Is High Expression of Claudin-7 in Advanced Colorectal Carcinoma Associated with a Poor Survival Rate? A Comparative Statistical and Artificial Intelligence Study

Simple Summary

The need for predictive and prognostic biomarkers in colorectal carcinoma (CRC) brought us to an era where the use of artificial intelligence (AI) models is increasing. We investigated the expression of Claudin-7, a tight junction component, which plays a crucial role in maintaining the integrity of normal epithelial mucosa, and its potential prognostic role in advanced CRCs by drawing a parallel between statistical and AI algorithms. Claudin-7 immunohistochemical expression was evaluated in the tumor core and invasion front of CRCs and correlated with clinicopathological parameters and survival using statistical and AI algorithms. The Kaplan–Meier univariate survival analysis showed that the immunohistochemical overexpression of Claudin-7 in the tumor invasive front may represent a poor prognostic factor in advanced stages of CRCs. On the contrary, AI models could not predict the same outcome, probably because of the small number of patients included in our cohort.

Abstract

Aim: The need for predictive and prognostic biomarkers in colorectal carcinoma (CRC) brought us to an era where the use of artificial intelligence (AI) models is increasing. We investigated the expression of Claudin-7, a tight junction component, which plays a crucial role in maintaining the integrity of normal epithelial mucosa, and its potential prognostic role in advanced CRCs, by drawing a parallel between statistical and AI algorithms. Methods: Claudin-7 immunohistochemical expression was evaluated in the tumor core and invasion front of CRCs from 84 patients and correlated with clinicopathological parameters and survival. The results were compared with those obtained by using various AI algorithms. Results: the Kaplan–Meier univariate survival analysis showed a significant correlation between survival and Claudin-7 intensity in the invasive front (p = 0.00), a higher expression being associated with a worse prognosis, while Claudin-7 intensity in the tumor core had no impact on survival. In contrast, AI models could not predict the same outcome on survival. Conclusion: The study showed through statistical means that the immunohistochemical overexpression of Claudin-7 in the tumor invasive front may represent a poor prognostic factor in advanced stages of CRCs, contrary to AI models which could not predict the same outcome, probably because of the small number of patients included in our cohort.

Modulation of microRNAs and claudin-7 in Caco-2 cell line treated with Blastocystis sp., subtype 3 soluble total antigen

Background

Blastocystis sp., is a eukaryote of the large intestine, which is reported from almost all countries. The pathogenesis of this protist is not clear. The current study aimed to analyze the effects of Blastocystis sp., ST3 soluble total antigen (B3STA) on the microRNAs (miRNAs) involved in the gut permeability and also pro-inflammatory cytokines, occludin, and claudin-7.

Methods

Blastocystis sp., ST3 isolated from stool sample was purified, and its soluble total antigen was extracted using freeze and thawing. The Caco-2 cell line was treated with B3STA for 24 h and the expression levels of mir-16, mir-21, mir-29a, mir-223, and mir-874 were analyzed. In addition, the expression levels of il-8, il-15, occludin, and claudin-7 genes were assessed.

Results

B3STA significantly upregulated the expression of mir-223, and mir-874, and downregulated mir-29a. The expression of mir-16 and mir-21 was not significant. In addition, the expression of il-8 and il-15 was not significant. B3STA significantly decreased the expression level of claudin-7 (P-value < 0.0001), but the expression of occludin was not significant. Our results showed significant correlation between all studied miRNAs, except mir-29a, with downregulation of claudin-7.

Conclusions

This is the first study investigating the effects of Blastocystis sp., ST3 isolated from symptomatic subjects on the expression levels of miRNAs involved in the gut permeability. Our results demonstrated that B3STA may change miRNA expression, which are involved in the gut barrier integrity, and downregulates claudin-7, which is known as sealing factor.

Intestinal Claudin-7 deficiency impacts the intestinal microbiota in mice with colitis

Background

Intestinal epithelial cells form a physical barrier that protects the intestine against the intestinal microbiota through tight junctions (TJs) and adhesive junctions, while barrier disruption may lead to inflammatory bowel disease (IBD). Claudin-7 (Cldn7) has been implicated in this protection as an important member of TJs. Here, we experimentally study the effect of Cldn7 deletion on intestinal microbiota in colitis.

Methods

Colitis model was established based on inducible intestinal conditional Cldn7 gene knockout mice (Cldn7fl/fl; villin-CreERT2), by feeding with dextran sodium sulfate (DSS). AB-PAS staining and immunohistochemical staining of Muc2 mucin were used to detect the effect of Cldn7 deficiency on the mucus layer of mice with colitis, and fluorescence in situ hybridization was used to detect how Cldn7 promotes spatial separation of the gut microbiota from the host. The microbiota population was characterized by high-throughput 16S rRNA gene sequencing of DNA extracted from fecal samples.

Results

Compared with the controls, Cldn7 knockout increased susceptibility to colitis, including greater degree of weight loss, colon shortening, and a significantly higher disease activity index score. DSS-treated Cldn7 knockout mice promoted the migration of bacteria to the intestinal epithelium to some extent by damaging the intestinal mucus layer. Sequencing of 16S rRNA showed that DSS-treated Cldn7 knockout mice reduced the gut microbiota diversity and had greater relative abundance of Escherichia coli. LEfSe analysis indicated that Escherichia coli may be the key bacteria in Cldn7 knockout mice during DSS-induced colitis. Furthermore, the Tax4Fun analysis predicted that DSS-treated Cldn7 knockout mice enriched for microbiota impacting infectious diseases, immune system and metabolic functions.

Conclusions

Our data suggests an association between intestinal Cldn7 knockout and microbiota dysbiosis during inflammatory events.

N-glycosylation status of Trop2 impacts its surface density, interaction with claudin-7 and exosomal release

Trophoblast antigen 2 (Trop2) is a type I transmembrane protein post-translationally modified by N-linked glycosylation. It was originally detected in trophoblasts but was later shown to be frequently overexpressed in many epithelial cancers. Recently, anti-Trop2 antibody-drug conjugate has been FDA approved for the treatment of metastatic triple-negative breast and urothelial carcinomas, making it an important tumor antigen. The current study explored the significance of N-glycosylation of Trop2 by substituting specific N-glycan addition sites by site-directed mutagenesis. The mutant proteins were characterized in transiently transfected HEK293 cells. The N-glycosylation mutants did not affect protein expression, stability, dimerization ability and matriptase mediated cleavage. However, N¹²⁰A and N²⁰⁸A mutants showed decreased interaction with its binding partner claudin-7. Our earlier reported Trop2 mutant V¹⁹⁴A, which shows aberrant glycosylation, also displayed hampered interaction with claudin-7. To further characterize the mutants, stable clones expressing wild type and mutant Trop2 were generated in OVCAR3 cell line. Interestingly, surface biotinylation assay showed significantly higher surface expression of N¹²⁰A and N²⁰⁸A mutants whereas surface localization was drastically reduced for V¹⁹⁴A Trop2 mutant. Though overexpression of wild type Trop2 did not cause any change in fibronectin-mediated FAK (Focal adhesion kinase) signaling; expression of N¹²⁰A mutant, surprisingly downregulated FAK signaling. Furthermore, exosomal release of Trop2 was also decreased in N¹²⁰A and N²⁰⁸A mutants. This data suggests that site-specific N-glycan addition determines Trop2 surface density, claudin-7 interaction and exosomal release.

IRF2-induced Claudin-7 suppresses cell proliferation, invasion and migration of oral squamous cell carcinoma

Oral squamous cell carcinoma (OSCC) is a common type of malignant tumor worldwide. Claudin-7 (CLDN7) has been reported to exhibit low expression in tissues of patients with OSCC; however, the underlying mechanisms of CLDN7 remain to be elucidated. The present study aimed to investigate the effects of CLDN7 on the progression of OSCC and identify its potential regulatory mechanisms. CLDN7 and interferon regulatory factor-2 (IRF2) expression in several OSCC cell lines were detected using reverse transcription-quantitative PCR (RT-qPCR) and western blotting. Following CLDN7 overexpression, cell proliferation, invasion and migration were determined using a Cell Counting Kit-8, colony formation, Transwell and wound healing assays, respectively. The potential binding sites of IRF2 on the CLDN7 promoter were analyzed using the PROMO and JASPAR databases, which were verified via chromatin immunoprecipitation and RT-qPCR assays. The effects of IRF2 and CLDN7 on the biological functions of OSCC cells were examined by transfection with short hairpin RNA (shRNA) against CLDN7 (sh-CLDN7), or IRF2 and CLDN7 overexpression plasmids. The results revealed that CLDN7 and IRF2 expression were significantly downregulated in OSCC cell lines, and CLDN7 overexpression reduced the proliferation, invasion and migration of OSCC cells. Additionally, IRF2 was confirmed to combine with the CLDN7 promoter. CLDN7 silencing reversed the inhibitory effects of IRF2 overexpression on the proliferation, invasion and migration of OSCC cells. Taken together, these findings demonstrated that IRF2-induced CLDN7 upregulation suppressed the proliferation, invasion and migration of OSCC cells, suggesting the possibility of CLDN7 and IRF2 as novel targets for the treatment of OSCC.

Claudin-7 in keratinocytes is downregulated by the inhibition of HMG-CoA reductase and is highly expressed in the stratum granulosum of the psoriatic epidermis

BACKGROUND

Cholesterol is de novo synthesized in the upper epidermis and plays an important role in maintaining the normality of skin. Studying the impact of the inhibition of cholesterol de novo synthesis in the epidermis may help understand how skin homeostasis is regulated.

OBJECTIVE

In this study, we created a gene expression profile to investigate the effect of hydroxymethylglutaryl-coenzyme A (HMG-CoA) reductase inhibitors on epidermal homeostasis.

METHODS

A microarray analysis was performed using normal keratinocytes with or without HMG-CoA reductase inhibitor (pitavastatin) treatment. Real-time PCR confirmed the reproducibility of genes with altered expression in keratinocytes treated with HMG-CoA reductase inhibitors. Among these genes, we focused on reduced expression of claudin 7 histologically confirmed by immunohistochemical staining, in situ hybridization, and immunoelectron microscopy.

RESULTS

Claudin-7 was highly expressed in the stratum granulosum of psoriatic lesions but was not expressed in the normal epidermis. Immunoelectron microscopy revealed that claudin-7 was localized in the keratohyalin granules of psoriatic lesions.

CONCLUSION

These results indicate that claudin-7 expression was regulated by HMG-CoA reductase in the epidermis and might play a pathogenic role in the keratohyalin granules found in the epidermal granular layer of psoriasis.

Claudin-7 deficiency promotes stemness properties in colorectal cancer through Sox9-mediated Wnt/β-catenin signalling

Background

Colorectal cancer (CRC) is a common malignant tumour of the digestive tract that is characterized by high patient morbidity and mortality rates. Claudin-7 (Cldn7), a tight junction protein, was recently reported to function as a candidate tumour suppressor gene in CRC. Our previous study demonstrated that the large intestine of C57/BL6 mice showed intestinal adenomas and abnormal Ki67 expression and distribution in the intestinal crypt when Cldn7 was knocked out. The aim of this study was to further investigate whether Cldn7 deficiency has non-tight junction functions, affects intestinal stemness properties, promotes CRC and to determine the specific mechanism.

Methods

Cell proliferation assays, migration assays, apoptosis assays, tumour sphere formation assays in vitro, and subcutaneous xenograft models in vivo were used to determine the effects of Cldn7 knockdown on the biological characteristics of CRC stem cells. Western blotting, qPCR and immunofluorescence staining were performed to identify the epithelial-mesenchymal transition and the activation of Wnt/β-catenin pathway in CRC stem cells. Cldn7 inducible conditional gene knockout mice and immunohistochemical staining further verified this hypothesis in vivo. The mechanism and target of Cldn7 were determined by performing a chromatin immunoprecipitation (ChIP) assay and coimmunoprecipitation (CoIP) assay.

Results

Cldn7 knock down in CRC stem cells promoted cell proliferation, migration, and globular growth in serum-free medium and the ability to form xenograft tumours; cell apoptosis was inhibited, while the cellular epithelial-mesenchymal transition was also observed. These changes in cell characteristics were achieved by activating the Wnt/β-catenin pathway and promoting the expression of downstream target genes after β-catenin entry into the nucleus, as observed in CRC cell lines and Cldn7 gene knockout mouse experiments. Using ChIP and CoIP experiments, we initially found that Cldn7 and Sox9 interacted at the protein level to activate the Wnt/β-catenin pathway.

Conclusions

Based on our research, Cldn7 deficiency confers stemness properties in CRC through Sox9-mediated Wnt/β-catenin signalling. This result clarifies that Cldn7 plays an inhibitory role in CRC and reveals a possible molecular mechanism, which is conducive to further research on Cldn7 and cancer stem cells.

The effect of transient receptor potential vanilloid 4 on the intestinal epithelial barrier and human colonic cells was affected by tyrosine-phosphorylated claudin-7

TRPV4 is a type of nonselective cation channel, and activation of TRPV4 in the gastrointestinal tract causes experimental colitis in mice. A previous study found that tyrosine-phosphorylated claudin-7 is increased in experimental colitis. The relationship between tyrosine-phosphorylated claudin-7 and TRPV4 remains undefined. In the present study, we developed a claudin-7 mutant by replacing tyrosine with glutamic acid at position 210, named cld7-Y210E colonic cells. We found that activation of TRPV4 by GSK1016790A increased the permeability of control colonic cell monolayers, which was decreased by the TRPV4 antagonist HC067047. In monolayers of cld7-Y210E colonic cells, no differences in permeability were found between GSK1016790A and HC067047 treatments. GSK1016790A increased the aggregation of claudin-7 at the cell membrane in control colonic cells, and the effect was diminished by HC067047. In cld7-Y210E colonic cells, neither GSK1016790A nor HC067047 apparently changed the aggregation of claudin-7. Neither GSK1016790A nor HC067047 altered the TRPV4 protein level in vector colonic cells. In cld7-wild colonic cells, GSK1016790A did not alter the TRPV4 protein level, while HC067047 increased the TRPV4 protein level. The TRPV4 protein level was increased in cld7-Y210E colonic cells, decreased by GSK1016790A and further decreased by HC067047. Calcium influx was not significantly changed in the control colonic cells treated with GSK1016790A. However, GSK1016790A significantly increased calcium influx in cld7-Y210E colonic cells. We concluded that tyrosine-phosphorylated claudin-7 affects the TRPV4-modulated intestinal epithelial barrier, TRPV4-mediated calcium influx, and the protein expression of TRPV4 in human colonic cells. We suggest that tyrosine-phosphorylated claudin-7 affects the TRPV4-modulated intestinal epithelial barrier, which might be related to TRPV4 expression and TRPV4-mediated calcium influx.

Claudin-7 Modulates Cl- and Na+ Homeostasis and WNK4 Expression in Renal Collecting Duct Cells

Claudin-7 knockout (CLDN7^-/-) mice display renal salt wasting and dehydration phenotypes. To address the role of CLDN7 in kidneys, we established collecting duct (CD) cell lines from CLDN7^+/+ and CLDN7^-/- mouse kidneys. We found that deletion of CLDN7 increased the transepithelial resistance (TER) and decreased the paracellular permeability for Cl^- and Na⁺ in CLDN7^-/- CD cells. Inhibition of transcellular Cl^- and Na⁺ channels has no significant effect on TER or dilution potentials. Current-voltage curves were linear in both CLDN7^+/+ and CLDN7^-/- CD cells, indicating that the ion flux was through the paracellular pathway. The impairment of Cl^- and Na⁺ permeability phenotype can be rescued by CLDN7 re-expression. We also found that WNK4 (its mutations lead to hypertension) expression, but not WNK1, was significantly increased in CLDN7^-/- CD cell lines as well as in primary CLDN7^-/- CD cells, suggesting that the expression of WNK4 was modulated by CLDN7. In addition, deletion of CLDN7 upregulated the expression level of the apical epithelial sodium channel (ENaC), indicating a potential cross-talk between paracellular and transcellular transport systems. This study demonstrates that CLDN7 plays an important role in salt balance in renal CD cells and modulating WNK4 and ENaC expression levels that are vital in controlling salt-sensitive hypertension.

Non-tight junction-related function of claudin-7 in interacting with integrinβ1 to suppress colorectal cancer cell proliferation and migration

Purpose

We conducted a preliminarily exploration of the role and possible mechanism of the non-tight junction-related function of claudin-7 in the occurrence and development of colorectal cancer.

Methods

We selected the colorectal cancer cell line HCT116, constructed a stably transfected claudin-7 knockdown cell line via RNAi and lentiviral infection, and determined the claudin-7 knockdown efficiency. We assessed the biological behavior changes (cell viability, apoptosis, and migration) in the stably transfected HCT116 cells and observed structural changes in the tight junction by transmission electron microscopy. We used a subcutaneous tumor formation model to assess the tumorigenicity of HCT116 cells after claudin-7 knockdown. We assessed the expression and localization of integrinβ1 in the stably transfected cell line by immunofluorescence staining and investigated the interaction between integrinβ1 and claudin-7 by co-immunoprecipitation.

Results

After the knockdown of claudin-7 the expression, the viability and migration ability of HCT116 cells increased and apoptosis decreased. Transmission electron microscopy indicated that the intercellular tight junction structure did not change substantially. Furthermore, the tumor growth in nude mice was enhanced. Immunofluorescence staining showed that integrinβ1 and claudin-7 were co-expressed and co-localized on the cell membrane, and immunoprecipitation suggested that claudin-7 interacts with integrinβ1.

Conclusion

Claudin-7 may inhibit the proliferation and migration of tumor cells by interacting with integrinβ1, subsequently participating in the development of colorectal cancer.

Claudin-7 gene knockout causes destruction of intestinal structure and animal death in mice

BACKGROUND

Claudin-7, one of the important components of cellular tight junctions, is currently considered to be expressed abnormally in colorectal inflammation and colorectal cancer. However, there is currently no effective animal model to study its specific mechanism. Therefore, we constructed three lines of Claudin-7 knockout mice using the Cre/LoxP system.

AIM

To determine the function of the tumor suppressor gene Claudin-7 by generating three lines of Claudin-7 gene knockout mice.

METHODS

We crossed Claudin-7-floxed mice with CMV-Cre, vil1-Cre, and villin-CreERT2 transgenic mice, and the offspring were self-crossed to obtain conventional Claudin-7 knockout mice, conditional (intestinal specific) Claudin-7 knockout mice, and inducible conditional Claudin-7 knockout mice. Intraperitoneal injection of tamoxifen into the inducible conditional Claudin-7 knockout mice can induce the knockout of Claudin-7. PCR and agarose gel electrophoresis were used to identify mouse genotypes, and Western blot was used to confirm the knockout of Claudin-7. The mental state, body length, and survival time of these mice were observed. The dying mice were sacrificed, and hematoxylin-eosin (HE) staining and immunohistochemical staining were performed to observe changes in intestinal structure and proliferation markers.

RESULTS

We generated Claudin-7-floxed mice and three lines of Claudin-7 gene knockout mice using the Cre/LoxP system successfully. Conventional and intestinal specific Claudin-7 knockout mice were stunted and died during the perinatal period, and intestinal HE staining in these mice revealed mucosal gland structure disappearance and connective tissue hyperplasia with extensive inflammatory cell infiltration. The inducible conditional Claudin-7 knockout mice had a normal phenotype at birth, but after the induction with tamoxifen, they exhibited a dying state. Intestinal HE staining showed significant inflammatory cell infiltration, and atypical hyperplasia and adenoma were also observed. Intestinal immunohistochemistry analysis showed abnormal expression and distribution of Ki67, and the normal intestinal proliferation balance was disrupted. The intestinal crypt size in inducible conditional Claudin-7 knockout mice was increased compared with control mice (small intestine: 54.1 ± 2.96 vs 38.4 ± 1.63; large intestine: 44.7 ± 1.93 vs 27.4 ± 0.60; P < 0.001).

CONCLUSION

The knockout of Claudin-7 in vivo causes extensive inflammation, atypical hyperplasia, and adenoma in intestinal tissue as well as animal death in mice. Claudin-7 may act as a tumor suppressor gene in the development of colorectal cancer.

Claudin-7 downregulation induces metastasis and invasion in colorectal cancer via the promotion of epithelial-mesenchymal transition. Biochem Biophys Res Commun. 2019;508:797-804. [PMID: 30528239 DOI: 10.1016/j.bbrc.2018.10.049]

The dysregulation of the tight junctions (TJs) protein claudin-7 is closely related to the development and metastasis of colorectal cancer (CRC). The aim of this study was to investigate the expression of claudin-7 and characterize the relationship between claudin-7 expression and epithelial-mesenchymal transition (EMT) in CRC. In this study, the expression of claudin-7, E-cadherin, vimentin and snail-1 was detected by immunohistochemistry (IHC) in a set of 80 CRC specimens comprising 20 specimens each of well-differentiated, moderately differentiated, poorly differentiated and liver metastases tissues. The correlation between claudin-7 and EMT-related proteins in the stably transfected claudin-7 knockdown HCT116 cell line was analyzed by IHC, immunofluorescence (IF), Western blotting (WB) and nude mouse xenograft models. The results revealed that the expression of claudin-7 was downregulated as CRC tissue differentiation grade decreased, and that low claudin-7 expression corresponded to the downregulation of E-cadherin (r = 0.725, p < 0.001) and upregulation of vimentin (r = -0.376, p = 0.001) and snail-1 (r = -0.599, p < 0.001). Additionally, in the claudin-7 knockdown HCT116 cell line, the staining intensity and expression of E-cadherin was decreased, while the immunoreactivity and expression of vimentin and snail-1 was increased. Futhermore, the result of tumor formation experiment was consistent with CRC tissues. In conclusion, the expression of claudin-7 in CRC is downregulated as differentiation grade decreases. Claudin-7 downregulation may promote the invasion and metastasis of CRC by regulating EMT. Our results provide new perspectives for a potential therapeutic target for CRC.

Immunoreactivity patterns of tight junction proteins are useful for differential diagnosis of human salivary gland tumors

The expression pattern of tight junction proteins (TJPs) varies among organs and tumor types. In this study, we examined the immunoreactivity of claudin (CLDN)-1, -4, and -7, and JAM-A in salivary gland tumors (SGTs) by histological types and cell types to estimate their usefulness as differential diagnostic markers. Immunoreactivity of CLDN1 was higher in ductal epithelium cells of SGTs than in non-tumor tissues. Conversely, immunoreactivity of CLDN1 was significantly decreased in basal/myoepithelium cells of SGTs compared with that in non-tumor tissues. There was no significant difference between the immunoreactivity of CLDN1 in benign tumors and that in malignant tumors. Immunoreactivity of CLDN4, CLDN7, and JAM-A in ductal epithelium cells was higher in many SGTs than in non-tumor tissues. There was a difference depending on the histological type of SGT in immunoreactivity of CLDN4, CLDN7, and JAM-A in basaloid/myoepithelial cells. It was possible to classify SGTs by a hierarchical clustering using immunoreactivity of TJPs. The results suggest that an immunohistochemical marker panel including these TJPs may be useful for differential diagnosis of SGTs and that CLDN1 is associated with tumorigenesis of SGTs.

Immunohistochemical quantification of expression of a tight junction protein, claudin-7, in human lung cancer samples using digital image analysis method

BACKGROUND AND OBJECTIVES

Tight junction proteins are correlated with cancer development. As the pivotal proteins in epithelial cells, altered expression and distribution of different claudins have been reported in a wide variety of human malignancies. We have previously reported that claudin-7 was strongly expressed in benign bronchial epithelial cells at the cell-cell junction while expression of claudin-7 was either altered with discontinued weak expression or completely absent in lung cancers. Based on these results, we continued working on the expression pattern of claudin-7 and its relationship with lung cancer development. We herein proposed a new Digital Image Classification, Fragmentation index, Morphological analysis (DICFM) method for differentiating the normal lung tissues and lung cancer tissues based on the claudin-7 immunohistochemical staining.

METHODS

Seventy-seven lung cancer samples were obtained from the Second Affiliated Hospital of Zhejiang University and claudin-7 immunohistochemical staining was performed. Based on C++ and Open Source Computer Vision Library (OpenCV, version 2.4.4), the DICFM processing module was developed. Intensity and fragmentation of claudin-7 expression, as well as the morphological parameters of nuclei were calculated. Evaluation of results was performed using Receiver Operator Characteristic (ROC) analysis.

RESULTS

Agreement between these computational results and the results obtained by two pathologists was demonstrated. The intensity of claudin-7 expression was significantly decreased while the fragmentation was significantly increased in the lung cancer tissues compared to the normal lung tissues and the intensity was strongly positively associated with the differentiation of lung cancer cells. Moreover, the perimeters of the nuclei of lung cancer cells were significantly greater than that of the normal lung cells, while the parameters of area and circularity revealed no statistical significance.

CONCLUSIONS

Taken together, our DICFM approach may be applied as an appropriate approach to quantify the immunohistochemical staining of claudin-7 on the cell membrane and claudin-7 may serve as a marker for identification of lung cancer.

Developmental Expression of Claudins in the Mammary Gland

Claudins are a large family of membrane proteins whose classic function is to regulate the permeability of tight junctions in epithelia. They are tetraspanins, with four alpha-helices crossing the membrane, two extracellular loops, a short cytoplasmic N-terminus and a longer and more variable C-terminus. The extracellular ends of the helices are known to undergo side-to-side (cis) interactions that allow the formation of claudin polymers in the plane of the membrane. The extracellular loops also engage in head-to-head (trans) interactions thought to mediate the formation of tight junctions. However, claudins are also present in intracellular structures, thought to be vesicles, with less well-characterized functions. Here, we briefly review our current understanding of claudin structure and function followed by an examination of changes in claudin mRNA and protein expression and localization through mammary gland development. Claudins-1, 3, 4, 7, and 8 are the five most prominent members of the claudin family in the mouse mammary gland, with varied abundance and intracellular localization during the different stages of post-pubertal development. Claudin-1 is clearly localized to tight junctions in mammary ducts in non-pregnant non-lactating animals. Cytoplasmic puncta that stain for claudin-7 are present throughout development. During pregnancy claudin-3 is localized both to the tight junction and basolaterally while claudin-4 is found only in sparse puncta. In the lactating mouse both claudin-3 and claudin-8 are localized at the tight junction where they may be important in forming the paracellular barrier. At involution and under challenge by lipopolysaccharide claudins -1, -3, and -4 are significantly upregulated. Claudin-3 is still colocalized with tight junction molecules but is also distributed through the cytoplasm as is claudin-4. These largely descriptive data provide the essential framework for future mechanistic studies of the function and regulation of mammary epithelial cell claudins.

Generation of an inducible Claudin-7 conditional knockout mouse line

AIM: To create an inducible Claudin-7 conditional knockout (ICKO) mouse line using the Cre/LoxP system and analyze the phenotype after inducing knockout in the intestine.

METHODS: Claudin-7 conditional knockout targeted vector was constructed and then transfected into embryonic stem (ES) cells by electroporation. The targeted ES cells were screened by positive-negative selection, and identified by PCR and Southern blot. The screened targeted ES cells were microinjected into the blastula of C57BL/6N mice. Chimerical mice were generated after transplanting the blastula into the host mice, and then the Claudin-7-floxed mice were generated by crossing between the chimerical mice and C57BL/6N mice. Claudin-7 ICKO mice could be obtained by crossing between Pvillin-CreERT2 transgenic mice and Claudin-7-floxed mice. A further phenotype analysis was made by HE staining.

RESULTS: We obtained Claudin-7-floxed mice and Cldn7fl/flVillin-CreERT2 homozygous mice successfully. The deletion of Claudin-7 gene expression in mouse intestinal epithelial cells was successfully induced by tamoxifen. After tamoxifen induction, the mice developed dehydration, the degree of living activity decreased, and death occurred.

CONCLUSION: We have successfully created an inducible Claudin-7 conditional knockout mouse line and induced the gene deletion in the intestine using tamoxifen, which may be used as a model of intestinal inflammation.

Expression of claudin-7 and loss of claudin-18 correlate with poor prognosis in gastric cancer

BACKGROUND

The purpose of this study was to evaluate the expression of claudin-3, claudin-7, and claudin-18 in gastric cancer and to determine the significance of these proteins for patient outcome.

MATERIALS AND METHODS

A total of 134 samples were obtained from surgically resected specimens from patients who were diagnosed with gastric carcinoma at a single institution. Paraffin tissue sections from tissue microarray blocks were examined with immunohistochemistry for the expression of claudin-3, claudin-7, and claudin-18.

RESULTS

In normal gastric tissues, positive immunoreactivity was detected for claudin-18 but not for claudin-3 or claudin-7. Claudin-3 and claudin-7 were expressed in 25.4% and 29.9% of the gastric cancer tissues, respectively. However, 51.5% of gastric cancer tissues exhibited reduced expression of claudin-18. Claudin-7 expression was significantly lower in cases with diffuse histologic type and positive lymphatic invasion. There was a significant inverse correlation between claudin-18 expression and perineural invasion. In the survival analysis, the overall survival time was shorter in patients with claudin-7 expression than in those without claudin-7 expression. However, the overall survival was longer in patients with claudin-18 expression than in those without claudin-18 expression.

CONCLUSIONS

Our data suggest that the up-regulation of claudin-3 and claudin-7 and the down-regulation of claudin-18 may play a role in the carcinogenesis of gastric cancer. Furthermore, the expression of claudin-7 and the loss of claudin-18 may be independent indicators of a poor prognosis in patients with gastric cancer.

Lack of claudin-7 is a strong predictor of regional recurrence in oral and oropharyngeal squamous cell carcinoma

OBJECTIVES

Adequate treatment of oral and oropharyngeal squamous cell carcinoma (OSCC) is dependent on correctly predicting the presence of lymph node metastases. Current methods to diagnose nodal metastases partly result in overtreatment with associated morbidity and undertreatment with decreased disease-free survival. E-cadherin has been studied extensively as potential marker for lymph node metastases. EpCAM and claudin-7 have a functional relationship with E-cadherin, forming a complex that promotes tumourigenicity in vitro. We hypothesize that the co-expression patterns of these related molecules is a better prognostic marker for nodal status and regional recurrences.

MATERIALS AND METHODS

We constructed separate tissue microarrays of tumour centre and tumour invasive front of 227 OSCC with complete clinicopathological and follow-up data, including HPV status, and performed immunohistochemistry for these molecules.

RESULTS

Lack of E-cadherin and presence of cytoplasmic EpCAM expression in the tumour front were predictive for nodal metastasis, but no co-expression pattern was found clinically relevant. Lack of claudin-7 in the tumour centre was highly and independently predictive for shorter regional disease-free survival (HR=0.19; 95%CI: 0.06-0.62) and disease-specific survival (HR=0.43; 95%CI: 0.21-0.87). High-risk HPV was not associated with any marker.

CONCLUSIONS

The expression of E-cadherin and EpCAM, depending on the specific tumour sublocalization, is predictive for nodal status. However, co-expression did not improve the prediction of nodal status, indicating that the proposed in vitro complex is not functional in clinical samples. Additionally, lack of claudin-7 expression in the tumour centre may be used to identify patients with increased risk for regional recurrence.

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

Objectives

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

Materials and methods

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

Results

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

Conclusions

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