Wnt-signalling pathway in ovarian epithelial tumours: increased expression of beta-catenin and GSK3beta.
ABSTRACT: Beta-catenin is involved in both cell-cell adhesion and in transcriptional regulation by the Wingless/Wnt signalling pathway. Alterations of components of this pathway have been suggested to play a central role in tumorigenesis. The present study investigated, by immunohistochemistry and immunoblotting, the protein expression and localisation of beta-catenin, adenomatous polyposis coli (APC), glycogen synthase kinase 3beta (GSK3beta) and lymphocyte enhancer factor-1 (Lef-1) in normal human ovaries and in epithelial ovarian tumours in vivo and in vitro. Immortalised human ovarian surface epithelium and ovarian cancer cell cells (OVCAR-3) expressed beta-catenin, APC, GSK3beta and Lef-1. Nuclear staining of beta-catenin and Lef-1 were demonstrated only in OVCAR-3 cells. There were significant increases of beta-catenin and GSK3beta, while APC was reduced in ovarian cancer compared to the normal ovary. Beta-catenin and Lef-1 were coimmunoprecipitated in ovarian tumours, but not in the normal ovary. Nuclear localisation of beta-catenin or Lef-1 could not be demonstrated in the normal ovary or in the ovarian tumours. The absence of nuclear localisation of beta-catenin could be due to an increased binding to the cadherin-alpha-catenin cell adhesion complex. In fact, we have earlier reported an increased expression of E-cadherin in ovarian adenocarcinomas. In summary, this study demonstrates an increase in the expression of components of the Wingless/Wnt pathway in malignant ovarian tumours. The increase suggests a role for this signalling pathway in cell transformation and in tumour progression. However, it remains to be demonstrated whether it is an increased participation of beta-catenin in transcriptional regulation, or in the stabilisation of cellular integrity, or both, that is the crucial event in ovarian tumorigenesis.
Project description:Central nervous system primitive neuroectodermal tumours (CNS PNET) are high-grade, predominantly paediatric, brain tumours. Previously they have been grouped with medulloblastomas owing to their histological similarities. The WNT/beta-catenin pathway has been implicated in many tumour types, including medulloblastoma. On pathway activation beta-catenin (CTNNB1) translocates to the nucleus, where it induces transcription of target genes. It is commonly upregulated in tumours by mutations in the key pathway components APC and CTNNB1. WNT/beta-catenin pathway status was investigated by immunohistochemical analysis of CTNNB1 and the pathway target cyclin D1 (CCND1) in 49 CNS PNETs and 46 medulloblastomas. The mutational status of APC and CTNNB1 (beta-catenin) was investigated in 33 CNS PNETs and 22 medulloblastomas. CTNNB1 nuclear localisation was seen in 36% of CNS PNETs and 27% of medulloblastomas. A significant correlation was found between CTNNB1 nuclear localisation and CCND1 levels. Mutations in CTNNB1 were identified in 4% of CNS PNETs and 20% of medulloblastomas. No mutations were identified in APC. A potential link between the level of nuclear staining and a better prognosis was identified in the CNS PNETs, suggesting that the extent of pathway activation is linked to outcome. The results suggest that the WNT/beta-catenin pathway plays an important role in the pathogenesis of CNS PNETs. However, activation is not caused by mutations in CTNNB1 or APC in the majority of CNS PNET cases.
Project description:In response to activation of the Wnt signaling pathway, beta-catenin accumulates in the nucleus, where it cooperates with LEF/TCF (for lymphoid enhancer factor and T-cell factor) transcription factors to activate gene expression. The mechanisms by which beta-catenin undergoes this shift in location and participates in activation of gene transcription are unknown. We demonstrate here that beta-catenin can be imported into the nucleus independently of LEF/TCF binding, and it may also be exported from nuclei. We have introduced a small deletion within beta-catenin (Delta19) that disrupts binding to LEF-1, E-cadherin, and APC but not axin. This Delta19 beta-catenin mutant localizes to the nucleus because it may not be efficiently sequestered in the cytoplasm. The nuclear localization of Delta19 definitively demonstrates that the mechanisms by which beta-catenin localizes in the nucleus are completely independent of LEF/TCF factors. beta-Catenin and LEF-1 complexes can activate reporter gene expression in a transformed T-lymphocyte cell line (Jurkat) but not in normal T lymphocytes, even though both factors are nuclear. Thus, localization of both factors to the nucleus is not sufficient for activation of gene expression. Excess beta-catenin can squelch reporter gene activation by LEF-1-beta-catenin complexes but not activation by the transcription factor VP16. Taken together, these data suggest that a third component is necessary for gene activation and that this third component may vary with cell type.
Project description:We have investigated how Wnt and vitamin D receptor signals regulate epidermal differentiation. Many epidermal genes induced by beta-catenin, including the stem cell marker keratin 15, contain vitamin D response elements (VDREs) and several are induced independently of TCF/Lef. The VDR is required for beta-catenin induced hair follicle formation in adult epidermis, and the vitamin D analog EB1089 synergizes with beta-catenin to stimulate hair differentiation. Human trichofolliculomas (hair follicle tumours) are characterized by high nuclear beta-catenin and VDR, whereas infiltrative basal cell carcinomas (BCCs) have high beta-catenin and low VDR levels. In mice, EB1089 prevents beta-catenin induced trichofolliculomas, while in the absence of VDR beta-catenin induces tumours resembling BCCs. We conclude that VDR is a TCF/Lef-independent transcriptional effector of the Wnt pathway and that vitamin D analogues have therapeutic potential in tumors with inappropriate activation of Wnt signalling.
Project description:beta-catenin is the major effector of the canonical Wnt signaling pathway. Mutations in components of the pathway that stabilize beta-catenin result in augmented gene transcription and play a major role in many human cancers. We employed microarrays to identify transcriptional targets of deregulated beta-catenin in a human epithelial cell line (293) engineered to produce mutant beta-catenin and in ovarian endometrioid adenocarcinomas characterized with respect to mutations affecting the Wnt/beta-catenin pathway. Two genes strongly induced in both systems-FGF20 and DKK1-were studied in detail. Elevated levels of FGF20 RNA were also observed in adenomas from mice carrying the Apc(Min)allele. Both XFGF20 and Xdkk-1 are expressed early in Xenopus embryogenesis under the control of the Wnt signaling pathway. Furthermore, FGF20 and DKK1 appear to be direct targets for beta-catenin/TCF transcriptional regulation via LEF/TCF-binding sites. Finally, by using small inhibitory RNAs specific for FGF20, we show that continued expression of FGF20 is necessary for maintenance of the anchorage-independent growth state in RK3E cells transformed by beta-catenin, implying that FGF-20 may be a critical element in oncogenesis induced by the Wnt signaling pathway.
Project description:The activation of Wnt/beta-catenin signalling has an important function in gastrointestinal tumorigenesis. It has been suggested that the promotion of Wnt/beta-catenin activity beyond the threshold is important for carcinogenesis. We herein investigated the role of macrophages in the promotion of Wnt/beta-catenin activity in gastric tumorigenesis. We found beta-catenin nuclear accumulation in macrophage-infiltrated dysplastic mucosa of the K19-Wnt1 mouse stomach. Moreover, macrophage depletion in Apc(Delta716) mice resulted in the suppression of intestinal tumorigenesis. These results suggested the role of macrophages in the activation of Wnt/beta-catenin signalling, which thus leads to tumour development. Importantly, the conditioned medium of activated macrophages promoted Wnt/beta-catenin signalling in gastric cancer cells, which was suppressed by the inhibition of tumour necrosis factor (TNF)-alpha. Furthermore, treatment with TNF-alpha induced glycogen synthase kinase 3beta (GSK3beta) phosphorylation, which resulted in the stabilization of beta-catenin. We also found that Helicobacter infection in the K19-Wnt1 mouse stomach caused mucosal macrophage infiltration and nuclear beta-catenin accumulation. These results suggest that macrophage-derived TNF-alpha promotes Wnt/beta-catenin signalling through inhibition of GSK3beta, which may contribute to tumour development in the gastric mucosa.
Project description:BACKGROUND: A novel member of the Wnt signalling pathway, Chibby, was recently identified. This protein inhibits Wnt/beta-catenin mediated transcriptional activation by competing with Lef-1 (the transcription factor and target of beta-catenin) to bind to beta-catenin. This suggests that Chibby could be a tumour suppressor protein. The C22orf2 gene coding Chibby is located on chromosome 22, a region recurrently lost in colorectal cancer. Activation of the Wnt pathway is a major feature of colorectal cancer and occurs through inactivation of APC or activation of beta-catenin. All of this led us to analyse the possible implication of Chibby in colorectal carcinogenesis. METHODS: First, 36 tumour and matched normal colonic mucosa DNA were genotyped with five microsatellite markers located on chromosome 22 to search for loss of heterozygosity. Then, mutation screening of the C22orf2 coding sequence and splice sites was performed in the 36 tumour DNA. Finally, expression of Chibby was analysed by quantitative RT-PCR on 10 patients, 4 with loss of heterozygosity (LOH) on chromosome 22. RESULTS: Loss of heterozygosity involving the C22orf2 region was detected in 11 out of 36 patients (30%). Sequencing analysis revealed a known variant, rs3747174, in exon 5: T321C leading to a silent amino acid polymorphism A107A. Allelic frequencies were 0.69 and 0.31 for T and C variants respectively. No other mutation was detected. Among the 10 patients studied, expression analysis revealed that Chibby is overexpressed in 2 tumours and underexpressed in 1. No correlations were found with 22q LOH status. CONCLUSION: As no somatic mutation was detected in C22orf2 in 36 colorectal tumour DNA, our results do not support the implication of Chibby as a tumour suppressor in colorectal carcinogenesis. This was supported by the absence of underexpression of Chibby among the tumour samples with 22q LOH. The implication of other Wnt pathway members remains to be identified to explain the part of colorectal tumours without mutation in APC and beta-catenin.
Project description:A novel member of the human frizzled (Fz) gene family was cloned and found to be specifically expressed in 3 of 13 well differentiated (23%), 13 of 20 moderately differentiated (62%), and 12 of 14 poorly differentiated (86%) squamous cell esophageal carcinomas compared with the adjacent uninvolved normal mucosa. The FzE3 cDNA encodes a protein of 574 amino acids and shares high sequence homology with the human FzD2 gene particularly in the putative ligand binding region of the cysteine-rich extracellular domain. Functional analysis revealed that transfection and expression of the FzE3 cDNA in esophageal carcinoma cells stimulates complex formation between adenomatous polyposis coli (APC) and beta-catenin followed by nuclear translocation of beta-catenin. Furthermore, cotransfection of a mutant construct encoding a FzE3 protein with a C-terminal truncation completely inhibited the interaction of APC with beta-catenin in cells. Finally, coexpression of FzE3 with Lef-1 transcription factor enhanced beta-catenin translocation to the nucleus. These observations suggest that FzE3 gene expression may down-regulate APC function and enhance beta-catenin mediated signals in poorly differentiated human esophageal carcinomas.
Project description:Axin and the adenomatous polyposis coli (APC) tumor suppressor protein are components of the Wnt/Wingless growth factor signaling pathway. In the absence of Wnt signal, Axin and APC regulate cytoplasmic levels of the proto-oncogene beta-catenin through the formation of a large complex containing these three proteins, glycogen synthase kinase 3beta (GSK3beta) and several other proteins. Both Axin and APC are known to be critical for beta-catenin regulation, and truncations in APC that eliminate the Axin-binding site result in human cancers. A protease-resistant domain of Axin that contains the APC-binding site is a member of the regulators of G-protein signaling (RGS) superfamily. The crystal structures of this domain alone and in complex with an Axin-binding sequence from APC reveal that the Axin-APC interaction occurs at a conserved groove on a face of the protein that is distinct from the G-protein interface of classical RGS proteins. The molecular interactions observed in the Axin-APC complex provide a rationale for the evolutionary conservation seen in both proteins.
Project description:In most colorectal tumours, APC mutation stabilises beta-catenin and mimics elements of Wnt growth factor signalling, but the high frequency of epigenetic loss of Wnt antagonists indicates an additional role for ligand-mediated Wnt signalling. Here, we have investigated the expression of key components of beta-catenin-independent Wnt response pathways to determine whether their profiles change during the transition from normal mucosa to colorectal adenomas. Transcription of the Wnt/planar cell polarity pathway determinant NKD1 (naked cuticle homologue 1) was induced in adenomas by a median 135-fold and in cancers by 7.4-fold. While some Frizzleds (FZDs) were downregulated in adenomas, the Wnt/Ca(2+) receptors FZD3 and FZD6 were induced by a median factor of 6.5 and 4.6, respectively. Naked cuticle homologue 1, FZD3 and FZD6 expression were coordinated in pre-malignant disease, but this relationship was lost in invasive cancers, where FZD induction was seen less frequently. Naked cuticle homologue 1 expression was associated with nuclear localisation of phospho-c-Jun in adenomas. In cultured cells, NKD1 transcription was induced by lithium chloride but FZD3 expression required Wnt growth factor treatment. These data show that Wnt responses are consistently directed towards both beta-catenin-independent routes in early colorectal tumorigenesis and elements of this are retained in more advanced cancers. These beta-catenin-independent Wnt signalling pathways may provide novel targets for chemoprevention of early colorectal tumours.
Project description:Wnt signals control decisive steps in development and can induce the formation of tumors. Canonical Wnt signals control the formation of the embryonic axis, and are mediated by stabilization and interaction of beta-catenin with Lef/Tcf transcription factors. An alternative branch of the Wnt pathway uses JNK to establish planar cell polarity in Drosophila and gastrulation movements in vertebrates. We describe here the vertebrate protein Diversin that interacts with two components of the canonical Wnt pathway, Casein kinase Iepsilon (CKIepsilon) and Axin/Conductin. Diversin recruits CKIepsilon to the beta-catenin degradation complex that consists of Axin/Conductin and GSK3beta and allows efficient phosphorylation of beta-catenin, thereby inhibiting beta-catenin/Tcf signals. Morpholino-based gene ablation in zebrafish shows that Diversin is crucial for axis formation, which depends on beta-catenin signaling. Diversin is also involved in JNK activation and gastrulation movements in zebrafish. Diversin is distantly related to Diego of Drosophila, which functions only in the pathway that controls planar cell polarity. Our data show that Diversin is an essential component of the Wnt-signaling pathway and acts as a molecular switch, which suppresses Wnt signals mediated by the canonical beta-catenin pathway and stimulates signaling via JNK.