Claudin-3 and claudin-4 expression in ovarian epithelial cells enhances invasion and is associated with increased matrix metalloproteinase-2 activity

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

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

Claudin expression is maintained in mucoepidermoid carcinoma of the salivary gland

OBJECTIVE

The aim of the present study was to investigate the expression of claudin-1, -3, -4, -5 and -7 proteins in mucoepidermoid carcinoma of oral cavity and analyze whether EGF may interfere in the expression of the genes that encode claudins using in vitro models.

MATERIAL AND METHODS

Using immunohistochemistry, the expression of claudins was searched in 36 histologically graded cases of mucoepidermoid carcinoma. The association of expression of claudins with clinical-pathological parameters was evaluated. An in vitro step investigated the influence of EGF on gene expression of claudins by real time RT-PCR technique.

RESULTS

Claudin-1, -3, -4, -5, and -7 were highly expressed in most mucoepidermoid carcinomas. These expressions were compared with clinicopathological parameters. High expression of claudin-1 was associated with patients over 40 years-old (p = 0.05) and Caucasians (p = 0.024). In vitro experiments demonstrated a tendency for Claudin gene expression increase after EGF stimulus.

CONCLUSIONS

The expression of claudins is maintained in mucoepidermoid carcinoma cells and EGF could be related with this expression. Our results point out to a fundamental biological importance to CLDNs in normal and neoplastic tissue. The expression patterns of CLDNs does not yet allow a clinical application, but the biological knowledge will ground evidence to new studies towards possible target-therapies.

Intracellular Fate and Impact on Gene Expression of Doxorubicin/Cyclodextrin-Graphene Nanomaterials at Sub-Toxic Concentration

The graphene road in nanomedicine still seems very long and winding because the current knowledge about graphene/cell interactions and the safety issues are not yet sufficiently clarified. Specifically, the impact of graphene exposure on gene expression is a largely unexplored concern. Herein, we investigated the intracellular fate of graphene (G) decorated with cyclodextrins (CD) and loaded with doxorubicin (DOX) and the modulation of genes involved in cancer-associated canonical pathways. Intracellular fate of GCD@DOX, tracked by FLIM, Raman mapping and fluorescence microscopy, evidenced the efficient cellular uptake of GCD@DOX and the presence of DOX in the nucleus, without graphene carrier. The NanoString nCounter™ platform provided evidence for 34 (out of 700) differentially expressed cancer-related genes in HEp-2 cells treated with GCD@DOX (25 µg/mL) compared with untreated cells. Cells treated with GCD alone (25 µg/mL) showed modification for 16 genes. Overall, 14 common genes were differentially expressed in both GCD and GCD@DOX treated cells and 4 of these genes with an opposite trend. The modification of cancer related genes also at sub-cytotoxic G concentration should be taken in consideration for the rational design of safe and effective G-based drug/gene delivery systems. The reliable advantages provided by NanoString^® technology, such as sensibility and the direct RNA measurements, could be the cornerstone in this field.

Proteomic analysis of transitional cell carcinoma-like variant of tubo-ovarian high-grade serous carcinoma

The current World Health Organization classification does not distinguish transitional cell carcinoma of the ovary (TCC) from conventional tubo-ovarian high-grade serous carcinoma (HGSC), despite evidence suggesting improved prognosis for patients with TCC; instead, it is considered a morphologic variant of HGSC. The immunohistochemical (IHC) markers applied to date do not distinguish between TCC and HGSC. Therefore, we sought to compare the proteomic profiles of TCC and conventional HGSC to identify proteins enriched in TCC. Prognostic biomarkers in HGSC have proven to be elusive, and our aim was to identify biomarkers of TCC as a way of reliably and reproducibly identifying patients with a favorable prognosis and better response to chemotherapy compared with those with conventional HGSC. Quantitative global proteome analysis was performed on archival material of 12 cases of TCC and 16 cases of HGSC using SP3 (single-pot, solid phase-enhanced, sample preparation)-Clinical Tissue Proteomics, a recently described protocol for full-proteome analysis from formalin-fixed paraffin-embedded tissues. We identified 430 proteins that were significantly enriched in TCC over HGSC. Unsupervised co-clustering perfectly distinguished TCC from HGSC based on protein expression. Pathway analysis showed that proteins associated with cell death, necrosis, and apoptosis were highly expressed in TCCs, whereas proteins associated with DNA homologous recombination, cell mitosis, proliferation and survival, and cell cycle progression pathways had reduced expression. From the proteomic analysis, three potential biomarkers for TCC were identified, claudin-4 (CLDN4), ubiquitin carboxyl-terminal esterase L1 (UCHL1), and minichromosome maintenance protein 7 (MCM7), and tested by IHC analysis on tissue microarrays. In agreement with the proteomic analysis, IHC expression of those proteins was stronger in TCC than in HGSC (p < 0.0001). Using global proteomic analysis, we are able to distinguish TCC from conventional HGSC. Follow-up studies will be necessary to confirm that these molecular and morphologic differences are clinically significant.

Claudin expression profile in flat wart and cutaneous squamous cell carcinoma in epidermodysplasia verruciformis

Epidermodysplasia verruciformis (EV) is a genodermatosis related to human beta-papillomavirus (beta-HPV), with a high risk of cutaneous squamous cell carcinoma (cSCC). Claudins are transmembrane proteins expressed in epithelia and may be altered during carcinogenesis. For a better understanding of the role of beta-HPV in cutaneous carcinogenesis, this claudin expression study was conducted on lesions of patients with and without EV. In this study, claudins-1, -2, -3, -4, -5, -7 and -11 expressions were analyzed by applying the immunohistochemistry technique, in samples of 108 normal skin, 39 flat warts and 174 cSCC. The cSCC samples were organized in tissue microarrays. We found that claudin-1 and claudin-3 focal expressions were associated with cSCC (p < 0.001), and claudin-2 focal or negative expression with flat wart (p < 0.001), in EV and NEV (non-EV) groups. For claudin-5, EV group showed a lower chance of focal and negative expression (p < 0.001), and its negative expression was associated with flat wart (p < 0.001) and lower mean age (p < 0.001). Claudins-4, -7 and -11 showed a diffuse expression in almost all studied samples. Our findings suggest that claudin-5 increased expression observed on normal skin, flat wart and cSCC showed association with EV. Claudin-1 and -3 down expression were also observed, but they could not be related to beta-HPV infection.

Current insights into the metastasis of epithelial ovarian cancer - hopes and hurdles

BACKGROUND

Ovarian cancer is the most lethal gynecologic cancer and the fifth leading cause of cancer-related mortality in women worldwide. Despite various attempts to improve the diagnosis and therapy of ovarian cancer patients, the survival rate for these patients is still dismal, mainly because most of them are diagnosed at a late stage. Up to 90% of ovarian cancers arise from neoplastic transformation of ovarian surface epithelial cells, and are usually referred to as epithelial ovarian cancer (EOC). Unlike most human cancers, which are disseminated through blood-borne metastatic routes, EOC has traditionally been thought to be disseminated through direct migration of ovarian tumor cells to the peritoneal cavity and omentum via peritoneal fluid. It has recently been shown, however, that EOC can also be disseminated through blood-borne metastatic routes, challenging previous thoughts about ovarian cancer metastasis.

CONCLUSIONS

Here, we review our current understanding of the most updated cellular and molecular mechanisms underlying EOC metastasis and discuss in more detail two main metastatic routes of EOC, i.e., transcoelomic metastasis and hematogenous metastasis. The emerging concept of blood-borne EOC metastasis has led to exploration of the significance of circulating tumor cells (CTCs) as novel and non-invasive prognostic markers in this daunting cancer. We also evaluate the role of tumor stroma, including cancer associated fibroblasts (CAFs), tumor associated macrophages (TAMs), endothelial cells, adipocytes, dendritic cells and extracellular matrix (ECM) components in EOC growth and metastasis. Lastly, we discuss therapeutic approaches for targeting EOC. Unraveling the mechanisms underlying EOC metastasis will open up avenues to the design of new therapeutic options. For instance, understanding the molecular mechanisms involved in the hematogenous metastasis of EOC, the biology of CTCs, and the detailed mechanisms through which EOC cells take advantage of stromal cells may help to find new opportunities for targeting EOC metastasis.

Zinc finger protein 703 induces EMT and sorafenib resistance in hepatocellular carcinoma by transactivating CLDN4 expression

Metastasis is one of the most common reasons of hepatocellular carcinoma (HCC) death; however, the molecular mechanism underlying HCC metastasis remains incompletely defined. Here we report a new function of Zinc Finger Protein 703 (ZNF703), a member of the NET/NlZ family of zinc finger transcription factors, in promoting hepatocellular carcinoma metastasis. We demonstrated that the overexpression of ZNF703 in human HCC tissue is correlated with tumor metastasis and recurrence, it is also related with the prognosis and survival rate of patients. ZNF703 overexpression promotes HCC progression in vitro and in vivo, whereas ZNF703 knockdown has the opposite effect. In addition, ZNF703 induces epithelialmesenchymal transition (EMT) via directly binding to the CLDN4 promoter and transactivating CLDN4 expression. Downregulation of CLDN4 can attenuate ZNF703-mediated HCC metastasis, whereas upregulation of CLDN4 can reverse the decreased metastasis induced by ZNF703 knockdown. Our data revealed that ZNF703 expression is correlated with CLDN4 level, the overexpression of both ZNF703 and CLDN4 are leaded to poorer prognosis of patients with HCC. Moreover, ZNF703 knockdown can enhance the sensitivity of HCC cell to sorafenib, whereas ZNF703 overexpression has the opposite effect. These results suggested that ZNF703 might be a potential target for cancer therapies and a candidate prognostic biomarker for predicting whether patients with HCC are befitting for sorafenib treatment.

Amyloid precursor-like protein 2 interacts with claudin-7 and affects ovarian cancer cell survival

Aim:

In our previous report, we identified roles of CLDN7 in regulation of cell signaling. The goal of this study was to identify proteins interacting with CLDN7 in ovarian cancer.

Methods:

The yeast two-hybrid system was used to identify proteins directly interacting with CLDN7 and cell survival was tested using colony formation assay.

Results:

Amyloid precursor-like protein 2 (APLP2) was found directly associated with CLDN7 in ovarian cancer cell line OVCA420. In addition, APLP2 showed increased expression in ovarian cancer cell lines and tumor tissue samples compared with non-neoplastic ovarian tissues. Knockdown of CLDN7 led to increased expression of APLP2 at both the mRNA and protein levels. Knockdown of APLP2 was associated with decreased cell survival in ovarian cancer cells.

Conclusion:

We show a direct interaction of CLDN7 with APLP2. These findings suggest novel regulatory role for APLP2 in ovarian cancer, a role that appears to be mediated by CLDN7.

We conducted this study to find other proteins interacting with CLDN7. CLDN7 is a tight junction protein and increased expression of CLDN7 has been reported in several cancers, including ovarian cancer. Using a yeast two-hybrid approach, we identified amyloid precursor-like protein 2 (APLP2) directly interacting with CLDN7. Like CLDN7, increased levels of APLP2 proteins were found in both ovarian cancer cell lines and ovarian cancer tissue samples. We also identified functional role of APLP2 in ovarian cancer where lowering APLP2 protein levels led to decreased cell survival in ovarian cancer cell line, OVCA420.

Tight Junction Proteins and the Biology of Hepatobiliary Disease

Tight junctions (TJ) are intercellular adhesion complexes on epithelial cells and composed of integral membrane proteins as well as cytosolic adaptor proteins. Tight junction proteins have been recognized to play a key role in health and disease. In the liver, TJ proteins have several functions: they contribute as gatekeepers for paracellular diffusion between adherent hepatocytes or cholangiocytes to shape the blood-biliary barrier (BBIB) and maintain tissue homeostasis. At non-junctional localizations, TJ proteins are involved in key regulatory cell functions such as differentiation, proliferation, and migration by recruiting signaling proteins in response to extracellular stimuli. Moreover, TJ proteins are hepatocyte entry factors for the hepatitis C virus (HCV)—a major cause of liver disease and cancer worldwide. Perturbation of TJ protein expression has been reported in chronic HCV infection, cholestatic liver diseases as well as hepatobiliary carcinoma. Here we review the physiological function of TJ proteins in the liver and their implications in hepatobiliary diseases.

Development of Human Monoclonal Antibody for Claudin-3 Overexpressing Carcinoma Targeting

Most malignant tumors originate from epithelial tissues in which tight junctions mediate cell-cell interactions. Tight junction proteins, especially claudin-3 (CLDN3), are overexpressed in various cancers. Claudin-3 is exposed externally during tumorigenesis making it a potential biomarker and therapeutic target. However, the development of antibodies against specific CLDN proteins is difficult, because CLDNs are four-transmembrane domain proteins with high homology among CLDN family members and species. Here, we developed a human IgG1 monoclonal antibody (h4G3) against CLDN3 through scFv phage display using CLDN3-overexpressing stable cells and CLDN3-embedded lipoparticles as antigens. The h4G3 recognized the native conformation of human and mouse CLDN3 without cross-reactivity to other CLDNs. The binding kinetics of h4G3 demonstrated a sub-nanomolar affinity for CLDN3 expressed on the cell surface. The h4G3 showed antibody-dependent cellular cytotoxicity (ADCC) according to CLDN3 expression levels in various cancer cells by the activation of FcγRIIIa (CD16a). The biodistribution of h4G3 was analyzed by intravenous injection of fluorescence-conjugated h4G3 which showed that it localized to the tumor site in xenograft mice bearing CLDN3-expressing tumors. These results indicate that h4G3 recognizes CLDN3 specifically, suggesting its value for cancer diagnosis, antibody-drug conjugates, and potentially as a chimeric antigen receptor (CAR) for CLDN3-expressing pan-carcinoma.

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.

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

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

Virtual screening of National Cancer Institute database for claudin-4 inhibitors: Synthesis, biological evaluation, and molecular dynamics studies

Claudin-4 (CLDN4) is a vital member of tight-junction proteins that is often overexpressed in cancer and other malignancies. The three-dimensional structure of human CLDN4 was constructed based on homology modeling approach. A total of 265 242 molecules from the National Cancer Institute (NCI) database has been utilized as a dataset for this study. In the present work, structure-based virtual screening is performed with the NCI database using Glide. By molecular docking, 10 candidate molecules with high scoring functions, which binds to the active site of CLDN4 were identified. Subsequently, molecular dynamics simulations of membrane protein were used for optimization of the top-three lead compounds (NCI110039, NCI344682, and NCI661251) with CLDN4 in a dynamic system. The lead molecule from NCI database NCI11039 (purpurogallin carboxylic acid) was synthesized and cytotoxic properties were evaluated with A549, MCF7 cell lines. Our docking and dynamics simulations predicted that ARG31, ASN142, ASP146, and ARG158 as critically important residues involved in the CLDN4 activity. Finally, three lead candidates from the NCI database were identified as potent CLDN4 inhibitors. Cytotoxicity assays had proved that purpurogallin carboxylic acid had an inhibitory effect towards breast (MCF7) and lung (A549) cancer cell lines. Computational insights and in vitro (cytotoxicity) studies reported in this study are expected to be helpful for the development of novel anticancer agents.

Methods for Systematic Identification of Membrane Proteins for Specific Capture of Cancer-Derived Extracellular Vesicles

Analysis of cancer-derived extracellular vesicles (EVs) in biofluids potentially provides a source of disease biomarkers. At present there is no procedure to systematically identify which antigens should be targeted to differentiate cancer-derived from normal host cell-derived EVs. Here, we propose a computational framework that integrates information about membrane proteins in tumors and normal tissues from databases: UniProt, The Cancer Genome Atlas, the Genotype-Tissue Expression Project, and the Human Protein Atlas. We developed two methods to assess capture of EVs from specific cell types. (1) We used palmitoylated fluorescent protein (palmtdTomato) to label tumor-derived EVs. Beads displaying antibodies of interest were incubated with conditioned medium from palmtdTomato-expressing cells. Bound EVs were quantified using flow cytometry. (2) We also showed that membrane-bound Gaussia luciferase allows the detection of cancer-derived EVs in blood of tumor-bearing animals. Our analytical and validation platform should be applicable to identify antigens on EVs from any tumor type.

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.

A novel PAK4-CEBPB-CLDN4 axis involving in breast cancer cell migration and invasion

Claudin-4 (CLDN4), a crucial member of tight junction proteins, is aberrantly expressed in breast cancer cells and contributes to cell migration and invasion. However, the mechanisms controlling CLDN4 expression in breast cancer are poorly understood. Here, we reported that CLDN4 expression correlated positively with p21-activated kinase 4 (PAK4) expression in human breast cancer tissues. Knockdown of PAK4 in MDA-MB-231 and ZR-75-30 cells suppressed CLDN4 expression and significantly inhibited cell migration and invasion. Conversely, restoration of CLDN4 expression in PAK4-knockdown cells reversed the inhibition of migration and invasion. We identified CCAAT/enhancer-binding protein β (CEBPB) as a novel transcriptional regulator of CLDN4 and confirmed that CEBPB bound to the -1093 to -991 bp region of the CLDN4 promoter. Importantly, we found that PAK4 enhanced CEBPB phosphorylation on Thr-235. In summary, we showed that PAK4-mediated CEBPB activation upregulated CLDN4 expression to promote breast cancer cell migration and invasion. Our results might contribute to understanding the mechanisms of CLDN4 regulation and suggest PAK4-CEBPB-CLDN4 axis as a potential therapeutic target for breast cancer.

Afadin cooperates with Claudin-2 to promote breast cancer metastasis

Claudin-2 promotes breast cancer liver metastasis by enabling seeding and early cancer cell survival. We now demonstrate that the PDZ-binding motif of Claudin-2 is necessary for anchorage-independent growth of cancer cells and is required for liver metastasis. Several PDZ domain-containing proteins were identified that interact with the PDZ-binding motif of Claudin-2 in liver metastatic breast cancer cells, including Afadin, Arhgap21, Pdlim2, Pdlim7, Rims2, Scrib, and ZO-1. We specifically examined the role of Afadin as a potential Claudin-2-interacting partner that promotes breast cancer liver metastasis. Afadin associates with Claudin-2, an interaction that requires the PDZ-binding motif of Claudin-2. Loss of Afadin also impairs the ability of breast cancer cells to form colonies in soft agar and metastasize to the lungs or liver. Immunohistochemical analysis of Claudin-2 and/or Afadin expression in 206 metastatic breast cancer tumors revealed that high levels of both Claudin-2 and Afadin in primary tumors were associated with poor disease-specific survival, relapse-free survival, lung-specific relapse, and liver-specific relapse. Our findings indicate that signaling downstream from a Claudin-2/Afadin complex enables the efficient formation of breast cancer metastases. Moreover, combining Claudin-2 and Afadin as prognostic markers better predicts the potential of breast cancer to metastasize to soft tissues.

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.

Ovarian Tumor Cell Expression of Claudin-4 Reduces Apoptotic Response to Paclitaxel

A significant factor contributing to poor survival rates for patients with ovarian cancer is the insensitivity of tumors to standard-of-care chemotherapy. In this study, we investigated the effect of claudin-4 expression on ovarian tumor cell apoptotic response to cisplatin and paclitaxel. We manipulated claudin-4 gene expression by silencing expression [short hairpin RNA (shRNA)] in cells with endogenously expressed claudin-4 or overexpressing claudin-4 in cells that natively do not express claudin-4. In addition, we inhibited claudin-4 activity with a claudin mimic peptide (CMP). We monitored apoptotic response by caspase-3 and Annexin V binding. We examined proliferation rate by counting the cell number over time as well as measuring the number of mitotic cells. Proximity ligation assays, immunoprecipitation (IP), and immunofluorescence were performed to examine interactions of claudin-4. Western blot analysis of tubulin in cell fractions was used to determine the changes in tubulin polymerization with changes in claudin-4 expression. Results show that claudin-4 expression reduced epithelial ovarian cancer (EOC) cell apoptotic response to paclitaxel. EOCs without claudin-4 proliferated more slowly with enhanced mitotic arrest compared with the cells expressing claudin-4. Furthermore, our results indicate that claudin-4 interacts with tubulin, having a profound effect on the structure and polymerization of the microtubule network. In conclusion, we demonstrate that claudin-4 reduces the ovarian tumor cell response to microtubule-targeting paclitaxel and disrupting claudin-4 with CMP can restore apoptotic response. IMPLICATIONS: These results suggest that claudin-4 expression may provide a biomarker for paclitaxel response and can be a target for new therapeutic strategies to improve response.

Anti-claudin-4 extracellular domain antibody enhances the antitumoral effects of chemotherapeutic and antibody drugs in colorectal cancer

Claudin-4 (CLDN4) is a major epithelial tight junction protein overexpressed in many cancers to maintain the tumor environment. In this report, we aimed to determine the efficacy of targeting CLDN4 in colorectal cancer (CRC) using an anti-CLDN4 extracellular domain antibody, 4D3. CLDN4 was upregulated in CRC metastatic foci. CLDN4 expression in CRC cells was reduced by upregulation of TNFα, which was induced by Clostridium perfringens enterotoxin produced by gut flora. In a nude mouse liver metastasis model, inhibition of metastasis was increased by combination treatment with 5-fluorouracil (FU) and 4D3 compared to that with 5-FU alone. Moreover, combination treatment with 4D3 and anti-epithelial growth factor receptor (EGFR) antibody C225 resulted in more pronounced inhibition of in vitro sphere formation and tumor growth in nude mice compared to that observed with C225 alone. Moreover, the time interval between the administration of 4D3 and that of C225 was important for maximizing the C225-induced inhibition of EGFR phosphorylation. In a nude mouse model, sequential treatment with 4D3 and C225 with a 6-h time interval resulted in more pronounced inhibition of tumor growth than concurrent treatment. These findings suggest that the targeting of CLDN4 enhances the antitumoral effects of chemotherapeutic agents and molecular targeting antibodies when used in combination.

CLDN18.1 attenuates malignancy and related signaling pathways of lung adenocarcinoma in vivo and in vitro

Claudins are a family of transmembrane proteins integral to the structure and function of tight junctions (TJ). Disruption of TJ and alterations in claudin expression are important features of invasive and metastatic cancer cells. Expression of CLDN18.1, the lung-specific isoform of CLDN18, is markedly decreased in lung adenocarcinoma (LuAd). Furthermore, we recently observed that aged Cldn18 -/- mice have increased propensity to develop LuAd. We now demonstrate that CLDN18.1 expression correlates inversely with promoter methylation and with LuAd patient mortality. In addition, when restored in LuAd cells that have lost expression, CLDN18.1 markedly attenuates malignant properties including xenograft tumor growth in vivo as well as cell proliferation, migration, invasion and anchorage-independent colony formation in vitro. Based on high throughput analyses of Cldn18 -/- murine lung alveolar epithelial type II cells, as well as CLDN18.1-repleted human LuAd cells, we hypothesized and subsequently confirmed by Western analysis that CLDN18.1 inhibits insulin-like growth factor-1 receptor (IGF-1R) and AKT phosphorylation. Consistent with recent data in Cldn18 -/- knockout mice, expression of CLDN18.1 in human LuAd cells also decreased expression of transcriptional co-activator with PDZ-binding motif (TAZ) and Yes-associated protein (YAP) and their target genes, contributing to its tumor suppressor activity. Moreover, analysis of LuAd cells in which YAP and/or TAZ are silenced with siRNA suggests that inhibition of TAZ, and possibly YAP, is also involved in CLDN18.1-mediated AKT inactivation. Taken together, these data indicate a tumor suppressor role for CLDN18.1 in LuAd mediated by a regulatory network that encompasses YAP/TAZ, IGF-1R and AKT signaling.

Impaired Localization of Claudin-11 in Endometriotic Epithelial Cells Compared to Endometrial Cells

Claudins are the major components of tight junctions and are often deregulated in human cancer, permitting escape of cancer cells along with the acquisition of invasive properties. Similarly, endometrial cells also show invasive capabilities; however, the role of tight junctions in endometriosis has only rarely been examined. In this study, we analyzed the protein expression and localization of claudin-7 and claudin-11 in human eutopic and ectopic endometrium and endometrial cell lines. We identified claudin-7 primarily at the basolateral junctions of the glandular epithelial cells in eutopic endometrium as well as in the ectopic lesions in nearly all glands and cysts. Quantification of claudin-7 localization by HSCORE showed a slight increase in peritoneal and deep infiltrating endometriosis (DIE) compared to eutopic endometrium. In contrast, claudin-11 was localized mainly in the apicolateral junctions in nearly all glandular epithelial cells of the eutopic endometrium. Interestingly, we observed a deregulation of claudin-11 localization to a basal or basolateral localization in ovarian (P < .001), peritoneal (P < .01), and DIE (P < .05) and a moderately decreased abundance in ovarian endometriosis. In endometrial cell lines, claudin-7 was only present in epithelial Ishikawa cells, and silencing by small-interfering RNA increased cell invasiveness. In contrast, claudin-11 could be demonstrated in Ishikawa and endometriotic 12Z and 49Z cells. Silencing of claudin-11 decreased invasiveness of 12Z slightly but significantly in 49Z. We suggest that although claudin-7 and claudin-11 can be found in nearly all eutopic and ectopic epithelial cells, the impaired localization of claudin-11 in ectopic endometrium might contribute to the pathogenesis of endometriosis.

Claudin-4 Expression is Associated With Survival in Ovarian Cancer But Not With Chemotherapy Response

The tight junction protein claudin-4 has been reported to be overexpressed in advanced ovarian cancer. We investigated the prognostic significance of claudin-4 overexpression and whether claudin-4 expression could predict platinum response in primary ovarian carcinoma (OC). Claudin-4 expression was evaluated by immunohistochemistry in a tissue microarray of 140 OCs. Multivariable Cox-regression models were used to assess the effect of claudin-4 overexpression on progression-free survival and overall survival (OS). Kaplan-Meier survival analyses and the logrank test were performed comparing claudin-4 high and low groups. The association between claudin-4 expression and platinum resistance was assessed using risk ratios and the Pearson χ test. A dataset of >1500 epithelial ovarian cancers was used to study the association between CLDN4 mRNA and survival. Of 140 evaluable cases, 71 (51%) displayed high claudin-4 expression. Claudin-4 overexpression predicted shorter 5-yr progression-free survival and OS in univariable analyses [hazard ratio (HR)=1.6 (1.1-2.5), P=0.020 and HR=1.6 (1.0-2.4), P=0.041, respectively]. Hazard of relapse was similar [HR=1.5 (1.0-2.4)] after adjustment for age, stage, type, and BRCA1/2 status in a multivariable analysis, but the evidence was slightly weaker (P=0.076). Validation in an external cohort confirmed the association between high expression of CLDN4 and poor 10-yr OS [HR=1.3 (1.1-1.5), P<0.001]. However, no confident association between claudin-4 and platinum sensitivity was found in our cohort [risk ratio=1.2 (0.7-2.0), P=0.3]. These findings suggest that high expression of claudin-4 may have a prognostic value in OC. The role of claudin-4 in the development of platinum resistance remains unclear.

MicroRNA-466 (miR-466) functions as a tumor suppressor and prognostic factor in colorectal cancer (CRC)

MicroRNAs (miRNAs) have an important role in the regulation of tumor development and metastasis. In this study, we investigated the clinical and prognostic value as well as biological function of miR-466 in colorectal cancer (CRC). Tumor and adjacent healthy tissues were obtained from 100 patients diagnosed with CRC. miR-466 expression was determined by quantitative reverse transcription polymerase chain reaction (qRT-PCR). mRNA and protein levels of cyclin D1, apoptosis regulator BAX (BAX), and matrix metalloproteinase-2 (MMP-2) were analyzed by qRT-PCR and Western blot, respectively, in SW-620 CRC cells transfected with miR-466 mimics or negative control miRNA. Effects of miR-466 on SW-620 cell proliferation, cell cycle and apoptosis, and invasion were investigated using CCK-8 assay, flow cytometry and Transwell assay, respectively. miR-466 expression was significantly downregulated in tumor tissues compared to matched adjacent non-tumor tissues. Low expression of miR-466 was significantly correlated with the tumor size, Tumor Node Metastasis stage, lymph node metastasis, and distant metastasis. The overall survival of CRC patients with low miR-466 expression was significantly shorter compared to high-miR-466 expression group (log-rank test: p = 0.0103). Multivariate analysis revealed that low miR-466 expression was associated with poor prognosis in CRC patients. The ectopic expression of miR-466 suppressed cell proliferation and migration/invasion, as well as induced G0/G1 arrest and apoptosis in SW-620 cells. Moreover, the ectopic expression of miR-466 decreased the expression of cyclin D1 and MMP-2, but increased BAX expression in SW-620 cells. In conclusion, our findings demonstrated that miR-466 functions as a suppressor miRNA in CRC and may be used as a prognostic factor in these patients.

Salivary exosomes as potential biomarkers in cancer

Over the past decade, there has been emerging research in the field of extracellular vesicles, especially those originating from endosomes, referred to as 'exosomes. Exosomes are membrane-bound nanovesicles secreted by most cell types upon fusion of multivesicular bodies (MVBs) to the cell plasma membrane. These vesicles are present in almost all body fluids such as blood, urine, saliva, breast milk, cerebrospinal and peritoneal fluids. Exosomes participate in intercellular communication by transferring the biologically active molecules like proteins, nucleic acids, and lipids to neighboring cells. Exosomes are enriched in the tumour microenvironment and growing evidence demonstrates that exosomes mediate cancer progression and metastasis. Given the important biological role played by these nanovesicles in cancer pathogenesis, these can be used as ideal non-invasive biomarkers in detecting and monitoring tumours as well as therapeutic targets. The scope of the current review is to provide an overview of exosomes with a special focus on salivary exosomes as potential biomarkers in head and neck cancers.

Identification of genes associated with matrix metalloproteinases in invasive lung adenocarcinoma

The aim of the present study was to identify genes with similar function to that of matrix metalloproteinases (MMPs) in invasive lung adenocarcinoma (AC) and to screen the transcription factors that regulate MMPs. The gene expression dataset GSE2514, including 20 invasive lung AC samples and 19 adjacent normal lung samples, was downloaded from the Gene Expression Omnibus database. Differentially expressed genes (DEGs) were screened using the limma package in R. Genes with similar function to MMPs were identified by K-means clustering. Their correlations with MMPs were validated using Pearson correlation analysis. The expression of MMPs in lung cancer and normal tissues was evaluated by western blot analysis. Protein-protein interaction (PPI) network and transcriptional regulatory network analyses were performed with Retrieval of Interacting Genes and Database for Annotation, Visualization and Integrated Discovery, respectively. As a result, 269 DEGs were identified between invasive lung AC samples and normal lung samples, including 78 upregulated and 191 downregulated genes. Four MMPs (MMP1, MMP7, MMP9 and MMP12), which were upregulated in lung AC, were clustered into one group with other genes, including NAD(P)H quinone oxidoreductase 1, claudin 3 (CLDN3), S100 calcium-binding protein P, serine protease inhibitor Kazal type 1, collagen type XI α 1 chain, periostin and desmoplakin (DSP), following cluster analysis. Pearson correlation analysis further confirmed correlations between MMP9-CLDN3, MMP9-DSP and MMP12-DSP. PPI network analysis also indicated multiple interactions between MMPs-associated genes. Furthermore, MMPs were commonly regulated by CCAAT/enhancer binding protein α transcription factor. These findings may provide further insight into the mechanisms of MMPs in invasive lung AC.

Imaging of Claudin-4 in Pancreatic Ductal Adenocarcinoma Using a Radiolabelled Anti-Claudin-4 Monoclonal Antibody

PURPOSE

Despite its widespread use, the positron emission tomography (PET) radiotracer 2-deoxy-2-[18F]fluoro-D-glucose ([18F]FDG) has been shown in clinical settings to be ineffective for improving early diagnosis of pancreatic ductal adenocarcinoma (PDAC). A promising biomarker for PDAC detection is the tight junction protein claudin-4. The purpose of this study was to evaluate a new single-photon emission computed tomography (SPECT) imaging agent, [111In]anti-claudin-4 mAb, with regard to its ability to allow visualisation of claudin-4 in a xenograft and a genetically engineered mouse model of PDAC.

PROCEDURES

The ability of [111In]anti-claudin-4 mAb to selectively target claudin-4 was assessed using two human xenograft tumour models with differential claudin-4 status in mice. [111In]anti-claudin-4 mAb was also used to detect PDAC development in genetically engineered KPC mice. The PDAC status of these mice was confirmed with [18F]FDG-PET, magnetic resonance imaging (MRI), histology, and immunofluorescence microscopy.

RESULTS

High uptake of [111In]anti-claudin-4 mAb was observed in PDAC xenografts in mice, reaching 16.9 ± 4.5 % of injected dose per gram (% ID/g) at 72 h post-injection. This uptake was mediated specifically by the expression of claudin-4. Uptake of [111In]anti-claudin-4 mAb also enabled clear visualisation of spontaneous PDAC formation in KPC mice.

CONCLUSIONS

[111In]anti-claudin-4 mAb allows non-invasive detection of claudin-4 upregulation during development of PDAC and could potentially be used to aid in the early detection and characterisation of this malignancy.

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.

Nuclear Phosphatidylinositol-Phosphate Type I Kinase α-Coupled Star-PAP Polyadenylation Regulates Cell Invasion

Star-PAP, a nuclear phosphatidylinositol (PI) signal-regulated poly(A) polymerase (PAP), couples with type I PI phosphate kinase α (PIPKIα) and controls gene expression. We show that Star-PAP and PIPKIα together regulate 3′-end processing and expression of pre-mRNAs encoding key anti-invasive factors (KISS1R, CDH1, NME1, CDH13, FEZ1, and WIF1) in breast cancer. Consistently, the endogenous Star-PAP level is negatively correlated with the cellular invasiveness of breast cancer cells. While silencing Star-PAP or PIPKIα increases cellular invasiveness in low-invasiveness MCF7 cells, Star-PAP overexpression decreases invasiveness in highly invasive MDA-MB-231 cells in a cellular Star-PAP level-dependent manner. However, expression of the PIPKIα-noninteracting Star-PAP mutant or the phosphodeficient Star-PAP (S6A mutant) has no effect on cellular invasiveness. These results strongly indicate that PIPKIα interaction and Star-PAP S6 phosphorylation are required for Star-PAP-mediated regulation of cancer cell invasion and give specificity to target anti-invasive gene expression. Our study establishes Star-PAP–PIPKIα-mediated 3′-end processing as a key anti-invasive mechanism in breast cancer.

Methylated claudin-11 associated with metastasis and poor survival of colorectal cancer

As one of crucial epigenetic modification, DNA methylation plays an important role during the carcinogenesis of colorectal cancer (CRC). In the current study, we used a human genome methylation array to detect the aberrant methylation genes in CRC. We further identified the hypermethylation of claudin-11 (CLDN11) and proved inverse correlation between CLDN11 methylation and its expression in CRC. In vitro experiments showed debased migration ability of colonic cancer cells in accompany with the converted methylation of CLDN11 after colonic cancer cells treated with demethylation agent, 5-aza-2'-deoxycytidine. Besides, our results also represented that hypermethylation of CLDN11 was associated with increased metastatic potential of CRC and with low progression free survival (PFS) of CRC. In conclusion, our findings supported that the hypermethylated CLDN11 is associated with metastasis of CRC and prognosis of poor survival of CRC.

Nuclear expression of claudin-3 in human colorectal adenocarcinoma cell lines and tissues

Claudins are members of a large family of transmembrane proteins, which are essential for the formation of tight junctions and have a significant effect on the biological behavior of tumor progression. Previous studies have demonstrated that several claudins show aberrant expression patterns in numerous types of cancer. The present study investigated the expression and localization of claudin-3 and claudin-7 in human colorectal adenocarcinoma cell lines and tissues. The protein expression levels of claudin-3 and claudin-7 were determined using immunocytochemical and immunohistochemical staining. Claudin-3, but not claudin-7, exhibited nuclear localization in the human colorectal adenocarcinoma Caco-2 and SW620 cell lines. Surgically resected colorectal adenocarcinoma tissue specimens were obtained, and the associations between the expression of claudin-3 or claudin-7 and various clinicopathological parameters were analyzed. The membranous expression rates of claudin-3 and claudin-7 were 58.0 and 50.0%, while their nuclear expression rates were 22.0 and 2.0%, respectively. The membranous expression of claudin-3 and claudin-7 was not associated with any clinicopathological factors, whereas the nuclear expression of claudin-3 was associated with histological type and was significantly increased in colorectal mucinous adenocarcinomas compared with that in well- to moderately-differentiated colorectal adenocarcinomas (P<0.01). However, no associations were observed between the nuclear expression of claudin-7 and any clinicopathological parameter. In conclusion, the nuclear expression of claudin-3 in colorectal mucinous adenocarcinoma may be involved in the biological transformation of tumors. The results from the present study indicated that claudin-3 is an important protein associated with histological type and has potential as a prognostic marker. Although the mechanisms underlying the nuclear localization of claudin-3 in tumorigenesis have not yet been elucidated in detail, the present results indicated the potential of claudin-3 as a histopathological biomarker for colorectal adenocarcinomas.

Claudin-3 expression increases the malignant potential of lung adenocarcinoma cells: role of epidermal growth factor receptor activation

Claudins are essential for the formation and maintenance of tight junctions (TJ). The altered expression of claudin proteins has been described in a variety of malignancies. However, the alteration of these proteins in lung adenocarcinoma (ADC) are poorly understood. Therefore, we report, based on the protein expression analysis of a total of 275 patient samples, that claudin-3 (CLDN3) expression is significantly increased in ADC tissues and is associated with cancer progression, correlating significantly with the poor survival of ADC patients (p=0.041&0.029). More importantly, forcing CLDN3 expression in ADC cells without endogenous CLDN3 expression resulted in significant increases in the cell proliferation, anchorage-dependent growth, migration and drug-resistance. In addition, epidermal growth factor (EGF) signaling pathway modulates the expression of claudins in a number of solid tumors. However, the mechanism of tight junction regulation by EGF in ADC remains unclear. To investigate this mechanisms, ADC cell lines were treated with EGF and its inhibitor. EGF unregulated CLDN3 expression via the MEK/ERK or PI3K/Akt signaling pathways and was required for the maintenance of baseline CLDN3 expression. Furthermore, downregulation of CLDN3 expression in ADC cell was found to prevent the EGF-induced increase in cell proliferation. In conclusion, our results demonstrate a novel role of CLDN3 overexpression in promoting the malignant potential of lung adenocarcinoma. This function is potentially regulated by the EGF-activated MEK/ERK and PI3K-Akt pathways.

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.

HpSlyD inducing CDX2 and VIL1 expression mediated through TCTP protein may contribute to intestinal metaplasia in the stomach

Helicobacter pylori infection is the most important risk factor for gastric intestinal metaplasia (IM). Our previous study demonstrated that infection with H. pylori HpslyD-positive strains associated with IM. To further investigate the signalling pathway involved in HpSlyD-induced IM, CDX2 and VIL1 expressions were determined before and after HpSlyD application. TCTP was knocked down by siRNA or overexpressed by plasmid transfection. An HpSlyD binding protein was used to block HpSlyD's enzymatic activity. The expression of CDX2 and TCTP in gastric diseases was measured by immunohistochemistry. Our results showed HpSlyD induced CDX2 and VIL1 expressions. TCTP protein expression was markedly increased after application of HpSlyD and in an HpSlyD-expressing stable cell line. Downregulation of TCTP protein led to decreased HpSlyD-induced CDX2 and VIL1. Overexpression of TCTP protein improved the expression of CDX2 and VIL1. Co-application of HpSlyD and FK506 led to significant reductions in CDX2, VIL1, and TCTP expression. Immunohistochemistry demonstrated that CDX2 and TCTP expression was higher in HpslyD-positive specimens compared with HpslyD-negative ones. Expression of CDX2 was positively correlated with TCTP in HpslyD-positive cells. Our study is the first to show that HpSlyD induction of CDX2 and VIL1 expression mediated through TCTP may contribute to IM in the stomach.

Effect of Clostridium perfringens enterotoxin on gastric cancer cells SGC7901 which highly expressed claudin-4 protein

AIM

To investigate the effects of Clostridium perfringens enterotoxin (CPE) on gastric cancer cells which highly expressed claudin-4 (CL4) protein.

METHODS

In this study, we detected expression of CL4 protein in different gastric cancer cell lines. Then, we investigated the effects of CPE on SGC7901 cells which highly expressed CL4 protein and the effects of CPE on subcutaneous tumor in nude mice models.

RESULTS

CL4 are highly expressed in SGC7901 cells. CPE expressed significant cytotoxicity in SGC7901 cells. Suppression of CL4 expression significantly decreased CPE-mediated cytotoxicity. CPE also inhibited tumor growth in subcutaneous tumor xenograft models.

CONCLUSION

CPE showed CL4 mediated cytotoxicity on gastric cancer cells SGC7901 and inhibited tumor growth in nude mice models.

Non-canonical functions of claudin proteins: Beyond the regulation of cell-cell adhesions

Tight junctions form a barrier to the diffusion of apical and basolateral membrane proteins thus regulating membrane polarity. They also regulate the paracellular movement of ions and water across epithelial and endothelial cells so that functionally they constitute an important permselective barrier. Permselectivity at tight junctions is regulated by claudins, which confer anion or cation permeability, and tightness or leakiness, by forming several highly regulated pores within the apical tight junction complex. One interesting feature of claudins is that they are, more often than not, localized to the basolateral membrane, in intracellular cytoplasmic vesicles, or in the nucleus rather than to the apical tight junction complex. These intracellular pools of claudin molecules likely serve important functions in the epithelium. This review will address the widespread prevalence of claudins that are not associated with the apical tight junction complex and discuss the important and emerging non-traditional functions of these molecules in health and disease.

Regulation of intestinal permeability: The role of proteases

The gastrointestinal barrier is - with approximately 400 m2 - the human body's largest surface separating the external environment from the internal milieu. This barrier serves a dual function: permitting the absorption of nutrients, water and electrolytes on the one hand, while limiting host contact with noxious luminal antigens on the other hand. To maintain this selective barrier, junction protein complexes seal the intercellular space between adjacent epithelial cells and regulate the paracellular transport. Increased intestinal permeability is associated with and suggested as a player in the pathophysiology of various gastrointestinal and extra-intestinal diseases such as inflammatory bowel disease, celiac disease and type 1 diabetes. The gastrointestinal tract is exposed to high levels of endogenous and exogenous proteases, both in the lumen and in the mucosa. There is increasing evidence to suggest that a dysregulation of the protease/antiprotease balance in the gut contributes to epithelial damage and increased permeability. Excessive proteolysis leads to direct cleavage of intercellular junction proteins, or to opening of the junction proteins via activation of protease activated receptors. In addition, proteases regulate the activity and availability of cytokines and growth factors, which are also known modulators of intestinal permeability. This review aims at outlining the mechanisms by which proteases alter the intestinal permeability. More knowledge on the role of proteases in mucosal homeostasis and gastrointestinal barrier function will definitely contribute to the identification of new therapeutic targets for permeability-related diseases.

Expression of claudin 1, 4 and 7 in thyroid neoplasms

The distinction of thyroid carcinoma from benign thyroid neoplasm, as well as the subtyping of papillary carcinoma (PC) and follicular carcinoma (FC), may be performed histopathologically in the majority of cases. However, in certain cases, it is difficult to histopathologically distinguish between PC and FC, as well as follicular adenoma (FA), FC and the dominant nodule of multinodular goiter (MNG-DN). The present study aimed to determine the roles of the expression levels of the tight junction proteins claudin 1, 4 and 7 in the differential diagnosis of PC, FC, FA, MNG-DN, medullary carcinoma (MC) and anaplastic carcinoma (AC). The current study included 114 cases of histopathologically diagnosed thyroid neoplasia, which were distributed as follows: 29 FA, 18 MNG-DN, 47 PC, 10 FC, 5 MC and 5 AC. The expression levels of claudin 1, 4 and 7 were examined using immunohistochemical methods. The results revealed a significant difference in claudin 1 expression between malignant and benign thyroid neoplasms (P<0.001). Claudin 1 expression was not detected in any of the MNG-DN cases, and no significant difference in claudin 1 expression levels was identified between FA and FC (P=0.653). However, a statistically significant difference was observed between FC and PC (P<0.001). Claudin 4 expression did not differ between malignant and benign thyroid neoplasms, neither between MNG-DN, FA and FC, nor between FC and PC (P=0.068, P=0.502 and P=0.481, respectively). Claudin 7 exhibited positive immunohistochemical staining in 107 patients (94%); however, no significant difference in claudin 7 expression §levels was identified between malignant and benign thyroid neoplasms among MNG-DN, FA and FC (malignant, P=0.135; benign, P=0.470). Claudin 7 exhibited positive staining in all PC and FC cases. Therefore, claudin 1 expression levels may be useful in distinguishing cases of FC and PC with overlapping histopathological features, and provide a novel immunohistochemical marker for the subtyping of thyroid carcinoma.

The role of claudins in cancer metastasis

TJs are large intercellular adhesion complexes that maintain cell polarity in normal epithelia and endothelia. During the metastatic process, TJs must be 'loosened' or dismantled in cancer cells to enable migration and dissemination. Diminished TJ integrity must also occur within endothelial cells to allow intravasation and extravasation of cancer cells across endothelial barriers. Claudins are critical components of TJs, forming homo- and heteromeric interactions between the adjacent cells, which have been implicated as key modulators of carcinogenesis and metastasis. Numerous epithelial-derived cancers display altered claudin expression patterns and certain claudins can now be used as biomarkers to predict patient prognosis. Moreover, claudins have been functionally implicated in numerous steps of the metastatic cascade. The distinct roles played by claudins during the cancer progression to metastatic disease are just starting to be elucidated. A more complete understanding of the mechanisms through which claudins augment cancer metastasis is required to develop new therapeutic agents against this family of proteins. In this review, we will summarize the relationship between the claudin expression and clinical outcomes in diverse cancers, discuss tumor intrinisic roles through which claudins regulate metastasis and explore claudin-mediated functions within stromal cells that influence the metastatic process. Finally, we will consider possible strategies for targeting claudins that have the potential to improve the management of metastatic cancer.

Claudin-6 enhances cell invasiveness through claudin-1 in AGS human adenocarcinoma gastric cancer cells

Claudins participate in tissue barrier function. The loss of this barrier is associated to metalloproteases-related extracellular matrix and basal membranes degradation. Claudin-1 is a pro-MMP-2 activator and claudin-6 transfected AGS (AGS-Cld6) cells are highly invasive. Our aim was to determine if claudin-6 was direct or indirectly associated with MMP-2 activation and cell invasiveness. Cytofluorometry, cell fractioning, immunoprecipitation, gelatin-zymography, cell migration and invasiveness assays were performed, claudin-2, -6, -7 and -9 transfected AGS cells, anti-MMP-2, -9 and -14, anti-claudins specific antibodies and claudin-1 small interfering RNA were used. The results showed a significant (p<0.001) overexpression of claudin-1 in AGS-Cld6 cell membranes. A strong MMP-2 activity was identified in culture supernatants of AGS-Cld6. Claudin-1 co-localized with MMP-2 and MMP-14; interestingly a significant increase in cell membrane and cytosol MMP-14 expression was detected in AGS-Cld6 cells (p<0.05). Silencing of claudin-1 in AGS-Cld6 cells showed a 60% MMP-2 activity decrease in culture supernatants and a significant decrease (p<0.05) in cell migration and invasiveness. Our results suggest that claudin-6 induces MMP-2 activation through claudin-1 membrane expression, which in turn promotes cell migration and invasiveness.

Claudin-4 activity in ovarian tumor cell apoptosis resistance and migration

Background

Claudin-4 is a transmembrane protein expressed at high levels in the majority of epithelial ovarian tumors, irrespective of subtype, and has been associated with tumor cells that are both chemoresistant and highly mobile. The objective of this study was to determine the functional role that claudin-4 plays in apoptosis resistance and migration as well as the therapeutic utility of targeting claudin-4 activity with a small mimic peptide.

Methods

We examined claudin-4 activity in human ovarian tumor cell lines (SKOV3, OVCAR3, PEO4) using in vitro caspase and scratch assays as well as an in vivo mouse model of ovarian cancer. Claudin-4 activity was disrupted by treating cells with a small peptide that mimics the DFYNP sequence in the second extracellular loop of claudin-4. Claudin-4 expression was also altered using shRNA-mediated gene silencing.

Results

Both the disruption of claudin-4 activity and the loss of claudin-4 expression significantly increased tumor cell caspase-3 activation (4 to 10-fold, respectively) in response to the apoptotic inducer staurosporine and reduced tumor cell migration by 50 %. The mimic peptide had no effect on cells that lacked claudin-4 expression. Female athymic nude mice bearing ZsGreen-PEO4 ovarian tumors showed a significant decrease in ovarian tumor burden, due to increased apoptosis, after treatment with intraperitoneal injections of 4 mg/kg mimic peptide every 48 h for three weeks, compared to control peptide treated mice.

Conclusion

Claudin-4 functionally contributes to both ovarian tumor cell apoptosis resistance and migration and targeting extracellular loop interactions of claudin-4 may have therapeutic implications for reducing ovarian tumor burden.

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.

Evaluation of a novel human IgG1 anti-claudin3 antibody that specifically recognizes its aberrantly localized antigen in ovarian cancer cells and that is suitable for selective drug delivery

Membrane protein claudin3 has been recently suggested as a marker for biologically aggressive tumors and a possible target for the therapeutic delivery of active anti-cancer compounds. Claudin3-binding molecules such as the Clostridium perfringens enterotoxin (CPE), CPE-related molecules, and murine and chimeric antibodies have shown promising antitumor efficacy in preclinical oncological settings. We first engineered a fully human anti-claudin3 IgG1 antibody (IgGH6) by fusing the human IgG1 Fc-domain to the anti-claudin3 scFvH6 previously isolated from a pre-immune phage display library. The construct was expressed in mammalian cells and specifically targeted claudin3 endogenously expressed on the surface of different human ovarian cancer cell lines. No detectable cross-reactivity with other homologous claudins was observed. The epitope recognized by IgGH6 is located within the minor extracellular domain of claudin3 and becomes accessible only in tumor cells characterized by incomplete junction formation. Confocal microscopy experiments demonstrated that IgGH6 was actively internalized in tumor cells after binding to native claudin3 and co-localized, likely within intracellular vesicles, with the C-CPE peptide. Preliminary results indicate that IgGH6 accumulated in vivo in free claudin3 ovarian carcinoma xenografts. For its selective uptake in tumor cells and its human nature, IgGH6 represents a valuable candidate for antibody-drug conjugate therapeutic applications in ovarian cancer patients.

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.

[Еxpression of claudin-1, 3, and 4 in colorectal cancer and polyps]

Claudins are a family of transmembrane tight junctions proteins. It is proven that claudins undergo structural and functional alteration in malignant cells. However, very few researches are pursued on this topic, the data provided by different researchers are controversial. The aim of this study was to evaluate expression of tight junction proteins in cancer and benign polyps of the colon and rectum.

MATERIAL AND METHODS

Specimens of 32 colorectal adenocarcinomas and biopsy specimens of 86 polypoid lesions of the colon and rectum were selected from diagnostic material. Polyps were divided into 6 groups following the 2010 WHO classification of premalignant lesions of the colon and rectum. Immunohistochemical labeling with claudin-1, claudin-3 and claudin-4 antibodies was performed in all cases. We used G. Sheehan et al. (2007) method to evaluate the expression of claudins in neoplasm as well as in adjacent normal mucosa in each slide.

RESULTS

Immunohistochemical staining with claudins antibodies had membranous pattern; claudins expression in adjacent normal mucosa was uniformly close to maximum. Serrated lesions showed the lowest level of expression of claudin-1 among other groups (p<0,05). In the group of adenocarcinomas we found moderate negative correlation between claudin-1 expression level and grade of adenocarcinoma. Claudin-3 expression level was significantly higher in adenocarcinomas compared to serrated lesions (p=0,025) and in conventional adenomas compared to serrated lesions (p=0,034). Expression of claudin-4 was strong in most cases, except for tubular adenomas that showed moderate expression in most cases.

CONCLUSION

We found no statistically significant difference between levels of expression of claudin-1, claudin-3 and claudin-4 expression levels among adenocarcinomas, hyperplastic polyps, sessile serrated adenomas, traditional serrated adenomas, tubular and tubular-villous adenomas. But we detected significant difference after enlargement of the groups. This fact may argue for general development pathway of hyperplastic polyps and sessile serrated adenomas, and of tubular and tubular-villous adenomas. Expression of claudin-1 and claudin-3 revealed difference of serrated lesions from conventional adenomas and adenocarcinomas, that confirms conception of independent «serrated» pathway of cancerogenesis.

Analysis of the distribution and expression of claudin-1 tight junction protein in the oral cavity

BACKGROUND

Claudins are the main sealing proteins of the intercellular tight junctions and play an important role in cancer cell progression and dissemination. The authors have previously shown that overexpression of claudin-1 is associated with angiolymphatic and perineural invasion, consistent with aggressive tumor behavior and with advanced stage disease in oral squamous cell carcinomas (OSCCs). Our goal in this study was to examine claudin-1 expression in a tissue microarray of OSCCs taken from multiple sites within the oral cavity.

MATERIALS AND METHODS

This study examined and compared the expression of claudin-1 by immunohistochemistry in 60 tissue samples (49 OSCCs and 10 cases of non-neoplastic tissue, single core per case) were analyzed for claudin-1 expression by immunohistochemistry. The tumors included SCCs from the tongue (n=28), the cheek (n=9), gingival (n=4), lip (n=3), and oral cavity (n=5). Nonmalignant normal oral mucosa from the tongue (unmatched cases, n=2). Cancer adjacent tissue samples were taken from the tongue (n=6), gingival (n=2), and palate (n=1).

RESULTS

This study demonstrates the expression of claudin-1 protein across a sample of OSCCs originating from multiple locations in the oral cavity. The highest expression of claudin-1 was observed in well-differentiated OSCCs, whereas poorly differentiated OSCCs exhibited mostly negative staining for claudin-1. In addition, we hereby report differential pattern of expression among tumors of different sites within the oral cavity, and between benign and cancerous samples. Our understanding of the exact function and role of claudin-1 in tumorigenesis is expanding exponentially.

Claudin-18 inhibits cell proliferation and motility mediated by inhibition of phosphorylation of PDK1 and Akt in human lung adenocarcinoma A549 cells

Abnormal expression of claudin subtypes has been reported in various cancers. However, the pathological role of each claudin has not been clarified in detail. Claudin-18 was absent in human non-small cell and small cell lung cancers, although it is expressed in normal lung tissues. Here, we examined the effect of claudin-18 expression on the expression of junctional proteins, cell proliferation, and cell motility using human lung adenocarcinoma A549 cells. Real-time PCR and western blotting showed that exogenous expression of claudin-18 had no effect on the expression of junctional proteins including claudin-1, zonula occludens-1 (ZO-1), occludin, and E-cadherin. Claudin-18 was mainly distributed in cell-cell contact areas concomitant with ZO-1. Cell proliferation was significantly decreased at 48 and 72h after seeding of claudin 18-expressing cells. Claudin-18 suppressed cell motility, whereas it increased cell death in anoikis. Claudin-18 decreased phosphorylated (p)-3-phosphoinositide-dependent protein kinase-1 (PDK1) and p-Akt levels without affecting p-epidermal growth factor receptor and p-phosphatidylinositol-3 kinase (PI3K) levels. Furthermore, claudin-18 was bound with PDK1 and suppressed the nuclear localization of PDK1. We suggest that claudin-18 suppresses the abnormal proliferation and motility of lung epithelial cells mediated by inhibition of the PI3K/PDK1/Akt signaling pathway.