Overexpression Of Beta-catenin Research Articles

Accelerated Liver Regeneration and Hepatocarcinogenesis in Mice Overexpressing Serine-45 Mutant β-Catenin

The Wnt/beta-catenin pathway is implicated in the pathogenesis of hepatocellular cancer (HCC). We developed a transgenic mouse (TG) in the FVB strain that overexpresses Ser45-mutated-beta-catenin in hepatocytes to study the effects on liver regeneration and cancer. In the two independent TG lines adult mice show elevated beta-catenin at hepatocyte membrane with no increase in the Wnt pathway targets cyclin-D1 or glutamine synthetase. However, TG hepatocytes upon culture exhibit a 2-fold increase in thymidine incorporation at day 5 (D5) when compared to hepatocytes from wildtype FVB mice (WT). When subjected to partial hepatectomy (PH), dramatic increases in the number of hepatocytes in S-phase are evident in TG at 40 and WT at 72 hours. Coincident with the earlier onset of proliferation, we observed nuclear translocation of beta-catenin along with an increase in total and nuclear cyclin-D1 protein at 40 hours in TG livers. To test if stimulation of beta-catenin induces regeneration, we used hydrodynamic delivery of Wnt-1 naked DNA to control mice, which prompted an increase in Wnt-1, beta-catenin, and known targets, glutamine synthetase (GS) and cyclin-D1, along with a concomitant increase in cell proliferation. beta-Catenin-overexpressing TG mice, when followed up to 12 months, showed no signs of spontaneous tumorigenesis. However, intraperitoneal delivery of diethylnitrosamine (DEN), a known carcinogen, induced HCC at 6 months in TG mice only. Tumors in TG livers showed up-regulation of beta-catenin, cyclin-D1, and unique genetic aberrations, whereas other canonical targets were unremarkable. beta-Catenin overexpression offers growth advantage during liver regeneration. Also, whereas no spontaneous HCC is evident, beta-catenin overexpression makes TG mice susceptible to DEN-induced HCC.

β-Catenin is involved in alterations in mitochondrial activity in non-transformed intestinal epithelial and colon cancer cells

Background:Alteration in respiratory activity and mitochondrial DNA (mtDNA) transcription seems to be an important feature of cancer cells. Leukotriene D4 (LTD4) is a proinflammatory mediator implicated in the pathology of chronic inflammation and cancer. We have shown earlier that LTD4 causes translocation of β-catenin both to the mitochondria, in which it associates with the survival protein Bcl-2 identifying a novel role for β-catenin in cell survival, and to the nucleus in which it activates the TCF/LEF transcription machinery.Methods:Here we have used non-transformed intestinal epithelial Int 407 cells and Caco-2 colon cancer cells, transfected or not with wild type and mutated (S33Y) β-catenin to analyse its effect on mitochondria activity. We have measured the ATP/ADP ratio, and transcription of the mtDNA genes ND2, ND6 and 16 s in these cells stimulated or not with LTD4.Results:We have shown for the first time that LTD4 triggers a cellular increase in NADPH dehydrogenase activity and ATP/ADP ratio. In addition, LTD4 significantly increased the transcription of mtDNA genes. Overexpression of wild-type β-catenin or a constitutively active β-catenin mutant mimicked the effect of LTD4 on ATP/ADP ratio and mtDNA transcription. These elevations in mitochondrial activity resulted in increased reactive oxygen species levels and subsequent activations of the p65 subunit of NF-κB.Conclusions:The present novel data show that LTD4, presumably through β-catenin accumulation in the mitochondria, affects mitochondrial activity, lending further credence to the idea that inflammatory signalling pathways are intrinsically linked with potential oncogenic signals.

Gardner's syndrome (familial adenomatous polyposis): a cilia-related disorder

Familial adenomatous polyposis (FAP) is an autosomal dominant form of intestinal polyposis and colorectal cancer caused by germ-line mutations in the adenomatous polyposis coli (APC) gene. The term Gardner's syndrome is used to describe extracolonic manifestations, such as osteomas, skin cysts, congenital hypertrophy of the retinal pigmented epithelium (CHRPE), and desmoid tumours (aggressive fibromatosis), that are especially prominent in families with FAP. We postulate that a ciliary dysfunction is the underlying pathogenetic mechanism of extraintestinal manifestations in patients with FAP. This postulation is based on the presence of common clinical manifestations (ie, cysts, retinal abnormalities, and fibrosis) in Gardner's syndrome and cilia-related disorders. Additionally, both APC and the cilia have degradation of beta-catenin as the common downstream target in the Wnt-signalling pathway. Mutations in APC causing Gardner's syndrome are clustered in a region encoding a series of amino-acid repeats responsible for the binding to beta-catenin. Proofs of principle that beta-catenin could be the key mediator of the ciliary disorder also rely in the findings that overexpression of beta-catenin induces polycystic kidney disease, and CHRPE phenotypes in animal models. Other candidates for the common link between Gardner's syndrome and cilia-related disorders are the APC-binding proteins: end-binding protein 1 (EB1) and kinesin-family-member 3a (KIF3a), both of which are ciliary proteins involved in intraflagellar transport. Finally, pathogenetic similarities between some ciliopathies and extraintestinal tumours in FAP suggest a cilia defect. Understanding extracolonic manifestations in the context of FAP as a ciliary disorder might add new therapeutic options for patients with Gardner's syndrome.

Alterations in the temporal expression and function of cadherin‐7 inhibit cell migration and condensation during chondrogenesis of chick limb mesenchymal cells in vitro

Endochondral bone formation requires a complex interplay among immature mesenchymal progenitor cells to form the cartilaginous anlagen, which involves migration, aggregation and condensation. Even though condensation of chondrogenic progenitors is an essential step in this process, its mechanism(s) has not been well studied. Here, we show that cadherin-7 plays a central role in cellular condensation by modulating cell motility and migration. In this study, many mesenchymal cells failed to migrate, and precartilage condensation was inhibited, after knockdown of endogenous cadherin-7 levels. Exposure of mesenchymal cells to SB203580 (a specific inhibitor of p38MAPK), LiCl (an inhibitor of GSK-3beta) or overexpression of beta-catenin resulted in inhibition of cadherin-7 levels and, subsequently, suppression of cell migration. Collectively, our results suggest that cadherin-7 controls cell migration in chick limb bud mesenchymal cells, and that p38MAPK and GSK signals are responsible for regulating cadherin-7-mediated cell migration.

Transcriptional activation of the β‐catenin gene at the invasion front of colorectal liver metastases

beta-Catenin is a pivotal molecule of the Wnt-signalling pathway, involved in regulation of developmental and oncogenic processes as well as in intercellular adhesion. So far, beta-catenin has been thought to be regulated mainly at the protein level. Here, we provide evidence for a transcriptional mechanism of beta-catenin regulation at the invasion front of colorectal liver metastases. In a nude mouse/LS174T cell xenograft model of colorectal liver metastases, we observed beta-catenin up-regulation at the mRNA and protein levels and a 13.7-fold increase of beta-catenin promoter activity in the cancer cells of the invasion front. In addition, the promoter activity was five-fold higher in the interior of the tumour than in cells growing in cell culture. In vitro studies revealed binding of TCF-4 to the beta-catenin promoter and reduced promoter activity by over-expression of dominant negative TCF-4, or beta-catenin knock-down and increased activity by beta-catenin over-expression, indicating that beta-catenin acts as co-transcription factor of its own promoter. In 55% (7/13) of clinical specimens, beta-catenin mRNA was markedly elevated in the cancer cells of the invasion front. Elevation of mRNA was paralleled by increased nuclear and cytoplasmic beta-catenin protein concentrations. These data indicate that transcriptional regulation contributes to the dynamic changes of beta-catenin levels upon the confrontation of tumour cells with the host microenvironment.

Pitx2, a β-catenin-regulated transcription factor, regulates the differentiation of outer root sheath cells cultured in vitro

Beta-catenin exerts its crucial role in hair follicle development and hair growth cycle. Although the importance of Wnt/beta-catenin is well recognized, the downstream effectors of beta-catenin have not been clearly elucidated yet. The aim of this study is to identify the beta-catenin-regulated genes in cultured human hair outer root sheath (ORS) cells. We transduced ORS cells with adenovirus harboring the expression cassette for constitutive active form of beta-catenin, then performed cDNA microarray. Overexpression of beta-catenin led to the upregulation of hair cell differentiation markers such as keratin 16 and 17. In addition, the expression of Pitx2, a bicoid-type homeodomain transcription factor, was also increased by overexpression of beta-catenin in ORS cells cultured in vitro. To investigate the potential role of Pitx2, we made the recombinant adenovirus expressing Pitx2, then transduced into the cultured ORS cells. Interestingly, Pitx2 induced the expression of keratin 16 and 17, indicating that Pitx2 activates ORS cells towards the follicular differentiation pathway preferentially. Our results implicate the potential importance of Pitx2 as a beta-catenin downstream modulator in hair growth control.

WNT/β-Catenin Signaling Is Involved in Regulation of Osteoclast Differentiation by Human Immunodeficiency Virus Protease Inhibitor Ritonavir: Relationship to Human Immunodeficiency Virus-Linked Bone Mineral Loss

Untreated human immunodeficiency virus (HIV) infection is accompanied by reduced bone mineral density, which appears to be exacerbated by certain HIV protease inhibitors (PIs). The mechanisms leading to this apparent paradox, however, remain unclear. We have previously shown that, the HIV envelope glycoprotein gp120 used at levels similar those in plasmas of untreated HIV(+) patients, induced expression of the osteoclast (OC) differentiation factor RANKL in CD4+ T cells. In addition, the HIV PI ritonavir abrogated the interferon-gamma-mediated degradation of the RANKL nuclear adapter protein TRAF6, a physiological block to RANKL activity. Here, using oligonucleotide microarrays and quantitative polymerase chain reaction, we explored potential upstream mechanisms for these effects. Ritonavir, but not the HIV PIs indinavir or nelfinavir, up-regulated the production of transcripts for OC growth factors and the non-canonical Wnt Proteins 5B and 7B as well as activated promoters of nuclear factor-kappaB signaling, but suppressed genes involved in canonical Wnt signaling. Similarly, ritonavir blocked the cytoplasmic to nuclear translocation of beta-catenin, the molecular node of the Wnt signaling pathway, in association with enhanced beta-catenin ubiquitination. Exposure of OC precursors to LiCl, an inhibitor of the canonical Wnt antagonist GSK-3beta, suppressed OC differentiation, as did adenovirus-mediated overexpression of beta-catenin. These data identify, for the first time, a biologically relevant role for Wnt signaling via beta-catenin in isolated OC precursors and the modulation of Wnt signaling by ritonavir. The reversal of these ritonavir-mediated changes by interferon-gamma provides a model for possible intervention in this metabolic complication of HIV therapy.

Altered {beta}-catenin accumulation in hepatocellular carcinomas of diethylnitrosamine-exposed rhesus macaques.

Chemical exposures are important risks for development of hepatocellular carcinoma (HCC). One such chemical, diethylnitrosamine (DENA), is present in food products as well as in industrial and research settings. Further examination of tumors induced by DENA may yield clues to human risk. HCC from seven rhesus macaques exposed to DENA was selected from a tissue archive to examine for evidence of Wnt/beta-catenin signaling events, which are frequently associated with HCC. DENA exposure durations ranged from 8 to 207 months, and total accumulated dose ranged from 0.7 to 4.08 mg. Unexposed colony breeder macaques served as controls. Previously unrecognized HCC metastases were discovered in lungs of three macaques. Overexpression of beta-catenin and glutamine synthetase was detected by immunohistochemistry in six confirmed primary HCC and all metastatic HCC, which implicated Wnt/beta-catenin activation. Concomitant beta-catenin gene mutation was detected in one primary HCC; similar findings have been reported in human and rodent HCC. Neither beta-catenin mutation nor beta-catenin overexpression appeared to influence metastatic potential. Accumulation of intracellular proteins involved in Wnt/beta-catenin signaling during HCC oncogenesis in rhesus macaques exposed to DENA appears to include other mechanisms, in addition to mutation of beta-catenin gene.

Overexpression of osteopontin independently correlates with vascular invasion and poor prognosis in patients with hepatocellular carcinoma

This study retrospectively evaluated the immunohistochemical expression of 3 cell adhesion molecules (CAMs), E-cadherin, beta-catenin, and osteopontin, according to tumor grade in 125 surgically resected specimens of hepatocellular carcinoma (HCC). The aims of this study were to identify factors associated with vascular invasion and to elucidate the prognostic value of CAMs. The median follow-up time was 110 months. The levels of E-cadherin, beta-catenin, and osteopontin immunoreactivity were significantly associated with Edmondson-Steiner grade but not with tumor size. There was increased loss of E-cadherin, nonnuclear overexpression of beta-catenin, and overexpression of osteopontin in tumors of higher histologic grade. Vascular invasion was found in 44 (35%) of 125 resected specimens. Logistic regression analysis identified 3 tumor-related factors that were independently associated with vascular invasion-tumor size more than 3 cm, Edmondson-Steiner grades III to IV, and overexpression of osteopontin. Among the tested CAMs, osteopontin (P = .0110) and E-cadherin (P = .0287) were significant prognostic factors by univariate analysis. The Cox proportional hazard regression analysis revealed that Edmondson-Steiner grades III to IV (relative risk [RR], 3.028; P < .001), the presence of vascular invasion (RR, 1.964; P = .011), overexpression of osteopontin (RR, 1.755; P = .034), serum alpha-fetoprotein level more than 20 ng/mL (RR, 1.834; P = .037), and Child-Pugh classification B to C (RR, 1.880; P = .040) were found to be independently significant factors associated with survival after hepatectomy. These results suggest that overexpression of osteopontin independently correlates with vascular invasion and thus predicts poor survival for patients with HCC, whereas aberrant expression of E-cadherin or beta-catenin does not.

Morules in endometrioid proliferations of the uterus and ovary consistently express the intestinal transcription factor CDX2

To undertake an immunohistochemical analysis of squamous elements in endometrioid proliferations of the uterus and ovary and to compare the immunophenotype of typical squamous elements and so-called squamous morules. Cases of uterine or ovarian endometrioid glandular lesions with squamous elements were stained with CDX2, beta-catenin, oestrogen receptor (ER), CD10, p63 and high-molecular-weight cytokeratin LP34. Thirteen cases had typical squamous elements and 18 cases morules. Morules typically exhibited diffuse nuclear CDX2 and beta-catenin immunoreactivity and were positive for CD10 and LP34. They were usually ER- and p63-. In contrast, typical squamous elements were usually positive for ER, CD10, p63 and LP34. They were usually CDX2- or focally positive and exhibited no nuclear immunoreactivity for beta-catenin. Ten endometrioid carcinomas not exhibiting squamous differentiation were immunoreactive for CDX2; one was focally positive. Electron microscopy in two ovarian endometrioid adenocarcinomas with extensive morular differentiation showed that the morules exhibited epithelial features, but no overt evidence of squamous differentiation. Typical squamous elements and morules have an overlapping but differing immunophenotype. Morules exhibit no firm immunohistochemical or ultrastructural evidence of squamous differentiation, although immature squamous differentiation cannot be excluded. Nuclear beta-catenin positivity is in keeping with the observation that endometrioid glandular lesions with morules are often associated with beta-catenin gene mutation. The explanation for diffuse nuclear positivity with the intestinal transcription factor CDX2 in morules is not clear, but may be a result of overexpression of nuclear beta-catenin. We suggest that the term morular metaplasia is used instead of squamous morules.

Frizzled‐1 is involved in the neuroprotective effect of Wnt3a against Aβ oligomers

The activation of the canonical Wnt signaling pathway protects hippocampal neurons against the toxicity of Alzheimer's amyloid-beta-peptide (Abeta), however, the role played by the Wnt receptors Frizzleds, has not been studied. We report here that Frizzled-1 mediates the activation of the canonical Wnt/beta-catenin pathway by Wnt3a in PC12 cells. In addition, the protective effect of Wnt3a against the toxicity of Abeta oligomers was modulated by Frizzled-1 expression levels in both PC12 cells and hippocampal neurons. Over-expression of Frizzled-1 significantly increased cell survival induced by Wnt3a and diminished caspase-3 activation, while knocking-down Frizzled-1 expression by antisense oligonucleotides decreased the Wnt3a protection. Over-expression of wild-type beta-catenin, but not a transcriptionally inactive mutated version, prevented the toxicity of Abeta suggesting that the transcription of Wnt target genes may be involved in these events. This was confirmed by co-transfecting both Frizzled-1 and the inactive form of beta-catenin, which does not elicited protection levels similar to those showed with endogenous beta-catenin. Our results indicate that Wnt3a protects from Abeta-oligomers toxicity by activating the canonical Wnt signaling pathway through the Frizzled-1 receptor, suggesting a therapeutic potential for this signaling pathway in the treatment of Alzheimer's disease.

β‐catenin gene alterations in a variety of so‐called calcifying odontogenic cysts

Calcifying odontogenic cysts (COCs) evidence a variety of histopathological features, in addition to biological behaviors. Several systems have been proposed for the classification of COCs. However, the molecular changes underlying their development remain largely unknown. In an effort to elucidate the participation of beta-catenin gene mutation in COC development, we evaluated the genetic alterations and expression of beta-catenin in different COC subtypes with archival paraffin blocks. beta-catenin gene mutations were detected in all subtypes. Immunohistochemically, all cases of COCs evidenced cytoplasmic and nuclear beta-catenin expression. Beta-catenin gene mutations and beta-catenin overexpression have been identified as characteristics of COCs. Therefore, the constitutive activation of Tcf/Lef-dependent transcription appears to be intimately involved in their development. These findings indicate that aberrations of the Wnt signaling pathway may perform a crucial role in the development and differentiation status of the odontogenic epithelium in COCs via the deregulation of cell proliferation.

Transcriptional silencing of Dickkopf gene family by CpG island hypermethylation in human gastrointestinal cancer

To clarify alterations of Dickkopfs (Dkks) and Kremen2 (Krm2) in gastrointestinal cancer. We investigated the expression profiles and epigenetic alterations of Dkks and Krm2 genes in gastrointestinal cancer using RT-PCR, tissue microarray analysis, and methylation specific PCR (MSP). Cancer cells were treated with the demethylating agent and/or histone deacetylase inhibitor. WST-8 assays and in vitro invasion assays after treatment with specific siRNA for those genes were performed. Dkks and Krm2 expression levels were reduced in a certain subset of the gastrointestinal cancer cell lines and cancer tissues. This was correlated with promoter hypermethylation. There were significant correlations between Dkks over-expression levels and beta-catenin over-expression in colorectal cancer. In colorectal cancers with beta-catenin over-expression, Dkk-1 expression levels were significantly lower in those with lymph node metastases than in those without. Down-regulation of Dkks expression by siRNA resulted in a significant increase in cancer cell growth and invasiveness in vitro. Down-regulation of the Dkks associated to promoter hypermethylation appears to be frequently involved in gastrointestinal tumorigenesis.

Retinoic acid metabolizing factor xCyp26c is specifically expressed in neuroectoderm and regulates anterior neural patterning in Xenopus laevis

Anterior-posterior neural patterning is determined during gastrulation when head structure is induced. Induction of anterior neural structures requires inhibition of Wnt signaling by several Wnt antagonists. We performed microarray analysis to isolate genes regulated by canonical Wnt signaling and abundantly expressed in the anterior neuroectoderm at the early neurula stage. We identified xCyp26c, a Cyp26 (RA-metabolizing protein)-family gene. In situ hybridization showed xCyp26c expression restricted to the anterior region of neurula, while xCyp26a was expressed in both anterior and posterior regions. At the tadpole stage, xCyp26c was also expressed in restricted sets of cranial nerves. Microarray, RT-PCR and in situ hybridization analyses revealed decreased xCyp26c expression with overexpression of beta-catenin, suggesting regulation by Wnt/beta-catenin signaling. We also assessed the effects of retinoic acid (RA) on xCyp26c expression. Embryos treated with 10(-7) M RA showed an anterior shift in the spatial expression of xCyp26c, reflecting a posteriorization effect. Conversely, expression patterns in embryos treated with more than 10(-6) M RA were less affected and remained restricted to the most anterior region. Moreover, injection of xCyp26c mRNA into animal poles caused head defects, and exogenous expression of xCyp26c rescued the posteriorizing effect of RA treatment. Taken together, these results implicated a role for xCyp26c in anterior patterning via RA signaling.

Lack of thrombospondin-1 increases angiogenesis in a model of chronic inflammatory bowel disease

Vascular abnormalities and expression of pro-angiogenic factors are observed in inflammatory bowel diseases (IBD). In this study, the role of thrombospondin-1 (TSP-1), an antiangiogenic protein, was analyzed using the dextran sulfate sodium (DSS) model for IBD. Wild-type (WT) and thrombospondin-1-deficient (TSP-1(-/-)) mice were subjected to four cycles (7 days) of DSS. Basic fibroblast growth factor (bFGF), vascular endothelial growth factor (VEGF), transforming growth factor beta 1 (TGFbeta-1), and pro-apoptotic proteins such as Fas and its ligand (FasL) were determined by enzyme-linked immunosorbent assay. Double immunohistochemistry for cluster of differential 31 (CD31) and panendothelial cell antigen-32 antibodies was performed for detecting blood vessels. The terminal deoxynucleotidyl transferase-mediated dUTP nick end-labeling assay was also performed for identifying apoptotic cells. Inflammation, dysplasia, microvascular density (MVD), apoptotic indices (AI), protein 53 (p53), and beta-catenin expression were determined. VEGF and bFGF protein levels and MVD were higher in the TSP-1(-/-) mice (p = 0.0312, p = 0.0246, and p = 0.0085, respectively). AI in the endothelial cells (EC) and FasL levels were significantly lower in TSP-1(-/-) compared to WT mice (p = 0.0042 and p = 0.0362, respectively). Dysplasia was detected in 66% of TSP-1(-/-) mice compared to 14% in WT mice. Hscores of ss-catenin and areas overexpressing p53 were higher in TSP-1(-/-) mice (p = 0.0002 and p = 0.0339, respectively). TSP-1 may decrease angiogenesis by reducing the levels of pro-angiogenic factors and inducing apoptosis in EC through the Fas or FasL pathway. These findings, along with the increased overexpression of p53 and beta-catenin in TSP-1(-/-) mice, underline its role in carcinogenesis.

Overexpression of E‐cadherin and β‐Catenin proteins in metastatic prostate cancer cells in bone

The expression of E-cadherin in the intercellular adhesion of metastatic prostate cancer cells in bone, which is the most prevalent site of metastatic growth, remains elusive. The aim of the study was to compare the concurrent membranous expression of E-cadherin and beta-catenin proteins, the state which is known to be associated with the cellular adhesion function of E-cadherin, in prostate biopsy tissue specimens by immunohistochemical staining method. The expression patterns of E-cadherin or beta-catenin were classified as homogeneous (most cells exhibiting positively), heterogeneous (a few scattered patches of cells with positivity) or negative. Benign prostate hyperplasia cells exhibited homogeneous expression of both E-cadherin and beta-catenin in 9 of 11 (82%), whereas the primary prostate cancer cells were homogeneously positive for both proteins only in 4 of 22 (18%) of the cases. The results are similar to those reported in literature. However, in contrast to the primary cancer, a significantly increased frequency of the metastatic prostate cancer cells in bone exhibited homogeneous expression of E-cadherin and beta-catenin in 12 of 17 (71%) of the cases. A statistically significant association was observed between the overexpression of both proteins and the metastatic prostate cancer cells in bone (Fisher's exact P < 0.001). The result of the study demonstrated for the first time that the membranous overexpression of E-cadherin and beta-catenin are significantly associated with the metastatic prostate cancer cells in bone and that the high frequency of expression suggest their involvement in the intercellular adhesion of the metastatic cells in bone.

Axin1 and Axin2 Are Regulated by TGF‐β and Mediate Cross‐talk between TGF‐β and Wnt Signaling Pathways

Chondrocyte maturation during endochondral bone formation is regulated by a number of signals that either promote or inhibit maturation. Among these, two well-studied signaling pathways play crucial roles in modulating chondrocyte maturation: transforming growth factor-beta (TGF-beta)/Smad3 signaling slows the rate of chondrocyte maturation, while Wingless/INT-1-related (Wnt)/beta-catenin signaling enhances the rate of chondrocyte maturation. Axin1 and Axin2 are functionally equivalent and have been shown to inhibit Wnt/beta-catenin signaling and stimulate TGF-beta signaling. Here we show that while Wnt3a stimulates Axin2 in a negative feedback loop, TGF-beta suppresses the expression of both Axin1 and Axin2 and stimulates beta-catenin signaling. In Axin2 -/- chondrocytes, TGF-beta treatment results in a sustained increase in beta-catenin levels compared to wild-type chondrocytes. In contrast, overexpression of Axin enhanced TGF-beta signaling while overexpression of beta-catenin inhibited the ability of TGF-beta to induce Smad3-sensitive reporters. Finally, the suppression of the Axins is Smad3-dependent since the effect is absent in Smad3 -/- chondrocytes. Altogether these findings show that the Axins act to integrate signals between the Wnt/beta-catenin and TGF-beta/Smad pathways. Since the suppression Axin1 and Axin2 expression by TGF-beta reduces TGF-beta signaling and enhances Wnt/beta-catenin signaling, the overall effect is a shift from TGF-beta toward Wnt/beta-catenin signaling and an acceleration of chondrocyte maturation.

The first Sino-German symposium on cancer research, Shanghai May 2007

This meeting report gives a short overview on the contributions of 17 leading scientists from China and Germany. The symposium was supported by the SinoGermany Science Center Bejing, the Deutsche Forschungsgemeinschaft and the National Science Foundation, China. It intended to foster communication and collaboration of researchers from both countries. The “Migrating Cancer Stem Cell”—Concept was discussed by Thomas Brabletz (Dept. of Surgery Univ. of Freiburg). Most colorectal adenocarcinomas (CRC) have mutations in the APC gene leading to overexpression of the Wnt-pathway effector beta-catenin. By acting as a transcriptional activator, nuclear beta-catenin is decisively involved in two fundamental processes in embryonic development: epithelial to mesenchymal transition (EMT) and generation of stem cells (e.g., in intestine development). We have previously shown that nuclear beta-catenin accumulates in tumor cells at the invasive front undergoing an EMT. The amount of these cells strongly correlates with clinical outcome and metastasis formation. In contrast, tumor cells in central tumor areas are differentiated and often show membranous, E-cadherin-bound beta-catenin. Strikingly, also, metastases show again a differentiated phenotype lacking nuclear beta-catenin, indicating a regulatory role of the tumor environment for malignant progression. Based on the developmental functions of beta-catenin and our data, we propose that both primary tumors and metastases are derived from the pool of EMT-associated “migrating cancer stem cells” at the tumor host interface, which are defined by strong nuclear beta-catenin accumulation and expression of its target genes. This gives these cells a feature, which drives malignant tumor progression including metastasis: The unusual combination of abilities allowing simultaneously to migrate and behave as a cancer stem cell. Molecular Targets in Cancer Therapy—New Possibilities and Old Limitations were reported by Reinhard Buettner (Inst. of Pathology, University of Bonn). Increasing knowledge on molecular pathogenesis of malignant tumors and activated signaling pathways has led to the concept of targeted therapies. Small molecularly designed molecules target specifically oncoproteins, and thereby modulate growth, apoptosis, or invasion of cancer cells. Currently, most experiences exit with membrane-coupled growth factor receptors and their intracellularly coupled signaling kinases. In cancer cells, these tyrosine kinase-triggered signaling pathways are frequently altered and causally involved in malignant transformation. Indeed, some of the tyrosine Virchows Arch (2007) 451:1099–1104 DOI 10.1007/s00428-007-0488-2

Crosstalk between NF‐κB/p65 and β‐catenin/TCF4/p300 signalling pathways through alterations in GSK‐3β expression during trans‐differentiation of endometrial carcinoma cells

Beta-catenin/TCF4/p300 signalling loops play an important role in trans-differentiation towards the morular phenotype of endometrial carcinomas. Crosstalk between NF-kappaB and beta-catenin pathways has been proposed and we focused here on associations between these two pathways during trans-differentiation. In normal endometrium, nuclear phosphorylated p65 (pp65), the active form NF-kappaB subunit, was found to be significantly increased in the secretory phase, correlating positively with vimentin and E-cadherin and inversely with Snail mRNA expression. On transfection of p65, vimentin, E-cadherin, and Snail were transcriptionally altered, indicating possible roles in establishment and maintenance of the secretory phenotype. In endometrial carcinomas with morules, levels of nuclear pp65, Snail mRNA, vimentin, and cytoplasmic TNF-alpha were reduced during trans-differentiation, correlating inversely with nuclear beta-catenin. Nuclear accumulation of GSK-3beta, along with beta-catenin, was observed in morules. In cell lines, overexpression of p65 inhibited beta-catenin/TCF4-mediated transcription, while transfection of GSK-3beta resulted in repression of TNF-alpha-induced NF-kappaB activity. Moreover, nuclear GSK-3beta was increased by overexpression of beta-catenin, as well as induction of G1-cell cycle arrest. These findings provide evidence that a shift from NF-kappaB to beta-catenin signalling pathways through alterations in GSK-3beta expression may be essential for the induction of trans-differentiation of endometrial carcinoma cells, leading to a shut-down of mesenchymal markers.

Functional Interaction of DNA Topoisomerase IIα With the β-Catenin and T-Cell Factor-4 Complex

The Wnt signaling pathway is activated constitutively in the majority of colorectal cancers as a result of mutation in either the adenomatous polyposis coli or the CTNNB1 gene, and blockage of the pathway has been considered feasible as molecular therapy against colorectal cancer. DNA topoisomerase IIalpha (Topo IIalpha) is a component of the beta-catenin/T-cell factor-4 (TCF-4) nuclear complex. We examined the functional significance of Topo IIalpha in Wnt signaling. The physical and functional interaction between Topo IIalpha and the beta-catenin/TCF-4 nuclear complex was evaluated by immunoprecipitation, immunofluorescence microscopy, 2-hybrid assay, and luciferase reporter assay. Amino acids 951-1301 of Topo IIalpha were necessary for binding to beta-catenin. Over expression of Topo IIalpha enhanced the TCF/lymphoid enhancer factor transcriptional activity in a dose-dependent manner, and knockdown of Topo IIalpha by RNA interference conversely attenuated the transcriptional activity. The Topo II inhibitors, merbarone and etoposide, suppressed the beta-catenin-mediated TCF/lymphoid enhancer factor transcriptional activity. The catalytic activity of Topo II was augmented by overexpression of beta-catenin as measured by the decatenation of kinetoplast DNA. Topo IIalpha was highly expressed and colocalized with beta-catenin in tumor cells of patients with familial adenomatous polyposis syndrome and patients with sporadic colorectal cancer. Topo IIalpha interacts with beta-catenin as a novel transcriptional co-activator. A new drug targeting the interaction of Topo IIalpha with beta-catenin as well as its catalytic activity might be more effective for suppressing aberrant Wnt signaling and proliferation of colorectal cancer cells than the current Topo II inhibitors.