Claudin-1, -2, -3, -4, -7, -8, and -10 protein expression in biliary tract cancers

Tight junction proteins and biliary diseases

PURPOSE OF REVIEW

In the pathophysiological context of cholangiopathies and more broadly of hepatopathies, while it is conceptually clear that the maintenance of inter-cholangiocyte and inter-hepatocyte tight junction integrity would be crucial for liver protection, only scarce studies have been devoted to this topic. Indeed, in the liver, alteration of tight junctions, the intercellular adhesion complexes that control paracellular permeability would result in leaky bile ducts and bile canaliculi, allowing bile reflux towards hepatic parenchyma, contributing to injury during the disease process.

RECENT FINDINGS

Last decades have provided a great deal of information regarding both tight junction structural organization and signaling pathways related to tight junctions, providing clues about potential intervention to modulate paracellular permeability during cholangiopathies pathogenesis. Interestingly, several liver diseases have been reported to be associated with abnormal expression of one or several tight junction proteins. However, the question remains unanswered if these alterations would be primarily involved in the disease pathogenesis or if they would occur secondarily in the pathological course.

SUMMARY

In this review, we provide an overview of tight junction disruptions described in various biliary diseases that should pave the way for defining new therapeutic targets in this field.

CLDN1 Arg81His founder variant causes ichthyosis, leukocyte vacuoles, alopecia, and sclerosing cholangitis (ILVASC) syndrome in Moroccan Jews

Neonatal ichthyosis and sclerosing cholangitis syndrome (NISCH), also known as ichthyosis, leukocyte vacuoles, alopecia, and sclerosing cholangitis (ILVASC), is an extremely rare disease of autosomal recessive inheritance, resulting from loss of function of the tight junction protein claudin-1. Its clinical presentation is highly variable, and is characterized by liver and ectodermal involvement. Although most ILVASC cases described to date were attributed to homozygous truncating variants in CLDN1, a single missense variant CLDN1 p.Arg81His, associated with isolated skin ichthyosis phenotype, has been recently reported in a family of Moroccan Jewish descent. We now describe seven patients with ILVASC, originating from four non consanguineous families of North African Jewish ancestry (including one previously reported family), harboring CLDN1 p.Arg81His variant, and broaden the phenotypic spectrum attributed to this variant to include teeth, hair, and liver/bile duct involvement, characteristic of ILVASC. Furthermore, we provide additional evidence for pathogenicity of the CLDN1 p.Arg81His variant by transmission electron microscopy of the affected skin, revealing distorted tight junction architecture, and show through haplotype analysis in the vicinity of the CLDN1 gene, that this variant represents a founder variant in Jews of Moroccan descent with an estimated carrier frequency of 1:220.

Claudin-10 Expression Is Increased in Endometriosis and Adenomyosis and Mislocalized in Ectopic Endometriosis

Claudins, as the major components of tight junctions, are crucial for epithelial cell-to-cell contacts. Recently, we showed that in endometriosis, the endometrial epithelial phenotype is highly conserved, with only minor alterations. For example, claudin-11 is strongly expressed; however, its localization in the endometriotic epithelial cells was impaired. In order to better understand the role of claudins in endometrial cell-to-cell contacts, we analyzed the tissue expression and localization of claudin-10 by immunohistochemistry analysis and two scoring systems. We used human tissue samples (n = 151) from the endometrium, endometriosis, and adenomyosis. We found a high abundance of claudin-10 in nearly all the endometrial (98%), endometriotic (98−99%), and adenomyotic (90−97%) glands, but no cycle-specific differences and no differences in the claudin-10 positive endometrial glands between cases with and without endometriosis. A significantly higher expression of claudin-10 was evident in the ectopic endometrium of deep-infiltrating (p < 0.01) and ovarian endometriosis (p < 0.001) and in adenomyosis in the cases with endometriosis (p ≤ 0.05). Interestingly, we observed a shift in claudin-10 from a predominant apical localization in the eutopic endometrium to a more pronounced basal/cytoplasmic localization in the ectopic endometria of all three endometriotic entities but not in adenomyosis. Significantly, despite the impaired endometriotic localization of claudin-10, the epithelial phenotype was retained. The significant differences in claudin-10 localization between the three endometriotic entities and adenomyosis, in conjunction with endometriosis, suggest that most of the aberrations occur after implantation and not before. The high similarity between the claudin-10 patterns in the eutopic endometrial and adenomyotic glands supports our recent conclusions that the endometrium is the main source of endometriosis and adenomyosis.

Research progress of tight junction protein claudin-3 in hepatobiliary systemic diseases

Claudin-3 is an important member of the claudin family of tight junction proteins and is the most abundant tight junction protein in the hepatobiliary system. It plays an important role in building tight junctions of hepatobiliary cells, and maintaining cellular barrier function and molecular delivery function. Dysregulation of hepatic claudin-3 expression leads to disruption of hepatobiliary system junctions, metabolic function, barrier function, proliferation capacity, and molecular delivery function, and is closely related to the development of various hepatobiliary diseases such as hepatic malignancies, cholesterol stones, and chronic liver diseases. In this paper, we review the progress in the research of claudin-3 in hepatobiliary diseases.

Clinical relevance of biomarkers in cholangiocarcinoma: critical revision and future directions

Cholangiocarcinoma (CCA) is a malignant tumour arising from the biliary system. In Europe, this tumour frequently presents as a sporadic cancer in patients without defined risk factors and is usually diagnosed at advanced stages with a consequent poor prognosis. Therefore, the identification of biomarkers represents an utmost need for patients with CCA. Numerous studies proposed a wide spectrum of biomarkers at tissue and molecular levels. With the present paper, a multidisciplinary group of experts within the European Network for the Study of Cholangiocarcinoma discusses the clinical role of tissue biomarkers and provides a selection based on their current relevance and potential applications in the framework of CCA. Recent advances are proposed by dividing biomarkers based on their potential role in diagnosis, prognosis and therapy response. Limitations of current biomarkers are also identified, together with specific promising areas (ie, artificial intelligence, patient-derived organoids, targeted therapy) where research should be focused to develop future biomarkers.

Advanced Bile Duct Cancers: A Focused Review on Current and Emerging Systemic Treatments

Cancers arising in the biliary tract are rare, with varied incidence depending on geographical location. As clinical presentation is typically vague with non-specific symptoms, a large proportion of patients present with unresectable or metastatic disease at diagnosis. When unresectable, the mainstay of treatment is cytotoxic chemotherapy; however, despite this, 5-year overall survival remains incredibly poor. Diagnostic molecular pathology, using next-generation sequencing, has identified a high prevalence of targetable alterations in bile duct cancers, which is transforming care. Substantial genomic heterogeneity has been identified depending on both the anatomical location and etiology of disease, with certain alterations enriched for subtypes. In addition, immune checkpoint inhibitors with anti-PD-1/PD-L1 antibodies in combination with chemotherapy are now poised to become the standard first-line treatment option in this disease. Here, we describe the established role of cytotoxic chemotherapy, targeted precision treatments and immunotherapy in what is a rapidly evolving treatment paradigm for advanced biliary tract cancer.

Immunocytochemistry of effusions: Processing and commonly used immunomarkers

Definitive cytopathological interpretation of some of the effusion fluids may not be possible based on cytomorphological evaluation alone. As discussed in other reviews, this is due to various reasons specifically applicable to effusion fluids including remarkably wide morphologic spectrum of reactive mesothelial cells overlapping with some well to moderately differentiated metastatic carcinoma. The challenge is subject to various factors including level of interpreter training or experience, institutional demographics (such as type of prevalent diseases, predominant sex and age group), technical advances in ancillary support, and expertise in cytopreparatory processing. In such cases immunohistochemistry performed on cell-block sections is simple objective adjunct with or without other ancillary techniques. Ongoing increase in number of immunomarkers along with rabbit monoclonal antibodies with relatively higher affinity is further refining this field. SCIP (subtractive coordinate immunoreactivity pattern) approach, discussed as separate dedicated review article, facilitates refined interpretation of immunoreactivity pattern in coordinate manner on various serial sections of cell-blocks. However, many variables such as delay after specimen collection, specimen processing related factors including fixation and storage; ambient conditions under which paraffin blocks are archived (for retrospective testing); antigen retrieval method; duration of antigen retrieval step; antibody clone and dilution; and antibody application time are common with application of immunohistochemistry in other areas. This review is dedicated to highlight technical aspects including processing of effusion specimens for optimum immunocytochemical evaluation along with commonly used immunomarkers in effusion cytopathology. This review focuses on the technical and general information about various immunomarkers.

Role of Barrier Integrity and Dysfunctions in Maintaining the Healthy Gut and Their Health Outcomes

Mucosal surface layers are the critical borders throughout epithelial membranes. These epithelial cells segregate luminal material from external environments. However, mucosal linings are also accountable for absorbing nutrients and requiring specific barrier permeability. These functional acts positioned the mucosal epithelium at the epicenter of communications concerning the mucosal immune coordination and foreign materials, such as dietary antigens and microbial metabolites. Current innovations have revealed that external stimuli can trigger several mechanisms regulated by intestinal mucosal barrier system. Crucial constituents of this epithelial boundary are physical intercellular structures known as tight junctions (TJs). TJs are composed of different types transmembrane proteins linked with cytoplasmic adaptors which helps in attachment to the adjacent cells. Disruption of this barrier has direct influence on healthy or diseased condition, as barrier dysfunctions have been interrelated with the initiation of inflammation, and pathogenic effects following metabolic complications. In this review we focus and overview the TJs structure, function and the diseases which are able to influence TJs during onset of disease. We also highlighted and discuss the role of phytochemicals evidenced to enhance the membrane permeability and integrity through restoring TJs levels.

Dual β-Catenin and γ-Catenin Loss in Hepatocytes Impacts Their Polarity through Altered Transforming Growth Factor-β and Hepatocyte Nuclear Factor 4α Signaling

Hepatocytes are highly polarized epithelia. Loss of hepatocyte polarity is associated with various liver diseases, including cholestasis. However, the molecular underpinnings of hepatocyte polarization remain poorly understood. Loss of β-catenin at adherens junctions is compensated by γ-catenin and dual loss of both catenins in double knockouts (DKOs) in mice liver leads to progressive intrahepatic cholestasis. However, the clinical relevance of this observation, and further phenotypic characterization of the phenotype, is important. Herein, simultaneous loss of β-catenin and γ-catenin was identified in a subset of liver samples from patients of progressive familial intrahepatic cholestasis and primary sclerosing cholangitis. Hepatocytes in DKO mice exhibited defects in apical-basolateral localization of polarity proteins, impaired bile canaliculi formation, and loss of microvilli. Loss of polarity in DKO livers manifested as epithelial-mesenchymal transition, increased hepatocyte proliferation, and suppression of hepatocyte differentiation, which was associated with up-regulation of transforming growth factor-β signaling and repression of hepatocyte nuclear factor 4α expression and activity. In conclusion, concomitant loss of the two catenins in the liver may play a pathogenic role in subsets of cholangiopathies. The findings also support a previously unknown role of β-catenin and γ-catenin in the maintenance of hepatocyte polarity. Improved understanding of the regulation of hepatocyte polarization processes by β-catenin and γ-catenin may potentially benefit development of new therapies for cholestasis.

Multiplexed Imaging Strategy to Distinguish Indeterminant Biliary Strictures: An Ex Vivo Study

Introduction

Indeterminant biliary strictures can be either malignant or benign. Biliary intraepithelial neoplasia (BilIN) is the precursor lesion to cholangiocarcinoma, a deadly bile duct cancer. Current diagnostic methods are limited by inadequate amounts of cells and tissues collected.

Aim

We aim to demonstrate use of fluorescently-labeled peptides specific for EGFR, claudin-1, and ErbB2 to perform multiplexed imaging of biliary neoplasia.

Methods

Formalin fixed and paraffin embedded specimens resected from human biliary strictures were sectioned. A gastrointestinal pathologist used standard criteria to score immunohistochemistry from biliary neoplasia and adjacent normal epithelium from the same specimen. Peptides specific for EGFR, claudin-1, and ErbB2 were fluorescently-labeled with FITC, Cy5, and IRDye800, respectively. The fluorophores were chosen to provide spectral separation to distinguish the individual targets. Immuno fluorescence images were collected using confocal microscopy.

Results

Target expression was validated using immunohistochemistry. Staining was visualized on the surface of biliary duct epithelial cells and not in the stroma. Greater fluorescence intensity was observed for peptide binding to biliary neoplasia by comparison with normal. The mean ratio for neoplasia-to-normal was 1.4, 1.7, and 1.6, respectively, and the average intensities were significantly greater for neoplasia than normal for each peptide. Peptides and antibody binding co-localized with correlation of ρ=0.64, 0.51 and 0.62, respectively.

Conclusions

A panel of fluorescently-labeled peptides can distinguish BilIN and cholangiocarcinoma from normal biliary epithelium, and may be used for multiplexed imaging of indeterminant biliary strictures.

Genotoxic Effect of Salmonella Paratyphi A Infection on Human Primary Gallbladder Cells

Bacterial infections are increasingly being recognized as risk factors for the development of adenocarcinomas. The strong epidemiological evidence linking Helicobacter pylori infection to stomach cancer has paved the way to the demonstration that bacterial infections cause DNA damage in the host cells, initiating transformation. In this regard, the role of bacterial genotoxins has become more relevant. Salmonella enterica serovars Typhi and Paratyphi A have been clinically associated with gallbladder cancer. By harnessing the stem cell potential of cells from healthy human gallbladder explant, we regenerated and propagated the epithelium of this organ in vitro and used these cultures to model S. Paratyphi A infection. This study demonstrates the importance of the typhoid toxin, encoded only by these specific serovars, in causing genomic instability in healthy gallbladder cells, posing intoxicated cells at risk of malignant transformation.

Carcinoma of the gallbladder (GBC) is the most frequent tumor of the biliary tract. Despite epidemiological studies showing a correlation between chronic infection with Salmonella enterica Typhi/Paratyphi A and GBC, the underlying molecular mechanisms of this fatal connection are still uncertain. The murine serovar Salmonella Typhimurium has been shown to promote transformation of genetically predisposed cells by driving mitogenic signaling. However, insights from this strain remain limited as it lacks the typhoid toxin produced by the human serovars Typhi and Paratyphi A. In particular, the CdtB subunit of the typhoid toxin directly induces DNA breaks in host cells, likely promoting transformation. To assess the underlying principles of transformation, we used gallbladder organoids as an infection model for Salmonella Paratyphi A. In this model, bacteria can invade epithelial cells, and we observed host cell DNA damage. The induction of DNA double-strand breaks after infection depended on the typhoid toxin CdtB subunit and extended to neighboring, non-infected cells. By cultivating the organoid derived cells into polarized monolayers in air-liquid interphase, we could extend the duration of the infection, and we observed an initial arrest of the cell cycle that does not depend on the typhoid toxin. Non-infected intoxicated cells instead continued to proliferate despite the DNA damage. Our study highlights the importance of the typhoid toxin in causing genomic instability and corroborates the epidemiological link between Salmonella infection and GBC.

E7 oncoprotein from human papillomavirus 16 alters claudins expression and the sealing of epithelial tight junctions

Tight junctions (TJs) are cell-cell adhesion structures frequently altered by oncogenic transformation. In the present study the role of human papillomavirus (HPV) 16 E7 oncoprotein on the sealing of TJs was investigated and also the expression level of claudins in mouse cervix and in epithelial Madin-Darby Canine Kidney (MDCK) cells. It was found that there was reduced expression of claudins -1 and -10 in the cervix of 7-month-old transgenic K14E7 mice treated with 17β-estradiol (E₂), with invasive cancer. In addition, there was also a transient increase in claudin-1 expression in the cervix of 2-month-old K14E7 mice, and claudin-10 accumulated at the border of cells in the upper layer of the cervix in FvB mice treated with E₂, and in K14E7 mice treated with or without E₂. These changes were accompanied by an augmented paracellular permeability of the cervix in 2- and 7-monthold FvB mice treated with E₂, which became more pronounced in K14E7 mice treated with or without E₂. In MDCK cells the stable expression of E7 increased the space between adjacent cells and altered the architecture of the monolayers, induced the development of an acute peak of transepithelial electrical resistance accompanied by a reduced expression of claudins -1, -2 and -10, and an increase in claudin-4. Moreover, E7 enhances the ability of MDCK cells to migrate through a 3D matrix and induces cell stiffening and stress fiber formation. These observations revealed that cell transformation induced by HPV16 E7 oncoprotein was accompanied by changes in the pattern of expression of claudins and the degree of sealing of epithelial TJs.

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.

Epithelial Claudin Proteins and Their Role in Gastrointestinal Diseases

Our bodies are protected from the external environment by mucosal barriers that are lined by epithelial cells. The epithelium plays a critical role as a highly dynamic, selective semipermeable barrier that separates luminal contents and pathogens from the rest of the body and controlling the absorption of nutrients, fluid and solutes. A series of protein complexes including the adherens junction, desmosomes, and tight junctions function as the principal barrier in paracellular diffusion and regulators of intracellular solute, protein, and lipid transport. Tight junctions are composed of a series of proteins called occludins, junctional adhesion molecules, and claudins that reside primarily as the most apical intercellular junction. Here we will review one of these protein families, claudins, and their relevance to gastrointestinal and liver diseases.

Blood-Bile Barrier: Morphology, Regulation, and Pathophysiology

The term blood-bile barrier (BBlB) refers to the physical structure within a hepatic lobule that compartmentalizes and hence segregates sinusoidal blood from canalicular bile. Thus, this barrier provides physiological protection in the liver, shielding the hepatocytes from bile toxicity and restricting the mixing of blood and bile. BBlB is primarily composed of tight junctions; however, adherens junction, desmosomes, gap junctions, and hepatocyte bile transporters also contribute to the barrier function of the BBlB. Recent findings also suggest that disruption of BBlB is associated with major hepatic diseases characterized by cholestasis and aberrations in BBlB thus may be a hallmark of many chronic liver diseases. Several molecular signaling pathways have now been shown to play a role in regulating the structure and function and eventually contribute to regulation of the BBlB function within the liver. In this review, we will discuss the structure and function of the BBlB, summarize the methods to assess the integrity and function of BBlB, discuss the role of BBlB in liver pathophysiology, and finally, discuss the mechanisms of BBlB regulation. Collectively, this review will demonstrate the significance of the BBlB in both liver homeostasis and hepatic dysfunction.

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.

Cholangiocarcinoma: Classification, Histopathology and Molecular Carcinogenesis

Cholangiocarcinoma (CC) is the second most common tumor of the liver, originating from the biliary system with increasing incidence and mortality worldwide. Several new classifications review the significance of tumor localization, site of origin, proliferation and biomarkers in the intrahepatic, perihilar and distal forms of the lesion. Based on growth pattern mass-forming, periductal-infiltrating, intraductal, undefined and mixed types are differentiated. There are further subclassifications which are applied for the histological features, in particular for intrahepatic CC. Recognition of the precursors and early lesions of CC including biliary intraepithelial neoplasia (BilIN), intraductal papillary neoplasm of the bile ducts (IPNB), biliary mucinous cystic neoplasm (MCNB) and the candidate precursors, such as bile duct adenoma and von Meyenburg complex is of increasing significance. In addition to the previously used biliary markers detected by immunohistochemistry, several new markers have been added to the differentiation of both the benign and malignant lesions, which can be used to aid in the subclassification in association with the outcome of CC. Major aspects of biliary carcinogenesis have been revealed, yet, the exact way of this diverse process is still unclear. The factors contributing to molecular cholangiocarcinogenesis include various risk factors, different anatomical localizations, multiple cellular origins, genetic and epigenetic alterations, tumor microenvironment, heterogeneity and clonal evolution. Driver mutations have been identified, implying that they are optimal candidates for targeted therapy. The most promising therapeutic candidates have entered clinical trials.

Epithelial-to-mesenchymal transition in gallbladder cancer: from clinical evidence to cellular regulatory networks

Gallbladder cancer (GBC), with late diagnosis, rapid disease progression and early metastasis, is a highly aggressive malignant tumor found worldwide. Patients with GBC have poor survival, low curative resection rates and early recurrence. For such a lethal tumor, uncovering the mechanisms and exploring new strategies to prevent tumor progression and metastasis are critically important. Epithelial-to-mesenchymal transition (EMT) has a prominent role in the early steps of tumor progression and metastasis by initiating polarized epithelial cell transition into motile mesenchymal cells. Accumulating evidence suggests that EMT can be modulated by the cooperation of multiple mechanisms affecting common targets. Signaling pathways, transcriptional and post-transcriptional regulation and epigenetic alterations are involved in the stepwise EMT regulatory network in GBC. Loss of epithelial markers, acquisition of mesenchymal markers and dysregulation of EMT-inducing transcription factors (EMT-TFs) have been observed and are associated with the clinicopathology and prognosis of GBC patients. Therefore, EMT may be a detectable and predictable event for predicting GBC progression and metastasis in the clinic. In this review, we will provide an overview of EMT from the clinical evidence to cellular regulatory networks that have been studied thus far in clinical and basic GBC studies.

Claudin-2 Expression Levels in Ulcerative Colitis: Development and Validation of an In-Situ Hybridisation Assay for Therapeutic Studies

Ulcerative colitis is a chronic inflammatory disease affecting the colon and is characterized by epithelial damage and barrier dysfunction. Upregulation of the tight junction protein claudin-2 by cytokines is hypothesized to contribute to the dysregulation of the epithelial barrier. New therapeutic agents which block the action of cytokines are being investigated in patients with ulcerative colitis. In order to understand the potential of these therapies, it is important to have reliable assays that can assess downstream endpoints that reflect drug mechanism of action. The aim of the current study was therefore to establish & validate an assay to reproducibly assess the expression and distribution of claudin-2 in human colon biopsy samples. Initially, the potential to measure claudin-2 protein by immunohistochemistry (IHC) was investigated. To identify suitable reagents to develop an IHC assay, pre-established criteria were used to screen five commercial antibodies by Western blotting, immunofluorescence and immunohistochemistry on claudin-2 positive and negative cells and healthy and ulcerative colitis colon tissue. Despite some of these antibodies specifically detecting claudin-2 using some of these techniques, none of the antibodies showed the expected specific staining pattern in formalin fixed human colon samples. As an alternative method to detect claudin-2 expression and distribution in formalin fixed biopsy sections, an in situ hybridization assay was developed. This assay underwent a novel tiered approach of validation to establish that it was fit-for-purpose, and suitable for clinical deployment. In addition, to understand the possible relationship of claudin-2 in the context of disease severity, expression was compared to the Geboes score. Overall, the microscopical Geboes score correlated with the claudin-2 biomarker score for samples that retained crypt morphology; samples with the highest Geboes score were not specifically distinguished, probably due to crypt destruction. In summary, we have applied a strategy for identifying target-specific antibodies in formalin fixed biopsy samples and highlighted that (published) antibodies may not correctly identify the intended antigen in tissues fixed using this method. Furthermore, we have developed and, for the first time, validated an in situ hybridization assay for detection of claudin-2 mRNA, suitable for use as a supportative method in clinical trials. Using our validated assay, we have demonstrated that increased claudin-2 expression correlates with the severity of ulcerative colitis, where crypt destruction is not seen.

Sex-Dependent Claudin-1 Expression in the Liver of Euthyroid and Hypothyroid Mice

BACKGROUND

In the liver the tight junction protein claudin-1 plays an important role in bile secretion by maintaining the paracellular barrier of bile canaliculi and the bile duct. A diminished bile excretion has been found in hypothyroid patients, and the prevalence of gallstones is increased in hypothyroidism. This association, however, only applies for men and is in contrast to the well-established female preponderance of biliary disease in the general population.

OBJECTIVES

We hypothesized that hypothyroidism could lead to altered claudin-1 expression in the liver, and that this effect may be sex specific.

METHODS

We characterized claudin-1 expression and localization in livers of euthyroid and hypothyroid male and female C57BL/6NTac mice by real-time PCR, Western blot and immunofluorescence.

RESULTS

Claudin-1 is expressed in canalicular regions and the bile ducts of the murine liver. Livers of female mice showed lower claudin-1 expression than male livers. In hypothyroid livers, female animals showed an elevated claudin-1 expression, whereas reduced claudin-1 expression was found in male animals compared to the euthyroid controls.

CONCLUSION

We demonstrate a correlation between claudin-1 expression and hypothyroidism in the murine liver. Furthermore, a sex-dependent alteration of claudin-1 expression was found.

Claudin-related intestinal diseases

With up to 200 m(2) the human intestine is the organ with the largest absorptive surface of the body. It is lined by a single layer of epithelial cells that separates the host from the environment. The intestinal epithelium provides both, selective absorption of nutrients, ions, and water but also a highly effective barrier function which includes the first line of defense against environmental antigens. The paracellular part of this barrier function is provided by tight junction (TJ) proteins, especially the large family of claudins. Changes in abundance or molecular structure of claudins can generally result in three typical effects, (i) decreased absorptive passage, (ii) increased secretory passage of small solutes and water causing leak flux diarrhea and (iii) increased absorptive passage of macromolecules which may induce inflammatory processes. Several intestinal diseases are associated with such changes that can result in intestinal inflammation and symptoms like weight loss, abdominal pain or diarrhea. This review summarizes our current knowledge on barrier dysfunction and claudin dysregulation in several intestinal diseases gastroenterologists are often faced with, like inflammatory bowel disease, microscopic colitis, celiac disease, irritable bowel syndrome, gallstones and infectious diseases like HIV enteropathy, Campylobacter jejuni and Clostridium perfringens infection.

Expression of Tight Junction Components in Hepatocyte-Like Cells Differentiated from Human Embryonic Stem Cells

Human embryonic stem cells can be differentiated in vitro into a wide variety of progeny cells by addition of different morphogens and growth factors. Our aim was to monitor the expression pattern of tight junction (TJ) components and various cellular markers during differentiation of stem cell lines toward the hepatic lineage. Human embryonic stem cell lines (HUES1, HUES9) were differentiated into endoderm-like cells, and further differentiated to hepatocyte-like cells. Gene expressions of Oct3/4, Nanog, alpha-fetoprotein, albumin, cytokeratins (CK-7, CK-8, CK-18, CK-19), ATP-binding cassette (ABC) transporters (ABCC2, ABCC7, ABCG2), and various TJ components, including claudin-1, claudin-4, claudin-5, claudin-7, and tricellulin, as well as an extracellular matrix component, agrin were monitored during hepatic differentiation by real-time quantitative PCR. The differentiated cells exhibit epithelial morphology and functional assessments similar to that of hepatocytes. The expression level of stem cell marker genes (Oct3/4 and Nanog) significantly and gradually decreased, while liver-associated genes (alpha-fetoprotein, albumin) reached their highest expression at the end of the differentiation. The endoderm-like cells expressed claudin-1, which declined eventually. The expression levels of cholangiocyte markers including claudin-4, CK-7, CK-19, and agrin gradually increased and reached their highest level at the final stage of differentiation. In contrast, these cells did not express notable level of claudin-7, CK-8 and tricellulin. The marker set used for monitoring differentiation revealed both hepatocyte and cholangiocyte characteristics of the differentiated cells at the final stage. This is the first report describing the expression level changes of various TJ components, and underlining their importance in hepatic differentiation.

miR-1303 targets claudin-18 gene to modulate proliferation and invasion of gastric cancer cells

BACKGROUND

MicroRNAs have emerged as important gene regulators and are recognized as important molecules in carcinogenesis. However, the effects of microRNA-1303 (miR-1303) on gastric cancer (GC) cells and the upstream regulation of GC-associated claudin-18 gene (CLDN18) remain unclear. miR-1303 may be involved in the tumorigenesis of GC by targeting CLDN18.

AIMS

The purpose of this study was to explore the effect of miR-1303 targeting of CLDN18 on the proliferation, migration and invasion of human GC cells.

METHODS

The expression of miR-1303 and claudin-18 in GC tissues and gastric cancer cell lines were detected by qRT-PCR and western blotting, respectively. CCK8 and colony formation assays were performed to study the influence of miR-1303 on the proliferation of the GC cell lines. Transwell and wound-healing assays were carried out to investigate the effect of miR-1303 on the invasion and migration of GC cell lines. Luciferase reporter assays, restore assays and western blotting were used to demonstrate whether CLDN18 is a direct target of miR-1303.

RESULTS

miR-1303 was significantly overexpressed whereas claudin-18 was downregulated in GC tissues and cell lines, which was significantly associated with tumor size, location invasion, histologic type and tumor-node-metastasis stage. Cell proliferation rates were reduced, and cell invasion and migratory ability was significantly restricted in miR-1303 inhibitor-transfected groups. miR-1303 could bind to the putative binding sites in CLDN18 mRNA 3'-UTR and visibly lower the expression of claudin-18. The introduction of claudin-18 without 3'-UTR restored the miR-1303 promoting migration function.

CONCLUSIONS

Downregulation of miR-1303 can inhibit proliferation, migration and invasion of GC cells by targeting CLDN18.

Tricellulin expression and its prognostic significance in primary liver carcinomas

Numerous data suggest that altered expression of tight junction proteins such as occludin and claudins plays important role in carcinogenesis. However, little is known about tricellulin, a transmembrane tight junction protein concentrated where three epithelial cells meet. We aimed to characterize tricellulin expression in normal and cirrhotic liver in comparison to primary hepatic neoplasms. Tricellulin expression of 20 control livers, 12 cirrhotic livers, 32 hepatocellular carcinomas (HCC), and 20 intrahepatic cholangiocarcinomas (iCCC) was investigated by immunohistochemistry and Western blotting. Co-localization of tricellulin with claudin-1, -4, and MRP2 was studied using double immunofluorescence. Scattered tricellulin immunopositivity was restricted to biliary pole of hepatocytes confirmed by co-localization with MRP2. Moreover, spotted-like reaction was observed between bile duct epithelial cells. In 40 % of HCCs marked tricellulin overexpression was measured regardless of tumor grades. In iCCCs, however, tricellulin expression decreased parallel with dedifferentiation. In HCCs high tricellulin expression, in iCCCs low tricellulin expression correlated with poor prognosis. Co-localization with MRP2 might substantiate that tricellulin plays role in blood-biliary barrier. Overexpressed tricellulin in a subset of HCCs correlated with unfavorable prognosis. Similar to ductal pancreatic adenocarcinoma, higher grades of iCCCs were associated with decreased tricellulin expression correlating with poor prognosis.

The claudin family of proteins in human malignancy: a clinical perspective

Tight junctions, or zonula occludens, are the most apical component of the junctional complex and provide one form of cell-cell adhesion in epithelial and endothelial cells. Nearly 90% of malignant tumors are derived from the epithelium. Loss of cell-cell adhesion is one of the steps in the progression of cancer to metastasis. At least three main tight junction family proteins have been discovered: occludin, claudin, and junctional adhesion molecule (JAM). Claudins are the most important structural and functional components of tight junction integral membrane proteins, with at least 24 members in mammals. They are crucial for the paracellular flux of ions and small molecules. Overexpression or downregulation of claudins is frequently observed in epithelial-derived cancers. However, molecular mechanisms by which claudins affect tumorigenesis remain largely unknown. As the pivotal proteins in epithelial cells, altered expression and distribution of different claudins have been reported in a wide variety of human malignancies, including pancreatic, colonic, lung, ovarian, thyroid, prostate, esophageal, and breast cancers. In this review, we will give the readers an overall picture of the changes in claudin expression observed in various cancers and their mechanisms of regulation. Downregulation of claudins contributes to epithelial transformation by increasing the paracellular permeability of nutrients and growth factors to cancerous cells. In the cases of upregulation of claudin expression, the barrier function of the cancerous epithelia changes, as they often display a disorganized arrangement of tight junction strands with increased permeability to paracellular markers. Finally, we will summarize the literature suggesting that claudins may become useful biomarkers for cancer detection and diagnosis as well as possible therapeutic targets for cancer treatment.

Bile duct epithelial tight junctions and barrier function

Bile ducts play a crucial role in the formation and secretion of bile as well as excretion of circulating xenobiotic substances. In addition to its secretory and excretory functions, bile duct epithelium plays an important role in the formation of a barrier to the diffusion of toxic substances from bile into the hepatic interstitial tissue. Disruption of barrier function and toxic injury to liver cells appear to be involved in the pathogenesis of a variety of liver diseases such as primary sclerosing cholangitis, primary biliary cirrhosis and cholangiocarcinoma. Although the investigations into understanding the structure and regulation of tight junctions in gut, renal and endothelial tissues have expanded rapidly, very little is known about the structure and regulation of tight junctions in the bile duct epithelium. In this article we summarize the current understanding of physiology and pathophysiology of bile duct epithelium, the structure and regulation of tight junctions in canaliculi and bile duct epithelia and different mechanisms involved in the regulation of disruption and protection of bile duct epithelial tight junctions. This article will make a case for the need of future investigations toward our understanding of molecular organization and regulation of canalicular and bile duct epithelial tight junctions.

Distinct claudin expression profiles of hepatocellular carcinoma and metastatic colorectal and pancreatic carcinomas

Tight junction proteins, including claudins, are often dysregulated during carcinogenesis and tumor progression. Moreover, the claudin expression pattern usually varies between different tumor entities. We aimed to investigate claudin expression profiles of primary and metastatic liver malignancies. We analyzed claudin-1, -2, -3, -4, and -7 expression by quantitative immunohistochemistry and real-time RT-PCR, respectively. Twenty hepatocellular carcinomas (HCCs) and liver metastases of 20 colorectal adenocarcinomas (CRLMs) and 15 pancreatic adenocarcinomas (PLMs) were studied together with paired surrounding non-tumorous liver samples and 5 normal liver samples. Strong claudin-3 and -7 immunohistochemical positivities were detected in CRLM samples, each with significantly stronger staining when compared with HCC and PLM groups. Claudin-1 protein was found highly expressed in CRLM, in contrast to lower expression in PLM and HCC. CRLMs and PLMs also were strongly positive for claudin-4, while being virtually undetectable in HCC. Claudin-2 showed strong positivity in non-tumorous liver tissue, whereas significantly weaker positivity was observed in all tumors. Differences in mRNA expression were mostly similar to those found by immunohistochemistry. In conclusion, HCC and both CRLM and PLM display distinct claudin expression profiles, which might provide better understanding of the pathobiology of these lesions and might be used for differential diagnosis.

Claudins and the modulation of tight junction permeability

Claudins are tight junction membrane proteins that are expressed in epithelia and endothelia and form paracellular barriers and pores that determine tight junction permeability. This review summarizes our current knowledge of this large protein family and discusses recent advances in our understanding of their structure and physiological functions.

Diagnostic utility of von Hippel-Lindau gene product, maspin, IMP3, and S100P in adenocarcinoma of the gallbladder

Our recent study demonstrated the up-regulation of maspin, IMP3, and S100P and down-regulation of von Hippel-Lindau gene product (pVHL) in ductal adenocarcinoma of the pancreas. Distinction of adenocarcinoma of the gallbladder from benign/reactive glandular epithelium can be challenging if based on hematoxylin and eosin-stained sections alone. Immunohistochemical stains for pVHL, maspin, IMP3, and S100P were performed on 82 gallbladder specimens, including adenocarcinoma (n = 33) and normal/reactive gallbladder (n = 49). The results demonstrated (1) only 6.0% of adenocarcinoma cases were focally positive for pVHL, and all normal and most reactive cases (85%) were diffusely positive for pVHL; (2) maspin, IMP3, and S100P were positive in 100%, 81.8%, and 75.8% of adenocarcinoma cases, respectively; in contrast, 53.1%, 12.2%, and 30.6% of normal/reactive cases were only focally and weakly positive for maspin, IMP3, and S100P, respectively; and (3) 90.3% of adenocarcinoma cases were pVHL-negative and positive for 2 or more positive markers, whereas none of the benign/reactive cases showed this staining profile. This study demonstrates that the immunostaining profile of pVHL-/IMP3+/maspin+/S100P+ is useful in the distinction of adenocarcinoma of the gallbladder from normal/reactive conditions.

Enhancer of zeste homologue 2 (EZH2) is a reliable immunohistochemical marker to differentiate malignant and benign hepatic tumors

BACKGROUND

The immunohistochemical demonstration of Enhancer of zeste homologue 2 (EZH2) proved to be a useful marker in several tumor types. It has been described to distinguish reliably hepatocellular carcinomas from liver adenomas and other benign hepatocellular lesions. However, no other types of malignant liver tumors were studied so far.

METHODS

To evaluate the diagnostic value of this protein in hepatic tumors we have investigated the presence of EZH2 by immunohistochemistry in hepatocellular carcinomas and other common hepatic tumors.EZH2 expression was examined in 44 hepatocellular carcinomas, 23 cholangiocarcinomas, 31 hepatoblastomas, 16 other childhood tumor types (rhabdomyosarcoma, neuroblastoma, Wilms' tumor and rhabdoid tumor), 17 metastatic liver tumors 24 hepatocellular adenomas, 15 high grade dysplastic nodules, 3 biliary cystadenomas, 3 biliary hamartomas and 3 Caroli's diseases.

RESULTS

Most of the malignant liver tumors were positive for EZH2, but neither of the adenomas, cirrhotic/dysplastic nodules, reactive and hamartomatous biliary ductules stained positively.

CONCLUSIONS

Our immunostainings confirm that EZH2 is a sensitive marker of hepatocellular carcinoma, but its specificity is very low, since almost all the investigated malignant liver tumors were positive regardless of their histogenesis. Based on these results EZH2 is a sensitive marker of malignancy in hepatic tumors. In routine surgical pathology EZH2 could be most helpful to diagnose cholangiocarcinomas, because as far as we know this is the first marker to distinguish transformed and reactive biliary structures. Although hepatoblastomas also express EZH2, the diagnostic significance of this observation seems to be quite limited whereas, the structurally similar, other blastic childhood tumors are also positive.

VIRTUAL SLIDES

The virtual slide(s) for this article can be found here: http://www.diagnosticpathology.diagnomx.eu/vs/1173195902735693.

Claudin-1 involved in neonatal ichthyosis sclerosing cholangitis syndrome regulates hepatic paracellular permeability

Neonatal ichthyosis and sclerosing cholangitis (NISCH) syndrome is a liver disease caused by mutations of CLDN1 encoding Claudin-1, a tight-junction (TJ) protein. In this syndrome, it is speculated that cholestasis is caused by Claudin-1 absence, leading to increased paracellular permeability and liver injuries secondary to paracellular bile regurgitation. We studied the role of claudin-1 in hepatic paracellular permeability. A NISCH liver and polarized rat cell lines forming TJs, the hepatocellular Can 10 and the cholangiocellular normal rat choloangiocyte (NRC), were used. In contrast to NRC, Can 10 does not express claudin-1. Can 10 cells were transfected with a plasmid encoding Claudin-1, and stable Claudin-1-expressing clones were isolated. Claudin-1 expression was silenced by transfection with short interfering RNA in Can 10 clones and with short hairpin RNA in NRC. Claudin-1 expression was evaluated by quantitative reverse-transcriptase polymerase chain reaction, immunoblotting, and immunolocalization. Paracellular permeability was assessed by fluorescein isothiocyanate-dextran passage in both lines and by transepithelial resistance measurements in NRC. In the NISCH liver, Claudin-1 was not detected in hepatocytes or cholangiocytes. In Claudin-1 expressing Can 10 clones, Claudin-1 was localized at the TJ and paracellular permeability was decreased, compared to parental Can 10 cells, this decrease correlating with claudin-1 levels. Silencing of Claudin-1 in Can 10 clones increased paracellular permeability to a level similar to that of parental cells. Similarly, we observed an increase of paracellular permeability in NRC cells silenced for claudin-1 expression.

CONCLUSION

Defect in claudin-1 expression increases paracellular permeability in polarized hepatic cell lines, supporting the hypothesis that paracellular bile leakage through deficient TJs is involved in liver pathology observed in NISCH syndrome.

Tricellulin expression in normal and neoplastic human pancreas

AIMS

  Tricellulin is a member of the family of tight junction proteins, which are found concentrated mainly at tricellular contacts. Altered expression of several tight junction components has been observed during carcinogenesis. In the present study, we have analysed the expression of tricellulin in normal human pancreas, and in primary exocrine and endocrine pancreatic tumours.

METHODS AND RESULTS

  A total of 96 cases were studied: 20 normal pancreas, 58 pancreatic ductal adenocarcinomas, 15 pancreatic endocrine neoplasms, and three acinar cell carcinomas. Immunohistochemistry (analysed by digital morphometry), immunofluorescence, western blot analysis and reverse transcription polymerase chain reaction were performed. Tricellulin was localized apically in normal ducts and acini as intensive, spotty immunopositivity at tricellular contacts, whereas weaker signals were observed at the junction between two cells. Islets of Langerhans were negative. Well-differentiated ductal adenocarcinomas significantly overexpressed tricellulin as compared with poorly differentiated adenocarcinomas. Acinar cell carcinomas expressed tricellulin in tumour cells. All endocrine tumours were tricellulin-negative.

CONCLUSIONS

  This is the first report to describe the tricellulin expression profile in normal and neoplastic human pancreas. Both normal and neoplastic pancreatic exocrine tissues expressed tricellulin, whereas no expression was seen in normal or neoplastic endocrine cells. Tricellulin expression in pancreatic ductal adenocarcinomas showed a significant negative correlation with the degree of differentiation.

Dynamic distribution of claudin proteins in pancreatic epithelia undergoing morphogenesis or neoplastic transformation

BACKGROUND

The assembly of distinct proteins into tight junctions results in the formation of a continuous barrier that regulates the paracellular flux of water, ions, and small molecules across epithelia. The claudin protein family encompasses numerous major structural components of tight junctions. These proteins specify the permeability characteristics of tight junctions and consequently, some of the physiological properties of epithelia. Furthermore, defective claudin expression has been found to correlate with some diseases, tumor progression, and defective morphogenesis. Investigating the pattern of claudin expression during embryogenesis or in certain pathological conditions is necessary to begin disclosing the role of these proteins in health and disease.

RESULTS

This study analyzed the expression of several claudins during mouse pancreas organogenesis and in pancreatic intraepithelial neoplasias of mouse and human origin.

CONCLUSIONS

Our results underscored a distinctive, dynamic distribution of certain claudins in both the developing pancreas and the pancreatic epithelium undergoing neoplastic transformation.

Expression of tight junction molecules in breast carcinomas analysed by array PCR and immunohistochemistry

In the past few decades an enormous amount of data became known to clarify the molecular composition and architecture of tight junctions (TJs). Despite the efforts, the expression and function of several TJ genes and proteins in breast carcinoma are still not known and some of the data are contradictory. The expression of forty-four TJ associated genes was examined at mRNA level in eighteen invasive ductal breast carcinoma samples and corresponding normal breast tissues by using low density array PCR. Expressions of claudins (CLDNs) 5, 10, 16, 17, and 18, and ZO-1, ZO-2 were evaluated by immunohistochemistry as well. Using immunohistochemical phenotype as a surrogate for the genetic subtype, 11 luminal A, 3 luminal B, 3 triple negative and one HER2+ cases were included. Ten genes were significantly downregulated in tumors compared with normal breast tissues (CLDNs 5, 10, 16, 18, 19, CTNNAL1, JAM-B, ZO-1, ZO-2 and PARD3), whereas one gene (CLDN17) was significantly up-regulated in tumors when compared with normal breast. At protein level CLDNs 5, 10, 16, 18, ZO-1 and ZO-2 were downregulated in tumors as compared with normal breast tissue. CLDN17 showed variable expression in tumor tissues in comparison to normal breast. In the single HER2+ tumor when compared with the other subtypes CLDNs 5, 16, 17, 18, CTNNAL1, JAM-B, ZO-1, ZO-2 and PARD3 genes were found to be upregulated. We found altered TJ genes and proteins whose expression has not yet been associated with breast carcinoma. Our findings show a tendency of TJ genes and proteins to be downregulated in breast cancer. Further studies are necessary to examine whether the downregulation of the above mentioned TJ associated genes and proteins may contribute to the malignant progression of invasive ductal breast carcinomas.

Regulation of intrahepatic biliary duct morphogenesis by Claudin 15-like b

The intrahepatic biliary ducts transport bile produced by the hepatocytes out of the liver. Defects in biliary cell differentiation and biliary duct remodeling cause a variety of congenital diseases including Alagille Syndrome and polycystic liver disease. While the molecular pathways regulating biliary cell differentiation have received increasing attention (Lemaigre, 2010), less is known about the cellular behavior underlying biliary duct remodeling. Here, we have identified a novel gene, claudin 15-like b (cldn15lb), which exhibits a unique and dynamic expression pattern in the hepatocytes and biliary epithelial cells in zebrafish. Claudins are tight junction proteins that have been implicated in maintaining epithelial polarity, regulating paracellular transport, and providing barrier function. In zebrafish cldn15lb mutant livers, tight junctions are observed between hepatocytes, but these cells show polarization defects as well as canalicular malformations. Furthermore, cldn15lb mutants show abnormalities in biliary duct morphogenesis whereby biliary epithelial cells remain clustered together and form a disorganized network. Our data suggest that Cldn15lb plays an important role in the remodeling process during biliary duct morphogenesis. Thus, cldn15lb mutants provide a novel in vivo model to study the role of tight junction proteins in the remodeling of the biliary network and hereditary cholestasis.

Claudins 10 and 18 are predominantly expressed in lung adenocarcinomas and in tumors of nonsmokers

AIMS

We investigated the expression of claudins 18 and 10 in a large set of primary lung carcinomas.

METHODS AND RESULTS

Immunohistochemical expression of claudin 18 was seen in 12.7 % and claudin 10 in 12.5 % of lung carcinomas. Their expression significantly associated with each other (p<0.001). The expression of claudin 18 and 10 was most prominent in lung adenocarcinomas which displayed positivity in 21.2% and 23.4 % of cases. Female patients had more often claudin 18 and 10 positive tumors, also separately in adenocarcinomas. Interestingly, claudin 10 (p=0.036) and claudin 18 (p=0.001) were more common in tumours of nonsmokers. In adenocarcinomas claudin 18 predicted a better survival (p=0.032). In Cox multivariate analysis, claudin 18 had an independent prognostic value (p=0.027).

CONCLUSION

The results show that both claudins are most commonly expressed in lung adenocarcinomas and they are more occasionally detected in other histological tumour types. Curiously, female patients and non-smokers express these claudins more commonly suggesting that they may play a part in the carcinogenesis of tobacco unrelated carcinoma. Claudin 18 associated with a better survival in lung adenocarcinoma and had an independent prognostic value and may thus be used in the evaluation of patient prognosis.

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

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

[The clinical significance of Claudin-7 and slug expression in lung squamous cell carcinoma and adenocarcinoma]

背景与目的

Claudins是紧密连接的骨架蛋白，Claudin-7是Claudins家族成员之一。本研究旨在观察Claudin-7和Slug在肺鳞癌和腺癌中的表达及其与临床病理因素的关系，并探讨Claudin-7和Slug的相互关系。

方法

采用免疫组织化学SP法检测101例原发性肺鳞癌、腺癌组织中Claudin-7和Slug的表达，同时应用Western blot检测30例新鲜肺癌组织及其配对的癌旁组织中Claudin-7和Slug的表达情况。

结果

Claudin-7在肺癌中的表达明显低于正常肺组织，并且与分化程度和淋巴结转移有关（P < 0.05），Slug在肺癌中的表达明显高于正常肺组织，除与分化程度和淋巴结转移有关外，还与TNM分期有关（P < 0.05），肺鳞癌、腺癌中Claudin-7与Slug的表达具有负相关性（r=-0.566, 8）。

结论

肺鳞癌、腺癌中Claudin-7的低表达与Slug的高表达可能是肺组织恶性转变和转移的有关标志物之一。

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.

Claudin-18 in biliary neoplasms. Its significance in the classification of intrahepatic cholangiocarcinoma

Claudin-18 (CLDN18), a tight junction protein specific to stomach and lung, is aberrantly expressed in preinvasive and invasive neoplasms of the pancreas. To investigate the significance of CLDN18 expression in biliary neoplasms, immunohistochemical analysis was performed. CLDN18 expression was frequently observed in the epithelial cells of extrahepatic bile duct carcinomas (90%, n = 99), intrahepatic intraductal papillary neoplasms of the bile duct (IPNBs, 100%, n = 11), and extrahepatic IPNBs (89%, n = 9), while it was less frequent in intrahepatic cholangiocarcinomas (ICCs, 43%, n = 83). Interestingly, CLDN18 expression was also frequently observed in precancerous lesions such as biliary intraepithelial neoplasias (78%, n = 18). Among ICCs, CLDN18-positive cases showed higher frequencies of periductal infiltrative growth, perineural invasion, and lymph node metastasis. Multivariable analysis demonstrated that positive CLDN18 expression was an independent risk factor for lymph node metastasis in ICCs. Furthermore, CLDN18 expression was associated with poor overall survival by univariable analysis, as well as lymph node metastasis. These results suggest that CLDN18 may play an important role in biliary carcinogenesis, and especially in ICCs, it is associated with aggressive behavior and serves as a useful marker for the classification of ICC.

Markers of bile duct tumors

Biliary tract carcinomas are relatively rare, representing less than 1% of cancers. However, their incidence has increased in Japan and in industrialized countries like the USA. Biliary tract tumors have a poor prognosis and a high mortality rate because they are usually detected late in the course of the disease; therapeutic treatment options are often limited and of minimal utility. Recent studies have shown the importance of serum and molecular markers in the diagnosis and follow up of biliary tract tumors. This review aims to introduce the main features of the most important serum and molecular markers of biliary tree tumors. Some considerable tumor markers are cancer antigen 125, carbohydrate antigen 19-9, carcinoembryonic antigen, chromogranin A, mucin 1, mucin 5, alpha-fetoprotein, claudins and cytokeratins.

Laboratory methods in the study of endometrial Claudin-4

Immunohistochemistry is a suitable method for the detection of proteins from the Claudin family and several antibodies are commercially available for the detection of Claudin congeners. Immunodetection of Caludin-4 in the paraffin-embedded specimens might be a useful tool for studying the role of these proteins in the cyclic transformation of the endometrium and its role in the endometrial receptivity; furthermore, other components of the junctional zone involved in the transformational process of the endometrium can be detected by means of immunohistochemistry/immunofluorescence with several polyclonal or monoclonal antibodies. The aim of this chapter is to comprehensively overview the materials and methods to perform the endometrial biopsy and to detect Claudin-4 in paraffin-embedded samples of endometrium. Additionally, the interpretation of the results is addressed.

Calcium inhibits paracellular sodium conductance through claudin-2 by competitive binding

Claudins form paracellular pores at the tight junction in epithelial cells. Profound depletion of extracellular calcium is well known to cause loosening of the tight junction with loss of transepithelial resistance. However, moderate variations in calcium concentrations within the physiological range can also regulate transepithelial permeability. To investigate the underlying molecular mechanisms, we studied the effects of calcium on the permeability of claudin-2, expressed in an inducible MDCK I cell line. We found that in the physiological range, calcium acts as a reversible inhibitor of the total conductance and Na(+) permeability of claudin-2, without causing changes in tight junction structure. The effect of calcium is enhanced at low Na(+) concentrations, consistent with a competitive effect. Furthermore, mutation of an intrapore negatively charged binding site, Asp-65, to asparagine partially abrogated the inhibitory effect of calcium. This suggests that calcium competes with Na(+) for binding to Asp-65. Other polyvalent cations had similar effects, including La(3+), which caused severe and irreversible inhibition of conductance. Brownian dynamics simulations demonstrated that such inhibition can be explained if Asp-65 has a relatively high charge density, thus favoring binding of Ca(2+) over that of Na(+), reducing Ca(2+) permeation by inhibiting its dissociation from this site, and decreasing Na(+) conductance through repulsive electrostatic interaction with Ca(2+). These findings may explain why hypercalcemia inhibits Na(+) reabsorption in the proximal tubule of the kidney.

[Study of claudins and prognostic factors in some gastrointestinal diseases]

Gastrointestinal tumors are highly ranked regarding tumoral mortality worldwide. The development and progression of gastrointestinal (GI) diseases go hand in hand with the changes of tight junctions (TJ). Claudins (CLDN) are the main TJ proteins, showing different expression by the different tissues, with the expressed CLDN profile being representative. I. We explored the changes of CLDN expression in Barrett's esophagus and related adenocarcinoma. CLDN2 and -3 expression in Barrett's esophagus was higher than in normal foveolar epithelium. Adenocarcinoma showed higher CLDN2 and -3 expression compared with normal and Barrett's epithelia. The similar CLDN expression profile of Barrett's esophagus and adenocarcinoma supports their sequential development. II. Gastric intestinal metaplasia showed higher expression of CLDN2, -3 and -4 as compared with normal antral foveolar mucosa. Tumors of small and large bowels exhibited higher CLDN2 expression when compared with normal epithelia. Colorectal adenoma and adenocarcinoma could not be differentiated according to their CLDN profile. Intestinal metaplasias of Barrett's esophagus and stomach show similar CLDN profile to small bowel epithelium. III. Studies on duodenal mucosa in celiac disease in childhood demonstrated CLDN2 and -3 expression to be higher than in normal mucosa. The expression was significantly higher in the distal part of the duodenum samples. This and the serious histological findings suggest that the distal duodenum is more adequate for biopsy testing. IV. Beside the epithelial cells, mesenchymal tumors express intercellular junctional proteins. Expression of claudins in gastrointestinal stromal tumors (GIST) and other mesenchymal neoplasia was also studied. The CLDN profile was found to be representative to the individual tumor. GIST, angiosarcoma, hemangioma, leiomyosarcoma and leiomyoma showed expression of various CLDNs. CLDN2 was detected in all entities. CLDN1, however, was found positive in leiomyosarcoma only. Leiomyoma, on the other hand, expressed only CLDN2. GISTs and leiomyosarcomas showed CLDN2, -3, -4, -5 and -7-expression. The angiogenic tumors revealed CLDN2 and -5 expression. The similar CLDN profile observable in GIST and leiomyosarcoma is suggestive of a histogenetic relationship. Smooth muscle and vessel tumors of different dignity could also be separated from each other based on CLDN profile.