APC, beta-Catenin and hTCF-4; an unholy trinity in the genesis of colorectal cancer

Specific small interfering RNAs (siRNAs) for targeting the metastasis, immune responses, and drug resistance of colorectal cancer cells (CRC)

Colorectal cancer (CRC) involves various genetic alterations, with liver metastasis posing a significant clinical challenge. Furthermore, CRC cells mostly show an increase in resistance to traditional treatments like chemotherapy. It is essential to investigate more advanced and effective therapies to prevent medication resistance and metastases and extend patient life. As a result, it is anticipated that small interfering RNAs (siRNAs) would be exceptional instruments that can control gene expression by RNA interference (RNAi). In eukaryotes, RNAi is a biological mechanism that destroys specific messenger RNA (mRNA) molecules, thereby inhibiting gene expression. In the management of CRC, this method of treatment represents a potential therapeutic agent. However, it is important to acknowledge that siRNA therapies have significant issues, such as low serum stability and nonspecific absorption into biological systems. Delivery mechanisms are thus being created to address these issues. In the current work, we address the potential benefits of siRNA therapy and outline the difficulties in treating CRCby focusing on the primary signaling pathways linked to metastasis as well as genes implicated in the multi-drug resistance (MDR) process.

Blocking the Wnt/β‑catenin signaling pathway to treat colorectal cancer: Strategies to improve current therapies (Review)

Colorectal cancer (CRC) is one of the most common malignant tumor types occurring in the digestive system. The incidence of CRC has exhibits yearly increases and the mortality rate among patients with CRC is high. The Wnt/β‑catenin signaling pathway, which is associated with carcinogenesis, is abnormally activated in CRC. Most patients with CRC have adenomatous polyposis coli mutations, while half of the remaining patients have β‑catenin gene mutations. Therefore, targeting the Wnt/β‑catenin signaling pathway for the treatment of CRC is of clinical value. In recent years, with in‑depth research on the Wnt/β‑catenin signaling pathway, inhibitors have been developed that are able to suppress or hinder the development and progression of CRC. In the present review, the role of the Wnt/β‑catenin signaling pathway in CRC is summarized, the research status on Wnt/β‑catenin pathway inhibitors is outlined and potential targets for inhibition of this pathway are presented.

Regulation of epithelial-mesenchymal transition and organoid morphogenesis by a novel TGFβ-TCF7L2 isoform-specific signaling pathway

Alternative splicing contributes to diversification of gene function, yet consequences of splicing on functions of specific gene products is poorly understood. The major transcription factor TCF7L2 undergoes alternative splicing but the biological significance of TCF7L2 isoforms has remained largely to be elucidated. Here, we find that the TCF7L2 E-isoforms maintain, whereas the M and S isoforms disrupt morphogenesis of 3D-epithelial cell-derived organoids via regulation of epithelial-mesenchymal transition (EMT). Remarkably, TCF7L2E2 antagonizes, whereas TCF7L2M2/S2 promotes EMT-like effects in epithelial cells induced by transforming growth factor beta (TGFβ) signaling. In addition, we find TGFβ signaling reduces the proportion of TCF7L2E to TCF7L2M/S protein in cells undergoing EMT. We also find that TCF7L2 operates via TGFβ-Smad3 signaling to regulate EMT. Collectively, our findings unveil novel isoform-specific functions for the major transcription factor TCF7L2 and provide novel links between TCF7L2 and TGFβ signaling in the control of EMT-like responses and epithelial tissue morphogenesis.

The genetic factors associated with Wnt signaling pathway in colorectal cancer

Colorectal cancer (CRC) is a common cancer with poor prognosis and high mortality. There is growing information about the factors involved in the pathogenesis of CRC. However, the knowledge of the predisposing factors is limited. The development of CRC is strongly associated with the Wingless/Integrated (Wnt) signaling pathway. This pathway comprises several major target proteins, including LRP5/6, GSK3β, adenomatous polyposis coli (APC), axis inhibition protein (Axin), and β-catenin. Genetic variations in these components of the Wnt signaling pathway may lead to the activation of β-catenin, potentially increasing the proliferation of colorectal cells. Because of the potentially important role of the Wnt signaling pathway in CRC, we aimed to review the involvement of different mutations in the main downstream proteins of this pathway, including LRP5/6, APC, GSK3β, Axin, and β-catenin. Determination of the genetic risk factors involved in the progression of CRC may lead to novel approaches for the early diagnosis of CRC and the identification of potential therapeutic targets in the treatment of CRC.

Biochemical and molecular aspects of 1,2-dimethylhydrazine (DMH)-induced colon carcinogenesis: a review

1,2-dimethylhydrazine (DMH) is a member in the class of hydrazines, strong DNA alkylating agent, naturally present in cycads. DMH is widely used as a carcinogen to induce colon cancer in animal models. Exploration of DMH-induced colon carcinogenesis in rodent models provides the knowledge to perceive the biochemical, molecular, and histological mechanisms of different stages of colon carcinogenesis. The procarcinogen DMH, after a series of metabolic reactions, finally reaches the colon, there produces the ultimate carcinogen and reactive oxygen species (ROS), which further alkylate the DNA and initiate the development of colon carcinogenesis. The preneolpastic lesions and histopathological observations of DMH-induced colon tumors may provide typical understanding about the disease in rodents and humans. In addition, this review discusses about the action of biotransformation and antioxidant enzymes involved in DMH intoxication. This understanding is essential to accurately identify and interpret alterations that occur in the colonic mucosa when evaluating natural or pharmacological compounds in DMH-induced animal colon carcinogenesis.

Role of adenomatous polyposis coli (APC) gene mutations in the pathogenesis of colorectal cancer; current status and perspectives

Colorectal cancer (CRC) is one of the most common forms of solid tumors in the world with high rates of mortality and morbidity. Most cases of CRCs are initiated by inactivating mutations in a tumor suppressor gene, adenomatous polyposis coli (APC), leading to constitutive activation of the Wnt signaling pathway. This review summarizes the roles of somatic and germline mutations of the APC gene in hereditary as well as sporadic forms of CRC. We also discuss the diagnostic and prognostic value of the APC gene in the pathogenesis of CRC for a better understanding of CRC disease.

Mismatch Repair Protein MSH2 Expression and Prognosis of Colorectal Cancer Patients

Introduction and aims

The role of genetic factors in the etiology and prognosis of patients with sporadic colorectal cancer is controversial. We have therefore investigated the biological and clinicopathological influence of immunohistochemical MSH2 expression in colorectal cancer.

Patients and methods

A total of 49 consecutive patients with unselected colorectal cancer operated on in our unit were included in the study. All tumors were resected and tumor specimens were evaluated for MSH2 expression. Clinicopathological data and patient survival were correlated with MSH2 staining. Uni- and multivariate analyses were performed. The minimum follow-up period was five years.

Results

Curative resection was performed in 34 patients (64.9%), 14 of whom subsequently relapsed. At the end of the overall follow-up 25 (51%) patients had died, 21 of cancer-related causes. Twenty-eight patients (57.1%) were negative for MSH2 staining. Only vascular invasion was significantly correlated with MSH2 expression (lower median values; p=0.04). The overall median survival was 47.9 months (95% CI=27–86.6%). Multivariate analysis of variables in relation to survival showed that T stage (p=0.001), N stage (p<0.001) and MSH2 expression (p=0.01) were independent factors for survival.

Conclusions

Reduced MSH2 expression is frequent in unselected colorectal cancer patients. Only vascular invasion was correlated with MSH2 expression in this study. Survival was related to TN stage and MSH2 staining.

Wnt, RSPO and Hippo Signalling in the Intestine and Intestinal Stem Cells

In this review, we address aspects of Wnt, R-Spondin (RSPO) and Hippo signalling, in both healthy and transformed intestinal epithelium. In intestinal stem cells (ISCs), the Wnt pathway is essential for intestinal crypt formation and renewal, whereas RSPO-mediated signalling mainly affects ISC numbers. In human colorectal cancer (CRC), aberrant Wnt signalling is the driving mechanism initiating this type of neoplasia. The signalling role of the RSPO-binding transmembrane proteins, the leucine-rich-repeat-containing G-protein-coupled receptors (LGRs), is possibly more pleiotropic and not only limited to the enhancement of Wnt signalling. There is growing evidence for multiple crosstalk between Hippo and Wnt/β-catenin signalling. In the ON state, Hippo signalling results in serine/threonine phosphorylation of Yes-associated protein (YAP1) and tafazzin (TAZ), promoting formation of the β-catenin destruction complex. In contrast, YAP1 or TAZ dephosphorylation (and YAP1 methylation) results in β-catenin destruction complex deactivation and β-catenin nuclear localization. In the Hippo OFF state, YAP1 and TAZ are engaged with the nuclear β-catenin and participate in the β-catenin-dependent transcription program. Interestingly, YAP1/TAZ are dispensable for intestinal homeostasis; however, upon Wnt pathway hyperactivation, the proteins together with TEA domain (TEAD) transcription factors drive the transcriptional program essential for intestinal cell transformation. In addition, in many CRC cells, YAP1 phosphorylation by YES proto-oncogene 1 tyrosine kinase (YES1) leads to the formation of a transcriptional complex that includes YAP1, β-catenin and T-box 5 (TBX5) DNA-binding protein. YAP1/β-catenin/T-box 5-mediated transcription is necessary for CRC cell proliferation and survival. Interestingly, dishevelled (DVL) appears to be an important mediator involved in both Wnt and Hippo (YAP1/TAZ) signalling and some of the DVL functions were assigned to the nuclear DVL pool. Wnt ligands can trigger alternative signalling that directly involves some of the Hippo pathway components such as YAP1, TAZ and TEADs. By upregulating Wnt pathway agonists, the alternative Wnt signalling can inhibit the canonical Wnt pathway activity.

Effects on the transcriptome upon deletion of a distal element cannot be predicted by the size of the H3K27Ac peak in human cells

Genome-wide association studies (GWAS) have identified single nucleotide polymorphisms (SNPs) associated with increased risk for colorectal cancer (CRC). A molecular understanding of the functional consequences of this genetic variation is complicated because most GWAS SNPs are located in non-coding regions. We used epigenomic information to identify H3K27Ac peaks in HCT116 colon cancer cells that harbor SNPs associated with an increased risk for CRC. Employing CRISPR/Cas9 nucleases, we deleted a CRC risk-associated H3K27Ac peak from HCT116 cells and observed large-scale changes in gene expression, resulting in decreased expression of many nearby genes. As a comparison, we showed that deletion of a robust H3K27Ac peak not associated with CRC had minimal effects on the transcriptome. Interestingly, although there is no H3K27Ac peak in HEK293 cells in the E7 region, deletion of this region in HEK293 cells decreased expression of several of the same genes that were downregulated in HCT116 cells, including the MYC oncogene. Accordingly, deletion of E7 causes changes in cell culture assays in HCT116 and HEK293 cells. In summary, we show that effects on the transcriptome upon deletion of a distal regulatory element cannot be predicted by the size or presence of an H3K27Ac peak.

Modulation of P-glycoprotein efflux pump: induction and activation as a therapeutic strategy

P-glycoprotein (P-gp) is an ATP-dependent efflux pump encoded by the MDR1 gene in humans, known to mediate multidrug resistance of neoplastic cells to cancer therapy. For several decades, P-gp inhibition has drawn many significant research efforts in an attempt to overcome this phenomenon. However, P-gp is also constitutively expressed in normal human epithelial tissues and, due to its broad substrate specificity, to its cellular polarized expression in many excretory and barrier tissues, and to its great efflux capacity, it can play a crucial role in limiting the absorption and distribution of harmful xenobiotics, by decreasing their intracellular accumulation. Such a defense mechanism can be of particular relevance at the intestinal level, by significantly reducing the intestinal absorption of the xenobiotic and, consequently, avoiding its access to the target organs. In this review, the current knowledge on this important efflux pump is summarized, and a new focus is brought on the therapeutic interest of inducing and/or activating P-gp for limiting the toxicity caused by its substrates. Several in vivo and in vitro studies validating the use of such a therapeutic strategy are discussed. An extensive literature search for reported P-gp inducers/activators and for the experimental models used in their characterization was conducted. Those studies demonstrate that effective antidotal pathways can be achieved by efficiently promoting the P-gp-mediated efflux of deleterious xenobiotics, resulting in a significant reduction in their intracellular levels and, consequently, in a significant reduction of their toxicity.

LincRNA-p21 enhances the sensitivity of radiotherapy for human colorectal cancer by targeting the Wnt/β-catenin signaling pathway

Recent studies show that long intergenic noncoding RNA-p21 (lincRNA-p21) is aberrantly expressed in several types of cancer, including colorectal cancer (CRC), one of the most common cancers in the world. Radiotherapy is considered as a standard preoperative treatment approach to reduce local recurrence for local advanced rectal cancer. However, a considerable number of rectal cancers are resistant to radiotherapy. In the present study, we evaluated the role of lincRNA‑p21 in radiotherapy for CRC and detected the possible molecular mechanism. By expression profile analysis, we demonstrated that lincRNA-p21 decreases in CRC cell lines and tissue samples, which contributes to the elevation of β-catenin in CRC. We further showed that lincRNA‑p21 increases following X-ray treatment, and enforced expression of the lincRNA enhances the sensitivity of radiotherapy for CRC by promoting cell apoptosis. Suppression of the β-catenin signaling pathway and elevation of the pro-apoptosis gene Noxa expression may help explain the role of lincRNA-p21 in CRC radiotherapy. The present study not only deepens our understanding of the mechanism of radiotherapy for CRC, but it also provides a potential target for CRC radiotherapy.

Oxidative DNA damage and β-catenin expression in colorectal cancer evolution

PURPOSE

Oxidative DNA damage is one of the mechanisms associated to initial colorectal carcinogenesis, but how it interacts with β-catenin, an adherence protein related to cancer evolution, is not clear. This study investigates the relationship between oxidative DNA damage and β-catenin expression in normal mucosa and colon tumor tissue (adenoma and adenocarcinoma) in colorectal adenocarcinoma evolution.

METHOD

One hundred and 13 samples were studied. Hematoxylin-eosin determined histological grade. β-Catenin expression was analyzed by immunohistochemistry. The oxidative DNA damage was evaluated using comet assay technique. The coefficient for rejection of the nullity hypothesis was taken to 5 %. Kruskal-Wallis, Spearman test, and partial correlation were used to analyze the data.

RESULTS

There was oxidative DNA damage increase in colorectal cancer evolution (p < 0.01). Histological grade was correlated with oxidative DNA damage (p < 0.01). There were differences in β-catenin expression among normal, adenoma, and adenocarcinoma tissue with progressive increase of β-catenin expression (p < 0.00). Histological grade was correlated to β-catenin expression (p < 0.00). There was a relationship (p < 0.00) between β-catenin and histological grade while controlling for the effect of oxidative DNA damage.

CONCLUSION

The findings of this study make it possible to establish a relationship between oxidative DNA damage and β-catenin expression in normal mucosa and colorectal tumor tissue. Additionally, they show a causal relationship between variations of β-catenin in different tissues analyzed while controlling for the effect of oxidative DNA damage.

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.

Wnt/β-catenin signaling mediates the antitumor activity of magnolol in colorectal cancer cells

Abnormal activation of the canonical Wnt/β-catenin pathway and up-regulation of the β-catenin/T-cell factor (TCF) response to transcriptional signaling play a critical role early in colorectal carcinogenesis. Therefore, Wnt/β-catenin signaling is considered an attractive target for cancer chemotherapeutic or chemopreventive agents. Small molecules derived from the natural products were used in our cell-based reporter gene assay to identify potential inhibitors of Wnt/β-catenin signaling. Magnolol, a neolignan from the cortex of Magnolia obovata, was identified as a promising candidate because it effectively inhibited β-catenin/TCF reporter gene (TOPflash) activity. Magnolol also suppressed Wnt3a-induced β-catenin translocation and subsequent target gene expression in human embryonic kidney 293 cells. To further investigate the precise mechanisms of action in the regulation of Wnt/β-catenin signaling by magnolol, we performed Western blot analysis, real-time reverse transcriptase-polymerase chain reactions, and an electrophoretic mobility shift assay in human colon cancer cells with aberrantly activated Wnt/β-catenin signaling. Magnolol inhibited the nuclear translocation of β-catenin and significantly suppressed the binding of β-catenin/TCF complexes onto their specific DNA-binding sites in the nucleus. These events led to the down-regulation of β-catenin/TCF-targeted downstream genes such as c-myc, matrix metalloproteinase-7, and urokinase-type plasminogen activator in SW480 and HCT116 human colon cancer cells. In addition, magnolol inhibited the invasion and motility of tumor cells and exhibited antitumor activity in a xenograft nude mouse model bearing HCT116 cells. These findings suggest that the growth inhibition of magnolol against human colon cancer cells can be partly attributed to the regulation of the Wnt/β-catenin signaling pathway.

Endoplasmic reticulum calcium pumps and cancer cell differentiation

The endoplasmic reticulum (ER) is a major intracellular calcium storage pool and a multifunctional organelle that accomplishes several calcium-dependent functions involved in many homeostatic and signaling mechanisms. Calcium is accumulated in the ER by Sarco/Endoplasmic Reticulum Calcium ATPase (SERCA)-type calcium pumps. SERCA activity can determine ER calcium content available for intra-ER functions and for calcium release into the cytosol, and can shape the spatiotemporal characteristics of calcium signals. SERCA function therefore constitutes an important nodal point in the regulation of cellular calcium homeostasis and signaling, and can exert important effects on cell growth, differentiation and survival. In several cell types such as cells of hematopoietic origin, mammary, gastric and colonic epithelium, SERCA2 and SERCA3-type calcium pumps are simultaneously expressed, and SERCA3 expression levels undergo significant changes during cell differentiation, activation or immortalization. In addition, SERCA3 expression is decreased or lost in several tumor types when compared to the corresponding normal tissue. These observations indicate that ER calcium homeostasis is remodeled during cell differentiation, and may present defects due to decreased SERCA3 expression in tumors. Modulation of the state of differentiation of the ER reflected by SERCA3 expression constitutes an interesting new aspect of cell differentiation and tumor biology.

The LMP7-K allele of the immunoproteasome exhibits reduced transcript stability and predicts high risk of colon cancer

Destruction of cancer cells by cytotoxic T lymphocytes depends on immunogenic tumor peptides generated by proteasomes and presented by human leukocyte antigen (HLA) molecules. Functional differences arising from alleles of immunoproteasome subunits have not been recognized so far. We analyzed the genetic polymorphism of the immunoproteasome subunits LMP2 and LMP7 and of the transporters associated with antigen processing (TAP1 and TAP2) in two independently collected panels of colorectal carcinoma patients (N(1) = 112, N(2) = 62; controls, N = 165). High risk of colon cancer was associated with the LMP7-K/Q genotype (OR = 8.10, P = 1.10 × 10(-11)) and low risk with the LMP7-Q/Q genotype (OR = 0.10, P = 5.97 × 10(-13)). The basis for these distinct associations of LMP7 genotypes was functionally assessed by IFN-γ stimulation of colon carcinoma cell lines (N = 10), followed by analyses of mRNA expression of HLA class I, TAP1, TAP2, and LMP7, with real-time PCR. Whereas induction of HLA-B, TAP1, and TAP2 was comparable in all cell lines, transcript amounts of LMP7-Q increased 10-fold, but of LMP7-K only 3.8-fold. This correlated with a reduced transcript stability of LMP7-K (t(1/2) ≈ 7 minutes) compared with LMP7-Q (t(1/2) ≈ 33 minutes). In addition, LMP7-Q/Q colon carcinoma cells increased (the peptide based) HLA class I surface expression significantly after IFN-γ stimulation, whereas LMP7-Q/K and LMP7-K/K carcinoma cells showed minimal (<20%) changes. These results suggest that the presence of LMP7-K can reduce the formation of immunoproteasomes and thus peptide processing, followed by reduced peptide-HLA presentation, a crucial factor in the immune response against cancer.

Expression of trefoil factor family-3 and β-catenin in different types of colorectal mucosal lesions

AIM: To analyze the expression of trefoil factor family-3 (TFF3) and β-catenin in different types of colorectal mucosal lesions and to explore their role in the development and progression of colorectal adenocarcinoma and adenoma.

METHODS: The expression of TFF3 and β-catenin was detected by immunohistochemistry in 20 normal colorectal mucosa specimens, 30 colorectal polyp specimens, 20 colorectal adenoma (CRA) specimens, 20 colorectal adenoma (with atypical hyperplasia, CRAAH) specimens, and 40 colorectal adenocarcinoma (CRCA) specimens. The differences in the expression of TFF3 and β-catenin in different types of colorectal mucosal lesions were compared.

RESULTS: The positive rate of TFF3 expression was significantly lower in CRA and CRAAH (P < 0.05), but higher in CRCA. The abnormal expression of β-catenin were gradually increasing along with the sequence of CRA→CRAAH→CRAC, the membrane expressing deletion and ectopic expression were both higher in CRAC than in CRCP and CRA (60.00% vs 0.00%, 15.00%; 75.00% vs 0.00%, 40.00%, all P < 0.05). TFF3 expression was not correlated with tumor location or differentiation in CRAC, but was related to lymph node metastasis and Duke's stage (both P < 0.05). β-catenin expression was not correlated with tumor location or lymph node metastasis, but was related to tumor differentiation. Ectopic expression of β-catenin was related to Duke's stage (P < 0.05). There were significantly positive correlations between TFF3 expression and abnormal expression and loss of membrane expression of β-catenin in CRA (r = 0.427, P = 0.006; r = 0.577, P = 0.000) but not in CRAC (r = 0.015, P = 0.951; r = 0.385, P = 0.094). There was a significantly positive correlation between loss of membrane expression and ectopic expression of β-catenin in CRAC and CRA (r = 0.638, P = 0.000; r = 0.514, P = 0.020).

CONCLUSION: The expression of TFF3 and β-catenin is closely related with the development and progression of CRAC. They may be involved in an early event in colorectal carcinogenesis. TFF3 is related to the abnormal expression of β-catenin, both of which may be involved in the development and progression of CRAC.

Endoplasmic reticulum calcium pumps and cancer

Endoplasmic reticulum calcium homeostasis is involved in a multitude of signaling, as well as "house-keeping" functions that control cell growth, differentiation or apoptosis in every human/eukaryotic cell. Calcium is actively accumulated in the endoplasmic reticulum by Sarco/Endoplasmic Reticulum Calcium transport ATPases (SERCA enzymes). SERCA-dependent calcium transport is the only calcium uptake mechanism in this organelle, and therefore the regulation of SERCA function by the cell constitutes a key mechanism to adjust calcium homeostasis in the endoplasmic reticulum depending on the cell type and its state of differentiation. The direct pharmacological modulation of SERCA activity affects cell differentiation and survival. SERCA expression levels can undergo significant changes during cell differentiation or tumorigenesis, leading to modified endoplasmic reticulum calcium storage. In several cell types such as cells of hematopoietic origin or various epithelial cells, two SERCA genes (SERCA2 and SERCA3) are simultaneously expressed. Expression levels of SERCA3, a lower calcium affinity calcium pump are highly variable. In several cell systems SERCA3 expression is selectively induced during differentiation, whereas during tumorigenesis and blastic transformation SERCA3 expression is decreased. These observations point at the existence of a cross-talk, via the regulation of SERCA3 levels, between endoplasmic reticulum calcium homeostasis and the control of cell differentiation, and show that endoplasmic reticulum calcium homeostasis itself can undergo remodeling during differentiation. The investigation of the anomalies of endoplasmic reticulum differentiation in tumor and leukemia cells may be useful for a better understanding of the contribution of calcium signaling to the establishment of malignant phenotypes.

Cytoplasmic beta-catenin accumulation is a good prognostic marker in upper and lower gastrointestinal adenocarcinomas

AIMS

beta-Catenin is an important molecule in cancer biology. Membranous beta-catenin enhances cellular differentiation and inhibits invasion by its action on E-cadherin. The aim was to ascertain whether the cellular expression of these molecules in colorectal and oesophageal cancer specimens is associated with survival in patients with gastrointestinal cancer.

METHODS AND RESULTS

Tumour samples from 149 patients undergoing resection for colorectal adenocarcinoma and 147 patients undergoing resection for oesophageal adenocarcinoma were retrospectively analysed using immunohistochemical techniques to assess beta-catenin expression. Increasing beta-catenin expression in the cytoplasm was associated with improved survival for colorectal cancer cases on both univariate (P = 0.003) and multivariate (P = 0.01) analysis. In addition, increased expression in the most recent cohort of oesophageal adenocarcinoma patients was associated with improved TNM staging (P = 0.007). Membrane expression was weakly associated with survival in colorectal cancer on univariate analysis (P = 0.09), but not on multivariate analysis (P = 0.21). Complete absence of beta-catenin expression at all three sites was associated with reduced 5-year survival in colorectal cancer.

CONCLUSIONS

This is one of the largest prognostic studies of beta-catenin in gastrointestinal adenocarcinoma. It shows that low levels of cytoplasmic beta-catenin expression are associated with reduced survival in patients with colorectal cancer as well as worse TNM staging in oesophageal adenocarcinoma (a recognized surrogate end-point for survival). We believe this is the first time that this has been reported. This finding should be tested prospectively in oncological trials to validate whether the presence of cytoplasmic beta-catenin could be used as a prognostic marker for less aggressive disease.

Quercetin inhibit human SW480 colon cancer growth in association with inhibition of cyclin D1 and survivin expression through Wnt/beta-catenin signaling pathway

AIM

The Wnt signaling pathway plays a pivotal role in cellular developmental processes and human carcinogenesis. The aim of this study was to investigate the effects of quercetin on the growth of the colon carcinoma cell line and the regulation effect of quercetin on the Wnt/beta-catenin signaling pathway.

METHODS

MTT assay was used to determine the reduction of cell viability of quercetin on SW480 cells and clone 26 cells. The apoptotic rate and cell-cycle analysis after treatment with quercetin was determined by flow cytometry. Effects of quercetin on mRNA expression of cyclin D(1) and survivin were detected by semiquantitative RT-PCR. After treatment with quercetin, the protein expression of cyclin D(1) and survivin in SW480 cells was analyzed by Western blot analysis. We built a Wnt/beta-catenin signaling pathway reporter gene model. The regulation effect of quercetin on the Wnt/beta-catenin signaling transcription was investigated by using this reporter gene model.

RESULTS

Quercetin reduced cell viability in a dose- and time-dependent manner in SW480 and clone 26 cells. The percentages of SW480 cells and clone 26 cells at G(2)/M phase were increased significantly after treatment with 40 approximately 80 micromol/L quercetin for 48 hours. Quercetin induced the apoptosis of SW480 cells in a dose-dependent manner at the concentration of 20, 40, 60, anf 80 micromol/L. However, quercetin only induced the apoptosis of clone 26 cells at the concentration of 80 micromol/L. Quercetin downregulated transcriptional activity of beta-catenin/Tcf in SW480 cells transiently transfected with the TCF-4 reporter gene. Within 24 hours of treatment, a 160-mumol/L concentration of quercetin reduced beta-catenin/Tcf transcriptional activity by about 18-fold. Cyclin D(1) and the survivin gene were downregulated markedly by quercetin in a dose-dependent manner at both the transcription and protein expression levels.

CONCLUSION

The results indicate that the molecular mechanism underlying the antitumor effect of quercetin in SW480 colon cancer cells is related to the inhibition of expression of cyclin D(1) and survivin as well as the Wnt/beta-catenin signaling pathway. Therefore, the Wnt/beta-catenin signaling pathway could be qualified as one of the promising targets for innovative treatment strategies of colorectal cancer.

MAD2B, a novel TCF4-binding protein, modulates TCF4-mediated epithelial-mesenchymal transdifferentiation

T cell factor 4 (TCF4) interacts with beta-catenin in the WNT signaling pathway and transactivates downstream target genes involved in cancer progression. To identify proteins that regulate TCF4-mediated biological responses, we performed a yeast two-hybrid screen to search for a TCF4-binding protein(s) and found that MAD2B interacts with TCF4. We confirmed that MAD2B is a TCF4-binding protein by co-immunoprecipitation. Using the TOPFLASH reporter assay, we found that MAD2B blocks TCF4-mediated transactivation. The MAD2B binding regions of TCF4 were identified by TCF4 deletion mapping and electrophoretic mobility shift assay analysis. TCF4 and MAD2B interactions abolished the DNA binding ability of TCF4. Knockdown of MAD2B in SW480 colorectal cancer cells led to the conversion of epithelial cells to a mesenchymal fibroblastoid phenotype (epithelial-mesenchymal transdifferentiation). An E-cadherin promoter reporter analysis showed that MAD2B modulates TCF4-mediated E-cadherin expression. MAD2B knockdown blocked E-cadherin expression and significantly induced mesenchymal markers, such as N-cadherin and vimentin. Mesenchymal induction was accompanied by F-actin redistribution and the appearance of a fibroblastoid phenotype. MAD2B knockdown also increased both mRNA and protein levels of Slug, a known TCF4-induced E-cadherin transcriptional repressor. A chromatin immunoprecipitation assay showed that MAD2B silencing enhances the ability of TCF4 to bind the Slug promoter. Thus, MAD2B is a novel TCF4-interacting protein. This study provides the first evidence for the involvement of MAD2B in TCF4-mediated epithelial-mesenchymal transdifferentiation.

Prevalence of mutations in APC, CTNNB1, and BRAF in Tunisian patients with sporadic colorectal cancer

Sporadic colorectal tumorigenesis is caused by alterations in the Wnt (APC, CTNNB1) and Ras pathways. Our objective was to analyze the occurrence of these genetic alterations in relation to tumor and patient characteristics. The prevalence of somatic alteration in the hot-spot regions of the APC, BRAF, and CTNNB1 genes was investigated in 48 unselected and unrelated Tunisian patients with sporadic colorectal cancer, and the association between the molecular features at these genes in relation to tumor and patient characteristics (age at diagnosis, sex, tumor localization, stage, and differentiation) was analyzed. Loss of heterozygosity was observed at the APC locus in 52% of the analyzed tumors. 6 novel mutations were detected by polymerase chain reaction sequencing in the mutation cluster region of the APC gene. No mutations were observed in the CTNNB1 gene in any tumor, but 8% of tumors harbored mutation in the BRAF gene. Clinicopathological analyses showed an association between APC point mutations and the earliest occurrence of sporadic colorectal cancer. The findings confirm the heterogeneity of APC gene alteration and also reveal a particular profile of this pathology among Tunisian patients that confirms the epidemiological data for this country.

Modification of the associations between lifestyle, dietary factors and colorectal cancer risk by APC variants

In a large Scottish case-control study, we investigated the effects of adenomatous polyposis coli (APC) Asp1822Val (rs459552) and APC Glu1317Gln substitutions on colorectal cancer (CRC) risk and whether these associations were influenced by lifestyle and dietary factors. We did not observe any associations between the variants and CRC risk in the whole population. Post-menopausal women taking hormone replacement therapy (HRT) and participants who consumed a diet low in total fat, saturated fatty acids, monounsaturated fatty acids (MUFAs) and trans fatty acids had a lower risk of CRC [odds ratio (95% confidence interval): 0.53 (0.41, 0.68); 0.84 (0.72, 0.98); 0.72 (0.62, 0.85); 0.85 (0.73, 1.00) and 0.78 (0.67, 0.92), respectively]. This risk reduction was stronger in those homozygous for the variant APC 1822 allele with significant interaction relationships for HRT, red meat and MUFA intakes (P for interaction case-only design: 0.02, 0.002 and 0.02, respectively). Low n3 polyunsaturated fatty acids intake was associated with an increased CRC risk for the wild-type and heterozygous APC 1822 individuals but with a decreased CRC risk in those homozygous for the variant allele (P for interaction case-only design: 0.09). The interaction relationships with the APC 1317 variant were of the same direction though not significant, possibly due to the low frequency of the variant allele. Our results confirm the findings of three recent case-control studies suggesting a number of possible biological mechanisms. However, further large-scale studies are necessary in order to replicate these findings and confirm the role of these APC gene variants and their interaction with dietary and lifestyle exposures in colorectal carcinogenesis.

Osteopontin: regulation in tumor metastasis

Osteopontin is a secreted phosphoprotein that has been implicated as an important mediator of tumor metastasis and has been investigated for use as a biomarker for advanced disease and as a potential therapeutic target in the regulation of cancer metastasis. The OPN DNA sequence is highly conserved and the protein contains several important functional domains including alpha(v)beta integrin and CD44 binding sites. High levels of OPN expression correlate with tumor invasion, progression or metastasis in multiple cancer. Studies demonstrate that osteopontin mediates the molecular mechanisms which determine metastatic spread, such as prevention of apoptosis, extracellular matrix proteolysis and remodeling, cell migration, evasion of host-immune cells and neovascularization. Transcriptional regulation of OPN is complex and involves multiple pathways, including AP-1, Myc, v-Src, Runx/CBF, TGF-B/BMPs/Smad/Hox, and Wnt/ss-catenin/APC/GSK-3ss/Tcf-4. The current state of knowledge of OPN biology suggests that it is an attractive target for therapeutic modulation of metastatic disease.

Effect of exercise on biological pathways in ApcMin/+ mouse intestinal polyps

Many epidemiological studies have demonstrated that level of exercise is associated with reduced colorectal cancer risk. Treadmill training can decrease Apc(Min/+) mouse intestinal polyp number and size, but the mechanisms remain unclear. Understanding the molecular changes in the tumor following exercise training may provide insight on the mechanism by which exercise decreases Apc(Min/+) mouse polyp formation and growth. The purpose of this study was to determine if exercise can modulate Apc(Min/+) mouse intestinal polyp cellular signaling related to tumor formation and growth. Male Apc(Min/+) mice were randomly assigned to control (n = 20) or exercise (n = 20) treatment groups. Exercised mice ran on a treadmill at a moderate intensity (18 m/min, 60 min, 6 days/wk, 5% grade) for 9 wk. Polyps from Apc(Min/+) mice were used to quantify markers of polyp inflammation, apoptosis, and beta-catenin signaling. Exercise decreased the number of macrophages in polyps by 35%. Related to apoptosis, exercise decreased the number of terminal deoxynucleotidyl transferase-mediated dUTP nick-end labeling (TUNEL)-positive cells by 73% in all polyps. Bax protein expression in polyps was decreased 43% by exercise. beta-Catenin phosphorylation was elevated 3.3-fold in polyps from exercised mice. Moderate-intensity exercise training alters cellular pathways in Apc(Min/+) mouse polyps, and these changes may be related to the exercise-induced reduction in polyp formation and growth.

The forkhead box M1 transcription factor contributes to the development and growth of mouse colorectal cancer

BACKGROUND & AIMS

In this study, we used Forkhead Box m1b (Foxm1b) transgenic mice and conditional Foxm1 knock-out mice to examine the role of Foxm1 in colon cancer development and proliferation.

METHODS

To induce mouse colorectal cancer, we used a single intraperitoneal injection of azoxymethane (AOM) followed by three 1-week cycles of 2.5% dextran sodium sulfate (DSS) water, each cycle separated by 2 weeks. For these colon tumor studies, we used either Rosa26-Foxm1b transgenic mice that ubiquitously expressed the human Foxm1b complementary DNA or mice in which the Foxm1 fl/fl targeted allele was deleted in colonic epithelial cells using the gut-specific Villin-Cre recombinase transgene (Villin-Cre). Colorectal tumor number and bromodeoxyuridine labeling were determined in Rosa26-Foxm1b mice, Villin-Cre Foxm1-/-, mice and wild-type mice after 12 weeks of AOM/DDS exposure. We also used Foxm1 small interfering RNA-depleted human DLD1 and mouse CT26 colon cancer cell lines to examine DNA replication and anchorage-independent growth.

RESULTS

After 12 weeks of treatment with AOM/DSS, Rosa26 Foxm1b transgenic mice showed an increase in the number and size of colorectal tumors compared with wild-type mice. Likewise, a significant reduction in the development and growth of colorectal tumors was found in Villin-Cre Foxm1-/- mice compared with Foxm1 fl/fl mice after AOM/DSS treatment, which was associated with decreased expression of cyclin A2, cyclin B1, survivin, and T-cell factor 4 genes. Moreover, Foxm1-depleted colon cancer cell lines showed reduced DNA replication and anchorage-independent growth.

CONCLUSIONS

These studies suggest that Foxm1 is critical for the proliferation and growth of colorectal cancer.

Caffeic acid phenethyl ester induces growth arrest and apoptosis of colon cancer cells via the beta-catenin/T-cell factor signaling

Caffeic acid phenethyl ester, an active component of propolis, has been implicated in the regulation of cell growth and apoptosis, although the exact mechanism of this activity has not been elucidated. In this study, we explored the effects of caffeic acid phenethyl ester on growth, cell cycle, apoptosis and beta-catenin/T-cell factor signaling in human colon cancer cells. Using two human sporadic colon cancer cell lines (HCT116 and SW480), we assayed for cell growth inhibition, cell cycle and apoptosis induction. We also assayed for beta-catenin and downstream target genes (cyclin D1 and c-myc) mRNA and protein expression by reverse transcriptase-polymerase chain reaction and Western blot analysis. Beta-catenin localization was detected by indirect immunofluorescence. Beta-catenin/T-cell factor transcriptional activity was determined by transient transfection and reporter gene assay. Caffeic acid phenethyl ester completely inhibited growth, and induced G1 phase arrest and apoptosis in a dose-dependent manner in both HCT116 and SW480 cells. Treatment of human colon cancer cells with apoptotic concentrations of caffeic acid phenethyl ester resulted in a dose-dependent and time-dependent loss of total beta-Catenin protein, associated with decreased nuclear beta-catenin. Caffeic acid phenethyl ester reduced the expression of cyclin D1 and c-myc in a dose-dependent and time-dependent manner. We proved that caffeic acid phenethyl ester markedly suppressed the transcriptional activity of beta-catenin/T-cell factor in both HCT116 and SW480 cells depending on the concentration of caffeic acid phenethyl ester. These results indicate that caffeic acid phenethyl ester is an excellent inhibitor of beta-catenin/T-cell factor signaling in colon cancer cell lines and suggest that caffeic acid phenethyl ester merits further study as an agent against colorectal cancers.

Altered expression of beta-catenin, E-cadherin, cycloxygenase-2, and p53 protein by ovine intestinal adenocarcinoma cells

Around 1.6% of sheep in New Zealand develop small-intestinal adenocarcinomas. These neoplasms typically develop widespread metastases. The common development of these neoplasms and their subsequent behavior suggests that sheep could be a useful animal model of human colonic cancer. However, for an animal model of human disease to be relevant, similar genetic mutations should be present. Genetic mutations within human colonic cancers frequently result in expression of cycloxygenase-2 (COX-2), loss of membranous expression of beta-catenin and E-cadherin, and accumulation of p53 protein within the neoplastic cells. Immunohistochemistry was used to investigate the presence of these 4 proteins within 26 ovine intestinal adenocarcinomas. Loss of membranous beta-catenin reactivity was observed in 14 of 26 ovine intestinal adenocarcinomas (54%). The loss of membranous beta-catenin reactivity was accompanied by cytoplasmic and nuclear reactivity in 2 neoplasms. Loss of E-cadherin was observed within 8 of 26 neoplasms (31%). Neoplastic cell expression of COX-2 was observed in 12 of 26 neoplasms (46%), whereas cells within 3 of 26 neoplasms (11%) contained visible p53 protein. In conclusion, all 4 proteins that commonly have altered expression in human colonic cancers were also altered in a proportion of the ovine intestinal adenocarcinomas. These results provide additional evidence that sheep could be useful for the study of human colonic cancer.

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Inhibitory effect of caffeic acid phenethyl ester on the growth of SW480 colorectal tumor cells involves beta-catenin associated signaling pathway down-regulation

AIM

To study the anti-tumor effect of caffeic acid phenethyl ester (CAPE) and the influence of CAPE on beta-catenin associated signaling pathway in SW480 colorectal cancer (CRC) cells.

METHODS

SW480 cells were treated with CAPE at serial concentrations. The proliferative status of cells was measured by methabenzthiazuron (MTT) assay. Cell cycle and cell apoptosis were analyzed using flow cytometry (FCM). Western blotting assay was used to evaluate the protein level of beta-catenin, c-myc and cyclinD1. Beta-catenin localization was determined by indirect immunofluorescence.

RESULTS

CAPE displayed a strong inhibitory effect in a significant dose- and time-dependent manner on SW480 cell growth. FCM analysis showed that the ratio of G0/G1 phase cells increased, S phase ratio decreased and apoptosis rate increased after SW480 cells were exposed to CAPE for 24 h. Pretreatment of SW480 cells with CAPE significantly suppressed beta-catenin, c-myc and cyclinD1 protein expression. CAPE treatment was associated with decreased accumulation of beta-catenin protein in nucleus and cytoplasm, and concurrently increased its accumulation on the surface of cell membrane.

CONCLUSION

CAPE can inhibit SW480 cell proliferation by inducing cell cycle arrest and apoptosis. Decreased beta-catenin and the associated signaling pathway target gene expression may mediate the anti-tumor effects of CAPE.

Expression des pompes calciques de type SERCA au cours de la différenciation cellulaire et de la tumorigenèse: application à la carcinogenèse colique

Calcium homeostasis of the endoplasmic reticulum (ER) is involved in intracellular signaling pathways and is implicated in major cell functions such as cell growth, differentiation, protein synthesis and apoptosis. The accumulation of calcium in the ER is performed by specific sarco/endoplasmic reticulum calcium transport ATPases (SERCA iso-enzymes). The expression of biochemically distinct SERCA isoforms is cell type dependent and developmentally regulated. This review summarizes pertinent data about the modulation of the expression of SERCA enzymes during the differentiation of normal and tumor cells. These data support the implication of SERCA pumps and especially SERCA3 in the differentiation program of cancer and leukemia cells. During the multi-step process of colon carcinogenesis, the decrease of SERCA3 expression seems to be linked to enhanced APC/ss-catenin/TCF4 signaling and deficient Sp1-like factor-dependent transcription.

DNA methylation of multiple tumor-related genes in association with overexpression of DNA methyltransferase 1 (DNMT1) during multistage carcinogenesis of the pancreas

To evaluate the significance of alterations in DNA methylation during multistage carcinogenesis of the pancreas, tissue samples of 13 peripheral pancreatic duct epithelia showing no remarkable histological changes without inflammatory background (DE), 20 peripheral pancreatic duct epithelia showing no remarkable histological changes with inflammatory background (DEI), 40 pancreatic intraepithelial neoplasias (PanIN) and 147 areas of ductal carcinoma were microdissected from surgically resected specimens from 58 patients and were embedded into agarose beads. The embedded tissue samples were subjected to methylation-specific PCR (MSP) to evaluate the DNA methylation status of the p14, p15, p16, p73, APC, hMLH1, MGMT, BRCA1, GSTP1, TIMP-3, CDH1 and DAPK-1 genes. The prevalence of DNA methylation of at least one of the 12 genes and the average number of methylated genes were significantly higher in both DEI (60% and 0.85 +/- 0.88, P = 0.0151 and P = 0.0224, respectively) and PanIN (67.5% and 0.95 +/- 0.85, P = 0.0014 and P = 0.0028, respectively) than in DE (15.4% and 0.15 +/- 0.38), and were further increased in ductal carcinoma (98.3% and 2.50 +/- 1.35, P < 0.0001 and P < 0.0001, respectively). The BRCA1, APC, p16 and TIMP-3 genes were frequently methylated in ductal carcinoma (60.3, 58.6, 39.3 and 30.9%, respectively). Considerable heterogeneity of DNA methylation status was observed among multiple microdissected areas from individual ductal carcinomas, and the number of methylated genes per area was significantly correlated with poorer tumor differentiation (P = 0.0249). The average number of methylated genes in ductal carcinomas was significantly correlated with DNMT1 protein expression level (P = 0.0093). These data suggest that accumulation of DNA methylation of multiple tumor-related genes is involved in multistage carcinogenesis of the pancreas from early precancerous stages to malignant progression and that DNMT1 protein overexpression may be responsible for this aberrant DNA methylation.

Genetic detection of lymph node micrometastases: a selection criterion for liver transplantation in patients with liver metastases after colorectal cancer

BACKGROUND

Liver transplantation for nonresectable liver metastases from colorectal cancer was abandoned in 1994 on account of high recurrence rates. The aim of this study was to investigate whether the genetic detection of micrometastases in histologically negative lymph nodes of the primary colon cancer could be applied to select patients for liver transplantation.

METHODS

We analyzed 21 patients with colorectal cancer who had undergone liver transplantation between 1983 and 1994 for liver metastases. Eleven patients were histologically lymph node negative at the time of surgery; ten patients with lymph node metastases served as control group. DNA sequencing was used to screen tumor material for p53 and K-ras mutations. Mutant allele-specific amplification (MASA) was then used to search for micrometastases in DNA from regional lymph nodes of the primary colorectal cancer.

RESULTS

p53 and K-ras mutations were detected in 12 (57%) and 3 (14%) of 21 patients in the colorectal cancer, respectively. The mutations were confirmed in the corresponding liver metastases. Of 11 patients with histologically negative lymph nodes, nine were eligible for MASA due to presence of p53 or K-ras mutation. MASA revealed six of nine patients to be genetically positive for micrometastases. Three patients were both genetically and histologically negative. These three patients showed a significantly longer overall survival (P = 0.011) of 4, 5, and 20 years, respectively.

CONCLUSIONS

We conclude that the genetic detection of micrometastases by MASA could be a powerful prognostic indicator for selecting patients with colorectal liver metastases who could benefit from liver transplantation.

Examination of actin and microtubule dependent APC localisations in living mammalian cells

BACKGROUND

The trafficking of the adenomatous polyposis coli (APC) tumour suppressor protein in mammalian cells is a perennially controversial topic. Immunostaining evidence for an actin-associated APC localisation at intercellular junctions has been previously presented, though live imaging of mammalian junctional APC has not been documented.

RESULTS

Using live imaging of transfected COS-7 cells we observed intercellular junction-associated pools of GFP-APC in addition to previously documented microtubule-associated GFP-APC and a variety of minor localisations. Although both microtubule and junction-associated populations could co-exist within individual cells, they differed in their subcellular location, dynamic behaviour and sensitivity to cytoskeletal poisons. GFP-APC deletion mutant analysis indicated that a protein truncated immediately after the APC armadillo repeat domain retained the ability to localise to adhesive membranes in transfected cells. Supporting this, we also observed junctional APC immunostaining in cultures of human colorectal cancer cell line that express truncated forms of APC.

CONCLUSION

Our data indicate that APC can be found in two spatially separate populations at the cell periphery and these populations can co-exist in the same cell. The first localisation is highly dynamic and associated with microtubules near free edges and in cell vertices, while the second is comparatively static and is closely associated with actin at sites of cell-cell contact. Our imaging confirms that human GFP-APC possesses many of the localisations and behaviours previously seen by live imaging of Xenopus GFP-APC. However, we report the novel finding that GFP-APC puncta can remain associated with the ends of shrinking microtubules. Deletion analysis indicated that the N-terminal region of the APC protein mediated its junctional localisation, consistent with our observation that truncated APC proteins in colon cancer cell lines are still capable of localising to the cell cortex. This may have implications for the development of colorectal cancer.

The loss of sarco/endoplasmic reticulum calcium transport ATPase 3 expression is an early event during the multistep process of colon carcinogenesis

Calcium accumulation in the endoplasmic reticulum is accomplished by sarco/endoplasmic reticulum calcium transport ATPases (SERCA enzymes). To better characterize the role of SERCA3 in colon carcinogenesis, its expression has been investigated in colonic epithelium, benign lesions, adenomas, and adenocarcinomas. In addition, the regulation of SERCA3 expression was analyzed in the context of the adenomatous polyposis coli/beta-catenin/T-cell factor 4 (TCF4) pathway and of specificity protein 1 (Sp1)-like factor-dependent transcription. We report that SERCA3 expression increased along the crypts as cells differentiated in normal colonic mucosa and in hyperplastic polyps, was moderately and heterogeneously expressed in colonic adenomas with expression levels inversely correlated with the degree of dysplasia, was barely detectable in well and moderately differentiated adenocarcinomas, and was absent in poorly differentiated tumors. Inhibition of Sp1-like factor-dependent transcription blocked SERCA3 expression during cell differentiation, and SERCA3 expression was induced by the expression of dominant-negative TCF4 in colon cancer cells. These data link SERCA3 expression to the state of differentiation of colonic epithelial cells, and relate SERCA3 expression, already decreased in adenomas, to enhanced adenomatous polyposis coli/beta-catenin/TCF4-dependent signaling and deficient Sp1-like factor-dependent transcription. In conclusion, intracellular calcium homeostasis becomes progressively anomalous during colon carcinogenesis as reflected by deficient SERCA3 expression.

Effect of caffeic acid phenethyl ester on proliferation and apoptosis of colorectal cancer cells in vitro

AIM: To study the effect of caffeic acid phenethyl ester (CAPE) on proliferation, cell cycle, apoptosis and expression of β-catenin in cultured human colorectal cancer (CRC) cell line HCT116.

METHODS: HCT116 cells were treated with CAPE at serial concentrations of 80, 40, 20, 10, 5, 2.5 mg/L. The proliferative status of HCT116 cells was measured by using methaben-zthiazuron (MTT) assay. Cell cycle was analyzed by using flow cytometry (FCM) with propidium iodide (PI) labeling method. The rate of apoptosis was detected by using FCM with annexin V-FITC and PI double labeling method. β-catenin levels were determined by Western blotting. β-catenin localization in HCT116 was determined by indirect immunofluorescence.

RESULTS: After HCT116 cells were exposed to CAPE (80, 40, 20, 10, 5, and 2.5 mg/L) for 24, 48, 72, 96 h, CAPE displayed a strong growth inhibitory effect in a dose- and time-dependent manner against HCT116 cells. FCM analysis showed that the ratio of G₀/G₁ phase cells increased, S phase ratio decreased and apoptosis rate increased after HCT116 cells were exposed to CAPE (10, 5, and 2.5 mg/L) for 24 h. CAPE treatment was associated with decreased cytoplasmic β-catenin, nuclear β-catenin and a concurrent increase in β-catenin protein expression at cell-cell junctions.

CONCLUSION: CAPE could inhibit HCT116 cell proliferation and induce cell cycle arrest and apoptosis. Decreased β-catenin protein expression may mediate the anti-proliferative effects of CAPE.

Ionomycin downregulates beta-catenin/Tcf signaling in colon cancer cell line

Functional activation of beta-catenin/Tcf signaling plays an important role in the early events in colorectal carcinogenesis. We examined the effect of ionomycin against beta-catenin/Tcf signaling in colon cancer cells. Reporter gene assay showed that ionomycin inhibited beta-catenin/Tcf signaling efficiently. In addition, the inhibition of beta-catenin/Tcf signaling by ionomycin in HEK293 cells transiently transfected with a constitutively mutant beta-catenin gene, whose product is not phosphorylated by GSK3beta, indicates that its inhibitory mechanism is related to beta-catenin itself or downstream components. To investigate the precise inhibitory mechanism, we performed immunoprecipitation analysis, western blot and electrophoretic mobility shift assay. As a result, our data reveal that the association of beta-catenin and Tcf-4 is disrupted and the amount of beta-catenin product in the nucleus is decreased by ionomycin in a concentration-dependent manner. Moreover, ionomycin strongly suppressed the binding of the Tcf complexes to its specific DNA-binding sites. The significance of the current work is that ionomycin is a negative regulator of beta-catenin/Tcf signaling in colon cancer cells and its inhibitory mechanism is related to the decreased nuclear beta-catenin products and to the suppressed binding of Tcf complexes to consensus DNA.

COX-2: a molecular target for colorectal cancer prevention

Cyclooxygenase (COX), a key enzyme in the prostanoid biosynthetic pathway, has received considerable attention due to its role in human cancers. Observational and randomized controlled studies in many different population cohorts and settings have demonstrated protective effects of nonsteroidal anti-inflammatory drugs (NSAIDs; the inhibitors of COX activity) for colorectal cancers (CRCs). COX-2, the inducible isoform of cyclooxygenase, is overexpressed in early and advanced CRC tissues, which portends a poor prognosis. Experimental studies have thus identified important mechanisms and pathways by which COX-2 plays an important role in carcinogenesis. Selective COX-2 inhibitors have been approved for use as adjunctive therapy for patients with familial polyposis. The role of COX-2 inhibitors is currently being evaluated for use in wider populations.

APC Asp1822Val and Gly2502Ser Polymorphisms and Risk of Colorectal Cancer and Adenoma

Mutation of the adenomatous polyposis coli (APC) tumor suppressor gene is an important initiating factor in the early stages of the adenoma-carcinoma sequence. The aim of this study was to investigate the two most common APC variants (Asp1822Val and Gly2502Ser) and their association with colorectal cancer and adenoma and whether these relationships are influenced by dietary and lifestyle factors. We analyzed 556 adenoma cases and 557 matched controls and 197 cancer cases and 490 matched controls nested within the Nurses' Health Study cohort, 274 cancer cases and 456 matched controls nested within the Physicians' Health Study cohort, and 375 adenoma cases and 724 matched controls nested within the Health Professionals Follow-up Study cohort. APC Asp1822Val and Gly2502Ser polymorphisms were not associated with risk of colorectal cancer or adenoma. For colorectal cancer, a significant interaction was found between Asp1822Val genotype and postmenopausal hormone (PMH) use among postmenopausal women (P(interaction) = 0.03). Current PMH use was associated with reduced risk overall and a statistically significant lower risk of colorectal cancer among carriers of one or two copies of the APC 1822Val allele (relative risk, 0.46; 95% confidence interval, 0.24-0.88) relative to wild-type never or past PMH users. Our results suggest that cigarette smoking, alcohol intake, and family history of colorectal cancer were positively associated and regular aspirin intake was inversely associated with colorectal adenoma in men and women. No gene-environment interactions were observed with these risk factors or with other dietary risk factors previously hypothesized to interact with the APC Asp1822Val polymorphism.

Quercetin, a potent inhibitor against beta-catenin/Tcf signaling in SW480 colon cancer cells

Dysregulation of Wnt/beta-catenin pathway plays a central role in early events in colorectal carcinogenesis. We examined the effect of quercetin, a famous anti-tumor agent, against beta-catenin/Tcf signaling in SW480 cells. Quercetin inhibited the transcriptional activity of beta-catenin/Tcf in SW480 and also in HEK293 cells transiently transfected with constitutively active mutant beta-catenin gene, whose product is not induced to be degraded by APC-Axin-GSK3beta complex, so we concluded that its inhibitory mechanism was related to beta-catenin itself or downstream components. To investigate the precise inhibitory mechanism, we performed EMSA showing that binding of the Tcf complexes to its specific DNA-binding sites was strongly suppressed by quercetin. Immunoprecipitation analysis also showed that the binding of beta-catenin to Tcf-4 was also disrupted by quercetin. Western blot analysis proved these decreased bindings resulted from decreased level of beta-catenin and Tcf-4 product in nucleus caused by quercetin. Together, we suggest that quercetin is an excellent inhibitor of beta-catenin/Tcf signaling in SW480 cell lines, and the reduced beta-catenin/Tcf transcriptional activity is due to the decreased nuclear beta-catenin and Tcf-4 proteins.

Mutation analysis of DKK1 and in vivo evidence of predominant p53-independent DKK1 function in gliomas

DKK1 protein belongs to a family of inhibitors of the Wnt/beta1-catenin signaling pathway. Sporadic mutations affecting almost each major player of the Wnt/beta1-catenin pathway have been described in a variety of human carcinomas. DKK1 translation can be induced by p53, thereby linking TP53 and Wnt/beta1-catenin signaling pathways. These findings raise questions in regard to human gliomas, which similar to carcinomas carry a high rate of mutations in TP53. To analyze DKK1 for its role in initiation or progression, we screened a series of 73 brain tumors for structural alterations in the entire coding sequence by single-strand conformation polymorphism and direct sequencing. While several sequence variants were detected, there were no obvious mutations affecting DKK1. Further, we analyzed the prevalence of mRNA from TP53, DKK1 and CTNNB1 and of p53 and beta1-catenin protein in a series of human gliomas with and without mutations in TP53. Transcription and expression of CTNNB1/beta1-catenin and DKK1 proved to be independent of TP53/p53. These data support in vivo function of DKK1, independent of p53, in human gliomas with no major impact on their pathogenesis.

RNA-mediated gene silencing of the RON receptor tyrosine kinase alters oncogenic phenotypes of human colorectal carcinoma cells

Altered expression of receptor tyrosine kinases contributes to tumorigenic behaviors of epithelial cancers. In this study, the pathogenic roles of receptor tyrosine kinase RON (recepteur d'origine nantais) in regulating oncogenic phenotypes in colorectal epithelial cells were studied. Increased expression of RON and its variants resulted in colony formation and motile activities of colonic epithelial AA/C1 cells as evident in soft-agar and migration assays, respectively. These results suggest that overexpression of wild-type RON mediates the transformed phenotypes in immortalized colon epithelial cells. In colorectal cancer cells (HT-29, HCT116, and SW620) that naturally express RON, the RON gene expression was silenced by RNA interference. The introduction of RON-specific small interfering (si) RNA significantly affected cancer cell proliferation, motility, and led to increased apoptotic cell death. Focus-forming activities and anchorage-independent growth of colon cancer cells were also dramatically reduced. Moreover, it was demonstrated in tumor growth assays that silencing RON gene expression significantly reduces tumorigenic activities of SW620 cells in vivo. By analysing signaling proteins involved in colon carcinogenesis, we found that the effect of RON-specific siRNA is associated with diminished expression of beta-catenin, a critical component in the Wnt signaling pathway. Taken together, our results demonstrate that altered expression of RON in colon cancer cells is required to maintain tumorigenic phenotypes. Thus, silencing RON gene expression could have potential to reverse malignant activities of colon tumors in vivo.

APC gene loss of heterozygosity, mutations, E1317Q, and I1307K germ-line variants in sporadic colon cancer in Croatia

Colorectal carcinomas are characterized by multiple genetic aberrations that occur during tumorigenesis. Several tumor suppressor genes associated with colorectal carcinoma have been identified: MCC, APC, p53, nm23-H1, DCC, DPC4. We examined 73 cases of sporadic human colon cancer and corresponding normal tissue samples to evaluate the loss of heterozygosity (LOH) at the APC gene loci. The purpose of this study was also to evaluate whether the LOH at the APC gene is associated with clinicopathological characteristics in sporadic colon cancer. We also investigated presence and the frequency of the most common APC gene mutations and APC E1317Q and I1307K germ-line variants in Croatian colorectal cancer patients. Five markers in all patients were found to be heterozygous and informative for LOH analysis. LOH at the APC locus was detected in 30.1% of tumors were examined. The majority of APC gene LOH was observed in Dukes' B (55.6%) and in the moderately differentiated tumors (42.9%). Only 1309 APC gene mutation was detected in our samples. In one tumor sample, a new sporadic mutation of the APC gene in codon 1374 was detected. APC E1317Q and I1307K germ-line variants were not detected in our population. But APC E1317Q sporadic mutation was found in one tumor sample.

Spontaneous immortalization of clinically normal colon-derived fibroblasts from a familial adenomatous polyposis patient

Normal human diploid cells do not spontaneously immortalize in culture, but instead enter replicative senescence after a finite number of population doublings. Ablation of key checkpoint arrest or cancer-suppressor genes, through dominantly inherited germline mutation (p53+/-, Li-Fraumeni) or viral oncogene expression (SV40 large T, HPV16/18, and E6/E7) can lead to escape from senescence, additional doublings, and entrance into crisis phase, where immortal clones emerge at low frequency. In the vast majority of cases, telomerase is reactivated and telomeres are stabilized. Here we describe the spontaneous immortalization of clinically normal fibroblasts derived from colonic stroma of a familial adenomatous polyposis (FAP) patient. The preimmortal (C26C) and the spontaneously immortalized derivative (C26Ci) cells are heterozygous for a characterized germline mutation in exon 15 of the adenomatous polyposis coli gene. Immortalization was accompanied by spontaneous reactivation of endogenous telomerase and establishment of telomeres at presenescent lengths. Normal checkpoint behavior is retained and a diploid karyotype is maintained. These cells provide a valuable new addition to the limited number of spontaneously immortalized human cell types, particularly fibroblast cells, and will be useful in experimentally determining the functional pathways in neoplastic development and in the identification of potential molecular targets for cancer chemoprevention.

The role of Osteopontin in tumor metastasis

Osteopontin (OPN) is a glyco-phosphoprotein that is expressed and secreted by numerous human cancers. OPN functions in cell adhesion, chemotaxis, macrophage-directed interleukin-10 (IL-10) suppression, stress-dependent angiogenesis, prevention of apoptosis, and anchorage-independent growth of tumor cells by regulating cell-matrix interactions and cellular signaling through binding with integrin and CD44 receptors. While constitutive expression of OPN exists in several cell types, induced expression has been detected in T-lymphocytes, epidermal cells, bone cells, macrophages, and tumor cells in remodeling processes such as inflammation, ischemia-reperfusion, bone resorption, and tumor progression. Recently, substantial evidence has linked OPN with the regulation of metastatic spread by tumor cells. However, the molecular mechanisms that define the role of OPN in tumor metastasis are incompletely understood. Transcriptional regulators that contribute to the induction of OPN expression have received significant attention as potential modulators of the OPN-mediated metastatic phenotype. The following review will discuss the molecular structure of OPN, the evidence for its functional role in tumor cell metastasis, the downstream signals that activate invasive mechanisms, and the recent reports concerning regulation of OPN transcription.

Induction of HSF1 expression is associated with sporadic colorectal cancer

AIM: To explore the activation of signal transduction pathways related with the carcinogenesis of sporadic colon cancers.

METHODS: A gene array monitoring the activation of 8 signal transduction pathways (PathwayFinder GEArray) was used to screen the differentially expressed genes between colorectal cancer and normal colon tissues. The differentially expressed genes were further analyzed by RT-PCR, using RNA derived from colorectal cancer and normal colon tissue of 35 patients.

RESULTS: The expression of HSF1, HSF27, HSP90 and iNOS was increased in colon cancer tissues compared to normal colon tissue using PathwayFinder GEArray. The RT-PCR results showed that the expression of HSF1 was increased in 86% (30/35) patients and the expression of iNOS was increased in 63% (22/35) patients.

CONCLUSION: The induction of HSF1 gene expression is associated with sporadic colon cancer. HSF1 induces heat shock stress signaling pathway, which might play a role in the carcinogenesis of sporadic colorectal cancer.

Immunolocalization of protein 4.1B/DAL-1 during neoplastic transformation of mouse and human intestinal epithelium

Recently, we have reported that the protein 4.1B immunolocalization occurred only in matured columnar epithelial cells of normal rat intestines. This finding suggested that protein 4.1B expression could be examined for a possible change during neoplastic transformation of the intestinal mucosa. In the present study, we first present the distribution of mouse protein 4.1B in normal intestinal epithelial cells and tumor cells using the adenomatous polyposis coli (Apc) mutant mouse model. A low level of protein 4.1B expression coincided with the phenotypic transition to carcinoma. To examine the protein 4.1B expression in human intestinal mucosa, we used another antibody against an isoform of the human protein 4.1B, DAL-1 (differentially expressed adenocarcinoma of the lung). Human DAL-1 was also expressed in matured epithelial cells in human colons, with a definite expression gradient along the crypt axis. In human colorectal cancer cells, however, DAL-1 expression was not detected. These results suggest that mouse protein 4.1B and human DAL-1 might have a striking analogy of functions, which may be integrally involved in epithelial proliferation. We propose that loss of protein 4.1B/DAL-1 expression might be a marker of intestinal tumors, indicative of a tumor suppressor function in the intestinal mucosa.

Sodium butyrate induces apoptosis in human hepatoma cells by a mitochondria/caspase pathway, associated with degradation of β-catenin, pRb and Bcl-XL

Butyrate can promote programmed cell death in a number of tumour cells in vitro. This paper provides evidence that butyrate induces apoptosis in human hepatoma HuH-6 and HepG2 cells but is ineffective in Chang liver cells, an immortalised non-tumour cell line. In both HuH-6 and HepG2 cells, apoptosis appeared after a lag period of approximately 16 h and increased rapidly during the second day of treatment. In particular, the effect was stronger in HuH-6 cells, which were, therefore, chosen for ascertaining the mechanism of butyrate action. In HuH-6 cells, beta-catenin seemed to exert an important protective role against apoptosis, since pretreatment with beta-catenin antisense ODN reduced the content of beta-catenin and anticipated the onset of apoptosis at 8 h of exposure to butyrate. Moreover, in HuH-6 cells, butyrate induced loss of mitochondrial membrane potential, release of cytochrome c from mitochondria, activation of caspase 9 and caspase 3, and degradation of poly(ADP-ribose) polymerase. In addition, during the second day of treatment, beta-catenin, pRb, and cyclins D and E were diminished and the phosphorylated form of pRb disappeared. Also, the content of the anti-apoptotic factor Bcl-XL fell markedly during this period, while that of the pro-apoptotic factor Bcl-Xs increased. These effects were accompanied by an increase in both Bcl-XL and Bcl-Xs mRNA transcripts, as ascertained by reverse transcriptase-polymerase chain reaction. Our results suggest that caspases have a crucial role in butyrate-induced apoptosis. This conclusion is supported by the observation that the inhibitors of caspases, benzyloxy carbonyl-Val-Ala-Asp-fluoromethylketone and benzyloxy carbonyl-Asp-Glu-Val-Asp-fluoromethylketone, prevented apoptosis and the decrease in Bcl-XL, pRb, cyclins and beta-catenin. These effects were most probably responsible for the increased sensitivity of the cells to butyrate-induced apoptosis, which was observed on the second day of treatment.