GATA family transcription factors activate lactase gene promoter in intestinal Caco-2 cells

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

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

Aberrant expression of GATA binding protein 6 correlates with poor prognosis and promotes metastasis in cholangiocarcinoma

AIM

GATA6, a zinc-finger transcription factor, functions as a tumour promoter or suppresser according to different tumour origins. We investigated the clinical significance of GATA6 and its role in invasion and metastasis in cholangiocarcinoma (CCA).

METHODS

Expression of GATA6 in 87 cancerous, 24 paracancerous, 32 lymph-node metastatic and 8 liver metastatic samples from 87 CCA patients undergoing surgical resection was detected by immunohistochemistry. Impact of GATA6 on invasion, metastasis and 67kDa laminin receptor expression (67LR) was evaluated in CCA cells by shRNA lentivirus or expressed-plasmid transfection.

RESULTS

Aberrant expression of GATA6 in CCAs was significantly associated with lymph-node metastasis. GATA6 expression was higher in lymph-node and liver metastatic tissues compared with primary cancerous tissues. Kaplan-Meier analysis showed GATA6 expression correlated with poor overall survival and early recurrence in CCAs. Cox analysis suggested GATA6 was an independent prognostic marker for overall survival and recurrence-free survival. CCA cell invasion and migration were decreased by GATA6 knockdown and enhanced by GATA6 overexpression in vitro. Knockdown of GATA6 reduced CCA cell metastasis by xenotransplantation into nude mice. 67LR, which is overexpressed in CCAs and promotes invasion and metastasis through several pathways, positively correlated with GATA6 expression in 87 CCAs. Both mRNA and protein levels of 67LR were regulated by GATA6 in CCA cells. Moreover, ChIP analysis showed GATA6 bound to 67LR gene promoter in CCA cells.

CONCLUSION

Aberrant expression of GATA6 correlates with poor prognosis and promotes invasion and metastasis in CCA.

MYC-induced epigenetic activation of GATA4 in lung adenocarcinoma

Human lung cancer is a disease with high incidence and accounts for most cancer-related deaths in both men and women. Metastasis is a common event in non-small cell lung carcinoma (NSCLC), diminishing the survival chance of the patients with this type of tumor. It has been shown that MYC is involved in the development of metastasis from NSCLC, but the mechanism underlying this switch remained to be identified. Here, we focus on GATA4 as a MYC target in the development of metastasis with origin in lung adenocarcinoma, the most common type of NSCLC. Epigenetic alterations at the GATA4 promoter level were observed after MYC expression in lung adenocarcinoma in vivo and in vitro. Such alterations include site-specific demethylation that accompanies the displacement of the MYC-associated zinc finger protein (MAZ) from the GATA4 promoter, which leads to GATA4 expression. Histone modification analysis of the GATA4 promoter revealed a switch from repressive histone marks to active histone marks after MYC binding, which corresponds to active GATA4 expression. Our results thus identify a novel epigenetic mechanism by which MYC activates GATA4 leading to metastasis in lung adenocarcinoma, suggesting novel potential targets for the development of antimetastatic therapy.

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

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

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

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

Control of intestinal promoter activity of the cellular migratory regulator gene ELMO3 by CDX2 and SP1

An important aspect of the cellular differentiation in the intestine is the migration of epithelial cells from the crypt to the villus tip. As homeodomaine transcription factor CDX2 has been suggested to influence cell migration, we performed a genome-wide promoter analysis for CDX2 binding in the differentiated human intestinal cancer cell line Caco-2 in order to identify CDX2-regulated genes involved in cellular migration. The engulfment and cell motility 3 (ELMO3) gene was identified as a potential CDX2 target gene. ELMO3 is an essential upstream regulator of the GTP-binding protein RAC during cell migration. However, no information is available about the transcriptional regulation of the ELMO3 gene. The aim of this study was to investigate the potential role of CDX2 in the regulation of the ELMO3 promoter activity. Electrophoretic mobility shift assays showed that CDX2 bound to conserved CDX2 sequences and mutations of the CDX2-binding sites, significantly reduced the promoter activity. Reporter gene assays demonstrated that the region mediating ELMO3 basal transcriptional activity to be located between -270 and -31 bp. Sequence analysis revealed no typical TATA-box, but four GC-rich sequences. In vitro analyses (electrophoretic mobility shift assays and promoter analyses) demonstrate that the SP1-binding sites are likely to play an important role in regulating the ELMO3 promoter activity. Furthermore, we showed here that CDX2 and SP1 can activate the ELMO3 promoter. Taken together, the present study reports the first characterization of the ELMO3 promoter and suggests a significant role of CDX2 in the basal transcriptional regulation of the intestine-specific expression of ELMO3, possibly through interaction with SP1.

Evolutionary conservation of glucose-dependent insulinotropic polypeptide (GIP) gene regulation and the enteroinsular axis

Glucose-dependent insulinotropic polypeptide (GIP), an important component of the enteroinsular axis, is a potent stimulator of insulin secretion, functioning to maintain nutrient efficiency. Although well-characterized in mammals, little is known regarding GIP transcriptional regulation in Danio rerio (Dr). We previously demonstrated that DrGIP is expressed in the intestine and the pancreas, and we therefore cloned the Dr promoter to compare GIP transcriptional regulation in Dr and mammals. Although no significant homology was indentified between the highly conserved mammalian promoter and the DrGIP promoter, 1072-bp of the DrGIP promoter conferred tissue-specific expression in mammalian cell lines. Deletional analysis of the DrGIP promoter identified two regions that, when deleted, reduced transcription by 75% and 95%, respectively. Mutational analysis of the upstream region suggested involvement of an Nkx binding site, although we were unable to identify the factor binding to this site. The cis element in the downstream region was found to be a GATA binding site. Lastly, overexpression and shRNA experiments identified PAX4 as a potential repressor of DrGIP expression. These findings provide evidence that despite the identification of species-specific transcriptional regulators and differences in GIP expression patterns between D. rerio and mammals, a moderate degree of regulatory conservation appears to exist.

Enhanced expression of transcription factor GATA-4 in inflammatory bowel disease and its possible regulation by TGF-beta1

BACKGROUND

Transforming growth factor beta 1 (TGF-beta1) promotes epithelial healing in inflammatory bowel disease. We hypothesized that GATA-4, a transcription factor cooperating with TGF-beta signaling pathway, is upregulated by TGF-beta1 in the inflamed intestinal epithelium.

METHODS

Normal and inflamed intestinal samples were subjected to immunohistochemistry for GATA-4/6 and the TGF-beta signaling pathway components Smad2/3/4. Proliferation and apoptosis were analyzed using Ki-67 and in situ DNA 3'-end labeling assays and Bax and Bcl-2 immunohistochemistry. Furthermore, GATA-4 was assessed in intestinal Caco-2 cells stimulated with TGF-beta1, or interleukin-6 and tumor necrosis factor alpha.

RESULTS

GATA-4 was detected in only 20% of normal intestinal samples, but was upregulated in corresponding inflamed regions. GATA-6 expression remained unchanged during inflammation. TGF-beta1 and Smad3/4, but not Smad2, were expressed concomitantly with GATA-4 in inflamed bowel mucosa. In intestinal Caco-2 cells, TGF-beta1 upregulated GATA-4 and Smad2/3/4, whereas treatment with control cytokines had no effect. Inflammation was associated with increased epithelial cell apoptosis and the enhancement of Bcl-2, but not Bax.

CONCLUSIONS

We surmise GATA-4 expression is upregulated in inflamed intestine correlating with the activation of TGF-beta signaling pathway. We speculate that TGF-beta1 drives GATA-4 expression during intestinal inflammation, these two components cooperating to promote epithelial healing.

Lactose digestion and the evolutionary genetics of lactase persistence

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

GATA4 is essential for jejunal function in mice

BACKGROUND & AIMS

Although the zinc-finger transcription factor GATA4 has been implicated in regulating jejunal gene expression, the contribution of GATA4 in controlling jejunal physiology has not been addressed.

METHODS

We generated mice in which the Gata4 gene was specifically deleted in the small intestinal epithelium. Measurements of plasma cholesterol and phospholipids, intestinal absorption of dietary fat and cholesterol, and gene expression were performed on these animals.

RESULTS

Mice lacking GATA4 in the intestine displayed a dramatic block in their ability to absorb cholesterol and dietary fat. Comparison of the global gene expression profiles of control jejunum, control ileum, and GATA4 null jejunum by gene array analysis revealed that GATA4 null jejunum lost expression of 53% of the jejunal-specific gene set and gained expression of 47% of the set of genes unique to the ileum. These alterations in gene expression included a decrease in messenger RNAs (mRNAs) encoding lipid and cholesterol transporters as well as an increase in mRNAs encoding proteins involved in bile acid absorption.

CONCLUSIONS

Our data demonstrate that GATA4 is essential for jejunal function including fat and cholesterol absorption and confirm that GATA4 plays a pivotal role in determining jejunal vs ileal identity.

GATA-4 upregulates glucose-dependent insulinotropic polypeptide expression in cells of pancreatic and intestinal lineage

A thorough examination of glucose-dependent insulinotropic polypeptide (GIP) expression has been hampered by difficulty in isolating widely dispersed, GIP-producing enteroendocrine K-cells. To elucidate the molecular mechanisms governing the regulation of GIP expression, 14 intestinal and pancreatic cell lines were assessed for their suitability for studies examining GIP expression. Both STC-1 cells and the pancreatic cell line betaTC-3 were found to express GIP mRNA and secrete biologically active GIP. However, levels of GIP mRNA and bioactive peptide and the activity of transfected GIP reporter constructs were significantly lower in betaTC-3 than STC-1 cells. When betaTC-3 cells were analyzed for transcription factors known to be important for GIP expression, PDX-1 and ISL-1, but not GATA-4, were detected. Double staining for GIP-1 and GATA-4 in mouse duodenum demonstrated GATA-4 expression in intestinal K-cells. Exogenous expression of GATA-4 in betaTC-3 cells led to marked increases in both GIP transcription and secretion. Lastly suppression of GATA-4 via RNA interference, in GTC-1 cells, a subpopulation of STC-1 cells with high endogenous GIP expression resulted in a marked an attenuation of GIP promoter activity. Our data support the hypothesis that GATA-4 may function to augment or enhance GIP expression rather than act as an initiator of GIP transcription.

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

BACKGROUND

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

METHODS

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

RESULTS

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

CONCLUSIONS

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

Oncogenic Ras upregulates NADPH oxidase 1 gene expression through MEK-ERK-dependent phosphorylation of GATA-6

Ras oncogene upregulates the expression of nicotinamide adenine dinucleotide phosphate oxidase (Nox) 1 via the Raf/MEK/ERK pathway, leading to the elevated production of reactive oxygen species that is essential for maintenance of Ras-transformation phenotypes. However, the precise transcriptional control mechanism underlying Ras-induced Nox1 expression remains to be elucidated. Here we demonstrated that via the MEK/ERK pathway, Ras signaling enhances the activity of the functional Nox1 promoter (nt -321 to -1) in colon cancer CaCo-2 cells and thereby induces the formation of the specific protein-DNA complexes in the two GATA-binding site-containing regions (nt -161 to -136 and -125 to -100). Supershift assays with GATA antibodies, protein analyses and chromatin immunoprecipitation revealed that GATA-6 is a component of the specific protein-DNA complexes at the Nox1 promoter. GATA-6 was able to trans-activate the Nox1 promoter but not a promoter in which the GATA-binding sites are mutated. Moreover, GATA-6 was phosphorylated at serine residues by MEK-activated ERK, which increased GATA-6 DNA binding, correlating with suppression of the Nox1 promoter activity by an MEK inhibitor PD98059. Finally, the site-directed mutation of the consensus ERK phosphorylation site (PYS(120)P to PYA(120)P) of GATA-6 abolished its trans-activation activity, suppressing of the growth of CaCo-2 cells. On the basis of these results, we propose that oncogenic Ras signaling upregulates the transcription of Nox1 through MEK-ERK-dependent phosphorylation of GATA-6.

Transcription factors GATA-4 and GATA-6 in normal and neoplastic human gastrointestinal mucosa

BACKGROUND

Human gastrointestinal mucosa regenerates vigorously throughout life, but the factors controlling cell fate in mature mucosa are poorly understood. GATA transcription factors direct cell proliferation and differentiation in many organs, and are implicated in tumorigenesis. GATA-4 and GATA-6 are considered crucial for the formation of murine gastrointestinal mucosa, but their role in human gastrointestinal tract remains unexplored. We studied in detail the expression patterns of these two GATA factors and a GATA-6 down-stream target, Indian hedgehog (Ihh), in normal human gastrointestinal mucosa. Since these factors are considered important for proliferation and differentiation, we also explored the possible alterations in their expression in gastrointestinal neoplasias. The expression of the carcinogenesis-related protein Indian hedgehog was also investigated in comparison to GATA factors.

METHODS

Samples of normal and neoplastic gastrointestinal tract from children and adults were subjected to RNA in situ hybridization with 33P labelled probes and immunohistochemistry, using an avidin-biotin immunoperoxidase system. The pathological tissues examined included samples of chronic and atrophic gastritis as well as adenomas and adenocarcinomas of the colon and rectum.

RESULTS

GATA-4 was abundant in the differentiated epithelial cells of the proximal parts of the gastrointestinal tract but was absent from the distal parts. In contrast, GATA-6 was expressed throughout the gastrointestinal epithelium, and in the distal gut its expression was most intense at the bottom of the crypts, i.e. cells with proliferative capacity. Both factors were also present in Barrett's esophagus and metaplasia of the stomach. GATA-6 expression was reduced in colon carcinoma. Ihh expression overlapped with that of GATA-6 especially in benign gastrointestinal neoplasias.

CONCLUSION

The results suggest differential but overlapping functions for GATA-4 and GATA-6 in the normal gastrointestinal mucosa. Furthermore, GATA-4, GATA-6 and Ihh expression is altered in premalignant dysplastic lesions and reduced in overt cancer.

Using genomics to understand intestinal biology

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

Promoter and 3'-untranslated-region haplotypes in the vitamin d receptor gene predispose to osteoporotic fracture: the rotterdam study

Polymorphisms of the vitamin D receptor gene (VDR) have been shown to be associated with several complex diseases, including osteoporosis, but the mechanisms are unknown and study results have been inconsistent. We therefore determined sequence variation across the major relevant parts of VDR, including construction of linkage disequilibrium blocks and identification of haplotype alleles. We analyzed 15 haplotype-tagging SNPs in relation to 937 clinical fractures recorded in 6,148 elderly whites over a follow-up period of 7.4 years. Haplotype alleles of the 5' 1a/1e, 1b promoter region and of the 3' untranslated region (UTR) were strongly associated with increased fracture risk. For the 16% of subjects who had risk genotypes at both regions, their risk increased 48% for clinical fractures (P = .0002), independent of age, sex, height, weight, and bone mineral density. The population-attributable risk varied between 1% and 12% for each block and was 4% for the combined VDR risk genotypes. Functional analysis of the variants demonstrated 53% lower expression of a reporter construct with the 1e/1a promoter risk haplotype (P = 5 x 10(-7)) in two cell lines and 15% lower mRNA level of VDR expression constructs carrying 3'-UTR risk haplotype 1 in five cell lines (P = 2 x 10(-6)). In a further analysis, we showed 30% increased mRNA decay in an osteoblast cell line for the construct carrying the 3'-UTR risk haplotype (P = .02). This comprehensive candidate-gene analysis demonstrates that the risk allele of multiple VDR polymorphisms results in lower VDR mRNA levels. This could impact the vitamin D signaling efficiency and might contribute to the increased fracture risk we observed for these risk haplotype alleles.

The effect of cytostatic drug treatment on intestine-specific transcription factors Cdx2, GATA-4 and HNF-1α in mice

Chemotherapy-induced intestinal damage is a very important dose-limiting side effect for which there is no definitive prophylaxis or treatment. This is in part due to the lack of understanding of its pathophysiology and impact on intestinal differentiation. The objective of this study was to investigate the gene expression of the small intestinal transcription factors HNF-1alpha, Cdx2, GATA-4 in an experimental model of methotrexate (MTX)-induced intestinal damage, and to correlate these alterations with histological damage, epithelial proliferation and differentiation. HNF-1alpha, Cdx2 and GATA-4 are critical transcription factors in epithelial differentiation, and in combination they act as promoting factors of the sucrase-isomaltase (SI) gene, an enterocyte-specific differentiation marker which is distinctly downregulated after MTX treatment. Mice received two doses of MTX i.v. on two consecutive days and were sacrificed 1, 3 and 7 or 9 days after final injection. Segments of the jejunum were taken for morphological, immunohistochemical and quantitative analyses. Intestinal damage was most severe at day 3 and was associated with decreased expression of the transcriptional factors HNF-1alpha, Cdx2 and GATA-4, which correlated well with decreased expression of SI, and seemed inversely correlated with enhanced proliferation of epithelial crypt cells. During severe damage, the epithelium was preferentially concerned with proliferation rather than differentiation, most likely in order to restore the small intestinal barrier function rather than maintaining its absorptive function. Since HNF-1alpha, Cdx2 and GATA-4 are critical for intestine-specific gene expression and therefore crucial in epithelial differentiation, these results may explain, at least in part, why intestinal differentiation is compromised during MTX treatment.

Molecular genetics of adult-type hypolactasia

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

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

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

Genetic variation and lactose intolerance: detection methods and clinical implications

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

Control of differentiation-induced calbindin-D9k gene expression in Caco-2 cells by cdx-2 and HNF-1alpha

Calbindin D9k (CaBP) is critical for intestinal calcium absorption; its in vivo expression is restricted to differentiated enterocytes of the small intestine. Our goal was to identify factors controlling the transcriptional regulation of this gene in the human intestine. Both the natural gene and a 4600-bp promoter construct were strongly regulated by differentiation (>100-fold) but not by treatment with 1,25(OH)2 vitamin D (<2-fold) in the Caco-2 clone TC7. Deletion-mutation studies revealed that conserved promoter sequences for cdx-2 (at -3158 bp) and hepatocyte nuclear factor (HNF)-1 (at -3131 and at -98 bp) combined to control CaBP expression during differentiation. Other putative response elements were not important for CaBP regulation in TC7 cells (CCAAT enhancer binding protein, pancreatic duodenal homebox-1 (pdx-1), a proximal cdx-2 element). Mutation of the distal HNF-1 site had the greatest impact on CaBP gene expression through disruption of HNF-1alpha binding; both basal and differentiation-mediated CaBP expression was reduced by 80%. In contrast, mutation of the distal cdx-2 element reduced only basal CaBP expression. Whereas a 60% reduction of CaBP mRNA in the duodenum of HNF-1alpha null mice confirmed the physiological importance of HNF-1alpha for CaBP gene regulation, additional studies showed that maximal CaBP expression requires the presence of both HNF-1alpha and cdx-2. Our data suggest that cdx-2 is a permissive factor that influences basal CaBP expression in enterocytes and that HNF-1alpha modulates CaBP gene expression during cellular differentiation.

GATA-4, GATA-5, and GATA-6 activate the rat liver fatty acid binding protein gene in concert with HNF-1alpha

Transcriptional regulation by GATA-4, GATA-5, and GATA-6 in intestine and liver was explored using a transgene constructed from the proximal promoter of the rat liver fatty acid binding protein gene (Fabpl). An immunohistochemical survey detected GATA-4 and GATA-6 in enterocytes, GATA-6 in hepatocytes, and GATA-5 in neither cell type in adult animals. In cell transfection assays, GATA-4 or GATA-5 but not GATA-6 activated the Fabpl transgene solely through the most proximal of three GATA binding sites in the Fabpl promoter. However, all three factors activated transgenes constructed from each Fabpl site upstream of a minimal viral promoter. GATA factors interact with hepatic nuclear factor (HNF)-1alpha, and the proximal Fabpl GATA site adjoins an HNF-1 site. GATA-4, GATA-5, or GATA-6 bounded to HNF-1alpha in solution, and all cooperated with HNF-1alpha to activate the Fabpl transgene. Mutagenizing all Fabpl GATA sites abrogated transgene activation by GATA factors, but GATA-4 activated the mutagenized transgene in the presence of HNF-1alpha. These in vitro results suggested GATA/HNF-1alpha interactions function in Fabpl regulation, and in vivo relevance was determined with subsequent experiments. In mice, the Fabpl transgene was active in enterocytes and hepatocytes, a transgene with mutagenized HNF-1 site was silent, and a transgene with mutagenized GATA sites had identical expression as the native transgene. Mice mosaic for biallelic Gata4 inactivation lost intestinal but not hepatic Fabpl expression in Gata4-deficient cells but not wild-type cells. These results demonstrate GATA-4 is critical for intestinal gene expression in vivo and suggest a specific GATA-4/HNF-1alpha physical and functional interaction in Fabpl activation.

Complex regulation of the lactase-phlorizin hydrolase promoter by GATA-4

Lactase-phlorizin hydrolase (LPH), a marker of intestinal differentiation, is expressed in absorptive enterocytes on small intestinal villi in a tightly regulated pattern along the proximal-distal axis. The LPH promoter contains binding sites that mediate activation by members of the GATA-4, -5, and -6 subfamily, but little is known about their individual contribution to LPH regulation in vivo. Here, we show that GATA-4 is the principal GATA factor from adult mouse intestinal epithelial cells that binds to the mouse LPH promoter, and its expression is highly correlated with that of LPH mRNA in jejunum and ileum. GATA-4 cooperates with hepatocyte nuclear factor (HNF)-1alpha to synergistically activate the LPH promoter by a mechanism identical to that previously characterized for GATA-5/HNF-1alpha, requiring physical association between GATA-4 and HNF-1alpha and intact HNF-1 binding sites on the LPH promoter. GATA-4 also activates the LPH promoter independently of HNF-1alpha, in contrast to GATA-5, which is unable to activate the LPH promoter in the absence of HNF-1alpha. GATA-4-specific activation requires intact GATA binding sites on the LPH promoter and was mapped by domain-swapping experiments to the zinc finger and basic regions. However, the difference in the capacity between GATA-4 and GATA-5 to activate the LPH promoter was not due to a difference in affinity for binding to GATA binding sites on the LPH promoter. These data indicate that GATA-4 is a key regulator of LPH gene expression that may function through an evolutionarily conserved mechanism involving cooperativity with an HNF-1alpha and/or a GATA-specific pathway independent of HNF-1alpha.

Transcriptional regulation of the lactase-phlorizin hydrolase promoter by PDX-1

Lactase-phlorizin hydrolase gene expression is spatially restricted along the anterior-posterior gut axis. Lactase gene transcription is maximal in the distal duodenum and jejunum in adult mammals and is barely detectable in the proximal duodenum. By contrast, pancreatic duodenal homeobox-1 (PDX-1) protein is expressed maximally in the proximal duodenum. This study aimed to determine the role of PDX-1 in regulating lactase gene promoter activity in intestinal epithelial cells. Caco-2 cells were cotransfected with lactase promoter-reporter constructs in the presence of a PDX-1 expression vector and assayed for luciferase activity. PDX-1 cotransfection results in repression of lactase promoter activity. Sequence analysis of the lactase promoter revealed a putative PDX-1 DNA binding site in the proximal 100-bp lactase gene promoter. EMSAs demonstrated that PDX-1 can interact with the lactase promoter binding site but not with a site in which the core PDX-1 binding sequence TAAT is mutated. Site-directed mutagenesis of the PDX-1 core binding site in the lactase promoter-reporter construct suggests that PDX-1 can function independently of DNA binding to its consensus binding site. Stable overexpression of PDX-1 results in repression of the endogenous human lactase gene in differentiated Caco-2 cells. Given the contrasting spatial expression pattern, PDX-1 may function to specify the anterior boundary of lactase expression in the small intestine and is thus a candidate regulator of anterior spatial restriction in the gut.

Rapid induction of GATA transcription factors in developing mouse intestine following glucocorticoid administration

In the developing intestine, transcription of alpha-glucosidase genes such as sucrase-isomaltase and trehalase is stimulated by glucocorticoid administration. The consequent increase of their respective mRNAs is characterized by a 12-h lag, suggesting that the response to glucocorticoids represents a secondary effect. We hypothesized that the primary response of the tissue to glucocorticoids includes induction of one or more intestinal transcription factors. To investigate this hypothesis, we identified a region in the mouse trehalase promoter (located at nucleotides -406 to -377 from the transcription start site) with potential binding sites for three transcription factors: Cdx-2, GATA, and C/EBP. Gel shifts were performed using labeled oligonucleotides from this region with nuclear extracts from jejunums of either control 8-day-old mouse pups or littermates treated with dexamethasone (DEX) 4 h before death. A specific shifted band was observed with DEX extracts but not with control extracts. Supershift assays indicated the presence of GATA-4 and GATA-6 but not GATA-5 nor Cdx-2, C/EBP alpha, C/EBP beta, or C/EBP delta. GATA binding was further implicated by competition studies with mutated oligonucleotides. Finally, Western blot analysis showed GATA-4 and GATA-6 proteins in DEX but not control nuclear extracts. For GATA-4, the same pattern was demonstrated with whole cell extracts and with the cytosol fraction. We conclude that expression of GATA-4 and GATA-6 proteins in the suckling mouse jejunum is stimulated by DEX. This novel finding constitutes an important first step in understanding the molecular mechanism of glucocorticoid action on the developing intestine.

Genetics of lactase persistence and lactose intolerance

The enzyme lactase that is located in the villus enterocytes of the small intestine is responsible for digestion of lactose in milk. Lactase activity is high and vital during infancy, but in most mammals, including most humans, lactase activity declines after the weaning phase. In other healthy humans, lactase activity persists at a high level throughout adult life, enabling them to digest lactose as adults. This dominantly inherited genetic trait is known as lactase persistence. The distribution of these different lactase phenotypes in human populations is highly variable and is controlled by a polymorphic element cis-acting to the lactase gene. A putative causal nucleotide change has been identified and occurs on the background of a very extended haplotype that is frequent in Northern Europeans, where lactase persistence is frequent. This single nucleotide polymorphism is located 14 kb upstream from the start of transcription of lactase in an intron of the adjacent gene MCM6. This change does not, however, explain all the variation in lactase expression.

Cdx1 inhibits the proliferation of human colon cancer cells by reducing cyclin D1 gene expression

The transcription factor Cdx1 regulates intestine-specific gene expression and enterocyte differentiation. It has been hypothesized to play a role in regulating intestinal cell proliferation; however, the mechanism for this effect remains elusive. In a prior study, we demonstrated that Cdx1 expression reduced the proliferation of a nontransformed intestinal cell line. This study tests the hypothesis that Cdx1 expression inhibits colon cancer cell proliferation by reducing cyclin D1 gene expression. Cdx1 expression markedly reduced cancer cell proliferation and DNA synthesis and induced an accumulation of cells in G0/G1. A transcriptionally inactive Cdx1 mutant could not elicit this effect, suggesting that it required Cdx1 transcriptional activity. Cdx1 expression increased the hypophosphorylation of the retinoblastoma (pRb) and p130 proteins. Reductions in G1 cyclin-dependant kinase (cdk) activity accompanied this effect. Cyclin D1 mRNA and protein levels were diminished by Cdx1 expression. Restoration of cyclin D1 expression reversed the G0/G1 block and induced pRb hyperphosphorylation. Lastly, Cdx1 expression did not alter cyclin D1 mRNA stability but did reduce cyclin D1 promoter activity, suggesting that Cdx1 acts to diminish cyclin D1 gene transcription. We conclude that Cdx1 reduces the proliferation of human colon cancer cells by reducing cyclin D1 gene transcription.

High-level activation by a duodenum-specific enhancer requires functional GATA binding sites

The purine metabolic gene adenosine deaminase (ADA) is expressed at high levels in a well-defined spatiotemporal pattern in the villous epithelium of proximal small intestine. A duodenum-specific enhancer module responsible for this expression pattern has been identified in the second intron of the human ADA gene. It has previously been shown that binding of the factor PDX-1 is essential for function of this enhancer. The studies presented here examine the proposed roles of GATA factors in the enhancer. Site-directed mutagenesis of the enhancer's GATA binding sites crippled enhancer function in 10 lines of transgenic mice, with 9 of the lines demonstrating <1% of normal activity. Detailed studies along the longitudinal axis of mouse small intestine indicate that GATA-4 and GATA-5 mRNA levels display a reciprocal pattern, with low levels of GATA-6 throughout. Interestingly, gel shift studies with duodenal nuclear extracts showed binding only by GATA-4.

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

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

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

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