Repressed E-cadherin expression in the lower crypt of human small intestine: a cell marker of functional relevance

Primary Cilium Identifies a Quiescent Cell Population in the Human Intestinal Crypt

Primary cilia are sensory antennae located at the cell surface which mediate a variety of extracellular signals involved in development, tissue homeostasis, stem cells and cancer. Primary cilia are found in an extensive array of vertebrae cells but can only be generated when cells become quiescent. The small intestinal epithelium is a rapidly self-renewing tissue organized into a functional unit called the crypt–villus axis, containing progenitor and differentiated cells, respectively. Terminally differentiated villus cells are notoriously devoid of primary cilia. We sought to determine if intestinal crypts contain a quiescent cell population that could be identified by the presence of primary cilia. Here we show that primary cilia are detected in a subset of cells located deep in the crypts slightly above a Paneth cell population. Using a normal epithelial proliferative crypt cell model, we show that primary cilia assembly and activity correlate with a quiescent state. These results provide further evidence for the existence of a quiescent cell population in the human small intestine and suggest the potential for new modes of regulation in stem cell dynamics.

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.

Summary: Inhibition of Src family kinases leads to a sharp reduction in YAP1 expression and an increase in CDX2 and HNF4α, two regulators of intestinal cell differentiation, while its paralog TAZ appears not to be directly involved.

In vitro models replicating the human intestinal epithelium for absorption and metabolism studies: A systematic review

Absorption, distribution, metabolism and excretion (ADME) studies represent a fundamental step in the early stages of drug discovery. In particular, the absorption of orally administered drugs, which occurs at the intestinal level, has gained attention since poor oral bioavailability often led to failures for new drug approval. In this context, several in vitro preclinical models have been recently developed and optimized to better resemble human physiology in the lab and serve as an animal alternative to accomplish the 3Rs principles. However, numerous models are ineffective in recapitulating the key features of the human small intestine epithelium and lack of prediction potential for drug absorption and metabolism during the preclinical stage. In this review, we provide an overview of in vitro models aimed at mimicking the intestinal barrier for pharmaceutical screening. After briefly describing how the human small intestine works, we present i) conventional 2D synthetic and cell-based systems, ii) 3D models replicating the main features of the intestinal architecture, iii) micro-physiological systems (MPSs) reproducing the dynamic stimuli to which cells are exposed in the native microenvironment. In this review, we will highlight the benefits and drawbacks of the leading intestinal models used for drug absorption and metabolism studies.

Intestinal Crypt Organoid: Isolation of Intestinal Stem Cells, In Vitro Culture, and Optical Observation

The isolation and culture of intestinal stem cells (ISCs) was first demonstrated in the very recent decade with the identification of ISC marker Lgr5. The growth of ISCs into crypt organoids provides an in vitro model for studying the mucosal physiology, intestinal cancer tumorigenesis, and intestinal regeneration. Here, we describe two different isolation protocols and demonstrate a fixation method that aids in the confocal observation of the organoids.

mTORC1 Prevents Epithelial Damage During Inflammation and Inhibits Colitis-Associated Colorectal Cancer Development

Epithelial cells lining the intestinal mucosa constitute a selective-semipermeable barrier acting as first line of defense in the organism. The number of those cells remains constant during physiological conditions, but disruption of epithelial cell homeostasis has been observed in several pathologies. During colitis, epithelial cell proliferation decreases and cell death augments. The mechanism responsible for these changes remains unknown. Here, we show that the pro-inflammatory cytokine IFNγ contributes to the inhibition of epithelial cell proliferation in intestinal epithelial cells (IECs) by inducing the activation of mTORC1. Activation of mTORC1 in response to IFNγ was detected in IECs present along the crypt axis and in colonic macrophages. mTORC1 inhibition enhances cell proliferation, increases DNA damage in IEC. In macrophages, mTORC1 inhibition strongly reduces the expression of pro-inflammatory markers. As a consequence, mTORC1 inhibition exacerbated disease activity, increased mucosal damage, enhanced ulceration, augmented cell infiltration, decreased survival and stimulated tumor formation in a model of colorectal cancer CRC associated to colitis. Thus, our findings suggest that mTORC1 signaling downstream of IFNγ prevents epithelial DNA damage and cancer development during colitis.

Hnf4α is a key gene that can generate columnar metaplasia in oesophageal epithelium

Barrett's metaplasia is the only known morphological precursor to oesophageal adenocarcinoma and is characterized by replacement of stratified squamous epithelium by columnar epithelium. The cell of origin is uncertain and the molecular mechanisms responsible for the change in cellular phenotype are poorly understood. We therefore explored the role of two transcription factors, Cdx2 and HNF4α in the conversion using primary organ cultures. Biopsy samples from cases of human Barrett's metaplasia were analysed for the presence of CDX2 and HNF4α. A new organ culture system for adult murine oesophagus is described. Using this, Cdx2 and HNF4α were ectopically expressed by adenoviral infection. The phenotype following infection was determined by a combination of PCR, immunohistochemical and morphological analyses. We demonstrate the expression of CDX2 and HNF4α in human biopsy samples. Our oesophageal organ culture system expressed markers characteristic of the normal SSQE: p63, K14, K4 and loricrin. Ectopic expression of HNF4α, but not of Cdx2 induced expression of Tff3, villin, K8 and E-cadherin. HNF4α is sufficient to induce a columnar-like phenotype in adult mouse oesophageal epithelium and is present in the human condition. These data suggest that induction of HNF4α is a key early step in the formation of Barrett's metaplasia and are consistent with an origin of Barrett's metaplasia from the oesophageal epithelium.

Novel regenerative peptide TP508 mitigates radiation-induced gastrointestinal damage by activating stem cells and preserving crypt integrity

In recent years, increasing threats of radiation exposure and nuclear disasters have become a significant concern for the United States and countries worldwide. Exposure to high doses of radiation triggers a number of potentially lethal effects. Among the most severe is the gastrointestinal (GI) toxicity syndrome caused by the destruction of the intestinal barrier, resulting in bacterial translocation, systemic bacteremia, sepsis, and death. The lack of effective radioprotective agents capable of mitigating radiation-induced damage has prompted a search for novel countermeasures that can mitigate the effects of radiation post exposure, accelerate tissue repair in radiation-exposed individuals, and prevent mortality. We report that a single injection of regenerative peptide TP508 (rusalatide acetate, Chrysalin) 24 h after lethal radiation exposure (9 Gy, LD100/15) appears to significantly increase survival and delay mortality by mitigating radiation-induced intestinal and colonic toxicity. TP508 treatment post exposure prevents the disintegration of GI crypts, stimulates the expression of adherens junction protein E-cadherin, activates crypt cell proliferation, and decreases apoptosis. TP508 post-exposure treatment also upregulates the expression of DCLK1 and LGR5 markers of stem cells that have been shown to be responsible for maintaining and regenerating intestinal crypts. Thus, TP508 appears to mitigate the effects of GI toxicity by activating radioresistant stem cells and increasing the stemness potential of crypts to maintain and restore intestinal integrity. These results suggest that TP508 may be an effective emergency nuclear countermeasure that could be delivered within 24 h post exposure to increase survival and delay mortality, giving victims time to reach clinical sites for advanced medical treatment.

Biochanin A and prunetin improve epithelial barrier function in intestinal CaCo-2 cells via downregulation of ERK, NF-κB, and tyrosine phosphorylation

The single-layered gut epithelium represents the primary line of defense against environmental stressors; thereby monolayer integrity and tightness are essentially required to maintain gut health and function. To date only a few plant-derived phytochemicals have been described as affecting intestinal barrier function. We investigated the impact of 28 secondary plant compounds on the barrier function of intestinal epithelial CaCo-2/TC-7 cells via transepithelial electrical resistance (TEER) measurements. Apart from genistein, the compounds that had the biggest effect in the TEER measurements were biochanin A and prunetin. These isoflavones improved barrier tightness by 36 and 60%, respectively, compared to the untreated control. Furthermore, both isoflavones significantly attenuated TNFα-dependent barrier disruption, thereby maintaining a high barrier resistance comparable to nonstressed cells. In docking analyses exploring the putative interaction with the tyrosine kinase EGFR, these novel modulators of barrier tightness showed very similar values compared to the known tyrosine kinase inhibitor genistein. Both biochanin A and prunetin were also identified as potent reducers of NF-κB and ERK activation, zonula occludens 1 tyrosine phosphorylation, and metalloproteinase-mediated shedding activity, which may account for the barrier-improving ability of these isoflavones.

ERK-associated changes in E2F4 phosphorylation, localization and transcriptional activity during mitogenic stimulation in human intestinal epithelial crypt cells

Background

The transcription factor E2F4 controls proliferation of normal and cancerous intestinal epithelial cells. E2F4 localization in normal human intestinal epithelial cells (HIEC) is cell cycle-dependent, being cytoplasmic in quiescent differentiated cells but nuclear in proliferative cells. However, the intracellular signaling mechanisms regulating such E2F4 localization remain unknown.

Results

Treatment of quiescent HIEC with serum induced ERK1/2 activation, E2F4 phosphorylation, E2F4 nuclear translocation and G1/S phase transition while inhibition of MEK/ERK signaling by U0126 prevented these events. Stimulation of HIEC with epidermal growth factor (EGF) also led to the activation of ERK1/2 but, in contrast to serum or lysophosphatidic acid (LPA), EGF failed to induce E2F4 phosphorylation, E2F4 nuclear translocation and G1/S phase transition. Furthermore, Akt and GSK3β phosphorylation levels were markedly enhanced in serum- or LPA-stimulated HIEC but not by EGF. Importantly, E2F4 phosphorylation, E2F4 nuclear translocation and G1/S phase transition were all observed in response to EGF when GSK3 activity was concomitantly inhibited by SB216763. Finally, E2F4 was found to be overexpressed, phosphorylated and nuclear localized in epithelial cells from human colorectal adenomas exhibiting mutations in APC and KRAS or BRAF genes, known to deregulate GSK3/β-catenin and MEK/ERK signaling, respectively.

Conclusions

The present results indicate that MEK/ERK activation and GSK3 inhibition are both required for E2F4 phosphorylation as well as its nuclear translocation and S phase entry in HIEC. This finding suggests that dysregulated E2F4 nuclear localization may be an instigating event leading to hyperproliferation and hence, of tumor initiation and promotion in the colon and rectum.

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.

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.

Tension, free space, and cell damage in a microfluidic wound healing assay

We use a novel, microfluidics-based technique to deconstruct the classical wound healing scratch assay, decoupling the contribution of free space and cell damage on the migratory dynamics of an epithelial sheet. This method utilizes multiple laminar flows to selectively cleave cells enzymatically, and allows us to present a 'damage free' denudation. We therefore isolate the influence of free space on the onset of sheet migration. First, we observe denudation directly to measure the retraction in the cell sheet that occurs after cell-cell contact is broken, providing direct and quantitative evidence of strong tension within the sheet. We further probe the mechanical integrity of the sheet without denudation, instead using laminar flows to selectively inactivate actomyosin contractility. In both cases, retraction is observed over many cell diameters. We then extend this method and complement the enzymatic denudation with analogies to wounding, including gradients in signals associated with cell damage, such as reactive oxygen species, suspected to play a role in the induction of movement after wounding. These chemical factors are evaluated in combination with the enzymatic cleavage of cells, and are assessed for their influence on the collective migration of a non-abrasively denuded epithelial sheet. We conclude that free space alone is sufficient to induce movement, but this movement is predominantly limited to the leading edge, leaving cells further from the edge less able to move towards the wound. Surprisingly, when coupled with a gradient in ROS to simulate the chemical effects of abrasion however, motility was not restored, but further inhibited.

Integrin signaling, cell survival, and anoikis: distinctions, differences, and differentiation

Cell survival and apoptosis implicate an increasing complexity of players and signaling pathways which regulate not only the decision-making process of surviving (or dying), but as well the execution of cell death proper. The same complex nature applies to anoikis, a form of caspase-dependent apoptosis that is largely regulated by integrin-mediated, cell-extracellular matrix interactions. Not surprisingly, the regulation of cell survival, apoptosis, and anoikis furthermore implicates additional mechanistic distinctions according to the specific tissue, cell type, and species. Incidentally, studies in recent years have unearthed yet another layer of complexity in the regulation of these cell processes, namely, the implication of cell differentiation state-specific mechanisms. Further analyses of such differentiation state-distinct mechanisms, either under normal or physiopathological contexts, should increase our understanding of diseases which implicate a deregulation of integrin function, cell survival, and anoikis.

Survival advantages conferred to colon cancer cells by E-selectin-induced activation of the PI3K-NFκB survival axis downstream of Death receptor-3

Background

Extravasation of circulating cancer cells is a key event of metastatic dissemination that is initiated by the adhesion of cancer cells to endothelial cells. It requires interactions between adhesion receptors on endothelial cells and their counter-receptors on cancer cells. Notably, E-selectin, a major endothelial adhesion receptor, interacts with Death receptor-3 present on metastatic colon carcinoma cells. This interaction confers metastatic properties to colon cancer cells by promoting the adhesion of cancer cells to endothelial cells and triggering the activation of the pro-migratory p38 and pro-survival ERK pathways in the cancer cells. In the present study, we investigated further the mechanisms by which the E-selectin-activated pathways downstream of DR3 confer a survival advantage to colon cancer cells.

Methods

Cell survival has been ascertained by using the WST-1 assay and by evaluating the activation of the PI3 kinase/NFκB survival axis. Apoptosis has been assayed by determining DNA fragmentation by Hoechst staining and by measuring cleavage of caspases-8 and -3. DR3 isoforms have been identified by PCR. For more precise quantification, targeted PCR reactions were carried out, and the amplified products were analyzed by automated chip-based microcapillary electrophoresis on an Agilent 2100 Bioanalyzer instrument.

Results

Interaction between DR3-expressing HT29 colon carcinoma cells and E-selectin induces the activation of the PI3K/Akt pathway. Moreover, p65/RelA, the anti-apoptotic subunit of NFκB, is rapidly translocated to the nucleus in response to E-selectin. This translocation is impaired by the PI3K inhibitor LY294002. Furthermore, inhibition of the PI3K/Akt pathway increases the cleavage of caspase 8 in colon cancer cells treated with E-selectin and this effect is still further increased when both ERK and PI3K pathways are concomitantly inhibited. Intriguingly, metastatic colon cancer cell lines such as HT29 and SW620 express higher levels of a splice variant of DR3 that has no trans-membrane domain and no death domain.

Conclusion

Colon cancer cells acquire an increased capacity to survive via the activation of the PI3K/NFκB pathway following the stimulation of DR3 by E-selectin. Generation of a DR3 splice variant devoid of death domain can further contribute to protect against apoptosis.

Integrin alpha8beta1 confers anoikis susceptibility to human intestinal epithelial crypt cells

We previously reported that integrin alpha8beta1 is expressed in human intestinal epithelial crypt cells (HIECs) and represents one of the major RGD-binding integrins expressed by these cells. Moreover, the depletion of alpha8beta1 affects vinculin, but not paxillin, localization at focal adhesion points. In the present study, we show that the integrin alpha8 shRNA-mediated knockdown in HIECs leads to a decrease in anoikis susceptibility under cell suspension culture conditions, marked by a reduction in PARP cleavage and propidium iodide incorporation. Moreover, alpha8beta1-depleted HIECs exhibited an illicitly sustained activation of Fak and PI3-K/Akt-1 under anoikis conditions, rendering them refractory to anoikis. To this effect, colon cancer cells exhibiting resistance to anoikis not only displayed a loss of alpha8beta1 expression, but forced expression of alpha8beta1 in these cells decreased their resistance to anoikis. Consequently, alpha8beta1 is a prerequisite for the proper conduct of anoikis in normal HIECs, whereas its loss contributes to the illicit acquisition of anoikis resistance.

Mesenchymal-to-epithelial transition of intercalating cells in Drosophila renal tubules depends on polarity cues from epithelial neighbours

The intercalation of mesenchymal cells into epithelia, through mesenchymal-to-epithelial transition (MET), underlies organogenesis, for example, in nephrogenesis, and tissue regeneration, during cell renewal and wound repair. Despite its importance, surprisingly little is known about the mechanisms that bring about MET in comparison with the related and much-studied, reverse process, epithelial-to-mesenchymal transition (EMT). We analyse the molecular events that regulate MET as stellate cells integrate into the established epithelium of the developing renal tubules in Drosophila. We show that stellate cells polarise as they integrate between epithelial principal cells and that the normal, localised expression of cell polarity proteins in principal cells is required for stellate cells to become epithelial. While the basolateral and apical membranes act as cues for stellate cell polarity, adherens junction integrity is required to regulate their movement through the epithelium; in the absence of these junctions stellate cells continue migrating into the tubule lumen. We also show that expression of basolateral proteins in stellate cells is a prerequisite for their ingression between principal cells. We present a model in which the contacts with successive principal cell membrane domains made by stellate cells as they integrate between them act as a cue for the elaboration of stellate cell polarity. We suggest that the formation of zonula adherens junctions between new cell neighbours establishes their apico-basal positions and stabilises them in the epithelium.

Cooperation between HNF-1alpha, Cdx2, and GATA-4 in initiating an enterocytic differentiation program in a normal human intestinal epithelial progenitor cell line

In the intestinal epithelium, the Cdx, GATA, and HNF transcription factor families are responsible for the expression of differentiation markers such as sucrase-isomaltase. Although previous studies have shown that Cdx2 can induce differentiation in rat intestinal IEC-6 cells, no data are available concerning the direct implication of transcription factors on differentiation in human normal intestinal epithelial cell types. We investigated the role of Cdx2, GATA-4, and HNF-1alpha using the undifferentiated human intestinal epithelial crypt cell line HIEC. These transcription factors were tested on proliferation and expression of polarization and differentiation markers. Ectopic expression of Cdx2 or HNF-1alpha, alone or in combination, altered cell proliferation abilities through the regulation of cyclin D1 and p27 expression. HNF-1alpha and GATA-4 together induced morphological modifications of the cells toward polarization, resulting in the appearance of functional features such as microvilli. HNF-1alpha was also sufficient to induce the expression of cadherins and dipeptidylpeptidase, whereas in combination with Cdx2 it allowed the expression of the late differentiation marker sucrase-isomaltase. Large-scale analysis of gene expression confirmed the cooperative effect of these factors. Finally, although DcamKL1 and Musashi-1 expression were downregulated in differentiated HIEC, other intestinal stem cell markers, such as Bmi1, were unaffected. These observations show that, in cooperation with Cdx2, HNF-1alpha acts as a key factor on human intestinal cells to trigger the onset of their functional differentiation program whereas GATA-4 appears to promote morphological changes.

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.

Polycystin-1 is a microtubule-driven desmosome-associated component in polarized epithelial cells

In this study, we have analyzed the expression and localization of polycystin-1 in intestinal epithelial cells, a system lacking primary cilia. Polycystin-1 was found to be expressed in the epithelium of the small intestine during development and levels remained elevated in the adult. Dual-labelling indirect immunofluorescence revealed polycystin-1 at sites of cell-cell contact co-localizing with the desmosomes both in situ as well as in polarized Caco-2/15 cells. In unpolarized cultures of Caco-2/15 cells, polycystin-1 was recruited to the cell surface early during initiation of cell junction assembly. In isolated Caco-2/15 cells and HIEC-6 cell cultures, where junctional complexes are absent, polycystin-1 was found predominantly associated with the cytoskeletal elements of the intermediate filaments and microtubule networks. More precisely, polycystin-1 was seen as brightly labelled puncta decorating the keratin-18 positive filaments as well as the beta-tubulin positive microtubules, which was particularly obvious in the lamellipodia. Treatment with the microtubule-disrupting agent, nocodazole, eliminated the microtubule association of polycystin-1 but did not seem to affect its association with keratin or the desmosomes. Taken together these data suggest that polycystin-1 is involved with the establishment of cell-cell junctions in absorptive intestinal epithelial cells and exploits the microtubule-based machinery in order to be transported to the plasma membrane.

Dysregulation of cadherins in the intercalated disc of the spontaneously hypertensive stroke-prone rat

The structural integrity of cardiac cells is maintained by the Ca(2+)-dependent homophilic cell-cell adhesion of cadherins. N-cadherin is responsible for this adhesion under normal physiological conditions. The role of cadherins in adverse cardiac pathology is less clear. We studied the hearts of the stroke-prone spontaneously hypertensive (SHRSP) rat as a genetic model of cardiac hypertrophy and compared them to Wistar-Kyoto control animals. Western blotting of protein homogenates from 12-week old SHRSP animals indicated that similar levels of beta, gamma-, and alpha-catenin and T, N and R-cadherin were expressed in the control and SHRSP animals. However, dramatically higher levels of E-cadherin were detected in SHRSP animals compared to controls at 6, 12 and 18 weeks of age. This was confirmed by quantitative Taqman PCR and immunohistochemistry. E-cadherin was located at the intercalated disc of the myocytes in co-localisation with connexin 43. Adenoviral overexpression of E-cadherin in rat H9c2 cells and primary rabbit myocytes resulted in a significant reduction in myocyte cell diameter and breadth. E-cadherin overexpression resulted in re-localisation of beta-catenin to the cell surface particularly to cell-cell junctions. Subsequent immunohistochemistry of the hearts of WKY and SHRSP animals also revealed increased levels of beta-catenin in the intercalated disc in the SHRSP compared to WKY. Therefore, remodelling of the intercalated disc in the hearts of SHRSP animals may contribute to the altered function observed in these animals.

Regulation of intestinal epithelial cells transcriptome by enteric glial cells: impact on intestinal epithelial barrier functions

BACKGROUND

Emerging evidences suggest that enteric glial cells (EGC), a major constituent of the enteric nervous system (ENS), are key regulators of intestinal epithelial barrier (IEB) functions. Indeed EGC inhibit intestinal epithelial cells (IEC) proliferation and increase IEB paracellular permeability. However, the role of EGC on other important barrier functions and the signalling pathways involved in their effects are currently unknown. To achieve this goal, we aimed at identifying the impact of EGC upon IEC transcriptome by performing microarray studies.

RESULTS

EGC induced significant changes in gene expression profiling of proliferating IEC after 24 hours of co-culture. 116 genes were identified as differentially expressed (70 up-regulated and 46 down-regulated) in IEC cultured with EGC compared to IEC cultured alone. By performing functional analysis of the 116 identified genes using Ingenuity Pathway Analysis, we showed that EGC induced a significant regulation of genes favoring both cell-to-cell and cell-to-matrix adhesion as well as cell differentiation. Consistently, functional studies showed that EGC induced a significant increase in cell adhesion. EGC also regulated genes involved in cell motility towards an enhancement of cell motility. In addition, EGC profoundly modulated expression of genes involved in cell proliferation and cell survival, although no clear functional trend could be identified. Finally, important genes involved in lipid and protein metabolism of epithelial cells were shown to be differentially regulated by EGC.

CONCLUSION

This study reinforces the emerging concept that EGC have major protective effects upon the IEB. EGC have a profound impact upon IEC transcriptome and induce a shift in IEC phenotype towards increased cell adhesion and cell differentiation. This concept needs to be further validated under both physiological and pathophysiological conditions.

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.

E2F4 expression is required for cell cycle progression of normal intestinal crypt cells and colorectal cancer cells

The generation of knock-out mice for E2F4 gene expression has suggested a role for this transcription factor in establishing and/or maintaining the intestinal crypt compartment. Having previously demonstrated that E2F4 is cytoplasmic in quiescent-differentiated cells but nuclear in growth factor-stimulated proliferative cells, the present study was aimed at determining the role of E2F4 in the control of human intestinal epithelial proliferation. Results herein demonstrate that lentiviral infection of an shRNA which specifically knocked-down E2F4 expression slowed down G1/S phase transition and the proliferation rate of normal human intestinal epithelial cells (HIEC) and of colon cancer cells. Protein expression of Cdk2, cyclins D1 and A, Cdc25A and c-myc was markedly down-regulated in shE2F4-expressing cells; by contrast, expression of the cell cycle inhibitors p21(Cip/Waf) and p27(Kip1) was increased. In addition, the expression of many genes involved in DNA synthesis was down-regulated in shE2F4-expressing cells, whereas no modulation in E2F1 expression was observed. A decrease in E2F4 in colon cancer cell lines also resulted in a reduction in soft-agar growth capacity. Immunofluorescence experiments in human fetal intestine revealed that cells expressing high nuclear levels of E2F4 also expressed cyclin A protein. Lastly, E2F4 and its target cyclin A were up-regulated and mostly nuclear in human colorectal tumor cells in comparison to the corresponding benign epithelium. These results indicate that nuclear E2F4 may be determinant in the promotion of proliferation of human intestinal epithelial crypt cells and colorectal cancer cells.

Tracking the cell hierarchy in the human intestine using biochemical signatures derived by mid-infrared microspectroscopy

Markers of gastrointestinal (GI) stem cells remain elusive. We employed synchrotron Fourier-transform infrared (FTIR) microspectroscopy to derive mid-infrared (IR) spectra along the length of human GI crypts. Tissue sections (10-μm thick) were floated onto BaF2 windows and image maps were acquired of small intestine and large bowel crypts in transmission mode with an aperture of ≤10 μm×10 μm. Counting upwards in a step-size (≤10 μm) fashion from the crypt base, IR spectra were extracted from the image maps and each spectrum corresponding to a particular location was identified. Spectra were analyzed using principal component analysis plus linear discriminant analysis. Compared to putative crypt base columnar/Paneth cells, those assigned as label-retaining cells were chemically more similar to putative large bowel stem cells and, the small intestine transit-amplifying cells were closest to large bowel transit-amplifying cells; interestingly, the base of small intestine crypts was the most chemically-distinct. This study suggests that in the complex cell lineage of human GI crypts, chemical similarities as revealed by FTIR microspectroscopy between regions putatively assigned as stem cell, transit-amplifying and terminally-differentiated facilitates identification of cell function.

Beta-catenin mediates alteration in cell proliferation, motility and invasion of prostate cancer cells by differential expression of E-cadherin and protein kinase D1

We have previously demonstrated that Protein Kinase D1 (PKD1) interacts with E-cadherin and is associated with altered cell aggregation and motility in prostate cancer (PC). Because both PKD1 and E-cadherin are known to be dysregulated in PC, in this study we investigated the functional consequences of combined dysregulation of PKD1 and E-cadherin using a panel of human PC cell lines. Gain and loss of function studies were carried out by either transfecting PC cells with full-length E-cadherin and/or PKD1 cDNA or by protein silencing by siRNAs, respectively. We studied major malignant phenotypic characteristics including cell proliferation, motility, and invasion at the cellular level, which were corroborated with appropriate changes in representative molecular markers. Down regulation or ectopic expression of either E-cadherin or PKD1 significantly increased or decreased cell proliferation, motility, and invasion, respectively, and combined down regulation cumulatively influenced the effects. Loss of PKD1 or E-cadherin expression was associated with increased expression of the pro-survival molecular markers survivin, beta-catenin, cyclin-D, and c-myc, whereas overexpression of PKD1 and/or E-cadherin resulted in an increase of caspases. The inhibitory effect of PKD1 and E-cadherin on cell proliferation was rescued by coexpression with beta-catenin, suggesting that beta-catenin mediates the effect of proliferation by PKD1 and E-cadherin. This study establishes the functional significance of combined dysregulation of PKD1 and E-cadherin in PC and that their effect on cell growth is mediated by beta-catenin.

Hereditary diffuse gastric cancer and lost cell polarity: a short path to cancer

The mechanisms that underlie the initiation of human cancer are poorly understood. Here, we describe the development of hereditary diffuse gastric cancer and argue that it arises from the disruption of the regenerative processes that are inherent to all epithelial tissues. This model supports the cancer stem cell hypothesis, in which tumors contain a subpopulation of cells with the key stem cell characteristics of capacity for self renewal, differentiation and limitless replication. We argue that epigenetic modifications induced by common environmental and physiological pressures are able to initiate this disruption. The carcinogenic effects of these modifications are potentially reversible through the use of epigenetic therapies such as DNA demethylating agents and histone deacetylation inhibitors.

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.

Oligosaccharides from human milk influence growth-related characteristics of intestinally transformed and non-transformed intestinal cells

Human milk oligosaccharides (HMO) are considered to influence the composition of the gut microflora in breastfed infants. We investigated direct effects of milk HMO fractions or individual oligosaccharides on proliferation, differentiation and apoptosis in transformed human intestinal cells (HT-29 and Caco-2) and non-transformed small intestinal epithelial crypt cells of fetal origin (human intestinal epithelial cells; HIEC). We observed growth inhibition induced by neutral and acidic HMO fractions in HT-29, Caco-2 and HIEC cells in a dose dependent manner. However, the effects varied between cell lines, i.e. HT-29 and Caco-2 cells were more sensitive than HIEC cells. In HT-29, all 16 individual neutral and acidic oligosaccharides except from the two fucosyllactoses had an inhibitory effect on cell growth. Regarding the induction of differentiation in HT-29 and HIEC cells a threshold concentration was observed at 7.5 mg/ml for neutral and acidic HMO fractions. Among individual oligosaccharides, only sialyllactoses induced differentiation in HT-29 and HIEC cells; no effect neither of fractions nor of individual oligosaccharides was found in Caco-2 cells. A strong induction of apoptosis was only detected in HT-29 and HIEC cells for neutral oligosaccharide but not for acidic fractions. HMO were shown to induce growth inhibition in intestinal cells through two different mechanisms, by suppressing cell cycle progression through induction of differentiation and/or by influencing apoptosis. As the development and maturation of digestive and absorptive processes depend on differentiation our experiments show that oligosaccharides are effective at influencing various stages in gastrointestinal development in vitro.

Fourier transform infrared microspectroscopy identifies symmetric PO(2)(-) modifications as a marker of the putative stem cell region of human intestinal crypts

Complex biomolecules absorb in the mid-infrared (lambda = 2-20 microm), giving vibrational spectra associated with structure and function. We used Fourier transform infrared (FTIR) microspectroscopy to "fingerprint" locations along the length of human small and large intestinal crypts. Paraffin-embedded slices of normal human gut were sectioned (10 microm thick) and mounted to facilitate infrared (IR) spectral analyses. IR spectra were collected using globar (15 microm x 15 microm aperture) FTIR microspectroscopy in reflection mode, synchrotron (<or=10 microm x 10 microm aperture) FTIR microspectroscopy in transmission mode or near-field photothermal microspectroscopy. Dependent on the location of crypt interrogation, clear differences in spectral characteristics were noted. Epithelial-cell IR spectra were subjected to principal component analysis to determine whether wavenumber-absorbance relationships expressed as single points in "hyperspace" might on the basis of multivariate distance reveal biophysical differences along the length of gut crypts. Following spectroscopic analysis, plotted clusters and their loadings plots pointed toward symmetric (nu(s))PO(2)(-) (1,080 cm(-1)) vibrations as a discriminating factor for the putative stem cell region; this proved to be a more robust marker than other phenotypic markers, such as beta-catenin or CD133. This pattern was subsequently confirmed by image mapping and points to a novel approach of nondestructively identifying a tissue's stem cell location. nu(s)PO(2)(-), probably associated with DNA conformational alterations, might facilitate a means of identifying stem cells, which may have utility in other tissues where the location of stem cells is unclear.

Apical junction complex protein expression in the canine colon: differential expression of claudin-2 in the colonic mucosa in dogs with idiopathic colitis

Canine idiopathic lymphocytic-plasmacytic colitis (LPC) is a well-recognized clinical and pathological entity in the dog, associated with altered immune cell populations and cytokine expression profiles. Clinical and experimental data indicate that alterations in the permeability of the intestinal epithelium contribute to the pathogenesis of a range of related conditions. The apical junction complex plays a significant role in regulating epithelial paracellular permeability, and we have characterized the distribution of a number of its component tight junction (ZO-1, occludin, claudin-2) and adherens junction (E-cadherin and beta-catenin) proteins in normal colon and colon from dogs with idiopathic LPC. ZO-1, occludin, E-cadherin, and beta-catenin exhibited a distribution in normal canine colon similar to that described previously in humans and rodents. In contrast to the situation in humans, claudin-2-specific labeling was observed in the normal canine colonic crypt epithelium, decreasing in intensity from the distal to the proximal crypt and becoming barely detectable at the luminal surface of the colon. There was little evidence for significant changes in ZO-1, occludin, E-cadherin, or beta-catenin expression in dogs affected by idiopathic LPC. However, claudin-2 expression markedly increased in the proximal crypt and luminal colonic epithelium in affected dogs, suggesting a role in the pathogenesis of canine LPC.

Differential expression of E-cadherin in metastatic lesions comparing to primary oral squamous cell carcinoma

BACKGROUND

The main cause of treatment failure in resectable oral squamous cell carcinoma (OSCC) is metastasis. E-cadherin (E-cad) plays a principal role in cell adhesion and motility, and is associated with OSCC progression. The aim of this study was to investigate the clinical significance of E-cad expression in OSCC with lymph node metastasis which had radical neck dissection done.

METHOD

Immunohistochemistry was used to detect E-cad expression in normal oral mucosa (NOM) (n = 10), oral precancerous lesions (OPLs) (n = 20), primary OSCC (n = 45), and their paired metastatic lesions (n = 45). E-cad immunoreactivity correlated with the clinicopathologic features.

RESULTS

E-cadherin immunoreactivity was progressively reduced in the NOM followed by OPLs and primary OSCC (58%). It decreased significantly in the advanced stages of OSCC. However, the increase in E-cad immunoreactivity was observed in the majority (60%) of metastatic lesions in relation to primary OSCC. Patients with such increased or positive immunoreactivity of E-cad in metastatic lesions exhibited worse prognosis.

CONCLUSION

The findings suggested a dynamic change in E-cad immunoreactivity during tumorigenesis and metastasis of OSCC. In a multivariate analysis, E-cad immunoreactivity in metastasis lesions (odds ratio 3.74, 95% CI 1.15-14.67; P = 0.040) implied the potential role of mortality predictors for OSCC cases with nodal involvement.

Gene expression profiles of normal proliferating and differentiating human intestinal epithelial cells: a comparison with the Caco-2 cell model

cDNA microarray technology enables detailed analysis of gene expression throughout complex processes such as differentiation. The aim of this study was to analyze the gene expression profile of normal human intestinal epithelial cells using cell models that recapitulate the crypt-villus axis of intestinal differentiation in comparison with the widely used Caco-2 cell model. cDNA microarrays (19,200 human genes) and a clustering algorithm were used to identify patterns of gene expression in the crypt-like proliferative HIEC and tsFHI cells, and villus epithelial cells as well as Caco-2/15 cells at two distinct stages of differentiation. Unsupervised hierarchical clustering analysis of global gene expression among the cell lines identified two branches: one for the HIEC cells versus a second comprised of two sub-groups: (a) the proliferative Caco-2 cells and (b) the differentiated Caco-2 cells and closely related villus epithelial cells. At the gene level, supervised hierarchical clustering with 272 differentially expressed genes revealed distinct expression patterns specific to each cell phenotype. We identified several upregulated genes that could lead to the identification of new regulatory pathways involved in cell differentiation and carcinogenesis. The combined use of microarray analysis and human intestinal cell models thus provides a powerful tool for establishing detailed gene expression profiles of proliferative to terminally differentiated intestinal cells. Furthermore, the molecular differences between the normal human intestinal cell models and Caco-2 cells clearly point out the strengths and limitations of this widely used experimental model for studying intestinal cell proliferation and differentiation.

Survivin identifies keratinocyte stem cells and is downregulated by anti-beta1 integrin during anoikis

Survivin belongs to the family of inhibitor of apoptosis proteins and is involved in regulation of cell death as well as cell division. Here, we show that wild-type (WT) survivin is expressed in a subpopulation of basal keratinocytes in normal human skin at the cytoplasmic level. WT survivin is highly expressed in keratinocyte stem cells (KSCs), whereas its mRNA level decreases in transit amplifying (TA) cells and disappears in postmitotic (PM) cells. Likewise, WT survivin protein is expressed in KSCs, almost undetectable in TA cells, and absent in PM cells. Real time polymerase chain reaction demonstrates that the putative antiapoptotic isoforms survivin-2B and survivin-DeltaEx3 are expressed at the highest levels in KSCs, whereas they tend to decrease in TA cells and disappear in PM cells. On the contrary, the putative proapoptotic variants of survivin, survivin-3B, and survivin-2alpha tend to be high in PM and TA cells and are almost absent in KSCs. By confocal microscopy, survivin is predominantly expressed at the nuclear level in KSCs, which proliferate significantly better than TA cells, which, in turn, express mostly cytosolic WT survivin. Blocking beta1 integrin signal downregulates WT survivin mRNA and protein expression and induces apoptosis (anoikis) in KSCs. On the other hand, inhibition of beta1 integrin upregulates mRNA expression of survivin-2alpha. Taken together, these results indicate that survivin identifies human KSCs. Expression of nuclear survivin could reflect the different behavior between KSCs in vitro and in vivo, in terms of proliferation. Finally, survivin could be part of the "niche" protection by preventing anoikis in KSCs.

Increased apoptosis and accelerated epithelial migration following inhibition of hedgehog signaling in adaptive small bowel postresection

The intestinal epithelium undergoes a marked adaptive response following loss of functional small bowel surface area characterized by increased crypt cell proliferation and increased enterocyte migration from crypt to villus tip, resulting in villus hyperplasia and enhanced nutrient absorption. Hedgehog (Hh) signaling plays a critical role in regulating epithelial-mesenchymal interactions during morphogenesis of the embryonic intestine. Our previous studies showed that blocking Hh signaling in neonatal mice results in increased small intestinal epithelial crypt cell proliferation and altered enterocyte fat absorption and morphology. Hh family members are also expressed in the adult intestine, but their role in the mature small bowel is unclear. With the use of a model of intestinal adaptation following partial small bowel resection, the role of Hh signaling in the adult gut was examined by determining the effects of blocking Hh signaling on the regenerative response following loss of functional surface area. Hh-inactivating monoclonal antibodies or control antibodies were administered to mice that sustained a 50% intestinal resection. mRNA analyses of the preoperative ileum by quantitative real-time PCR revealed that Indian hedgehog was the most abundant Hh family member. The Hh receptor Patched was more abundant than Patched 2. Analyses of downstream targets of Hh signaling demonstrated that Gli3 was twofold more abundant than Gli1 and Gli2 and that bone morphogenetic protein (BMP)2 was most highly expressed compared with BMP1, -4, and -7. Following intestinal resection, the expression of Hh, Patched, Gli, and most BMP genes was markedly downregulated in the remnant ileum, and, in anti-Hh antibody-treated mice, expression of Patched 2 and Gli 1 was further suppressed. In Hh antibody-treated mice following resection, the enterocyte migration rate from crypt to villus tip was increased, and by 2 wk postoperation, apoptosis was increased in the adaptive gut. However, crypt cell proliferation, villus height, and crypt depth were not augmented. These data indicate that Hh signaling plays a role in adult gut epithelial homeostasis by regulating epithelial cell migration from crypt to villus tip and by enhancing apoptosis.

Reciprocal inhibition of Cd(2+) and Ca(2+) uptake in human intestinal crypt cells for voltage-independent Zn-activated pathways

Cadmium-Ca-Zn interactions for uptake have been studied in human intestinal crypt cells HIEC. Our results failed to demonstrate any significant cross-inhibition between Cd and Ca uptake under single metal exposure conditions. However, they revealed a strong reciprocal inhibition for a Zn-stimulated mechanism of transport. Optimal stimulation was observed under exposure conditions that favor an inward-directed Zn gradient, suggesting activation by extracellular rather than intracellular Zn. The effect of Zn on the uptake of Ca was concentration-dependent, and zinc-induced stimulation of Cd uptake resulted in a 3- and 5.8-fold increase in the K(m) and V(max) values, respectively. Neither basal nor Zn-stimulated Ca uptakes were sensitive to membrane depolarization. However, the stimulated component of uptake was inhibited by the trivalent cations Gd(3+), and La(3+) and to a lesser extent by Mg(2+) and Ba(2+). RT-PCR analysis as well as uptake measurement performed with extracellular ATP and/or suramin do not support the involvement of purinergic P2X receptor channels. Uptake and fluorescence data led to the conclusion that Zn is unlikely to trigger Ca influx in response to Ca release from thapsigargin-sensitive intracellular pools. Our data show that Zn may potentiate Cd accumulation in intestinal crypt cells through mechanism that still needs to be clarified.

Molecular biology of the small intestine

PURPOSE OF REVIEW

A concise report of published research is presented here that has provided new insights into the molecular and cell biology of the small intestine.

RECENT FINDINGS

The precise control of cell renewal lineage commitment, differentiation and apoptosis along the crypt-villus axis are regulated by paracrine and autocrine signaling pathways that include Wnt, Hedgehog and Notch ligands. The downstream signaling pathways and transcriptional control of gene expression are being elucidated. Conditional loss of functional c-myc in the intestinal mucosa may have no effect on the normal homeostasis of this tissue. Manipulation of CUGBP2 expression may modulate the response of normal intestine to radiation therapy.

SUMMARY

The cellular interactions at various levels in the small intestine are being understood and would provide a framework for interventional translational research in coming years.

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.

Cripto-1: a multifunctional modulator during embryogenesis and oncogenesis

It is increasingly evident that genes known to perform critical roles during early embryogenesis, particularly during stem cell renewal, pluripotentiality and survival, are also expressed during the development of cancer. In this regard, oncogenesis may be considered as the recapitulation of embryogenesis in an inappropriate temporal and spatial manner. The epidermal growth factor-Cripto-1/FRL1/cryptic family of proteins consists of extracellular and cell-associated proteins that have been identified in several vertebrate species. During early embryogenesis, epidermal growth factor-Cripto-1/FRL1/cryptic proteins perform an obligatory role as coreceptors for the transforming growth factor-beta subfamily of proteins, which includes Nodal. Cripto-1 has also been shown to function as a ligand through a Nodal/Alk4-independent signaling pathway that involves binding to glypican-1 and the subsequent activation through src of phosphoinositol-3 kinase/Akt and ras/mitogen-activated protein kinase intracellular pathways. Expression of Cripto-1 is increased in several human cancers and its overexpression is associated with the development of mammary tumors in mice. Here, we review the role of Cripto-1 during embryogenesis, cell migration, invasion and angiogenesis and how these activities may relate to cellular transformation and tumorigenesis. We also briefly discuss evidence suggesting that Cripto-1 may be involved in stem cell maintenance.