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

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

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

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.

Current and emerging approaches to define intestinal epithelium-specific transcriptional networks

Upon developmental or environmental cues, the composition of transcription factors in a transcriptional regulatory network is deeply implicated in controlling the signature of the gene expression and thereby specifies the cell or tissue type. Novel methods including ChIP-chip and ChIP-Seq have been applied to analyze known transcription factors and their interacting regulatory DNA elements in the intestine. The intestine is an example of a dynamic tissue where stem cells in the crypt proliferate and undergo a differentiation process toward the villus. During this differentiation process, specific regulatory networks of transcription factors are activated to target specific genes, which determine the intestinal cell fate. The expanding genomewide mapping of transcription factor binding sites and construction of transcriptional regulatory networks provide new insight into how intestinal differentiation occurs. This review summarizes the current overview of the transcriptional regulatory networks driving epithelial differentiation in adult intestine. The novel technologies that have been implied to study these networks are presented and their prospects for implications in future research are also addressed.

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.

Enterocytes’ tight junctions: From molecules to diseases

Tight junctions (TJs) are structures between cells where cells appear in the closest possible contact. They are responsible for sealing compartments when epithelial sheets are generated. They regulate the permeability of ions, (macro) molecules and cells via the paracellular pathway. Their structure at the electron microscopic level has been well known since the 1970s; however, only recently has their macromolecular composition been revealed. This review first examines the major macromolecular components of the TJs (occludin, claudins, junctional adhesion molecule and tricellulin) and then the associated macromolecules at the intracellular plaque [zonula occludens (ZO)-1, ZO-2, ZO-3, AF-6, cingulin, 7H6]. Emphasis is given to their interactions in order to begin to understand the mode of assembly of TJs. The functional significance of TJs is detailed and several mechanisms and factors involved are discussed briefly. Emphasis is given to the role of intestinal TJs and the alterations observed or speculated in diverse disease states. Specifically, intestinal TJs may exert a pathogenetic role in intestinal (inflammatory bowel disease, celiac disease) and extraintestinal diseases (diabetes type 1, food allergies, autoimmune diseases). Additionally, intestinal TJs may be secondarily disrupted during the course of diverse diseases, subsequently allowing the bacterial translocation phenomenon and promoting the systemic inflammatory response, which is often associated with clinical deterioration. The major questions in the field are highlighted.

Molecular mechanisms of Barrett's esophagus

Barrett's esophagus (BE) is defined as the metaplastic conversion of esophageal squamous epithelium to intestinalized columnar epithelium. As a premalignant lesion of esophageal adenocarcinoma (EAC), BE develops as a result of chronic gastroesophageal reflux disease (GERD). Many studies have been conducted to understand the molecular mechanisms of this disease. This review summarizes recent results involving squamous and intestinal transcription factors, signaling pathways, stromal factors, microRNAs, and other factors in the development of BE. A conceptual framework is proposed to guide future studies. We expect elucidation of the molecular mechanisms of BE to help in the development of improved management of GERD, BE, and EAC.

Cdx regulates Dll1 in multiple lineages

Vertebrate Cdx genes encode homeodomain transcription factors related to caudal in Drosophila. The murine Cdx homologues Cdx1, Cdx2 and Cdx4 play important roles in anterior-posterior patterning of the embryonic axis and the intestine, as well as axial elongation. While our understanding of the ontogenic programs requiring Cdx function has advanced considerably, the molecular bases underlying these functions are less well understood. In this regard, Cdx1-Cdx2 conditional mutants exhibit abnormal somite formation, while loss of Cdx1-Cdx2 in the intestinal epithelium results in a shift in differentiation toward the Goblet cell lineage. The aim of the present study was to identify the Cdx-dependent mechanisms impacting on these events. Consistent with prior work implicating Notch signaling in these pathways, we found that expression of the Notch ligand Dll1 was reduced in Cdx mutants in both the intestinal epithelium and paraxial mesoderm. Cdx members occupied the Dll1 promoter both in vivo and in vitro, while genetic analysis indicated interaction between Cdx and Dll1 pathways in both somitogenesis and Goblet cell differentiation. These findings suggest that Cdx members operate upstream of Dll1 to convey different functions in two distinct lineages.

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.