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

Genetics of Lactose Intolerance: An Updated Review and Online Interactive World Maps of Phenotype and Genotype Frequencies

In humans the ability to digest milk lactose is conferred by a β-galactosidase enzyme called lactase-phlorizin hydrolase (LPH). While in some humans (approximately two-thirds of humankind) the levels of this enzyme decline drastically after the weaning phase (a trait known as lactase non-persistence (LNP)), some other individuals are capable of maintaining high levels of LPH lifelong (lactase persistence (LP)), thus being able to digest milk during adulthood. Both lactase phenotypes in humans present a complex genetic basis and have been widely investigated during the last decades. The distribution of lactase phenotypes and their associated single nucleotide polymorphisms (SNPs) across human populations has also been extensively studied, though not recently reviewed. All available information has always been presented in the form of static world maps or large dimension tables, so that it would benefit from the newly available visualization tools, such as interactive world maps. Taking all this into consideration, the aims of the present review were: (1) to gather and summarize all available information on LNP and LP genetic mechanisms and evolutionary adaptation theories, and (2) to create online interactive world maps, including all LP phenotype and genotype frequency data reported to date. As a result, we have created two online interactive resources, which constitute an upgrade over previously published static world maps, and allow users a personalized data exploration, while at the same time accessing complete reports by population or ethnicity.

The Hippo Pathway Effector YAP1 Regulates Intestinal Epithelial Cell Differentiation

The human intestine is covered by epithelium, which is continuously replaced by new cells provided by stem cells located at the bottom of the glands. The maintenance of intestinal stem cells is supported by a niche which is composed of several signaling proteins including the Hippo pathway effectors YAP1/TAZ. The role of YAP1/TAZ in cell proliferation and regeneration is well documented but their involvement on the differentiation of intestinal epithelial cells is unclear. In the present study, the role of YAP1/TAZ on the differentiation of intestinal epithelial cells was investigated using the HT29 cell line, the only multipotent intestinal cell line available, with a combination of knockdown approaches. The expression of intestinal differentiation cell markers was tested by qPCR, Western blot, indirect immunofluorescence and electron microscopy analyses. The results show that TAZ is not expressed while the abolition of YAP1 expression led to a sharp increase in goblet and absorptive cell differentiation and reduction of some stem cell markers. Further studies using double knockdown experiments revealed that most of these effects resulting from YAP1 abolition are mediated by CDX2, a key intestinal cell transcription factor. In conclusion, our results indicate that YAP1/TAZ negatively regulate the differentiation of intestinal epithelial cells through the inhibition of CDX2 expression.

GATA factor transcriptional activity: Insights from genome-wide binding profiles

The members of the GATA family of transcription factors have homologous zinc fingers and bind to similar sequence motifs. Recent advances in genome-wide technologies and the integration of bioinformatics data have led to a better understanding of how GATA factors regulate gene expression; GATA-factor-induced transcriptional and epigenetic changes have now been analyzed at unprecedented levels of detail. Here, we review the results of genome-wide studies of GATA factor occupancy in human and murine cell lines and primary cells (as determined by chromatin immunoprecipitation sequencing), and then discuss the molecular mechanisms underlying the mediation of transcriptional and epigenetic regulation by GATA factors.

MiR-26a and miR-26b downregulate the expression of sucrase-isomaltase enzyme: A new chapter in diabetes treatment

Type II diabetes is a metabolic disease that has affected 460 million people around the globe and become a heavy burden on health care system. Diabetic patients suffer from hyperglycemia and hyperinsulinemia which can damage vital organs in body like heart, kidneys, eyes and nervous system. Different strategies have been introduced to control or lessen these diabetic complications in which one of the most promising approaches is the inhibition of intestinal sucrase-isomaltase (SI). Inhibition of this enzyme will block the release of glucose into bloodstream and lead to reduced postprandial hyperglycemia. MicroRNAs are small regulatory molecules that play critical roles in different cellular pathways and molecular mechanisms. It is proved that microRNAs have significant effects on cellular mechanisms involved in diabetes and can be used as biomarkers for diagnosis of this metabolic disease. Based on bioinformatics analysis miR-26a and miR-26b can interact with a conserved 3'-UTR region of SI mRNA which lead to a hypothesis that these miRs may have negative regulatory effect on this enzyme. In this study, we investigated the impact of high glucose conditions on expression of sucrase-isomaltase, miR-26a and miR-26b in caco-2 cell line. It is proved that in a simulated diabetic condition there is a reverse correlation between the expression pattern of these miRs and SI. QRT-PCR method was used to evaluate the expression of our target molecules. Interestingly, transfection of miR-26a and miR-26b in caco-2 cell line reduced the transcription of SI mRNA and decreased the sucrase and maltase activity of its active sites. To sum up, our results demonstrate the first evidence of the significant effect of miR-26a and miR-26b on SI expression and activity. We proved that these microRNAs may directly inhibit this enzyme and can be used as a new scaffold in search of finding novel treatments for type II diabetes.

The UDP-Glycosyltransferase (UGT) Superfamily: New Members, New Functions, and Novel Paradigms

UDP-glycosyltransferases (UGTs) catalyze the covalent addition of sugars to a broad range of lipophilic molecules. This biotransformation plays a critical role in elimination of a broad range of exogenous chemicals and by-products of endogenous metabolism, and also controls the levels and distribution of many endogenous signaling molecules. In mammals, the superfamily comprises four families: UGT1, UGT2, UGT3, and UGT8. UGT1 and UGT2 enzymes have important roles in pharmacology and toxicology including contributing to interindividual differences in drug disposition as well as to cancer risk. These UGTs are highly expressed in organs of detoxification (e.g., liver, kidney, intestine) and can be induced by pathways that sense demand for detoxification and for modulation of endobiotic signaling molecules. The functions of the UGT3 and UGT8 family enzymes have only been characterized relatively recently; these enzymes show different UDP-sugar preferences to that of UGT1 and UGT2 enzymes, and to date, their contributions to drug metabolism appear to be relatively minor. This review summarizes and provides critical analysis of the current state of research into all four families of UGT enzymes. Key areas discussed include the roles of UGTs in drug metabolism, cancer risk, and regulation of signaling, as well as the transcriptional and posttranscriptional control of UGT expression and function. The latter part of this review provides an in-depth analysis of the known and predicted functions of UGT3 and UGT8 enzymes, focused on their likely roles in modulation of levels of endogenous signaling pathways.

N-Glycomic and Transcriptomic Changes Associated with CDX1 mRNA Expression in Colorectal Cancer Cell Lines

The caudal-related homeobox protein 1 (CDX1) is a transcription factor, which is important in the development, differentiation, and homeostasis of the gut. Although the involvement of CDX genes in the regulation of the expression levels of a few glycosyltransferases has been shown, associations between glycosylation phenotypes and CDX1 mRNA expression have hitherto not been well studied. Triggered by our previous study, we here characterized the N-glycomic phenotype of 16 colon cancer cell lines, selected for their differential CDX1 mRNA expression levels. We found that high CDX1 mRNA expression associated with a higher degree of multi-fucosylation on N-glycans, which is in line with our previous results and was supported by up-regulated gene expression of fucosyltransferases involved in antenna fucosylation. Interestingly, hepatocyte nuclear factors (HNF)4A and HNF1A were, among others, positively associated with high CDX1 mRNA expression and have been previously proven to regulate antenna fucosylation. Besides fucosylation, we found that high CDX1 mRNA expression in cancer cell lines also associated with low levels of sialylation and galactosylation and high levels of bisection on N-glycans. Altogether, our data highlight a possible role of CDX1 in altering the N-glycosylation of colorectal cancer cells, which is a hallmark of tumor development.

Schlafen 3 Mediates the Differentiating Effects of Cdx2 in Rat IEC-Cdx2L1 Enterocytes

AIM

Mature, differentiated enterocytes are essential for normal gut function and critical to recovery from pathological conditions. Little is known about the factors that regulate intestinal epithelial cell differentiation in the adult intestine. The transcription factor, Cdx2, involved in enterocytic differentiation, remains expressed in the adult. Since we have implicated Slfn3 in differentiation in vivo and in vitro, we examined whether it also mediated differentiation in the IEC-Cdx2-L1 cell model of differentiation.

MATERIALS AND METHODS

IEC-Cdx2-L1 cells, permanently transfected with Cdx2 under the control of isopropyl-β-D-thiogalactoside (IPTG), were stimulated to differentiate by 16-day exposure to IPTG. Transcript levels of Cdx2, Slfn 3, and villin were determined by quantitative reverse transcriptase-polymerase chain reaction of mRNA isolated from IPTG-treated and control cells. Slfn3 expression was lowered with specific siRNA to investigate the role of Slfn3 in Cdx2-driven villin expression in IPTG-differentiated cells.

RESULTS

Slfn3 and villin expression were significantly greater in IPTG-treated cells. Slfn3 siRNA lowered Slfn3 expression and abolished the IPTG-induced rise in villin expression (p < .05 by ANOVA); Cdx2 expression was unaffected by Slfn3 siRNA.

DISCUSSION

The data indicate that the presence of Slfn3 is required for Cdx2 to induce villin expression, and thus differentiation. However, Slfn3 must also promote differentiation of Cdx2 independently since IEC-6 cells that do not normally express Cdx2 can be differentiated by a variety of Slfn3-dependent mechanisms.

Transcriptional regulation of human UDP-glucuronosyltransferase genes

Glucuronidation is an important metabolic pathway for many small endogenous and exogenous lipophilic compounds, including bilirubin, steroid hormones, bile acids, carcinogens and therapeutic drugs. Glucuronidation is primarily catalyzed by the UDP-glucuronosyltransferase (UGT) 1A and two subfamilies, including nine functional UGT1A enzymes (1A1, 1A3-1A10) and 10 functional UGT2 enzymes (2A1, 2A2, 2A3, 2B4, 2B7, 2B10, 2B11, 2B15, 2B17 and 2B28). Most UGTs are expressed in the liver and this expression relates to the major role of hepatic glucuronidation in systemic clearance of toxic lipophilic compounds. Hepatic glucuronidation activity protects the body from chemical insults and governs the therapeutic efficacy of drugs that are inactivated by UGTs. UGT mRNAs have also been detected in over 20 extrahepatic tissues with a unique complement of UGT mRNAs seen in almost every tissue. This extrahepatic glucuronidation activity helps to maintain homeostasis and hence regulates biological activity of endogenous molecules that are primarily inactivated by UGTs. Deciphering the molecular mechanisms underlying tissue-specific UGT expression has been the subject of a large number of studies over the last two decades. These studies have shown that the constitutive and inducible expression of UGTs is primarily regulated by tissue-specific and ligand-activated transcription factors (TFs) via their binding to cis-regulatory elements (CREs) in UGT promoters and enhancers. This review first briefly summarizes published UGT gene transcriptional studies and the experimental models and tools utilized in these studies, and then describes in detail the TFs and their respective CREs that have been identified in the promoters and/or enhancers of individual UGT genes.

Role of GATA factors in development, differentiation, and homeostasis of the small intestinal epithelium

The small intestinal epithelium develops from embryonic endoderm into a highly specialized layer of cells perfectly suited for the digestion and absorption of nutrients. The development, differentiation, and regeneration of the small intestinal epithelium require complex gene regulatory networks involving multiple context-specific transcription factors. The evolutionarily conserved GATA family of transcription factors, well known for its role in hematopoiesis, is essential for the development of endoderm during embryogenesis and the renewal of the differentiated epithelium in the mature gut. We review the role of GATA factors in the evolution and development of endoderm and summarize our current understanding of the function of GATA factors in the mature small intestine. We offer perspective on the application of epigenetics approaches to define the mechanisms underlying context-specific GATA gene regulation during intestinal development.

Spdef deletion rescues the crypt cell proliferation defect in conditional Gata6 null mouse small intestine

Background

GATA transcription factors are essential for self-renewal of the small intestinal epithelium. Gata4 is expressed in the proximal 85% of small intestine while Gata6 is expressed throughout the length of small intestine. Deletion of intestinal Gata4 and Gata6 results in an altered proliferation/differentiation phenotype, and an up-regulation of SAM pointed domain containing ETS transcription factor (Spdef), a transcription factor recently shown to act as a tumor suppressor. The goal of this study is to determine to what extent SPDEF mediates the downstream functions of GATA4/GATA6 in the small intestine. The hypothesis to be tested is that intestinal GATA4/GATA6 functions through SPDEF by repressing Spdef gene expression. To test this hypothesis, we defined the functions most likely regulated by the overlapping GATA6/SPDEF target gene set in mouse intestine, delineated the relationship between GATA6 chromatin occupancy and Spdef gene regulation in Caco-2 cells, and determined the extent to which prevention of Spdef up-regulation by Spdef knockout rescues the GATA6 phenotype in conditional Gata6 knockout mouse ileum.

Results

Using publicly available profiling data, we found that 83% of GATA6-regulated genes are also regulated by SPDEF, and that proliferation/cancer is the function most likely to be modulated by this overlapping gene set. In human Caco-2 cells, GATA6 knockdown results in an up-regulation of Spdef gene expression, modeling our mouse Gata6 knockout data. GATA6 occupies a genetic locus located 40 kb upstream of the Spdef transcription start site, consistent with direct regulation of Spdef gene expression by GATA6. Prevention of Spdef up-regulation in conditional Gata6 knockout mouse ileum by the additional deletion of Spdef rescued the crypt cell proliferation defect, but had little effect on altered lineage differentiation or absorptive enterocytes gene expression.

Conclusion

SPDEF is a key, immediate downstream effecter of the crypt cell proliferation function of GATA4/GATA6 in the small intestine.

Thyroid and glucocorticoid hormones induce expression of lactase-phlorizin hydrolase gene in CDX-2/HNF-1α co-transfected IEC-6 cells

Thyroid and glucocorticoid hormones and several transcriptional factors such as caudal type homeobox (CDX)-2 and hepatocyte nuclear factor (HNF)-1α are important for the differentiation of small intestinal absorptive cells and the consequent expression of genes related to the digestion/absorption of carbohydrates. In this study, we investigated whether thyroid and glucocorticoid hormones enhanced the expression of lactase-phlorizin hydrolase (LPH) gene, an intestine-specific gene that encodes an enzyme for lactose digestion, in small intestinal stem-like IEC-6 cells co-transfected with CDX-2 and HNF-1α using a retrovirus system. Changes in expression of intestine-specific genes caused by treatment with thyroid and/or glucocorticoid hormones were monitored in empty vector-transfected cells and in CDX-2/HNF-1α co-transfected cells by qRT-PCR. Stable co-transfection with CDX-2 and HNF-1α evoked the expression of the LPH gene in IEC-6 cells. Furthermore, treatment with a thyroid hormone, triiodothyronine, and a glucocorticoid receptor agonist, dexamethasone, significantly enhanced expression of the LPH, CDX-2 and HNF-1α genes in CDX-2/HNF-1α co-transfected IEC-6 cells. These results suggest that thyroid and glucocorticoid hormones synergistically enhance expression of the LPH gene in CDX-2/HNF-1α co-transfected IEC-6 cells.

GATA6 is required for proliferation, migration, secretory cell maturation, and gene expression in the mature mouse colon

Controlled renewal of the epithelium with precise cell distribution and gene expression patterns is essential for colonic function. GATA6 is expressed in the colonic epithelium, but its function in the colon is currently unknown. To define GATA6 function in the colon, we conditionally deleted Gata6 throughout the epithelium of small and large intestines of adult mice. In the colon, Gata6 deletion resulted in shorter, wider crypts, a decrease in proliferation, and a delayed crypt-to-surface epithelial migration rate. Staining techniques and electron microscopy indicated deficient maturation of goblet cells, and coimmunofluorescence demonstrated alterations in specific hormones produced by the endocrine L cells and serotonin-producing cells. Specific colonocyte genes were significantly downregulated. In LS174T, the colonic adenocarcinoma cell line, Gata6 knockdown resulted in a significant downregulation of a similar subset of goblet cell and colonocyte genes, and GATA6 was found to occupy active loci in enhancers and promoters of some of these genes, suggesting that they are direct targets of GATA6. These data demonstrate that GATA6 is necessary for proliferation, migration, lineage maturation, and gene expression in the mature colonic epithelium.

PER1 modulates SGLT1 transcription in vitro independent of E-box status

BACKGROUND AND AIMS

The intestine demonstrates profound circadian rhythmicity in glucose absorption in rodents, mediated entirely by rhythmicity in the transcription, translation, and function of the sodium glucose co-transporter SGLT1 (Slc5a1). Clock genes are rhythmic in the intestine and have been implicated in the regulation of rhythmicity of other intestinal genes; however, their role in the regulation of SGLT1 is unknown. We investigated the effects of one clock gene, PER1, on SGLT1 transcription in vitro.

METHODS

Caco-2 cells were stably transfected with knockdown vectors for PER1 and mRNA expression of clock genes and SGLT1 determined using quantitative polymerase chain reaction (qPCR). Chinese hamster ovary (CHO) cells were transiently cotransfected with combinations of the PER1 expression vectors and the wild-type SGLT1-luciferase promoter construct or the promoter with mutated E-box sequences.

RESULTS

Knockdown of PER1 increased native SGLT1 expression in Caco-2 enterocytes, while promoter studies confirmed that the inhibitory activity of PER1 on SGLT1 occurs via the proximal 1 kb of the SGLT1 promoter. E-box sites exerted a suppressive effect on the SGLT1 promoter; however, mutation of E-boxes had little effect on the inhibitory activity of PER1 on the SGLT1 promoter suggesting that the actions of PER1 on SGLT1 are independent of E-boxes.

CONCLUSIONS

Our findings suggest that PER1 exerts an indirect suppressive effect on SGLT1, possibly acting via other clock-controlled genes binding to non-E-box sites on the SGLT1 promoter. Understanding the regulation of rhythmicity of SGLT1 may lead to new treatments for the modulation of SGLT1 expression in conditions such as malabsorption, diabetes, and obesity.

PIAS1 is a GATA4 SUMO ligase that regulates GATA4-dependent intestinal promoters independent of SUMO ligase activity and GATA4 sumoylation

GATA4 confers cell type-specific gene expression on genes expressed in cardiovascular, gastro-intestinal, endocrine and neuronal tissues by interacting with various ubiquitous and cell-type-restricted transcriptional regulators. By using yeast two-hybrid screening approach, we have identified PIAS1 as an intestine-expressed GATA4 interacting protein. The physical interaction between GATA4 and PIAS1 was confirmed in mammalian cells by coimmunoprecipitation and two-hybrid analysis. The interacting domains were mapped to the second zinc finger and the adjacent C-terminal basic region of GATA4 and the RING finger and the adjoining C-terminal 60 amino acids of PIAS1. PIAS1 and GATA4 synergistically activated IFABP and SI promoters but not LPH promoters suggesting that PIAS1 differentially activates GATA4 targeted promoters. In primary murine enterocytes PIAS1 was recruited to the GATA4-regulated IFABP promoter. PIAS1 promoted SUMO-1 modification of GATA4 on lysine 366. However, sumoylation was not required for the nuclear localization and stability of GATA4. Further, neither GATA4 sumoylation nor the SUMO ligase activity of PIAS1 was required for coactivation of IFABP promoter by GATA4 and PIAS1. Together, our results demonstrate that PIAS1 is a SUMO ligase for GATA4 that differentially regulates GATA4 transcriptional activity independent of SUMO ligase activity and GATA4 sumoylation.

Feeding rats dietary resistant starch reduces both the binding of ChREBP and the acetylation of histones on the Thrsp gene in the jejunum

We have previously reported that the thyroid hormone-responsive spot 14 protein (Thrsp) gene is expressed in rat jejunum. In this study, we found that jejunal mRNA and protein expressions of Thrsp were markedly reduced in rats fed a diet containing a high amount of resistant starch (RS), which is an indigestible starch, for 7 days, compared with those fed a regular starch diet. Furthermore, we found that the binding of carbohydrate response element binding protein (ChREBP), which is a key transcription factor for the Thrsp gene, and the acetylation of histones H3 and H4, which is one of the histone modifications for transactivation, on the Thrsp gene were reduced by feeding the RS diet. These results suggest that the reduction of jejunal Thrsp gene expression by feeding a diet rich in less-digestible starch is associated with decreases in the binding of ChREBP and the acetylation of histones on the gene.

The -14010*C variant associated with lactase persistence is located between an Oct-1 and HNF1α binding site and increases lactase promoter activity

In most people worldwide intestinal lactase expression declines in childhood. In many others, particularly in Europeans, lactase expression persists into adult life. The lactase persistence phenotype is in Europe associated with the -13910*T single nucleotide variant located 13,910 bp upstream the lactase gene in an enhancer region that affects lactase promoter activity. This variant falls in an Oct-1 binding site and shows greater Oct-1 binding than the ancestral variant and increases enhancer activity. Several other variants have been identified very close to the -13910 position, which are associated with lactase persistence in the Middle East and Africa. One of them, the -14010*C, is associated with lactase persistence in Africa. Here we show by deletion analysis that the -14010 position is located in a 144 bp region that reduces the enhancer activity. In transfections the -14010*C allele shows a stronger enhancer effect than the ancestral -4010*G allele. Binding sites for Oct-1 and HNF1α surrounding the -14010 position were identified by gel shift assays, which indicated that -14010*C has greater binding affinity to Oct-1 than -14010*G.

Genome-wide analysis of CDX2 binding in intestinal epithelial cells (Caco-2)

The CDX2 transcription factor is known to play a crucial role in inhibiting proliferation, promoting differentiation and the expression of intestinal specific genes in intestinal cells. The overall effect of CDX2 in intestinal cells has previously been investigated in conditional knock-out mice, revealing a critical role of CDX2 in the formation of the normal intestinal identity. The identification of direct targets of transcription factors is a key problem in the study of gene regulatory networks. The ChIP-seq technique combines chromatin immunoprecipitation (ChIP) with next generation sequencing resulting in a high throughput experimental method of identifying direct targets of specific transcription factors. The method was applied to CDX2, leading to the identification of the direct binding of CDX2 to several known and novel target genes in the intestinal cell. Examination of the transcript levels of selected genes verified the regulatory role of CDX2 binding. The results place CDX2 as a key node in a transcription factor network controlling the proliferation and differentiation of intestinal cells.

Cooperation between HNF-1alpha, Cdx2, and GATA-4 in initiating an enterocytic differentiation program in a normal human intestinal epithelial progenitor cell line

In the intestinal epithelium, the Cdx, GATA, and HNF transcription factor families are responsible for the expression of differentiation markers such as sucrase-isomaltase. Although previous studies have shown that Cdx2 can induce differentiation in rat intestinal IEC-6 cells, no data are available concerning the direct implication of transcription factors on differentiation in human normal intestinal epithelial cell types. We investigated the role of Cdx2, GATA-4, and HNF-1alpha using the undifferentiated human intestinal epithelial crypt cell line HIEC. These transcription factors were tested on proliferation and expression of polarization and differentiation markers. Ectopic expression of Cdx2 or HNF-1alpha, alone or in combination, altered cell proliferation abilities through the regulation of cyclin D1 and p27 expression. HNF-1alpha and GATA-4 together induced morphological modifications of the cells toward polarization, resulting in the appearance of functional features such as microvilli. HNF-1alpha was also sufficient to induce the expression of cadherins and dipeptidylpeptidase, whereas in combination with Cdx2 it allowed the expression of the late differentiation marker sucrase-isomaltase. Large-scale analysis of gene expression confirmed the cooperative effect of these factors. Finally, although DcamKL1 and Musashi-1 expression were downregulated in differentiated HIEC, other intestinal stem cell markers, such as Bmi1, were unaffected. These observations show that, in cooperation with Cdx2, HNF-1alpha acts as a key factor on human intestinal cells to trigger the onset of their functional differentiation program whereas GATA-4 appears to promote morphological changes.

Selective activation of tumor growth-promoting Ca2+ channel MS4A12 in colon cancer by caudal type homeobox transcription factor CDX2

Colon cancer-associated MS4A12 is a novel colon-specific component of store-operated Ca²⁺ (SOC) entry sensitizing cells for epidermal growth factor (EGF)-mediated effects on proliferation and chemotaxis. In the present study, we investigated regulation of the MS4A12 promoter to understand the mechanisms responsible for strict transcriptional restriction of this gene to the colonic epithelial cell lineage. DNA-binding assays and luciferase reporter assays showed that MS4A12 promoter activity is governed by a single CDX homeobox transcription factor binding element. RNA interference (RNAi)-mediated silencing of intestine-specific transcription factors CDX1 and CDX2 and chromatin immunoprecipitation (ChIP) in LoVo and SW48 colon cancer cells revealed that MS4A12 transcript and protein expression is essentially dependent on the presence of endogenous CDX2. In summary, our findings provide a rationale for colon-specific expression of MS4A12. Moreover, this is the first report establishing CDX2 as transactivator of tumor growth-promoting gene expression in colon cancer, adding to untangle the complex and conflicting biological functions of CDX2 in colon cancer and supporting MS4A12 as important factor for normal colonic development as well as for the biology and treatment of colon cancer.

Mapping of HNF4alpha target genes in intestinal epithelial cells

BACKGROUND

The role of HNF4alpha has been extensively studied in hepatocytes and pancreatic beta-cells, and HNF4alpha is also regarded as a key regulator of intestinal epithelial cell differentiation. The aim of the present work is to identify novel HNF4alpha target genes in the human intestinal epithelial cells in order to elucidate the role of HNF4alpha in the intestinal differentiation progress.

METHODS

We have performed a ChIP-chip analysis of the human intestinal cell line Caco-2 in order to make a genome-wide identification of HNF4alpha binding to promoter regions. The HNF4alpha ChIP-chip data was matched with gene expression and histone H3 acetylation status of the promoters in order to identify HNF4alpha binding to actively transcribed genes with an open chromatin structure.

RESULTS

1,541 genes were identified as potential HNF4alpha targets, many of which have not previously been described as being regulated by HNF4alpha. The 1,541 genes contributed significantly to gene ontology (GO) pathways categorized by lipid and amino acid transport and metabolism. An analysis of the homeodomain transcription factor Cdx-2 (CDX2), the disaccharidase trehalase (TREH), and the tight junction protein cingulin (CGN) promoters verified that these genes are bound by HNF4alpha in Caco2 cells. For the Cdx-2 and trehalase promoters the HNF4alpha binding was verified in mouse small intestine epithelium.

CONCLUSION

The HNF4alpha regulation of the Cdx-2 promoter unravels a transcription factor network also including HNF1alpha, all of which are transcription factors involved in intestinal development and gene expression.

Intestinal hormones and growth factors: effects on the small intestine

There are various hormones and growth factors which may modify the intestinal absorption of nutrients, and which might thereby be useful in a therapeutic setting, such as in persons with short bowel syndrome. In part I, we focus first on insulin-like growth factors, epidermal and transferring growth factors, thyroid hormones and glucocorticosteroids. Part II will detail the effects of glucagon-like peptide (GLP)-2 on intestinal absorption and adaptation, and the potential for an additive effect of GLP2 plus steroids.

Lactose digestion and the evolutionary genetics of lactase persistence

It has been known for some 40 years that lactase production persists into adult life in some people but not in others. However, the mechanism and evolutionary significance of this variation have proved more elusive, and continue to excite the interest of investigators from different disciplines. This genetically determined trait differs in frequency worldwide and is due to cis-acting polymorphism of regulation of lactase gene expression. A single nucleotide polymorphism located 13.9 kb upstream from the lactase gene (C-13910 > T) was proposed to be the cause, and the -13910*T allele, which is widespread in Europe was found to be located on a very extended haplotype of 500 kb or more. The long region of haplotype conservation reflects a recent origin, and this, together with high frequencies, is evidence of positive selection, but also means that -13910*T might be an associated marker, rather than being causal of lactase persistence itself. Doubt about function was increased when it was shown that the original SNP did not account for lactase persistence in most African populations. However, the recent discovery that there are several other SNPs associated with lactase persistence in close proximity (within 100 bp), and that they all reside in a piece of sequence that has enhancer function in vitro, does suggest that they may each be functional, and their occurrence on different haplotype backgrounds shows that several independent mutations led to lactase persistence. Here we provide access to a database of worldwide distributions of lactase persistence and of the C-13910*T allele, as well as reviewing lactase molecular and population genetics and the role of selection in determining present day distributions of the lactase persistence phenotype.

GATA4 mediates gene repression in the mature mouse small intestine through interactions with friend of GATA (FOG) cofactors

GATA4, a transcription factor expressed in the proximal small intestine but not in the distal ileum, maintains proximal-distal distinctions by multiple processes involving gene repression, gene activation, and cell fate determination. Friend of GATA (FOG) is an evolutionarily conserved family of cofactors whose members physically associate with GATA factors and mediate GATA-regulated repression in multiple tissues. Using a novel, inducible, intestine-specific Gata4 knock-in model in mice, in which wild-type GATA4 is specifically inactivated in the small intestine, but a GATA4 mutant that does not bind FOG cofactors (GATA4ki) continues to be expressed, we found that ileal-specific genes were significantly induced in the proximal small intestine (P<0.01); in contrast, genes restricted to proximal small intestine and cell lineage markers were unaffected, indicating that GATA4-FOG interactions contribute specifically to the repression function of GATA4 within this organ. Fog1 mRNA displayed a proximal-distal pattern that parallels that of Gata4, and FOG1 protein was co-expressed with GATA4 in intestinal epithelial cells, implicating FOG1 as the likely mediator of GATA4 function in the small intestine. Our data are the first to indicate FOG function and expression in the mammalian small intestine.

Cytokeratin and CDX-2 expression in Barrett's esophagus

OBJECTIVE

Barrett's esophagus (BE) is a premalignant condition of the distal esophagus. For diagnostic purposes it is important to find biomarkers that can specifically identify BE, for instance to differentiate BE epithelial cells from gastric cardia epithelial cells in brush cytology specimens. The objective of this study was to determine the specificity of CDX-2 and a set of cytokeratins (CKs) as specific markers for BE as compared with normal squamous esophageal and gastric cardia tissue.

MATERIAL AND METHODS

Immunohistochemistry (IHC) with specific antibodies against CDX-2, and a set of CKs was performed on fresh frozen consecutive tissue sections of normal squamous, gastric cardia and non-dysplastic BE of 80 patients.

RESULTS

IHC results showed CK8, CK18 and CK20 expression in both BE and gastric cardia, while CK7 was seen in all BE but also in 26% of gastric cardia biopsies. CK10/13 was only expressed in normal squamous epithelium. CDX-2 nuclear staining was found in 87.5% of the BE biopsies, whereas normal squamous esophagus and cardia biopsies were negative.

CONCLUSIONS

CDX-2 in combination with a set of CKs can be used as biomarkers to distinguish between BE and normal squamous esophagus. In order to distinguish BE from cardia tissue, a combination of CDX-2 and CK7 is most informative.

Defining the transcriptional regulation of the intestinal sodium-glucose cotransporter using RNA-interference mediated gene silencing

BACKGROUND

The sodium glucose cotransporter (SGLT1) is responsible for all active intestinal glucose uptake. Hepatocyte nuclear factors 1 alpha and beta (HNF 1 alpha and HNF 1 beta) activate the SGLT1 promoter, whereas GATA-binding protein 5 (GATA-5) and caudal-type homeobox protein 2 (CDX2) regulate transcription of other intestinal genes. We investigated SGLT1 regulation by these transcription factors using promoter studies and RNA interference.

METHODS

Chinese hamster ovary (CHO) cells were transiently cotransfected with an SGLT1-luciferase promoter construct and combinations of expression vectors for HNF 1 alpha, HNF 1 beta, CDX2, and GATA-5. Caco-2 cells were stably transfected with knockdown vectors for either HNF 1 alpha or HNF 1 beta. mRNA levels of HNF 1 alpha, HNF 1 beta, and SGLT1 were determined using quantitative polymerase chain reaction (qPCR).

RESULTS

HNF 1 alpha, GATA-5, and HNF 1 beta significantly activated the SGLT1 promoter (P < .05). Cotransfection of GATA-5 with HNF 1 alpha had an additive effect, whereas HNF 1 beta and CDX2 antagonized HNF 1 alpha and GATA-5. SGLT1 expression was significantly reduced in HNF 1 alpha or HNF 1 beta knockdowns (P < .001). HNF alpha knockdown significantly reduced HNF 1 beta expression and vice versa (P < .005).

CONCLUSIONS

HNF 1 alpha and HNF 1 beta are important transcription factors for endogenous SGLT1 expression by cultured enterocytes. GATA-5 and CDX2 also regulate SGLT1 promoter activity and show cooperativity with the HNF1s. We, therefore, propose a multifactorial model for SGLT1 regulation, with interactions between HNF1, GATA-5, and CDX2 modulating intestinal glucose absorption.

Transcriptional regulation of the fatty acid binding protein 2 (FABP2) gene by the hepatic nuclear factor 1 alpha (HNF-1alpha)

The human fatty acid binding protein (FABP2) is involved in intestinal absorption and intracellular trafficking of long-chain fatty acids. Here we investigate transcriptional regulation of FABP2 by the endodermal hepatic nuclear factor 1 alpha (HNF-1alpha). In electromobility shift and supershift assays we show the presence of two adjacent HNF-1alpha binding sites within the FABP2 promoter regions -185 to -165 and -169 to -149. HNF-1alpha activates an FABP2 promoter luciferase construct by 3.5 and 20-fold in Caco-2 and Hela cells, respectively. Mutational analysis of HNF-1alpha elements resulted in about 50% reduction of basal and HNF-1alpha induced activity of FABP2 promoter constructs, predominantly caused by deletion of the -185 to -165 site. Thus, our data suggest a major role of HNF-1alpha in control of FABP2 expression in intestine via a functional HNF-1alpha recognition element within FABP2 promoter region -185 to -165.

Role of the GATA family of transcription factors in endocrine development, function, and disease

The WGATAR motif is a common nucleotide sequence found in the transcriptional regulatory regions of numerous genes. In vertebrates, these motifs are bound by one of six factors (GATA1 to GATA6) that constitute the GATA family of transcriptional regulatory proteins. Although originally considered for their roles in hematopoietic cells and the heart, GATA factors are now known to be expressed in a wide variety of tissues where they act as critical regulators of cell-specific gene expression. This includes multiple endocrine organs such as the pituitary, pancreas, adrenals, and especially the gonads. Insights into the functional roles played by GATA factors in adult organ systems have been hampered by the early embryonic lethality associated with the different Gata-null mice. This is now being overcome with the generation of tissue-specific knockout models and other knockdown strategies. These approaches, together with the increasing number of human GATA-related pathologies have greatly broadened the scope of GATA-dependent genes and, importantly, have shown that GATA action is not necessarily limited to early development. This has been particularly evident in endocrine organs where GATA factors appear to contribute to the transcription of multiple hormone-encoding genes. This review provides an overview of the GATA family of transcription factors as they relate to endocrine function and disease.

Epigenetic silencing of CDX2 is a feature of squamous esophageal cancer

CDX2, a mammalian homologue of the homeobox gene 'caudal,' is expressed in gut epithelia and plays an important role in establishing the intestinal phenotype during development. Mice heterozygously disrupted for CDX2 develop disorganized polypoid hamartomas with glandular epithelium and stratified squamous metaplasia resembling foregut mucosa. Since no genetic disruptions of CDX2 have been reported to explain loss of gene function, we examined whether epigenetic mechanisms altered CDX2 expression. Eleven of 17 squamous esophageal cancer cell lines lacked expression of CDX2 that was restored following treatment with 5-aza-2'-deoxycytidine, while all colorectal cancer cell lines expressed CDX2. Loss of expression was associated with DNA methylation in the 5' region of CDX2 determined by methylation specific PCR and bisulfite sequencing. Methylation of CDX2 was rare in primary colorectal (1 of 44 tumors, 2%) and esophageal adenocarcinoma neoplasms (2 of 43 tumors, 5%), but was common in esophageal squamous carcinoma (24 of 45 tumors, 49%). No CDX2 methylation was found in normal tissues. Using semi-quantitative RT-PCR, expression of CDX2 was found in low level in normal esophagus, at higher levels in primary adenocarcinoma of the esophagus, but not in primary squamous cancers of the esophagus. Restoration of CDX2 in silenced cell lines resulted in expression of the CDX2 target gene MUC2, a gene important in glandular differentiation. Our results suggest that the inactivation of CDX2 in esophageal cancer associated with DNA methylation may be an important determinant of the squamous or non-adenomatous phenotype.

Using genomics to understand intestinal biology

The use of microarrays to evaluate the transcriptome has transformed our view of biology. In addition to the focused, hypothesis-testing studies that we have traditionally conducted in cell biology, we are now able to see global changes within the entire system of the cell in response to a treatment. By examining a biological question under multiple complementary perturbations model systems (e.g. yeast, C. Elegans) have revealed new complexity that would have been impossible to see on a gene-by-gene approach. Unfortunately, beyond the use of transcript profiles to define the molecular signature of diseases (e.g. cancer), transcriptomics has not been extensively used to study intestinal biology. This review will provide a roadmap for effective use of gene expression profiling for biological research and will review some of the microarray work that has been done to better understand the nature of intestinal development and enterocyte differentiation.

Cooperation between GATA4 and TGF-beta signaling regulates intestinal epithelial gene expression

Members of the transforming growth factor-beta (TGF-beta) family have been shown to play an important role in the regulation of gut epithelial gene expression. We have used the intestinal alkaline phosphatase (IAP) and intestinal fatty acid binding protein (IFABP) promoters to dissect the mechanisms by which TGF-beta1 signaling regulates gut epithelial gene expression. TGF-beta signaling alone was not sufficient for activation of IAP and IFABP promoters. However, TGF-beta signaling cooperated with the gut epithelial transcription factor GATA4 to synergistically activate IAP and IFABP promoters. Coexpression of GATA4 along with the TGF-beta1 signal transducing downstream effectors such as Smad2, 3, and 4 resulted in synergistic activation of both IAP and IFABP promoters. This synergistic activation was reduced by simultaneous expression of dominant-negative Smad4. -40 and -89 GATA binding sites in the IFABP promoter were required for the synergistic activation by Smad2, 3, and 4 and GATA4. GATA4 and Smad2, 3, and 4 physically associated with each other and this interaction was mediated through the MH2 domain of Smad2, 3, and 4 and the second zinc finger and the COOH-terminal basic domain of GATA4. The COOH-terminal activation domain and the Smad-interacting second zinc finger domain of GATA4 were required for the synergistic activation of the IFABP promoter. Naturally occurring oncogenic mutations within the GATA4-interacting MH2 domain of Smad2 reduced the coactivation of IFABP promoter by Smad2 and GATA4. Our results suggest that the TGF-beta signaling regulates gut epithelial gene expression by targeting GATA4.

Gata4 and Hnf1alpha are partially required for the expression of specific intestinal genes during development

The terminal differentiation phases of intestinal development in mice occur during cytodifferentiation and the weaning transition. Lactase-phlorizin hydrolase (LPH), liver fatty acid binding protein (Fabp1), and sucrase-isomaltase (SI) are well-characterized markers of these transitions. With the use of gene inactivation models in mature mouse jejunum, we have previously shown that a member of the zinc finger transcription factor family (Gata4) and hepatocyte nuclear factor-1alpha (Hnf1alpha) are each indispensable for LPH and Fabp1 gene expression but are both dispensable for SI gene expression. In the present study, we used these models to test the hypothesis that Gata4 and Hnf1alpha regulate LPH, Fabp1, and SI gene expression during development, specifically focusing on cytodifferentiation and the weaning transition. Inactivation of Gata4 had no effect on LPH gene expression during either cytodifferentiation or suckling, whereas inactivation of Hnf1alpha resulted in a 50% reduction in LPH gene expression during these same time intervals. Inactivation of Gata4 or Hnf1alpha had a partial effect ( approximately 50% reduction) on Fabp1 gene expression during cytodifferentiation and suckling but no effect on SI gene expression at any time during development. Throughout the suckling period, we found a surprising and dramatic reduction in Gata4 and Hnf1alpha protein in the nuclei of absorptive enterocytes of the jejunum despite high levels of their mRNAs. Finally, we show that neither Gata4 nor Hnf1alpha mediates the glucocorticoid-induced precocious maturation of the intestine but rather are downstream targets of this process. Together, these data demonstrate that specific intestinal genes have differential requirements for Gata4 and Hnf1alpha that are dependent on the developmental time frame in which they are expressed.

Carbohydrate/fat ratio in the diet alters histone acetylation on the sucrase-isomaltase gene and its expression in mouse small intestine

A diet with a high carbohydrate/fat ratio enhances jejunal SI gene expression. Using ChIP assay, we revealed that the acetylation of histone H3 on transcriptional region and H4 on promoter region, respectively, of mouse SI gene are high. The acetylation of histone H3 and H4 as well as binding of HNF-1 and Cdx-2 on SI gene, was enhanced by increase in carbohydrate/fat ratio in the diet. These suggest that induction of SI gene by the diet rich in carbohydrate is associated with acetylation of histone H3 and H4 as well as binding of HNF-1 and Cdx-2 on SI gene.

Role of eIF3a (eIF3 p170) in intestinal cell differentiation and its association with early development

Eukaryotic initiation factor 3a (eIF3a) has been suggested to play a regulatory role in mRNA translation. Decreased eIF3a expression has been observed in differentiated cells while higher levels have been observed in cancer cells. However, whether eIF3a plays any role in differentiation and development is currently unknown. Here, we investigated eIF3a expression during mouse development and its role in differentiation of colon epithelial cells. We found that eIF3a expression was higher in fetal tissues compared with postnatal ones. Its expression in intestine, stomach, and lung abruptly stopped on the 18th day in gestation but persisted in liver, kidney, and heart throughout the postnatal stage at decreased levels. Similarly, eIF3a expression in colon cancer cell lines, HT-29 and Caco-2, drastically decreased prior to differentiation. Enforced eIF3a expression inhibited while knocking it down using small interference RNA promoted Caco-2 differentiation. Thus, eIF3a may play some roles in development and differentiation and that the decreased eIF3a expression may be a pre-requisite of intestinal epithelial cell differentiation.

CDX2 promotes anchorage-independent growth by transcriptional repression of IGFBP-3

CDX2 is a Drosophila caudal-related homeobox transcription factor that is important for the establishment and maintenance of intestinal epithelial cells. We have reported that CDX2 promotes tumorigenicity in a subset of human colorectal cancer cell lines. Here, we present evidence that CDX2 negatively regulates the well-documented growth inhibitor insulin-like growth factor binding protein-3 (IGFBP-3). Specifically, CDX2 binds to the IGFBP-3 gene promoter and can repress IGFBP-3 transcription, protein expression and secretion. Furthermore, inhibition of IGFBP-3 partially rescues the decreased anchorage-independent growth phenotype observed in CDX2 knockout cells. These data demonstrate for the first time that (1) CDX2 can function as a transcriptional repressor, and (2) one mechanism by which CDX2 promotes anchorage-independent growth is by transcriptional repression of IGFBP-3.

Gata4 is essential for the maintenance of jejunal-ileal identities in the adult mouse small intestine

Gata4, a member of the zinc finger family of GATA transcription factors, is highly expressed in duodenum and jejunum but is nearly undetectable in distal ileum of adult mice. We show here that the caudal reduction of Gata4 is conserved in humans. To test the hypothesis that the regional expression of Gata4 is critical for the maintenance of jejunal-ileal homeostasis in the adult small intestine in vivo, we established an inducible, intestine-specific model that results in the synthesis of a transcriptionally inactive Gata4 mutant. Synthesis of mutant Gata4 in jejuna of 6- to 8-week-old mice resulted in an attenuation of absorptive enterocyte genes normally expressed in jejunum but not in ileum, including those for the anticipated targets liver fatty acid binding protein (Fabp1) and lactase-phlorizin hydrolase (LPH), and a surprising induction of genes normally silent in jejunum but highly expressed in ileum, specifically those involved in bile acid transport. Inactivation of Gata4 resulted in an increase in the goblet cell population and a redistribution of the enteroendocrine subpopulations, all toward an ileal phenotype. The gene encoding Math1, a known activator of the secretory cell fate, was induced approximately 75% (P < 0.05). Gata4 is thus an important positional signal required for the maintenance of jejunal-ileal identities in the adult mouse small intestine.

Cooperative interactions among intestinal GATA factors in activating the rat liver fatty acid binding protein gene

GATA-4, GATA-5, and GATA-6 are endodermal zinc-finger transcription factors that activate numerous enterocytic genes. GATA-4 and GATA-6 but not GATA-5 are present in adult murine small intestinal enterocytes, and we now report the simultaneous presence of all three GATA factors in murine small intestinal enterocytes before weaning age. An immunohistochemical survey detected enterocytic GATA-4 and GATA-6 at birth and 1 wk of age and GATA-5 at 1 wk but not birth. Interactions among GATA factors were explored utilizing a transgene constructed from the proximal promoter of the rat liver fatty acid binding protein gene (Fabp1). GATA-4 and GATA-5 but not GATA-6 activate the Fabp1 transgene through a cognate binding site at -128. A dose-response assay revealed a maximum in transgene activation by both factors, where additional factor did not further increase transgene activity. However, at saturated levels of GATA-4, additional transgene activation was achieved by adding GATA-5 expression construct, and vice versa. Similar cooperativity occurred with GATA-5 and GATA-6. Identical interactions were observed with a target transgene consisting of a single GATA site upstream of a minimal promoter. Furthermore, GATA-4 and GATA-5 or GATA-5 and GATA-6 bound to each other in solution. These results are consistent with tethering of one GATA factor to the Fabp1 promoter through interaction with a second GATA factor to produce increased target gene activation. Cooperative target gene activation was specific to an intestinal cell line and may represent a mechanism by which genes are activated in the small intestinal epithelium during the period before weaning.

Hepatocyte nuclear factor-1alpha is required for expression but dispensable for histone acetylation of the lactase-phlorizin hydrolase gene in vivo

Hepatocyte nuclear factor-1alpha (HNF-1alpha) is a modified homeodomain-containing transcription factor that has been implicated in the regulation of intestinal genes. To define the importance and underlying mechanism of HNF-1alpha for the regulation of intestinal gene expression in vivo, we analyzed the expression of the intestinal differentiation markers and putative HNF-1alpha targets lactase-phlorizin hydrolase (LPH) and sucrase-isomaltase (SI) in hnf1alpha null mice. We found that in adult jejunum, LPH mRNA in hnf1alpha(-/-) mice was reduced 95% compared with wild-type controls (P < 0.01, n = 4), whereas SI mRNA was virtually identical to that in wild-type mice. Furthermore, SI mRNA abundance was unchanged in the absence of HNF-1alpha along the length of the adult mouse small intestine as well as in newborn jejunum. We found that HNF-1alpha occupies the promoters of both the LPH and SI genes in vivo. However, in contrast to liver and pancreas, where HNF-1alpha regulates target genes by recruitment of histone acetyl transferase activity to the promoter, the histone acetylation state of the LPH and SI promoters was not affected by the presence or absence of HNF-1alpha. Finally, we showed that a subset of hypothesized intestinal target genes is regulated by HNF-1alpha in vivo and that this regulation occurs in a defined tissue-specific and developmental context. These data indicate that HNF-1alpha is an activator of a subset of intestinal genes and induces these genes through an alternative mechanism in which it is dispensable for chromatin remodeling.

Cdx2 modulates proliferation in normal human intestinal epithelial crypt cells

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

Transcriptional regulation of the NADPH oxidase isoform, Nox1, in colon epithelial cells: role of GATA-binding factor(s)

Nonphagocytic NADPH oxidases (Noxs) are major sources of reactive oxygen species (ROS) and exist as a family of isoenzymes with tissue-restricted expression and functions. Nox1, expressed in colon epithelium and vascular smooth muscle, is suggested to be involved in innate immune defense and cell growth or proliferation. The transcriptional regulation of Nox1 appears to be particularly important in the modulation of its activity but the underlying mechanisms are unknown. Here we have identified the functional Nox1 promoter in human colon epithelial Caco-2 cells, and show that a 520-bp genomic fragment encompassing the CAP site is sufficient to direct high levels of expression of a linked reporter gene in these cells. Deletion analyses together with electrophoretic mobility-shift assays (EMSAs) suggest that maximal promoter activity is dependent on a GATA-binding site, conserved between human and mouse, within the proximal promoter region. The ability of mouse GATA factors to transactivate the Nox1 promoter was demonstrated in Cos-7 cells and site-directed mutagenesis of the conserved GATA-binding site further demonstrates that the regulation of Nox1 transcription is mediated by the direct binding of a GATA factor to the Nox1 proximal promoter. We also identified more distal, upstream regions which act to repress significantly expression from the Nox1 promoter.

Spatio-temporal patterns of intestine-specific transcription factor expression during postnatal mouse gut development

The small intestine matures from a primitive tube into morphologically and functionally distinct regions during gut development. Maximal expression of the genes encoding the digestive enzymes lactase-phlorizin hydrolase and sucrase-isomaltase is spatially restricted to distinct segments along the anterior-posterior axis of the small intestine and is temporally regulated during postnatal maturation. Transcription factors capable of interacting with the intestinal lactase and sucrase gene promoters are candidate regulators of spatio-temporal patterning during gut development and maturation. We aimed to quantitatively examine and compare the relative expression levels of a set of intestine-specific transcription factors along the anterior-posterior gut axis during postnatal maturation. Our analysis was focused on the transcription factors capable of regulating the intestinal lactase and sucrase-isomaltase genes. A real-time PCR protocol was used to quantitatively examine and compare spatially and temporally the relative transcript abundance levels for intestine-specific factors during postnatal intestinal maturation. Distinct spatial expressions patterns were detected along the length of the small intestine for PDX-1, Cdx-2, GATA-4, GATA-5, GATA-6, HNF-1alpha, HNF-1beta and CDP transcription factor genes. There is a general decline in transcript abundance for the factor genes during postnatal maturation. Defining the spatio-temporal expression patterns for intestine-specific transcription factor genes contributes to investigation of the roles that factor gradients play in mediating gut development and differentiation.

T-13910 DNA variant associated with lactase persistence interacts with Oct-1 and stimulates lactase promoter activity in vitro

Two phenotypes exist in the human population with regard to expression of lactase in adults. Lactase non-persistence (adult-type hypolactasia and lactose intolerance) is characterized by a decline in the expression of lactase-phlorizin hydrolase (LPH) after weaning. In contrast, lactase-persistent individuals have a high LPH throughout their lifespan. Lactase persistence and non-persistence are associated with a T/C polymorphism at position -13,910 upstream the lactase gene. A nuclear factor binds more strongly to the T-13,910 variant associated with lactase persistence than the C-13,910 variant associated with lactase non-persistence. Oct-1 and glyceraldehyde-3-phosphate dehydrogenase were co-purified by DNA affinity purification using the sequence of the T-13,910 variant. Supershift analyses show that Oct-1 binds directly to the T-13,910 variant, and we suggest that GAPDH is co-purified due to interactions with Oct-1. Expression of Oct-1 stimulates reporter gene expression from the T and the C-13,910 variant/LPH promoter constructs only when it is co-expressed with HNF1alpha. Binding sites for other intestinal transcription factors (GATA-6, HNF4alpha, Fox and Cdx-2) were identified in the region of the -13,910 T/C polymorphism. Three of these sites are required for the enhancer activity of the -13,910 region. The data suggest that the binding of Oct-1 to the T-13,910 variant directs increased lactase promoter activity and this might provide an explanation for the lactase persistence phenotype in the human population.

Differential expression of claudin-2 along the human intestine: Implication of GATA-4 in the maintenance of claudin-2 in differentiating cells

Claudins, and particularly claudin-2, are important regulatory components of tight junction permeability. A better understanding of the involvement of claudin-2 in intestinal barrier functions requires the characterization of its distribution and regulation in the intestine. Interestingly, the claudin-2 gene promoter harbors a number of similarities to that of sucrase-isomaltase, a marker of enterocyte differentiation. We thus investigated the expression of claudin-2 in relation to the transcription factors CDX2, HNF-1alpha, and GATA-4 in the human intestine. The characterization of claudin-2 and the expression of the above transcription factors were performed by immunofluorescence, Western blot, and RT-PCR in the developing human intestinal epithelium. The functional role of CDX2, HNF-1alpha, and GATA-4 on claudin-2 regulation was also examined by ectopic expression studies in intestinal cell models. Claudin-2 was detected in both crypt and villus cells of the small intestine but restricted to undifferentiated crypt cells in the colon. CDX2 and HNF-1alpha were expressed along the entire intestine whereas GATA-4 was undetectable in the colon. Accordingly, in the colonic Caco-2 cell model, claudin-2 was found to be present only in undifferentiated cells. Like in the colonic epithelium, GATA-4 was found to be also lacking in Caco-2 cells while CDX2 and HNF-1alpha were present at significant levels. Cotransfection experiments showed that the claudin-2 promoter was activated by CDX2, HNF-1alpha, and GATA-4 in a cooperative manner. Furthermore, forced GATA-4 expression in Caco-2 cells enhances maintenance of claudin-2 expression during differentiation. These observations suggest that optimal claudin-2 expression in the gut relies on the presence of GATA-4, suggesting a role for this factor in intestinal regionalization.

Molecular genetics of adult-type hypolactasia

Adult-type hypolactasia (lactase non-persistence; primary lactose malabsorption) is characterized by the down-regulation of the lactase enzyme activity in the intestinal wall after weaning. The down-regulation is genetically determined and a mutation has occurred that has made part of mankind tolerate milk (lactase persistence). A DNA-variant, single nucleotide polymorphism C/T-13910 located 13 910 base pairs (bp) upstream of the lactase gene (LCT) at chromosome 2q21-22 has been shown to associate with the lactase persistence/non-persistence trait both in family and case-control studies. The C/T-13910 variant is located in a non-coding region in the genome in intron 13 of the minichromosome maintenance type 6 gene (MCM6). Significant correlation between the C/T-13910-variant and lactase activity in the intestinal biopsy specimens has been demonstrated. Molecular epidemiological studies on the prevalence of the C/C-13910 genotype associated with low lactase activity are in agreement with the prevalence figures for adult type hypolactasia in>70 diverse ethnic groups studied. Recent functional studies have suggested that this variant has an enhancer effect over the lactase gene. Based on the biochemical, functional, genetic and molecular epidemiological studies of the C/T-13910 variant, genetic testing for adult type hypolactasia has been introduced into clinical practice in Finland. Identification of the genetic change has highlighted the role of non-coding variants in the regulation of common genes and created new tools to study the mechanism of lactase enzyme activation.

The murine Muc2 mucin gene is transcriptionally regulated by the zinc-finger GATA-4 transcription factor in intestinal cells

MUC2, the major mucin in the intestine, is expressed early during development and shows an altered expression pattern in intestinal bowel diseases. However, the mechanisms responsible for MUC2 expression in the intestine during these events are largely unknown. Having found putative GATA binding sites in the murine Muc2 promoter and that GATA-4 is expressed in Muc2-expressing goblet cells of the mouse small intestine, we undertook to study its regulation by this transcription factor. A panel of deletion mutants made in pGL3 vector and covering 2.2kb of the promoter were used to transfect the murine CMT-93 colorectal cancer cell line. The role of GATA-4 on Muc2 gene regulation was investigated by RT-PCR and co-transfections in the presence of expression vectors encoding either wild-type or mutated GATA-4 or by mutating the GATA-4 site identified within Muc2 promoter. Four GATA-4 cis-elements were identified in the promoter by EMSA and Muc2 promoter was efficiently activated when GATA-4 was overexpressed in the cells with a loss of transactivation when those sites were either mutated or a mutated form of GATA-4 was used. Altogether, these results identify Muc2, a goblet cell marker, as a new target gene of GATA-4 and point out an important role for this factor in Muc2 expression in the intestine.

Genetic variation and lactose intolerance: detection methods and clinical implications

The maturational decline in lactase activity renders most of the world's adult human population intolerant of excessive consumption of milk and other dairy products. In conditions of primary or secondary lactase deficiency, the lactose sugars in milk pass through the gastrointestinal tract undigested or are partially digested by enzymes produced by intestinal bacterial flora to yield short chain fatty acids, hydrogen, carbon dioxide, and methane. The undigested lactose molecules and products of bacterial digestion can result in symptoms of lactose intolerance, diarrhea, gas bloat, flatulence, and abdominal pain. Diagnosis of lactose intolerance is often made on clinical grounds and response to an empiric trail of dietary lactose avoidance. Biochemical methods for assessing lactose malabsorption in the form of the lactose breath hydrogen test and direct lactase enzyme activity performed on small intestinal tissue biopsy samples may also be utilized. In some adults, however, high levels of lactase activity persist into adulthood. This hereditary persistence of lactase is common primarily in people of northern European descent and is attributed to inheritance of an autosomal-dominant mutation that prevents the maturational decline in lactase expression. Recent reports have identified genetic polymorphisms that are closely associated with lactase persistence and nonpersistence phenotypes. The identification of genetic variants associated with lactase persistence or nonpersistence allows for molecular detection of the genetic predisposition towards adult-onset hypolactasia by DNA sequencing or restriction fragment length polymorphism analysis. The role for such genetic detection in clinical practice seems limited to ruling out adult-onset hypolactasia as a cause of intolerance symptoms but remains to be fully defined. Attention should be paid to appropriate interpretation of genetic detection in order to avoid potentially harmful reduction in dairy intake or misdiagnosis of secondary lactase deficiency.