Extracellular matrix components and integrins in relationship to human intestinal epithelial cell differentiation

Collagen IV regulates Caco-2 cell spreading and p130Cas phosphorylation by FAK-dependent and FAK-independent pathways

We previously observed that collagen IV regulates Caco-2 intestinal epithelial cell spreading and migration via Src-dependent p130(Cas) phosphorylation and stimulates focal adhesion kinase (FAK). However, the role of FAK and the related kinase, Pyk2, in Caco-2 spreading and migration is unclear. FAK- or Pyk2-specific siRNAs reduced protein levels by 90%. However, when detached cells were replated on collagen IV neither individual nor combined FAK and Pyk2 siRNAs affected the cell spreading rate. As combined FAK and Pyk2 siRNAs increased p130(Cas) protein levels, we cotransfected cells with 1 nm p130(Cas) siRNA to partially reduce p130(Cas) protein to control levels. Although p130(Cas) Tyr(P)(249) phosphorylation was reduced by 60%, cell spreading was unaffected. Combined siRNA reduction of FAK, Pyk2 and p130(Cas) increased cell spreading by 20% compared to p130(Cas) siRNA alone, suggesting that FAK and Pyk2 negatively regulate spreading in addition to stimulating spreading via p130(Cas). FAK-binding mutant SH3 domain-deleted rat p130(Cas) was not phosphorylated after adhesion and, unlike full-length p130(Cas), did not restore spreading after human-specific p130(Cas) siRNA knockdown of endogenous p130(Cas). Together, these data suggest that FAK positively regulates Caco-2 spreading on collagen IV via p130(Cas) phosphorylation, but also suggests that FAK may negatively regulate spreading through other mechanisms and the presence of additional FAK-independent pathways regulating p130(Cas).

Laminins in the developing and adult human small intestine: relation with the functional absorptive unit

The expression of the five laminin alpha-chains was analyzed in the developing and mature human small intestine at the protein and transcript levels in order to further delineate specific involvement of individual laminins in relation to the epithelial cell state as defined along the functional crypt-villus axis. The results show that all of the alpha-laminin transcripts are expressed in significant amounts in the small intestine relative to a panel of other tissues and organs. Further analysis of their expression by indirect immunofluorescence and semi-quantitative and quantitative RT-PCR demonstrates a close correlation between transcript and protein expression, distinct epithelial and mesenchymal origins, as well as differential occurrence in intestinal basement membranes according to developmental stage, along the crypt-villus axis and in compartment-related experimental intestinal cell models. Taken together, the data point out the prime importance of alpha2-, alpha3-, and alpha5-containing laminins for the development and maintenance of the functional human intestinal epithelium.

Hepatocyte nuclear factor 4alpha is essential for embryonic development of the mouse colon

BACKGROUND & AIMS

Hepatocyte nuclear factor 4 alpha (HNF4alpha) is a transcription factor that has been shown to be required for hepatocyte differentiation and development of the liver. It has also been implicated in regulating expression of genes that act in the epithelium of the lower gastrointestinal tract. This implied that HNF4alpha might be required for development of the gut.

METHODS

Mouse embryos were generated in which Hnf4a was ablated in the epithelial cells of the fetal colon by using Cre-loxP technology. Embryos were examined by using a combination of histology, immunohistochemistry, DNA microarray, reverse-transcription polymerase chain reaction, electrophoretic mobility shift assays, and chromatin immunoprecipitation analyses to define the consequences of loss of HNF4alpha on colon development.

RESULTS

Embryos were recovered at E18.5 that lacked HNF4alpha in their colons. Although early stages of colonic development occurred, HNF4alpha-null colons failed to form normal crypts. In addition, goblet-cell maturation was perturbed and expression of an array of genes that encode proteins with diverse roles in colon function was disrupted. Several genes whose expression in the colon was dependent on HNF4alpha contained HNF4alpha-binding sites within putative transcriptional regulatory regions and a subset of these sites were occupied by HNF4alpha in vivo.

CONCLUSIONS

HNF4alpha is a transcription factor that is essential for development of the mammalian colon, regulates goblet-cell maturation, and is required for expression of genes that control normal colon function and epithelial cell differentiation.

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

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

Laminin-5-integrin interaction signals through PI 3-kinase and Rac1b to promote assembly of adherens junctions in HT-29 cells

Human intestinal cell differentiation is mediated by signaling pathways that remain largely undefined. We and others have shown that cell migration and differentiation along the crypt-villus axis is associated with temporal and spatial modulations of the repertoire, as well as with the function of integrins and E-cadherins and their substrates. Cross-talk between integrin and cadherin signaling was previously described and seems to coordinate this differentiation process. Here, we report that engagement of alpha6 and, to a lesser extent, alpha3 integrin subunits after HT-29 cell adhesion on laminin 5 increases the expression of E-cadherin, which then organizes into nascent adherens junctions. We further identify that phosphoinositide 3-kinase (PI 3-kinase) activation plays a key role in this cross-talk. Indeed, integrin-dependent adhesion on laminin 5 stimulates PI 3-kinase activity. Immunofluorescence and immunoprecipitation experiments revealed that activated PI 3-kinase is recruited at cell-cell contacts. Using LY294002, an inhibitor of PI 3-kinase activity, we found that this activation is essential for E-cadherin connection with the cytoskeleton and for biogenesis of adherens junctions. Finally, we demonstrated that PI 3-kinase could signal through Rac1b activation to control adherens junction assembly. Our results provide a mechanistic insight into integrin-cadherin cross-talk and identify a novel role for PI 3-kinase in the establishment of adherens junctions.

p130cas but not paxillin is essential for Caco-2 intestinal epithelial cell spreading and migration on collagen IV

We have previously observed that collagen IV regulates Caco-2 intestinal epithelial cell spreading and migration via Src kinase and stimulates Src-dependent tyrosine phosphorylation of p130cas. We observed that collagen IV also stimulated Src-dependent phosphorylation of both paxillin Tyr31 and paxillin Tyr118. Caco-2 transfection with paxillin or p130cas siRNAs inhibited expression of these proteins by more than 90% for at least 5 days after transfection. Although p130cas siRNA inhibited cell spreading on collagen IV by 33%, three different paxillin siRNAs did not inhibit cell spreading. p130cas siRNA did not affect Src Tyr416 or Src Tyr527 phosphorylation, FAK Tyr397 phosphorylation, or Src-dependent phosphorylation of FAK Tyr925, suggesting that p130cas did not inhibit cell spreading by altering FAK or Src activity. Rat p130cas expression after siRNA knock-out of endogenous human p130cas in Caco-2 cells reduced cell spreading inhibition by 71%. In contrast, expression of rat p130cas from which the Src-phosphorylated substrate domain was deleted did not rescue siRNA inhibition of cell spreading. Combined treatment with siRNAs to Crk and CrkL, which bind to the p130cas substrate domain, inhibited cell spreading by 54%. Both p130cas siRNA and the combined Crk/CrkL siRNAs strongly inhibited (52 and 46% inhibition, respectively) Caco-2 sheet migration on collagen IV and noticeably inhibited lamellipodial extension, whereas paxillin siRNA only inhibited migration by 18% and did not noticeably affect lamellipodial extension. These results suggest that Src may regulate Caco-2 migration on collagen IV via both p130cas and paxillin but that Src phosphorylation of p130cas is more important for this process.

Gene therapy for barrett's esophagus: adenoviral gene transfer in different intestinal models

Adenoviral gene therapy could potentially be used for treatment of patients with a Barrett's esophagus. In order to study the feasibility of this approach it is important to study adenoviral intestinal transduction both in vitro and in vivo. In the present study, we used differentiating Caco-2 cells, closed intestinal loops and a Barrett's esophagus rat model to test transduction of adenoviruses expressing green fluorescent protein. We observed a decreased adenoviral transduction from 18.6 to 2.3% in undifferentiated and differentiated Caco-2 cells, respectively. This could be improved by the use of the mucolytic agent N-acetylcysteine (NAC) and the polycation diethylaminoethyl-dextran (DEAE-dextran), which improved transduction in differentiated cells five- and ten-fold, respectively. Also an RGD-retargeted adenovirus showed an improved transduction in differentiated cells. In closed intestinal loops adenoviral transduction was limited and the use of NAC and DEAE-dextran or RGD targeting had little effect. The Barrett's esophagus rat model consisted of an esophagojejunostomy, which results in a Barrett's esophagus and esophageal tumors within 6 months. Adenoviral transduction in this model was limited and mainly localized in the basal layer of normal esophagus and stromal tissue of a Barrett's segment. We conclude that although the adenovirus shows promising results in vitro, the current adenoviral vectors are probably not suitable for patients with Barrett's esophagus.

ADAM-15 inhibits wound healing in human intestinal epithelial cell monolayers

The disintegrin metalloproteases (or ADAMs) are membrane-anchored glycoproteins that have been implicated in cell-cell or cell-matrix interactions and in proteolysis of molecules on the cell surface. The expression and/or the pathophysiological implications of ADAMs are not known in intestinal epithelial cells. Therefore, our aim was to investigate the expression and the role of ADAMs in intestinal epithelial cells. Expression of ADAMs was assessed by RT-PCR, Western blot analysis, and immunufluorescence experiments. Wound-healing experiments were performed by using the electric cell substrate impedence sensing technology. Our results showed that ADAMs-10, -12, and -15 mRNA are expressed in the colonic human cell lines Caco2-BBE and HT29-Cl.19A. An ADAM-15 complementary DNA cloned from Caco2-BBE poly(A)+ RNA, and encompassing the entire coding region, was found to be shorter and to present a different region encoding the cytoplasmic tail compared with ADAM-15 sequence deposited in the database. In Caco2-BBE cells and colonic epithelial cells, ADAM-15 protein was found in the apical, basolateral, and intracellular compartments. We also showed that the overexpression of ADAM-15 reduced cell migration in a wound-healing assay in Caco2-BBE monolayers. Our data show that 1) ADAM-15 is expressed in human intestinal epithelia, 2) a new variant of ADAM-15 is expressed in a human intestinal epithelial cell line, and 3) ADAM-15 is involved in intestinal epithelial cells wound-healing processes. Together, these results suggest that ADAM-15 may have important pathophysiological roles in intestinal cells.

Early loss of E-cadherin from cell-cell contacts is involved in the onset of Anoikis in enterocytes

Anoikis, i.e. apoptosis induced by detachment from the extracellular matrix, is thought to be involved in the shedding of enterocytes at the tip of intestinal villi. Mechanisms controlling enterocyte survival are poorly understood. We investigated the role of E-cadherin, a key protein of cell-cell adhesion, in the control of anoikis of normal intestinal epithelial cells, by detaching murine villus epithelial cells from the underlying basement membrane while preserving cell-cell interactions. We show that upon the loss of anchorage, normal enterocytes execute a program of apoptosis within minutes, via a Bcl-2-regulated and caspase-9-dependent pathway. E-cadherin is lost early from cell-cell contacts. This process precedes the execution phase of detachment-induced apoptosis as it is only weakly modulated by Bcl-2 overexpression or caspase inhibition. E-cadherin loss, however, is efficiently prevented by lysosome and proteasome inhibitors. We also found that a blocking anti-E-cadherin antibody increases the rate of anoikis, whereas the activation of E-cadherin using E-cadherin-Fc chimera proteins reduces anoikis. In conclusion, our results stress the striking sensitivity of normal enterocytes to the loss of anchorage and the contribution of E-cadherin to the control of their survival/apoptosis balance. They open new perspectives on the key role of this protein, which is dysregulated in the intestinal epithelium in both inflammatory bowel disease and cancer.

Protein kinase C-alpha phosphorylation of specific serines in the connecting segment of the beta 4 integrin regulates the dynamics of type II hemidesmosomes

Although the regulation of hemidesmosome dynamics during processes such as epithelial migration, wound healing, and carcinoma invasion is important, the mechanisms involved are poorly understood. The integrin alpha 6 beta 4 is an essential component of the hemidesmosome and a target of such regulation. Epidermal growth factor (EGF) can induce hemidesmosome disassembly by a mechanism that involves serine phosphorylation of the beta 4 integrin subunit. Using a combination of biochemical and mutational analyses, we demonstrate that EGF induces the phosphorylation of three specific serine residues (S(1356), S(1360), and S(1364)) located within the connecting segment of the beta 4 subunit and that phosphorylation on these residues accounts for the bulk of beta 4 phosphorylation stimulated by EGF. Importantly, phosphorylation of these serines is critical for the ability of EGF to disrupt hemidesmosomes. Using COS-7 cells, which assemble hemidesmosomes type II upon exogenous expression of the alpha 6 beta 4 integrin, we observed that expression of a beta 4 construct containing Ser-->Ala mutations of S(1356), S(1360), and S(1364) reduced the ability of EGF to disrupt hemidesmosomes and that this effect appears to involve cooperation among these phosphorylation sites. Moreover, expression of Ser-->Asp mutants that mimic constitutive phosphorylation reduced hemidesmosome formation. Protein kinase C-alpha (PKC-alpha) is the kinase responsible for phosphorylating at least two of these serines, based on in vitro kinase assays, peptide mapping, and mutational analysis. Together, these results highlight the importance of serine phosphorylation in regulating type II hemidesmosome disassembly, implicate a cluster of serine residues within the connecting segment of beta 4, and argue for a key role for PKC-alpha in regulating these structures.

Collagen IV regulates Caco-2 migration and ERK activation via alpha1beta1- and alpha2beta1-integrin-dependent Src kinase activation

Our previous work indicates intestinal epithelial cell ERK activation by collagen IV, a major component of the intestinal epithelial basement membrane, requires focal adhesion kinase (FAK) and suggests FAK and ERK may have important roles in regulating intestinal epithelial cell migration. We therefore sought to identify FAK downstream targets regulating intestinal epithelial cell spreading, migration, and ERK activation on collagen IV and the integrins involved. Both dominant-negative Src and Src inhibitor PP2 strongly inhibited collagen IV ERK activation in Caco-2 intestinal epithelial cells. Collagen IV stimulated Grb2 binding site FAK Y925 phosphorylation, which was inhibited by PP2 and required FAK Y397 autophosphorylation. Additionally, FAK Y925F expression blocked collagen IV ERK activation. alpha(1)beta(1)- Or alpha(2)beta(1)-integrin blockade with alpha(1)- or alpha(2)-integrin subunit antibodies indicated that either integrin can mediate adhesion, cell spreading, and FAK, Src, and ERK activation on collagen IV. Both dominant-negative Src and PP2 inhibited Caco-2 spreading on collagen IV. PP2 inhibited p130(Cas) tyrosine phosphorylation, but dominant-negative p130(Cas) did not inhibit cell spreading. PP2 inhibited Caco-2 migration on collagen IV much more strongly than the mitogen-activated protein kinase kinase inhibitor PD-98059, which completely inhibited collagen IV ERK activation. These results suggest a pathway for collagen IV ERK activation requiring Src phosphorylation of FAK Y925 not previously described for this matrix protein and suggest either alpha(1)beta(1)- or alpha(2)beta(1)-integrins can regulate Caco-2 spreading and ERK activation on collagen IV via Src. Additionally, these results suggest Src regulates Caco-2 migration on collagen IV primarily through ERK-independent pathways.

Enterophilin-1 Interacts with Focal Adhesion Kinase and Decreases β1 Integrins in Intestinal Caco-2 Cells

Intestinal cell growth and differentiation are tightly regulated by growth factors and extracellular matrix components along the crypt-villus axis. We previously described enterophilin-1 (Ent-1) as a new intestinal protein associated with growth arrest and enterocyte differentiation. Ent-1 interacted with sorting nexin 1 and decreased cell surface epidermal growth factor receptor. Because beta(1) integrins are mostly found in vivo in the proliferative crypt cells, we investigated the role of Ent-1 in the fate of beta(1) integrin subunits. In undifferentiated intestinal Caco-2 cells, overexpression of Ent-1 induces a marked decrease of alpha(5)beta(1) integrin pools, whereas alpha(2)beta(1) integrin is weakly affected. Conversely, overexpression of sorting nexin 1 has no effect on integrin levels despite its ability to interact with Ent-1. Interestingly, we identified focal adhesion kinase as a new Ent-1 partner using yeast two-hybrid screening and co-precipitation experiments. Furthermore by confocal microscopy, we observed that Ent-1 and beta(1) integrins partly co-localize on vesicular structures, suggesting a role for Ent-1 in integrin trafficking. Because focal adhesion kinase is able to bind both Ent-1 and beta(1) integrins, the kinase might act as a molecular bridge between the two proteins. Altogether, these results support a role of Ent-1 in regulating beta(1) integrin expression that could favor intestinal differentiation.

Kruppel-like factors regulate the Lama1 gene encoding the laminin alpha1 chain

Laminin-1 (alpha1beta1gamma1), a basement membrane (BM) constituent, has been associated with differentiation processes and also with malignant progression. In the intestinal tissue, the alpha1 chain is expressed and secreted in the subepithelial BM during the developmental period; in the adult rodent tissue, it is restricted to the BM of the dividing cells. To understand how laminin alpha1 chain expression is regulated, we cloned and characterized a 2-kb promoter region of the Lama1 mouse gene. Analysis of the promoter was conducted in the Caco2-TC7 intestinal epithelial cells by transient transfection of serially deleted and site-directed mutated promoter constructs, by electrophoretic mobility shift assays, and expression of selected transcription factors. We determined that a proximal region, which includes an Sp1-binding GC box and a Krüppel-like element, was important for the promoter activity. This region is conserved between the human and mouse genes. Interestingly, two Krüppel-like factors KLF4 and KLF5 exhibit opposing effects on the Lama1 promoter activity that are decreased and increased, respectively, in the intestinal epithelial cells. These data corroborate the complementary expression of KLF4 and KLF5 along the intestinal crypt-villus axis and the parallel expression of KLF5 and laminin alpha1 chain in the crypt region. Finally, we showed that glucocorticoids stimulate the promoter activity. This study is the first characterization of the Lama1 promoter; we identified regulatory elements that may account for the expression pattern of the endogenous protein in the mouse intestine.

Fibronectin blocks p38 and jnk activation by cyclic strain in Caco-2 cells

Diverse repetitive forces deform the intestinal epithelium and basement membrane. Such repetitive deformation induces intestinal epithelial proliferation, differentiation, and intracellular signaling. Although at least some deformation-induced signals probably involve integrins, the matrix-dependence of these signals is poorly understood. We compared rapid strain activation of p38 and jnk in human Caco-2 intestinal epithelial cells cultured on collagen I, collagen IV, laminin, and tissue fibronectin. These signals were inhibited in cells on a fibronectin substrate, but activated by strain on collagens and laminin. Furthermore, adding 300 microg/ml plasma fibronectin (approximately the concentration found in plasma) to the culture medium inhibited strain activation of p38 and jnk in cells cultured on collagen. Since tissue and plasma fibronectin levels vary in acute or chronic inflammatory or infectious conditions, these results suggest that tissue or plasma fibronectin may modulate the intestinal epithelial response to repetitive deformation.

Regulation of the intestinal epithelial response to cyclic strain by extracellular matrix proteins

Repetitive mechanical deformation may stimulate intestinal epithelial proliferation. Because the extracellular matrix modulates static intestinal epithelial biology, we examined whether matrix proteins influence intestinal epithelial responses to deformation. Human Caco-2BBE cells and nontransformed human enterocytes (HIPEC) were subjected to 10% average cyclic strain at 10 cycles/min on flexible membranes precoated with matrix proteins without or with plasma fibronectin or functional anti-integrin antibodies in the medium. Strain stimulated proliferation, focal adhesion kinase, extracellular signal-regulated protein kinase (ERK), p38, and Jun N-terminal kinase similarly on collagen I or IV, and more weakly on laminin, but had no effect on fibronectin. MEK blockade (PD98059) prevented strain-stimulated proliferation on collagen but did not affect proliferation on fibronectin. Adding tissue fibronectin to a collagen substrate or plasma fibronectin to the media suppressed strain s mitogenic and signal effects, but not those of epidermal growth factor. Functional antibodies to the alpha5 or alpha(v) integrin subunit blocked strain's effects on Caco-2 proliferation and ERK activation, although ligation of the alpha2 or alpha6 subunit did not. Repetitive strain also stimulated, and fibronectin inhibited, human intestinal primary epithelial cell proliferation. Repetitive deformation stimulates transformed and nontransformed human intestinal epithelial proliferation in a matrix-dependent manner. Tissue or plasma fibronectin may regulate the intestinal epithelial response to strain via integrins containing alpha5 or alpha(v).

The alpha2 and alpha3 integrins are required for morphologic differentiation of an intestinal epithelial cell line

BACKGROUND

The molecular mechanisms controlling intestinal epithelial cell differentiation are poorly defined because of the difficulty of growing normal intestinal cells. We have taken advantage of the ability of the Caco-2 cell line to acquire a glandular phenotype in 3-dimensional (3-D) culture systems to investigate the role of alpha2 and alpha3 integrins in morphologic differentiation.

METHODS

Caco-2 cells transfected with sense or antisense DNA constructs of alpha2 or alpha3 integrins were grown in 3-D Matrigel or collagen I in the presence or absence of integrin function-blocking antibodies. We used light and confocal microscopy, BrDU incorporation, TUNEL assay, a fluorometric adhesion assay, FACS analysis, and Western blot analysis to study the effect of extracellular matrix (ECM) and integrins on morphology, polarization, proliferation, apoptosis, cell adhesion, and integrin expression.

RESULTS

Compared to collagen I, Caco-2 cells cultured in 3-D Matrigel display cytoskeletal and adherens junction rearrangements and decreased proliferation consistent with cellular differentiation. These changes, which are inhibited by alpha2 and alpha3 blocking monoclonal antibodies and alpha2 and alpha3 antisense DNA transfection, were associated with an increase in alpha3 integrin expression.

CONCLUSIONS

We demonstrated that signaling through both constitutively expressed alpha2 integrin and Matrigel-induced alpha3 integrin expression is required to acquire a differentiated phenotype in Caco-2 cells.

Changes in epithelial cell turnover and extracellular matrix in human small intestine after TPN

BACKGROUND

The atrophy and architectural remodeling of the jejunal mucosa arising in adults receiving total parenteral nutrition (TPN) has been suggested to originate from a disturbance in tissue homeostasis. The present study aims at examining (1) whether there are differences in proliferation and apoptosis of epithelial cells between enterally and parenterally nourished patients and (2) whether the distribution pattern of extracellular matrix (ECM) proteins known to influence cell turnover along the the crypt-villus axis is changed after TPN.

METHODS

The mitotic frequency and the proliferation index [using an antibody against Ki-67 antigen (MIB 1)] were determined on epoxy semithin and paraffin sections, respectively. Morphological techniques and the TUNEL assay were applied to detect apoptotic events. Immunolocalization of collagen IV, laminin, fibronectin, tenascin, and collagen VI was performed on cryosections.

RESULTS

After TPN the cell renewal was significantly enhanced, while epithelial cell death was drastically reduced. The comparison of TPN and EN patients revealed differences in the distribution patterns of the ECM proteins laminin, fibronectin, and tenascin along the crypt-villus axis. Moreover, after TPN an increased expression of collagen types IV and VI was observed.

CONCLUSIONS

TPN in human adults is associated with alterations in epithelial cell turnover and changes in expression and/or localization of ECM proteins. Thus, the inverted route of nutrient supply in patients might modify environmental tissue conditions, which may influence the interactions between intestinal epithelial cells and the extracellular matrix.

Neurogenin 3 is essential for the proper specification of gastric enteroendocrine cells and the maintenance of gastric epithelial cell identity

The notch signaling pathway is essential for the endocrine cell fate in various tissues including the enteroendocrine system of the gastrointestinal tract. Enteroendocrine cells are one of the four major cell types found in the gastric epithelium of the glandular stomach. To understand the molecular basis of enteroendocrine cell development, we have used gene targeting in mouse embryonic stem cells to derive an EGFP-marked null allele of the bHLH transcription factor, neurogenin 3 (ngn3). In ngn3(-/-) mice, glucagon secreting A-cells, somatostatin secreting D-cells, and gastrin secreting G-cells are absent from the epithelium of the glandular stomach, whereas the number of serotonin-expressing enterochromaffin (EC) cells is decreased dramatically. In addition, ngn3(-/-) mice display intestinal metaplasia of the gastric epithelium. Thus, ngn3 is required for the differentiation of enteroendocrine cells in the stomach and the maintenance of gastric epithelial cell identity.

Inactivation of the transcription factor Elf3 in mice results in dysmorphogenesis and altered differentiation of intestinal epithelium

BACKGROUND & AIMS

The mammalian small intestine is lined by a highly specialized epithelium that functions in the digestion and absorption of nutrients. The molecular mechanisms that direct intestinal epithelial cell morphogenesis and terminal differentiation are poorly understood. We have previously identified Elf3 (E74-like factor-3) as a member of the ETS transcription factor family strongly expressed in small intestinal epithelium. The aim of this study is to investigate the biological roles of Elf3 in vivo.

METHODS

Mice with a null mutation of Elf3 were generated through targeted gene disruption. Characterization of intestinal development was performed by histologic and immunohistochemical techniques.

RESULTS

Targeted disruption of Elf3 resulted in fetal lethality of about 30% at around embryonic day 11.5. Seventy percent of the Elf3-deficent progeny were born and displayed severe alterations of tissue architecture in the small intestine, manifested by poor villus formation and abnormal morphogenesis and terminal differentiation of absorptive enterocytes and mucus-secreting goblet cells. Crypt cell proliferation, however, appeared intact in Elf3-deficient mice.Elf3-deficient enterocytes express markedly reduced levels of the transforming growth factor beta type II receptor (TGF-beta RII), an inducer of intestinal epithelial differentiation.

CONCLUSIONS

Elf3 is an important regulator of morphogenesis and terminal differentiation of epithelial cell lineages in the small intestine.

Laminins and TGF-beta maintain cell polarity and functionality of human gastric glandular epithelium

The human gastric glandular epithelium produces a gastric lipase enzyme (HGL) that plays an important role in digestion of dietary triglycerides. To assess the involvement of extracellular matrix components and transforming growth factor-beta1 (TGF-beta1) in the regulation of this enzymic function, normal gastric epithelial cells were cultured on collagen type I, Matrigel, and laminins (LN)-1 and -2 with or without TGF-beta1. Epithelial morphology and HGL expression were evaluated using microscopy techniques, enzymic assays, Western blot, Northern hybridization, and RT-PCR. A correlation was observed between the cell polarity status and the level of HGL expression. TGF-beta1 alone or individual matrix components stimulated cell spreading and caused a downfall of HGL activity and mRNA. By contrast, Matrigel preserved the morphological features of differentiated epithelial cells and maintained HGL expression. The combination of LNs with TGF-beta1 (two constituents of Matrigel) exerted similar beneficial effects on epithelial cell polarity and evoked a 10-fold increase of HGL levels that was blunted by a neutralizing antibody against the alpha(2)-integrin subunit and by mitogen-activated protein kinase (MAPK) inhibitors PD-98059 (p42/p44) or SB-203580 (p38). This investigation demonstrates for the first time that a powerful synergism between a growth factor and basement membrane LNs positively influences cell polarity and functionality of the human gastric glandular epithelium through an activation of the alpha(2)beta(1)-integrin and effectors of two MAPK pathways.

Integrin-mediated functional polarization of Caco-2 cells through E-cadherin—actin complexes

Enterocyte differentiation is a dynamic process during which reinforcement of cell-cell adhesion favours migration along the crypt-to-villus axis. Functional polarization of Caco-2 cells, the most commonly used model to study intestinal differentiation, is assessed by dome formation and tightness of the monolayer and is under the control of the extracellular matrix (ECM). Furthermore, our biochemical and confocal microscopy data demonstrate that the ECM dramatically reinforces E-cadherin targeting to the upper lateral membrane, formation of the apical actin cytoskeleton and its colocalization with E-cadherin in functional complexes. In our model, these effects were produced by native laminin-5-enriched ECM as well as by type IV collagen or laminin 2, which suggests a common pathway of induction through integrin receptors. Indeed, these effects were antagonized by blocking anti-β1-and anti-α6-integrin antibodies and directly induced by a stimulating anti-β1-integrin antibody. These results demonstrate that integrin-dependent cell to ECM adhesion reinforces E-cadherin-dependent cell-cell adhesion in Caco-2 cells and further support the notion that enterocyte differentiation is supported by a molecular crosstalk between the two adhesion systems of the cell.

Foxl1 controls the Wnt/beta-catenin pathway by modulating the expression of proteoglycans in the gut

Foxl1 is a winged helix transcription factor expressed in the mesenchyme of the gastrointestinal tract. Foxl1 null mice display severe structural defects in the epithelia of the stomach, duodenum, and jejunum. Here we addressed the molecular mechanisms by which Foxl1 controls gastrointestinal differentiation. First we showed that the abnormalities found in the epithelia of the null mice are the result of an increase in the number of proliferating cells and not a change in the rate of cell migration. Next we investigated the regulatory circuits affected by Foxl1. We focused on the Wnt/beta-catenin signaling pathway as a possible target of Foxl1 as it has been shown to play a central role in gastrointestinal proliferation. We demonstrated that Foxl1 activates the Wnt/beta-catenin pathway by increasing extracellular proteoglycans, which act as co-receptors for Wnt. Thus we establish that Foxl1 is involved in the regulation of the Wnt/beta-catenin pathway, providing a novel link in mesenchymal/epithelial cross-talk in the gut. Moreover, we provide the first example implicating proteoglycans in the regulation of cellular proliferation in the gastrointestinal tract.

RhoA-dependent switch between alpha2beta1 and alpha3beta1 integrins is induced by laminin-5 during early stage of HT-29 cell differentiation

Integrin-mediated interactions between the basement membrane and epithelial cells control the differentiation of epithelia. We characterized the modulation of adhesive behaviors to basement membrane proteins and of integrin function in the human colon adenocarcinoma HT-29 cell line, which differentiates into enterocytes after the substitution of galactose for glucose in the medium. We demonstrate an increased capability of these cells to adhere to collagen type IV during the early stage of differentiation. This effect occurs without any changes in integrin cell surface expression but rather results from an alpha2beta1/alpha3beta1 integrin switch, alpha3beta1 integrin becoming the major collagen receptor. The increase in laminin-5 secretion and deposit on the matrix is a key factor in the mechanism regulating cell adhesion, because it is responsible for the activation of alpha3beta1 integrin. Furthermore, down-regulation of RhoA GTPase activity occurs during HT-29 cell differentiation and correlates with the activation of the integrin alpha3beta1. Indeed, C3 transferase, a RhoA GTPase inhibitor, induces a similar alpha2beta1/alpha3beta1 switch in undifferentiated HT-29 cells. These results indicate that the decrease in RhoA activation is the biochemical mechanism underlying this integrin switch observed during cell differentiation. The physiological relevance of such modulation of integrin activity in the functioning of the crypt-villus axis is discussed.

CDX-1 and CDX-2 are expressed in human colonic mucosa and are down-regulated in patients with Hirschsprung's disease associated enterocolitis

Caudal type homeobox gene-1 and -2 (CDX-1 and CDX-2), homologues of the Drosophila homeobox gene caudal, encode transcription factors in endoderm derived tissues of the intestine. CDX genes control proliferation and differentiation of intestinal mucosal cells and colon cancer cells. Hirschsprung's Disease (HD) or congenital intestinal aganglionosis, a major developmental anomaly of intestine, which causes functional intestinal obstruction, is frequently associated with enterocolitis. Aetiology of HD-associated enterocolitis (HDEC) remains obscure. Reduction of gut mucosal enteroendocrine cells, and inefficient transfer of the secretory immunoglobulin A across the gut mucosal cell were shown to be associated with enterocolitis in HD patients suggesting that mucosa may directly involve in the pathophysiology of HDEC. This study aims to ascertain whether the CDX-1 and CDX-2 genes, that control the proliferation and differentiation of mucosal cells, play a role in HDEC. Using semi-quantitative reverse transcription-polymerase chain reaction (RT-PCR) and in situ hybridisation, we analysed the expression of CDX-1 and CDX-2 genes in colon specimens of normal controls, necrotising enterocolitis (NEC) infants, and HD patients with and without enterocolitis. We showed for the first time that CDX-1 and CDX-2 genes were expressed in the colonic mucosal epithelium in normal, NEC and in HD infants. However, the expressions of both genes were reduced in patients with HDEC. Our findings suggest that reduced expression of CDX-1 and CDX-2 genes in mucosa may be associated with the development of HDEC.

p27(Kip1) is an inducer of intestinal epithelial cell differentiation

Constant renewal of the intestinal epithelium is a highly coordinated process that has been subject to intense investigation, but its regulatory mechanisms are still essentially unknown. In this study, we have demonstrated that forced expression of the cyclin-dependent kinase inhibitors (CKIs) p27(Kip1) and p21(Cip1/WAF1) in human intestinal epithelial cells led to expression of differentiation markers at both the mRNA and protein levels. Cell differentiation was temporally dissociated from inhibition of retinoblastoma protein phosphorylation and growth arrest, already established 1 day after infection with recombinant adenoviruses. p27(Kip1) proved significantly more efficient than p21(Cip1/WAF1) in induction of cell differentiation. In contrast, forced expression of p16(INK4a) resulted in growth arrest without induction of differentiation markers. These results implicate both p27(Kip1) and p21(Cip1/WAF1) in the differentiation-timing process, but p21(Cip1/WAF1) may act indirectly by increasing p27(Kip1) levels. These results also suggest that induction of intestinal epithelial cell differentiation by CKIs is not related to their effects on the cell cycle and may involve interactions with cellular components other than cyclins and cyclin-dependent kinases.

Unaltered distribution of laminins, fibronectin, and tenascin in celiac intestinal mucosa

Extensive remodeling of the extracellular matrix (ECM) occurs in inflammatory tissues. The celiac lesion in the small intestine is characterized by inflammation accompanied by profound morphological alterations. We used immunohistochemistry to determine the distribution of laminin, fibronectin, and tenascin isoforms in small intestinal biopsies of untreated patients with celiac disease. In normal mucosa, the distribution of laminin isoforms defines three epithelial basement membrane (BM) zones. We found that the organization of these zones was maintained in the celiac mucosa. Thus, components of laminin-5 (alpha3 and beta3) were found in the surface epithelial BM, laminin alpha2 chain was found selectively at crypt bottoms, and laminin alpha5 chain was the sole alpha-type chain in middle crypt BMs. Likewise, the distribution of fibronectin and tenascin resembled that of the normal gut. The organization of pericryptal fibroblasts and lamina propria smooth muscle strands, as defined by immunostaining for alpha-smooth muscle actin, also remained unchanged in the celiac mucosa. Unexpectedly, major ECM changes were not detected in the celiac lesion.

Basement membrane laminin-5 is deposited in colorectal adenomas and carcinomas and serves as a ligand for alpha3beta1 integrin

Interplay between laminin-5 (Ln-5) and its integrin (Int) receptors alpha2beta1, alpha3beta1 and alpha6beta4 has been implicated in the progression and invasion of carcinomas. In this study we found abundant immunoreactivity for chains of Ln-5 (alpha3-beta3-gamma2) and Ln-10 (alpha5-beta1-gamma1), as well as for type VII collagen, in basement membranes (BM) of colorectal adenomas. In carcinomas of all differentiation grades, Lns were seen in tumor BMs, whereas type VII collagen was almost absent. Ln-5 appeared to accumulate along the invading edges of carcinomas, while Ln-10 was mostly absent. Immunoreactivity for Ln al chain, a component of Lns-1 and -3, was not seen in adenomas or carcinomas. Immunoreactivity for alpha2, alpha6, beta1 and beta4 Ints was found in all tumors and that for alpha3 Int in all adenomas and most of the carcinomas, often in colocalization with Ln-5. Immunoblotting of carcinoma tissues showed that the gamma2 chain of Ln-5 was present as typical Mr 105000 and 155000 isoforms. Immunoprecipitation experiments showed production of Ln-5 by cultured colon carcinoma cells. In quantitative cell adhesion experiments, function-blocking MAbs to alpha3 and beta1 Int subunits, but not those to Int alpha2 or alpha6 subunits, significantly inhibited the adhesion of cells to Ln-5. Our results suggest that BM composition in colorectal adenomas reflects the properties of surface epithelial BM of colorectal mucosa. In invading carcinomas, trimeric Ln-5, produced by carcinoma cells, is a major BM component and the cells use the alpha3beta1 Int complex for adhesion to Ln-5.

Altered expression of laminins in Crohn's disease small intestinal mucosa

Laminins are a large family of heterotrimeric basement membrane molecules that mediate crucial cell functions such as adhesion, proliferation, migration, and differentiation. Up to now, three distinct laminins have been identified in the normal human small intestinal epithelium. Laminin-1 (alpha1beta1gamma1) and laminin-5 (alpha3beta3gamma2) are mainly expressed at the base of villus cells, whereas laminin-2 (alpha2beta1gamma1) is restricted to the bottom of the crypts. The expression of these molecules has not yet been studied in Crohn's disease (CD), but it could be altered, in light of the important changes occurring in the architecture of the crypt-villus axis under the active state of the disease. To test this hypothesis, the expression of laminin alpha1, alpha2, and alpha3 subunits was analyzed in control, inflamed, and corresponding uninflamed CD small intestinal specimens by indirect immunofluorescence and reverse transcriptase-polymerase chain reaction. Surprisingly, alpha1 and alpha3 remained strongly expressed by all villus cells, whereas alpha2, normally expressed in the bottom of the crypts in control and uninflamed CD specimens, was lacking in inflamed CD specimens. However, this loss of alpha2 expression was associated with a significant up-regulation of both alpha1 and alpha3 expression in the crypts of inflamed CD specimens. A significant up-regulation of the alpha1 subunit was also observed in the crypts of uninflamed CD specimens. At the transcript levels, alpha1 was found significantly higher in inflamed than uninflamed CD specimens. Taken together, these observations identify important alterations in laminin expression in the small intestine with CD and suggest that compositional changes in the epithelial basement membrane may play a role in this disease.

Restricted distribution of laminin alpha1 chain in normal adult mouse tissues

The distribution of laminin alpha1 chain in adult mouse tissue was determined by immunofluorescence using monoclonal antibody 200, reacting with the globular carboxyterminus E3 fragment of alpha1 chain. Strong reactivity was noted only in a few tissues. Reactivity was restricted to epithelial basement membranes. Expression was noted in several epithelial basement membranes of the urinary tract, and male and female reproductive organs. In addition, expression was seen in some parts of the nervous system. Expression was seen in pia mater which surrounds the brain, and in the extracellular matrices covering the vitreous chamber and the lens of the eye. Staining was seen in the adrenal gland cortex, with strongest staining in the zona glomerulosa. Staining was negative in all other studied epithelial basement membranes, such as the lung (trachea or lung epithelium), epidermis, and all parts of the gastrointestinal tract (liver, gut) except for weak staining in the ventricle and Brunner's glands. No expression was seen in basement membranes of fat, Schwann, or endothelial cells in any studied parts of the body. Both small- and large-size vessel walls were negative both in endothelial basement membranes and blood vessel walls, with the exception of some larger brain blood vessels in locations where epithelial cells have invaginated. Neither smooth muscle, myocardium or striated muscle expressed alpha1 chain. We conclude that alpha1-containing heterotrimers including laminin-1 (alpha1beta1gamma1) have a very restricted tissue distribution.

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.

Confocal laser scanning microscopy of chondrocytes in vitro: cytoskeletal changes after quinolone treatment

The use of quinolone antibiotics would be significant for chronically diseased children (e.g., cystic fibrosis) as a prophylactic long-term treatment. However, quinolones were shown to cause cartilage damage in experimental animals when administered during certain developmental stages. In the present study, the effect of quinolones on chondrocytes was studied in a cell culture model in order to avoid animal experiments, to investigate the influence of single factors, and to open up the possibility to test human tissue. Chondrocytes were obtained from hip joint cartilage of 3 to 4-weeks-old rats and cultured in control medium or quinolone-supplemented medium. It was shown that quinolones heavily disturbed adhesion of chondrocytes to the culture dish, accompanied by changes in cell shape and cytoskeletal morphology. Reduction of filamentous actin (stress fibers) and disintegration of vimentin fibers was demonstrated by immunofluorescence and evaluated by confocal laser scanning microscopy. In contrast, distribution and amount of the adhesion molecule integrin alpha 1 did not change. Results of the present study indicate that quinolones disturb the adherence mechanism of chondrocytes and lead to cytoskeleton changes.

Epithelial vs mesenchymal contribution to the extracellular matrix in the human intestine

The basement membrane (BM) underlying the epithelium of the intestine is generally believed to be of both epithelial and mesenchymal origin but the exact contribution of each tissue has not been directly examined in the human. In this study, we have used a newly described procedure to dissociate the human intestine into pure epithelial and corresponding mesenchymal fractions. Northern blot and RT-PCR analyses of the fractions for the presence of transcripts encoding extracellular matrix molecules revealed that the epithelium produces the formal BM molecules such as the alpha 1, alpha 2, and beta 1 chains of laminin-1 and laminin-2 and the alpha 5(IV) and alpha 6(IV) chains of collagen as well as fibronectin, a BM-associated molecule. Interestingly, the alpha 1(IV) chain of collagen, which associates with the alpha 2(IV) chain to form the main BM collagen network, as well as tenascin-C and decorin, two BM-associated molecules, was found to be exclusively of mesenchymal origin. Taken together, these data support the concept that in the human, as in experimental animals, the intestinal BM is composed of components produced from both the epithelium and the mesenchyme.