Claudin-7 expression induces mesenchymal to epithelial transformation (MET) to inhibit colon tumorigenesis. Oncogene. 2015;34:4570-4580. [PMID: 25500541 DOI: 10.1038/onc.2014.385]

Transcription factor ZEB1 coordinating with NuRD complex to promote oncogenesis through glycolysis in colorectal cancer

Background

Colorectal cancer (CRC) is an aggressive primary intestinal malignancy with the third-highest incidence and second-highest mortality among all cancer types worldwide. Transcription factors (TFs) regulate cell development and differentiation owing to their ability to recognize specific DNA sequences upstream of genes. Numerous studies have demonstrated a strong correlation between TFs, the etiology of tumors, and therapeutic approaches. Here, we aimed to explore prognosis-related TFs and comprehend their carcinogenic mechanisms, thereby offering novel insights into the diagnosis and management of CRC.

Materials and Methods

Differentially expressed TFs between CRC and normal tissues were identified leveraging The Cancer Genome Atlas database, Weighted correlation network analysis and Cox regression analysis were performed to identify prognosis-related TFs. The cellular functions of hub TF zinc finger E-box binding homeobox 1 (ZEB1) were determined using by 5-ethynyl-2'-deoxyuridine and cell invasion assays in CRC cells. RNA-sequencing, Kyoto Encyclopedia of Genes and Genomes enrichment, and gene set enrichment analyses were used to identify the cellular processes in which ZEB1 participates. Immunoaffinity purification, silver staining mass spectrometry, and a chromatin immunoprecipitation assay were conducted to search for proteins that might interact with ZEB1 and the target genes they jointly regulate.

Results

Thirteen central TFs related to prognosis were identified through bioinformatics analysis techniques. Among these TFs, ZEB1 emerged as the TF most closely associated with CRC, as determined through a combination of regulatory network diagrams, survival curves, and phenotype analyses. ZEB1 promotes CRC cell growth by recruiting the NuRD(MTA1) complex, and the ZEB1/NuRD(MTA1) complex transcriptionally represses glycolysis-associated tumor suppressor genes.

Conclusion

Our study not only identified a hub biomarker related to CRC prognosis but also revealed the specific molecular mechanisms through which ZEB1 affects cancer progression. These insights provide crucial evidence for the diagnosis of CRC and potential treatment opportunities.

Colonic crypt stem cell functions are controlled by tight junction protein claudin-7 through Notch/Hippo signaling

The tight junction protein claudin-7 is essential for tight junction function and intestinal homeostasis. Cldn7 deletion in mice leads to an inflammatory bowel disease-like phenotype exhibiting severe intestinal epithelial damage, weight loss, inflammation, mucosal ulcerations, and epithelial hyperplasia. Claudin-7 has also been shown to be involved in cancer metastasis and invasion. Here, we test our hypothesis that claudin-7 plays an important role in regulating colonic intestinal stem cell function. Conditional knockout of Cldn7 in the colon led to impaired epithelial cell differentiation, hyperproliferative epithelium, a decrease in active stem cells, and dramatically altered gene expression profiles. In 3D colonoid culture, claudin-7-deficient crypts were unable to survive and form spheroids, emphasizing the importance of claudin-7 in stem cell survival. Inhibition of the Hippo pathway or activation of Notch signaling partially rescued the defective stem cell behavior. Concurrent Notch activation and Hippo inhibition resulted in restored colonoid survival, growth, and differentiation to the level comparable to those of wild-type derived crypts. In this study, we highlight the essential role of claudin-7 in regulating Notch and Hippo signaling-dependent colonic stem cell functions, including survival, self-renewal, and differentiation. These new findings may shed light on potential avenues to explore for drug development in colorectal cancer.

Low expression of RACK1 is associated with metastasis and worse prognosis in cholangiocarcinoma

Background

Cholangiocarcinoma is a poorly prognostic malignant tumor, and the metastatic stage of cancer is not an early stage when diagnosed. Lymph node metastasis is common in the early stage. Ribosomal receptor for activated C-kinase 1 (RACK1) has found involved in the oncogenesis of various tumors and in the epithelial-mesenchymal transition (EMT). Nevertheless, its role in cholangiocarcinoma remains unknown.

Material and methods

The possible correlation between RACK1 and tumor prognosis was analyzed in cholangiocarcinoma patients. The GEO and TCGA databases were used to evaluate the level of RACK1 in cholangiocarcinoma. The RBE and HCCC-9810 cell lines were used to examine the effects of RACK1 in the behavior of tumor cells in vitro.

Results

The Kaplan-Meier analysis indicated that low expression of RACK1 was associated with poor prognosis and RACK1 was negatively related to lymph node metastasis, which were verified in databases TCGA and GEO; downregulation of RACK1 via RNA interference correlated with changes in the expression of EMT biomarkers and promoted the migration of cholangiocarcinoma cell lines.

Conclusion

The protein expression of RACK1 is significantly higher in cholangiocarcinoma tissues than in peritumoral tissues, however, the high RACK1 expression indicates better overall survival and less risk for lymph node metastasis. In vitro, RACK1 may suppress the migratory ability of cholangiocarcinoma cells by inhibiting EMT.

Rab25 suppresses colon cancer cell invasion through upregulating claudin‑7 expression

Ras‑related protein 25 (Rab25) is a member of small GTPase and is implicated in cancer cell progression of various types of cancer. Growing evidence suggests the context‑dependent role of Rab25 in cancer invasiveness. Claudin‑7 is a tight junction protein and has been known to suppress cancer cell invasion. Although Rab25 was reported to repress cancer aggressiveness through recycling β1 integrin to the plasma membrane, the detailed underlying mechanism remains to be elucidated. The present study identified the critical role of claudin‑7 in Rab25‑induced suppression of colon cancer invasion. 3D Matrigel system and modified Boyden chamber analysis showed that enforced expression of Rab25 attenuated colon cancer cell invasion. In addition, Rab25 inactivated epidermal growth factor receptor (EGFR) and increased E‑cadherin expression. Unexpectedly, it was observed that Rab25 induces claudin‑7 expression through protein stabilization. In addition, ectopic claudin‑7 expression reduced EGFR activity and Snail expression as well as colon cancer cell invasion. However, silencing of claudin‑7 expression reversed the tumor suppressive role of Rab25, thereby increasing colon cancer cell invasiveness. Collectively, the present data indicated that Rab25 inactivates EGFR and colon cancer cell invasion by upregulating claudin‑7 expression.

Tight Junction Claudins and Occludin Are Differentially Regulated and Expressed in Genomically Defined Subsets of Colon Cancer

Metastatic colon cancer remains incurable despite improvements in survival outcomes. New therapies based on the discovery of colon cancer genomic subsets could improve outcomes. Colon cancers from genomic studies with publicly available data were examined to define the expression and regulation of the major tight junction proteins claudins and occludin in genomic groups. Putative regulations of the promoters of tight junction genes by colon-cancer-deregulated pathways were evaluated in silico. The effect of claudin mRNA expression levels on survival of colon cancer patients was examined. Common mutations in colon-cancer-related genes showed variable prevalence in genomically identified groups. Claudin genes were rarely mutated in colon cancer patients. Genomically identified groups of colon cancer displayed distinct regulation of claudins and occludin at the mRNA level. Claudin gene promoters possessed clustered sites of binding sequences for transcription factors TCF4 and SMADs, consistent with a key regulatory role of the WNT and TGFβ pathways in their expression. Although an effect of claudin mRNA expression on survival of colon cancer patients as a whole was not prominent, survival of genomic subsets was significantly influenced by claudin mRNA expression. mRNA expression of the main tight junction genes showed differential regulation in various genomically defined subgroups of colon cancer. These data pinpoint a distinct role of claudins and pathways that regulate them in these subgroups and suggest that subgroups of colon cancer should be considered in future efforts to therapeutically target claudins.

Trans-Compartmental Regulation of Tight Junction Barrier Function

Tight junctions (TJs) are the most apical components of junctional complexes in epithelial and endothelial cells. Barrier function is one of the major functions of TJ, which restricts the ions and small water-soluble molecules from passing through the paracellular pathway. Adherens junctions (AJs) play an important role in cell-cell adhesion and cell signaling. Gap junctions (GJs) are intercellular channels regulating electrical and metabolic signals between cells. It is well known that TJ integral membrane proteins, such as claudins and occludins, are the molecular building blocks responsible for TJ barrier function. However, recent studies demonstrate that proteins of other junctional complexes can influence and regulate TJ barrier function. Therefore, the crosstalk between different cell junctions represents a common means to modulate cellular activities. In this review, we will discuss the interactions among TJ, AJ, and GJ by focusing on how AJ and GJ proteins regulate TJ barrier function in different biological systems.

Expression of Claudins in Preneoplastic Conditions of the Gastrointestinal Tract: A Review

Premalignant lesions of the gastrointestinal tract are a group of disorders which act as the harbinger of malignant tumors. They are the ground-zero of neoplastic transformation, and their identification and management offer patients the best opportunity of blocking the progress of cancer. However, diagnoses of some of these conditions are hard to make, and their clinical importance is difficult to assess. Recent reports indicated that several claudin proteins have altered expressions in many cancers, including esophageal, gastric, colon, liver, and pancreatic cancers. The early identification of the aberrant expression of these proteins could lead to the early diagnosis and management of gastrointestinal tumors. Specifically, claudins -1, -2, -3, -4, and -18 are frequently overexpressed in gastrointestinal preneoplastic lesions. These altered expressions have shown clinical value in several tumors, providing diagnostic and prognostic information. In this article, we review the literature on the aberrant expression of claudins in preneoplastic lesions of the gastrointestinal tract. Additionally, we summarize their diagnostic and prognostic implications.

IL-22-Activated MUC13 Impacts on Colonic Barrier Function through JAK1/STAT3, SNAI1/ZEB1 and ROCK2/MAPK Signaling

Overexpression of the transmembrane mucin MUC13, as seen in inflammatory bowel diseases (IBD), could potentially impact barrier function. This study aimed to explore how inflammation-induced MUC13 disrupts epithelial barrier integrity by affecting junctional protein expression in IBD, thereby also considering the involvement of MUC1. RNA sequencing and permeability assays were performed using LS513 cells transfected with MUC1 and MUC13 siRNA and subsequently stimulated with IL-22. In vivo intestinal permeability and MUC13-related signaling pathways affecting barrier function were investigated in acute and chronic DSS-induced colitis wildtype and Muc13^-/- mice. Finally, the expression of MUC13, its regulators and other barrier mediators were studied in IBD and control patients. Mucin knockdown in intestinal epithelial cells affected gene expression of several barrier mediators in the presence/absence of inflammation. IL-22-induced MUC13 expression impacted barrier function by modulating the JAK1/STAT3, SNAI1/ZEB1 and ROCK2/MAPK signaling pathways, with a cooperating role for MUC1. In response to DSS, MUC13 was protective during the acute phase whereas it caused more harm upon chronic colitis. The pathways accounting for the MUC13-mediated barrier dysfunction were also altered upon inflammation in IBD patients. These novel findings indicate an active role for aberrant MUC13 signaling inducing intestinal barrier dysfunction upon inflammation with MUC1 as collaborating partner.

Claudins: The Newly Emerging Targets in Breast Cancer

Claudin-low breast cancers are recently described entities showing low expression of certain claudins and cell adhesion molecules. Claudins constitute the backbone of tight junctions (TJs) formed between 2 cells. Their dysregulation plays a vital role in tumorigenesis. First part of the article focuses on the role of claudins in the TJ organization, their structural-functional characteristics, and post-transcriptional and translational modifications. The latter part of the review attempts to summarize existing knowledge regarding the status of claudins in breast cancer. The article also provides an overview of the effect of claudins on tumor progression, metastasis, stemness, chemotherapy resistance, and their crosstalk with relevant signaling pathways in breast cancer. Claudins can act as 2-edged swords in tumors. Some claudins have either tumor-suppressive/ promoting action, while others work as both in a context-dependent manner. Claudins regulate many important events in breast cancer. However, the intricacies involved in their activity are poorly understood. Post-translational modifications in claudins and their impact on TJ integrity, function, and tumor behavior are still unclear. Although their role in adverse events in breast cancer is recognized, their potential to serve as relevant targets for future therapeutics, especially for difficult-to-treat subtypes of the above malignancy, remains to be explored.

Three-Dimensional Culture of Murine Colonic Crypts to Study Intestinal Stem Cell Function Ex Vivo

The intestinal epithelium regenerates every 5-7 days, and is controlled by the intestinal epithelial stem cell (IESC) population located at the bottom of the crypt region. IESCs include active stem cells, which self-renew and differentiate into various epithelial cell types, and quiescent stem cells, which serve as the reserve stem cells in the case of injury. Regeneration of the intestinal epithelium is controlled by the self-renewing and differentiating capabilities of these active IESCs. In addition, the balance of the crypt stem cell population and maintenance of the stem cell niche are essential for intestinal regeneration. Organoid culture is an important and attractive approach to studying proteins, signaling molecules, and environmental cues that regulate stem cell survival and functions. This model is less expensive, less time-consuming, and more manipulatable than animal models. Organoids also mimic the tissue microenvironment, providing in vivo relevance. The present protocol describes the isolation of colonic crypts, embedding these isolated crypt cells into a three-dimensional gel matrix system and culturing crypt cells to form colonic organoids capable of self-organization, proliferation, self-renewal, and differentiation. This model allows one to manipulate the environment-knocking out specific proteins such as claudin-7, activating/deactivating signaling pathways, etc.-to study how these effects influence the functioning of colonic stem cells. Specifically, the role of tight junction protein claudin-7 in colonic stem cell function was examined. Claudin-7 is vital for maintaining intestinal homeostasis and barrier function and integrity. Knockout of claudin-7 in mice induces an inflammatory bowel disease-like phenotype exhibiting intestinal inflammation, epithelial hyperplasia, weight loss, mucosal ulcerations, epithelial cell sloughing, and adenomas. Previously, it was reported that claudin-7 is required for intestinal epithelial stem cell functions in the small intestine. In this protocol, a colonic organoid culture system is established to study the role of claudin-7 in the large intestine.

CYP1B1 Augments the Mesenchymal, Claudin-Low, and Chemoresistant Phenotypes of Triple-Negative Breast Cancer Cells

Cytochrome P4501B1 (CYP1B1) is elevated in breast cancer. Studies indicate a relationship between CYP1B1 and aggressive cancer phenotypes. Here, we report on in vitro studies in triple-negative breast cancer cell lines, where knockdown (KD) of CYP1B1 was used to determine the influence of its expression on invasive cell phenotypes. CYP1B1 KD in MDA-MB-231 cells resulted in the loss of mesenchymal morphology, altered expression of epithelial-mesenchymal genes, and increased claudin (CLDN) RNA and protein. CYP1B1 KD cells had increased cell-to-cell contact and paracellular barrier function, a reduced rate of cell proliferation, abrogation of migratory and invasive activity, and diminished spheroid formation. Analysis of clinical breast cancer tumor samples revealed an association between tumors exhibiting higher CYP1B1 RNA levels and diminished overall and disease-free survival. Tumor expression of CYP1B1 was inversely associated with CLDN7 expression, and CYP1B1HI/CLDN7LOW identified patients with lower median survival. Cells with CYP1B1 KD had an enhanced chemosensitivity to paclitaxel, 5-fluorouracil, and cisplatin. Our findings that CYP1B1 KD can increase chemosensitivity points to therapeutic targeting of this enzyme. CYP1B1 inhibitors in combination with chemotherapeutic drugs may provide a novel targeted and effective approach to adjuvant or neoadjuvant therapy against certain forms of highly metastatic breast cancer.

Is High Expression of Claudin-7 in Advanced Colorectal Carcinoma Associated with a Poor Survival Rate? A Comparative Statistical and Artificial Intelligence Study

AIM

The need for predictive and prognostic biomarkers in colorectal carcinoma (CRC) brought us to an era where the use of artificial intelligence (AI) models is increasing. We investigated the expression of Claudin-7, a tight junction component, which plays a crucial role in maintaining the integrity of normal epithelial mucosa, and its potential prognostic role in advanced CRCs, by drawing a parallel between statistical and AI algorithms.

METHODS

Claudin-7 immunohistochemical expression was evaluated in the tumor core and invasion front of CRCs from 84 patients and correlated with clinicopathological parameters and survival. The results were compared with those obtained by using various AI algorithms.

RESULTS

the Kaplan-Meier univariate survival analysis showed a significant correlation between survival and Claudin-7 intensity in the invasive front (p = 0.00), a higher expression being associated with a worse prognosis, while Claudin-7 intensity in the tumor core had no impact on survival. In contrast, AI models could not predict the same outcome on survival.

CONCLUSION

The study showed through statistical means that the immunohistochemical overexpression of Claudin-7 in the tumor invasive front may represent a poor prognostic factor in advanced stages of CRCs, contrary to AI models which could not predict the same outcome, probably because of the small number of patients included in our cohort.

Dual role of E-cadherin in cancer cells

E-cadherin is the main component of epithelial adherens junctions (AJs), which play a crucial role in the maintenance of stable cell-cell adhesion and overall tissue integrity. Down-regulation of E-cadherin expression has been found in many carcinomas, and loss of E-cadherin is generally associated with poor prognosis in patients. During the last decade, however, numerous studies have shown that E-cadherin is essential for several aspects of cancer cell biology that contribute to cancer progression, most importantly, active cell migration. In this review, we summarize the available data about the input of E-cadherin in cancer progression, focusing on the latest advances in the research of the various roles E-cadherin-based AJs play in cancer cell dissemination. The review also touches upon the "cadherin switching" in cancer cells where N- or P-cadherin replace or are co-expressed with E-cadherin and its influence on the migratory properties of cancer cells.

Differential Expression of Claudin in Odontogenic Cysts

Objective  This study aimed to analyze claudin-1, -4, and -7 expression in different types of odontogenic cysts (odontogenic keratocysts [OKCs], dentigerous cysts [DCs], calcifying odontogenic cysts [COCs], and radicular cysts [RCs]) as well as its association with OKC recurrence.

Materials and Methods  Seventy samples of odontogenic cysts samples were immunohistochemically stained to detect claudin-1, -4, and -7 expression. Patient information and OKC recurrence data were recorded. The staining was analyzed semiquantitatively and categorized based on the pattern and percentage of positively stained cystic epithelial cells.

Statistical Analysis  Expression of different claudins between groups was analyzed using the Kruskal–Wallis test with Dunn's test, followed by post hoc pairwise comparison. The association between claudin expression and OKC recurrence was analyzed by the Mann–Whitney U test. Correlations among claudin expression were examined with Spearman's correlation coefficient. Level of significance was at p  < 0.005.

Results  Claudin-1 was widely expressed in every odontogenic cyst. Most DCs (50%) expressed claudin-1 in more than 75% of cells, as did RCs (65%), while most OKCs (50%) expressed claudin-1 in 26 to 50% of cells. Most COCs (50%) expressed claudin-1 in 51 to 75% of cells. Every sample of OKC and RC was positive for claudin-4, but no sample showed staining in more than 51% of cells. Every odontogenic cyst was positive for claudin-7. DCs (35%), OKCs (55%), and RCs (40%) mostly showed staining in 26 to 50% of cells. High claudin-1 expression was shown in COCs, DCs, and RCs, while low expression of claudin-4 was shown in every odontogenic cyst. For claudin-7, the expression is high only in COCs. Claudin-1 and -4 was significantly different among each odontogenic cyst. High expression of claudin-1 was correlated with OKC recurrence. The correlations of claudin-1 with claudin-7 expression and claudin-4 with claudin-7 expression were significant in DCs. In COCs, claudin-1 and claudin-7 expression was significantly correlated.

Conclusions  The expression of claudin-1, -4, and -7 was present in every odontogenic cyst, but the proportion of positive staining cells was different. Expression of claudin-1 is associated with OKC recurrence. Dysregulation of claudin expression may play a pathogenic role in cyst pathogenesis.

The gastrointestinal microbiota in colorectal cancer cell migration and invasion

Colorectal carcinoma is the third most common cancer in developed countries and the second leading cause of cancer-related mortality. Interest in the influence of the intestinal microbiota on CRC emerged rapidly in the past few years, and the close presence of microbiota to the tumour mass creates a unique microenvironment in CRC. The gastrointestinal microbiota secrete factors that can contribute to CRC metastasis by influencing, for example, epithelial-to-mesenchymal transition. Although the role of EMT in metastasis is well-studied, mechanisms by which gastrointestinal microbiota contribute to the progression of CRC remain poorly understood. In this review, we will explore bacterial factors that contribute to the migration and invasion of colorectal carcinoma and the mechanisms involved. Bacteria involved in the induction of metastasis in primary CRC include Fusobacterium nucleatum, Enterococcus faecalis, enterotoxigenic Bacteroides fragilis, Escherichia coli and Salmonella enterica. Examples of prominent bacterial factors secreted by these bacteria include Fusobacterium adhesin A and Bacteroides fragilis Toxin. Most of these factors induce EMT-like properties in carcinoma cells and, as such, contribute to disease progression by affecting cell-cell adhesion, breakdown of the extracellular matrix and reorganisation of the cytoskeleton. It is of utmost importance to elucidate how bacterial factors promote CRC recurrence and metastasis to increase patient survival. So far, mainly animal models have been used to demonstrate this interplay between the host and microbiota. More human-based models are needed to study the mechanisms that promote migration and invasion and mimic the progression and recurrence of CRC.

Intestinal Barrier, Claudins and Mycotoxins

The intestinal barrier is the main barrier against all of the substances that enter the body. Proper functioning of this barrier guarantees maintained balance in the organism. Mycotoxins are toxic, secondary fungi metabolites, that have a negative impact both on human and animal health. It was postulated that various mycotoxins may affect homeostasis by disturbing the intestinal barrier. Claudins are proteins that are involved in creating tight junctions between epithelial cells. A growing body of evidence underlines their role in molecular response to mycotoxin-induced cytotoxicity. This review summarizes the information connected with claudins, their association with an intestinal barrier, physiological conditions in general, and with gastrointestinal cancers. Moreover, this review also includes information about the changes in claudin expression upon exposition to various mycotoxins.

A Claudin-Based Molecular Signature Identifies High-Risk, Chemoresistant Colorectal Cancer Patients

Identifying molecular characteristics that are associated with aggressive cancer phenotypes through gene expression profiling can help predict treatment responses and clinical outcomes. Claudins are deregulated in colorectal cancer (CRC). In CRC, increased claudin-1 expression results in epithelial-to-mesenchymal transition and metastasis, while claudin-7 functions as a tumor suppressor. In this study, we have developed a molecular signature based on claudin-1 and claudin-7 associated with poor patient survival and chemoresistance. This signature was validated using an integrated approach including publicly available datasets and CRC samples from patients who either responded or did not respond to standard-of-care treatment, CRC cell lines, and patient-derived rectal and colon tumoroids. Transcriptomic analysis from a patient dataset initially yielded 23 genes that were differentially expressed along with higher claudin-1 and decreased claudin-7. From this analysis, we selected a claudins-associated molecular signature including PIK3CA, SLC6A6, TMEM43, and ASAP-1 based on their importance in CRC. The upregulation of these genes and their protein products was validated using multiple CRC patient datasets, in vitro chemoresistant cell lines, and patient-derived tumoroid models. Additionally, blocking these genes improved 5-FU sensitivity in chemoresistant CRC cells. Our findings propose a new claudin-based molecular signature that associates with poor prognosis as well as characteristics of treatment-resistant CRC including chemoresistance, metastasis, and relapse.

Hypomethylated RRBP1 Potentiates Tumor Malignancy and Chemoresistance in Upper Tract Urothelial Carcinoma

Ribosome-binding protein 1 (RRBP1) is a potential oncogene in several cancer types. However, the correlation between RRBP1 expression and the prognosis of patients with upper tract urothelial carcinoma (UTUC) remains unclear. In this study, we identified that RRBP1 is associated with carcinogenesis and metastasis in UTUC using a methylation profiling microarray. High correlations between RRBP1 and cancer stages, nodal metastasis status, molecular subtypes, and prognosis in bladder urothelial cancer (BLCA) were found. Aberrant DNA methylation in the gene body region of RRBP1 was determined in UTUC tissues by methylation-specific PCR. RRBP1 expression was significantly increased in UTUC tissues and cell lines, as determined by real-time PCR and immunohistochemistry. RRBP1 depletion significantly reduced BFTC909 cell growth induced by specific shRNA. On the other hand, molecular subtype analysis showed that the expression of RRBP1 was associated with genes related to cell proliferation, epithelial-mesenchymal transition, and basal markers. A patient-derived organoid model was established to analyze patients' responses to different drugs. The expression of RRBP1 was related to chemoresistance. Taken together, these results provide the first evidence that RRBP1 gene body hypomethylation predicts RRBP1 high expression in UTUC. The data highlight the importance of RRBP1 in UTUC malignancy and chemotherapeutic tolerance.

Claudins as biomarkers of differential diagnosis and prognosis of tumors

Claudins are a superfamily of transmembrane proteins, the optimal expression and localization of which are important for the normal physiological function of the epithelium and any imbalance may have pathological consequences. Not only insufficient but also excessive production of claudins in cancer cells, as well as their aberrant localization, equally manifest the formation of a malignant phenotype. Many works are distinguished by contradictory data, which demonstrate the action of the same claudins both in the role of tumor-growth suppressors and promoters in the same cancers. The most important possible causes of significant discrepancies in the results of the works are a considerable variability of sampling and the absence of a consistent approach both to the assessment of the immune reactivity of claudins and to the differential analysis of their subcellular localization. Combined, these drawbacks hinder the histological assessment of the link between claudins and tumor progression. In particular, ambiguous expression of claudins in breast cancer subtypes, revealed by various authors in immunohistochemical analysis, not only fails to facilitate the identification of the claudin-low molecular subtype but rather complicates these efforts. Research into the role of claudins in carcinogenesis has undoubtedly confirmed the potential value of this class of proteins as significant biomarkers in some cancer types; however, the immunohistochemical approach to the assessment of claudins still has limitations, needs standardization, and, to date, has not reached a diagnostic or a prognostic value.

Colon epithelial cell TGFβ signaling modulates the expression of tight junction proteins and barrier function in mice

Defective barrier function is a predisposing factor in inflammatory bowel disease (IBD) and colitis-associated cancer (CAC). Although TGFβ signaling defects have been associated with IBD and CAC, few studies have examined the relationship between TGFβ and intestinal barrier function. Here, we examine the role of TGFβ signaling via SMAD4 in modulation of colon barrier function. The Smad4 gene was conditionally deleted in the intestines of adult mice and intestinal permeability assessed using an in vivo 4 kDa FITC-Dextran (FD4) permeability assay. Mouse colon was isolated for gene expression (RNA-sequencing), Western blot, and immunofluorescence analysis. In vitro colon organoid culture was utilized to assess junction-related gene expression by qPCR and transepithelial resistance (TER). In silico analyses of human IBD and colon cancer databases were performed. Mice lacking intestinal expression of Smad4 demonstrate increased colonic permeability to FD4 without gross mucosal damage. mRNA/protein expression analyses demonstrate significant increases in Cldn2/Claudin 2 and Cldn8/Claudin 8, and decreases in Cldn3, Cldn4, and Cldn7/Claudin 7 with intestinal SMAD4 loss in vivo without changes in Claudin protein localization. TGFβ1/BMP2 treatment of polarized SMAD4+ colonoids increases TER. Cldn2, Cldn4, Cldn7, and Cldn8 are regulated by canonical TGFβ signaling, and TGFβ-dependent regulation of these genes is dependent on nascent RNA transcription (Cldn2, Cldn4, Cldn8) but not nascent protein translation (Cldn4, Cldn8). Human IBD/colon cancer specimens demonstrate decreased SMAD4, CLDN4, CLDN7, and CLDN8 and increased CLDN2 compared with healthy controls. Canonical TGFβ signaling modulates the expression of tight junction proteins and barrier function in mouse colon.NEW & NOTEWORTHY We demonstrate that canonical TGFβ family signaling modulates the expression of critical tight junction proteins in colon epithelial cells, and that expression of these tight junction proteins is associated with maintenance of colon epithelial barrier function in mice.

Chimeric Claudins: A New Tool to Study Tight Junction Structure and Function

The tight junction (TJ) is a structure composed of multiple proteins, both cytosolic and membranal, responsible for cell–cell adhesion in polarized endothelium and epithelium. The TJ is intimately connected to the cytoskeleton and plays a role in development and homeostasis. Among the TJ’s membrane proteins, claudins (CLDNs) are key to establishing blood–tissue barriers that protect organismal physiology. Recently, several crystal structures have been reported for detergent extracted recombinant CLDNs. These structural advances lack direct evidence to support quaternary structure of CLDNs. In this article, we have employed protein-engineering principles to create detergent-independent chimeric CLDNs, a combination of a 4-helix bundle soluble monomeric protein (PDB ID: 2jua) and the apical—50% of human CLDN1, the extracellular domain that is responsible for cell–cell adhesion. Maltose-binding protein-fused chimeric CLDNs (MBP-CCs) used in this study are soluble proteins that retain structural and functional aspects of native CLDNs. Here, we report the biophysical characterization of the structure and function of MBP-CCs. MBP-fused epithelial cadherin (MBP-eCAD) is used as a control and point of comparison of a well-characterized cell-adhesion molecule. Our synthetic strategy may benefit other families of 4-α-helix membrane proteins, including tetraspanins, connexins, pannexins, innexins, and more.

Patient-derived xenografts of central nervous system metastasis reveal expansion of aggressive minor clones

BACKGROUND

The dearth of relevant tumor models reflecting the heterogeneity of human central nervous system metastasis (CM) has hindered development of novel therapies.

METHODS

We established 39 CM patient-derived xenograft (PDX) models representing the histological spectrum, and performed phenotypic and multi-omic characterization of PDXs and their original patient tumors. PDX clonal evolution was also reconstructed using allele-specific copy number and somatic variants.

RESULTS

PDXs retained their metastatic potential, with flank-implanted PDXs forming spontaneous metastases in multiple organs, including brain, and CM subsequent to intracardiac injection. PDXs also retained the histological and molecular profiles of the original patient tumors, including retention of genomic aberrations and signaling pathways. Novel modes of clonal evolution involving rapid expansion by a minor clone were identified in 2 PDXs, including CM13, which was highly aggressive in vivo forming multiple spontaneous metastases, including to brain. These PDXs had little molecular resemblance to the patient donor tumor, including reversion to a copy number neutral genome, no shared nonsynonymous mutations, and no correlation by gene expression.

CONCLUSIONS

We generated a diverse and novel repertoire of PDXs that provides a new set of tools to enhance our knowledge of CM biology and improve preclinical testing. Furthermore, our study suggests that minor clone succession may confer tumor aggressiveness and potentiate brain metastasis.

Role of tight junctions in the epithelial-to-mesenchymal transition of cancer cells

The epithelial-mesenchymal transition (EMT) is an essential step in cancer progression. Epithelial cells possess several types of cell-cell junctions, and tight junctions are known to play important roles in maintaining the epithelial program. EMT is characterized by a loss of epithelial markers, including E-cadherin and tight junction proteins. Somewhat surprisingly, the evidence is accumulating that upregulated expression of tight junction proteins plays an important role in the EMT of cancer cells. Tight junctions have distinct tissue-specific and cancer-specific regulatory mechanisms, enabling them to play different roles in EMT. Tight junctions and related signaling pathways are attractive targets for cancer treatments; signal transduction inhibitors and monoclonal antibodies for tight junction proteins may be used to suppress EMT, invasion, and metastasis. Here we review the role of bicellular and tricellular tight junction proteins during EMT. Further investigation of regulatory mechanisms of tight junctions during EMT in cancer cells will inform the development of biomarkers for predicting prognosis as well as novel therapies.

The p53-inducible CLDN7 regulates colorectal tumorigenesis and has prognostic significance

Most colorectal cancer (CRC) are characterized by allele loss of the genes located on the short arm of chromosome 17 (17p13.1), including the tumor suppressor p53 gene. Although important, p53 is not the only driver of chromosome 17p loss. In this study, we explored the biological and prognostic significance of genes around p53 on 17p13.1 in CRC. The Cancer Genome Atlas (TCGA) were used to identify differentially expressed genes located between 1000 kb upstream and downstream of p53 gene. The function of CLDN7 was evaluated by both in vitro and in vivo experiments. Quantitative real-time PCR, western blot, and promoter luciferase activity, immunohistochemistry were used to explore the molecular drivers responsible for the development and progression of CRC. The results showed that CLDN7, located between 1000 kb upstream and downstream of p53 gene, were remarkably differentially expressed in tumor and normal tissues. CLDN7 expression also positively associated with p53 level in different stages of the adenoma-carcinoma sequence. Both in vitro and in vivo assays showed that CLDN7 inhibited cell proliferation in p53 wild type CRC cells, but had no effects on p53 mutant CRC cells. Mechanistically, p53 could bind to CLDN7 promoter region and regulate its expression. Clinically, high CLDN7 expression was negatively correlated with tumor size, invasion depth, lymphatic metastasis and AJCC III/IV stage, but was positively associated with favorable prognosis of CRC patients. Collectively, our work uncovers the tumor suppressive function for CLDN7 in a p53-dependent manner, which may mediate colorectal tumorigenesis induced by p53 deletion or mutation.

Gold/alpha-lactalbumin nanoprobes for the imaging and treatment of breast cancer

Theranostic agents should ideally be renally cleared and biodegradable. Here, we report the synthesis, characterization and theranostic applications of fluorescent ultrasmall gold quantum clusters that are stabilized by the milk metalloprotein alpha-lactalbumin. We synthesized three types of these nanoprobes that together display fluorescence across the visible and near-infrared spectra when excited at a single wavelength through optical colour coding. In live tumour-bearing mice, the near-infrared nanoprobe generates contrast for fluorescence, X-ray computed tomography and magnetic resonance imaging, and exhibits long circulation times, low accumulation in the reticuloendothelial system, sustained tumour retention, insignificant toxicity and renal clearance. An intravenously administrated near-infrared nanoprobe with a large Stokes shift facilitated the detection and image-guided resection of breast tumours in vivo using a smartphone with modified optics. Moreover, the partially unfolded structure of alpha-lactalbumin in the nanoprobe helps with the formation of an anti-cancer lipoprotein complex with oleic acid that triggers the inhibition of the MAPK and PI3K-AKT pathways, immunogenic cell death and the recruitment of infiltrating macrophages. The biodegradability and safety profile of the nanoprobes make them suitable for the systemic detection and localized treatment of cancer.

Regulation of Src Family Kinases during Colorectal Cancer Development and Its Clinical Implications

Src family kinases (SFKs) are non-receptor kinases that play a critical role in the pathogenesis of colorectal cancer (CRC). The expression and activity of SFKs are upregulated in patients with CRC. Activation of SFKs promotes CRC cell proliferation, metastases to other organs and chemoresistance, as well as the formation of cancer stem cells (CSCs). The enhanced expression level of Src is associated with decreased survival in patients with CRC. Src-mediated regulation of CRC progression involves various membrane receptors, modulators, and suppressors, which regulate Src activation and its downstream targets through various mechanisms. This review provides an overview of the current understanding of the correlations between Src and CRC progression, with a special focus on cancer cell proliferation, invasion, metastasis and chemoresistance, and formation of CSCs. Additionally, this review discusses preclinical and clinical strategies to improve the therapeutic efficacy of drugs targeting Src for treating patients with CRC.

CDX2 expression and perioperative patient serum affects the adhesion properties of cultured colon cancer cells

Background

Colon cancer is one of the most commonly diagnosed types of cancer with surgical resection of the tumor being the primary choice of treatment. However, the surgical stress response induced during treatment may be related to a higher risk of recurrence. The aim of this study was to examine the effect of surgery on adhesion of cultured colon cancer cells with or without expression of the tumour suppressor CDX2.

Method

We enrolled 30 patients undergoing elective, curatively intended laparoscopic surgery for colon cancer in this study. Blood samples were drawn 1 day prior to surgery and 24 h after surgery. The samples of pre- and postoperative serum was applied to wild type colon cancer LS174T cells and CDX2 inducible LS174T cells and adhesion was measured with Real-Time Cell-Analysis iCELLigence using electrical impedance as a readout to monitor changes in the cellular adhesion.

Results

Adhesion abilities of wild type LS174T cells seeded in postoperative serum was significantly increased compared to cells seeded in preoperative serum. When seeding the CDX2 inducible LS174T cells without CDX2 expression in pre- and postoperative serum, no significant difference in adhesion was found. However, when inducing CDX2 expression in these cells, the adhesion abilities in pre- and postoperative serum resembled those of the LS174T wild type cell line.

Conclusions

We found that the adhesion of colon cancer cells was significantly increased in postoperative versus preoperative serum, and that CDX2 expression affected the adhesive ability of cancer cells. The results of this study may help to elucidate the pro-metastatic mechanisms in the perioperative phase and the role of CDX2 in colon cancer metastasis.

Relationship between apical junction proteins, gene expression and cancer

The apical junctional complex (AJC) is a cell-cell adhesion system present at the upper portion of the lateral membrane of epithelial cells integrated by the tight junction (TJ) and the adherens junction (AJ). This complex is crucial to initiate and stabilize cell-cell adhesion, to regulate the paracellular transit of ions and molecules and to maintain cell polarity. Moreover, we now consider the AJC as a hub of signal transduction that regulates cell-cell adhesion, gene transcription and cell proliferation and differentiation. The molecular components of the AJC are multiple and diverse and depending on the cellular context some of the proteins in this complex act as tumor suppressors or as promoters of cell transformation, migration and metastasis outgrowth. Here, we describe these new roles played by TJ and AJ proteins and their potential use in cancer diagnostics and as targets for therapeutic intervention.

Tight Junction Protein Claudin-7 Is Essential for Intestinal Epithelial Stem Cell Self-Renewal and Differentiation

BACKGROUND & AIMS

Claudin-7 (Cldn7) is a tight junction (TJ) membrane protein located at the apical TJ and basolateral side of intestinal epithelial cells. Deletion of Cldn7 by gene targeting leads to the inflammatory bowel disease-like phenotype in mice, which includes weight loss, diarrhea, mucosa ulceration, and severe intestinal epithelial damage. In this study, we test our hypothesis that Cldn7 plays a critical role in regulating intestinal crypt stem cell functions.

METHODS

Gene expression microarray, quantitative reverse-transcription polymerase chain reaction, in situ hybridization, histologic examinations, immunoblotting, 3-dimensional organoid culture, and various treatments to rescue Cldn7-deficient organoid defects were conducted using global Cldn7 knockout mice and inducible, conditional Cldn7 knockout mice.

RESULTS

Gene deletion of Cldn7 in intestines showed significant alteration of expression profiles with striking down-regulation of intestinal crypt stem cell markers such as Olfm4, dislocated proliferative cells, and disrupted epithelial cell differentiation. In addition, the isolated Cldn7-deficient crypts where the stem cells reside were either unable to survive at all or formed defective spheroids, highlighting the functional impairment of crypt stem cells in the absence of Cldn7. Remarkably, the Cldn7-expressing organoids with buddings underwent rapid cell degeneration within days after turning off Cldn7 expression in the culture. We identified that activation of Wnt/β-catenin signaling rescued the organoid defects caused by Cldn7 deletion.

CONCLUSIONS

In this study, we show that Cldn7 is indispensable in controlling Wnt/β-catenin signaling-dependent intestinal epithelial stem cell survival, self-renewal, and cell differentiation. This study could open a door to study roles of TJ proteins in stem cell regulations in other tissues and organs.

Role of Claudin Proteins in Regulating Cancer Stem Cells and Chemoresistance-Potential Implication in Disease Prognosis and Therapy

Claudins are cell–cell adhesion proteins, which are expressed in tight junctions (TJs), the most common apical cell-cell adhesion. Claudin proteins help to regulate defense and barrier functions, as well as differentiation and polarity in epithelial and endothelial cells. A series of studies have now reported dysregulation of claudin proteins in cancers. However, the precise mechanisms are still not well understood. Nonetheless, studies have clearly demonstrated a causal role of multiple claudins in the regulation of epithelial to mesenchymal transition (EMT), a key feature in the acquisition of a cancer stem cell phenotype in cancer cells. In addition, claudin proteins are known to modulate therapy resistance in cancer cells, a feature associated with cancer stem cells. In this review, we have focused primarily on highlighting the causal link between claudins, cancer stem cells, and therapy resistance. We have also contemplated the significance of claudins as novel targets in improving the efficacy of cancer therapy. Overall, this review provides a much-needed understanding of the emerging role of claudin proteins in cancer malignancy and therapeutic management.

A Novel Zebrafish Model of Metastasis Identifies the HSD11β1 Inhibitor Adrenosterone as a Suppressor of Epithelial-Mesenchymal Transition and Metastatic Dissemination

Metastasis of cancer cells is multi-step process and dissemination is an initial step. Here we report a tamoxifen-controllable Twist1a-ER^T2 transgenic zebrafish line as a new animal model for metastasis research, and demonstrate that this model can serve as a novel platform for discovery of antimetastasis drugs targeting metastatic dissemination of cancer cells. By crossing Twist1a-ER^T2 with xmrk (a homolog of hyperactive form of EGFR) transgenic zebrafish, which develops hepatocellular carcinoma, approximately 80% of the double transgenic zebrafish showed spontaneous cell dissemination of mCherry-labeled hepatocytes from the liver to the entire abdomen region and the tail region. The dissemination is accomplished in 5 days through induction of an epithelial-to-mesenchymal transition. Using this model, we conducted in vivo drug screening and identified three hit drugs. One of them, adrenosterone, an inhibitor for hydroxysteroid (11-beta) dehydrogenase 1 (HSD11β1), has a suppressor effect on cell dissemination in this model. Pharmacologic and genetic inhibition of HSD11β1 suppressed metastatic dissemination of highly metastatic human cell lines in a zebrafish xenotransplantation model. Through downregulation of Snail and Slug, adrenosterone-treated cells recovered expression of E-cadherin and other epithelial markers and lost partial expression of mesenchymal markers compared with vehicle-treated cells. Taken together, our model offers a useful platform for the discovery of antimetastasis drugs targeting metastatic dissemination of cancer cells. IMPLICATIONS: This study describes a transgenic zebrafish model for liver tumor metastasis and it has been successfully used for identification of some drugs to inhibit metastatic dissemination of human cancer cells.

Catechin and Procyanidin B2 Modulate the Expression of Tight Junction Proteins but Do Not Protect from Inflammation-Induced Changes in Permeability in Human Intestinal Cell Monolayers

The possibility of counteracting inflammation-related barrier defects with dietary compounds such as (poly)phenols has raised much interest, but information is still scarce. We have investigated here if (+)-catechin (CAT) and procyanidin B₂ (PB₂), two main dietary polyphenols, protect the barrier function of intestinal cells undergoing inflammatory stress. The cell model adopted consisted of co-cultured Caco-2 and HT29-MTX cells, while inflammatory conditions were mimicked through the incubation of epithelial cells with the conditioned medium of activated macrophages (MCM). The epithelial barrier function was monitored through trans-epithelial electrical resistance (TEER), and ROS production was assessed with dichlorofluorescein, while the expression of tight-junctional proteins and signal transduction pathways were evaluated with Western blot. The results indicated that MCM produced significant oxidative stress, the activation of NF-κB and MAPK pathways, a decrease in occludin and ZO-1 expression, and an increase in claudin-7 (CL-7) expression, while TEER was markedly lowered. Neither CAT nor PB₂ prevented oxidative stress, transduction pathways activation, ZO-1 suppression, or TEER decrease. However, PB₂ prevented the decrease in occludin expression and both polyphenols produced a huge increase in CL-7 abundance. It is concluded that, under the conditions adopted, CAT and PB₂ do not prevent inflammation-dependent impairment of the epithelial barrier function of intestinal cell monolayers. However, the two compounds modify the expression of tight-junctional proteins and, in particular, markedly increase the expression of CL-7. These insights add to a better understanding of the potential biological activity of these major dietary flavan-3-ols at intestinal level.

Claudin Family Participates in the Pathogenesis of Inflammatory Bowel Diseases and Colitis-Associated Colorectal Cancer

Claudins are a multigene transmembrane protein family comprising at least 27 members. In gastrointestinal tract, claudins are mainly located in the intestinal epithelia; many types of claudins form a network of strands in tight junction plaques within the intercellular space of neighboring epithelial cells and build paracellular selective channels, while others act as signaling proteins and mediates cell behaviors. Claudin dysfunction may contribute to epithelial permeation disorder and multiple intestinal diseases. Over recent years, the importance of claudins in the pathogenesis of inflammatory bowel diseases (IBD) has gained focus and is being investigated. This review analyzes the expression pattern and regulatory mechanism of claudins based on existing evidence and elucidates the fact that claudin dysregulation correlates with increased intestinal permeability, sustained activation of inflammation, epithelial-to-mesenchymal transition (EMT), and tumor progression in IBD as well as consequent colitis-associated colorectal cancer (CAC), possibly shedding new light on further etiologic research and clinical treatments.

Identification of claudin-2, -6, -11 and -14 as prognostic markers in human breast carcinoma

The development of cancer occurs with various genomic and epigenetic modifications that act as indicators for early diagnosis and treatment. Recent data have shown that the abnormal expression of the claudin (CLDN) tight junction (TJ) proteins is involved in the tumorigenesis of numerous human cancers. Real-time quantitative PCR and western blotting were used to explore the differences in the expression of the CLDN TJ proteins in breast carcinoma tissues and non-neoplastic tissues. The results showed that CLDN5, CLDN9, CLDN12 and CLDN13 were not expressed in breast carcinoma tissues or non-neoplastic tissues. CLDN1, CLDN3, CLDN8 and CLDN10 were expressed in breast carcinoma and non-neoplastic tissues, but there was no significant difference between the expression of these CLDN proteins among them. The expression of CLDN2, -6, -11 and -14 varied between the breast carcinoma and non-neoplastic tissues. Moreover, 86 samples of breast carcinoma and non-neoplastic tissues were examined for the expression of CLDN2, -6, -11 and -14 by streptavidin-peroxidase immunohistochemical staining. The data revealed that the CLDN2, CLDN6, and CLDN14 were expressed in the cell membrane and the expression levels of these proteins were downregulated in breast carcinoma. The CLDN11 was expressed in cell cytoplasm and the expression level of CLDN11 was upregulated compared with those in non-neoplastic tissues. Consistent with these findings, the expression of CLDN2, CLDN6 and CLDN14 were downregulated, while the expression of CLDN11 was upregulated in breast carcinoma compared with those in non-neoplastic tissues. Furthermore, the associations between these CLDNs and clinicopathologic indicators were analyzed, and these CLDN expressions were revealed to be associated with distant metastasis and to predict a poor prognosis. In conclusion, our data showed that the expression levels of CLDN2, -6, -11 and -14 differed between breast carcinoma tissues and histologically non-neoplastic tissues, and the expression levels of these CLDNs may be useful as molecular markers for the diagnosis of breast carcinoma as well as for the determination of metastasis and prognosis.

Identification of specific modules and significant genes associated with colon cancer by weighted gene co‑expression network analysis

Colon cancer is one of the most commonly diagnosed malignancies and is a leading cause of cancer‑associated mortality. The aim of the present study was to investigate the molecular mechanisms underlying colon cancer and identify potentially significant genes associated with the disease using weighted gene co‑expression network analysis (WGCNA). The test datasets used were downloaded from The Cancer Genome Atlas (TCGA) database. WGCNA was applied to analyze microarray data obtained from colon adenocarcinoma samples to identify significant modules and highly associated genes. A gene co‑expression network was constructed and different gene modules were selected. Functional and pathway enrichment analyses were performed to investigate the molecular mechanisms of colon cancer. In addition, highly connected hub genes associated with the most significant module were selected for further analysis. Nine specific modules associated with colon cancer were identified, of which the turquoise module was observed to exhibit the greatest association with the disease. Pathway enrichment analysis of the turquoise module suggested that genes in the turquoise module were associated with 'RNA polymerase' and 'purine metabolism'. Furthermore, gene ontology enrichment analysis revealed the top 30 hub genes with a higher degree in the turquoise module, such as σ‑non‑opioid intracellular receptor 1, transmembrane protein 147  TMEM147) and carbamoyl‑phosphate synthetase 2, aspartate transcarbamylase, and dihydroorotase, were predominantly enriched in the biological processes 'translation' and 'gene expression'. Experimental verification demonstrated that the expression of TMEM147 in colon cancer was significantly increased compared with the control. Therefore, the results suggested that genes associated with RNA polymerase and the purine metabolic pathways may be substantially involved in the pathogenesis of colon cancer. Furthermore, TMEM147 may represent a biomarker for colon cancer.

Identification of claudin‑1, ‑3, ‑7 and ‑8 as prognostic markers in human laryngeal carcinoma

Various genomic and epigenetic modifications that occur during the development of cancer act as potential biomarkers for early diagnosis and treatment. Previous studies have demonstrated abnormal expression of the claudin (CLDN) tight junction (TJ) proteins in numerous types of human cancer. Reverse transcription-quantitative polymerase chain reaction and western blotting were employed to investigate variations in the expression of the CLDN TJ proteins in laryngeal non-neoplastic tissues and laryngeal squamous carcinoma tissues. It was revealed that CLDN2, CLDN4, CLDN5, CLDN6, CLDN9, CLDN11 and CLDN12 were undetectable in laryngeal squamous carcinoma tissues and laryngeal non-neoplastic tissues. Additionally, CLDN10 was expressed in laryngeal squamous carcinoma tissues and laryngeal non-neoplastic tissues; however, no significant difference was reported. Conversely, the expression levels of CLDN1 and CLDN7 mRNA and protein were downregulated in laryngeal squamous carcinoma tissues compared with in adjacent non-neoplastic tissues, whereas those of CLDN3 and CLDN8 were upregulated. A total of 80 samples of laryngeal squamous carcinoma and non-neoplastic tissues were analyzed for the expression of CLDN1, −3, −7 and −8 via streptavidin-peroxidase immunohistochemical staining. It was revealed that the expression levels of CLDN1 and CLDN7 were downregulated in laryngeal squamous carcinoma tissues compared with in non-neoplastic mucosal tissues, whereas those of CLDN3 and CLDN8 were upregulated. Furthermore, the associations between CLDN expression and the clinicopathological factors of patients were analyzed. The expression levels of CLDN3 and CLDN7 were reported to be associated with distant metastasis and serve as potential predictors of poor prognosis. In conclusion, the findings of the present study demonstrated that the expression levels of CLDN1, −3, −7 and −8 varied between laryngeal squamous carcinoma tissues and non-neoplastic tissues. The expression levels of these CLDNs may be useful molecular markers for the diagnosis of laryngeal carcinoma, and determining the metastasis and prognosis of this disease.

The chromatin remodeling protein BRM regulates the transcription of tight junction proteins: Implication in breast cancer metastasis

Claudins are a group of cell tight junction proteins that play versatile roles in cancer biology. Recent studies have correlated down-regulation of Claudins with augmented breast cancer malignancy and poor prognosis. The mechanism underlying repression of Claudin transcription in breast cancer cells is not well understood. Here we report that expression levels of Brahma (BRM) were down-regulated in triple negative breast cancer cells (MDA-231) compared to the less malignant MCF-7 cells and in high-grade human breast cancer specimens compared to low-grade ones. TGF-β treatment in MCF-7 cells repressed BRM transcription likely through targeting C/EBPβ. BRM over-expression suppressed whereas BRM knockdown promoted TGF-β induced migration and invasion of MCF-7 cells. BRM down-regulation was accompanied by the loss of a panel of Claudins in breast cancer cells. BRM directly bound to the promoter region of Claudin genes via interacting with Sp1 and activated transcription by modulating histone modifications. Together, our data have identified a novel epigenetic pathway that links Claudin transcription to breast cancer metastasis.

Claudin gene expression profiles and clinical value in colorectal tumors classified according to their molecular subtype

Purpose

Colorectal cancer (CRC) is a heterogeneous disease that can be classified into distinct molecular subtypes. The aims of this study were 1) to compare claudin (CLDN) gene expression in CRC samples and normal colon mucosa, and then in the different CRC molecular subtypes, and 2) to assess their prognostic value.

Patients and methods

CLDN expression in CRC samples was analyzed using gene expression data for a cohort of 143 primary CRC samples, and compared in the same CRC samples classified into different molecular subtypes (C1 to C6 according to the Marisa's classification, and CMS1 to CMS4 of the consensus classification). Comparison of CLDN expression in normal and tumor colon samples was also made on a smaller number of samples. Then, the relationship between CLDN expression profiles and overall survival (OS) and progression-free survival was examined.

Results

Compared with normal mucosa, CLDN1 and CLDN2 were upregulated, whereas CLDN5, 7, 8, and 23 were downregulated in CRC samples. Variations in CLDN expression profiles were observed mainly in the CMS2/C1 and CMS4/C4 subtypes. Overall, expression of CLDN2 or CLDN4 alone had a strong prognostic value that increased when they were associated. In the CMS4/C4 subtypes, lower expressions of CLDN11, CLDN12, and CLDN23 were associated with longer OS. Conversely, in the CMS2 and C1 subtypes, low CLDN23 expression was associated with shorter OS and progression-free survival, suggesting a dual role for CLDN23 as a tumor suppressor/promoter in CRC. CLDN6 and CLDN11 had a prognostic value in the CMS2 and C4 subtypes, respectively.

Conclusion

This analysis of CLDN gene expression profiles and prognostic value in CRC samples classified according to their molecular subtype shows that CRC heterogeneity must be taken into account when assessing CLDN potential value as prognostic markers or therapeutic targets.

Non-tight junction-related function of claudin-7 in interacting with integrinβ1 to suppress colorectal cancer cell proliferation and migration

Purpose

We conducted a preliminarily exploration of the role and possible mechanism of the non-tight junction-related function of claudin-7 in the occurrence and development of colorectal cancer.

Methods

We selected the colorectal cancer cell line HCT116, constructed a stably transfected claudin-7 knockdown cell line via RNAi and lentiviral infection, and determined the claudin-7 knockdown efficiency. We assessed the biological behavior changes (cell viability, apoptosis, and migration) in the stably transfected HCT116 cells and observed structural changes in the tight junction by transmission electron microscopy. We used a subcutaneous tumor formation model to assess the tumorigenicity of HCT116 cells after claudin-7 knockdown. We assessed the expression and localization of integrinβ1 in the stably transfected cell line by immunofluorescence staining and investigated the interaction between integrinβ1 and claudin-7 by co-immunoprecipitation.

Results

After the knockdown of claudin-7 the expression, the viability and migration ability of HCT116 cells increased and apoptosis decreased. Transmission electron microscopy indicated that the intercellular tight junction structure did not change substantially. Furthermore, the tumor growth in nude mice was enhanced. Immunofluorescence staining showed that integrinβ1 and claudin-7 were co-expressed and co-localized on the cell membrane, and immunoprecipitation suggested that claudin-7 interacts with integrinβ1.

Conclusion

Claudin-7 may inhibit the proliferation and migration of tumor cells by interacting with integrinβ1, subsequently participating in the development of colorectal cancer.

Tight Junction Proteins and Signaling Pathways in Cancer and Inflammation: A Functional Crosstalk

The ability of epithelial cells to organize through cell–cell adhesion into a functioning epithelium serves the purpose of a tight epithelial protective barrier. Contacts between adjacent cells are made up of tight junctions (TJ), adherens junctions (AJ), and desmosomes with unique cellular functions and a complex molecular composition. These proteins mediate firm mechanical stability, serves as a gatekeeper for the paracellular pathway, and helps in preserving tissue homeostasis. TJ proteins are involved in maintaining cell polarity, in establishing organ-specific apical domains and also in recruiting signaling proteins involved in the regulation of various important cellular functions including proliferation, differentiation, and migration. As a vital component of the epithelial barrier, TJs are under a constant threat from proinflammatory mediators, pathogenic viruses and bacteria, aiding inflammation and the development of disease. Inflammatory bowel disease (IBD) patients reveal loss of TJ barrier function, increased levels of proinflammatory cytokines, and immune dysregulation; yet, the relationship between these events is partly understood. Although TJ barrier defects are inadequate to cause experimental IBD, mucosal immune activation is changed in response to augmented epithelial permeability. Thus, the current studies suggest that altered barrier function may predispose or increase disease progression and therapies targeted to specifically restore the barrier function may provide a substitute or supplement to immunologic-based therapies. This review provides a brief introduction about the TJs, AJs, structure and function of TJ proteins. The link between TJ proteins and key signaling pathways in cell proliferation, transformation, and metastasis is discussed thoroughly. We also discuss the compromised intestinal TJ integrity under inflammatory conditions, and the signaling mechanisms involved that bridge inflammation and cancer.

Testing the gene expression classification of the EMT spectrum

The epithelial-mesenchymal transition (EMT) plays a central role in cancer metastasis and drug resistance-two persistent clinical challenges. Epithelial cells can undergo a partial or full EMT, attaining either a hybrid epithelial/mesenchymal (E/M) or mesenchymal phenotype, respectively. Recent studies have emphasized that hybrid E/M cells may be more aggressive than their mesenchymal counterparts. However, mechanisms driving hybrid E/M phenotypes remain largely elusive. Here, to better characterize the hybrid E/M phenotype (s) and tumor aggressiveness, we integrate two computational methods-(a) RACIPE-to identify the robust gene expression patterns emerging from the dynamics of a given gene regulatory network, and (b) EMT scoring metric-to calculate the probability that a given gene expression profile displays a hybrid E/M phenotype. We apply the EMT scoring metric to RACIPE-generated gene expression data generated from a core EMT regulatory network and classify the gene expression profiles into relevant categories (epithelial, hybrid E/M, mesenchymal). This categorization is broadly consistent with hierarchical clustering readouts of RACIPE-generated gene expression data. We also show how the EMT scoring metric can be used to distinguish between samples composed of exclusively hybrid E/M cells and those containing mixtures of epithelial and mesenchymal subpopulations using the RACIPE-generated gene expression data.

Claudin-7 modulates cell-matrix adhesion that controls cell migration, invasion and attachment of human HCC827 lung cancer cells

Claudins are a family of tight junction proteins, and serve important roles in epithelial barrier, selective ion transports and cancer metastasis. Although the exact role of claudin-7 in human lung cancer has not been completely elucidated, recent clinical studies have demonstrated that claudin-7 is associated with the survival of patients with lung cancer. Our previous studies have demonstrated that claudin-7 forms a protein complex with integrin β1 in human lung cancer cells. The knockdown (KD) of claudin-7 by short hairpin RNA (shRNA) reduced integrin β1 expression and increased the cell proliferative rate, whereas claudin-7 re-expression in the KD cells decreased the cell proliferation. It is unknown as to whether claudin-7 and integrin β1 regulate cell proliferation and invasion synergistically or independently. In the present study, it was observed that ectopic expression of integrin β1 in claudin-7 KD lung cancer cells did not reduce the cell proliferation. However, integrin β1-transfected cells migrated more effectively in wound healing and cell invasion assays and were more adhesive in a cell attachment assay when compared with those of claudin-7 KD cells. This indicates that claudin-7 controls cell proliferation, while cell attachment and motility were regulated partially through integrin β1. Additionally, claudin-7 overexpression in claudin-7 KD cells resulted in an improved ability to attach to the surface of cell culture plates and a higher expression of focal adhesion proteins when compared with claudin-7 non-KD control cells, which supports the role of claudin-7 in cell adhesion and motility. Taken together, these data suggest that claudin-7 regulates cell motility through integrin β1, providing additional insight into the roles of claudins in carcinogenesis and cancer cell metastasis.

Claudin-7 downregulation induces metastasis and invasion in colorectal cancer via the promotion of epithelial-mesenchymal transition

The dysregulation of the tight junctions (TJs) protein claudin-7 is closely related to the development and metastasis of colorectal cancer (CRC). The aim of this study was to investigate the expression of claudin-7 and characterize the relationship between claudin-7 expression and epithelial-mesenchymal transition (EMT) in CRC. In this study, the expression of claudin-7, E-cadherin, vimentin and snail-1 was detected by immunohistochemistry (IHC) in a set of 80 CRC specimens comprising 20 specimens each of well-differentiated, moderately differentiated, poorly differentiated and liver metastases tissues. The correlation between claudin-7 and EMT-related proteins in the stably transfected claudin-7 knockdown HCT116 cell line was analyzed by IHC, immunofluorescence (IF), Western blotting (WB) and nude mouse xenograft models. The results revealed that the expression of claudin-7 was downregulated as CRC tissue differentiation grade decreased, and that low claudin-7 expression corresponded to the downregulation of E-cadherin (r = 0.725, p < 0.001) and upregulation of vimentin (r = -0.376, p = 0.001) and snail-1 (r = -0.599, p < 0.001). Additionally, in the claudin-7 knockdown HCT116 cell line, the staining intensity and expression of E-cadherin was decreased, while the immunoreactivity and expression of vimentin and snail-1 was increased. Futhermore, the result of tumor formation experiment was consistent with CRC tissues. In conclusion, the expression of claudin-7 in CRC is downregulated as differentiation grade decreases. Claudin-7 downregulation may promote the invasion and metastasis of CRC by regulating EMT. Our results provide new perspectives for a potential therapeutic target for CRC.

Downregulation of CLDN7 due to promoter hypermethylation is associated with human clear cell renal cell carcinoma progression and poor prognosis

BACKGROUND

Metastasis is the primary cause of death in renal cell carcinoma (RCC). Loss of cell-to-cell adhesion, including tight junctions (TJs) is the initial step in the process of metastasis. Claudin-7 (CLDN7) is a major component of TJs. However, the clinical significance and its regulation of kidney tumorigenesis remain poorly understood.

METHODS

A total of 120 fresh clear cell RCC (ccRCC) specimens and 144 primary RCC and adjacent nonmalignant renal paraffin specimens were obtained from Department of Urology, Peking University First Hospital. Expression of CLDN7 in ccRCC tissues and cell lines were determined using bioinformatic data mining, quantitative real-time PCR (qRT-PCR), Western blotting and immunostaining. The clinical significance of CLDN7 expression and promoter DNA methylation status was analyzed in ccRCC patients from Peking University First Hospital and The Cancer Genome Atlas. Additionally, the methylation specific-PCR, bisulfite genomic sequencing and demethylation analysis of CLDN7 were performed. Biological functions of CLDN7 were investigated by examining cell proliferation using MTS assays and EdU incorporation assays, cell migration by in vitro wound healing assays and transwell migration assays, cell invasion by transwell invasion assays, and cell apoptosis by flow cytometry. Mouse model experiments were performed to confirm the effects of CLDN7 on tumor growth and metastasis in vivo. The molecular mechanism of CLDN7 function was investigated using gene-set enrichment analysis (GSEA) and high-throughput cDNA sequencing (RNA-Seq) and confirmed by qRT-PCR, Western blot and immunostaining in vitro and in vivo.

RESULTS

Our findings revealed that CLDN7 is frequently downregulated via hypermethylation of its promoter in ccRCC. CLDN7 can help predict aggressive tumor status and poor prognosis in ccRCC patients. Interestingly, hypermethylation of the CLDN7 promoter was related to advanced ccRCC status and poor prognosis. Moreover, overexpression of CLDN7 induced cell apoptosis, suppressed proliferation, migration and invasion abilities of ccRCC cells both in vitro and in vivo. Additionally, GSEA and RNA-Seq results showed that CLDN7 had negative effects in cancer-associated signaling pathways and (epithelial-mesenchymal transition) EMT-related pathways. These results were validated by qRT-PCR, Western blot and immunostaining.

CONCLUSIONS

We have demonstrated a previously undescribed role of CLDN7 as a ccRCC suppressor and suggest that loss of CLDN7 potentiates EMT and tumor progression. CLDN7 may serve as a functional tumor suppressor in tumor progression and a potential biomarker and target in patients with ccRCC.

Emerging clinical significance of claudin-7 in colorectal cancer: a review

Tight junctions (TJs) play an important role in maintaining cell polarity and regulating cell permeability. In recent years, many studies have shown that TJ proteins, especially claudin-7, are closely related to inflammation and the development of various malignant tumors. Claudin-7 plays a significant role in maintaining the physiological functions and pathological conditions of the TJ barrier. The dysregulation of claudin-7 plays a tumor suppressor role or conversely has carcinogenic effects in different target tissues or cells, but the exact underlying mechanism is still unclear. In this review, we will summarize the expression pattern of claudin-7 in tumors, focusing on the expression and regulation of claudin-7 in colorectal cancer and discussing the correlation between claudin-7 and invasion, metastasis and epithelial–mesenchymal transition (EMT) in colorectal cancer. The construction of Cldn7^−/− mice and conventional claudin-7 knockout mouse models has helped determine the mechanisms by which claudin-7 promotes tumorigenesis. Elucidation of the expression and subcellular localization of claudin-7 under pathological conditions will help develop claudin-7 as a useful biomarker for detecting and diagnosing cancer, and thus may help combat the occurrence, development, and invasion of cancers.

MASTL induces Colon Cancer progression and Chemoresistance by promoting Wnt/β-catenin signaling

BACKGROUND

Chemotherapeutic agents that modulate cell cycle checkpoints and/or tumor-specific pathways have shown immense promise in preclinical and clinical studies aimed at anti-cancer therapy. MASTL (Greatwall in Xenopus and Drosophila), a serine/threonine kinase controls the final G2/M checkpoint and prevents premature entry of cells into mitosis. Recent studies suggest that MASTL expression is highly upregulated in cancer and confers resistance against chemotherapy. However, the role and mechanism/s of MASTL mediated regulation of tumorigenesis remains poorly understood.

METHODS

We utilized a large patient cohort and mouse models of colon cancer as well as colon cancer cells to determine the role of Mastl and associated mechanism in colon cancer.

RESULTS

Here, we show that MASTL expression increases in colon cancer across all cancer stages compared with normal colon tissue (P < 0.001). Also, increased levels of MASTL associated with high-risk of the disease and poor prognosis. Further, the shRNA silencing of MASTL expression in colon cancer cells induced cell cycle arrest and apoptosis in vitro and inhibited xenograft-tumor growth in vivo. Mechanistic analysis revealed that MASTL expression facilitates colon cancer progression by promoting the β-catenin/Wnt signaling, the key signaling pathway implicated in colon carcinogenesis, and up-regulating anti-apoptotic proteins, Bcl-xL and Survivin. Further studies where colorectal cancer (CRC) cells were subjected to 5-fluorouracil (5FU) treatment revealed a sharp increase in MASTL expression upon chemotherapy, along with increases in Bcl-xL and Survivin expression. Most notably, inhibition of MASTL in these cells induced chemosensitivity to 5FU with downregulation of Survivin and Bcl-xL expression.

CONCLUSION

Overall, our data shed light on the heretofore-undescribed mechanistic role of MASTL in key oncogenic signaling pathway/s to regulate colon cancer progression and chemo-resistance that would tremendously help to overcome drug resistance in colon cancer treatment.

Severe Intestinal Inflammation in the Small Intestine of Mice Induced by Controllable Deletion of Claudin-7

BACKGROUND

As a potential tumor suppressor gene, Claudin-7 (Cldn7), which is a component of tight junctions, may play an important role in colorectal cancer occurrence and development.

AIMS

To generate a knockout mouse model of inducible conditional Cldn7 in the intestine and analyze the phenotype of the mice after induction with tamoxifen.

METHODS

We constructed Cldn7-flox transgenic mice and crossed them with Villin-CreERT2 mice. The Cldn7 inducible conditional knockout mice appeared normal and were well developed at birth. We induced Cldn7 gene deletion by injecting different dosages of tamoxifen into the mice and then conducted a further phenotypic analysis.

RESULTS

After induction for 5 days in succession at a dose of 200 µl tamoxifen in sunflower oil at 10 mg/ml per mouse every time, the mice appeared dehydrated, had a lower temperature, and displayed inactivity or death. The results of hematoxylin-eosin staining showed that the intestines of the Cldn7 inducible conditional knockout mice had severe intestinal defects that included epithelial cell sloughing, necrosis, inflammation and hyperplasia. Owing to the death of ICKO mice, we adjusted the dose of tamoxifen to a dose of 100 µl in sunflower oil at 10 mg/ml per mouse (aged more than 8 weeks old) every 4 days. And we could induce atypical hyperplasia and adenoma in the intestine. Immunofluorescent staining indicated that the intestinal epithelial structure was destroyed. Electron microscopy experimental analysis indicated that the intercellular gap along the basolateral membrane of Cldn7 inducible conditional knockout mice in the intestine was increased and that contact between the cells and matrix was loosened.

CONCLUSIONS

We generated a model of intestinal Cldn7 inducible conditional knockout mice. Intestinal Cldn7 deletion induced by tamoxifen initiated inflammation and hyperplasia in mice.

Na+/H+ exchanger NHE1 regulation modulates metastatic potential and epithelial-mesenchymal transition of triple-negative breast cancer cells

In triple-negative breast cancer (TNBC), the high recurrence rate, increased invasion and aggressive metastatic formation dictate patient survival. We previously demonstrated a critical role for the Na+/H+ exchanger isoform 1 (NHE1) in controlling metastasis of triple-negative cells. Here, we investigated the effect of changes to three regulatory loci of NHE1. Two via the Ras/Raf/ERK/p90RSK pathway: p90RSK/14-3-3 (S703A) and ERK1/2 (S766,770,771A, SSSA) and a third via a calmodulin-binding domain (K641,R643,645,647E, 1K3R4E). MDA-MB-231 cells with a mutation at the p90RSK site (S703A-NHE1) changed from a wild-type mesenchymal morphology to a smaller epithelial-like phenotype with a loss of expression of mesenchymal marker vimentin. S703A cells also had reduced metastatic potential and markedly decreased rates of migration, invasion, spheroid growth, anchorage-dependent and soft agar colony formation. Similarly, BI-D1870, a specific inhibitor of p90RSK, significantly inhibited the metastatic potential of highly invasive MDA-MB-231 and moderately invasive MDA-MB-468 TNBC cells, but was minimally effective in non-invasive Hs578T TNBC cells. In contrast, invasion and spheroid growth were unaffected in cells containing NHE1 with mutations interfering with its activation by ERK1/2 (SSSA), though rates of migration and colony formation were reduced. Cells with a constitutive activation of NHE1 via the 1K3R4E mutation exhibited higher rates of migration, invasion, and spheroid growth. Taken together, our data demonstrate the critical role of NHE1 in metastasis, and suggest a novel link between NHE1 and the expression and cytosolic organization of vimentin, a key factor in epithelial-mesenchymal transition, that is dependent on p90RSK/14-3-3-mediated activation of the exchanger.

Integration of pan-cancer transcriptomics with RPPA proteomics reveals mechanisms of epithelial-mesenchymal transition

Integrating data from multiple regulatory layers across cancer types could elucidate additional mechanisms of oncogenesis. Using antibody-based protein profiling of 736 cancer cell lines, along with matching transcriptomic data, we show that pan-cancer bimodality in the amounts of mRNA, protein, and protein phosphorylation reveals mechanisms related to the epithelial-mesenchymal transition (EMT). Based on the bimodal expression of E-cadherin, we define an EMT signature consisting of 239 genes, many of which were not previously associated with EMT. By querying gene expression signatures collected from cancer cell lines after small-molecule perturbations, we identify enrichment for histone deacetylase (HDAC) inhibitors as inducers of EMT, and kinase inhibitors as mesenchymal-to-epithelial transition (MET) promoters. Causal modeling of protein-based signaling identifies putative drivers of EMT. In conclusion, integrative analysis of pan-cancer proteomic and transcriptomic data reveals key regulatory mechanisms of oncogenic transformation.

Profiling molecular and phenotypic characteristics of large collections of cancer cell lines can be used to identify distinct and common oncogenic pathways across cancer types. So far, most large-scale data obtained from cancer cell lines have been at the genomic, transcriptomic, and phenotypic levels. Recently, high-quality data at the level of cell signaling through protein abundances and phosphorylation sites has become available. By integrating this newly generated protein data with prior transcriptomic data, and by visualizing all cancer cell lines using dimensionality reduction techniques, pan-cancer cell lines are strikingly shown to organize into a gradient of epithelial to mesenchymal types. Interestingly, many of the measured proteins and transcripts display bimodality; the expression of genes, proteins, and protein phosphorylations is either high or low, strongly suggesting that they act as molecular switches. Focusing on further characterizing molecular switches of epithelial-mesenchymal transitions, we identify candidate regulators and small molecules that can induce or reverse such transition, as well as potential causal relationships between proteins. Since the mesenchymal state of tumors is known to be associated with metastasis and later-stage cancer development, better understanding the regulatory mechanisms of epithelial-to-mesenchymal transition can lead to improved targeted therapeutics.