DNA-methylation-dependent alterations of claudin-4 expression in human bladder carcinoma

Claudins in genitourinary tract neoplasms: mechanisms, prognosis, and therapeutic prospects

Genitourinary (GU) cancers are among the most prevalent neoplasms in the world, with bladder cancers constituting 3% of global cancer diagnoses. However, several pathogenetic mechanisms remain controversial and unclear. Claudins, for example, have been shown to play a significant role in several cancers of the human body. Their role in GU cancers has not been extensively studied. Aberrant expression of claudins -1, -2, -3, -4, -7, and -11 has been expressed in urothelial cell carcinomas. In prostate cancers, altered levels of claudins -1, -2, -3, -4, and -5 have been reported. Furthermore, the levels of claudins -1, -2, -3, -4, -6, -7, -8, and -10 have been studied in renal cell carcinomas. Specifically, claudins -7 and -8 have proven especially useful in differentiating between chromophobe renal cell carcinomas and oncocytomas. Several of these claudins also correlate with clinicopathologic parameters and prognosis in GU cancers. Although mechanisms underpinning aberrant expression of claudins in GU cancers are unclear, epigenetic changes, tumor necrosis factor-ɑ, and the p63 protein have been implicated. Claudins also provide therapeutic value through tailored immunotherapy via molecular subtyping and providing therapeutic targets, which have shown positive outcomes in preclinical studies. In this review, we aim to summarize the literature describing aberrant expression of claudins in urothelial, prostatic, and renal cell carcinomas. Then, we describe the mechanisms underlying these changes and the therapeutic value of claudins. Understanding the scope of claudins in GU cancers paves the way for several diagnostic, prognostic, and therapeutic innovations.

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.

Effect of zearalenone on aflatoxin B1-induced intestinal and ovarian toxicity in pregnant and lactating rats

Aflatoxin B1 (AFB1) and zearalenone (ZEN) cause serious damage to mammals, but few studies have investigated the impacts of these toxins on pregnant and lactating mammals. This study investigated the effects of ZEN on AFB1-induced intestinal and ovarian toxicity in pregnant and lactating rats. Based on the results, AFB1 reduces the digestion, absorption, and antioxidant capacity in the intestine, increases intestinal mucosal permeability, destroys intestinal mechanical barriers, and increases pathogenic bacteria' relative abundances. Simultaneously, ZEN can exacerbate the intestinal injury caused by AFB1. The intestines of the offspring were also damaged, but the damage was less severe than that observed for the dams. While AFB1 activates various signalling pathways in the ovary and affects genes related to endoplasmic reticulum stress, apoptosis, and inflammation, ZEN may exacerbate or antagonize the AFB1 toxicity on gene expression in the ovary through key node genes and abnormally expressed genes. Our study found that mycotoxins can not only directly damage the ovaries and affect gene expression in the ovaries but can also impact ovarian health by disrupting intestinal microbes. Mycotoxins are an important environmental pathogenic factor for intestinal and ovarian disease in pregnancy and lactation mammals.

Intravesical Contrast-Enhanced MRI: A Potential Tool for Bladder Cancer Surveillance and Staging

This review article gives an overview of the current state of the art of bladder cancer imaging and then discusses in depth the scientific and technical merit of a novel imaging approach, tracing its evolution from murine cancer models to cancer patients. While the poor resolution of soft tissue obtained by widely available imaging options such as abdominal sonography and radiation-based CT leaves them only suitable for measuring the gross tumor volume and bladder wall thickening, dynamic contrast-enhanced magnetic resolution imaging (DCE MRI) is demonstrably superior in resolving muscle invasion. However, major barriers still exist in its adoption. Instead of injection for DCE-MRI, intravesical contrast-enhanced MRI (ICE-MRI) instills Gadolinium chelate (Gadobutrol) together with trace amounts of superparamagnetic agents for measurement of tumor volume, depth, and aggressiveness. ICE-MRI leverages leaky tight junctions to accelerate passive paracellular diffusion of Gadobutrol (604.71 Daltons) by treading the paracellular ingress pathway of fluorescein sodium and of mitomycin (<400 Daltons) into bladder tumor. The soaring cost of diagnosis and care of bladder cancer could be mitigated by reducing the use of expensive operating room resources with a potential non-surgical imaging option for cancer surveillance, thereby reducing over-diagnosis and over-treatment and increasing organ preservation.

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-3 Loss of Expression Is a Prognostic Marker in Castration-Resistant Prostate Cancer

Castration-resistant prostate cancer (CRPC) development is the foremost concern after treatment of patients with high risk with locally advanced or metastatic prostate cancer. Androgen receptor (AR) is the main driver of CRPC development, through its interaction with epigenetic modifier genes, placing epigenetics modifications in the forefront of CRPC development. Comparing the DNA methylation and expression profile of androgen-sensitive and -refractory prostate cancer cells, we describe the epigenetic silencing of claudin-3 (CLDN3) in AR positive cells resistant to androgen deprivation (LNCaP-abl). CLDN3 silencing was associated with DNA methylation, loss of histone acetylation and H3K27 methylation, and was re-expressed by the combined treatment with the epigenetic modulators Aza and SAHA. From a functional point of view, CLDN3 loss was associated with increased cellular invasion. Immunohistochemical analysis showed decreased CLDN3 expression in samples from CRPC patients. Interestingly, CLDN3 expression was significantly decreased in samples from patients with high total Gleason score (≥8) and locally advanced tumors. Finally, CLDN3 loss of expression was associated with worse disease-free survival and time to clinical progression. In conclusion, our findings strongly indicate that epigenetic silencing of CLDN3 is a common event in CRPC that could be useful as a molecular marker for the prognosis of prostate cancer patients and to discriminate aggressive from indolent prostate tumors.

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.

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.

The urothelium: a multi-faceted barrier against a harsh environment

All mucosal surfaces must deal with the challenge of exposure to the outside world. The urothelium is a highly specialized layer of stratified epithelial cells lining the inner surface of the urinary bladder, a gruelling environment involving significant stretch forces, osmotic and hydrostatic pressures, toxic substances, and microbial invasion. The urinary bladder plays an important barrier role and allows the accommodation and expulsion of large volumes of urine without permitting urine components to diffuse across. The urothelium is made up of three cell types, basal, intermediate, and umbrella cells, whose specialized functions aid in the bladder's mission. In this review, we summarize the recent insights into urothelial structure, function, development, regeneration, and in particular the role of umbrella cells in barrier formation and maintenance. We briefly review diseases which involve the bladder and discuss current human urothelial in vitro models as a complement to traditional animal studies.

Claudin-4 Immunoexpression in Urothelial Carcinomas

The involvement of claudins in urothelial carcinogenesis is controversial. In this study, we analyzed Claudin-4 immunoexpression in 50 cases of bladder urothelial carcinomas depending on the main prognostic parameters of the lesions represented by the tumor grade and tumor extension. Claudin-4 immunoexpression scores were significantly higher in high-grade urothelial carcinomas and in tumors with invasion in muscularis propria. The results obtained indicate the involvement of Claudin-4 in the progression of urothelial bladder carcinomas.

The Urothelium: Life in a Liquid Environment

The urothelium, which lines the renal pelvis, ureters, urinary bladder, and proximal urethra, forms a high-resistance but adaptable barrier that surveils its mechanochemical environment and communicates changes to underlying tissues including afferent nerve fibers and the smooth muscle. The goal of this review is to summarize new insights into urothelial biology and function that have occurred in the past decade. After familiarizing the reader with key aspects of urothelial histology, we describe new insights into urothelial development and regeneration. This is followed by an extended discussion of urothelial barrier function, including information about the roles of the glycocalyx, ion and water transport, tight junctions, and the cellular and tissue shape changes and other adaptations that accompany expansion and contraction of the lower urinary tract. We also explore evidence that the urothelium can alter the water and solute composition of urine during normal physiology and in response to overdistension. We complete the review by providing an overview of our current knowledge about the urothelial environment, discussing the sensor and transducer functions of the urothelium, exploring the role of circadian rhythms in urothelial gene expression, and describing novel research tools that are likely to further advance our understanding of urothelial biology.

Targeting claudin-overexpressing thyroid and lung cancer by modified Clostridium perfringens enterotoxin

Clostridium perfringens enterotoxin (CPE) can be used to eliminate carcinoma cells that overexpress on their cell surface CPE receptors - a subset of claudins (e.g., Cldn3 and Cldn4). However, CPE cannot target tumors expressing solely CPE-insensitive claudins (such as Cldn1 and Cldn5). To overcome this limitation, structure-guided modifications were used to generate CPE variants that can strongly bind to Cldn1, Cldn2 and/or Cldn5, while maintaining the ability to bind Cldn3 and Cldn4. This enabled (a) targeting of the most frequent endocrine malignancy, namely, Cldn1-overexpressing thyroid cancer, and (b) improved targeting of the most common cancer type worldwide, non-small-cell lung cancer (NSCLC), which is characterized by high expression of several claudins, including Cldn1 and Cldn5. Different CPE variants, including the novel mutant CPE-Mut3 (S231R/S313H), were applied on thyroid cancer (K1 cells) and NSCLC (PC-9 cells) models. In vitro, CPE-Mut3, but not CPEwt, showed Cldn1-dependent binding and cytotoxicity toward K1 cells. For PC-9 cells, CPE-Mut3 improved claudin-dependent cytotoxic targeting, when compared to CPEwt. In vivo, intratumoral injection of CPE-Mut3 in xenograft models bearing K1 or PC-9 tumors induced necrosis and reduced the growth of both tumor types. Thus, directed modification of CPE enables eradication of tumor entities that cannot be targeted by CPEwt, for instance, Cldn1-overexpressing thyroid cancer by using the novel CPE-Mut3.

Synthesis, 18F-labelling and radiopharmacological characterisation of the C-terminal 30mer of Clostridium perfringens enterotoxin as a potential claudin-targeting peptide

The cell surface receptor claudin-4 (Cld-4) is upregulated in various tumours and represents an important emerging target for both diagnosis and treatment of solid tumours of epithelial origin. The C-terminal fragment of the Clostridium perfringens enterotoxin cCPE_290-319 appears as a suitable ligand for targeting Cld-4. The synthesis of this 30mer peptide was attempted via several approaches, which has revealed sequential SPPS using three pseudoproline dipeptide building blocks to be the most efficient one. Labelling with fluorine-18 was achieved on solid phase using N-succinimidyl 4-[¹⁸F]fluorobenzoate ([¹⁸F]SFB) and 4-[¹⁸F]fluorobenzoyl chloride as ¹⁸F-acylating agents, which was the most advantageous when [¹⁸F]SFB was reacted with the resin-bound 30mer containing an N-terminal 6-aminohexanoic spacer. Binding to Cld-4 was demonstrated via surface plasmon resonance using a protein construct containing both extracellular loops of Cld-4. In addition, cell binding experiments were performed for ¹⁸F-labelled cCPE_290-319 with the Cld-4 expressing tumour cell lines HT-29 and A431 that were complemented by fluorescence microscopy studies using the corresponding fluorescein isothiocyanate-conjugated peptide. The 30mer peptide proved to be sufficiently stable in blood plasma. Studying the in vivo behaviour of ¹⁸F-labelled cCPE_290-319 in healthy mice and rats by dynamic PET imaging and radiometabolite analyses has revealed that the peptide is subject to substantial liver uptake and rapid metabolic degradation in vivo, which limits its suitability as imaging probe for tumour-associated Cld-4.

DNA demethylation of claudin-4 suppresses migration and invasion in laryngeal squamous carcinoma cells

Claudin-4 (CLDN4) is a member of the claudin transmembrane protein family, which consists of integral membrane proteins that are components of the epithelial cell tight junctions; these tight junctions regulate movement of solutes and ions through the paracellular space. CLDN4 is also a differentiation marker and is believed to indicate an epithelial phenotype. However, the role of CLDN4 in laryngeal squamous carcinoma is still unclear. Here, we showed that CLDN4 expression was down-regulated in laryngeal squamous carcinoma tissues and negatively correlated with methyl-CpG-binding protein 2. In addition, CLDN4 was hypermethylated in HEp-2 cells. DNA demethylation of CLDN4 by 5-aza-2'-deoxycytidine suppressed migration and invasion of HEp-2 cells, whereas CLDN4 silencing restored the migration and invasion of HEp-2 cells. Therefore, CLDN4 plays a key role in laryngeal squamous carcinoma progression.

HDAC-4 regulates claudin-2 expression in EGFR-ERK1/2 dependent manner to regulate colonic epithelial cell differentiation

In normal colon, claudin-2 expression is restricted to the crypt bottom containing the undifferentiated and proliferative colonocytes. Claudin-2 expression is also upregulated in colorectal cancer (CRC) and promotes carcinogenesis. However, cellular mechanism/s regulated by increased claudin-2 expression during the CRC and mechanism/s regulating this increase remain poorly understood. Epigenetic mechanisms help regulate expression of cancer-associated genes and inhibition of Histone Deacetylases (HDACs) induces cell cycle arrest and differentiation. Accordingly, based on a comprehensive in vitro and in vivo analysis we here report that Histone Deacetylases regulate claudin-2 expression in causal association with colonocyte dedifferentiation to promote CRC. Detailed differentiation analyses using colon cancer cells demonstrated inverse association between claudin-2 expression and epithelial differentiation. Genetic manipulation studies revealed the causal role of HDAC-4 in regulating claudin-2 expression during this process. Further analysis identified transcriptional regulation as the underlying mechanism, which was dependent on HDAC-4 dependent modulation of the EGFR-ERK1/2 signaling. Accordingly, colon tumors demonstrated marked upregulation of the HDAC-4/ERK1/2/Claudin-2 signaling. Taken together, we demonstrate a novel role for HDAC-4/EGFR/ERK1/2 signaling in regulating claudin-2 expression to modulate colonocyte differentiation. These findings are of clinical significance and highlight epigenetic regulation as potential mechanism to regulate claudin-2 expression during mucosal pathologies including CRC.

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.

A cCPE-based xenon biosensor for magnetic resonance imaging of claudin-expressing cells

The majority of malignant tumors originate from epithelial cells, and many of them are characterized by an overexpression of claudins (Cldns) and their mislocalization out of tight junctions. We utilized the C-terminal claudin-binding domain of Clostridium perfringens enterotoxin (cCPE), with its high affinity to specific members of the claudin family, as the targeting unit for a claudin-sensitive cancer biosensor. To overcome the poor sensitivity of conventional relaxivity-based magnetic resonance imaging (MRI) contrast agents, we utilized the superior sensitivity of xenon Hyper-CEST biosensors. We labeled cCPE for both xenon MRI and fluorescence detection. As one readout module, we employed a cryptophane (CrA) monoacid and, as the second, a fluorescein molecule. Both were conjugated separately to a biotin molecule via a polyethyleneglycol chemical spacer and later via avidin linked to GST-cCPE. Nontransfected HEK293 cells and HEK293 cells stably expressing Cldn4-FLAG were incubated with the cCPE-based biosensor. Fluorescence-based flow cytometry and xenon MRI demonstrated binding of the biosensor specifically to Cldn4-expressing cells. This study provides proof of concept for the use of cCPE as a carrier for diagnostic contrast agents, a novel approach for potential detection of Cldn3/-4-overexpressing tumors for noninvasive early cancer detection.

Expression of claudin-11 by tumor cells in cutaneous squamous cell carcinoma is dependent on the activity of p38δ

The incidence of cutaneous squamous cell carcinoma (cSCC) is rapidly increasing, and the prognosis of patients with metastatic disease is poor. There is an emerging need to identify molecular markers for predicting aggressive behaviour of cSCC. Here, we have examined the role of tight junction (TJ) components in the progression of cSCC. The expression pattern of mRNAs for TJ components was determined with RNA sequencing and oligonucleotide array-based expression analysis from cSCC cell lines (n=8) and normal human epidermal keratinocytes (NHEK, n=5). The expression of CLDN11 was specifically elevated in primary cSCC cell lines (n=5), but low or absent in metastatic cSCC cell lines (n=3) and NHEKs. Claudin-11 was detected in cell-cell contacts of primary cSCC cells in culture by indirect immunofluorescence analysis. Analysis of a large panel of tissue samples from sporadic UV-induced cSCC (n=65), cSCC in situ (n=56), actinic keratoses (n=31), seborrhoeic keratoses (n=7) and normal skin (n=16) by immunohistochemistry showed specific staining for claudin-11 in intercellular junctions of keratinizing tumor cells in well and moderately differentiated cSCCs, whereas no staining for claudin-11 was detected in poorly differentiated tumors. The expression of claudin-11 in cSCC cells was dependent on the activity of p38δ MAPK and knock-down of claudin-11 enhanced cSCC cell invasion. These findings provide evidence for the role of claudin-11 in regulation of cSCC invasion and suggest loss of claudin-11 expression in tumor cells as a biomarker for advanced stage of cSCC.

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.

DNA methylation of claudin-6 promotes breast cancer cell migration and invasion by recruiting MeCP2 and deacetylating H3Ac and H4Ac

Background

Claudin-6 (CLDN6), a member of claudin transmembrane protein family, has recently been reported to be undetectable or at low levels in human breast cancer cell lines and tissues and plays a role in suppression of migration and invasion in breast cancer cells. In addition, it is reported that CLDN6 expression is regulated by DNA methylation in various human cancers and cell lines. However, it is unclear how DNA methylation regulates CLDN6 expression. Here we show the mechanism by which DNA methylation regulates CLDN6 expression in human breast cancer cell line MCF-7.

Methods

RT-PCR, Western blot and immunofluorescent staining were utilized to investigate CLDN6 expression in breast cancer tissues and MCF-7 cells. Methylation-Specific PCR (MSP) was applied to determine DNA methylation status in CLDN6 gene promoter region. Wound-healing assay and invasion assay were utilized to test mobility of MCF-7 cells treated with 5-aza-dC (DNA methyltransferase inhibitor). MeCP2 binding, H3Ac and H4Ac in CLDN6 promoter region were analyzed by ChIP assay. Nuclease accessibility assay was performed for analysis of the chromatin conformation of CLDN6 gene. To study the role of CLDN6 in malignant progression, we used RNAi to knockdown CLDN6 expression in MCF-7 cells treated with 5-aza-dC, and examined the mobility of MCF-7 cells by wound-healing assay and invasion assay.

Results

5-aza-dC and TSA (histone deacetylase inhibitor) application induced CLDN6 expression in MCF-7 cells respectively and synergistically. 5-aza-dC treatment induced CLDN6 demethylation, inhibited MeCP2 binding to CLDN6 promoter and increased H3Ac and H4Ac in the promoter. In addition, TSA increased H4Ac, not H3Ac in the promoter. The chromatin structure of CLDN6 gene became looser than the control group after treating with 5-aza-dC in MCF-7 cells. 5-aza-dC up-regulated CLDN6 expression and suppressed migration and invasion in MCF-7 cells, whereas CLDN6 silence restored tumor malignance in MCF-7 cells.

Conclusions

DNA methylation down-regulates CLDN6 expression through MeCP2 binding to the CLDN6 promoter, deacetylating H3 and H4, and altering chromatin structure, consequently promoting migratory and invasive phenotype in MCF-7 cells.

Claudin-4 is required for vasculogenic mimicry formation in human breast cancer cells

Vasculogenic mimicry (VM) refers to the unique capability of aggressive tumor cells to mimic the pattern of embryonic vasculogenic networks. Claudins are aberrantly expressed in aggressive breast cancer. However, the relationship between claudins and VM formation is not clear. We examined VM in two human breast cancer cell lines with different aggressive capabilities (MDA-MB-231 and MCF-7 cells) and one human umbilical vein endothelial cell line (HUVEC). Both HUVEC and MDA-MB-231 cells formed vascular channels in Matrigel cultures, while MCF-7 cells did not. Western blot analysis revealed a possible correlation between claudin-4 and -6 expression in breast cancer cell lines and tumor aggressiveness, with protein levels correlating with the ability to form vascular channels. Treatment of MDA-MB-231 and HUVEC cells with claudin-4 monoclonal antibodies completely inhibited the ability of cells to form vascular channels. Moreover, knockdown of claudin-4 by short hairpin RNA completely inhibited tubule formation in MDA-MB-231 cells. Overexpression of claudin-4 in MCF-7 cells induced formation of vascular channels. Immunocytochemistry revealed that membranous claudin-4 protein was significantly associated with vascular channel formation. Collectively, these results indicate that claudin-4 may play a critical role in VM in human breast cancer cells, opening new opportunities to improve aggressive breast cancer therapy.

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.

The impact of CLAUDIN-1 on follicular thyroid carcinoma aggressiveness

CLAUDIN-1 belongs to the family of transmembrane tight junction proteins tightening the paracellular cleft of epithelial cells. In human malignancies, CLAUDIN-1 is often dysregulated and located in subcellular compartments, particularly in the nucleus where it may influence cellular behaviour. Here, we studied CLAUDIN-1 in relation to the biological characteristics of follicular thyroid carcinoma (FTC). CLAUDIN-1 immuno-staining showed loss of membrane expression and increased nuclear CLAUDIN-1 localization in FTC metastases. CLAUDIN-1 function was further investigated in two different follicular thyroid carcinoma cell lines: FTC-133 isolated from a regional lymph node metastasis and FTC-238 derived from a lung metastasis. In both cell lines CLAUDIN-1 expression was demonstrated in the cell nuclei with a significantly higher protein expression in FTC-238 compared to FTC-133 cells. Interestingly, in vitro scratch assay revealed enriched nuclear CLAUDIN-1 expression near the scratch. Furthermore, the increase of the pathogenic character of FTC-133 cells by RASV12 transfection was associated with elevated CLAUDIN-1 expression and enhanced cell migration, invasion and proliferation. Likewise over-expression of nuclear CLAUDIN-1 in FTC-133 cells resulted in increased cell migration and invasion. Conversely, CLAUDIN-1 downregulation in FTC-238 cells by siRNA resulted in decreased cell migration and invasion and was accompanied by reduced phosphoPKC expression. Moreover, activation and inhibition of PKC resulted in CLAUDIN-1 up- and downregulation in FTC cells respectively. These data suggest an impact of CLAUDIN-1 on follicular thyroid carcinoma aggressiveness, which could potentially be influenced by PKC activity.

CLDN3 inhibits cancer aggressiveness via Wnt-EMT signaling and is a potential prognostic biomarker for hepatocellular carcinoma

Hepatocellular carcinoma (HCC) is one of the most common fatal malignancies but the molecular genetic basis of this disease remains unclear. By using genome-wide methylation profiling analysis, we identified CLDN3 as an epigenetically regulated gene in cancer. Here, we investigated its function and clinical relevance in human HCC. CLDN3 downregulation occurred in 87/114 (76.3%) of primary HCCs, where it was correlated significantly with shorter survival of HCC patients (P=0.021). Moreover, multivariate cyclooxygenase regression analysis showed that CLDN3 was an independent prognostic factor for overall survival (P=0.014). Absent expression of CLDN3 was also detected in 67% of HCC cell lines, which was significantly associated with its promoter hypermethylation. Ectopic expression of CLDN3 in HCC cells could inhibit cell motility, cell invasiveness, and tumor formation in nude mice. Mechanistic investigations suggested through downregulation of GSK3B, CTNNB1, SNAI2, and CDH2, CLDN3 could significantly suppress metastasis by inactivating the Wnt/β-catenin-epithelial mesenchymal transition (EMT) axis in HCC cells. Collectively, our findings demonstrated that CLDN3 is an epigenetically silenced metastasis suppressor gene in HCC. A better understanding of the molecular mechanism of CLDN3 in inhibiting liver cancer cell metastasis may lead to a more effective management of HCC patients with the inactivation of CLDN3.

CLDN3 inhibits cancer aggressiveness via Wnt-EMT signaling and is a potential prognostic biomarker for hepatocellular carcinoma

Hepatocellular carcinoma (HCC) is one of the most common fatal malignancies but the molecular genetic basis of this disease remains unclear. By using genome-wide methylation profiling analysis, we identified CLDN3 as an epigenetically regulated gene in cancer. Here, we investigated its function and clinical relevance in human HCC. CLDN3 downregulation occurred in 87/114 (76.3%) of primary HCCs, where it was correlated significantly with shorter survival of HCC patients (P=0.021). Moreover, multivariate cyclooxygenase regression analysis showed that CLDN3 was an independent prognostic factor for overall survival (P=0.014). Absent expression of CLDN3 was also detected in 67% of HCC cell lines, which was significantly associated with its promoter hypermethylation. Ectopic expression of CLDN3 in HCC cells could inhibit cell motility, cell invasiveness, and tumor formation in nude mice. Mechanistic investigations suggested through downregulation of GSK3B, CTNNB1, SNAI2, and CDH2, CLDN3 could significantly suppress metastasis by inactivating the Wnt/β-catenin-epithelial mesenchymal transition (EMT) axis in HCC cells. Collectively, our findings demonstrated that CLDN3 is an epigenetically silenced metastasis suppressor gene in HCC. A better understanding of the molecular mechanism of CLDN3 in inhibiting liver cancer cell metastasis may lead to a more effective management of HCC patients with the inactivation of CLDN3.

Claudin11 Promoter Hypermethylation Is Frequent in Malignant Melanoma of the Skin, but Uncommon in Nevus Cell Nevi

Epigenetic inactivation of tumor-related genes is an important characteristic in the pathology of human cancers, including melanomagenesis. We analyzed the epigenetic inactivation of Claudin 11 (CLDN11) in malignant melanoma (MM) of the skin, including six melanoma cell lines, 39 primary melanoma, 41 metastases of MM and 52 nevus cell nevi (NCN). CLDN11 promoter hypermethylation was found in 19 out of 39 (49%) of the primary MM and in 21 out of 41 (51%) of the MM metastases, but only in eight out of 52 (15%) of NCN (p = 0.001 and p = 0.0003, respectively). Moreover, a significant increase in the methylation level of CLDN11 from primary melanomas to MM metastases was revealed (p = 0.003). Methylation of CLDN11 was significantly more frequent in skin metastases (79%) compared to brain metastases (31%; p = 0.007). CLDN11 methylation was also found in five out of six MM cell lines (83%) and its promoter hypermethylation correlated with a reduced expression. Treatment of MM cell lines with a DNA methylation inhibitor reactivated CLDN11 transcription by its promoter demethylation. In summary, CLDN11 proved to be an epigenetically inactivated tumor related gene in melanomagenesis, and analysis of CLDN11 methylation level represents a potential tool for assisting in the discrimination between malignant melanoma and nevus cell nevi.

Claudin-4 controls the proliferation, apoptosis, migration and in vivo growth of MCF-7 breast cancer cells

Previous studies have shown that the expression of claudin-4 is upregulated in breast cancer. The aim of the present study was to investigate the role and the regulation of claudin-4 in MCF-7 breast cancer cells. For the in vitro experiments, MCF-7 cells were treated with recombinant vectors carrying cDNA for claudin-4 overexpression or short hairpin RNAs (shRNAs) for claudin-4 silencing. Cell proliferation was determined by an MTT assay and cell migration ability was measured by a wound-healing assay. The cell cycle profile and apoptotic rate were analyzed using flow cytometry. The effect of methylation status on claudin-4 expression was determined by PCR and western blotting. For the in vivo tumorigenesis analysis, MCF-7 cells with or without claudin-4 silencing were transplanted into nude mice. In vivo cell growth was evaluated 14 days after transplantation. We found that claudin-4 overexpression increased MCF-7 cell proliferation and migration, and reduced the rate of cell apoptosis. Silencing of claudin-4 induced the opposite effects in MCF-7 cells. In addition, claudin-4 expression was upregulated by demethylation. Moreover, the size of tumor formation was reduced in nude mice transplanted with claudin-4 silenced MCF-7 cells. These observations suggested that claudin-4, which was regulated by methylation status, plays an important role in breast cancer growth and malignancy via the control of cell proliferation, migration and apoptosis.

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.

Claudin-7 expression induces mesenchymal to epithelial transformation (MET) to inhibit colon tumorigenesis

In normal colon, claudin-7 is one of the highly expressed claudin proteins and its knockdown in mice results in altered epithelial cell homeostasis and neonatal death. Notably, dysregulation of the epithelial homeostasis potentiates oncogenic transformation and growth. However, the role of claudin-7 in the regulation of colon tumorigenesis remains poorly understood. Using a large colorectal cancer (CRC) patient database and mouse models of colon cancer, we found claudin-7 expression to be significantly downregulated in cancer samples. Most notably, forced claudin-7 expression in poorly differentiated and highly metastatic SW620 colon cancer cells induced epithelial characteristics and inhibited their growth in soft agar and tumor growth in vivo. By contrast, knockdown of claudin-7 in HT-29 or DLD-1 cells induced epithelial-to-mesenchymal transition (EMT), colony formation, xenograft-tumor growth in athymic mice and invasion. Importantly, a claudin-7 signature gene profile generated by overlapping the DEGs (differentially expressed genes in a high-throughput transcriptome analysis using claudin-7-manipulated cells) with human claudin-7 signature genes identified high-risk CRC patients. Furthermore, Rab25, a colon cancer suppressor and regulator of the polarized cell trafficking constituted one of the highly upregulated DEGs in claudin-7 overexpressing cells. Notably, silencing of Rab25 expression counteracted the effects of claudin-7 expression and not only increased proliferation and cell invasion but also increased the expression of p-Src and mitogen-activated protein kinase-extracellular signal-regulated kinase 1/2 that were suppressed upon claudin-7 overexpression. Of interest, CRC cell lines, which exhibited decreased claudin-7 expression, also exhibited promoter DNA hypermethylation, a modification associated with transcriptional silencing. Taken together, our data demonstrate a previously undescribed role of claudin-7 as a colon cancer suppressor and suggest that loss of claudin-7 potentiates EMT to promote colon cancer, in a manner dependent on Rab25.

Enhancing mammary differentiation by overcoming lineage-specific epigenetic modification and signature gene expression of fibroblast-derived iPSCs

Recent studies have shown that induced pluripotent stem cells (iPSCs) retain a memory of their origin and exhibit biased differentiation potential. This finding reveals a severe limitation in the application of iPSCs to cell-based therapy because it means that certain cell types are not available for reprogramming for patients. Here we show that the iPSC differentiation process is accompanied by profound gene expression and epigenetic modifications that reflect cells' origins. Under typical conditions for mammary differentiation, iPSCs reprogrammed from tail-tip fibroblasts (TF-iPSCs) activated a fibroblast-specific signature that was not compatible with mammary differentiation. Strikingly, under optimized conditions, including coculture with iPSCs derived from the mammary epithelium or in the presence of pregnancy hormones, the fibroblast-specific signature of TF-iPSCs obtained during differentiation was erased and cells displayed a mammary-specific signature with a markedly enhanced ability for mammary differentiation. These findings provide new insights into the precise control of differentiation conditions that may have applications in personalized cell-based therapy.

Renal tubular Sirt1 attenuates diabetic albuminuria by epigenetically suppressing Claudin-1 overexpression in podocytes

Sirtuin 1 (Sirt1), a NAD(+)-regulated deacetylase with numerous known positive effects on cellular and whole-body metabolism, is expressed in the renal cortex and medulla. It is known to have protective effects against age-related disease, including diabetes. Here we investigated the protective role of Sirt1 in diabetic renal damage. We found that Sirt1 in proximal tubules (PTs) was downregulated before albuminuria occurred in streptozotocin-induced or obese (db/db) diabetic mice. PT-specific SIRT1 transgenic and Sirt1 knockout mice showed prevention and aggravation of the glomerular changes that occur in diabetes, respectively, and nondiabetic knockout mice exhibited albuminuria, suggesting that Sirt1 in PTs affects glomerular function. Downregulation of Sirt1 and upregulation of the tight junction protein Claudin-1 by SIRT1-mediated epigenetic regulation in podocytes contributed to albuminuria. We did not observe these phenomena in 5/6 nephrectomized mice. We also demonstrated retrograde interplay from PTs to glomeruli using nicotinamide mononucleotide (NMN) from conditioned medium, measurement of the autofluorescence of photoactivatable NMN and injection of fluorescence-labeled NMN. In human subjects with diabetes, the levels of SIRT1 and Claudin-1 were correlated with proteinuria levels. These results suggest that Sirt1 in PTs protects against albuminuria in diabetes by maintaining NMN concentrations around glomeruli, thus influencing podocyte function.

Emerging roles of claudins in human cancer

Claudins are major integral membrane proteins of tight junctions. Altered expression of several claudin proteins, in particular claudin-1, -3, -4 and -7, has been linked to the development of various cancers. Although their dysregulation in cancer suggests that claudins play a role in tumorigenesis, the exact underlying mechanism remains unclear. The involvement of claudins in tumor progression was suggested by their important role in the migration, invasion and metastasis of cancer cells in a tissue-dependent manner. Recent studies have shown that they play a role in epithelial to mesenchymal transition (EMT), the formation of cancer stem cells or tumor-initiating cells (CSCs/TICs), and chemoresistance, suggesting that claudins are promising targets for the treatment of chemoresistant and recurrent tumors. A recently identified claudin-low breast cancer subtype that is characterized by the enrichment of EMT and stem cell-like features is significantly associated with disease recurrence, underscoring the importance of claudins as predictors of tumor recurrence. The critical role of epigenetic mechanisms in the regulation of claudin expression indicates the possible application of epigenetic therapy to target claudins. A better understanding of the emerging role of claudins in CSC/TICs and chemoresistance may help to develop therapies against recurrent cancers.

Claudins and gastric carcinogenesis

Gastric carcinoma arises from aberrant growth of normal gastric mucosa. There is increasing evidence that claudins (CLDNs) may play a critical role in the significant steps of gastric tumorigenesis, from metaplasia to metastasis. The CLDN family which consists of at least 27 member proteins is known to mediate selective permeability in cellular tight junctions. It is now established that CLDNs are differentially altered in gastric cancer and CLDN proteins are believed to play different roles in the growth and progression of gastric cancer.

Methylation of the claudin 1 promoter is associated with loss of expression in estrogen receptor positive breast cancer

Downregulation of the tight junction protein claudin 1 is a frequent event in breast cancer and is associated with recurrence, metastasis, and reduced survival, suggesting a tumor suppressor role for this protein. Tumor suppressor genes are often epigenetically silenced in cancer. Downregulation of claudin 1 via DNA promoter methylation may thus be an important determinant in breast cancer development and progression. To investigate if silencing of claudin 1 has an epigenetic etiology in breast cancer we compared gene expression and methylation data from 217 breast cancer samples and 40 matched normal samples available through the Cancer Genome Atlas (TCGA). Moreover, we analyzed claudin 1 expression and methylation in 26 breast cancer cell lines. We found that methylation of the claudin 1 promoter CpG island is relatively frequent in estrogen receptor positive (ER+) breast cancer and is associated with low claudin 1 expression. In contrast, the claudin 1 promoter was not methylated in most of the ER-breast cancers samples and some of these tumors overexpress claudin 1. In addition, we observed that the demethylating agents, azacitidine and decitabine can upregulate claudin 1 expression in breast cancer cell lines that have a methylated claudin 1 promoter. Taken together, our results indicate that DNA promoter methylation is causally associated with downregulation of claudin 1 in a subgroup of breast cancer that includes mostly ER+ tumors, and suggest that epigenetic therapy to restore claudin 1 expression might represent a viable therapeutic strategy in this subtype of breast cancer.

Down-regulated claudin-7 immunoexpression in urothelial carcinoma of the urinary bladder

Objectives

To analyse the gene-expression level of claudin-7 in urothelial carcinoma (UC) of the urinary bladder, and its relationship with clinicopathological variables.

Materials and methods

This study included 68 specimens of UC of the bladder, comprising 35 with non-muscle-invasive (NMI), stage Ta–T1, and 33 with muscle-invasive (MI) tumours, T2–T4, and 26 of normal urothelium (NU). Total RNA was extracted and 1 μg was reverse transcribed using a cDNA kit. RT-PCR was conducted using SYBR Green I dye to examine the expression levels of the target gene (claudin-7) and the housekeeping gene glyceraldehyde-3-phosphate dehydrogenase. Using confocal-laser scanning light microscopy, immunohistochemistry (IHC) was used to validate the RT-PCR data. The correlation between claudin-7 and the clinicopathological variables was assessed.

Results

Claudin-7 was down-regulated in UC samples compared to NU samples (P < 0.001). NMI (Ta–T1) tumours had significantly higher claudin-7 expression than MI (⩾pT2) tumours (P = 0.012). There was no significant difference between patients with G1-2 tumours and those with G3 tumours (P = 0.19). There was no significant difference between patients with recurrent NMI UC and those with no recurrence (P = 0.61). IHC showed a lower expression of claudin-7 in the UC samples than NU samples, and in MI UC than in NMI UC.

Conclusions

These results indicate that a reduced expression of claudin-7 correlates with the invasiveness and progression of UC of the urinary bladder. Further studies are needed to validate claudin-7 as a marker for UC.

Claudins and alveolar epithelial barrier function in the lung

The alveolar epithelium of the lung constitutes a unique interface with the outside environment. This thin barrier must maintain a surface for gas transfer while being continuously exposed to potentially hazardous environmental stimuli. Small differences in alveolar epithelial barrier properties could therefore have a large impact on disease susceptibility or outcome. Moreover, recent work has focused attention on the alveolar epithelium as central to several lung diseases, including acute lung injury and idiopathic pulmonary fibrosis. Although relatively little is known about the function and regulation of claudin tight junction proteins in the lung, new evidence suggests that environmental stimuli can influence claudin expression and alveolar barrier function in human disease. This review considers recent advances in the understanding of the role of claudins in the breakdown of the alveolar epithelial barrier in disease and in epithelial repair.

Regulation of tight junctions in human normal pancreatic duct epithelial cells and cancer cells

To investigate the regulation of tight junction molecules in normal human pancreatic duct epithelial (HPDE) cells and pancreatic cancer cells, we introduced the human telomerase reverse transcriptase (hTERT) gene into HPDE cells in primary culture and compared them to pancreatic cancer cell lines. The hTERT-transfected HPDE cells were positive for PDE markers and expressed claudin-1, claudin-4, claudin-7, and claudin-18, occludin, tricellulin, marvelD3, JAM-A, zonula occludens (ZO)-1, and ZO-2. The tight junction molecules, including claudin-4 and claudin-18 of normal HPDE cells, were in part regulated via a protein kinase C signal pathway by transcriptional control. In addition, claudin-18 in normal HPDE cells and pancreatic cancer cells was markedly induced by a PKC activator, and claudin-18 in pancreatic cancer cells was also modified by DNA methylation. In the marvel family of normal HPDE cells and pancreatic cancer cells, tricellulin was upregulated via a c-Jun N-terminal kinase pathway, and marvelD3 was downregulated during Snail-induced epithelial-mesenchymal transition.

Bufalin prevents the migration and invasion of T24 bladder carcinoma cells through the inactivation of matrix metalloproteinases and modulation of tight junctions

Bufalin, a cardiotonic steroid extracted from toad venom, has generally been known to possess a range of biological activities; however, only a few studies have reported the anti-metastatic activity of bufalin. In the present study, we investigated the inhibitory effects of bufalin on cell migration and invasion, two critical cellular processes that are often deregulated during metastasis, using the human bladder cancer cell line, T24. Within the concentration range that was not cytotoxic, bufalin markedly inhibited the cell motility and invasiveness of T24 cells. The inhibitory effects of bufalin on cell invasiveness were associated with the tightening of tight junctions (TJs), which was demonstrated by an increase in transepithelial electrical resistance (TER). Bufalin treatment also repressed the levels of claudin proteins (claudin-2, -3 and -4) and the major components of TJs that play key roles in the control and selectivity of paracellular transport. Furthermore, the activities of matrix metalloproteinase (MMP)‑2 and -9 in T24 cells were dose‑dependently inhibited by treatment with bufalin and this also correlated with a decrease in their mRNA and protein expression levels; however, the mRNA and protein levels of the tissue inhibitor of metalloproteinase (TIMP)‑1 and -2 were increased. In addition, these effects were related to the increased phosphorylation of the extracellular signal-regulated protein kinase (ERK) pathway. The inhibition of ERK (PD98059) significantly prevented the bufalin‑induced suppression of T24 cell migration. These findings suggest that bufalin inhibits the migration and invasion of T24 cells by modulating the activity of TJs and MMPs, possibly in association with the activation of ERK.

Immunohistochemical features of claudin-low intrinsic subtype in metaplastic breast carcinomas

PURPOSE

The claudin-low molecular subtype of breast cancer includes triple negative invasive carcinomas, with a high frequency of metaplastic and medullary features. The aim of this study was to evaluate the immunohistochemistry expression of claudins in a series of metaplastic breast carcinomas. We also assessed other claudin-low features, such as the cancer stem cell-like and epithelial-to-mesenchymal transition phenotypes.

RESULTS

The majority of the cases showed weak or negative staining for membrane claudins expression. We found 76.9% (10/13) low expressing cases for claudin-1, 84.6% (11/13) for claudin-3 and claudin-4, and 92.3% (12/13) for claudin-7. Regarding the cancer stem cell marker ALDH1, 30.8% (4/13) showed positive staining. We also showed that the majority of the cases presented a CD44(+)CD24(-/low) phenotype, positivity for vimentin and lack of E-cadherin expression. Interestingly, these claudin-low molecular features were specific of the mesenchymal component of metaplastic breast carcinomas, since its frequency was very low in other breast cancer molecular subtypes, as luminal, HER2-overexpressing and non-metaplastic triple negative tumors.

CONCLUSIONS

The negative/low expression of claudins and E-cadherin, high levels of vimentin, and the breast cancer stem cell phenotype suggests that metaplastic breast carcinomas have similar features to the ones included in the claudin-low molecular subtype, specially their mesenchymal components.

Claudin-4 as therapeutic target in cancer

BACKGROUND

Intercellular junctional complexes such as adherens junctions and tight junctions are critical regulators of cellular polarity, paracellular permeability and metabolic and structural integrity of cellular networks. Abundant expression analysis data have yielded insights into the complex pattern of differentially expressed cell-adhesion proteins in epithelial cancers and provide a useful platform for functional, preclinical and clinical evaluation of novel targets.

SCOPE OF REVIEW

This review will focus on the role of claudin-4, an integral constituent of tight junctions, in the pathophysiology of epithelial malignancies with particular focus pancreatic cancer, and its potential applicability for prognostic, diagnostic and therapeutic approaches.

MAJOR CONCLUSIONS

Claudin-4 expression is widely dysregulated in epithelial malignancies and in a number of premalignant precursor lesions. Although the functional implications are only starting to unravel, claudin-4 seems to play an important role in tumour cell invasion and metastasis, and its dual role as receptor of Clostridium perfringens enterotoxin (CPE) opens exciting avenues for molecular targeted approaches.

GENERAL SIGNIFICANCE

Claudin-4 constitutes a promising molecular marker for prognosis, diagnosis and therapy of epithelial malignancies.

Claudins and ki-67: potential markers to differentiate low- and high-grade transitional cell carcinomas of the urinary bladder

Updated classification of urothelial cell cancer differentiates low-grade and high-grade cancers, which determines potential clinical outcome. Substantial interobserver variability necessitates new biomarkers to ensure classification. Claudins' specific expression pattern characterizes normal tissues, different tumor types, and defined grades of tumor differentiation. The aim of this study was to examine the expression pattern of claudins and proliferation marker Ki-67 in low-grade and high-grade urothelial cell cancers compared with independent control samples of non-tumorous urothelium, as well as to reveal the predictive usefulness of claudins. The expression of claudins-1, -2, -3, -4, -5, -7, and -10 and Ki-67 was studied with quantitative immunohistochemistry and real-time RT-PCR with relative quantification in 103 samples: 86 urothelial cell cancers (27 low grade, 59 high grade) and 17 non-tumorous urothelia. Results were analyzed regarding overall survival and recurrence-free period as well. High-grade tumors overall showed significantly higher claudin-4 and Ki-67 and significantly lower claudin-7 expression when compared with low-grade ones. High-grade tumors revealed significantly shorter overall survival in Kaplan-Meier analysis. Claudin-4, claudin-7, and Ki-67 might be used as potential markers to differentiate low-grade and high-grade urothelial cell cancers, thereby possibly enhancing accuracy of pathological diagnosis and adding further information to clinical outcome.

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

The tight junction (TJ) protein claudin-4 is aberrantly upregulated in gastric cancer, but its clinical significance and the molecular mechanisms underlying claudin-4 overexpression in gastric cancer remain unclear. Here, we investigated its roles and epigenetic mechanisms regulating CLDN4 expression in gastric cancer. We show that increased membranous expression of claudin-4 in gastric carcinoma is associated with better patient prognosis, whereas cytoplasmic claudin-4 expression did not show a significant association with prognosis. Consistent with the correlation of increased membranous claudin-4 with favorable clinicopathological factors, claudin-4 overexpression inhibited the migration and invasion of gastric cancer cells; in contrast, it did not affect cell growth. Claudin-4 expression also increased the barrier function of TJs. Claudin-4 upregulation was strongly correlated with DNA hypomethylation in both gastric tissues and gastric cancer cells. Moreover, CLDN4 expression was repressed in normal gastric tissues in association with bivalent histone modifications, and loss of repressive histone methylations and gain of active histone modifications were associated with CLDN4 overexpression in gastric cancer cells. Interestingly, CLDN4 repression could be markedly derepressed by combined treatments that simultaneously target both histone modifications and DNA demethylation in CLDN4-hypermethylated cells, whereas concomitant changes in histone methylations and acetylations are required for CLDN4 induction in CLDN4-repressed cells with low DNA methylation. Taken together, this study reveals that membranous claudin-4 expression is associated with gastric cancer progression and that it is an independent positive prognosis marker in gastric carcinoma. Furthermore, our findings suggest that epigenetic derepression may be a possible mechanism underlying CLDN4 overexpression in gastric cancer and that claudin-4 may have potential as a promising target for the treatment of gastric cancer.

Transcriptional regulation of claudin-18 via specific protein kinase C signaling pathways and modification of DNA methylation in human pancreatic cancer cells

Since claudin-18 (Cldn18) is overexpressed in precursor lesion PanIN and pancreatic duct carcinoma, it serves as a diagnostic marker and a target of immunotherapy. The stomach isoform of Cldn18, Cldn18a2 is regulated via a PKC/MAPK/AP-1-dependent pathway in PKC activator 12-O-tetradecanoylphorbol 13-acetate (TPA)-stimulated gastric cancer cells. However, little is known about how Cldn18 is regulated, not only in pancreatic duct carcinoma but also in normal human pancreatic duct epithelial cells (HPDE cells). In the present study, four pancreatic cancer cell lines, HPAF-II, HPAC, PANC-1 and BXPC3, and hTERT-HPDE cells in which the hTERT gene was introduced into HPDE cells in primary culture, were treated with TPA. In all human pancreatic cancer cell lines and hTERT-HPDE cells, Cldn18 mRNA indicated as Cldn18a2 was markedly induced by TPA and in well- or moderately differentiated human pancreatic cancer cells HPAF-II and HPAC and hTERT-HPDE cells, the protein was also strongly increased. The upregulation of Cldn18 by TPA in human pancreatic cancer cell lines was prevented by inhibitors of PKCδ, PKCε, and PKCα, whereas the upregulation of Cldn18 by TPA in hTERT-HPDE cells was prevented by inhibitors of PKCδ, PKCθ, and PKCα. Furthermore, a CpG island was identified within the coding sequence of the Cldn18 gene and treatment with the demethylating agent 5-azadeoxycytidine enhanced upregulation of Cldn18 by TPA in HPAF-II and HPAC, but not hTERT-HPDE cells. Our findings suggest that in human pancreatic cancer cells, Cldn18 is primarily regulated at the transcriptional level via specific PKC signaling pathways and modified by DNA methylation.

Expression of claudins and their prognostic significance in noninvasive urothelial neoplasms of the human urinary bladder

The members of the claudin family are major integral transmembrane protein constituents of tight junctions. Normal and neoplastic tissues can be characterized by unique qualitative and quantitative distribution of claudin subtypes, which may be related to clinicopathological features. Differential diagnosis and prognosis of nonmuscle invasive tumor entities of urinary bladder epithelium are often challenging. The aim was to investigate the expression profile of claudins in inverted urothelial papillomas (IUPs), urothelial papillomas (UPs), papillary urothelial neoplasms of low malignant potential (PUNLMPs), and intraepithelial (Ta), low-grade urothelial cell carcinomas (LG-UCCs) in order to reveal potential prognostic and differential diagnostic values of certain claudins. Claudin-1, -2, -4, and -7 protein expressions detected by immunohistochemistry and clinical data were analyzed in 15 IUPs, 20 UPs, 20 PUNLMPs, and 20 LG-UCCs. UPs, PUNLMPs, and LG-UCCs showed significantly decreased claudin-1 expression in comparison to IUPs. LG-UCCs expressing claudin-4 over the median were associated with significantly shorter recurrence-free survival. PUNLMPs expressing claudin-1 over the median revealed significantly longer recurrence-free survival. High claudin-1 protein expression might help to differentiate IUP from UPs, PUNLMPs, and LG-UCCs. High claudin-4 expression may determine an unfavorable clinical course of LG-UCCs, while high claudin-1 expression in PUNLMP was associated with markedly better clinical outcome.

Low expression of claudin-4 is associated with poor prognosis in esophageal squamous cell carcinoma

BACKGROUND

Claudins are 22-27 kDa sized adhesion molecules that constitute tight junctions. Their expression levels are often tissue-specific, and their altered degrees of expression have been reported in a variety of cancers. In addition, the prognostic significance of claudin expression has been implicated in various human cancers. However, the prognostic significance of claudin-4 expression in esophageal squamous cell carcinoma (ESCC) remains to be clarified.

MATERIALS AND METHODS

We investigated the prognostic significance of claudin-4 expression in 164 cases of ESCC using immunohistochemisty. We also evaluated claudin-4 mRNA expression levels using quantitative real-time reverse transcription polymerase chain reaction (RT-PCR) and analyzed its specific promoter methylation status using quantitative methylation-specific PCR.

RESULTS

According to clinicopathological parameters, low claudin-4 expression was found to be significantly associated with histological differentiation (P = 0.003), invasion depth (P = 0.002), and lymph node metastasis (P = 0.024). Low claudin-4 expression showed unfavorable influences on disease-free survival (P = 0.0115) and overall survival (OS) (P = 0.0009). In multivariate analysis, low claudin-4 expression was an independent predictor of poor OS (P = 0.007). Claudin-4 mRNA levels assessed using real-time RT-PCR were consistent with the protein levels determined using immunohistochemistry. Furthermore, this study demonstrates that loss of claudin-4 is associated with promoter hypermethylation.

CONCLUSIONS

Our study indicates that claudin-4 expression is deregulated in ESCC, implying its potential use as a prognostic biomarker in ESCC.