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Hans Clevers

Publications and source records attributed to Hans Clevers.

At least 19 recordsLinked to original sources
PubMed2026

Modeling reptile virus infection in vitro using Python regius airway organoids.

Zoonoses pose substantial global health risks, highlighting the need to better understand animal-to-human transmission. Reptiles are increasingly recognized as hosts of diverse pathogens, including numerous viruses, yet the diversity and prevalence of reptile pathogens, as well as their potential risk to humans, remain poorly understood. Here, we establish and characterize airway organoids derived from Python regius, providing an in vitro model to study reptile airway infection. Through de novo assembly of a Python regius reference genome, we characterize airway organoids at single-cell resolution, which suggests the presence of diverse cell populations including ionocytes, ciliated, secretory, goblet, endocrine, tuft, and basal cells. The organoids support productive infection with Ball Python Nidovirus (BPNV) and mount a robust epithelial antiviral response through the induction of interferon-stimulated genes, cytokines, and genes involved in chemical defense. As a proof-of-concept, treating organoids with antiviral drugs during infection reduces BPNV levels, highlighting the model's utility for drug testing. By providing a reductionist system of the serpentes airway, these organoids constitute a physiologically relevant in vitro model to study reptile viruses and host-pathogen interactions in their native host.

Animals↗
PubMed2007

WNT signaling in the normal intestine and colorectal cancer.

The intestinal epithelium is a self-renewing tissue that represents a unique model for studying interconnected cellular processes such as proliferation, differentiation, cell migration and carcinogenesis. This review covers work from the past decade and highlights the importance of the canonical Wnt pathway in regulating multiple aspects of intestinal homeostasis. Numerous in vivo studies combined with gene profiling experiments have shown that Wnt signaling promotes maintenance of epithelial stem cells and early progenitors by driving transcription of genes associated with proliferation. These studies also revealed strong similarities between the genetic program initiated by Wnt signals in normal crypt progenitors and in colorectal cancer cells. More recently it has become apparent that Wnts do not act alone but rather cooperate with Notch signals in maintaining progenitor cell populations. Processes associated with differentiated epithelial cells also appear to be regulated by Wnt signals. For instance, Paneth cells employ active Wnt signals for terminal differentiation. Moreover, through transcriptional regulation of members of the Eph and Ephrin families, Wnt signaling promotes compartmentalization of epithelial cells along the crypt-villus axis. The Eph/Ephrin system also operates to limit progression of colorectal cancer beyond the early stages.

Animals↗
PubMed2007

Mapping the consequence of Notch1 proteolysis in vivo with NIP-CRE.

The four highly conserved Notch receptors receive short-range signals that control many biological processes during development and in adult vertebrate tissues. The involvement of Notch1 signaling in tissue self-renewal is less clear, however. We developed a novel genetic approach N(1)IP-CRE (Notch1 Intramembrane Proteolysis) to follow, at high resolution, the descendents of cells experiencing Notch1 activation in the mouse. By combining N(1)IP-CRE with loss-of-function analysis, Notch activation patterns were correlated with function during development, self-renewal and malignancy in selected tissues. Identification of many known functions of Notch1 throughout development validated the utility of this approach. Importantly, novel roles for Notch1 signaling were identified in heart, vasculature, retina and in the stem cell compartments of self-renewing epithelia. We find that the probability of Notch1 activation in different tissues does not always indicate a requirement for this receptor and that gradients of Notch1 activation are evident within one organ. These findings highlight an underappreciated layer of complexity of Notch signaling in vivo. Moreover, NIP-CRE represents a general strategy applicable for monitoring proteolysis-dependent signaling in vivo.

Amino Acid Sequence↗
PubMed2006

Wnt/beta-catenin signaling in development and disease.

A remarkable interdisciplinary effort has unraveled the WNT (Wingless and INT-1) signal transduction cascade over the last two decades. Wnt genes encode small secreted proteins that are found in all animal genomes. Wnt signaling is involved in virtually every aspect of embryonic development and also controls homeostatic self-renewal in a number of adult tissues. Germline mutations in the Wnt pathway cause several hereditary diseases, and somatic mutations are associated with cancer of the intestine and a variety of other tissues.

Adult↗
PubMed2006

Rapid loss of intestinal crypts upon conditional deletion of the Wnt/Tcf-4 target gene c-Myc.

Inhibition of the mutationally activated Wnt cascade in colorectal cancer cell lines induces a rapid G1 arrest and subsequent differentiation. This arrest can be overcome by maintaining expression of a single Tcf4 target gene, the proto-oncogene c-Myc. Since colorectal cancer cells share many molecular characteristics with proliferative crypt progenitors, we have assessed the physiological role of c-Myc in adult crypts by conditional gene deletion. c-Myc-deficient crypts are lost within weeks and replaced by c-Myc-proficient crypts through a fission process of crypts that have escaped gene deletion. Although c-Myc(-/-) crypt cells remain in the cell cycle, they are on average much smaller than wild-type cells, cycle slower, and divide at a smaller cell size. c-Myc appears essential for crypt progenitor cells to provide the necessary biosynthetic capacity to successfully progress through the cell cycle.

Animals↗
PubMed2006

The inner nuclear membrane protein emerin regulates beta-catenin activity by restricting its accumulation in the nucleus.

Emerin is a type II inner nuclear membrane (INM) protein of unknown function. Emerin function is likely to be important because, when it is mutated, emerin promotes both skeletal muscle and heart defects. Here we show that one function of Emerin is to regulate the flux of beta-catenin, an important transcription coactivator, into the nucleus. Emerin interacts with beta-catenin through a conserved adenomatous polyposis coli (APC)-like domain. When GFP-emerin is expressed in HEK293 cells, beta-catenin is restricted to the cytoplasm and beta-catenin activity is inhibited. In contrast, expression of an emerin mutant, lacking its APC-like domain (GFP-emerinDelta), dominantly stimulates beta-catenin activity and increases nuclear accumulation of beta-catenin. Human fibroblasts that are null for emerin have an autostimulatory growth phenotype. This unusual growth phenotype arises through enhanced nuclear accumulation and activity of beta-catenin and can be replicated in wild-type fibroblasts by transfection with constitutively active beta-catenin. Our results support recent findings that suggest that INM proteins can influence signalling pathways by restricting access of transcription coactivators to the nucleus.

Cell Line↗
PubMed2006

AU-rich elements and alternative splicing in the beta-catenin 3'UTR can influence the human beta-catenin mRNA stability.

Beta-catenin, the central player of the Wnt signaling cascade, is a well-known oncogene. The regulation of beta-catenin protein stability has been studied extensively while other mechanisms that control cellular levels of beta-catenin have hardly been addressed. In this study, we show that there are three beta-catenin mRNA splice variants that differ solely in their 3'-untranslated region (3'UTR) due to alternative splicing or retaining of an intron. The three isoforms were found to be ubiquitously expressed though in different quantities. Upon induction of the beta-catenin protein in peripheral blood mononuclear leukocytes (PBMC), the beta-catenin mRNA is induced in an isoform-specific manner. All three variants occur in the cytoplasm and contribute to the synthesis of beta-catenin acting as a transcriptional coactivator but have different cytoplasmic stabilities in Hela cells. AU-rich elements (AREs), sequence elements implicated in the regulation of mRNA stability, are found in each of the three transcripts. Surprisingly, the AREs contribute to stabilization of the beta-catenin mRNA transcripts in a splicing-dependent manner. The isoform most affected is the one found to be most induced when beta-catenin protein accumulates. These results suggest that alternative splicing and AREs can act together in regulating beta-catenin mRNA stability and thereby provide a step of controlling the cellular beta-catenin concentration.

3' Untranslated Regions↗
PubMed2006

Transcriptional regulation of CD4 gene expression by T cell factor-1/beta-catenin pathway.

By interacting with MHC class II molecules, CD4 facilitates lineage development as well as activation of Th cells. Expression of physiological levels of CD4 requires a proximal CD4 enhancer to stimulate basic CD4 promoter activity. T cell factor (TCF)-1/beta-catenin pathway has previously been shown to regulate thymocyte survival via up-regulating antiapoptotic molecule Bcl-xL. By both loss and gain of function studies, in this study we show additional function of TCF-1/beta-catenin pathway in the regulation of CD4 expression in vivo. Mice deficient in TCF-1 displayed significantly reduced protein and mRNA levels of CD4 in CD4+ CD8+ double-positive (DP) thymocytes. A transgene encoding Bcl-2 restored survival but not CD4 levels of TCF-1(-/-) DP cells. Thus, TCF-1-regulated survival and CD4 expression are two separate events. In contrast, CD4 levels were restored on DP TCF-1(-/-) cells by transgenic expression of a wild-type TCF-1, but not a truncated TCF-1 that lacks a domain required for interacting with beta-catenin. Furthermore, forced expression of a stabilized beta-catenin, a coactivator of TCF-1, resulted in up-regulation of CD4. TCF-1 or stabilized beta-catenin greatly stimulated activity of a CD4 reporter gene driven by a basic CD4 promoter and the CD4 enhancer. However, mutation of a potential TCF binding site located within the enhancer abrogated TCF-1 and beta-catenin-mediated activation of CD4 reporter. Finally, recruitment of TCF-1 to CD4 enhancer was detected in wild-type but not TCF-1 null mice by chromatin-immunoprecipitation analysis. Thus, our results demonstrated that TCF/beta-catenin pathway enhances CD4 expression in vivo by recruiting TCF-1 to stimulate CD4 enhancer activity.

Animals↗
PubMed2006

Transcription factor target practice.

In this issue of Cell, Hallikas et al. (2006) and Wei et al. (2006) describe different ways of identifying direct targets of transcription factors and their corresponding regulatory sequences in the genome. Although still under development, these studies provide an efficient way to decipher regulatory networks.

Animals↗
PubMed2006

EphB/EphrinB receptors and Wnt signaling in colorectal cancer.

Eph receptors and their ephrin ligands mediate cell repulsion during embryonic development. In the intestinal epithelium, EphB receptors are Wnt signaling target genes that control cell compartmentalization along the crypt axis. Recent findings have shown that this family of receptors are key players during colorectal cancer progression. Here, we review the current knowledge of the EphB/ephrinB system in the intestinal epithelium and we discuss their tumor suppressor role in the context of the multistep progression of colorectal cancer.

Animals↗
PubMed2006

Mining the Wnt pathway for cancer therapeutics.

Aberrant activation of the Wnt pathway is implicated in driving the formation of various human cancers, particularly those of the digestive tract. Inhibition of aberrant Wnt pathway activity in cancer cell lines efficiently blocks their growth, highlighting the great potential of therapeutics designed to achieve this in cancer patients. Here we provide an overview of the promise and pitfalls of current drug development strategies striving to inhibit the Wnt pathway and present new opportunities for therapeutic intervention.

Animals↗
PubMed2006

From gut homeostasis to cancer.

The mammalian intestine has one of the highest turnover rates in the body. The intestinal epithelium is completely renewed in less than a week. It is divided into spatially distinct compartments in the form of finger-like projections and invaginations that are dedicated to specific functions. Intestinal cells are constantly produced from a stem cell reservoir that gives rise to proliferating transient amplifying cells, which subsequently differentiate and migrate to the correct compartment before dying after having fulfilled their physiological function. In recent years, a substantial body of evidence has accumulated to support the concept that signaling pathways known to be crucial for embryonic development of multiple organisms play a critical role in tightly regulating and controlling the self-renewing process of the intestine. Moreover, the same pathways appear to be deregulated in several hereditary and sporadic colorectal cancer syndromes due to activating and/or inactivating mutations of key components of such pathways. In this review we discuss recent findings demonstrating that differentiation and homeostasis of the intestine are controlled by developmental pathways such as Wnt, Notch, TGF-beta and Hedgehog, and illustrate how their deregulation contributes to intestinal neoplasia.

Animals↗
PubMed2005

The rac activator Tiam1 is a Wnt-responsive gene that modifies intestinal tumor development.

Mutations in the canonical Wnt signaling pathway leading to its activation are known to cause the majority of intestinal tumors. However, few genes targeted by this pathway have been demonstrated to affect tumor development in vivo. Here we show that Tiam1, a selective Rac GTPase activator, is a Wnt-responsive gene expressed in the base of intestinal crypts and up-regulated in mouse intestinal tumors and human colon adenomas. Moreover, by comparing tumor development in APC mutant Min (multiple intestinal neoplasia) mice expressing or lacking Tiam1, we found that Tiam1 deficiency significantly reduces the formation and growth of polyps in vivo. However, invasion of malignant intestinal tumors is enhanced by a lack of Tiam1. In line with this, knock-down of Tiam1 reduced the growth potential of human colorectal cancer cells and their ability to form E-cadherin-based adhesions, a prerequisite for local invasion of tumor cells. Our data indicate a novel cross-talk between Tiam1-Rac and canonical Wnt-signaling pathways that influences intestinal tumor formation and progression.

Adenoma↗
PubMed2005

Notch and Wnt inhibitors as potential new drugs for intestinal neoplastic disease.

Colorectal cancer is a major cause of death in the western world. Recent advances in treatment comprise variations on the classical themes of surgical resection combined with chemotherapy using cytotoxic drugs and radiation therapy. Because this therapy is only moderately successful, novel approaches to the treatment of colorectal cancer are required. Our rapidly increasing knowledge of molecular signalling pathways that are deregulated in colorectal cancer might provide a platform from which to develop new rational cancer therapies. Here, we give an update on the roles of the Wnt and Notch signalling pathways in the self renewal of the intestinal epithelium and the consequences of Wnt deregulation in colorectal cancer. We focus on the potential of recently identified small-molecule inhibitors of the Wnt pathway and gamma-secretase inhibitors of the Notch pathway as novel colon cancer therapeutics.

Amyloid Precursor Protein Secretases↗
PubMed2005

Down-regulation of Rap1 activity is involved in ephrinB1-induced cell contraction.

Ephrins are cell surface ligands that activate Eph receptor tyrosine kinases. This ligand-receptor interaction plays a central role in the sorting of cells. We have previously shown that the ephrinB-EphB signalling pathway is also involved in the migration of intestinal precursor cells along the crypts. Using the colon cell line DLD1 expressing the EphB2 receptor, we showed that stimulation of these cells with soluble ephrinB1 results in a rapid retraction of cell extensions and a detachment of cells. On ephrinB1 stimulation, the small GTPases Rho and Ras are activated and Rap1 is inactivated. Importantly, when a constitutively active Rap1 mutant was introduced into these cells, ephrinB1-induced retraction was inhibited. From these results, we conclude that down-regulation of Rap1 is a prerequisite for ephrin-induced cell retraction in colon cells.

Cell Adhesion↗
PubMed2005

EphB receptor activity suppresses colorectal cancer progression.

Most sporadic colorectal cancers are initiated by activating Wnt pathway mutations, characterized by the stabilization of beta-catenin and constitutive transcription by the beta-catenin/T cell factor-4 (Tcf-4) complex. EphB guidance receptors are Tcf4 target genes that control intestinal epithelial architecture through repulsive interactions with Ephrin-B ligands. Here we show that, although Wnt signalling remains constitutively active, most human colorectal cancers lose expression of EphB at the adenoma-carcinoma transition. Loss of EphB expression strongly correlates with degree of malignancy. Furthermore, reduction of EphB activity accelerates tumorigenesis in the colon and rectum of Apc(Min/+) mice, and results in the formation of aggressive adenocarcinomas. Our data demonstrate that loss of EphB expression represents a critical step in colorectal cancer progression.

Adenoma↗
PubMed2005

Notch/gamma-secretase inhibition turns proliferative cells in intestinal crypts and adenomas into goblet cells.

The self-renewing epithelium of the small intestine is ordered into stem/progenitor crypt compartments and differentiated villus compartments. Recent evidence indicates that the Wnt cascade is the dominant force in controlling cell fate along the crypt-villus axis. Here we show a rapid, massive conversion of proliferative crypt cells into post-mitotic goblet cells after conditional removal of the common Notch pathway transcription factor CSL/RBP-J. We obtained a similar phenotype by blocking the Notch cascade with a gamma-secretase inhibitor. The inhibitor also induced goblet cell differentiation in adenomas in mice carrying a mutation of the Apc tumour suppressor gene. Thus, maintenance of undifferentiated, proliferative cells in crypts and adenomas requires the concerted activation of the Notch and Wnt cascades. Our data indicate that gamma-secretase inhibitors, developed for Alzheimer's disease, might be of therapeutic benefit in colorectal neoplastic disease.

Adenoma↗