Claudin3 is localized outside the tight junctions in human carcinomas

Finding the junction between claudins and endometrial carcinoma

Endometrial carcinoma (EC) defines a heterogeneous group of neoplastic diseases originating from the transformation of endometrial cells that constitute the internal lining of the uterus. To date several molecular targets have been analysed to describe the natural course of the disease, claudins being among these. Claudins are the main components of tight junctions (TJs), and their main functions are ascribed to the compartmentalization of tissues and cell-cell communication by means of intracellular ions diffusion: these features are typical of epithelial cells. Their overexpression, mis-localization or loss contribute to the malignancy of EC cells. This review collected all available data regarding the expression, regulation and claudin-related signaling pathways to provide a comprehensive view on the influence of claudin in EC progression. Further, the translational potential of claudin differential expression was explored, indicating that their role in personalized medicine could also contribute to EC therapy besides their employment for diagnosis and prognosis.

Claudin-3 facilitates the progression and mediates the tumorigenic effects of TGF-β in glioblastoma multiforme

Glioblastoma multiforme (GBM) is a significantly malignant and lethal brain tumor with an average survival time of less than 12 months. Several researches had shown that Claudin-3 (CLDN3) is overexpressed in various cancers and might be important in their growth and spread. In this study, we used qRT-PCR, western blotting, immunohistochemistry, and immunofluorescence staining assays to investigate the expression levels of various proteins. To explore the proliferation abilities of GBM cells, we conducted the CCK-8 and EdU-DNA formation assays. Wound healing and transwell assays were used to investigate the capacities of invasion and migration of GBM cells. Additionally, we constructed an intracranial xenograft model of GBM to study the in vivo role of CLDN3. Our study devoted to investigate the function of CLDN3 in the pathogenesis and progression of GBM. Our study revealed that CLDN3 was upregulated in GBM and could stimulate tumor cell growth and epithelial-mesenchymal transition (EMT) in both laboratory and animal models. We also discovered that CLDN3 expression could be triggered by transforming growth factor-β (TGF-β) and reduced by specific inhibitors of the TGF-β signaling pathway, such as ITD-1. Further analysis revealed that increased CLDN3 levels enhanced TGF-β-induced growth and EMT in GBM cells, while reducing CLDN3 levels weakened these effects. Our study demonstrated the function of CLDN3 in facilitating GBM growth and metastasis and indicated its involvement in the tumorigenic effects of TGF-β. Developing specific inhibitors of CLDN3 might, therefore, represent a promising new approach for treating this devastating disease.

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 localization in epithelial ovarian cancer

Claudin-4, a protein with the structure of classic claudins most often found in cell-cell junctions, is frequently overexpressed in epithelial cancers where its localization has not been studied. In this study we aimed to find out where this membrane protein is localized in an ovarian tumor model, OVCAR3 cells, that express high levels of the protein. Immunohistochemical studies showed claudin-4 staining in a perinuclear region, at most plasma membranes and in cytoplasmic puncta. Native claudin-4 did not overlap with phosphorylated claudin-4, which was partially located in focal adhesions. Using claudin-4 BioID technology we confirmed that large amounts of claudin-4 are localized to the Golgi compartment, including in dispersed Golgi in cells where claudin-4 is partially knocked down and in dividing cells. Claudin-4 appears to be present in the vicinity of several types of cell-cell junctions, but there is no evidence that it forms tight junctions in these tumor cells. Both claudin-4, the Golgi marker GM130, and the plasma membrane receptor Notch2 were found in dispersed Golgi in dividing cells. This definition of the cellular architecture of claudin-4 should provide a framework for better understanding of the function of claudin-4 in tumor cells and its molecular interactions.

Claudin-6 increases SNAI1, NANOG and SOX2 gene expression in human gastric adenocarcinoma AGS cells

BACKGROUND

Gastric cancer is a heterogeneous disease associated to deregulated gastric epithelia tight junction barrier function and di novo expression of claudin-6; these changes are associated with epithelial-mesenchymal transition, enhanced invasiveness, metastatic progression, resistance to chemotherapy, and poor prognosis. Gastric cancer stem cells represent a rare population of cells within the tumor implicated in tumor growth and higher tumorigenic capacity. The possible relation between claudin-6 expression and the expression of some markers associated to epithelial mesenchymal transition and cancer stem cells in gastric cancer cells have never been explored.

METHODS AND RESULTS

CD44, CD24, Twist, Villin, DCLK1, claudin-6, NANOG, E-Cadherin, SOX2, and SNAI1 expression was evaluated by immunofluorescence and cytofluorometry in wild type and Claudin-6 transfected AGS cells. Cell migration assays were also performed. Differentially expressed genes and biological processes analysis was performed to determine gene preponderance. The results showed that claudin-6 overexpression enriched the CD44 + /CD24- subpopulation with an overall increase in the expression and the number of CD44 + cells. A significant increase in NANOG, SOX2 and SNAI1 expression and enhanced cell migration was observed in claudin-6 transfected cells. Transcriptome analysis revealed 271 genes involved in enhanced biological processes with only 31 with a significantly p value; thirteen of those genes are closely associated to epithelial mesenchymal transition processes and folding and unfolding processes of proteins in the endoplasmic reticulum.

CONCLUSIONS

The pro-tumorigenic effect of claudin-6 in gastric cancer could be associated to dedifferentiation of epithelial cells and an increase in di novo cancer stem cell genesis.

Context-Dependent Roles of Claudins in Tumorigenesis

The barrier and fence functions of the claudin protein family are fundamental to tissue integrity and human health. Increasing evidence has linked claudins to signal transduction and tumorigenesis. The expression of claudins is frequently dysregulated in the context of neoplastic transformation. Studies have uncovered that claudins engage in nearly all aspects of tumor biology and steps of tumor development, suggesting their promise as targets for treatment or biomarkers for diagnosis and prognosis. However, claudins can be either tumor promoters or tumor suppressors depending on the context, which emphasizes the importance of taking various factors, including organ type, environmental context and genetic confounders, into account when studying the biological functions and targeting of claudins in cancer. This review discusses the complicated roles and intrinsic and extrinsic determinants of the context-specific effects of claudins in cancer.

The Claudin-Low Subtype of High-Grade Serous Ovarian Carcinoma Exhibits Stem Cell Features

Claudin-low cancer (CL) represents a rare and biologically aggressive variant of epithelial tumor. Here, we identified a claudin-low molecular profile of ovarian high-grade serous carcinoma (HGSOC), which exhibits the main characteristics of the homonym breast cancer subtype, including low epithelial differentiation and high mesenchymal signature. Hierarchical clustering and a centroid based algorithm applied to cell line collection expression dataset labeled 6 HGSOC cell lines as CL. These have a high energy metabolism and are enriched in CD44+/CD24- mesenchymal stem-like cells expressing low levels of cell-cell adhesion molecules (claudins and E-Cadherin) and high levels of epithelial-to-mesenchymal transition (EMT) induction transcription factors (Zeb1, Snai2, Twist1 and Twist2). Accordingly, the centroid base algorithm applied to large retrospective collections of primary HGSOC samples reveals a tumor subgroup with transcriptional features consistent with the CL profile, and reaffirms EMT as the dominant biological pathway functioning in CL-HGSOC. HGSOC patients carrying CL profiles have a worse overall survival when compared to others, likely to be attributed to its undifferentiated/stem component. These observations highlight the lack of a molecular diagnostic in the management of HGSOC and suggest a potential prognostic utility of this molecular subtyping.

Low Expression of Claudin-7 as Potential Predictor of Distant Metastases in High-Grade Serous Ovarian Carcinoma Patients

High-grade serous ovarian carcinoma (HGSOC) usually spreads directly into the peritoneal cavity following a transcoelomic dissemination route, although distant hematogenous metastasis exist and have been reported. However, no tumor markers can currently predict the risk of distant metastases in HGSOC. Claudins, belonging to tight-junction proteins, are dysregulated in HGSOC and functionally related to cancer progression. Here we analyzed claudin-3, -4, and -7 expression as potential markers of distant metastases. Using quantitative RT-PCR and immunohistochemistry we assessed the expression of claudins in primary HGSOC tissues, normal ovarian, and normal fallopian tube epithelia and correlated it with clinicopathological features, including the site of metastasis and the route of dissemination. Gene set enrichment analysis was performed on microarray-generated gene expression data to investigate key pathways in patients with distant metastases. We found the overall expression level of claudin-3, -4, and -7 mRNA decreased in HGSOC compared to normal tubal epithelium, currently considered the potential site of origin of many HGSOC. The reduced expression of claudin-7 is significantly associated with the development of distant metastases (p = 0.016), mainly by hematogenous route (p = 0.025). In patients with diminished expression of claudin-7, immunohistochemical staining revealed a heterogeneous pattern of membranous staining with discontinuous expression of claudin-7 along the cell border, indicative of a dischoesive architecture. The estimated reduction in the probability of distant disease is of 39% per unit increase in the level of claudin-7 (p = 0.03). Genes involved in epithelial to mesenchymal transition, hypoxia, and angiogenesis processes resulted strongly associated to hematogenous recurrence. Our data suggest a potential role of claudin-7 in discriminating distant metastatic events in HGSOC patients. The quantification of its expression levels could be a useful tool to identify patient deserving a personalized follow-up in terms of clinical and radiological assessment.

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.