Regulation of sucrase and lactase in developing rats: role of nuclear factors that bind to two gene regulatory elements

Schlafen 12 mediates the effects of butyrate and repetitive mechanical deformation on intestinal epithelial differentiation in human Caco-2 intestinal epithelial cells

Intestinal epithelial differentiation may be stimulated by diverse pathways including luminal short-chain fatty acids and repetitive mechanical deformation engendered by villous motility and peristalsis. Schlafen 12 (SLFN12) is a cytosolic protein that stimulates sucrase-isomaltase (SI) expression. We hypothesized that two disparate differentiating stimuli, butyrate and repetitive deformation, would each stimulate SLFN12 expression in human Caco-2 intestinal epithelial cells and that increased SLFN12 expression would contribute to the differentiating activity of the human Caco-2 intestinal epithelial cells. We stimulated Caco-2 cells with 1-2 mM butyrate or repetitive mechanical deformation at 10 cycles/min at an average 10% strain, and measured SLFN12 and SI expression by qRT-PCR. Sodium butyrate enhanced SLFN12 expression at both 1 mM and 2 mM although SI expression was only significantly increased at 2 mM. Repetitive deformation induced by cyclic mechanical strain also significantly increased both SLFN12 and SI gene expression. Reducing SLFN12 by siRNA decreased basal, deformation-stimulated, and butyrate-stimulated SLFN12 levels, compared to control cells treated with non-targeting siRNA, although both deformation and butyrate were still able to stimulate SLFN12 expression in siRNA-treated cells compared to control cells treated with the same siRNA. This attenuation of the increase in SLFN12 expression in response to mechanical strain or butyrate was accompanied by parallel attenuation of SI expression. Butyrate stimulated SI-promoter activity, and reducing SLFN12 by siRNA attenuated butyrate-induced SI-promoter activity. These data suggest that SLFN12 mediates at least in part the stimulation by both butyrate and repetitive mechanical deformation of sucrase-isomaltase, a late stage differentiation marker in human intestinal epithelial cells.

Differential expression of Homeobox C11 protein in water buffalo Bubalus bubalis and its putative 3D structure

BACKGROUND

The Homeobox (Hox) family complex contains 39 genes, clustered into four groups (A-D) all expressing in sequential manner. The HOX proteins are transcriptional factors involved in regulation of pattern formation of the anterio-posterior body axis across the species. Most of the Hox family genes have been studied with respect to their organization and expression during the embryonic stages. However, expression pattern of Homeobox C11 (Hoxc11) gene in the 5' region, particularly in higher mammals remains largely unexplored.

RESULTS

We cloned and expressed Homeobox C11 (Hoxc11) gene from water buffalo Bubalus bubalis. The recombinant HOXC11 protein expressed as inclusion bodies was solubilized in Tris buffer (10 mM, pH-6.5) and purified using Ni-NTA affinity column. The purity and molecular weight of HOXC11 protein (~33 kDa) were confirmed by SDS-PAGE and western blot analysis. Employing immunohistochemistry approach, we localized HOXC11 protein in the nuclei across the tissues of buffalo. Western blot analysis showed highest expression of HOXC11 protein in kidney and lung although its possible renal and respiratory roles are not yet established. Electrophoretic mobility shift assay (EMSA) demonstrated the specific binding of HOXC11 protein with the promoter element, CE-LPH1 of lactase-phlorizin hydrolase (LPH) gene showing reduced mobility of the protein-DNA complex, corroborating with earlier report on the possible role of this protein in intestinal functions. In silico analysis of HOXC11 showed predominance of α helices and presence of six conserved domains. We deduced the putative 3D structure of HOXC11 protein and fifteen possible DNA interacting residues within the homeodomain.

CONCLUSIONS

Present study augments our understanding on the specific expression of HOXC11 protein in kidney and lung in water buffalo. The fifteen DNA interacting residues reported herein provide an opportunity to establish much broader structural and functional perspectives of HOXC11 protein in the context of genome analysis in general and animal biotechnology in particular.

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

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

Cdx genes, inflammation, and the pathogenesis of intestinal metaplasia

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

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

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

50 years of hypnosis in medicine and clinical health psychology: a synthesis of cultural crosscurrents

In 2008, the 50th anniversary of ASCH, hypnosis is used increasingly for healthcare applications in hospitals, clinics, and psychotherapy practice. A substantial body of research demonstrates the efficacy of hypnosis as part of the integrative treatment of many conditions that traditional medicine has found difficult to treat (e.g., Pinnell & Covino, 2000; Elkins, Jensen, & Patterson, 2007). The practice of hypnosis in healthcare has been altered and centrally influenced by the rapid growth of technological medicine in the 1950's, the AIDS epidemic and development of psychoneuroimmunology, revolutionary developments in genetics and neuroimaging technology, and the progression from alternative to integrative medicine. We have come to develop more detailed expectations about the beneficial effects of hypnotic interventions for health problems. We have also come to know that in these populations hypnosis can lead not only to reduced anxiety but also specifically altered physiological parameters.

Oral polyamine administration modifies the ontogeny of hexose transporter gene expression in the postnatal rat intestine

Gastrointestinal mucosal polyamines influence enterocyte proliferation and differentiation during small intestinal maturation in the rat. Studies in postnatal rats have shown that ornithine decarboxylase (ODC) protein and mRNA peak before the maximal expression of brush-border membrane (BBM) sucrase-isomaltase (SI) and the sugar transporters sodium-dependent glucose transporter 1 (SGLT1) and glucose transporter 2 (GLUT2). This study was undertaken to test the hypothesis that the oral administration of spermidine in postnatal rats upregulates the expression of ODC, thereby enhancing the expression of SI and SGLT1 in the brush-border membrane as well as basolateral membrane-facilitative GLUT2 and Na(+)-K(+)-ATPase. Northern and Western blot analyses were performed with antibodies and cDNA probes specific for SI, SGLT1, GLUT2, alpha(1)- and beta(1)-subunits of Na(+)-K(+)-ATPase, and ODC. Postnatal rats fed 6 mumol spermidine daily for 3 days from days 7 to 9 were killed either on postnatal day 10 (Sp10) or day 13 following a 3-day washout period (Sp13). Sp10 rats showed a precocious increase in the abundance of mRNAs for SI, SGLT1, and GLUT2 and Na(+)-K(+)-ATPase activity and alpha(1)- and beta(1)-isoform gene expression compared with controls. ODC activity and protein and mRNA abundance were also increased in Sp10 animals. The increased expression of these genes was not sustained in Sp13 rats, suggesting that these effects were transient. Thus, 3 days of oral polyamine administration induces the precocious maturation of glucose transporters in the postnatal rat small intestine, which may be mediated by alterations in ODC expression.

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

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

De-phosphorylation of TRalpha-1 by p44/42 MAPK inhibition enhances T(3)-mediated GLUT5 gene expression in the intestinal cell line Caco-2 cells

Thyroid hormone and p44/42 MAPK inactivation are important in intestinal differentiation. We demonstrated not only that treatment with p44/42 MAPK inhibitor U0126 in intestinal cell line Caco-2 cells reduced the phosphorylation of serine and threonine residues of TRalpha-1, but also that T(3) and U0126 synergistically induced GLUT5 gene expression. EMSA demonstrated that the binding activity of TRalpha-1-RXR heterodimer on GLUT5-TRE in nuclear proteins of Caco-2 cells was synergistically enhanced by co-incubation in vitro with T(3) and CIAP, which strongly de-phosphorylates proteins. ChIP and transfection assays revealed that co-treatment of T(3) and U0126 induces TRalpha-1-RXR binding to GLUT5-TRE on the human GLUT5 enhancer region, and recruitment of the transcriptional complex in cells. These results suggest that inactivation of p44/42 MAPK enhances T(3)-induced GLUT5 gene expression in Caco-2 cells through increasing TRalpha-1 transactivity and binding activity to the GLUT5-TRE, probably due to de-phosphorylation of TRalpha-1.

Temporal regulation of enhancer function in intestinal epithelium: a role for Onecut factors

An intestine-specific gene regulatory region was previously identified near the second exon of the human adenosine deaminase (ADA) gene. In mammalian intestine, ADA is expressed at high levels only along the villi of the duodenal epithelium, principally if not exclusively in enterocytes. Within the ADA intestinal regulatory region, a potent duodenum-specific enhancer was identified that controls this pattern of expression. This enhancer has been shown to rely on PDX-1, GATA factors, and Cdx factors for its function. Upstream of the enhancer, a separate temporal regulatory region was identified that has no independent enhancer capability but controls the timing of enhancer activation. DNase I footprinting and electrophoretic mobility shift assays were used to begin to characterize temporal region function at the molecular level. In this manner, binding sites for the Onecut (OC) family of factors, YY1, and NFI family members were identified. Identification of the OC site was especially interesting, because almost nothing is known about the function of OC factors in intestine. In transgenic mice, mutation of the OC site to ablate binding resulted in a delay of 2-3 weeks in enhancer activation in the developing postnatal intestine, a result very similar to that observed previously when the entire temporal region was deleted. In mammals, the OC family is comprised of OC-1/HNF-6, OC-2, and OC-3. An examination of intestinal expression patterns showed that all three OC factors are expressed at detectable levels in adult mouse duodenum, with OC-2 predominant. In postnatal day 2 mice only OC-2 and OC-3 were detected in intestine, with OC-2 again predominant.

Adult-type hypolactasia and regulation of lactase expression

A common genetically determined polymorphism in the human population leads to two distinct phenotypes in adults, lactase persistence and adult-type hypolactasia (lactase non-persistence). All healthy newborn children express high levels of lactase and are able to digest large quantities of lactose, the main carbohydrate in milk. Individuals with adult-type hypolactasia lose their lactase expression before adulthood and consequently often become lactose intolerant with associated digestive problems (e.g. diarrhoea). In contrast, lactase persistent individuals have a lifelong lactase expression and are able to digest lactose as adults. Lactase persistence can be regarded as the mutant phenotype since other mammals down-regulate their lactase expression after weaning (the postweaning decline). This phenomenon does not occur in lactase persistent individuals. The regulation of lactase expression is mainly transcriptional and it is well established that adult-type hypolactasia is inherited in an autosomal recessive manner, whereas persistence is dominant. The recent findings of single nucleotide polymorphisms associated with lactase persistence have made it possible to study the potential mechanisms underlying adult-type hypolactasia. This work has led to the identification of gene-regulatory sequences located far from the lactase gene (LCT). The present review describes the recent advances in the understanding of the regulation of lactase expression and the possible mechanisms behind adult-type hypolactasia.

Hypnosis and irritable bowel syndrome: a review of efficacy and mechanism of action

Irritable bowel syndrome (IBS) is a functional gastrointestinal disorder characterized by abdominal pain, distension, and an altered bowel habit for which no cause can be found. Despite its prevalence, there remains a significant lack of efficacious medical treatments for IBS to date. In this paper we reviewed a total of 14 published studies (N=644) on the efficacy of hypnosis in treating IBS (8 with no control group and 6 with a control group). We concluded that hypnosis consistently produces significant results and improves the cardinal symptoms of IBS in the majority of patients, as well as positively affecting non-colonic symptoms. When evaluated according to the efficacy guidelines of the Clinical Psychology Division of American Psychological Association, the use of hypnosis with IBS qualifies for the highest level of acceptance as being both efficacious and specific. In reviewing the research on the mechanism of action as to how hypnosis works to reduce symptoms of IBS, some evidence was found to support both physiological and psychological mechanisms of action.

Regulatory regions in the rat lactase-phlorizin hydrolase gene that control cell-specific expression

OBJECTIVES

Lactase-phlorizin hydrolase (LPH) is an enterocyte-specific gene whose expression has been well-characterized, not only developmentally but also along the crypt-villus axis and along the length of the small bowel. Previous studies from the authors' laboratory have demonstrated that 2 kb of the 5'-flanking region of the rat LPH gene control the correct tissue, cell, and crypt-villus expression in transgenic animals.

METHODS

To examine further the regulation conferred by this region, protein-DNA interactions were studied using DNase I footprint analyses in LPH-expressing and nonexpressing cell lines. Functional delineation of this 5'-flanking sequence was performed using deletion analysis in transient transfection assays.

RESULTS

Studies revealed a generally positive activity between -74 and -37 bp, a cell-specific negative region between -210 and -95 bp, and additional elements further toward the 5'-terminus that conferred a highly cell-specific response in reporter activity. Computer analysis of distal regions encompassing identified footprints revealed potential binding sites for various intestinal transcription factors. Co-transfection and electromobility shift assay experiments indicated binding of HNF3beta at three sites relevant to LPH expression.

CONCLUSIONS

The data demonstrate that the cell specificity of LPH gene expression depends upon both positive and negative interactions among elements in the first 2 kb of the LPH 5'-flanking region.

An enhancer activates the pig lactase phlorizin hydrolase promoter in intestinal cells

Lactase phlorizin hydrolase is a small intestinal-specific brush border protein commonly used as a specific marker of differentiated enterocytes. A number of transcription factors involved in the enterocyte-specific expression of lactase phlorizin hydrolase have been identified. An upstream regulatory region, which we have named the "LPH enhancer", located at position -894 to -798 in the porcine lactase phlorizin hydrolase gene, is necessary for high differentiation-dependent LPH expression in intestinal cells. The LPH enhancer was studied by mutation analysis, transfection experiments and electrophoretical mobility shift assays. The LPH enhancer is active in intestinal cells (Caco-2) and not in non-intestinal cells (HeLa). The LPH enhancer is only able to enhance expression when it is located in front of an intestinal-specific promoter such as the lactase phlorizin hydrolase promoter or the sucrase-isomaltase promoter. In front of an SV40-derived promoter the LPH enhancer has no stimulatory effect. In addition to the lack of promoter-promiscuity, the LPH enhancer is not a classical enhancer in the sense that it is not orientation-independent and it cannot function when located 3' of a reporter gene. The LPH enhancer contains at least three cis-elements (at -894 to -880, -880 to -875 and -833 to -814) with functional importance for the LPH enhancer activity.

Novel interaction at the Cdx-2 binding sites of the lactase-phlorizin hydrolase promoter

Cdx-2 is an intestine-specific homeodomain-containing transcription factor that activates the promoters of intestinal genes through specific interactions with the consensus, TTTAT/C. Here, we demonstrate that Cdx-2 interacts with the lactase-phlorizin hydrolase (LPH) promoter at cis-element (CE)-LPH1a (-54 to -40 bp) as well as the LPH TATA-box. Affinity comparisons between SIF-1, CE-LPH1a, and the LPH TATA-box revealed that the TATA-box has the lowest affinity for Cdx-2. Characterization of CE-LPH1a using EMSAs revealed binding of a novel, non-Cdx-2 complex in multiple cell lines that bind to sequence that is different from that of the Cdx-2 binding site. Heterologous promoter analysis in transient transfection assays revealed a repressor function for this protein, and thus, it was designated as nuclear factor-LPH1/repressor (NF-LPH1/R). These data are consistent with the hypothesis that NF-LPH1/R represses LPH gene expression in non-Cdx-2-producing cells, and that this repression is released in cells that synthesize Cdx-2, such as those in the intestinal epithelium.

Ontogeny of MAP kinases in rat small intestine: premature stimulation by insulin of BBM hydrolases is regulated by ERKs but not by p-38 MAP kinase

Although mitogen-activating protein (MAP) kinases are crucial signal transduction molecules regulating cellular proliferation, differentiation, and morphology, their ontogenic changes in the small intestine have not been analyzed. Also, it remains unknown which pathway of activated MAP kinases regulates the expression of brush border membrane hydrolases during growth. Therefore, we have analyzed the mucosal distribution, ontogeny, and responses to insulin and to inhibitors of p44, p42, and p38 MAP kinases in immature and mature enterocytes using Western blot analysis and autoradiography after immunoprecipitation, immunohistochemistry, and in vitro phosphorylation assays. Between d 10 and 40 postpartum, diphosphorylated active p44/p42 extracellular regulated protein kinases (ERKs) increased in abundance compared with total immunoprecipitated ERKs, and were highly responsive to exogenous insulin. In concordance, ERK total activity increased by 4-fold during the same period of growth and was further enhanced 2-fold by exogenous insulin. In weaning rats, ERKs were mainly located in membranes of villus cells and with less intensity in crypt cells. By contrast, p38 MAP kinase was unresponsive to insulin and was confined to nuclei. Administration to sucklings of PD 098059, a specific inhibitor of ERKs, not only inhibited the premature stimulation of sucrase, lactase, and maltase total activities in response to exogenous insulin, but also depressed the natural expression of these brush border membrane enzymes in the absence of insulin stimulation. In concordance, administration of SB 203580, a specific inhibitor of p38 MAP kinase, failed to inhibit both the response of brush border membrane hydrolases to insulin and their natural expression in the absence of insulin stimulation. We conclude that the ontogenic expression of brush border membrane hydrolases and their premature stimulation by insulin are regulated at least in part by the activation of p44/p42 ERKs but not by p38 MAP kinase.

Bile acids regulate the ontogenic expression of ileal bile acid binding protein in the rat via the farnesoid X receptor

BACKGROUND & AIMS

In the rat, an increase in ileal bile acid binding protein (IBABP) expression occurs during the third postnatal week. In vitro studies suggest that bile acids (BAs) increase IBABP transcription by activating the BA receptor, farnesoid X receptor (FXR). Thus, we investigated the role of BAs on the ontogenic expression of IBABP and whether FXR may mediate these effects.

METHODS

Suckling rats were gavage-fed taurocholate for 3 days or were allowed to develop normally. Ileums were collected for Northern and Western blot analyses. Electrophoretic mobility shift assays for functional FXR were performed using nuclear extracts from ileums of both adult and developing rats.

RESULTS

Taurocholate gavage significantly elevated IBABP messenger RNA and protein levels in suckling animals. Gelshift assays using adult ileal nuclear extracts incubated with a radiolabeled consensus inverted repeat-1 oligonucleotide (response element for FXR) revealed a high-molecular weight DNA/protein complex. Cold competition and supershift assays showed that this complex is sequence specific and confirmed that FXR is a component of the complex. Gelshift assays with nuclear extracts from rat ileum at different ages revealed absence of the DNA/protein complex in the second postnatal week when there is lack of IBABP expression and presence of these complexes at later ages when there is normally high expression. Western blot analyses showed FXR and its heterodimer partner, retinoid X receptor alpha, protein levels are low in the ileum during the suckling period and increase during the third postnatal week.

CONCLUSIONS

BAs play a role in the normal developmental expression of IBABP through FXR activation, and decreased functional FXR in ileal nuclei during the suckling period may account, in part, for the lack of IBABP expression at this time.

Regulation of intestine-specific spatiotemporal expression by the rat lactase promoter

Lactase gene transcription is spatially restricted to the proximal and middle small intestine of the developing mouse. To identify regions of the lactase gene involved in mediating the spatiotemporal expression pattern, transgenic mice harboring 0.8-, 1.3-, and 2.0-kb fragments of the 5'-flanking region cloned upstream of a firefly-luciferase reporter were generated. Transgene expression was assessed noninvasively in living mice using a sensitive low light imaging system. Two independent, 1.3- and 2.0-kb, lactase promoter-reporter transgenic lines expressed appropriate high levels of luciferase activity in the small intestine (300-3,000 relative light units/microg) with maximal expression in the middle segments. Post-weaned 30-day transgenic offspring also demonstrated an appropriate 4-fold maturational decline in luciferase expression in the small intestine. The pattern of the 2.0-kb promoter transgene mRNA abundance most closely mimicked that of the endogenous lactase gene with respect to spatiotemporal restriction. In contrast, a 0.8-kb promoter-reporter construct expressed low level luciferase activity (<25 relative light units/microg) in multiple organs and throughout the gastrointestinal tract in transgenic mice. Thus, a distinct 5'-region of the lactase promoter directs intestine-specific expression in the small intestine of transgenic mice, and regulatory sequences have been localized to a 1.2-kb region upstream of the lactase transcription start site. In addition, we have demonstrated that in vivo bioluminescence imaging can be utilized for assessment of intestinal expression patterns of a luciferase reporter gene driven by lactase promoter regions in transgenic mice.

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.

5-HT (serotonin) physiology and related drugs

Alone among organs of the body, the gut is able to mediate reflexes in the absence of input from the brain or spinal cord. This ability appears to be caused by the secretion of serotonin (5-HT) by enterochromaffin (EC) cells of the mucosal epithelium. This 5-HT is secreted into the wall of the gut, where it stimulates the mucosal processes of intrinsic and extrinsic primary afferent neurons. The intrinsic primary afferents, which are activated by 5-HT1P/4 receptors, initiate peristaltic and secretory reflexes. The extrinsic primary afferent neurons send distress and other signals to the central nervous system. Extrinsic nerves are activated by 5-HT(3) receptors. The 5-HT that is involved in mucosal signaling is inactivated by uptake into mucosal epithelial cells, which are mediated by an integral membrane protein called the serotonin reuptake transporter (SERT). The epithelial SERT is the same molecule as that which transports 5-HT in the central and enteric nervous systems. Increasing evidence suggests that abnormal enteric release or inactivation of 5-HT is involved in the pathogenesis of irritable bowel syndrome (IBS). Spread of 5-HT to inappropriate sites in IBS may activate 5-HT(3) receptors on extrinsic afferent fibers and motor neurons, giving rise to visceral hypersensitivity and abnormal motility, respectively. A potent 5-HT(3) antagonist, such as alosetron, can prevent both of these effects and is therefore useful in treating IBS. 5-HT also appears to function as a growth factor in the development of enteric neurons. The developmental effects of 5-HT are mediated by the 5-HT(2B) receptor, which is developmentally regulated. The importance of serotonergic mechanisms in enteric physiology probably accounts for the gastrointestinal "side effects" of compounds that inhibit SERT. The newly discovered role of 5-HT in enteric neuronal development suggests that drugs that interfere with the action or inactivation of 5-HT should be used in pregnancy only with extreme caution, if at all.

The homeodomain protein Cdx2 regulates lactase gene promoter activity during enterocyte differentiation

BACKGROUND & AIMS

Lactase is the intestinal disaccharidase responsible for digestion of lactose, the predominant carbohydrate in milk. Transcription of the lactase gene is activated during enterocyte differentiation. We have characterized the interaction between the lactase promoter and Cdx2, a homeodomain protein involved in regulating intestinal development and differentiation.

METHODS

Nuclear protein bound to the lactase gene cis element, CE-LPH1, was analyzed by electrophoretic mobility shift assays and supershifts with Cdx2 antibody. Lactase promoter activities were assayed in cells transfected with luciferase reporter constructs and a Cdx2 expression construct.

RESULTS

Electrophoretic mobility shift assay with CE-LPH1 yields a specific DNA/protein complex that requires the caudal-related protein binding site, TTTAC. The complex is recognized by Cdx2 antibody and is more abundant in differentiated enterocytes. A Cdx2 expression construct is able to activate transcription driven by the wild-type, but not a mutated, promoter and results in increased endogenous lactase messenger RNA.

CONCLUSIONS

The homeodomain protein Cdx2 interacts with the lactase promoter and is capable of activating transcription of the endogenous gene. In contrast to a previous report, Cdx2 interaction with the lactase promoter correlates with enterocyte differentiation. These conclusions are consistent with the role of Cdx2 in regulating intestinal cell differentiation.

The Cdx-1 and Cdx-2 homeobox genes in the intestine

The past years have witnessed an increasing number of reports relative to homeobox genes in endoderm-derived tissues. In this review, we focus on the caudal-related Cdx-1 and Cdx-2 homeobox genes to give an overview of the in vivo, in vitro, and ex vivo approaches that emphasize their primary role in intestinal development and in the control of intestinal cell proliferation, differentiation, and identity. The participation of these genes in colon tumorigenesis and their identification as important actors of the oncogenic process are also discussed.

Development of the human gastrointestinal tract: twenty years of progress

A combination of approaches has begun to elucidate the mechanisms of gastrointestinal development. This review describes progress over the last 20 years in understanding human gastrointestinal development, including data from both human and experimental animal studies that address molecular mechanisms. Rapid progress is being made in the identification of genes regulating gastrointestinal development. Genes directing initial formation of the endoderm as well as organ-specific patterning are beginning to be identified. Signaling pathways regulating the overall right-left asymmetry of the gastrointestinal tract and epithelial-mesenchymal interactions are being clarified. In searching for extrinsic developmental regulators, numerous candidate trophic factors have been proposed, but compelling evidence remains elusive. A critical gene that initiates pancreas development has been identified, as well as a number of genes regulating liver, stomach, and intestinal development. Mutations in genes affecting neural crest cell migration have been shown to give rise to Hirschsprung's disease. Considerable progress has been achieved in understanding specific phenomena, such as the transcription factors regulating expression of sucrase-isomaltase and fatty acid-binding protein. The challenge for the future is to integrate these data into a more complete understanding of the physiology of gastrointestinal development.

Expression of intestinal brush-border membrane hydrolases and ferritin after segmental ischemia-reperfusion in rats

Jejunal expression of three brush-border membrane (BBM) enzymes, intestinal alkaline phosphatase (IAP), lactose-phlorizin hydrolase (LPH), and sucrase-isomaltase (SI), and a cytosolic protein, ferritin (Ft), was investigated after transient segmental ischemia-reperfusion (I/R). I/R reduced mucosal IAP, LPH, and SI mRNAs to 36%, 11%, and 38% of normal jejunal levels after 3 h of reperfusion and to 22%, 8%, and 51% of normal jejunal levels after 6 h of reperfusion, respectively. Intriguingly, in the internal control jejunum IAP and LPH mRNAs also decreased significantly. LPH and SI mRNA rapidly recovered to levels significantly higher than those of normal jejunum at 12 h, whereas IAP mRNA levels did not recover until 48 h. Enzyme activity paralleled changes in mRNA levels in the ischemic reperfused jejunum. Electrophoretic mobility shift assays showed that I/R significantly increased SI footprinting 1 (SIF1) binding activity. The mobility of one of the DNA-protein complexes was further retarded in the presence of anti-Cdx-2 antibody, suggesting that either Cdx-2 or a related protein was interacting with the SIF1 sequences. Similar to BBM enzymes, cytosolic Ft mRNA and protein were significantly decreased at 3 and 6 h after I/R. By 12 h, Ft mRNA, but not Ft protein, had increased to higher than normal levels. We conclude that a rapid recovery of BBM mRNAs and enzymes occurs in regenerating mucosa after upper villus damage. The increase of SIF1 binding protein activity after I/R may enhance SI, and perhaps LPH, gene transcription. The expression of Ft is regulated at both pretranslational and translational levels.

Guinea pig 5-HT transporter: cloning, expression, distribution, and function in intestinal sensory reception

Studies of the guinea pig small intestine have suggested that serotonin (5-HT) may be a mucosal transmitter that stimulates sensory nerves and initiates peristaltic and secretory reflexes. We tested the hypothesis that guinea pig villus epithelial cells are able to inactivate 5-HT because they express the same 5-HT transporter as serotonergic neurons. A full-length cDNA, encoding a 630-amino acid protein (89.2% and 90% identical, respectively, to the rat and human 5-HT transporters) was cloned from the guinea pig intestinal mucosa. Evidence demonstrating that this cDNA encodes the guinea pig 5-HT transporter included 1) hybridization with a single species of mRNA ( approximately 3.7 kb) in Northern blots of the guinea pig brain stem and mucosa and 2) uptake of [3H]5-HT by transfected HeLa cells via a saturable, high-affinity (Michaelis constant 618 nM, maximum velocity 2.4 x 10(-17) mol . cell-1 . min-1), Na+-dependent mechanism that was inhibited by chlorimipramine > imipramine > fluoxetine > desipramine > zimelidine. Expression of the 5-HT transporter in guinea pig raphe and enteric neurons and the epithelium of the entire crypt-villus axis was demonstrated by in situ hybridization and immunocytochemistry. Inhibition of mucosal 5-HT uptake potentiates responses of submucosal neurons to mucosal stimulation. The epithelial reuptake of 5-HT thus appears to be responsible for terminating mucosal actions of 5-HT.

The HOXC11 homeodomain protein interacts with the lactase-phlorizin hydrolase promoter and stimulates HNF1alpha-dependent transcription

The lactase-phlorizin hydrolase (LPH) gene is expressed specifically in the enterocytes of the small intestine. LPH levels are high in newborn mammals, but decrease after weaning. We have previously suggested that the promoter element CE-LPH1, located at -40 to -54, plays an important role in this down-regulation, because the DNA binding activity of a nuclear factor that binds to this site is present specifically in small intestinal extracts and is down-regulated after weaning. In an effort to clone CE-LPH1-binding factors, a yeast one-hybrid genetic selection was used, resulting in the isolation of a partial cDNA encoding the human homeodomain protein HOXC11. The full-length HOXC11 sequence was obtained by rapid amplification of cDNA ends. It was shown in a yeast assay and by electrophoretic mobility shift assay that HOXC11 binds to the CE-LPH1 element with similar specificity to the endogenous intestinal factor. Two HOXC11 transcript sizes were identified by Northern blot analysis. The larger transcript (2.1 kilobase pairs) is likely to contain a translational start site in good context and is present in HeLa cells. The shorter 1.7-kilobase pair transcript, present in HeLa and Caco-2 cells, probably encodes a protein lacking 114 amino acids at the N-terminal end. Both forms of HOXC11 potentiate transcriptional activation of the LPH promoter by HNF1alpha. The expression of HOXC11 mRNA in human fetal intestine suggests a role in early intestinal development.

Premature stimulation of rat sucrase-isomaltase (SI) by exogenous insulin and the analog B-Asp10 is regulated by a receptor-mediated signal triggering SI gene transcription

The mechanism(s) by which insulin enhance prematurely the activity of brush border membrane (BBM) hydrolases in rat immature intestine is unknown. Therefore, we have compared the responses of four BBM enzymes [sucrase-isomaltase (SI), maltase, lactase-phloridzine hydrolase (LPH), and aminopeptidase] with exogenous insulin, the analog B-Asp10, IGF-I, and antireceptor MAb [insulin-receptor (IR) MAb] given to preweaning pups. Low doses of insulin caused a precocious induction of SI and of SI mRNA and stimulated maltase activity without effect on LPH nor on aminopeptidase activities. IGF-I given at the same dose as that of insulin had no detectable effect on these enzymes. Administration to sucklings of IR MAb prevented the effect of endogenous insulin by inhibiting the expression of SI and maltase without effect on LPH activity. B-Asp10, an insulin analogue that exhibits in vitro a 3.5-fold increase in receptor affinity with sustained signaling of the receptor tyrosine kinase, caused an overexpression of SI by 3.5-fold and of maltase by 1.5-fold compared with equivalent doses of normal insulin. The premature increases in SI activity, SI mRNA, and maltase activity in response to insulin were dose-dependent and were associated with dose-dependent increases in intracellular spermine and spermidine concentrations. In conclusion, these data suggest that the premature induction of SI by insulin is mediated by a dose-dependent signal initiated by binding of the hormone to its intestinal receptor, which after transduction into the cell indirectly triggers the transcription of the SI gene, possibly by changes in intracellular polyamine concentrations.

Human adult-onset lactase decline: an update

Human adult-onset lactase decline is a biologic feature characteristic of the maturing intestine in the majority of the world's population. The digestion and absorption of lactose, the major carbohydrate in milk and also the main substrate for lactase, is often variable, a consequence of lactase levels, gastric emptying rate, and colonic salvage. Although commercially available "lactase" products alleviate symptoms in many lactose-intolerant people, a greater understanding of this variability in lactose tolerance could lead to interventions that reduce the rate of gastric emptying and/or increase the proliferation of lactose-metabolizing bacteria in the colon, leading to more efficient lactose utilization. Adult-onset lactase decline appears to be a risk factor for developing osteoporosis, owing to avoidance of dairy products or interference of undigested lactose with calcium absorption. Elderly with both adult-onset lactase decline and atrophic gastritis or those undergoing anti-ulcer treatment may have an increased risk of low calcium absorption owing to the lack of gastric acid that facilitates calcium uptake. Thus, lactose-intolerant elders should monitor their calcium nutrition status carefully.