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

Identification of an intestine-specific promoter and inducible expression of bacterial α-galactosidase in mammalian cells by a lac operon system

Background

α-galactosidase has been widely used in animal husbandry to reduce anti-nutritional factors (such as α-galactoside) in feed. Intestine-specific and substrate inducible expression of α-galactosidase would be highly beneficial for transgenic animal production.

Methods

To achieve the intestine-specific and substrate inducible expression of α-galactosidase, we first identified intestine-specific promoters by comparing the transcriptional activity and tissue specificity of four intestine-specific promoters from human intestinal fatty acid binding protein, rat intestinal fatty acid binding protein, human mucin-2 and human lysozyme. We made two chimeric constructs combining the promoter and enhancer of human mucin-2, rat intestinal trefoil factor and human sucrase-isomaltase. Then a modified lac operon system was constructed to investigate the induction of α-galactosidase expression and enzyme activity by isopropyl β-D-1-thiogalactopyranoside (IPTG) and an α-galactosidase substrate, α-lactose.

We declared that the research carried out on human (Zhai Yafeng) was in compliance with the Helsinki Declaration, and experimental research on animals also followed internationally recognized guidelines.

Results

The activity of the human mucin-2 promoter was about 2 to 3 times higher than that of other intestine-specific promoters. In the lac operon system, the repressor significantly decreased (P < 0.05) luciferase activity by approximately 6.5-fold and reduced the percentage of cells expressing green fluorescent protein (GFP) by approximately 2-fold. In addition, the expression level of α-galactosidase mRNA was decreased by 6-fold and α-galactosidase activity was reduced by 8-fold. In line with our expectations, IPTG and α-lactose supplementation reversed (P < 0.05) the inhibition and produced a 5-fold increase of luciferase activity, an 11-fold enhancement in the percentage of cells with GFP expression and an increase in α-galactosidase mRNA abundance (by about 5-fold) and α-galactosidase activity (by about 7-fold).

Conclusions

We have successfully constructed a high specificity inducible lac operon system in an intestine-derived cell line, which could be of great value for gene therapy applications and transgenic animal production.

Assessing the pathological relevance of SPINK1 promoter variants

The SPINK1 gene, encoding the human pancreatic secretory trypsin inhibitor, is one of the major genes involved in predisposition to chronic pancreatitis (CP). In this study we have assessed the potential functional impact of 11 SPINK1 promoter variants by means of both luciferase reporter gene assay and electrophoretic mobility shift assay (EMSA), using human pancreatic COLO-357 cells as an expression system. The 11 promoter variants were found to be separable into three distinct categories on the basis of the reporter gene assay results viz loss-of-function, gain-of-function and functionally neutral. These findings, which were validated by EMSA, concurred with data from previous deletion studies and DNase I footprinting assays. Further, binding sites for two transcription factors, HNF1 and PTF1, were newly identified within the SPINK1 promoter by virtue of their being affected by specific variants. Combining the functional data with epidemiological data (derived by resequencing the SPINK1 promoter region in French, German and Indian CP patients and controls), then allowed us to make meaningful inferences as to each variant's likely contribution to CP. We conclude that only the three promoter variants associated with a loss-of-function (ie, −53C>T, −142T>C and −147A>G) are likely to be disease-predisposing alterations.

Hnf1alpha (MODY3) controls tissue-specific transcriptional programs and exerts opposed effects on cell growth in pancreatic islets and liver

Heterozygous HNF1A mutations cause pancreatic-islet beta-cell dysfunction and monogenic diabetes (MODY3). Hnf1alpha is known to regulate numerous hepatic genes, yet knowledge of its function in pancreatic islets is more limited. We now show that Hnf1a deficiency in mice leads to highly tissue-specific changes in the expression of genes involved in key functions of both islets and liver. To gain insights into the mechanisms of tissue-specific Hnf1alpha regulation, we integrated expression studies of Hnf1a-deficient mice with identification of direct Hnf1alpha targets. We demonstrate that Hnf1alpha can bind in a tissue-selective manner to genes that are expressed only in liver or islets. We also show that Hnf1alpha is essential only for the transcription of a minor fraction of its direct-target genes. Even among genes that were expressed in both liver and islets, the subset of targets showing functional dependence on Hnf1alpha was highly tissue specific. This was partly explained by the compensatory occupancy by the paralog Hnf1beta at selected genes in Hnf1a-deficient liver. In keeping with these findings, the biological consequences of Hnf1a deficiency were markedly different in islets and liver. Notably, Hnf1a deficiency led to impaired large-T-antigen-induced growth and oncogenesis in beta cells yet enhanced proliferation in hepatocytes. Collectively, these findings show that Hnf1alpha governs broad, highly tissue-specific genetic programs in pancreatic islets and liver and reveal key consequences of Hnf1a deficiency relevant to the pathophysiology of monogenic diabetes.

Expression of drug-metabolizing enzymes, nuclear transcription factors and ABC transporters in Caco-2 cells

1. Caco-2 cells are frequently used in intestinal drug absorption and metabolism studies, but little is known about the effects of drugs on the simultaneous expression of genes coding for drug-metabolizing enzymes (DMEs), nuclear transcription factors and ABC transporters. 2. The gene expression and enzyme activities of control and Aroclor 1254-treated cultures were therefore explored, the latter being a powerful inducer of DMEs. Fourteen- and 80-fold induction of CYP1A1 and CYP1A2 mRNA were shown, whereas expression of other DMEs was either increased (CYP2C8-2C19, 10-fold; CYP3A5, twofold; FMO1, 2 and 5, twofold; epoxide hydrolase, threefold) or repressed (CYP2D6 and CYP2E1 to 75% of control values). 3. Notably, gene copies of CYP3A4 and CYP2B6/7 were below the limit of detection, but a three- and 10-fold induction of HNF 1alpha + beta, HNF-4alpha4 and a similar 10-fold increase in STAT 3 and 4 was observed. 4. Similarly, c/EBP transcripts were only detected in treated cell cultures, but MRP1, its isoforms 3-5 as well as MDR-1 were increased threefold after dosing with Aroclor 1254. 5. Overall, CYP gene expression correlated well with the cognate enzyme activity using testosterone as a marker substrate.

Histone H3 modifications and Cdx-2 binding to the sucrase-isomaltase (SI) gene is involved in induction of the gene in the transition from the crypt to villus in the small intestine of rats

Expression of the sucrase-isomaltase (SI) gene is induced in cells transitioning from the crypt to the villus of rat jejunum. In the present study, we revealed by ChIP assay using a cryostat sectioning technique that binding of the di-acetylated histone H3 at lysine 9/14 and the transcriptional factor Cdx-2 to the promoter region on the SI gene, as well as mRNA, increased in the transient process. Additionally, di-/tri-methylation of histone H3 at lysine 9/14 on the promoter region of the SI gene rapidly decreased with increasing mRNA. These results suggest that induction of the SI gene during the transition from the crypt to the villi is associated with changes in histone H3 modifications from methylation at lysine 9 to di-acetylation at lysine 9/14, as well as increased binding of Cdx-2 to the SI promoter region.

Alternate mRNA processing of the hepatocyte nuclear factor genes and its role in monogenic diabetes

Variation in mRNA processing has the capacity to exert fine control over gene expression in most cell types. The hepatic nuclear factor genes, like approximately 74% of the genome, produce multiple transcripts. Hepatic nuclear factor isoforms exhibit both spatial and temporal variation in expression. In this review, the known isoforms of the hepatocyte nuclear factor-1α, hepatocyte nuclear factor-1β and hepatocyte nuclear factor-4α genes are described and their properties are compared. Finally, data are discussed regarding the influence of hepatocyte nuclear factor-1α alternate mRNA processing on the clinical phenotype of maturity-onset diabetes of the young.

Disaccharide digestion: clinical and molecular aspects

Sugars normally are absorbed in the small intestine. When carbohydrates are malabsorbed, the osmotic load produced by the high amount of low molecular weight sugars and partially digested starches in the small intestine can cause symptoms of intestinal distention, rapid peristalsis, and diarrhea. Colonic bacteria normally metabolize proximally malabsorbed dietary carbohydrate through fermentation to small fatty acids and gases (ie, hydrogen, methane, and carbon dioxide). When present in large amounts, the malabsorbed sugars and starches can be excreted in the stool. Sugar intolerance is the presence of abdominal symptoms related to the proximal or distal malabsorption of dietary carbohydrates. The symptoms consist of meal-related abdominal cramps and distention, increased flatulence, borborygmus, and diarrhea. Infants and young children with carbohydrate malabsorption show more intense symptoms than adults; the passage of undigested carbohydrates through the colon is more rapid and is associated with detectable carbohydrates in copious watery acid stools. Dehydration often follows feeding of the offending sugar. In this review we present the clinical and current molecular aspects of disaccharidase digestion.

E-cadherin-dependent Transcriptional Control of Apolipoprotein A-IV Gene Expression in Intestinal Epithelial Cells

Cell-matrix and cell-cell adhesion play a central role in the control of cell proliferation, differentiation, and gene expression. Integrins and E-cadherin are the key components involved in these processes in epithelial cells. We recently showed that integrin-dependent adhesion to the extracellular matrix reinforces the formation of E-cadherin-actin complexes inducing the polarization of Caco-2 enterocytes and increases the expression of a marker of enterocyte differentiation, the apolipoprotein A-IV (apoA-IV) gene. By impairing or enhancing E-cadherin-dependent cell adhesion, we demonstrate in the present study its involvement in the transcriptional activation of the apoA-IV gene in Caco-2 cells. This control requires the regulatory sequence that we have previously identified as necessary and sufficient to drive and restrict apoA-IV gene expression in enterocytes in vivo. Furthermore, using chimeric E-cadherin-Fc homophilic ligand-coated surfaces, we show that a direct activation of E-cadherin triggers the transcriptional activation of the apoA-IV promoter. Finally, E-cadherin-dependent cell-cell adhesion controls the nuclear abundance of the transcription factor hepatic nuclear factor 4alpha, which is involved in the enterocyte-specific expression of apoA-IV gene. Altogether, our results suggest that E-cadherin controls enterocyte-specific expression of genes, such as the apoA-IV gene, through the control of hepatic nuclear factor 4alpha nuclear abundance.

Intestinal glucose-dependent expression of glucose-6-phosphatase: involvement of the aryl receptor nuclear translocator transcription factor

Glucose-6-phosphatase (G6Pase) catalyzes the release of glucose from glucose 6-phosphate. This enzyme was mainly studied in the liver, but while detected in the small intestine little is known about the regulation of its intestinal expression. This study describes the mechanisms of the glucose-dependent regulation of G6Pase expression in intestinal cells. Results obtained in vivo and in Caco-2/TC7 enterocytes showed that glucose increases the G6Pase mRNA level. In Caco-2/TC7 cells, glucose stabilized G6Pase mRNA and activated the transcription of the gene, meaning that glucose-dependent G6Pase expression involved both transcriptional and post-transcriptional mechanisms. Reporter-gene studies showed that, although the -299/+57 region of the human G6Pase promoter was sufficient to trigger the glucose response in the hepatoma cell line HepG2, the -1157/-1133 fragment was required for maximal activation of glucose-6-phosphatase gene transcription in Caco-2/TC7 cells. This fragment binds the aryl receptor nuclear translocator (ARNT), cAMP-responsive element-binding protein, and upstream stimulatory factor transcription factors. The DNA binding activity of these transcription factors was increased in nuclear extracts of differentiated cells from the intestinal villus of mice fed sugar-rich diets as compared with mice fed a no-sugar diet. A direct implication of ARNT in the activation of G6Pase gene transcription by glucose has been observed in Caco-2/TC7 cells using RNA interference experiments. These results support a physiological role for G6Pase in the control of nutrient absorption in the small intestine.

HNF-4-dependent induction of apolipoprotein A-IV gene transcription by an apical supply of lipid micelles in intestinal cells

Apolipoprotein (apo) A-IV, a component of triglyceride-rich lipoproteins secreted by the small intestine, has been shown to play an important role in the control of lipid homeostasis. Numerous studies have described the induction of apoA-IV gene expression by lipids, but the molecular mechanisms involved in this process remain unknown. In this study, we have demonstrated that a lipid bolus induced transcription of the apoA-IV gene in transgenic mice and that the regulatory region of the apoA-IV gene, composed of the apoC-III enhancer and the apoA-IV promoter (eC3-A4), was responsible for this induction. In enterocyte Caco-2/TC7 cells, a permanent supply of lipids at the basal pole induced expression of the apoA-IV gene both at the transcriptional level and through mRNA stabilization. ApoA-IV gene transcription and protein secretion were further induced by an apical supply of complex lipid micelles mimicking the composition of duodenal micelles, and this effect was not reproduced by apical delivery of different combinations of micelle components. Only induction of the apoA-IV gene by lipid micelles involved the participation of hepatic nuclear factor (HNF)-4, as demonstrated using a dominant negative form of this transcription factor. Accordingly, lipid micelles increased the DNA binding activity of HNF-4 on the eC3-A4 region. These results emphasize the importance of physiological delivery of dietary lipids on apoA-IV gene expression and the implication of HNF-4 in this regulation.

Intestinal bile acid transport: biology, physiology, and pathophysiology

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

Activity of hepatocyte nuclear factor 1alpha and hepatocyte nuclear factor 1beta isoforms is differently affected by the inhibition of protein phosphatases 1/2A

Phosphorylation/dephosphorylation processes are known to control the activity of several transcription factors. The nutrition-dependent expression of sucrase-isomaltase and Na+/glucose co-transporter 1, two proteins implicated in the intestinal absorption of glucose, has been shown to be closely related to modifications of hepatocyte nuclear factor 1 (HNF1) activity. This study was conducted to determine whether phosphorylation/dephosphorylation processes could control HNF1 activity. We show that expression of the gene encoding sucrase-isomaltase is inhibited in the enterocytic Caco-2 clone TC7 by okadaic acid at a concentration that is known to inhibit protein phosphatases 1/2A and that does not affect cell viability. At the same concentration, phosphorylation of the HNF1alpha and HNF1beta isoforms is greatly enhanced and their DNA-binding capacity is decreased. The phosphorylation state of HNF1beta isoforms directly affects their DNA-binding capacity. In contrast, the decreased DNA-binding activity of the HNF1alpha isoforms, which was observed after the inhibition of protein phosphatases 1/2A, is due to a net decrease in their total cellular and nuclear amounts. Such an effect results from a decrease in both the HNF1alpha mRNA levels and the half-life of the protein. This is the first evidence for the implication of protein phosphatases 1/2A in the control of the activity of HNF1 isoforms. Moreover, these results emphasize a physiological role for the balance between phosphatases and kinases in the nutrition-dependent regulation of HNF1-controlled genes.

Regulation of the human Na(+)-glucose cotransporter gene, SGLT1, by HNF-1 and Sp1

The Na(+)-glucose cotransporter (SGLT1) is expressed primarily by small intestinal epithelial cells and transports the monosaccharides glucose and galactose across the apical membrane. Here we describe the isolation and characterization of 5.3 kb of the 5'-flanking region of the SGLT1 gene by transiently transfecting reporter constructs into a variety of epithelial cell lines. A fragment (nt -235 to +22) of the promoter showed strong activity in the intestinal cell line Caco-2 but was inactive in a nonintestinal epithelial cell line (Chinese hamster ovary). Within this region, three cis-elements, a hepatocyte nuclear factor-1 (HNF-1) and two GC box sites are critical for maintaining the gene's basal level of expression. The two GC boxes bind to several members of the Sp1 family of transcription factors and, in the presence of HNF-1, synergistically upregulate transactivation of the promoter. A novel 16-bp element just downstream of one GC box was also shown to influence the interaction of Sp1 to its binding site. In summary, we report the identification and characterization of the human SGLT1 minimal promoter and the critical role that HNF-1 and Sp1-multigene members have in enhancing the basal level of its transcription in Caco-2 cells.