogenesis. A rat intestinal epithelial cell line IEC6 became elongated, extended protrusions at cell periphery, and increased stress fibers and focal contacts upon the induction of beta-catenin protein stabilized by deletion of the N-terminal glycogen synthase kinase-3beta (GSKbeta) phosphorylation sites (beta-catenin DeltaN89). We used the GeneChiptrade mark oligonucleotide microarray system to examine approximately 24 000 genes and identified 13 genes whose expression was altered during the course of this morphological transformation. Those genes included known negative regulators of the Wnt signaling pathway, Sfrp4 and Axin2; extracellular matrix and related molecule, Hxb and Crtl1; cell adhesion and cytoskeletal proteins, Podxl, Igaf4, and Itab6; and molecules involved in the insulin and insulin-like growth factor (IGF) signaling pathways, Enpp1, Igfbp2, and Sgk. We report the finding that insulin-like growth factor-binding protein-2 (IGFBP2) is a direct target gene of the beta-catenin and TCF/LEF complexes. The IGFBP2 protein interacts with integrins. Disruption of the multigene network system regulating cell adhesion and cytoskeleton may be crucial in the initiation of colorectal carcinogenesis.

Epithelial-Connective Tissue Cross-Talk Is Essential for Regeneration of Intestinal Epithelium

Epithelial cells of the gastrointestine undergo a rapid cell-renewal and originate from stem cells throughout the life of the organisms. Previous studies have provided a solid body of evidence to show that the epithelial cell-renewal is under the strict control of cell-cell and cell-extracellular matrix (ECM) interactions between the epithelium and the connective tissue. Especially, the microenvironment around the stem cells called "niche" is thought to play important roles in this control, and its disruption leads to diseases or disorders such as cancer in the human gastrointestine. Although understanding how the niche affects the stem cells is clinically important, its mechanisms still remain mostly unknown at the molecular level, possibly due to difficulties in the identification of the stem cells in the gastrointestine. Recent progress in cell and molecular biology is gradually beginning to shed light on some of the key signaling pathways in the cell-renewal of the intestinal epithelium, such as Wnt/T-cell factor (TCF)/beta-catenin, Notch, Sonic hedgehog (Shh)/bone morphogenetic protein (BMP) signaling pathways, which are also involved in embryonic organogenesis and/or adult carcinogenesis. At present, only fragmentary information is available on their precise functions in the intestine. Nevertheless, there is a growing body of evidence that such signaling pathways have conservative functions in the intestine throughout terrestrial vertebrates, suggesting the usefulness of experimental animals to clarify molecular mechanisms regulating epithelial cell-renewal. In this article, I review some recent findings in this field, with particular focus on our studies using the Xenopus laevis intestine, where the stem cells form the mammalian-type intestinal epithelium under the control of connective tissue during metamorphosis. This Xenopus experimental system will certainly serve as a useful model for the study of the intestinal niche, whose clarification is urgently needed in regenerative medicine.

CDX1 expression is reduced in colorectal carcinoma and is associated with promoter hypermethylation

The CDX1 homeobox gene encodes a transcription factor specifically expressed in normal intestinal and colonic epithelia, and CDX1 gene expression is affected during colorectal tumour progression. In this study, real-time quantitative RT-PCR was used to investigate CDX1 expression in 26 colorectal carcinomas. Reduced expression of CDX1 was observed in 19 of 26 colon carcinomas compared to matched normal colonic mucosa: the decrease in CDX1 expression ranged between 0.10 and 0.79 (21-90% decrease; mean 64.75% +/-22; p = 0.001). Mutation and loss of heterozygosity (LOH) analyses were then used to determine if reduced CDX1 expression was due to genetic alteration. No CDX1 gene mutations, but two known polymorphisms in exon 1, were observed. LOH was observed in 33% of the tumours investigated but this was not related to CDX1 expression. Since aberrant promoter methylation is a well-known mechanism that participates in gene silencing, the methylation status of the CDX1 5' CpG island promoter was also investigated. PCR amplification of bisulphite-treated DNA followed by cloning was performed in 7 carcinomas that showed low expression of CDX1 and in 1 colonic carcinoma without reduced expression. Promoter hypermethylation occurred in carcinomas in which CDX1 reduced expression was present. These results suggest that CDX1 promoter hypermethylation is one of the molecular mechanisms that accounts for reduced CDX1 gene expression in colorectal carcinoma.

Reduction of menin expression enhances cell proliferation and is tumorigenic in intestinal epithelial cells

Menin, the product of the tumor suppressor gene MEN1, is widely expressed in mammalian endocrine and non-endocrine tissues, including intestine. Its known abundant expression in several types of cells with high proliferative capacity led us to investigate the physiological function of the protein menin in intestinal epithelium, one of the most rapidly growing epithelia. Here we showed that the Men1 gene is mainly expressed in the crypt compartment of the proximal small intestine and that its expression was increased during fasting in vivo, both suggesting a role of menin in the control of cell growth. Indeed, specific reduction of menin expression by transfected antisense cDNA in the rat duodenal crypt-like cell line, IEC-17, increased cell proliferation. The latter is correlated to a loss of cell-cycle arrest in G(1) phase by resting cells and an overexpression of cyclin D1 and cyclin-dependent kinase (Cdk)-4. Furthermore, these cells lost the inhibition of proliferation induced by transforming growth factor-beta1, associated with a decrease of transforming growth factor-beta type II receptor expression. As a result of deregulated proliferation, antisense menin transfected IEC-17 cells became tumorigenic as shown in vitro as well as in vivo in immunosuppressed animals. These results indicate that menin contributes to proliferation control in intestinal epithelial cells. The present study reveals an unknown physiological function for menin in intestine that may be important in the regulation of epithelial homeostasis.

Oct-3/4 is a dose-dependent oncogenic fate determinant

The Oct-3/4 transcription factor sustains embryonic stem (ES) cell self-renewal and is a dose-dependent cell fate determinant. In the adult male, its expression is restricted to type A spermatogonia. We show that Oct-3/4 is expressed in all human testicular germ cell tumors (GCTs) tested, even in the early premalignant component. We demonstrate that Oct-3/4 dictates ES cells' oncogenic potential in a dose-dependent manner; high levels increase the malignant potential of ES cell-derived tumors while Oct-3/4 inactivation induces regression of the malignant component. Oct-3/4 expression in a heterologous cell system transforms nontumorigenic cells and endows tumorigenicity in nude mice. Our findings suggest that Oct-3/4 is not only a distinctive immunohistochemical marker for GCTs, but also plays a critical role in the genesis of these tumors.

Cdx1 inhibits the proliferation of human colon cancer cells by reducing cyclin D1 gene expression

The transcription factor Cdx1 regulates intestine-specific gene expression and enterocyte differentiation. It has been hypothesized to play a role in regulating intestinal cell proliferation; however, the mechanism for this effect remains elusive. In a prior study, we demonstrated that Cdx1 expression reduced the proliferation of a nontransformed intestinal cell line. This study tests the hypothesis that Cdx1 expression inhibits colon cancer cell proliferation by reducing cyclin D1 gene expression. Cdx1 expression markedly reduced cancer cell proliferation and DNA synthesis and induced an accumulation of cells in G0/G1. A transcriptionally inactive Cdx1 mutant could not elicit this effect, suggesting that it required Cdx1 transcriptional activity. Cdx1 expression increased the hypophosphorylation of the retinoblastoma (pRb) and p130 proteins. Reductions in G1 cyclin-dependant kinase (cdk) activity accompanied this effect. Cyclin D1 mRNA and protein levels were diminished by Cdx1 expression. Restoration of cyclin D1 expression reversed the G0/G1 block and induced pRb hyperphosphorylation. Lastly, Cdx1 expression did not alter cyclin D1 mRNA stability but did reduce cyclin D1 promoter activity, suggesting that Cdx1 acts to diminish cyclin D1 gene transcription. We conclude that Cdx1 reduces the proliferation of human colon cancer cells by reducing cyclin D1 gene transcription.

Cdx1 homeobox gene during human colon cancer progression

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

Effect of gastrin on differentiation of rat intestinal epithelial cells in vitro

AIM: To investigate the effect of gastrin on differentiation of IEC-6 cell line in vitro.

METHODS: IEC-6 cells were incubated with gastrin. On day 7 after treatment, cell morphology was examined by light microscope, and on day 20, the cellular ultrastructures were examined by electron microscope. After exposure to gastrin for 6 hours, villin mRNA was analyzed by reverse transcription-polymerase chain reaction, and on day 7, the expression of villin was examined by immunocytochemical analysis with laser confocal microscope.

RESULTS: After exposure to gastrin, IEC-6 cells showed differentiated phenotypes as villas enterocytes and contained an abundance of plasma, small nuclei with nucleoli, and were arranged regularly. There were numerous microvilli around edge of the cells, and several cells showed columnar structures. Villin mRNA expression in cytoplasm was increased in comparison with control.

CONCLUSION: Differentiated characteristics of villus enterocytes and phenotypic changes of rat intestinal epithelial cells (IEC-6) are induced by gastrin, and the effects of gastrin are correlated to increased villin expression.

Molecular and cellular biology of small intestinal differentiation, gene expression and hormonal responses

Many recent publications have looked at the function of the small intestine at the molecular and cellular level. Hundreds of genes are expressed predominantly in the gastrointestinal tract and many are found in only one segment. The developmental interactions between mesenchymal and epithelial cells are now better understood, as are the processes that determine the fate of the products of the stem cell division. The pattern of the principal transcription factors that regulate the expression of genes in the intestine is becoming clearer. The mechanism of action of hormones and growth factors on the intestine is the subject of considerable research, especially concerning the glucagon-like peptides and epidermal growth factor. Genomic factors, which can affect nutritional requirements by altering intestinal function, will be increasingly recognized.

Human growth hormone-regulated HOXA1 is a human mammary epithelial oncogene

Increased mammary epithelial expression of the human growth hormone (hGH) gene is associated with the acquisition of pathological proliferation. We report here that autocrine hGH production by human mammary carcinoma cells increased the expression and transcriptional activity of the homeobox domain containing protein HOXA1. Forced expression of HOXA1 in human mammary carcinoma cells resulted in increased total cell number primarily by the promotion of cell survival mediated by the transcriptional up-regulation of Bcl-2. HOXA1 also abrogated the apoptotic response of mammary carcinoma cells to doxorubicin. Forced expression of HOXA1 in mammary carcinoma cells, in a Bcl-2-dependent manner, resulted in dramatic enhancement of anchorage-independent proliferation and colony formation in soft agar. Finally, forced expression of HOXA1 was sufficient to result in the oncogenic transformation of immortalized human mammary epithelial cells with aggressive in vivo tumor formation. Herein, we have therefore provided a molecular mechanism by which autocrine hGH stimulation of human mammary epithelial cells may result in oncogenic transformation.

Developmental regulation of apolipoprotein B mRNA editing is an autonomous function of small intestine involving homeobox gene Cdx1

Apolipoprotein B mRNA editing is developmentally regulated in the human and rodent small intestine, changing from <1% at day 14 to approximately 90% by day 20 in the rat fetus. This regulation is coincident with the developmental formation of the crypt-to-villus axis functional unit, a continuous and rapidly renewing system involving cell generation, migration, and differentiation. Utilizing small intestine isografts implanted into the subcutaneous tissue of adult recipients, apolipoprotein B mRNA editing was developmentally up-regulated, parallel to that seen with an intact control. In contrast, apoB mRNA expression remains nearly constant in the isograft, unlike the normal intact small intestine. Immunohistochemical analyses demonstrated that apoB-48 protein existed predominantly in well differentiated enterocytes along the villus surface whereas apoB-100 was in the lamina propria and crypts. ApoB mRNA editing levels were very low in the crypt-like rat intestinal cell line, IEC-6 ( approximately 0.3%), but very high in well differentiated enterocytes ( approximately 91.5%). The expression of homeobox gene Cdx1 increased 18-fold in small intestine in vivo during the same time course when apoB mRNA editing increased from approximately 2 to approximately 90%. The overexpression of Cdx1 in IEC-6 cells increased apoB mRNA editing over 10-fold compared with the vector control. This increase was associated with a significant increase of activating factor ACF, a component of the apoB mRNA editing complex. Taken together, these data suggest that the developmental regulation of apoB mRNA editing is an autonomous cytodifferentiation function of small intestine for which homeobox gene Cdx1 may play an important role.

The homeobox gene Cdx1 belongs to the p53-p21(WAF)-Bcl-2 network in intestinal epithelial cells

Because the Cdx1 homeobox gene stimulates proliferation and induces transformation and tumorigenesis, it has been investigated whether it is involved in the complex network comprising p53, p21(WAF), and Bcl-2 in intestinal epithelial cells. Non-transformed intestinal IEC-6 cells and colon adenocarcinoma SW480 cells were used to study the putative molecular relationship between Cdx1, p53, p21(WAF), and Bcl-2. Wild-type p53 inhibited the transcriptional activity of the Cdx1 promoter whereas the inactive mutant p53(mut22/23) had no effect. Induction of Cdx1 expression had no direct effect on p53 expression and activity. However, it inhibited the transcriptional activity of the p21(WAF) promoter through Cdx1 binding to the p21(WAF) TATA-box and increased the transcriptional activity of the Bcl-2 promoter P2 through a consensus Cdx-binding site. Finally, compared to control cells, Cdx1-overexpressing cells were more resistant to adriamycin-induced apoptosis, probably because they do not show concomitant decrease in endogenous Bcl-2 level. In conclusion, Cdx1 is a negatively regulated target of p53 in intestinal cells. Its regulation of p21(WAF) and Bcl-2 is opposite to that of p53 and is p53-independent. Cdx1 belongs to the regulatory networks of apoptosis, proliferation, and differentiation. These results emphasize the oncogenic potential of Cdx1.

Opposing effects of Krüppel-like factor 4 (gut-enriched Krüppel-like factor) and Krüppel-like factor 5 (intestinal-enriched Krüppel-like factor) on the promoter of the Krüppel-like factor 4 gene

KLF4 (Krüppel-like factor 4 or gut-enriched Krüppel-like factor, GKLF) and KLF5 (Krüppel-like factor 5 or intestinal-enriched Krüppel-like factor, IKLF) are two closely related members of the zinc finger-containing Krüppel-like factor family of transcription factors. Although both genes are expressed in the intestinal epithelium, their distributions are different: Klf4 is primarily expressed in the terminally differentiated villus cells while Klf5 is primarily in the proliferating crypt cells. Previous studies show that Klf4 is a negative regulator of cell proliferation and Klf5 is a positive regulator of cell proliferation. In this study, we demonstrate that Klf5 binds to a number of cis-DNA elements that have previously been shown to bind to Klf4. However, while Klf4 activates the promoter of its own gene, Klf5 suppresses the Klf4 promoter. Moreover, Klf5 abrogates the activating effect of Klf4 on the Klf4 promoter and Klf4 abrogates the inhibitory effect of Klf5 on the same promoter. An explanation of this competing effect is due to physical competition of the two proteins for binding to cognate DNA sequence. The complementary tissue localization of expression of Klf4 and Klf5 and the opposing effect of the two Klfs on the Klf4 promoter activity may provide a basis for the coordinated regulation of expression of the Klf4 gene in the intestinal epithelium.

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

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