Expression profile of tight junction protein claudin 3 and claudin 4 in ovarian serous adenocarcinoma with prognostic correlation

Spatial expression of claudin 18.2 in matched primaries and metastases of tubo-ovarian carcinoma of all subtypes

Physiologically, claudin 18 splice variant 2 (CLDN18.2) expression is restricted to the gastric epithelium, but its expression has been detected in solid cancers. Zolbetuximab, a chimeric IgG1 antibody targeting CLDN18.2, has demonstrated promising effects in patients suffering from CLDN18.2-positive, HER2-negative locally advanced gastric cancer and is currently being studied further. To date, little is known about CLDN18.2 expression in other histological subtypes of tubo-ovarian carcinoma (TOC) and their matching metastases.Using a cohort of all histological TOC subtypes, we investigated the immunohistochemical (IHC) CLDN18.2 expression in both TOCs (n = 536), their matching metastatic tissue (n = 385) and in 93 metastases without primary. Tissue microarrays comprised both the tumor center and periphery. IHC positivity was defined as biomarker expression of ≥ 75% in tumor cells with moderate-to-strong membranous staining.Overall CLDN18.2 positivity was 4.1% (21/515) in the TOC centers and 3.6% (18/498) in their peripheries. In primaries of mucinous tubo-ovarian carcinoma (MTOC), CLDN18.2 positivity rates were 45% (18/40) and 36.6% (15/41), respectively. Positivity rates for the corresponding metastases were 33% (4/12, center) and 27% (3/11, periphery). The expression was relatively homogenous throughout all tumor sites. With no expression in 99.5% of nonmucinous tumors, CLDN18.2 positivity was almost exclusively seen in the mucinous subtype.In tubo-ovarian carcinoma, CLDN18.2 expression was, with rare exceptions, restricted to the mucinous subtype. Among them, 33% of metastasized MTOCs presented with CLDN18.2 positivity. Hence, CLDN18.2 might display a promising target for personalized therapy in patients with advanced MTOC.

Chronic Inhalation Exposure to Antimony Trioxide Exacerbates the MAPK Signaling in Alveolar Bronchiolar Carcinomas in B6C3F1/N Mice

Antimony trioxide (AT) is used as a flame retardant in fabrics and plastics. Occupational exposure in miners and smelters is mainly through inhalation and dermal contact. Chronic inhalation exposure to AT particulates in B6C3F1/N mice and Wistar Han rats resulted in increased incidences and tumor multiplicities of alveolar/bronchiolar carcinomas (ABCs). In this study, we demonstrated Kras (43%) and Egfr (46%) hotspot mutations in mouse lung tumors (n = 80) and only Egfr (50%) mutations in rat lung tumors (n = 26). Interestingly, there were no differences in the incidences of these mutations in ABCs from rats and mice at exposure concentrations that did and did not exceed the pulmonary overload threshold. There was increased expression of p44/42 mitogen-activated protein kinase (MAPK) (Erk1/2) protein in ABCs harboring mutations in Kras and/or Egfr, confirming the activation of MAPK signaling. Transcriptomic analysis indicated significant alterations in MAPK signaling such as ephrin receptor signaling and signaling by Rho-family GTPases in AT-exposed ABCs. In addition, there was significant overlap between transcriptomic data from mouse ABCs due to AT exposure and human pulmonary adenocarcinoma data. Collectively, these data suggest chronic AT exposure exacerbates MAPK signaling in ABCs and, thus, may be translationally relevant to human lung cancers.

Potential roles of claudin-3 and claudin-4 in ovarian cancer management

BACKGROUND

Ovarian cancer has the highest mortality amongst all gynaecological malignancies, with around two-thirds of patients diagnosed with advanced disease due to late presentation. Furthermore, around 90% of patients develop recurrence and eventually become chemoresistant. Therefore, there is a high demand to identify biomarkers specific to this disease for screening for early detection, as well as new therapeutic targets. Tight junctions (TJs) regulate paracellular permeability and are vital in establishing epithelial cell polarity. One hallmark of tumorigenesis is the loss of TJs, with loss of cell-to-cell adhesion. Claudins are integral TJ membrane proteins, which have been found to play a critical role in maintaining the TJ's barrier function. Furthermore, claudin-3 (CLDN3) and claudin-4 (CLDN4) are overexpressed in ovarian cancer. This article aims to explore the biological role of CLDN3 and CLDN4 and their potential in different aspects of the management of ovarian cancer.

MAIN BODY

CLDN3 and CLDN4 have been shown to be effective markers for the early detection of ovarian cancer. Whilst there is difficulty in screening for both claudins in serum, their assessment by gene expression analysis and immunohistochemical methods shows promising potential as diagnostic and prognostic biomarkers for ovarian cancer. The localisation and overexpression of claudins, such as CLDN3, have been shown to correlate with poorer survival outcomes. The added value of combining claudins with other markers such as CA125 for diagnosis has also been highlighted. Therapeutically, CLDN3 and more so CLDN4 have been shown to be effective targets of Clostridium perfringens enterotoxin (CPE). Interestingly, CPE has also been shown to resensitise chemoresistant tumours to therapy.

CONCLUSIONS

This review presents the diagnostic and prognostic potential of CLDN3 and CLDN4 and their emerging role as therapeutic targets in ovarian cancer. Clinical trials are required to validate the promising results of the in vitro and in vivo studies for CLDN3 and CLDN4, possibly adding onto current ovarian cancer management.

Targeting claudins in cancer: diagnosis, prognosis and therapy

Increasing evidence has linked claudins to signal transduction and tumorigenesis. The expression of claudins is frequently dysregulated in the context of neoplastic transformation, suggesting their promise as biomarkers for diagnosis and prognosis or targets for treatment. Claudin binders (Clostridium perfringens enterotoxin and monoclonal antibody) have been tested in preclinical experiments, and some of them have progressed into clinical trials involving patients with certain cancers. However, the clinical development of many of these agents has not advanced to clinical applications. Herein, I review the current status of preclinical and clinical investigations of agents targeting claudins for diagnosis, prognosis and therapy. I also discuss the potential of combining claudin binders with other currently approved therapeutic agents.

Claudins as biomarkers of differential diagnosis and prognosis of tumors

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

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

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

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.

Claudins: New Players in Human Fertility and Reproductive System Cancers

Claudins are major integral proteins of tight junctions (TJs), the apical cell-cell adhesions that enable maintaining polarity of epithelial cells, their differentiation, and cell signaling. A number of studies have indicated that claudins might play a crucial role in both physiology and pathogenesis. Their tissue-specific expression was originally linked to the development of different types of cancer and triggered a hope to use them as diagnostic or prognostic markers. However, it seems that their expression is more complex than that, and undoubtedly, claudins participate in one of the most important molecular events in cells. This review summarizes the recent research evaluating the role of claudins in fertility and the most common endocrine-dependent cancers in the reproductive system and highlights the crucial role of claudins both in human fertility and the most common cancers.

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.

Epigenetic Biomarkers in the Management of Ovarian Cancer: Current Prospectives

Ovarian cancer (OC) causes significant morbidity and mortality as neither detection nor screening of OC is currently feasible at an early stage. Difficulty to promptly diagnose OC in its early stage remains challenging due to non-specific symptoms in the early-stage of the disease, their presentation at an advanced stage and poor survival. Therefore, improved detection methods are urgently needed. In this article, we summarize the potential clinical utility of epigenetic signatures like DNA methylation, histone modifications, and microRNA dysregulation, which play important role in ovarian carcinogenesis and discuss its application in development of diagnostic, prognostic, and predictive biomarkers. Molecular characterization of epigenetic modification (methylation) in circulating cell free tumor DNA in body fluids offers novel, non-invasive approach for identification of potential promising cancer biomarkers, which can be performed at multiple time points and probably better reflects the prevailing molecular profile of cancer. Current status of epigenetic research in diagnosis of early OC and its management are discussed here with main focus on potential diagnostic biomarkers in tissue and body fluids. Rapid and point of care diagnostic applications of DNA methylation in liquid biopsy has been precluded as a result of cumbersome sample preparation with complicated conventional methods of isolation. New technologies which allow rapid identification of methylation signatures directly from blood will facilitate sample-to answer solutions thereby enabling next-generation point of care molecular diagnostics. To date, not a single epigenetic biomarker which could accurately detect ovarian cancer at an early stage in either tissue or body fluid has been reported. Taken together, the methodological drawbacks, heterogeneity associated with ovarian cancer and non-validation of the clinical utility of reported potential biomarkers in larger ovarian cancer populations has impeded the transition of epigenetic biomarkers from lab to clinical settings. Until addressed, clinical implementation as a diagnostic measure is a far way to go.

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.

High-level cytoplasmic claudin 3 expression is an independent predictor of poor survival in triple-negative breast cancer

Background

The subtype of claudin-low breast cancer can be reliably determined only by gene-expression profiling. Attempts have been made to develop immunohistochemical surrogates, which nearly always focus on membranous claudin expression.

Methods

We assessed the immunohistochemical expression of both membranous and cytoplasmic claudins 3, 4 and 7 in a series of 197 non-metastatic breast cancers, enriched with triple-negative breast cancers (TNBCs; 60%). The expression of epithelial-to-mesenchymal transition-regulating transcription factors Sip1, Zeb1 and vimentin had previously been determined in the same material.

Results

In multivariate analysis, strong cytoplasmic claudin 3 expression was associated with poor relapse-free survival (RFS), disease-free survival, distant disease-free survival, breast cancer-specific survival and overall survival among TNBC patients (for RFS, RR 5.202, 95% CI 1.210–22.369, p = 0.027, vs. T-class, RR 0.663, 95% CI 0.168–2.623, p = 0.558, and N-class, RR 3.940, 95% CI 0.933–16.631, p = 0.062). Cytoplasmic claudin 3 expression was also associated with strong nuclear Sip1 expression (p = 0.000053), TNBC phenotype (p = 0.012) and within them, non-basal-like phenotype (p = 0.026). Cytoplasmic claudin 7 was associated with dismal RFS (RR 6.328, 95% CI 1.401–28.593, p = 0.016, vs. T-class, RR 0.692, 95% CI 0.242–1.982, p = 0.493, and N-class, RR 2.981, 95% CI 1.1016–8.749, p = 0.047). Low cytoplasmic expression of claudins 3, 4 and 7 together also predicted poor RFS (RR 6.070, 95% CI 1.347–27.363, p = 0.019, vs. T-class, RR 0.677, 95% CI 0.237–1.934, p = 0.467, and N-class, RR 3.167, 95% CI 1.079–9.290, p = 0.036).

Conclusions

Immunohistochemical expression levels of cytoplasmic claudins 3 and 7 appear to be novel prognostic factors in TNBC.

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

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

Prognosis genes in gastric adenocarcinoma identified by cross talk genes in disease‑related pathways

The aim of the present study was to investigate the prognostic value of genes that participate in the development of gastric adenocarcinoma, via exploring gene cross talk in disease-related pathways. Differentially expressed genes (DEGs) in the gastric samples were identified by analyzing the expression data downloaded from the GEO database. The DEGs were subjected to the human protein-protein interaction (PPI) network to construct the PPI network of DEGs, which was then used for the identification of key genes in cancer samples via the expression deviation score and degree in the network. A total of 635 DEGs, including 432 downregulated and 203 upregulated ones were screened in the gastric adenocarcinomas samples. The PPI network of DEGs comprised 590 DEGs and 4,299 interaction pairs. A total of 200 key genes were obtained, which were significantly enriched in six downregulated and six upregulated pathways. Cross talk genes in the connected pathways were analyzed, and the Kyoto Encyclopedia of Genes and Genomes pathways hsa00980 (Metabolism of xenobiotics by cytochrome P450) and hsa00982 (Drug metabolism) were reported to share 8 cross talk genes: ADH7, ALDH3A1, GSTA1, GSTA2, UGT2B17, UGT2B10, ADH1B and CYP2C18. Among all cross talk genes, ADH7, ALDH3A1 and CLDN3 were the most specific genes. The high- and low-risk samples identified by the prognosis model presented a remarkable difference in total survival time, indicating its robustness and sensitivity as the prognosis genes for gastric adenocarcinoma. ADH7, ALDH3A1, GSTA1, GSTA2, UGT2B17, UGT2B10, ADH1B, CYP2C18ADH7, ALDH3A1 and CLDN3 may be used as the prognosis markers and target biomarkers for chemotherapies in gastric adenocarcinoma.

SCF/C-Kit/JNK/AP-1 Signaling Pathway Promotes Claudin-3 Expression in Colonic Epithelium and Colorectal Carcinoma

Claudin-3 is a major protein of tight junctions (TJs) in the intestinal epithelium and is critical for maintaining cell-cell adhesion, barrier function, and epithelium polarity. Recent studies have shown high claudin-3 levels in several solid tumors, but the regulation mechanism of claudin-3 expression remains poorly understood. In the present study, colorectal cancer (CRC) tissues, HT-29 and DLD-1 CRC cell lines, CRC murine model (C57BL/6 mice) and c-kit loss-of-function mutant mice were used. We demonstrated that elevated claudin-3 levels were positively correlated with highly expressed c-kit in CRC tissues based upon analysis of protein expression. In vitro, claudin-3 expression was clearly increased in CRC cells by overexpressed c-kit or stimulated by exogenous recombinant human stem cell factor (rhSCF), while significantly decreased by the treatment with c-kit or c-Jun N-terminal kinase (JNK) inhibitors. Chromatin immunoprecipitation (ChIP) and luciferase reporter assay showed that SCF/c-kit signaling significantly promoted activator protein-1 (AP-1) binding with CLDN-3 promoter and enhanced its transcription activity. Furthermore, decreased expression of claudin-3 was obtained in the colonic epithelium from the c-Kit loss-of-function mutant mice. In conclusion, SCF/c-kit-JNK/AP-1 signaling pathway significantly promoted claudin-3 expression in colonic epithelium and CRC, which could contribute to epithelial barrier function maintenance and to CRC development.

Paradigms lost-an emerging role for over-expression of tight junction adhesion proteins in cancer pathogenesis

Tight junctions (TJ) are multi-protein complexes located at the apicalmost tip of the lateral membrane in polarised epithelial and endothelial cells. Their principal function is in mediating intercellular adhesion and polarity. Accordingly, it has long been a paradigm that loss of TJ proteins and consequent deficits in cell-cell adhesion are required for tumour cell dissemination in the early stages of the invasive/metastatic cascade. However it is becoming increasingly apparent that TJ proteins play important roles in not just adhesion but also intracellular signalling events, activation of which can contribute to, or even drive, tumour progression and metastasis. In this review, we shall therefore highlight cases wherein the gain of TJ proteins has been associated with signals promoting tumour progression. We will also discuss the potential of overexpressed TJ proteins to act as therapeutic targets in cancer treatment. The overall purpose of this review is not to disprove the fact that loss of TJ-based adhesion contributes to the progression of several cancers, but rather to introduce the growing body of evidence that gain of TJ proteins may have adhesion-independent consequences for promoting progression in other cancers.

Androgen-dependent sertoli cell tight junction remodeling is mediated by multiple tight junction components

Sertoli cell tight junctions (SCTJs) of the seminiferous epithelium create a specialized microenvironment in the testis to aid differentiation of spermatocytes and spermatids from spermatogonial stem cells. SCTJs must be chronically broken and rebuilt with high fidelity to allow the transmigration of preleptotene spermatocytes from the basal to adluminal epithelial compartment. Impairment of androgen signaling in Sertoli cells perturbs SCTJ remodeling. Claudin (CLDN) 3, a tight junction component under androgen regulation, localizes to newly forming SCTJs and is absent in Sertoli cell androgen receptor knockout (SCARKO) mice. We show here that Cldn3-null mice do not phenocopy SCARKO mice: Cldn3(-/-) mice are fertile, show uninterrupted spermatogenesis, and exhibit fully functional SCTJs based on imaging and small molecule tracer analyses, suggesting that other androgen-regulated genes must contribute to the SCARKO phenotype. To further investigate the SCTJ phenotype observed in SCARKO mutants, we generated a new SCARKO model and extensively analyzed the expression of other tight junction components. In addition to Cldn3, we identified altered expression of several other SCTJ molecules, including down-regulation of Cldn13 and a noncanonical tight junction protein 2 isoform (Tjp2iso3). Chromatin immunoprecipitation was used to demonstrate direct androgen receptor binding to regions of these target genes. Furthermore, we demonstrated that CLDN13 is a constituent of SCTJs and that TJP2iso3 colocalizes with tricellulin, a constituent of tricellular junctions, underscoring the importance of androgen signaling in the regulation of both bicellular and tricellular Sertoli cell tight junctions.

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.

Claudin 1 expression characterizes human uterine cervical reserve cells

Stem cells participate in cervical carcinogenesis but their function and exact features are still not clear. One type of stem-like cells are endocervical reserve cells (RCs), and their association with other normal/altered cervical cells is not exactly known. Epithelial cells are attached to each other by tight junctions. Their dominant components are the claudin proteins, which show changed expression in cancer; however, no data are available on their pattern. Expressions of various claudins (1, 2, 3, 4, 7), occludin, cytokeratins 5/6 and 7, and p63 were analyzed in 60 paraffin-embedded cervical samples. Immunohistochemical reactions were evaluated semiquantitatively and statistically. Claudin 1 was as high in RCs as in cervical intraepithelial neoplasia (CIN) and higher than in suprabasal squamous epithelial cells, contrary to the negative glandular and squamous basal cells. Claudin 2 was positive in all cell types except parabasal cells, whereas claudins 4 and 7 were weakly positive and claudin 3 was negative in all cell types. Occludin was positive in RCs, basal/parabasal cells, and CIN, whereas glandular cells were negative. This is a first report that describes the intermediate claudin pattern of RCs, demonstrating that it differs from that of cervical glandular and squamous basal cells, but showing an expression similar to the strong claudin 1 expression detected in cervical neoplastic cells.

Regulation of the Epithelial-Mesenchymal Transition by Claudin-3 and Claudin-4

The mechanisms that control intracellular adhesion are central to the process of invasion and metastasis. Claudin-3 (CLDN3) and claudin-4 (CLDN4) are major structural molecules of the tight junctions that link epithelial cells. Our prior work has demonstrated that knockdown of the expression of either CLDN3 or CLDN4 produces marked changes in the phenotype of ovarian carcinoma cells including increases in growth rate in vivo, migration, invasion, metastasis, and drug resistance, similar to those produced by the epithelial-to-mesenchymal transition (EMT). We postulated that these changes may result from the ability of CLDN3 or CLDN4 to suppress EMT. In this study we found that knockdown of either CLDN3 or CLDN4 increased cell size and resulted in flattened morphology. While knockdown of CLDN3 or CLDN4 did not alter the expression of vimentin, it significantly down-regulated the level of E-cadherin and up-regulated N-cadherin expression. Conversely, over-expression of CLDN3 or CLDN4 in a cell line that does not express endogenous CLDN3 or CLDN4 decreased N-cadherin expression. Re-expression of E-cadherin in the CLDN3 or CLDN4 knockdown cells reduced migration, invasion and tumor growth in vivo. Loss of either CLDN3 or CLDN4 resulted in activation of the PI3K pathway as evidenced by increased Akt phosphorylation, elevated cellular PIP3 content and PI3K activity as well as up-regulation of the mRNA and protein levels of the transcription factor Twist. Taken together, these findings suggest that CLDN3 and CLDN4 function to sustain an epithelial phenotype and that their loss promotes EMT.

Claudins overexpression in ovarian cancer: potential targets for Clostridium Perfringens Enterotoxin (CPE) based diagnosis and therapy

Claudins are a family of tight junction proteins regulating paracellular permeability and cell polarity with different patterns of expression in benign and malignant human tissues. There are approximately 27 members of the claudin family identified to date with varying cell and tissue-specific expression. Claudins-3, -4 and -7 represent the most highly differentially expressed claudins in ovarian cancer. While their exact role in ovarian tumors is still being elucidated, these proteins are thought to be critical for ovarian cancer cell invasion/dissemination and resistance to chemotherapy. Claudin-3 and claudin-4 are the natural receptors for the Clostridium perfringens enterotoxin (CPE), a potent cytolytic toxin. These surface proteins may therefore represent attractive targets for the detection and treatment of chemotherapy-resistant ovarian cancer and other aggressive solid tumors overexpressing claudin-3 and -4 using CPE-based theranostic agents.

Tight junction proteins claudin-3 and claudin-4 control tumor growth and metastases

The extent of tight junction (TJ) formation is one of many factors that regulate motility, invasion, and metastasis. Claudins are required for the formation and maintenance of TJs. Claudin-3 (CLDN3) and claudin-4 (CLDN4) are highly expressed in the majority of ovarian cancers. We report here that CLDN3 and CLDN4 each serve to constrain the growth of human 2008 cancer xenografts and limit metastatic potential. Knockdown of CLDN3 increased in vivo growth rate by 2.3-fold and knockdown of CLDN4 by 3.7-fold in the absence of significant change in in vitro growth rate. Both types of tumors exhibited increase in birth rate as measured by Ki67 staining and decrease in death rate as reflected by terminal deoxynucleotidyl transferase dUTP nick end labeling (TUNEL) staining. Knockdown of either claudin did not alter expression of other TJ protein but did reduce TJ formation as measured by transepithelial resistance and paracellular flux of dextran, enhance migration and invasion in in vitro assays, and increase lung colonization following intravenous injection. Knockdown of CLDN3 and CLDN4 increased total lung metastatic burden by 1.7-fold and 2.4-fold, respectively. Loss of either CLDN3 or CLDN4 resulted in down-regulation of E-cadherin mRNA and protein, increased inhibitory phosphorylation of glycogen synthase kinase-3β (GSK-3β), and activation of β-catenin pathway signaling as evidenced by increases in nuclear β-catenin, the dephosphorylated form of the protein, and transcriptional activity of β-catenin/T-cell factor (TCF). We conclude that both CLDN3 and CLDN4 mediate interactions with other cells in vivo that restrain growth and metastatic potential by sustaining expression of E-cadherin and limiting β-catenin signaling.

Claudin expression in high-grade invasive ductal carcinoma of the breast: correlation with the molecular subtype

Claudin proteins are a major component of the tight junctions. Dysregulation of claudin protein expression has been described in a number of malignancies. Gene expression profiling has stratified breast cancers into distinct molecular subtypes: luminal, HER2 positive (HER2+), and basal-like. Recently, a novel claudin-low molecular subtype has been described. In this study, we correlated the expression patterns of claudins with the molecular subtypes of breast cancer. On the basis of immunohistochemical expression, 226 grade 3 invasive ductal carcinomas were stratified into 65 luminal (estrogen receptor positive (ER+)), 65 HER2+, 86 basal-like, including 14 metaplastic carcinomas (ER-, HER2-, CK5/6, and/or epidermal growth factor receptor positive), and 10 unclassified. Tissue microarrays were analyzed for the expression of claudins 1, 3, 4, 7, and 8 by immunohistochemistry and scored semiquantitatively. High levels of expression were detected in 17% of all cases for claudin 1, 32% claudin 3, 41% claudin 4, 44% claudin 7, and 40% claudin 8. Luminal cancers exhibited increased claudins 7 and 8; basal-like tumors demonstrated increased expression of claudins 1 and 4. Low expression of all five claudins was detected in 30 of 226 cases (13%) and this group was designated 'claudin-low'. The majority of the claudin-low subgroup were basal-like cancers (23 of 30, 77%). In contrast, only 1 of 30 (3%) claudin-low tumors was of the luminal phenotype and 6 of 30 cases (20%) were HER2+ (P<0.001). Within the basal-like subgroup, 64% of the metaplastic and 19% of the non-metaplastic tumors were claudin-low. The claudin-low group was strongly associated with disease recurrence (P=0.0093). In conclusion, this study is the first to examine comprehensively the differential expression of claudins 1, 3, 4, 7, and 8 in the molecular subtypes of high-grade breast cancer. Claudin-low subtype is a frequent phenomenon in metaplastic and basal-like breast cancer and appears to be a strong predictor of disease recurrence.

Prognostic biomarkers in ovarian cancer

Epithelial ovarian cancer (EOC) remains the most lethal gynecological malignancy despite several decades of progress in diagnosis and treatment. Taking advantage of the robust development of discovery and utility of prognostic biomarkers, clinicians and researchers are developing personalized and targeted treatment strategies. This review encompasses recently discovered biomarkers of ovarian cancer, the utility of published prognostic biomarkers for EOC (especially biomarkers related to angiogenesis and key signaling pathways), and their integration into clinical practice.

Epithelial-mesenchymal transition in ovarian carcinoma

Ovarian cancer is the most lethal gynecologic malignancy, with the majority of patients dying within 5 years of diagnosis. This poor survival of patients diagnosed with this malignancy is attributed to diagnosis at advanced stage, when the tumor has metastasized, and to chemotherapy resistance, either primary or developing along tumor progression. However, ovarian carcinomas, constituting the vast majority of ovarian cancers, additionally have unique biology, one aspect of which is the ability to co-express epithelial and mesenchymal determinants. epithelial–mesenchymal transition (EMT), a physiological process by which mesenchymal cells are formed and migrate to target organs during embryogenesis, is involved in cancer cell invasion and metastasis. However, these changes do not fully occur in ovarian carcinoma, and are even reversed in tumor cells present in malignant peritoneal and pleural effusions. This review summarizes current knowledge in this area, including the characteristics of EMT related to adhesion, transcriptional regulation and chemoresistance, and their clinical relevance, as well as the recently observed regulation of EMT by microRNA.

Expression of claudin 10 protein in hepatocellular carcinoma: impact on survival

PURPOSE

To investigate the expression of claudin 10 in hepatocellular carcinoma (HCC) and the impact on angiogenesis and the postoperative survival of HCC patients.

METHODS

The expression of claudin 10 protein was analyzed on samples from 99 HCC patients undergoing hepatectomy with immunohistochemistry and 31 fresh specimens with Western blotting. We examined the relationship between claudin 10 expression with clinicopathological factors, microvessel density (MVD), and postoperative survival.

RESULTS

Western blotting and immunohistochemical staining showed that claudin 10 protein was highly expressed in HCC, compared with paraneoplastic liver tissue and normal liver tissue (P < 0.01). Claudin 10 protein expression levels were significantly higher in HCC specimens with microscopic venous invasion (P < 0.01). MVD in HCC increased with enhanced claudin 10 expression (P < 0.01). Kaplan-Meier survival analysis revealed that HCC patients with high claudin 10 expression had significantly shorter overall survival (P = 0.01). Multivariate analysis showed that claudin 10 expression was an independent prognostic indicator for postoperative overall survival of HCC patients (P < 0.01).

CONCLUSIONS

Claudin 10 protein is highly expressed in HCC tissue and is closely related to angiogenesis. Claudin 10 protein could be a useful marker to predict poor prognosis of HCC patients after hepatectomy.

Translational application of epigenetic alterations: ovarian cancer as a model

Cancer is a disease initiated and driven by the accumulation and interplay of genetic and epigenetic mutations of genes involved in the regulation of cell growth and signaling. Dysregulation of these genes and pathways in a cell leads to a growth advantage and clonal expansion. The epigenetic alterations involved in the initiation and progression of cancer are DNA methylation and histone modifications which interact to remodel chromatin, as well as RNA interference. These alterations can be used as candidate targets in molecular tests for risk, early detection, prognosis, prediction of response to therapy, and monitoring, as well as new therapeutic targets in cancer. In this review, we discuss the rationale, studies to date, and issues in the translational application of epigenetics using epithelial ovarian cancer as a specific example of all types of cancer.

Immunohistochemical profiles of claudin-3 in primary and metastatic prostatic adenocarcinoma

Background

Claudins are integral membrane proteins that are involved in forming cellular tight junctions. One member of the claudin family, claudin-3, has been shown to be overexpressed in breast, ovarian, and pancreatic cancer. Here we use immunohistochemistry to evaluate its expression in benign prostatic hyperplasia (BPH), prostatic intraepithelial neoplasia (PIN), normal tissue adjacent to prostatic adenocarcinoma (NAC), primary prostatic adenocarcinoma (PCa), and metastatic prostatic adenocarcinoma (Mets).

Methods

Tissue microarrays were immunohistochemically stained for claudin-3, with the staining intensities subsequently quantified and statistically analyzed using a one-way ANOVA with subsequent Tukey tests for multiple comparisons or a nonparametric equivalent. Fifty-three cases of NAC, 17 cases of BPH, 35 cases of PIN, 107 cases of PCa, and 55 cases of Mets were analyzed in the microarrays.

Results

PCa and Mets had the highest absolute staining for claudin-3. Both had significantly higher staining than BPH (p < 0.05 in both cases) and NAC (p < 0.05 in both cases). PIN had a lower, but non-significant, staining score than PCa and Mets, but a statistically higher score than both BPH and NAC (p < 0.05 for both cases). No significant differences were observed between PCa, Mets, and PIN.

Conclusions

To our knowledge, this represents one of the first studies comparing the immunohistochemical profiles of claudin-3 in PCa and NAC to specimens of PIN, BPH, and Mets. These findings provide further evidence that claudin-3 may serve as an important biomarker for prostate cancer, both primary and metastatic, but does not provide evidence that claudin-3 can be used to predict risk of metastasis.

Derepression of CLDN3 and CLDN4 during ovarian tumorigenesis is associated with loss of repressive histone modifications

Unlike epigenetic silencing of tumor suppressor genes, the role of epigenetic derepression of cancer-promoting genes or oncogenes in carcinogenesis remains less well understood. The tight junction proteins claudin-3 and claudin-4 are frequently overexpressed in ovarian cancer and their overexpression was previously reported to promote the migration and invasion of ovarian epithelial cells. Here, we show that the expression of claudin-3 and claudin-4 is repressed in ovarian epithelial cells in association with promoter ‘bivalent’ histone modifications, containing both the activating trimethylated histone H3 lysine 4 (H3K4me3) mark and the repressive mark of trimethylated histone H3 lysine 27 (H3K27me3). During ovarian tumorigenesis, derepression of CLDN3 and CLDN4 expression correlates with loss of H3K27me3 in addition to trimethylated histone H4 lysine 20 (H4K20me3), another repressive histone modification. Although CLDN4 repression was accompanied by both DNA hypermethylation and repressive histone modifications, DNA methylation was not required for CLDN3 repression in immortalized ovarian epithelial cells. Moreover, activation of both CLDN3 and CLDN4 in ovarian cancer cells was associated with simultaneous changes in multiple histone modifications, whereas H3K27me3 loss alone was insufficient for their derepression. CLDN4 repression was robustly reversed by combined treatment targeting both DNA demethylation and histone acetylation. Our study strongly suggests that in addition to the well-known chromatin-associated silencing of tumor suppressor genes, epigenetic derepression by the conversely related loss of repressive chromatin modifications also contributes to ovarian tumorigenesis via activation of cancer-promoting genes or candidate oncogenes.

Possible angiogenic roles for claudin-4 in ovarian cancer

Claudin proteins are frequently overexpressed in various tumors such as breast, prostate and ovarian cancer. While their functions in cancer have not been completely elucidated, roles in survival, adhesion and invasion have been suggested. In order to clarify the roles of claudins in ovarian cancer, we have performed gene expression profiling of ovarian surface epithelial cells overexpressing claudin-4 and compared the expression patterns to the parental, non-expressing cells. Claudin-4 expression leads to the differential expression of several genes, including many that have previously been implicated in angiogenesis. In particular, angiogenic cytokines, such as IL-8, were found elevated while genes of the angiostatic interferon pathway were found downregulated. In vitro assays show that claudin-4-expressing cells produce factors that can stimulate angiogenesis as measured by tube formation and migration in HUVEC cells. In addition, an in vivo mouse dorsal skinfold assay confirms that cells expressing claudin-4 secrete factors that can mediate angiogenesis in the dorsal skin of mice. Our data suggest a novel function for claudin-4 in cancer and provide an additional rationale for its common overexpression in human tumors.

Claudin-containing exosomes in the peripheral circulation of women with ovarian cancer

Background

The absence of highly sensitive and specific serum biomarkers makes mass screening for ovarian cancer impossible. The claudin proteins are frequently overexpressed in ovarian cancers, but their potential as prognostic, diagnostic, or detection markers remains unclear. Here, we have explored the possible use of these proteins as screening biomarkers for ovarian cancer detection.

Methods

Claudin protein shedding from cells was examined by immunoblotting of conditioned culture media. The presence of claudins in exosomes released from ovarian cancer cells was demonstrated by sucrose gradient separation and immunogold electron microscopy experiments. Claudin-4-containing exosomes in the plasma of ovarian cancer patients were evaluated in a pilot panel of 63 ovarian cancer patients and 50 healthy volunteers. The CA125 marker was also assessed in these samples and compared with claudin-4 positivity.

Results

We show that full-length claudins can be shed from ovarian cancer cells in culture and found in the media as part of small lipid vesicles known as exosomes. Moreover, 32 of 63 plasma samples from ovarian cancer patients exhibited the presence of claudin-4-containing exosomes. In contrast, only one of 50 samples from individuals without cancer exhibited claudin-4-positive exosomes. In our small panel, at a specificity of 98%, the claudin-4 and CA125 tests had sensitivities of 51% and 71%, respectively. The two tests did not appear to be independent and were strongly correlated.

Conclusion

Our work shows for the first time that claudin-4 can be released from ovarian cancer cells and can be detected in the peripheral circulation of ovarian cancer patients. The development of sensitive assays for the detection of claudin-4 in blood will be crucial in determining whether this approach can be useful, alone or in combination with other screening methods, for the detection of ovarian cancer.

Microarray analysis of RNA extracted from formalin-fixed, paraffin-embedded and matched fresh-frozen ovarian adenocarcinomas

Background

Gene expression profiling of formalin-fixed, paraffin-embedded (FFPE) samples represents a valuable approach for advancing oncology diagnostics and enhancing retrospective clinical studies; however, at present, this methodology still requires optimization and thus has not been extensively used. Here, we utilized thorough quality control methods to assess RNA extracted from FFPE samples and then compared it to RNA extracted from matched fresh-frozen (FF) counterparts. We preformed genome-wide expression profiling of FF and FFPE ovarian serous adenocarcinoma sample pairs and compared their gene signatures to normal ovary samples.

Methods

RNA from FFPE samples was extracted using two different methods, Ambion and Agencourt, and its quality was determined by profiling starting total RNA on Bioanalyzer and by amplifying increasing size fragments of beta actin (ACTB) and claudin 3 (CLDN3) by reverse-transcriptase polymerase chain reaction. Five matched FF and FFPE ovarian serous adenocarcinoma samples, as well as a set of normal ovary samples, were profiled using whole genome Agilent microarrays. Reproducibility of the FF and FFPE replicates was measured using Pearson correlation, whereas comparison between the FF and FFPE samples was done using a Z-score analysis.

Results

Data analysis showed high reproducibility of expression within each FF and FFPE method, whereas matched FF and FFPE pairs demonstrated lower similarity, emphasizing an inherent difference between the two sample types. Z-score analysis of matched FF and FFPE samples revealed good concordance of top 100 differentially expressed genes with the highest correlation of 0.84. Genes characteristic of ovarian serous adenocarcinoma, including a well known marker CLDN3, as well as potentially some novel markers, were identified by comparing gene expression profiles of ovarian adenocarcinoma to those of normal ovary.

Conclusion

Conclusively, we showed that systematic assessment of FFPE samples at the RNA level is essential for obtaining good quality gene expression microarray data. We also demonstrated that profiling of not only FF but also of FFPE samples can be successfully used to identify differentially expressed genes characteristic of ovarian carcinoma.

Genome profiling of ovarian adenocarcinomas using pangenomic BACs microarray comparative genomic hybridization

Background

Routine cytogenetic investigations for ovarian cancers are limited by culture failure and poor growth of cancer cells compared to normal cells. Fluorescence in situ Hybridization (FISH) application or classical comparative genome hybridization techniques are also have their own limitations in detecting genome imbalance especially for small changes that are not known ahead of time and for which FISH probes could not be thus designed.

Methods

We applied microarray comparative genomic hybridization (A-CGH) using one mega base BAC arrays to investigate chromosomal disorders in ovarian adenocarcinoma in patients with familial history.

Results

Our data on 10 cases of ovarian cancer revealed losses of 6q (4 cases mainly mosaic loss), 9p (4 cases), 10q (3 cases), 21q (3 cases), 22q (4 cases) with association to a monosomy X and gains of 8q and 9q (occurring together in 8 cases) and gain of 12p. There were other abnormalities such as loss of 17p that were noted in two profiles of the studied cases. Total or mosaic segmental gain of 2p, 3q, 4q, 7q and 13q were also observed. Seven of 10 patients were investigated by FISH to control array CGH results. The FISH data showed a concordance between the 2 methods.

Conclusion

The data suggest that A-CGH detects unique and common abnormalities with certain exceptions such as tetraploidy and balanced translocation, which may lead to understanding progression of genetic changes as well as aid in early diagnosis and have an impact on therapy and prognosis.