Loss of Smad4 correlates with loss of the invasion suppressor E-cadherin in advanced colorectal carcinomas

Association between the expression of epithelial-mesenchymal transition (EMT)-related markers and oncologic outcomes of colorectal cancer

BACKGROUND

Epithelial-mesenchymal transition (EMT) is a key step in the development of colorectal cancer (CRC) that confers metastatic capabilities to cancer cells. The present study aimed to assess the immunohistochemical (IHC) expression and impact of EMT markers, including E-cadherin, Vimentin, β-catenin, and SMAD4, on the oncologic outcomes of CRC.

METHODS

This was a retrospective review of 118 CRC patients. Tissue slides were retrieved from the slide archive and five tissue microarray construction blocks were constructed. IHC for E-cadherin, Vimentin, β-catenin, and SMAD4 was done. The main outcome was the association between abnormal marker expression and overall survival (OS), and disease-free survival (DFS).

RESULTS

Adenocarcinomas accounted for 71.2% of tumors, whereas 25.4% and 3.4% were mucinous and signet ring cell carcinomas. The rates of lymphovascular invasion and perineural invasion were 72.9% and 20.3%, respectively. There was a positive, significant correlation, and association between the four markers. Abnormal expression of E-cadherin was associated with significantly lower OS (p < 0.0001) and similar DFS (p = 0.06). Abnormal Vimentin expression was associated with a significantly higher rate of distant metastasis (p = 0.005) and significantly lower OS and DFS (p < 0.0001). Abnormal expression of β-catenin was associated with significantly lower OS (p < 0.0001) and similar DFS (p = 0.15). Abnormal expression of SMAD4 was associated with significantly lower OS and DFS (p < 0.0001). Abnormal expression of all four markers was associated with a higher disease recurrence, lower OS, and lower DFS.

CONCLUSION

Abnormal expression of each marker was associated with lower OS, whereas abnormal expression of Vimentin and SMAD4 only was associated with lower DFS.

Tumor Progression from a Fibroblast Activation Protein Perspective: Novel Diagnostic and Therapeutic Scenarios for Colorectal Cancer

In 2020, the Global Cancer Observatory estimated the incidence of colorectal cancer (CRC) at around 10.7% coupled with a mortality rate of 9.5%. The explanation for these values lies in the tumor microenvironment consisting of the extracellular matrix and cancer-associated fibroblasts (CAFs). Fibroblast activation protein (FAP) offers a promising target for cancer therapy since its functions contribute to tumor progression. Immunohistochemistry examination of FAP, fibronectin ED-B, and CXCR4 in primary tumors and their respective synchronous and/or metachronous metastases along with semiquantitative analysis have been carried out on histological samples of 50 patients diagnosed with metastatic CRC. The intensity of FAP, articulated by both "Intensity %" and "Intensity score", is lower in the first metastasis compared to the primary tumor with a statistically significant correlation. No significant correlations have been observed regarding fibronectin ED-B and CXCR4. Tumors that produce FAP have an ambivalent relationship with this protein. At first, they exploit FAP, but later they reduce its expressiveness. Although our study has not directly included FAP-Inhibitor (FAPI) PET/CT, the considerable expression of FAP reveals its potential as a diagnostic and therapeutic tool worthy of further investigation. This dynamic relationship between cancer and FAP has substantial diagnostic and therapeutic implications.

Prostate apoptosis response-4 and tumor suppression: it's not just about apoptosis anymore

The tumor suppressor prostate apoptosis response-4 (Par-4) has recently turned ‘twenty-five’. Beyond its indisputable role as an apoptosis inducer, an increasing and sometimes bewildering, new roles for Par-4 are being reported. These roles include its ability to regulate autophagy, senescence, and metastasis. This growing range of responses to Par-4 is reflected by our increasing understanding of the various mechanisms through which Par-4 can function. In this review, we summarize the existing knowledge on Par-4 tumor suppressive mechanisms, and discuss how the interaction of Par-4 with different regulators influence cell fate. This review also highlights the new secretory pathway that has emerged and the likely discussion on its clinical implications.

Role of Epithelial-Mesenchymal Plasticity in Pseudomyxoma Peritonei: Implications for Locoregional Treatments

The mechanisms by which neoplastic cells disseminate from the primary tumor to metastatic sites, so-called metastatic organotropism, remain poorly understood. Epithelial-mesenchymal transition (EMT) plays a role in cancer development and progression by converting static epithelial cells into the migratory and microenvironment-interacting mesenchymal cells, and by the modulation of chemoresistance and stemness of tumor cells. Several findings highlight that pathways involved in EMT and its reverse process (mesenchymal-epithelial transition, MET), now collectively called epithelial-mesenchymal plasticity (EMP), play a role in peritoneal metastases. So far, the relevance of factors linked to EMP in a unique peritoneal malignancy such as pseudomyxoma peritonei (PMP) has not been fully elucidated. In this review, we focus on the role of epithelial-mesenchymal dynamics in the metastatic process involving mucinous neoplastic dissemination in the peritoneum. In particular, we discuss the role of expression profiles and phenotypic transitions found in PMP in light of the recent concept of EMP. A better understanding of EMP-associated mechanisms driving peritoneal metastasis will help to provide a more targeted approach for PMP patients selected for locoregional interventions involving cytoreductive surgery and hyperthermic intraperitoneal chemotherapy.

The Small GTPase RAC1B: A Potent Negative Regulator of-and Useful Tool to Study-TGFβ Signaling

RAC1 and its alternatively spliced isoform, RAC1B, are members of the Rho family of GTPases. Both isoforms are involved in the regulation of actin cytoskeleton remodeling, cell motility, cell proliferation, and epithelial-mesenchymal transition (EMT). Compared to RAC1, RAC1B exhibits a number of distinctive features with respect to tissue distribution, downstream signaling and a role in disease conditions like inflammation and cancer. The subcellular locations and interaction partners of RAC1 and RAC1B vary depending on their activation state, which makes RAC1 and RAC1B ideal candidates to establish cross-talk with cancer-associated signaling pathways-for instance, interactions with signaling by transforming growth factor β (TGFβ), a known tumor promoter. Although RAC1 has been found to promote TGFβ-driven tumor progression, recent observations in pancreatic carcinoma cells surprisingly revealed that RAC1B confers anti-oncogenic properties, i.e., through inhibiting TGFβ-induced EMT. Since then, an unexpected array of mechanisms through which RAC1B cross-talks with TGFβ signaling has been demonstrated. However, rather than being uniformly inhibitory, RAC1B interacts with TGFβ signaling in a way that results in the selective blockade of tumor-promoting pathways, while concomitantly allowing tumor-suppressive pathways to proceed. In this review article, we are going to discuss the specific interactions between RAC1B and TGFβ signaling, which occur at multiple levels and include various components such as ligands, receptors, cytosolic mediators, transcription factors, and extracellular inhibitors of TGFβ ligands.

Targeting RICTOR Sensitizes SMAD4-Negative Colon Cancer to Irinotecan

Deciphering molecular targets to enhance sensitivity to chemotherapy is becoming a priority for effectively treating cancers. Loss of function mutations of SMAD4 in colon cancer are associated with metastatic progression and resistance to 5-fluorouracil (5-FU), the most extensively used drug of almost all chemotherapy combinations used in the treatment of metastatic colon cancer. Here, we report that SMAD4 deficiency also confers resistance to irinotecan, another common chemotherapeutic frequently used alone or in combination with 5-FU against colon cancer. Mechanistically, we find that SMAD4 interacts with and inhibits RICTOR, a component of the mTORC2 complex, resulting in suppression of downstream effector phosphorylation of AKT at Serine 473. In silico meta-analysis of publicly available gene expression datasets derived from tumors indicates that lower levels of SMAD4 or higher levels of RICTOR/AKT, irrespective of the SMAD4 status, correlate with poor survival, suggesting them as strong prognostic biomarkers and targets for therapeutic intervention. Moreover, we find that overexpression of SMAD4 or depletion of RICTOR suppresses AKT signaling and increases sensitivity to irinotecan in SMAD4-deficient colon cancer cells. Consistent with these observations, pharmacologic inhibition of AKT sensitizes SMAD4-negative colon cancer cells to irinotecan in vitro and in vivo. Overall, our study suggests that hyperactivation of the mTORC2 pathway is a therapeutic vulnerability that could be exploited to sensitize SMAD4-negative colon cancer to irinotecan. IMPLICATIONS: Hyperactivation of the mTORC2 pathway in SMAD4-negative colon cancer provides a mechanistic rationale for targeted inhibition of mTORC2 or AKT as a distinctive combinatorial therapeutic opportunity with chemotherapy for colon cancer.

Mechanisms of Metastasis in Colorectal Cancer and Metastatic Organotropism: Hematogenous versus Peritoneal Spread

Metastasis is the major cause of death in patients with colorectal carcinoma (CRC). The most common sites of metastasis are the liver and the peritoneum. Peritoneal carcinomatosis is often considered the end stage of the disease after the tumor has spread to the liver. However, almost half of CRC patients with peritoneal carcinomatosis do not present with liver metastasis. This brings up the question of whether peritoneal spread can still be considered as the end stage of a metastasized CRC or whether it should just be interpreted as a site of metastasis alternative to the liver. This review tries to discuss this question and summarize the current status of literature on potential characteristics in tumor biology in the primary tumor, i.e., factors (transcription factors and direct and indirect E-cadherin repressors) and pathways (WNT, TGF-β, and RAS) modulating EMT, regulation of EMT on a posttranscriptional and posttranslational level (miRNAs), and angiogenesis. In addition to tumor-specific characteristics, factors in the tumor microenvironment, immunological markers, ways of transport of tumor cells, and adhesion molecules appear to differ between hematogenous and peritoneal spread. Factors such as integrins and exosomal integrins, cancer stem cell phenotype, and miRNA expression appear to contribute in determining the metastatic route. We went through each step of the metastasis process comparing hematogenous to peritoneal spread. We identified differences with respect to organotropism, epithelial-mesenchymal transition, angiogenesis and inflammation, and tumor microenvironment which will be further elucidated in this review. A better understanding of the underlying mechanisms and contributing factors of metastasis development in CRC has huge relevance as it is the foundation to help find specific targets for treatment of CRC.

Linking stemness with colorectal cancer initiation, progression, and therapy

The discovery of cancer stem cells caused a paradigm shift in the concepts of origin and development of colorectal cancer. Several unresolved questions remain in this field though. Are colorectal cancer stem cells the cause or an effect of the disease? How do cancer stem cells assist in colorectal tumor dissemination to distant organs? What are the molecular or environmental factors affecting the roles of these cells in colorectal cancer? Through this review, we investigate the key findings until now and attempt to elucidate the origins, physical properties, microenvironmental niches, as well as the molecular signaling network that support the existence, self-renewal, plasticity, quiescence, and the overall maintenance of cancer stem cells in colorectal cancer. Increasing data show that the cancer stem cells play a crucial role not only in the establishment of the primary colorectal tumor but also in the distant spread of the disease. Hence, we will also look at the mechanisms adopted by cancer stem cells to influence the development of metastasis and evade therapeutic targeting and its role in the overall disease prognosis. Finally, we will illustrate the importance of understanding the biology of these cells to develop improved clinical strategies to tackle colorectal cancer.

Effect of STC2 gene silencing on colorectal cancer cells

Stanniocalcin 2 (STC2), a secretory glycoprotein hormone, regulates many biological processes including cell proliferation, apoptosis, tumorigenesis and atherosclerosis. However, the effect of STC2 on proliferation, migration and epithelial-mesenchymal transition (EMT) progression in human colorectal cancer (CRC) cells remains poorly understood. The expression level of STC2 was determined by quantitative real-time polymerase chain reaction (qPCR) and western blot analysis. Cell Counting Kit-8 (CCK-8) was used to detect the viability of SW480 cells. The invasion and migration of cells were identified by wound healing and Transwell assays. The mRNA and protein expression levels of β-catenin, matrix metalloproteinase (MMP)-2, MMP-9, E-cadherin and vimentin were assessed by qPCR and western blot analysis. In the present study, it was demonstrated that STC2 was highly expressed in the CRC cell lines. After silencing of STC2, the cell viability, migration and invasion were significantly reduced. Silencing of STC2 in the CRC Sw480 cells increased the expression of E-cadherin and decreased the expression of vimentin, MMP-2 and MMP-9, compared to those in the normal and empty vector group. Furthermore, the expression of β-catenin in the STC2 gene silenced group was suppressed, and the expression of β-catenin was reversed by Wnt activator, SB216763. These results demonstrated that STC2 participates in the development and progression of CRC by promoting CRC cell proliferation, survival and migration and activating the Wnt/β-catenin signaling pathway.

Novel biomarkers for patient stratification in colorectal cancer: A review of definitions, emerging concepts, and data

Colorectal cancer (CRC) treatment has become more personalised, incorporating a combination of the individual patient risk assessment, gene testing, and chemotherapy with surgery for optimal care. The improvement of staging with high-resolution imaging has allowed more selective treatments, optimising survival outcomes. The next step is to identify biomarkers that can inform clinicians of expected prognosis and offer the most beneficial treatment, while reducing unnecessary morbidity for the patient. The search for biomarkers in CRC has been of significant interest, with questions remaining on their impact and applicability. The study of biomarkers can be broadly divided into metabolic, molecular, microRNA, epithelial-to-mesenchymal-transition (EMT), and imaging classes. Although numerous molecules have claimed to impact prognosis and treatment, their clinical application has been limited. Furthermore, routine testing of prognostic markers with no demonstrable influence on response to treatment is a questionable practice, as it increases cost and can adversely affect expectations of treatment. In this review we focus on recent developments and emerging biomarkers with potential utility for clinical translation in CRC. We examine and critically appraise novel imaging and molecular-based approaches; evaluate the promising array of microRNAs, analyze metabolic profiles, and highlight key findings for biomarker potential in the EMT pathway.

Prognostic value of loss of heterozygosity and sub-cellular localization of SMAD4 varies with tumor stage in colorectal cancer

Background

Although loss of heterozygosity (LOH) at chromosome location 18q21 and decreased expression of SMAD4 in invasive colorectal cancers (CRCs) correlate with poor patient survival, the prognostic value of LOH at 18q21 and sub-cellular localization of SMAD4 have not been evaluated in relation to tumor stage.

Methods

Genomic DNA samples from 209 formalin-fixed, paraffin-embedded sporadic CRC tissues and their matching controls were analyzed for 18q21 LOH, and corresponding tissue sections were evaluated by immunohistochemistry for expression of SMAD4 and assessed for its sub-cellular localization (nuclear vs. cytoplasmic). In addition, 53 frozen CRCs and their matching control tissues were analyzed for their mutational status and mRNA expression of SMAD4. The phenotypic expression pattern and LOH status were evaluated for correlation with patient survival by the use of Kaplan-Meier and Cox regression models.

Results

LOH of 18q21 was detected in 61% of the informative cases. In 8% of the cases, missense point mutations were detected in Smad4. In CRCs, relative to controls, there was increased SMAD4 staining in the cytoplasm (74%) and decreased staining in the nuclei (37%). LOH of 18q21 and high cytoplasmic localization of SMAD4 were associated with shortened overall survival of Stage II patients, whereas low nuclear expression of SMAD4 was associated with worse survival, but only for patients with Stage III CRCs.

Conclusions

LOH of 18q21 and high cytoplasmic localization of SMAD4 in Stage II CRCs and low nuclear SMAD4 in Stage III CRCs are predictors of shortened patient survival.

MicroRNA-1285-5p influences the proliferation and metastasis of non-small-cell lung carcinoma cells via downregulating CDH1 and Smad4

Abnormal expression of microRNAs has been reported to regulate gene expression and cancer cell growth, invasion, and migration. Recently, upregulation of hsa-miR-1285 was demonstrated in bronchoalveolar lavage fluid samples from patients with lung cancer and downregulation in plasma level of stage-I lung cancer patients. However, the function and the underlying mechanism of miR-1285 in non-small-cell lung carcinoma have not been elucidated. In this study, we found that miR-1285-5p, the mature form of miR-1285, was significantly upregulated in human non-small-cell lung carcinoma cell lines A549 and SK-MES-1. Additionally, cells transfected with the miR-1285-5p inhibitor LV-anti-miR-1285-5p demonstrated significantly inhibited proliferation and invasion and depressed migration. Further analysis demonstrated that the miR-1285-5p precursor LV-miR-1285-5p attenuated the expression of Smad4 and cadherin-1 (CDH1) but that LV-anti-miR-1285-5p showed opposite results. A luciferase reporter assay confirmed that miR-1285-5p targeted Smad4 and CDH1. Mechanism analyses revealed that silence of Smad4 and CDH1 significantly attenuated the inhibitory effects of LV-anti-miR-1285-5p on non-small-cell lung carcinoma growth and invasion. Taken together, our data suggest that miR-1285-5p functions as a tumor promoter in the development of non-small-cell lung carcinoma by targeting Smad4 and CDH1, indicating a novel therapeutic strategy for non-small-cell lung carcinoma patients.

Transforming Growth Factor β Superfamily Signaling in Development of Colorectal Cancer

Transforming growth factor (TGF)-β cytokines signal via a complex network of pathways to regulate proliferation, differentiation, adhesion, migration, and other functions in many cell types. A high percentage of colorectal tumors contain mutations that disrupt TGF-β family member signaling. We review how TGF-β family member signaling is altered during development of colorectal cancer, models of study, interaction of pathways, and potential therapeutic strategies.

Role of phytochemicals in the inhibition of epithelial–mesenchymal transition in cancer metastasis

Epithelial–mesenchymal transition (EMT) development is controlled by several signaling pathways including Hedgehog, Wnt, fibroblast growth factors (FGF), hepatocyte growth factor/scatter factor (HGF),etc. Phytochemicals is very promising therapeutic candidate that inhibit the progression of EMT by inhibiting the signaling pathways.

Epithelial-mesenchymal transition in colorectal cancer metastasis: A system review

Tumor metastasis is a multi-step process by which tumor cells disseminate from their primary site and form secondary tumors at a distant site. And metastasis is the major cause of death in the vast majority of cancer patients. However, the mechanisms underlying each step remain obscure. In the past decade, a developmental program epithelial-to-mesenchymal transition (EMT) has been increasingly recognized to play pivotal and intricate roles in promoting carcinoma invasion and metastasis. The EMT process is very complex and controlled by various families of transcriptional regulators through different signaling pathways. In this system review, we focus on the molecular network of the EMT program and its malignant phenotypes associated with metastasis in colorectal cancer (CRC), including cancer stem cells, tumor budding, circulating tumor cells and drug resistance. A better understanding of the molecular regulation of the dynamic EMT program during tumor metastasis will help to provide much-needed therapeutic interventions to target this program when treating metastatic CRC.

RhoC is essential in TGF-β1 induced epithelial-mesenchymal transition in cervical cancer cells

Epithelial-mesenchymal transition (EMT) is a critical process in the promotion of epithelial tumor progression and metastasis. The present study aimed to investigate the role of Ras homolog gene family, member C (RhoC) guanosine triphosphatase (GTPase) in transforming growth factor (TGF)-β1 induced EMT. EMT occurred in human cervical carcinoma SiHa cells following TGF-β1 stimulation for 4 days, as demonstrated by the appearance of mesenchymal morphology, reorganization of the actin cytoskeleton, reduced E-cadherin expression and increased Vimentin expression, which was associated with increased RhoC expression and activity. However, EMT was not observed in cells that were pretreated with RhoC siRNA prior to TGF-β1 stimulation. Downregulation of RhoC 4 days following TGF-β1 stimulation was not able to reverse the existing EMT. In addition, TGF-β1 promoted the invasion of the control SiHa cells but not that of the cells in which RhoC was downregulated. In conclusion, RhoC expression is activated by TGF-β1, and sufficient RhoC expression levels are essential for TGF-β1-induced EMT.

OTUB1 promotes metastasis and serves as a marker of poor prognosis in colorectal cancer

Background

OTUB1 (OTU deubiquitinase, ubiquitin aldehyde binding 1) is a deubiquitinating enzyme (DUB) that belongs to the OTU (ovarian tumor) superfamily. The aim of this study was to clarify the role of OTUB1 in colorectal cancer (CRC) and to identify the mechanism underlying its function.

Methods

Two hundred and sixty CRC samples were subjected to association analysis of OTUB1 expression and clinicopathological variables using immunohistochemical (IHC) staining. Overexpression of OTUB1 was achieved in SW480 and DLD-1 cells, and downregulation of OTUB1 was employed in SW620 cells. Then, migration and invasion assays were performed, and markers of the epithelial-mesenchymal transition (EMT) were analyzed. In addition, hepatic metastasis models in mice were used to validate the function of OTUB1 in vivo.

Results

OTUB1 was overexpressed in CRC tissues, and the expression level of OTUB1 was associated with metastasis. A high expression level of OTUB1 was also associated with poor survival, and OTUB1 served as an independent prognostic factor in multivariate analysis. OTUB1 also promoted the metastasis of CRC cell lines in vitro and in vivo by regulating EMT.

Conclusions

OTUB1 promotes CRC metastasis by facilitating EMT and acts as a potential distant metastasis marker and prognostic factor in CRC. Targeting OTUB1 may be helpful for the treatment of CRC.

Electronic supplementary material

The online version of this article (doi:10.1186/1476-4598-13-258) contains supplementary material, which is available to authorized users.

SMAD4 suppresses AURKA-induced metastatic phenotypes via degradation of AURKA in a TGFβ-independent manner

SMAD4 has been suggested to inhibit the activity of the WNT/β-catenin signaling pathway in cancer. However, the mechanism by which SMAD4 antagonizes WNT/β-catenin signaling in cancer remains largely unknown. Aurora A kinase (AURKA), which is frequently overexpressed in cancer, increases the transcriptional activity of β-catenin/T-cell factor (TCF) complex by stabilizing β-catenin through the inhibition of GSK-3β. Here, SMAD4 modulated AURKA in a TGFβ-independent manner. Overexpression of SMAD4 significantly suppressed AURKA function, including colony formation, migration, and invasion of cell lines. In addition, SMAD4 bound to AURKA induced degradation of AURKA by the proteasome. A luciferase activity assay revealed that the transcriptional activity of the β-catenin/TCF complex was elevated by AURKA, but decreased by SMAD4 overexpression. Moreover, target gene analysis showed that SMAD4 abrogated the AURKA-mediated increase of β-catenin target genes. However, this inhibitory effect of SMAD4 was abolished by overexpression of AURKA or silencing of AURKA in SMAD4-overexpressed cells. Meanwhile, the SMAD4-mediated repression of AURKA and β-catenin was independent of TGFβ signaling because blockage of TGFβR1 or restoration of TGFβ signaling did not prevent suppression of AURKA and β-catenin signaling by SMAD4. These results indicate that the tumor-suppressive function of SMAD4 is mediated by downregulation of β-catenin transcriptional activity via AURKA degradation in a TGFβ-independent manner.

IMPLICATIONS

SMAD4 interacts with AURKA and antagonizes its tumor-promoting potential, thus demonstrating a novel mechanism of tumor suppression.

A three-dimensional in vitro model of tumor cell intravasation

Metastasis is the cause of over 90% of all human cancer deaths. Early steps in the metastatic process include: the formation of new blood vessels, the initiation of epithelial-mesenchymal transition (EMT), and the mobilization of tumor cells into the circulation. There are ongoing efforts to replicate the physiological landscape of human tumor tissue using three-dimensional in vitro culture models; however, few systems are able to capture the full range of authentic, complex in vivo events such as neovascularization and intravasation. Here we introduce the Prevascularized Tumor (PVT) model to investigate early events of solid tumor progression. PVT spheroids are composed of endothelial and tumor cells, and are embedded in a fibrin matrix containing fibroblasts. The PVT model facilitates two mechanisms of vessel formation: robust sprouting angiogenesis into the matrix, and contiguous vascularization within the spheroid. Furthermore, the PVT model enables the intravasation of tumor cells that is enhanced under low oxygen conditions and is also dependent on the key EMT transcription factor Slug. The PVT model provides a significant advance in the mimicry of human tumors in vitro, and may improve investigation and targeting of events in the metastatic process.

Low expression of transforming growth factor beta-1 in cancer tissue predicts a poor prognosis for patients with stage III rectal cancers

OBJECTIVE

Transforming growth factor beta (TGF-β) plays an important role in tumorigenesis and metastasis. It works as a tumor suppressor in the normal colon, but acts as a cancer promoter during the late stages of colorectal carcinogenesis. High expression of TGF-β is known to be associated with advanced stages, tumor recurrence and decreased survival of patients. We investigated the expression of TGF-β and its signaling axis molecules and evaluated their prognostic significance in patients with stage III rectal cancers.

METHODS

Tissues from 201 cases of stage III rectal cancer were subjected to immunohistochemistry for TGF-β1, type II TGF-β receptor, Smad3, Smad4 and Smad7 proteins. The immunoactivities of these molecules were evaluated and the results were compared with clinicopathological variables including patient survival.

RESULTS

Low expression of TGF-β1 protein was correlated with a decreased disease-free survival in univariate Kaplan-Meier (p = 0.003) and multivariate Cox regression (HR 9.188 and 95% CI 1.256-67.198, p = 0.029) analyses. The loss of Smad4 protein expression was associated with a reduction in disease-free survival in the univariate analysis, but this finding was not significant after the multivariate analysis.

CONCLUSION

Low expression of TGF-β1 protein is associated with a poor prognosis for patients with stage III rectal cancers.

Usefulness of plasma epigenetic changes of five major genes involved in the pathogenesis of colorectal cancer

PURPOSE

The purpose of present study was to investigate the methylation status of the promoter region in five genes (mothers against decapentaplegic homolog 4, fragile histidine triad protein, death-associated protein kinase 1, adenomatous polyposis coli (APC), and E-cadherin), which are known to be involved in the pathogenesis of colorectal cancer (CRC) and its clinicopathological significance.

METHODS

The study subjects were 60 CRC patients, 40 patients with adenomatous colorectal polyp and 60 healthy control individuals. We further enrolled a total of 16 patients (two patients with Crohn's disease, two patients with ulcerative colitis, one patient with serrated adenoma, and 11 patients with colorectal cancer). The methylation states of the five genes were determined in peripheral blood plasma using methylation-specific polymerase chain reaction single-strand conformation polymorphism analysis.

RESULTS

This study showed the most sensitive epigenetic markers, E-cadherin (60 %), followed by APC (57 %), for detecting CRC. E-cadherin and APC had similar specificities and amplified 84 and 86 %, respectively, of CRC patients compared to non-CRC patients. Additionally, APC was the only marker to be significantly increased (OR = 6.67, 95 % CI = 1.19-23.4, P = 0.045) and the most sensitive (57 %) and specific (89 %) marker in stage I CRC. Though we have not examined the paired cancer tissues and plasma, there was relatively high concordant rate (60-80 %) in our limited number of colorectal cancer patients.

CONCLUSIONS

Five genes, promoter methylation, in plasma were statistically significant risk factors in CRC patients. In this study, E-cad and APC genes may be particularly useful epigenetic biomarkers in plasma for the detection of CRC. Additionally, APC may able to identify early potential CRC.

Epithelial mesenchymal transition in colorectal cancer: Seminal role in promoting disease progression and resistance to neoadjuvant therapy

BACKGROUND

Epithelial mesenchymal transition (EMT) may be physiological as part of embryological development, or pathological as part of cancer development. It is one of the key initiating events in the metastatic cascade. EMT has profound effects on tumour cell invasiveness, proliferation and motility. In the present article we aimed to review the potential role of EMT as a process to explain colorectal cancer progression and resistance to neoadjuvant therapy.

METHODS

Extensive literature searches were performed in Pubmed, EMBASE and Google Scholar databases to identify relevant articles published before March 2012.

RESULTS

There is adequate evidence to support the complex upstream signalling alterations needed for EMT to occur in colorectal cancers. Changes of EMT are likely to be found at the tumour invasive front: the deepest, growing tumour margin. Loss of E-cadherin at the cell membrane causes loss of cellular integrity, with subsequent migration of malignant cells and tumour budding. These processes are associated with metastases and recurrence of colorectal cancer. There is early evidence from a limited number of studies that resistance to neoadjuvant therapy in colorectal cancer is associated with changes of EMT. However, there is a lack of supporting evidence originating from human colorectal cancer tissues.

CONCLUSIONS

Emerging evidence demonstrates that development of EMT in colorectal cancer leads to an aggressive phenotype that may promote metastatic spread, and augment treatment resistance during neoadjuvant therapy. A clearer understanding of the processes and role of EMT in colorectal cancer may also highlight novel therapeutic strategies.

Developmental pathways in colon cancer: crosstalk between WNT, BMP, Hedgehog and Notch

A hallmark of cancer is reactivation/alteration of pathways that control cellular differentiation during developmental processes. Evidence indicates that WNT, Notch, BMP and Hedgehog pathways have a role in normal epithelial cell differentiation, and that alterations in these pathways accompany establishment of the tumorigenic state. Interestingly, there is recent evidence that these pathways are intertwined at the molecular level, and these nodes of intersection may provide opportunities for effective targeted therapies. This review will highlight the role of the WNT, Notch, BMP and Hedgehog pathways in colon cancer.

Smad4-mediated signaling inhibits intestinal neoplasia by inhibiting expression of β-catenin

BACKGROUND & AIMS

Mutational inactivation of adenomatous polyposis coli (APC) is an early event in colorectal cancer (CRC) progression that affects the stability and increases the activity of β-catenin, a mediator of Wnt signaling. Progression of CRC also involves inactivation of signaling via transforming growth factor β and bone morphogenetic protein (BMP), which are tumor suppressors. However, the interactions between these pathways are not clear. We investigated the effects of loss of the transcription factor Smad4 on levels of β-catenin messenger RNA (mRNA) and Wnt signaling.

METHODS

We used microarray analysis to associate levels of Smad4 and β-catenin mRNA in colorectal tumor samples from 250 patients. We performed oligonucleotide-mediated knockdown of Smad4 in human embryonic kidney (HEK293T) and in HCT116 colon cancer cells and transgenically expressed Smad4 in SW480 colon cancer cells. We analyzed adenomas from (APC(Δ1638/+)) and (APC(Δ1638/+)) × (K19Cre(ERT2)Smad4(lox/lox)) mice by using laser capture microdissection.

RESULTS

In human CRC samples, reduced levels of Smad4 correlated with increased levels of β-catenin mRNA. In Smad4-depleted cell lines, levels of β-catenin mRNA and Wnt signaling increased. Inhibition of BMP or depletion of Smad4 in HEK293T cells increased binding of RNA polymerase II to the β-catenin gene. Expression of Smad4 in SW480 cells reduced Wnt signaling and levels of β-catenin mRNA. In mice with heterozygous disruption of Apc(APC(Δ1638/+)), Smad4-deficient intestinal adenomas had increased levels of β-catenin mRNA and expression of Wnt target genes compared with adenomas from APC(Δ1638/+) mice that expressed Smad4.

CONCLUSIONS

Transcription of β-catenin is inhibited by BMP signaling to Smad4. These findings provide important information about the interaction among transforming growth factor β, BMP, and Wnt signaling pathways in progression of CRC.

Immunohistochemical expression profile of β-catenin, E-cadherin, P-cadherin, laminin-5γ2 chain, and SMAD4 in colorectal serrated adenocarcinoma

The immunohistochemical expression of cell adhesion molecules in colorectal serrated adenocarcinoma is still unknown. The immunostaining patterns of β-catenin, E-cadherin, P-cadherin, laminin 5γ2, and SMAD4 and their relationship to survival were studied in different tumor areas, namely, tumor center and invasive front, the latter comprising tumor bud and non-tumor bud clusters, as described in a previous study of 66 serrated adenocarcinomas and matched conventional carcinomas. Compared with conventional carcinomas, serrated adenocarcinomas showed significantly reduced nuclear β-catenin, membranous E-cadherin, and nuclear SMAD4 but an increased cytoplasmic expression of laminin-5γ2 at the invasive front that was particularly pronounced in the tumor buds. E-cadherin loss at the invasive front was identified as an independent prognostic factor for a poorer outcome in serrated adenocarcinoma. Serrated adenocarcinoma shows a distinct immunohistochemical profile at the invasive front compared with conventional carcinoma, which may account for its less favorable outcome. The lower frequency of nuclear β-catenin in SAC, especially in right-sided tumors, suggests that molecular mechanisms other than the canonical Wnt/β-catenin pathway may have a role in tumor bud formation.

Prognostic value of reduced SMAD4 expression in patients with metastatic colorectal cancer under oxaliplatin-containing chemotherapy: a translational study of the AIO colorectal study group

BACKGROUND

SMAD4 is a polypeptide with tumor suppressor function being investigated as a prognostic biomarker in Union Internationale Contre le Cancer stages II and III in previous studies, but its role as a prognostic marker in stage IV colorectal cancer (CRC) is still undefined. We investigated the prognostic value of reduced SMAD4 expression in patients with metastatic (mCRC) under first-line oxaliplatin-containing combination chemotherapy.

PATIENTS AND METHODS

Tumor samples were obtained from patients who took part in a prospective randomized phase III chemotherapy trial of the Arbeitsgemeinschaft Internistische Onkologie of the German Cancer Society colorectal study group, comparing the use of capecitabine plus oxaliplatin with infusional 5-fluorouracil (5-FU) plus oxaliplatin as first-line therapy in mCRC. SMAD4 expression was determined by immunohistochemistry.

RESULTS

Tumor tissues from 230 patients were obtained. Reduced SMAD4 expression was identified in 34% of samples. Patients with reduced nuclear SMAD4 expression in tumor tissue showed a shorter progression-free survival (PFS; 7.0 months vs. 8.9 months; P = .024) and overall survival (OS; 13.9 months vs. 17.8 months; P = .044) compared with patients retaining SMAD4 expression. The effect of SMAD4 expression on PFS and OS could be demonstrated in univariate and multivariate analyses.

CONCLUSION

Our data demonstrate the importance of reduced SMAD4 expression in patients with mCRC receiving chemotherapy with oxaliplatin and 5-FU.

Keratin 23, a novel DPC4/Smad4 target gene which binds 14-3-3ε

Background

Inactivating mutations of SMAD4 are frequent in metastatic colorectal carcinomas. In previous analyses, we were able to show that restoration of Smad4 expression in Smad4-deficient SW480 human colon carcinoma cells was adequate to suppress tumorigenicity and invasive potential, whereas in vitro cell growth was not affected. Using this cellular model system, we searched for new Smad4 targets comparing nuclear subproteomes derived from Smad4 re-expressing and Smad4 negative SW480 cells.

Methods

High resolution two-dimensional (2D) gel electrophoresis was applied to identify novel Smad4 targets in the nuclear subproteome of Smad4 re-expressing SW480 cells. The identified candidate protein Keratin 23 was further characterized by tandem affinity purification. Immunoprecipitation, subfractionation and immunolocalization studies in combination with RNAi were used to validate the Keratin 23-14-3-3ε interaction.

Results

We identified keratins 8 and 18, heat shock proteins 60 and 70, plectin 1, as well as 14-3-3ε and γ as novel proteins present in the KRT23-interacting complex. Co-immunoprecipitation and subfractionation analyses as well as immunolocalization studies in our Smad4-SW480 model cells provided further evidence that KRT23 associates with 14-3-3ε and that Smad4 dependent KRT23 up-regulation induces a shift of the 14-3-3ε protein from a nuclear to a cytoplasmic localization.

Conclusion

Based on our findings we propose a new regulatory circuitry involving Smad4 dependent up-regulation of KRT23 (directly or indirectly) which in turn modulates the interaction between KRT23 and 14-3-3ε leading to a cytoplasmic sequestration of 14-3-3ε. This cytoplasmic KRT23-14-3-3 interaction may alter the functional status of the well described 14-3-3 scaffold protein, known to regulate key cellular processes, such as signal transduction, cell cycle control, and apoptosis and may thus be a previously unappreciated facet of the Smad4 tumor suppressive circuitry.

Smad4 inactivation promotes malignancy and drug resistance of colon cancer

SMAD4 is localized to chromosome 18q21, a frequent site for loss of heterozygosity in advanced stage colon cancers. Although Smad4 is regarded as a signaling mediator of the TGFβ signaling pathway, its role as a major suppressor of colorectal cancer progression and the molecular events underlying this phenomenon remain elusive. Here, we describe the establishment and use of colon cancer cell line model systems to dissect the functional roles of TGFβ and Smad4 inactivation in the manifestation of a malignant phenotype. We found that loss of function of Smad4 and retention of intact TGFβ receptors could synergistically increase the levels of VEGF, a major proangiogenic factor. Pharmacologic inhibition studies suggest that overactivation of the TGFβ-induced MEK-Erk and p38-MAPK (mitogen-activated protein kinase) auxiliary pathways are involved in the induction of VEGF expression in SMAD4 null cells. Overall, SMAD4 deficiency was responsible for the enhanced migration of colon cancer cells with a corresponding increase in matrix metalloprotease 9 enhanced hypoxia-induced GLUT1 expression, increased aerobic glycolysis, and resistance to 5'-fluoruracil-mediated apoptosis. Interestingly, Smad4 specifically interacts with hypoxia-inducible factor (HIF) 1α under hypoxic conditions providing a molecular basis for the differential regulation of target genes to suppress a malignant phenotype. In summary, our results define a molecular mechanism that explains how loss of the tumor suppressor Smad4 promotes colorectal cancer progression. These findings are also consistent with targeting TGFβ-induced auxiliary pathways, such as MEK-ERK, and p38-MAPK and the glycolytic cascade, in SMAD4-deficient tumors as attractive strategies for therapeutic intervention.

Tumor-associated Macrophages (TAM) and Inflammation in Colorectal Cancer

Experimental and epidemiological studies indicate a strong link between chronic inflammation and tumor progression. Human colorectal cancer (CRC), a major cause of cancer-related death in Western countries, represents a paradigm for this link. Key features of cancer-related inflammation in CRC are the activation of transcription factors (e.g. NF-κB, STAT3), the expression of inflammatory cytokines and chemokines (e.g. TNFα, IL-6, CCL2, CXCL8) as well as a prominent leukocyte infiltrate. While considerable evidence indicates that the presence of lymphocytes of adaptive immunity may positively influence patient survival and clinical outcome in CRC, the role of tumor-associated macrophages (TAM) and of other lymphoid populations (e.g. Th17, Treg) is still unclear. In this review we will summarize the different and controversial effects that TAM play in CRC-related inflammation and progression of disease. The characterization of the most relevant inflammatory pathways in CRC is instrumental for the identification of new target molecules that could lead to improved diagnosis and treatment.

Role of TGF-beta1, its receptor TGFbetaRII, and Smad proteins in the progression of colorectal cancer

AIM

In the current study, we investigated the expression of TGF-beta1, its receptor TGFbetaRII, and the signaling proteins Smad4 and Smad7 in colorectal cancer tissue in relation to infiltration with antigen-presenting cells and some clinical and pathologic parameters of disease progression in patients with colorectal cancer (CRC).

MATERIALS AND METHODS

The immunohistochemical expression of TGF-beta1, TGFbetaRII, Smad4, Smad7, HLA-DR antigen, CD1a, CD83, and CD68 was evaluated in 142 patients (50 females and 92 males) with CRC, followed-up for 6-8 years period.

RESULTS

In our study, 127 (89.4%) out of 142 colorectal cancers displayed cytoplasmic TGF-beta1 immunoreactivity. Common-mediator Smad4 was detected in the tumor cytoplasm in 124 cancers (79.5%) and inhibitory Smad7 immunostaining was observed in 110 (77.4%) tumor specimens. TGFbetaRII was expressed on tumor cell membranes in 119 (76.3%) of the cancers. The increased TGF-beta1 expression in tumor cytoplasm was related to low CD68(+)- and CD83(+)-cell infiltration in tumor tissues. Patients with TGF-beta1 overexpression had worse prognosis after surgical therapy compared to those with low expression of TGF-beta1. The observed association was more pronounced for the patients in T1-T2 stage (p = 0.0015).

CONCLUSIONS

The expression of TGF-beta1, its receptor TGFbetaRII, and signaling proteins Smad4 and Smad7 was observed in the majority of colorectal cancer specimens. Our results suggest that TGF-beta1 production by tumor cells may affect the tumor environment via suppression of tumor-infiltrating immune cells and probably contributes to tumor cells aggressiveness through autocrine activation of Smad signaling.

Significance of expression of metastasis-related factors uPA, MMP-2, MMP-9 and TGF-β1 in gastrointestinal stromal tumors

AIM: To investigate the significance of expression of urokinase-type plasminogen activator (uPA), matrix metalloproteinase-2 (MMP-2), matrix metalloproteinase-9 (MMP-9) and transforming growth factor-β1 (TGF-β1) in gastrointestinal stromal tumors (GISTs).

METHODS: The expression of uPA, MMP-2, MMP-9 and TGF-β1 mRNAs and proteins in 124 GISTs specimens was detected by reverse transcription-polymerase chain reaction (RT-PCR) and Western blot, respectively.

RESULTS: In gastrointestinal stromal tumors, the mRNA expression of uPA, MMP-2, MMP-9 and TGF-β1 is closely correlated with tumor stage (NIH classification), mucosal invasion and lymphatic metastasis. The mRNA expression levels of uPA, MMP-2, MMP-9 and TGF-β1 were up-regulated with increasing tumor stage, showing significant differences among low-, moderate- and high-risk GISTs. The positive rates of uPA, MMP-2, MMP-9 and TGF-β1 mRNA expression was not correlated with age, sex and histological type. Similar results were obtained for the expression of uPA, MMP-2, MMP-9 and TGF-β1 proteins in GISTs. The expression of uPA protein is positively correlated with that of TGF-β1, MMP-2 and MMP-9 (r = 0.356, 0.323 and 0.346, respectively).

CONCLUSION: The positive activation of TGF-β1 in GISTs possibly up-regulates uPA expression which in turn activates MMP-2 and MMP-9. The activation of MMP-2 and MMP-9 may lead to the degradation of extracellular matrix degradation and promote tumor invasion and metastasis.

The tumor microenvironment in colorectal carcinogenesis

Colorectal cancer is the second leading cause of cancer-related mortality in the United States. Therapeutic developments in the past decade have extended life expectancy in patients with metastatic disease. However, metastatic colorectal cancers remain incurable. Numerous agents that were demonstrated to have significant antitumor activity in experimental models translated into disappointing results in extending patient survival. This has resulted in more attention being focused on the contribution of tumor microenvironment to the progression of a number of solid tumors including colorectal cancer. A more complete understanding of interactions between tumor epithelial cells and their stromal elements will enhance therapeutic options and improve clinical outcome. Here we will review the role of various stromal components in colorectal carcinogenesis and discuss the potential of targeting these components for the development of future therapeutic agents.

Development and progression of colorectal neoplasia

A variety of genetic and molecular alterations underlie the development and progression of colorectal neoplasia (CRN). Most of these cancers arise sporadically due to multiple somatic mutations and genetic instability. Genetic instability includes chromosomal instability (CIN) and microsatellite instability (MSI), which is observed in most hereditary non-polyposis colon cancers (HNPCCs) and accounts for a small proportion of sporadic CRN. Although many biomarkers have been used in the diagnosis and prediction of the clinical outcomes of CRNs, no single marker has established value. New markers and genes associated with the development and progression of CRNs are being discovered at an accelerated rate. CRN is a heterogeneous disease, especially with respect to the anatomic location of the tumor, race/ethnicity differences, and genetic and dietary interactions that influence its development and progression and act as confounders. Hence, efforts related to biomarker discovery should focus on identification of individual differences based on tumor stage, tumor anatomic location, and race/ethnicity; on the discovery of molecules (genes, mRNA transcripts, and proteins) relevant to these differences; and on development of therapeutic approaches to target these molecules in developing personalized medicine. Such strategies have the potential of reducing the personal and socio-economic burden of CRNs. Here, we systematically review molecular and other pathologic features as they relate to the development, early detection, diagnosis, prognosis, progression, and prevention of CRNs, especially colorectal cancers (CRCs).

Smad4 restoration leads to a suppression of Wnt/beta-catenin signaling activity and migration capacity in human colon carcinoma cells

Recent studies have reported that Smad4 has a TGF-beta-independent function as a tumor suppressor in cooperating with beta-catenin/Lef to regulate target gene expression. The objective of this research was to study the role of Smad4 in colon cancer migration and its potential mechanism. In our study, stable colon cancer cells that have increased Smad4 expression were created using a eukaryotic vector containing Smad4-pcDNA3.1(+). Smad4 restoration directly suppressed the Wnt/beta-catenin signal activity in SW480 cells by down-regulating beta-catenin expression and altering its localization from cytoplasm and nucleus to the plasma membrane. Up-regulation of Smad4 also increased the expression of E-cadherin and decreased the transcriptional activity of beta-catenin/Tcf target genes, such as claudin-1 and MMP-7. SW480 cells with increased Smad4 expression had decreased in vitro cell migration. The data suggested that restoration of Smad4 in Smad4-deficient cells may provide a potential therapeutic strategy for intervention of colon cancer migration and metastasis.

Divergent mechanisms underlie Smad4-mediated positive regulation of the three genes encoding the basement membrane component laminin-332 (laminin-5)

BACKGROUND

Functional inactivation of the tumor suppressor Smad4 in colorectal and pancreatic carcinogenesis occurs coincident with the transition to invasive growth. Breaking the basement membrane (BM) barrier, a prerequisite for invasive growth, can be due to tumor induced proteolytic tissue remodeling or to reduced synthesis of BM molecules by incipient tumor cells. Laminin-332 (laminin-5), a heterotrimeric BM component composed of alpha 3-, beta 3- and gamma 2-chains, has recently been identified as a target structure of Smad4 and represents the first example for expression control of an essential BM component by a tumor and invasion suppressor. Biochemically Smad4 is a transmitter of signals of the TGFbeta superfamily of cytokines. We have reported previously, that Smad4 functions as a positive transcriptional regulator of constitutive and of TGFbeta-induced transcription of all three genes encoding Laminin-332, LAMA3, LAMB3 and LAMC2.

METHODS

Promoter-reporter constructs harboring 4 kb upstream regions, each of the three genes encoding Laminin-322 as well as deletion and mutations constructs were established. Promoter activities and TGFbeta induction were assayed through transient transfections in Smad4-negative human cancer cells and their stable Smad4-positive derivatives. Functionally relevant binding sites were subsequently confirmed through chromatin immunoprecipitation.

RESULTS

Herein, we report that Smad4 mediates transcriptional regulation through three different mechanisms, namely through Smad4 binding to a functional SBE site exclusively in the LAMA3 promoter, Smad4 binding to AP1 (and Sp1) sites presumably via interaction with AP1 family components and lastly a Smad4 impact on transcription of AP1 factors. Whereas Smad4 is essential for positive regulation of all three genes, the molecular mechanisms are significantly divergent between the LAMA3 promoter as compared to the LAMB3 and LAMC2 promoters.

CONCLUSION

We hypothesize that this divergence in modular regulation of the three promoters may lay the ground for uncoupled regulation of Laminin-332 in Smad4-deficient tumor cells in response to stromally expressed cytokines acting on budding tumor cells.

High-level inducible Smad4-reexpression in the cervical cancer cell line C4-II is associated with a gene expression profile that predicts a preferential role of Smad4 in extracellular matrix composition

Background

Smad4 is a tumour suppressor frequently inactivated in pancreatic and colorectal cancers. We have recently reported loss of Smad4 in every fourth carcinoma of the uterine cervix. Smad4 transmits signals from the TGF-β superfamily of cytokines and functions as a versatile transcriptional co-modulator. The prevailing view suggests that the tumour suppressor function of Smad4 primarily resides in its capability to mediate TGF-β growth inhibitory responses. However, accumulating evidence indicates, that the acquisition of TGF-β resistance and loss of Smad4 may be independent events in the carcinogenic process. Through inducible reexpression of Smad4 in cervical cancer cells we wished to shed more light on this issue and to identify target genes implicated in Smad4 dependent tumor suppression.

Methods

Smad4-deficient human C4-II cervical carcinoma cells were used to establish inducible Smad4 reexpression using the commercial Tet-on™ system (Clontech). The impact of Smad4 reexpression on cell growth was analysed in vitro and in vivo. Transcriptional responses were assessed through profiling on cDNA macroarrays (Clontech) and validated through Northern blotting.

Results

Clones were obtained that express Smad4 at widely varying levels from approximately physiological to 50-fold overexpression. Smad4-mediated tumour suppression in vivo was apparent at physiological expression levels as well as in Smad4 overexpressing clones. Smad4 reexpression in a dose-dependent manner was associated with transcriptional induction of the extracellular matrix-associated genes, BigH3, fibronectin and PAI-1, in response to TGF-β. Smad4-dependent regulation of these secreted Smad4 targets is not restricted to cervical carcinoma cells and was confirmed in pancreatic carcinoma cells reexpressing Smad4 after retroviral transduction and in a stable Smad4 knockdown model. On the other hand, the classical cell cycle-associated TGF-β target genes, c-myc, p21 and p15, remained unaltered.

Conclusion

Our results show that Smad4-mediated tumour suppression in cervical cancer cells is not due to restoration of TGF-β growth inhibitory responses. Rather, tumour cell-ECM interactions may be more relevant for Smad4-mediated tumour suppression. C4-II cells with a high level inducible Smad4 expression may serve as a model to indicate further Smad4 targets responsive to diverse environmental stimuli operative in vivo.

Moderate folate depletion modulates the expression of selected genes involved in cell cycle, intracellular signaling and folate uptake in human colonic epithelial cell lines

Folate deficiency may affect gene expression by disrupting DNA methylation patterns or by inducing base substitution, DNA breaks, gene deletions and gene amplification. Changes in expression may explain the inverse relationship observed between folate status and risk of colorectal cancer. Three cell lines derived from the normal human colon, HCEC, NCM356 and NCM460, were grown for 32-34 days in media containing 25, 50, 75 or 150 nM folic acid, and the expression of genes involved in cell-cycle checkpoints, intracellular signaling, folate uptake and cell adhesion and migration was determined. Expression of Folate Receptor 1 was increased with decreasing media folate in all cell lines, as was p53, p21, p16 and beta-catenin. With decreasing folate, the expression of both E-cadherin and SMAD-4 was decreased in NCM356. APC was elevated in NCM356 but unchanged in the other lines. No changes in global methylation were detected. A significant increase in p53 exon 7-8 strand breaks was observed with decreasing folate in NCM460 cells. The changes observed are consistent with DNA damage-induced activation of cell-cycle checkpoints and cellular adaptation to folate depletion. Folate-depletion-induced changes in the Wnt/APC pathway as well as in genes involved in cell adhesion, migration and invasion may underlie observed relationships between folate status and cancer risk.

Aberrant expression of Smad4, a TGF-beta signaling molecule, in oral squamous cell carcinoma

Although carcinogenesis of oral squamous cell carcinoma (OSCC) has been studied by many investigators in the past decade, the available evidence about its molecular mechanism is inconclusive. The objective of the present study was to compare expression of Smad4, a signaling molecule of the transforming growth factor beta (TGF-beta) pathway, between OSCC and normal oral mucosa. We assayed expression of Smad4 in OSCC and normal oral mucosa by performing immunohistochemistry using paraffin-embedded tissue samples. We also compared expression of Smad4 protein between OSCC lines and normal oral keratinocytes, using Western blot analysis. Smad4 expression was observed in only 60% of OSCC tissue samples, whereas it was observed in 82% of normal oral mucosa samples. Reduced Smad4 expression was clearly observed in all OSCC lines, compared with normal oral keratinocytes. These findings suggest that aberration of the TGF-beta pathway, as indicated by a reduction or absence of Smad4 expression, promotes carcinogenesis of OSCC.

Inactivation of SMAD4 tumor suppressor gene during gastric carcinoma progression

PURPOSE

Mothers against decapentaplegic homologue 4 (SMAD4) is a tumor suppressor gene associated with gastrointestinal carcinogenesis. The aim of the present study is to more precisely characterize its role in the development and progression of human gastric carcinoma.

EXPERIMENTAL DESIGN

The expression of SMAD4 was investigated in 283 gastric adenocarcinomas and related lesions, as well as in 9 gastric carcinoma cell lines. We also analyzed the methylation status of SMAD4 gene by using methylation-specific PCR, examined loss of heterozygosity (LOH) of this gene locus by using a vicinal marker, and detected exon mutation of SMAD4 through exon-by-exon amplification. Moreover, we assessed whether MG132, a proteasome inhibitor, affected the SMAD4 protein level.

RESULTS

We found loss of SMAD4 protein expression in the cytoplasm (36 of 114, 32%) and in the nucleus (46 of 114, 40%) of gastric cancer cells. The loss of nuclear SMAD4 expression in primary tumors correlated significantly with poor survival, and was an independent prognostic marker in multivariate analysis. We also found a substantial decrease in SMAD4 expression at both the RNA and protein level in several human gastric carcinoma cell lines. In addition, we found that LOH (20 of 70, 29%) and promoter hypermethylation (4 of 73, 5%) were associated with the loss of SMAD4 expression. SMAD4 protein levels were also affected in certain gastric carcinoma cell lines following incubation with MG132.

CONCLUSION

Taken together, our results indicate that the loss of SMAD4, especially loss of nuclear SMAD4 expression, is involved in gastric cancer progression. The loss of SMAD4 in gastric carcinomas was due to several mechanisms, including LOH, hypermethylation, and proteasome degradation.

Smad4 regulates claudin-1 expression in a transforming growth factor-beta-independent manner in colon cancer cells

We have recently reported that the expression of a tight junction protein, claudin-1, is increased during colon carcinogenesis and particularly metastatic colorectal cancer. Manipulation of claudin-1 levels in colon cancer cells showed a positive correlation between claudin-1 expression and tumor growth and metastasis. However, the mechanisms underlying the increased claudin-1 expression in colorectal cancer remains unknown. The tumor suppressor Smad4 is a central intracellular signal transduction component of the transforming growth factor-beta (TGF-beta) family of cytokines. Loss of Smad4 protein expression is correlated with poor prognosis and is frequently observed in invasive and metastatic colorectal carcinoma. In the present study, we report an inverse relationship between Smad4 and claudin-1 expression in human colorectal carcinoma tumor samples and in human colon cancer cell lines. We found that the expression of Smad4 in Smad4-deficient but claudin-1-positive SW480 or HT29 colon cancer cell lines down-regulates claudin-1 expression through transcriptional repression by modulating beta-catenin/T-cell factor/lymphocyte enhancer factor activity. Furthermore, this Smad4-dependent inhibition of claudin-1 expression is independent of TGF-beta signaling because Smad4 expression alone is insufficient to restore TGF-beta signaling in the SW480 cells, and the selective TGF-beta receptor kinase inhibitor LY364947 did not prevent the Smad4 suppression of claudin-1 protein expression in either SW480 or HT29 cells. Taken together, these findings suggest a novel mechanism underlying Smad4 tumor-suppressive function through regulation of a potential metastatic modulator, claudin-1, in a TGF-beta-independent manner.

Mucosal integrity and barrier function in the pathogenesis of early lesions in Crohn's disease

Crohn's disease aetiology is multifactorial and remains enigmatic. However, animal models show that disease heterogeneity is probable, in that more than one defective mucosal mechanism can produce the same clinical phenotype. For example, Crohn's-like lesions are reported after compromise of mucosal integrity per se in the presence of an intact immune system, through altered expression of mucosal adhesion molecules, such as cadherins and tight junction proteins, highlighting the importance of the mucosal barrier in the disease process. Key to mucosal damage is the trigger of an inflammatory cascade after luminal antigen processing, a role classically ascribed to M cells in the surface follicle associated epithelium. Direct luminal antigen sampling has recently been proposed, however, by extension of dendritic cell (DC) processes through the intact gut epithelium, and it follows that early mucosal damage could result from de novo lymphoid recruitment. Cytokines, such as tumour necrosis factor alpha (TNFalpha), are known to drive inflammation, but emerging data suggest additional important roles for TNFalpha influencing mucosal barrier efficacy by altering adhesion molecule expression, influencing epithelial apoptosis, and affecting tight junction functionality.

Gene expression profiling of colorectal adenomas and early invasive carcinomas by cDNA array analysis

It is generally accepted that most colorectal carcinomas arise in pre-existing adenomas. Morphologically, colorectal adenomas can be divided into two groups, protruded type and flat type. The aim of this study was to clarify relevant alterations of gene expression associated with the early stage of colorectal carcinogenesis. Using cDNA array, we analysed the expression profiles of 550 cancer-related genes in 36 colorectal adenomas (18 flat-type and 18 protruded-type adenomas) and 14 early invasive carcinomas. Among the 550 genes, we chose 32 genes the average expression levels of which were at least three-fold up- or downregulated in tumour tissues compared with levels in matched normal tissues. A total of 13 and 19 genes were identified as up- and downregulated genes in tumour tissues, respectively. Among the upregulated genes, the average expression levels of E1AF, bone morphogenic protein (BMP)-4, insulin-like growth factor (IGF)-2, inducible nitric oxide synthase (iNOS), tissue inhibitors of metalloproteinase (TIMP)-1, Smad4, and nm23 in tumour tissues were over five times higher than those in matched normal tissues. Colorectal adenomas and early invasive carcinomas were divided into two major clusters by clustering analysis. Moreover, flat- and protruded-type adenomas were divided into two major clusters by clustering analysis. The expression profiles obtained by the cDNA array clearly indicate that colorectal adenomas and early invasive carcinomas have specific expression profiles. Likewise, the gene expression profiles of flat- and protruded-type adenomas are different. These results indicate that molecular classification of early colorectal tumours by a cDNA array is feasible.