Claudin-4 overexpression is associated with epigenetic derepression in gastric carcinoma

Gastric Cancer Signaling Pathways and Therapeutic Applications

Gastric cancer (GC) is a prevalent malignant tumor and ranks as the second leading cause of death among cancer patients worldwide. Due to its hidden nature and difficulty in detection, GC has a high incidence and poor prognosis. Traditional treatment methods such as systemic chemotherapy, radiotherapy, and surgical resection are commonly used, but they often fail to achieve satisfactory curative effects, resulting in a very low 5-year survival rate for GC patients. Currently, targeted therapy and immunotherapy are prominent areas of research both domestically and internationally. These methods hold promise for the treatment of GC. This article focuses on the signaling pathways associated with the development of GC, as well as the recent advancements and applications of targeted therapy and immunotherapy. The aim is to provide fresh insights for the clinical treatment of GC.

Claudins-Promising Biomarkers for Selected Gastrointestinal (GI) Malignancies?

Despite recent() improvements in diagnostic ability() and treatment() strategies for patients() with neoplastic disease(), gastrointestinal (GI) cancers(), such() as colorectal, gastric, pancreatic, and oesophageal cancers(), are still common() malignancies and the leading() cause() of cancer() deaths worldwide(), with a high frequency of recurrence and metastasis as well as poor patient() prognosis. There is a link() between the secretion of proteolytic enzymes that degrade the extracellular matrix and the pathogenesis of GI tumours. Recent() findings have focused() on the potential() significance() of selected claudins (CLDNs) in the pathogenesis and prognosis of GI cancers(). Tight junctions (TJs) have been proven to play an important role() in maintaining cell() polarity and permeability. A number of authors have recently() revealed that TJ proteins, particularly() selected CLDNs, are related() to inflammation and the development() of various tumours, including GI malignancies. This review() presents general() characteristics and the involvement() of selected CLDNs in the progression() of GI malignancies, with a focus() on the potential() application() of these proteins in the diagnosis() and prognosis of colorectal cancer() (CRC), gastric cancer() (GC), pancreatic cancer() (PC), and oesophageal cancer() (EC). Our review() indicates that selected CLDNs, particularly() CLDN1, 2, 4, 7, and 18, play a significant() role() in the development() of GI tumours and in patient() prognosis. Furthermore, selected CLDNs may be of value() in the design() of therapeutic() strategies for the treatment() of recurrent tumours.

Expression patterns of claudins in cancer

Claudins are four-transmembrane proteins, which were found in tight junctions. They maintain cell barriers and regulate cell differentiation and proliferation. They are involved in maintaining cellular polarity and normal functions. Different claudins show different expression patterns. The expression level and localization of claudins are altered in various cancers. They promote or inhibit proliferation, invasion, and migration of cancer cells through multiple signaling pathways. Therefore, claudins may serve as diagnostic markers, novel therapeutic targets, and prognostic risk factors. The important roles of claudins in cancer aroused our great interest. In the present review, we provide a summary of insights into expression patterns of claudins in cancer, which is more comprehensive and provides new ideas for further research.

Tight junction proteins related to blood-brain barrier and their regulatory signaling pathways in ischemic stroke

Tight junctions (TJs) are crucial for intercellular connections. The abnormal expression of proteins related to TJs can result in TJ destruction, structural damage, and endothelial and epithelial cell dysfunction. These factors are associated with the occurrence and progression of several diseases. Studies have shown that blood-brain barrier (BBB) damage and dysfunction are the prominent pathological features of stroke. TJs are directly associated with the BBB integrity. In this article, we first discuss the structure and function of BBB TJ-related proteins before focusing on the crucial events that cause TJ dysfunction and BBB damage, as well as the regulatory mechanisms that affect the qualitative and quantitative expression of TJ proteins during ischemic stroke. Multiple regulatory mechanisms, including phosphorylation, matrix metalloproteinases (MMPs), and microRNAs, regulate TJ-related proteins and affect BBB permeability. Some signaling pathways and mechanisms have been demonstrated to have dual functions. Hopefully, our understanding of the regulation of BBB TJs in ischemic stroke will be applied to the development of targeted medications and therapeutic therapies.

The role of salinity on genome-wide DNA methylation dynamics in European sea bass gills

Epigenetic modifications, like DNA methylation, generate phenotypic diversity in fish and ultimately lead to adaptive evolutionary processes. Euryhaline marine species that migrate between salinity-contrasted habitats have received little attention regarding the role of salinity on whole-genome DNA methylation. Investigation of salinity-induced DNA methylation in fish will help to better understand the potential role of this process in salinity acclimation. Using whole-genome bisulfite sequencing, we compared DNA methylation patterns in European sea bass (Dicentrarchus labrax) juveniles in seawater and after freshwater transfer. We targeted the gill as a crucial organ involved in plastic responses to environmental changes. To investigate the function of DNA methylation in gills, we performed RNAseq and assessed DNA methylome-transcriptome correlations. We showed a negative correlation between gene expression levels and DNA methylation levels in promoters, first introns and first exons. A significant effect of salinity on DNA methylation dynamics with an overall DNA hypomethylation in freshwater-transferred fish compared to seawater controls was demonstrated. This suggests a role of DNA methylation changes in salinity acclimation. Genes involved in key functions as metabolism, ion transport and transepithelial permeability (junctional complexes) were differentially methylated and expressed between salinity conditions. Expression of genes involved in mitochondrial metabolism (tricarboxylic acid cycle) was increased, whereas the expression of DNA methyltransferases 3a was repressed. This study reveals novel links between DNA methylation, mainly in promoters and first exons/introns, and gene expression patterns following salinity change.

Gastric precancerous lesions:occurrence, development factors, and treatment

Patients with gastric precancerous lesions (GPL) have a higher risk of gastric cancer (GC). However, the transformation of GPL into GC is an ongoing process that takes several years. At present, several factors including H.Pylori (Hp), flora imbalance, inflammatory factors, genetic variations, Claudin-4, gastric stem cells, solute carrier family member 26 (SLC26A9), bile reflux, exosomes, and miR-30a plays a considerable role in the transformation of GPL into GC. Moreover, timely intervention in the event of GPL can reduce the risk of GC. In clinical practice, GPL is mainly treated with endoscopy, acid suppression therapy, Hp eradication, a cyclooxygenase-2 inhibitor, aspirin, and diet. Currently, the use of traditional Chinese medicine (TCM) or combination with western medication to remove Hp and the use of TCM to treat GPL are common in Asia, particularly China, and have also demonstrated excellent clinical efficacy. This review thoroughly discussed the combining of TCM and Western therapy for the treatment of precancerous lesions as conditions allow. Consequently, this review also focuses on the causes of the development and progression of GPL, as well as its current treatment. This may help us understand GPL and related treatment.

Immune-related risk prognostic model for clear cell renal cell carcinoma: Implications for immunotherapy

Clear cell renal cell carcinoma (ccRCC) is associated with complex immune interactions. We conducted a comprehensive analysis of immune-related differentially expressed genes in patients with ccRCC using data from The Cancer Genome Atlas and ImmPort databases. The immune-related differentially expressed genes underwent functional and pathway enrichment analysis, followed by COX regression combined with LASSO regression to construct an immune-related risk prognostic model. The model comprised 4 IRGs: CLDN4, SEMA3G, CAT, and UCN. Patients were stratified into high-risk and low-risk groups based on the median risk score, and the overall survival rate of the high-risk group was significantly lower than that of the low-risk group, confirming the reliability of the model from various perspectives. Further comparison of immune infiltration, tumor mutation load, and immunophenoscore (IPS) comparison between the 2 groups indicates that the high-risk group could potentially demonstrate a heightened sensitivity towards immunotherapy checkpoints PD-1, CTLA-4, IL-6, and LAG3 in ccRCC patients. The proposed model not only applies to ccRCC but also shows potential in developing into a prognostic model for renal cancer, thus introducing a novel approach for personalized immunotherapy in ccRCC.

Twist1‑mediated transcriptional activation of Claudin‑4 promotes cervical cancer cell migration and invasion

Claudin-4, a member of the claudin multigene family, participates in events associated with mesenchymal-like activity of cancerous cells. Claudin-4 expression is upregulated in cervical cancer tissue compared with that in adjoining non-neoplastic tissue. However, the mechanisms that regulate Claudin-4 expression in cervical cancer are poorly understood. Moreover, whether Claudin-4 contributes to the migration and invasion of cervical cancer cells remains unclear. By western blotting, reverse transcription-qPCR, bioinformatics analysis, dual-luciferase reporter assay, chromatin immunoprecipitation assay, wound healing assay and Transwell migration/invasion assay, the present study confirmed that Claudin-4 was a downstream target of Twist1, a helix-loop-helix transcriptional factor, the activity of which has a positive correlation with Claudin-4 expression. Mechanistically, Twist1 directly binds to Claudin-4 promoter, resulting in the transactivation of expression. The depletion of the Twist1-binding E-Box1 domain on Claudin-4 promoter via CRISPR-Cas9 knockout system downregulates Claudin-4 expression and suppresses the ability of cervical cancer cells to migrate and invade by elevating E-cadherin levels and lowering N-cadherin levels. Following activation by transforming growth factor-β, Twist1 induces Claudin-4 expression, thus enhancing migration and invasion of cervical cancer cells. In summary, the present data suggested that Claudin-4 was a direct downstream target of Twist1 and served a critical role in promoting Twist1-mediated cervical cancer cell migration and invasion.

cCPE Fusion Proteins as Molecular Probes to Detect Claudins and Tight Junction Dysregulation in Gastrointestinal Cell Lines, Tissue Explants and Patient-Derived Organoids

Claudins regulate paracellular permeability, contribute to epithelial polarization and are dysregulated during inflammation and carcinogenesis. Variants of the claudin-binding domain of Clostridium perfringens enterotoxin (cCPE) are highly sensitive protein ligands for generic detection of a broad spectrum of claudins. Here, we investigated the preferential binding of YFP- or GST-cCPE fusion proteins to non-junctional claudin molecules. Plate reader assays, flow cytometry and microscopy were used to assess the binding of YFP- or GST-cCPE to non-junctional claudins in multiple in vitro and ex vivo models of human and rat gastrointestinal epithelia and to monitor formation of a tight junction barrier. Furthermore, YFP-cCPE was used to probe expression, polar localization and dysregulation of claudins in patient-derived organoids generated from gastric dysplasia and gastric cancer. Live-cell imaging and immunocytochemistry revealed cell polarity and presence of tight junctions in glandular organoids (originating from intestinal-type gastric cancer and gastric dysplasia) and, in contrast, a disrupted diffusion barrier for granular organoids (originating from discohesive tumor areas). In sum, we report the use of cCPE fusion proteins as molecular probes to specifically and efficiently detect claudin expression, localization and tight junction dysregulation in cell lines, tissue explants and patient-derived organoids of the gastrointestinal tract.

Claudin-4: A New Molecular Target for Epithelial Cancer Therapy

Claudin-4 (CLDN4) is a key component of tight junctions (TJs) in epithelial cells. CLDN4 is overexpressed in many epithelial malignancies and correlates with cancer progression. Changes in CLDN4 expression have been associated with epigenetic factors (such as hypomethylation of promoter DNA), inflammation associated with infection and cytokines, and growth factor signaling. CLDN4 helps to maintain the tumor microenvironment by forming TJs and acts as a barrier to the entry of anticancer drugs into tumors. Decreased expression of CLDN4 is a potential marker of epithelial-mesenchymal transition (EMT), and decreased epithelial differentiation due to reduced CLDN4 activity is involved in EMT induction. Non-TJ CLDN4 also activates integrin beta 1 and YAP to promote proliferation, EMT, and stemness. These roles in cancer have led to investigations of molecular therapies targeting CLDN4 using anti-CLDN4 extracellular domain antibodies, gene knockdown, clostridium perfringens enterotoxin (CPE), and C-terminus domain of CPE (C-CPE), which have demonstrated the experimental efficacy of this approach. CLDN4 is strongly involved in promoting malignant phenotypes in many epithelial cancers and is regarded as a promising molecular therapeutic target.

Tight Junction Protein Signaling and Cancer Biology

Tight junctions (TJs) are intercellular protein complexes that preserve tissue homeostasis and integrity through the control of paracellular permeability and cell polarity. Recent findings have revealed the functional role of TJ proteins outside TJs and beyond their classical cellular functions as selective gatekeepers. This is illustrated by the dysregulation in TJ protein expression levels in response to external and intracellular stimuli, notably during tumorigenesis. A large body of knowledge has uncovered the well-established functional role of TJ proteins in cancer pathogenesis. Mechanistically, TJ proteins act as bidirectional signaling hubs that connect the extracellular compartment to the intracellular compartment. By modulating key signaling pathways, TJ proteins are crucial players in the regulation of cell proliferation, migration, and differentiation, all of which being essential cancer hallmarks crucial for tumor growth and metastasis. TJ proteins also promote the acquisition of stem cell phenotypes in cancer cells. These findings highlight their contribution to carcinogenesis and therapeutic resistance. Moreover, recent preclinical and clinical studies have used TJ proteins as therapeutic targets or prognostic markers. This review summarizes the functional role of TJ proteins in cancer biology and their impact for novel strategies to prevent and treat cancer.

Claudin and pancreatic cancer

Due to the lack of timely and accurate screening modalities and treatments, most pancreatic cancer (PCa) patients undergo fatal PCa progression within a short period since diagnosis. The claudin(CLDN) family is expressed specifically as tight junction structure in a variety of tumors, including PCa, and affects tumor progression by changing the cell junctions. Thus far, many of the 27 members of the claudin family, including claudin-18.2 and claudin-4, have significantly aberrantly expression in pancreatic tumors. In addition, some studies have confirmed the role of some claudin proteins in the diagnosis and treatment of pancreatic tumors. By targeting different targets of claudin protein and combining chemotherapy, further enhance tumor cell necrosis and inhibit tumor invasion and metastasis. Claudins can either promote or inhibit the development of pancreatic cancer, which indicates that the diagnosis and treatment of different kinds of claudins require to consider different biological characteristics. This literature summarizes the functional characteristics and clinical applications of various claudin proteins in Pca cells, with a focus on claudin-18.2 and claudin-4.

The role and mechanism of claudins in cancer

Claudins are a tetraspan membrane protein multigene family that plays a structural and functional role in constructing tight junctions. Claudins perform crucial roles in maintaining cell polarity in epithelial and endothelial cell sheets and controlling paracellular permeability. In the last two decades, increasing evidence indicates that claudin proteins play a major role in controlling paracellular permeability and signaling inside cells. Several types of claudins are dysregulated in various cancers. Depending on where the tumor originated, claudin overexpression or underexpression has been shown to regulate cell proliferation, cell growth, metabolism, metastasis and cell stemness. Epithelial-to-mesenchymal transition is one of the most important functions of claudin proteins in disease progression. However, the exact molecular mechanisms and signaling pathways that explain why claudin proteins are so important to tumorigenesis and progression have not been determined. In addition, claudins are currently being investigated as possible diagnostic and treatment targets. Here, we discuss how claudin-related signaling pathways affect tumorigenesis, tumor progression, and treatment sensitivity.

Transcriptomic Analysis of Testicular Gene Expression in a Dog Model of Experimentally Induced Cryptorchidism

Cryptorchidism, a condition in which testes fail to descend from the abdomen into the scrotum, is a risk factor for infertility and germ cell cancer. Normally, tight junctions between adjacent Sertoli cells in the testes form a blood–testes barrier that regulates spermatogenesis; however, the effect of cryptorchidism on tight junctions is not well-understood. We established a model of heat-induced testicular damage in dogs using surgical cryptorchidism. We sequenced RNA to investigate whether certain transcripts are expressed at higher rates in heat-damaged versus normally descended testes. Claudins, cell adhesion molecules, were relatively highly expressed in cryptorchid testes: claudins 2, 3, 5, 11, and 18 were significantly increased in cryptorchid testes and reduced by orchiopexy. SOX9-positive Sertoli cells were present in the seminiferous tubules in both cryptorchid and control testes. Using real-time PCR and Western blot analysis to compare Sertoli cells cultured at 34 °C and 37 °C, we found that Sertoli cell claudins 2, 3, 5, 11, and 18 were significantly increased at 37 °C; however, accumulation was higher in the G0/G1 phase in Sertoli cells cultured at 34 °C. These results indicate that testicular hyperthermia caused by cryptorchidism affects claudin expression, regulated germ cell death, and the proliferation of Sertoli cells.

High Expression of Claudin-4 Is Associated with Synchronous Tumors in Patients with Early Gastric Cancer

Claudin (CLDN) is a tight junction protein found in human epithelial cells and its altered expression is known to be associated with the progression of gastric cancer. We aimed to investigate the differential expression of CLDN-4 in early gastric cancer (EGC) according to its clinicopathological characteristics. We enrolled 53 patients with EGC who underwent surgical gastric resection from January 2007 to December 2018. The staining intensity of the tumor cells was scored as 0–3, and the percentage of staining was scored as 0–5; high expression was defined if the intensity plus percentage score was 7 or 8, and low expression was defined if the score was 0–6. Among the 53 patients, 16 (30.2%) showed low CLDN-4 expression, while 37 (69.8%) had high CLDN-4 expression. High CLDN-4 expression was significantly associated with intestinal-type EGC (low: 12.5% vs. high: 56.8%, p = 0.003), open-type atrophic change (low: 60.0% vs. high: 90.9%, p = 0.011), and the presence of synchronous tumors (0 vs. 32.4%, p = 0.010), and all 12 EGCs with synchronous tumors showed high CLDN-4 expression. However, expression of CLDN-3, a typical intestinal phenotype CLDN, was neither correlated with CLDN-4 expression nor associated with synchronous tumors. Taken together, high CLDN-4 expression may be considered as an auxiliary tool for screening synchronous tumors in patients with EGC.

Hypomethylation of CLDN4 Gene Promoter Is Associated with Malignant Phenotype in Urinary Bladder Cancer

The tight junction (TJ) protein claudin-4 (CLDN4) is overexpressed in bladder urothelial carcinoma (BUC) and correlates with cancer progression. However, the mechanism of CLDN4 upregulation and promotion of malignant phenotype is not clear. Here, we analyzed 157 cases of BUC and investigated the hypomethylation of CpG island in the CLDN4 promoter DNA and its correlation with cancer progression. In hypomethylated cases, CLDN4 expression, cell proliferation, stemness, and epithelial-mesenchymal transition were increased. Treatment of three human BUC cell lines with the demethylating agent aza-2′-deoxycytidine (AZA) led to excessive CLDN4 expression, and, specifically, to an increase in CLDN4 monomer that is not integrated into the TJ. The TJ-unintegrated CLDN4 was found to bind integrin β1 and increase stemness, drug resistance, and metastatic ability of the cells as well as show an anti-apoptosis effect likely via FAK phosphorylation, which reduces upon knockdown of CLDN4. Thus, CLDN4 is overexpressed in BUC by an epigenetic mechanism and the high expression enhances the malignant phenotype of BUC via increased levels of TJ-unintegrated CLDN4. CLDN4 promoter DNA methylation is expected to be a novel indicator of BUC malignant phenotype and a new therapeutic target.

Claudins and Gastric Cancer: An Overview

Simple Summary

Gastric cancer (GC) is one of the most common cancers and the third leading cause of cancer deaths worldwide, with a high frequency of recurrence and metastasis, and a poor prognosis. This review presents novel biological and clinical significance of claudin (CLDN) expression in GC, especially CLDN18, and clinical trials centered around CLDN18.2. It also presents new findings for other CLDNs.

Abstract

Despite recent improvements in diagnostic ability and treatment strategies, advanced gastric cancer (GC) has a high frequency of recurrence and metastasis, with poor prognosis. To improve the treatment results of GC, the search for new treatment targets from proteins related to epithelial–mesenchymal transition (EMT) and cell–cell adhesion is currently being conducted. EMT plays an important role in cancer metastasis and is initiated by the loss of cell–cell adhesion, such as tight junctions (TJs), adherens junctions, desmosomes, and gap junctions. Among these, claudins (CLDNs) are highly expressed in some cancers, including GC. Abnormal expression of CLDN1, CLDN2, CLDN3, CLDN4, CLDN6, CLDN7, CLDN10, CLDN11, CLDN14, CLDN17, CLDN18, and CLDN23 have been reported. Among these, CLDN18 is of particular interest. In The Cancer Genome Atlas, GC was classified into four new molecular subtypes, and CLDN18–ARHGAP fusion was observed in the genomically stable type. An anti-CLDN18.2 antibody drug was recently developed as a therapeutic drug for GC, and the results of clinical trials are highly predictable. Thus, CLDNs are highly expressed in GC as TJs and are expected targets for new antibody drugs. Herein, we review the literature on CLDNs, focusing on CLDN18 in GC.

Identification of stage-specific differentially expressed genes and SNPs in gastric cancer employing RNA-Seq based transcriptome profiling

We analysed over 400 million reads obtained from Illumina sequencing of six pairs of libraries representing two each of stage I, II, and III gastric tumors and corresponding normal tissues to identify differentially expressed genes (DEGs), single nucleotide polymorphisms (SNPs), and transcription factors (TFs). In total, 2207 DEGs including 972 upregulated genes and 1235 downregulated genes were detected. Of these, several stage-specific signature genes were identified. The protein-protein interaction networks involving DEGs and TFs were constructed. The KEGG pathway analysis of SNP harbouring genes revealed their involvement in different cancer related pathways like apoptosis, mTOR pathway, and MAPK signaling pathway. The SNP analysis showed implication of host genes in GO categories like immune system process, regulation of signaling, response to stress, and transport. A biased chromosomal distribution of DEGs and SNP harbouring genes was observed. Our study would provide further insights into the complex regulatory mechanisms operating during gastric tumorigenesis.

Knocking down claudin receptors leads to a decrease in prostate cancer cell migration, cell growth, cell viability and clonogenic cell survival

Prostate cancer is the most common solid organ malignancy in the United States, and has the highest probability of all cancers in becoming invasive. New molecular targets are needed to define and impede the growth and progression of advanced prostate cancers. Claudins (Cldns) are transmembrane proteins that regulate paracellular permeability and cell polarity, and their levels are elevated in many human cancers such as breast, ovarian, pancreatic, and prostatic cancers. Previously, we found that Cldn3 and Cldn4 are expressed in aggressive high-grade human prostate cancer specimens. We and others have shown that there are higher levels of Cldn3 and Cldn4 in metastatic human prostate cancer cells than in normal human prostate cells. The result of targeting Cldn3 and Cldn4 expression on the growth and viability of prostate cancer cells has not been elucidated. Human prostate cancer PC3 and LNCaP cells were transfected with Cldn3 or -4 small interfering RNAs (siRNAs). Cldn3/Cldn4 siRNA treatment resulted in a greater than 85% decrease in the protein levels of Cldn3 and Cldn4, which was accompanied by a 30–40% decrease in prostate cancer cell growth and a 60–65% reduction in cell viability. There was decreased cell migration with Cldn3 and Cldn4 siRNA in both PC3 and LNCaP cells and a 60–75% decrease in the number of clones when treated with siCldn3 or siCldn4 compared to control. Knocking down Cldn3/Cldn4 affects prostate cancer cell growth and survival and may have therapeutic implications.

Targeting PVT1 Exon 9 Re-Expresses Claudin 4 Protein and Inhibits Migration by Claudin-Low Triple Negative Breast Cancer Cells

PVT1 is a long non-coding RNA transcribed from a gene located at the 8q24 chromosomal region that has been implicated in multiple cancers including breast cancer (BC). Amplification of the 8q24 chromosomal region is a common event in BC and is associated with poor clinical outcomes. Claudin-low (CL) triple negative breast cancer (TNBC) is a subtype of BC with a particularly dismal outcome. We assessed PVT1 exon 9 expression in the T47D estrogen receptor positive BC cell line, and in the MDA MB 468 and MDA MB 231 TNBC cell lines, followed by the assessment of the expression of claudins 1, 3, 4 and 7, in MDA MB 468 and MDA MB 231 (TNBC) cells. We found that MDA MB 231 TNBC cells significantly express less claudin 1, 3, 4, and 7 than MDA MB 468 TNBC cells. PVT1 exon 9 is significantly upregulated in MDA MB 231 CL TNBC cells, and significantly downregulated in MDA MB 468 claudin high (CH) TNBC cells, in comparison to T47D estrogen receptor positive BC cells. We then analyzed the functional consequences of siRNA targeting of PVT1 exon 9 expression in the MDA MB 231 CL TNBC cells. Notably, siRNA targeting of PVT1 exon 9 expression in the MDA MB 231 CL TNBC cells led to a significant reduction in migration and the re-expression of claudin 4. Taken together, our data indicate that PVT1 exon 9 regulates claudin 4 expression and migration in CL TNBC cells, and may have clinical implications in CL TNBC.

The role of claudin-4 in the development of gastric cancer

Gastric cancer is one of most challenging cancers and a significant cause of death worldwide. Gastric cancer is, associated with a high incidence and recurrence rate of metastatic disease and poor survival for those with metastatic disease. Claudin-4 is a transmembrane protein that plays an important role in tight junctions. Increasing experimental research has demonstrated that claudin-4 plays an important role in the progression of gastric cancer, including the occurrence of epithelial to mesenchymal transition, intestinal metaplasia, and gastric cancer. In addition, claudin-4 regulates cell proliferation, invasion, migration and apoptosis. Claudin-4 may represent a potential biomarker for gastric cancer patient prognosis and is useful in the classification of gastric cancer. Therefore, in this review, we summarize current information on claudin-4 and gastric cancer, describing the role of claudin-4 in gastric cancer progression and its application in clinical treatment to provide a basis for further research and promote the claudin-4 gene as a potential target to diagnose and treat gastric cancer.

Effect of Perfluorooctanoic Acid on the Epigenetic and Tight Junction Genes of the Mouse Intestine

Perfluorooctanoic acid (PFOA) has been implicated in various toxicities including neurotoxicity, genotoxicity, nephrotoxicity, epigenetic toxicity, immunotoxicity, reproductive toxicity, and hepatotoxicity. However, information on the accumulation of PFOA in the intestine and its toxic effects on intestinal epigenetics and tight junction (TJ) genes is sparse. CD1 mice were dosed with PFOA (1, 5, 10, or 20 mg/kg/day) for 10 days, and its accumulation and induced alterations in the expression of epigenetic and tight junction genes in the small intestine and colon were evaluated using LC-MS and qPCR techniques. PFOA reduced the expression levels of DNA methyltransferases (Dnmt1, Dnmt3a, Dnmt3b) primarily in the small intestine whereas, in the colon, a decrease was observed only at high concentrations. Moreover, ten-eleven translocation genes (Tet2 and Tet3) expression was dysregulated in the small intestine, whereas in the colon Tets remained unaffected. The tight junction genes Claudins (Cldn), Occludin (Ocln), and Tight Junction Protein (Tjp) were also heavily altered in the small intestine. TJs responded differently across the gut, in proportion to PFOA dosing. Our study reveals that PFOA triggers DNA methylation changes and alters the expression of genes essential for maintaining the physical barrier of intestine, with more profound effects in the small intestine compared to the colon.

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.

CLDN1 induces autophagy to promote proliferation and metastasis of esophageal squamous carcinoma through AMPK/STAT1/ULK1 signaling

Tight junction is a structural constitution in cell-cell adhesion and play an important role in the maintenance of permeability and integrity of normal epithelial cell barrier. The protein encoded by Claudin 1 (CLDN1), a member of the claudin family, is an integral membrane protein and a component of tight junction strands. CLDN1 has been proved to regulate the proliferation and metastasis of multiple tumors, but little is known about its role in esophageal squamous cell carcinoma (ESCC). Here, we found that CLDN1 was aberrantly increased in ESCC tissues and cell lines, and mainly distributed in the nucleus of tumor cells. Furthermore, we confirmed that CLDN1 promoted the proliferation and metastasis of ESCC by triggering autophagy both in vitro and in vivo. Mechanically, we validated that CLDN1-induced autophagy via increasing Unc-51 like autophagy activating kinase 1 (ULK1) expression through AMP-activated protein kinase (AMPK)/signal transducer and activator of transcription 1 (STAT1) signaling pathway in ESCC cells. Taken together, our findings demonstrated that aberrant expression and distribution of CLDN1 promoted the proliferation and metastasis of esophageal squamous carcinoma by triggering autophagy through AMPK/STAT1/ULK1 signaling pathway.

Tight junction proteins in gastrointestinal and liver disease

Over the past two decades a growing body of evidence has demonstrated an important role of tight junction (TJ) proteins in the physiology and disease biology of GI and liver disease. On one side, TJ proteins exert their functional role as integral proteins of TJs in forming barriers in the gut and the liver. Furthermore, TJ proteins can also be expressed outside TJs where they play important functional roles in signalling, trafficking and regulation of gene expression. A hallmark of TJ proteins in disease biology is their functional role in epithelial-to-mesenchymal transition. A causative role of TJ proteins has been established in the pathogenesis of colorectal cancer and gastric cancer. Among the best characterised roles of TJ proteins in liver disease biology is their function as cell entry receptors for HCV-one of the most common causes of hepatocellular carcinoma. At the same time TJ proteins are emerging as targets for novel therapeutic approaches for GI and liver disease. Here we review our current knowledge of the role of TJ proteins in the pathogenesis of GI and liver disease biology and discuss their potential as therapeutic targets.

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.

Claudin1 promotes the proliferation, invasion and migration of nasopharyngeal carcinoma cells by upregulating the expression and nuclear entry of β-catenin

The aim of the present study was to measure the expression of Claudin (CLDN) 1 in nasopharyngeal carcinoma (NPC) and to determine its biological function and mechanism of action. Reverse transcription-quantitative polymerase chain reaction and western blotting were performed to measure the expression of CLDN1 mRNA and protein, respectively, in the immortalized human nasopharyngeal epithelial cell line NP69 and NPC-TW01 cells. Subsequently, small interfering RNA against CLDN1 and the LV-GFP-PURO-CLDN1 lentivirus were transfected into NPC-TW01 cells. Western blotting was used to determine the effects of CLDN1 down- and upregulation on the expression of the epithelial mesenchymal transition (EMT) markers E-cadherin and vimentin. In addition, the effect of CLDN1 on the expression of β-Catenin was determined. The results demonstrated that levels of CLDN1 mRNA and protein in NPC cells were significantly higher than in NP69 cells. Furthermore, the downregulation of CLDN1 inhibited the proliferation, invasion and migration of NPC-TW01 cells. The results of western blotting demonstrated that the downregulation of CLDN1 resulted in the upregulation of E-cadherin and inhibition of vimentin in NPC-TW01 cells. By contrast, the overexpression of CLDN1 resulted in the downregulation of E-cadherin and upregulation of vimentin in NPC-TW01 cells. The downregulation of β-catenin attenuated the cancer-promoting effect of CLDN1 on NPC-TW01 cells, whereas the upregulation of β-catenin reversed the tumor-suppressing effect of CLDN1 downregulation on NPC-TW01 cells. The results of the present study therefore demonstrate that CLDN1 expression is elevated in NPC cells. As an oncogene, CLDN1 promotes the proliferation, invasion and migration of NPC cells by upregulating the expression and nuclear entry of β-catenin.

Methylation of the claudin‑3 promoter predicts the prognosis of advanced gastric adenocarcinoma

Claudin-3 expression is associated with gastric cancer progression, but the role of epigenetic modifications remains unclear. We investigated methylation of the claudin-3 promoter and expression profiles in gastric adenocarcinoma and their associations with clinicopathological characteristics and prognosis of the patients. A total of 122 patients with advanced gastric cancer [stage IIB-IV, with lymph node (LN) metastasis] were enrolled. Each patient provided 4 tissue samples: normal gastric epithelium, intestinal metaplasia, primary tumor and metastatic LN. Claudin-3 protein expression was examined by immunohistochemistry. Claudin-3 promoter methylation was determined by methylation-specific PCR and verified by bisulfite sequencing PCR. Claudin-3 mRNA expression was measured by real-time PCR in a subset of cases, and its correlation with protein expression was analyzed using Spearman correlation. Kaplan-Meier survival analysis was performed (log-rank test). Factors associated with survival were identified by Cox regression. The strong expression rate of claudin-3 in intestinal metaplasia, primary tumor, metastatic LN and normal gastric epithelium was 91.8, 58.2, 30.3 and 13.9%, respectively. The promoter hypermethylation rate in intestinal metaplasia, primary tumor, normal gastric epithelium and metastatic LN was 5.7, 27.9, 36.9 and 49.2%, respectively. Claudin-3 mRNA and protein expression were positively correlated (P<0.001) with normal gastric epithelium (r_s=0.745), intestinal metaplasia (r_s=0.876), primary gastric adenocarcinoma (r_s=0.915) and metastatic LN (r_s=0.819). Claudin-3 mRNA expression was negatively correlated with claudin-3 promoter methylation. Median patient survival was 38, 22 and 11 months in the hypomethylated, partially methylated and hypermethylated groups, respectively (P<0.001). Claudin-3 promoter methylation status (HR: 5.67; 95% CI: 2.27–14.17) but not claudin-3 expression was an independent predictor of survival. Claudin-3 promoter hypermethylation reduces claudin-3 expression and independently predicts poor prognosis.

ESRP1 is overexpressed in ovarian cancer and promotes switching from mesenchymal to epithelial phenotype in ovarian cancer cells

Epithelial splicing regulatory protein 1 (ESRP1) and 2 (ESRP2), epithelial cell-specific regulators of alternative splicing, are downregulated during the epithelial-mesenchymal transition (EMT). These factors have roles in tumor progression and metastasis in some cancers; however, their expression and function in ovarian cancer (OC) remain unclear. We found that ESRP1 and ESRP2 mRNAs were expressed at higher levels in OC cells than in immortalized ovarian surface epithelial (IOSE) cells, and confirmed their overexpression in OC tissues at the protein level. The Cancer Genome Atlas (TCGA) data analysis revealed frequent gene amplification of ESRP1 in OC tissues; however, we detected no significant correlation between ESRP1 gene copy number and gene expression in OC cells. Importantly, expression of ESRP1 and ESRP2 was inversely correlated with DNA methylation in OC cells, and ESRP2 overexpression in OC tissues was significantly associated with DNA hypomethylation. Notably, survival analysis using TCGA data from 541 OC tissues revealed that high ESRP1 expression was significantly associated with shorter 5-year survival of patients. Ectopic ESRP1 expression in mesenchymal OC cells promoted cell proliferation but suppressed cell migration. Furthermore, we found that ESRP1 drives a switch from mesenchymal to epithelial phenotype characterized by reduced cell migration in association with induction of epithelial cell-specific variant of CD44 and ENAH. Taken together, our findings suggest that an epigenetic mechanism is involved in ESRP1 overexpression, and that ESRP1 has a role in OC progression.

TLR2 activation induced by H. pylori LPS promotes the differential expression of claudin-4, -6, -7 and -9 via either STAT3 and ERK1/2 in AGS cells

Gastric carcinogenesis has been associated to H. pylori virulence factors that induce a chronic inflammation process. Lipopolysaccharides play a role in chronic inflammatory responses via TLR2- and TLR4-dependent signaling pathways. Similarly, cellular invasiveness, metastatic potential and prognosis are usually associated to claudin-4, -6, -7 and -9 expression in gastric carcinogenesis. Therefore, the aim of this study was to determine if H. pylori LPS exerts an influence on carcinogenesis-related claudin expression and if it was directly regulated through the TLR2 pathway. Human antrum gastric adenocarcinoma AGS cells exposed or not to H. pylori LPS were used. Polyclonal anti-claudin-4, -6, -7 and -9, anti-TLR2, anti-pERK1/2 as well as rabbit monoclonal anti-pNFκB p65 and mouse monoclonal anti-CdX2 were used. ERK1/2 inhibitor UO126 and STAT3 inhibitor Stattic were also used. Western blot, immunofluorescence and confocal experiments were performed in whole cells as well as total protein, nuclear and cell membrane fractions. The results showed that H. pylori LPS increased the expression of TLR2 in a time dependent bi-phasic manner (<12 and >12h exposure). Immunofluorescence using AGS monolayers corroborated the double phase TLR2 expression mainly on the cell membrane but a detectable signal was also determined in the cytoplasm of the cells. Activation of NFkB was downstream and depended on TLR2 expression as a statistically significant increase in pNFkB, that followed a pattern highly similar to the TLR2 expression was observed on the cell membrane fraction. The increase in TLR2 expression was accompanied by dramatically increased claudin-4 expression in cultures exposed from 30m to 8h to LPS. Increased expression of claudin-6, -7 and -9 also increases in >12h LPS exposure times. The increase in claudins expression was also dependent on NFkB activation. The results also showed an increase in pSTAT3 that followed a bi-phasic pattern that began 30min after stimulation and was compatible with the increase in TLR2 expression. The expression of the claudin-4 related CDX2 transcription factor did not followed the biphasic pattern. The results also showed that claudin-4 expression was STAT3 dependent whereas claudin-6, 7 and 9 expressions was ERK1/2 dependent. Our results suggest that H. pylori LPS induces TLR2 expression in the AGS cells, and that the longer the exposure to LPS, the greater the expression of TLR2 in the cell membrane. Consequently the expression of claudin-4, -6, -7 and -9 also increases.

Genes co-amplified with ERBB2 or MET as novel potential cancer-promoting genes in gastric cancer

Gastric cancer (GC), one of the most common cancers worldwide, has a high mortality rate due to limited treatment options. Identifying novel and promising molecular targets is a major challenge that must be overcome if treatment of advanced GC is to be successful. Here, we used comparative genomic hybridization and gene expression microarrays to examine genome-wide DNA copy number alterations (CNAs) and global gene expression in 38 GC samples from old and young patients. We identified frequent CNAs, which included copy number gains on chromosomes 3q, 7p, 8q, 20p, and 20q and copy number losses on chromosomes 19p and 21p. The most frequently gained region was 7p21.1 (55%), whereas the most frequently deleted region was 21p11.1 (50%). Recurrent highly amplified regions 17q12 and 7q31.1-7q31.31 harbored two well-known oncogenes: ERBB2 and MET. Correlation analysis of CNAs and gene expression levels identified CAPZA2 (co-amplified with MET) and genes GRB7, MIEN1, PGAP3, and STARD3 (co-amplified with ERBB2) as potential candidate cancer-promoting genes (CPGs). Public dataset analysis confirmed co-amplification of these genes with MET or ERBB2 in GC tissue samples, and revealed that high expression (except for PGAP3) was significantly associated with shorter overall survival. Knockdown of these genes using small interfering RNA led to significant suppression of GC cell proliferation and migration. Reduced GC cell proliferation mediated by CAPZA2 knockdown was attributable to attenuated cell cycle progression and increased apoptosis. This study identified novel candidate CPGs co-amplified with MET or ERBB2, and suggests that they play a functional role in GC.

CANcer-specific Evaluation System (CANES): a high-accuracy platform, for preclinical single/multi-biomarker discovery

The recent creation of enormous, cancer-related “Big Data” public depositories represents a powerful means for understanding tumorigenesis. However, a consistently accurate system for clinically evaluating single/multi-biomarkers remains lacking, and it has been asserted that oft-failed clinical advancement of biomarkers occurs within the very early stages of biomarker assessment. To address these challenges, we developed a clinically testable, web-based tool, CANcer-specific single/multi-biomarker Evaluation System (CANES), to evaluate biomarker effectiveness, across 2,134 whole transcriptome datasets, from 94,147 biological samples (from 18 tumor types). For user-provided single/multi-biomarkers, CANES evaluates the performance of single/multi-biomarker candidates, based on four classification methods, support vector machine, random forest, neural networks, and classification and regression trees. In addition, CANES offers several advantages over earlier analysis tools, including: 1) survival analysis; 2) evaluation of mature miRNAs as markers for user-defined diagnostic or prognostic purposes; and 3) provision of a “pan-cancer” summary view, based on each single marker. We believe that such “landscape” evaluation of single/multi-biomarkers, for diagnostic therapeutic/prognostic decision-making, will be highly valuable for the discovery and “repurposing” of existing biomarkers (and their specific targeted therapies), leading to improved patient therapeutic stratification, a key component of targeted therapy success for the avoidance of therapy resistance.

Non-coding RNAs participate in the regulatory network of CLDN4 via ceRNA mediated miRNA evasion

Thousands of genes have been well demonstrated to play important roles in cancer progression. As genes do not function in isolation, they can be grouped into "networks" based on their interactions. In this study, we discover a network regulating Claudin-4 in gastric cancer. We observe that Claudin-4 is up-regulated in gastric cancer and is associated with poor prognosis. Claudin-4 reinforce proliferation, invasion, and EMT in AGS, HGC-27, and SGC-7901 cells, which could be reversed by miR-596 and miR-3620-3p. In addition, lncRNA-KRTAP5-AS1 and lncRNA-TUBB2A could act as competing endogenous RNAs to affect the function of Claudin-4. Our results suggest that non-coding RNAs play important roles in the regulatory network of Claudin-4. As such, non-coding RNAs should be considered as potential biomarkers and therapeutic targets against gastric cancer.Non-coding RNAs can modify the expression of proteins in cancer networks. Here the authors reveal a regulatory network in gastric cancer whereby claudin-4 expression is reduced by specific miRNAs, which are in turn bound by specific lncRNAs acting as competing endogenous RNAs (ceRNAs), resulting in increased claudin-4 expression.

Expression of claudin 1, claudin 4, and claudin 7 in colorectal cancer and its relation with CLDN DNA methylation patterns

Altered claudin expression has been described in colon, prostatic, ovarian, and breast carcinoma. However, the role of epigenetic modifications in these genes and their role in colorectal cancer is unknown. We aimed our study to investigate whether claudin protein expression and methylation of CLDN can influence the tumorigenesis of colorectal cancer. A total of 31 patients diagnosed with colorectal carcinoma was used in this study. Immunohistochemical staining was used to study protein expression in both tumor and the adjacent nonneoplastic mucosa of claudin 1, 4, and 7. To detect the DNA methylation pattern of CLDN1, 4, and 7, genomic DNA was extracted from both the tumor and the adjacent nonneoplastic mucosa. Methylation analysis was carried out using bisulfite pyrosequencing. Cell membrane staining intensity of all claudins was found significantly lower in colorectal cancer tissues when compared to paired normal mucosa (p ≤ 0.001). For claudin 4, the percentage of cells staining positively was also significantly reduced (p = 0.04). In normal mucosa, cytoplasm showed no staining for claudins in any patient, whereas in paired colorectal cancer tissues, significant cytoplasmic staining appeared both for claudin 1 (p = 0.04) and claudin 4 (p = 0.01). Tumor samples were significantly hypomethylated in CLDN1 (p < 0.05). In conclusion, our results show that CLDN1 is significantly hypomethylated in tumor samples and that the membrane staining intensity for claudin 1, 4, and 7 is significantly lower in colorectal cancer tissues than in adjacent nonneoplastic tissue. Colorectal cancer cells showed dystopic cytoplasmic location of claudins.

Expression of claudin-11, -23 in different gastric tissues and its relationship with the risk and prognosis of gastric cancer

Claudins play an important role in regulating the permeability of epithelial and endothelial cells and in the maintenance of cell polarity. We aimed to investigate expression of claudin-11, -23 in different gastric tissues and its relationship with clinicopathologic parameters and prognosis of gastric cancer. We compared their expression levels in the paired cancerous tissues versus those in the adjacent noncancerous tissues by real-time PCR, western blotting and immunohistochemistry. The results showed that the expression of claudin-11, -23 was greatly increased in paracancerous gastric tissue compared with cancerous tissue. We also compared their expression levels of tissues from gastric cancer, superficial gastritis, and atrophic gastritis by immunohistochemistry. The results indicated that the expression of claudin-11 and 23 was significantly higher in superficial gastritis than that in atrophic gastritis and gastric cancer. The expression of claudin-23 was significantly lower in atrophic gastritis than that in gastric cancer, but no obviously difference was observed for claudin-11. As for analysis of clinicopathologic parameters of gastric cancer, logistic multiple regression indicated that claudin-11 was significantly associated with sex, smoking, alcohol, H. pylori infection and Borrmann classification while claudin-23 was significantly associated with vessel cancer embolus. Cox multivariate survival analysis indicated that gastric cancer patients with negative claudin-23 expression had significantly longer overall survival. In conclusion, the expression of claudin-11, -23 was remarkably downregulated in gastric cancer. Abnormal expression of these proteins was significantly correlated with some clinicopathologic parameters. In particular, claudin-23 positive expression was associated with poor prognostic outcomes of gastric cancer patients and may therefore serve as an independent prognosticator of patient survival.

Epigenomic profiling of primary gastric adenocarcinoma reveals super-enhancer heterogeneity

Regulatory enhancer elements in solid tumours remain poorly characterized. Here we apply micro-scale chromatin profiling to survey the distal enhancer landscape of primary gastric adenocarcinoma (GC), a leading cause of global cancer mortality. Integrating 110 epigenomic profiles from primary GCs, normal gastric tissues and cell lines, we highlight 36,973 predicted enhancers and 3,759 predicted super-enhancers respectively. Cell-line-defined super-enhancers can be subclassified by their somatic alteration status into somatic gain, loss and unaltered categories, each displaying distinct epigenetic, transcriptional and pathway enrichments. Somatic gain super-enhancers are associated with complex chromatin interaction profiles, expression patterns correlated with patient outcome and dense co-occupancy of the transcription factors CDX2 and HNF4α. Somatic super-enhancers are also enriched in genetic risk SNPs associated with cancer predisposition. Our results reveal a genome-wide reprogramming of the GC enhancer and super-enhancer landscape during tumorigenesis, contributing to dysregulated local and regional cancer gene expression.

Claudins in cancer: bench to bedside

The claudin family, in mammals, encoded by at least 27 members of a single ancestral gene, CLDN, is the main constituent as integral membrane proteins of tight junctions. It has been shown that the expression levels of claudins are often decreased or that their expressions are absent in human neoplasias. These findings are consistent with the well-accepted concept that carcinogenesis is accompanied by the disruption or loss of functional tight junctions. In contrast, accumulating data have showed elevated or aberrant expression of claudins in various cancers, indicating specific roles of claudins in tumorigenesis. Importantly, dysregulated claudins play an oncogenic role or conversely have a tumor-suppressive effect depending on target tissues or cell types, and thus, they contribute to tumor development and progression. Although tight junctions are intercellular structures in epithelial cells, specific roles of claudins in cancer are supported by the evidence that TJs are not simple static constituents for establishing cell adhesion structures but are also cell signaling components that have functions in receiving environmental cues and transmitting signals inside cells. Since the expression profile of claudins is associated with patients' outcome and prognosis in several cancer types, an understanding of the expression pattern and subcellular localization of claudins in various pathologies will lead to the establishment of claudins as useful biomarkers for the detection and diagnosis of cancers.

Role of TGF-β-induced Claudin-4 expression through c-Jun signaling in non-small cell lung cancer

Claudin-4 has been identified as an integral member of tight junctions and has been found to be upregulated in various types of cancers especially in metastatic cancers. However, the molecular mechanism of the upregulation of Claudin-4 and its role in lung tumorigenesis are unknown. The aim of the present study is to investigate the role of Claudin-4 on migration and tumorigenicity of lung cancer cells and to examine the regulatory effects of TGF-β on Claudin-4 expression. We have observed that TGF-β induces the expression of Claudin-4 dramatically in lung cell lines in a time dependent manner. TGF-β-induced Smad signaling is important for enhancing Claudin-4 mRNA level through inducing its promoter activity. Treatment with curcumin, a c-Jun inhibitor, or stable knockdown of c-Jun abrogates TGF-β-induced Claudin-4 expression suggesting an involvement of the c-Jun pathway. Notably, TGF-β-induced Claudin-4 expression through c-Jun pathway plays a role in TGF-β-mediated motility and tumorigenicity of these cells. In support of these observations, we have uncovered that Claudin-4 is upregulated in 14 of 24 (58%) lung tumors when compared with normal lung tissue. This is the first study to show how TGF-β regulates the expression of Claudin-4 through c-Jun signaling and how this pathway contributes to the migratory and tumorigenic phenotype of lung tumor cells.

Clinicopathological significance of claudin 4 expression in gastric carcinoma: a systematic review and meta-analysis

Background

The prognostic significance of claudin 4 (CLDN4) in patients with gastric cancer (GC) is controversial. This meta-analysis aims to assess the correlation between CLDN4 expression and clinicopathological characteristics and assess the prognostic significance of CLDN4 in GC.

Methods

We searched the PubMed and Embase databases. We performed the meta-analysis with odds ratio (OR), hazard ratio (HR), and 95% confidence interval (CI) as effect values.

Results

Fourteen studies containing 2,106 patients with GC were analyzed. The overall analysis showed that CLDN4 expression was associated with increasing pT category, tumor size, and lymph node metastasis in patients with GC (pT3–T4 vs pT1–T2: OR =1.56, 95% CI =1.13–2.16; P<0.01; large tumor size vs small tumor size: OR =1.64, 95% CI =1.15–2.34; P<0.01; positive lymph node metastasis vs negative lymph node metastasis: OR =1.49, 95% CI =1.12–1.97; P<0.01). CLDN4 expression was associated with histological differentiation (differentiated type vs undifferentiated type: OR =2.90, 95% CI =1.32–6.37; P=0.01; Lauren intestinal type vs diffuse type: OR =3.51, 95% CI =1.48–8.28; P<0.01). CLDN4 expression was also strongly associated with sex and age. This meta-analysis found no significant association between CLDN4 expression and prognosis for overall survival in patients with GC (HR =0.74, 95% CI =0.43–1.27; P=0.28).

Conclusion

Present study indicates that aberrant CLDN4 expression plays an important role in the clinicopathological characteristics of GC.

Expression pattern and prognostic significance of claudin 1, 4 and 7 in pancreatic cancer

BACKGROUND

Tight junctions (TJs) organise paracellular permeability and they have an important role in epithelial and endothelial cell polarity and permanence of barrier function. It has been demonstrated that the Claudin family constitutes an important component of them. In this study, we assessed expression patterns of of Claudin1, 4 and 7 and whether they have any relation with prognosis in patients with pancreatic cancer.

MATERIALS AND METHODS

Expression patterns of Claudin 1,4 and 7 were examined by immunohistochemistry in 25 patients with a histopathological diagnosis of pancreatic cancer using a semiquantitative scoring of the extent and intensity of staining. After grouping the staining scores as low (final score 0-2) and high (final score 3-9) the relation between expression of Claudin 1,4 and 7 and survival was evaluated.

RESULTS

There was no significant relation between expression of Claudin 1,4 and 7 and gender and stage. No statistically significant relation was found between Claudin 1 and 4 expression and survival whereas a statistically significant relation was found between decrease in Claudin 7 expression and decrease in survival.

CONCLUSIONS

Claudins have important functions other than their popular function known as adhesion. Supporting this hypothesis, we found a statistically significant relationship between increased Claudin 7 expression and increased survival time, and this suggests that Claudin 7 may exert different tumorigenic effects in pancreatic cancer other than its well- known adhesion effect.

Claudin-1 enhances tumor proliferation and metastasis by regulating cell anoikis in gastric cancer

Claudin-1 (CLDN1) is overexpressed in gastric cancer and correlated with tumor invasion, metastasis and poor outcome. Here, we both down and up regulated CLDN1 expression in gastric cancer cells to elucidate its role in gastric carcinogenesis and tumor progression. We found that deficiency of CLDN1 inhibited cells migration, invasion, and colony formation in vitro and tumorigenicity, metastasis in vivo. Also, CLDN1 promoted cell aggregation and increased anoikis resistance. Down or up regulation of CLDN1 was accompanied with changes of membrane β-catenin expression as well as Akt and Src activities. When β-catenin was up-regulated in CLDN1-KD cells, cell aggregation and anoikis resistance were restored, and Akt and Src signal pathways were re-activated. Taken together, these findings suggest that CLDN1 is oncogenic in gastric cancer and its malignant potential may be attributed in part to regulation of anoikis, by mediating membrane β-catenin-regulated cell-cell adhesion and cell survival.

Tight junction protein claudin 4 in gastric carcinoma and its relation to lymphangiogenic activity

BACKGROUND AND STUDY AIMS

Gastric cancer is the second most common cause of cancer-related death worldwide. Claudins are a family of tight junction proteins that are biologically relevant in many cancer progression steps. This study aimed to investigate the expression of the intestinal claudin (claudin 4) in gastric carcinoma and to evaluate its relation to the different clinicopathologic prognostic parameters, especially lymphangiogenesis (production of new lymphatic vessels, measured by lymphovascular density (LVD)) and lymphovascular invasion (LVI).

PATIENTS AND METHODS

Fifty-five gastric carcinoma specimens were immunohistochemically stained for claudin 4 and D2-40 (for detection of lymphatic vessel endothelium).

RESULTS

High expression of claudin 4 was detected in 26 of 55 (47.3%) cases. Low expression of claudin 4 was related to poorly differentiated type (p=0.001), non-intestinal (diffuse) type (p=0.001), deeper tumour invasion (p<0.001), lymph node metastasis (p=0.001), and higher stage (p=0.001). In addition, higher LVD was related to poorly differentiated types (p=0.001), non-intestinal type (p=0.001), lymph node metastasis (p=0.015), and higher tumour, node, metastasis (TNM) stage (p=0.001). LVI was related to lymph node metastasis (p=0.025), higher TNM stage (p=0.001), and LVD (p=0.001). Claudin 4 significantly correlated with both LVD (p=0.009) and LVI (p=0.009).

CONCLUSIONS

High expression of claudin 4 was associated with the more differentiated intestinal-type gastric carcinoma and lost in poorly differentiated diffuse type. So, claudin 4 may be used as one of the differentiating markers between the two major types of gastric carcinoma (intestinal vs. diffuse). LVD and LVI were related to higher incidence of lymph node metastasis and therefore could be used as predictive markers for lymph node metastasis in limited specimens during early gastric carcinoma to determine the need for more invasive surgery. Low expression of claudin 4 was related to lymphangiogenesis. This may shed light on the relation of tight junction protein expression and lymphangiogenesis.

Tight junction disruption: Helicobacter pylori and dysregulation of the gastric mucosal barrier

Long-term chronic infection with Helicobacter pylori (H. pylori) is a risk factor for gastric cancer development. In the multi-step process that leads to gastric cancer, tight junction dysfunction is thought to occur and serve as a risk factor by permitting the permeation of luminal contents across an otherwise tight mucosa. Mechanisms that regulate tight junction function and structure in the normal stomach, or dysfunction in the infected stomach, however, are largely unknown. Although conventional tight junction components are expressed in gastric epithelial cells, claudins regulate paracellular permeability and are likely the target of inflammation or H. pylori itself. There are 27 different claudin molecules, each with unique properties that render the mucosa an intact barrier that is permselective in a way that is consistent with cell physiology. Understanding the architecture of tight junctions in the normal stomach and then changes that occur during infection is important but challenging, because most of the reports that catalog claudin expression in gastric cancer pathogenesis are contradictory. Furthermore, the role of H. pylori virulence factors, such as cytotoxin-associated gene A and vacoulating cytotoxin, in regulating tight junction dysfunction during infection is inconsistent in different gastric cell lines and in vivo, likely because non-gastric epithelial cell cultures were initially used to unravel the details of their effects on the stomach. Hampering further study, as well, is the relative lack of cultured cell models that have tight junction claudins that are consistent with native tissues. This summary will review the current state of knowledge about gastric tight junctions, normally and in H. pylori infection, and make predictions about the consequences of claudin reorganization during H. pylori infection.

CD24 Overexpression Is Associated with Poor Prognosis in Luminal A and Triple-Negative Breast Cancer

CD24 is associated with unfavourable prognoses in various cancers, but the prevalence of CD24 expression and its influence on clinical outcome in subtypes of breast cancers remain unclear. CD24 expression was analyzed by immunohistochemistry in 747 breast cancer tissues, and DNA methylation and histone modification status in the promoter region of CD24 were assessed using bisulfite sequencing and chromatin immunoprecipitation assay. 213 (28.5%) samples exhibited high CD24 expression in the membrane and/or cytoplasm of breast cancer cells, and CD24 overexpression was significantly correlated with the presence of lymph node metastasis and more advanced pathological stage. Patients with CD24-high tumours had significantly shorter patient survival than those with CD24-low tumours. Importantly, multivariate analysis that included tumour size, lymph node metastasis and chemotherapy demonstrated that high CD24 expression is independently associated with poorer survival in luminal A and triple-negative breast cancer (TNBC) subtypes. Furthermore, CD24 gene expression was associated with histone acetylation independent of DNA methylation, suggesting its epigenetic regulation in breast cancer. Our results suggest that CD24 overexpression is an independent unfavourable prognostic factor in breast cancer, especially for luminal A and TNBC subtypes, and CD24 may be a promising therapeutic target for specific subtypes of breast cancer.

Pro-chemotherapeutic effects of antibody against extracellular domain of claudin-4 in bladder cancer

Bladder cancer displays an aggressive phenotype in the muscle-invasive phase, and is associated with a high mortality rate. Therefore, novel molecular therapeutic targets are needed to improve patient survival. A monoclonal antibody against the extracellular domain of the claudin-4 (CLDN4) tight junction protein was established by immunizing rats with a plasmid vector encoding human CLDN4. A hybridoma clone, producing a rat monoclonal antibody recognizing CLDN4 (clone 4D3), was obtained. Immunohistochemistry by using the 4D3 antibody showed that CLDN4 expression was associated with local invasion, nodal metastasis, distant metastasis, and advanced stage in 86 cases of bladder cancer. The 4D3 antibody inhibited growth, invasion, and survival, associated with abrogation of the intratumoral microenvironment; lowered concentrations of epidermal growth factor and vascular endothelial growth factor were found in three-dimensional cultures of T24 and RT4 cells. In combination with cisplatin therapy, 4D3 enhanced cisplatin cytotoxicity by increasing cellular permeability, leading to increased intracellular cisplatin concentrations. In mouse models of subcutaneous tumors and lung metastasis, 4D3 enhanced tumor growth inhibition, alone and with concurrent cisplatin treatment. The anti-tumor activity of the newly established 4D3 antibody suggests that it may be a powerful tool in CLDN4-targeting therapy, and in combination with chemotherapy.

Prognostic and clinical significance of claudin-4 in gastric cancer: a meta-analysis

BACKGROUND

The current reports on the association of claudin-4 expression with gastric cancer outcome were inconsistent. Thus, we conducted a meta-analysis to assess the association of claudin-4 expression with the prognosis and clinical parameters more precisely.

METHODS

Systematic searches on PubMed, Embase, and Cochrane Library prior to December 2014 were performed. The pooled hazard ratio (HR) with its 95 % confidence interval (95 %CI) was used to assess the prognostic value of claudin-4 expression with gastric cancer patients, and the pooled odds ratio (OR) with its 95 %CI was used to assess the association with clinical parameters.

RESULTS

Nine studies with a total of 1265 gastric cancer patients were included. Overall, the pooled results showed that over-expression of claudin-4 was associated with a poor survival in gastric cancer patients (HR: 2.01, 95 % CI: 1.62-2.50). Over-expression of claudin-4 was also associated with advanced stage (OR: 1.96, 95 % CI: 1.08-3.56) and lymphoid node metastasis (OR: 1.72, 95 % CI: 1.05-2.81) of gastric cancer patients. No significant publication bias was found among the studies (P > 0.05).

CONCLUSIONS

This meta-analysis shows that over-expression of claudin-4 is associated with progress of gastric cancer and poor prognosis of gastric cancer patients.

Genome-wide DNA methylation identifies trophoblast invasion-related genes: Claudin-4 and Fucosyltransferase IV control mobility via altering matrix metalloproteinase activity

Previously we showed that extravillous cytotrophoblast (EVT) outgrowth and migration on a collagen gel explant model were affected by exposure to decidual natural killer cells (dNK). This study investigates the molecular causes behind this phenomenon. Genome wide DNA methylation of exposed and unexposed EVT was assessed using the Illumina Infinium HumanMethylation450 BeadChip array (450 K array). We identified 444 differentially methylated CpG loci in dNK-treated EVT compared with medium control (P < 0.05). The genes associated with these loci had critical biological roles in cellular development, cellular growth and proliferation, cell signaling, cellular assembly and organization by Ingenuity Pathway Analysis (IPA). Furthermore, 23 mobility-related genes were identified by IPA from dNK-treated EVT. Among these genes, CLDN4 (encoding claudin-4) and FUT4 (encoding fucosyltransferase IV) were chosen for follow-up studies because of their biological relevance from research on tumor cells. The results showed that the mRNA and protein expressions of both CLDN4 and FUT4 in dNK-treated EVT were significantly reduced compared with control (P < 0.01 for both CLDN4 and FUT4 mRNA expression; P < 0.001 for CLDN4 and P < 0.01 for FUT4 protein expression), and were inversely correlated with DNA methylation. Knocking down CLDN4 and FUT4 by small interfering RNA reduced trophoblast invasion, possibly through the altered matrix metalloproteinase (MMP)-2 and/or MMP-9 expression and activity. Taken together, dNK alter EVT mobility at least partially in association with an alteration of DNA methylation profile. Hypermethylation of CLDN4 and FUT4 reduces protein expression. CLDN4 and FUT4 are representative genes that participate in modulating trophoblast mobility.

Regulation of the expression of claudin 23 by the enhancer of zeste 2 polycomb group protein in colorectal cancer

Altered epigenetic mechanisms, similar to gene mutations, contribute to the pathogenesis and molecular heterogeneity of neoplasms, including colorectal cancer (CRC). Enhancer of zeste 2 (EZH2) is a histone methyltransferase, which is involved in epigenetic gene silencing and is aberrantly expressed in CRC. Therefore, the identification of the genes regulated by EZH2 in CRC is important to improve current understanding of its role in cancer epigenetics. The present study used chromatin immunoprecipitation (ChIP) followed by deep sequencing to assess genome-wide EZH2‑DNA interactions in healthy or CRC mucosa samples. In total, 86.9/61.6 and 92.5/62.6 million tags were sequenced/mapped in healthy and CRC mucosa samples, respectively. The EZH2-binding densities were correlated with transcriptomic datasets and this demonstrated that the claudin-23 (CLDN23) gene, which encodes a component of cell-cell adhesion structures, was occupied by EZH2 and significantly silenced in CRC tissue. The measurement of DNA methylation at the CLDN23 promoter using pyrosequencing excluded the possibility that silencing of this gene in CRC patient samples was a result of DNA hypermethylation. Following treatment of the Colo205 and HT-29 CRC cell lines, with the EZH2 inhibitor, GSK126, the level of histone H3 lysine 27 trimethylation (H3K27me3) was reduced and the mRNA and protein expression levels of CLDN23 were increased. ChIP analysis confirmed that the level of H3K27m3 along the CLDN23 gene was decreased in the GSK126-treated cell lines. Furthermore, ChIP analysis of these samples detected histone H3 lysine 4 trimethylation (H3K4me3) at the CLDN23 promoter, demonstrating that the balance between H3K27me3 and H3K4me3 may underlie the regulation of the expression of CLDN23. The present study demonstrated an epigenetic link between the activity of the EZH2 methyltransferase at the CLDN23 locus and the expression of CLDN23 in CRC tissue.

Matrix metalloproteinases and gastrointestinal cancers: Impacts of dietary antioxidants

The process of carcinogenesis is tightly regulated by antioxidant enzymes and matrix degrading enzymes, namely, matrix metalloproteinases (MMPs). Degradation of extracellular matrix (ECM) proteins like collagen, proteoglycan, laminin, elastin and fibronectin is considered to be the prerequisite for tumor invasion and metastasis. MMPs can degrade essentially all of the ECM components and, most MMPs also substantially contribute to angiogenesis, differentiation, proliferation and apoptosis. Hence, MMPs are important regulators of tumor growth both at the primary site and in distant metastases; thus the enzymes are considered as important targets for cancer therapy. The implications of MMPs in cancers are no longer mysterious; however, the mechanism of action is yet to be explained. Herein, our major interest is to clarify how MMPs are tied up with gastrointestinal cancers. Gastrointestinal cancer is a variety of cancer types, including the cancers of gastrointestinal tract and organs, i.e., esophagus, stomach, biliary system, pancreas, small intestine, large intestine, rectum and anus. The activity of MMPs is regulated by its endogenous inhibitor tissue inhibitor of metalloproteinase (TIMP) which bind MMPs with a 1:1 stoichiometry. In addition, RECK (reversion including cysteine-rich protein with kazal motifs) is a membrane bound glycoprotein that inhibits MMP-2, -9 and -14. Moreover, α2-macroglobulin mediates the uptake of several MMPs thereby inhibit their activity. Cancerous conditions increase intrinsic reactive oxygen species (ROS) through mitochondrial dysfunction leading to altered protease/anti-protease balance. ROS, an index of oxidative stress is also involved in tumorigenesis by activation of different MAP kinase pathways including MMP induction. Oxidative stress is involved in cancer by changing the activity and expression of regulatory proteins especially MMPs. Epidemiological studies have shown that high intake of fruits that rich in antioxidants is associated with a lower cancer incidence. Evidence indicates that some antioxidants inhibit the growth of malignant cells by inducing apoptosis and inhibiting the activity of MMPs. This review is discussed in six subchapters, as follows.