Frequent alterations in the Wnt signaling pathway in colorectal cancer with microsatellite instability

Recapitulating the adenoma-carcinoma sequence by selection of four spontaneous oncogenic mutations in mismatch-repair-deficient human colon organoids

Carcinogenesis results from the sequential acquisition of oncogenic mutations that convert normal cells into invasive, metastasizing cancer cells. Colorectal cancer exemplifies this process through its well-described adenoma-carcinoma sequence, modeled previously using clustered regularly interspaced short palindromic repeats (CRISPR) to induce four consecutive mutations in wild-type human gut organoids. Here, we demonstrate that long-term culture of mismatch-repair-deficient organoids allows the selection of spontaneous oncogenic mutations through the sequential withdrawal of Wnt agonists, epidermal growth factor (EGF) agonists and the bone morphogenetic protein (BMP) antagonist Noggin, while TP53 mutations were selected through the addition of Nutlin-3. Thus, organoids sequentially acquired mutations in AXIN1 and AXIN2 (Wnt pathway), TP53, ACVR2A and BMPR2 (BMP pathway) and NRAS (EGF pathway), gaining complete independence from stem cell niche factors. Quadruple-pathway (Wnt, EGF receptor, p53 and BMP) mutant organoids formed solid tumors upon xenotransplantation. This demonstrates that carcinogenesis can be recapitulated in a DNA repair-mutant background through in vitro selection that targets four consecutive cancer pathways.

Wnt/β-catenin signaling pathway in carcinogenesis and cancer therapy

The Wnt/β-catenin signaling pathway plays a crucial role in various physiological processes, encompassing development, tissue homeostasis, and cell proliferation. Under normal physiological conditions, the Wnt/β-catenin signaling pathway is meticulously regulated. However, aberrant activation of this pathway and downstream target genes can occur due to mutations in key components of the Wnt/β-catenin pathway, epigenetic modifications, and crosstalk with other signaling pathways. Consequently, these dysregulations contribute significantly to tumor initiation and progression. Therapies targeting the Wnt/β-catenin signaling transduction have exhibited promising prospects and potential for tumor treatment. An increasing number of medications targeting this pathway are continuously being developed and validated. This comprehensive review aims to summarize the latest advances in our understanding of the role played by the Wnt/β-catenin signaling pathway in carcinogenesis and targeted therapy, providing valuable insights into acknowledging current opportunities and challenges associated with targeting this signaling pathway in cancer research and treatment.

Elevated expression of Axin2 in intestinal metaplasia and gastric cancers

BACKGROUND

The Wnt signaling pathway regulates crucial cellular processes, including stem cell development and tissue repair. Dysregulation of this pathway, particularly β-catenin stabilization, is linked to colorectal carcinoma and other tumors. Axin2, a critical component in the pathway, plays a role in β-catenin regulation. This study examines Axin2 expression in normal gastric mucosa and various gastric pathologies.

METHODS

Formalin-fixed and paraffin-embedded tissue samples from normal stomach, gastritis, intestinal metaplasia (IM), and gastric carcinoma were collected. Axin2 and β-catenin expression were evaluated using RNA in situ hybridization and immunohistochemistry, respectively. Histo-scores (H-scores) were calculated to quantify expression levels of Axin2. Associations between Axin2 expression and clinicopathological variables were examined.

RESULTS

Axin2 expression was examined in normal stomach, gastritis, and IM tissues. Axin2 expression was mainly observed in the surface and isthmus areas in the normal stomach and gastritis, whereas Axin2 expression was markedly higher at the bases of IM. Axin2 H-scores were significantly elevated in IM (mean ± standard deviation [SD], 87.0 ± 38.9) compared to normal (mean ± SD, 18.0 ± 4.5) and gastritis tissues (mean ± SD, 33.0 ± 18.6). In total, 30% of gastric carcinomas showed higher Axin2 expression. Axin2 expression did not have significant associations with age, sex, Lauren classification, histological differentiation, invasion depth, and lymph node metastasis. However, a strong positive correlation was observed between Axin2 and nuclear β-catenin in gastric carcinomas (p < .001).

CONCLUSIONS

Axin2 expression was significantly increased in IM compared to normal and gastritis cases. In addition, Axin2 showed a strong positive association with nuclear β-catenin expression in gastric carcinomas, demonstrating a close relationship with abnormal Wnt/β-catenin signaling pathway.

Common and ethnic-specific genetic determinants of hemoglobin concentration between Taiwanese Han Chinese and European Whites: findings from comparative two-stage genome-wide association studies

Human iron nutrition is a result of interplays between genetic and environmental factors. However, there has been scarcity of data on the genetic variants associated with altered iron homeostasis and ethnic-specific associations are further lacking. In this study, we compared between the Taiwanese Han Chinese (HC) and European Whites the genetic determinants of hemoglobin (Hb) concentration, a biochemical parameter that in part reflects the amount of functional iron in the body. Through sex-specific two-stage genome-wide association studies (2S-GWAS), we observed the consistent Hb-association of SNPs in TMPRSS6 (chr 22), ABO (chr 9), and PRKCE (chr 2) across sexes in both ethnic groups. Specific to the Taiwanese HC, the Hb-association of AXIN1, together with other loci near the chr 16 alpha-globin gene cluster, was found novel. On the other hand, majority of the Hb-associated SNPs among Europeans were identified along the chr 6 major histocompatibility complex (MHC) region, which has established roles in immune system control. We report here strong Hb-associations of HFE and members of gene families (SLC17; H2A, H2B, H3, H4, H1; TRIM; ZSCAN, ZKSCAN, ZNF; HLA; BTN, OR), numerous SNPs in/nearby CARMIL1, PRRC2A, PSORS1C1, NOTCH4, TSBP1, C6orf15, and distinct associations with non-coding RNA genes. Our findings provide evidence for both common and ethnic-specific genetic determinants of Hb between East Asians and Caucasians. These will help to further our understanding of the iron and/or erythropoiesis physiology in humans and to identify high risk subgroups for iron imbalances - a primary requirement to meet the goal of precision nutrition for optimal health.

The multidimensional role of the Wnt/β-catenin signaling pathway in human malignancies

Several signaling pathways have been identified as important for developmental processes. One of such important cascades is the Wnt/β-catenin signaling pathway, which can regulate various physiological processes such as embryonic development, tissue homeostasis, and tissue regeneration; while its dysregulation is implicated in several pathological conditions especially cancers. Interestingly, deregulation of the Wnt/β-catenin pathway has been reported to be closely associated with initiation, progression, metastasis, maintenance of cancer stem cells, and drug resistance in human malignancies. Moreover, several genetic and experimental models support the inhibition of the Wnt/β-catenin pathway to answer the key issues related to cancer development. The present review focuses on different regulators of Wnt pathway and how distinct mutations, deletion, and amplification in these regulators could possibly play an essential role in the development of several cancers such as colorectal, melanoma, breast, lung, and leukemia. Additionally, we also provide insights on diverse classes of inhibitors of the Wnt/β-catenin pathway, which are currently in preclinical and clinical trial against different cancers.

Cancer Genomic Profiling in Colorectal Cancer: Current Challenges in Subtyping Colorectal Cancers Based on Somatic and Germline Variants

Colorectal cancer (CRC) is a heterogeneous disease caused by the accumulation of multistep genetic alterations under the influence of genomic instability. Different backgrounds of genomic instability, such as chromosomal instability, microsatellite instability, hypermutated-single nucleotide variants, and genome stable-induced transformation in the colonic epithelium, can result in adenomas, adenocarcinomas, and metastatic tumors. Characterization of molecular subtypes and establishment of treatment policies based on each subtype will lead to better treatment outcomes and an improved selection of molecularly targeted agents. In Japan, cancer precision medicine has been introduced in the National Health Insurance program through the addition of the cancer genomic profiling (CGP) examination. It has also become possible to access a large amount of genomic information, including information on pathogenic somatic and germline variants, incomparable to conventional diagnostic tests. This information enables us to apply research data to clinical decision-making, benefiting patients and their healthy family members. In this article, we discuss the important molecules and signaling pathways presumed to be the driver genes of CRC progression and the signal transduction system in which they are involved. Molecular subtypes of CRC based on CGP examinations and gene expression profiles have been established in The Cancer Genome Atlas Network with the advent of next-generation sequencing technology. We will also discuss the recommended management of secondary/germline findings, pathogenic germline variants, and presumed germline pathogenic variants obtained from CGP examination and review the current challenges to better understand these data in a new era of cancer genomic medicine.

Effects of Lactobacillus acidophilus and Bifidobacterium bifidum Probiotics on the Expression of MicroRNAs 135b, 26b, 18a and 155, and Their Involving Genes in Mice Colon Cancer

A wide range of sources supports that the link between diet and colorectal cancer may be due to an imbalance of the intestinal microflora. In this case, it seems that the probiotics may have a possible molecular mechanism via microRNAs (miRNAs). The present study is aimed to evaluate the effects of Lactobacillus acidophilus and Bifidobacterium bifidum probiotics on the expression of miRNAs 135b, 26b, 18a, and 155 and their target genes, including APC, PTEN, KRAS, and PU.1 in mouse azoxymethane (AOM)-induced colon cancer. Thirty-eight male BALB/c mice were randomly divided into four groups: the control, AOM, Lactobacillus acidophilus, and Bifidobacterium bifidum to deliberate the effects of the probiotics on the miRNAs and their target genes. Except for the control group, the rest groups were weekly given AOM (15 mg/kg, s.c) in three consecutive weeks to induce mouse colon cancer. The animals were given 1.5 g powders of L. acidophilus (1 × 10⁹ cfu/g) and B. bifidum (1 × 10⁹ cfu/g) in 30 cc drinking water in the related groups for 5 months. At the end of the study, the animals were sacrificed and their blood and colon samples were removed for the molecular analyses. The results showed that the expression of the miR-135b, miR-155, and KRAS was increased in the AOM group compared to the control group in both the plasma and the colon tissue samples, and the consumption of the probiotics decreased their expression. Moreover, the miR-26b, miR-18a, APC, PU.1, and PTEN expressions were decreased in the AOM group compared to the control group and the consumption of the probiotics increased their expressions. It seems that Lactobacillus acidophilus and Bifidobacterium bifidum though increasing the expression of the tumor suppressor miRNAs and their target genes and decreasing the oncogenes can improve colon cancer treatment.

Human Colorectal Cancer from the Perspective of Mouse Models

Colorectal cancer (CRC) is a heterogeneous disease that includes both hereditary and sporadic types of tumors. Tumor initiation and growth is driven by mutational or epigenetic changes that alter the function or expression of multiple genes. The genes predominantly encode components of various intracellular signaling cascades. In this review, we present mouse intestinal cancer models that include alterations in the Wnt, Hippo, p53, epidermal growth factor (EGF), and transforming growth factor β (TGFβ) pathways; models of impaired DNA mismatch repair and chemically induced tumorigenesis are included. Based on their molecular biology characteristics and mutational and epigenetic status, human colorectal carcinomas were divided into four so-called consensus molecular subtype (CMS) groups. It was shown subsequently that the CMS classification system could be applied to various cell lines derived from intestinal tumors and tumor-derived organoids. Although the CMS system facilitates characterization of human CRC, individual mouse models were not assigned to some of the CMS groups. Thus, we also indicate the possible assignment of described animal models to the CMS group. This might be helpful for selection of a suitable mouse strain to study a particular type of CRC.

Identification of miRNA profiling in prediction of tumor recurrence and progress and bioinformatics analysis for patients with primary esophageal cancer: Study based on TCGA database

OBJECT

This study focused on the identification of prognostic miRNAs for the prediction of tumor recurrence and progress in esophageal cancer.

METHODS

MiRNA profiling and clinical characteristics of esophageal cancer patients was downloaded from the TCGA database. Univariate analysis was performed to select potential prognostic miRNAs and covariates. LASSO based logistic regression was conducted to identify the prognostic miRNAs given covariates. Bioinformatics analysis including gene ontology, disease ontology and pathway enrichment analysis were performed. A nomogram was generated based on multivariate logistic regression to illustrate the association between the identified miRNAs and the risk of tumor recurrence and progress.

RESULTS

A total of 1881 miRNAs and 10 clinical characteristics were obtained from TCGA database. 18 miRNAs were finally identified in which 6 miRNAs were identified for the first time to be associated with the tumor recurrence and progress of esophageal cancer given covariates. Bioinformatics analysis suggested that the identified miRNAs were associated with the tumor recurrence and progress of esophageal cancer. The association between identified miRNAs and risk of tumor recurrence and progress were presented in a nomogram.

CONCLUSION

The 6 newly identified miRNAs may be potential biomarkers for the prediction of tumor recurrence and progress of esophageal cancer.

Wnt Effector TCF4 Is Dispensable for Wnt Signaling in Human Cancer Cells

T-cell factor 4 (TCF4), together with β-catenin coactivator, functions as the major transcriptional mediator of the canonical wingless/integrated (Wnt) signaling pathway in the intestinal epithelium. The pathway activity is essential for both intestinal homeostasis and tumorigenesis. To date, several mouse models and cellular systems have been used to analyze TCF4 function. However, some findings were conflicting, especially those that were related to the defects observed in the mouse gastrointestinal tract after Tcf4 gene deletion, or to a potential tumor suppressive role of the gene in intestinal cancer cells or tumors. Here, we present the results obtained using a newly generated conditional Tcf4 allele that allows inactivation of all potential Tcf4 isoforms in the mouse tissue or small intestinal and colon organoids. We also employed the clustered regularly interspaced short palindromic repeats (CRISPR)/Cas9 system to disrupt the TCF4 gene in human cells. We showed that in adult mice, epithelial expression of Tcf4 is indispensable for cell proliferation and tumor initiation. However, in human cells, the TCF4 role is redundant with the related T-cell factor 1 (TCF1) and lymphoid enhancer-binding factor 1 (LEF1) transcription factors.

Independent prognostic genes and mechanism investigation for colon cancer

PROPOSE

We aimed to explore the potential molecular mechanism and independent prognostic genes for colon cancer (CC).

METHODS

Microarray datasets GSE17536 and GSE39582 were downloaded from Gene Expression Omnibus. Meanwhile, the whole CC-related dataset were downloaded from The Cancer Genome Atlas (TCGA) database. Differentially expressed mRNA (DEMs) were identified between cancer tissue samples and para-carcinoma tissue samples in TCGA dataset, followed by the KEGG pathway and GO function analyses. Furthermore, the clinical prognostic analysis including overall survival (OS) and disease-free survival (DFS) were performed in all three datasets.

RESULTS

A total of 633 up- and 321 down-regulated mRNAs were revealed in TCGA dataset. The up-regulated mRNAs were mainly assembled in functions including extracellular matrix and pathways including Wnt signaling. The down-regulated mRNAs were mainly assembled in functions like Digestion and pathways like Drug metabolism. Furthermore, up-regulation of UL16-binding protein 2 (ULBP2) was associated with OS in CC patients. A total of 12 DEMs including Surfactant Associated 2 (SFTA2) were potential DFS prognostic genes in CC patients. Meanwhile, the GRP and Transmembrane Protein 37 (TMEM37) were two outstanding independent DFS prognostic genes in CC.

CONCLUSIONS

ULBP2 might be a potential novel OS prognostic biomarker in CC, while GRP and TMEM37 could be served as the independent DFS prognostic genes in CC. Furthermore, functions including extracellular matrix and digestion, as well as pathways including Wnt signaling and drug metabolism might play important roles in the process of CC.

Manipulation of DNA Repair Proficiency in Mouse Models of Colorectal Cancer

Technical and biological innovations have enabled the development of more sophisticated and focused murine models that increasingly recapitulate the complex pathologies of human diseases, in particular cancer. Mouse models provide excellent in vivo systems for deciphering the intricacies of cancer biology within the context of precise experimental settings. They present biologically relevant, adaptable platforms that are amenable to continual improvement and refinement. We discuss how recent advances in our understanding of tumorigenesis and the underlying deficiencies of DNA repair mechanisms that drive it have been informed by using genetically engineered mice to create defined, well-characterized models of human colorectal cancer. In particular, we focus on how mechanisms of DNA repair can be manipulated precisely to create in vivo models whereby the underlying processes of tumorigenesis are accelerated or attenuated, dependent on the composite alleles carried by the mouse model. Such models have evolved to the stage where they now reflect the initiation and progression of sporadic cancers. The review is focused on mouse models of colorectal cancer and how insights from these models have been instrumental in shaping our understanding of the processes and potential therapies for this disease.

LGALS3 and AXIN1 gene variants playing role in the Wnt/ β-catenin signaling pathway are associated with mucinous component and tumor size in colorectal cancer

The Wnt pathway alterations have been identified in colorectal and many other cancer types. It has been reported that galectin-3 (which is encoded by the LGALS3 gene) alters the signaling mechanism in the Wnt/ β-catenin pathway by binding to β-catenin in colon and other cancers. AXIN1 is mainly responsible for the assembly of the β-catenin destruction complex in the Wnt pathway. This study investigated the relationship of rs4644 and rs4652 variants of the LGALS3 gene and rs214250 variants of the AXIN1 gene to histopathological and clinical properties. Our study included a total of 236 patients, of whom 119 had colorectal cancer (42 women, 77 men) and 117 were healthy controls. Polymerase chain reaction restriction fragment length polymorphism (PCR-RFLP) and allele-specific oligonucleotide (ASO) PCR methods were used. In addition, the serum galectin-3 level was studied with the enzyme-linked immunosorbent assay (ELISA) method. For the rs4644 variant of the LGALS3 gene, the CC genotype a mucinous component was significantly more common than those without a mucinous component (p=0.026). C allele frequency of the rs214250 variant of the AXIN1 gene was significantly correlated to tumor size in the advanced tumor stage (p=0.022). The CCAACT haplotype was more common in colorectal cancer patients (p=0.022). Serum galectin-3 level was higher in the patient group compared to the control group (5.9± 0.69 ng/ml vs. 0.79±0.01 ng/ml; p<0.001). In conclusion, variants of LGALS3 and AXIN1 genes affect tumor sizes and the mucinous component via Wnt/ β-catenin pathway in the pathogenesis of colorectal cancer.

A survey of tandem repeat instabilities and associated gene expression changes in 35 colorectal cancers

BACKGROUND

Colorectal cancer is a major contributor to cancer morbidity and mortality. Tandem repeat instability and its effect on cancer phenotypes remain so far poorly studied on a genome-wide scale.

RESULTS

Here we analyze the genomes of 35 colorectal tumors and their matched normal (healthy) tissues for two types of tandem repeat instability, de-novo repeat gain or loss and repeat copy number variation. Specifically, we study for the first time genome-wide repeat instability in the promoters and exons of 18,439 genes, and examine the association of repeat instability with genome-scale gene expression levels. We find that tumors with a microsatellite instable (MSI) phenotype are enriched in genes with repeat instability, and that tumor genomes have significantly more genes with repeat instability compared to healthy tissues. Genes in tumor genomes with repeat instability in their promoters are significantly less expressed and show slightly higher levels of methylation. Genes in well-studied cancer-associated signaling pathways also contain significantly more unstable repeats in tumor genomes. Genes with such unstable repeats in the tumor-suppressor p53 pathway have lower expression levels, whereas genes with repeat instability in the MAPK and Wnt signaling pathways are expressed at higher levels, consistent with the oncogenic role they play in cancer.

CONCLUSIONS

Our results suggest that repeat instability in gene promoters and associated differential gene expression may play an important role in colorectal tumors, which is a first step towards the development of more effective molecular diagnostic approaches centered on repeat instability.

Targeting Wnt signaling in colorectal cancer. A Review in the Theme: Cell Signaling: Proteins, Pathways and Mechanisms

The evolutionarily conserved Wnt signaling pathway plays essential roles during embryonic development and tissue homeostasis. Notably, comprehensive genetic studies in Drosophila and mice in the past decades have demonstrated the crucial role of Wnt signaling in intestinal stem cell maintenance by regulating proliferation, differentiation, and cell-fate decisions. Wnt signaling has also been implicated in a variety of cancers and other diseases. Loss of the Wnt pathway negative regulator adenomatous polyposis coli (APC) is the hallmark of human colorectal cancers (CRC). Recent advances in high-throughput sequencing further reveal many novel recurrent Wnt pathway mutations in addition to the well-characterized APC and β-catenin mutations in CRC. Despite attractive strategies to develop drugs for Wnt signaling, major hurdles in therapeutic intervention of the pathway persist. Here we discuss the Wnt-activating mechanisms in CRC and review the current advances and challenges in drug discovery.

NKD1 marks intestinal and liver tumors linked to aberrant Wnt signaling

The activity of the Wnt pathway undergoes complex regulation to ensure proper functioning of this principal signaling mechanism during development of adult tissues. The regulation may occur at several levels and includes both positive and negative feedback loops. In the present study we employed one of such negative feedback regulators, naked cuticle homolog 1 (Nkd1), to follow the Wnt pathway activity in the intestine and liver and in neoplasia originated in these organs. Using lineage tracing in transgenic mice we localized Nkd1 mRNA to the bottom parts of the small intestinal crypts and hepatocytes surrounding the central vein of the hepatic lobule. Furthermore, in two mouse models of intestinal tumorigenesis, Nkd1 expression levels were elevated in tumors when compared to healthy tissue. We utilized a collection of human intestinal polyps and carcinomas to confirm that NKD1 represents a robust marker of neoplastic growth. In addition, expression analysis of NKD1 in liver cancer showed that high expression levels of the gene distinguish a subclass of hepatocellular carcinomas related to aberrant Wnt signaling. Finally, our results were confirmed by bioinformatic analysis of large publicly available datasets that included gene expression profiling and high-throughput sequencing data of human colon and liver cancer specimens.

AXIN1 and AXIN2 variants in gastrointestinal cancers

Mutations in the APC (adenomatous polyposis coli) gene, which encodes a multi-functional protein with a well-defined role in the canonical Wnt pathway, underlie familial adenomatous polypsosis, a rare, inherited form of colorectal cancer (CRC) and contribute to the majority of sporadic CRCs. However, not all sporadic and familial CRCs can be explained by mutations in APC or other genes with well-established roles in CRC. The AXIN1 and AXIN2 proteins function in the canonical Wnt pathway, and AXIN1/2 alterations have been proposed as key defects in some cancers. Here, we review AXIN1 and AXIN2 sequence alterations reported in gastrointestinal cancers, with the goal of vetting the evidence that some of the variants may have key functional roles in cancer development.

Downregulation of WIF-1 and Wnt5a in patients with colorectal carcinoma: clinical significance

Activation of the wingless-type (Wnt) signaling pathway is common in various human cancers including colorectal cancer (CRC). Wnt inhibitory factor-1 (WIF-1) is a secreted antagonist that can bind Wnt ligands and therefore inhibits the Wnt signaling pathway. In this study, we aimed to analyze the expression of two members of Wnt signaling (WIF-1 and Wnt5a) in Tunisian patients with sporadic CRC. WIF-1 was frequently methylated in tumor tissues (87.95 %) compared to normal mucosa (39.54 %) and correlated with distant metastasis and vascular invasion (P = 0.001 and 0.037, respectively). The unmethylated profile of the WIF-1 promoter conferred a benefit to patients in terms of overall survival (P log rank = 0.024). In addition, in the group of patients with methylated WIF-1 promoter, the overall survival rate was significantly prolonged for those with small tumor size (<5 cm) and absence of distant metastasis (P log rank = 0.007 and 0.036, respectively). Aberrant CpG methylation of the WIF-1 promoter leads to transcriptional silencing of this tumor suppressor gene in tumor tissues (P = 0.001). Furthermore, we showed that the level of Wnt5a mRNA was significantly lower in tumor compared to normal tissues (P = 0.031) and lower still in those showing more aggressive behavior (presence of lymph nodes and advanced TNM stage). Our finding supports that WIF-1 is frequently methylated and that Wnt5a acts as a tumor suppressor gene in CRC. Loss of WIF-1 and Wnt5a functions results in more aggressive behavior of the disease.

Wnt signaling in adult intestinal stem cells and cancer

Signaling initiated by secreted glycoproteins of the Wnt family regulates many aspects of embryonic development and it is involved in homeostasis of adult tissues. In the gastrointestinal (GI) tract the Wnt pathway maintains the self-renewal capacity of epithelial stem cells. The stem cell attributes are conferred by mutual interactions of the stem cell with its local microenvironment, the stem cell niche. The niche ensures that the threshold of Wnt signaling in the stem cell is kept in physiological range. In addition, the Wnt pathway involves various feedback loops that balance the opposing processes of cell proliferation and differentiation. Today, we have compelling evidence that mutations causing aberrant activation of the Wnt pathway promote expansion of undifferentiated progenitors and lead to cancer. The review summarizes recent advances in characterization of adult epithelial stem cells in the gut. We mainly focus on discoveries related to molecular mechanisms regulating the output of the Wnt pathway. Moreover, we present novel experimental approaches utilized to investigate the epithelial cell signaling circuitry in vivo and in vitro. Pivotal aspects of tissue homeostasis are often deduced from studies of tumor cells; therefore, we also discuss some latest results gleaned from the deep genome sequencing studies of human carcinomas of the colon and rectum.

Axin gene methylation status correlates with radiosensitivity of lung cancer cells

Background

We previously reported that Axin1 (Axin) is down-regulated in many cases of lung cancer, and X-ray irradiation increased Axin expression and inhibited lung cancer cells. The mechanisms, however, were not clear.

Methods

Four lung cancer cell lines were used to detect the methylation status of Axin with or without X-ray treatment. Real-time PCR was used to quantify the expression of Axin, and western blot analysis was applied to measure protein levels of Axin, β-catenin, Cyclin D1, MMP-7, DNMTS, MeCP2 and acetylated histones. Flow cytometric analysis, colony formation assay, transwell assay and xenograft growth experiment were used to study the biological behavior of the cells with hypermethylated or unmethylated Axin gene after X-ray treatment.

Results

Hypermethylated Axin gene was detected in 2 of 4 cell lines, and it correlated inversely with Axin expression. X-ray treatment significantly up-regulated Axin expression in H446 and H157 cells, which possess intrinsic hypermethylation of the Axin gene (P<0.01), but did not show up-regulation in LTE and H460 cells, which have unmethylated Axin gene. 2Gy X-ray significantly reduced colony formation (from 71% to 10.5%) in H157 cells, while the reduction was lower in LTE cells (from 71% to 20%). After X-ray irradiation, xenograft growth was significantly decreased in H157 cells (from 1.15 g to 0.28 g) in comparison with LTE cells (from 1.06 g to 0.65 g). Significantly decreased cell invasiveness and increased apoptosis were also observed in H157 cells treated with X-ray irradiation (P<0.01). Down-regulation of DNMTs and MeCP2 and up-regulation of acetylated histones could be detected in lung cancer cells.

Conclusions

X-ray-induced inhibition of lung cancer cells may be mediated by enhanced expression of Axin via genomic DNA demethylation and histone acetylation. Lung cancer cells with a different methylation status of the Axin gene showed different radiosensitivity, suggesting that the methylation status of the Axin gene may be one important factor to predict radiosensitivity of the tumor.

Abnormal hypermethylation and clinicopathological significance of Axin gene in lung cancer

Axin is an important negative regulator of Wnt pathway. We have reported that reduced expression of Axin could be detected in lung cancer tissues, but the mechanism is not clear. By analyzing the genomic sequence, we note that Axin gene promoter is rich in CpGs. Little is known about the methylation status of Axin gene in lung cancer. So, nested MSP and RT-PCR were used to study the methylation status and mRNA expression of Axin gene in lung cancer tissues and cell lines. The results showed that hypermethylated Axin gene promoter and reduced mRNA expression level of Axin could be detected in lung cancer tissues but not in their paired autologous normal lung tissues (P < 0.01). The hypermethylated Axin gene promoter significantly correlated with the degree of differentiation (P = 0.03), lymph node metastasis (P = 0.048) and TNM classifications (P = 0.032). Demethylation reagent 5-aza-2-deoxycytidine significantly up-regulate Axin expression in BE1 cells (with hypermethylated Axin gene promoter) but not in H460 cells (with unmethylated Axin gene promoter). MTT (3(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide) and transwell matrigel invasion assay showed that 5-aza-2-deoxycytidine treatment inhibited cell growth and invasion more significantly in BE1 cells than that in H460 cells. Our data indicate that hypermethylated Axin gene significantly correlates with the progression of lung cancer and might serve as a new target of clinical therapy for lung cancer patients in future.

Evidence for possible non-canonical pathway(s) driven early-onset colorectal cancer in India

Two genetic instability pathways viz. chromosomal instability, driven primarily by APC mutation induced deregulated Wnt signaling, and microsatellite instability (MSI) caused by mismatch repair (MMR) inactivation, together account for >90% of late-onset colorectal cancer (CRC). Our understanding of early-onset sporadic CRC is however comparatively limited. In addition, most seminal studies have been performed in the western population and analyses of tumorigenesis pathway(s) causing CRC in developing nations have been rare. We performed a comparative analysis of early and late-onset CRC from India with respect to common genetic aberrations including Wnt, KRAS, and p53 (constituting the classical CRC progression sequence) in addition to MSI. Our results revealed the absence of Wnt and MSI in a significant proportion of early-onset as against late-onset CRC in India. In addition, KRAS mutation frequency was significantly lower in early-onset CRC indicating that a significant proportion of CRC in India may follow tumorigenesis pathways distinct from the classical CRC progression sequence. Our study has therefore revealed the possible existence of non-canonical tumorigenesis pathways in early-onset CRC in India.

Epigenetic and genetic analysis of WNT signaling pathway in sporadic colorectal cancer patients from Iran

The WNT signaling is deregulated in most human colorectal cancers (CRC). Promoter methylation has been proposed as an alternative mechanism to inactivate genes in tumors. To gain insight into the methylation silencing of the WNT pathway during colorectal carcinogenesis, we examined the aberrant methylation profile of four genes, APC, Axin1, Axin2, and GSK3β in an unselected series of 112 sporadic colorectal tumors by methylation specific PCR. It has been suggested that the Axin2 C148T SNP is associated with the risk of developing certain types of cancers. To assess the contribution of Axin2 SNP to CRC susceptibility, we examined the Axin2 C148T genotype in CRC patients and 170 healthy controls by PCR-RFLP. The frequency of CRCs with at least one gene methylated was 18.75%. Promoter methylation of Axin2 and APC genes was detected in 7.1 and 11.9% of tumors, respectively. No aberrant methylation was found in Gsk3β and Axin1 gene in these tumor series. The methylation status of APC had no significant association with clinical parameters. But, promoter methylation of Axin2 was sex-related, occurring more frequently in females (P = 0.002). The frequency of Axin2 C148T genotypes were similar in patients and controls. Moreover, we observed no association between the Axin2 SNP and risk of CRC in patients stratified by age, sex, and smoking status. However, the heterozygote CT genotype was associated with a reduced CRC risk in distal patients compared with proximal patients (OR = 0.3; 95% CI 0.1-0.9, P = 0.04). Our findings indicate that Axin1 and GSK3β methylation play a minor role in colorectal carcinogenesis.

Acinar cell carcinoma of the pancreas: new genetic and treatment insights into a rare malignancy

BACKGROUND

Acinar cell carcinoma (ACC) of the pancreas is a rare neoplasm, accounting for 1% of all pancreatic neoplasms. There remains a lack of data regarding the use of systemic therapy in this disease. We present a series of 40 consecutive cases of ACC of the pancreas treated at Memorial Sloan-Kettering Cancer Center, with an emphasis on evaluation of activity of new therapeutic agents.

METHODS

Patients reviewed at our institution from January 2000 through January 2011 were identified from an institutional database with prior institutional review board approval. Pathology was confirmed in all cases as ACC or a closely related entity.

RESULTS

Forty patients were identified; 29 were male (73%). The median age at diagnosis was 65 years (range, 16-87 years). The median overall survival (OS) time for patients with localized, resectable disease was 56.9 months and the OS time for patients with metastatic ACC (n = 18) was 19.6 months. Six patients with metastatic or recurrent ACC had a partial response to chemotherapy and five patients had stable disease for ≥6 months on systemic chemotherapy. Clinical observation was made of a patient with ACC and hereditary nonpolyposis colorectal cancer and a patient with ACC and a BRCA1 germline mutation.

CONCLUSIONS

ACC is moderately chemoresponsive to agents that have activity in pancreatic adenocarcinoma and colorectal carcinoma. A potential association between germline mutations in DNA mismatch repair genes and ACC warrants further evaluation.

Deranged Wnt signaling is frequent in hereditary nonpolyposis colorectal cancer

The Wnt signaling pathway is frequently deranged in colorectal cancer and is a key target for future preventive and therapeutic approaches. Colorectal cancers associated with the hereditary nonpolyposis colorectal cancer (HNPCC) syndrome are characterized by wide-spread microsatellite instability, but show few gross genomic alterations. We characterized expression of the Wnt signaling pathway markers β-catenin, E-cadherin, TCF-4, and PTEN using immunohistochemical staining in colorectal cancers from individuals with HNPCC. Reduced membranous staining for β-catenin was found in 64% and for E-cadherin in 80% with strong correlation between these markers (P = 0.001). Nuclear β-catenin staining was detected in 19% of the tumors. Overexpression of TCF-4, which is activated by β-catenin, was found in 89% and downregulation of PTEN, which suppresses nuclear accumulation of β-catenin, was present in 54% of the tumors. In summary, altered expression of target molecules in the Wnt signaling pathway was demonstrated in the vast majority of the HNPCC-associated tumors, which support deranged Wnt-signaling as a central tumorigenic mechanism also in MMR defective colorectal cancer.

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.

Methylation by protein arginine methyltransferase 1 increases stability of Axin, a negative regulator of Wnt signaling

Axin, a negative regulator of Wnt signaling, is a key scaffold protein for the β-catenin destruction complex. It has been previously shown that multiple post-translational modification enzymes regulate the level of Axin. Here, we provide evidence that protein arginine methyltransferase 1 (PRMT1) directly interacts with and methylates the 378th arginine residue of Axin both in vitro and in vivo. We found that the transient expression of PRMT1 led to an increased level of Axin and that knockdown of endogenous PRMT1 by short hairpin RNA reduced the level of Axin. These results suggest that methylation by PRMT1 enhanced the stability of Axin. Methylation of Axin by PRMT1 also seemingly enhanced the interaction between Axin and glycogen synthase kinase 3β, leading to decreased ubiquitination of Axin. Consistent with the role of PRMT1 in the regulation of Axin, knockdown of PRMT1 enhanced the level of cytoplasmic β-catenin as well as β-catenin-dependent transcription activity. In summary, we show that the methylation of Axin occurred in vivo and controlled the stability of Axin. Therefore, methylation of Axin by PRMT1 may serve as a finely tuned regulation mechanism for Wnt/β-catenin signaling.

Somatic mutations and germline sequence variants in patients with familial colorectal cancer

It is estimated that up to 35% of colorectal cancers (CRC) can be explained by hereditary factors. However, genes predisposing to highly penetrant CRC syndromes account for only a small fraction of all cases. Thus, most CRCs still remain molecularly unexplained. A recent systematic sequencing study on well-annotated human protein coding genes identified 280 somatically mutated candidate cancer genes (CAN genes) in breast and colorectal cancer. It is estimated that 8% of all reported cancer genes show both somatic and germline mutations. Therefore, the identified CAN genes serve as a distinct set of candidates for being involved in hereditary susceptibility. The aim of this study was to evaluate the role of colorectal CAN genes in familial CRC. Samples from 45 familial CRCs without known cancer predisposing mutations were screened for somatic and germline variants in 15 top-ranked CAN genes. Six of the genes were found to be somatically mutated in our tumor series. We identified 22 nonsynonymous somatic mutations of which the majority was of missense type. In germline, three novel nonsynonymous variants were identified in the following genes: CSMD3, EPHB6 and C10orf137, and none of the variants were present in 890 population-matched healthy controls. It is possible that the identified germline variants modulate predisposition to CRC. Functional validation and larger sample sets, however, will be required to clarify the role of the identified germline variants in CRC susceptibility.

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.

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.

Approach to early-onset colorectal cancer: clinicopathological, familial, molecular and immunohistochemical characteristics

AIM

To characterize clinicopathological and familial features of early-onset colorectal cancer (CRC) and compare features of tumors with and without microsatellite instability (MSI).

METHODS

Forty-five patients with CRC aged 45 or younger were included in the study. Clinical information, a three-generation family history, and tumor samples were obtained. MSI status was analyzed and mismatch repair genes were examined in the MSI families. Tumors were included in a tissue microarray and an immunohistochemical study was carried out with a panel of selected antibodies.

RESULTS

Early onset CRC is characterized by advanced stage at diagnosis, right colon location, low-grade of differentiation, mucin production, and presence of polyps. Hereditary forms represent at least 21% of cases. Eighty-one percent of patients who died during follow-up showed a lack of expression of cyclin E, which could be a marker of poor prognosis. beta-catenin expression was normal in a high percentage of tumors.

CONCLUSION

Early-onset CRC has an important familial component, with a high proportion of tumors showing microsatellite stable. Cyclin E might be a poor prognosis factor.

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.

Identification of an MSI-H tumor-specific cytotoxic T cell epitope generated by the (-1) frame of U79260(FTO)

Microsatellite instability (MSI-H) induced by defects of the DNA mismatch repair system results in insertion or deletion of single nucleotides at short repetitive DNA sequences. About 15% of sporadic and approximately 90% of hereditary nonpolyposis colorectal cancers display MSI-H. When affecting coding regions, MSI-H results in frameshift mutations and expression of corresponding frameshift peptides (FSPs). Functional tumor promoting relevance has been demonstrated for a growing number of genes frequently hit by MSI-H. Contrary, immune reactions against FSPs are involved in the immune surveillance of MSI-H cancers. Here, we provide conclusive data that the (−1) frame of U79260(FTO) encodes an HLA-A0201-restricted cytotoxic T cell epitope (FSP11; TLSPGWSAV). T cells specific for FSP11 efficiently recognized HLA-A0201^(pos) tumor cells harboring the mutated reading frame. Considering the exceptionally high mutation rate of U79260(FTO) in MSI-H colorectal carcinoma (81.8%), this recommends that FSP11 be a component of future vaccines.

Differential colorectal carcinogenesis: Molecular basis and clinical relevance

Colorectal cancer (CCR) is one of the most frequent cancers in developed countries. It poses a major public health problem and there is renewed interest in understanding the basic principles of the molecular biology of colorectal cancer. It has been established that sporadic CCRs can arise from at least two different carcinogenic pathways. The traditional pathway, also called the suppressor or chromosomal instability pathway, follows the Fearon and Vogelstein model and shows mutation in classical oncogenes and tumour suppressor genes, such as K-ras, adenomatous polyposis coli, deleted in colorectal cancer, or p53. Alterations in the Wnt pathway are also very common in this type of tumour. The second main colorectal carcinogenesis pathway is the mutator pathway. This pathway is present in nearly 15% of all cases of sporadic colorectal cancer. It is characterized by the presence of mutations in the microsatellite sequences caused by a defect in the DNA mismatch repair genes, mostly in hMLH1 or hMSH2. These two pathways have clear molecular differences, which will be reviewed in this article, but they also present distinct histopathological features. More strikingly, their clinical behaviours are completely different, having the “mutator” tumours a better outcome than the “suppressor” tumours.

Frameshift mutations of Wnt pathway genes AXIN2 and TCF7L2 in gastric carcinomas with high microsatellite instability

Frameshift mutations of genes with mononucleotide repeats are features of colorectal and gastric cancers with microsatellite instability (MSI). Deregulation of Wnt pathway is involved in the mechanisms of cancer development, and mutations of the Wnt-pathway genes have frequently been detected in cancers, indicating somatic mutations are important deregulation mechanisms of the Wnt signaling in cancer development. Both AXIN2 and TCF7L2 genes in the Wnt pathway possess mononucleotide repeats in their coding sequences and are considered as candidate tumor suppressor genes. The aim of this study was to see whether AXIN2 and TCF7L2 are altered by frameshift mutations in gastric carcinomas with MSI. For this, we analyzed human AXIN2 exon 8 and TCF7L2 exon 14 in 32 gastric carcinomas with high MSI, 13 gastric carcinomas with low MSI, and 47 gastric carcinomas without MSI by a single-strand conformation polymorphism analysis. Overall, we detected 9 AXIN2 and 6 TCF7L2 frameshift mutations in the mononucleotide repeats in the cancers with MSH-H, and all of them were found in MSH-H cancers (AXIN2, 28.1%; TCF7L2, 18.8%). Of the 32 high MSI cancers, 13 cancers (40.6%) harbored at least one of AXIN2 and TCF7L2 mutation, whereas 19 cancers (59.4%) harbored neither. The present data indicate that frameshift mutations in both AXIN2 and TCF7L2 genes are common in gastric carcinomas with high MSI and suggest that these mutations may contribute to development of gastric cancers with high MSI by deregulating the Wnt signaling in the affected cancer cells.

Concomitant activation of Wnt pathway and loss of mismatch repair function in human melanoma

Constitutive activation of the Wnt pathway plays a key role in the development of colorectal cancer and has also been implicated in the pathogenesis of other malignancies. Deregulation of Wnt signaling mainly occurs through genetic alterations of APC, the beta-catenin gene (CTNNB1), AXIN1 and AXIN2, leading to stabilization of beta-catenin. Physiologically, AXIN2 is transcriptionally induced on Wnt signaling activation and acts as a negative feedback regulator of the pathway. In colorectal cancer, mutations in CTNNB1 and AXIN2 occur preferentially in tumors with inactivation of the mismatch repair (MMR) genes MSH2, MLH1, or PMS2. In this study, the expression of beta-catenin and AXIN2, and the mutational status of CTNNB1, APC, and AXIN2 were evaluated in two MMR-deficient (PR-Mel and MR-Mel) and seven MMR-proficient human melanoma cell lines. Only PR-Mel and MR-Mel cells showed nuclear accumulation of beta-catenin and expression of the AXIN2 gene, and hence, constitutive activation of Wnt signaling. Mutational analysis identified a somatic heterozygous missense mutation in CTNNB1 exon three and a germline heterozygous deletion within AXIN2 exon seven in PR-Mel cells, and a somatic biallelic deletion within APC in MR-Mel cells. Deregulation of Wnt signaling and a defective MMR system were also present in the original tumor of PR and MR patients. Thus, we describe additional melanomas with mutations in CTNNB1 and APC, identify for the first time a germline AXIN2 mutation in a melanoma patient and suggest that inactivation of the MMR system and deregulation of the Wnt/beta-catenin signaling pathway cooperate to promote melanoma development and/or progression.

Differential Wnt pathway gene expression and E-cadherin truncation in sporadic colorectal cancers with and without microsatellite instability

PURPOSE

Alterations in the Wnt pathway play a major role in colorectal cancer with high (MSI-H) or low microsatellite instability (MSS/MSI-L). However, the differential impact of the Wnt pathway components on these tumors is poorly understood. MMP-3 (stromelysin-1) promoter is a target of the mutator phenotype in sporadic colorectal cancer. Among MMP-3 targets, we investigated E-cadherin integrity status in both groups of tumors. Because beta-catenin is the main effector of the Wnt pathway, we have also investigated the differential cellular status of beta-catenin.

EXPERIMENTAL DESIGN

Expression profiles of 114 genes related to the Wnt pathway were analyzed by oligo microarrays in 48 tumors classified by their MSI status. In addition, we analyzed 48 sporadic colorectal cancers for E-cadherin integrity status. We performed investigation of beta-catenin and cyclin D1 by immunohistochemistry using tissue arrays containing 96 tumors.

RESULTS

Our data show that a group of genes that negatively regulate Wnt signaling are downregulated in MSS/MSI-L as compared with MSI-H colorectal tumors. E-cadherin truncation was significantly higher in MSS/MSI-L as compared with MSI-H tumors. Moreover, MSI-H tumors showed low or null beta-catenin nuclear presence, whereas the group of tumors classified as MSS or MSI-L displayed a high content of the nuclear beta-catenin location.

CONCLUSIONS

Our results suggest that the differential expression of genes that negatively regulate the Wnt pathway, as well as the status of E-cadherin and beta-catenin in MSI-H or MSS/MSI-L colorectal tumors, shed some light on the different clinical behavior showed by the two groups.

Mutations in components of the Wnt signaling pathway in gastric cancer

AIM: To explore the contribution of AXIN1, AXIN2 and beta-catenin, components of Wnt signaling pathway, to the carcinogenesis of gastric cancer (GC), we examined AXIN1, AXIN2 exon7 and CTNNB1 (encoding beta-catenin) exon3 mutations in 70 GCs.

METHODS: The presence of mutations was identified by polymerase chain reaction (PCR)-based denaturing high-performance liquid chromatography and direct DNA sequencing. Beta-catenin expression was detected by immunohistochemical analysis.

RESULTS: Among the 70 GCs, 5 (7.1%) had mutations in one or two of these three components. A frameshift mutation (1 bp deletion) in exon7 of AXIN2 was found in one case. Four cases, including the case with a mutation in AXIN2, had frameshift mutations and missense mutations in AXIN1. Five single nucleotide polymorphisms (SNPs), 334 C>T, 874 C>T, 1396 G>A, 1690 C>T and 1942 T>G, were identified in AXIN1. A frameshift mutation (27 bp deletion) spanning exon3 of CTNNB1 was observed in one case. All four cases with mutations in AXIN1 and AXIN2 showed nuclear beta-catenin expression.

CONCLUSION: These data indicate that the mutations in AXIN1 and AXIN2 may contribute to gastric carcinogenesis.

The many ways of Wnt in cancer

More than 20 years ago, the oncogenicity of a Wnt ligand was revealed in a series of experiments originating with random proviral integration in mice. The significance of Wnt signaling in human cancer has since been buttressed by the identification of mutations in genes coding for the Wnt pathway components Axin, APC, and beta-catenin. This review summarizes the reported genetic defects in the Wnt pathway, with an emphasis on their functional contribution to human tumor progression.

Colorectal cancer and genetic alterations in the Wnt pathway

In colorectal tumours, Wnt pathway genetics continues to be dominated by mutations in the adenomatous polyposis coli (APC) gene. Germline mutations cause familial adenomatous polyposis and at least two-thirds of sporadic colorectal tumours also acquire APC mutations, quite possibly as the initiating events in tumorigenesis. These mutations almost always cause loss of the C-terminal functions of the APC protein - probably involved in microtubule binding, cell polarity and chromosome segregation - and deletion of the SAMP repeats that are important for binding to axin and formation of the beta-catenin phosphorylation complex. The truncated APC proteins are, in general, stable and almost certainly retain some activity in beta-catenin binding. The 'two hits' at APC are coselected so as to produce an optimal activation of Wnt signalling (just-right hypothesis). In a minority of colorectal tumours, Wnt activation can occur through mutations that affect phosphorylation sites within exon 3 of beta-catenin, causing protein stabilization. In other tumours, epigenetic transcriptional silencing or mutation of the secreted frizzled-related proteins may modulate Wnt levels. Mutations in the Wnt components AXIN1, AXIN2 and TCF4 have been found in microsatellite-unstable colon cancers, but it is not clear in every case whether these changes are functional. Therapeutic modulation of the Wnt pathway remains an attractive therapeutic possibility for colorectal carcinomas.

Combined immunohistochemistry of beta-catenin, cytokeratin 7, and cytokeratin 20 is useful in discriminating primary lung adenocarcinomas from metastatic colorectal cancer

Background

It is important to discriminate between primary and secondary lung cancer. However, often, the discriminating diagnosis of primary lung acinar adenocarcinoma and lung metastasis of colorectal cancer based on morphological and pathological findings is difficult. The purpose of this study was to evaluate the clinical usefulness of immunohistochemistry of β-catenin, cytokeratin (CK) 7, and CK20 for the discriminating diagnosis of lung cancer.

Methods

We performed immunohistochemistry of β-catenin, CK7, and CK20 in 19 lung metastasis of colorectal cancer samples, 10 corresponding primary colorectal cancer samples and 11 primary lung acinar adenocarcinoma samples and compared the levels of accuracy of the discriminating diagnosis by using antibodies against these antigens.

Results

Positive staining of β-catenin was observed in all the lung metastasis of colorectal cancer samples as well as in the primary colorectal cancer samples but in none of the primary lung acinar adenocarcinoma samples. Positive staining of CK7 was observed in 90.9% of the primary lung acinar adenocarcinoma samples and in 5.3% of the lung metastasis of colorectal cancer samples, but in none of the primary colorectal cancer samples. Positive staining of CK20 was observed in all the primary colorectal cancer samples and in 84.2% of the lung metastasis of colorectal cancer samples, but in none of the primary lung acinar adenocarcinoma samples.

Conclusion

Combined immunohistochemistry of β-catenin, CK7, and CK20 is useful for making a discriminating diagnosis between lung metastasis of colorectal cancer and primary lung acinar adenocarcinoma. This method will enable accurate diagnosis of a lung tumor and will be useful for selecting appropriate therapeutic strategies, including chemotherapeutic agents and operation methods.

Genetic and cellular characterizations of human TCF4 with microsatellite instability in colon cancer and leukemia cell lines

It has been reported that the mutational inactivation of the adenomatous polyposis coli (APC) and beta-catenin genes play important roles in colorectal carcinogenesis. However, alteration of the components in the Wnt signaling pathway in colorectal cancer (CRC) with microsatellite instability (MSI) has been elucidated. To define the precise role of the Wnt signaling components in CRC and leukemia cell lines with MSI, mutational analyses of the T cell factor 4 (TCF4) genes were performed. Here we describe for the first time a TCF4 MSI+ phenotype in leukemia cell lines except in colon cancer cell lines. Moreover, we found that these cell lines exhibited deletion and insertion of 1-2A in an (A)9 repeat so as to result in (A)7, (A)8, (A)10 and (A)11 repeat, respectively. To characterize the cellular function of these special TCF4 mutant clones, transient transfection and fluorescent microscopy were analyzed and the results revealed that the TCF4 frameshift gene products all localized in nuclei. Surprisingly, these TCF4 frameshift mutants lost transcriptional activity with beta-catenin and down-regulate the target gene expression. These results delineate a novel role for MSI+TCF4 in leukemia and colon cancer progression.

Mutations within Wnt pathway genes in sporadic colorectal cancers and cell lines

Wnt signaling pathway activation via mutation of genetic components, commonly adenomatous polyposis coli (APC), has a major role in colorectal cancer (CRC). Most components have not been assessed for mutation in sporadic CRC. We have analyzed AXIN2, CK1alpha, DKK1, GSK-3beta, SOX17, LRP6 and PPP2R1B, beta-catenin and APC in a collection of sporadic CRCs (n = 47) and CRC cell lines (CLs; n = 26). The CRC set was enriched for microsatellite unstable cancers (MSI+, 30%, 14/47). Somatic mutation was not found in CK1alpha, DKK1, LRP6, beta-catenin or GSK-3beta; but heterozygous frame-shift mutations, and an in-frame deletion mutation were detected in exon 7 of AXIN2 (CRCs, 11%, 5/47; CLs, 8%, 2/26). Our data refute a previous suggestion that a CRC-related mutational hot-spot occurred in the Huntington elongation A subunit TOR (HEAT) repeat 2 of PPP2R1B; this "hotspot" is, more likely, a rare germline polymorphism. An early investigation proposing a high mutational frequency in HEAT repeat 13 was not substantiated. A heterozygous SOX17 mutation (L194P) was also found in a cell line. APC gene mutations were identified in 64% (30/47) of cancers and 7% of these (2/30) had an additional mutation in another Wnt gene. Overall, 70% (33/47) of CRCs had a somatic mutation in a Wnt pathway gene. The number of tumors containing such a mutation was not significantly higher in MSI+ (57%, 8/14) compared to MSI- (76%, 25/33) cancers (p = 0.3, Fisher's exact test); APC mutation was significantly increased in the MSI- subgroup (p = 0.02, Fisher's exact test). Further, mutational screening of other Wnt pathway genes is warranted.

Mutations in APC, CTNNB1 and K-ras genes and expression of hMLH1 in sporadic colorectal carcinomas from the Netherlands Cohort Study

Background

The early to intermediate stages of the majority of colorectal tumours are thought to be driven by aberrations in the Wnt (APC, CTNNB1) and Ras (K-ras) pathways. A smaller proportion of cancers shows mismatch repair deficiency. The aim of this study was to analyse the co-occurrence of these genetic alterations in relation to tumour and patient characteristics.

Methods

In a group of 656 unselected sporadic colorectal cancer patients, aberrations in the APC, K-ras, CTNNB1 genes, and expression of hMLH1 were investigated. Additionally, tumours were divided in groups based on molecular features and compared with respect to patient's age at diagnosis, sex, family history of colorectal cancer, tumour sub-localisation, Dukes' stage and differentiation.

Results

Mutations at the phosphorylation sites (codons 31, 33, 37, and 45) in the CTNNB1 gene were observed in tumours from only 5/464 patients. Tumours with truncating APC mutations and activating K-ras mutations in codons 12 and 13 occurred at similar frequencies (37% (245/656) and 36% (235/656), respectively). Seventeen percent of tumours harboured both an APC and a K-ras mutation (109/656). Nine percent of all tumours (58/656) lacked hMLH1 expression. Patients harbouring a tumour with absent hMLH1 expression were older, more often women, more often had proximal colon tumours that showed poorer differentiation when compared to patients harbouring tumours with an APC and/or K-ras mutation.

Conclusion

CTNNB1 mutations seem to be of minor importance in sporadic colorectal cancer. The main differences in tumour and patient characteristics are found between groups of patients based on mismatch repair deficiency.

Genetic and epigenetic changes of components affecting the WNT pathway in colorectal carcinomas stratified by microsatellite instability

An unselected series of 310 colorectal carcinomas, stratified according to microsatellite instability (MSI) and DNA ploidy, was examined for mutations and/or promoter hypermethylation of five components of the WNT signaling cascade [APC, CTNNB1 (encoding beta-catenin), AXIN2, TCF4, and WISP3] and three genes indirectly affecting this pathway [CDH1 (encoding E-cadherin), PTEN, and TP53]. APC and TP53 mutations were each present more often in microsatellite-stable (MSS) tumors than in those with MSI (P < .001 for both). We confirmed that the aneuploid MSS tumors frequently contained TP53 mutations (P < .001), whereas tumors with APC mutations and/or promoter hypermethylation revealed no associations to ploidy. Mutations in APC upstream of codons 1020 to 1169, encoding the beta-catenin binding site, were found in 15/144 mutated tumors and these patients seemed to have poor clinical outcome (P = .096). Frameshift mutations in AXIN2, PTEN, TCF4, and WISP3 were found in 20%, 17%, 46%, and 28% of the MSI tumors, respectively. More than half of the tumors with heterozygote mutations in AXIN2 were concurrently mutated in APC. The present study showed that more than 90% of all samples had alteration in one or more of the genes investigated, adding further evidence to the vital importance of activated WNT signaling in colorectal carcinogenesis.

The links between axin and carcinogenesis

The products of the two mammalian Axin genes (Axin1 and its homologue Axin2) are essential for the degradation of beta catenin, a component of Wnt signalling that is frequently dysregulated in cancer cells. Axin is a multidomain scaffold protein that has many functions in biological signalling pathways. Overexpression of mutant [corrected] axin results in axis duplication in mouse embryos. Wnt signalling activity determines dorsal-ventral axis formation in vertebrates, implicating axin as a negative regulator of this signalling pathway. In addition, Wnts modulate pattern formation and the morphogenesis of most organs by influencing and controlling cell proliferation, motility, and fate. Defects in different components of the Wnt signalling pathway promote tumorigenesis and tumour progression. Recent biochemical studies of axins indicate that these molecules are the primary limiting components of this pathway. This review explores the intriguing connections between defects in axin function and human diseases.

Immunohistochemical and sequencing analyses of the Wnt signaling components in Japanese anaplastic thyroid cancers

We investigated the status of the components and target genes of the Wnt signaling pathway in Japanese anaplastic thyroid cancers (ATCs) in the present study. Nuclear and cytoplasmic positive staining of beta-catenin, which might indicate the existence of alterations in the Wnt signaling pathway, were found in 40.9% and 63.6% of the 22 ATC samples, respectively. The beta-catenin, adenomatous polyposis coli (APC) and Axin 1 gene mutations were observed in 4.5%, 9.0%, and 81.8% of the 22 ATC samples, respectively. Overexpression of cyclin D1 and c-myc, which are the target genes of the Wnt signaling pathway, was observed in 27.3% and 59.1% of the ATC samples, respectively. There was no significant correlation between nuclear or cytoplasmic positive staining of beta-catenin and nuclear positive staining of cyclin D1 or c-myc. Taken together, the results of beta-catenin immunohistochemistry suggest that alterations in the Wnt signaling pathway are associated with carcinogenesis of ATC, but the frequency of beta-catenin gene mutation in our series is lower than that previously reported. Furthermore, cyclin D1 and c-myc frequently accumulated in ATC, independently of dysfunction in the Wnt signaling pathway.