The canonical Wnt signalling pathway and its APC partner in colon cancer development

Important molecular genetic markers of colorectal cancer

Colorectal cancer (CRC) ranks third in the incidences of cancer morbidity and mortality worldwide. CRC is rather heterogeneous with regard to molecular genetic characteristics and pathogenic pathways. A wide spectrum of biomarkers is used for molecular subtype determination, prognosis, and estimation of sensitivity to different drugs in practice. These biomarkers can include germline and somatic mutations, chromosomal aberrations, genomic abnormalities, gene expression alterations at mRNA or protein level and changes in DNA methylation status. In the present review we discuss the most important and well-studied CRC biomarkers, and their potential clinical significance and current approaches to molecular classification of colorectal tumors.

Methylation status of the APC and RASSF1A promoter in cell-free circulating DNA and its prognostic role in patients with colorectal cancer

DNA methylation is the most frequent epigenetic alteration. Using methylation-specific polymerase chain reaction (MSP), the methylation status of the adenomatous polyposis coli (APC) and Ras association domain family 1 isoform A (RASSF1A) genes was examined in cell-free circulating DNA from 155 plasma samples obtained from patients with early and advanced colorectal cancer (CRC). APC and RASSF1A hypermethylation was frequently observed in both early and advanced disease, and was significantly associated with a poorer disease outcome. The methylation status of the APC and RASSF1A promoters was investigated in cell-free DNA of patients with CRC. Using MSP, the promoter methylation status of APC and RASSF1A was examined in 155 blood samples obtained from patients with CRC, 88 of whom had operable CRC (oCRC) and 67 had metastatic CRC (mCRC). The frequency of APC methylation in patients with oCRC was 33%. Methylated APC promoter was significantly associated with older age (P=0.012), higher stage (P=0.014) and methylated RASSF1A status (P=0.050). The frequency of APC methylation in patients with mCRC was 53.7%. In these patients, APC methylation was significantly associated with methylated RASSF1A status (P=0.016). The frequency of RASSF1A methylation in patients with oCRC was 25%. Methylated RASSF1A in oCRC was significantly associated with higher stage (P=0.021). The frequency of RASSF1A methylation in mCRC was 44.8%. Methylated RASSF1A in mCRC was associated with moderate differentiation (P=0.012), high levels of carcinoembryonic antigen (P=0.023) and methylated APC status (P=0.016). Patients with an unmethylated APC gene had better survival in both early (81±5 vs. 27±4 months, P<0.001) and advanced disease (37±7 vs. 15±3 months, P<0.001), compared with patients with methylated APC. Patients with an unmethylated RASSF1A gene had better survival in both early (71±6 vs. 46±8 months, P<0.001) and advanced disease (28±4 vs. 16±3 months, P<0.001) than patients with methylated RASSF1A. The observed significant correlations between APC and RASSF1A promoter methylation status and survival may be indicative of a prognostic role for these genes in CRC, which requires additional testing in larger studies.

Colorectal cancer risk genes are functionally enriched in regulatory pathways

Colorectal cancer (CRC) is a common complex disease caused by the combination of genetic variants and environmental factors. Genome-wide association studies (GWAS) have been performed and reported some novel CRC susceptibility variants. However, the potential genetic mechanisms for newly identified CRC susceptibility variants are still unclear. Here, we selected 85 CRC susceptibility variants with suggestive association P < 1.00E-05 from the National Human Genome Research Institute GWAS catalog. To investigate the underlying genetic pathways where these newly identified CRC susceptibility genes are significantly enriched, we conducted a functional annotation. Using two kinds of SNP to gene mapping methods including the nearest upstream and downstream gene method and the ProxyGeneLD, we got 128 unique CRC susceptibility genes. We then conducted a pathway analysis in GO database using the corresponding 128 genes. We identified 44 GO categories, 17 of which are regulatory pathways. We believe that our results may provide further insight into the underlying genetic mechanisms for these newly identified CRC susceptibility variants.

Combined changes in Wnt signaling response and contact inhibition induce altered proliferation in radiation-treated intestinal crypts

Wnt concentration gradients operate in many tissues. Modeling of proliferation in control and irradiated intestinal crypts shows that the Wnt concentrations that cells experience when they are born set their proliferative fate and cell cycle duration. The simulations also predict the initial proportion of cells damaged by tumor-promoting radiation.

Curative intervention is possible if colorectal cancer is identified early, underscoring the need to detect the earliest stages of malignant transformation. A candidate biomarker is the expanded proliferative zone observed in crypts before adenoma formation, also found in irradiated crypts. However, the underlying driving mechanism for this is not known. Wnt signaling is a key regulator of proliferation, and elevated Wnt signaling is implicated in cancer. Nonetheless, how cells differentiate Wnt signals of varying strengths is not understood. We use computational modeling to compare alternative hypotheses about how Wnt signaling and contact inhibition affect proliferation. Direct comparison of simulations with published experimental data revealed that the model that best reproduces proliferation patterns in normal crypts stipulates that proliferative fate and cell cycle duration are set by the Wnt stimulus experienced at birth. The model also showed that the broadened proliferation zone induced by tumorigenic radiation can be attributed to cells responding to lower Wnt concentrations and dividing at smaller volumes. Application of the model to data from irradiated crypts after an extended recovery period permitted deductions about the extent of the initial insult. Application of computational modeling to experimental data revealed how mechanisms that control cell dynamics are altered at the earliest stages of carcinogenesis.

Mouse Crumbs3 sustains epithelial tissue morphogenesis in vivo

The human apical protein CRB3 (Crb3 in mouse) organizes epithelial cell polarity. Loss of CRB3 expression increases the tumorogenic potential of cultured epithelial cells and favors metastasis formation in nude mice. These data emphasize the need of in vivo models to study CRB3 functions. Here, we report the phenotypic analysis of a novel Crb3 knockout mouse model. Crb3-deficient newborn mice show improper clearance of airways, suffer from respiratory distress and display perinatal lethality. Crb3 is also essential to maintain apical membrane identity in kidney epithelial cells. Numerous kidney cysts accompany these polarity defects. Impaired differentiation of the apical membrane is also observed in a subset of cells of the intestinal epithelium. This results in improper remodeling of adhesive contacts in the developing intestinal epithelium, thereby leading to villus fusion. We also noted a strong increase in cytoplasmic β-catenin levels in intestinal epithelial cells. β-catenin is a mediator of the Wnt signaling pathway, which is overactivated in the majority of colon cancers. In addition to clarifying the physiologic roles of Crb3, our study highlights that further functional analysis of this protein is likely to provide insights into the etiology of diverse pathologies, including respiratory distress syndrome, polycystic kidney disease and cancer.

Role of miR-140 in embryonic bone development and cancer

Bone is increasingly viewed as an endocrine organ with key biological functions. The skeleton produces hormones and cytokines, such as FGF23 and osteocalcin, which regulate an extensive list of homoeostatic functions. Some of these functions include glucose metabolism, male fertility, blood cell production and calcium/phosphate metabolism. Many of the genes regulating these functions are specific to bone cells. Some of these genes can be wrongly expressed by other malfunctioning cells, driving the generation of disease. The miRNAs are a class of non-coding RNA molecules that are powerful regulators of gene expression by suppressing and fine-tuning target mRNAs. Expression of one such miRNA, miR-140, is ubiquitous in chondrocyte cells during embryonic bone development. Activity in cells found in the adult breast, colon and lung tissue can silence genes required for tumour suppression. The realization that the same miRNA can be both normal and detrimental, depending on the cell, tissue and time point, provides a captivating twist to the study of whole-organism functional genomics. With the recent interest in miRNAs in bone biology and RNA-based therapeutics on the horizon, we present a review on the role of miR-140 in the molecular events that govern bone formation in the embryo. Cellular pathways involving miR-140 may be reactivated or inhibited when treating skeletal injury or disorder in adulthood. These pathways may also provide a novel model system when studying cancer biology of other cells and tissues.

Elevated Coexpression of KITENIN and the ErbB4 CYT-2 Isoform Promotes the Transition from Colon Adenoma to Carcinoma Following APC loss

PURPOSE AND EXPERIMENTAL DESIGN

The molecular events in the malignant progression of colon adenoma after loss of adenomatous polyposis coli (APC) are not fully understood. KITENIN (KAI1 C-terminal interacting tetraspanin) increases the invasiveness of colorectal cancer cells, and we identified a novel EGFR-independent oncogenic signal of EGF that works under coexpressed KITENIN and ErbB4. Here we tested whether elevated KITENIN and ErbB4 contribute to further progression of intestinal adenoma following APC loss.

RESULTS

The intestinal tissues of villin-KITENIN transgenic mice in which villin-driven KITENIN expression induces increased c-Jun expression exhibit mild epithelial cell proliferation but no epithelial lineage changes compared with those of nontransgenic mice. Among the four ErbB4 isoforms, JM-a/CYT-2 and JM-b/CYT-2 exhibited the highest AP-1 activity when cells coexpressing KITENIN and each isoform were stimulated by EGF. Interestingly, predominant overexpression of the ErB4-CYT-2 mRNA as well as increased EGFR expression were observed in intestinal adenoma of APC(min/+) mice, which makes the microenvironment of activated EGF signaling. When we crossed villin-KITENIN mice with APC(min/+) mice, intestinal tumor tissues in the crossed mice showed the characteristics of early-stage invading adenocarcinoma. In patients with colorectal cancer, ErbB4-CYT-2 mRNA expression was significantly greater in tumor tissues than in normal adjacent tissues, but no significant differences in tumor tissue expression were found between different colorectal cancer stages. Furthermore, the mRNA expression of KITENIN and that of ErbB4-CYT-2 were positively correlated in human colorectal cancer tissue.

CONCLUSIONS

Elevated coexpression of KITENIN and ErbB4-CYT-2 promotes the transition of colon adenoma to adenocarcinoma within an APC loss-associated tumor microenvironment.

Selenium and inflammatory bowel disease

Dietary intake of the micronutrient selenium is essential for normal immune functions. Selenium is cotranslationally incorporated as the 21st amino acid, selenocysteine, into selenoproteins that function to modulate pathways involved in inflammation. Epidemiological studies have suggested an inverse association between selenium levels and inflammatory bowel disease (IBD), which includes Crohn's disease and ulcerative colitis that can potentially progress to colon cancer. However, the underlying mechanisms are not well understood. Here we summarize the current literature on the pathophysiology of IBD, which is multifactorial in origin with unknown etiology. We have focused on a few selenoproteins that mediate gastrointestinal inflammation and activate the host immune response, wherein macrophages play a pivotal role. Changes in cellular oxidative state coupled with altered expression of selenoproteins in macrophages drive the switch from a proinflammatory phenotype to an anti-inflammatory phenotype to efficiently resolve inflammation in the gut and restore epithelial barrier integrity. Such a phenotypic plasticity is accompanied by changes in cytokines, chemokines, and bioactive metabolites, including eicosanoids that not only mitigate inflammation but also partake in restoring gut homeostasis through diverse pathways involving differential regulation of transcription factors such as nuclear factor-κB and peroxisome proliferator-activated receptor-γ. The role of the intestinal microbiome in modulating inflammation and aiding in selenium-dependent resolution of gut injury is highlighted to provide novel insights into the beneficial effects of selenium in IBD.

Protein kinase D1 attenuates tumorigenesis in colon cancer by modulating β-catenin/T cell factor activity

Over 80% of colon cancer development and progression is a result of the dysregulation of β-catenin signaling pathway. Herein, for the first time, we demonstrate that a serine-threonine kinase, Protein Kinase D1 (PKD1), modulates the functions of β-catenin to suppress colon cancer growth. Analysis of normal and colon cancer tissues reveals downregulation of PKD1 expression in advanced stages of colon cancer and its co-localization with β-catenin in the colon crypts. This PKD1 downregulation corresponds with the aberrant expression and nuclear localization of β-catenin. In-vitro investigation of the PKD1-β-catenin interaction in colon cancer cells reveal that PKD1 overexpression suppresses cell proliferation and clonogenic potential and enhances cell-cell aggregation. We demonstrate that PKD1 directly interacts with β-catenin and attenuates β-catenin transcriptional activity by decreasing nuclear β-catenin levels. Additionally, we show that inhibition of nuclear β-catenin transcriptional activity is predominantly influenced by nucleus targeted PKD1. This subcellular modulation of β-catenin results in enhanced membrane localization of β-catenin and thereby increases cell-cell adhesion. Studies in a xenograft mouse model indicate that PKD1 overexpression delayed tumor appearance, enhanced necrosis and lowered tumor hypoxia. Overall, our results demonstrate a putative tumor-suppressor function of PKD1 in colon tumorigenesis via modulation of β-catenin functions in cells.

Genetic dissection of the Mom5 modifier locus and evaluation of Mom5 candidate genes

Germline mutations in the adenomatous polyposis coli (APC) gene cause familial adenomatous polyposis (FAP), a hereditary colon cancer syndrome in which affected individuals may develop 100-1000s of colonic adenomas. In families affected by FAP, adenoma number can vary markedly between individuals, despite the fact that these individuals carry the same APC mutation. In at least some FAP pedigrees, evidence suggests that these phenotypic differences are caused by segregating modifier alleles that impact adenoma number. However, identifying these modifiers in the human population is difficult, therefore mouse models are essential. Using the Apc (Min/+) mouse colon cancer model, we previously mapped one such modifier, Mom5, to a 25 Mbp region of chromosome 5 that contains hundreds of genes. The purpose of the present study was to refine the Mom5 interval and evaluate candidate genes for the Mom5 modifier of intestinal neoplasia. Recombinant mice were used to narrow the Mom5 interval to 8.1 Mbp containing 70 genes. In silico and gene expression analyses were utilized to identify and evaluate potential candidate genes that reside within this interval. These analyses identified seven genes within the Mom5 interval that contain variants between the B6 and 129P2 strains. These genes represent the most likely candidates for the Mom5 modifier.

LGR5 promotes the proliferation of colorectal cancer cells via the Wnt/β-catenin signaling pathway

Leucine-rich repeat-containing G-protein coupled receptor 5 (LGR5) is an established cancer stem cell marker and is a target gene of the Wnt/β-catenin signaling pathway, a critical pathway in the process of tumor initiation and growth. In the present study, the mRNA expression levels of LGR5, adenomatous polyposis coli (APC) and β-catenin were detected in 20 colorectal cancer (CRC) tissues and matched healthy mucosa samples using reverse transcription-quantitative polymerase chain reaction. HT-29 CRC cell line was treated with siRNA-Lgr5; the APC, β-catenin and LGR5 RNA expressions were detected and cell viability was measured using a CCK8 assay. The results revealed that LGR5 was significantly overexpressed in CRC tissue compared with healthy mucosa (P<0.05). Furthermore, knockdown of LGR5 by small interfering RNA decreased the expression of APC and β-catenin in HT29 colon cancer cells as well as inhibited the proliferation of HT29 cells. These findings demonstrated that LGR5 expression is critical for the promotion of neoplastic CRC cell proliferation, indicating that LGR5 may be a novel therapeutic target for CRC.

The pathological role of microRNAs and inflammation in colon carcinogenesis

Evidence of an association between inflammation, microRNAs (miRNAs) and tumorigenesis has emerged in recent years. Patients with inflammatory bowel disease (IBD) are at an increased risk for colorectal cancer (CRC) development, suggesting that inflammatory mediators play a causative role in colon carcinogenesis. MiRNAs are small (19-22 nucleotides) non-coding RNA molecules that regulate gene expression at the post-transcriptional level by base-pairing to specific messenger RNAs (mRNAs), promoting their degradation or suppressing translation. MiRNAs can act as inflammatory mediators, oncogenes or tumor suppressors in different cellular environments. MiRNAs also serve as biomarkers and therapeutic targets in CRC. The risk of CRC is also influenced by miRNA polymorphisms and binding sites. Their functions as early diagnostic biomarkers or prognostic classifiers has been demonstrated. Here, we reviewed recent findings on miRNAs and inflammation in colon carcinogenesis and discussed the potential for miRNAs and inflammation-related genes as biomarkers and therapeutic targets in CRC.

Is resistant starch protective against colorectal cancer via modulation of the WNT signalling pathway?

Epidemiological and experimental evidence suggests that non-digestible carbohydrates (NDC) including resistant starch are protective against colorectal cancer. These anti-neoplastic effects are presumed to result from the production of the SCFA, butyrate, by colonic fermentation, which binds to the G-protein-coupled receptor GPR43 to regulate inflammation and other cancer-related processes. The WNT pathway is central to the maintenance of homeostasis within the large bowel through regulation of processes such as cell proliferation and migration and is frequently aberrantly hyperactivated in colorectal cancers. Abnormal WNT signalling can lead to irregular crypt cell proliferation that favours a hyperproliferative state. Butyrate has been shown to modulate the WNT pathway positively, affecting functional outcomes such as apoptosis and proliferation. Butyrate's ability to regulate gene expression results from epigenetic mechanisms, including its role as a histone deacetylase inhibitor and through modulating DNA methylation and the expression of microRNA. We conclude that genetic and epigenetic modulation of the WNT signalling pathway may be an important mechanism through which butyrate from fermentation of resistant starch and other NDC exert their chemoprotective effects.

Synthesis, Structure-Activity Relationship, and Mechanistic Investigation of Lithocholic Acid Amphiphiles for Colon Cancer Therapy

We report a structure-activity relationship of lithocholic acid amphiphiles for their anticancer activities against colon cancer. We synthesized ten cationic amphiphiles differing in nature of cationic charged head groups using lithocholic acid. We observed that anticancer activities of these amphiphiles against colon cancer cell lines are contingent on nature of charged head group. Lithocholic acid based amphiphile possessing piperidine head group (LCA-PIP1 ) is ~10 times more cytotoxic as compared to its precursor. Biochemical studies revealed that enhanced activity of LCA-PIP1 as compared to lithocholic acid is due to greater activation of apoptosis.LCA-PIP1 induces sub G0 arrest and causes cleavage of caspases. A single dose of lithocholic acid-piperidine derivative is enough to reduce the tumor burden by 75% in tumor xenograft model.

Evolution of network biomarkers from early to late stage bladder cancer samples

We use a systems biology approach to construct protein-protein interaction networks (PPINs) for early and late stage bladder cancer. By comparing the networks of these two stages, we find that both networks showed very significantly different mechanisms. To obtain the differential network structures between cancer and noncancer PPINs, we constructed cancer PPIN and noncancer PPIN network structures for the two bladder cancer stages using microarray data from cancer cells and their adjacent noncancer cells, respectively. With their carcinogenesis relevance values (CRVs), we identified 152 and 50 significant proteins and their PPI networks (network markers) for early and late stage bladder cancer by statistical assessment. To investigate the evolution of network biomarkers in the carcinogenesis process, primary pathway analysis showed that the significant pathways of early stage bladder cancer are related to ordinary cancer mechanisms, while the ribosome pathway and spliceosome pathway are most important for late stage bladder cancer. Their only intersection is the ubiquitin mediated proteolysis pathway in the whole stage of bladder cancer. The evolution of network biomarkers from early to late stage can reveal the carcinogenesis of bladder cancer. The findings in this study are new clues specific to this study and give us a direction for targeted cancer therapy, and it should be validated in vivo or in vitro in the future.

Expression of Indian hedgehog is negatively correlated with APC gene mutation in colorectal tumors

The regulatory mechanism of Indian hedgehog (IHH) in colorectal carcinogenesis has not been elucidated. In the current study, the expression of IHH were investigated in 7 digestive tract cancer cell lines, and in 10 normal colorectal mucosas (NCs), 30 hyperplastic polyps (HPs), 35 colorectal adenomas (ADs), and 40 colorectal adenocarcinomas (CAs) by semi-quantitative RT-PCR and immunohistochemical staining. Moreover, the mutational status of adenomatous polyposis coli (APC) and β-catenin in these tumors were analyzed by direct sequencing. IHH mRNA was lost in the 4 colon cancer cell lines harboring APC mutation. IHH mRNA was significantly decreased in CAs (0.17 ± 0.22), compared with that in ADs (0.38 ± 0.35) and HPs (0.56 ± 0.38, P < 0.05). IHH protein was expressed at a very low level or absent in both ADs (7.51 ± 11.92) and CAs (5.15 ± 9.21) in comparison to that in HPs (19.47 ± 17.91) and NCs (42.40 ± 13.67, P < 0.05). Moreover, APC mutations were negatively correlated with IHH mRNA expression (Spearman's R = -0.636, P < 0.01) and IHH protein expression (Spearman's R = -0.426, P < 0.01). In conclusion, down-regulation of IHH expression might be an early event during the carcinogenesis of colorectal cancer. The activation of Wnt signaling by APC mutation might contribute to the down-regulation or loss of IHH expression in colorectal tumors.

Core and specific network markers of carcinogenesis from multiple cancer samples

Cancer is the leading cause of death worldwide and is generally caused by mutations in multiple proteins or the dysregulation of pathways. Understanding the causes and the underlying carcinogenic mechanisms can help fight this disease. In this study, a systems biology approach was used to construct the protein-protein interaction (PPI) networks of four cancers and the non-cancers by their corresponding microarray data, PPI modeling and database-mining. By comparing PPI networks between cancer and non-cancer samples to find significant proteins with large PPI changes during carcinogenesis process, core and specific network markers were identified by the intersection and difference of significant proteins, respectively, with carcinogenesis relevance values (CRVs) for each cancer. A total of 28 significant proteins were identified as core network markers in the carcinogenesis of four types of cancer, two of which are novel cancer-related proteins (e.g., UBC and PSMA3). Moreover, seven crucial common pathways were found among these cancers based on their core network markers, and some specific pathways were particularly prominent based on the specific network markers of different cancers (e.g., the RIG-I-like receptor pathway in bladder cancer, the proteasome pathway and TCR pathway in liver cancer, and the HR pathway in lung cancer). Additional validation of these network markers using the literature and new tested datasets could strengthen our findings and confirm the proposed method. From these core and specific network markers, we could not only gain an insight into crucial common and specific pathways in the carcinogenesis, but also obtain a high promising PPI target for cancer therapy.

Targeting mTOR network in colorectal cancer therapy

The mechanistic target of rapamycin (mTOR) integrates growth factor signals with cellular nutrient and energy levels and coordinates cell growth, proliferation and survival. A regulatory network with multiple feedback loops has evolved to ensure the exquisite regulation of cell growth and division. Colorectal cancer is the most intensively studied cancer because of its high incidence and mortality rate. Multiple genetic alterations are involved in colorectal carcinogenesis, including oncogenic Ras activation, phosphatidylinositol 3-kinase pathway hyperactivation, p53 mutation, and dysregulation of wnt pathway. Many oncogenic pathways activate the mTOR pathway. mTOR has emerged as an effective target for colorectal cancer therapy. In vitro and preclinical studies targeting the mTOR pathway for colorectal cancer chemotherapy have provided promising perspectives. However, the overall objective response rates in major solid tumors achieved with single-agent rapalog therapy have been modest, especially in advanced metastatic colorectal cancer. Combination regimens of mTOR inhibitor with agents such as cytotoxic chemotherapy, inhibitors of vascular endothelial growth factor, epidermal growth factor receptor and Mitogen-activated protein kinase kinase (MEK) inhibitors are being intensively studied and appear to be promising. Further understanding of the molecular mechanism in mTOR signaling network is needed to develop optimized therapeutic regimens. In this paper, oncogenic gene alterations in colorectal cancer, as well as their interaction with the mTOR pathway, are systematically summarized. The most recent preclinical and clinical anticancer therapeutic endeavors are reviewed. New players in mTOR signaling pathway, such as non-steroidal anti-inflammatory drug and metformin with therapeutic potentials are also discussed here.

different Roles for the axin interactions with the SAMP versus the second twenty amino acid repeat of adenomatous polyposis coli

Wnt signalling is prevented by the proteosomal degradation of β-catenin, which occurs in a destruction complex containing adenomatous polyposis coli (APC), APC-like (APCL), Axin and Axin2. Truncating mutations of the APC gene result in the constitutive stabilisation of β-catenin and the initiation of colon cancer, although tumour cells tolerate the expression of wild-type APCL. Using the colocalisation of overexpressed Axin, APC and APCL constructs as a readout of interaction, we found that Axin interacted with the second twenty amino acid repeat (20R2) of APC and APCL. This interaction involved a domain adjacent to the C-terminal DIX domain of Axin. We identified serine residues within the 20R2 of APCL that were involved in Axin colocalisation, the phosphorylation of truncated APCL and the down-regulation of β-catenin. Our results indicated that Axin, but not Axin2, displaced APC, but not APCL, from the cytoskeleton and stimulated its incorporation into bright cytoplasmic dots that others have recognised as β-catenin destruction complexes. The SAMP repeats in APC interact with the N-terminal RGS domain of Axin. Our data showed that a short domain containing the first SAMP repeat in truncated APC was required to stimulate Axin oligomerisation. This was independent of Axin colocalisation with 20R2. Our data also suggested that the RGS domain exerted an internal inhibitory constraint on Axin oligomerisation. Considering our data and those from others, we discuss a working model whereby β-catenin phosphorylation involves Axin and the 20R2 of APC or APCL and further processing of phospho-β-catenin occurs upon the oligomerisation of Axin that is induced by binding the SAMP repeats in APC.

RIP140 increases APC expression and controls intestinal homeostasis and tumorigenesis

Deregulation of the Wnt/APC/β-catenin signaling pathway is an important consequence of tumor suppressor APC dysfunction. Genetic and molecular data have established that disruption of this pathway contributes to the development of colorectal cancer. Here, we demonstrate that the transcriptional coregulator RIP140 regulates intestinal homeostasis and tumorigenesis. Using Rip140-null mice and mice overexpressing human RIP140, we found that RIP140 inhibited intestinal epithelial cell proliferation and apoptosis. Interestingly, following whole-body irradiation, mice lacking RIP140 exhibited improved regenerative capacity in the intestine, while mice overexpressing RIP140 displayed reduced recovery. Enhanced RIP140 expression strongly repressed human colon cancer cell proliferation in vitro and after grafting onto nude mice. Moreover, in murine tissues and human cancer cells, RIP140 stimulated APC transcription and inhibited β-catenin activation and target gene expression. Finally, RIP140 mRNA and RIP140 protein levels were decreased in human colon cancers compared with those in normal mucosal tissue, and low levels of RIP140 expression in adenocarcinomas from patients correlated with poor prognosis. Together, these results support a tumor suppressor role for RIP140 in colon cancer.

p53 protein regulates Hsp90 ATPase activity and thereby Wnt signaling by modulating Aha1 expression

The p53 tumor suppressor gene encodes a homotetrameric transcription factor which is activated in response to a variety of cellular stressors, including DNA damage and oncogene activation. p53 mutations occur in >50% of human cancers. Although p53 has been shown to regulate Wnt signaling, the underlying mechanisms are not well understood. Here we show that silencing p53 in colon cancer cells led to increased expression of Aha1, a co-chaperone of Hsp90. Heat shock factor-1 was important for mediating the changes in Aha1 levels. Increased Aha1 levels were associated with enhanced interactions with Hsp90, resulting in increased Hsp90 ATPase activity. Moreover, increased Hsp90 ATPase activity resulted in increased phosphorylation of Akt and glycogen synthase kinase-3β (GSK3β), leading to enhanced expression of Wnt target genes. Significantly, levels of Aha1, Hsp90 ATPase activity, Akt, and GSK3β phosphorylation and expression of Wnt target genes were increased in the colons of p53-null as compared with p53 wild type mice. Using p53 heterozygous mutant epithelial cells from Li-Fraumeni syndrome patients, we show that a monoallelic mutation of p53 was sufficient to activate the Aha1/Hsp90 ATPase axis leading to stimulation of Wnt signaling and increased expression of Wnt target genes. Pharmacologic intervention with CP-31398, a p53 rescue agent, inhibited recruitment of Aha1 to Hsp90 and suppressed Wnt-mediated gene expression in colon cancer cells. Taken together, this study provides new insights into the mechanism by which p53 regulates Wnt signaling and raises the intriguing possibility that p53 status may affect the efficacy of anticancer therapies targeting Hsp90 ATPase.

Prevalence and molecular characterisation of the sessile serrated adenoma in a subset of the Chinese population

AIMS

The incidence and mortality rates from right-sided colorectal cancers (CRCs) have not decreased in recent years. It is very likely that a significant proportion of these cancers evolve from undetected sessile serrated adenomas (SSAs). The prevalence and molecular features of the SSAs in the Chinese population have seldom been investigated.

METHODS

We retrospectively reviewed the colonoscopy database and pathology archives in our medical centre. Adenomatous polyposis coli (APC) and β-catenin expressions were examined in 28 right hyperplastic polyps (RHPs) and 21 SSAs by immunohistochemical staining. The mutations of BRAF, KRAS, APC and β-CATENIN were analysed by direct sequencing. The methylation status of APC promoter in these polyps was analysed by methylation-specific PCR and bisulfite sequencing. Samples of left hyperplastic polyps, traditional adenomas and CRC were used as controls.

RESULTS

SSAs accounted for 4.9% of serrated polyps and 1.0% of all colorectal polyps. BRAF((V600E)) mutations were found in 14.3% of SSAs and 7.1% of RHPs. Nuclear accumulation of β-catenin was seen in 28.6% of SSAs and 17.9% of RHPs. APC mutations were detected in 57.1% of SSAs and 67.9% of RHPs. APC methylation was detected in 14.3% of RHPs and 23.8% of SSAs.

CONCLUSIONS

The prevalence of SSAs in a subset of the Chinese population is much lower than that in the Western population. BRAF((V600E)) mutation is not a frequent event in right colon serrated polyps in a subset of the Chinese population. APC mutation is possibly the main cause for the Wnt signalling activation in right colon serrated polyps.

Involvement of CDX2 in the cross talk between TNF-α and Wnt signaling pathway in the colon cancer cell line Caco-2

Tumor necrosis factor-α (TNF-α) is highly upregulated in inflammation and reduces the expression of the intestinal transcription factor, Caudal-related homeobox transcription factor 2 (CDX2). Wnt/β-catenin signaling is critical for intestinal cell proliferation, but a decreased CDX2 expression has influence on the Wnt signaling-related genes and progression of colorectal cancer. Although several inflammatory signaling pathways, including TNF-α, have been reported to promote Wnt/β-catenin activity and development of cancer, the underlying molecular mechanisms remain unclear. The aim was to investigate the signaling pathways involved in the TNF-α-mediated downregulation of CDX2, and its influence on Wnt/β-catenin signaling components in colon cancer cells. The expression of TNF-α and CDX2 at the invasive front were evaluated by immunohistochemical staining and showed reduced CDX2-positive cells in tumor buddings in areas with TNF-α expression in the surrounding inflammatory cells. In vitro studies revealed that TNF-α treatment showed a dose-dependent decrease of CDX2 messenger RNA (mRNA) and protein expression in Caco-2 cells. Inhibition of nuclear factor-kappaB or p38 pathways showed that these are involved in the TNF-α-dependent downregulation of CDX2. Furthermore, TNF-α-mediated downregulation of CDX2 was found to significantly decrease the mRNA levels of adenomatous polyposis coli (APC), axis inhibition protein 2 (AXIN2) and glycogen synthase kinase-3 beta (GSK3β), whereas the mRNA levels of Wnt targets were significantly elevated in TNF-α-treated Caco-2 cells. These findings were associated with reduced binding of CDX2 to promoter or enhancer regions of APC, AXIN2 and GSK3β. In conclusion, it was found that TNF-α induces the expression of Wnt signaling components through a downregulation of the CDX2 expression that might have a tumor-promoting effect on colon cancer cells.

Myofibroblast-derived SFRP1 as potential inhibitor of colorectal carcinoma field effect

Epigenetic changes of stromal-epithelial interactions are of key importance in the regulation of colorectal carcinoma (CRC) cells and morphologically normal, but genetically and epigenetically altered epithelium in normal adjacent tumor (NAT) areas. Here we demonstrated retained protein expression of well-known Wnt inhibitor, secreted frizzled-related protein 1 (SFRP1) in stromal myofibroblasts and decreasing epithelial expression from NAT tissues towards the tumor. SFRP1 was unmethylated in laser microdissected myofibroblasts and partially hypermethylated in epithelial cells in these areas. In contrast, we found epigenetically silenced myofibroblast-derived SFRP1 in CRC stroma. Our results suggest that the myofibroblast-derived SFRP1 protein might be a paracrine inhibitor of epithelial proliferation in NAT areas and loss of this signal may support tumor proliferation in CRC.

Expression and localization of axin 2 in colorectal carcinoma and its clinical implication

PURPOSE

Aberrant activation of the Wnt/β-catenin pathway plays a major role in the development of colorectal carcinoma (CRC). Axin 2 is a key protein of this pathway and is upregulated in CRC. Here, we investigated RNA- and protein expression of axin 2 in CRC tissues at the single cell level. Moreover, the association of axin 2 with prognosis and survival was investigated in a large cohort of CRC patients (n = 280).

METHODS

Localization and expression of axin 2 and β-catenin was investigated using in situ hybridization and immunohistochemical staining. The quantitative expression levels of axin 2 were determined using RT-qPCR. The association of axin 2 expression with prognosis and survival of the patients was determined by statistical analysis (logrank test, Kaplan-Meier).

RESULTS

Our results confirmed the upregulation of axin 2 in CRC and showed that it is broadly expressed in the cytoplasm of the tumor epithelial cells both, in the tumor center and at the invasion front. Axin 2 was rarely expressed by tumor stromal cells and only weakly by normal colonic epithelial cells. Staining of β-catenin and axin 2 in consecutive CRC tissue sections revealed that nuclear translocation of β-catenin in the tumor front was not associated with changes in the cytoplasmic localization of axin 2. Axin 2 did not show any association with proven prognostic factors or survival of the CRC patients.

CONCLUSION

The generally increased expression of axin 2 in all tumor stages as compared to normal tissue suggests an initiating pathogenic function in the development of CRC.

A systematic approach to therapeutic target selection in oesophago-gastric cancer

OBJECTIVE

The success of personalised therapy depends on identification and inhibition of the oncogene(s) on which that tumour is dependent. We aimed to determine whether a receptor tyrosine kinase (RTK) array could be used to select the most effective therapeutic strategies in molecularly heterogeneous oesophago-gastric adenocarcinomas.

DESIGN

Gene expression profiling from oesophago-gastric tumours (n=75) and preinvasive stages (n=57) identified the active signalling pathways, which was confirmed using immunohistochemistry (n=434). RTK arrays on a cell line panel (n=14) determined therapeutic targets for in vitro cytotoxic testing. Feasibility of this personalised approach was tested in tumour samples (n=46).

RESULTS

MAPK was the most frequently activated pathway (32/75 samples (42.7%)) with progressive enrichment in preinvasive disease stages (p<0.05) and ERK phosphorylation in 148/434 (34.3%) independent samples. Cell lines displayed a range of RTK activation profiles. When no RTKs were activated, tyrosine kinase inhibitors (TKIs) and a Mek inhibitor were not useful (MKN1). In lines with a dominant phosphorylated RTK (OE19, MKN45 and KATOIII), selection of this TKI or Mek in nM concentrations induced cytotoxicity and inhibited Erk and Akt phosphorylation. In cells lines with complex activation profiles (HSC39 and OE33), a combination of TKIs or Mek inhibition (in nM concentrations) was necessary for cytotoxicity and inhibition of Erk and Akt phosphorylation. Human tumours demonstrated diverse activation profiles and 65% of cases had two or more active RTKs.

CONCLUSIONS

The MAPK pathway is commonly activated in oesophago-gastric cancer following activation of a variety of RTKs. Molecular phenotyping can inform a rational choice of targeted therapy.

Differential expression of IL-17, 22 and 23 in the progression of colorectal cancer in patients with K-ras mutation: Ras signal inhibition and crosstalk with GM-CSF and IFN-γ

Recent studies have suggested that aberrant K-ras signaling is responsible for triggering immunological responses and inflammation-driven tumorigenesis. Interleukins IL-17, IL-22, and IL-23 have been reported in various types of malignancies, but the exact mechanistic role of these molecules remains to be elucidated. Given the role of K-ras and the involvement of interleukins in colorectal tumorigenesis, research efforts are reported for the first time, showing that differentially expressed interleukin IL-17, IL-22, and IL-23 levels are associated with K-ras in a stage-specific fashion along colorectal cancer progression. Specifically, a) the effect of K-ras signaling was investigated in the overall expression of interleukins in patients with colorectal cancer and healthy controls, and b) an association was established between mutant K-ras and cytokines GM-CSF and IFN-γ. The results indicate that specific interleukins are differentially expressed in K-ras positive patients and the use of K-ras inhibitor Manumycin A decreases both interleukin levels and apoptosis in Caco-2 cells by inhibiting cell viability. Finally, inflammation-driven GM-CSF and IFN-γ levels are modulated through interleukin expression in tumor patients, with interleukin expression in the intestinal lumen and cancerous tissue mediated by aberrant K-ras signaling. Collectively, the findings a) indicate that interleukin expression is influenced by ras signaling and specific interleukins play an oncogenic promoter role in colorectal cancer, highlighting the molecular link between inflammation and tumorigenesis, and b) accentuate the interwoven molecular correlations as leads to new therapeutic approaches in the future.

Candidate serum biomarkers for early intestinal cancer using 15N metabolic labeling and quantitative proteomics in the ApcMin/+ mouse

Current screening procedures for colorectal cancer are imperfect and highly invasive and result in increased mortality rates due to low compliance. The goal of the experiments reported herein is to identify potential blood-based biomarkers indicative of early stage intestinal cancers using the ApcMin/+ mouse model of intestinal cancer as an experimental system. Serum proteins from tumor-bearing ApcMin/+ mice were quantitatively compared to tumor-free Apc+/+ wild-type mice via in anima metabolic labeling with 14N/15N-labeled Spirulina algae and an LTQ Orbitrap mass spectrometer. Out of 1116 total serum proteins quantified, this study identified 40 that were differentially expressed and correlated with the increase in intestinal neoplasms. A subset of these differentially expressed proteins underwent a secondary quantitative screen using selected reaction monitoring-mass spectrometry with stable isotope-labeled peptides. Using both quantitative techniques, we identified MGAM and COL1A1 as downregulated and ITIH3 and F5 as upregulated in serum. All but COL1A1 were similarly differentially expressed in the mRNA of neoplastic colonic tissues of ApcMin/+ mice compared to normal wild-type tissue. These differentially expressed proteins identified in the ApcMin/+ mouse model have provided a set of candidate biomarkers for future validation screens in humans.

The APC p.I1307K polymorphism is a significant risk factor for CRC in average risk Ashkenazi Jews

BACKGROUND

The p.I1307K adenomatous polyposis coli (APC) gene variant, prevalent among Ashkenazi Jews, may increase the risk for colorectal neoplasia. We studied the clinical importance of screening for this polymorphism in 3305 Israelis undergoing colonoscopy.

PATIENTS AND METHODS

Clinical data regarding potential risk factors for colorectal cancer (CRC) were collected from individuals undergoing colonoscopic examination at the Tel-Aviv medical center. The APC p.I1307K was detected using real-time PCR (polymerase chain reaction) from DNA extracted from peripheral mononuclear cells.

RESULTS

The overall prevalence of the p.I1307K polymorphism was 8.0% (10.1% among Ashkenazi and 2.7% among Sephardic Jews, p<0.001). The overall adjusted odds ratio (OR) for colorectal neoplasia among carriers was 1.51 (95% confidence intervals (CI), 1.16-1.98). Among average risk Ashkenazi Jews, the adjusted OR was 1.75 (95% CI 1.26-2.45). A multiplicative interaction was identified between Ashkenazi ethnicity and APC p.I1307K carrier status (P(INTERACTION) = 0.055). The histopathological features of adenomas and carcinomas did not differ between carriers and non-carriers.

CONCLUSIONS

The APC p.I1307K gene variant is an important risk factor for colorectal neoplasia in average risk Ashkenazi Jews. Carriers in this group should be considered for screening colonoscopy at the age of 40, to be repeated every 5 years, similar to recommendations in individuals with family history of colorectal cancer.

Association of common gene variants in the WNT/β-catenin pathway with colon cancer recurrence

Wnt/β-catenin signaling has a central role in the development and progression of most colon cancers (CCs). Germline variants in Wnt/β-catenin pathway genes may result in altered gene function and/or activity, thereby causing inter-individual differences in relation to tumor recurrence capacity and chemoresistance. We investigated germline polymorphisms in a comprehensive panel of Wnt/β-catenin pathway genes to predict time to tumor recurrence (TTR) in patients with stage III and high-risk stage II CC. A total of 234 patients treated with 5-fluorouracil-based chemotherapy were included in this study. Whole-blood samples were analyzed for putative functional germline polymorphisms in SFRP3, SFRP4, DKK2, DKK3, Axin2, APC, TCF7L2, WNT5B, CXXC4, NOTCH2 and GLI1 genes by PCR-based restriction fragment-length polymorphism or direct DNA sequencing. Polymorphisms with statistical significance were validated in an independent study cohort. The minor allele of WNT5B rs2010851 T>G was significantly associated with a shorter TTR (10.7 vs 4.9 years; hazard ratio: 2.48; 95% CI, 0.96-6.38; P=0.04) in high-risk stage II CC patients. This result remained significant in multivariate Cox's regression analysis. This study shows that the WNT5B germline variant rs2010851 was significantly identified as a stage-dependent prognostic marker for CC patients after 5-fluorouracil-based adjuvant therapy.

Functional comparison of human adenomatous polyposis coli (APC) and APC-like in targeting beta-catenin for degradation

Truncating mutations affect the adenomatous polyposis coli (APC) gene in most cases of colon cancer, resulting in the stabilization of β-catenin and uncontrolled cell proliferation. We show here that colon cancer cell lines express also the paralog APC-like (APCL or APC2). RNA interference revealed that it controls the level and/or the activity of β-catenin, but it is less efficient and binds less well to β-catenin than APC, thereby providing one explanation as to why the gene is not mutated in colon cancer. A further comparison indicates that APCL down-regulates the β-catenin level despite the lack of the 15R region known to be important in APC. To understand this discrepancy, we performed immunoprecipitation experiments that revealed that phosphorylated β-catenin displays a preference for binding to the 15 amino acid repeats (15R) rather than the first 20 amino acid repeat of APC. This suggests that the 15R region constitutes a gate connecting the steps of β-catenin phosphorylation and subsequent ubiquitination/degradation. Using RNA interference and domain swapping experiments, we show that APCL benefits from the 15R of truncated APC to target β-catenin for degradation, in a process likely involving heterodimerization of the two partners. Our data suggest that the functional complementation of APCL by APC constitutes a substantial facet of tumour development, because the truncating mutations of APC in colorectal tumours from familial adenomatous polyposis (FAP) patients are almost always selected for the retention of at least one 15R.

Cancer risks and immunohistochemical profiles linked to the Danish MLH1 Lynch syndrome founder mutation

Founder mutations with a large impact in distinct populations have been described in Lynch syndrome. In Denmark, the MLH1 c.1667+2_1667_+8TAAATCAdelinsATTT mutation accounts for 25 % of the MLH1 mutant families. We used the national Danish hereditary nonpolyposis colorectal cancer register to estimate the cumulative lifetime risks for Lynch syndrome-associated cancer in 16 founder mutation families with comparison to 47 other MLH1 mutant families. The founder mutation conferred comparable risks for colorectal cancer (relative risks, RR, of 0.99 for males and 0.79 for females) and lower risks for extracolonic cancer (RR of 0.69 for endometrial cancer and 0.39 for all other extracolonic cancers). We also characterized expression of key Wnt-signaling proteins in colorectal cancers with the founder mutation. Aberrant staining affected β-catenin in 59 %, E-cadherin in 68 %, TCF-4 in 94 % and Cyclin D1 in 68 % with extensive inter-tumor variability despite the same underlying germline mutation. In conclusion, the Danish MLH1 founder mutation that accounts for a significant proportion of Lynch syndrome and is associated with a lower risk for extracolonic cancers.

Treatment with Jian-pi-qing-re-huo-xue detection regulates SW480 cell apoptosis by altering Wnt/β-catenin expression

AIM: To investigate the effect of treatment with Jian-pi-qing-re-huo-xue decoction on SW480 cell proliferation and apoptosis and the expression of β-catenin, TCF-4, c-myc and cyclin D1.

METHODS: SW480 cells were divided into a blank group, an intervention group and a control group, which were incubated with fetal calf serum, different concentrations of serum containing Jian-pi-qing-re-huo-xue decoction, or serum containing mesalamine for 24 h, respectively. The proliferation and apoptosis of SW480 cells were detected by MMT assay and flow cytometry, respectively. The mRNA and protein expression of β-catenin, TCF-4, c-myc, and cyclin D1 was assayed by real-time PCR and Western blot.

RESULTS: Compared to the blank group, the survival of SW480 cells was reduced in the intervention group (P < 0.05). When the dilution concentration of Jian-pi-qing-re-huo-xue decoction was 5%, 10%, 15%, 20% and 30%, the reduced rate of cell growth was 28%, 44.58%, 65.86%, 57.86% and 49.89%, respectively. However, this inhibitory effect was not concentration-dependent (P > 0.05). Intervention with Jian-pi-qing-re-huo-xue decoction significantly increased the percentage of cells at S phase and decreased that of cells at G1 in a concentration-dependent manner compared to the control group (both P < 0.05). β-catenin was more abundantly expressed in the nucleus in the blank group. In the intervention group, the ectopic expression of β-catenin in the cytoplasm and nucleus declined, and membrane expression increased (P < 0.05). Treatment with Jian-pi-qing-re-huo-xue decoction induced cell apoptosis and down-regulated the expression of β-catenin, TCF-4, c-myc, and cyclin D1 compared to the blank group (P < 0.01), and the effect was more significant when middle concentration of serum containing the decoction was used.

CONCLUSION: Jian-pi-qing-re-huo-xue decoction exerts a distinct preventive and therapeutic effect on colon cancer possibly by altering the expression of Wnt/β-catenin, affecting cell cycle progression and inducing cell apoptosis.

β-Sitosterol and flavonoids isolated from Bauhinia malabarica found during screening for Wnt signaling inhibitory activity

Screening with a cell-based luciferase assay was conducted to identify bioactive natural products which inhibit Wnt signaling activity-guided separation of an MeOH extract of Bauhinia malabarica (Caesalpiniaceae) leaves yielded five compounds, which were identified as β-sitosterol (1), quercetin (2), 6,8-C-dimethyl kaempferol-3-O-rhamnopyranoside (3), hyperin (4), and 6,8-C-dimethyl kaempferol-3-methyl ether (5). The tested compounds 1, 3, and 5 exhibited Wnt signaling inhibitory activity, with IC50 values of 0.77, 0.74, and 16.6 μM, respectively.

Differentiation-inducing factor-1 suppresses the expression of c-Myc in the human cancer cell lines

Differentiation-inducing factor-1 (DIF-1), a morphogen for Dictyostelium discoideum, inhibits the proliferation of human cancer cell lines by suppressing the Wnt/β-catenin signaling pathway. In this study, we examined the effect of DIF-1 on c-Myc, a target gene product of the Wnt/β-catenin signaling pathway, mainly using HCT-116 colon cancer cells. DIF-1 strongly reduced the amount of c-Myc protein in time- and concentration-dependent manners and reduced c-Myc mRNA expression by inhibiting promoter activity through the TCF binding sites. The effect of DIF-1 on c-Myc was also confirmed using the human cervical cell line HeLa. Pretreatment with the proteasome inhibitor MG132 or glycogen synthase kinase-3β (GSK-3β) inhibitors (LiCl and SB216763) attenuated the effect of DIF-1, suggesting that DIF-1 induced c-Myc protein degradation through GSK-3β activation. Furthermore, we examined whether c-Myc was involved in the anti-proliferative effect of DIF-1 using c-Myc-overexpressing cells and found that c-Myc was associated with the anti-proliferative effect of this compound. These results suggest that DIF-1 inhibits c-Myc expression by inhibiting promoter activity and inducing protein degradation via GSK-3β activation, resulting in the inhibition of cell proliferation. Since c-Myc seems to be profoundly involved in accelerated proliferation of various malignant tumors, DIF-1 may have a potential to develop into a novel anti-cancer agent.

Inflammation and colorectal cancer: colitis-associated neoplasia

Connection between inflammation and cancer is a rapidly developing field. Epidemiological data suggests that inflammation along with distinct arms of host immune system plays a very important role in the development and progression of many different cancers. Inflammatory bowel disease (IBD) is an important risk factor for the development of colon cancer, namely, colitis-associated cancer (CAC). The molecular mechanisms by which inflammation promotes cancer development are still being uncovered and may differ between CAC and other forms of colorectal cancer. Recent work has shed light on the role of distinct immune cells, cytokines, and other immune mediators in virtually all of the steps of colonic tumorigenesis, including tumor initiation and promotion as well as progression and metastasis. The close proximity of colonic tumors to the myriad of intestinal microbes, as well as instrumental role of microbiota in IBD, introduces microbes as new players capable of triggering inflammation and possibly promoting tumorigenesis. Various mechanisms of CAC tumorigenesis as well as new possible hints for the future approaches for prevention and therapy are discussed in this review.

Analysis of APC and IGFBP7 promoter gene methylation in Swedish and Vietnamese colorectal cancer patients

The tumour suppressor gene adenomatous polyposis coli (APC) is a key component that drives colorectal carcinogenesis. The reported DNA methylation in the promoter of APC varies greatly among studies of colorectal cancer (CRC) in different populations. Insulin-like growth factor binding protein 7 (IGFBP7), also known as IGFBP-related protein 1 (IGFBP-rP1), is expressed in various tissue types, including the lung, brain, prostate and gastrointestinal tract, and has been suggested to play a tumour suppressor role against colorectal carcinogenesis. Studies have indicated that IGFBP7 is inactivated by DNA methylation in human colon, lung and breast cancer. In the present study, we used the methylation-specific polymerase chain reaction to study the methylation status of the APC and IGFBP7 gene promoters in cancerous and paired normal tissue to evaluate its impact on clinical factors and association with ethnicity, represented by Swedish and Vietnamese CRC patients. We also investigated the distribution of CpG islands and the CpG dinucleotide density of each CpG island in the regions which were the subject of our investigation. Overall, normal tissue from Swedish patients exhibited a significantly higher frequency of IGFBP7 gene methylation in comparison with that of Vietnamese patients. Moreover, a significantly higher number of cancer tissues from Vietnamese individuals showed higher levels of methylation versus the paired normal tissue compared with that of Swedish patients. When we studied the methylation in cancer compared with the matched normal tissue in individuals, we found that a significantly higher number of Vietnamese patients had a higher degree of IGFBP7 gene methylation in cancer versus matched normal tissue in comparison with Swedish patients. Taken together, our results suggest that the methylation of the APC and IGFBP7 gene promoter region in cancerous tissue, in combination with the predominance of methylation in normal tissue, may serve as a prognostic factor in CRC patients.

Cancer syndromes and therapy by stop-codon readthrough

Several hereditary cancer syndromes are associated with nonsense mutations that create premature termination codons (PTC). Therapeutic strategies involving readthrough induction partially restore expression of proteins with normal function from nonsense-mutated genes, and small molecules such as aminoglycosides and PTC124 have exhibited promising results for treating patients with cystic fibrosis and Duchenne muscular dystrophy. Transgenic expression of suppressor-tRNAs and depleting translation termination factors are, among others, potential strategies for treating PTC-associated diseases. In this review, the potential of using readthrough strategies as a therapy for cancer syndromes is discussed, and we consider the effect of nonsense-mediated decay and other factors on readthrough efficiency.

Wnt signaling in gut organogenesis

Wnt signaling regulates some aspect of development of nearly all endoderm-derived organs and Wnts mediate both differentiation and proliferation at different steps during visceral organogenesis. Wnt2b induces liver formation in zebrafish 1 and may combine with other inducers, Fibroblast Growth Factors 1 & 4 and Bone Morphogenetic Protein 4, to specify the mammalian liver.2-5 Later in development, Wnts are critical for liver expansion and, finally, for terminal hepatocyte differentiation,6-12 as reviewed elsewhere in this issue (Monga). Likewise, in the pancreas, Wnts drive proliferation of exocrine and endocrine cells13,14 and promote acinar cell differentiation,13,15 as reviewed in the chapter by Murtaugh. Here we examine the intricate involvement of Wnt signaling in growth and differentiation of the digestive tract.

Inhibition of Tcf-4 induces apoptosis and enhances chemosensitivity of colon cancer cells

Aberrant activation of β-catenin/Tcf-4 signaling has been implicated in human carcinogenesis, including colorectal cancer. In this study, we compared the effects of Tcf-4 knockdown with β-catenin knockdown on cell proliferation, apoptosis, and chemosensitivity in SW480 and HCT116 colon cancer cells using adenoviral vector-mediated short hairpin RNA (shRNA). Our results show that, compared to β-catenin knockdown, Tcf-4 knockdown more effectively inhibited colony formation, induced apoptosis, and increased 5-FU and oxaliplatin-mediated cytotoxicity in colon cancer cells. We further investigated the mechanisms involved in the different efficacies observed with β-catenin and Tcf-4 knockdown in colon cancer cells. FOXO4 is a member of the subfamily of mammalian FOXO forkhead transcription factors and plays a major role in controlling cellular proliferation, apoptosis, and DNA repair. Our data showed that the protein level of FOXO4 did not change after treatment with both β-catenin and Tcf-4 shRNA. However, β-catenin shRNA was found to increase the accumulation of phosphorylated FOXO4 S193 and decrease the expression of FOXO target genes p27Kip1 and MnSOD, whereas Tcf-4 shRNA showed the opposite effect. Therefore, compared to β-catenin knockdown, Tcf-4 knockdown shows better efficacy for inhibiting proliferation and inducing apoptosis of colorectal cancer cells, which may be related to increased FOXO4 transcriptional activity. These results suggest that Tcf-4 is an attractive potential therapeutic target for colorectal cancer therapy.

The Wnt/β-catenin/T-cell factor 4 pathway up-regulates high-mobility group A1 expression in colon cancer

High-mobility group A1 (HMGA1) encodes proteins that act as mediators in viral integration, modification of chromatin structure, neoplastic transformation and metastatic progression. Because HMGA1 is overexpressed in most cancers and has transcriptional relationships with several Wnt-responsive genes, we explored the involvement of HMGA1 in Wnt/β-catenin/TCF-4 signalling. In adenomatous polyposis coli (APC(Min/+)) mice, we observed significant up-regulation of HMGA1 mRNA and protein in intestinal tumours when compared with normal intestinal mucosa. Conversely, restoration of Wnt signalling by the zinc induction of wild-type APC resulted in HMGA1 down-regulation in HT-29 cells. Because APC mutations are associated with mobilization of the β-catenin/TCF-4 transcriptional complex and subsequent activation of downstream oncogenic targets, we analyzed the 5'-flanking sequence of HMGA1 for putative TCF-4 binding elements. We identified two regions that specifically bind the β-catenin/TCF-4 complex in vitro and in vivo, identifying HMGA1 as an immediate target of the β-catenin/TCF-4 signalling pathway in colon cancer. Collectively, these findings strongly implicate Wnt/β-catenin/TCF-4 signalling in regulating HMGA1 to further expand the extensive regulatory network affected by Wnt/β-catenin/TCF-4 signalling.

Association of APC and REEP5 gene polymorphisms with major depression disorder and treatment response to antidepressants in a Han Chinese population

OBJECTIVE

Despite the high prevalence of depression and its considerable impact on the population, knowledge about the pathogenesis of the illness and the antidepressant treatment response is still unknown.

METHODS

A total of 397 patients with major depression disorder (MDD) and 473 normal controls were employed in the present research. Twelve single nucleotide polymorphisms (SNPs) within the adenomatous polyposis coli (APC) and receptor accessory protein (REEP5) genes were selected for genotyping using the GoldenGate genotyping assay. A total of 165 MDD patients completed a 6-week antidepressant treatment. Responders were defined as patients with at least a 50% reduction in Hamilton Rating Scale for Depression total scores posttreatment.

RESULTS

Two SNPs (rs2464805 and rs563556) within the APC gene exhibited a statistically significant association with MDD when analyzed by genotype and allele frequencies. Three SNPs (rs495794, rs153549 and rs153560) in the REEP5 gene showed significant statistical differences between the responders and nonresponders.

CONCLUSIONS

The APC gene may be one of the susceptibility genes for MDD as well as a genetic link between psychiatric disease and cancer. REEP5 gene polymorphisms may influence antidepressant treatment response in MDD.

Analysis of bacteria from intestinal tract of FAP patients for the presence of APC-like sequences

Background

Familial adenomatous polyposis (FAP) is a hereditary disease induced by germ-line mutations in the tumor suppressor APC gene. These initiate the early stages of the adenoma-carcinoma sequence in familial, but also in sporadic (in 80% to 90%), colon tumorigenesis. We found the presence of APC-like sequences in bacteria of FAP patients.

Material/Methods

We analyzed bacteria isolated from FAP patients’ rectal swabs. Total bacterial DNA was isolated and analyzed for detection of APC-like sequences using PCR. We also tested DNA homology rate and APC-like protein production.

Results

We collected blood samples and rectal swabs from patients with confirmed diagnosis of FAP. They were analyzed for presence of sections from exon 15 of the APC gene. Most positive results were found in sections located exactly in the area called the MCR (mutation cluster region), where the highest frequency of APC gene mutations were identified. By sequencing PCR products from bacteria in section F–G together with a patient’s DNA sample and human APC gene, we found a more than 90% DNA homology rate. We also confirmed production of APC-like protein using Western blotting.

Conclusions

Our results suggested two hypotheses. The APC-like protein might have same function as a truncated APC product, which is synthesized in most cases of mutations of APC gene in the MCR region in colorectal cancer cells. Alternatively, we can consider the possible existence of horizontal transfer of genetic information between eukaryotic and prokaryotic cells. Our study can be considered as a pilot project. For confirmation of our hypotheses, further research is needed.

A common role for various human truncated adenomatous polyposis coli isoforms in the control of beta-catenin activity and cell proliferation

The tumour suppressor gene adenomatous polyposis coli (APC) is mutated in most colorectal cancer cases, leading to the synthesis of truncated APC products and the stabilization of β-catenin. Truncated APC is almost always retained in tumour cells, suggesting that it serves an essential function. Here, RNA interference has been used to down-regulate truncated APC in several colorectal cancer cell lines expressing truncated APCs of different lengths, thereby performing an analysis covering most of the mutation cluster region (MCR). The consequences on proliferation in vitro, tumour formation in vivo and the level and transcriptional activity of β-catenin have been investigated. Down-regulation of truncated APC results in an inhibition of tumour cell population expansion in vitro in 6 cell lines out of 6 and inhibition of tumour outgrowth in vivo as analysed in one of these cell lines, HT29. This provides a general rule explaining the retention of truncated APC in colorectal tumours and defines it as a suitable target for therapeutic intervention. Actually, we also show that it is possible to design a shRNA that targets a specific truncated isoform of APC without altering the expression of wild-type APC. Down-regulation of truncated APC is accompanied by an up-regulation of the transcriptional activity of β-catenin in 5 out of 6 cell lines. Surprisingly, the increased signalling is associated in most cases (4 out of 5) with an up-regulation of β-catenin levels, indicating that truncated APC can still modulate wnt signalling through controlling the level of β-catenin. This control can happen even when truncated APC lacks the β-catenin inhibiting domain (CiD) involved in targeting β-catenin for proteasomal degradation. Thus, truncated APC is an essential component of colorectal cancer cells, required for cell proliferation, possibly by adjusting β-catenin signalling to the “just right” level.

Vitamin D and cancer: a review of molecular mechanisms

The population-based association between low vitamin D status and increased cancer risk can be inconsistent, but it is now generally accepted. These relationships link low serum 25OHD (25-hydroxyvitamin D) levels to cancer, whereas cell-based studies show that the metabolite 1,25(OH)2D (1,25-dihydroxyvitamin D) is a biologically active metabolite that works through vitamin D receptor to regulate gene transcription. In the present review we discuss the literature relevant to the molecular events that may account for the beneficial impact of vitamin D on cancer prevention or treatment. These data show that although vitamin D-induced growth arrest and apoptosis of tumour cells or their non-neoplastic progenitors are plausible mechanisms, other chemoprotective mechanisms are also worthy of consideration. These alternative mechanisms include enhancing DNA repair, antioxidant protection and immunomodulation. In addition, other cell targets, such as the stromal cells, endothelial cells and cells of the immune system, may be regulated by 1,25(OH)2D and contribute to vitamin D-mediated cancer prevention.