Regulation of sucrase-isomaltase gene expression along the crypt-villus axis of rat small intestine

Loss of Slfn3 induces a sex-dependent repair vulnerability after 50% bowel resection

Bowel resection accelerates enterocyte proliferation in the remaining gut with suboptimal absorptive and digestive capacity because of a proliferation-associated decrease in functional differentiation markers. We hypothesized that although schlafen 3 (Slfn3) is an important regulator of enterocytic differentiation, Slfn3 would have less impact on bowel resection adaptation, where accelerated proliferation takes priority over differentiation. We assessed proliferation, cell shedding, and enterocyte differentiation markers from resected and postoperative bowel of wild-type (WT) and Slfn3-knockout (Slfn3KO) mice. Villus length and crypt depth were increased in WT mice and were even longer in Slfn3KO mice. Mitotic marker, Phh3+, and the proliferation markers Lgr5, FoxL1, and platelet-derived growth factor-α (PDGFRα) were increased after resection in male WT, but this was blunted in male Slfn3KO mice. Cell-shedding regulators Villin1 and TNFα were downregulated in female mice and male WT mice only, whereas Gelsolin and EGFR increased expression in all mice. Slfn3 expression increased after resection in WT mice, whereas other Slfn family members 1, 2, 5, 8, and 9 had varied expressions that were affected also by sex difference and loss of Slfn3. Differentiation markers sucrase isomaltase, Dpp4, Glut2, and SGLT1 were all decreased, suggesting that enterocytic differentiation effort is incompatible with rapid proliferation shift in intestinal adaptation. Slfn3 absence potentiates villus length and crypt depth, suggesting that the differentiating stimulus of Slfn3 signaling may restrain mucosal mass increase through regulating Villin1, Gelsolin, EGFR, TNFα, and proliferation markers. Therefore, Slfn3 may be an important regulator not only of "normal" enterocytic differentiation but also in response to bowel resection.NEW & NOTEWORTHY The differentiating stimulus of Slfn3 signaling restrains an increase in mucosal mass after bowel resection, and there is a Slfn3-sex interaction regulating differentiation gene expression and intestinal adaptation. This current study highlights the combinatory effects of gender and Slfn3 genotype on the gene expression changes that contribute to the adaptation in intestinal cellular milleu (i.e. villus and crypt structure) which are utilized to compensate for the stress-healing response that the animals display in intestinal adaptation.

Glucose sensing and signalling; regulation of intestinal glucose transport

Epithelial cells lining the inner surface of the intestinal epithelium are in direct contact with a lumenal environment that varies dramatically with diet. It has long been suggested that the intestinal epithelium can sense the nutrient composition of lumenal contents. It is only recently that the nature of intestinal nutrient-sensing molecules and underlying mechanisms have been elucidated. There are a number of nutrient sensors expressed on the luminal membrane of endocrine cells that are activated by various dietary nutrients. We showed that the intestinal glucose sensor, T1R2+T1R3 and the G-protein, gustducin are expressed in endocrine cells. Eliminating sweet transduction in micein vivoby deletion of either gustducin or T1R3 prevented dietary monosaccharide- and artificial sweetener-induced up-regulation of the Na+/glucose cotransporter, SGLT1 observed in wild-type mice. Transgenic mice, lacking gustducin or T1R3 had deficiencies in secretion of glucagon-like peptide 1 (GLP-1) and, glucose-dependent insulinotrophic peptide (GIP). Furthermore, they had an abnormal insulin profile and prolonged elevation of postprandial blood glucose in response to orally ingested carbohydrates. GIP and GLP-1 increase insulin secretion, while glucagon-like peptide 2 (GLP-2) modulates intestinal growth, blood flow and expression of SGLT1. The receptor for GLP-2 resides in enteric neurons and not in any surface epithelial cells, suggesting the involvement of the enteric nervous system in SGLT1 up-regulation. The accessibility of the glucose sensor and the important role that it plays in regulation of intestinal glucose absorption and glucose homeostasis makes it an attractive nutritional and therapeutic target for manipulation.

Bone morphogenetic protein signaling is essential for terminal differentiation of the intestinal secretory cell lineage

BACKGROUND & AIMS

Bone morphogenetic proteins (Bmps) are morphogens known to play key roles in gastrointestinal development and pathology. Most Bmps are produced primarily by the mesenchymal compartment and activate their signaling pathways following a paracrine or autocrine route. The aim of this study was to investigate the role of epithelial Bmp signaling in intestinal morphogenesis and maintenance of adult epithelial cell functions.

METHODS

With the use of tissue-specific gene ablation, we generated mice lacking the Bmp receptor type IA (Bmpr1a) exclusively in the intestinal epithelium. Bmpr1a mutant and control mice were sacrificed for histology, immunofluorescence, Western blot analysis, electron microscopy, and quantitative polymerase chain reaction.

RESULTS

As well as showing increased proliferation and altered intestinal epithelial morphology, Bmpr1a mutant mice revealed that epithelial Bmp signaling is associated with impaired terminal differentiation of cells from the secretory lineage but not with the determination of cell fate. Loss of Bmp signaling exclusively in the epithelial compartment is not sufficient for the initiation of the de novo crypt phenomenon associated with juvenile polyposis syndrome.

CONCLUSIONS

Epithelial Bmp signaling plays an important role in the terminal differentiation of the intestinal secretory cell lineage but not in de novo crypt formation. These findings emphasize the importance of delineating the contribution of the stroma vs the epithelium in gastrointestinal physiology and pathology.

Loss of cathepsin L activity promotes claudin-1 overexpression and intestinal neoplasia

Intestinal epithelial integrity and polarity are maintained by cohesive interactions between cells via the formation of tight junctions. Irregularities in tight junctions have only recently been found to be associated with the initiation and progression of intestinal neoplasia. The claudin family of proteins is integral to the structure and function of the tight junction but little is known of the molecular events that regulate the expression of these components. The present report identifies cathepsin L, classically a lysosomal cysteine protease, as being induced during intestinal epithelial cell polarization and differentiation. Inhibition of intracellular cathepsin L activity results in the accumulation of disorganized cell layers and a decline in the expression of differentiation markers in cultured intestinal epithelial cells. This coincides with a rapid up-regulation of claudin-1 protein accumulation. Mutant mice defective in cathepsin L activity (furless) display an elevated level of intestinal claudin-1 and claudin-2 expression. Loss of cathepsin L activity leads to a marked increase in tumor multiplicity in the intestine of Apc(Min) mice. Given the traditionally viewed biological role of cathepsin L in the processing of lysosomal content as well as in pathological extracellular matrix remodeling, the results here demonstrate an as yet unsuspected intracellular role for this protease in normal intestinal epithelial polarization and initiation of neoplasia.

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.

Decreased sucrase and lactase activity in iron deficiency is accompanied by reduced gene expression and upregulation of the transcriptional repressor PDX-1

Disaccharidases are important digestive enzymes whose activities can be reduced by iron deficiency. We hypothesise that this is due to reduced gene expression, either by impairment to enterocyte differentiation or by iron-sensitive mechanisms that regulate mRNA levels in enterocytes. Iron-deficient Wistar rats were generated by dietary means. The enzyme activities and kinetics of sucrase and lactase were tested as well as the activity of intestinal alkaline phosphatase (IAP)-II because it is unrelated to carbohydrate digestion. mRNA levels of beta-actin, sucrase, lactase, and the associated transcription factors pancreatic duodenal homeobox (PDX)-1, caudal-related homeobox (CDX)-2, GATA-binding protein (GATA)-4, and hepatocyte nuclear factor (HNF)-1 were measured by real-time PCR. Spatial patterns of protein and gene expression were assessed by immunofluorescence and in situ hybridization, respectively. It was found that iron-deficient rats had significantly lower sucrase (19.5% lower) and lactase (56.8% lower) but not IAP-II activity than control rats. Kinetic properties of both enzymes remained unchanged from controls, suggesting a decrease in the quantity of enzyme present. Sucrase and lactase mRNA levels were reduced by 44.5% and 67.9%, respectively, by iron deficiency, suggesting that enzyme activity is controlled primarily by gene expression. Iron deficiency did not affect the pattern of protein and gene expression along the crypt to villus axis. Expression of PDX-1, a repressor of sucrase and lactase promoters, was 4.5-fold higher in iron deficiency, whereas CDX-2, GATA-4, and HNF-1 levels were not significantly different. These data suggest that decreases in sucrase and lactase activities result from a reduction in gene expression, following from increased levels of the transcriptional repressor PDX-1.

Opposing roles for p21(waf1/cip1) and p27(kip1) in enterocyte differentiation, proliferation, and migration

BACKGROUND

Originating from proliferating stem cells of the intestinal crypt, enterocytes differentiate as they migrate up the crypt-villus axis. A regulatory role of the cyclin-dependent kinase inhibitors p21(waf1/cip1) and p27(kip1) in these processes has been suggested by in vitro models. We sought to determine the effect of p21(waf1/cip1) and p27(kip1) deficiency on enterocyte differentiation, proliferation and migration.

METHODS

Three strains of mice including control (C57Bl/6), p27(kip1)-null, and p21(waf1/cip1)-null were studied. Enterocyte differentiation was evaluated by immunostaining for intestinal alkaline phosphatase, by colorimetric assaying for intestinal alkaline phosphatase and sucrase enzyme activity, and by polymerase chain reaction for intestinal fatty acid-binding protein and villin-messenger RNA in enterocytes extracted by laser capture microdissection. Rates of enterocyte proliferation and migration were determined by 5-bromo 2-deoxyuridine immunostaining after a 50% small-bowel resection (SBR).

RESULTS

Compared with controls, p27(kip1)-null mice demonstrated minimal differentiation but maintained a normal proliferative response to SBR. Contrarily, p21(waf1/cip1)-null mice demonstrated greater enterocyte differentiation without significant increases in enterocyte proliferation after SBR.

CONCLUSIONS

These findings suggest that p21(waf1/cip1) and p27(kip1) have distinctive and opposing roles in the pathogenesis of enterocyte differentiation, proliferation, and migration.

Laminin isoforms: biological roles and effects on the intracellular distribution of nuclear proteins in intestinal epithelial cells

Laminins are structurally and functionally major components of the extracellular matrix. Four isoforms of laminins (laminin-1, -2, -5 and -10) are expressed in a specific pattern along the crypt-villus axis of the intestine. Previous works indicated that expression of these isoforms is developmentally regulated and that laminins could modulate the behaviour of intestinal cells, but the exact role of each isoform remained unclear. Here, we report the first systematic analysis of the cellular functions of the four isoforms using the human colon adenocarcinoma Caco2/TC7 cell line as a model. We compared the respective abilities of each isoform to modulate adhesion, proliferation and differentiation of intestinal epithelial cells. We found that the isoforms were functionally distinct, with laminin-10 being the most adhesive substratum, laminin-2, laminin-5 and laminin-10 enhancing cellular proliferation and at the opposite, laminin-1 stimulating intestinal cell differentiation. To begin to characterise the molecular events induced by the different isoforms, we examined by immunofluorescence the intracellular distribution of several nuclear proteins, recently highlighted by a nuclear proteomic approach. We observed clear nucleocytoplasmic redistribution of these proteins, which depended on the laminin isoform. These results provide evidence for a distinct functional role of laminins in intestinal cell functions characterised by specific localisation of nuclear proteins.

Protection of the Peyer's patch-associated crypt and villus epithelium against methotrexate-induced damage is based on its distinct regulation of proliferation

The crypt and villus epithelium associated with Peyer's patches (PPs) is largely spared from methotrexate (MTX)-induced damage, compared with the non-patch (NP) epithelium. To assess the mechanism(s) preventing damage to the PP epithelium after MTX treatment, epithelial proliferation, apoptosis, and cell functions were studied in a rat-MTX model. Small intestinal segments containing PPs were excised after MTX treatment. Epithelial proliferation and apoptosis were assessed by detection of incorporated BrdU and cleaved caspase-3, respectively. Epithelial functions were determined by the expression of cell type-specific gene products at mRNA and protein level. Before and after MTX treatment, the number of BrdU-positive cells was higher in PP crypts than in NP crypts. BrdU incorporation was diminished in NP crypts, while in PP crypts incorporation was hardly affected. In PP and NP crypts, similar and increased levels of cleaved caspase-3-positive cells were observed after MTX. The enterocyte markers, sucrase-isomaltase, sodium-glucose co-transporter 1, glucose transporters 2 and 5, and intestinal and liver fatty acid binding protein, were down-regulated after MTX in NP epithelium but not in PP epithelium. In contrast, expression of the goblet cell markers, Muc2 and trefoil factor 3, and the Paneth cell marker, lysozyme, was maintained after MTX in both PP and NP epithelium. In conclusion, as MTX-induced apoptosis was similar in PP and NP crypts, the protection of the PP epithelium seems to be based on differences in the regulation of epithelial proliferation. Enterocyte function in the PP epithelium was unaffected by MTX treatment. Goblet and Paneth cell function was maintained in both NP and PP epithelium.

Hepatocyte nuclear factor-1 alpha, GATA-4, and caudal related homeodomain protein Cdx2 interact functionally to modulate intestinal gene transcription. Implication for the developmental regulation of the sucrase-isomaltase gene

Sucrase-isomaltase (SI), an intestine-specific gene, is induced in the differentiated small intestinal villous epithelium during the suckling-weaning transition in mice. We have previously identified cis-acting elements within a short evolutionarily conserved SI promoter. However, the nature and profile of expression of the interacting proteins have not been fully characterized during this developmental transition. Herein, we show that hepatocyte nuclear factor-1 alpha (HNF-1 alpha), GATA-4, and caudal related homeodomain proteins Cdx2 and Cdx1 are the primary transcription factors from the adult mouse intestinal epithelium to interact with the SIF3, GATA, and SIF1 elements of the SI promoter. We wanted to study whether HNF-1 alpha, GATA-4, and Cdx2 can cooperate in the regulation of SI gene expression. Immunolocalization experiments revealed that HNF-1 alpha is detected in rare epithelial cells of suckling mice and becomes progressively more expressed in the villous epithelial cells during the suckling-weaning transition. GATA-4 protein is expressed exclusively in villous differentiated epithelial cells of the proximal small intestine, decreases in expression in the ileum, and becomes undetectable in the colon. HNF-1 alpha, GATA-4, and Cdx2 interact in vitro and in vivo. These factors activate SI promoter activity in cotransfection experiments where GATA-4 requires the presence of both HNF-1 alpha and Cdx2. These findings imply a combinatory role of HNF-1 alpha, Cdx2, and GATA-4 for the time- and position-dependent regulation of SI transcription during development.

Chapter 16 Production and gene expression of brush border disaccharidases and peptidases during development in pigs and calves

This chapter reviews the expression of intestinal brush-border disaccharidases (maltase-glucoamylase, sucrase-isomaltase, lactase, and trehalase) and peptidases (aminopeptidases A and N and dipeptidyl peptidase IV) during development in growing animals. It describes the roles of intestinal enzymes, focussing on complementarity with salivary, gastric, and pancreatic digestive enzymes and their hydrolytic function in the process of absorption. Gene expression of the enzymes and nutritional regulation of their expression appear during postnatal development up to maturity. After translation of the specific mRNA, a single precursor of maltaseglucoamylase (pro-MG), rich in mannose, is produced in the rough endoplasmic reticulum (RER). In contrast to the relatively small number of carbohydrases, the number of peptidases found in enterocytes in the small intestine is large, because of the large number of different peptide bonds in oligopeptides produced by the action of pancreatic proteases. The digestive function (disaccharidase and peptidase activities) of the enterocytes and their microvilli begins when structural differentiation is complete, that is, during the period of migration over the cryptvillus junction. Modern techniques and investigations are expected to yield relevant data for elaborating feeding strategies that take into account the complex interactions between the diet, the microflora, the luminal milieu and the physiology of the small intestine, including the optimal functioning of the immunological and endocrine systems.

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

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

A silencer inhibitor confers specific expression of intestinal trefoil factor in gobletlike cell lines

Intestinal trefoil factor (ITF) is selectively expressed in intestinal goblet cells. Previous studies identified cis-regulatory elements in the proximal promoter of ITF, but these were insufficient to recapitulate the exquisite tissue- and cell-specific expression of native ITF in vivo. Preliminary studies suggested that goblet cell-specific expression of murine ITF requires elements far upstream that include a silencer element that effectively prevents ITF expression in non-goblet cells. Transient transfection studies using native or mutant ITF 5'-flanking sequences identified a region that restores expression in goblet cells. This element, designated goblet cell silencer inhibitor (GCSI) element, enables human and murine goblet cell-like cell lines to override the silencing effect of more proximal elements. The GCSI has no intrinsic enhancer activity and regulates expression only when the silencer element is present. Ligation of GCSI and silencer elements to sucrase-isomaltase conferred goblet cell-specific expression. Goblet cells but not non-goblet cells possess a nuclear protein that binds to the GCSI regulatory element (GCSI binding protein; GCSI-BP). Both transient transfection and gel mobility shift assay studies localize the GCSI and GCSI-BP to -2216 to -2204. We conclude that goblet cell-specific transcription of ITF in vivo depends on a regulatory element designated GCSI.

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

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

Lactase-phlorizin hydrolase and sucrase-isomaltase genes are expressed differently along the villus-crypt axis of rat jejunum

Lactase-phlorizin hydrolase (LPH) and sucrase-isomaltase (SI) are two disaccharidases specifically expressed in small intestinal absorptive cells. We previously showed that the transcripts of both genes are elevated within 12 h of carbohydrate intake. To examine at which locus of villus-crypt axis this response to dietary carbohydrate occurs, 6-wk-old rats were fed a low-carbohydrate diet (5% energy) for 7 d, and then force-fed either the low-carbohydrate diet or a sucrose (40% energy) diet during the last 6 h. Cryostat sectioning of jejunal segments followed by RNA blot hybridizations of the transcripts revealed that, unlike SI mRNA which was expressed maximally in the lower villus, maximal LPH mRNA level was attained at the upper villus. The distribution of the respective immunoreactive protein and the enzymatic activity was shifted more toward the villus tips for LPH than for SI. Force-feeding the sucrose diet caused an abrupt increase in SI mRNA level in the lower villus within 3 h, while the rise in LPH mRNA level occurred in the mid- and upper-villus. The diet-induced increases in the LPH mRNA and SI mRNA levels were abolished along the entire villus by the administration of actinomycin D. These results suggest that LPH gene is maximally expressed in more apical villus cells than SI gene, and that dietary sucrose elicits enhancement of the gene expressions in the villus cells which are accumulating the respective transcripts.

Regulation and expression of multidrug resistance (MDR) transcripts in the intestinal epithelium

A paucity of information exists on the regulation of gene expression in the undifferentiated intestine. The intestinal epithelium is one of the few normal tissues expressing the multidrug resistance (MDR) genes that confer the multidrug resistant phenotype to a variety of tumours. Expression of mdr1a has been observed in the primitive rat intestinal epithelial cell line, IEC-18. It is hypothesized that characterization of MDR gene expression in IEC-18 cells will provide insight into gene regulation in undifferentiated intestinal cells. A series of hamster mdr1a promoter deletion constructs was studied in IEC-18 and a region with 12-13-fold enhancer activity was identified. This region was shown to function in an orientation- and promoter context-independent manner, specifically in IEC-18 cells. Unexpectedly, Northern probing revealed a greater expression of mdr1b than mdr1a in IEC-18 cells. A quantitative reverse transcription polymerase chain reaction assay was used to compare the relative expression of MDR genes in IEC cells, fetal intestine, and in the undifferentiated and differentiated components of adult intestinal epithelium. MDR transcript levels in IEC cells were found to resemble those of fetal intestine and small intestinal crypts, where a conversion from mixed mdr1a/mdr1b to predominantly mdr1a expression occurs as cells mature. This work describes two contributions to the field of gene regulation in the undifferentiated intestine--first, the initial characterization of a putative mdr1a enhancer region with specificity for primitive intestinal cells and secondly, the first report of mdr1b detection in the intestine and its expression in primitive cell types.

Dissociation between growth arrest and differentiation in Caco-2 subclone expressing high levels of sucrase

Growth arrest and cell differentiation are generally considered temporally and functionally linked phenomena in small intestinal crypt cells and colon tumor cell lines (Caco-2, HT-29). We have derived a Caco-2 subclone (NGI3) that deviates from such a paradigm. In striking contrast with the parental cells, proliferative and subconfluent NGI3 cells were found to express sucrase-isomaltase (SI) mRNA and to synthesize relatively high levels of SI, dipeptidyl peptidase IV, and aminopeptidase N (APN). In postconfluent cells, little difference was seen in SI mRNA levels between Caco-2 and NGI3 cells, but the latter still expressed much higher levels of SI that could be attributed to higher rates of translation. APN expression was also greatly enhanced in NGI3 cells. To determine whether high levels of brush-border enzymes correlated with expression of cell-cycle regulatory proteins, we investigated their relative cellular levels in growing and growth-arrested cells. The results showed that the cyclin-dependent kinase inhibitors (p21 and p27) and D-type cyclins (D1 and D3) were all induced in postconfluent cells, but NGI3 cells expressed much higher levels of p21. This study demonstrated that cell growth and expression of differentiated traits are not mutually exclusive in intestinal epithelial cells and provided evidence indicating that posttranscriptional events play an important role in regulation of SI expression.

Secretion of human meprin from intestinal epithelial cells depends on differential expression of the alpha and beta subunits

Human meprin (N-benzoyl-l-tyrosyl-p-aminobenzoic acid hydrolase, EC 3.4.24.18), an astacin-type metalloprotease, is expressed by intestinal epithelial cells as a dimeric protein complex of alpha and beta subunits. In transfected cells, intracellular proteolytic removal of the membrane anchor from the alpha subunit results in its secretion, while the beta subunit and alpha/beta heterodimers are retained at the cell membrane. We investigated the consequence of differential intracellular processing of alpha and beta subunits in the human small and large intestine using subunit-specific immunohistochemistry, in situ hybridization and biosynthetic studies in organ culture. In the ileum, both subunits localize to the brush-border membrane of villus enterocytes. In contrast, the beta subunit is not expressed in the colon, which leads to the secretion of the alpha subunit. We conclude that differential expression of meprin alpha and beta subunits is a unique means of targeting the proteolytic activity of the alpha subunit either to the brush-border membrane in the ileum or to the lumen in the colon, suggesting dual functions of cell-associated and luminal meprin. Meprin alpha and beta subunits are also coexpressed in distinct lamina propria leukocytes, suggesting an additional role for this protease in leukocyte function in the intestinal mucosa.

Keratinocyte growth factor down-regulates expression of the sucrase-isomaltase gene in Caco-2 intestinal epithelial cells

The molecular mechanisms that regulate the proliferation and differentiation of intestinal mucosal epithelial cells are not well understood. Keratinocyte growth factor (KGF) is an epithelial cell-specific growth factor that may be involved in the maintenance of mucosal epithelial populations and in mediating epithelial repair after injury. The sucrase-isomaltase (SI) gene, which encodes an enterocyte brush border disaccharidase, has served as a model for study of intestinal-specific gene expression and differentiation. KGF down-regulated SI mRNA and protein expression in Caco-2 intestinal epithelial cells but not the expression of other brush border enzymes. The down-regulation was dose- and time-dependent and specifically blocked by anti-KGF antibodies. Transfection experiments using SI promoter constructs demonstrated that KGF decreased SI gene transcription. In contrast, the stability of SI mRNA was not affected by incubation of Caco-2 cells with KGF. Electrophoretic mobility shift analysis demonstrated that binding of nuclear proteins to the SI footprint (SIF) 3 and SIF4 regulatory elements within the SI promoter region was increased in Caco-2 cells that had been incubated with KGF. In transfection experiments using a construct in which tandem copies of the SIF4-binding site were inserted upstream of the SV40 promoter and luciferase gene, incubation with KGF resulted in a significant decrease in luciferase activity. However, transfection with a similar construct containing tandem copies of SIF3 had no significant effect on SV40 promoter activity following KGF treatment. SIF4 may bind E4BP4, a previously identified transcriptional repressor protein. This factor may in part mediate the decrease in SI transcription by KGF in Caco-2 cells.

Two HNF-1 binding sites govern the glucose repression of the human sucrase-isomaltase promoter

We have previously shown, using the Caco-2 clone PF11, that glucose represses transcription of the human sucrase-isomaltase (SI) gene and that the -370/+30 fragment of the SI gene conferred glucose-regulated expression on a heterologous gene. Different fragments beginning at the already characterized SI footprint (SIF) 1 (-53/-37), SIFR (-153/-129) or SIF3 (-176/-156) elements [Wu, Chen, Forslund and Traber (1994) J. Biol. Chem. 269, 17080-17085] were tested, in comparison with the -370/+30 fragment, for their capacity to inhibit reporter gene expression under high-glucose (25 mM) conditions. Unlike SIF1 and SIFR, the addition of the HNF (hepatocyte nuclear factor)-1-binding element SIF3 to the promoter fragment was required for repression under high-glucose conditions. This effect was enhanced when the SI promoter was extended to position -370, indicating that the -370/-176 region contains elements that may co-operate with SIF3 to increase the metabolic control of the SI promoter. We have characterized an additional HNF-1-binding site near to and upstream from SIF3; SIF4. By mutagenesis of the three HNF-1-binding elements we show that the two distal HNF-1-recognition sites are the most important for the glucose regulation of the SI gene. Moreover, this glucose regulation was abolished in PF11 cells overexpressing vHNF-1C (variant HNF, an isoform of the HNF-1 family). We thus propose that the differential binding of HNF-1-family proteins to their DNA targets on the SI promoter constitutes the molecular mechanism that controls the glucose regulation of the SI gene transcription.

Vitamin A up-regulates expression of bone-type alkaline phosphatase in rat small intestinal crypt cell line and fetal rat small intestine

Vitamin A is a potent inducer for liver/bone/kidney alkaline phosphatase (L/B/K ALP) in a variety of tissues. However, the evidence for induction of L/B/K ALP by vitamin A in small intestine is limited. In this study, we investigated the influence of vitamin A on L/B/K ALP expression in rat small intestinal crypt IEC-6 cells and fetal rat small intestine. Treatment of IEC-6 cells with all-trans retinoic acid (RA) increased the levels of activity, protein and mRNA of L/B/K ALP, whereas enterocyte-specific proteins, including intestinal ALP, sucrase-isomaltase and glucose transporter-2, were not induced. The reverse transcription-polymerase chain reaction technique revealed that this L/B/K ALP transcript had the bone-type but not the liver-type leader exon. IEC-6 cells constitutively expressed mRNAs of all subtypes of retinoic acid receptor (RAR) and retinoid X receptor (RXR) at varied concentrations. Among these receptor mRNAs, RARbeta mRNA quickly responded to RA treatment, and the level was doubled within 4 h. Gel mobility shift assay showed that RA induced an RXRE-binding activity in IEC-6 cells. The L/B/K ALP transcript, expressed in fetal rat small intestine, also contained the bone-type leader exon. Intragastric administration of 10 mg retinyl acetate to pregnant rats from gestational d 7 to 15 increased the levels of this transcript and enzyme in 15-d fetal rat small intestine. Our results suggest that vitamin A may be an important regulator for L/B/K ALP expression in fetal rat small intestine as well as in IEC-6 cells.

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.

Circadian periodicity of intestinal Na+/glucose cotransporter 1 mRNA levels is transcriptionally regulated

Intestinal expression of the high affinity Na+/glucose cotransporter 1 (SGLT1), which absorbs dietary glucose and galactose, exhibits both circadian periodicity in its activity and induction by dietary carbohydrate. Because the daily variation in SGLT1 activity is established by the feeding schedule (whether ad libitum or imposed) and persists in the absence of food, this variation has been described as anticipatory. To delineate the mechanisms regulating SGLT1, its expression was examined in rats maintained in a 12-h photoperiod with free access to chow. SGLT1 mRNA levels varied significantly, with the maximum abundance occurring near the onset of dark and the minimum near the onset of light. The SGLT1 transcription rate was 7-fold higher in the morning (1000-1100 h) than in the afternoon (1600-1700 h). An element for hepatocyte nuclear factor 1 (HNF-1) was identified in the SGLT1 promoter that formed different complexes with small intestinal nuclear extracts, depending on the time when the source animal was killed. Serological tests indicated that HNF-1alpha was present in complexes throughout the day, while HNF-1beta binding exhibited circadian periodicity. We propose that exchange of HNF-1 dimerization partners contributes to circadian changes in SGLT1 transcription. Because SGLT1 mRNA levels also varied in rhesus monkeys (offset by approximately one-half day from rats), a similar mechanism appears to be present in primates.

Regulation of the PepT1 peptide transporter in the rat small intestine in response to 5-fluorouracil-induced injury

BACKGROUND & AIMS

The oligopeptide transport system of the small intestine is resistant to mucosal injury. The mechanism of this resistance was investigated by examining the activity level and expression of the peptide transporter PepT1 in the intestine of rats treated with 5-fluorouracil.

METHODS

The expression and localization of PepT1 were examined by immunoblot analysis of brush border membrane vesicles and immunohistochemical analysis of intestinal sections with PepT1-specific rabbit polyclonal antibodies. Also, Northern blot analysis was used for the expression of PepT1 messenger RNA (mRNA).

RESULTS

Although the amounts of sucrase and an Na+-dependent glucose transporter protein in intestinal vesicles decreased markedly after 5-fluorouracil treatment, the amount of PepT1 protein remained largely unaffected. Immunohistochemical analysis also showed that the PepT1 immunoreactivity level was preserved in the brush border membrane of the remaining villi of 5-fluorouracil-treated rats. Levels of amino acid, glucose, and phosphate transporter mRNAs were profoundly depressed in 5-fluorouracil-treated animals, whereas the level of PepT1 mRNA conversely increased.

CONCLUSIONS

The resistance of intestinal peptide transport to tissue injury may be attributable to increased synthesis of PepT1 rather than to a change in the kinetic properties of the residual absorbing cells.

Asymmetrical localization of mRNAs in enterocytes of human jejunum

Intracellular localization of specific mRNAs is known to be a mechanism for targeting proteins to specific sites within the cell. Previous studies from this laboratory have demonstrated co-localization of mRNAs and proteins for a number of genes in absorptive enterocytes of fetal rat intestine. The present study was undertaken to examine in human enterocytes the intracellular localization patterns of mRNAs for the microvillous membrane proteins lactase-phlorizin hydrolase (LPH), sucrase-isomaltase (SI), and intestinal alkaline phosphatase (IAP), and the cytoskeletal protein beta-actin. In sections of human jejunum, mRNAs were localized by in situ hybridization using digoxigenin-labeled anti-sense RNA probes. Both LPH and SI mRNAs were localized to the apical region of villous enterocytes, whereas IAP and beta-actin mRNAs were detected both apically and basally relative to the nucleus. Therefore, in contrast to LPH, SI, and beta-actin mRNAs, which co-localize with their encoded proteins, that of IAP is present in the basal region of the cell where IAP protein has not directly been demonstrated to be present. Absorptive enterocytes from humans possess the mechanisms for intracellular mRNA localization, but not all mRNAs co-localize with their encoded proteins.

A novel alkaline phosphatase-based isolation method allows characterization of intraepithelial lymphocytes from villi tip and crypt regions of murine small intestine

The isolation of intestinal intraepithelial lymphocytes (IEL) is a major prerequisite for the investigation of cellular and molecular cross-talk in the intestinal mucosa. Since intestinal epithelial cells exhibit distinct functional features at the villi tip and crypt levels, such differences could extend to IEL. We developed a mechanical procedure for isolation of IEL from these distinct epithelial sites to test our hypothesis. Cells isolated from the intestinal epithelium by sequential incubations under stirring were segregated based upon their alkaline phosphatase (AP) activity since villi tip and crypt fractions expressed high and low AP activity, respectively. IEL preparations obtained after a further purification step in Percoll gradient contained > 90% Integrin alpha IEL chain+, CD3+ T cells, and no Ig+ cells. Villi tip IEL preparations possessed increased numbers of low density IEL when compared to crypt IEL, suggesting that distinct IEL-epithelial cell interactions occur at the intestinal villi tip and crypt levels.

Total intestinal lactase and sucrase activities are reduced in aged rats

Lactase-phlorizin hydrolase (LPH) and sucrase-isomaltase (SI) are intestinal microvillus membrane hydrolases that play important roles in carbohydrate digestion. Although the expression of these enzymes during postnatal development has been characterized, the effect of old age on disaccharidase activity is poorly understood. In the present investigation, we examined the effect of aging on lactase and sucrase activities and their mRNA levels in the small intestines of 3-, 12- and 24- mo-old rats by sampling from nine equidistant segments of small intestine. Total intestinal disaccharidase activity or mRNA abundance was determined from areas under the proximal-to-distal curves. Rats 24 mo of age had total intestinal lactase and sucrase activities that were 12 and 38% lower, respectively, than the 3-mo-old animals (P < 0.05). In contrast, total LPH and SI mRNA abundance did not change significantly. Thus, total intestinal lactase and sucrase activities decrease with age in a manner that likely involves a posttranscriptional process. The age-related decline in disaccharidase activity, if extrapolated to humans, may have important implications for the digestion of carbohydrate contained in the diet of the elderly.

Transcriptional and translational control over sodium-glucose-linked transporter (SGLT1) gene expression in adult rat small intestine

We have measured SGLT1 mRNA content and SGLT1-mediated glucose transport at different positions along the small intestine of control and streptozotocin diabetic rats and shown both parameters to be similar but higher in jejunal compared with ileal tissue. No such correlation was seen when comparing measurements of SGLT1 mRNA along jejunal villi with previous estimates of SGLT1 protein and SGLT1-mediated glucose transport [Debnam et al., Eur. J. Physiol. 430 (1995) 151-159]. This is the first time it has been possible to directly relate these three aspects of SGLT1 gene expression in a single species. Results are discussed in terms of a possible time rather than positional control over translation of SGLT1 mRNA.

An enhancer with cell-type dependent activity is located between the myeloid and epithelial aminopeptidase N (CD 13) promoters

The 5' flanking region of the gene encoding the small intestinal brush-border peptidase aminopeptidase N (APN) was screened for the presence of enhancer regions. A 300 bp region with enhancer activity was identified 2.7 kb upstream of the transcriptional start site which is used in epithelial cells. The enhancer stimulated transcription from a heterologous promoter (the simian virus 40 early promoter) in a position- and orientation-independent manner. The activity of the enhancer is cell-type dependent and it is active in liver (HepG2), intestinal (Caco-2) and myeloid (K562) cells. As the epithelial APN promoter is active in the first two cell-types and the myeloid APN promoter in the last, the results may suggest that the enhancer, through a cooperation with either of the promoters, is important for the tissue-specific expression of APN. A detailed analysis of the enhancer led to the identification of four functionally important regions that are protected against DNase I digestion by Caco-2 nuclear extract. Sequence analysis suggests that two of the regions may interact with members of the Ets transcription factor family (Ets is a transformation-specific protein first discovered in the E26 avian erythroblastosis virus), one region with a CCAAT enhancer-binding protein and one region with Sp1, a transcriptional activator first described as a factor binding to the simian virus 40 early promoter.

Glucose-dependent transcriptional regulation of the human sucrase-isomaltase (SI) gene

We have previously shown that the transcription of the human sucrase-isomaltase (SI) gene was negatively regulated by glucose. Using two clonal metabolic variants of the human colon adenocarcinoma cell line Caco-2 we demonstrate here that: 1) although similar growth-related variations of phosphoenolpyruvate carboxykinase (PEPCK), frutose 1,6-diphosphatase (F1, 6-dPase), pyruvate kinase (PK) and SI mRNA levels are observed, only F1,6-dPase, PK and SI mRNA levels vary in the same way in response to modifications of glucose utilization; and 2) regulatory elements responsible for the glucose-dependent transcription of the SI gene are located within the -370/+30 region of the promoter.

Guinea pig intestinal phospholipase B: protein expression during enterocyte maturation and effects of N-oligosaccharide removal on enzymatic activities and protein stability

Guinea pig phospholipase B (PLB) is an intestinal brush-border hydrolase displaying a broad substrate specificity towards various dietary lipids. PLB was detected by immunoblotting as a single 140-kDa polypeptide in all cell populations isolated from guinea pig intestinal mucosa, but increased in parallel to its activity from undifferentiated to mature cells, the specific activity of the enzyme remaining constant. Moreover, N-glycosylation, which contributed to 23% of the apparent molecular mass, was identical along the cell differentiation axis. In all cell fractions, N-linked sugar chains were of the complex type, since they were removed by N-glycosidase F, whereas PLB remained insensitive to endoglycosidase H. Moreover, lack of O-glycosylation was demonstrated by the insensitivity of PLB to O-glycosidase and by its failure to interact with Helix pomatia lectin after prior treatment with neuraminidase or alpha-fucosidase. Enzymatic removal of sugar chains reduced phospholipase A2, lysophospholipase and diacylglycerol lipase activities by 27-35%, kinetic analysis indicating a decrease in apparent Vmax values for the three enzymatic activities, whereas the Km remained unchanged. Finally, the carbohydrate-depleted form of PLB did not display gross changes in thermal stability, in contrast to PLB from microorganisms previously investigated. Our data indicate that the high level of PLB N-glycosylation is poorly related to its biological function. Whether carbohydrate chains are involved in proper targeting of the enzyme to the brush-border membrane remains to be established.

Rabbit sucrase-isomaltase contains a functional intestinal receptor for Clostridium difficile toxin A

The intestinal effects of Clostridium difficile toxin A are inidated by toxin binding to luminal enterocyte receptors. We reported previously that the rabbit ileal brush border (BB) receptor is a glycoprotein with an alpha-d-galactose containing trisaccharide in the toxin-binding domain (1991. J. Clin. Invest. 88:119-125). In this study we characterized the rabbit ileal BB receptor for this toxin. Purified toxin receptor peptides of 19 and 24 amino acids showed 100% homology with rabbit sucrase-isomaltase (SI). Guinea pig receptor antiserum reacted in Western blots with rabbit SI and with the purified toxin receptor. Antireceptor IgG blocked in vitro binding of toxin A to rabbit ileal villus cell BB. Furthermore, anti-SI IgG inhibited toxin A-induced secretion (by 78.1%, P < 0.01), intestinal permeability (by 80.8%, P < 0.01), and histologic injury (P < 0.01) in rabbit ileal loops in vivo. Chinese hamster ovary cells transfected with SI cDNA showed increased intracellular calcium increase in response to native toxin (holotoxin) or to a recombinant 873-amino acid peptide representing the receptor binding domain of toxin A. These data suggest that toxin A binds specifically to carbohydrate domains on rabbit ileal SI, and that such binding is relevant to signal transduction mechanisms that mediate in vitro and in vivo toxicity.

A limited upstream region of the human sucrase-isomaltase gene confers glucose-regulated expression on a heterologous gene

We have previously shown that glucose can exert a repressive effect on the transcription of the sucrase-isomaltase (SI) gene in the differentiated enterocyte-like human colon carcinoma cell lines HT-29 and Caco-2. To characterize the region through which glucose exerts this effect, three different-length fragments of the 5'-flanking region of the human SI gene were linked to the reporter gene luciferase in an episomal vector carrying a hygromycin resistance gene. These fragments were used for transfection into a clone of the Caco-2 cell line, PF11, which has high glucose consumption and only expresses SI at high levels when cultured in the presence of a low supply of glucose. By using the stably transformed PF11 cells grown either in standard high glucose (25 mM) or in low glucose (1 mM) it was possible to show that the smallest fragment of the SI promoter, extending from bases -370 to +30, contains all the information required for the glucose repression of the reporter gene luciferase.

Kinetics of neurotensin gene expression in the developing gut

BACKGROUND

Expression of the gene encoding neurotensin (NT/N) is regulated in a strict temporal- and spatial-specific pattern during gut development; the mechanisms (that is, transcriptional versus posttranscriptional) responsible for this expression pattern are not known. The purpose of this study was to determine whether developmental changes in NT/N expression reflect alternations in gene transcription.

METHODS

Sensitive ribonuclease protection assays were performed with a rat NT/N genomic probe containing the entire sequence of both exon 1 and intron 1 hybridized with RNA from fetal (day 19) and postnatal (days 14, 28, and 60) rat jejunum and ileum; signals were quantitated densitometrically.

RESULTS

Mature (exon 1) and precursor (exon 1 + intron 1) NT/N RNA, initially low in the fetus, increased dramatically by postnatal day 14 and attained maximal levels by day 28. NT/N RNA levels remained stable in the ileum of the 60-day-old rat but decreased in the jejunum, consistent with the typical expression pattern in the gut.

CONCLUSIONS

Concomitant changes in expression of precursor and mature NT/N RNA suggest that NT/N gene regulation occurs at the level of transcription in the gut during development. Identifying the factors that regulate NT/N gene transcription is crucial to our understanding of how neurotensin functions in the gut.

An intestine-specific homeobox gene regulates proliferation and differentiation

Precise regulation of cellular proliferation, differentiation, and senescence results in the continuous renewal of the intestinal epithelium with maintenance of a highly ordered tissue architecture. Here we show that an intestine-specific homeobox gene, Cdx2, is a transcription factor that regulates both proliferation and differentiation in intestinal epithelial cells. Conditional expression of Cdx2 in IEC-6 cells, an undifferentiated intestinal cell line, led to arrest of proliferation for several days followed by a period of growth resulting in multicellular structures containing a well-formed columnar layer of cells. The columnar cells had multiple morphological characteristics of intestinal epithelial cells. Enterocyte-like cells were polarized with tight junctions, lateral membrane interdigitations, and well-organized microvilli with associated glycocalyx located at the apical pole. Remarkably, there were also cells with a goblet cell-like ultrastructure, suggesting that two of the four intestinal epithelial cell lineages may arise from IEC-6 cells. Molecular evidence for differentiation was shown by demonstrating that cells expressing high levels of Cdx2 expressed sucrase-isomaltase, an enterocyte-specific gene which is a well-defined target for the Cdx2 protein. Taken together, our data suggest that Cdx2 may play a role in directing early processes in intestinal cell morphogenesis and in the maintenance of the differentiated phenotype by supporting transcription of differentiated gene products. We propose that Cdx2 is part of a regulatory network that orchestrates a developmental program of proliferation, morphogenesis, and gene expression in the intestinal epithelium.

Regulation of sucrase-isomaltase gene expression in human intestinal epithelial cells by inflammatory cytokines

Using metabolic labeling techniques in human intestinal epithelial cell lines in tissue culture and in situ hybridization techniques in normal and inflamed (Crohn's) intestine, recent studies have shown that there is synthesis of acute phase proteins in enterocytes. Moreover, these studies have shown that acute phase protein biosynthesis in enterocytes is regulated by inflammatory cytokines in a manner characteristic of the physiologic acute phase response. In the course of these studies it was noticed that one inflammatory cytokine, interleukin-6 (IL-6), mediated selective down-regulation of the enterocyte-specific, differentiation-dependent integral membrane protein sucrase-isomaltase (SI) in the Caco2 intestinal epithelial cell line. In the current study we examined the effect of several other inflammatory cytokines interleukin-1 (IL-1 beta), tumor necrosis factor alpha (TNF alpha), and interferon gamma (IFN gamma) on synthesis of SI in Caco2 cells, examined the possibility that inflammatory cytokines affect the synthesis of other enterocyte integral membrane proteins using lactase as a prototype, and examined the possibility that SI gene expression was down-regulated in villous enterocytes in vivo during the local inflammatory response of Crohn's disease. The results show that IL-6 and IFN gamma each mediate a decrease and TNF alpha mediates an increase in synthesis of SI in Caco2 cells. The magnitude of down-regulation by IL-6 and IFN gamma is significantly greater than the up-regulation by TNF alpha. IL-1 beta has no effect on synthesis of SI. Synthesis of lactase is not affected by any of the cytokines. There is a marked specific decrease in SI gene expression in villous enterocytes in acutely inflamed Crohn's ileum as compared to adjacent uninflamed ileum and normal ileum. Taken together, these data show that inflammatory cytokines have specific and selective effects on the expression of the brush border hydrolase SI in tissue culture and in vivo and provide evidence for a previously unrecognized mechanism for disaccharidase deficiency in intestinal inflammation.

Patterns of gene expression along the crypt-villus axis in mouse jejunal epithelium

BACKGROUND

There is considerable interest in gene expression along the crypt-villus axis of the small intestinal epithelium, particularly in the identification of genes expressed in intestinal crypts.

METHODS

In an attempt to identify crypt-expressed genes, single-stranded cDNA made from normal mouse jejunal epithelium was used in subtractive hybridization against single-stranded cDNA from epithelium from which crypt cells were depleted by 2,000 rads of gamma irradiation. Partial DNA sequence and in situ hybridization of 72 resulting clones were determined.

RESULTS

The sequence of 45 clones matched previously published genes. Gene expression patterns fell into three categories: expression throughout the crypt-villus axis, expression restricted to the villus, and expression restricted to the crypt. Clones in the first two categories could be further divided into three subgroups: those with uniform expression, those with an increasing gradient of expression, and those with a decreasing gradient of expression along the crypt-villus axis. Twenty two clones showed a stronger expression in crypt and lower villus cells, four of these were differentially localized to the crypt. Two of the crypt localized clones were uniformly expressed throughout the crypt, expression of one was stronger in the lower crypt, and expression of the remaining clone was enhanced Paneth cells. We report the full-length cDNA sequence of the Paneth-cell-enhanced clone.

CONCLUSIONS

The screen isolated crypt-expressed genes that may prove useful tools in the study of crypt biology. In a companion report, we characterize one of the crypt clones.

Expression and glycosylation of the filamentous brush border glycocalyx (FBBG) during rabbit enterocyte differentiation along the crypt-villus axis

The filamentous brush border glycocalyx forming the ‘enteric surface coat’ of the intestinal epithelium is composed in rabbits of a 400 kDa mucin-type glycoprotein, which was purified using the 3A4 monoclonal antibody. This monoclonal antibody recognizes a filamentous brush border glycocalyx-specific glycosidic structure containing an O-acetylated sialic acid, which is absent from all the other glycoproteins in the epithelium, with the exception of certain goblet cell mucins. Here we establish that only 50% of the rabbits tested synthesized this glycosidic structure. Upon immunolabeling surface epithelia and sections of jejunum from these rabbits, the carbohydrate epitope recognized by the 3A4 mAb was found to be present on the filamentous brush border glycocalyx of a variable number of enterocytes, which were patchily distributed over all the villi. This heterogeneous expression of 3A4 antigenicity, which was also observed in the crypts, suggests the existence of differences between the patterns of differentiation of enterocytes, which results in the expression of different pools of glycosyltransferases and/or acetyl transferases. In mature enterocytes, the 3A4 determinants were present only on the filamentous brush border glycocalyx, which is anchored solely to the membrane microdomain at the tip of brush border microvilli. However, expression of 3A4 antigenicity begins in the median third of crypts, in enterocytes with a short, thin brush border devoid of apical filamentous brush border glycocalyx. Here the 3A4 epitopes were present over the whole brush border membrane.(ABSTRACT TRUNCATED AT 250 WORDS)

Regulation of GLUT5 gene expression in rat intestinal mucosa: regional distribution, circadian rhythm, perinatal development and effect of diabetes

1. GLUT5 gene expression was studied in small intestine under a variety of conditions characterized by altered intestinal absorption of monosaccharides. 2. RNA-blotting studies showed that GLUT5 mRNA was abundantly expressed in rat and rabbit intestine and kidney, but it was not detected in heart or brown adipose tissue. GLUT5 mRNA levels were higher in the upper segments of the small intestine (duodenum and proximal jejunum) than in the lower segments (distal jejunum and ileum). 3. The intestinal expression of GLUT5 mRNA in rat proximal jejunum showed circadian rhythm. A 12-fold increase in GLUT5 mRNA levels was detected at the end of the light cycle and at the beginning of the dark cycle when compared with the early light period. In keeping with this, GLUT5 protein content in brush-border membranes was also increased at the beginning of the dark cycle compared with that in the light period. 4. In streptozotocin-induced diabetes an 80% increase in GLUT5 mRNA levels in mucosa from the proximal jejunum was detected under conditions in which enhanced intestinal absorption of monosaccharides has been reported. 5. The intestinal expression of GLUT5 mRNA showed regulation during perinatal development. Levels of GLUT5 mRNA were low during fetal life, increased progressively during the postnatal period and reached levels comparable with the adult state after weaning. Weaning on to a high-fat diet partially prevented the induction of GLUT5 gene expression. 6. Our results indicate that GLUT5 gene expression is tightly regulated in small intestine. Regulation involves maximal expression in the upper part of the small intestine, circadian rhythm, developmental regulation dependent on the fat and carbohydrate content in the diet at weaning and enhanced expression in streptozotocin-induced diabetes. Furthermore, changes observed in intestinal GLUT5 expression correlate with reported alterations in intestinal absorption of fructose. This suggests a regulatory role for GLUT5 in fructose uptake by absorptive enterocytes.

Intestinal brush border glycohydrolases: structure, function, and development

The hydrolytic enzymes of the intestinal brush border membrane are essential for the degradation of nutrients to absorbable units. Particularly, the brush border glycohydrolases are responsible for the degradation of di- and oligosaccharides into monosaccharides, and are thus crucial for the energy-intake of humans and other mammals. This review will critically discuss all that is known in the literature about intestinal brush border glycohydrolases. First, we will assess the importance of these enzymes in degradation of dietary carbohydrates. Then, we will closely examine the relevant features of the intestinal epithelium which harbors these glycohydrolases. Each of the glycohydrolytic brush border enzymes will be reviewed with respect to structure, biosynthesis, substrate specificity, hydrolytic mechanism, gene regulation and developmental expression. Finally, intestinal disorders will be discussed that affect the expression of the brush border glycohydrolases. The clinical consequences of these enzyme deficiency disorders will be discussed. Concomitantly, these disorders may provide us with important details regarding the functions and gene expression of these enzymes under specific (pathogenic) circumstances.

Cloning and sequencing of a full-length rat sucrase-isomaltase-encoding cDNA

Sucrase-isomaltase (SI) has been widely used as a marker enzyme to study cellular differentiation in the small intestine. We isolated a 6.1-kb SI cDNA clone (GC1.4) from a size-fractionated cDNA library from rat intestine. Sequencing of this cDNA clone showed 6066 nucleotides (nt) with an open reading frame (ORF) of 1841 amino acids (aa). The nt sequence correctly predicts several known aa stretches in the protein. The deduced as sequence showed 78 and 75% overall identity with the rabbit and human SI, respectively. At the active sites of both S and I, the rat nt sequence encodes stretches of 14 and 16 aa, respectively, which show 100% identity to rabbit and human SI. In the region immediately beyond the transmembrane domain, the rat sequence encodes an extra 10 aa, as compared to rabbit and human. This 10-aa insertion consists almost entirely of Pro, Ser and Thr, and may be responsible for additional O-glycosylations of rat SI. The cDNA contains a 3'-UTR (untranslated region) of 499 nt with polyadenylation signal sequence and a poly(A) tract. The ATG start codon was found 41 nt downstream from the 5' end of the cDNA. Primer extension experiments showed the cap site to be 61 nt upstream from the start codon. The results indicate that our cDNA clone lacks only 20 nt in the 5'-UTR. Given that this cDNA encodes the entire coding region of SI, it should be useful in elucidating the regulatory mechanisms of SI biosynthesis, localization and targeting during rat intestinal development and differentiation.

A homeodomain protein related to caudal regulates intestine-specific gene transcription

The continually renewing epithelium of the intestinal tract arises from the visceral endoderm by a series of complex developmental transitions. The mechanisms that establish and maintain the processes of cellular renewal, cell lineage allocation, and tissue restriction and spatial assignment of gene expression in this epithelium are unknown. An understanding of the regulation of intestine-specific gene regulation may provide information on the molecular mechanisms that direct these processes. In this regard, we show that intestine-specific transcription of sucrase-isomaltase, a gene that is expressed exclusively in differentiated enterocytes, is dependent on binding of a tissue-specific homeodomain protein (mouse Cdx-2) to an evolutionarily conserved promoter element in the sucrase-isomaltase gene. This protein is a member of the caudal family of homeodomain genes which appear to function in early developmental events in Drosophila melanogaster, during gastrulation in many species, and in intestinal endoderm. Unique for this homeodomain gene family, we show that mouse Cdx-2 binds as a dimer to its regulatory element and that dimerization in vitro is dependent on redox potential. These characteristics of the interaction of Cdx-2 with its regulatory element provide for a number of potential mechanisms for transcriptional regulation. Taken together, these findings suggest that members of the Cdx gene family play a fundamental role both in the establishment of the intestinal phenotype during development and in maintenance of this phenotype via transcriptional activation of differentiated intestinal genes.

A homeodomain protein related to caudal regulates intestine-specific gene transcription

The continually renewing epithelium of the intestinal tract arises from the visceral endoderm by a series of complex developmental transitions. The mechanisms that establish and maintain the processes of cellular renewal, cell lineage allocation, and tissue restriction and spatial assignment of gene expression in this epithelium are unknown. An understanding of the regulation of intestine-specific gene regulation may provide information on the molecular mechanisms that direct these processes. In this regard, we show that intestine-specific transcription of sucrase-isomaltase, a gene that is expressed exclusively in differentiated enterocytes, is dependent on binding of a tissue-specific homeodomain protein (mouse Cdx-2) to an evolutionarily conserved promoter element in the sucrase-isomaltase gene. This protein is a member of the caudal family of homeodomain genes which appear to function in early developmental events in Drosophila melanogaster, during gastrulation in many species, and in intestinal endoderm. Unique for this homeodomain gene family, we show that mouse Cdx-2 binds as a dimer to its regulatory element and that dimerization in vitro is dependent on redox potential. These characteristics of the interaction of Cdx-2 with its regulatory element provide for a number of potential mechanisms for transcriptional regulation. Taken together, these findings suggest that members of the Cdx gene family play a fundamental role both in the establishment of the intestinal phenotype during development and in maintenance of this phenotype via transcriptional activation of differentiated intestinal genes.

Cellular localization of the class I alcohol dehydrogenase transcript in adult rat tissues

The mammalian class I alcohol dehydrogenase is the principal enzyme responsible for ethanol metabolism. While it is regarded primarily as a liver-specific enzyme, class I alcohol dehydrogenase is known to be present in a number of extrahepatic tissues. The purpose of the current study is to define the tissue and cellular distribution of the dehydrogenase transcript in four rat tissues previously shown to contain high levels of mRNA: the liver, the proximal small intestine, the colon and the testis. Localization of the transcript was examined in formalin-fixed, paraffin-embedded rat tissues by in situ hybridization using radioactively labelled antisense rat alcohol dehydrogenase RNA probe. In the liver, the dehydrogenase message is localized primarily to the perivenous hepatocytes. In the proximal small intestine and the colon, the message follows a vertical gradient of distribution along the crypt-villus and the crypt-surface epithelium axes, respectively, with the base of the crypt exhibiting the greatest concentration. In the testis, the message is localized primarily to cells in the interstitium. These findings illustrate a highly compartmentalized nature of distribution of the class I alcohol dehydrogenase transcript in the tissues studied and may help to elucidate the metabolic functions of this enzyme in these tissues.

Restriction of lactase gene expression along the proximal-to-distal axis of rat small intestine occurs during postnatal development

BACKGROUND/AIMS

Developmental changes of lactase activity along the proximal-to-distal axis of the small intestine are poorly understood. A study of delineate lactase gene expression at the cellular level was undertaken.

METHODS

The topographical regulation of lactase was studied in conjunction with sucrase-isomaltase in proximal, middle, and distal segments of 0-, 7-, 14-, 16-, 18-, 21-, and 28-day-old and adult rats using in sity hybridization, immunohistochemistry, and ribonuclease protection assays.

RESULTS

From 0 to 16 days, lactase messenger RNA (mRNA) and protein were abundant along the total length of the small intestine. However, at weaning, lactase mRNA and protein were no longer detectable in the terminal ileum. After 28 days, zones of reduced lactase expression were found in the duodenum and terminal ileum. These zones demonstrated expression of lactase protein in scattered enterocytes along the villus (patchy expression). In contrast, sucrase-isomaltase was first detected at 16 days, with patchy expression along the total small intestine; at 21 days it was abundant.

CONCLUSIONS

Concordant changes in both lactase mRNA and protein detection during development suggest that the horizontal gradient of lactase enzyme expression is dependent on lactase mRNA abundance. Furthermore, zones of patchy lactase expression appear around weaning and flank the area of high lactase expression in the midintestine. Patchy expression is also found for sucrase-isomaltase before weaning.

Two intestinal specific nuclear factors binding to the lactase-phlorizin hydrolase and sucrase-isomaltase promoters are functionally related oligomeric molecules

Lactase-phlorizin hydrolase (LPH) and sucrase-isomaltase (SI) are enterocyte-specific gene products. The identification of regulatory cis-elements in the promoter of these two genes has enabled us to carry out comparative studies of the corresponding intestinal-specific nuclear factors (NF-LPH1 and SIF1-BP). Electrophoretic mobility shift assays demonstrated that the two nuclear factors compete for binding on the same cis-elements. The molecular size of the DNA binding polypeptide is estimated to be approximately 50 kDa for both factors. In the native form the factors are found as 250 kDa oligomeric complexes. Based on these results NF-LPH1 and SIF1-BP are suggested to be either identical or closely related molecules.