Mutations in AXIN2 cause colorectal cancer with defective mismatch repair by activating beta-catenin/TCF signalling

Maintenance of adenomatous polyposis coli (APC)-mutant colorectal cancer is dependent on Wnt/beta-catenin signaling

Persistent expression of certain oncogenes is required for tumor maintenance. This phenotype is referred to as oncogene addiction and has been clinically validated by anticancer therapies that specifically inhibit oncoproteins such as BCR-ABL, c-Kit, HER2, PDGFR, and EGFR. Identifying additional genes that are required for tumor maintenance may lead to new targets for anticancer drugs. Although the role of aberrant Wnt pathway activation in the initiation of colorectal cancer has been clearly established, it remains unclear whether sustained Wnt pathway activation is required for colorectal tumor maintenance. To address this question, we used inducible β-catenin shRNAs to temporally control Wnt pathway activation in vivo. Here, we show that active Wnt/β-catenin signaling is required for maintenance of colorectal tumor xenografts harboring APC mutations. Reduced tumor growth upon β-catenin inhibition was due to cell cycle arrest and differentiation. Upon reactivation of the Wnt/β-catenin pathway colorectal cancer cells resumed proliferation and reacquired a crypt progenitor phenotype. In human colonic adenocarcinomas, high levels of nuclear β-catenin correlated with crypt progenitor but not differentiation markers, suggesting that the Wnt/β-catenin pathway may also control colorectal tumor cell fate during the maintenance phase of tumors in patients. These results support efforts to treat human colorectal cancer by pharmacological inhibition of the Wnt/β-catenin pathway.

Colorectal cancers choosing sides

In contrast to the majority of sporadic colorectal cancer which predominantly occur in the distal colon, most mismatch repair deficient tumours arise at the proximal side. At present, these regional preferences have not been explained properly. Recently, we have screened colorectal tumours for mutations in Wnt-related genes focusing specifically on colorectal location. Combining this analysis with published data, we propose a mechanism underlying the side-related preferences of colorectal cancers, based on the specific acquired genetic defects in β-catenin signalling.

HEF1, a novel target of Wnt signaling, promotes colonic cell migration and cancer progression

Misregulation of the canonical Wnt/β-catenin pathway and aberrant activation of Wnt signaling target genes are common in colorectal cancer (CRC) and contribute to cancer progression. Altered expression of human enhancer of filamentation 1 (HEF1; also known as NEDD9 or Cas-L) has been implicated in progression of melanoma, breast, and CRC. However, the regulation of HEF1 and the role of HEF1 in CRC tumorigenesis are not fully understood. We here identify HEF1 as a novel Wnt signaling target. The expression of HEF1 was upregulated by Wnt-3a, β-catenin, and Dvl2 in a dose-dependent manner, and was suppressed following β-catenin downregulation by shRNA. In addition, elevated HEF1 mRNA and protein levels were observed in CRC cell lines and primary tumor tissues, as well as in the colon and adenoma polyps of Apc(Min/+) mice. Moreover, HEF1 levels in human colorectal tumor tissues increased with the tumor grade. Chromatin immunoprecipitation (ChIP) assays and promoter analyses revealed three functional T-cell factor (TCF)-binding sites in the promoter of HEF1 responsible for HEF1 induction by Wnt signaling. Ectopic expression of HEF1 increased cell proliferation and colony formation, while downregulation of HEF1 in SW480 cells by shRNA had the opposite effects and inhibited the xenograft tumor growth. Furthermore, overexpression of HEF1 in SW480 cells promoted cell migration and invasion. Together, our results determined a novel role of HEF1 as a mediator of the canonical Wnt/β-catenin signaling pathway for cell proliferation, migration, and tumorigenesis, as well as an important player in colorectal tumorigenesis and progression. HEF1 may represent an attractive candidate for drug targeting in CRC.

Novelty of Axin 2 and lack of Axin 1 gene mutation in colorectal cancer: a study in Kashmiri population

Colorectal cancer is (CRC) one of the leading causes of mortality and morbidity. Various genetic factors have been reported to be involved in the development of colorectal cancers including Axin gene. Axin, a major scaffold protein, plays an important role in various bio signaling pathways. We aim to study mutational pattern of Axin gene in colorectal cancer patients of Kashmiri population. The paired tumor and adjacent normal tissue specimens of 50 consecutive patients with CRC were used in our study. The DNA preparations were evaluated for the occurrence of Axin 1 and Axin 2 gene mutations by direct DNA sequencing. We analyzed exon 1a, 1b, 1c, 2, 4, 6, and 10 of Axin 1 and exon 7 of Axin 2. In this study, we found a novel mutation of G>T (GCT>TCT) transversion in exon 7 of Axin 2 gene at codon G695T (p.alanine > serine) at a frequency of 6% (3/50). In the same exon of Axin 2 gene a single nucleotide polymorphism (SNP) was detected in codon L688L (CCT>CTT) at a frequency of 36% (18/50). In exon 1c of Axin 1 a SNP was detected at codon D726D (GAT>GAC) at a frequency of 62.5% (31/50). Both the SNPs were synonymous hence do not lead to change of amino acid. Although Axin 1 and Axin 2 gene mutations have been found to be involved in the development of colorectal cancers, it seems to be a relatively rare event in Kashmiri population. However, an interesting finding of this study is the novelty of Axin 2 gene mutations which may be a predisposing factor in ethnic Kashmiri population to CRC.

Alteration of the β-catenin pathway in spiradenoma

BACKGROUND

Although skin carcinogenesis has been widely investigated, only limited information is available for epidermal tumors, while even less is known about other skin structures. Alterations in the β-catenin pathway have been reported in several epidermal tumors, while little is known about in adnexal tumors. This study was performed to assess alterations in the β-catenin pathway associated with adnexal tumors, and to investigate the mechanisms underlying these alterations.

METHODS

β-Catenin expression in 48 adnexal tumors (trichoepithelioma, trichofolliculoma, pilomatricoma, syringoma, eccrine poroma, spiradenoma, sebaceous hyperplasia and nevus sebaceus) was assessed using immunohistochemistry. The tumors showing intense nuclear reactivity for β-catenin were further evaluated by immunohistochemistry for β-catenin degradation complex such as adenomatosis polyposis coli (APC), Axin and glycogen synthase kinase 3β (GSK-3β).

RESULTS

Intense nuclear immunoreactivity for β-catenin was observed in pilomatricoma and spiradenoma. Among 12 eccrine spiradenomas, APC was downregulated in 2 (16.7%) cases, and Axin and GSK-3β were downregulated in 11 (91.7%) and 10 (83.3%) cases, respectively.

CONCLUSIONS

This is the first reported analysis of the role of alterations in the β-catenin pathway in spiradenoma. We suggest that downregulation of Axin and GSK-3β in the β-catenin pathway may be an important signaling alteration in the development of spiradenoma.

Wnt/β-catenin Signaling in Normal and Cancer Stem Cells

The ability of Wnt ligands to initiate a signaling cascade that results in cytoplasmic stabilization of, and nuclear localization of, β-catenin underlies their ability to regulate progenitor cell differentiation. In this review, we will summarize the current knowledge of the mechanisms underlying Wnt/β-catenin signaling and how the pathway regulates normal differentiation of stem cells in the intestine, mammary gland, and prostate. We will also discuss how dysregulation of the pathway is associated with putative cancer stem cells and the potential therapeutic implications of regulating Wnt signaling.

Targeting the Wnt/β-catenin signaling pathway in human cancers

INTRODUCTION

The Wnt/β-catenin signaling pathway plays a pivotal role in the regulation of cell growth, cell development and the differentiation of normal stem cells. Constitutive activation of the Wnt/β-catenin signaling pathway is found in many human cancers, and is thus an attractive target for anti-cancer therapy. Specific inhibitors of this pathway have been keenly researched and developed.

AREAS COVERED

This review discusses the potential of inhibiting the Wnt/β-catenin signaling pathway, as a therapeutic approach for cancer, along with an overview of the development of specific inhibitors.

EXPERT OPINION

Cancer stem cells (CSCs) play a significant role in the development and recurrence of several cancers, and Wnt/β-catenin signaling is important for the proliferation of CSCs. Inhibition of Wnt/β-catenin signaling is therefore a promising treatment approach. Progress has been made in the development of screening methods to identify Wnt/β-catenin signaling inhibitors. Biomarker-based screening is an effective and promising method for the identification of compounds of interest.

Frequent truncating mutation of TFAM induces mitochondrial DNA depletion and apoptotic resistance in microsatellite-unstable colorectal cancer

The mitochondrial transcription factor A (TFAM) is required for mitochondrial DNA (mtDNA) replication and transcription. Disruption of TFAM results in heart failure and premature aging in mice. But very little is known about the role of TFAM in cancer development. Here, we report the identification of frequent frameshift mutations in the coding mononucleotide repeat of TFAM in sporadic colorectal cancer (CRC) cell lines and in primary tumors with microsatellite instability (MSI), but not in microsatellite stable (MSS) CRC cell lines and tumors. The presence of the TFAM truncating mutation, in CRC cells with MSI, reduced the TFAM protein level in vivo and in vitro and correlated with mtDNA depletion. Furthermore, forced overexpression of wild-type TFAM in RKO cells carrying a TFAM truncating mutation suppressed cell proliferation and inhibited RKO cell-induced xenograft tumor growth. Moreover, these cells showed more susceptibility to cisplatin-induced apoptosis due to an increase of cytochrome b (Cyt b) expression and its release from mitochondria. An interaction assay between TFAM and the heavy-strand promoter (HSP) of mitochondria revealed that mutant TFAM exhibited reduced binding to HSP, leading to reduction in Cyt b transcription. Collectively, these data provide evidence that a high incidence of TFAM truncating mutations leads to mitochondrial copy number reduction and mitochondrial instability, distinguishing most CRC with MSI from MSS CRC. These mutations may play an important role in tumorigenesis and cisplatin-induced apoptotic resistance of most microsatellite-unstable CRCs.

AXIN2-associated autosomal dominant ectodermal dysplasia and neoplastic syndrome

We describe a family with a novel, inherited AXIN2 mutation (c.1989G>A) segregating in an autosomal dominant pattern with oligodontia and variable other findings including colonic polyposis, gastric polyps, a mild ectodermal dysplasia phenotype with sparse hair and eyebrows, and early onset colorectal and breast cancers. This novel mutation predicts p.Trp663X, which is a truncated protein that is missing the last three exons, including the DIX (Disheveled and AXIN interacting) domain. This nonsense mutation is predicted to destroy the inhibitory action of AXIN2 on WNT signaling. Previous authors have described an unrelated family with autosomal dominant oligodontia and a variable colorectal phenotype segregating with a nonsense mutation of AXIN2, as well as a frameshift AXIN2 mutation in an unrelated individual with oligodontia. Our report provides additional evidence supporting an autosomal dominant AXIN2-associated ectodermal dysplasia and neoplastic syndrome.

Wnt signaling and colon carcinogenesis: beyond APC

Activation of the Wnt signaling pathway via mutation of the adenomatous polyposis coli gene (APC) is a critical event in the development of colon cancer. For colon carcinogenesis, however, constitutive signaling through the canonical Wnt pathway is not a singular event. Here we review how canonical Wnt signaling is modulated by intracellular LEF/TCF composition and location, the action of different Wnt ligands, and the secretion of Wnt inhibitory molecules. We also review the contributions of non-canonical Wnt signaling and other distinct pathways in the tumor micro environment that cross-talk to the canonical Wnt pathway and thereby influence colon cancer progression. These ‘non-APC’ aspects of Wnt signaling are considered in relation to the development of potential agents for the treatment of patients with colon cancer. Regulatory pathways that influence Wnt signaling highlight how it might be possible to design therapies that target a network of signals beyond that of APC and β-catenin.

Defining the cancer master switch

BACKGROUND

Recent research has focused on signaling cascades and their interactions yielding considerable insight into which genetic pathways are targeted and how they tend to be altered in tumors. Therapeutic interventions now can be designed based on the knowledge of pathways vital to tumor growth and survival. These critical targets for intervention, master switches for cancer, are termed so because the tumor attempts to "flip the switch" in a way that promotes its survival, whereas molecular therapy aims to "switch off" signals important for tumor-related processes.

METHODS

Literature review.

CONCLUSIONS

Defining useful targets for therapy depends on identifying pathways that are crucial for tumor growth, survival, and metastasis. Because not all signaling cascades are created equal, selecting master switches or targets for intervention needs to be done in a systematic fashion. This discussion proposes a set of criteria to define what it means to be a cancer master switch and provides examples to illustrate their application.

Novel synthetic antagonists of canonical Wnt signaling inhibit colorectal cancer cell growth

Canonical Wnt signaling is deregulated in several types of human cancer where it plays a central role in tumor cell growth and progression. Here we report the identification of 2 new small molecules that specifically inhibit canonical Wnt pathway at the level of the destruction complex. Specificity was verified in various cellular reporter systems, a Xenopus double-axis formation assay and a gene expression profile analysis. In human colorectal cancer (CRC) cells, the new compounds JW67 and JW74 rapidly reduced active β-catenin with a subsequent downregulation of Wnt target genes, including AXIN2, SP5, and NKD1. Notably, AXIN2 protein levels were strongly increased after compound exposure. Long-term treatment with JW74 inhibited the growth of tumor cells in both a mouse xenograft model of CRC and in Apc(Min) mice (multiple intestinal neoplasia, Min). Our findings rationalize further preclinical and clinical evaluation of these new compounds as novel modalities for cancer treatment.

The leukemia-associated Mllt10/Af10-Dot1l are Tcf4/β-catenin coactivators essential for intestinal homeostasis

Wnt signaling maintains the undifferentiated state of intestinal crypt progenitor cells by inducing the formation of nuclear TCF4/β-catenin complexes. In colorectal cancer, activating mutations in Wnt pathway components cause inappropriate activation of TCF4/β-catenin-driven transcription. Despite the passage of a decade after the discovery of TCF4 and β-catenin as the molecular effectors of the Wnt signal, few transcriptional activators essential and unique to the regulation of this transcription program have been found. Using proteomics, we identified the leukemia-associated Mllt10/Af10 and the methyltransferase Dot1l as Tcf4/β-catenin interactors in mouse small intestinal crypts. Mllt10/Af10-Dot1l, essential for transcription elongation, are recruited to Wnt target genes in a β-catenin-dependent manner, resulting in H3K79 methylation over their coding regions in vivo in proliferative crypts of mouse small intestine in colorectal cancer and Wnt-inducible HEK293T cells. Depletion of MLLT10/AF10 in colorectal cancer and Wnt-inducible HEK293T cells followed by expression array analysis identifies MLLT10/AF10 and DOT1L as essential activators to a large extent dedicated to Wnt target gene regulation. In contrast, previously published β-catenin coactivators p300 and BRG1 displayed a more pleiotropic target gene expression profile controlling Wnt and other pathways. tcf4, mllt10/af10, and dot1l are co-expressed in Wnt-driven tissues in zebrafish and essential for Wnt-reporter activity. Intestinal differentiation defects in apc-mutant zebrafish can be rescued by depletion of Mllt10 and Dot1l, establishing these genes as activators downstream of Apc in Wnt target gene activation in vivo. Morpholino-depletion of mllt10/af10-dot1l in zebrafish results in defects in intestinal homeostasis and a significant reduction in the in vivo expression of direct Wnt target genes and in the number of proliferative intestinal epithelial cells. We conclude that Mllt10/Af10-Dot1l are essential, largely dedicated activators of Wnt-dependent transcription, critical for maintenance of intestinal proliferation and homeostasis. The methyltransferase DOT1L may present an attractive candidate for drug targeting in colorectal cancer.

AXIN2 polymorphism and its association with prostate cancer in a Turkish population

Polymorphism of AXIN2, a component of Wnt signaling, has been shown to play a role in tumorigenesis and dysregulated in cancer cells. In order to find out if AXIN2 polymorphism is a risk factor for prostate cancer, we analyzed eight polymorphic regions of this gene in 84 patients with prostate cancer and compared the results with 100 healthy controls in a Turkish population using PCR-RFLP methods. The genotype frequencies and risk factors of prostate cancer and control groups were analyzed by Chi-square test. We found a statistically significant result between prostate cancer risk and AXIN2 Intron2-956+16A/G (rs35285779) SNP. The frequency of the homozygous G/G (0%) and heterozygous A/G (18%) genotypes was significantly less in patients with prostate cancer than in healthy controls (7 and 32%, respectively) (P<0.05) for this SNP. When compared with the wild-type A/A genotype of the controls, prostate cancer patients with the A/G and G/G genotype showed reduced risk of cancer; the adjusted odds ratio (OR) for patients with the homozygous G/G genotype was 0.87 (95% CI: 0.81-0.95) and for heterozygous A/G genotype was 0.42 (95% CI: 0.20-0.85). We found no statistically significant association between controls and prostate cancer for other seven SNPs of AXIN2 including Exon1-148 C/T (rs2240308), Exon1-432 T/C (rs2240308), Exon5-1365 G/A (rs9915936), Exon5-1386 C/T (rs1133683), Intron5-1712+19 T/G, Exon7-2062 C/T, and Intron7-2141+73 G/A (rs4072245) (P>0.05). These results suggest that the AXIN2 Intron2 rs35285779 SNP is associated with development of prostate cancer as a protective SNP, while an association between other seven SNPs of the AXIN2 and risk of prostate cancer was not observed.

Drug discovery approaches to target Wnt signaling in cancer stem cells

Cancer stem cells (CSCs) represent a unique subset of cells within a tumor that possess self-renewal capacity and pluripotency, and can drive tumor initiation and maintenance. First identified in hematological malignancies, CSCs are now thought to play an important role in a wide variety of solid tumors such as NSCLC, breast and colorectal cancer. The role of CSCs in driving tumor formation illustrates the dysregulation of differentiation in tumorigenesis. The Wnt, Notch and Hedgehog (HH) pathways are developmental pathways that are commonly activated in many types of cancer. While substantial progress has been made in developing therapeutics targeting Notch and HH, the Wnt pathway has remained an elusive therapeutic target. This review will focus on the clinical relevance of the Wnt pathway in CSCs and tumor cell biology, as well as points of therapeutic intervention and recent advances in targeting Wnt/β-catenin signaling.

Colorectal cancers show distinct mutation spectra in members of the canonical WNT signaling pathway according to their anatomical location and type of genetic instability

It is unclear whether the mutation spectra in WNT genes vary among distinct types of colorectal tumors. We have analyzed mutations in specific WNT genes in a cohort of 52 colorectal tumors and performed a meta-analysis of previous studies. Notably, significant differences were found among the mutation spectra. We have previously shown that in familial adenomatous polyposis, APC somatic mutations are selected to provide the "just-right" level of WNT signaling for tumor formation. Here, we found that APC mutations encompassing at least two beta-catenin down-regulating motifs (20 a.a. repeats) are significantly more frequent in microsatellite unstable (MSI-H) than in microsatellite stable (MSS) tumors where truncations retaining less than two repeats are more frequent (P = 0.0009). Moreover, in cases where both APC hits are detected, selection for mutations retaining a cumulative number of two 20 a.a. repeats became apparent in MSI-H tumors (P = 0.001). This type of mutations were also more frequent in proximal versus distal colonic tumors, regardless of MSI status (P = 0.0008). Among MSI-H tumors, CTNNB1 mutations were significantly more frequent in HNPCC than in sporadic lesions (28% versus 6%, P < 10-6) and were preferentially detected in the proximal colon, independently of MSI status (P = 0.017). In conclusion, the observed spectra of WNT gene mutations in colorectal tumors are likely the result from selection of specific levels of beta-catenin signaling, optimal for tumor formation in the context of specific anatomical locations and forms of genetic instability. We suggest that this may underlie the preferential location of MMR deficient tumors in the proximal colon.

Mutations in the WTX-gene are found in some high-grade microsatellite instable (MSI-H) colorectal cancers

BACKGROUND

Genetically, colorectal cancers (CRCs) can be subdivided into tumors with chromosomal instability (CIN) or microsatellite instability (MSI). In both types of CRCs genes that are involved in the degradation of beta-CATENIN are frequently mutated. Whereas in CIN CRCs APC (Adenomatous Polyposis Coli) is affected in most cases, high grade MSI (MSI-H) CRCs frequently display mutations in various genes, like the APC-, AXIN2- or CTNNBI (beta-CATENIN) gene itself. Recently in Wilms tumors, WTX (Wilms tumor gene on the X-chromosome) was discovered as another gene involved in the destruction of beta-CATENIN. As the WTX-gene harbors a short T6-microsatellite in its N-terminal coding region, we hypothesized that frameshift-mutations might occur in MSI-H CRCs in the WTX gene, thus additionally contributing to the stabilization of beta-CATENIN in human CRCs.

METHODS

DNA was extracted from 632 formalin-fixed, paraffin-embedded metastatic CRCs (UICCIV) and analyzed for MSI-H by investigating the stability of the highly sensitive microsatellite markers BAT25 and BAT26 applying fluorescence capillary electrophoresis (FCE). Then, in the MSI-H cases, well described mutational hot spot regions from the APC-, AXIN2- and CTNNBI genes were analyzed for genomic alterations by didesoxy-sequencing while the WTX T6-microsatellite was analyzed by fragment analysis. Additionally, the PCR products of T5-repeats were subcloned and mutations were validated using didesoxy-sequencing. Furthermore, the KRAS and the BRAF proto-oncogenes were analyzed for the most common activating mutations applying pyro-sequencing. mRNA expression of WTX from MSI-H and MSS cases and a panel of colorectal cancer cell lines was investigated using reverse transcription (RT-) PCR and FCE.

RESULTS

In our cohort of 632 metastatic CRCs (UICCIV) we identified 41 MSI-H cases (6.5%). Two of the 41 MSI-H cases (4.8%) displayed a frameshift mutation in the T6-repeat resulting in a T5 sequence. Only one case, a male patient, expressed the mutated WTX gene while being wild type for all other investigated genes.

CONCLUSION

Mutations in the WTX-gene might compromise the function of the beta-CATENIN destruction complex in only a small fraction of MSI-H CRCs thus contributing to the process of carcinogenesis.

Serrated adenoma: a distinct form of non-polypoid colorectal neoplasia?

Until recently, 2 major forms of colorectal polyp were recognized: the adenoma and the hyperplastic polyp. Adenomas were known to represent a precursor to colorectal cancer, whereas hyperplastic polyps were viewed as nonneoplastic, having no potential for progression to malignancy. We now recognize, however, that the lesions diagnosed as hyperplastic polyps in the past represent a heterogeneous group of polyps, some of which truly are hyperplastic, and others that truly have a significant risk for transformation to colorectal cancer. These polyps have a characteristic serrated architecture, and include not only hyperplastic polyps but also the recently recognized serrated adenomas. Serrated adenomas occur in 2 forms: the traditional serrated adenoma, which is usually a polypoid lesion endoscopically, and the sessile serrated adenoma, a flat or slightly raised, usually right-sided lesion. Serrated adenomas of both types show characteristic molecular alterations not commonly seen in traditional colorectal adenomas, and probably progress to colorectal cancer by means of a different pathway, the so-called serrated neoplasia pathway. The morphologic features of serrated colorectal lesions, the molecular alterations that characterize them, and their role in colorectal cancer development are discussed.

The chromosomal instability pathway in colon cancer

The acquisition of genomic instability is a crucial feature in tumor development and there are at least 3 distinct pathways in colorectal cancer pathogenesis: the chromosomal instability (CIN), microsatellite instability, and CpG island methylator phenotype pathways. Most cases of colorectal cancer arise through the CIN pathway, which is characterized by widespread imbalances in chromosome number (aneuploidy) and loss of heterozygosity. It can result from defects in chromosomal segregation, telomere stability, and the DNA damage response, although the full complement of genes underlying CIN remains incompletely described. Coupled with the karyotypic abnormalities observed in CIN tumors are the accumulation of a characteristic set of mutations in specific tumor suppressor genes and oncogenes that activate pathways critical for colorectal cancer initiation and progression. Whether CIN creates the appropriate milieu for the accumulation of these mutations or vice versa remains a provocative and unanswered question. The goal of this review is to provide an updated perspective on the mechanisms that lead to CIN and the key mutations that are acquired in this pathway.

The chromosomal instability pathway in colon cancer

The acquisition of genomic instability is a crucial feature in tumor development and there are at least 3 distinct pathways in colorectal cancer pathogenesis: the chromosomal instability (CIN), microsatellite instability, and CpG island methylator phenotype pathways. Most cases of colorectal cancer arise through the CIN pathway, which is characterized by widespread imbalances in chromosome number (aneuploidy) and loss of heterozygosity. It can result from defects in chromosomal segregation, telomere stability, and the DNA damage response, although the full complement of genes underlying CIN remains incompletely described. Coupled with the karyotypic abnormalities observed in CIN tumors are the accumulation of a characteristic set of mutations in specific tumor suppressor genes and oncogenes that activate pathways critical for colorectal cancer initiation and progression. Whether CIN creates the appropriate milieu for the accumulation of these mutations or vice versa remains a provocative and unanswered question. The goal of this review is to provide an updated perspective on the mechanisms that lead to CIN and the key mutations that are acquired in this pathway.

Deficiency of the LIM-only protein FHL2 reduces intestinal tumorigenesis in Apc mutant mice

Background

The four and a half LIM-only protein 2 (FHL2) is capable of shuttling between focal adhesion and nucleus where it signals through direct interaction with a number of proteins including β-catenin. Although FHL2 activation has been found in various human cancers, evidence of its functional contribution to carcinogenesis has been lacking.

Methodology/Principal Findings

Here we have investigated the role of FHL2 in intestinal tumorigenesis in which activation of the Wnt pathway by mutations in the adenomatous polyposis coli gene (Apc) or in β-catenin constitutes the primary transforming event. In this murine model, introduction of a biallelic deletion of FHL2 into mutant Apc^Δ14/+ mice substantially reduces the number of intestinal adenomas but not tumor growth, suggesting a role of FHL2 in the initial steps of tumorigenesis. In the lesions, Wnt signalling is not affected by FHL2 deficiency, remaining constitutively active. Nevertheless, loss of FHL2 activity is associated with increased epithelial cell migration in intestinal epithelium, which might allow to eliminate more efficiently deleterious cells and reduce the risk of tumorigenesis. This finding may provide a mechanistic basis for tumor suppression by FHL2 deficiency. In human colorectal carcinoma but not in low-grade dysplasia, we detected up-regulation and enhanced nuclear localization of FHL2, indicating the activation of FHL2 during the development of malignancy.

Conclusions/Significance

Our data demonstrate that FHL2 represents a critical factor in intestinal tumorigenesis.

Variable FZD7 expression in colorectal cancers indicates regulation by the tumour microenvironment

Recent evidence shows that a sub-population of Wnt/beta-catenin target genes is specifically induced in different tissue contexts. FZD7 is a putative Wnt/beta-catenin target gene and although it is highly expressed in well-differentiated colorectal cancer tumour cells, its expression is decreased in de-differentiated tumour cells at the invasive front despite elevated Wnt/beta-catenin signalling in this area. This variable expression of FZD7 implicates additional regulation by the microenvironment; however, this has not been investigated. To begin to elucidate the role of extracellular matrix in regulating FZD7 expression, we generated a FZD7 promoter reporter and analysed FZD7 promoter activity in colorectal cancer cells grown on different matrices. We demonstrate that the FZD7 promoter is regulated by beta-catenin in colorectal cancer cells and observed decreased promoter activity in cells grown on fibronectin but not collagen I or collagen IV. Thus, expression of FZD7 in colorectal cancer may be regulated by fibronectin in the microenvironment.

Association of mitotic regulation pathway polymorphisms with pancreatic cancer risk and outcome

BACKGROUND

Mitosis is a highly regulated process that serves to ensure the fidelity of cell division. The disruption of mitotic regulators leading to aneuploidy and polyploidy is commonly observed in cancer cells. Single nucleotide polymorphisms (SNP) in regulators of mitosis may promote chromosome missegregation and influence pancreatic cancer and/or survival.

METHODS

Thirty-four SNPs, previously associated with breast cancer risk, from 33 genes involved in the regulation of mitosis, were investigated for associations with pancreatic cancer risk in 1,143 Caucasian patients with pancreatic adenocarcinoma and 1,097 unaffected controls from the Mayo Clinic. Associations with survival from pancreatic cancer were also assessed using 1,030 pancreatic cancer cases with known outcome.

RESULTS

Two SNPs in the APC (rs2431238) and NIN (rs10145182) loci, of 34 examined, were significantly associated with pancreatic cancer risk (P = 0.035 and P = 0.038, respectively). Further analyses of individuals categorized by smoking and body mass index identified several SNPs displaying significant associations (P < 0.05) with pancreatic cancer risk, including APC rs2431238 in individuals with high body mass index (>/=30; P = 0.031) and NIN rs10145182 in ever smokers (P = 0.01). In addition, survival analyses detected significant associations between SNPs in EIF3S10 and overall survival (P = 0.009), SNPs from five genes and survival in resected cancer cases (P < 0.05), and SNPs from two other genes (P < 0.05) and survival of locally advanced cancer cases.

CONCLUSION

Common variation in genes encoding regulators of mitosis may independently influence pancreatic cancer susceptibility and survival.

Wnt signaling stabilizes the DIXDC1 protein through decreased ubiquitin-dependent degradation

Wnt signaling plays key roles in development, cell growth, differentiation, polarity formation, neural development, and carcinogenesis. DIX Domain Containing 1 (DIXDC1), a novel component of the Wnt pathway, was recently cloned. DIXDC1 is the human homolog of Ccd1, a positive regulator of the Wnt signaling pathway during zebrafish neural patterning. Little has been known about DIXDC1 gene expression regulation. In the present study, we showed that the DIXDC1 protein was induced upon Wnt-3a stimulation, whereas the DIXDC1 mRNA level was not significantly increased after Wnt-3a treatment. Positive DIXDC1 staining was detected in colon cancer cells and was colocalized with beta-catenin staining. However, the DIXDC1 mRNA expression decreased in human colon cancer cells compared to the matched normal colon epithelial cells. Our further investigation showed that the DIXDC1 protein was degraded through the proteasome pathway, and the activation of canonical Wnt signaling decreased the ubiquitin-dependent degradation of both the ectopic and endogenous DIXDC1 protein. In order to explore the possible mechanism of the ubiquitination of DIXDC1, we found that the phosphorylation of DIXDC1 was inhibited by Wnt-3a. Collectively, these results indicate that canonical Wnt/beta-catenin pathway activation might upregulate DIXDC1 through a post-translational mechanism by inhibiting the ubiquitin-mediated degradation of the DIXDC1 protein.

TAB2 scaffolds TAK1 and NLK in repressing canonical Wnt signaling

The TAK1-NLK cascade is a mitogen-activated protein kinase-related pathway that plays an inhibitory role in canonical Wnt/beta-catenin signaling through regulating the LEF1/TCF family transcriptional factors. TAB2 (TAK1-binding protein 2) is a putative TAK1 interacting protein that is involved in the regulation of TAK1. Here, we found that TAB2 could directly interact with NLK and function as a scaffold protein to facilitate the interaction between TAK1 and NLK. Knocking down TAB2 using small interfering RNA abolished the interaction of TAK1 with NLK in mammalian cells. The intermediate region (residues 292-417) of TAB2 was mapped for its binding to NLK. TAB2-DeltaM, a TAB2 mutant lacking this region, showed a lower affinity for NLK and became defective in its scaffolding function. In addition, TAB2, but not TAB2-DeltaM, mediated TAK1-dependent activation of NLK and LEF1 polyubiquitylation, resulting in the inhibition of canonical Wnt signaling. Moreover, Wnt3a stimulation led to an increase in the interaction of TAB2 with NLK and the formation of a TAK1.TAB2.NLK complex, suggesting that this TAK1-TAB2-NLK pathway may constitute a negative feedback mechanism for canonical Wnt signaling.

MAP3K1 functionally interacts with Axin1 in the canonical Wnt signalling pathway

A central point of regulation in the Wnt/β-catenin signalling pathway is the formation of the β-catenin destruction complex. Axin1, an essential negative regulator of Wnt signalling, serves as a scaffold within this complex and is critical for rapid turnover of β-catenin. To examine the mechanism by which Wnt signalling disables the destruction complex, we used an immunoprecipitation-coupled proteomics approach to identify novel endogenous binding partners of Axin1. We found mitogen-activated protein kinase kinase kinase 1 (MAP3K1) as an Axin1 interactor in Ls174T colorectal cancer (CRC) cells. Importantly, confirmation of this interaction in HEK293T cells indicated that the Axin1-MAP3K1 interaction is induced and modulated by Wnt stimulation. siRNA depletion of MAP3K1 specifically abrogated TCF/LEF-driven transcription and Wnt3A-driven endogenous gene expression in both HEK293T as well as DLD-1 CRC. Expression of ubiquitin ligase mutants of MAP3K1 abrogated TCF/LEF transcription, whereas kinase mutants had no effect in TCF-driven activity, highlighting the essential role of the MAP3K1 E3 ubiquitin ligase activity in regulation of the Wnt/β-catenin pathway. These results suggest that MAP3K1, previously reported as an Axin1 inter-actor in c-Jun NH2-terminal kinase pathway, is also involved in the canonical Wnt signalling pathway and positively regulates expression of Wnt target genes.

Genetic dissection of differential signaling threshold requirements for the Wnt/beta-catenin pathway in vivo

Contributions of null and hypomorphic alleles of Apc in mice produce both developmental and pathophysiological phenotypes. To ascribe the resulting genotype-to-phenotype relationship unambiguously to the Wnt/β-catenin pathway, we challenged the allele combinations by genetically restricting intracellular β-catenin expression in the corresponding compound mutant mice. Subsequent evaluation of the extent of resulting Tcf4-reporter activity in mouse embryo fibroblasts enabled genetic measurement of Wnt/β-catenin signaling in the form of an allelic series of mouse mutants. Different permissive Wnt signaling thresholds appear to be required for the embryonic development of head structures, adult intestinal polyposis, hepatocellular carcinomas, liver zonation, and the development of natural killer cells. Furthermore, we identify a homozygous Apc allele combination with Wnt/β-catenin signaling capacity similar to that in the germline of the Apc^min mice, where somatic Apc loss-of-heterozygosity triggers intestinal polyposis, to distinguish whether co-morbidities in Apc^min mice arise independently of intestinal tumorigenesis. Together, the present genotype–phenotype analysis suggests tissue-specific response levels for the Wnt/β-catenin pathway that regulate both physiological and pathophysiological conditions.

Germline or somatic mutations in genes are the underlying cause of many human diseases, most notably cancer. Interestingly though, even in situations where every cell of every tissue of an organism carries the same mutation (as is the case for germline mutations), some tissues are more susceptible to the development of disease over time than others. For example, in familial adenomatous polyposis (FAP), affected persons carry different germline mutations in the APC gene and are prone to developing cancers of the colon and the rectum—and, less frequently, cancers in other tissues such as stomach, liver, and bones. Here we utilize a panel of mutant mice with truncating or hypomorphic mutations in the Apc gene, resulting in different levels of activation of the Wnt/β-catenin pathway. Our results reveal that different pathophysiological outcomes depend on different permissive signaling thresholds in embryonic, intestinal, and liver tissues. Importantly, we demonstrate that reducing Wnt pathway activation by 50% is enough to prevent the manifestation of embryonic abnormalities and disease in the adult mouse. This raises the possibility of developing therapeutic strategies that modulate the activation levels of this pathway rather than trying to “repair” the mutation in the gene itself.

Controlling destiny through chemistry: small-molecule regulators of cell fate

Controlling cell fate is essential for embryonic development, tissue regeneration, and the prevention of human disease. With each cell in the human body sharing a common genome, achieving the appropriate spectrum of stem cells and their differentiated lineages requires the selective activation of developmental signaling pathways, the expression of specific target genes, and the maintenance of these cellular states through epigenetic mechanisms. Small molecules that target these regulatory processes are therefore valuable tools for probing and manipulating the molecular mechanisms by which stem cells self-renew, differentiate, and arise from somatic cell reprogramming. Pharmacological modulators of cell fate could also help remediate human diseases caused by dysregulated cell proliferation or differentiation, heralding a new era in molecular therapeutics.

A coordinated phosphorylation by Lats and CK1 regulates YAP stability through SCF(beta-TRCP)

The Yes-associated protein (YAP) transcription coactivator is a key regulator of organ size and a candidate human oncogene. YAP is inhibited by the Hippo pathway kinase cascade, at least in part via phosphorylation of Ser 127, which results in YAP 14-3-3 binding and cytoplasmic retention. Here we report that YAP is phosphorylated by Lats on all of the five consensus HXRXXS motifs. Phosphorylation of Ser 381 in one of them primes YAP for subsequent phosphorylation by CK1delta/epsilon in a phosphodegron. The phosphorylated phosphodegron then recruits the SCF(beta-TRCP) E3 ubiquitin ligase, which catalyzes YAP ubiquitination, ultimately leading to YAP degradation. The phosphodegron-mediated degradation and the Ser 127 phosphorylation-dependent translocation coordinately suppress YAP oncogenic activity. Our study identified CK1delta/epsilon as new regulators of YAP and uncovered an intricate mechanism of YAP regulation by the Hippo pathway via both S127 phosphorylation-mediated spatial regulation (nuclear-cytoplasmic shuttling) and the phosphodegron-mediated temporal regulation (degradation).

DNA methylation of developmental genes in pediatric medulloblastomas identified by denaturation analysis of methylation differences

DNA methylation might have a significant role in preventing normal differentiation in pediatric cancers. We used a genomewide method for detecting regions of CpG methylation on the basis of the increased melting temperature of methylated DNA, termed denaturation analysis of methylation differences (DAMD). Using the DAMD assay, we find common regions of cancer-specific methylation changes in primary medulloblastomas in critical developmental regulatory pathways, including Sonic hedgehog (Shh), Wingless (Wnt), retinoic acid receptor (RAR), and bone morphogenetic protein (BMP). One of the commonly methylated loci is the PTCH1-1C promoter, a negative regulator of the Shh pathway that is methylated in both primary patient samples and human medulloblastoma cell lines. Treatment with the DNA methyltransferase inhibitor 5-aza-2'-deoxycytidine (5-aza-dC) increases the expression of PTCH1 and other methylated loci. Whereas genetic mutations in PTCH1 have previously been shown to lead to medulloblastoma, our study indicates that epigenetic silencing of PTCH1, and other critical developmental loci, by DNA methylation is a fundamental process of pediatric medulloblastoma formation. This finding warrants strong consideration for DNA demethylating agents in future clinical trials for children with this disease.

Mutations in the human naked cuticle homolog NKD1 found in colorectal cancer alter Wnt/Dvl/beta-catenin signaling

Background

Mutation of Wnt signal antagonists Apc or Axin activates β-catenin signaling in many cancers including the majority of human colorectal adenocarcinomas. The phenotype of apc or axin mutation in the fruit fly Drosophila melanogaster is strikingly similar to that caused by mutation in the segment-polarity gene, naked cuticle (nkd). Nkd inhibits Wnt signaling by binding to the Dishevelled (Dsh/Dvl) family of scaffold proteins that link Wnt receptor activation to β-catenin accumulation and TCF-dependent transcription, but human NKD genes have yet to be directly implicated in cancer.

Methodology/Principal Findings

We identify for the first time mutations in NKD1 - one of two human nkd homologs - in a subset of DNA mismatch repair-deficient colorectal tumors that are not known to harbor mutations in other Wnt-pathway genes. The mutant Nkd1 proteins are defective at inhibiting Wnt signaling; in addition, the mutant Nkd1 proteins stabilize β-catenin and promote cell proliferation, in part due to a reduced ability of each mutant Nkd1 protein to bind and destabilize Dvl proteins.

Conclusions/Significance

Our data raise the hypothesis that specific NKD1 mutations promote Wnt-dependent tumorigenesis in a subset of DNA mismatch-repair-deficient colorectal adenocarcinomas and possibly other Wnt-signal driven human cancers.

The kinase TNIK is an essential activator of Wnt target genes

Wnt signalling maintains the undifferentiated state of intestinal crypt/progenitor cells through the TCF4/beta-catenin-activating transcriptional complex. In colorectal cancer, activating mutations in Wnt pathway components lead to inappropriate activation of the TCF4/beta-catenin transcriptional programme and tumourigenesis. The mechanisms by which TCF4/beta-catenin activate key target genes are not well understood. Using a proteomics approach, we identified Tnik, a member of the germinal centre kinase family as a Tcf4 interactor in the proliferative crypts of mouse small intestine. Tnik is recruited to promoters of Wnt target genes in mouse crypts and in Ls174T colorectal cancer cells in a beta-catenin-dependent manner. Depletion of TNIK and expression of TNIK kinase mutants abrogated TCF-LEF transcription, highlighting the essential function of the kinase activity in Wnt target gene activation. In vitro binding and kinase assays show that TNIK directly binds both TCF4 and beta-catenin and phosphorylates TCF4. siRNA depletion of TNIK followed by expression array analysis showed that TNIK is an essential, specific activator of Wnt transcriptional programme. This kinase may present an attractive candidate for drug targeting in colorectal cancer.

DIXDC1 targets p21 and cyclin D1 via PI3K pathway activation to promote colon cancer cell proliferation

DIXDC1 is the human homolog of Ccd1, a recently identified DIX domain containing protein in zebrafish. It is a positive regulator in the Wnt signaling pathway functioning downstream of Wnt and upstream of Axin. Since Wnt pathway activation is correlated with human colon cancer formation and progression, the biological role of DIXDC1 in human colon cancer was examined. In the current study, up-regulation of DIXDC1 protein was detected in human colorectal adenocarcinoma tissues and was found to be correlated well with high cell proliferation index. Ectopic over-expression of DIXDC1 resulted in increased cell proliferation in vitro and accelerated tumorigenesis on nude mice in vivo. We also showed that DIXDC1 promoted G0/G1 to S phase transition concomitantly with up-regulation of cyclin D1 and down-regulation of p21 protein. DIXDC1 over-expression cells showed activation of the PI3K/AKT pathway. Both siRNA knockdown of DIXDC1 and blocking the PI3K pathway using a specific inhibitor caused G1/S phase arrest, as well as down-regulation of cyclin D1 and up-regulation of p21 in DIXDC1 over-expression colon cancer cells. Collectively, this study demonstrates that over-expression of DIXDC1 might target p21 and cyclin D1 to promote colon cancer cell proliferation and tumorigenesis at least partially through activation of the PI3K/Akt pathway.

HMGA1 is induced by Wnt/beta-catenin pathway and maintains cell proliferation in gastric cancer

The development of stomach cancer is closely associated with chronic inflammation, and the Wnt/beta-catenin signaling pathway is activated in most cases of this cancer. High-mobility group A (HMGA) proteins are oncogenic chromatin factors that are primarily expressed not only in undifferentiated tissues but also in various tumors. Here we report that HMGA1 is induced by the Wnt/beta-catenin pathway and maintains proliferation of gastric cancer cells. Specific knockdown of HMGA1 resulted in marked reduction of cell growth. The loss of beta-catenin or its downstream c-myc decreased HMGA1 expression, whereas Wnt3a treatment increased HMGA1 and c-myc transcripts. Furthermore, Wnt3a-induced expression of HMGA1 was inhibited by c-myc knockdown, suggesting that HMGA1 is a downstream target of the Wnt/beta-catenin pathway. Enhanced expression of HMGA1 coexisted with the nuclear accumulation of beta-catenin in about 30% of gastric cancer tissues. To visualize the expression of HMGA1 in vivo, transgenic mice expressing endogenous HMGA1 fused to enhanced green fluorescent protein were generated and then crossed with K19-Wnt1/C2mE mice, which develop gastric tumors through activation of both the Wnt and prostaglandin E2 pathways. Expression of HMGA1-enhanced green fluorescent protein was normally detected in the forestomach, along the upper border of the glandular stomach, but its expression was also up-regulated in cancerous glandular stomach. These data suggest that HMGA1 is involved in proliferation and gastric tumor formation via the Wnt/beta-catenin pathway.

Stem cells, self-renewal, and differentiation in the intestinal epithelium

The mammalian intestine is covered by a single layer of epithelial cells that is renewed every 4-5 days. This high cell turnover makes it a very attractive and comprehensive adult organ system for the study of cell proliferation and differentiation. The intestine is composed of proliferative crypts, which contain intestinal stem cells, and villi, which contain differentiated specialized cell types. Through the recent identification of Lgr5, an intestinal stem cell marker, it is now possible to visualize stem cells and study their behavior and differentiation in a much broader context. In this review we describe the identification of intestinal stem cells. We also discuss genetic studies that have helped to elucidate those signals important for progenitor cells to differentiate into one of the specialized intestinal epithelial cell types. These studies describe a genetic hierarchy responsible for cell fate commitment in normal gut physiology. Where relevant we also mention aberrant deregulation of these molecular pathways that results in colon cancer.

Wnt/beta-catenin signaling: components, mechanisms, and diseases

Signaling by the Wnt family of secreted glycolipoproteins via the transcriptional coactivator beta-catenin controls embryonic development and adult homeostasis. Here we review recent progress in this so-called canonical Wnt signaling pathway. We discuss Wnt ligands, agonists, and antagonists, and their interactions with Wnt receptors. We also dissect critical events that regulate beta-catenin stability, from Wnt receptors to the cytoplasmic beta-catenin destruction complex, and nuclear machinery that mediates beta-catenin-dependent transcription. Finally, we highlight some key aspects of Wnt/beta-catenin signaling in human diseases including congenital malformations, cancer, and osteoporosis, and discuss potential therapeutic implications.

Wnt/beta-catenin signaling: components, mechanisms, and diseases

Signaling by the Wnt family of secreted glycolipoproteins via the transcriptional coactivator beta-catenin controls embryonic development and adult homeostasis. Here we review recent progress in this so-called canonical Wnt signaling pathway. We discuss Wnt ligands, agonists, and antagonists, and their interactions with Wnt receptors. We also dissect critical events that regulate beta-catenin stability, from Wnt receptors to the cytoplasmic beta-catenin destruction complex, and nuclear machinery that mediates beta-catenin-dependent transcription. Finally, we highlight some key aspects of Wnt/beta-catenin signaling in human diseases including congenital malformations, cancer, and osteoporosis, and discuss potential therapeutic implications.

Wnt/beta-catenin signaling: components, mechanisms, and diseases

Signaling by the Wnt family of secreted glycolipoproteins via the transcriptional coactivator beta-catenin controls embryonic development and adult homeostasis. Here we review recent progress in this so-called canonical Wnt signaling pathway. We discuss Wnt ligands, agonists, and antagonists, and their interactions with Wnt receptors. We also dissect critical events that regulate beta-catenin stability, from Wnt receptors to the cytoplasmic beta-catenin destruction complex, and nuclear machinery that mediates beta-catenin-dependent transcription. Finally, we highlight some key aspects of Wnt/beta-catenin signaling in human diseases including congenital malformations, cancer, and osteoporosis, and discuss potential therapeutic implications.

Requirement of cell cycle and apoptosis regulator 1 for target gene activation by Wnt and beta-catenin and for anchorage-independent growth of human colon carcinoma cells

Aberrant Wnt signaling promotes oncogenesis by increasing cellular levels of beta-catenin, which associates with DNA-bound transcription factors and activates Wnt target genes. However, the molecular mechanism by which beta-catenin mediates gene expression is still poorly understood. Here, we show that cell cycle and apoptosis regulator 1 (CCAR1), which was recently shown to function as a transcriptional coactivator for nuclear receptors, also interacts with beta-catenin and enhances the ability of beta-catenin to activate expression of transiently transfected reporter genes. Furthermore, association of CCAR1 with the promoter of an endogenous Wnt/beta-catenin target gene in a colon cancer cell line depends on the presence of beta-catenin. Depletion of CCAR1 inhibits expression of several Wnt/beta-catenin target genes and suppresses anchorage-independent growth of the colon cancer cell line. Thus, CCAR1 is a novel component of Wnt/beta-catenin signaling that plays an important role in transcriptional regulation by beta-catenin and that, therefore, may represent a novel target for therapeutic intervention in cancers involving aberrantly activated Wnt/beta-catenin signaling.

Serrated polyps and colorectal cancer: new pathway to malignancy

Until recently, two major forms of colorectal epithelial polyp were recognized: the adenoma and the hyperplastic polyp. Adenomas were perceived to represent the precursor to colorectal cancer, whereas hyperplastic polyps were viewed as innocuous lesions with no potential for progression to malignancy. We now recognize, however, that the lesions formerly classified as hyperplastic actually represent a heterogeneous group of polyps, some of which have a significant risk for neoplastic transformation. These serrated polyps include not only hyperplastic polyps but also traditional serrated adenomas and sessile serrated adenomas. These polyps demonstrate characteristic molecular alterations not commonly seen in colorectal adenomas, and they probably progress to colorectal cancer by means of a new pathway: the serrated neoplasia pathway. The morphologic features of serrated colorectal lesions, the molecular alterations that characterize them, and their role in colorectal cancer development are discussed herein.

Axin localizes to mitotic spindles and centrosomes in mitotic cells

Wnt signaling plays critical roles in cell proliferation and carcinogenesis. In addition, numerous recent studies have shown that various Wnt signaling components are involved in mitosis and chromosomal instability. However, the role of Axin, a negative regulator of Wnt signaling, in mitosis has remained unclear. Using monoclonal antibodies against Axin, we found that Axin localizes to the centrosome and along mitotic spindles. This localization was suppressed by siRNA specific for Aurora A kinase and by Aurora kinase inhibitor. Interestingly, Axin over-expression altered the subcellular distribution of Plk1 and of phosphorylated glycogen synthase kinase (GSK3beta) without producing any notable changes in cellular phenotype. In the presence of Aurora kinase inhibitor, Axin over-expression induced the formation of cleavage furrow-like structures and of prominent astral microtubules lacking midbody formation in a subset of cells. Our results suggest that Axin modulates distribution of Axin-associated proteins such as Plk1 and GSK3beta in an expression level-dependent manner and these interactions affect the mitotic process, including cytokinesis under certain conditions, such as in the presence of Aurora kinase inhibitor.

An investigation of WNT pathway activation and association with survival in central nervous system primitive neuroectodermal tumours (CNS PNET)

Central nervous system primitive neuroectodermal tumours (CNS PNET) are high-grade, predominantly paediatric, brain tumours. Previously they have been grouped with medulloblastomas owing to their histological similarities. The WNT/β-catenin pathway has been implicated in many tumour types, including medulloblastoma. On pathway activation β-catenin (CTNNB1) translocates to the nucleus, where it induces transcription of target genes. It is commonly upregulated in tumours by mutations in the key pathway components APC and CTNNB1. WNT/β-catenin pathway status was investigated by immunohistochemical analysis of CTNNB1 and the pathway target cyclin D1 (CCND1) in 49 CNS PNETs and 46 medulloblastomas. The mutational status of APC and CTNNB1 (β-catenin) was investigated in 33 CNS PNETs and 22 medulloblastomas. CTNNB1 nuclear localisation was seen in 36% of CNS PNETs and 27% of medulloblastomas. A significant correlation was found between CTNNB1 nuclear localisation and CCND1 levels. Mutations in CTNNB1 were identified in 4% of CNS PNETs and 20% of medulloblastomas. No mutations were identified in APC. A potential link between the level of nuclear staining and a better prognosis was identified in the CNS PNETs, suggesting that the extent of pathway activation is linked to outcome. The results suggest that the WNT/β-catenin pathway plays an important role in the pathogenesis of CNS PNETs. However, activation is not caused by mutations in CTNNB1 or APC in the majority of CNS PNET cases.

Wnt/beta-catenin pathway in hepatocellular carcinoma pathogenesis and liver physiology

The Wnt/beta-catenin pathway is a key developmental pathway for which alterations have been described in various human cancers. The aberrant activation of this pathway is a major event in human hepatocellular carcinoma. Several laboratories have shown that the Wnt/beta-catenin pathway plays an essential role in all phases of liver development and maturation, and is required for the metabolic function of this organ. In this review, we summarize current knowledge regarding the role of the Wnt/beta-catenin pathway in hepatocellular carcinoma pathogenesis and liver biology, and the possibilities for developing new therapeutic interventions based on this knowledge.

Comparison of the effects of 40% oxygen and two atmospheric absolute air pressure conditions on stress-induced premature senescence of normal human diploid fibroblasts

The pressure during hyperbaric oxygen treatment may increase oxygen toxicity via an augmented oxygen pressure in the gas. Nevertheless, only a few reports have been published on the effect of cells grown under 2 atmospheric absolute (ATA) pressure. To evaluate the effect of pressure on oxygen toxicity and to study effects in addition to oxygen toxicity, we designed an experiment to compare the effects of normobaric mild hyperoxia (NMH, 40% oxygen) and hyperbaric air condition (HA, air with 2 ATA) on human diploid fibroblasts (HDF) in a hyperbaric incubator. HDFs in both the NMH and the HA condition had a similar oxidative stress response and exhibited premature senescence. To investigate differences in gene profiling in cells grown in the NMH and HA conditions, samples from cells exposed to each condition were applied to microarrays. We found no expression difference in genes related to aging and deoxyribonucleic acid damage, but the expression of genes including cell adhesion, stress response, and transcription were significantly increased in fibroblasts that were responsive to pressure. Among 26 statistically reliable genes, the expression of apoptosis related genes such as ADAM22, Bax, BCL2L14, and UBD, as well as tumor suppressor-related genes like Axin2 and ATF, and also mitogen-activated protein kinase-related genes like mitogen-activated protein kinase kinase kinase 1, histamine receptor, and RAB24, were significantly changed in cells responsive to pressure-induced oxidative stress.

PCAF acetylates {beta}-catenin and improves its stability

beta-Catenin plays an important role in development and tumorigenesis. However, the effect of a key acetyltransferase p300/CBP-associated factor (PCAF) on beta-catenin signaling is largely unknown. In this study, we found PCAF could increase the beta-catenin transcriptional activity, induce its nuclear translocation, and up-regulate its protein level by inhibiting its ubiquitination and improving its stability. Further studies showed that PCAF directly binds to and acetylates beta-catenin. The key ubiquitination sites Lys-19 and Lys-49 of beta-catenin were shown as the critical residues for PCAF-induced acetylation and stabilization. Knockdown of PCAF in colon cancer cells markedly reduced the protein level, transcriptional activity, and acetylation level of beta-catenin; promoted cell differentiation; inhibited cell migration; and repressed xenografted tumorigenesis and tumor growth in nude mice. All these data demonstrate that PCAF acetylates beta-catenin and regulates its stability, and they raise the prospect that therapies targeting PCAF may be of clinical use in beta-catenin-driven diseases, such as colon cancer.