The caudal-related homeodomain protein Cdx1 inhibits proliferation of intestinal epithelial cells by down-regulation of D-type cyclins

HOXA5 inhibits adipocytes proliferation through transcriptional regulation of Ccne1 and blocking JAK2/STAT3 signaling pathway in mice

The highly regulated proliferation of adipocytes plays a momentous role in fat development and obesity. Hoxa5 is an important member of Hox family, its encoded protein is an important transcription factor related to development. And its differential expression in different adipose tissues seems to indicate that Hoxa5 may be involved in the regulation of adipocyte proliferation. In order to evaluate the regulation mechanism of Hoxa5 on adipocyte proliferation, we constructed a variety of Hoxa5 expression vectors in vivo and in vitro to explore its mechanism on adipocyte proliferation and its potential impact on obesity. We have observed that the overexpression of Hoxa5 strongly reduces cell counts, and Hoxa5 can inhibit cell proliferation and block cell cycle progression by regulating the expression of genes such as Cyclin E, Cycling D1 and p53. Most importantly, we demonstrated that Hoxa5 exerts its effect by regulating the signaling pathway of Janus kinase 2 (JAK2) signal transduction and transcription 3 (STAT3) activator, as well as binding to the promoter region of Ccne1 and inhibiting the transcription of Ccne1.This study provides an in-depth understanding of the potential molecular mechanism of Hoxa5 inhibiting adipocyte proliferation. Our results suggest the importance of Hoxa5 in the treatment of obesity.

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

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

Math1/Atoh1 contributes to intestinalization of esophageal keratinocytes by inducing the expression of Muc2 and Keratin-20

BACKGROUND

Esophageal intestinal metaplasia, also known as Barrett's esophagus, is the replacement of the normal epithelium with one that resembles the intestine morphologically. Generally, this includes intestinal mucin-secreting goblet cells. Barrett's esophagus is an important risk factor for adenocarcinoma development. In-vitro models for Barrett's esophagus have not, to date, focused on the induction of goblet cells in Barrett's epithelium.

AIMS

To explore the contribution of Math1/Atoh1 to induction of Barrett's esophagus and intestinal mucin-secreting goblet cells from normal human esophageal epithelium.

METHODS

We explored the level and pattern of Math1/Atoh1 mRNA and protein expression in human Barrett's esophagus. Then, using retroviral-mediated gene expression, we induced Math1 mRNA and protein expression in a human esophageal keratinocyte cell line. We evaluated the effects of this ectopic Math1 expression on cell proliferation and gene expression patterns in cells cultured under two-dimensional and three-dimensional tissue-engineering conditions.

RESULTS

Math1/Atoh1 mRNA and protein are detected in human Barrett's esophagus specimens, but the mRNA levels vary substantially. In the keratinocyte expression studies, we observed that Math1/Atoh1 ectopic expression significantly reduced cell proliferation and altered cell morphology. Moreover, Math1/Atoh1 expression is associated with a more intestinalized gene expression pattern that is distinct from that reported in after studies using other intestinal transcription factors. Most significantly, we observe the induction of the Barrett's esophagus markers Mucin-2 and Keratin-20 with Math1/Atoh1 expression.

CONCLUSIONS

We conclude that ectopic Math1/Atoh1 expression makes unique contributions to intestinalization of the esophageal epithelium in Barrett's esophagus.

Cox2 and β-catenin/T-cell factor signaling intestinalize human esophageal keratinocytes when cultured under organotypic conditions

The incidence of esophageal adenocarcinoma (EAC) is rising in the United States. An important risk factor for EAC is the presence of Barrett esophagus (BE). BE is the replacement of normal squamous esophageal epithelium with a specialized columnar epithelium in response to chronic acid and bile reflux. However, the emergence of BE from squamous keratinocytes has not yet been demonstrated. Our research has focused on this. Wnt and cyclooxygenase 2 (Cox2) are two pathways whose activation has been associated with BE and progression to EAC, but their role has not been tested experimentally. To explore their contribution, we engineered a human esophageal keratinocyte cell line to express either a dominant-active Wnt effector CatCLef or a Cox2 complementary DNA. In a two-dimensional culture environment, Cox2 expression increases cell proliferation and migration, but neither transgene induces known BE markers. In contrast, when these cells were placed into three-dimensional organotypic culture conditions, we observed more profound effects. CatCLef-expressing cells were more proliferative, developed a thicker epithelium, and upregulated Notch signaling and several BE markers including NHE2. Cox2 expression also increased cell proliferation and induced a thicker epithelium. More importantly, we observed cysts form within the epithelium, filled with intestinal mucins including Muc5B and Muc17. This suggests that Cox2 expression in a three-dimensional culture environment induces a lineage of mucin-secreting cells and supports an important causal role for Cox2 in BE pathogenesis. We conclude that in vitro modeling of BE pathogenesis can be improved by enhancing Wnt signaling and Cox2 activity and using three-dimensional organotypic culture conditions.

Ectopic Cdx2 expression in murine esophagus models an intermediate stage in the emergence of Barrett's esophagus

Barrett's esophagus (BE) is an intestinal metaplasia that occurs in the setting of chronic acid and bile reflux and is associated with a risk for adenocarcinoma. Expression of intestine-specific transcription factors in the esophagus likely contributes to metaplasia development. Our objective was to explore the effects of an intestine-specific transcription factor when expressed in the mouse esophageal epithelium. Transgenic mice were derived in which the transcription factor Cdx2 is expressed in squamous epithelium using the murine Keratin-14 gene promoter. Effects of the transgene upon cell proliferation and differentiation, gene expression, and barrier integrity were explored. K14-Cdx2 mice express the Cdx2 transgene in esophageal squamous tissues. Cdx2 expression was associated with reduced basal epithelial cell proliferation and altered cell morphology. Ultrastructurally two changes were noted. Cdx2 expression was associated with dilated space between the basal cells and diminished cell-cell adhesion caused by reduced Desmocollin-3 mRNA and protein expression. This compromised epithelial barrier function, as the measured trans-epithelial electrical resistance (TEER) of the K14-Cdx2 epithelium was significantly reduced compared to controls (1189 Ohm*cm(2) ±343.5 to 508 Ohm*cm(2)±92.48, p = 0.0532). Secondly, basal cells with features of a transitional cell type, intermediate between keratinocytes and columnar Barrett's epithelial cells, were observed. These cells had reduced keratin bundles and increased endoplasmic reticulum levels, suggesting the adoption of secretory-cell features. Moreover, at the ultrastructural level they resembled "Distinctive" cells associated with multilayered epithelium. Treatment of the K14-Cdx2 mice with 5'-Azacytidine elicited expression of BE-associated genes including Cdx1, Krt18, and Slc26a3/Dra, suggesting the phenotype could be advanced under certain conditions. We conclude that ectopic Cdx2 expression in keratinocytes alters cell proliferation, barrier function, and differentiation. These altered cells represent a transitional cell type between normal squamous and columnar BE cells. The K14-Cdx2 mice represent a useful model to study progression from squamous epithelium to BE.

Pathophysiology of intestinal metaplasia of the stomach: emphasis on CDX2 regulation

IM (intestinal metaplasia) of the stomach is a pre-neoplastic lesion that usually follows Helicobacter pylori infection and that confers increased risk for gastric cancer development. After setting the role played by CDX2 (Caudal-type homeobox 2) in the establishment of gastric IM, it became of foremost importance to unravel the regulatory mechanisms behind its de novo expression in the stomach. In the present paper, we review the basic pathology of gastric IM as well as the current knowledge on molecular pathways involved in CDX2 regulation in the gastric context.

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.

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.

Intestine-specific expression of green fluorescent protein-tagged cathepsin B: proof-of-principle experiments

We hypothesized that tissue-specific expression of cathepsin B-enhanced green fluorescent protein (CB-EGFP) can be driven by the A33-antigen promoter that contains positive cis-regulatory elements, including caudal-related homeobox (CDX) binding sites. The intestine-specific transcription factor Cdx1 is crucial for A33-antigen promoter activation and could thereby induce expression of CB-EGFP. This concept was tested by construction of the vector pA33-CathB-EGFP encoding CB-EGFP downstream of the A33-antigen promoter. Its Cdx1 dependence, as an indication of its intestine-specific expression, was tested in Cdx1-negative CHO-K1 cells. Cdx1 expression was achieved upon transfection with pCdx1-DsRed-Express and was indicated by red fluorescence of the simultaneously translated reporter protein. Immunolabeling with Cdx1-specific antibodies showed correct targeting of the transcription factor to its point of action in nuclei of transfected cells. Co-transfection experiments with plasmids pA33-CathB-EGFP and pCdx1-DsRed-Express confirmed the hypothesis that Cdx1 indeed activates CB-EGFP expression in a manner dependent on the A33-antigen promoter. Co-localization with compartment-specific markers and subcellular fractionation confirmed CB-EGFP trafficking along the expected route to endolysosomal compartments. Hence, the A33-antigen promoter represents a potent tool for induction of Cdx1-dependent CB-EGFP expression in vitro. Our proof-of-principle studies confirm the suitability of this approach in visualizing protease transport in Cdx1-positive tissues of the gastrointestinal tract.

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.

Cdx1, a dispensable homeobox gene for gut development with limited effect in intestinal cancer

The homeobox gene Cdx1 is involved in anteroposterior patterning in embryos and its expression selectively persists in the intestinal epithelium throughout life. In human colon cancers, Cdx1 is overexpressed in few cases and lost in the majority of adenocarcinomas. We used mouse models of gain and loss-of-function to investigate the role of Cdx1 in intestinal development and cancers. Transgenic mice overexpressing Cdx1 and knockout mice exhibited a morphologically normal intestine. Cell proliferation, specification into the four differentiated lineages and migration along the crypt-villus axis were unchanged compared to wild-type mice. Changing Cdx1 caused an inverse and dose-dependent modification of the expression of the paralogous gene Cdx2, indicating that Cdx1 fine-tunes Cdx2 activity. Transgenenic and knockout mice failed to spontaneously develop tumours. Overexpressing Cdx1 was without incidence on the frequency of intestinal tumours induced chemically by azoxymethane treatment or genetically in Apc(Delta14/+) mice. However, it augmented the severity of the tumours in Apc(Delta14/+) mice. Inversely, the loss-of-function of Cdx1 in knockout mice was without incidence on the growth of tumours induced by azoxymethane. We conclude that Cdx1 is dispensable for intestinal development and that its overexpression could increase malignancy in early stages of tumourigenesis.

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.

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.

The human mucin MUC4 is transcriptionally regulated by caudal-related homeobox, hepatocyte nuclear factors, forkhead box A, and GATA endodermal transcription factors in epithelial cancer cells

The human gene MUC4 encodes a large transmembrane mucin that is developmentally regulated and expressed along the undifferentiated pseudostratified epithelium, as early as 6.5 weeks during fetal development. Immunohistochemical analysis of Muc4 expression in developing mouse lung and gastrointestinal tract showed a different spatio-temporal pattern of expression before and after cytodifferentiation. The molecular mechanisms governing MUC4 expression during development are, however, unknown. Hepatocyte nuclear factors (HNF), forkhead box A (FOXA), GATA, and caudal-related homeobox transcription factors (TFs) are known to control cell differentiation of gut endoderm derived-tissues during embryonic development. They also control the expression of cell- and tissue-specific genes and may thus control MUC4 expression. To test this hypothesis, we studied and deciphered the molecular mechanisms responsible for MUC4 transcriptional regulation by these TFs. Experiments using small interfering RNA, cell co-transfection, and site-directed mutagenesis indicated that MUC4 is regulated at the transcriptional level by CDX-1 and -2, HNF-1 alpha and -1 beta, FOXA1/A2, HNF-4 alpha and -4 gamma, and GATA-4, -5, and -6 factors in a cell-specific manner. Binding of TFs was assessed by chromatin immunoprecipitation, and gel-shift assays. Altogether, these results demonstrate that MUC4 is a target gene of endodermal TFs and thus point out an important role for these TFs in regulating MUC4 expression during epithelial differentiation during development, cancer, and repair.

A functional role of Cdx2 in beta-catenin signaling during transdifferentiation in endometrial carcinomas

Nuclear beta-catenin is required for changes in morphology from glandular to morular phenotypes of endometrial carcinoma (Em Ca) cells, with activation of p14(ARF)/p53/p21(Waf1) and alteration of p16(INK4A)/pRb pathways. Having demonstrated previously that the homeodomain transcription factor Cdx2 increases markedly during intestinal epithelial cell differentiation, we have examined its effects in beta-catenin signaling during transdifferentiation of Em Ca cells. In clinical cases, Cdx2 immunoreactivity, along with increased mRNA signals, was found to overlap with nuclear accumulation of beta-catenin and p21(Waf1) in morules, demonstrating an inverse correlation with cell proliferation. In cell lines, over-expression of active form beta-catenin resulted in a significant increase in endogenous Cdx2 expression at both mRNA and protein levels. Furthermore, the Cdx2 promoter was activated by T-cell factor 4 (TCF4) -independent activated beta-catenin, as well as Cdx2 itself, through the region from -39 to +9 bp relative to transcription start site. Cells over-expressing exogenous Cdx2 showed high levels of p21(Waf1) expression due to stabilization of the mRNA status, resulting in significant decrease in the proliferation rate, in contrast to the lack of apparent changes in morphology. Moreover, transfected Cdx2 could inhibit beta-catenin/TCF4-mediated transcriptional activation of target genes, including p14(ARF) and cyclin D1, probably through indirect mechanisms. These data suggest that over-expression of Cdx2 mediated by nuclear beta-catenin and Cdx2 itself can cause an inhibition of Em Ca cell proliferation through up-regulation of p21(Waf1) expression, modulating beta-catenin/TCF4-mediated transcription. We therefore conclude that an association between Cdx2 and beta-catenin signaling may participate in induction of transdifferentiation of Em Ca cells.

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.

Thyroid hormone receptor alpha1 directly controls transcription of the beta-catenin gene in intestinal epithelial cells

Thyroid hormones, T3 and T4, are known regulators of intestine development. The best characterized example is the remodeling of the gastrointestinal tract during amphibian metamorphosis. Thyroid hormones act via nuclear receptors, the TRs, which are T3-dependent transcription factors. We previously showed that intestinal epithelial cell proliferation is controlled by thyroid hormones and the TRalpha gene. To analyze the mechanisms responsible, we studied the expression of genes belonging to and/or activated by the Wnt/beta-catenin pathway, a major actor in the control of physiological and pathological epithelial proliferation in the intestine. We show that T3-TRalpha1 controls the transcription of the beta-catenin gene in an epithelial cell-autonomous way. This is parallel to positive regulation of proliferation-controlling genes such as type D cyclins and c-myc, known targets of the Wnt/beta-catenin. In addition, we show that the regulation of the beta-catenin gene is direct, as TR binds in vitro and in chromatin in vivo to a specific thyroid hormone-responsive element present in intron 1 of this gene. This is the first report concerning in vivo transcriptional control of the beta-catenin gene. As Wnt/beta-catenin plays a crucial role in intestinal tumorigenesis, our observations open a new perspective on the study of TRs as potential tumor inducers.

A consensus Oct1 binding site is required for the activity of the Xenopus Cdx4 promoter

Cdx homeodomain transcription factors have multiple roles in early vertebrate development. Furthermore, mis-regulation of Cdx expression has been demonstrated in metaplasias and cancers of the gut epithelium. Given the importance of Cdx genes in development and disease, the mechanisms underlying their expression are of considerable interest. We report an analysis of the upstream regulatory regions from the amphibian Xenopus laevis Cdx4 gene. We show that a GFP reporter containing 2.8 kb upstream of the transcription start site is expressed in the posterior of transgenic embryos. Deletion analysis of the upstream sequence reveals that a 247-bp proximal promoter fragment will drive posterior expression in transgenic embryos. We show that 63 bp of upstream sequence, that includes a consensus site for POU-domain octamer-binding proteins, retains significant promoter activity. Co-expression of the octamer-binding protein Oct1 induces expression from a Cdx4 reporter and mutation of the octamer site abolishes activity of the same reporter. We show that the octamer site is highly conserved in the promoters of the human, mouse, chicken, and zebrafish Cdx4 genes and within the promoters of amphibian Cdx1 and Cdx2. These data suggest a conserved function for octamer-binding proteins in the regulation of Cdx family members.

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.

The Short Stature Homeodomain Protein SHOX Induces Cellular Growth Arrest and Apoptosis and Is Expressed in Human Growth Plate Chondrocytes

Mutations in the homeobox gene SHOX cause growth retardation and the skeletal abnormalities associated with Léri-Weill, Langer, and Turner syndromes. Little is known about the mechanism underlying these SHOX-related inherited disorders of bone formation. Here we demonstrate that SHOX expression in osteogenic stable cell lines, primary oral fibroblasts, and primary chondrocytes leads to cell cycle arrest and apoptosis. These events are associated with alterations in the expression of several cellular genes, including pRB, p53, and the cyclin kinase inhibitors p21(Cip1) and p27(Kip1). A SHOX mutant, such as seen in Léri-Weill syndrome patients, does not display these activities of the wild type protein. We have also shown that endogenous SHOX is mainly expressed in hypertrophic/apoptotic chondrocytes of the growth plate, strongly suggesting that the protein plays a direct role in regulating the differentiation of these cells. This study provides the first insight into the biological function of SHOX as regulator of cellular proliferation and viability and relates these cellular events to the phenotypic consequences of SHOX deficiency.

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.

The tumor suppressor adenomatous polyposis coli and caudal related homeodomain protein regulate expression of retinol dehydrogenase L

Development of normal colon epithelial cells proceeds through a systematic differentiation of cells that emerge from stem cells within the base of colon crypts. Genetic mutations in the adenomatous polyposis coli (APC) gene are thought to cause colon adenoma and carcinoma formation by enhancing colonocyte proliferation and impairing differentiation. We currently have a limited understanding of the cellular mechanisms that promote colonocyte differentiation. Herein, we present evidence supporting a lack of retinoic acid biosynthesis as a mechanism contributing to the development of colon adenomas and carcinomas. Microarray and reverse transcriptase-PCR analyses revealed reduced expression of two retinoid biosynthesis genes: retinol dehydrogenase 5 (RDH5) and retinol dehydrogenase L (RDHL) in colon adenomas and carcinomas as compared with normal colon. Consistent with the adenoma and carcinomas samples, seven colon carcinoma cell lines also lacked expression of RDH5 and RDHL. Assessment of RDH enzymatic activity within these seven cell lines showed poor conversion of retinol into retinoic acid when compared with normal cells such as normal human mammary epithelial cells. Reintroduction of wild type APC into an APC-deficient colon carcinoma cell line (HT29) resulted in increased expression of RDHL without affecting RDH5. APC-mediated induction of RDHL was paralleled by increased production of retinoic acid. Investigations into the mechanism responsible for APC induction of RDHL indicated that beta-catenin fails to repress RDHL. The colon-specific transcription factor CDX2, however, activated an RDHL promoter construct and induced endogenous RDHL. Finally, the induction of RDHL by APC appears dependent on the presence of CDX2. We propose a novel role for APC and CDX2 in controlling retinoic acid biosynthesis and in promoting a retinoid-induced program of colonocyte differentiation.

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.

Transcriptional control of the cell cycle in mammary gland development and tumorigenesis

Over the past several years it has become increasingly evident that normal development and cancer share many properties. Both processes involve alterations in cell proliferation and differentiation, cell death, neovascularization, and cell motility and invasion. Thus, genes involved in normal development are frequently utilized in neoplasia. During development, numerous transcriptional regulatory mechanisms are used to ensure tight control over cellular proliferation. In this review we focus on a number of transcription factor families (homeobox, STAT, and Ets), and on inhibitors of transcription factors (Id), which have been implicated in controlling the cell cycle not only in normal mammary gland development but also in breast tumorigenesis.

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.

Control of gut differentiation and intestinal-type gastric carcinogenesis

Gastric cancer is one of the world's most common cancers. Its carcinogenic pathway is mainly associated with Helicobacter pylori infection, subsequent inflammation and tissue regeneration. During the regeneration process, cells deviate from the normal pathway of gastric differentiation to an 'intestinal phenotype', which is thought to be precancerous and associated with the intestinal type of gastric cancer. Inappropriate activation of intestine-specific transcription factors could contribute to the occurrence of the intestinal-type cancer of the stomach.

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 proline-rich homeodomain protein, PRH, is a tissue-specific inhibitor of eIF4E-dependent cyclin D1 mRNA transport and growth

The translation initiation factor eIF4E is involved in the modulation of cellular growth. In the nucleus, where eIF4E is associated with PML nuclear bodies, eIF4E mediates nucleocytoplasmic transport of specific transcripts, and this contributes to its transformation activity. Surprisingly, we found that a trans cription factor, the proline-rich homeodomain protein PRH, is a negative regulator of eIF4E in myeloid cells, interacting with eIF4E through a conserved binding site typically found in translational regulators. Through this interaction, PRH inhibits eIF4E-dependent mRNA transport and subsequent transformation. These activities of PRH are independent of its transcriptional functions. Further, we found that 199 homeodomain proteins contain potential eIF4E-binding sites. Thus, there could be many tissue-specific regulators of eIF4E. These findings provide a model for regulation of a general factor, eIF4E, in tissue- specific contexts, and suggest that its regulation is important in differentiation and development.

GeneChip microarrays facilitate identification of Protease Nexin-1 as a target gene of the Prx2 (S8) homeoprotein

The paired-related homeobox genes, Prx1 and Prx2, are important for normal skeletal and cardiovascular development as well as adult vascular remodeling. The identification and characterization of Prx downstream targets is crucial to understanding their function in normal developmental processes and congenital malformations. To identify Prx2 regulated genes, stably transfected NIH3T3 clones expressing Prx2 sense or antisense transcripts were generated. Expression profiles initially were established for two of the clones using Affymetrix GeneChip arrays. Over 6,400 genes were screened by the microarray approach, and approximately 500 genes differed in expression by a factor of two or more. Fifteen genes were chosen for further analysis. RT-PCR of the two transfectants used in the GeneChip analysis demonstrated that five out of the 15 genes were differentially expressed. However, after screening additional stable transfectant clones only one of the 15 genes, Protease Nexin-1 (PN-1), was differentially expressed. Subsequent Northern blot, RT-PCR, and further GeneChip analysis of additional stable transfectants confirmed that PN-1 expression is increased at least fivefold when Prx2 is overexpressed. It was demonstrated that Prx2 directly regulates PN-1 because (1) Prx2 binds to a cis element in the PN-1 promoter in vitro, and (2) Prx2 regulates the PN-1 promoter in transient transfection assays. The GeneChip analysis generated a prioritized list of other potential targets. The utility and limitations of cell culture models combined with microarray analysis for elucidating complex regulatory cascades are discussed.

The caudal homeodomain protein activates Drosophila E2F gene expression

The Drosophila caudal homeobox gene is required for definition of the anteroposterior axis and for gut development, and CDX1 and CDX2, human homologs, play crucial roles in the regulation of cell proliferation and differentiation in the intestine. Most studies have indicated tumor suppressor functions of Cdx2, with inhibition of proliferation, while the effects of Cdx1 are more controversial. The influence of Drosophila Caudal on cell proliferation is unknown. In this study, we found three potential Caudal binding sequences in the 5'-flanking region of the Drosophila E2F (DE2F) gene and showed by transient transfection assays that they are involved in Caudal transactivation of the dE2F gene promoter. Analyses with transgenic flies carrying an E2F-lacZ fusion gene, with and without mutation in the Caudal binding site, indicated that the Caudal binding sites are required for expression of dE2F in living flies. Caudal-induced E2F expression was also confirmed with a GAL4-UAS system in living flies. In addition, ectopic expression of Caudal with heat-shock promotion induced melanotic tumors in larvae. These results suggest that Caudal is involved in regulation of proliferation through transactivation of the E2F gene in Drosophila.

Cell cycle inhibition by FoxO forkhead transcription factors involves downregulation of cyclin D

The FoxO forkhead transcription factors FoxO4 (AFX), FoxO3a (FKHR.L1), and FoxO1a (FKHR) represent important physiological targets of phosphatidylinositol-3 kinase (PI3K)/protein kinase B (PKB) signaling. Overexpression or conditional activation of FoxO factors is able to antagonize many responses to constitutive PI3K/PKB activation including its effect on cellular proliferation. It was previously shown that the FoxO-induced cell cycle arrest is partially mediated by enhanced transcription and protein expression of the cyclin-dependent kinase inhibitor p27(kip1) (R. H. Medema, G. J. Kops, J. L. Bos, and B. M. Burgering, Nature 404:782-787, 2000). Here we have identified a p27(kip1)-independent mechanism that plays an important role in the antiproliferative effect of FoxO factors. Forced expression or conditional activation of FoxO factors leads to reduced protein expression of the D-type cyclins D1 and D2 and is associated with an impaired capacity of CDK4 to phosphorylate and inactivate the S-phase repressor pRb. Downregulation of D-type cyclins involves a transcriptional repression mechanism and does not require p27(kip1) function. Ectopic expression of cyclin D1 can partially overcome FoxO factor-induced cell cycle arrest, demonstrating that downregulation of D-type cyclins represents a physiologically relevant mechanism of FoxO-induced cell cycle inhibition.

DNA methylation down-regulates CDX1 gene expression in colorectal cancer cell lines

CDX1 is a homeobox protein that inhibits proliferation of intestinal epithelial cells and regulates intestine-specific genes involved in differentiation. CDX1 expression is developmentally and spatially regulated, and its expression is aberrantly down-regulated in colorectal cancers and colon cancer-derived cell lines. However, very little is known about the molecular mechanism underlying the regulation of CDX1 gene expression. In this study, we characterized the CDX1 gene structure and identified that its gene promoter contained a typical CpG island with a CpG observed/expected ratio of 0.80, suggesting that the CDX1 gene is a target of aberrant methylation. Alterations of DNA methylation in the CDX1 gene promoter were investigated in a series of colorectal cancer cell lines. Combined Bisulfite Restriction Analysis (COBRA) and bisulfite sequencing analysis revealed that the CDX1 promoter is methylated in CDX1 non-expressing colorectal cancer cell lines but not in human normal colon tissue and T84 cells, which express CDX1. Treatment with 5'-aza-2'-deoxycytidine (5-azaC), a DNA methyltransferase inhibitor, induced CDX1 expression in the colorectal cancer cell lines. Furthermore, de novo methylation was determined by establishing stably transfected clones of the CDX1 promoter in SW480 cells and demethylation by 5-azaC-activated reporter gene expression. These results indicate that aberrant methylation of the CpG island in the CDX1 promoter is one of the mechanisms that mediate CDX1 down-regulation in colorectal cancer cell lines.

Cloning of the human claudin-2 5'-flanking region revealed a TATA-less promoter with conserved binding sites in mouse and human for caudal-related homeodomain proteins and hepatocyte nuclear factor-1alpha

Claudin-2 is a structural component of tight junctions in the kidneys, liver, and intestine, but the mechanisms regulating its expression have not been defined. The 5'-flanking region of the claudin-2 gene contains binding sites for intestine-specific Cdx homeodomain proteins and hepatocyte nuclear factor (HNF)-1, which are conserved in human and mouse. Both Cdx1 and Cdx2 activated the claudin-2 promoter in the human intestinal epithelial cell line Caco-2. HNF-1alpha augmented the Cdx2-induced but not Cdx1-induced transcriptional activation of the human claudin-2 promoter. In mice, HNF-1alpha was required for claudin-2 expression in the villus epithelium of the ileum and within the liver but not in the kidneys, indicating an organ-specific function of HNF-1alpha in the regulation of claudin-2 gene expression. Tight junction structural components, which determine epithelial polarization and intestinal barrier function, can be regulated by homeodomain proteins that control the differentiation of the intestinal epithelium.

Ectopic expression of homeodomain protein CDX2 in intestinal metaplasia and carcinomas of the stomach

The roles of CDX2 and CDX1 homeobox genes during gastric carcinogenesis remain poorly defined. We have studied the expression of CDX2/1 in gastric cancers and intestinal metaplasia (IM) of 69 gastric carcinoma patients by immunohistochemistry. CDX2/1 were shown to be ectopically overexpressed in IM in 41 (85%) of 48, and 47 (90%) of 52 cases, respectively. The expression of CDX2/1 was detected in 38 (55%) and 51 (74%) of the 69 gastric carcinomas, respectively. The histological type of the gastric carcinomas was independently associated with CDX2 expression, but not with that of CDX1, with higher CDX2 expression in intestinal type (differentiated type) than in diffuse type (undifferentiated type) gastric carcinomas. Our results thus suggest that CDX2 and CDX1 may play a role during IM formation and gastric carcinogenesis.

Phosphorylation of the serine 60 residue within the Cdx2 activation domain mediates its transactivation capacity

BACKGROUND & AIMS

Cdx2 is critical in intestinal proliferation and differentiation. Modulation of Cdx2 function in response to cellular signaling is to be elucidated. We hypothesize that phosphorylation of the Cdx2 activation domain can modulate its function.

METHODS

The Cdx2 activation domain was delineated in transient transfections using different portions of Cdx2 fused to the Gal4-DNA binding domain. In vivo phosphorylation was studied by metabolic labeling with (32)P-orthophosphate. To study a potential phosphorylation site, polyclonal antibodies were generated: CNL was raised against amino acids 54-66 of Cdx2 and P-Cdx2-S60 against the same epitope in which serine 60 was phosphorylated.

RESULTS

A critical region for transactivation resides within amino acids 60-70. Substitution of serine 60 with alanine reduces incorporation of (32)P-orthophosphate substantially. S60-phosphorylation decreases Cdx2 transactivation. Phosphorylation of serine 60 can be inhibited with the mitogen-activated protein kinase inhibitors PD98059 or UO126. P-Cdx2-S60 recognizes phosphorylated serine 60 mainly in proliferative compartment of the intestinal epithelial layer. In contrast, CNL recognizes Cdx2 predominantly in the differentiated compartment.

CONCLUSIONS

The Cdx2 activation domain is phosphorylated at serine 60 via the mitogen-activated protein kinase pathway. S60-phosphorylated and S60-nonphosphorylated Cdx2 have different transcriptional activity, as well as different spatial expression patterns in the intestinal epithelium.

Expression of homeobox-containing genes in cDNA libraries derived from cattle oocytes and preimplantation stage embryo

The homeobox-containing gene family plays a pivotal role in regulating, patterning, and axial morphogenesis in the developing embryo. But there is still very little known about the expression and function of these genes in mammalian oocytes and preimplantation stage embryos. In this study we have used degenerate primers corresponding to the highly conserved regions of Antennapedia class homeodomains as a rapid and an efficient method to survey bovine cDNA libraries derived from unfertilised oocytes, single 2-cell, 4-cell, 8-cell, morula, and blastocyst stage embryos for the presence of homeobox sequences. Our results provide, for the first time, evidence for the transcription of Hoxa3 and Hoxd1 in oocytes; Cdx1 and Cdx2 in the 2-cell; Cdx1, Hoxa1, Hoxd1, and Hoxd4 in the 4-cell; Cdx1, Hoxa1, and Hoxc9 in the 8-cell; Cdx2, Hoxb9, and Hoxc9 in the morula; Cdx2, Hoxb7, Hoxb9, and Hoxc9 in blastocyst stage cattle embryos. These are candidate genes for the developmental capacity of in vivo and in vitro produced bovine embryos.

CDX-1 and CDX-2 are expressed in human colonic mucosa and are down-regulated in patients with Hirschsprung's disease associated enterocolitis

Caudal type homeobox gene-1 and -2 (CDX-1 and CDX-2), homologues of the Drosophila homeobox gene caudal, encode transcription factors in endoderm derived tissues of the intestine. CDX genes control proliferation and differentiation of intestinal mucosal cells and colon cancer cells. Hirschsprung's Disease (HD) or congenital intestinal aganglionosis, a major developmental anomaly of intestine, which causes functional intestinal obstruction, is frequently associated with enterocolitis. Aetiology of HD-associated enterocolitis (HDEC) remains obscure. Reduction of gut mucosal enteroendocrine cells, and inefficient transfer of the secretory immunoglobulin A across the gut mucosal cell were shown to be associated with enterocolitis in HD patients suggesting that mucosa may directly involve in the pathophysiology of HDEC. This study aims to ascertain whether the CDX-1 and CDX-2 genes, that control the proliferation and differentiation of mucosal cells, play a role in HDEC. Using semi-quantitative reverse transcription-polymerase chain reaction (RT-PCR) and in situ hybridisation, we analysed the expression of CDX-1 and CDX-2 genes in colon specimens of normal controls, necrotising enterocolitis (NEC) infants, and HD patients with and without enterocolitis. We showed for the first time that CDX-1 and CDX-2 genes were expressed in the colonic mucosal epithelium in normal, NEC and in HD infants. However, the expressions of both genes were reduced in patients with HDEC. Our findings suggest that reduced expression of CDX-1 and CDX-2 genes in mucosa may be associated with the development of HDEC.

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

The Cdx1 homeobox gene encodes for an intestine-specific transcription factor involved in the control of proliferation and differentiation of epithelial cells. Although it has been indicated that Cdx1 may act as a proto-oncogene in cultured fibroblasts, its direct role in the regulation of intestinal tumorigenesis has not been demonstrated. Here we show that expression of Cdx1 in an intestinal epithelial cell line (IEC-6) induces anchorage-independent growth in soft agar and promotes the formation of adenocarcinoma in vivo. The phenotype of Cdx1-induced tumors was exacerbated when IEC-6/Cdx1 cells were injected together with matrigel containing mitogens and extracellular matrix components. These changes were correlated with an increase in the GTP-bound form of Ras, modulation of Cdc42 and Rho-A activities, and accumulation of phosphatidyl inositol 3 (PI3) kinase products. Moreover, combined inhibition of Ras/Rho and PI3 kinase signaling by synthethic inhibitors blocked colony formation of IEC-6/Cdx1 cells in soft agar. Taken together, these results demonstrate a direct involvement of Cdx1, and its collaboration with Ras, Rho and PI3 kinase pathways, in transformation and tumorigenesis of intestinal epithelial cells.

Enterophilins, a new family of leucine zipper proteins bearing a b30.2 domain and associated with enterocyte differentiation

Enterocyte terminal differentiation occurs at the crypt-villus junction through the transcriptional activation of cell-specific genes, many of which code for proteins of the brush border membrane such as intestinal alkaline phosphatase, sucrase-isomaltase, or the microvillar structural protein villin. Several studies have shown that this sharp increase in specific mRNA levels is intimately associated with arrest of cell proliferation. We isolated several clones from a guinea pig intestine cDNA library. They encode new proteins characterized by an original structure associating a carboxyl-terminal B30.2/RFP-like domain and a long leucine zipper at the amino terminus. The first member of this novel gene family codes for a 65-kDa protein termed enterophilin-1, which is specifically expressed in enterocytes before their final differentiation. Enterophilin-1 is the most abundant in the small intestine but is still present in significant amounts in colonic enterocytes. In Caco-2 cells, a similar 65-kDa protein was recognized by a specific anti-enterophilin-1 antibody, and its expression was positively correlated with cell differentiation status. In addition, transfection of HT-29 cells with enterophilin-1 full-length cDNA slightly inhibited cell growth and promoted an increase in alkaline phosphatase activity. Taken together, these data identify enterophilins as a new family of proteins associated with enterocyte differentiation.

Stem cells and the regulation of proliferation, differentiation and patterning in the intestinal epithelium: emerging insights from gene expression patterns, transgenic and gene ablation studies

Tissues that undergo self-renewal such as the skin, the haematopoeitic system and the intestine are all maintained and renewed by a small group of multipotent stem cells. The stem cells of the intestinal epithelium are located in the crypts and give rise to its four main lineages located mainly in the finger like projections- the villi. An increasing number of genes are now being identified as either being necessary for or involved in the maintenance of intestinal stem cells and regulating differentiation along the crypt-villus axis. These developmental regulatory genes include among others, Tcf-4, Cdx-1 Fkh6, HFH11 and Nkx2-3. Other genes such as the integrins, and Indian hedgehog (Ihh) also affect function of the progenitor cells of the intestinal epithelium. This mini-review will focus on the more recent data on expression patterns of genes in the intestinal epithelium and the direct or indirect effects of their ablation on proliferation and differentiation.

Molecular and cellular biology of small-bowel mucosa

Study of the molecular and cellular biology of the small-intestinal mucosa is providing insights into the remarkable properties of this unique tissue. With its structured pattern of cell proliferation, differentiation, and apoptosis, and its ability to adapt following exposure to luminal nutrients or injury from surgery or pathogens, it functions in a regulated but responsive manner. We review recent publications on factors affecting development, gene expression, cell turnover, and adaptation.

Clusterin gene transcription is activated by caudal-related homeobox genes in intestinal epithelium

Caudal-related homeobox (Cdx) proteins play an important role in development and differentiation of the intestinal epithelium. Using cDNA differential display, we identified clusterin as a prominently induced gene in a Cdx2-regulated cellular model of intestinal differentiation. Transfection experiments and DNA-protein interaction assays showed that clusterin is an immediate downstream target gene for Cdx proteins. The distribution of clusterin protein in the intestine was assessed during development and in the adult epithelium using immunohistochemistry. In the adult mouse epithelium, clusterin protein was localized in both crypt and villus compartments but not in interstitial cells of the intestinal mucosa. Together, these data suggest that clusterin is a direct target gene for Cdx homeobox proteins, and the pattern of clusterin protein expression suggests that it is associated with the differentiated state in the intestinal epithelium.