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H Clevers

Publications and source records attributed to H Clevers.

At least 19 recordsLinked to original sources
PubMed2006

Interplay between VHL/HIF1alpha and Wnt/beta-catenin pathways during colorectal tumorigenesis.

Activation of the Wnt signaling pathway initiates the transformation of colorectal epithelial cells, although the transition to metastatic cancer requires angiogenesis. We have investigated the expression of the von Hippel-Lindau (VHL) tumor suppressor in the intestines from humans and mice. Here, we show that VHL expression is regulated by TCF4 and is restricted to the proliferative compartment at the bottom of intestinal crypts. Accordingly, VHL is completely absent from the proliferative intestinal pockets of Tcf4(-/-) perinatal mice. We observed complementary staining of the hypoxia-inducible factor (HIF) 1alpha to VHL in normal intestinal epithelium as well as in all stages of colorectal cancer (CRC). To the best of our knowledge, this is the first report demonstrating the presence of nuclear HIF1alpha in normoxic healthy adult tissue. Although we observed upregulated levels of VHL in very early CRC lesions from sporadic and familial adenomatous polyposis patients - presumably due to activated Wnt signaling - a clear reduction of VHL expression is observed in later stages of CRC progression, coinciding with stabilization of HIF1alpha. As loss of VHL in later stages of CRC progression results in stabilization of HIF, these data provide evidence that selection for VHL downregulation provides a proangiogenic impulse for CRC progression.

Adenocarcinoma↗
PubMed2006

Mucosal prolapse in the pathogenesis of Peutz-Jeghers polyposis.

Germline mutations in LKB1 cause the rare cancer prone disorder Peutz-Jeghers syndrome (PJS). Gastrointestinal hamartomatous polyps constitute the major phenotypic trait in PJS. Hamartomatous polyps arising in PJS patients are generally considered to lack premalignant potential although rare neoplastic changes in these polyps and an increased gastrointestinal cancer risk in PJS are well documented. These conflicting observations are resolved in the current hypothesis by providing a unifying explanation for these contrasting features of PJS polyposis. We postulate that a genetic predisposition to epithelial prolapse underlies the formation of the polyps associated with PJS. Conventional sporadic adenomas arising in PJS patients will similarly show mucosal prolapse and carry the associated histological features.

AMP-Activated Protein Kinase Kinases↗
PubMed2003

Retraction.

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Retraction Notice↗
PubMed2001

The chromatin remodelling factor Brg-1 interacts with beta-catenin to promote target gene activation.

Wnt-induced formation of nuclear Tcf-beta-catenin complexes promotes transcriptional activation of target genes involved in cell fate decisions. Inappropriate expression of Tcf target genes resulting from mutational activation of this pathway is also implicated in tumorigenesis. The C-terminus of beta-catenin is indispensable for the transactivation function, which probably reflects the presence of binding sites for essential transcriptional coactivators such as p300/CBP. However, the precise mechanism of transactivation remains unclear. Here we demonstrate an interaction between beta-catenin and Brg-1, a component of mammalian SWI/SNF and Rsc chromatin-remodelling complexes. A functional consequence of reintroduction of Brg-1 into Brg-1-deficient cells is enhanced activity of a Tcf-responsive reporter gene. Consistent with this, stable expression of inactive forms of Brg-1 in colon carcinoma cell lines specifically inhibits expression of endogenous Tcf target genes. In addition, we observe genetic interactions between the Brg-1 and beta-catenin homologues in flies. We conclude that beta-catenin recruits Brg-1 to Tcf target gene promoters, facilitating chromatin remodelling as a prerequisite for transcriptional activation.

Amino Acid Substitution↗
PubMed2001

The epithelial cellular adhesion molecule (Ep-CAM) is a ligand for the leukocyte-associated immunoglobulin-like receptor (LAIR).

Human leukocyte-associated immunoglobulin-like receptor (LAIR)-1 is expressed on many cells of the immune system and is predicted to mediate inhibitory functions based on the presence of immunoreceptor tyrosine-based inhibitory motifs (ITIMs) in its cytoplasmic domain. Although the role of LAIR-1 in the regulation of immune responses in vivo is unknown, LAIR-1 cross-linking by monoclonal antibody inhibits various immune cell functions in vitro. Here, we identify the colon carcinoma-associated epithelial cellular adhesion molecule (Ep-CAM) as a ligand for LAIR-1 and LAIR-2, a related soluble LAIR-1 family member. Ep-CAM interacts with the LAIR molecules through its first epidermal growth factor domain; Ep-CAM--specific antibodies can abrogate the binding. Intraepithelial T lymphocytes express LAIR-1 and thus may interact with Ep-CAM present on human intestinal epithelium. We propose that LAIR-1--Ep-CAM interaction may contribute to mucosal tolerance and that LAIR-2 possibly modulates this function.

Antigens, Neoplasm↗
PubMed2001

All Tcf HMG box transcription factors interact with Groucho-related co-repressors.

Tcf/Lef family transcription factors are the downstream effectors of the Wingless/Wnt signal transduction pathway. Upon Wingless/Wnt signalling, beta-catenin translocates to the nucleus, interacts with Tcf (1-3) and thus activates transcription of target genes (4,5). Tcf factors also interact with members of the Groucho (Grg/TLE) family of transcriptional co-repressors (6). We have now tested all known mammalian Groucho family members for their ability to interact specifically with individual Tcf/Lef family members. Transcriptional activation by any Tcf could be repressed by Grg-1, Grg-2/TLE-2, Grg-3 and Grg-4 in a reporter assay. Specific interactions between Tcf and Grg proteins may be achieved in vivo by tissue- or cell type-limited expression. To address this, we determined the expression of all Tcf and Grg/TLE family members in a panel of cell lines. Within any cell line, several Tcfs and TLEs are co-expressed. Thus, redundancy in Tcf/Grg interactions appears to be the rule. The 'long' Groucho family members containing five domains are repressors of Tcf-mediated transactivation, whereas Grg-5, which only contains the first two domains, acts as a de-repressor. As previously shown for Drosophila Groucho, we show that long Grg proteins interact with histone deacetylase-1. Although Grg-5 contains the GP homology domain that mediates HDAC binding in long Grg proteins, Grg-5 fails to bind this co-repressor, explaining how it can de-repress transcription.

Amino Acid Sequence↗
PubMed2001

Mutant E-cadherin breast cancer cells do not display constitutive Wnt signaling.

Participation of E-cadherin in the Wnt signaling pathway was suggested because of the dual role of beta-catenin in cell adhesion and the Wnt signaling cascade. Whereas beta-catenin interacts at the cell membrane with the cell adhesion protein E-cadherin, in the nucleus it activates Wnt target genes through formation of transcriptionally active complexes with members of the Tcf/Lef family of transcription factors. Here, we analyzed by PCR and direct cycle sequencing 26 human breast cancer cell lines for alterations in the E-cadherin gene. Genetic alterations were identified in eight cell lines. Five cell lines had truncating mutations, whereas three cell lines had in-frame deletions in the gene transcript and expressed mutant E-cadherin proteins at the cell membrane. Involvement of E-cadherin in the Wnt pathway was evaluated through determination of the activity of a Tcf reporter gene, which had been transiently transfected into 15 breast cancer cell lines. None of six E-cadherin mutant cell lines and four cell lines that exhibit transcriptional silencing of the E-cadherin gene showed Tcf-mediated transcriptional activation. E-cadherin wild-type cell line DU4475 exhibited constitutive Tcf-beta-catenin signaling activity and was found to express truncated APC proteins. These results indicate that if cellular transformation occurred through mutation of E-cadherin, it is not mediated via constitutive activation of the Wnt signaling pathway.

Breast Neoplasms↗
PubMed2001

Wnt signaling is required for thymocyte development and activates Tcf-1 mediated transcription.

T cell factor / lymphocyte enhancer factor (Tcf/Lef) transcription factors complex with the transcriptional co-activator beta-catenin to transduce Wnt signals in a variety of developmental systems. The prototypic family member Tcf-1 is highly expressed in T lineage cells. Tcf1-/- mice are defective in cell cycling of early thymocyte stages. Here, we show that the interaction of beta-catenin with Tcf-1 is required for full thymocyte development. This interaction may be established by signals mediated by Wnt1 and Wnt4, leading to increased Tcf-dependent transcriptional activity in thymocytes, as demonstrated in Tcf-LacZ reporter mice. Transduction of fetal thymocytes with Wnt1 and Wnt4 results in increased survival in an in vitro cell culture system. Retroviral expression of soluble Wnt receptor mutants that block Wnt signaling inhibits thymocyte development. These results imply an important role for the Wnt cascade in thymocyte development.

Animals↗
PubMed2001

Mutations in the APC tumour suppressor gene cause chromosomal instability.

Two forms of genetic instability have been described in colorectal cancer: microsatellite instability and chromosomal instability. Microsatellite instability results from mutations in mismatch repair genes; chromosomal instability is the hallmark of many colorectal cancers, although it is not completely understood at the molecular level. As truncations of the Adenomatous Polyposis Coli (APC) gene are found in most colorectal tumours, we thought that mutations in APC might be responsible for chromosomal instability. To test this hypothesis, we examined mouse embryonic stem (ES) cells homozygous for Min (multiple intestinal neoplasia) or Apc1638T alleles. Here we show that Apc mutant ES cells display extensive chromosome and spindle aberrations, providing genetic evidence for a role of APC in chromosome segregation. Consistent with this, APC accumulates at the kinetochore during mitosis. Apc mutant cells form mitotic spindles with an abundance of microtubules that inefficiently connect with kinetochores. This phenotype is recapitulated by the induced expression of a 253-amino-acid carboxy-terminal fragment of APC in microsatellite unstable colorectal cancer cells. We conclude that loss of APC sequences that lie C-terminal to the beta-catenin regulatory domain contributes to chromosomal instability in colorectal cancer.

Adenomatous Polyposis Coli Protein↗
PubMed2001

APC, signal transduction and genetic instability in colorectal cancer.

Colorectal cancer arises through a gradual series of histological changes, each of which is accompanied by a specific genetic alteration. In general, an intestinal cell needs to comply with two essential requirements to develop into a cancer: it must acquire selective advantage to allow for the initial clonal expansion, and genetic instability to allow for multiple hits in other genes that are responsible for tumour progression and malignant transformation. Inactivation of APC--the gene responsible for most cases of colorectal cancer--might fulfil both requirements.

Animals↗
PubMed2001

The beta-catenin--TCF-1 pathway ensures CD4(+)CD8(+) thymocyte survival.

The association of trans-acting T cell factors (TCFs) or lymphoid enhancer factor 1 (LEF-1) with their coactivator beta-catenin mediates transient transcriptional responses to extracellular Wnt signals. We show here that T cell maturation depends on the presence of the beta-catenin--binding domain in TCF-1. This domain is necessary to mediate the survival of immature CD4(+)CD8(+) double-positive (DP) thymocytes. Accelerated spontaneous thymocyte death in the absence of TCF-1 correlates with aberrantly low expression of the anti-apoptotic protein Bcl-x(L). Increasing anti-apoptotic effectors in thymocytes by the use of a Bcl-2 transgene rescued TCF-1-deficient DP thymocytes from apoptosis. Thus, TCF-1, upon association with beta-catenin, transiently ensures the survival of immature T cells, which enables them to generate and edit T cell receptor (TCR) alpha chains and attempt TCR-mediated positive selection.

Animals↗
PubMed2001

Ectopic Wnt signal determines the eyeless phenotype of zebrafish masterblind mutant.

masterblind (mbl) is a zebrafish mutation characterised by the absence or reduction in size of the telencephalon, optic vesicles and olfactory placodes. We show that inhibition of Gsk3beta in zebrafish embryos either by overexpression of dominant negative dn gsk3beta mRNA or by lithium treatment after the midblastula transition phenocopies mbl. The loss of anterior neural tissue in mbl and lithium-treated embryos is preceded by posteriorization of presumptive anterior neuroectoderm during gastrulation, which is evident from the anterior shift of marker genes Otx2 and Wnt1. Heterozygous mbl embryos showed increased sensitivity to inhibition of GSK3beta by lithium or dn Xgsk3beta that led to the loss of eyes. Overexpression of gsk3beta mRNA rescued eyes and the wild-type fgf8 expression of homozygous mbl embryos. emx1 that delineates the telencephalon is expanded and shifted ventroanteriorly in mbl embryos. In contrast to fgf8, the emx1 expression domain was not restored upon overexpression of gsk3beta mRNA. These experiments place mbl as an antagonist of the Wnt pathway in parallel or upstream of the complex consisting of Axin, APC and Gsk3beta that binds and phosphorylates beta-catenin, thereby destabilising it. mbl maps on LG 3 close to a candidate gene axin1. In mbl we detected a point mutation in the conserved minimal Gsk3beta-binding domain of axin1 leading to a leucine to glutamine substitution at position 399. Overexpression of wild-type axin1 mRNA rescued mbl completely, demonstrating that mutant axin1 is responsible for the mutant phenotype. Overexpression of mutant L399Q axin1 in wild-type embryos resulted in a dose-dependent dominant negative activity as demonstrated by the loss of telencephalon and eyes. We suggest that the function of Axin1/Mbl protein is to antagonise the Wnt signal and in doing so to establish and maintain the most anterior CNS. Our findings provide new insights into the mechanisms by which the Wnt pathway generates anteroposterior polarity of the neural plate.

Animals↗
PubMed2000

Sequence-specific high mobility group box factors recognize 10-12-base pair minor groove motifs.

Sequence-specific high mobility group (HMG) box factors bind and bend DNA via interactions in the minor groove. Three-dimensional NMR analyses have provided the structural basis for this interaction. The cognate HMG domain DNA motif is generally believed to span 6-8 bases. However, alignment of promoter elements controlled by the yeast genes ste11 and Rox1 has indicated strict conservation of a larger DNA motif. By site selection, we identify a highly specific 12-base pair motif for Ste11, AGAACAAAGAAA. Similarly, we show that Tcf1, MatMc, and Sox4 bind unique, highly specific DNA motifs of 12, 12, and 10 base pairs, respectively. Footprinting with a deletion mutant of Ste11 reveals a novel interaction between the 3' base pairs of the extended DNA motif and amino acids C-terminal to the HMG domain. The sequence-specific interaction of Ste11 with these 3' base pairs contributes significantly to binding and bending of the DNA motif.

Amino Acid Sequence↗
PubMed2000

Roles of Sox4 in central nervous system development.

The transcription factor-encoding gene, Sox4, is expressed in a wide range of tissues and has been shown to be functionally involved in heart, B-cell and reproductive system development. Sox4 shows a high degree of sequence homology with another group C Sox gene, Sox11, which is predominantly expressed in the CNS. Since the expression of Sox4 in the CNS has not been described we have carried out such a study. Sox4 and Sox11 expression increased simultaneously in the same early differentiating cells of the developing CNS except in the external granule layer of the cerebellum where Sox11 expression preceded that of Sox4. As development proceeded, their expression always appeared to relate to the maturational stage of the cell population, with Sox11 expression more transient than Sox4, except in the spinal cord where the reverse was true. Sox4 knock-out mice have been shown to die of a heart defect half way through gestation with no observable CNS phenotype. Our more detailed analysis showed no abnormality in the spatial restriction of expression of Sox2, Sox11, Mash1, neurogenin1 or neurogenin2, although the level of expression of Sox11 and Mash1 appeared a little different from the wild-type, implying that Sox4 might indeed have a functional role in CNS development. However, since Sox4 and Sox11 expression is so similar, we propose that Sox11 might compensate for the loss of Sox4 function in the CNS such that the phenotype is extremely mild in the Sox4 null mutant.

Aging↗
PubMed2000

Differential expression of the Groucho-related genes 4 and 5 during early development of Xenopus laevis.

Recently, we demonstrated that the Xenopus Wnt effector XTcf-3 interacts with Groucho-related transcriptional repressors (Roose et al., 1998. Nature 395, 608-612). A long form of the Groucho-related genes, XGrg-4, was shown to repress axis formation in the Xenopus embryo, whereas a short form, XGrg-5, acted as a potentiator. In this study, the temporal and spatial expression of XGrg-4 and XGrg-5 is described in Xenopus laevis embryos. Both genes are maternally expressed. In the gastrula, transcripts of both genes are present in the animal as well as the vegetal region. At later stages, XGrg-4 and XGrg-5 show specific patterns of expression in the central nervous system (CNS), cranial ganglia, eyes, otic vesicles, stomodeal-hypophyseal anlage, cement gland, head mesenchyme, branchial arches, neural crest and derivatives, somites, pronephros, pronephric duct, heart and tailbud. Differences in the expression of XGrg-4 and XGrg-5 were found in the CNS, cranial ganglia, olfactory placodes, stomodeal-pharyngeal anlage, cement gland, head mesenchyme and ectoderm.

Animals↗