AXIN1 mutations in hepatocellular carcinomas, and growth suppression in cancer cells by virus-mediated transfer of AXIN1

EBP50, a beta-catenin-associating protein, enhances Wnt signaling and is over-expressed in hepatocellular carcinoma

Wnt signaling mediated by beta-catenin plays crucial roles in the development of hepatocellular carcinoma and other cancers such as colorectal cancer. beta-Catenin associates with T-cell factor (TCF) transcription factors and functions as a transcriptional activator in the nucleus. By protein interaction screening, we identified EBP50, a cytoplasmic protein with 2 PDZ domains, as a beta-catenin-associating molecule. EBP50 interacted with beta-catenin through its carboxyl-PDZ domain in vitro and in vivo. Northern blot and RT-PCR analysis revealed an increase of EBP50 messenger RNA (mRNA) in hepatocellular carcinoma (HCC) cell lines and surgical specimens of human HCC. Over-expression of EBP50 protein with focal nuclear localization was detected in human HCC. In human HCC and colorectal cancer cell lines, EBP50 enhanced beta-catenin/TCF-dependent transcription in a dose-dependent manner. In an HCC cell line, over-expression of the carboxyl PDZ domain resulted in a decrease of endogenous beta-catenin/TCF transactivation. EBP50 promoted beta-catenin-mediated transactivation only in cells in which beta-catenin was already stabilized, suggesting that EBP50 may work with stabilized beta-catenin for transcriptional regulation. In conclusion, the EBP50/beta-catenin complex promotes Wnt signaling, and over-expression of EBP50 may work cooperatively with beta-catenin in the development of liver cancer.

Caught up in a Wnt storm: Wnt signaling in cancer

The Wnt signaling pathway, named for its most upstream ligands, the Wnts, is involved in various differentiation events during embryonic development and leads to tumor formation when aberrantly activated. Molecular studies have pinpointed activating mutations of the Wnt signaling pathway as the cause of approximately 90% of colorectal cancer (CRC), and somewhat less frequently in cancers at other sites, such as hepatocellular carcinoma (HCC). Ironically, Wnts themselves are only rarely involved in the activation of the pathway during carcinogenesis. Mutations mimicking Wnt stimulation-generally inactivating APC mutations or activating beta-catenin mutations-result in nuclear accumulation of beta-catenin which subsequently complexes with T-cell factor/lymphoid enhancing factor (TCF/LEF) transcription factors to activate gene transcription. Recent data identifying target genes has revealed a genetic program regulated by beta-catenin/TCF controlling the transcription of a suite of genes promoting cellular proliferation and repressing differentiation during embryogenesis, carcinogenesis, and in the post-embryonic regulation of cell positioning in the intestinal crypts. This review considers the spectra of tumors arising from active Wnt signaling and attempts to place perspective on recent data that begin to elucidate the mechanisms prompting uncontrolled cell growth following induction of Wnt signaling.

Reduced expression of Axin correlates with tumour progression of oesophageal squamous cell carcinoma

Axin is a negative regulator of the Wnt signalling pathway, and genetic alterations of AXIN1 have been suggested to be an important factor of carcinogenesis in some tumours. The objective of this study was to clarify the clinicopathologic and prognostic significance of Axin in oesophageal squamous cell carcinoma (SCC). Immunohistochemical staining for Axin was performed on surgical specimens obtained from 81 patients with oesophageal SCC. Western and Northern blottings were performed on proteins and RNA from oesophageal SCC cell lines. Then polymerase chain reaction-single-strand conformational analysis (PCR-SSCP) was performed on DNA from oesophageal SCC patients and cell lines. Axin expression was found to be correlated inversely with depth of invasion, lymph node metastasis, and lymphatic invasion. Although univariate analysis showed Axin to be a negative predictor, multivariate analysis showed that it was not an independent prognostic marker. In all but one of the seven cell lines examined, the levels of protein expression were equivalent to RNA expression. PCR-SSCP showed that five patients and three cell lines had polymorphisms in exon 4 or 5 of the AXIN1 gene, but none of the 81 patients with oesophageal SCC had mutations. Our findings suggest that reduced expression of Axin is correlated with tumour progression of oesophageal SCC. However, additional studies will be necessary to elucidate the mechanism responsible for loss of Axin expression in tumour cells.

A functional screen in human cells identifies UBF2 as an RNA polymerase II transcription factor that enhances the beta-catenin signaling pathway

beta-Catenin signaling plays an important role in the development of many organisms and has a key part in driving the malignant transformation of epithelial cells comprising a variety of cancers. beta-Catenin can activate gene expression through its association with transcription factors of the lymphoid enhancer factor 1 (LEF-1)/T-cell factor (TCF) family. We designed a screen in human cells to identify novel genes that activate a beta-catenin-LEF/TCF-responsive promoter and isolated the high-mobility group box transcription factor, UBF2. UBF1 and UBF2 are splice variants of a common precursor RNA. Although UBF1 has been shown to activate RNA polymerase I-regulated genes, the function of UBF2 has remained obscure. Here, we show for the first time that both UBF1 and UBF2 activate RNA polymerase II-regulated promoters. UBF2 associates with LEF-1, as shown by coimmunoprecipitation experiments, and potentiates transcriptional activation stimulated by LEF-1/beta-catenin from a synthetic promoter with multimerized LEF/TCF binding sites and a natural cyclin D1 promoter with consensus LEF/TCF binding sites. Downregulation of endogenous UBF expression using an RNA interference approach reduces transcriptional activation of a beta-catenin-LEF/TCF-responsive promoter by means of overexpressed beta-catenin, further implicating UBF as a transcriptional enhancer of the beta-catenin pathway.

Analysis of chromosomal instability in pulmonary or liver metastases and matched primary hepatocellular carcinoma after orthotopic liver transplantation

To investigate the genetic mechanism of metastatic spread in hepatocellular carcinoma (HCC), we analyzed genomic changes in lung or liver metastases and the corresponding primary tumors (83 tumor samples) in 18 patients who underwent orthotopic liver transplantation. We studied the incidence of microsatellite instability (MSI) and loss of heterozygosity (LOH) involving 8 highly polymorphic microsatellite markers and the polyA tract, Bat26. We also sought alterations of p53 and beta-catenin gene mutations. High MSI (>30-40% of the loci analyzed) was found only in primary tumors (11%), whereas LOH was observed in 50% of primary and in 39% of recurrent tumors. p53 mutations were found in 2 cases of primary HCC but not in the corresponding metastases. P53 was overexpressed in 4 primary HCC (22%) and 7 metastases (39%). The percentage of beta-catenin gene mutations was low (6%). Lung metastases retained the D16S402 microsatellite abnormalities observed in the primary tumors, whereas recurrent liver tumor did not (p = 0.02). In conclusion, LOH and P53 protein overexpression, rather than mutations in the p53 or beta-catenin genes or MSI, seem to be involved in the spreading of HCC, suggesting the presence of metastasis suppressor genes in the vicinity of the chromosomal loci in question.

Spectrum of molecular changes during hepatocarcinogenesis induced by DEN and other chemicals in Fisher 344 male rats [Mechanisms of Ageing and Development 123 (2002) 1665-1680]

Unlike other tissues such as breast, colon and renal cell carcinoma, it is not an easy task to single out any representative oncogene or tumor suppressor genes in the development of hepatocellular carcinoma (HCC), which play a pivotal role. To investigate putatively altered main pathways in HCC, F344 male rats were treated with a single injection of N-nitrosodiethylamine (DEN), followed by either twice/week injections of nodularin for 10 weeks or thioacetamide (TAA) in drinking water for 39 weeks. p53 expression was dramatic in both hepatocytes and mesenchymal cells after a single injection of DEN, however, PCR-SSCP assay could not detect any p53 mutation during the development of hepatocellular adenoma (HCA). The data indicate that wtp53 response was mostly for removal of damaged cells during the initiation of carcinogenesis. When treated with DEN-TAA, induction of gankyrin expression during hepatic fibrosis preceded the loss of pRB protein, accompanied with significant expressions of G1phase cyclins and CDKs. Moreover, p16(INK4A) exon 1 was hypermethylated during the development of poorly differentiated HCCs. These changes would result in complete inactivation of the pRB regulatory pathway during hepatocarcinogenesis. Induction of TGF-beta1 expression with loss of its receptor expression occurred rapidly in the altered hepatocytes by DEN-nodularin treatment.

CONCLUSION

Therefore, escape from TGF-beta1 induced apoptosis and severe degradation of pRB protein during the early stage of carcinogenesis can perform a symphony to proliferate and to transform the altered hepatocytes to tumor cells. Inactivation of p16(INK4A) and p53 genes at the later stage of carcinogenesis would endow HCC with malignancy, which is highly resistant to any therapeutic trials.

Wnt/beta-catenin/tcf signaling: a critical pathway in gastrointestinal tumorigenesis

Cancers of the gastrointestinal tract, including the liver, bile ducts, and pancreas, constitute the largest group of malignant tumors. Colorectal cancer is one of the most common neoplastic diseases in Western countries and one of the leading causes of cancer-related deaths. Inactivation of the adenomatous polyposis coli (APC) tumor-suppressor gene during early adenoma formation is thought to be the first genetic event in the process of colorectal carcinogenesis followed by mutations in oncogenes like K-Ras and tumor-suppressor genes like p53. Identification of the interaction of APC with the proto-oncogene beta-catenin has linked colorectal carcinogenesis to the Wnt-signal transduction pathway. The main function of APC is thought to be the regulation of free beta-catenin in concert with the glycogen synthase kinase 3beta (GSK-3beta) and Axin proteins. Loss of APC function, inactivation of Axin or activating beta-catenin mutations result in the cellular accumulation of beta-catenin. Upon translocation to the nucleus beta-catenin serves as an activator of T-cell factor (Tcf)-dependent transcription leading to an increased expression of several specific target genes including c-Myc, cyclin D1, MMP-7, and ITF-2. While APC mutations are almost exclusively found in colorectal cancers, deregulation of Wnt/beta-catenin/Tcf signaling is also common in other gastrointestinal and extra-gastrointestinal human cancers. In a fraction of hepatocellular carcinomas the Wnt pathway is deregulated by inactivation of Axin or stabilizing mutations of beta-catenin. The majority of hepatoblastomas and a group of gastric cancers also carry beta-catenin mutations. Clearly, this pathway harbors great potential for future applications in cancer diagnostics, staging, and therapy.

Ectopic expression of Axin blocks neuronal differentiation of embryonic carcinoma P19 cells

Axin regulates Wnt signaling through down-regulation of beta-catenin. To test the role of Wnt signaling in neuronal differentiation, embryonal carcinoma P19 cells (P19 EC), which can be stimulated to differentiate into a neuron-like phenotype in response to retinoic acid (RA), were used. Reverse transcription-PCR and Western blot analysis showed that Axin is expressed in undifferentiated cells, whereas the level is clearly reduced during RA-induced neuronal differentiation. Interestingly, Axin levels were not reduced during endodermal differentiation of P19 EC cells and F9 EC cells by RA, suggesting that the reduction of the Axin level is a specific property of neuronal differentiation. Western analysis showed that the cytoplasmic level of beta-catenin increased during neuronal differentiation of P19 EC cells. Indirect immunofluorescence with beta-catenin antibody showed that the localization of beta-catenin was changed from membrane in undifferentiated cells to nuclei in neuronal P19 EC cells. Induced expression of Axin during endodermal and early neuronal differentiation, using the Tet-On system, did not block normal differentiation. However, maintenance of the Axin level blocked neuronal differentiation and inhibited expression of a neuron-specific marker protein, beta III-tubulin. Also, ectopic induction of a beta-catenin signaling inhibitor, ICAT, inhibited expression of beta III-tubulin. In contrast, addition of Wnt-3A-conditioned medium during the neuronal differentiation period enhanced the expression of beta III-tubulin. Overall, our data show that Wnt-3a/canonical beta-catenin signaling through the down-regulation of Axin may play an important role in neuronal differentiation.

EGR2 induces apoptosis in various cancer cell lines by direct transactivation of BNIP3L and BAK

EGR2 plays a key role in the PTEN-induced apoptotic pathway. Using adenovirus-mediated gene transfer to 39 cancer cell lines, we found that EGR2 could induce apoptosis in a large proportion of these lines by altering the permeability of mitochondrial membranes, releasing cytochrome c and activating caspase-3, -8, and -9. Analysis by cDNA microarray and subsequent functional studies revealed that EGR2 directly transactivates expression of BNIP3L and BAK. Our results helped to clarify the molecular mechanism of the apoptotic pathway induced by PTEN-EGR2, and suggested that EGR2 may be an excellent target molecule for gene therapy to treat a variety of cancers.

The Wnt signaling pathway and its role in tumor development

Cancer development depends on the aberrant activation of signal transduction pathways that control cell growth and survival and play important roles in normal embryonic development. This review will focus on one of the most powerful pathways, the canonical Wnt signal transduction cascade, which has been originally described in vertebrate and non-vertebrate embryogenesis and subsequently associated with the development of a multitude of different tumor types, mainly of gastrointestinal origin. In recent years, a variety of novel interacting components and functions have been identified in the Wnt pathway revealing not only the complexity of Wnt signaling but also its potency. Here we will concentrate on the role of the Wnt pathway in cancer development with emphasis placed on the molecular defects known to promote neoplastic transformation in humans and in animal models.

Dysregulation of beta-catenin expression correlates with tumor differentiation in pancreatic duct adenocarcinoma

BACKGROUND

beta-Catenin functions as an integral part of the E-cadherin/catenin adhesion complex to maintain epithelial cell integrity. beta-Catenin also functions as part of the Wnt signal transduction pathway to transmit growth-promoting signals to the nucleus via its interactions with Tcf/Lef transcription factors. Previous reports have demonstrated altered beta-catenin expression in numerous tumor types; however, reports regarding beta-catenin expression in pancreatic cancer have been conflicting.

METHODS

beta-Catenin expression was examined in 10 pancreatic cancer cell lines by Western and Northern analysis and by immunofluorescence. Expression was also examined by immunohistochemistry in 57 primary pancreatic cancers and 7 foci of carcinoma-in-situ.

RESULTS

Reduced expression of beta-catenin was observed in 4 of 10 pancreatic cancer cell lines. Reduced membranous expression was noted in 32 pancreatic cancers (56%) and correlated with loss of tumor differentiation. Nuclear beta-catenin expression was identified in two tumors (4%). beta-Catenin expression was present in all seven foci of carcinoma-in-situ; however, nuclear expression was predominant in four of the seven cases.

CONCLUSIONS

Alterations in beta-catenin expression are common in pancreatic cancer; however, signaling and adhesion functions may be perturbed at different times during tumor progression. Therefore, dysregulation of beta-catenin may contribute to the development and progression of this disease through distinct mechanisms.

Homozygous deletion scanning in hepatobiliary tumor cell lines reveals alternative pathways for liver carcinogenesis

Despite high rates of loss of heterozygosity affecting various chromosomes, the number of tumor suppressor genes (TSGs) found to be consistently involved in primary liver cancer is low. In the past decade, characterization of homozygous deletions (HDs) in tumors has become instrumental to identify new TSGs or to reveal the influence of a particular TSG on the development of a specific tumor type. We performed a detailed HD profiling at 238 critical loci on a collection of 57 hepatobiliary tumor cell lines (hepatocellular, cholangiocellular, and bile duct carcinomas, hepatoblastomas, and immortalized hepatocytes). We identified HDs at 9 independent loci, the analysis of which was extended to 17 additional hepatobiliary tumor cell lines. In total, 34 homozygous losses involving 9 distinct genes were detected in the 74 cell lines analyzed. Besides expected deletions at the p16-INK4A/p14-ARF, FHIT, AXIN1, and p53 genes, we detected HDs at the PTEN, NF2, STK11, BAX, and LRPDIT genes that were formerly not known to be implicated in human liver tumorigenesis. In conclusion, our data suggest that these genes may represent novel liver tumor suppressive targets. Additional tumorigenic pathways should be carefully considered in hepatocarcinogenesis.

Differences between the interaction of beta-catenin with non-phosphorylated and single-mimicked phosphorylated 20-amino acid residue repeats of the APC protein

The tumour suppressor protein adenomatous polyposis coli (APC) regulates the level and the intracellular localisation of the proto-oncoprotein beta-catenin. There are indications that a region comprising seven homologous 20-amino acid residue repeats within the APC protein is responsible for the interaction with beta-catenin and that the phosphorylation of conserved serine residues within these repeats increases the affinity for beta-catenin. We used biophysical methods to analyse the beta-catenin binding of single repeats or repeat combinations as non-phosphorylated or phosphorylated recombinant proteins. The non-phosphorylated repeats showed similar affinities, no matter whether they were tested as single recombinant repeats or in combination with neighbouring repeats. This result makes a cooperative influence between the repetitive motifs unlikely. The phosphorylation of the APC protein was mimicked by specific serine/aspartate mutations, which align to serine residues in the cytoplasmic beta-catenin binding domain of E-cadherin. Remarkably, the mimicked phosphorylation of a serine, which is not involved in beta-catenin interaction in the E-cadherin/beta-catenin complex, led to a significant increase in the APC affinity for beta-catenin. These results indicate structural differences between the E-cadherin/beta-catenin and the APC/beta-catenin complexes and provide quantitative evidence for the importance of the APC phosphorylation for its interaction with beta-catenin.

Deleted in liver cancer (DLC) 2 encodes a RhoGAP protein with growth suppressor function and is underexpressed in hepatocellular carcinoma

Hepatocellular carcinoma (HCC) is a major malignancy in many parts of the world, especially in Asia and Africa. Loss of heterozygosity (LOH) on the long arm of chromosome 13 has been reported in HCC. In search of tumor suppressor genes in this region, here we have identified DLC2 (for deleted in liver cancer 2) at 13q12.3 encoding a novel Rho family GTPase-activating protein (GAP). DLC2 mRNA is ubiquitously expressed in normal tissues but was significantly underexpressed in 18% (8/45) of human HCCs. DLC2 is homologous to DLC1, a previously identified tumor suppressor gene at 8p22-p21.3 frequently deleted in HCC. DLC2 encodes a novel protein with a RhoGAP domain, a SAM (sterile alpha motif) domain related to p73/p63, and a lipid-binding StAR-related lipid transfer (START) domain. Biochemical analysis indicates that DLC2 protein has GAP activity specific for small GTPases RhoA and Cdc42. Expression of the GAP domain of DLC2 sufficiently inhibits the Rho-mediated formation of actin stress fibers. Introduction of human DLC2 into mouse fibroblasts suppresses Ras signaling and Ras-induced cellular transformation in a GAP-dependent manner. Taken together, our findings suggest a role for DLC2 in growth suppression and hepatocarcinogenesis.

Nuclear export of the APC tumour suppressor controls beta-catenin function in transcription

The adenomatous polyposis coli (APC) protein is inactivated in most colorectal tumours. APC loss is an early event in tumorigenesis, and causes an increase of nuclear beta-catenin and its transcriptional activity. This is thought to be the driving force for tumour progression. APC shuttles in and out of the nucleus, but the functional significance of this has been controversial. Here, we show that APC truncations are nuclear in colorectal cancer cells and adenocarcinomas, and this correlates with loss of centrally located nuclear export signals. These signals confer efficient nuclear export as measured directly by fluorescence loss in photobleaching (FLIP), and they are critical for the function of APC in reducing the transcriptional activity of beta-catenin in complementation assays of APC mutant colorectal cancer cells. Importantly, targeting a functional APC construct to the nucleus causes a striking nuclear accumulation of beta-catenin without changing its transcriptional activity. Our evidence indicates that the rate of nuclear export of APC, rather than its nuclear import or steady-state levels, determines the transcriptional activity of beta-catenin.

Wnt signaling in hepatocellular carcinoma: analysis of mutation and expression of beta-catenin, T-cell factor-4 and glycogen synthase kinase 3-beta genes

BACKGROUND AND AIMS

Hepatocellular carcinoma (HCC) is a common killer cancer in the world. Recently, abnormal activation of the Wnt pathway has been found to be involved in the carcinogenesis of several human cancers including HCC. The goal of the present study was to investigate the mechanism of inappropriate activation of the Wnt pathway in hepatocarcinogenesis.

METHODS

We analyzed the alterations of three key components of the Wnt pathway: beta-catenin, glycogen synthase kinase (GSK)-3beta and T-cell factor (Tcf)-4 in 34 HCC and paracancerous normal liver by immunohistochemistry, polymerase chain reaction (PCR)-single-strand conformation polymorphism (SSCP), direct sequencing, and quantitative real-time reverse transcription (RT)-PCR.

RESULTS

We found that 61.8% (21/34) of all HCC examined showed an abnormal beta-catenin protein accumulation in the cytoplasm or nuclei. The RT-PCR-SSCP and direct sequencing showed that beta-catenin exon 3 mutations existed in 44.1% (15/34) of the HCC. No mutations of GSK-3beta or Tcf-4 were detected in HCC. Moreover, messenger RNA of beta-catenin and Tcf-4, but not GSK-3beta, was found to be overexpressed in HCC. On analyzing the relationship between alterations of beta-catenin or Tcf-4 and C-myc or Cyclin D1 expression, we found that mutations of beta-catenin, as well as overexpression of beta-catenin or the Tcf-4 gene were independently correlated with C-myc gene overexpression in HCC.

CONCLUSION

Our present findings strongly suggest that mutations of beta-catenin, as well as overexpression of beta-catenin and the Tcf-4 gene, independently activate the Wnt pathway in HCC, with the target gene most likely to be C-myc.

Tumor formation by genetic mutations in the components of the Wnt signaling pathway

The genetics of development and cancer have converged in the identification of intra- and extra-cellular signaling pathways that are aberrantly regulated in cancer, and are also central to embryonic patterning. The Wnt signaling pathway has provided an outstanding example of this. The genes for beta-catenin, APC, and Axin in the Wnt signaling pathway are often mutated in human cancers. In all such cases, the common denominator is the activation of gene transcription by beta-catenin. The resulting gene expression profile should provide a significant clue to the developmental mechanisms of cancers carrying defects in the Wnt signaling pathway. In this review, the functions of beta-catenin, APC and Axin, and the alterations of the three genes in human cancers are described.

Prolyl isomerase Pin1: a catalyst for oncogenesis and a potential therapeutic target in cancer

Phosphorylation of proteins on serine or threonine residues preceding proline (Ser/Thr-Pro) is a major intracellular signaling mechanism. The phosphorylated Ser/Thr-Pro motifs in a certain subset of phosphoproteins are isomerized specifically by the peptidyl-prolyl cis-trans isomerase Pin1. This post-phosphorylation isomerization can lead to conformational changes in the substrate proteins and modulate their functions. Pin1 interacts with a number of mitotic phosphoproteins, and plays a critical role in mitotic regulation. Recent work indicates that Pin1 is overexpressed in many human cancers and plays an important role in oncogenesis. Pin1 regulates the expression of cyclin D1 by cooperating with Ras signaling and inhibiting the interaction of beta-catenin with the tumor suppressor APC and also directly stabilizing cyclin D1 protein. Furthermore, PIN1 is an E2F target gene essential for the Neu/Ras-induced transformation of mammary epithelial cells. Pin1 is also a critical regulator of the tumor suppressor p53 during DNA damage response. Given its role in cell growth control and oncogenesis, Pin1 could represent a new anti-cancer target.

SIAH1 inactivation correlates with tumor progression in hepatocellular carcinomas

Accumulation of loss of heterozygosity (LOH) on chromosome 16 is frequently observed in human hepatocellular carcinomas (HCCs). To identify tumor-suppressor genes (TSGs) involved in hepatocarcinogenesis, we performed deletion mapping of chromosome 16 in 59 HCCs. Three commonly deleted regions, located in 16q12.1, 16q22.1, and 16q24.2, were observed. Because there has been no study on LOH at locus 16q12.1 in HCCs, we focused on this region. By searching the Human Genome Database at the National Center for Biotechnology Information web site, we identified 14 known genes in 16q12.1 as TSG candidates. Among these, the expression of SIAH1 was markedly downregulated in HCCs, and inactivation of SIAH1 expression was associated with LOH at 16q12.1. A mutation analysis of SIAH1 revealed no somatic mutations, but one single nucleotide polymorphism was found among the 35 HCCs investigated. Subsequently, we evaluated the relation between SIAH1 expression, confirmed by semiquantitative RT-PCR, and clinicopathological parameters in HCCs. SIAH1 was significantly downregulated in advanced HCCs, including poorly differentiated tumors, larger tumors, and tumors in advanced stages. These findings suggest that inactivation of SIAH1 plays an important role in HCC progression.

Overexpression of orphan G-protein-coupled receptor, Gpr49, in human hepatocellular carcinomas with beta-catenin mutations

To identify the genes responsible for carcinogenesis and progression of hepatocellular carcinoma (HCC), we screened differentially expressed genes in several human HCC cell lines. Among these genes, Gpr49 was up-regulated in PLC/PRF/5 and HepG2. Gpr49 is a member of the glycoprotein hormone receptor subfamily, which includes the thyroid-stimulating hormone receptor (TSHR). However, Gpr49 remains to be an orphan G-protein-coupled receptor. By real-time quantitative reverse transcriptase polymerase chain reaction (RT-PCR) analysis, overexpression (>3-fold increase compared with the corresponding noncancerous liver tissue) of Gpr49 mRNA was observed in 18 of 38 (47%) HCCs compared with corresponding noncancerous livers. Clinicopathologically, overexpression of Gpr49 was frequently observed in HCC with mutation in beta-catenin exon 3 (14 of 16 cases, 87.5%). Moreover, introduction of mutant beta-catenin into mouse hepatocytes in culture caused up-regulation of the Gpr49 mouse homologue. Therefore, Gpr49 is likely to be a target gene activated by Wnt-signaling in HCC. In conclusion, although much is still unknown, Gpr49 may be critically involved in the development of HCCs with beta-catenin mutations and has the potential to be a new therapeutic target in the treatment of HCC.

AXIN1 mutations but not deletions in cerebellar medulloblastomas

Medulloblastoma is a malignant, invasive embryonal tumour of the cerebellum which manifests preferentially in children. A subset of cases is associated with colon cancer and APC germline mutations (Turcot syndrome), and APC and beta-catenin point mutations occur in up to 10% of sporadic cases, indicating the involvement of the Wnt pathway in the development of medulloblastoma. In 39 sporadic cerebellar medulloblastomas screeened for alterations in the AXIN1 gene, another component of the Wnt pathway, we found missense AXIN1 mutations in two tumours, CCC-->TCC at codon 255 (exon 1, Pro-->Ser) and TCT-->TGT at codon 263 (exon 1, Ser-->Cys). Furthermore, the A allele at the G/A polymorphism at nucleotide 16 in intron 4 was significantly over-represented in medulloblastomas (39 cases; G 0.76 vs-A 0.24) compared to healthy individuals (86 cases; G 0.91 vs A 0.09; P=0.0027). RT-PCR revealed large deletions in the AXIN1 gene in 5/12 (42%) medulloblastomas, consistent with a previous report. However, we observed such deletions at a similar frequency also in normal brain tissue (6/12, 50%). Since there are multiple complementary, inverted sequences present in the AXIN1 gene, these large deletions may represent RT-PCR errors due to stem-loop secondary structures.

Beta-catenin antisense studies in embryonic liver cultures: role in proliferation, apoptosis, and lineage specification

BACKGROUND & AIMS

Wnt/beta-catenin pathway activation occurs during liver growth in hepatoblastomas, hepatocellular cancers, and liver regeneration. The aim of this study was to investigate the role of beta-catenin, a key component of the Wnt pathway, in liver development as well as its normal distribution in developing liver.

METHODS

Embryonic liver cultures and beta-catenin antisense phosphorodiamidate morpholino oligomer (PMO) were used to elucidate the role of beta-catenin in liver development. Livers from embryos at 10 days of gestational development were cultured in the presence of antisense or control PMO for 72 hours and analyzed.

RESULTS

Beta-catenin shows stage-specific localization and distinct distribution compared with known markers in developing liver. A substantial decrease in beta-catenin protein was evident in the organs cultured in the presence of antisense. Beta-catenin inhibition decreased cell proliferation and increased apoptosis in these organ cultures. Presence of antisense resulted in loss of CK19 immunoreactivity of the bipotential stem cells. Beta-catenin inhibition also promoted c-kit immunoreactivity of the hepatocytes.

CONCLUSIONS

We conclude that the PMO antisense to beta-catenin effectively inhibits synthesis of its protein. Beta-catenin modulates cell proliferation and apoptosis in developing liver. It may play a significant role in early biliary lineage commitment of the bipotential stem cells and also seems to be important in hepatocyte maturation.

Runnin' with the Dvl: proteins that associate with Dsh/Dvl and their significance to Wnt signal transduction

Wnt proteins transmit myriad intercellular signals crucial for the development and homeostasis of metazoan animals from Hydra to human. Abnormal Wnt signaling causes a growing number of diseases, including cancer and osteoporosis. Depending on the context, a given Wnt signal may denote: cell proliferation or apoptosis; cell fate determination, differentiation, or stem cell maintenance; a variety of changes in cell behavior; and/or coordinated interactions with its neighbors. Which event(s) occur in Wnt-responsive cells depends critically on the ability of Dishevelled (Dsh)/Dvl proteins to interpret distinct types of intracellular, receptor-generated stimuli and transmit them to at least two distinct sets of effector molecules, all while apparently ignoring a third type of Wnt-generated Ca(2+) signal. The three conserved domains present in Dsh/Dvl proteins uniquely function in each Wnt pathway, in part by association with 18 (and counting) Dsh/Dvl-associated proteins. The latest data suggest that Dsh/Dvl proteins organize dynamic, pathway-specific subcellular signaling complexes that ensure correct information routing, signal amplification, and dynamic control through feedback regulation. The biochemical and cell biological mechanisms by which Dsh/Dvl proteins accomplish these remarkable tasks remain obscure.

Patterns of beta-catenin expression in gastric carcinoma: clinicopathological relevance and mutation analysis

Studies on the expression of beta-catenin (beta-ct) in gastric carcinoma have provided conflicting results, and the role played by beta-ct mutations in gastric carcinogenesis remains unclear. In an attempt to clarify the aforementioned issues we undertook the retrospective study of 157 gastric carcinomas by using immunohistochemistry and molecular genetics. Reduced/absent membranous beta-ct expression was significantly associated with isolated-cell/diffuse histotype both in "pure" diffuse gastric carcinomas and in the isolated-cell/diffuse component of mixed carcinomas. Cytoplasmic and/or nuclear beta-ct expression was particularly prevalent in mixed carcinomas and was significantly associated with lymphatic vessel invasion and lymph node metastases. beta-ct mutations were not detected in any case. We conclude that the pattern of beta-ct expression is closely related to gastric carcinoma histotype. The activation of Wnt/beta-ct pathway is associated with mixed gastric carcinoma and with features of clinical aggressiveness; the mechanism(s) underlying this pathway in gastric carcinoma are not due to beta-ct mutations and remain to be elucidated.

Nuclear accumulation of beta-catenin protein in Wilms' tumours

The wnt-signalling pathway plays an important role during both normal kidney development and Wilms' tumourigenesis. Activation of this pathway involves stabilization, intracellular accumulation, and nuclear translocation of the beta-catenin protein and may be caused by specific mutations in the beta-catenin gene itself. Such mutations have been found in about 15% of Wilms' tumours. This study has analysed the intracellular levels and subcellular distribution of beta-catenin protein in 36 primary Wilms' tumour specimens and has correlated these results with the mutational status of the beta-catenin gene. Immunohistochemistry detected faint cytoplasmic and strong membranous expression of beta-catenin protein in the epithelial compartment of all tumours examined. In contrast, nuclear immunoreactivity for beta-catenin was detected in 9 of 9 Wilms' tumours containing a mutation of the beta-catenin gene and in 15 of 27 Wilms' tumours without detectable beta-catenin mutation. Nuclear positivity, in each case, was found to be very strong, but was usually present only in a fraction of cells ranging from 5% to 10%. Among the different histological subcompartments, blastemal and mesenchymal cell nuclei preferentially stained positive, whereas cells of epithelial differentiation displayed nuclear localization of beta-catenin protein in only a single case. Furthermore, nuclear positive cells were found in Wilms' tumours of all stages and in tumours of both favourable and unfavourable histology. These data support the idea that activation of the wnt-signalling pathway is a key oncogenic step in Wilms' tumourigenesis and that it probably involves transcriptional activation of critical target genes, carried out by beta-catenin protein in the nucleus. The fact that nuclear immunoreactivity specific for beta-catenin was detected in a significant number of Wilms' tumours in the absence of beta-catenin mutations suggests that genetic defects affecting other members of the wnt-signalling pathway may contribute to the development of Wilms' tumours in those cases.

Ligand-dependent inhibition of beta-catenin/TCF signaling by androgen receptor

Beta-catenin signaling may contribute to prostate cancer (CaP) progression. Although beta-catenin is known to upregulate T cell factor (TCF) target gene expression in CaP cells, recent evidence demonstrates its capacity to enhance ligand-dependent androgen receptor (AR) function. Thus, we wished to further understand the interaction between these two pathways. We find in both CaP cells (CWR22-Rv1, LAPC-4, DU145) and non-CaP cells (HEK-293, TSU, SW480, HCT-116) that beta-catenin/TCF-related transcription (CRT), as measured by activation of a synthetic promoter and that of cyclin D1, is inhibited by androgen treatment. This inhibition is AR-dependent, as it only occurs in cells expressing AR endogenously or transiently, and is abrogated by AR antagonists. Additional analyses convey that the ligand-dependent nature of CRT suppression depends on transactivation-competent AR in the nucleus, but not on indirect effects stemming from AR target gene expression. Given the recent work identifying an AR/beta-catenin interaction, and from our finding that liganded AR does not prompt gross changes in the constitutive nuclear localization of TCF4 or mutant beta-catenin, we hypothesized that transcription factor (i.e. AR and TCF) competition for beta-catenin recruitment may explain, in part, androgen-induced suppression of CRT. To address this idea, we expressed an AR mutant lacking its DNA-binding domain (DBD). This receptor could not orchestrate ligand-dependent CRT repression, thereby providing support for those recent data implicating the AR DBD/LBD as necessary for beta-catenin interaction. Further supporting this hypothesis, TCF/LEF over-expression counteracts androgen-induced suppression of CRT, and requires beta-catenin binding activity to do so. Interestingly, TCF4 over-expression potently antagonizes AR function; however, this inhibition may occur independently of beta-catenin/TCF4 interaction. These results from TCF4 over-expression analyses, taken together, provide further evidence that AR-mediated suppression of CRT is a consequence of limiting amounts of beta-catenin, and not AR target gene expression. Our analyses point to a reciprocal balance between AR and CRT function that may shape critical processes during normal prostate development and tumor progression.

Cytoplasmic and/or nuclear accumulation of the beta-catenin protein is a frequent event in human osteosarcoma

The molecular events that precede the development of osteosarcoma, the most common primary malignancy of bone, are unclear, and concurrent molecular and genetic alterations associated with its pathogenesis have yet to be identified. Recent studies suggest that activation of beta-catenin signaling may play an important role in human tumorigenesis. To investigate the potential role of beta-catenin deregulation in human osteosarcoma, we analyzed a panel of 47 osteosarcoma samples for beta-catenin accumulation using immunohistochemistry. Potential activating mutations were investigated by sequencing exon 3 of the beta-catenin gene in genomic DNA isolated from tumor samples. Our findings revealed cytoplasmic and/or nuclear accumulation of beta-catenin in 33 of 47 samples (70.2%); however, mutation analysis failed to detect any genetic alterations within exon 3, suggesting that other regulatory mechanisms may play an important role in activating beta-catenin signaling in osteosarcoma. In our survival analysis, beta-catenin deregulation conferred a hazard ratio of 1.05, indicating that beta-catenin accumulation does not appear to be of prognostic value for osteosarcoma patients. When analyzed against other clinicopathologic parameters, beta-catenin accumulation correlated only with younger age at presentation (26.4 vs. 39.8 years). Nevertheless, our results demonstrate that the deregulation of beta-catenin signaling is a common occurrence in osteosarcoma that is implicated in the pathogenesis of osteosarcoma.

New targets of beta-catenin signaling in the liver are involved in the glutamine metabolism

Inappropriate activation of the Wnt/beta-catenin signaling has been implicated in the development of hepatocellular carcinoma (HCC), but exactly how beta-catenin works remains to be elucidated. To identify, in vivo, the target genes of beta-catenin in the liver, we have used the suppression subtractive hybridization technique and transgenic mice expressing an activated beta-catenin in the liver that developed hepatomegaly. We identified three genes involved in glutamine metabolism, encoding glutamine synthetase (GS), ornithine aminotransferase (OAT) and the glutamate transporter GLT-1. By Northern blot and immunohistochemical analysis we demonstrated that these three genes were specifically induced by activation of the beta-catenin pathway in the liver. In different mouse models bearing an activated beta-catenin signaling in the liver known to be associated with hepatocellular proliferation we observed a marked up-regulation of these three genes. The cellular distribution of GS and GLT-1 parallels beta-catenin activity. By contrast no up-regulation of these three genes was observed in the liver in which hepatocyte proliferation was induced by a signal-independent of beta-catenin. In addition, the GS promoter was activated in the liver of GS(+/LacZ) mice by adenovirus vector-mediated beta-catenin overexpression. Strikingly, the overexpression of the GS gene in human HCC samples was strongly correlated with beta-catenin activation. Together, our results indicate that GS is a target of the Wnt/beta-catenin pathway in the liver. Because a linkage of the glutamine pathway to hepatocarcinogenesis has already been demonstrated, we propose that regulation of these three genes of glutamine metabolism by beta-catenin is a contributing factor to liver carcinogenesis.

Abnormalities of the APC/beta-catenin pathway in endometrial cancer

The activation of the APC/beta-catenin signalling pathway due to beta-catenin mutations has been implicated in the development of a subset of endometrial carcinomas (ECs). However, up to 25% of ECs have beta-catenin nuclear accumulation without evidence of beta-catenin mutations, suggesting alterations of other molecules that can modulate the Wnt pathway, such as APC, gamma-catenin, AXIN1 and AXIN2. We investigated the expression pattern of beta- and gamma-catenin in a group of 128 endometrial carcinomas, including 95 endometrioid endometrial carcinomas (EECs) and 33 non-endometrioid endometrial carcinomas (NEECs). In addition, we evaluated the presence of loss of heterozygosity and promoter hypermethylation of the APC gene and mutations in the APC, beta- and gamma-catenin, AXIN1, AXIN2, and RAS genes, and phospho-Akt expression. No APC mutations were detected but LOH at the APC locus was found in 24.3% of informative cases. APC promoter 1A hypermethylation was observed in 46.6% of ECs, and was associated with the endometrioid phenotype (P=0.034) and microsatellite instability (P=0.008). Neither LOH nor promoter hypermethylation of APC was associated with nuclear catenin expression. Nuclear beta-catenin expression was found in 31.2% of EECs and 3% of NEECs (P=0.002), and was significantly associated with beta-catenin gene exon 3 mutations (P<0.0001). beta-catenin gene exon 3 mutations were associated with the endometrioid phenotype, and were detected in 14 (14.9%) EECs, but in none of the NEECs (P=0.02). gamma-catenin nuclear expression was found in 10 ECs; it was not associated with the histological type but was associated with more advanced stages (P=0.042). No mutations in gamma-catenin, AXIN1 and 2 genes were detected in this series. Neither RAS mutations nor phospho-Akt expression, which were found in 16 and 27.6% of the cases, respectively, were associated with beta-catenin nuclear expression. Our results demonstrated a high prevalence of alterations in molecules of the APC/beta-catenin pathway, but only mutations in beta-catenin gene are associated with aberrant nuclear localization of beta-catenin.

P53 mutation as a source of aberrant beta-catenin accumulation in cancer cells

beta-catenin is involved in both cell-cell interactions and wnt pathway-dependent cell fate determination through its interactions with E-cadherin and TCF/LEF transcription factors, respectively. Cytoplasmic/nuclear levels of beta-catenin are important in regulated transcriptional activation of TCF/LEF target genes. Normally, these levels are kept low by proteosomal degradation of beta-catenin through Axin1- and APC-dependent phosphorylation by CKI and GSK-3beta. Deregulation of beta-catenin degradation results in its aberrant accumulation, often leading to cancer. Accordingly, aberrant accumulation of beta-catenin is observed at high frequency in many cancers. This accumulation correlates with either mutational activation of CTNNB1 (beta-catenin) or mutational inactivation of APC and Axin1 genes in some tumors. However, there are many tumors that display beta-catenin accumulation in the absence of a mutation in these genes. Thus, there must be additional sources for aberrant beta-catenin accumulation in cancer cells. Here, we provide experimental evidence that wild-type beta-catenin accumulates in hepatocellular carcinoma (HCC) cells in association with mutational inactivation of p53 gene. We also show that worldwide p53 and beta-catenin mutation rates are inversely correlated in HCC. These data suggest that inactivation of p53 is an important cause of aberrant accumulation of beta-catenin in cancer cells.

SUMO-1 modification of the C-terminal KVEKVD of Axin is required for JNK activation but has no effect on Wnt signaling

Axin is a multifunctional protein, regulating Wnt signaling and the c-Jun N-terminal/stress-activated protein kinase (JNK/SAPK) pathway as well as tumorigenesis. In the present study, we found that Axin interacts with three SUMO-1 (small ubiquitin-related modifier) conjugating enzymes 3 (E3), PIAS1, PIASxbeta, and PIASy. The extreme C-terminal six amino acid residues of Axin are critical for the Axin/E3 interaction as deletion of the six residues (AxinDeltaC6) completely abolished the ability of Axin to interact with E3 enzymes. AxinDeltaC6 also failed to activate JNK, although it was intact in both its interaction with MEKK1 and homodimerization. Consistent with the presence of a doublet of the KV(E/D) sumoylation consensus motif at the C-terminal end (KVEKVD), we found that Axin is heavily sumoylated. Deletion of the C-terminal six amino acids drastically reduced sumoylation, indicating that the C-terminal six amino acids stretch is the main sumoylation site for Axin. Sumoylation-defective mutants failed to activate JNK but effectively destabilized beta-catenin and attenuated LEF1 transcriptional activity. In addition, we show that dominant negative Axin mutants blocked PIAS-mediated JNK activation, in accordance with the requirement of sumoylation for Axin-mediated JNK activation. Taken together, we demonstrate that sumoylation plays a role for Axin to function in the JNK pathway.

Analysis of the beta-catenin/T cell factor signaling pathway in 36 gastrointestinal and liver cancer cells

We investigated the frequency and mechanism of beta-catenin/T cell factor (Tcf) signaling activation in a panel of 36 human gastrointestinal and liver cancer cell lines. Reporter assay and electrophoretic mobility shift assay revealed that the beta-catenin/Tcf signaling was upregulated in 12 of 12 (100%) colorectal, 5 of 8 (68%) gastric, 2 of 7 (29%) hepatic, and none of 9 pancreatic cancer cell lines. The activation of the pathway was mainly due to the mutation of adenomatous polyposis coli (APC) or beta-catenin, and Tcf-4 was highly expressed in these cell lines with upregulated signaling. Nuclear beta-catenin was observed not only in the signaling-activated cell lines, but also in 14 of 25 (56%) primary gastric cancers, 15 of 20 (75%) colon cancers, 5 of 19 (26%) hepatocellular carcinomas, and none of 13 pancreatic cancers. The presence of signaling-upregulated gastric cancer cell lines with intact APC and beta-catenin suggests the involvement of other mechanisms than mutations of APC or beta-catenin.

Pro-apoptotic actions of exisulind and CP461 in SW480 colon tumor cells involve beta-catenin and cyclin D1 down-regulation

Exisulind and its analogues are inhibitors of cyclic GMP phosphodiesterases (PDEs) that have been shown to activate and induce protein kinase G, resulting in the induction of apoptosis in colon cancer cells. These drugs also reduce beta-catenin protein levels and decrease cyclin D1 mRNA levels in SW480 cells. Herein we report on studies pertaining to exisulind regulation of beta-catenin levels and activity in colon tumor cells. Exisulind and its higher-affinity PDE analogues, (Z)-5-fluoro-2-methyl-(4-pyridylidene)-3-(N-benzyl)-indenylacetamide hydrochloride (CP461) and (Z)-1H-indene-3-acetamide, 5-fluoro-2-methyl-N-(phenylmethyl)-1-[(3,4,5-trimethoxyphenyl)methylene] (CP248), reduced beta-catenin, including the nuclear beta-catenin in SW480 cells (EC(50) approximately 200 microM, 1 microM, and <1 microM, respectively). The 50% reduction of beta-catenin was seen in 8-14 hr. There was no change in beta-catenin mRNA. Exisulind-induced beta-catenin reduction was blocked by the proteasomal inhibitor MG132 (Z-leu-Leu-Leu-CHO), indicating that the effect of exisulind involved ubiquitin-proteasomal degradation. A consequence of reduced beta-catenin in SW480 cells was that exisulind, CP461, and CP248 caused a concentration- and time-dependent decrease in cyclin D1 levels (EC(50) approximately 300 microM, 1 microM, and <1 microM, respectively) in 4 hr. The effect was via decreased cyclin D1 mRNA levels. Exisulind-induced degradation of beta-catenin was not blocked by the inhibition of caspase-3 activity and/or apoptosis, and some SW480 cells showed a reduction in beta-catenin levels before the appearance of early apoptosis indicators. Expression of the N-terminal 170 amino acid fragment of beta-catenin reduced the effects of beta-catenin degradation, cyclin D1 reduction, and the apoptosis response to exisulind. These results indicate that exisulind-induced beta-catenin degradation precedes the induction of apoptosis and that the down-regulation of inappropriate beta-catenin-activated genes accounts in part for the pro-apoptotic effects of exisulind and CP461 in colon tumor cells.

Two cases of the caudal duplication anomaly including a discordant monozygotic twin

We present two unrelated patients with various duplications in the caudal region. One patient presented with a duplication of the distal spine from L4, left double ureter, duplication of the vagina and cervix, and duplication of the distal colon. The second patient was diagnosed with a duplication of the colon, bladder, vagina and uterus. The first patient had an unaffected monozygotic twin sister. Dominguez et al. [1993: Am J Dis Child 147:1048-1052] presented six similar cases, and introduced the name "caudal duplication syndrome." The pathogenesis of the caudal duplication anomaly is unclear. The possibility of a polytopic primary developmental field defect or a disruptive sequence are discussed. On the other hand, somatic or germline mutations in certain developmental genes could be involved, as illustrated by the mouse mutations disorganisation and fused. DNA-analysis of the AXIN1 gene, the human homologue of the gene responsible for fused, performed in our first patient, did not show any apparent pathogenic mutation.

Transcriptional activation of interleukin-8 by beta-catenin-Tcf4

Nuclear translocation of beta-catenin and its association with Tcf/Lef factors are key steps in transduction of the Wnt signal, which is aberrantly activated in a variety of human cancers. In a search for new beta-catenin-Tcf target genes, we analyzed beta-catenin-induced alterations of gene expression in primary human hepatocytes, after transduction of either dominant stable beta-catenin or its truncated, transactivation-deficient counterpart by means of a lentiviral vector. cDNA microarray analysis revealed a limited set of up-regulated genes, including known Wnt targets such as matrilysin and keratin-1. In this screen, we identified the CXC chemokine interleukin 8 (IL-8) as a direct target of beta-catenin-Tcf4. IL-8 is constitutively expressed in various cancers, and it has been implicated in tumor progression through its mitogenic, motogenic, and angiogenic activities. The IL-8 promoter contains a unique consensus Tcf/Lef site that is critical for IL-8 activation by beta-catenin. We show here that the p300 coactivator was required for efficient transactivation of beta-catenin on this promoter. Ectopic expression of beta-catenin in hepatoma cells promoted IL-8 secretion, which stimulated endothelial cell migration. These data define IL-8 as a Wnt target and suggest that IL-8 induction by beta-catenin might be implicated in developmental and tumorigenic processes.

Spectrum of molecular changes during hepatocarcinogenesis induced by DEN and other chemicals in Fischer 344 male rats

Unlike other tissues such as breast, colon and renal cell carcinoma, it is not an easy task to single out any representative oncogene or tumor suppressor genes in the development of hepatocellular carcinoma (HCC), which play a pivotal role. To investigate putatively altered main pathways in HCC, F344 male rats were treated with a single injection of N-nitrosodiethylamine (DEN), followed by either twice/week injections of nodularin for 10 weeks or thioacetamide (TAA) in drinking water for 39 weeks. p53 expression was dramatic in both hepatocytes and mesenchymal cells after a single injection of DEN, however, PCR-SSCP assay could not detect any p53 mutation during the development of hepatocellular adenoma. The data indicate that wtp53 response was mostly for removal of damaged cells during the initiation of carcinogenesis. When treated with DEN-TAA, induction of gankyrin expression during hepatic fibrosis preceded the loss of pRB protein, accompanied with significant expressions of G1 phase cyclins and CDKs. Moreover, p16(INK4A) exon 1 was hypermethylated during the development of poorly differentiated HCCs. These changes would result in complete inactivation of the pRB regulatory pathway during hepatocarcinogenesis. Induction of TGF-beta1 expression with loss of its receptor expression occurred rapidly in the altered hepatocytes by DEN-nodularin treatment.

CONCLUSION

Therefore, escape from TGF-beta1 induced apoptosis and severe degradation of pRB protein during the early stage of carcinogenesis can perform a symphony to proliferate and to transform the altered hepatocytes to tumor cells. Inactivation of p16(INK4A) and p53 genes at the later stage of carcinogenesis would endow HCC with malignancy, which is highly resistant to any therapeutic trials.

Genetic alterations in hepatoblastoma and hepatocellular carcinoma: common and distinctive aspects

Hepatoblastoma (HB) and hepatocellular carcinoma (HCC) are two different subtypes of primary tumors arising from liver parenchymal cells. These tumors differ by many histoclinical characteristics, and comparative analysis of genetic alterations in HB and HCC might provide some clues on the molecular oncogenic pathways leading to hepatocyte transformation. Recent outcomes have been provided by the assessment of global genetic changes in tumor cells, using conventional cytogenetic approaches, PCR-based microsatellite analysis and Comparative genomic Hybridization (CGH). Cytogenetic studies of HB, microsatellite analysis of HCC and recent CHG data have outlined common and distinctive characters between the two tumor types. HBs are characterized by a low number of chromosomal changes, consisting mainly of gains at chromosomes 1q, 2, 8q, 17q, and 20. By contrast, HCCs harbor multiple chromosomal abnormalities, predominantly losses, with increased chromosomal instability in tumors associated with hepatitis B virus infection. Common alterations in HB and HCC include gain of chromosomes 1q, 8q, and 17q, and loss of 4q. Another important common feature shared by the two tumor types is the frequent activation of Wnt/beta-catenin signaling by stabilizing mutations of beta-catenin. Immunohistochemical analysis of beta-catenin has demonstrated nuclear/cytoplasmic accumulation of the protein in most HBs and in more than one third of HCCs. Strikingly, beta-catenin mutations are associated with chromosomal stability in both tumor types. Together, these studies define different pathways in liver cell transformation, reflecting various developmental stages and multiple risk factors. A detailed understanding of the molecular hits underlying liver tumorigenesis, combined with clinicopathological parameters, will permit an accurate evaluation of major targets for prognostic and therapeutic intervention.

Presenilin couples the paired phosphorylation of beta-catenin independent of axin: implications for beta-catenin activation in tumorigenesis

The Alzheimer's disease-linked gene presenilin 1 (PS1) is required for intramembrane proteolysis of APP and Notch. In addition, recent observations strongly implicate PS1 as a negative regulator of the Wnt/beta-catenin signaling pathway, although the mechanism underlying this activity is unknown. Here, we show that presenilin functions as a scaffold that rapidly couples beta-catenin phosphorylation through two sequential kinase activities independent of the Wnt-regulated Axin/CK1alpha complex. Thus, presenilin deficiency results in increased beta-catenin stability in vitro and in vivo by disconnecting the stepwise phosphorylation of beta-catenin, both in the presence and absence of Wnt stimulation. These findings highlight an aspect of beta-catenin regulation outside of the canonical Wnt-regulated pathway and a function of presenilin separate from intramembrane proteolysis.

The beta-catenin/TCF-4 complex imposes a crypt progenitor phenotype on colorectal cancer cells

The transactivation of TCF target genes induced by Wnt pathway mutations constitutes the primary transforming event in colorectal cancer (CRC). We show that disruption of beta-catenin/TCF-4 activity in CRC cells induces a rapid G1 arrest and blocks a genetic program that is physiologically active in the proliferative compartment of colon crypts. Coincidently, an intestinal differentiation program is induced. The TCF-4 target gene c-MYC plays a central role in this switch by direct repression of the p21(CIP1/WAF1) promoter. Following disruption of beta-catenin/TCF-4 activity, the decreased expression of c-MYC releases p21(CIP1/WAF1) transcription, which in turn mediates G1 arrest and differentiation. Thus, the beta-catenin/TCF-4 complex constitutes the master switch that controls proliferation versus differentiation in healthy and malignant intestinal epithelial cells.

Regulation of epithelial cell migration and tumor formation by beta-catenin signaling

Cell migration requires precise control, which is altered or lost when tumor cells become invasive and metastatic. beta-catenin plays a dual role in this process: as a member of adherens junctions it is essential to link cadherins to the cytoskeleton thereby allowing tight intercellular adhesion, and as a member of the Wnt-signaling pathway, beta-catenin is translocated into the nucleus and serves together with the LEF1/TCF-transcription factors to drive gene expression necessary for the epithelial-to-mesenchymal transition (EMT). Activated beta-catenin signaling has been implicated in the genesis of a variety of tumors. Here we demonstrate a pivotal function for beta-catenin signaling in epithelial cell migration and tumorigenesis. Hepatocyte growth factor (HGF) and epidermal growth factor (EGF) induce beta-catenin signaling under conditions where they stimulate cell motility. Ectopic expression of either stabilized beta-catenin or a regulatable form of activated beta-catenin induces cell migration in different cell types and cooperates with EGF and HGF in this process. Activation of beta-catenin signaling induces expression of the new target gene osteopontin during migration. Cells expressing stabilized beta-catenin also exhibit significantly increased capability to form tumors in a nude mouse xenograft model. The data suggest that a critical threshold of beta-catenin signaling, activated by cooperative mechanisms, may be important during the EMT and tumorigenesis.

Oncogenic transformation by beta-catenin: deletion analysis and characterization of selected target genes

Genetic analysis of beta-catenin-induced oncogenic transformation in chicken embryo fibroblasts (CEF) revealed the following prerequisites for oncogenicity: (1) removal of the N terminal phosphorylation sites targeted by glycogen synthase kinase 3beta (GSK3beta), (2) retention of the N terminal transactivation domain, and (3) retention of the armadillo repeats. The C terminal transactivation domain played an ancillary role in the transformation of CEF. There was a rough correlation between the transforming activity of various beta-catenin constructs and their transactivation of the TOPFLASH reporter. Expression levels of the candidate target genes of beta-catenin-LEF, cyclin D1 and myc were not correlated with each other or with the transforming activity of beta-catenin constructs. A new target gene, coding for inositol hexakisphosphate kinase 2 (IP6K2) was identified. Its expression showed concordance with the transforming activity of beta-catenin constructs.

P53 gene and Wnt signaling in benign neoplasms: beta-catenin mutations in hepatic adenoma but not in focal nodular hyperplasia

Hepatocellular adenoma (HA) and focal nodular hyperplasia (FNH) are 2 rare, benign liver neoplasms that often are discovered incidentally. To date, few genetic changes have been found in these 2 benign lesions. However, the 2 pathways of p53 and Wnt signaling, which may be the most common molecular targets involved in liver tumorgenesis, were studied in HA and FNH. Ten HAs and 11 FNHs were analyzed for loss of heterozygosity (LOH) and sequencing analysis of mutation hot spots in exons 5 to 8 of the p53 gene. No LOH or mutant sequences were identified, indicating that p53 was not associated with these benign lesions. Genes in the Wnt signaling pathway, including beta-catenin, axin, and adenomatous polyposis coli (APC), also were studied. Polymerase chain reaction (PCR) amplification and direct sequencing of all samples of HA and FNH displayed no mutations in exon 3 of the beta-catenin gene. However, 3 HAs (30%) contained interstitial deletions from exon 3 to exon 4. Truncated forms of beta-catenin detected by Western blot and immunohistochemical analyses showed they had accumulated in the cytoplasm and nuclei. However, for the axin and APC genes, no genetic changes, including allelic loss, interstitial deletions and point mutations, were detected in any of the HAs and FNHs. In conclusion, beta-catenin, which participates in the Wnt signaling pathway, might play a more important role in the formation of HA than in that of FNH, but p53 is not associated with the development of either HA or FNH.

Calpain as an effector of the Gq signaling pathway for inhibition of Wnt/beta -catenin-regulated cell proliferation

Signaling pathways interact to integrate and regulate information flow in evoking complex cellular responses. We have studied the mechanisms and consequences of interactions between the Gq and Wnt/beta-catenin pathways. In human colon carcinoma SW480 cells, activation of the Gq pathway inhibits beta-catenin signaling as determined by transcriptional reporter and cell proliferation assays. Ca(2+) release from internal stores results in nuclear export and calpain-mediated degradation of beta-catenin in the cytoplasm. Galphaq does not inhibit the effects of constitutively activated DeltaN-XTCF3-VP16 chimera in SW480 cells. Similarly, in HEK293 cells the Gq pathway suppresses beta-catenin-T cell factor/lymphocyte enhancer factor-1 transcriptional activity induced by Wnt/Frizzled interaction or glycogen synthase kinase-3beta-resistant beta-catenin, but not DeltaN-XTCF3-VP16. We conclude that Gq signaling promotes nuclear export and calpain-mediated degradation of beta-catenin, which therefore contributes to the inhibition of Wnt/beta-catenin pathway.

A yeast model system for functional analysis of beta-catenin signaling

We have developed a novel Saccharomyces cerevisiae model system to dissect the molecular events of beta-catenin (beta-cat) signaling. Coexpression of mammalian beta-cat with TCF4 or LEF1 results in nuclear accumulation of these proteins and a functional complex that activates reporter gene transcription from constructs containing leukocyte enhancer factor (LEF)/T cell factor (TCF) response elements. Reporter transcription is constitutive, requires expression of both beta-cat and TCF4 or LEF1, and is not supported by mutated LEF/TCF binding elements or by TCF4 or LEF1 mutants. A cytoplasmic domain of E-cadherin or a functional fragment of adenomatous polyposis coli (APC) protein (APC-25) complexes with beta-cat, reduces beta-cat binding to TCF4, and leads to increased cytoplasmic localization of beta-cat and a reduction in reporter activation. Systematic mutation of putative nuclear export signal sequences in APC-25 decreases APC-25 binding to beta-cat and restores reporter gene transcription. Additional beta-cat signaling components, Axin and glycogen synthase kinase 3beta, form a multisubunit complex similar to that found in mammalian cells. Coexpression of the F-box protein beta-transducin repeat-containing protein reduces the stability of beta-cat and decreases reporter activation. Thus, we have reconstituted a functional beta-cat signal transduction pathway in yeast and show that beta-cat signaling can be regulated at multiple levels, including protein subcellular localization, protein complex formation, and protein stability.

Isolation of HELAD1, a novel human helicase gene up-regulated in colorectal carcinomas

To investigate the mechanisms of colorectal carcinogenesis, we searched for genes regulated by adenomatous polyposis coli gene product (APC) and identified a novel gene, termed HELAD1 (helicase, APC down-regulated 1). A recombinant polypeptide representing the ATPases associated with cellular activities (AAA) domain of the HELAD1 product showed 3' to 5' helicase activity and exonuclease activity in vitro. HELAD1 was abundantly expressed in 16 of 20 colon cancers examined but hardly detectable in corresponding non-cancerous mucosae. Treatment of colon-cancer cells with antisense oligonucleotides suppressed its expression and induced apoptosis. These data revealed an importance of HELAD1 in colorectal carcinogenesis and suggest that suppression of HELAD1 may be a promising therapeutic strategy.

Role of Wnt pathway in medulloblastoma oncogenesis

To clarify the roles of Wnt pathway in medulloblastoma oncogenesis, immunohistochemical staining of beta-catenin and Wnt-1 and genomic analyses of CTNNB1 (beta-catenin) and AXIN1 (axin 1) were examined in 23 sporadic cases. Accumulation of beta-catenin in tumor cells was immunohistochemically proven in 5 cases; 2 cases showed positive immunoreactivity for Wnt-1 and another 2 showed mutation of either CTNNB1 or AXIN1. AXIN1 mutation was in exon 3, corresponding to GSK-3beta binding site and CTNNB1 mutation was in exon 3, corresponding to its phosphorylation site. Disruption of these proteins could result in upregulation of the Wnt signaling and accumulation of beta-catenin, followed by cell proliferation and medulloblastoma oncogenesis.

Expression profiles of 109 apoptosis pathway-related genes in 82 mouse tissues and experimental conditions

Apoptosis is an important process in development and tissue homeostasis. To understand the similarities and differences in the apoptosis machinery in different normal, developmental, and diseased tissues, the expression profiles of 109 apoptosis-pathway-related genes in 82 mouse tissues and experimental conditions were examined using Incyte Mouse GEMI cDNA arrays. It has been found that the compositions of the apoptotic machinery vary among different tissues, developmental stages, and disease states, with subsets of apoptotic genes co-ordinately expressed in the 82 tissues and experimental conditions. Additional genes whose expression profiles resemble selected genes from the 109 apoptotic gene list were also identified. This study provides valuable information on possible molecular mechanisms of differential apoptotic responses to developmental signals, environmental stimuli, and therapeutic treatments in tissue-specific manner.