Clonal analysis of sucrase-isomaltase expression in the human colon adenocarcinoma Caco-2 cells

Reconsideration of the laminin receptor 67LR in colorectal cancer cells

The 67 kDa laminin receptor (67LR) was identified as the first laminin receptor shown to be involved in the carcinogenesis of various cancers, including colorectal cancer. While the exact composition of this 67 kDa receptor remains unknown, it has been reported to be formed by the 37 kDa ribosomal protein SA (RPSA) covalently attached to another unidentified protein. The goal of this study was to clarify the molecular structure of 67LR to enhance our understanding of its role in malignancies. Using cell fractionation of colorectal cancer cells, the 67 kDa immunoreactive protein corresponding to 67LR was found in the soluble protein fraction, while some of the 37 kDa RPSA exhibited plasma membrane-like properties. Proteomic analysis of the 67 kDa fraction revealed the absence of RPSA but identified the β-galactosidase-related 67 kDa elastin-binding protein (67EBP), another laminin binding receptor which presents amino acid sequence similarities that can explain the immune cross reactivity with RPSA. The downregulation of β-galactosidase through short hairpin RNA (shRNA) led to a reduction in both 67LR and 67EBP immunoreactive proteins, confirming the misidentification of 67LR and 67EBP in colorectal cancer cells. Based on these findings, we propose to redefine the 67LR as the RPSA-containing laminin receptor (RCLR) to avoid confusion with the 67EBP.

Integrin α7β1 represses intestinal absorptive cell differentiation

Intestinal epithelial cell differentiation is a highly controlled and orderly process occurring in the crypt so that cells migrating out to cover the villi are already fully functional. Absorptive cell precursors, which originate from the stem cell population located in the lower third of the crypt, are subject to several cycles of amplification in the transit amplifying (TA) zone, before reaching the terminal differentiation compartment located in the upper third. There is a large body of evidence that absorptive cell differentiation is halted in the TA zone through various epigenetic, transcriptional and intracellular signalling events or mechanisms allowing the transient expansion of this cell population but how these mechanisms are themself regulated remains obscure. One clue can be found in the epithelial cell-matrix microenvironment located all along the crypt-villus axis. Indeed, a previous study from our group revealed that α5-subunit containing laminins such as lamimin-511 and 512 inhibit early stages of differentiation in Caco-2/15 cells. Among potential receptors for laminin 511/512 is the integrin α7β1, which has previously been reported to be expressed in the human intestinal crypts and in early stages of Caco-2/15 cell differentiation. In this study, the effects of knocking down ITGA7 in Caco-2/15 cells were studied using shRNA and CRISPR/Cas9 strategies. Abolition of the α7 integrin subunit resulted in a significant increase in the level of differentiation and polarization markers as well as the morphological features of intestinal cells. Activities of focal adhesion kinase and Src kinase were both reduced in α7-knockdown cells while the three major intestinal pro-differentiation factors CDX2, HNFα1 and HNF4α were overexpressed. Two epigenetic events associated with intestinal differentiation, the reduction of tri-methylated lysine 27 on histone H3 and the increase of acetylation of histone H4 were also observed in α7-knockdown cells. On the other hand, the ablation of α7 had no effect on cell proliferation. In conclusion, these data indicate that integrin α7β1 acts as a major repressor of absorptive cell terminal differentiation in the Caco-2/15 cell model and suggest that the laminin-α7β1 integrin interaction occurring in the transit amplifying zone of the adult intestine is involved in the transient halting of absorptive cell terminal differentiation.

Fibrin(ogen) Is Constitutively Expressed by Differentiated Intestinal Epithelial Cells and Mediates Wound Healing

Fibrinogen is a large molecule synthesized in the liver and released in the blood. Circulating levels of fibrinogen are upregulated after bleeding or clotting events and support wound healing. In the context of an injury, thrombin activation drives conversion of fibrinogen to fibrin. Fibrin deposition contains tissue damage, stops blood loss, and prevents microbial infection. In most circumstances, fibrin needs to be removed to allow the resolution of inflammation and tissue repair, whereas failure of this may lead to the development of various disorders. However, the contribution of fibrinogen to tissue inflammation and repair is likely to be context-dependent. In this study, the concept that fibrin needs to be removed to allow tissue repair and to reduce inflammation is challenged by our observations that, in the intestine, fibrinogen is constitutively produced by a subset of intestinal epithelial cells and deposited at the basement membrane as fibrin where it serves as a substrate for wound healing under physiological conditions such as epithelial shedding at the tip of the small intestinal villus and surface epithelium of the colon as well as under pathological conditions that require rapid epithelial repair. The functional integrity of the intestine is ensured by the constant renewal of its simple epithelium. Superficial denuding of the epithelial cell layer occurs regularly and is rapidly corrected by a process called restitution that can be influenced by various soluble and insoluble factors. Epithelial cell interaction with the extracellular matrix greatly influences the healing process by acting on cell morphology, adhesion, and migration. The functional contribution of a fibrin(ogen) matrix in the intestine was studied under physiological and pathological contexts. Our results (immunofluorescence, immunoelectron microscopy, and quantitative PCR) show that fibrin(ogen) is a novel component of the basement membrane associated with the differentiated epithelial cell population in both the small intestine and colon. Fibrin(ogen) alone is a weak ligand for epithelial cells and behaves as an anti-adhesive molecule in the presence of type I collagen. Furthermore, the presence of fibrin(ogen) significantly shortens the time required to achieve closure of wounded epithelial cell monolayers and co-cultures in a PI3K-dependent manner. In human specimens with Crohn's disease, we observed a major accumulation of fibrin(ogen) throughout the tissue and at denuded sites. In mice in which fibrin formation was inhibited with dabigatran treatment, dextran sulfate sodium administration provoked a significant increase in the disease activity index and pathological features such as mucosal ulceration and crypt abscess formation. Taken together, these results suggest that fibrin(ogen) contributes to epithelial healing under both normal and pathological conditions.

Differential influence of YAP1 and TAZ on differentiation of intestinal epithelial cell: A review

Intestinal cell stemness, proliferation and differentiation are complex processes all occurring in distinct compartments of the crypt that need to be closely regulated to ensure proper epithelial renewal. The involvement of the Hippo pathway in intestinal epithelial proliferation and regeneration after injury via the regulation of its effectors YAP1 and TAZ has been well-documented over the last decade. The implication of YAP1 and TAZ on intestinal epithelial cell differentiation is less clear. Using intestinal cell models in which the expression of YAP1 and TAZ can be modulated, our group showed that YAP1 inhibits differentiation of the two main intestinal epithelial cell types, goblet and absorptive cells through a specific mechanism involving the repression of prodifferentiation transcription factor CDX2 expression. Further analysis provided evidence that the repressive effect of YAP1 on intestinal differentiation is mediated by regulation of the Hippo pathway by Src family kinase activity. Interestingly, the TAZ paralog does not seem to be involved in this process, which provides another example of the lack of perfect complementarity of the two main Hippo effectors.

Src family kinases inhibit differentiation of intestinal epithelial cells through the Hippo effector YAP1

Intestinal cell lineage differentiation is a tightly regulated mechanism that involves several intracellular signaling pathways affecting the expression of a variety of transcription factors, which ultimately regulate cell specific gene expression. Absorptive and goblet cells are the two main epithelial cell types of the intestine. Previous studies from our group using an shRNA knockdown approach have shown that YAP1, one of the main Hippo pathway effectors, inhibits the differentiation of these two cell types. In the present study, we show that YAP1 activity is regulated by Src family kinases (SFKs) in these cells. Inhibition of SFKs led to a sharp reduction in YAP1 expression at the protein level, an increase in CDX2 and the P1 forms of HNF4α and of absorptive and goblet cell differentiation specific markers. Interestingly, in Caco-2/15 cells which express both YAP1 and its paralog TAZ, TAZ was not reduced by the inhibition of SFKs and its specific knockdown rather impaired absorptive cell differentiation indicating that YAP1 and TAZ are not always interchangeable for regulating cell functions. This article has an associated First Person interview with the first author of the paper.

Peroxidized Linoleic Acid, 13-HPODE, Alters Gene Expression Profile in Intestinal Epithelial Cells

Lipid peroxides (LOOHs) abound in processed food and have been implicated in the pathology of diverse diseases including gut, cardiovascular, and cancer diseases. Recently, RNA Sequencing (RNA-seq) has been widely used to profile gene expression. To characterize gene expression and pathway dysregulation upon exposure to peroxidized linoleic acid, we incubated intestinal epithelial cells (Caco-2) with 100 µM of 13-hydroperoxyoctadecadienoic acid (13-HPODE) or linoleic acid (LA) for 24 h. Total RNA was extracted for library preparation and Illumina HiSeq sequencing. We identified 3094 differentially expressed genes (DEGs) in 13-HPODE-treated cells and 2862 DEGs in LA-treated cells relative to untreated cells. We show that 13-HPODE enhanced lipid metabolic pathways, including steroid hormone biosynthesis, PPAR signaling, and bile secretion, which alter lipid uptake and transport. 13-HPODE and LA treatments promoted detoxification mechanisms including cytochrome-P450. Conversely, both treatments suppressed oxidative phosphorylation. We also show that both treatments may promote absorptive cell differentiation and reduce proliferation by suppressing pathways involved in the cell cycle, DNA synthesis/repair and ribosomes, and enhancing focal adhesion. A qRT-PCR analysis of representative DEGs validated the RNA-seq analysis. This study provides insights into mechanisms by which 13-HPODE alters cellular processes and its possible involvement in mitochondrial dysfunction-related disorders and proposes potential therapeutic strategies to treat LOOH-related pathologies.

The Hippo Pathway Effector YAP1 Regulates Intestinal Epithelial Cell Differentiation

The human intestine is covered by epithelium, which is continuously replaced by new cells provided by stem cells located at the bottom of the glands. The maintenance of intestinal stem cells is supported by a niche which is composed of several signaling proteins including the Hippo pathway effectors YAP1/TAZ. The role of YAP1/TAZ in cell proliferation and regeneration is well documented but their involvement on the differentiation of intestinal epithelial cells is unclear. In the present study, the role of YAP1/TAZ on the differentiation of intestinal epithelial cells was investigated using the HT29 cell line, the only multipotent intestinal cell line available, with a combination of knockdown approaches. The expression of intestinal differentiation cell markers was tested by qPCR, Western blot, indirect immunofluorescence and electron microscopy analyses. The results show that TAZ is not expressed while the abolition of YAP1 expression led to a sharp increase in goblet and absorptive cell differentiation and reduction of some stem cell markers. Further studies using double knockdown experiments revealed that most of these effects resulting from YAP1 abolition are mediated by CDX2, a key intestinal cell transcription factor. In conclusion, our results indicate that YAP1/TAZ negatively regulate the differentiation of intestinal epithelial cells through the inhibition of CDX2 expression.

Glycomacropeptide Prevents Iron/Ascorbate-Induced Oxidative Stress, Inflammation and Insulin Sensitivity with an Impact on Lipoprotein Production in Intestinal Caco-2/15 Cells

Background. Metabolic Syndrome (MetS), a major worldwide concern for the public health system, refers to a cluster of key metabolic components, and represents a risk factor for diabetes and cardiovascular diseases. As oxidative stress (OxS) and inflammation are the major triggers of insulin sensitivity (IS), a cardinal MetS feature, the principal aim of the present work is to determine whether glycomacropeptide (GMP), a milk-derived bioactive peptide, exerts beneficial effects on their expression. Methods. Fully differentiated intestinal Caco-2/15 cells are used to evaluate the preventive action of 2 mg/mL GMP against OxS and inflammation induced by the mixture iron-ascorbate (Fe/Asc) (200 μM:2 mM). The potency of GMP of decreasing the production of lipoproteins, including chylomicrons (CM), very-low-density lipoproteins (VLDL) and low-density lipoproteins (LDL) is also assessed. Results. The administration of GMP significantly reduces malondialdehyde, a biomarker of lipid peroxidation, and raises superoxide dismutase 2 and glutathione peroxidase via the induction of the nuclear factor erythroid 2–related factor 2, a transcription factor, which orchestrates cellular antioxidant defenses. Similarly, GMP markedly lowers the inflammatory agents tumor necrosis factor-α and cyclooxygenase-2 via abrogation of the nuclear transcription factor-kB. Moreover, GMP-treated cells show a down-regulation of Fe/Asc-induced mitogen activated protein kinase pathway, suggesting greater IS. Finally, GMP decreases the production of CM, VLDL, and LDL. Conclusions. Our results highlight the effectiveness of GMP in attenuating OxS, inflammation and lipoprotein biogenesis, as well as improving IS, the key components of MetS. Further investigation is needed to elucidate the mechanisms mediating the preventive action of GMP.

Methods for Assessing Apoptosis and Anoikis in Normal Intestine/Colon and Colorectal Cancer

Caspase-dependent apoptosis, including its distinct cell death subroutine known as anoikis, perform essential roles during organogenesis, as well as in the maintenance and repair of tissues. To this effect, the continuous renewal of the human intestinal/colon epithelium is characterized by the exfoliation by anoikis of differentiated cells, whereas immature/undifferentiated cells may occasionally undergo apoptosis in order to evacuate daughter cells that are damaged or defective. Dysregulated epithelial apoptosis is a significant component of inflammatory bowel diseases. Conversely, the acquisition of a resistance to apoptosis represents one of the hallmarks of cancer initiation and progression, including for colorectal cancer (CRC). Furthermore, the emergence of anoikis resistance constitutes a critical step in cancer progression (including CRC), as well as a limiting one that enables invasion and metastasis.Considering the implications of apoptosis/anoikis dysregulation in gut physiopathology, it therefore becomes incumbent to understand the functional determinants that underlie such dysregulation-all the while having to monitor, assess, or evidence apoptosis and/or anoikis. In this chapter, methodologies that are typically used to assess caspase-dependent apoptosis and anoikis in intestinal/colonic normal and CRC cells, whether in vivo, ex vivo, or in cellulo, are provided.

The In Vitro Protective Role of Bovine Lactoferrin on Intestinal Epithelial Barrier

The intestinal epithelial barrier plays a key protective role in the gut lumen. Bovine lactoferrin (bLF) has been reported to improve the intestinal epithelial barrier function, but its impact on tight junction (TJ) proteins has been rarely described. Human intestinal epithelial crypt cells (HIECs) were more similar to those in the human small intestine, compared with the well-established Caco-2 cells. Accordingly, both HIECs and Caco-2 cells were investigated in this study to determine the effects of bioactive protein bLF on their growth promotion and intestinal barrier function. The results showed that bLF promoted cell growth and arrested cell-cycle progression at the G2/M-phase. Moreover, bLF decreased paracellular permeability and increased alkaline phosphatase activity and transepithelial electrical resistance, strengthening barrier function. Immunofluorescence, western blot and quantitative real-time polymerase chain reaction revealed that bLF significantly increased the expression of three tight junction proteins-claudin-1, occludin, and ZO-1-at both the mRNA and protein levels, and consequently strengthened the barrier function of the two cell models. bLF in general showed higher activity in Caco-2 cells, however, HIECs also exhibited desired responses to barrier function. Therefore, bLF may be incorporated into functional foods for treatment of inflammatory bowel diseases which are caused by loss of barrier integrity.

P1 promoter-driven HNF4α isoforms are specifically repressed by β-catenin signaling in colorectal cancer cells

HNF4α is a key nuclear receptor for regulating gene expression in the gut. Although both P1 and P2 isoform classes of HNF4α are expressed in colonic epithelium, specific inhibition of P1 isoforms is commonly found in colorectal cancer. Previous studies have suggested that P1 and P2 isoforms might regulate different cellular functions. Despite these advances, it remains unclear whether these isoform classes are functionally divergent in the context of human biology. Here, the consequences of specific inhibition of P1 or P2 isoform expression was measured in a human colorectal cancer cell transcriptome. Results indicate that P1 isoforms were specifically associated with the control of cell metabolism, whereas P2 isoforms globally supported aberrant oncogenic signalization, promoting cancer cell survival and progression. P1 promoter-driven isoform expression was found to be repressed by β-catenin, one of the earliest oncogenic pathways to be activated during colon tumorigenesis. These findings identify a novel cascade by which the expression of P1 isoforms is rapidly shut down in the early stages of colon tumorigenesis, allowing a change in HNF4α-dependent transcriptome, thereby promoting colorectal cancer progression.This article has an associated First Person interview with the first author of the paper.

MYC Regulates α6 Integrin Subunit Expression and Splicing Under Its Pro-Proliferative ITGA6A Form in Colorectal Cancer Cells

The α6 integrin subunit (ITGA6) pre-mRNA undergoes alternative splicing to form two splicing variants, named ITGA6A and ITGA6B. In primary human colorectal cancer cells, the levels of both ITGA6 and β4 integrin subunit (ITGB4) subunits of the α6β4 integrin are increased. We previously found that the upregulation of ITGA6 is a direct consequence of the increase of the pro-proliferative ITGA6A variant. However, the mechanisms that control ITGA6 expression and splicing into the ITGA6A variant over ITGA6B in colorectal cancer cells remain poorly understood. Here, we show that the promoter activity of the ITGA6 gene is regulated by MYC. Pharmacological inhibition of MYC activity with the MYC inhibitor (MYCi) 10058-F4 or knockdown of MYC expression by short hairpin RNA (shRNA) both lead to a decrease in ITGA6 and ITGA6A levels in colorectal cancer cells, while overexpression of MYC enhances ITGA6 promoter activity. We also found that MYC inhibition decreases the epithelial splicing regulatory protein 2 (ESRP2) splicing factor at both the mRNA and protein levels. Chromatin immunoprecipitation revealed that the proximal promoter sequences of ITGA6 and ESRP2 were occupied by MYC and actively transcribed in colorectal cancer cells. Furthermore, expression studies in primary colorectal tumors and corresponding resection margins confirmed that the up-regulation of the ITGA6A subunit can be correlated with the increase in MYC and ESRP2. Taken together, our results demonstrate that the proto-oncogene MYC can regulate the promoter activation and splicing of the ITGA6 integrin gene through ESRP2 to favor the production of the pro-proliferative ITGA6A variant in colorectal cancer cells.

Knockdown of laminin α5 stimulates intestinal cell differentiation

Interactions between cells and the extracellular matrix regulate a wide range of cell processes such as proliferation and differentiation. Laminins are major components of the basement membrane that actively participate in most biological functions via their interactions with a variety of specific cell receptors. The α5-containing laminins (LAMA5) are one of the three main types of laminins identified at the epithelial basal lamina in the adult intestine. The aim of the present study was to investigate the role of α5-containing laminins on intestinal cell proliferation and differentiation. Using an shRNA targeting approach, the effects of knocking down the expression of LAMA5 were investigated in the enterocytic-like Caco-2/15 cell line, a well-characterized model for intestinal cell differentiation. Surprisingly, the abolition of the laminin α5 chain resulted in a drastic increase in the differentiation marker sucrase-isomaltase which was correctly expressed at the apical pole of the cells as observed by indirect immunofluorescence. Transient increases of dipeptidylpeptidase IV, villin, CDX2, HNF-1α, HNF-4α and transepithelial resistance as well as an apparent redistribution of the junctional components ZO-1 and E-cadherin were also observed at early stages of differentiation but no specific effect was observed on cell proliferation as evaluated by BrdU incorporation. Taken together, these data suggest that α5-containing laminins repress intestinal differentiation in its early stages.

Plasma Lactoferrin Levels Positively Correlate with Insulin Resistance despite an Inverse Association with Total Adiposity in Lean and Severely Obese Patients

Context

Lactoferrin (Lf) is an important protein found on mucosal surfaces, within neutrophils and various cells, and in biological fluids. It displays multiple functions, including iron-binding as well as antimicrobial, immunomodulatory and anti-inflammatory activities. Although Lf ingestion has been suggested to cause adiposity reduction in murine models and humans, its relationship with insulin resistance (IR) has not been studied thoroughly.

Objective

To establish the association between circulating Lf levels, glucose status and blood lipid/lipoprotein profile.

Methods

Two independent cohorts were examined: lean to moderately obese women admitted for gynecological surgery (n = 53) and severely obese subjects undergoing biliopancreatic diversion (n = 62).

Results

Although body mass index (BMI) and total body fat mass were negatively associated with Lf, IR (assessed by the HOMA-IR index) was positively and independently associated with plasma Lf concentrations of the first cohort of lean to moderately obese women. These observations were validated in the second cohort in view of the positive correlation between plasma Lf concentrations and the HOMA-IR index, but without a significant association with the body mass index (BMI) of severely obese subjects. In subsamples of severely obese subjects matched for sex, age and BMI, but with either relatively low (1.89 ± 0.73) or high (13.77 ± 8.81) IR states (according to HOMA-IR), higher plasma Lf levels were noted in insulin-resistant vs insulin-sensitive subjects (P<0.05). Finally, Lf levels were significantly higher in lean to moderately obese women than in severely obese subjects (P<0.05).

Conclusion

Our findings revealed that plasma Lf levels are strongly associated with IR independently of total adiposity, which suggests an intriguing Lf regulation mechanism in conditions of obesity and IR.

New Insights In Intestinal Sar1B GTPase Regulation and Role in Cholesterol Homeostasis

Sar1B GTPase is a key component of Coat protein complex II (COPII)-coated vesicles that bud from the endoplasmic reticulum to export newly synthesized proteins. The aims of this study were to determine whether Sar1B responds to lipid regulation and to evaluate its role in cholesterol (CHOL) homeostasis. The influence of lipids on Sar1B protein expression was analyzed in Caco-2/15 cells by Western blot. Our results showed that the presence of CHOL (200 μM) and oleic acid (0.5 mM), bound to albumin, increases Sar1B protein expression. Similarly, supplementation of the medium with micelles composed of taurocholate with monooleylglycerol or oleic acid also stimulated Sar1B expression, but the addition of CHOL (200 μM) to micelle content did not modify its regulation. On the other hand, overexpression of Sar1B impacted on CHOL transport and metabolism in view of the reduced cellular CHOL content along with elevated secretion when incubated with oleic acid-containing micelles for 24 h, thereby disclosing induced CHOL transport. This was accompanied with higher secretion of free- and esterified-CHOL within chylomicrons, which was not the case when oleic acid was replaced with monooleylglycerol or when albumin-bound CHOL was given alone. The aforementioned cellular CHOL depletion was accompanied with a low phosphorylated/non phosphorylated HMG-CoA reductase ratio, indicating elevated enzymatic activity. Combination of Sar1B overexpression with micelle incubation led to reduction in intestinal CHOL transporters (NPC1L1, SR-BI) and metabolic regulators (PCSK9 and LDLR). The present work showed that Sar1B is regulated in a time- and concentration-dependent manner by dietary lipids, suggesting an adaptation to alimentary lipid flux. Our data also suggest that Sar1B overexpression contributes to regulation of CHOL transport and metabolism by facilitating rapid uptake and transport of CHOL.

Epigenetics in Intestinal Epithelial Cell Renewal

A controlled balance between cell proliferation and differentiation is essential to maintain normal intestinal tissue renewal and physiology. Such regulation is powered by several intracellular pathways that are translated into the establishment of specific transcription programs, which influence intestinal cell fate along the crypt-villus axis. One important check-point in this process occurs in the transit amplifying zone of the intestinal crypts where different signaling pathways and transcription factors cooperate to manage cellular proliferation and differentiation, before secretory or absorptive cell lineage terminal differentiation. However, the importance of epigenetic modifications such as histone methylation and acetylation in the regulation of these processes is still incompletely understood. There have been recent advances in identifying the impact of histone modifications and chromatin remodelers on the proliferation and differentiation of normal intestinal crypt cells. In this review we discuss recent discoveries on the role of the cellular epigenome in intestinal cell fate, development, and tissue renewal. J. Cell. Physiol. 231: 2361-2367, 2016. © 2016 The Authors. Journal of Cellular Physiology Published by Wiley Periodicals, Inc.

Active vitamin D potentiates the anti-neoplastic effects of calcium in the colon: A cross talk through the calcium-sensing receptor

Epidemiological studies suggest an inverse correlation between dietary calcium (Ca(2+)) and vitamin D intake and the risk of colorectal cancer (CRC). It has been shown in vitro that the active vitamin D metabolite, 1,25-dihydroxyvitamin D3 (1,25-D3) can upregulate expression of the calcium-sensing receptor (CaSR). In the colon, CaSR has been suggested to regulate proliferation of colonocytes. However, during tumorigenesis colonic CaSR expression is downregulated and we hypothesized that the loss of CaSR could influence the anti-tumorigenic effects of Ca(2+) and vitamin D. Our aim was to assess the impact of CaSR expression and function on the anti-neoplastic effects of 1,25-D3 in colon cancer cell lines. We demonstrated that in the healthy colon of mice, high vitamin D diet (2500 IU/kg diet) increased expression of differentiation and apoptosis markers, decreased expression of proliferation markers and significantly upregulated CaSR mRNA expression, compared with low vitamin D diet (100 IU/kg diet). To determine the role of CaSR in this process, we transfected Caco2-15 and HT29 CRC cells with wild type CaSR (CaSR-WT) or a dominant negative CaSR mutant (CaSR-DN) and treated them with 1,25-D3 alone, or in combination with CaSR activators (Ca(2+) and NPS R-568). 1,25-D3 enhanced the anti-proliferative effects of Ca(2+) and induced differentiation and apoptosis only in cells with a functional CaSR, which were further enhanced in the presence of NPS R-568, a positive allosteric modulator of CaSR. The mutant CaSR inhibited the anti-tumorigenic effects of 1,25-D3 suggesting that the anti-neoplastic effects of 1,25-D3 are, at least in part, mediated by the CaSR. Taken together, our data provides molecular evidence to support the epidemiological observation that both, vitamin D and calcium are needed for protection against malignant transformation of the colon and that their effect is modulated by the presence of a functional CaSR. This article is part of a Special Issue entitled '17th Vitamin D Workshop'.

Histone deacetylase inhibition impairs normal intestinal cell proliferation and promotes specific gene expression

Mechanisms that maintain proliferation and delay cell differentiation in the intestinal crypt are not yet fully understood. We have previously shown the implication of histone methylation in the regulation of enterocytic differentiation. In this study, we investigated the role of histone deacetylation as an important epigenetic mechanism that controls proliferation and differentiation of intestinal cells using the histone deacetylase inhibitor suberanilohydroxamic acid (SAHA) on the proliferation and differentiation of human and mouse intestinal cells. Treatment of newly confluent Caco-2/15 cells with SAHA resulted in growth arrest, increased histone acetylation and up-regulation of the expression of intestine-specific genes such as those encoding sucrase-isomaltase, villin and the ion exchanger SLC26A3. Although SAHA has been recently used in clinical trials for cancer treatment, its effect on normal intestinal cells has not been documented. Analyses of small and large intestines of mice treated with SAHA revealed a repression of crypt cell proliferation and a higher expression of sucrase-isomaltase in both segments compared to control mice. Expression of SLC26A3 was also significantly up-regulated in the colons of mice after SAHA administration. Finally, SAHA was also found to strongly inhibit normal human intestinal crypt cell proliferation in vitro. These results demonstrate the important implication of epigenetic mechanisms such as histone acetylation/deacetylation in the regulation of normal intestinal cell fate and proliferation.

miR-135b- and miR-146b-dependent silencing of calcium-sensing receptor expression in colorectal tumors

Studies have shown that the calcium-sensing receptor (CaSR) mediates the antitumorigenic effects of calcium against colorectal cancer (CRC). Expression of the CaSR in colorectal tumors is often reduced. We have reported previously that silencing of CaSR in CRC is caused in part by methylation of CaSR promoter 2 and loss of histone acetylation. We investigated the impact of aberrant microRNA expression on loss of CaSR expression. A microarray study in two Caco-2 subclones (Caco2/AQ and Caco2/15) that have similar genetic background, but different CaSR expression levels (Caco2/AQ expressing more CaSR than Caco2/15), identified 22 differentially expressed microRNAs that potentially target the CaSR. We validated these results by performing gain- and loss-of-function studies with the top candidates: miR-9, miR-27a, miR-135b, and miR-146b. Modulation of miR-135b or miR-146b expression by mimicking or inhibiting their expression regulated CaSR protein levels in two different colon cancer cell lines: Caco2/AQ (moderate endogenous CaSR expression) and HT29 (low endogenous CaSR levels). Inhibition of miR-135b and miR-146b expression led to high CaSR levels and significantly reduced proliferation. In samples of colorectal tumors we observed overexpression of miR-135b and miR-146b, and this correlated inversely with CaSR expression (miR-135b: r = -0.684, p < 0.001 and miR-146b: r = -0.448, p < 0.001), supporting our in vitro findings. We demonstrate that miR-135b and miR-146b target the CaSR and reduce its expression in colorectal tumors, reducing the antiproliferative and prodifferentiating actions of calcium. This provides a new approach for finding means to prevent CaSR loss, developing better treatment strategies for CRC.

Altered intestinal functions and increased local inflammation in insulin-resistant obese subjects: a gene-expression profile analysis

BACKGROUND

Metabolic alterations relevant to postprandial dyslipidemia were previously identified in the intestine of obese insulin-resistant subjects. The aim of the study was to identify the genes deregulated by systemic insulin resistance in the intestine of severely obese subjects.

METHODS

Transcripts from duodenal samples of insulin-sensitive (HOMA-IR < 3, n = 9) and insulin-resistant (HOMA-IR > 7, n = 9) obese subjects were assayed by microarray (Illumina HumanHT-12).

RESULTS

A total of 195 annotated genes were identified as differentially expressed between these two groups (Fold change > 1.2). Of these genes, 36 were found to be directly involved in known intestinal functions, including digestion, extracellular matrix, endocrine system, immunity and cholesterol metabolism. Interestingly, all differentially expressed genes (n = 8) implicated in inflammation and oxidative stress were found to be upregulated in the intestine of insulin-resistant compared to insulin-sensitive subjects. Metabolic pathway analysis revealed that several signaling pathways involved in immunity and inflammation were significantly enriched in differently expressed genes and were predicted to be activated in the intestine of insulin-resistant subjects. Using stringent criteria (Fold change > 1.5; FDR < 0.05), three genes were found to be significantly and differently expressed in the intestine of insulin-resistant compared to insulin-sensitive subjects: the transcripts of the insulinotropic glucose-dependant peptide (GIP) and of the β-microseminoprotein (MSMB) were significantly reduced, but that of the humanin like-1 (MTRNR2L1) was significantly increased.

CONCLUSION

These results underline that systemic insulin resistance is associated with remodeling of key intestinal functions. Moreover, these data indicate that small intestine metabolic dysfunction is accompanied with a local amplification of low-grade inflammatory process implicating several pathways. Genes identified in this study are potentially triggered throughout the development of intestinal metabolic abnormalities, which could contribute to dyslipidemia, a component of metabolic syndrome and diabetes.

The calcium-sensing receptor: A promising target for prevention of colorectal cancer

The inverse correlation between dietary calcium intake and the risk of colorectal cancer (CRC) is well known, but poorly understood. Expression of the calcium-sensing receptor (CaSR), a calcium-binding G protein-coupled receptor is downregulated in CRC leading us to hypothesize that the CaSR has tumor suppressive roles in the colon. The aim of this study was to understand whether restoration of CaSR expression could reduce the malignant phenotype in CRC. In human colorectal tumors, expression of the CaSR negatively correlated with proliferation markers whereas loss of CaSR correlated with poor tumor differentiation and reduced apoptotic potential. In vivo, dearth of CaSR significantly increased expression of proliferation markers and decreased levels of differentiation and apoptotic markers in the colons of CaSR/PTH double knock-out mice confirming the tumor suppressive functions of CaSR. In vitro CRC cells stably overexpressing wild-type CaSR showed significant reduction in proliferation, as well as increased differentiation and apoptotic potential. The positive allosteric modulator of CaSR, NPS R-568 further enhanced these effects, whereas treatment with the negative allosteric modulator, NPS 2143 inhibited these functions. Interestingly, the dominant-negative mutant (R185Q) was able to abrogate these effects. Our results demonstrate a critical tumor suppressive role of CaSR in the colon. Restoration of CaSR expression and function is linked to regulation of the balance between proliferation, differentiation, and apoptosis and provides a rationale for novel strategies in CRC therapy.

Colostrum whey down-regulates the expression of early and late inflammatory response genes induced byEscherichia coliandSalmonella entericaTyphimurium components in intestinal epithelial cells

Pathogenic invasion byEscherichia coliandSalmonellaeremains a constant threat to the integrity of the intestinal epithelium and can rapidly induce inflammatory responses. At birth, colostrum consumption exerts numerous beneficial effects on the properties of intestinal epithelial cells and protects the gastrointestinal tract of newborns from pathogenic invasion. The present study aimed to investigate the effect of colostrum on the early and late inflammatory responses induced by pathogens. The short-term (2 h) and long-term (24 h) effects of exposure to heat-killed (HK)E. coliandSalmonella entericaTyphimurium on gene expression in the porcine intestinal epithelial cell (IPEC-J2) model were first evaluated by microarray and quantitative PCR analyses. Luciferase assays were performed using a NF-κB-luc reporter construct to investigate the effect of colostrum whey treatment on the activation of NF-κB induced by HK bacteria. Luciferase assays were also performed using NF-κB-luc, IL-8-luc and IL-6-luc reporter constructs in human colon adenocarcinoma Caco-2/15 cells exposed to dose–response stimulations with HK bacteria and colostrum whey. Bovine colostrum whey treatment decreased the expression of early and late inflammatory genes induced by HK bacteria in IPEC-J2, as well as the transcriptional activation of NF-κB-luc induced by HK bacteria. Unlike that with colostrum whey, treatment with other milk fractions failed to decrease the activation of NF-κB-luc induced by HK bacteria. Lastly, the reduction of the HK bacteria-induced activation of NF-κB-luc, IL-8-luc and IL-6-luc by colostrum whey was dose dependent. The results of the present study indicate that bovine colostrum may protect and preserve the integrity of the intestinal mucosal barrier in the host by controlling the expression levels of early and late inflammatory genes following invasion by enteric pathogens.

A gene expression programme induced by bovine colostrum whey promotes growth and wound-healing processes in intestinal epithelial cells

Bovine colostrum is well known for its beneficial properties on health and development. It contains a wide variety of bioactive ingredients that are known to promote a number of cellular processes. Therefore the use of colostrum whey as a feed additive to promote intestinal health has been proposed, yet little is known about mechanisms implicated in its beneficial properties on intestinal epithelial cells. In the present paper, casein were removed from bovine colostrum and the remaining liquid, rich in bioactive compounds, was evaluated for its capacity to modulate cellular processes in porcine intestinal epithelial cell line IPEC-J2 and human colon adenocarcinoma cell line Caco-2/15. First, we verified the effect of colostrum whey and cheese whey on processes involved in intestinal wound healing, including cell proliferation, attachment, morphology and migration. Our results showed that colostrum whey promoted proliferation and migration, and decreased specifically the attachment of Caco-2/15 cells on the culture dish. On the other hand, cheese whey induced proliferation and morphological changes in IPEC-J2 cells, but failed to induce migration. The gene expression profile of IPEC-J2 cells following colostrum whey treatment was evaluated by microarray analysis. Results revealed that the expression of a significant number of genes involved in cell migration, adhesion and proliferation was indeed affected in colostrum whey-treated cells. In conclusion, colostrum specific bioactive content could be beneficial for intestinal epithelial cell homoeostasis by controlling biological processes implicated in wound healing through a precise gene expression programme.

Regulation of the calcium-sensing receptor expression by 1,25-dihydroxyvitamin D3, interleukin-6, and tumor necrosis factor alpha in colon cancer cells

Anti-proliferative effects of calcium in the colon are mediated, at least in part, via the calcium-sensing receptor (CaSR), a vitamin D target gene. The expression of CaSR decreases during colorectal tumor progression and the mechanisms regulating its expression are poorly understood. The CaSR promoter harbors vitamin D elements responsive to 1,25-dihydroxyvitamin D3 (1,25D3) and NF-κB, STAT, and SP1 binding sites accounting for responsiveness to proinflammatory cytokines. Therefore, in the current study we investigated the impact of 1,25D3, tumor necrosis factor alpha (TNFα), and interleukin (IL)-6 on CaSR expression in a differentiated (Caco2/AQ) and in a moderately differentiated (Coga1A) colon cancer cell line. 1,25D3 induced CaSR expression in both cell lines. Treatment with TNFα was accompanied by a 134-fold induction of CaSR in Coga1A (p<0.01). In Caco2/AQ cells the expression of CaSR was upregulated also by IL-6 (3.5-fold). Our data demonstrated transcriptional and translational activation of the CaSR by 1,25D3, TNFα, and IL-6 in a time- and cell line-dependent manner. This article is part of a Special Issue entitled '16th Vitamin D Workshop'.

Pathogenesis of human enterovirulent bacteria: lessons from cultured, fully differentiated human colon cancer cell lines

Hosts are protected from attack by potentially harmful enteric microorganisms, viruses, and parasites by the polarized fully differentiated epithelial cells that make up the epithelium, providing a physical and functional barrier. Enterovirulent bacteria interact with the epithelial polarized cells lining the intestinal barrier, and some invade the cells. A better understanding of the cross talk between enterovirulent bacteria and the polarized intestinal cells has resulted in the identification of essential enterovirulent bacterial structures and virulence gene products playing pivotal roles in pathogenesis. Cultured animal cell lines and cultured human nonintestinal, undifferentiated epithelial cells have been extensively used for understanding the mechanisms by which some human enterovirulent bacteria induce intestinal disorders. Human colon carcinoma cell lines which are able to express in culture the functional and structural characteristics of mature enterocytes and goblet cells have been established, mimicking structurally and functionally an intestinal epithelial barrier. Moreover, Caco-2-derived M-like cells have been established, mimicking the bacterial capture property of M cells of Peyer's patches. This review intends to analyze the cellular and molecular mechanisms of pathogenesis of human enterovirulent bacteria observed in infected cultured human colon carcinoma enterocyte-like HT-29 subpopulations, enterocyte-like Caco-2 and clone cells, the colonic T84 cell line, HT-29 mucus-secreting cell subpopulations, and Caco-2-derived M-like cells, including cell association, cell entry, intracellular lifestyle, structural lesions at the brush border, functional lesions in enterocytes and goblet cells, functional and structural lesions at the junctional domain, and host cellular defense responses.

Development of an epidermal growth factor derivative with EGFR blocking activity

The members of the epidermal growth factor (EGF)/ErbB family are prime targets for cancer therapy. However, the therapeutic efficiency of the existing anti-ErbB agents is limited. Thus, identifying new molecules that inactivate the ErbB receptors through novel strategies is an important goal on cancer research. In this study we have developed a shorter form of human EGF (EGFt) with a truncated C-terminal as a novel EGFR inhibitor. EGFt was designed based on the superimposition of the three-dimensional structures of EGF and the Potato Carboxypeptidase Inhibitor (PCI), an EGFR blocker previously described by our group. The peptide was produced in E. coli with a high yield of the correctly folded peptide. EGFt showed specificity and high affinity for EGFR but induced poor EGFR homodimerization and phosphorylation. Interestingly, EGFt promoted EGFR internalization and translocation to the cell nucleus although it did not stimulate the cell growth. In addition, EGFt competed with EGFR native ligands, inhibiting the proliferation of cancer cells. These data indicate that EGFt may be a potential EGFR blocker for cancer therapy. In addition, the lack of EGFR-mediated growth-stimulatory activity makes EGFt an excellent delivery agent to target toxins to tumours over-expressing EGFR.

Selective inhibition of the gliadin-specific, cell-mediated immune response by transamidation with microbial transglutaminase

CD is an immune-mediated enteropathy caused by the ingestion of wheat gluten. The modification of gluten by intestinal tTGase plays a crucial role in CD pathogenesis. In this study, we observed that extensive transamidation of wheat flour with K-C2H5 by mTGase yielded spf and K-gliadins fractions. By Western blot, we found that these modifications were associated with strongly reduced immune cross-reactivity. With the use of DQ8 tg mice as a model of gluten sensitivity, we observed a dramatic reduction in IFNγ production in gliadin-specific spleen cells challenged with spf and K-gliadins in vitro (n=12; median values: 813 vs. 29 and 99; control vs. spf and K-gliadins, P=0.012 for spf, and P=0.003 for K-gliadins). For spf, we also observed an increase in the IL-10/IFNγ protein ratio (n=12; median values: 0.3 vs. 4.7; control vs. spf, P=0.005). In intestinal biopsies from CD patients challenged in vitro with gliadins (n=10), we demonstrated further that K-gliadins dramatically reduced the levels of antigen-specific IFNγ mRNA in all specimens responsive to native gliadins (four of 10; P<0.05). As cytotoxic effects have been described for gliadins, we also studied GST and caspase-3 activities using the enterocytic Caco-2 cell line. We found that neither activities were modified by flour transamidation. Our results indicate that K-C2H5 cross-linking via mTGase specifically affects gliadin immunogenicity, reversing the inducible inflammatory response in models of gluten sensitivity without affecting other aspects of the biological activity of gliadins.

Insights into the pathogenesis of enteropathogenic E. coli using an improved intestinal enterocyte model

Enteropathogenic E. coli (EPEC) is a human pathogen that targets the small intestine, causing severe and often fatal diarrhoea in infants. A defining feature of EPEC disease is the loss (effacement) of absorptive microvilli (MV) from the surface of small intestinal enterocytes. Much of our understanding of EPEC pathogenesis is derived from studies using cell lines such as Caco-2 – the most extensively used small intestinal model. However, previous work has revealed fundamental differences between Caco-2 cells and in vivo differentiated enterocytes in relation to MV effacement. This, and the high heterogeneity and low transfection efficiency of the Caco-2 cell line prompted the isolation of several sub-clones (NCL-1–12) to identify a more tractable and improved in vivo-like cell model. Along with established Caco-2 clones (TC-7, BBE1), sub-clones were assessed for growth rate, apical surface morphology, epithelial barrier function and transfection efficiency. TC-7 cells provided the best all-round clone and exhibited highest levels of ectopic gene expression following cell polarisation. Novel alterations in EGFP-labelled mitochondria, that were not previously documented in non-polarised cell types, highlighted the potential of the TC-7 model for defining dynamic enterocyte-specific changes during infection. Crucially, the TC-7 cell line also mimicked ex vivo derived enterocytes with regard to MV effacement, enabling a better dissection of the process. Effacement activity caused by the EPEC protein Map in the Caco-2 but not ex vivo model, was linked to a defect in suppressing its Cdc42-dependent functionality. MV effacement activity of the EPEC protein EspF in the TC-7 model was dependent on its N-WASP binding motif, which is also shown to play an essential role in epithelial barrier dysfunction. Together, this study highlights the many advantages of using TC-7 cells as a small intestinal model to study host-pathogen interactions.

Glucose transporter 2 expression is down regulated following P2X7 activation in enterocytes

With the diabetes epidemic affecting the world population, there is an increasing demand for means to regulate glycemia. Dietary glucose is first absorbed by the intestine before entering the blood stream. Thus, the regulation of glucose absorption by intestinal epithelial cells (IECs) could represent a way to regulate glycemia. Among the molecules involved in glycemia homeostasis, extracellular ATP, a paracrine signaling molecule, was reported to induce insulin secretion from pancreatic β cells by activating P2Y and P2X receptors. In rat's jejunum, P2X7 expression was previously immunolocalized to the apex of villi, where it has been suspected to play a role in apoptosis. However, using an antibody recognizing the receptor extracellular domain and thus most of the P2X7 isoforms, we showed that expression of this receptor is apparent in the top two-thirds of villi. These data suggest a different role for this receptor in IECs. Using the non-cancerous IEC-6 cells and differentiated Caco-2 cells, glucose transport was reduced by more than 30% following P2X7 stimulation. This effect on glucose transport was not due to P2X7-induced cell apoptosis, but rather was the consequence of glucose transporter 2 (Glut2)'s internalization. The signaling pathway leading to P2X7-dependent Glut2 internalization involved the calcium-independent activation of phospholipase Cγ1 (PLCγ1), PKCδ, and PKD1. Although the complete mechanism regulating Glut2 internalization following P2X7 activation is not fully understood, modulation of P2X7 receptor activation could represent an interesting approach to regulate intestinal glucose absorption.

Src family kinase inhibitor PP2 accelerates differentiation in human intestinal epithelial cells

The proto-oncogene Src is an important protein tyrosine kinase involved in signaling pathways that control cell adhesion, growth, migration and survival. Here, we investigated the involvement of Src family kinases (SFKs) in human intestinal cell differentiation. We first observed that Src activity peaked in early stages of Caco-2/15 cell differentiation. Inhibition of SFKs with PP2, a selective SFK inhibitor, accelerated the overall differentiation program. Interestingly, all polarization and terminal differentiation markers tested, including sucrase-isomaltase, lactase-phlorizin hydrolase and E and Li-cadherins were found to be significantly up-regulated after only 3 days of treatment in the newly differentiating cells. Further investigation of the effects of PP2 revealed a significant up-regulation of the two main intestinal epithelial cell-specific transcription factors Cdx2 and HNF1α and a reduction of polycomb PRC2-related epigenetic repressing activity as measured by a decrease in H3K27me3, two events closely related to the control of cell terminal differentiation in the intestine. Taken together, these data suggest that SFKs play a key role in the control of intestinal epithelial cell terminal differentiation.

Modulatory role of PYY in transport and metabolism of cholesterol in intestinal epithelial cells

Background

Gastrointestinal peptides are involved in modulating appetite. Other biological functions attributed to them include the regulation of lipid homeostasis. However, data concerning PYY remain fragmentary. The objectives of the study were: (i) To determine the effect of PYY on intestinal transport and synthesis of cholesterol, the biogenesis of apolipoproteins (apos) and assembly of lipoproteins and (ii) To analyze whether the effects of PYY are similar according to whether cells are exposed to PYY on apical or basolateral surface.

Methodology/Principal Findings

Caco-2/15 cells were incubated with PYY (1–36) administered either to the apical or basolateral medium, at concentrations of 50 or 200 nM for 24 hours. De novo synthesis of cholesterol, cholesterol uptake, and assembly of lipoproteins were evaluated through the incorporation of [¹⁴C]-acetate, [¹⁴C]-cholesterol, and [¹⁴C]-oleate, respectively. Biogenesis of apos (A-I, A-IV, E, B-48 and B-100) was examined by the incorporation of [³⁵S]-methionine. The influence of PYY on protein and mRNA levels of many key mediators of lipid metabolism was analyzed by Western blot and PCR, respectively. Our results show that PYY influenced cholesterol metabolism in Caco-2/15 cells depending on the site of PYY delivery. Apical addition of PYY significantly lowered the incorporation of [¹⁴C]-cholesterol likely via the reduction of NPC1L1, stimulated intracellular cholesterol synthesis probably through an increase in SREBP-2 expression, whereas it concomitantly increased apo A-I synthesis and decreased LDL secretion. In contrast, basolateral PYY reduced the production of chylomicrons (CM) as well as the biogenesis of apos B-48 and B-100, while lowering the expression of the transcription factors RXRα and PPAR(α,β).

Conclusions/Significance

PYY is capable of influencing cholesterol homeostasis in intestinal Caco-2/15 cells depending on the site delivery. Apical PYY was able to decrease cholesterol uptake via NPC1L1 downregulation, whereas basolateral PYY diminished CM output through the biogenesis decline of apos B-48 and B-100.

Polycomb repressive complex 2 impedes intestinal cell terminal differentiation

The crypt-villus axis constitutes the functional unit of the small intestine, where mature absorptive cells are confined to the villi, and stem cells and transit amplifying and differentiating cells are restricted to the crypts. The polycomb group (PcG) proteins repress differentiation and promote self-renewal in embryonic stem cells. PcGs prevent transcriptional activity by catalysing epigenetic modifications, such as the covalent addition of methyl groups on histone tails, through the action of the polycomb repressive complex 2 (PRC2). Although a role for PcGs in the preservation of stemness characteristics is now well established, recent evidence suggests that they may also be involved in the regulation of differentiation. Using intestinal epithelial cell models that recapitulate the enterocytic differentiation programme, we generated a RNAi-mediated stable knockdown of SUZ12, which constitutes a cornerstone for PRC2 assembly and functionality, in order to analyse intestinal cell proliferation and differentiation. Expression of SUZ12 was also investigated in human intestinal tissues, revealing the presence of SUZ12 in most proliferative epithelial cells of the crypt and an increase in its expression in colorectal cancers. Moreover, PRC2 disruption led to a significant precocious expression of a number of terminal differentiation markers in intestinal cell models. Taken together, our data identified a mechanism whereby PcG proteins participate in the repression of the enterocytic differentiation program, and suggest that a similar mechanism exists in situ to slow down terminal differentiation in the transit amplifying cell population.

Anti-inflammatory effects of epidermal growth factor on the immature human intestine

The inflammatory response of the preterm infants' intestine underlines its inability to respond to hemodynamic stress, microbes, and nutrients. Recent evidence suggests that exogenous epidermal growth factor (EGF) exerts a therapeutic influence on neonatal enteropathies. However, the molecular mechanisms underlying the beneficial effects of EGF remain to be clarified. The purpose of this study was to evaluate the impact of EGF on the gene expression profiles of the developing human small and large intestine at midgestation in serum-free organ cultures using microarrays. The gene expression profiles of cultured human fetal ileal and colonic explants were investigated in the absence or presence of a physiological concentration of 50 ng/ml EGF for 48 h. Data were analyzed with the Ingenuity Pathway Analysis (IPA) software and confirmed by qPCR. We found a total of 6,474 differentially expressed genes in the two segments in response to EGF. IPA functional analysis revealed that in addition to differentially modulating distinct cellular, molecular, and physiological functions in the small and large intestine, EGF regulated the inflammatory response in both intestinal segments in a distinct manner. For instance, several intestinal-derived chemokines such as CCL2, CCL25, CXCL5, and CXCL10 were found to be differentially regulated by EGF in the immature ileum and colon. The findings showing the anti-inflammatory influence of exogenous EGF suggests a mechanistic basis for the beneficial effects of EGF on neonatal enteropathies. These results reinforce growing evidence that by midgestation, the human small intestine and colon rely on specific and distinct regulatory pathways.

Isolation, characterization, and culture of normal human intestinal crypt and villus cells

The intestinal epithelium is a highly dynamic tissue undergoing constant and rapid renewal. It consists of a functional villus compartment responsible for terminal digestion and nutrient absorption and a progenitor cell compartment located in the crypts that produce new cells. The mechanisms regulating cell proliferation in the crypt, their migration, and differentiation are still incompletely understood. Until recently, normal human intestinal cell models allowing the study of these mechanisms have been lacking. In our laboratory, using fetal human intestines obtained at mid-gestation, we have generated the first normal human intestinal epithelial crypt-like (HIEC) cell line and villus-like primary cultures of differentiated enterocytes (PCDE). In this chapter, we provide a detailed description of the methodologies used to generate and characterize these normal intestinal crypt and villus cell models.

Constitutive activation of the MEK/ERK pathway inhibits intestinal epithelial cell differentiation

The Ras/Raf/MEK/ERK cascade regulates intestinal epithelial cell proliferation. Indeed, while barely detectable in differentiated cells of the villi, ERK1/2-activated forms are detected in the nucleus of undifferentiated human intestinal crypt cells. In addition, we and others have reported that ERKs are selectively inactivated during enterocyte differentiation. However, whether inactivation of the ERK pathway is necessary for inhibition of both proliferation and induction of differentiation of intestinal epithelial cells is unknown. Human Caco-2/15 cells, undifferentiated crypt IEC-6 cells, and differentiating Cdx3-expressing IEC-6 cells were infected with retroviruses encoding either a hemagglutinin (HA)-tagged MEK1 wild type (wtMEK) or a constitutively active S218D/S222D MEK1 mutant (caMEK). Protein and gene expression was assessed by Western blotting, semiquantitative RT-PCR, and real-time PCR. Morphology was analyzed by transmission electron microscopy. We found that 1) IEC-6/Cdx3 cells formed multicellular layers after confluence and differentiated after 30 days in culture, as assessed by increased polarization, microvilli formation, expression of differentiation markers, and ERK1/2 inhibition; 2) while activated MEK prevented neither the inhibition of ERK1/2 activities nor the differentiation process in postconfluent Caco-2/15 cells, caMEK expression prevented ERK inhibition in postconfluent IEC-6/Cdx3 cells, thus leading to maintenance of elevated ERK1/2 activities; 3) caMEK-expressing IEC-6/Cdx3 cells exhibited altered multicellular structure organization, poorly defined tight junctions, reduced number of microvilli on the apical surface, and decreased expression of the hepatocyte nuclear factor 1α transcription factor and differentiation markers, namely apolipoprotein A-4, fatty acid-binding protein, calbindin-3, mucin 2, alkaline phosphatase, and sucrase-isomaltase; and 4) increased Cdx3 phosphorylation on serine-60 (S60) in IEC-6/Cdx3 cells expressing caMEK led to decreased Cdx2 transactivation potential. These results indicate that inactivation of the ERK pathway is required to ensure the full Cdx2/3 transcriptional activity necessary for intestinal epithelial cell terminal differentiation.

Collagen VI is a basement membrane component that regulates epithelial cell-fibronectin interactions

Collagen VI is a heterotrimer composed of three α chains (α1, α2, α3) widely expressed throughout various interstitial matrices. Collagen VI is also found near the basement membranes of many tissues where it serves as an anchoring meshwork. The aim of this study was to investigate the distribution and role of collagen VI at the epithelial-stromal interface in the intestine. Results showed that collagen VI is a bona fide epithelial basal lamina component and constitutes the major collagen type of epithelial origin in this organ. In vitro, collagen VI co-distributes with fibronectin. Targeted knockdown of collagen VI expression in intestinal epithelial cells was used to investigate its function. Depletion of collagen VI from the matrix led to a significant increase in cell spreading and fibrillar adhesion formation coinciding with an upregulation of fibronectin expression, deposition and organization as well as activation of myosin light chain phosphorylation by the myosin light chain kinase and Rho kinase dependent mechanisms. Plating cells deficient for collagen VI on collagen VI rescued the phenotype. Taken together, these data demonstrate that collagen VI is an important basal lamina component involved in the regulation of epithelial cell behavior most notably as a regulator of epithelial cell-fibronectin interactions.

The dual role of annexin II in targeting of brush border proteins and in intestinal cell polarity

Functional intestinal epithelium relies on complete polarization of enterocytes marked by the formation of microvilli and the accurate trafficking of glycoproteins to relevant membrane domains. Numerous transport pathways warrant the unique structural identity and protein/lipid composition of the brush border membrane. Annexin II (Ca(2+)-dependent lipid-binding protein) is an important component of one of the apical protein transport machineries, which involves detergent-resistant membranes and the actin cytoskeleton. Here, we investigate in intestinal Caco-2 cells the contribution of annexin II to the sorting and transport of brush border hydrolases and role in intestinal cell polarity. Downregulation of annexin II in Caco-2-A4 cell line results in a severe reduction of the levels of the brush border membrane resident enzyme sucrase isomaltase (SI) as well as structural components such as ezrin. This reduction is accompanied by a redistribution of these proteins to intracellular compartments and a striking morphological transition of Caco-2 cells to rudimentary epithelial cells that are characterized by an almost flat apical membrane with sparse and short microvilli. Concomitant with this alteration is the redistribution of the intermediate filament protein keratin 19 to the intracellular membranes in Caco-2-A4 cells. Interestingly, keratin 19 interacts with annexin II in wild type Caco-2 cells and this interaction occurs exclusively in lipid rafts. Our findings suggest a role for annexin II and K19 in differentiation and polarization of intestinal cells.

Lipophilic derivatives of leu-enkephalinamide: in vitro permeability, stability and in vivo nasal delivery

Leu-enkephalin is an endogenous pain modulating opioid pentapeptide. Its development as a potential pharmaceutic has been hampered by poor membrane permeability and susceptibility to enzymatic degradation. The addition of an unnatural amino acid containing a lipidic side chain at the N-terminus and the modification of the C-terminus to a carboxyamide was performed to enhance the nasal delivery of the peptide. Two lipidic derivatives with varying side chain lengths (C(8)-Enk-NH(2) (1), C(12)-Enk-NH(2) (2)) and their acetylated analogues were successfully synthesised. Caco-2 cell monolayer permeability and Caco-2 cell homogenate stability assays were performed. C(8)-Enk-NH(2) (1) and its acetylated analogue Ac-C8-Enk-NH(2) (3) exhibited apparent permeabilities (mean±SD) of 2.51±0.75×10(-6)cm/s and 1.06±0.62×10(-6), respectively. C12-Enk-NH(2) (2) exhibited an apparent permeability of 2.43±1.26×10(-6) cm/s while Ac-C12-Enk-NH(2) (4) was not permeable through the Caco-2 monolayers due to its poor solubility. All analogues exhibited improved Caco-2 homogenate stability compared to Leu-Enk-NH(2) with t(½) values of: C8-Enk-NH(2) (1): 31.7 min, C(12)-Enk-NH(2) (2): 14.7 min, Ac-C8-Enk-NH(2) (3): 83 min, Ac-C(12)-Enk-NH(2) (4): 27 min. However, plasma stability assays revealed that the diastereoisomers of C8-Enk-NH(2) (1) did not degrade at the same rate, with the l isomer (t(1/2)=8.9 min) degrading into Leu-enkephalinamide and then des-Tyr-Leu-Enk-NH(2), whereas the d isomer was stable (t(1/2)=120 min). In vivo nasal administration of C(8)-Enk-NH(2) to male rats resulted in concentrations of 5.9±1.84×10(-2) μM in the olfactory bulbs, 1.35±1.01×10(-2) μM in the brain and 6.53±1.87×10(-3) μM in the blood 10 min after administration.

Intestinal epithelial wound healing assay in an epithelial-mesenchymal co-culture system

Rapid and efficient healing of epithelial damage is critical to the functional integrity of the small intestine. Epithelial repair is a complex process that has largely been studied in cultured epithelium but to a much lesser extent in mucosa. We describe a novel method for the study of wound healing using a co-culture system that combined an intestinal epithelial Caco-2/15 cell monolayer cultured on top of human intestinal myofibroblasts, which together formed a basement membrane-like structure that contained many of the major components found at the epithelial-mesenchymal interface in the human intestine. To investigate the mechanism of restitution, small lesions were generated in epithelial cell monolayers on plastic or in co-cultures without disturbing the underlying mesenchymal layer. Monitoring of wound healing showed that repair was more efficient in Caco-2/15-myofibroblast co-cultures than in Caco-2/15 monolayers and involved the deposition of basement membrane components. Functional experiments showed that the addition of type I collagen or human fibronectin to the culture medium significantly accelerated wound closure on epithelial cell co-cultures. This system may provide a new tool to investigate the mechanisms that regulate wound healing in the intestinal epithelium.

The ethanol metabolite acetaldehyde increases paracellular drug permeability in vitro and oral bioavailability in vivo

Alcohol consumption leads to the production of the highly reactive ethanol metabolite, acetaldehyde, which may affect intestinal tight junctions and increase paracellular permeability. We examined the effects of elevated acetaldehyde within the gastrointestinal tract on the permeability and bioavailability of hydrophilic markers and drug molecules of variable molecular weight and geometry. In vitro permeability was measured unidirectionally in Caco-2 and MDCKII cell models in the presence of acetaldehyde, ethanol, or disulfiram, an aldehyde dehydrogenase inhibitor, which causes acetaldehyde formation when coadministered with ethanol in vivo. Acetaldehyde significantly lowered transepithelial resistance in cell monolayers and increased permeability of the low-molecular-weight markers, mannitol and sucrose; however, permeability of high-molecular-weight markers, polyethylene glycol and inulin, was not affected. In vivo permeability was assessed in male Sprague-Dawley rats treated for 6 days with ethanol, disulfiram, or saline alone or in combination. Bioavailability of naproxen was not affected by any treatment, whereas that of paclitaxel was increased upon acetaldehyde exposure. Although disulfiram has been shown to inhibit multidrug resistance-1 P-glycoprotein (P-gp) in vitro, our data demonstrate that the known P-gp substrate paclitaxel is not affected by coadministration of disulfiram. In conclusion, we demonstrate that acetaldehyde significantly modulates tight junctions and paracellular permeability in vitro as well as the oral bioavailability of low-molecular-weight hydrophilic probes and therapeutic molecules in vivo even when these molecules are substrates for efflux transporters. These studies emphasize the significance of ethanol metabolism and drug interactions outside of the liver.

Integrin-linked kinase regulates migration and proliferation of human intestinal cells under a fibronectin-dependent mechanism

Integrin-linked kinase (ILK) plays a role in integrin signaling-mediated extracellular matrix (ECM)–cell interactions and also acts as a scaffold protein in functional focal adhesion points. In the present study, we investigated the expression and roles of ILK in human intestinal epithelial cells (IECs) in vivo and in vitro. Herein, we report that ILK and its scaffold-function interacting partners, PINCH-1, α-parvin, and β-parvin, are expressed according to a decreasing gradient from the bottom of the crypt (proliferative/undifferentiated) compartment to the tip of the villus (non-proliferative/differentiated) compartment, closely following the expression pattern of the ECM/basement membrane component fibronectin. The siRNA knockdown of ILK in human IECs caused a loss of PINCH-1, α-parvin, and β-parvin expression, along with a significant decrease in cell proliferation via a loss of cyclin D1 and an increase in p27 and hypophosphorylated pRb expression levels. ILK knockdown severely affected cell spreading, migration, and restitution abilities, which were shown to be directly related to a decrease in fibronectin deposition. All ILK knockdown-induced defects were rescued with exogenously deposited fibronectin. Altogether, our results indicate that ILK performs crucial roles in the control of human intestinal cell and crypt–villus axis homeostasis—especially with regard to basement membrane fibronectin deposition—as well as cell proliferation, spreading, and migration. J. Cell. Physiol. 222: 387–400, 2010. © 2009 Wiley-Liss, Inc.

Intestinal epithelial cancer cell anoikis resistance: EGFR-mediated sustained activation of Src overrides Fak-dependent signaling to MEK/Erk and/or PI3-K/Akt-1

Herein, we investigated the survival roles of Fak, Src, MEK/Erk, and PI3-K/Akt-1 in intestinal epithelial cancer cells (HCT116, HT29, and T84), in comparison to undifferentiated and differentiated intestinal epithelial cells (IECs). We report that: (1) cancer cells display striking anoikis resistance, as opposed to undifferentiated/differentiated IECs; (2) under anoikis conditions and consequent Fak down-activation, cancer cells nevertheless exhibit sustained Fak-Src interactions and Src/MEK/Erk activation, unlike undifferentiated/differentiated IECs; however, HCT116 and HT29 cells exhibit a PI3-K/Akt-1 down-activation, as undifferentiated/differentiated IECs, whereas T84 cells do not; (3) cancer cells require MEK/Erk for survival, as differentiated (but not undifferentiated) IECs; however, T84 cells do not require Fak and HCT116 cells do not require PI3-K/Akt-1, in contrast to the other cells studied; (4) Src acts as a cornerstone in Fak-mediated signaling to MEK/Erk and PI3-K/Akt-1 in T84 cells, as in undifferentiated IECs, whereas PI3-K/Akt-1 is Src-independent in HCT116, HT29 cells, as in differentiated IECs; and (5) EGFR activity inhibition abrogates anoikis resistance in cancer cells through a loss of Fak-Src interactions and down-activation of Src/MEK/Erk (T84, HCT116, HT29 cells) and PI3-K/Akt-1 (T84 cells). Hence, despite distinctions in signaling behavior not necessarily related to undifferentiated or differentiated IECs, intestinal epithelial cancer cells commonly display an EGFR-mediated sustained activation of Src under anoikis conditions. Furthermore, such sustained Src activation confers anoikis resistance at least in part through a consequent sustenance of Fak-Src interactions and MEK/Erk activation, thus not only overriding Fak-mediated signaling to MEK/Erk and/or PI3-K/Akt-1, but also the requirement of Fak and/or PI3-K/Akt-1 for survival.

Integrin alpha8beta1 regulates adhesion, migration and proliferation of human intestinal crypt cells via a predominant RhoA/ROCK-dependent mechanism

Background. Integrins are transmembrane αβ heterodimer receptors that function as structural and functional bridges between the cytoskeleton and ECM (extracellular matrix) molecules. The RGD (arginine-glycine-aspartate tripeptide motif)-dependent integrin α8β1 has been shown to be involved in various cell functions in neuronal and mesenchymal-derived cell types. Its role in epithelial cells remains unknown.

Results. Integrin α8β1 was found to be expressed in the crypt cell population of the human intestine but was absent from differentiating and mature epithelial cells of the villus. The function of α8β1 in epithelial crypt cells was investigated at the cellular level using normal HIECs (human intestinal epithelial cells). Specific knockdown of α8 subunit expression using an shRNA (small-hairpin RNA) approach showed that α8β1 plays important roles in RGD-dependent cell adhesion, migration and proliferation via a RhoA/ROCK (Rho-associated kinase)-dependent mechanism as demonstrated by active RhoA quantification and pharmacological inhibition of ROCK. Moreover, loss of α8β1, through RhoA/ROCK, impairs FA (focal adhesion) complex integrity as demonstrated by faulty vinculin recruitment.

Conclusions. Integrin α8β1 is expressed in epithelial cells. In intestinal crypt cells, α8β1 is closely involved in the regulation of adhesion, migration and cell proliferation via a predominant RhoA/ROCK-dependent mechanism. These results suggest an important role for this integrin in intestinal crypt cell homoeostasis.

Integrin alpha6Bbeta4 inhibits colon cancer cell proliferation and c-Myc activity

BACKGROUND

Integrins are known to be important contributors to cancer progression. We have previously shown that the integrin beta4 subunit is up-regulated in primary colon cancer. Its partner, the integrin alpha6 subunit, exists as two different mRNA splice variants, alpha6A and alpha6B, that differ in their cytoplasmic domains but evidence for distinct biological functions of these alpha6 splice variants is still lacking.

METHODS

In this work, we first analyzed the expression of integrin alpha6A and alpha6B at the protein and transcript levels in normal human colonic cells as well as colorectal adenocarcinoma cells from both primary tumors and established cell lines. Then, using forced expression experiments, we investigated the effect of alpha6A and alpha6B on the regulation of cell proliferation in a colon cancer cell line.

RESULTS

Using variant-specific antibodies, we observed that alpha6A and alpha6B are differentially expressed both within the normal adult colonic epithelium and between normal and diseased colonic tissues. Proliferative cells located in the lower half of the glands were found to predominantly express alpha6A, while the differentiated and quiescent colonocytes in the upper half of the glands and surface epithelium expressed alpha6B. A relative decrease of alpha6B expression was also identified in primary colon tumors and adenocarcinoma cell lines suggesting that the alpha6A/alpha6B ratios may be linked to the proliferative status of colonic cells. Additional studies in colon cancer cells showed that experimentally restoring the alpha6A/alpha6B balance in favor of alpha6B caused a decrease in cellular S-phase entry and repressed the activity of c-Myc.

CONCLUSION

The findings that the alpha6Bbeta4 integrin is expressed in quiescent normal colonic cells and is significantly down-regulated in colon cancer cells relative to its alpha6Abeta4 counterpart are consistent with the anti-proliferative influence and inhibitory effect on c-Myc activity identified for this alpha6Bbeta4 integrin. Taken together, these findings point out the importance of integrin variant expression in colon cancer cell biology.

Hepatocyte nuclear factor 4alpha contributes to an intestinal epithelial phenotype in vitro and plays a partial role in mouse intestinal epithelium differentiation

Hepatocyte nuclear factor 4alpha (HNF4alpha) is a regulator of hepatocyte and pancreatic transcription. Hnf4alpha deletion in the mouse is embryonically lethal with severe defects in visceral endoderm formation. It has been concluded in the past that the role of Hnf4alpha in the developing colon was much less important than in the liver. However, the precise role of Hnf4alpha in the homeostasis of the small intestinal epithelium remains unclear. Our aim was to evaluate the potential of Hnf4alpha to support an intestinal epithelial phenotype. First, Hnf4alpha potential to dictate this phenotype was assessed in nonintestinal cell lines in vitro. Forced expression of Hnf4alpha in fibroblasts showed an induction of features normally restricted to epithelial cells. Combinatory expression of Hnf4alpha with specific transcriptional regulators of the intestine resulted in the induction of intestinal epithelial genes in this context. Second, the importance of Hnf4alpha in maintaining the homeostasis of the intestinal epithelium was investigated in mice. Mice conditionally deficient for intestinal Hnf4alpha developed normally throughout adulthood with an epithelium displaying normal morphological and functional structures with minor alterations. Subtle but statistical differences were observed at the proliferation and the cytodifferentiation levels. Hnf4alpha mutant mice displayed an increase in the number of goblet and enteroendocrine cells compared with controls. Given the fundamental role of this transcription factor in other tissues, these findings dispute the crucial role for this regulator in the maintenance of intestinal epithelial cell function at a period of time that follows cytodifferentiation but may suggest a functional role in instructing cells to become specific to the intestinal epithelium.