An intestine-specific homeobox gene regulates proliferation and differentiation

A novel colonic repressor element regulates intestinal gene expression by interacting with Cux/CDP

Intestinal gene regulation involves mechanisms that direct temporal expression along the vertical and horizontal axes of the alimentary tract. Sucrase-isomaltase (SI), the product of an enterocyte-specific gene, exhibits a complex pattern of expression. Generation of transgenic mice with a mutated SI transgene showed involvement of an overlapping CDP (CCAAT displacement protein)-GATA element in colonic repression of SI throughout postnatal intestinal development. We define this element as CRESIP (colon-repressive element of the SI promoter). Cux/CDP interacts with SI and represses SI promoter activity in a CRESIP-dependent manner. Cux/CDP homozygous mutant mice displayed increased expression of SI mRNA during early postnatal development. Our results demonstrate that an intestinal gene can be repressed in the distal gut and identify Cux/CDP as a regulator of this repression during development.

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

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

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.

Conversion of gastric mucosa to intestinal metaplasia in Cdx2-expressing transgenic mice

Gastric intestinal metaplasia occurs as a pathological condition in the gastric mucosa. To clarify how an intestine-specific homeobox gene, Cdx2, affects the morphogenesis of gastric mucosa, we generated transgenic mice expressing Cdx2 in parietal cells. Until Day 18 after birth, the number of parietal cells inthegastric mucosa of transgenic mice was the same as for their normal littermates. However, at Day 19, we detected several glands in which parietal cells disappeared and the proliferating zone moved from the isthmus to the base of the glands. Thereafter, parietal cells decreased gradually and disappeared at Day 37. All of the gastric mucosal cells, except for enterochromaffin-like (ECL) cells, were completely replaced by intestinal metaplasia, consisting of goblet cells, enteroendocrine cells, and absorptive cells expressing alkaline phosphatase. Pseudopyloric gland metaplasia was also formed. The transgenic mouse is a very useful model for clarifying physiological differentiation of gastric and intestinal cell lineages and analyzing the molecular events from intestinal metaplasia to adenocarcinoma.

Aberrant expression of CDX2 in the gastric mucosa with and without intestinal metaplasia: effect of eradication of Helicobacter pylori

BACKGROUND

The intestine-specific transcription factor CDX2 plays an important role in differentiation and maintenance of intestinal epithelial cells. Development and progression of intestinal metaplasia (IM) in the stomach is closely associated with Helicobacter pylori-gastritis. We investigated expression of CDX2 protein in the gastric mucosa with and without IM before and after eradication of H. pylori.

MATERIALS AND METHODS

The subjects comprised five normal controls and 29 H. pylori-positive patients (15 with antral IM and 14 without IM), who were followed for 12 months after eradication of H. pylori. Biopsies were taken from the greater curvatures of the antrum and middle body. Expression of CDX2 was evaluated immunohistochemically using anti-CDX2 antibody.

RESULTS

CDX2 expression was not found in controls. Strong nuclear staining was observed extensively in IM, but rarely in the gastric epithelium, except for the focal area in only four antral biopsies (three with and one without IM). Fine granular cytoplasmic staining was also observed in the perinuclear regions of IM and the gastric epithelial cells in half of the patients. In 13 of the 15 patients with IM, IM did not regress after eradication of H. pylori, and the extent of nuclear staining in IM did not change. The extent of cytoplasmic staining did not change either.

CONCLUSIONS

Our results indicate that CDX2 expression in the gastric mucosa is found in patients with chronic gastritis and is closely associated with IM. CDX2 expression in IM or the gastric epithelial cells did not disappear after eradication of H. pylori.

The zinc-finger transcription factor Klf4 is required for terminal differentiation of goblet cells in the colon

Klf4 (formerly GKLF) is a zinc-finger transcription factor expressed in the epithelia of the skin, lungs, gastrointestinal tract and several other organs. In vitro studies have suggested that Klf4 plays an important role in cell proliferation and/or differentiation. Mice homozygous for a null mutation in Klf4 die within 15 hours of birth and show selective perturbation of late-stage differentiation structures in the epidermis, but the function of Klf4 in the gastrointestinal tract has not been investigated. To address this issue, we have generated Klf4(-/-) mice by homologous recombination in embryonic stem cells. In this study, we provide the first in vivo evidence that Klf4 is a goblet cell-specific differentiation factor in the colon. Klf4(-/-) mice exhibit normal cell proliferation and cell death rates in the colon on postnatal day 1. However, Klf4(-/-) mice demonstrate a 90% decrease in the number of goblet cells in the colon, show abnormal expression of the goblet cell-specific marker Muc2 by in situ hybridization, have abnormal staining of the colonic epithelium with Alcian Blue for acidic mucins, and lack normal goblet cell morphology by ultrastructural analysis. All other epithelial cell types are present in the colon of Klf4(-/-) mice. In summary, Klf4 plays a crucial role in colonic epithelial cell differentiation in vivo.

Analysis of human cellular retinol-binding protein II promoter during enterocyte differentiation

Cellular retinol binding protein II (CRBP II) is a vitamin A-binding protein that is expressed specifically in small intestinal villus absorptive cells. Previous studies have shown that retinoic acid upregulates endogenous human CRBP II gene expression in differentiated Caco-2 cells. To better characterize the regulation of human CRBP II expression, we analyzed the ability of receptor-selective agonists to enhance transcription from the 5'-upstream flanking region of the human CRBP II gene. Stable transfection experiments showed that the proximal 2.8-kb region of the human CRBP II gene is sufficient for retinoic acid inducibility in differentiated Caco-2 cells. However, direct sequence analysis and transient transfection experiments indicate that, unlike the rat CRBP II promoter, the human CRBP II promoter is not a direct retinoid X receptor target. The results indicate that the retinoic acid responsiveness of the human CRBP II promoter is mediated by an indirect mechanism and that this mechanism is associated with enterocyte differentiation.

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

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

Combined expression of pancreatic duodenal homeobox 1 and islet factor 1 induces immature enterocytes to produce insulin

Immature rat intestinal stem cells (IEC-6) given the ability to express the transcription factor, pancreatic duodenal homeobox 1 (Pdx-1), yielded YK cells. Although these cells produced multiple enteroendocrine hormones, they did not produce insulin. Exposure of YK cells to 2 nmol/l betacellulin yielded BYK cells that showed the presence of insulin expression in cytoplasm and that secreted insulin into culture media. By examining the mechanism of differentiation in BYK cells, we found that another transcription factor, islet factor 1 (Isl-1) was newly expressed with the disappearance of Pax-6 expression in those cells after exposure to betacellulin. These results indicated that combined expression of Pdx-1 and Isl-1 in IEC-6 cells was required for the production of insulin. In fact, overexpression of both Pdx-1 and Isl-1 in IEC-6 cells (Isl-YK-12, -14, and -15 cells) gave them the ability to express insulin without exposure to betacellulin. Furthermore, implantation of the Isl-YK-14 cells into diabetic rats reduced the animals' plasma glucose levels; glucose levels dropped from 19.4 to 16.9 mmol/l 1 day after the injection of cells. As expected, the plasma insulin concentrations were 2.7 times higher in the diabetic rats injected with Isl-YK-14 cells compared to in controls. In summary, our results indicated that immature intestinal stem cells can differentiate into insulin-producing cells given the ability to express the transcription factors Pdx-1 and Isl-1.

Stimulation of the intestinal Cdx2 homeobox gene by butyrate in colon cancer cells

BACKGROUND

The transcription factor encoded by the intestinal Cdx2 homeobox gene and treatment with sodium butyrate (NaB), a byproduct of fibre fermentation by colonic bacteria, exert similar effects on colon cancer cell lines as they both inhibit cell growth and stimulate cell differentiation and apoptosis.

AIM

To investigate whether NaB regulates expression of the Cdx2 gene in colon cancer cell lines.

METHODS

Human adenocarcinoma cell lines Caco2 and HT29 were grown in the presence or absence of NaB. Cells were analysed for Cdx2 mRNA expression by reverse transcription-polymerase chain reaction, for protein expression by western blotting and electromobility shift assays, and for transcriptional activity of the Cdx2 promoter by transfection with luciferase reporter plasmids.

RESULTS

In HT29 and Caco2 cells, NaB stimulated Cdx2 mRNA and protein expression as well as transcriptional activity of the Cdx2 promoter. Stimulation of the activity of the Cdx2 promoter by NaB was dose and time dependent. The Cdx2 promoter contains discrete regions that participate in or inversely that blunt the stimulatory effect exerted by NaB. In addition, NaB stimulated the transcriptional activity of the Cdx2 promoter downregulated by oncogenic ras.

CONCLUSION

This study is the first report of an intestine specific transcription factor, Cdx2, stimulated by butyrate. Thus it provides a new mechanism whereby butyrate controls proliferation and differentiation of colon cancer cells.

Activation of K(+) channels and increased migration of differentiated intestinal epithelial cells after wounding

Early mucosal restitution occurs by epithelial cell migration to reseal superficial wounds after injury. Differentiated intestinal epithelial cells induced by forced expression of the Cdx2 gene migrate over the wounded edge much faster than undifferentiated parental cells in an in vitro model. This study determined whether these differentiated intestinal epithelial cells exhibit increased migration by altering voltage-gated K(+) (Kv) channel expression and cytosolic free Ca(2+) concentration ([Ca(2+)](cyt)). Stable Cdx2-transfected IEC-6 cells (IEC-Cdx2L1) with highly differentiated phenotype expressed higher basal levels of Kv1.1 and Kv1.5 mRNAs and proteins than parental IEC-6 cells. Neither IEC-Cdx2L1 cells nor parental IEC-6 cells expressed voltage-dependent Ca(2+) channels. The increased expression of Kv channels in differentiated IEC-Cdx2L1 cells was associated with an increase in whole cell K(+) currents, membrane hyperpolarization, and a rise in [Ca(2+)](cyt). The migration rates in differentiated IEC-Cdx2L1 cells were about four times those of parental IEC-6 cells. Inhibition of Kv channel expression by polyamine depletion decreased [Ca(2+)](cyt), reduced myosin stress fibers, and inhibited cell migration. Elevation of [Ca(2+)](cyt) by ionomycin promoted myosin II stress fiber formation and increased cell migration. These results suggest that increased migration of differentiated intestinal epithelial cells is mediated, at least partially, by increasing Kv channel activity and Ca(2+) influx during restitution.

Cdx2 ectopic expression induces gastric intestinal metaplasia in transgenic mice

BACKGROUND & AIMS

Intestinal-type gastric cancer is often preceded by intestinal metaplasia in humans. The genetic events responsible for the transdifferentiation that occurs in intestinal metaplasia are not well understood. Cdx2, a transcription factor whose expression is normally limited to the intestine, has been detected in gastric intestinal metaplasia. Cdx2 induces differentiation of intestinal epithelial cells in vitro; therefore, we sought to establish whether a causal relationship exists between Cdx2 activation and intestinal metaplasia.

METHODS

Cdx2 expression was directed to the gastric mucosa in transgenic mice using cis-regulatory elements of Foxa3 (Hnf3gamma). Transgenic mice were analyzed for histologic and gene expression changes.

RESULTS

Histologic examination of the gastric mucosa of the Foxa3/Cdx2 mice revealed the presence of alcian blue-positive intestinal-type goblet cells, a hallmark of intestinal metaplasia. In addition, Cdx2 induced the expression of intestine-specific genes.

CONCLUSIONS

Gastric expression of Cdx2 alone was sufficient to induce intestinal metaplasia in mice. These mice represent a powerful tool to investigate the molecular mechanisms that promote intestinal metaplasia. Moreover, as gastric cancer in humans is often preceded by intestinal metaplasia, the phenotype described here strongly suggests involvement of Cdx2 in the initiation of the process leading to intestinal neoplasia of the gastric mucosa.

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.

Cell differentiation is a key determinant of cathelicidin LL-37/human cationic antimicrobial protein 18 expression by human colon epithelium

Antimicrobial peptides are highly conserved evolutionarily and are thought to play an important role in innate immunity at intestinal mucosal surfaces. To better understand the role of the antimicrobial peptide human cathelicidin LL-37/human cationic antimicrobial protein 18 (hCAP18) in intestinal mucosal defense, we characterized the regulated expression and production of this peptide by human intestinal epithelium. LL-37/hCAP18 is shown to be expressed within epithelial cells located at the surface and upper crypts of normal human colon. Little or no expression was seen within the deeper colon crypts or within epithelial cells of the small intestine. Paralleling its expression in more differentiated epithelial cells in vivo, LL-37/hCAP18 mRNA and protein expression was upregulated in spontaneously differentiating Caco-2 human colon epithelial cells and in HCA-7 human colon epithelial cells treated with the cell differentiation-inducing agent sodium butyrate. LL-37/hCAP18 expression by colon epithelium does not require commensal bacteria, since LL-37/hCAP18 is produced with a similar expression pattern by epithelial cells in human colon xenografts that lack a luminal microflora. LL-37/hCAP18 mRNA was not upregulated in response to tumor necrosis factor alpha, interleukin 1alpha (IL-1alpha), gamma interferon, lipopolysaccharide, or IL-6, nor did the expression patterns and levels of LL-37/hCAP18 in the epithelium of the normal and inflamed colon differ. On the other hand, infection of HCA-7 cells with Salmonella enterica serovar Dublin or enteroinvasive Escherichia coli modestly upregulated LL-37/hCAP18 mRNA expression. We conclude that differentiated human colon epithelium expresses LL-37/hCAP18 as part of its repertoire of innate defense molecules and that the distribution and regulated expression of LL-37/hCAP18 in the colon differs markedly from that of other enteric antimicrobial peptides, such as defensins.

Cloning and expression of the Cdx family from the frog Xenopus tropicalis

The caudal-related (Cdx) homeodomain transcription factors have a conserved role in the development of posterior structures in both vertebrates and invertebrates. A particularly interesting finding is that Cdx proteins have an important function in the regulation of expression from a subset of Hox genes. In this study, we report the cloning of cDNAs from the Cdx genes of the amphibian Xenopus tropicalis. Xenopus tropicalis is a diploid species, related to the commonly used laboratory animal Xenopus laevis, and has attracted attention recently as a potential genetic model for animal development. The Xenopus tropicalis cDNAs, Xtcad1, Xtcad2, and Xtcad3, show between 88 and 94% sequence identity with their Xenopus laevis orthologues. This finding corresponds to between 90 and 95% identity at the level of derived amino acid sequence. We also present a detailed description of Xtcad1, Xtcad2, and Xtcad3 expression during normal development. In common with the Cdx genes of other vertebrates, the Xenopus tropicalis Cdx genes show overlapping and dynamic patterns of expression in posterior regions of the embryo through the early stages of development.

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.

Sucrase-isomaltase gene transcription requires the hepatocyte nuclear factor-1 (HNF-1) regulatory element and is regulated by the ratio of HNF-1 alpha to HNF-1 beta

The mouse sucrase-isomaltase (SI) gene is an enterocyte-specific gene expressed in a complex developmental pattern. We previously reported that a short, evolutionarily conserved gene promoter regulates developmental expression of SI in mouse small intestine. Herein, we investigated the role of a hepatocyte nuclear factor-1 (HNF-1) cis-acting element to regulate SI gene expression in vivo. Transgenic SI gene constructs with a mutated HNF-1 element (SIF3) revealed a strong reduction in promoter activity in comparison with a wild-type construct in mice and during Caco-2 cell differentiation. Nuclear proteins isolated from enterocytes showed increased binding of the HNF-1 alpha complex with a concomitant decrease in the HNF-1 beta-containing complex to the SIF3 element both during the suckling-weaning developmental transition and Caco-2 cell differentiation. These changes coincided with a strong induction of SI gene transcription. In transfection experiments, HNF-1 alpha activated the SI promoter via the SIF3 element, and co-expression of HNF-1 beta impaired this transcriptional activation. These findings demonstrate the essential role of the HNF-1 regulatory element to support SI gene transcription in vivo and suggest that the ratio of HNF-1 alpha to HNF-1 beta plays a role in the transcriptional activity of this gene during intestinal development.

Expression of the gut-enriched Krüppel-like factor (Krüppel-like factor 4) gene in the human colon cancer cell line RKO is dependent on CDX2

Gut-enriched Krüppel-like factor (GKLF or KLF4) is a zinc finger-containing, epithelial-specific transcription factor, that functions as a suppressor of cell proliferation. We previously showed that GKLF expression is decreased in intestinal and colonic adenomas, respectively, from multiple intestinal neoplasia (Min) mice and familial adenomatous polyposis (FAP) patients. This study shows that GKLF is induced upon activation of the adenomatous polyposis coli (APC) gene. However, among several human colon cancer cell lines surveyed, expression of GKLF is lowest in RKO, a line with wild-type APC and beta-catenin. RKO contains a mutated allele that encodes the putative tumor suppressor homeodomain protein, CDX2. We show that wild-type CDX2 activates the GKLF promoter and that the mutated CDX2 has a dominant negative effect on wild-type function. Our results may help explain the exceedingly low levels of GKLF expression detected in this cell line, which may in turn contribute to the tumor phenotype.

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.

Differential activation of intestinal gene promoters: functional interactions between GATA-5 and HNF-1 alpha

The effects of GATA-4, -5, and -6, hepatocyte nuclear factor-1 alpha (HNF-1 alpha) and -beta, and Cdx-2 on the rat and human lactase-phlorizin hydrolase (LPH) and human sucrase-isomaltase (SI) promoters were studied using transient cotransfection assays in Caco-2 cells. GATA factors and HNF-1 alpha were strong activators of the LPH promoters, whereas HNF-1 alpha and Cdx-2 were strong activators of the SI promoter, although GATA factors were also necessary for maximal activation of the SI gene. Cotransfection of GATA-5 and HNF-1 alpha together resulted in a higher activation of all three promoters than the sum of the activation by either factor alone, demonstrating functional cooperativity. In the human LPH promoter, an intact HNF-1 binding site was required for functional synergy. This study is the first to demonstrate 1) differential activation of the LPH and SI promoters by multiple transcription factors cotransfected singly and in combination and 2) that GATA and HNF-1 transcription factors cooperatively activate intestinal gene promoters. Synergistic activation is a mechanism by which higher levels of tissue-specific expression might be attained by overlapping expression of specific transcription factors.

Differentiation of immature enterocytes into enteroendocrine cells by Pdx1 overexpression

The development of a variety of enteroendocrine cells of the gut is poorly understood. We tested whether immature intestinal stem cells were switched to multiple enteroendocrine hormone-producing cells by in vitro transfer of a homeobox gene. We transfected the pancreatic-duodenal homeobox 1 gene (Pdx1) into IEC-6 cells, an embryonic intestinal epithelial cell line derived from a normal rat, and selected the cells that overexpressed Pdx1 by 150-fold compared with control. The cells were examined for differentiation into enteroendocrine cells by immunocytochemical and electron microscopic analyses. Transfected cells cultured on micropore filters formed a trabecular network piled up on monolayer cells. These trabecular cells showed nuclear localization of Pdx1 protein and contained well-developed rough endoplasmic reticulum as well as many secretory granules of pleomorphic shape in the cytoplasm. Antibodies against chromogranin A, serotonin, cholecystokinin, gastrin, and somatostatin stained these secretory granules in the cytoplasm. Furthermore, immunofluorescence double staining analysis showed that different hormones were produced within a cell. These results provide the evidence that immature intestinal epithelial cells can differentiate into multiple hormone-producing enteroendocrine cells in response to overexpression of Pdx1.

Intestinal epithelial cell differentiation involves activation of p38 mitogen-activated protein kinase that regulates the homeobox transcription factor CDX2

The intracellular signaling pathways responsible for cell cycle arrest and differentiation along the crypt-villus axis of the human small intestine remain largely unknown. p38 mitogen-activated protein kinases (MAPKs) have recently emerged as key modulators of various vertebrate cell differentiation processes. In order to elucidate further the mechanism(s) responsible for the loss of proliferative potential once committed intestinal cells begin to differentiate, the role and regulation of p38 MAPK with regard to differentiation were analyzed in both intact epithelium as well as in well established intestinal cell models recapitulating the crypt-villus axis in vitro. Results show that phosphorylated and active forms of p38 were detected primarily in the nuclei of differentiated villus cells. Inhibition of p38 MAPK signaling by 2-20 microm SB203580 did not affect E2F-dependent transcriptional activity in subconfluent Caco-2/15 or HIEC cells. p38 MAPK activity dramatically increased as soon as Caco-2/15 cells reached confluence, whereas addition of SB203580 during differentiation of Caco-2/15 cells strongly attenuated sucrase-isomaltase gene and protein expression as well as protein expression of villin and alkaline phosphatase. The binding of CDX2 to the sucrase-isomaltase promoter and its transcriptional activity were significantly reduced by SB203580. Pull-down glutathione S-transferase and immunoprecipitation experiments demonstrated a direct interaction of CDX3 with p38. Finally, p38-dependent phosphorylation of CDX3 was observed in differentiating Caco-2/15 cells. Taken together, our results indicate that p38 MAPK may be involved in the regulation of CDX2/3 function and intestinal cell differentiation.

Changes in cell proliferation and differentiation of adult rat small intestine epithelium after adrenalectomy: kinetic, biochemical, and morphological studies

The effects of 10-day bilateral adrenalectomy on morphometry, proliferation, and apoptosis were determined in the small intestine of 3-month-old Sprague-Dawley rats. The activities of sucrase, lactase, and its respective mRNA, aminopeptidase N, and intestinal alkaline phosphatase were also evaluated. Adrenalectomy lead to partial atrophy and disorganization of the epithelium, with an increased number of goblet and Paneth cells and a reduction of crypt cell proliferation paralleled by a marked increase in villus apoptosis. Biochemical assays revealed that aminopeptidase N and intestinal alkaline phosphatase activities were significantly decreased, whereas disaccharidases were increased by adrenalectomy. The corresponding induction of lactase mRNA suggests an active response of the epithelium. In conclusion, adrenalectomy modified maturation and the differentiation processes of the small intestinal mucosa, especially in the proximal part of the small intestine. This result points to an important role of adrenals and glucocorticoids in the trophic status of the adult small intestinal mucosa.

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.

Keratinocyte growth factor promotes goblet cell differentiation through regulation of goblet cell silencer inhibitor

BACKGROUND & AIMS

Keratinocyte growth factor (KGF) is an epithelial cell-specific growth factor. Previous reports demonstrated that KGF induces differentiation of epithelial cells of gastrointestinal tract in vivo, especially goblet cell-specific lineage stimulation. Intestinal trefoil factor (ITF) is selectively expressed in intestinal goblet cells and its expression correlates with intestinal goblet cell differentiation. In this study, we analyzed the mechanism of KGF modulation of goblet cell differentiation through characterization of its effects on ITF gene expression.

METHODS

Subclone H2 of the human colonic epithelial cell line HT-29, which can be induced to intestinal goblet cells, was treated with KGF and characterized by Northern and Western blot analyses, transient transfection assays, and electrophoretic mobility shift assays (EMSAs).

RESULTS

KGF promoted differentiation of H2 cells to goblet cells as reflected by induced ITF expression. Transient transfection assays revealed that KGF regulates mouse ITF transcription through the goblet cell silencer inhibitor (GCSI) element, which is essential for goblet cell-specific expression of ITF. EMSAs showed that KGF induces GCSI binding protein (GCSI-BP).

CONCLUSIONS

KGF promotes goblet cell differentiation through the induction of GCSI-BP, a goblet cell-specific transcription factor. GCSI-BP may play a central role in intestinal goblet cell differentiation.

Intestinal bile acid transport: biology, physiology, and pathophysiology

Intestinal reabsorption of bile salts plays a crucial role in human health and disease. This process is primarily localized to the terminal ileum and is mediated by a 48-kd sodium-dependent bile acid cotransporter (SLC10A2 = ASBT). ASBT is also expressed in renal tubule cells, cholangiocytes, and the gallbladder. Exon skipping leads to a truncated version of ASBT, which sorts to the basolateral surface and mediates efflux of bile salts. Inherited mutation of ASBT leads to congenital diarrhea secondary to bile acid malabsorption. Partial inhibition of ASBT may be useful in the treatment of hypercholesterolemia and intrahepatic cholestasis. During normal development in the rat ileum, ASBT undergoes a biphasic pattern of expression with a prenatal onset, postnatal repression, and reinduction at the time of weaning. The bile acid responsiveness of the ASBT gene is not clear and may be dependent on both the experimental model used and the species being investigated. Future studies of the transcriptional and posttranscriptional regulation of the ASBT gene and analysis of ASBT knockout mice will provide further insight into the biology, physiology, and pathophysiology of intestinal bile acid transport.

Cdx1 promotes cellular growth of epithelial intestinal cells through induction of the secretory protein PAP I

Expression of the Cdx1 homeobox gene in epithelial intestinal cells promotes cellular growth and differentiation. Cdx1and the Pancreatitis Associated Protein I (PAP I) are concomitantly expressed in the epithelial cells of the lower part of the intestinal crypts. Because Cdx1 is a transcription factor and PAP I, in other tissues, is a proliferative factor, we looked for a relationship between these two proteins in the intestinal-derived IEC-6 cells. After stable transfection with a Cdx1 expression vector, they produce high levels of the PAP I transcript and protein indicating a functional link between the two genes. Demonstration of Cdx1 binding to the PAP I promoter region and suppression of PAP I induction after deletion of the corresponding sequence indicated that Cdx1 is a transcription factor controlling PAP I gene expression in intestinal cells. By infecting IEC-6 cells with adenoviruses expressing PAP I, we demonstrated that PAP I induces mitosis in these cells. On the other hand, inhibition of the PAP I expression in the IEC-6 Cdxl-expressing cells using an antisense strategy confirmed the requirement of this protein for the effect of Cdx1 on cell growth. Finally, addition of the immunopurified PAP I to the culture medium promotes cell growth of the IEC-6 cells in a dose-dependent manner. Maximal effect was obtained at 1 ng/ml. Taken together these results demonstrate that PAP I is a target of the Cdx1 homeobox gene in intestinal cells which participates in the regulation of intestinal cell growth via an autocrine and/or paracrine mechanism.

Role of p27(Kip1) in human intestinal cell differentiation

BACKGROUND & AIMS

Growth arrest and differentiation are generally considered to be temporally and functionally linked phenomena in the intestinal epithelium.

METHODS

To delineate the mechanism(s) responsible for the loss of proliferative potential as committed intestinal cells start to differentiate, we have analyzed the regulation of G(1)-phase regulatory proteins in relation to differentiation in the intact epithelium as well as in well-established intestinal cell models that allow the recapitulation of the crypt-villus axis in vitro.

RESULTS

With intestinal cell differentiation, we have observed an induction of the cell cycle inhibitors p21(Cip), p27(Kip1), and p57(Kip2) expression with an increased association of p27(Kip1) and p57(Kip2) with cyclin-dependent kinase 2 (Cdk2). At the same time, there was an accumulation of the hypophosphorylated form of the pRb proteins and a strong decline in Cdk2 activity. Stable expression of a p27(Kip1) antisense complementary DNA in Caco-2/15 cells did not prevent growth arrest induced by confluence, but repressed villin, sucrase-isomaltase, and alkaline phosphatase expression.

CONCLUSIONS

Our results indicate that the growth arrest that precedes differentiation involves the activation of Rb proteins and the inhibition of Cdk2. Furthermore, intestinal cell differentiation apparently requires a function of p27(Kip1) other than that which leads to inhibition of Cdks.

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.

A duodenum-specific enhancer regulates expression along three axes in the small intestine

Adenosine deaminase (ADA) is expressed at high levels in the epithelium of proximal small intestine. Transgenic mice were used to characterize the regulatory region governing this activation. A duodenum-specific enhancer is located in intron 2 of the human ADA gene at the central site among a cluster of seven DNase I-hypersensitive sites present in duodenal DNA. Flanking DNA, including the remaining hypersensitive sites, is required for consistent high-level enhancer function. The enhancer activates expression in a pattern identical to endogenous ADA along both the anterior-posterior axis of the small intestine and the crypt-villus differentiation axis of the intestinal epithelium. Timing of activation by the central enhancer mimics endogenous mouse ADA activation, occurring at 2-3 wk of age. However, two upstream DNA segments, one proximal and one distal, collaborate to change enhancer activation to a perinatal time point. Studies with duodenal nuclear extracts identified five distinct DNase I footprints within the enhancer. Protected regions encompass six putative binding sites for the transcription factor PDX-1, as well as proposed CDX, hepatocyte nuclear factor-4, and GATA-type sites.

Regulation of intestinal regeneration: new insights

Intestinal regeneration is the process by which intestinal injury penetrating deep to the lamina propria heals. The regenerative process involves epithelial cell migration and proliferation, changes in cellular function, adaptation of subepithelial tissues, and contraction of the injured area. This requires interaction of multiple cell types. While many observations have been made about the process of regeneration, its regulation is not well understood. Previous studies, performed primarily in a serosal patch model, have identified many potential regulatory factors. These include location and size of the injury, other associated injury, e.g., resection, and a variety of agents that influence one or more of the primary processes involved. Epidermal growth factor (EGF), in particular, appears to play a role in many aspects of regeneration. Recent advances in the understanding of intestinal growth regulation have provided new insights into the regulation of intestinal regeneration. Developmental studies in genetically manipulated mice suggest a role for gene products not previously implicated in regeneration. The importance of apoptosis in growth regulation has recently been emphasized. Mesenchymal-epithelial interactions have gained greater appreciation. Finally, it has become clear that immune cells and cytokines are important factors in this process. Transforming growth factor-beta (TGFbeta) has been implicated as another important regulator of several of the processes involved in intestinal regulation. Improved understanding of the regulation of intestinal regeneration will lead to new therapeutic approaches to stimulate intestinal healing in the clinical setting.

Cdx1 and cdx2 expression during intestinal development

BACKGROUND & AIMS

The intestine-specific transcription factors Cdx1 and Cdx2 are candidate genes for directing intestinal development, differentiation, and maintenance of the intestinal phenotype. This study focused on the complex patterns of expression of Cdx1 and Cdx2 during mouse gastrointestinal development.

METHODS

Embryonic and postnatal mouse tissues were analyzed by immunohistochemistry to determine protein expression of Cdx1 and Cdx2 in the developing intestinal tract.

RESULTS

Cdx2 protein expression was observed at 9. 5 postcoitum (pc), whereas weak expression of Cdx1 protein was first seen at 12.5 pc in the distal developing intestine (hindgut). Expression of Cdx1 increased from 13.5 to 14.5 pc during the endoderm/epithelial transition with predominately distal expression. In contrast to Cdx1, there was intense expression of Cdx2 in all but the distal portions of the developing intestine. Cdx2 expression remained low in the distal colon throughout postnatal development. A gradient of expression formed in the crypt-villus axis, with Cdx1 primarily in the crypt and Cdx2 primarily in the villus.

CONCLUSIONS

Direct comparison of the patterns of Cdx1 and Cdx2 protein expression during development as performed in this study provides new insights into their potential functional roles. The relative expression of Cdx1 to Cdx2 protein may be important in the anterior to posterior patterning of the intestinal epithelium and in defining patterns of proliferation and differentiation along the crypt-villus axis.

Decreased expression of the gut-enriched Krüppel-like factor gene in intestinal adenomas of multiple intestinal neoplasia mice and in colonic adenomas of familial adenomatous polyposis patients

Gut-enriched Krüppel-like factor (GKLF) is a zinc finger-containing transcription factor, the expression of which is associated with growth arrest. We compared Gklf expression in intestinal and colonic adenomas to normal mucosa in multiple intestinal neoplasia (Min) mice and familial adenomatous polyposis (FAP) patients, respectively, using semi-quantitative RT-PCR. In Min mice, the level of Gklf transcript is highest in normal-appearing intestinal tissues and decreases as the size of the adenoma increases. In FAP patients, the level of GKLF transcript is lower in adenomas compared to paired normal-appearing mucosa from the same patient or normal colonic mucosa from control individuals without FAP. The possibility of DNA methylation as a cause for the decreased expression of Gklf in adenomas of Min mice was investigated by methylation-specific PCR. Results indicate that the Gklf gene is not methylated in either normal or tumorous tissues. The findings of our study are therefore consistent with the potential role of GKLF as a negative growth regulator of gut epithelial cells.

Human cell models to study small intestinal functions: recapitulation of the crypt-villus axis

The intestinal epithelium is continuously and rapidly renewed by a process involving cell generation, migration, and differentiation, from the stem cell population located at the bottom of the crypt to the extrusion of the terminally differentiated cells at the tip of the villus. Because of the lack of normal human intestinal cell models, most of our knowledge about the regulation of human intestinal cell functions has been derived from studies conducted on cell cultures generated from experimental animals and human colon cancers. However, important advances have been achieved over recent years in the generation of normal human intestinal cell models. These models include (a) intestinal cell lines with typical crypt cell proliferative noncommitted characteristics, (b) conditionally immortalized intestinal cell lines that can be induced to differentiate, and (c) primary cultures of differentiated villuslike cells that can be maintained in culture for up to 10 days. Each of these models should help in the investigation of the specific aspects of human intestinal function and regulation. Furthermore, taken together, these models provide an integrated system that allows an in vitro recapitulation of the entire crypt-villus axis of the normal human small intestine.

Overexpression of Cdx1 and Cdx2 homeogenes enhances expression of the HLA-I in HT-29 cells

We have previously reported that down-regulation of Cdx1 and Cdx2 mRNA expression is associated with colon carcinogenesis, and that coordinated reexpression of these genes in the HT29 colon cancer-derived cell line leads to a reduced malignant phenotype. Here we show that restoring Cdx1 and Cdx2 expression in HT29 cells enhanced the antigen presentation system, as reflected by a strong induction of the concentration of HLA-I molecules at the cell surface, resulting from increased expression of the HLA-I mRNA. Expression of the LMP2 proteasomal protein was also strongly induced by Cdx1 and Cdx2 at the transcriptional level, whereas TAP1 expression which is under the control of the same bidirectional promoter as LMP2 remained unchanged. Furthermore, expression of the adhesion molecule ICAM-1, which works in concert with HLA-I, and of the cell death promoter Fas was also increased upon Cdx1 and Cdx2 expression. Taken together, these results suggest that loss of Cdx1 and Cdx2 expression during colorectal carcinogenesis could favor the escape of tumor cells from the immune system. In conclusion, restoration of Cdx1 and Cdx2 expression should be considered in immunotherapeutic strategies for colorectal cancer.

Homeobox genes and gut development

The gut of vertebrates exhibits a common anteroposterior regional differentiation. The role of homeobox genes in establishing this pattern is inferred by their sites of expression. It is suggested that the primary source of positional information is in the endoderm, which subsequently establishes a 'dialogue' with the surrounding visceral layer of the lateral plate mesoderm. This results in the anatomical and physiological specialization of the adult gut.

Transcriptional regulation in intestinal development. Implications for colorectal cancer

Deciphering the complex mechanisms of intestinal epithelial development will require multiple cell and molecular approaches in both in vitro and whole animal systems. Additionally, the use of model organisms such as D. melanogaster, C. elegans, and zebrafish will help describe paradigms that may be investigated in mammals as well as serve as test systems for findings from mammals. This manuscript reviewed only one approach to understanding intestinal development. However, the Cdx story and the information to be mined from an understanding of SI gene transcription is not at an end. As the other pieces of the transcriptional puzzle of the SI gene are assembled there will be new information to generate hypotheses on the relationship of transcriptional mechanisms to cancer pathogenesis.

Transactivation and growth suppression by the gut-enriched Krüppel-like factor (Krüppel-like factor 4) are dependent on acidic amino acid residues and protein-protein interaction

Gut-enriched Krüppel-like factor (GKLF or KLF4) is a pleiotropic (activating and repressive) transcription factor. This study characterizes the mechanisms of transactivation by GKLF. Using a GAL4 fusion assay, the activating domain of murine GKLF was localized to the 109 amino acid residues in the N-terminus. Site-directed mutagenesis showed that two adjacent clusters of acidic residues within this region are responsible for the activating effect. Transactivation by GKLF involves intermolecular interactions as demonstrated by the ability of wild-type, but not mutated, GKLF to compete with the N-terminal activation domain. In addition, wild-type adenovirus E1A, but not a mutated E1A that failed to bind p300/CBP, inhibited transactivation by the N-terminal 109 amino acids of GKLF, suggesting that p300/CBP are GKLF's interacting partners. A physical interaction between GKLF and CBP was demonstrated by glutathione- S -transferase pull-down and by in vivo co-immuno-precipitation experiments. We also showed that the two acidic amino acid clusters are essential for this interaction, since GKLF with mutations in these residues failed to co-immunoprecipitate with CBP. Importantly, the same mutations abrogated the ability of GKLF to suppress cell growth as determined by a colony suppression assay. These studies therefore provide plausible evidence for a structural and functional correlation between the transactivating and growth-suppressing effects of GKLF.

Interaction between the homeodomain proteins Cdx2 and HNF1alpha mediates expression of the lactase-phlorizin hydrolase gene

Lactase-phlorizin hydrolase is a brush-border enzyme which is specifically expressed in the small intestine where it hydrolyses lactose, the main carbohydrate found in milk. We have previously demonstrated in transgenic mice that the tissue-specific and developmental expression of lactase is controlled by a 1 kb upstream region of the pig lactase gene. Two homeodomain transcription factors, caudal-related homeodomain protein (Cdx2) and hepatic nuclear factor 1alpha (HNF1alpha), are known to bind to regulatory cis elements in the promoters for several intestine-specific genes, including lactase, and are present in mammalian intestinal epithelia from an early stage in development. In the present study, we examined whether Cdx2 and HNF1alpha physically interact and co-operatively activate transcription from the lactase-phlorizin hydrolase promoter. We show that the presence of both factors leads to a much higher level of transcription than the sum of the activation by either factor alone. The N-terminal activation domain of Cdx2 is required for maximal synergy with HNF1alpha. With the use of pull-down assays, we demonstrate a direct protein-protein interaction between Cdx2 and HNF1alpha. The interaction domain includes the homeodomain region of both proteins. This is the first demonstration of a functional interaction between two transcription factors involved in the activation of a number of intestine-specific genes. Synergistic interaction between tissue-restricted factors is likely to be an important mechanism for reinforcing developmental and tissue-specific gene expression within the intestine.

Glucagon-like peptide-2 increases sucrase-isomaltase but not caudal-related homeobox protein-2 gene expression

To determine the effect of glucagon-like peptide-2 (GLP-2) on sucrase-isomaltase and caudal-related homeobox protein-2 (Cdx-2) gene expression, male Wistar rats were divided into total parenteral nutrition (TPN)-fed and GLP-2-treated, TPN-fed groups. TPN was given via a jugular line, inserted under anesthesia, for 7 days. The treatment group received 40 microg/day of GLP-2 intravenously with the TPN diet. The small intestine and colon were weighed and measured. Tissue was obtained from the jejunum, terminal ileum, and midcolon. RNA analysis, morphometry, and microdissection were performed. The weight of the small intestine of GLP-2-treated rats was greater than that of TPN-fed rats (P < 0.001). GLP-2 increased the mean metaphase arrests/crypt in both the jejunum and ileum (P < 0.001). Ileal expression of sucrase-isomaltase was increased by 1. 6-fold (P < 0.05). Jejunal expression was increased by a similar amount, although not significantly (P = 0.08). There was no change in Cdx-2 gene expression. Thus GLP-2 can maintain small intestinal morphology and function, but effects on gene expression are not mediated by gross changes in the level of the mRNA for the homeobox protein Cdx-2.

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

Cdx1 is a homeodomain transcription factor that regulates intestine-specific gene expression. Experimental evidence suggests that Cdx1 may be involved in cell cycle regulation, but its role is ill defined and the mechanisms have not been explored. We used stable transfection of inducible constructs and transient expression with a replication-deficient adenovirus to induce Cdx1 expression in rat IEC6 cells, a non-transformed intestinal epithelial cell line that does not express Cdx1 protein. Expression of Cdx1 markedly reduced proliferation of IEC6 cells with accumulation of cells in the G(0)/G(1) phase of the cell cycle. Cell cycle arrest was accompanied by an increase in the hypophosphorylated forms of the retinoblastoma protein (pRb) and the pRb-related p130 protein. Protein levels of multiple cyclin-dependent kinase inhibitors were either unchanged (p16, p18, p21, p27, and p57) or were not detected (p15 and p19). Most significantly, levels of cyclins D1 and D2 were markedly diminished with Cdx1 expression, but not cyclins D3, E, or the G(1) kinases. Additionally, cyclin-dependent kinase-4 activity was decreased in association with decreased cyclin D protein. We conclude that Cdx1 regulates intestinal epithelial cell proliferation by inhibiting progression through G(0)/G(1), most likely via modulation of cyclin D1 and D2 protein levels.

Expression of an intestine-specific transcription factor (CDX1) in intestinal metaplasia and in subsequently developed intestinal type of cholangiocarcinoma in rat liver

CDX1 is a caudal-type homeobox intestine-specific transcription factor that has been shown to be selectively expressed in epithelial cells in intestinal metaplasia of the human stomach and esophagus and variably expressed in human gastric and esophageal adenocarcinomas (Silberg DG, Furth EE, Taylor JK, Schuck T, Chiou T, Traber PG: Gastroenterology 1997, 113: 478-486). Through the use of immunohistochemistry and Western blotting, we investigated whether CDX1 is also uniquely associated with the intestinal metaplasia associated with putative precancerous cholangiofibrosis induced in rat liver during furan cholangiocarcinogenesis, as well as expressed in neoplastic glands in a subsequently developed intestinal type of cholangiocarcinoma. In normal, control adult rat small intestine, specific nuclear immunoreactivity for CDX1 was most prominent in enterocytes lining the crypts. In comparison, epithelium from intestinal metaplastic glands within furan-induced hepatic cholangiofibrosis and neoplastic epithelium from later developed primary intestinal-type cholangiocarcinoma each demonstrated strong nuclear immunoreactivity for CDX1. CDX1-positive cells were detected in hepatic cholangiofibrotic tissue as early as 3 weeks after the start of chronic furan treatment. We further determined that the percentages of CDX1-positive neoplastic glands and glandular nuclei are significantly higher in primary tumors than in a derived, transplantable cholangiocarcinoma serially-propagated in vivo. Western blotting confirmed our immunohistochemical results, and no CDX1 immunoreactivity was detected in normal adult rat liver or in hyperplastic biliary epithelial cells. These findings indicate that CDX1 is specifically associated with early intestinal metaplasia and a later developed intestinal-type of cholangiocarcinoma induced in the liver of furan-treated rats.

Differentiated intestinal epithelial cells exhibit increased migration through polyamines and myosin II

Early mucosal restitution is a rapid process by which differentiated intestinal epithelial cells migrate to reseal superficial wounds. However, most of the in vitro studies for restitution employ undifferentiated intestinal crypt cells as a model. The transcription factor, Cdx2, plays an important role in the regulation of intestinal epithelial differentiation. Forced expression of the Cdx2 gene in undifferentiated intestinal crypt cells induces the development of a differentiated phenotype. The current study was designed to determine changes in differentiated intestinal epithelial cell migration after wounding in the stable Cdx2-transfected IEC-6 cells and then to examine involvement of polyamines and nonmuscle myosin II in the process of cell motility. Cdx2-transfected IEC-6 cells were associated with a highly differentiated phenotype and exhibited increased cell migration after wounding. Migration of Cdx2-transfected IEC-6 cells were approximately four times that of nontransfected IEC-6 cells. Migration after wounding was associated with significant increases in polyamine synthesis. Depletion of cellular polyamines by 5 mM α-difluoromethylornithine (DFMO), a specific inhibitor of polyamine biosynthesis, inhibited cell migration without affecting the differentiated phenotype. DFMO also decreased levels of nonmuscle myosin II mRNA and protein and resulted in reorganization of myosin II, along with a marked reduction in stress fibers. Exogenous spermidine given together with DFMO not only returned nonmuscle myosin II levels and cellular distribution toward normal but also restored cell migration to control levels. These results indicate that 1) Cdx2-transfected IEC-6 cells exhibit increased cell migration after wounding and 2) cellular polyamines are absolutely required for stimulation of cell migration in association with their ability to modulate the structural organization of nonmuscle myosin II.

Cdx1 promotes differentiation in a rat intestinal epithelial cell line

BACKGROUND & AIMS

Homeobox genes are involved in establishing and maintaining differentiated patterns in adult tissues. Cdx1 might carry out that function in the intestinal epithelium because its expression is specific to that tissue and increases during development.

METHODS

Cdx1 expression was induced in IEC-6 intestinal epithelial cells by stable transfection, and subsequent changes in cell growth, resistance to apoptosis, migration, and differentiation were monitored.

RESULTS

Compared with control, IEC-6/Cdx1 cells proliferated more rapidly, were more resistant to apoptosis, and migrated 3-4 times faster, as shown by an in vitro wound assay. IEC-6/Cdx1 cells in culture formed multilayers. Morphology of the top layer was similar to that of columnar epithelium, with cells showing typical features of differentiated enterocytes, including complex junctions and well-developed microvilli with glycocalix. Expression of 2 markers of enterocyte differentiation, aminopeptidase N and villin, was induced in IEC-6/Cdx1 cells. Aminopeptidase N was targeted to the basolateral membrane, and villin was localized to the cytoplasm. Actin filaments, which were mostly present in transcytoplasmic stress fibers in control cells, were redistributed to the cortex in Cdx1-transfected cells.

CONCLUSIONS

Cdx1 expression in IEC-6 cells induces phenotypic changes characteristic of differentiating enterocytes, suggesting an important role for Cdx1 in the transition from stem cells to proliferating/transit cells.

Cell type-specific autoregulation of the Caudal-related homeobox gene Cdx-2/3

The caudal-related homeobox gene Cdx-2/3 is a critical "master" control gene in embryogenesis. Mice heterozygous for a null mutation in Cdx-2/3 exhibit multiple malfunctions including tail abnormalities, stunted growth, a homeotic shift in vertebrae, and the development of multiple intestinal adenomatous polyps, indicating that Cdx-2/3 is haplo-insufficient. In vitro studies have identified more than a half-dozen downstream target genes expressed in pancreatic and intestinal cells for this transcription factor. We have examined the transcriptional properties of the mouse Cdx-2/3 promoter. This promoter could be autoregulated in pancreatic and intestinal cells that express endogenous Cdx-2/3. In contrast, Cdx-2/3 transfection represses the Cdx-2/3 promoter in fibroblasts, which do not express endogenous Cdx-2/3. Since Cdx-2/3 activates proglucagon gene promoter in both pancreatic and intestinal cells and in fibroblasts, we suggest that some, yet to be identified, cell type-specific components are required for activating selected target gene promoters of Cdx-2/3, including the Cdx-2/3 promoter itself. Cdx-2/3 binds to the TATA box and another AT-rich motif, designated as DBS, within an evolutionarily conserved proximal element of the Cdx-2/3 promoter. The DBS motif is critical for the autoregulation, whereas the TATA box may act as an attenuating element for the autoregulatory loop. Finally, overexpression of Cdx-2/3 in a pancreatic cell line activated the expression of the endogenous Cdx-2/3. Taken together, our results indicate that the dose-dependent phenotype of Cdx-2/3 expression on its downstream targets in vivo could be regulated initially via a transcriptional network involving cell type-specific autoregulation of the Cdx-2/3 promoter.

Loss of Hoxa5 gene function in mice perturbs intestinal maturation

The Hox gene family of transcription factors constitutes candidate regulators in the molecular cascade of events that governs establishment of normal terminal differentiation along the duodenum to colon axis. One member of this family, Hoxa5, displays a dynamic pattern of expression during gut development. Hoxa5 transcripts are present in midgut mesenchyme at the time of remodeling, supporting a role for this gene in digestive tract specification. To study the role of Hoxa5 in proper intestinal development and maturation, we examined whether Hoxa5 mutant mice exhibit any defect in this process. We report here that even though Hoxa5 is not required for midgut morphogenesis, its loss of function perturbs the acquisition of adult mode of digestion, which normally is temporally coordinated with the process of spontaneous weaning. Impaired maturation of the digestive tract might be related to altered specification of intestinal epithelial cells. Our findings provide evidence that Hoxa5 expression in the gut mesoderm is important for the region-specific differentiation of the adjacent endoderm.

CDX2 is mutated in a colorectal cancer with normal APC/beta-catenin signaling

The majority of human colorectal cancers have elevated beta-catenin/TCF regulated transcription due to either inactivating mutations of the APC tumor suppressor gene or activating mutations of beta-catenin. Surprisingly, one commonly used colorectal cancer cell line was found to have intact APC and beta-catenin and no demonstrable beta-catenin/TCF regulated transcription. However, this line did possess a truncating mutation in one allele of CDX2, a gene whose inactivation has recently been shown to cause colon tumorigenesis in mice. Expression of CDX2 was found to be induced by restoring expression of wild type APC in a colorectal cancer cell line. These findings raise the intriguing possibility that CDX2 contributes to APC's tumor suppressive effects.

Factors involved in the duodenal expression of the human calbindin-D9k gene

Calbindin-D9k is expressed in the cytoplasm of intestinal cells, where it is critical for dietary calcium absorption. Two striking aspects of the expression of this gene are its vitamin-D dependency and regional differences in expression, with high levels only in duodenum. We report studies of the human calbindin-D9k promoter. Differences between the reported sequences of the human calbindin-D9k promoter were first clarified before undertaking a functional analysis of this sequence. Studies of the rat gene have indicated that several transcription factors, including the caudal-related homeobox factor (CDX-2), hepatic nuclear factor-4 and CCAAT-enhancer-binding protein alpha (C/EBPalpha), could interact with elements in the promoter. Although these elements are conserved in the human gene, we show here that their intestinal distribution makes them unlikely to be critical positive factors. The calbindin-D9k gene contains multiple potential binding sites for homeobox transcription factors; one of these, known as IPF-1 or PDX-1, co-localizes in the intestine with calbindin-D9k. We show in gel-shift assays that the sequence within a putative vitamin-D-response element in the human calbindin-D9k promoter can bind expressed IPF-1/PDX-1 protein, although we cannot confirm binding of the vitamin-D-receptor protein. CDX-2 binds to the region around the TATA box, as in the rat gene, and may act as a negative factor in the distal intestine. Transfection studies in Caco-2 and MCF-7 cells with heterologous reporter vectors containing up to 1303 bp of the gene showed that this functioned as a weak promoter and indicated the presence of suppressor sequences, but did not show vitamin-D responsiveness. This indicates that other elements are also needed for the control of human calbindin-D9k expression.