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

The inhibition of enterocyte proliferation by lithocholic acid exacerbates necrotizing enterocolitis through downregulating the Wnt/β-catenin signalling pathway

Objectives

Necrotizing enterocolitis (NEC) is a catastrophic gastrointestinal emergency in preterm infants, whose exact aetiology remains unknown. The role of lithocholic acid (LCA), a key component of secondary bile acids (BAs), in NEC is unclear.

Methods

Clinical data were collected to analyse the changes of BAs in NEC patients. In vitro studies, the cell proliferation and cell death were assessed. In vivo experiments, the newborn rats were administered with low or high dose of LCA and further induced NEC.

Results

Clinically, compared with control group, total BAs in the NEC patients were significantly higher when NEC occurred. In vitro, LCA treatment significantly inhibited the cell proliferation through arresting cell cycle at G1/S phase without inducing apoptosis or necroptosis. Mechanistically, the Wnt/β‐catenin pathway was involved. In vivo, LCA inhibited intestinal cell proliferation leading to disruption of intestinal barrier, and thereby increased the severity of NEC. Specifically, LCA supplementation caused higher levels of FITC‐labelled dextran in serum, reduced PCNA expression and inhibited the activity of Wnt/β‐catenin pathway in enterocytes. The LC–MS/MS test found that LCA was significantly higher in intestinal tissue of NEC group, and more obviously in the NEC‐L and NEC‐H group compared with the DM group.

Conclusion

LCA exacerbates NEC by inhibiting intestinal cell proliferation through downregulating the Wnt/β‐catenin pathway.

Improved detection of tumor suppressor events in single-cell RNA-Seq data

Tissue-specific transcription factors are frequently inactivated in cancer. To fully dissect the heterogeneity of such tumor suppressor events requires single-cell resolution, yet this is challenging because of the high dropout rate. Here we propose a simple yet effective computational strategy called SCIRA to infer regulatory activity of tissue-specific transcription factors at single-cell resolution and use this tool to identify tumor suppressor events in single-cell RNA-Seq cancer studies. We demonstrate that tissue-specific transcription factors are preferentially inactivated in the corresponding cancer cells, suggesting that these are driver events. For many known or suspected tumor suppressors, SCIRA predicts inactivation in single cancer cells where differential expression does not, indicating that SCIRA improves the sensitivity to detect changes in regulatory activity. We identify NKX2-1 and TBX4 inactivation as early tumor suppressor events in normal non-ciliated lung epithelial cells from smokers. In summary, SCIRA can help chart the heterogeneity of tumor suppressor events at single-cell resolution.

Association analysis using somatic mutations

Somatic mutations drive the growth of tumor cells and are pivotal biomarkers for many cancer treatments. Genetic association analysis using somatic mutations is an effective approach to study the functional impact of somatic mutations. However, standard regression methods are not appropriate for somatic mutation association studies because somatic mutation calls often have non-ignorable false positive rate and/or false negative rate. While large scale association analysis using somatic mutations becomes feasible recently—thanks for the improvement of sequencing techniques and the reduction of sequencing cost—there is an urgent need for a new statistical method designed for somatic mutation association analysis. We propose such a method with computationally efficient software implementation: Somatic mutation Association test with Measurement Errors (SAME). SAME accounts for somatic mutation calling uncertainty using a likelihood based approach. It can be used to assess the associations between continuous/dichotomous outcomes and individual mutations or gene-level mutations. Through simulation studies across a wide range of realistic scenarios, we show that SAME can significantly improve statistical power than the naive generalized linear model that ignores mutation calling uncertainty. Finally, using the data collected from The Cancer Genome Atlas (TCGA) project, we apply SAME to study the associations between somatic mutations and gene expression in 12 cancer types, as well as the associations between somatic mutations and colon cancer subtype defined by DNA methylation data. SAME recovered some interesting findings that were missed by the generalized linear model. In addition, we demonstrated that mutation-level and gene-level analyses are often more appropriate for oncogene and tumor-suppressor gene, respectively.

Cancer is a genetic disease that is driven by the accumulation of somatic mutations. Association studies using somatic mutations is a powerful approach to identify the potential impact of somatic mutations on molecular or clinical features. One challenge for such tasks is the non-ignorable somatic mutation calling errors. We have developed a statistical method to address this challenge and applied our method to study the gene expression traits associated with somatic mutations in 12 cancer types. Our results show that some somatic mutations affect gene expression in several cancer types. In particular, we show that the associations between gene expression traits and TP53 gene level mutation reveal some similarities across a few cancer types.

CDX2 expression is concordant between primary colorectal cancer lesions and corresponding liver metastases independent of chemotherapy: a single-center retrospective study in Japan

Objective

Loss of caudal-type homeobox transcription factor 2 (CDX2) expression in colorectal cancers (CRCs) has recently been proposed as a promising predictive biomarker for not only prognosis but also response to chemotherapy. However, the relationship between alterations in CDX2 expression during cancer progression and response to chemotherapy remains unclear. We herein aimed to determine the concordance of CDX2 expression between primary CRCs and corresponding liver metastases, in association with chemotherapy.

Results

Primary CRCs exhibited heterogeneous CDX2 expression. Seven of the 144 CRCs in the cohort (4.9%, 95% confidential interval, 2.0%–9.8%) were CDX2-negative. The concordance rate of the CDX2 expression status in patients who did not receive chemotherapy was 100% (P = 0.041), whereas the concordance rate among patients who received chemotherapy only after primary resection was 96.3% (P = 0.005). Moreover, the concordance rate in patients who received chemotherapy before both primary resection and liver metastasectomy was 100% (P < 0.001).

Conclusion

CDX2 expression status was highly concordant between primary CRCs and corresponding liver metastases, independent of chemotherapy, suggesting that the CDX2 expression status in CRCs was not affected by metastasis or chemotherapy.

Methods

A total of 144 consecutive patients with CRC who were treated at a single center in Japan between 2006 and 2014 were included. Formalin-fixed paraffin-embedded whole sections of surgically resected primary CRCs and corresponding liver metastases were assessed for CDX2 expression by immunohistochemistry.

Application of unique sequence index (USI) barcode to gene expression profiling in gastric adenocarcinoma

Accurate expression profiling is imperative for understanding the biological roles of mRNAs. Real-time PCR have been at the forefront of biological innovation in detection and monitoring of gene expression, however, fluorophore-labeled oligonucleotides and double-stranded DNA binding dyes, the two most frequently used dyes in RNA detection, are not very cost effective and have poor specificity, respectively. We have developed a cost effective and specific approach for mRNA expression profiling via added unique sequence index (USI) to cDNAs before amplification. USI is a barcode which enable the detection of each target RNA. Using this method, caudal type homeobox 1 (CDX1) and FAT atypical cadherin 4 (FAT4) expressions were investigated in tumoral and non-tumoral tissues of gastric cancer patients and compared with commercial ABI kit. Both methods indicated that FAT4 and CDX1 expression were significantly reduced in gastric cancer tissues compared with adjacent noncancerous tissues. Moreover, we have shown that this assay is highly sensitive, linear and reproducible. USI barcode not only provides a powerful tool for mRNA detection due to its sensitivity, specificity and cost-effectiveness, but also allows comfortable design for real-time qPCR assays within the least time and empowers the analysis of many transcripts of virtually any organism. Furthermore, USI barcode is highly affordable for large numbers of different samples or small sample sizes without microarray and expensive commercial platforms.

Impact of homeobox genes in gastrointestinal cancer

Homeobox genes, including HOX and non-HOX genes, have been identified to be expressed aberrantly in solid tumors. In gastrointestinal (GI) cancers, most studies have focused on the function of non-HOX genes including caudal-related homeobox transcription factor 1 (CDX1) and CDX2. CDX2 is a crucial factor in the development of pre-cancerous lesions such as Barrett’s esophagus or intestinal metaplasia in the stomach, and its tumor suppressive role has been investigated in colorectal cancers. Recently, several HOX genes were reported to have specific roles in GI cancers; for example, HOXA13 in esophageal squamous cell cancer and HOXB7 in stomach and colorectal cancers. HOXD10 is upregulated in colorectal cancer while it is silenced epigenetically in gastric cancer. Thus, it is essential to examine the differential expression pattern of various homeobox genes in specific tumor types or cell lineages, and understand their underlying mechanisms. In this review, we summarize the available research on homeobox genes and present their potential value for the prediction of prognosis in GI cancers.

Computational Identification of Key Regulators in Two Different Colorectal Cancer Cell Lines

Transcription factors (TFs) are gene regulatory proteins that are essential for an effective regulation of the transcriptional machinery. Today, it is known that their expression plays an important role in several types of cancer. Computational identification of key players in specific cancer cell lines is still an open challenge in cancer research. In this study, we present a systematic approach which combines colorectal cancer (CRC) cell lines, namely 1638N-T1 and CMT-93, and well-established computational methods in order to compare these cell lines on the level of transcriptional regulation as well as on a pathway level, i.e., the cancer cell-intrinsic pathway repertoire. For this purpose, we firstly applied the Trinity platform to detect signature genes, and then applied analyses of the geneXplain platform to these for detection of upstream transcriptional regulators and their regulatory networks. We created a CRC-specific position weight matrix (PWM) library based on the TRANSFAC database (release 2014.1) to minimize the rate of false predictions in the promoter analyses. Using our proposed workflow, we specifically focused on revealing the similarities and differences in transcriptional regulation between the two CRC cell lines, and report a number of well-known, cancer-associated TFs with significantly enriched binding sites in the promoter regions of the signature genes. We show that, although the signature genes of both cell lines show no overlap, they may still be regulated by common TFs in CRC. Based on our findings, we suggest that canonical Wnt signaling is activated in 1638N-T1, but inhibited in CMT-93 through cross-talks of Wnt signaling with the VDR signaling pathway and/or LXR-related pathways. Furthermore, our findings provide indication of several master regulators being present such as MLK3 and Mapk1 (ERK2) which might be important in cell proliferation, migration, and invasion of 1638N-T1 and CMT-93, respectively. Taken together, we provide new insights into the invasive potential of these cell lines, which can be used for development of effective cancer therapy.

mRNA expression profiles in circulating tumor cells of metastatic colorectal cancer patients

INTRODUCTION

The molecular characterization of circulating tumor cells (CTCs) is a promising tool for the repeated and non-invasive evaluation of predictive and prognostic factors. Challenges associated with CTC characterization using the only FDA approved method for CTC enumeration, the CellSearch technique, include the presence of an excess of leukocytes in CTC-enriched blood fractions. Here we aimed to identify colorectal tumor-specific gene expression levels in the blood of patients with and without detectable CTCs according to CellSearch criteria.

MATERIALS AND METHODS

Blood of 30 healthy donors (HDs) and 142 metastatic colorectal cancer (mCRC) patients was subjected to CellSearch CTC enumeration and isolation. In all samples, 95 mRNAs were measured by reverse transcriptase quantitative PCR (RT-qPCR). HD blood samples and patient samples with three or more CTCs were compared to identify CTC-specific mRNAs. Patient samples without detectable CTCs were separately analyzed.

RESULTS

Thirty-four CTC-specific mRNAs were higher expressed in patients with ≥3 CTCs compared with HDs (Mann-Whitney U-test P < 0.05). Among patients without detectable CTCs, a HD-unlike subgroup was identified which could be distinguished from HDs by the expression of epithelial genes such as KRT19, KRT20 and AGR2. Also, in an independent patient set, a similar HD-unlike group could be identified among the patients without detectable CTCs according to the CellSearch system.

CONCLUSION

Extensive molecular characterization of colorectal CTCs is feasible and a subgroup of patients without detectable CTCs according to CellSearch criteria bears circulating tumor load, which may have clinical consequences. This CTC-specific gene panel for mCRC patients may enable the exploration of CTC characterization as a novel means to further individualize cancer treatment.

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

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

Intestine-specific transcription factor Cdx2 induces E-cadherin function by enhancing the trafficking of E-cadherin to the cell membrane

Cdx2 is an intestine-specific transcription factor required for normal intestinal epithelium development. Cdx2 regulates the expression of intestine-specific genes and induces cell adhesion and columnar morphogenesis. Cdx2 also has tumor-suppressor properties, including the reduction of colon cancer cell proliferation and cell invasion, the latter due to its effects on cell adhesion. E-cadherin is a cell adhesion protein required for adherens junction formation and the establishment of intestinal cell polarity. The objective of this study was to elucidate the mechanism by which Cdx2 regulates E-cadherin function. Two colon cancer cell lines were identified in which Cdx2 expression was associated with increased cell-cell adhesion and diminished cell migration. In both cell lines, Cdx2 did not directly alter E-cadherin levels but increased its trafficking to the cell membrane compartment. Cdx2 enhanced this trafficking by altering receptor tyrosine kinase (RTK) activity. Cdx2 expression diminished phosphorylated Abl and phosphorylated Rac levels, which are downstream effectors of RTKs. Specific chemical inhibition or short interfering RNA (shRNA) knockdown of c-Abl kinase phenocopied Cdx2's cell-cell adhesion effects. In Colo 205 cells, Cdx2 reduced PDGF receptor and IGF-I receptor activation. This was mediated by caveolin-1, which was induced by Cdx2. Targeted shRNA knockdown of caveolin-1 restored PDGF receptor and reversed E-cadherin membrane trafficking, despite Cdx2 expression. We conclude that Cdx2 regulates E-cadherin function indirectly by disrupting RTK activity and enhancing E-cadherin trafficking to the cell membrane compartment. This novel mechanism advances Cdx2's prodifferentiation and antitumor properties and suggests that Cdx2 may broadly regulate RTK activity in normal intestinal epithelium by modulating membrane trafficking of proteins.

Modelling Barrett's oesophagus

Barrett's oesophagus is the replacement of normal squamous oesophageal epithelium with an intestinalized columnar epithelium. Although some insight has been gained as to what Barrett's oesophagus is, how this columnar epithelium emerges from within a stratified squamous epithelium remains an unanswered question. We have sought to determine whether oesophageal keratinocytes can be trans-differentiated into Barrett's oesophagus cells. Using an Affymetrix microarray, we found unexpectedly that gene-expression patterns in the Barrett's oesophagus were only slightly more similar to the normal small intestine than they were to the normal oesophagus. Thus gene-expression patterns suggest significant molecular similarities remain between Barrett's oesophagus cells and normal squamous oesophageal epithelium, despite their histological resemblance with intestine. We next determined whether directed expression of intestine-specific transcription factors could induce intestinalization of keratinocytes. Retroviral-mediated Cdx2 (Caudal-type homeobox 2) expression in immortalized human oesophageal keratinocytes engineered with human telomerase reverse transcriptase (EPC2-hTERT cells) could be established transiently, but not maintained, and was associated with a reduction in cell proliferation. Co-expression of cyclin D1 rescued proliferation in the Cdx2-expressing cells, but co-expression of dominant-negative p53 did not. Cdx2 expression in the EPC2-hTERT.D1 cells did not induce intestinalization. However, when combined with treatments that induce chromatin remodelling, there was a significant induction of Barrett's oesophagus-associated genes. Studies are ongoing to determine whether other intestinal transcription factors, either alone or in combination, can provoke greater intestinalization of oesophageal keratinocytes. We conclude that, on the basis of gene-expression patterns, Barrett's oesophagus epithelial cells may represent an intermediate between oesophageal keratinocytes and intestinal epithelial cells. Moreover, our findings suggest that it may be possible to induce Barrett's oesophagus epithelial cells from oesophageal keratinocytes by altering the expression of certain critical genes.

Cdx genes, inflammation, and the pathogenesis of intestinal metaplasia

Intestinal metaplasia (IM) is a biologically interesting and clinically relevant condition in which one differentiated type of epithelium is replaced by another that is morphologically similar to normal intestinal epithelium. Two classic examples of this are gastric IM and Barrett's esophagus (BE). In both, a chronic inflammatory microenvironment, provoked either by Helicobacter pylori infection of the stomach or acid and bile reflux into the esophagus, precedes the metaplasia. The Caudal-related homeodomain transcription factors Cdx1 and Cdx2 are critical regulators of the normal intestinal epithelial cell phenotype. Ectopic expression of Cdx1 and Cdx2 occurs in both gastric IM as well as in BE. This expression precedes the onset of the metaplasia and implies a causal role for these factors in this process. We review the observations regarding the role of chronic inflammation and the Cdx transcription factors in the pathogenesis of gastric IM and BE.

The intestine-specific transcription factor Cdx2 inhibits beta-catenin/TCF transcriptional activity by disrupting the beta-catenin-TCF protein complex

Cdx2 is an intestine-specific transcription factor known to regulate proliferation and differentiation. We have reported previously that Cdx2 limits the proliferation of human colon cancer cells by inhibiting the transcriptional activity of the beta-catenin-T-cell factor (TCF) bipartite complex. Herein we further elucidate this mechanism. Studies with a classic Cdx2 target gene and a canonical Wnt/beta-catenin/TCF reporter suggest that Cdx2 regulates these promoters by distinctly different processes. Specifically, inhibition of beta-catenin/TCF activity by Cdx2 does not require Cdx2 transcriptional activity. Instead, Cdx2 binds beta-catenin and disrupts its interaction with the DNA-binding TCF factors, thereby silencing beta-catenin/TCF target gene expression. Using Cdx2 mutants, we map the Cdx2 domains required for the inhibition of beta-catenin/TCF activity. We identify a subdomain in the N-terminus that is highly conserved and when mutated significantly reduces Cdx2 inhibition of beta-catenin/TCF transcriptional activity. Mutation of this subdomain also abrogates Cdx2's anti-proliferative effects in colon cancer cells. In summary, we conclude that Cdx2 binds beta-catenin and disrupts the beta-catenin-TCF complex. Considering the pivotal role of beta-catenin/TCF activity in driving proliferation of normal intestinal epithelial and colon cancer cells, our findings suggest a novel mechanism for Cdx2-mediated regulation of Wnt/beta-catenin signaling and cell proliferation.

Homeobox gene CDX2 inhibits human pancreatic cancer cell proliferation by down-regulating cyclin D1 transcriptional activity

OBJECTIVES

Homeobox gene caudal related homeobox gene 2 (CDX2) is an intestine-specific tumor suppressor gene. This study is intended to investigate the effect of CDX2 expression on cell proliferation and cyclin D1 expression in pancreatic cancer cells.

METHODS

Four pancreatic ductal adenocarcinoma cell lines (PancQGO-1, BxPC-3, MIAPaCa-2, CFPAC-1), 1 islet carcinoma cell line (QGP-1), and 1 adenosquamous carcinoma cell line (KP-3) were analyzed for CDX1 and CDX2 expression using real-time reverse transcription-polymerase chain reaction and Western blot analysis. Proliferation of pancreatic cancer cells was analyzed using WST-1 assay after CDX2 transfection. Luciferase assay was performed to examine the effects of CDX2 on cyclin D1 transcriptional activity.

RESULTS

CDX2 was expressed at a significantly higher level in QGP-1 cells than in KP-3 cells. Moreover, CDX2 was expressed at a middle level in 4 pancreatic ductal adenocarcinoma cells. Cell proliferation and cyclin D1 mRNA level were inhibited significantly after CDX2 transfection in pancreatic cancer cells. Furthermore, CDX2 inhibited exogenous nuclear factor kappaB-p65-induced luciferase gene expression in a dose-dependent manner. In addition, CDX2 inhibited pGL2HIVD1kappaB2-luciferase activity.

CONCLUSIONS

CDX2 might play a role in inhibiting cell proliferation and repressing cyclin D1 transcriptional activity through the proximal nuclear factor kappaB binding site in pancreatic cancer cells.

Induction of intestinalization in human esophageal keratinocytes is a multistep process

Barrett's esophagus (BE) is the replacement of normal squamous esophageal mucosa with an intestinalized columnar epithelium. The molecular mechanisms underlying its development are not understood. Cdx2 is an intestine-specific transcription factor that is ectopically expressed in BE, but its role in this process is unclear. Herein, we describe a novel cell culture model for BE. Retroviral-mediated Cdx2 expression in immortalized human esophageal keratinocytes [EPC-human telomerase reverse transcriptase (hTERT)] could transiently be established but not maintained and was associated with a reduction in cell proliferation. Coexpression of cyclin D1, but not a dominant-negative p53, rescued proliferation in the Cdx2-expressing cells. Cdx2 expression in the EPC-hTERT.D1 cells decreased cell proliferation but did not induce intestinalization. We investigated for other treatments to enhance intestinalization and found that acidic culture conditions uniformly killed EPC-hTERT.D1.Cdx2 cells. However, treatment with 5-aza-2-deoxycytidine (5-AzaC) to demethylate epigenetically silenced genes did appear to be tolerated. Multiple Cdx2 target genes, markers of intestinal differentiation and markers of BE, were induced by this 5-AzaC treatment. More interestingly, the expression level of several of these genes was enhanced only in the EPC-hTERT.D1-Cdx2 cells treated with 5-AzaC. Two of these, SLC26a3/DRA (downregulated in adenoma) and Na+/H+ exchanger 2 (NHE2), were not previously known to be elevated in BE; however, we confirmed their elevation in BE tissue samples. 5-AzaC treatment also induced cell senescence, even at low doses. We conclude that ectopic proliferation signals, alterations in epigenetic gene regulation and the inhibition of tumor suppressor mechanisms are required for Cdx2-mediated intestinalization of human esophageal keratinocytes in BE.

The frizzled-related sFRP2 gene is a target of thyroid hormone receptor alpha1 and activates beta-catenin signaling in mouse intestine

The thyroid hormone receptor TRalpha1 regulates intestinal development and homeostasis by controlling epithelial proliferation in the crypts. This involves positive control of the Wnt/beta-catenin pathway. To further investigate the effect of thyroid hormone-TRalpha1 signaling on the intestinal epithelium proliferating compartment, we performed a comparative transcription profile analysis on laser microdissected crypt cells recovered from wild type animals with normal or perturbed hormonal status, as well as from TR knock-out mice. Statistical analysis and an in silico approach allowed us to identify 179 differentially regulated genes and to group them into organized functional networks. We focused on the "cell cycle/cell proliferation" network and, in particular, on the Frizzled-related protein sFRP2, whose expression was greatly increased in response to thyroid hormones. In vitro and in vivo analyses showed that the expression of sFRP2 is directly regulated by TRalpha1 and that it activates beta-catenin signaling via Frizzled receptors. Indeed, sFRP2 stabilizes beta-catenin, activates its target genes, and enhances cell proliferation. In conclusion, these new data, in conjunction with our previous results, indicate a complex interplay between TRalpha1 and components of the Wnt/beta-catenin pathway. Moreover, we describe in this study a novel mechanism of action of sFRP2, responsible for the activation of beta-catenin signaling.

Repression of the desmocollin 2 gene expression in human colon cancer cells is relieved by the homeodomain transcription factors Cdx1 and Cdx2

Desmosomes are intracellular junctions that provide strong cell-cell adhesion in epithelia and cardiac muscle. Their disruption causes several human diseases and contributes to the epithelial-to-mesenchymal transition observed in cancer. Desmocollin 2 (DSC2) is a cadherin superfamily member and a critical component of desmosomes found in intestinal epithelium. However, the mechanism regulating DSC2 gene expression in intestinal cells is not known. Cdx1 and Cdx2 are homeodomain transcription factors that regulate intestine-specific gene expression. Cdx expression in the past has been associated with the induction of desmosomes. We now show that the DSC2 gene is a transcriptional target for Cdx1 and Cdx2. Colon cancer cell lines retaining Cdx2 expression typically express DSC2. Restoration of Cdx expression in Colo 205 cells induced DSC2 mRNA and protein and the formation of desmosomes. The 5'-flanking region of the DSC2 promoter contains two consensus Cdx-binding sites. Electrophoretic mobility shift assays show that Cdx1 and Cdx2 bind these sites in vitro, and chromatin immunoprecipitation confirmed Cdx2 binding in vivo. DSC2 promoter truncations established that these regions are Cdx responsive. The truncations also identify a region of the promoter in which potent transcriptional repressors act. This repressor activity is relieved by Cdx binding. We conclude that the homeodomain transcription factors Cdx1 and Cdx2 regulate DSC2 gene expression in intestinal epithelia by reversing the actions of a transcriptional repressor. The regulation of desmosomal junctions by Cdx contributes to normal intestinal epithelial columnar morphology and likely antagonizes the epithelial-to-mesenchymal transition necessary for the metastasis of colon cancer cells in humans.

Frameshift mutations of Wnt pathway genes AXIN2 and TCF7L2 in gastric carcinomas with high microsatellite instability

Frameshift mutations of genes with mononucleotide repeats are features of colorectal and gastric cancers with microsatellite instability (MSI). Deregulation of Wnt pathway is involved in the mechanisms of cancer development, and mutations of the Wnt-pathway genes have frequently been detected in cancers, indicating somatic mutations are important deregulation mechanisms of the Wnt signaling in cancer development. Both AXIN2 and TCF7L2 genes in the Wnt pathway possess mononucleotide repeats in their coding sequences and are considered as candidate tumor suppressor genes. The aim of this study was to see whether AXIN2 and TCF7L2 are altered by frameshift mutations in gastric carcinomas with MSI. For this, we analyzed human AXIN2 exon 8 and TCF7L2 exon 14 in 32 gastric carcinomas with high MSI, 13 gastric carcinomas with low MSI, and 47 gastric carcinomas without MSI by a single-strand conformation polymorphism analysis. Overall, we detected 9 AXIN2 and 6 TCF7L2 frameshift mutations in the mononucleotide repeats in the cancers with MSH-H, and all of them were found in MSH-H cancers (AXIN2, 28.1%; TCF7L2, 18.8%). Of the 32 high MSI cancers, 13 cancers (40.6%) harbored at least one of AXIN2 and TCF7L2 mutation, whereas 19 cancers (59.4%) harbored neither. The present data indicate that frameshift mutations in both AXIN2 and TCF7L2 genes are common in gastric carcinomas with high MSI and suggest that these mutations may contribute to development of gastric cancers with high MSI by deregulating the Wnt signaling in the affected cancer cells.

The anti-tumour agent, cisplatin, and its clinically ineffective isomer, transplatin, produce unique gene expression profiles in human cells

Cisplatin is a DNA-damaging anti-cancer agent that is widely used to treat a range of tumour types. Despite its clinical success, cisplatin treatment is still associated with a number of dose-limiting toxic side effects. The purpose of this study was to clarify the molecular events that are important in the anti-tumour activity of cisplatin, using gene expression profiling techniques. Currently, our incomplete understanding of this drug's mechanism of action hinders the development of more efficient and less harmful cisplatin-based chemotherapeutics. In this study the effect of cisplatin on gene expression in human foreskin fibroblasts has been investigated using human 19K oligonucleotide microarrays. In addition its clinically inactive isomer, transplatin, was also tested. Dualfluor microarray experiments comparing treated and untreated cells were performed in quadruplicate. Cisplatin treatment was shown to significantly up- or down-regulate a consistent subset of genes. Many of these genes responded similarly to treatment with transplatin, the therapeutically inactive isomer of cisplatin. However, a smaller proportion of these transcripts underwent differential expression changes in response to the two isomers. Some of these genes may constitute part of the DNA damage response induced by cisplatin that is critical for its anti-tumour activity. Ultimately, the identification of gene expression responses unique to clinically active compounds, like cisplatin, could thus greatly benefit the design and development of improved chemotherapeutics.

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.

Transient stress and stress enzyme responses have practical impacts on parameters of embryo development, from IVF to directed differentiation of stem cells

In this review, we discuss the expression, regulation, downstream mechanisms, and function of stress-induced stress enzymes in mammalian oocytes, peri-implantation embryos, and the stem cells derived from those embryos. Recent reports suggest that stress enzymes mediate developmental functions during early mammalian development, in addition to the homeostatic functions shared with somatic cells. Stress-induced enzymes appear to insure that necessary developmental events occur: many of these events may occur at a slower rate, although some may occur more rapidly. Developmental events induced by stress may be mediated by a single dominant enzyme, but there are examples of responses that require the integration of more than one stress enzyme. The discussion focuses on the consequences of stress as a function of duration and magnitude, and this includes an emerging understanding of the threshold levels of duration and magnitude that lead to pathology. Other topics discussed are the reversibility of the developmental as well as homeostatic consequences of stress, the further problems with readaptation after stress subsides, and the mechanisms and functions of stress enzymes during early mammalian development. The analyses are done with specific concern for their practical impact in assisted reproductive technology (ART) and stem cell technologies.

The homeodomain transcription factors Cdx1 and Cdx2 induce E-cadherin adhesion activity by reducing beta- and p120-catenin tyrosine phosphorylation

The homeodomain transcription factors Cdx1 and Cdx2 are regulators of intestine-specific gene expression. They also regulate intestinal cell differentiation and proliferation; however, these effects are poorly understood. Previously, we have shown that expression of Cdx1 or Cdx2 in human Colo 205 cells induces a mature colonocyte morphology characterized by the induction of a polarized, columnar shape with apical microvilli and strong cell-cell adhesion. To elucidate the mechanism underlying this phenomenon, we investigated the adherens junction complex. Cdx1 or Cdx2 expression reduced Colo 205 cell migration and invasion in vitro, suggesting a physiologically significant change in cadherin function. However, Cdx expression did not significantly effect E-cadherin, alpha-, beta-, or gamma-catenin, or p120-catenin protein levels. Additionally, no alteration in their intracellular distribution was observed. Cdx expression did not alter the coprecipitation of beta-catenin with E-cadherin; however, it did reduce p120-catenin-E-cadherin coprecipitation. Tyrosine phosphorylation of beta- and p120-catenin is known to disrupt E-cadherin-mediated cell adhesion and is associated with robust p120-catenin/E-cadherin interactions. We specifically investigated beta- and p120-catenin for tyrosine phosphorylation and found that it was significantly diminished by Cdx1 or Cdx2 expression. We restored beta- and p120-catenin tyrosine phosphorylation in Cdx2-expressing cells by knocking down the expression of protein tyrosine phosphatase 1B and noted a significant decline in cell-cell adhesion. We conclude that Cdx expression in Colo 205 cells induces E-cadherin-dependent cell-cell adhesion by reducing beta- and p120-catenin tyrosine phosphorylation. Ascertaining the mechanism for this novel Cdx effect may improve our understanding of the regulation of cell-cell adhesion in the colonic epithelium.

CDX2 has tumorigenic potential in the human colon cancer cell lines LOVO and SW48

CDX2 is a Drosophila caudal-related homeobox transcription factor that is important for the establishment and maintenance of intestinal epithelial cells. CDX2 is a marker of colon cancer, with strong staining in up to 90% of colonic adenocarcinomas. CDX2 heterozygous-null mice develop colonic neoplasms, which have suggested that CDX2 is a tumor suppressor. However, CDX2 has not been reported to affect xenograft growth. Furthermore, CDX2 is rarely mutated in colon cancer, which has led to suggestions that it may play only a minor role as a tumor suppressor in colon cancer. To understand the functional contributions of CDX2 to colon cancer, we disrupted CDX2 in LOVO and SW48 human colon cancer cell lines by targeted homologous recombination. Consistent with the literature, disruption of CDX2 enhanced anchorage-dependent cell proliferation. However, homozygous loss of CDX2 led to significant inhibition of anchorage-independent growth in LOVO cells, and cell lethality in SW48 cells. Further analyses revealed that disruption of CDX2 led to anchorage-independent G1 to S growth arrest and anoikis. In vivo xenograft studies confirmed that disruption of CDX2 inhibited LOVO tumor growth. These data demonstrate that CDX2 mediates anchorage-independent growth and survival. Thus, CDX2 has tumorigenic potential in the human colon cancer cell lines LOVO and SW48.

Cdx2 modulates proliferation in normal human intestinal epithelial crypt cells

The homeobox gene Cdx2 is involved in the regulation of the expression of intestine specific markers such as sucrase-isomaltase and lactase-phlorizin hydrolase. Previous studies performed with immortalized or transformed intestinal cell lines have provided evidence that Cdx2 can promote morphological and functional differentiation in these experimental models. However, no data exist concerning the implication of this factor in normal human intestinal cell physiology. In the present work, we have investigated the role of Cdx2 in normal human intestinal epithelial crypt (HIEC) cells that lack this transcription factor. The establishment of HIEC cells expressing Cdx2 in an inducible manner shows that forced expression of Cdx2 significantly alters the proliferation of intestinal crypt cells and stimulates dipeptidylpeptidase IV expression but is not sufficient to trigger intestinal terminal differentiation. These observations suggest that Cdx2 requires additional factors to activate the enterocyte differentiation program in normal undifferentiated cells.

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.

Regulation of RELM/FIZZ isoform expression by Cdx2 in response to innate and adaptive immune stimulation in the intestine

Host immune responses to commensal flora and enteric pathogens are known to influence gene expression in the intestinal epithelium. Although the Cdx family of caudal-related transcription factors represents critical regulators of gene expression in the intestinal epithelium, the effect of intestinal immune responses on Cdx expression and function has not been determined. We have shown that bacterial colonization and Th2 immune stimulation by intestinal nematode infection induce expression of the intestinal goblet cell-specific gene RELM beta. In this study, we investigated the transcriptional regulation of resistin-like molecule/found in inflammatory zone (RELM/FIZZ, RELM beta) and its isoforms RELM alpha and RELM gamma to ascertain the role of Cdx in modifying intestinal gene expression associated with innate and adaptive immune responses. Analysis of the RELM beta promoter showed that Cdx2 plays a critical role in basal gene activation in vitro. This was confirmed in vivo using transgenic mice, where ectopic gastric and hepatic expression of Cdx2 induces expression of RELM beta, but not RELM alpha or RELM gamma, exclusively in the stomach. Although there was no quantitative change in colonic Cdx2 mRNA expression, protein distribution, or phosphorylation of Cdx2, bacterial colonization induced expression of RELM beta, but not RELM alpha or RELM gamma. In contrast, parasitic nematode infections activated colonic expression of all three RELM isoforms without alteration in Cdx2 expression. These results demonstrated that Cdx2 participates in directing intestine-specific expression of RELM beta in the presence of commensal bacteria and that adaptive Th2 immune responses to intestinal nematode infections can activate intestinal goblet cell-specific gene expression independent of Cdx2.

Recent findings in the cell and molecular biology of the small intestine

PURPOSE OF REVIEW

Recently published research exploring new aspects of the molecular and cell biology of the small intestine is reviewed.

RECENT FINDINGS

The importance has become apparent of several paracrine and autocrine signaling pathways that regulate stem cell proliferation in the crypts and differentiation on the villus. These growth factor systems include: the Wnt pathway, with molecules such as Dickkopf, APC, beta-catenin and SOX9; the Hedgehog system; and members of the TGF-beta family such as bone morphogenetic proteins. Transcription factors activating the expression of genes in the intestine include CDX1, CDX2 and HNF1alpha and their actions are increasingly well characterized. Important findings are being made relating to the Toll-like receptors, which have a major role in innate immunity and intestinal homeostasis.

SUMMARY

Many new discoveries using increasingly sophisticated techniques have demonstrated the complexity of the cellular and molecular interactions in the intestinal mucosa.

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.

Cdx1 or Cdx2 expression activates E-cadherin-mediated cell-cell adhesion and compaction in human COLO 205 cells

A mature columnar intestinal epithelium develops late in embryogenesis and is maintained throughout the life of the organism. Although the mechanisms driving intestine-specific gene expression have been well studied, those promoting the acquisition of cell-cell junctions, columnar morphogenesis, and polarization have been less studied. The Cdx homeodomain transcription factors (Cdx1 and Cdx2) regulate intestine-specific gene expression and intestinal epithelial differentiation. We report here that Cdx expression induces E-cadherin activity and cell-cell adhesion in human COLO 205 cancer cells. Within days of Cdx1 or Cdx2 expression, a new homotypic cell-cell adhesion phenotype is induced. This is a specific response to Cdx, inasmuch as a Cdx1 mutant failed to elicit the effect. Additionally, Cdx-expressing COLO 205 cells demonstrate a reduced proliferative capacity and an increase in the mRNA expression of differentiation-associated genes. Electron micrographs of these cells demonstrate induction of tight, adherens, and desmosomal junctions, as well as a columnar shape and apical microvilli. Investigations of the adhesion phenotype determined that it was Ca(2+) dependent and could be blocked by an E-cadherin-blocking antibody. However, E-cadherin protein levels and intracellular distribution were unchanged. Cdx expression restored the ability of the cell membranes to adhere and undergo compaction. We conclude that Cdx1 or Cdx2 expression is sufficient to induce an E-cadherin-dependent adhesion of COLO 205 cells. This adhesion is associated with polarization and cell-cell membrane compaction, as well as induction of a differentiated gene-expression pattern. Ascertaining the mechanism for this novel Cdx effect may yield insight into the development of mature colonic epithelium.

Cdx1 inhibits human colon cancer cell proliferation by reducing beta-catenin/T-cell factor transcriptional activity

The cessation of proliferation and the induction of differentiation are highly coordinated processes that occur continuously in the intestinal crypts. The homeodomain transcription factors Cdx1 and Cdx2 regulate intestine-specific gene expression and enterocyte differentiation. Their roles in regulating proliferation are recognized but remain poorly understood. Previously, we demonstrated that Cdx1 expression diminished the proliferation of human colon cancer cells in part by reducing cyclin D1 gene expression. In order to elucidate further the molecular mechanisms underlying this phenomenon, we first hypothesized that Cdx1 or Cdx2 expression reduces colon cancer cell proliferation by inhibiting beta-catenin/T-cell factor (TCF) transcriptional activity. We report that Cdx1 or Cdx2 expression does inhibit beta-catenin/TCF transcriptional activity in colon cancer cells. This inhibitory effect is dose-dependent and is observed in different colon cancer cell lines, and the degree of inhibition correlates with the ability of Cdx1 to reduce cell proliferation. Cdx1 expression does not alter beta-catenin protein levels or intracellular distribution nor does it induce an inhibitory TCF isoform. We also find that Cdx1 expression is lost in Min mouse polyps with increased nuclear localization of beta-catenin, suggesting that Cdx1 does not support beta-catenin-mediated transformation. Finally, we show that colon cancer cells effectively reduce Cdx2-mediated inhibition of Wnt/beta-catenin/TCF transcriptional activity when compared with other model systems. This suggests that colon cancer and possibly crypt epithelial cells can modulate the effects of Cdx2 on beta-catenin signaling and proliferation. We conclude that Cdx1 and Cdx2 inhibit colon cancer cell proliferation by blocking beta-catenin/TCF transcriptional activity.

Putative intestine-specific enhancers located in 5' sequence of the CDX1 gene regulate CDX1 expression in the intestine

CDX1 is a homeobox transcription factor that plays a critical role in intestinal epithelial cell growth and differentiation. CDX1 gene expression is tightly regulated in a temporal and cell-type specific manner. However, very little is known about the regulatory mechanisms that direct CDX1 gene expression in the intestine. To elucidate these mechanisms, we employed a series of transgenic mouse studies using the 5' flanking sequences of the human CDX1 gene. Transgenic mice containing nucleotides between -5667 and +68 relative to the transcription start site of the CDX1 gene demonstrated ectopic expression of the transgene in the brain and gastric smooth muscle. However, transgenic expression of the nucleotides -15601 to +68 of the CDX1 gene was restricted to the intestinal epithelium, which was identical to endogenous CDX1 gene expression. Taken together, the upstream sequences between -15601 and -5667 contain regulatory elements that direct transgene expression specifically to the intestinal epithelium. Furthermore, DNase I hypersensitivity assays revealed two active chromatin regions in the CDX1 gene (hypertensive sites 1 and 2) located at approximately -5.8 and -6.8 kb upstream of the CDX1 gene, respectively, which may function as potential intestine-specific enhancers.