Members of the caudal family of homeodomain proteins repress transcription from the human apolipoprotein B promoter in intestinal cells

Transcriptomics analysis of Daheng broilers reveals that PLIN2 regulates chicken preadipocyte proliferation, differentiation and apoptosis

BACKGROUND

Intramuscular fat content, an important meat quality trait, strongly affects flavor, juiciness, and tenderness. Sex hormones regulate lipid metabolism, and female hormones stimulate fat deposition, thereby making the female chickens always fatter than males. In this study, the effect of sex on IMF deposition was screened following transcriptomics in chickens.

METHODS AND RESULTS

Results confirmed significantly higher IMF content of 150-day female chickens as compared to the male chickens. The female chickens manifested higher serum TG, LDL-C, and VLDL, and significantly lower HDL-C contents than male chickens. Moreover, differential expression of genes involved in lipid metabolism were obtained in the muscle and liver between female and male chicken, which could partly interpret the possible reasons for the sex-mediated differences of IMF content. Cellular results revealed that inhibition of PLIN2 significantly inhibited chicken preadipocyte proliferation and induces apoptosis of preadipocytes, as well as promoted adipocyte differentiation.

CONCLUSIONS

According to our results, PLIN2 may be considered as a molecular marker for poultry meat quality and applying this gene in early breed selection.

Overexpression of caudal-related homeobox transcription factor 2 inhibits the growth of transplanted colorectal tumors in nude mice

Caudal-related homeobox transcription factor 2 (CDX2) is a transcription factor, which is specifically expressed in the adult intestine. It is essential for the development and homeostasis of the intestinal epithelium and its functions as a tumor suppressor have been demonstrated in the adult colon. The present study aimed to examine the inhibitory effects of the overexpression of CDX2 on subcutaneously-transplanted tumors, derived from LoVo colon cancer cells, in nude mice, and to provide experimental evidence for the biotherapy of colon cancer. A pEGFP-C1-CDX2 eukaryotic expression vector was transfected into the LoVo cells via lipofection, and LoVo cells stably-expressing CDX2 (pEGFP-C1-CDX2 cells) were obtained using G418 selection. A nude mouse subcutaneously-transplanted tumor model was established by inoculating the nude mice with the pEGFP-C1-CDX2 cells, and the effects of overexpression of CDX2 on transplanted tumor growth in the LoVo cells were observed. Western blotting results demonstrated that the protein expression of CDX2 in the LoVo cells was higher in the pEGFP-C1-CDX2 cell group, compared with that in the pEGFP-C1 cell group and the untreated cell group. At 20 days post-inoculation with either pEGFP-C1-CDX2 or pEGFP-C1, the transplanted tumor masses were significantly lower in the pEGFP-C1-CDX2 group, compared with those in the pEGFP-C1 and untreated groups. Immunohistochemistry revealed that the expression levels of CDX2 and matrix metalloproteinase-2 (MMP-2) were detected in each group, and the protein expression of CDX2 was increased in the tumor tissues from the nude mice in the pEGFP-C1-CDX2 group. However the expression of MMP-2 was downregulated in the tumor tissues of the nude mice in the pEGFP-C1-CDX2 group. Taken together, these data suggested that pEGFP-C1-CDX2 cells exhibited suppressed tumor growth in vivo. Overexpression of CDX2 was observed in transplanted tumors in the pEGFP-C1-CDX2 group, and the gene expression of MMP-2 was reduced. These results indicate that CDX2 inhibited the growth of colorectal tumor cells, possibly by downregulating the gene expression.

Biology of intestinal metaplasia in 2008: more than a simple phenotypic alteration

This review concentrates on one main aspect of cancerization in the oesophagus and stomach: principally, intestinal metaplasia. There are at least two other important pathways that lead to cancer and do not need such a morphological transformation. One is the gastric type of carcinoma on the Lauren classification, which arises directly from the stem cell zone and is the signet ring form of cancer, while the other is spasmolytic polypeptide-expressing metaplasia (SPEM)--spasmolytic polypeptide (TFF2) expressing metaplasia, where the gastric glands become filled with TFF2-expressing cells and may also lead to gastric dysplasia and cancer. The development of intestinal metaplasia is complex. Here, we examine intestinal metaplasia in molecular terms, noting the over-expression of Cdx1, Cdx2, Pdx1, Oct1, TFF3 and the downregulation of Hedgehog signalling; Runx3 is deactivated by epigenetic silencing, and pathways such as Wnt and MARK/ERK are involved. These changes start to explain the principles of the development of intestinal metaplasia and suggest that the regulation of these genes is of importance in the development of gastric cancer.

Regulation of TFF3 expression by homeodomain protein CDX2

Although trefoil factor family 3 (TFF3) plays an important role in protecting the intestinal mucosa, the regulatory mechanisms of its expression are not fully understood. Since homeodomain protein CDX2 has been reported to be critically involved in the development and differentiation of intestinal epithelium, we examined whether CDX2 affects the expression of TFF3. The transcription of human TFF3 reporter genes was significantly up-regulated by the transient overexpression of CDX2 in COS-7 cells and AGS gastric cells. Electrophoretic mobility shift assay revealed the presence of at least two CDX-binding sites within the human TFF3 promoter. Deletion analysis showed the relative importance of the proximal CDX-binding site at -63. We also detected the up-regulation of endogenous TFF3 mRNA expression in AGS cells stably transfected with CDX2 expression vectors. These results suggest that CDX2 plays a key role in the expression of TFF3 in the intestine and perhaps in intestinal metaplasia of the stomach.

Increased CDX2 and decreased PITX1 homeobox gene expression in Barrett's esophagus and Barrett's-associated adenocarcinoma

BACKGROUND

The CDX2 (caudal-related homeobox gene 2) and PITX1 (pituitary homeobox 1) genes have essential roles in human development. Forced expression of Cdx2 alone in the murine stomach results in gastric intestinal metaplasia (IM). This study was undertaken to investigate the expression pattern of these critical morphogenesis genes in the Barrett's multistage carcinogenesis model.

METHODS

CDX2 and PITX1 messenger RNA (mRNA) expression levels, relative to the control gene beta-actin, were measured by reverse transcription-polymerase chain reaction in specimens of Barrett's IM (n = 21), dysplasia (n = 18), adenocarcinoma (n = 20), and matching normal squamous esophagus tissues (n = 39) collected from 19 patients with Barrett's esophagus and 20 patients with esophageal adenocarcinoma. CDX2 protein expression was assessed by immunohistochemistry in specimens of normal squamous esophagus (n = 13), IM (n = 10), dysplasia (n = 8,) and adenocarcinoma (n = 5).

RESULTS

The median relative CDX2 mRNA expression was approximately 200 times higher in Barrett's esophagus tissues (0.83) than in matching normal squamous esophagus (0.004) in the patients with Barrett's esophagus (P < .001). The mRNA expression in cancer tissues (0.49) was also higher than in matching normal squamous esophagus specimens (0.009, P < .001). There was no significant difference between the mRNA expression levels in Barrett's esophagus and adenocarcinoma. There was no CDX2 protein expression in normal squamous esophagus, but moderate to strong protein expression was seen in all Barrett's tissues and in a majority of the dysplasia and adenocarcinoma cells. Relative median PITX1 mRNA expression was decreased in Barrett's esophagus (8.02 for all specimens), compared with normal esophagus specimens (47.46 for all specimens, P < .001), and was further reduced in cancer specimens (2.21), compared with either Barrett's esophagus or normal esophagus (both P < .001). Wilcoxon testwas used for all P values shown.

CONCLUSIONS

CDX2 mRNA and CDX2 protein expression are upregulated in Barrett's IM tissues, compared with normal squamous esophagus, and remain elevated in dysplasia and adenocarcinoma tissues. In contrast, PITX1 mRNA expression is decreased in Barrett's esophagus, compared with matching normal squamous esophagus specimens, and is further decreased in Barrett's-associated cancer. These descriptive findings suggest a possible role for these genes in the Barrett's metaplasia-dysplasia-adenocarcinoma sequence.

C/EBP and Cdx family factors regulate liver fatty acid binding protein transgene expression in the small intestinal epithelium

A transgene constructed from the rat liver fatty acid binding protein gene (Fabp1) promoter is active in all murine small intestinal crypt and villus epithelial cells. Coincident Cdx and C/EBP transcription factor binding sites were identified spanning Fabp1 nucleotides -90 to -78. CDX-1, CDX-2, C/EBPalpha, and C/EBPbeta activated the Fabp1 transgene in CaCo-2 cells, and mutagenizing the -78 site prevented activation by these factors. CDX but not C/EBP factors bound to the site in vitro, although C/EBP factors competed with CDX factors for transgene activation. The -78 site adjoins an HNF-1 site, and CDX and C/EBP family factors cooperated with HNF-1alpha but not HNF-1beta to activate the transgene. Furthermore, CDX-1, CDX-2, C/EBPalpha, and C/EBPbeta bound to HNF-1alpha and HNF-1beta. The transgene with a mutagenized -78 site was silenced in vivo specifically in small intestinal crypt epithelial cells but remained active in villus cells. These results demonstrate functional interactions between HNF-1, C/EBP, and CDX family factors and suggest that these interactions may contribute to differential transcriptional regulation in the small intestinal crypt and villus compartments.

Cdx binding determines the timing of enhancer activation in postnatal duodenum

In mammalian intestine, adenosine deaminase (ADA) is expressed at high levels only along the villi of the duodenal epithelium. A duodenum-specific enhancer identified in the second intron of the human ADA gene controls this pattern of expression. This enhancer faithfully recapitulates this expression pattern in transgenic mice, when included in CAT reporter gene constructions. Multiple binding sites for PDX-1 and GATA factors were previously identified within the approximately 300-bp region that encompasses the enhancer. Mutation analyses demonstrated that binding of PDX-1 and of GATA-4 was absolutely essential for enhancer function. In the present study, we have identified additional enhancer binding sites for Cdx factors, for YY1, and for NFI family members. Detailed EMSA studies were used to confirm binding at these sites. This brings the number of confirmed binding sites within the enhancer to thirteen, with five different factors or family of factors contributing to the putative enhanceosome complex. Mutation analysis was utilized to examine the specific roles of the newly identified sites. Two sites were identified that bound both Cdx1 and Cdx2. Mutations were identified in these two sites that completely and specifically eliminated Cdx binding. In transgenic mice, these enhancer mutations dramatically changed the developmental timing of enhancer activation (delaying it by 2-3 weeks) without affecting other aspects of enhancer function. In the chromatin context of certain transgenic insertion sites, mutation of the two YY1 sites to specifically ablate binding caused a delay in enhancer activation similar to that observed with the Cdx mutations. No overt changes were observed from mutation of the NFI site.

HNF-1alpha and endodermal transcription factors cooperatively activate Fabpl: MODY3 mutations abrogate cooperativity

Hepatocyte nuclear factor (HNF)-1alpha plays a central role in intestinal and hepatic gene regulation and is required for hepatic expression of the liver fatty acid binding protein gene (Fabpl). An Fabpl transgene was directly activated through cognate sites by HNF-1alpha and HNF-1beta, as well as five other endodermal factors: CDX-1, C/EBPbeta, GATA-4, FoxA2, and HNF-4alpha. HNF-1alpha activated the Fabpl transgene by as much as 60-fold greater in the presence of the other five endodermal factors than in their absence, accounting for up to one-half the total transgene activation by the group of six factors. This degree of synergistic interaction suggests that multifactor cooperativity is a critical determinant of endodermal gene activation by HNF-1alpha. Mutations in HNF-1alpha that result in maturity onset diabetes of the young (MODY3) provide evidence for the in vivo significance of these synergistic interactions. An R131Q HNF-1alpha MODY3 mutant exhibits complete loss of synergistic activation in concert with the other endodermal transcription factors despite wild-type transactivation ability in their absence. Furthermore, whereas wild-type HNF-1alpha exhibited pairwise cooperative synergy with each of the other five factors, the R131Q mutant could synergize only with GATA-4 and C/EBPbeta. Selective loss of synergy with other endodermal transcription factors accompanied by retention of native transactivation ability in an HNF-1alpha MODY mutant suggests in vivo significance for cooperative synergy.

Differentiation-dependent induction of CYP1A1 in cultured rat small intestinal epithelial cells, colonocytes, and human colon carcinoma cells: basement membrane-mediated apoptosis

Rat small intestinal epithelial cells and human colon adenocarcinoma cells cultured on Matrigel expressed the differentiation specific enzyme, sucrase-isomaltase, as determined by indirect immunofluorescence. Rat small intestinal epithelial cells, rat colonocytes, and human colon adenocarcinoma cells developed an altered morphology when cultured on Matrigel and became apoptotic within 24-48 h. Benzo[a]pyrene and 2,3,7,8-tetrachlorodibenzo-p-dioxin caused a 2- and 5-fold induction, respectively, of ethoxyresorufin-o-deethylase activity in rat small intestinal epithelial cells cultured on Matrigel. Benzo[a]pyrene- or 2,3,7,8-tetrachlorodibenzo-p-dioxin-induced ethoxyresorufin-o-deethylase activity in rat small intestinal epithelial cells cultured on plastic was not detected. 2,3,7,8-tetrachlorodibenzo-p-dioxin treatment caused a 14-fold induction of transfected, rat CYP1A1-promoter-luciferase activity in rat small intestinal epithelial cells cultured on Matrigel. Benzo[a]pyrene and 2,3,7,8-tetrachlorodibenzo-p-dioxin treatment induced ethoxyresorufin-o-deethylase activity by 6- and 1.6-fold, respectively in rat colonocytes cultured on Matrigel. Induction of ethoxyresorufin-o-deethylase activity was not observed in rat colonocytes cultured on plastic. CYP1A1-promoter-luciferase activity was induced 3-fold by 2,3,7,8-tetrachlorodibenzo-p-dioxin in rat colonocytes cultured on Matrigel. Induction of CYP1A1-promoter-luciferase activity in rat small intestinal epithelial cells or rat colonocytes cultured on plastic was not observed. Ethoxyresorufin-o-deethylase activity in human colon adenocarcinoma cells, cultured on either plastic or Matrigel, was induced 7-fold by benzo[a]pyrene. 2,3,7,8-Tetrachlorodibenzo-p-dioxin-induced ethoxyresorufin-o-deethylase activity was 2-fold greater in human colon adenocarcinoma cells cultured on Matrigel compared to cells cultured on plastic. Extracellular matrix-mediated differentiation and apoptosis of intestinal cells provide in vitro systems for study of the regulation of CYP1A1 expression, carcinogen activation in the gut and mechanism(s) of apoptosis of colon cancer cells.

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

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

Heparin-binding EGF-like growth factor gene transcription regulated by Cdx2 in the intestinal epithelium

Development and differentiation of the intestinal epithelium appear to be regulated by various growth factors. Using cDNA microarrays, we identified heparin-binding EGF-like growth factor (HB-EGF) as one of the genes induced by intestinal-specific transcription factor Cdx2 in an intestinal undifferentiated rat cell line, intestinal epithelial cell (IEC)-6. Both Cdx2 and HB-EGF stimulated cell proliferation and migration, and their effects were inhibited partially by an EGF receptor-specific tyrosine kinase inhibitor, PD-153035. HB-EGF may function as one of the mediators of Cdx2 and may be associated with the proliferation and migration in the intestinal epithelium. The Cdx2 protein can bind to the Cdx2-binding element of the HB-EGF gene. Reporter gene analyses showed that the HB-EGF gene promoter is Cdx2 responsive and that the activity of the promoter in the IEC-6 cells depends on the number of consensus Cdx2-binding site-like sequences. These data indicate that HB-EGF gene expression can be regulated by Cdx2 and serves to mediate the control of Cdx2 of the proliferation and migration of IEC-6 cells.

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.

Analysis of dipeptidyl peptidase IV gene regulation in transgenic mice: DNA elements sufficient for promoter activity in the kidney, but not the intestine, reside on the proximal portion of the gene 5'-flanking region

The dipeptidyl peptidase IV (DPPIV) gene encodes a brush border membrane exopeptidase that is expressed in a tissue-restricted fashion. To examine the regulation of DPPIV transcription in various tissues in vivo, we examined the expression of DPPIV 5'-flanking region (promoter)-human growth hormone reporter constructs in transgenic mice. These mice exhibited cell-type specific reporter expression in kidney. Surprisingly, however, only very low to non-detectable levels of reporter were found in small intestine. These results indicate that DNA elements sufficient for DPPIV expression in kidney, but not intestine, reside in the 5'-flanking region of the gene.

Identification and characterization of a 315-base pair enhancer, located more than 55 kilobases 5' of the apolipoprotein B gene, that confers expression in the intestine

We recently reported that an 8-kilobase (kb) region, spanning from -54 to -62 kb 5' of the human apolipoprotein B (apoB) gene, contains intestine-specific regulatory elements that control apoB expression in the intestines of transgenic mice. In this study, we further localized the apoB intestinal control region to a 3-kb segment (-54 to -57 kb). DNaseI hypersensitivity studies uncovered a prominent DNaseI hypersensitivity site, located within a 315-base pair (bp) fragment at the 5'-end of the 3-kb segment, in transcriptionally active CaCo-2 cells but not in transcriptionally inactive HeLa cells. Transient transfection experiments with CaCo-2 and HepG2 cells indicated that the 315-bp fragment contained an intestine-specific enhancer, and analysis of the DNA sequence revealed putative binding sites for the tissue-specific transcription factors hepatocyte nuclear factor 3beta, hepatocyte nuclear factor 4, and CAAT enhancer-binding protein beta. Binding of these factors to the 315-bp enhancer was demonstrated in gel retardation experiments. Transfection of deletion mutants of the 315-bp enhancer revealed the relative contributions of these transcription factors in the activity of the apoB intestinal enhancer. The corresponding segment of the mouse apoB gene (located -40 to -83 kb 5' of the structural gene) exhibited a high degree of sequence conservation in the binding sites for the key transcriptional activators and also exhibited enhancer activity in transient transfection assays with CaCo-2 cells. In transgenic mouse expression studies, the 315-bp enhancer conferred intestinal expression to human apoB transgenes.

The nuclear matrix protein CDP represses hepatic transcription of the human cholesterol-7alpha hydroxylase gene

To date, the molecular mechanisms that govern hepatic-specific transcription of the human cholesterol 7alpha-hydroxylase (CYP7A1) gene are poorly understood. We recently reported that the region extending from -1888 to +46, which includes the promoter, is not capable of conferring expression to human CYP7A1 promoter lacZ transgenes in the livers of mice, but that expression is observed with transgenes containing the entire structural gene. To locate liver-specific elements in other segments of the human gene, DNase I hypersensitivity studies were performed with transcriptionally active, liver-derived HepG2 cells and with transcriptionally inactive HeLa cells. Three DNase I hypersensitivity sites were detected within the first intron of the human CYP7A1 gene, but only in HepG2 cells. Transient transfection experiments with HepG2 cells revealed a transcriptional repressor within intron 1. Five binding sites for the CAAT displacement protein (CDP) were detected within intron 1. Since CDP is a nuclear matrix protein, two methods were employed to localize nuclear matrix attachment sites within intron 1 of the human CYP7A1 gene. A matrix attachment site was found throughout the entirety of intron 1. Gel retardation experiments and cell transfection studies provided evidence for the repression mechanism. Repression is achieved by displacement by CDP of two hepatic activators, namely HNF-1alpha and C/EBPalpha, that bind to three different sites within intron 1. Additionally, CDP represses transactivation mediated by these two activators.

The human vasoactive intestinal peptide/pituitary adenylate cyclase-activating peptide receptor 1 (VPAC1) promoter: characterization and role in receptor expression during enterocytic differentiation of the colon cancer cell line Caco-2Cl.20

The basic organization of the human vasoactive intestinal peptide/pituitary adenylate cyclase-activating peptide receptor (VPAC) 1 promoter was investigated after cloning the 5'-flanking region (1.4 kb) of the VPAC1 gene from a human genomic library. Subsequent functional analysis of various deletions of the 5'-flanking sequence, subcloned upstream of a luciferase reporter gene, was carried out in HT-29 cells. The minimal promoter region identified encompasses the -205/+76 sequence and contains a crucial CCAAT box (-182/-178) and a GC-rich sequence. Moreover a region (-1348/-933) containing a silencer element was identified. We previously showed that the expression of the VPAC1 receptor binding site is strictly dependent upon the enterocytic differentiation of human colon cancer Caco-2 cells [Laburthe, Rousset, Rouyer-Fessard, Couvineau, Chantret, Chevalier and Zweibaum (1987) J. Biol. Chem. 262, 10180-10184]. In the present study we show that VPAC1 mRNA increases dramatically when Caco-2Cl.20 cells differentiate, as measured by RNase protection assays and reverse transcriptase-PCR. A single transcript species of 3 kb is detected in differentiated cells by Northern-blot analysis. Accumulation of VPAC1 receptor mRNA is due to a 5-fold increase of transcription rate (run-on assay) without a change in mRNA half-life (9 h). Stable transfections of various constructs in Caco-2Cl.20 cells and subsequent analysis of reporter gene expression, during the enterocytic differentiation process over 25 days of culture, further indicated that the -254/+76 5'-flanking sequence is endowed with the regulatory element(s) necessary for transcriptional regulation of VPAC1 during differentiation. Altogether, these observations provide the first characterization of the basic organization of the human VPAC1 gene promoter and unravel the crucial role of a short promoter sequence in the strict transcriptional control of VPAC1 expression during differentiation of human colon cancer Caco-2 cells.

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

BACKGROUND & AIMS

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

METHODS

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

RESULTS

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

CONCLUSIONS

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

The private hepatocyte nuclear factor-1alpha G319S variant is associated with plasma lipoprotein variation in Canadian Oji-Cree

We previously showed an extremely strong association between type 2 diabetes and a private polymorphism, namely G319S, in the hepatocyte nuclear transcription factor (HNF)-1alpha. Because HNF-1alpha is involved in the transcription of several apolipoprotein genes, we tested for an association between the private HNF1A G319S variant and plasma lipoproteins in a sample of 55 unrelated Oji-Cree subjects with type 2 diabetes and 175 unrelated Oji-Cree subjects without type 2 diabetes. In Oji-Cree subjects with type 2 diabetes, we found that the HNF1A G319S genotype was significantly associated with lower plasma concentrations of total cholesterol, low density lipoprotein cholesterol, and apolipoprotein (apo) B. In Oji-Cree subjects without type 2 diabetes, we found that the HNF1A G319S genotype was significantly associated with higher plasma concentrations of high density lipoprotein cholesterol and apo AI. There were no associations with plasma triglycerides or lipoprotein(a). Regression analysis indicated that the HNF1A genotype accounted for approximately 10% of the variation in the apo B-related traits in the diabetic subjects and for approximately 5% of the variation in the apo AI-related traits in the nondiabetic subjects. Furthermore, the regression model indicated that the HNF1A S319 allele affected these traits in a dominant manner in subjects with and without type 2 diabetes. These findings provide the first evidence that a rare variant in a nuclear transcription factor is associated with variation in plasma lipoprotein traits.

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

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

Transcriptional regulation of pig lactase-phlorizin hydrolase: involvement of HNF-1 and FREACs

BACKGROUND & AIMS

One-kilobase sequence of the upstream fragment of the pig lactase-phlorizin hydrolase gene has been shown to control small intestinal-specific expression and postweaning decline of lactase-phlorizin hydrolase in transgenic mice. The aim of this study was to identify the regulatory DNA elements and transcription factors controlling lactase-phlorizin hydrolase expression.

METHODS

The activity of different lactase-phlorizin hydrolase promoter fragments was investigated by transfection experiments using Caco-2 cells. Electrophoretic mobility shift assays and supershift analyses were used to characterize the interaction between intestinal transcription factors and the identified regulatory elements.

RESULTS

Functional analysis revealed three previously undescribed regulatory regions in the lactase-phlorizin hydrolase promoter: a putative enhancer between -894 and -798 binding hepatocyte nuclear factor (HNF)-1 at position -894 to -880; a repressor-binding element between -278 to -264 to which an HNF-3-like factor is able to bind; and an element between -178 to -164 that binds an activating transcription factor.

CONCLUSIONS

Identification of three new regulatory regions and HNF-1 and HNF-3-like transcription factor as players in the regulation of lactase-phlorizin hydrolase gene transcription has an impact on the understanding of the molecular mechanisms behind age-dependent, tissue-specific, differentiation-dependent, and regional regulation of expression in the intestine.

Identification of domains mediating transcriptional activation and cytoplasmic export in the caudal homeobox protein Cdx-3

The caudal genes have important functions in embryonic development and cell differentiation. The caudal-related protein Cdx-2/3 (the protein designated Cdx-2 in the mouse and Cdx-3 in the hamster) is expressed in the gastrointestinal epithelium and in islet and enteroendocrine cells, where it activates proglucagon gene transcription. We show here that Cdx-3 sequences amino-terminal to the homeodomain (amino acids 1-180) function as a heterologous transcriptional activation domain when fused to the LexA DNA binding domain. A Cdx-3-Pit-1 fusion protein containing only the first 83 amino acids of Cdx-3 linked to the POU domain of Pit-1 markedly stimulated the transcriptional activity of a Pit-1-responsive promoter. Analysis of the transcriptional properties of Cdx-3 mutants in fibroblasts and islet cells revealed distinct amino-terminal subdomains that function in a cell-specific manner. Point mutations within the amino-terminal A domain were associated with reduced transcriptional activity. Furthermore, internal deletions and selected point mutations within domain A, but not the B or C domains, resulted in accumulation of mutant Cdx-3 in the cytoplasm. Unexpectedly, mutation of an Asp-Lys-Asp motif within domain A identified a putative cytoplasmic membrane-associated export signal that mediates Cdx-3 compartmentalization. These experiments delineate unique activities for specific amino-terminal sequences that are functionally important for Cdx-3 biological activity.

Intestinal expression of the calbindin-D9K gene in transgenic mice. Requirement for a Cdx2-binding site in a distal activator region

The calbindin-D9K gene encodes a vitamin D-induced calcium-binding protein that is expressed as a marker of small intestine differentiation. We have shown that 4580 base pairs of its 5' DNA regulatory region can target reporter transgene expression in the intestine and cause this transgene to respond like the endogenous gene to vitamin D active metabolite and that the homeoprotein Cdx2 is bound to the TATA box in the intestine. We now show that the 4580 base pairs construct confers a differentiated pattern of reporter transgene expression in the intestine and that cooperation between the proximal promoter and a distal element located in an opened chromatin structure is responsible for the intestinal expression and vitamin D responsiveness of the transgene. Gel shift and footprinting assays using duodenal nuclear extracts indicate that this distal element contains a Cdx2-binding site. Finally, a mutation in this distal Cdx2-binding site dramatically decreases intestinal expression in transgenic mice. This report, using an in vivo approach, demonstrates the crucial role of Cdx2 for the transcription of an intestinal gene.

Differential regulation of basal and cyclic adenosine 3',5'-monophosphate-induced somatostatin gene transcription in neural cells by DNA control elements that bind homeodomain proteins

A number of genes encoding neuropeptides are expressed in the peripheral and central nervous systems, in different endocrine organs, and in specialized cells distributed along the gastrointestinal tract. Whether expression of the same neuropeptide gene in different tissues is regulated by similar transcriptional mechanisms or by mechanisms that differ in a cell-specific manner remains unclear. We report on promoter studies on the regulation of the somatostatin gene in immortalized neural precursor cells derived from developing rat forebrain. Expression of the somatostatin gene in these cells was determined by RT-PCR/Southern blot analysis, by immunocytochemistry, and by RIA. We show that in cerebrocortical and hippocampal cells, expression of the somatostatin gene is regulated by several negative and positive DNA cis-regulatory elements located throughout the promoter region. The somatostatin cAMP-response element appears to play a prominent role in neural somatostatin gene expression by acting as a strong enhancer even in the absence of cAMP stimulation. Site-directed mutagenesis followed by transient transfection assays indicated that SMS-TAAT1, SMS-TAAT2, and SMS-UE, three previously identified homeodomain protein-binding regulatory elements that enhance transcription in pancreatic cells, act as repressors of transcription in neural cells. Electrophoretic mobility shifts assays indicate that those elements bind protein complexes that differ between neural and pancreatic cells. Our results support the notion that expression of the somatostatin gene in neural cells occurs via transcriptional mechanisms that are different from those regulating expression of the same gene in pancreatic cells.

Colon carbonic anhydrase 1: transactivation of gene expression by the homeodomain protein Cdx2

The homeodomain protein, Cdx2, has been implicated in the transcriptional regulation of genes expressed in the small intestine. In vitro studies of the carbonic anhydrase 1 (CA1) colon promoter implied that Cdx2 may also play a role in the regulation of colon-specific gene expression. The current work follows up this proposal by examining the ability of Cdx2 to transactivate gene expression in cultured cells mediated by CA1 promoter sequences. The results show that Cdx2 exerts a positive regulatory effect by binding to a motif 87 bp upstream of the CA1 TATA box; this motif appears to act as an enhancer since gene activation is independent of its orientation.

Key role of the Cdx2 homeobox gene in extracellular matrix-mediated intestinal cell differentiation

To explore the role of homeobox genes in the intestine, the human colon adenocarcinoma cell line Caco2-TC7 has been stably transfected with plasmids synthesizing Cdx1 and Cdx2 sense and antisense RNAs. Cdx1 overexpression or inhibition by antisense RNA does not markedly modify the cell differentiation markers analyzed in this study. In contrast, Cdx2 overexpression stimulates two typical markers of enterocytic differentiation: sucrase-isomaltase and lactase. Cells in which the endogenous expression of Cdx2 is reduced by antisense RNA attach poorly to the substratum. Conversely, Cdx2 overexpression modifies the expression of molecules involved in cell-cell and cell-substratum interactions and in transduction process: indeed, E-cadherin, integrin-beta4 subunit, laminin-gamma2 chain, hemidesmosomal protein, APC, and alpha-actinin are upregulated. Interestingly, most of these molecules are preferentially expressed in vivo in the differentiated villi enterocytes rather than in crypt cells. Cdx2 overexpression also results in the stimulation of HoxA-9 mRNA expression, an homeobox gene selectively expressed in the colon. In contrast, Cdx2-overexpressing cells display a decline of Cdx1 mRNA, which is mostly found in vivo in crypt cells. When implanted in nude mice, Cdx2-overexpressing cells produce larger tumors than control cells, and form glandular and villus-like structures. Laminin-1 is known to stimulate intestinal cell differentiation in vitro. In the present study, we demonstrate that the differentiating effect of laminin-1 coatings on Caco2-TC7 cells is accompanied by an upregulation of Cdx2. To further document this observation, we analyzed a series of Caco2 clones in which the production of laminin-alpha1 chain is differentially inhibited by antisense RNA. We found a positive correlation between the level of Cdx2 expression, that of endogenous laminin-alpha1 chain mRNA and that of sucrase-isomaltase expression in these cell lines. Taken together, these results suggest (a) that Cdx1 and Cdx2 homeobox genes play distinct roles in the intestinal epithelium, (b) that Cdx2 provokes pleiotropic effects triggering cells towards the phenotype of differentiated villus enterocytes, and (c) that Cdx2 expression is modulated by basement membrane components. Hence, we conclude that Cdx2 plays a key role in the extracellular matrix-mediated intestinal cell differentiation.

Identification and characterization of the MUC2 (human intestinal mucin) gene 5'-flanking region: promoter activity in cultured cells

The initiation point for MUC2 gene transcription is located within a 7000-base GC-rich region of the mucin gene cluster found on chromosome 11p15.5. The promoter activity of the 5'-flanking region of the MUC2 gene was examined following its cloning into the luciferase-producing pGL2-Basic reporter vector. A short segment comprising bases -91 to -73 relative to the start of transcription was found to be important for basal promoter activity in all cell lines tested. Electrophoretic mobility shift assays demonstrated nuclear protein binding to this region, which contains the consensus CACCC motif (5'-GCCACACCC). This element has been shown to be functionally important in several promoters that are active in diverse cell types. Competition experiments using an Sp1 oligonucleotide and antibody supershift experiments indicated that both Sp1 and other Sp1 family members bind to this element. Inclusion of the region between bases -228 and -171 in pGL2-Basic constructs increased normalized luciferase reporter activity by almost 3-fold in C1a cells, which produce relatively high levels of MUC2 mRNA. Significantly lower levels of normalized luciferase activity resulted when the same construct was transfected into cultured cell lines that express low or undetectable levels of MUC2, suggesting a possible role for this region in conferring cell-type specificity of expression. We also demonstrate, using actinomycin D, that the MUC2 mRNA is long-lived, at least in cultured cells. Moreover, no evidence was found that the MUC2 mRNA turned over more rapidly in LS174T cells, which produce relatively low levels of MUC2 mRNA, as compared with C1a cells, which produce high levels of mRNA. Thus a long mRNA half-life appears to be an important mechanism involved in achieving elevated levels of MUC2 mRNA.

Changing intestinal connective tissue interactions alters homeobox gene expression in epithelial cells

In segmented organs, homeobox genes are involved in axial patterning and cell identity. Much less is known about their role in non-segmented endoderm derivatives such as the digestive epithelium. Using a xenograft model of fetal intestinal anlagen implanted under the skin of nude mice, we have investigated whether the expression of five homeobox genes (HoxA-4, HoxA-9, HoxC-8, Cdx-1 and Cdx-2) is modified when intestinal epithelium undergoes normal development or displays heterodifferentiation in association with heterotopic mesenchyme. In homotypic associations of fetal endoderm and mesenchyme that recapitulate normal development, the overall pattern of homeobox gene expression was maintained: HoxA-9 and HoxC-8 were the highest in the colon and ileum, respectively, and HoxA-4 was expressed all along the intestine; Cdx-1 and Cdx-2 exhibited an increasing gradient of expression from small intestine to colon. Yet, grafting per se caused a faint upregulation of HoxA-9 and HoxC-8 in small intestinal regions in which these genes are not normally expressed, while the endoderm-mesenchyme dissociation-association step provoked a decay of Cdx-1 in the colon. In heterotopic associations of colonic endoderm with small intestinal mesenchyme, the colonic epithelium exhibited heterodifferentiation to a small intestinal-like phenotype. In this case, we observed a decay of HoxA-9 expression and an upregulation of HoxC-8. Additionally, heterodifferentiation of the colonic epithelium was accompanied by a downregulation of Cdx-1 and Cdx-2 to a level similar to that found in the normal small intestine. To demonstrate that mesenchyme-derived cells can influence Cdx-1 and Cdx-2 expression in the bowel epithelium, fetal jejunal endoderm was associated with intestinal fibroblastic cell lines that either support small intestinal-like or colonic-like morphogenesis. A lower expression of both homeobox genes was shown in grafts presenting the small intestinal phenotype than in those showing glandular colonic-like differentiation. Taken together, these results suggest that homeobox genes participate in the control of the positional information and/or cell differentiation in the intestinal epithelium. They also indicate that the level of Cdx-1 and Cdx-2 homeobox gene expression is influenced by epithelial-mesenchymal cell interactions in the intestinal mucosa.

The caudal homeobox protein cdx-2/3 activates endogenous proglucagon gene expression in InR1-G9 islet cells

The proglucagon gene is expressed in a highly cell-specific manner in islet and enteroendocrine cells. DNA sequences within the proximal proglucagon G1 promoter region bind the homeobox protein cdx-2/3, and cdx-2/3 activates the proglucagon promoter in fibroblasts. We show here that cdx-2/3 activates the proglucagon promoter in both islet (InR1-G9) and enteroendocrine (STC-1 and GLUTag) cell lines. Furthermore, transfected cdx-2/3 increased the levels of endogenous proglucagon mRNA transcripts in both transient and stable transfections of InR1-G9 islet cells. The cdx-2/3-dependent induction of endogenous proglucagon mRNA transcripts in stable islet lines was associated with a corresponding increase in the transcriptional activity of proglucagon promoter-luciferase plasmids. An amino-terminally truncated cdx-2/3 derivative containing the homeodomain and carboxy-terminal region of the molecule inhibited both the cdx-2/3 activation of the proglucagon promoter and the induction of endogenous proglucagon mRNA transcripts. These observations demonstrate that cdx-2/3, acting through the proximal G1 element, is a major transcriptional determinant of cell-specific proglucagon gene expression in pancreatic islet cells.