The Wnt signaling pathway in solid childhood tumors

Crosstalk between PI3K/AKT/mTOR and WNT/β-Catenin signaling in GBM - Could combination therapy checkmate the collusion?

Glioblastoma multiforme is one of the calamitous primary glial brain tumors with extensive heterogeneity at cellular and molecular levels. While maximal surgical resection trailed by radio and chemotherapy employing temozolomide remains the gold-standard treatment for malignant glioma patients, the overall prognosis remains dismal and there exists an unmet need for effective therapeutic strategies. In this context, we hypothesize that proper understanding of signaling pathways responsible for glioblastoma multiforme proliferation would be the first trump card while searching for novel targeted therapies. Among the pathways aberrantly activated, PI3K/AKT/mTOR is the most significant pathway, that is clinically implicated in malignancies such as high-grade glioma. Further, the WNT/β-Catenin cascade is well-implicated in several malignancies, while its role in regulating glioma pathogenesis has only emerged recently. Nevertheless, oncogenic activation of both these pathways is a frequent event in malignant glioma that facilitates tumor proliferation, stemness and chemo-resistance. Recently, it has been reported that the cross-talk of PI3K/AKT/mTOR pathway with multiple signaling pathways could promote glioma progression and reduce the sensitivity of glioma cells to the standard therapy. However, very few studies had focused on the relationship between PI3K/AKT/mTOR and WNT/β-Catenin pathways in glioblastoma multiforme. Interestingly, in homeostatic and pathologic circumstances, both these pathways depict fine modulation and are connected at multiple levels by upstream and downstream effectors. Thus, gaining deep insights on the collusion between these pathways would help in discovering unique therapeutic targets for glioblastoma multiforme management. Hence, the current review aims to address, "the importance of inter-play between PI3K/AKT/mTOR and WNT/β-Catenin pathways", and put forward, "the possibility of combinatorially targeting them", for glioblastoma multiforme treatment enhancement.

Molecular Alterations in Solid Pseudopapillary Neoplasm of the Pancreas: The Achilles Heel in Conquering Pancreatic Tumorigenesis

Solid pseudopapillary neoplasms of the pancreas are overwhelmingly benign tumors predominately observed in women in the third decade of life. However, their malignant potential, based on local recurrences and metastases, has brought into question the available evidence on their biological behavior. Solid pseudopapillary neoplasms have distanced themselves from other pancreatic tumors with varying morphological appearance, immune profile, and histogenesis. In review of the literature, PubMed was queried using search strings, including "solid pseudopapillary neoplasm" and "molecular," and "immunohistochemistry." Alternative searches were also conducted given the variability in tumor name, including "solid pseudopapillary tumor" and "Frantz tumor." This article provides an in-depth review into the molecular pathways that contribute to the pathogenesis of solid pseudopapillary neoplasms. It also discusses the implications of existing molecular pathways toward tumor aggressiveness and recurrence potential.

Destined to Die: Apoptosis and Pediatric Cancers

Apoptosis (programmed cell death) is a systematic and coordinated cellular process that occurs in physiological and pathophysiological conditions. Sidestepping or resisting apoptosis is a distinct characteristic of human cancers including childhood malignancies. This review dissects the apoptosis pathways implicated in pediatric tumors. Understanding these pathways not only unraveled key molecules that may serve as potential targets for drug discovery, but also molecular nodes that integrate with other signaling networks involved in processes such as development. This review presents current knowledge of the complex regulatory system that governs apoptosis with respect to other processes in pediatric cancers, so that fresh insights may be derived regarding treatment resistance or for more effective treatment options.

Molecular dynamic simulation of mutated β-catenin in solid pseudopapillary neoplasia of the pancreas

Solid pseudopapillary neoplasia of the pancreas (SPN) is a rare pancreatic neoplasm that frequently harbors mutations in catenin β1 (CTNNB1, encoding β-catenin) as a part of its molecular pathogenesis. Mutations to CTNNB1 reported in SPN usually occur at the serine/threonine phosphorylation sites, including codons 33, 37 and 41, and the flanking residues of codon 33. On analysis of 3 cases of SPN, mutations to CTNNB1 were detected in codon 32 (D32A and D32Y). As this residue, aspartic acid, is not a direct phosphorylation site of the protein, molecular modeling tools were used to predict the influence of these mutations on the protein structure of β-catenin. A total of three MD simulations (wild-type, D32A, and D32Y) were performed to visualize the conformations of β-catenin under in vivo, aqueous-phase conditions at 37°C. In the wild-type protein, the secondary structure of residues P16-H28 remained helical; we therefore hypothesized that the helical structure of this protein fragment (residues M11-G50) was necessary for phosphorylation of S33 phosphorylation. The loss of the secondary structure in P16-H28 was observed in D32A, losing its helical structure and becoming a turn; however, in the D32Y mutant, the helical structure remained. The present demonstrated that structural changes in the mutated β-catenin protein at D32 could potentially explain the mechanism behind its defective phosphorylation in the pathogenesis of SPN.

Inhibition of β-catenin signaling suppresses pancreatic tumor growth by disrupting nuclear β-catenin/TCF-1 complex: critical role of STAT-3

Aberrant activation of β-catenin/TCF signaling is related to the invasiveness of pancreatic cancer. In the present study, we evaluated the effect of capsaicin on β-catenin/TCF signaling. In a concentration and time-dependent study, we observed that capsaicin treatment inhibits the activation of dishevelled (Dsh) protein DvI-1 in L3.6PL, PanC-1 and MiaPaCa-2 pancreatic cancer cells. Capsaicin treatment induced GSK-3β by inhibiting its phosphorylation and further activated APC and Axin multicomplex, leading to the proteasomal degradation of β-catenin. Expression of TCF-1 and β-catenin-responsive proteins, c-Myc and cyclin D1 also decreased in response to capsaicin treatment. Pre-treatment of cells with MG-132 blocked capsaicin-mediated proteasomal degradation of β-catenin. To establish the involvement of β-catenin in capsaicin-induced apoptosis, cells were treated with LiCl or SB415286, inhibitors of GSK-3β. Our results reveal that capsaicin treatment suppressed LiCl or SB415286-mediated activation of β-catenin signaling. Our results further showed that capsaicin blocked nuclear translocation of β-catenin, TCF-1 and p-STAT-3 (Tyr705). The immunoprecipitation results indicated that capsaicin treatment reduced the interaction of β-catenin and TCF-1 in the nucleus. Moreover, capsaicin treatment significantly decreased the phosphorylation of STAT-3 at Tyr705. Interestingly, STAT-3 over expression or STAT-3 activation by IL-6, significantly increased the levels of β-catenin and attenuated the effects of capsaicin in inhibiting β-catenin signaling. Finally, capsaicin mediated inhibition of orthotopic tumor growth was associated with inhibition of β-catenin/TCF-1 signaling. Taken together, our results suggest that capsaicin-induced apoptosis in pancreatic cancer cells was associated with inhibition of β-catenin signaling due to the dissociation of β-catenin/TCF-1 complex and the process was orchestrated by STAT-3.

Prostaglandin E2 promotes MYCN non-amplified neuroblastoma cell survival via β-catenin stabilization

Amplification of MYCN is the most well-known prognostic marker of neuroblastoma risk classification, but still is only observed in 25% of cases. Recent evidence points to the cyclic adenosine monophosphate (cAMP) elevating ligand prostaglandin E2 (PGE2 ) and β-catenin as two novel players in neuroblastoma. Here, we aimed to define the potential role of PGE2 and cAMP and its potential interplay with β-catenin, both of which may converge on neuroblastoma cell behaviour. Gain and loss of β-catenin function, PGE2 , the adenylyl cyclase activator forskolin and pharmacological inhibition of cyclooxygenase-2 (COX-2) were studied in two human neuroblastoma cell lines without MYCN amplification. Our findings show that PGE2 enhanced cell viability through the EP4 receptor and cAMP elevation, whereas COX-2 inhibitors attenuated cell viability. Interestingly, PGE2 and forskolin promoted glycogen synthase kinase 3β inhibition, β-catenin phosphorylation at the protein kinase A target residue ser675, β-catenin nuclear translocation and TCF-dependent gene transcription. Ectopic expression of a degradation-resistant β-catenin mutant enhances neuroblastoma cell viability and inhibition of β-catenin with XAV939 prevented PGE2 -induced cell viability. Finally, we show increased β-catenin expression in human high-risk neuroblastoma tissue without MYCN amplification. Our data indicate that PGE2 enhances neuroblastoma cell viability, a process which may involve cAMP-mediated β-catenin stabilization, and suggest that this pathway is of relevance to high-risk neuroblastoma without MYCN amplification.

Coupling G2/M arrest to the Wnt/β-catenin pathway restrains pancreatic adenocarcinoma

β-catenin plays a pivotal role in organogenesis and oncogenesis. Alterations in β-catenin expression are common in pancreatic cancer, which is an extremely aggressive malignancy with a notably poor prognosis. In this report, we analyzed the apoptotic activity of withanolide-D (witha-D), a steroidal lactone that was purified from an Indian medicinal plant, Withania somnifera, and its underlying mechanism of action. Witha-D induced apoptosis in pancreatic ductal adenocarcinoma cells by prompting cell-cycle arrest at the G2/M phase. This lactone abrogated β-catenin signaling in these cells regardless of disease grade, mutational status, and gemcitabine sensitivity. Witha-D also upregulated E-cadherin in most cells, thereby supporting the inversion of the epithelial-mesenchymal transition. Furthermore, the Akt/Gsk3β kinase cascade was identified as a critical mediator of G2/M regulation and β-catenin signaling. Witha-D deactivated Akt, which failed to promote Gsk3β deactivation phosphorylation. Consequently, activated Gsk3β facilitated β-catenin destruction in pancreatic carcinoma cells. The knockdown of Chk1 and Chk2 further activated Akt and reversed the molecular signal. Taken together, the results of the current study represent the first evidence of β-catenin signal crosstalk during the G2/M phase by functionally inactivating Akt via witha-D treatment in pancreatic cancer cells. In conclusion, this finding suggests the potential identification of a new lead molecule in the treatment of pancreatic adenocarcinoma.

Activated wnt signaling in stroma contributes to development of pancreatic mucinous cystic neoplasms

BACKGROUND & AIMS

Pancreatic mucinous cystic neoplasm (MCN), a cystic tumor of the pancreas that develops most frequently in women, is a potential precursor to pancreatic ductal adenocarcinoma. MCNs develop primarily in the body and tail of the pancreas and are characterized by the presence of a mucinous epithelium and ovarian-like subepithelial stroma. We investigated the involvement of Wnt signaling in KRAS-mediated pancreatic tumorigenesis and development of MCN in mice, and Wnt activation in human MCN samples.

METHODS

LSL-Kras(G12D), Ptf1a-cre mice were crossed with elastase-tva mice to allow for introduction of genes encoded by the replication-competent avian sarcoma-leukosis virus long-terminal repeat with splice acceptor viruses to pancreatic acinar cells and acinar cell progenitors, postnatally and sporadically. Repeat with splice acceptor viruses that expressed Wnt1 were delivered to the pancreatic epithelium of these mice; pancreatic lesions were analyzed by histopathology and immunohistochemical analyses. We analyzed levels of factors in Wnt signaling pathways in 19 MCN samples from patients.

RESULTS

Expression of Wnt1 in the pancreatic acinar cells and acinar cell progenitors of female mice led to development of unilocular or multilocular epithelial cysts in the pancreas body and tail, similar to MCN. The cystic lesions resembled the estrogen receptor- and progesterone receptor-positive ovarian-like stroma of MCN, but lacked the typical mucinous epithelium. Activated Wnt signaling, based on nuclear localization of β-catenin, was detected in the stroma but not cyst epithelium. Wnt signaling to β-catenin was found to be activated in MCN samples from patients, within the ovarian-like stroma, consistent with the findings in mice.

CONCLUSIONS

Based on studies of mice and pancreatic MCN samples from patients, the canonical Wnt signaling pathway becomes activated and promotes development of the ovarian-like stroma to contribute to formation of MCNs.

Tumor stem cells: A new approach for tumor therapy (Review)

Recent studies have demonstrated the existence of a minority of tumor cells possessing the stem cell properties of self-renewal and differentiation in leukemia and several solid tumors. However, these cells do not possess the normal regulatory mechanisms of stem cells. Following transplantation, they are capable of initiating tumorigenesis and are therefore known as 'tumor stem cells'. Cellular origin analysis of tumor stem cells has resulted in three hypotheses: Embryonal rest hypothesis, anaplasia and maturation arrest. Several signaling pathways which are involved in carcinogenesis, including Wnt/β-catenin, Notch and Oct-4 signaling pathways are crucial in normal stem cell self-renewal decisions, suggesting that breakdown in the regulation of self-renewal may be a key event in the development of tumors. Thus, tumors can be regarded as an abnormal organ in which stem cells have escaped from the normal constraints on self-renewal, thus, leading to abnormally differentiated tumor cells that lose the ability to form tumors. This new model for maligancies has significance for clinical research and treatment.

Notch, wnt, and hedgehog pathways in rhabdomyosarcoma: from single pathways to an integrated network

Rhabdomyosarcoma (RMS) is the most common type of soft tissue sarcoma in children. Regarding histopathological criteria, RMS can be divided into 2 main subtypes: embryonal and alveolar. These subtypes differ considerably in their clinical phenotype and molecular features. Abnormal regulation or mutation of signalling pathways that regulate normal embryonic development such as Notch, Hedgehog, and Wnt is a recurrent feature in tumorigenesis. Herein, the general features of each of the three pathways, their implication in cancer and particularly in RMS are reviewed. Finally, the cross-talking among these three pathways and the possibility of better understanding of the horizontal communication among them, leading to the development of more potent therapeutic approaches, are discussed.

Pancreatic ductal and acinar cell neoplasms in Carney complex: a possible new association

CONTEXT

Carney complex (CNC) is a rare disease inherited as an autosomal dominant trait, associated with various tumors, and caused most frequently by inactivation of the PRKAR1A gene.

OBJECTIVES

In our recent investigation of a large cohort of CNC patients, we identified several cases of pancreatic neoplasms. This possible association and PRKAR1A's possible involvement in pancreatic tumor have not been reported previously.

PATIENTS AND METHODS

Nine patients (2.5%) with CNC and pancreatic neoplasms in an international cohort of 354 CNC patients were identified; we studied six of them. Immunohistochemistry and PRKAR1A sequencing were obtained.

RESULTS

Three men and three women with a mean age of 49 yr (range 34-75 yr) had acinar cell carcinoma (n = 2), adenocarcinoma (n = 1), and intraductal pancreatic mucinous neoplasm (n = 3). Five patients had a germline PRKAR1A mutation, including two patients with acinar cell carcinoma, for whom mutations were found in a hemizygous state in the tumor, suggesting loss of heterozygosity. PRKAR1A expression was not detected in five of the six pancreatic neoplasms from CNC patients, whereas the protein was amply expressed on other sporadic pancreatic tumors and normal tissue.

CONCLUSION

An unexpectedly high prevalence of rare pancreatic tumors was found among CNC patients. Immunohistochemistry and loss-of-heterozygosity studies suggest that PRKAR1A could function as a tumor suppressor gene in pancreatic tissue, at least in the context of CNC. Clinicians taking care of CNC patients should be aware of the possible association of CNC with a potentially aggressive pancreatic neoplasm.

Altered microRNA Expression Patterns in Hepatoblastoma Patients

Liver cancers in children are rare representing only 1.1% of malignancies, with an annual incidence rate of 1.5 cases per million. Hepatoblastoma and hepatocellular carcinomas are the most common malignancies of the liver occurring in young people aged 15 years or younger. Molecular basis of both tumors are still unclear, and common markers (i.e., CTNNB1, APC, IGF-2) are not always useful in the characterization of sporadic forms; in this respect, microRNA recently associated with carcinogenesis could play a pivotal role in their onset. CTNNB1 and APC were analyzed by sequencing, and IGF-2 promoter methylation status was assessed by methylation-specific polymerase chain reaction. MicroRNA expression was assayed by microarray and quantitative reverse transcription-polymerase chain reaction in hepatoblastoma samples. Although few genomic alterations were detected in ours samples, an altered expression of somemicroRNA in hepatoblastoma was observed. Unsupervised clustering shows that microRNA profile can distinguish tumor from nontumor tissues. Further analyses of microRNA contents in hepatoblastoma compared with hepatocellular carcinoma highlighted four upregulated microRNA (miR-214, miR-199a, miR-150 [P < .01], and miR-125a [P < .05]) and one downregulated microRNA (miR-148a [P < .01]). In conclusion, although our samples were poorly informative from a genetic point of view, they showed a peculiar microRNA expression pattern compared with nontumor tissues and hepatocellular carcinoma. MicroRNA could represent valid markers for the classification of pediatric liver tumors.

Immunohistochemical evaluation of solid pseudopapillary tumors of the pancreas: the expression pattern of CD99 is highly unique

The aim of this study was to investigate CD99 as a new marker to characterize solid pseudopapillary tumors (SPTs), and to determine a specific panel of markers to identify the disease. We analyzed the clinicopathological characteristics and immunohistochemical features of 37 patients with SPT. All 37 tumors displayed intracytoplasmic dot-like immunoreactivity of CD99 in contrast to membranous staining in all pancreatic endocrine tumors and most of acinar cell carcinomas, along with negative immunostaining in ductal carcinomas. In addition, we observed a loss of expression of E-cadherin in all SPTs as well as in some other pancreatic tumors, and aberrant nuclear expression of β-catenin in most SPTs. Our findings demonstrated for the first time that the pattern of CD99 expression was highly specific for distinguishing SPTs from other pancreatic tumors. CD99 combined with E-cadherin/β-catenin and CD10 can be used as a relatively specific expression profile of SPTs.

Wnt4 induces nephronic tubules in metanephric mesenchyme by a non-canonical mechanism

Wnt4 and β-catenin are both required for nephrogenesis, but studies using TCF-reporter mice suggest that canonical Wnt signaling is not activated in metanephric mesenchyme (MM) during its conversion to the epithelia of the nephron. To better define the role of Wnt signaling, we treated rat metanephric mesenchymal progenitors directly with recombinant Wnt proteins. These studies revealed that Wnt4 protein, which is required for nephron formation, induces tubule formation and differentiation markers Lim1 and E-cadherin in MM cells, but does not activate a TCF reporter or up regulate expression of canonical Wnt target gene Axin-2 and has little effect on the stabilization of β-catenin or phosphorylation of disheveled-2. Furthermore, Wnt4 causes membrane localization of ZO-1 and occludin in tight junctions. To directly examine the role of β-catenin/TCF-dependent transcription, we developed synthetic cell-permeable analogs of β-catenin's helix C, which is required for transcriptional activation, in efforts to specifically inhibit canonical Wnt signaling. One inhibitor blocked TCF-dependent transcription and induced degradation of β-catenin but did not affect tubule formation and stimulated the expression of Lim1 and E-cadherin. Since a canonical mechanism appears not to be operative in tubule formation, we assessed the involvement of the non-canonical Ca(2+)-dependent pathway. Treatment of MM cells with Wnt4 induced an influx of Ca(2+) and caused phosphorylation of CaMKII. Moreover, Ionomycin, a Ca(2+)-dependent pathway activator, stimulated tubule formation. These results demonstrate that the canonical Wnt pathway is not responsible for mesenchymal-epithelial transition (MET) in nephron formation and suggest that the non-canonical calcium/Wnt pathway mediates Wnt4-induced tubulogenesis in the kidney.

Cushing's syndrome in an infant secondary to malignant adrenocortical tumors with somatic mutation of beta-catenin

A role of beta-catenin (CTNNB1) in the molecular pathogenesis of adrenocortical carcinoma (ACC) has been suspected in adult ACC and pediatric pigmented nodular adrenocortical disease, but it has never been reported in pediatric ACC. We present the case of a 4-month-old Thai infant who had Cushing's syndrome secondary to bilateral adrenal tumors with hepatic metastasis. The child was successfully treated with a bilateral adrenalectomy and wedge resection of the liver nodule. Histopathology revealed bilateral adrenocortical tumors with different histologic grades; the right tumor had a higher score, according to modified Weiss criteria. On molecular study, a deletion mutation of beta-catenin involving codons 44 to 45 was detected in the right adrenal tumor. The same mutation was found in peripheral blood before treatment; this mutation disappeared after tumor removal. The left tumor harbored wild-type beta-catenin. Immunohistochemistry showed nuclear accumulation of beta-catenin on the right adrenal tumor and the metastatic nodule. In summary, we present evidence that supports the role of the Wnt-signaling pathway in the carcinogenesis of pediatric adrenocortical carcinoma.

Nuclear accumulation of beta-catenin protein indicates activation of wnt signaling in chemically induced rat nephroblastomas

Aberrant wnt signaling caused by mutations in CTNNB1 occurs in about 15% of Wilms tumors, and these mutations appear to be dependent on the concomitant mutational inactivation of the zinc-finger protein WT1. Nuclear beta-catenin protein, a substitute marker of active wnt signaling, has been detected in an even higher proportion (>50%) of Wilms tumors, suggesting alternative genetic pathways leading to beta-catenin activation. Thus, targeting wnt signaling may become an important future therapeutic strategy in Wilms tumor patients. Currently, chemically induced rat nephroblastomas provide the only available rodent model for this tumor. To determine the contribution of active wnt signaling in this model, we investigated 24 chemically induced rat nephroblastomas for beta-catenin protein expression and for Ctnnb1 and WT1 mutations. Immunohistochemistry showed focal strong nuclear accumulation of beta-catenin protein in 18 of 24 tumors, although in a heterogenous pattern. Blastemal and mesenchymal compartments displayed nuclear-positive cells more frequently than areas of epithelial differentiation. Interestingly, we found no mutation of exon 3 of Ctnnb1 and no mutation within the zinc-finger region of WT1 in any of the 24 tumors analyzed. In conclusion, our findings suggest activation of wnt signaling in the majority (63%) of chemically induced rat nephroblastomas. Nuclear expression of beta-catenin in the absence of Ctnnb1 mutations implies, however, alternate mutational targets in rat nephroblastomas.

MSX1 induces the Wnt pathway antagonist genes DKK1, DKK2, DKK3, and SFRP1 in neuroblastoma cells, but does not block Wnt3 and Wnt5A signalling to DVL3

Neuroblastoma is the most common extra-cranial solid childhood cancer; it arises from neural crest-derived cells of the sympathetic nervous system. The anomalous regulation of embryonic developmental pathways like Delta-Notch and Wnt has been implicated in aberrant cell growth and differentiation in many (childhood) tumours. We have previously found regulation of Delta-Notch pathway genes by the MSX1 neural crest development gene in a neuroblastoma cell line, and significant correlations between these genes in neuroblastic tumours. However, a clear role for the Wnt pathway in neuroblastic tumours has not yet been determined. We now analyze the complete spectrum of genes regulated by inducible expression of MSX1 in the SJNB8 neuroblastoma cell line using Affymetrix expression profiling. We show that MSX1 induces the expression of four different Wnt pathway inhibitor genes: Dickkopf 1-3 (DKK1-3) and secreted frizzled-related protein 1 (SFRP1), and provide evidence that high expression of two of these genes correlates with good prognosis. We were able to demonstrate that both the canonical Wnt3 and the alternative Wnt5A ligands are highly expressed in neuroblastic tumours and cell lines, and specifically activate the DVL3 Wnt co-receptor protein in SJNB8 neuroblastoma cells. These results suggest involvement of MSX1 in Wnt signalling and demonstrate activity of the more upstream Wnt pathway in neuroblastic cells.

Beta-catenin mutation does not seem to have an effect on the tumorigenesis of pediatric rhabdomyosarcomas

Involvement of the Wnt signal transduction pathway has been shown in different pediatric embryonal tumors, such as hepatoblastoma, nephroblastoma, pancreatoblastoma, and medulloblastoma. There are few data available on the status of beta-catenin in rhabdomyosarcoma (RMS), another pediatric embryonal tumor. The aims of this study were 1st to verify the status of the exon 3 of CTNNB1 and 2nd to assess the usefulness of beta-catenin immunostaining in a small series of 8 embryonal RMS, 3 alveolar RMS, and 1 sclerosing RMS (SRMS). Sequence analysis revealed no mutations in the exon 3 of CTNNB1 in all the tumors studied. All RMS showed a cytoplasmic beta-catenin staining with cytoplasmic membrane reinforcement and no nuclear delocalization. We conclude that there is no evidence of beta-catenin mutation in the genesis of rhabdomyosarcoma and that beta-catenin does not represent a useful immunomarker to help distinguish between embryonal RMS and alveolar RMS.

Wilms tumor arising in a child with X-linked nephrogenic diabetes insipidus

We report on a child with X-linked nephrogenic diabetes insipidus (NDI) who developed Wilms tumor (WT). Nephrogenic diabetes insipidus is caused by mutations of the arginine vasopressin receptor (AVPR2) or aquaporin-II (AQP2) genes. Wilms tumor is also genetically heterogeneous and is associated with mutations of WT1 (15-20%), WTX (20-30%) and other loci. The boy presented at 5 months with failure to thrive, polyuria, hypernatremia and abdominal mass. Analysis of leukocyte DNA showed a novel missense mutation (Q174H) of the AVPR2 gene, which was not present in his mother. In cells (WitS) isolated from the tumor, WTX mRNA expression and coding sequence were intact. However, we identified a 44-kb homozygous deletion of the WT1 gene spanning exons 4 to 10. The WT1 deletion was not present in leukocyte DNA from the patient or his mother. We also noted strong beta-catenin (CTNNB1) expression in the tumor cells and identified a heterozygote missense Ser45Cys mutation of exon 3 of CTNNB1. However, the mutation was absent both in the constitutional DNA of the patient and his mother. The concurrence of WT and NDI has not been previously reported and may be unrelated. Nevertheless, this case nicely illustrates the sequence of events leading to sporadic Wilms tumor.

High expression of Snail mRNA in blood from hepatocellular carcinoma patients with extra-hepatic metastasis

The presence of circulating tumor cells (CTCs) in patients with hepatocellular carcinoma (HCC) suggests metastasis to extra-hepatic organs. Snail is a key regulator of epithelial mesenchymal transition, which is closely associated with tumor metastasis. The aim of this study was to investigate the presence of CTCs and evaluate the significance of Snail mRNA levels in peripheral blood of HCC patients with and without extra-hepatic metastasis. Sixty-six consecutive patients with HCC (30 without metastasis, 36 with metastasis) were prospectively enrolled, as were 30 with liver cirrhosis and 23 healthy subjects. CTCs were isolated by FACS using Ber-EP4 and anti-CD45 antibodies, and CTC identity confirmed by immunofluorescent cytokeratin staining. Snail mRNA levels were measured by quantitative real-time PCR of blood samples. CTCs, positive for pan-cytokeratin and Snail, were isolated from five HCC patients with metastasis. The mean amount of Snail mRNA in HCC with metastasis was 18.8-fold, 26.6-fold greater than HCC without metastasis, liver cirrhosis, respectively. When compared with healthy controls, the mean level of Snail mRNA in HCC without metastasis was 10.1-fold greater (P < 0.001). In six patients showing complete remission of HCC, Snail mRNA decreased to levels similar to those of healthy controls. This study suggests the possibility that circulating Snail mRNA levels may have been associated with extra-hepatic metastasis in HCC patients.

Overall expression of beta-catenin outperforms its nuclear accumulation in predicting outcomes of colorectal cancers

AIM: To examine the expression of beta-catenin in colorectal cancer and look for association with other clinico-pathological parameters.

METHODS: Tumor samples from 163 cases of colorectal cancer (CRC) who had undergone primary colectomy between May, 1998 and November, 2002 with complete follow-up data for either 5 years or until death were recruited for a beta-catenin immunohistochemical study. The percentage of immunoreacted tumor cells was defined as overall staining density (OSD) and percentage of cells having nuclear localization was counted as nuclear staining density (NSD). Univariate exploration used log-rank test and multivariate survival analysis used Cox’s hazard regression model.

RESULTS: Beta-catenin immunoreactivity was detected in 161 samples (98.8%), of which 131 cases had nuclear staining. High OSD (≥ 75%), detected in 123 cases (75.5%), was significantly associated with earlier clinical staging (P < 0.01), lower nodal status (P = 0.02), non-metastatic status (P < 0.01) and better differentiation (P = 0.02). Multivariate analysis found that high OSD was independently associated with better survival [Cox’s hazard ratio 0.51, 95% confidence interval (CI) 0.31-0.83]. Although high NSD (≥ 75%) was correlated with high pre-operative serum CEA (P = 0.03), well differentiation (P < 0.01), and increased staining intensity (P < 0.01), the parameter was not significantly associated with survival.

CONCLUSION: Unlike previous reports, the study did not find a predictive value of nuclear beta-catenin in CRC. Instead, the overall expression of beta-catenin in CRC showed an association with better differentiation and earlier staging. Moreover, the parameter also independently predicted superior survival.

Stabilization of beta-catenin induces pancreas tumor formation

BACKGROUND & AIMS

beta-Catenin signaling within the canonical Wnt pathway is essential for pancreas development. However, the pathway is normally down-regulated in the adult organ. Increased cytoplasmic and nuclear localization of beta-catenin can be detected in nearly all human solid pseudopapillary neoplasms (SPN), a rare tumor with low malignant potential. Conversely, pancreatic ductal adenocarcinoma (PDA) accounts for the majority of pancreatic tumors and is among the leading causes of cancer death. Whereas activating mutations within beta-catenin and other members of the canonical Wnt pathway are rare, recent reports have implicated Wnt signaling in the development and progression of human PDA. Here, we sought to address the role of beta-catenin signaling in pancreas tumorigenesis.

METHODS

Using Cre/lox technology, we conditionally activated beta-catenin in a subset of murine pancreatic cells in vivo.

RESULTS

Activation of beta-catenin results in the formation of large pancreatic tumors at a high frequency in adult mice. These tumors resemble human SPN based on morphologic and immunohistochemical comparisons. Interestingly, stabilization of beta-catenin blocks the formation of pancreatic intraepithelial neoplasia (PanIN) in the presence of an activating mutation in Kras that is known to predispose individuals to PDA. Instead, mice in which beta-catenin and Kras are concurrently activated develop distinct ductal neoplasms that do not resemble PanIN lesions.

CONCLUSIONS

These results demonstrate that activation of beta-catenin is sufficient to induce pancreas tumorigenesis. Moreover, they indicate that the sequence in which oncogenic mutations are acquired has profound consequences on the phenotype of the resulting tumor.

Wnt signaling pathway analysis in renal cell carcinoma in young patients

Renal cell carcinomas in young patients constitute a morphologically and genetically heterogeneous group. Twenty percent belong to the newly recognized Xp11.2 translocation-associated family and rare tumors arise from nephroblastoma. Aberrant Wnt signaling through beta-catenin mutation has been implicated in nephroblastoma pathogenesis and has been found to synergize with WT1 mutations. To characterize Wnt signaling activity in renal cell carcinomas in young patients, we gathered 34 tumors (three clear cell, ten Xp11.2 translocation associated, five papillary, two chromophobe, two collecting duct, one neuroblastoma associated, eight unclassified renal cell carcinomas, and three carcinomas combined with nephroblastoma) from patients less than 22 years. Expression of beta-catenin, its homologue gamma-catenin, and of WT1 was assessed by immunohistochemistry in 30 tumors, and sequence analysis of CTNNB1, CTNNG1, and WT1 genes was performed in 25 tumors. Cytoplasmic beta-catenin accumulation was demonstrated in two papillary carcinomas, one neuroblastoma-associated carcinoma, and two carcinomas arising from nephroblastoma. The pattern of gamma-catenin expression paralleled that of beta-catenin but its signal intensity was lower in 22, equal in 7, and stronger only in 1 tumor, respectively. Four tumors showed nuclear WT1 expression. One Xp11.2 translocation-associated carcinoma presented a rare intronic CTNNB1 single nucleotide polymorphism and cytoplasmic beta-catenin accumulation. There were no further CTNNB1 or CTNNG1 sequence alterations. A WT1 mutation was found in the nephroblastoma component of a carcinoma arising from nephroblastoma. These findings suggest Wnt signaling pathway activation only in a minority of renal cell carcinomas in young patients. CTNNB1 mutations are rare events. Cytoplasmic beta-catenin accumulation in an Xp11.2-associated carcinoma suggests potential interaction of Wnt signaling components with microphthalmia transcription factor family also in Xp11.2 translocation carcinomas. WT1 mutation in the nephroblastoma component of a mixed-type renal cell carcinoma provides direct evidence for clonal independence of nephroblastoma and carcinoma components in this exceptional tumor.

Stem cells: tissue regeneration and cancer

Regenerative medicine is the promised paradigm of replacement and repair of damaged or senescent tissues. As the building blocks for organ development and tissue repair, stem cells have unique and wide-ranging capabilities, thus delineating their potential application to regenerative medicine. The recognition that consistent patterns of molecular mechanisms drive organ development and postnatal tissue regeneration has significant implications for a variety of pediatric diseases beyond replacement biology. The observation that organ-specific stem cells derive all of the differentiated cells within a given tissue has led to the acceptance of a stem cell hierarchy model for tissue development, maintenance, and repair. Extending the tissue stem cell hierarchical model to tissue carcinogenesis may revolutionize the manner in which we conceptualize cancer therapeutics. In this review, the clinical promise of these technologies and the emerging concept of "cancer stem cells" are examined. A basic understanding of stem cell biology is paramount to stay informed of this emerging technology and the accompanying research in this area with the potential for clinical application.

Claudin-1 and claudin-2 differentiate fetal and embryonal components in human hepatoblastoma

Claudins (CLDNs), a family of transmembrane proteins, are major constituents of tight junctions (TJs). They have been shown to be differentially regulated in malignant tumors and play a role in carcinogenesis and progression. We aimed to explain the molecular mechanism underlying the main epithelial components of hepatoblastomas (HBs) based on the composition of TJs. Fourteen formalin-fixed, paraffin-embedded surgical resection specimens were analyzed by immunohistochemistry for CLDN-1, -2, -3, -4, -7; proliferating cell nuclear antigen (PCNA); Ki-67; beta-catenin; cytokeratin-7 (CK-7); and hepatocyte-specific antigen; messenger RNA was isolated for real-time reverse transcriptase polymerase chain reaction analysis of the CLDNs from dissected fetal and embryonal cell types. Significantly increased protein and messenger RNA expression of CLDN-1 and -2 was detected in the fetal compared with the embryonal component. Both cell types displayed negative or weak immunostainings for CLDN-3, -4, and -7. Hepatocyte-specific antigen was dominantly expressed in the fetal component. PCNA and Ki-67 labeling indices were significantly higher in embryonal compared with fetal cells. beta-catenin cytoplasmic/nuclear immunoreaction was frequent, although not showing significant differences between fetal and embryonal cells. Mutational analysis of beta-catenin detected mutation in two cases. Our results suggest that increased expression of CLDN-1 and -2 characterizes the more differentiated fetal component in HBs and is a reliable marker for differentiating fetal and embryonal cell types in HBs. The results proved that the embryonal and fetal components of HBs differ in such important feature as the protein composition of TJs. The expression of CLDN-1 and -2 is inversely correlated with cell proliferation. The more aggressive, rapidly proliferating embryonal phenotype is associated with the decrease/loss of CLDN-1 and -2. However, there are no data indicating association with the nuclear translocation of beta-catenin.

Absence of beta-catenin alteration in hepatic tumors induced by p-nitroanisole in Crj:BDF1 mice

In the present study, beta-catenin localization in hepatocellular neoplasms and hepatoblastomas, induced by oral administration of p-Nitroanisole (pNA) in Crj:BDF1 for 2 years, was evaluated by immunohistochemistry along with genetic alterations in exon 2 of beta-catenin by the polymerase chain reaction-single strand conformation polymorphism (PCR-SSCP) approach. Genomic DNA was isolated from paraffin sections of a total of 53 liver tumors. Immunohistochemical analysis revealed no abnormal accumulation of the beta-catenin protein in any of the cases. No mutations (0/13), 20% silent mutations (3/15) and 8% silent plus 12% functional mutations (2 + 3/25), not in the multiple phosphorylation sites of beta-catenin, were observed in hepatocellular adenomas, carcinomas and hepatoblastomas, respectively. The results indicate that beta-catenin does not play an important role in development of hepatic tumors induced by pNA in Crj:BDF1 mice.

Identification of a specific inhibitor of the dishevelled PDZ domain

The Wnt signaling pathways are involved in embryo development as well as in tumorigenesis. Dishevelled (Dvl) transduces Wnt signals from the receptor Frizzled (Fz) to downstream components in canonical and noncanonical Wnt signaling pathways. The Dvl PDZ domain is thought to play an essential role in both pathways, and we recently demonstrated that the Dvl PDZ domain binds directly to Fz receptors. In this study, using structure-based virtual ligand screening, we identified an organic molecule (NSC668036) from the National Cancer Institute small-molecule library that can bind to the Dvl PDZ domain. We then used molecular dynamics simulation to analyze the binding between the PDZ domain and NSC668036 in detail. In addition, we showed that, in Xenopus, as expected, NSC668036 inhibited the signaling induced by Wnt3A. This compound provides a basis for rational design of high-affinity inhibitors of the PDZ domain, which can block Wnt signaling by interrupting the Fz-Dvl interaction.

Negative regulation of retinal-neurite extension by beta-catenin signaling pathway

Although there have been many studies on the regulation of neurite extension in mouse brain, such a mechanism in neural retina has remained to be clarified. To delineate the role of Wnt signaling in retinal development, we used a retrovirus-vector-mediated expression system to express various mutants forms of Wnt signaling members in E17.5 mouse retinal explant cultures, which are an excellent system to examine retinal development in vitro. Expression of constitutively active beta-catenin or Lef-1 in the retinal cells resulted in failure of neurite extension, suggesting that beta-catenin negatively regulates neurite extension in the retina through Lef-1 transcriptional activity. However, proliferation and differentiation of retinal cells into mature retinal cells such as rod-photoreceptor cells and Muller glia cells were not affected by perturbation of the Wnt-Lef-1 pathway. As in retinal cells, activation of beta-catenin-Lef-1 signaling inhibited NGF-induced neurite extension in PC12 cells without affecting their proliferation. Interestingly, the Wnt-Lef-1 signaling pathway suppressed neurite extension without affecting Mek-1 signal activity, which is known to promote neurite extension. We found that MAPK was activated in retinal explant cultures, but that perturbation of MAPK signals did not affect neurite extension. Taken together, our data suggest that the Wnt pathway functions in proper neurite extension by opposing positive signals for promotion of neurite extension that are distinct from those of the MAPK pathway.

Overview of the molecular biology of hepatocellular neoplasms and hepatoblastomas of the mouse liver

The molecular pathogenesis of chemically induced hepatocellular neoplasms and hepatoblastomas in the B6C3FI mouse is unclear but may involve alterations in the fi-catenin/Wnt signaling pathway as was recently described for human liver neoplasms. The objectives of this research were to characterize the mutation frequency and spectrum of P-catenin mutations and the intracellular localization of I-catenin protein accumulation in chemically induced hepatoblastomas and hepatocellular neoplasms. In the majority of the hepatoblastomas examined by immunohistochemical methods, both nuclear and cytoplasmic localization of P-catenin protein were detected, whereas in hepatocellular adenomas and carcinomas and normal liver only membrane staining was observed. Genomic DNA was isolated from paraffin sections of each liver tumor. P-catenin exon 2 (corresponds to exon 3 in humans) genetic alterations were identified in the majority of hepatoblastomas from exposed mice. Deletion mutations were identified more frequently than point mutations in hepatoblastomas. Hepatocellular adenomas and carcinomas from treated mice had mutations in exon 2 of the B-catenin gene which ranged from 32-43%, while 10% P-catenin mutations were detected in spontaneous neoplasms. By immunohistochemical methods cyclin Dl was observed in most nuclei of hepatoblastomas and strong expression of cyclin Dl was confirmed by Western analysis regardless of treatment. The cumulative data suggests that P-catenin mutations with upregulation of the B-catenin protein and Wnt signaling most likely increased cyclin Dl expression. Cyclin D1 may provide an advantage during tumor progression of hepatocellular neoplasms and hepatoblastomas. The review will also focus on other genes which are important in mouse and human liver tumors.

Frequent loss of membranous E-cadherin in gastric cancers: A cross-talk with Wnt in determining the fate of β-catenin

The potential correlation of E-cadherin reduction and Wnt2 up-regulation in determining the intracellular distribution of beta-catenin in gastric cancers was investigated by the methods of frozen tissue array-based immunohistochemistry, Western blot and RT-PCR analysis. It was revealed that membranous E-cadherin was reduced frequently in the two major subtypes of gastric cancer (intestinal gastric cancer, i-GC and diffuse gastric cancer, d-GC) and closely correlated with the risk of lymphoid node metastasis (P < 0.05). The reduction of membranous E-cadherin was paralleled with cytosolic and nuclear accumulation of beta-catenin and the increased Wnt2 expression. These results indicate that the reduced E-cadherin is a common genetic phenotype of GCs and plays beneficial roles in tumor metastasis. Altered beta-catenin distribution may result from the imbalance of E-cadherin production and Wnt expression, which confers on gastric cancer cells more aggressive behaviors.