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Hans Clevers

Publications and source records attributed to Hans Clevers.

At least 37 records · Page 2Linked to original sources
PubMed2005

Cyclin D1 is not an immediate target of beta-catenin following Apc loss in the intestine.

Cyclin D1 is postulated to be a target of the canonical Wnt pathway and critical for intestinal adenoma development. We show here that, unlike cyclin D1 reporter assays, endogenous cyclin D1 levels are not affected following antagonism of the Wnt pathway in vitro, nor is cyclin D1 immediately up-regulated following conditional loss of Apc in vivo. Cyclin D1 levels do, however, increase in a delayed manner in a small subset of cells, suggesting such up-regulation occurs as a secondary event. We also analyzed the immediate consequences of Apc loss in a cyclin D1(-/-) background and failed to find any cyclin D1-dependent phenotypes. However, we did observe elevated cyclin D1 expression in lesions developing 20 days after Apc loss. In these circumstances, all adenomas (but not smaller lesions) showed cyclin D1 up-regulation. Finally in a smaller study, we analyzed whether cyclin D1 deficiency affected adenoma formation 20 days following induced loss of Apc. Unlike AhCre(+) Apc(fl/fl) mice (which all developed adenomas), doubly mutant AhCre(+) Apc(fl/fl) cyclin D1(-/-) mice only developed small lesions. Taken together, this argues that cyclin D1 up-regulation in intestinal neoplasia is important for tumor progression rather than initiation.

Adenoma↗
PubMed2005

Wnt signaling in the intestinal epithelium: from endoderm to cancer.

The Wnt pathway controls cell fate during embryonic development. It also persists as a key regulator of homeostasis in adult self-renewing tissues. In these tissues, mutational deregulation of the Wnt cascade is closely associated with malignant transformation. The intestinal epithelium represents the best-understood example for the closely linked roles of Wnt signaling in homeostatic self-renewal and malignant transformation. In this review, we outline current understanding of the physiological role of Wnt signaling in intestinal biology. From this perspective, we then describe how mutational subversion of the Wnt cascade leads to colorectal cancer.

Animals↗
PubMed2005

Wnt signalling in stem cells and cancer.

The canonical Wnt cascade has emerged as a critical regulator of stem cells. In many tissues, activation of Wnt signalling has also been associated with cancer. This has raised the possibility that the tightly regulated self-renewal mediated by Wnt signalling in stem and progenitor cells is subverted in cancer cells to allow malignant proliferation. Insights gained from understanding how the Wnt pathway is integrally involved in both stem cell and cancer cell maintenance and growth in the intestinal, epidermal and haematopoietic systems may serve as a paradigm for understanding the dual nature of self-renewal signals.

Animals↗
PubMed2005

Wnt control of stem cells and differentiation in the intestinal epithelium.

The intestinal epithelium represents a very attractive experimental model for the study of integrated key cellular processes such as proliferation and differentiation. The tissue is subjected to a rapid and perpetual self-renewal along the crypt-villus axis. Renewal requires division of multipotent stem cells, still to be morphologically identified and isolated, followed by transit amplification, and differentiation of daughter cells into specialized absorptive and secretory cells. Our understanding of the crucial role played by the Wnt/beta-catenin signaling pathway in controlling the fine balance between cell proliferation and differentiation in the gut has been significantly enhanced in recent years. Mutations in some of its components irreversibly lead to carcinogenesis in humans and in mice. Here, we discuss recent advances related to the Wnt/beta-catenin signaling pathway in regulating intestinal stem cells, homeostasis, and cancer. We emphasize how Wnt signaling is able to maintain a stem cell/progenitor phenotype in normal intestinal crypts, and to impose a very similar phenotype onto colorectal adenomas.

Animals↗
PubMed2005

Functional analysis of Peutz-Jeghers mutations reveals that the LKB1 C-terminal region exerts a crucial role in regulating both the AMPK pathway and the cell polarity.

Germline mutations of the LKB1 gene are responsible for the cancer-prone Peutz-Jeghers syndrome (PJS). LKB1 encodes a serine-threonine kinase that acts as a regulator of cell cycle, metabolism and cell polarity. The majority of PJS missense mutations abolish LKB1 enzymatic activity and thereby impair all functions assigned to LKB1. Here, we have investigated the functional consequences of recurrent missense mutations identified in PJS and in sporadic tumors which map in the LKB1 C-terminal non-catalytic region. We report that these C-terminal mutations neither disrupt LKB1 kinase activity nor interfere with LKB1-induced growth arrest. However, these naturally occuring mutations lessened LKB1-mediated activation of the AMP-activated protein kinase (AMPK) and impaired downstream signaling. Furthermore, C-terminal mutations compromise LKB1 ability to establish and maintain polarity of both intestinal epithelial cells and migrating astrocytes. Consistent with these findings, mutational analysis reveals that the LKB1 tail exerts an essential function in the control of cell polarity. Overall, our results ascribe a crucial regulatory role to the LKB1 C-terminal region. Our findings further indicate that LKB1 tumor suppressor activity is likely to depend on the regulation of AMPK signaling and cell polarization.

AMP-Activated Protein Kinase Kinases↗
PubMed2005

Self-renewal and cancer of the gut: two sides of a coin.

The intestinal epithelium follows the paradigms of stem cell biology established for other self-renewing tissues. With a unique topology, it constitutes a two-dimensional structure folded into valleys and hills: the proliferative crypts and the differentiated villi. Its unprecedented self-renewal rate appears reflected in a high susceptibility to malignant transformation. The molecular mechanisms that control homeostatic self-renewal and those that underlie colorectal cancer are remarkably symmetrical. Here, we discuss the biology of the intestinal epithelium, emphasizing the roles played by Wnt, bone morphogenic protein, and Notch signaling cascades in epithelial self-renewal and cancer.

Adenomatous Polyposis Coli↗
PubMed2005

Wnt signalling induces maturation of Paneth cells in intestinal crypts.

Wnt signalling, which is transduced through beta-catenin/TCF4, maintains the undifferentiated state of intestinal crypt progenitor cells. Mutational activation of the pathway initiates the adenomacarcinoma sequence. Whereas all other differentiated epithelial cells migrate from the crypt onto the villus, Paneth cells home towards the source of Wnt signals--that is, the crypt bottom. Here, we show that expression of a Paneth gene programme is critically dependent on TCF4 in embryonic intestine. Moreover, conditional deletion of the Wnt receptor Frizzled-5 abrogates expression of these genes in Paneth cells in the adult intestine. Conversely, adenomas in Apc-mutant mice and colorectal cancers in humans inappropriately express these Paneth-cell genes. These observations imply that Wnt signals in the crypt can separately drive a stem-cell/progenitor gene programme and a Paneth-cell maturation programme. In intestinal cancer, both gene programmes are activated simultaneously.

Animals↗
PubMed2005

FoxM1 is required for execution of the mitotic programme and chromosome stability.

Transcriptional induction of cell-cycle regulatory proteins ensures proper timing of subsequent cell-cycle events. Here we show that the Forkhead transcription factor FoxM1 regulates expression of many G2-specific genes and is essential for chromosome stability. Loss of FoxM1 leads to pleiotropic cell-cycle defects, including a delay in G2, chromosome mis-segregation and frequent failure of cytokinesis. We show that transcriptional activation of cyclin B by FoxM1 is essential for timely mitotic entry, whereas CENP-F, another direct target of FoxM1 identified here, is essential for precise functioning of the mitotic spindle checkpoint. Thus, our data uncover a transcriptional cluster regulated by FoxM1 that is essential for proper mitotic progression.

Animals↗
PubMed2005

Canonical Wnt signaling in differentiated osteoblasts controls osteoclast differentiation.

Inactivation of beta-catenin in mesenchymal progenitors prevents osteoblast differentiation; inactivation of Lrp5, a gene encoding a likely Wnt coreceptor, results in low bone mass (osteopenia) by decreasing bone formation. These observations indicate that Wnt signaling controls osteoblast differentiation and suggest that it may regulate bone formation in differentiated osteoblasts. Here, we study later events and find that stabilization of beta-catenin in differentiated osteoblasts results in high bone mass, while its deletion from differentiated osteoblasts leads to osteopenia. Surprisingly, histological analysis showed that these mutations primarily affect bone resorption rather than bone formation. Cellular and molecular studies showed that beta-catenin together with TCF proteins regulates osteoblast expression of Osteoprotegerin, a major inhibitor of osteoclast differentiation. These findings demonstrate that beta-catenin, and presumably Wnt signaling, promote the ability of differentiated osteoblasts to inhibit osteoclast differentiation; thus, they broaden our knowledge of the functions Wnt proteins have at various stages of skeletogenesis.

Animals↗
PubMed2005

Expression pattern of Wnt signaling components in the adult intestine.

BACKGROUND & AIMS: In the intestine, the canonical Wnt signaling cascade plays a crucial role in driving the proliferation of epithelial cells. Furthermore, aberrant activation of Wnt signaling is strongly associated with the development of colorectal cancer. Despite this evidence, little is known about the precise identity and localization of Wnts and their downstream effectors in the adult intestine. To address this issue, we examined the expression pattern of all Wnts, Frizzleds (Fzs), low-density lipoprotein receptor-related proteins, Wnt antagonists, and T-cell factors in the murine small intestine and colon and adenomas. METHODS: Embryonic, postnatal, and adult intestinal samples were subjected to in situ hybridization by using specific RNA probes for the various genes tested. RESULTS: Our analysis showed high expression of several signaling components (including Wnt-3, Wnt-6, Wnt-9b, Frizzled 4, Frizzled 6, Frizzled 7, low-density lipoprotein receptor-related protein 5, and secreted Frizzled-related protein 5) in crypt epithelial cells. We also detected Wnt-2b, Wnt-4, Wnt-5a, Wnt-5b, Frizzled 4, and Frizzled 6 in differentiated epithelial and mesenchymal cells of the small intestine and colon. Finally, several factors (Frizzled 4, T-cell factor 1, lymphoid enhancer factor, Dickkopf 2, Dickkopf 3, and Wnt-interacting factor) displayed differential expression in normal vs neoplastic tissue. CONCLUSIONS: Our study predicts a much broader role for Wnt signaling in gut development and homeostasis than was previously anticipated from available genetic studies and identifies novel factors likely involved in promoting canonical and noncanonical Wnt signals in the intestine.

Adult↗
PubMed2005

Wnt, stem cells and cancer in the intestine.

The intestinal epithelium is a self-renewing tissue which represents a unique model for studying interconnected cellular processes such as proliferation, differentiation, cell migration and carcinogenesis. Although the stem cells of the intestine have not yet been physically characterized or isolated, data over the past decade have strongly implicated the Wnt/beta-catenin signalling pathway in their maintenance and progression to cancer. This review will (i) describe the distinctive features of the intestinal epithelium in relation to stem-cell function, (ii) illustrate the major genetic alterations that can lead to cancer, and (iii) show how Wnt/beta-catenin signalling controls homoeostasis in this tissue.

Animals↗
PubMed2004

At the crossroads of inflammation and cancer.

Chronic inflammation and cancer are closely associated in the intestine. Anti-inflammatory medication reduces intestinal neoplasia, while colorectal cancer incidence is increased in ulcerative colitis. Cyclooxygenases are key to both diseases, yet the molecular basis of the association remains incompletely understood. Two recent Cell (Greten et al., 2004; Rakoff-Nahoum et al., 2004) papers illuminate roles of Toll-like receptors and the NF-kappaB pathway in the control of epithelial homeostasis in health and disease.

Animals↗
PubMed2004

SOX9 is an intestine crypt transcription factor, is regulated by the Wnt pathway, and represses the CDX2 and MUC2 genes.

TCF and SOX proteins belong to the high mobility group box transcription factor family. Whereas TCFs, the transcriptional effectors of the Wnt pathway, have been widely implicated in the development, homeostasis and disease of the intestine epithelium, little is known about the function of the SOX proteins in this tissue. Here, we identified SOX9 in a SOX expression screening in the mouse fetal intestine. We report that the SOX9 protein is expressed in the intestinal epithelium in a pattern characteristic of Wnt targets. We provide in vitro and in vivo evidence that a bipartite beta-catenin/TCF4 transcription factor, the effector of the Wnt signaling pathway, is required for SOX9 expression in epithelial cells. Finally, in colon epithelium-derived cells, SOX9 transcriptionally represses the CDX2 and MUC2 genes, normally expressed in the mature villus cells of the intestinal epithelium, and may therefore contribute to the Wnt-dependent maintenance of a progenitor cell phenotype.

Animals↗
PubMed2004

Loss of Apc in vivo immediately perturbs Wnt signaling, differentiation, and migration.

Although Apc is well characterized as a tumor-suppressor gene in the intestine, the precise mechanism of this suppression remains to be defined. Using a novel inducible Ahcre transgenic line in conjunction with a loxP-flanked Apc allele we, show that loss of Apc acutely activates Wnt signaling through the nuclear accumulation of beta-catenin. Coincidentally, it perturbs differentiation, migration, proliferation, and apoptosis, such that Apc-deficient cells maintain a "crypt progenitor-like" phenotype. Critically, for the first time we confirm a series of Wnt target molecules in an in vivo setting and also identify a series of new candidate targets within the same setting.

Adenomatous Polyposis Coli Protein↗
PubMed2004

Wnt signaling: Ig-norrin the dogma.

Secreted Wnt proteins trigger the intracellular Wnt signaling cascade upon engagement of dedicated Frizzled-Lrp receptor complexes. Unexpectedly, a non-Wnt ligand for this receptor complex has now been discovered. This novel ligand, Norrin, is mutated in the hereditary ocular Norrie syndrome.

Blindness↗
PubMed2004

Aberrant polycystin-1 expression results in modification of activator protein-1 activity, whereas Wnt signaling remains unaffected.

Polycystin-1, the polycystic kidney disease 1 gene product, has been implicated in several signaling complexes that are known to regulate essential cellular functions. We investigated the role of polycystin-1 in Wnt signaling and activator protein-1 (AP-1) activation. To this aim, a membrane-targeted construct encoding the conserved C-terminal region of mouse polycystin-1 reported to mediate signal transduction activity was expressed in human embryonic and renal epithelial cells. To ensure specificity and minimal cotransfection effects, we focused our study on the endogenous proteins that actually transduce the signals, beta-catenin and T-cell factor/lymphoid-enhancing factor for Wnt signaling and (phosphorylated) c-Jun, ATF2, and c-Fos for AP-1. Our data indicate that the C-terminal region of polycystin-1 activates AP-1 by inducing phosphorylation and expression of at least c-Jun and ATF2, whereas c-Fos was not affected. Under our experimental conditions, polycystin-1 did not modulate Wnt signaling. AP-1 activity was aberrant in human autosomal dominant polycystic kidney disease (ADPKD) renal cystic epithelial cells and in renal epithelial cells expressing transgenic full-length polycystin-1, resulting in decreased Jun-ATF and increased Jun-Fos activity, whereas Wnt signaling remained unaffected. Since our data indicate that aberrant polycystin-1 expression results in altered AP-1 activity, polycystin-1 may be required for adequate AP-1 activity.

Activating Transcription Factor 2↗
PubMed2004

Illegitimate WNT signaling promotes proliferation of multiple myeloma cells.

The unrestrained growth of tumor cells is generally attributed to mutations in essential growth control genes, but tumor cells are also influenced by signals from the environment. In multiple myeloma (MM), the factors and signals coming from the bone marrow microenvironment are possibly even essential for the growth of the tumor cells. As targets for intervention, these signals may be equally important as mutated oncogenes. Given their oncogenic potential, WNT signals form a class of paracrine growth factors that could act to influence MM cell growth. In this paper, we report that MM cells have hallmarks of active WNT signaling, whereas the cells have not undergone detectable mutations in WNT signaling genes such as adenomatous polyposis coli and beta-catenin (CTNNB1). We show that the malignant MM plasma cells overexpress beta-catenin, including its N-terminally unphosphorylated form, suggesting active beta-catenin/T cell factor-mediated transcription. Further accumulation and nuclear localization of beta-catenin, and/or increased cell proliferation, was achieved by stimulation of WNT signaling with either Wnt3a, LiCl, or the constitutively active S33Y mutant of beta-catenin. In contrast, by blocking WNT signaling by dominant-negative T cell factor, we can interfere with the growth of MM cells. We therefore suggest that MM cells are dependent on an active WNT signal, which may have important implications for the management of this incurable form of cancer.

Cell Division↗