Junctions gone bad: Claudins and loss of the barrier in cancer

Selective Role of TNFα and IL10 in Regulation of Barrier Properties of the Colon in DMH-Induced Tumor and Healthy Rats

Recently it has been reported that the tumor adjacent colon tissues of 1,2-dymethylhydrazine induced (DMH)-rats revealed a high paracellular permeability. We hypothesized that the changes might be induced by cytokines. Colorectal cancer is accompanied by an increase in tumor necrosis factor alpha (TNFα) and interleukin 10 (IL10) that exert opposite regulatory effects on barrier properties of the colon, which is characterized by morphological and functional segmental heterogeneity. The aim of this study was to analyze the level of TNFα and IL10 in the colon segments of DMH-rats and to investigate their effects on barrier properties of the proximal and distal parts of the colon in healthy rats. Enzyme immunoassay analysis showed decreased TNFα in tumors in the distal part of the colon and increased IL10 in proximal tumors and in non-tumor tissues. Four-hour intraluminal exposure of the colon of healthy rats with cytokines showed reduced colon barrier function dependent on the cytokine: TNFα decreased it mainly in the distal part of the colon, whereas IL10 decreased it only in the proximal part. Western blot analysis revealed a more pronounced influence of IL10 on tight junction (TJ) proteins expression by down-regulation of the TJ proteins claudin-1, -2 and -4, and up-regulation of occludin only in the proximal part of the colon. These data may indicate a selective role of the cytokines in regulation of the barrier properties of the colon and a prominent role of IL10 in carcinogenesis in its proximal part.

Hypomethylation of CLDN4 Gene Promoter Is Associated with Malignant Phenotype in Urinary Bladder Cancer

The tight junction (TJ) protein claudin-4 (CLDN4) is overexpressed in bladder urothelial carcinoma (BUC) and correlates with cancer progression. However, the mechanism of CLDN4 upregulation and promotion of malignant phenotype is not clear. Here, we analyzed 157 cases of BUC and investigated the hypomethylation of CpG island in the CLDN4 promoter DNA and its correlation with cancer progression. In hypomethylated cases, CLDN4 expression, cell proliferation, stemness, and epithelial-mesenchymal transition were increased. Treatment of three human BUC cell lines with the demethylating agent aza-2′-deoxycytidine (AZA) led to excessive CLDN4 expression, and, specifically, to an increase in CLDN4 monomer that is not integrated into the TJ. The TJ-unintegrated CLDN4 was found to bind integrin β1 and increase stemness, drug resistance, and metastatic ability of the cells as well as show an anti-apoptosis effect likely via FAK phosphorylation, which reduces upon knockdown of CLDN4. Thus, CLDN4 is overexpressed in BUC by an epigenetic mechanism and the high expression enhances the malignant phenotype of BUC via increased levels of TJ-unintegrated CLDN4. CLDN4 promoter DNA methylation is expected to be a novel indicator of BUC malignant phenotype and a new therapeutic target.

TGF-β induces GBM mesenchymal transition through upregulation of CLDN4 and nuclear translocation to activate TNF-α/NF-κB signal pathway

Glioblastoma (GBM) is the most common and aggressive primary malignant brain tumor. The unregulated expression of Claudin-4 (CLDN4) plays an important role in tumor progression. However, the biological role of CLDN4 in GBM is still unknown. This study aimed to determine whether CLDN4 mediates glioma malignant progression, if so, it would further explore the molecular mechanisms of carcinogenesis. Our results revealed that CLDN4 was significantly upregulated in glioma specimens and cells. The inhibition of CLND4 expression could inhibit mesenchymal transformation, cell invasion, cell migration and tumor growth in vitro and in vivo. Moreover, combined with in vitro analysis, we found that CLDN4 can modulate tumor necrosis factor-α (TNF-α) signal pathway. Meanwhile, we also validated that the transforming growth factor-β (TGF-β) signal pathway can upregulate the expression of CLDN4, and promote the invasion ability of GBM cells. Conversely, TGF-β signal pathway inhibitor ITD-1 can downregulate the expression of CLDN4, and inhibit the invasion ability of GBM cells. Furthermore, we found that TGF-β can promote the nuclear translocation of CLDN4. In summary, our findings indicated that the TGF-β/CLDN4/TNF-α/NF-κB signal axis plays a key role in the biological progression of glioma. Disrupting the function of this signal axis may represent a new treatment strategy for patients with GBM.

Effects of 1,2-Dimethylhydrazine on Barrier Properties of Rat Large Intestine and IPEC-J2 Cells

Colon cancer is accompanied by a decrease of epithelial barrier properties, which are determined by tight junction (TJ) proteins between adjacent epithelial cells. The aim of the current study was to analyze the expression of TJ proteins in a rat model of 1,2-dimethylhydrazine (DMH)-induced colorectal cancer, as well as the barrier properties and TJ protein expression of IPEC-J2 cell monolayers after incubation with DMH. Transepithelial electrical resistance and paracellular permeability for sodium fluorescein of IPEC-J2 were examined by an epithelial volt/ohm meter and spectrophotometry. The expression and localization of TJ proteins were analyzed by immunoblotting and immunohistochemistry. In the colonic tumors of rats with DMH-induced carcinogenesis, the expression of claudin-3 and -4 was significantly increased compared to controls. The transepithelial electrical resistance of IPEC-J2 cells increased, while paracellular permeability for sodium fluorescein decreased, accompanied by an increased expression of claudin-4. The increase of claudin-4 in rat colon after chronic DMH exposure was consistent with the acute effect of DMH on IPEC-J2 cells, which may indicate an essential role of this protein in colorectal cancer development.

Immune infiltration profiling in gastric cancer and their clinical implications

The abundance and type of immune cells in the tumor microenvironment (TME) significantly influence immunotherapy and tumor progression. However, the role of immune cells in the TME of gastric cancer (GC) is poorly understood. We studied the correlations, proportion, and infiltration of immune and stromal cells in GC tumors. Data analyses showed a significant association of infiltration levels of specific immune cells with the pathological characteristics and clinical outcomes of GC. Furthermore, based on the difference in infiltration levels of immune and stromal cells, GC patients were divided into two categories, those with "immunologically hot" (hot) tumors and those with "immunologically cold" (cold) tumors. The assay for transposase-accessible chromatin using sequencing and RNA sequencing analyses revealed that the hot and cold tumors had altered epigenomic and transcriptional profiles. Claudin-3 (CLDN3) was found to have high expression in the cold tumors and negatively correlated with CD8⁺ T cells in GC. Overexpression of CLDN3 in GC cells inhibited the expression of MHC-I and CXCL9. Finally, the differentially expressed genes between hot and cold tumors were utilized to generate a prognostic model, which predicted the overall survival of GC as well as patients with immunotherapy. Overall, we undertook a comprehensive analysis of the immune cell infiltration pattern in GC and provided an accurate model for predicting the prognosis of GC patients.

The claudin-transcription factor signaling pathway

Claudins (CLDNs) represent major transmembrane proteins of tight junctions and contribute to the barrier function. They also serve as anchors for several signaling proteins, but the underlying molecular basis has yet to be established. The present review covers the recent progress in our understanding of the CLDN signaling pathway in health and disease. We discuss the functional relevance of phosphotyrosine motifs in the C-terminal cytoplasmic domain of CLDNs and define mutual regulation between CLDNs and Src-family kinases (SFKs). In addition, we focus on the crosstalk between CLDN and transcription factor signaling. We also describe how aberrant CLDN–transcription factor signaling promotes or inhibits cancer progression. We propose that a link between various cell adhesion molecules and transcription factors coordinates a range of physiological and pathological events via activation or suppression of target genes.

Reduced Claudin-12 Expression Predicts Poor Prognosis in Cervical Cancer

Background: Within the claudin (CLDN) family, CLDN12 mRNA expression is altered in various types of cancer, but its clinicopathological relevance has yet to be established due to the absence of specific antibodies (Abs) with broad applications. Methods: We generated a monoclonal Ab (mAb) against human/mouse CLDN12 and verified its specificity. By performing immunohistochemical staining and semiquantification, we evaluated the relationship between CLDN12 expression and clinicopathological parameters in tissues from 138 cases of cervical cancer. Results: Western blot and immunohistochemical analyses revealed that the established mAb selectively recognized the CLDN12 protein. Twenty six of the 138 cases (18.8%) showed low CLDN12 expression, and the disease-specific survival (DSS) and recurrence-free survival rates were significantly decreased compared with those in the high CLDN12 expression group. We also demonstrated, via univariable and multivariable analyses, that the low CLDN12 expression represents a significant prognostic factor for the DSS of cervical cancer patients (HR 3.412, p = 0.002 and HR 2.615, p = 0.029, respectively). Conclusions: It can be concluded that a reduced CLDN12 expression predicts a poor outcome for cervical cancer. The novel anti-CLDN12 mAb could be a valuable tool to evaluate the biological relevance of the CLDN12 expression in diverse cancer types and other diseases.

Role of Nuclear Claudin-4 in Renal Cell Carcinoma

Claudin-4 (CLDN4) is a tight junction protein to maintain the cancer microenvironment. We recently reported the role of the CLDN4 not forming tight junction in the induction of epithelial-mesenchymal transition (EMT). Herein, we investigated the role of CLDN4 in renal cell carcinoma (RCC), focusing on CLDN4. CLDN4 expression in 202 RCCs was examined by immunostaining. CLDN4 phosphorylation and subcellular localization were examined using high metastatic human RCC SN12L1 and low metastatic SN12C cell lines. In 202 RCC cases, the CLDN4 expression decreased in the cell membrane and had no correlation with clinicopathological factors. However, CLDN4 was localized in the nucleus in 5 cases (2%), all of which were pT3. Contrastingly, only 6 of 198 nuclear CLDN4-negative cases were pT3. CLDN4 was found in the nuclear fraction of a highly metastatic human RCC cell line, SN12L1, but not in the low metastatic SN12C cells. In SN12L1 cells, phosphorylation of tyrosine and serine residues was observed in cytoplasmic CLDN4, but not in membranous CLDN4. In contrast, phosphorylation of serine residues was observed in nuclear CLDN4. In SN12L1 cells, CLDN4 tyrosine phosphorylation by EphA2/Ephrin A1 resulted in the release of CLDN4 from tight junction and cytoplasmic translocation. Furthermore, protein kinase C (PKC)-ε phosphorylated the CLDN4 serine residue, resulting in nuclear import. Contrarily, in SN12C cells that showed decreased expression of EphA2/Ephrin A1 and PKCε, the activation of EphA2/EphrinA1 and PKCε induced cytoplasmic and nuclear translocation of CLDN4, respectively. Furthermore, the nuclear translocation of CLDN4 promoted the nuclear translocation of Yes-associated protein (YAP) bound to CLDN4, which induced the EMT phenotype. These findings suggest that the release of CLDN4 by impaired tight junction might be a mechanism underlying the malignant properties of RCC. These findings suggest that the release of CLDN4 by impaired tight junction might be one of the mechanisms of malignant properties of RCC.

Targeting claudin-4 enhances chemosensitivity in breast cancer

Triple negative breast cancer (TNBC) is characterized by highly aggressive phenotype, limited treatment options and a poor prognosis. In the present study, we examined the therapeutic effect of anti–claudin (CLDN)‐4 extracellular domain antibody, 4D3, on TNBC. When the expression of CLDN4 and CLDN1 in invasive ductal carcinoma (IDC) was examined in 114 IDC (78 cases from 2004 to 2009 in a single center and 36 cases of tissues array), CLDN1 had lower expression than CLDN4 and was correlated with histological grade. In contrast, expression of CLDN4 was correlated with histological grade, receptor subtype, and stage. CLDN4 expression in human IDC cell lines MCF‐7 (luminal subtype) and MDA‐468 (TNBC) was at the same level. In both cells, paclitaxel (PTX)‐induced growth suppression was enhanced by 4D3. Furthermore, 4D3 increased both intracellular PTX concentration (in both cells) and apoptosis. In the mouse model, 4D3 promoted the antitumor effect of PTX on subcutaneous tumors and reduced lung metastasis. The combination of PTX and 4D3 reduced M2 macrophages and mesenchymal stem cells in the tumor. 4D3 also reduced stemness of the tumors and increased the intratumoral pH. Moreover, concurrent treatment with 4D3, PTX and tamoxifen, or with PTX and tamoxifen in MDA‐468 also showed the same level of antitumor activity and survival as MCF‐7. Furthermore, in a bone metastasis model, combination of PTX and bisphosphonate with 4D3 promoted tumor growth in both cells. Thus, CLDN4 targeting of the antibody facilitated existing therapeutic effects.

Claudin-9 enhances the metastatic potential of hepatocytes via Tyk2/Stat3 signaling

BACKGROUND/AIMS

We have previously identified a tight junction protein claudin-9 (CLDN9) as an upregulated gene in hepatocellular carcinoma (HCC) through an immunohistochemistry analysis. Here, we explore its function and clinical relevance in human HCC.

MATERIALS AND METHODS

Stable transfection of the hepatocyte line HL7702 with CLDN9 was confirmed by the real-time polymerase chain reaction (PCR), western blotting, and immunofluorescence. The impact of CLDN9 on the cell invasion and migration was assessed in vitro by a transwell assay and wound-healing experiment. Western blotting was used to determine the activation state of the Tyk2 (tyrosine kinase 2)/Stat3 (signal transducer and activator of transcription 3) pathway. Moreover, we used a Tyk2-RNAi assay to silence the expression of Tyk2 in CLDN9 expressing hepatocytes; subsequently, the impact of the Tyk2/Stat3 signaling pathway on the cell invasion and migration in vitro was assessed by a transwell assay and a wound-healing experiment. Furthermore, an immunohistochemistry method was utilized to explore the expression levels of CLDN9 and p-Stat3 in the HCC tissues and histologically non-neoplastic hepatic tissues.

RESULTS

We confirmed that the expression of CLDN9 significantly enhanced the metastatic ability of hepatocytes in vitro, and the activation of the Stat3 pathway by Tyk2 was an important mechanism by which CLDN9 promoted hepatocyte aggressiveness in HCC.

CONCLUSION

As an HCC proto-oncogene, CLDN9 affected the Stat3 signaling pathway via Tyk2 and ultimately enhanced the metastatic ability of hepatocytes.

Clostridium perfringens enterotoxin induces claudin-4 to activate YAP in oral squamous cell carcinomas

Claudin (CLDN)-4 expression has been associated with malignancy in various cancers. When CLDN4 expression was examined in oral squamous cell carcinoma (OSCC), 22 out of 57 (39%) cases showed immunoreactivity in the nucleus. Nuclear CLDN4-positive cases showed a stronger correlation with cancer progression than the negative cases. Intratumoral anaerobic bacterial DNA examination revealed nuclear CLDN4 expression in 81% of Clostridium perfringens-positive cases. Treatment of human oral squamous cell carcinoma cell lines HSC3 and HSC4 with Clostridium perfringens enterotoxin (CPE), induced CLDN4 nuclear translocation to enhance epithelial-mesenchymal transition (EMT), stemness, cell proliferation and invasive ability. In addition, CPE treatment suppressed phosphorylation of yes-associated protein-1 (YAP1) and promoted YAP1 nuclear translocation, resulting in increased expression of YAP1 target genes; cyclin D1 and connective tissue growth factor. Moreover, it was revealed that the complex of YAP1, CLDN4 and zona occludens-2 (ZO-2) was formed by CPE treatment, further suppressing YAP1 phosphorylation by LATS1 and activating it. Thus YAP activation in OSCC was regarded important in promoting malignant phenotypes. Our research suggested that the control of oral anaerobic bacteria may suppress YAP activation and in turn tumor progression.

Integrative Gene Expression Profiling Analysis to Investigate Potential Prognostic Biomarkers for Colorectal Cancer

BACKGROUND Despite noteworthy advancements in the multidisciplinary treatment of colorectal cancer (CRC) and deeper understanding in the molecular mechanisms of CRC, many of CRC patients with histologically identical tumors present different treatment response and prognosis. Thus, more evidence on novel predictive and prognostic biomarkers for CRC remains urgently needed. This study aims to identify potential prognostic biomarkers for CRC with integrative gene expression profiling analysis. MATERIAL AND METHODS Differential expression analysis of paired CRC and adjacent normal tissue samples in 6 microarray datasets was independently performed, and the 6 datasets were integrated by the robust rank aggregation method to detect consistent differentially expressed genes (DEGs). Aberrant expression patterns of these genes were further validated in RNA sequencing data. Then, gene set enrichment analysis (GSEA) was performed to investigate significantly dysregulated biological functions in CRC. Finally, univariate, LASSO and multivariate Cox regression models were built to identify key prognostic genes in CRC patients. RESULTS A total of 990 DEGs (495 downregulated and 495 upregulated genes) were acquired after integratedly analyzing the 6 microarray datasets, and 4131 DEGs (2050 downregulated and 2081 upregulated genes) were obtained from the RNA sequencing dataset. Subsequently, these DEGs were intersected and 885 consistent DEGs were finally identified, including 458 downregulated and 427 upregulated genes. Two risky prognostic genes (TIMP1 and LZTS3) and 5 protective prognostic genes (AXIN2, CXCL1, ITLN1, CPT2 and CLDN23) were identified, which were significantly associated with the prognosis of CRC. CONCLUSIONS The 7 genes that we identified would provide more evidence for further applying novel diagnostic and prognostic biomarkers in clinical practice to facilitate personalized treatment of CRC.

Targeting claudin-4 enhances chemosensitivity of pancreatic ductal carcinomas

Claudin (CLDN) family comprises of protein that form a tight junction, and is involved in regulating polarity and differentiation of cells. Here, we aimed to investigate the effects of inhibiting CLDN4 in pancreatic ductal carcinomas (PDC). We first examined 91 cases of human PDC by immunohistochemistry and found that CLDN4 expression was correlated with tumor invasion, nodal metastasis, and distant metastasis. Anti-CLDN4 extracellular domain antibody, previously established by us (4D3), inhibited the proliferation of MIA-PaCa-2 PDC cells and increased intracellular 5-fluorouracil (5-FU) concentration with lowering transepithelial electrical resistance. Concurrent treatment of 5-FU and 4D3 resulted in synergistic inhibition of growth of MIA-PaCa-2 cells in nude mice. In addition, MIA-PaCa-2 cell tumors treated with full-dose folfirinox (FFX) decreased tumor diameters to 50%; however, 60% of mice were dead from adverse effects. In contrast, half-dose FFX concomitant with 4D3 treatment decreased tumors equivalent to full-dose FFX, but without the adverse effects. These findings suggest that targeting CLDN4 might increase the effectiveness and safety of anticancer drug therapy in PDC.

Low Expression of Occludin in the Melanoma Patient

BACKGROUND & OBJECTIVE

Malignant melanoma is the fatal cutaneous neoplasm which is curable by the early diagnosis. The expression of occludin protein which is an integral membrane protein is altered in an epithelial-to-mesenchymal transition. Although, recent studies provide sufficient evidence supporting the functional importance of occludin in cancer, the prognostic significance of occludin expression levels in melanoma remains obscure. The aim of this study was to determine occludin expression level and its correlation with clinicopathological features of the patients with melanoma.

METHODS

The occludin mRNA level was compared between paraffin-embedded tissues of 40 patients with melanoma and 10 subjects with normal skin. The quality and quantity of the RNA was determined and occludin expression level was measured using Real-time PCR and ∆∆CT computational technique.

RESULTS

The occludin mRNA level reduced five-fold in the melanoma patients compared to the control group (P=0.000). No significant difference was observed between male and female cases (P=0.533). No significant correlation was observed between occludin mRNA level, mitotic count (P=0.252), and Breslow levels (P=0.171).

CONCLUSION

We can conclude that down-regulation of occludin expression in the patients with melanoma is a hallmark of cancer progression and it might be used as a prognostic factor. No significant correlation was found between occludin gene expression and clinicopathological characteristics including Clark level, Breslow staging, mitotic count, age and gender (P<0.05).

Impact of chemotherapy on the expression of claudins and cadherins in invasive breast cancer

The importance of the expression profile of claudins in the molecular classification of breast cancer (BC) is currently under investigation. Claudins, together with cadherins, serve an important role in the epithelial-mesenchymal transition and influence the chemosensitivity of cancer cells. Adjuvant chemotherapy is administered following surgical resection in selected cases of BC. Previous neoadjuvant chemotherapy may change the molecular profile of a tumour and subsequently also its chemosensitivity. In the current study, the expression of claudin-1, −3 and −4, E- and N-cadherin and the standard BC biomarkers [oestrogen receptor (ER), progesterone receptor (PR), human epidermal growth factor receptor 2 (HER2) and marker of proliferation Ki-67 (Ki-67)] in formalin-fixed, paraffin-embedded sections from 62 patients with invasive BC was analysed using immunohistochemistry prior to and following neoadjuvant chemotherapy. The results revealed increased expression of claudin-1 (P=0.03) and decreased expression of claudin-3 (P=0.005), PR (P<0.001) and Ki-67 (P=0.01) following the neoadjuvant therapy. No significant changes in the expression of ER, claudin-4 or E- and N-cadherin were observed following therapy. Furthermore, an association between the expression of claudin-1 and the standard BC markers (P<0.05) was identified. A high expression of claudin-1 was more frequently observed in the triple-negative BC cohort than in the cohort with positive ER, PR and/or HER2 before (P=0.04) and after chemotherapy (P=0.02). The expression of N-cadherin was associated with the expression of ER, PR, HER2 and tumour grade (P<0.05). A positive association between the expression of claudin-3 and E-cadherin (P=0.005) was observed. No association was found between the expression of E- and N-cadherin. In conclusion, significant changes in the expression of claudin-1 and −3 but not in the expression of claudin-4, E- and N-cadherin were observed in samples taken from patients with BC following chemotherapy. These findings indicate that claudins-1 and −3 serve a role in the response of BC to chemotherapy.

Regulation of Epithelial Cell Functions by the Osmolality and Hydrostatic Pressure Gradients: A Possible Role of the Tight Junction as a Sensor

Epithelia act as a barrier to the external environment. The extracellular environment constantly changes, and the epithelia are required to regulate their function in accordance with the changes in the environment. It has been reported that a difference of the environment between the apical and basal sides of epithelia such as osmolality and hydrostatic pressure affects various epithelial functions including transepithelial transport, cytoskeleton, and cell proliferation. In this paper, we review the regulation of epithelial functions by the gradients of osmolality and hydrostatic pressure. We also examine the significance of this regulation in pathological conditions especially focusing on the role of the hydrostatic pressure gradient in the pathogenesis of carcinomas. Furthermore, we discuss the mechanism by which epithelia sense the osmotic and hydrostatic pressure gradients and the possible role of the tight junction as a sensor of the extracellular environment to regulate epithelial functions.

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

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

Targeting claudin-4 enhances CDDP-chemosensitivity in gastric cancer

Claudins are major tight-junction proteins that mediate cellular polarity and differentiation. The present study investigated whether the 4D3 antibody to the human CLDN4 extracellular domain (that we previously established) is capable of modulating chemotherapeutic sensitivity in gastric cancer (GC). The results of the present study showed that CLDN4 was overexpressed in 137 of the 192 analyzed GC cases, and that CLDN4 expression was retained in tumors of a lower histological grade (more differentiated), and/or those that were caudal-type homeobox protein 2 (CDX2)-positive, but was reduced in more highly undifferentiated, and CDX2-negative GC cases. The study also compared the synergic effects of combining 4D3 with CDDP treatment and knocking down CLDN4 expression in MKN74 and TMK-1 human GC cells. Co-treatment with 4D3 increased anti-tumor effects of CDDP, whereas CLDN4 knockdown did not. In the TMK-1 cells, non-tight junction CLDN4 associated with integrin β1, increasing stem cell-associated proteins via FAK-c-SRC signals. The anti-tumoral effect of CDDP and 4D3 was examined in a nude mouse subcutaneous tumor model. In the two GC cell lines, concurrent treatment with 4D3 and CDDP synergistically inhibited cell proliferation and increased tumor necrosis and apoptosis to a greater degree than CDDP treatment alone. These findings suggest that 4D3 might increase chemotherapeutic sensitivity by evoking structural disintegration of tight-junction CLDN4 expressed in gastric cancer.

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

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

Increased expression of claudin-17 promotes a malignant phenotype in hepatocyte via Tyk2/Stat3 signaling and is associated with poor prognosis in patients with hepatocellular carcinoma

Background

Hepatocellular carcinoma (HCC) is the second leading cause of cancer death in Asia; however, the molecular mechanism in its tumorigenesis remains unclear. Abnormal expression of claudins (CLDNs), a family of tight junction (TJ) proteins, plays an important role in the metastatic phenotype of epithelial-derived tumors by affecting tight junction structure, function and related cellular signaling pathways. In a previous study, we used a tissue chip assay to identify CLDN17 as an upregulated gene in HCC. Here we aimed to use molecular biology technology to explore the effect of CLDN17 on the malignant phenotype of HCC and the underlying molecular mechanism, with the objective of identifying a new target for HCC treatment and the control of HCC metastasis.

Method

The expression levels of CLDN17 in HCC tissues and histologically non-neoplastic hepatic tissues were explored by immunohistochemistry. Stable transfection of the hepatocyte line HL7702 with CLDN17 was detected by real-time polymerase chain reaction (PCR), western blotting and immunofluorescence. The impact of CLDN17 on the malignant phenotype of HL7702 cells in vitro was assessed by a Cell Counting Kit-8 (CCK8) assay, a Transwell assay and a wound-healing experiment. Western blotting was utilized to detect the activation state of Tyrosine kinase 2 (Tyk2) / signal transducer and activator of transcription3 (Stat3) pathway. A Tyk2 RNA interference (RNAi) was utilized to determine the impact of the Tyk2/Stat3 signaling pathway on the malignant phenotype of hepatocytes.

Results

In this work, our research group first found that CLDN17 was highly expressed in HCC tissues and was associated with poor prognosis. In addition, we demonstrated that CLDN17 affected the Stat3 signaling pathway via Tyk2 and ultimately enhanced the migration ability of hepatocytes.

Conclusion

In conclusion, we confirmed that the upregulated expression of CLDN17 significantly enhances the migration ability of hepatocytes in vitro and we found that the activation of the Stat3 pathway by Tyk2 may an important mechanism by which CLDN17 promotes aggressiveness in hepatocytes.

Tight Junction barriers in human hair follicles - role of claudin-1

Barrier function of hair follicles (HFs) is of great interest because they might be an entry port for allergens/pathogens, but could on the other hand be used for drug delivery or vaccination. Therefore we investigated tight junction (TJ) barrier function in human HFs. We show that there is a TJ barrier in the outermost living layer bordering to the environment from the infundibulum to the lower central part and between Henle’s and Huxles layer of anagen HFs. In club hair typical for catagen and telogen HFs a TJ barrier is found surrounding the club. This demonstrates that there is a continuous TJ barrier along interfollicular epidermis and HFs in different phases of HF cycle. However, interestingly, in cell culture experiments we can show that barrier is less tight in HF keratinocytes compared to interfollicular keratinocytes. Knock-down of the TJ protein claudin-1, which we demonstrate here to be less expressed in HFs of lesional atopic dermatitis skin, results in impaired barrier function, decreased proliferation and increased apoptosis of hair keratinocytes. This is in line with a hair growth phenotype in claudin-1 deficient patients (NISCH syndrome) and corresponding knock-out mice and indicates an important role of claudin-1 in HF barrier function and growth.

Intestinal regulation of suppression of tumorigenicity 14 (ST14) and serine peptidase inhibitor, Kunitz type -1 (SPINT1) by transcription factor CDX2

The type II membrane-anchored serine protease, matriptase, encoded by suppression of tumorgenicity-14 (ST14) regulates the integrity of the intestinal epithelial barrier in concert with its inhibitor, HAI-1 encoded by serine peptidase inhibitor, Kunitz type -1 (SPINT1). The balance of the protease/inhibitor gene expression ratio is vital in preventing the oncogenic potential of matriptase. The intestinal cell lineage is regulated by a transcriptional regulatory network where the tumor suppressor, Caudal homeobox 2 (CDX2) is considered to be an intestinal master transcription factor. In this study, we show that CDX2 has a dual function in regulating both ST14 and SPINT1, gene expression in intestinal cells. We find that CDX2 is not required for the basal ST14 and SPINT1 gene expression; however changes in CDX2 expression affects the ST14/SPINT1 mRNA ratio. Exploring CDX2 ChIP-seq data from intestinal cell lines, we identified genomic CDX2-enriched enhancer elements for both ST14 and SPINT1, which regulate their corresponding gene promoter activity. We show that CDX2 displays both repressive and enhancing regulatory abilities in a cell specific manner. Together, these data reveal new insight into transcriptional mechanisms controlling the intestinal matriptase/inhibitor balance.

HER2 Basolateral versus Circumferential IHC Expression Is Dependent on Polarity and Differentiation of Epithelial Cells in Gastric/GE Adenocarcinoma

Aim

Antigenic expression in epithelial cells can be heterogeneous which may pose a problem in immunohistochemical (IHC) analysis of tumor markers, in particular, predictive markers like HER2. Studies have shown that epithelial cells have distinct apical and basolateral domains which are separated by tight junctions. The cell membrane in these two domains has a different composition of macromolecules and hence can have variable antigen expression on immunohistochemistry. In our study, we aimed to investigate this phenomenon of basolateral versus circumferential IHC staining of HER2 in gastric/GE adenocarcinoma.

Methods

We selected 45 cases of gastric/GE adenocarcinoma and evaluated equal number of specimens (15 each) showing well-differentiated, moderately differentiated, and poorly differentiated morphology. All cases had 3+ HER2 score as per CAP guidelines. HER2-membrane staining pattern in all specimens was analyzed.

Results

Cases with well-differentiated morphology showed only basolateral or lateral membrane staining in most cases. Poorly differentiated adenocarcinoma samples showed circumferential staining (both basolateral and luminal) in all cases with highly significant p value. Mixed staining pattern was observed in moderately differentiated cases. Diffuse expression of E-cadherin in well-differentiated adenocarcinoma and loss in poorly differentiated tumors were also statistically significant.

Conclusion

These findings suggest that HER2 in gastric epithelium has a polarized distribution which is maintained by the fence function of tight junctions. With progression to high grade cancer, the glandular structural differentiation in gastric mucosa is lost, along with disruption of tight junctions. This leads to loss of cell polarity and migration of antigens across the membrane.

Inactivation of the tight junction gene CLDN11 by aberrant hypermethylation modulates tubulins polymerization and promotes cell migration in nasopharyngeal carcinoma

BACKGROUND

Aberrant hypermethylation of cellular genes is a common phenomenon to inactivate genes and promote tumorigenesis in nasopharyngeal carcinoma (NPC).

METHODS

Methyl binding domain (MBD)-ChIP sequencing of NPC cells, microarray data of NPC biopsies and gene ontology analysis were conducted to identify a potential tumor suppressor gene CLDN11 that was both hypermethylated and downregulated in NPC. Bisulfite sequencing, qRT-PCR, immunohistochemistry staining of the NPC clinical samples and addition of methylation inhibitor, 5'azacytidine, in NPC cells were performed to verify the correlation between DNA hypermethylation and expression of CLDN11. Promoter reporter and EMSA assays were used to dissect the DNA region responsible for transcription activator binding and to confirm whether DNA methylation could affect activator's binding, respectively. CLDN11 was transiently overexpressed in NPC cells followed by cell proliferation, migration, invasion assays to characterize its biological roles. Co-immunoprecipitation experiments and proteomic approach were carried out to identify novel interacting protein(s) and the binding domain of CLDN11. Anti-tumor activity of the CLDN11 was elucidated by in vitro functional assay.

RESULTS

A tight junction gene, CLDN11, was identified as differentially hypermethylated gene in NPC. High methylation percentage of CLDN11 promoter in paired NPC clinical samples was correlated with low mRNA expression level. Immunohistochemistry staining of NPC paired samples tissue array demonstrated that CLDN11 protein expression was relatively low in NPC tumors. Transcription activator GATA1 bound to CLDN11 promoter region - 62 to - 53 and its DNA binding activity was inhibited by DNA methylation. Re-expression of CLDN11 reduced cell migration and invasion abilities in NPC cells. By co-immunoprecipitation and liquid chromatography-tandem mass spectrometry LC-MS/MS, tubulin alpha-1b (TUBA1B) and beta-3 (TUBB3), were identified as the novel CLDN11-interacting proteins. CLDN11 interacted with these two tubulins through its intracellular loop and C-terminus. Furthermore, these domains were required for CLDN11-mediated cell migration inhibition. Treatment with a tubulin polymerization inhibitor, nocodazole, blocked NPC cell migration.

CONCLUSIONS

CLDN11 is a hypermethylated and downregulated gene in NPC. Through interacting with microtubules TUBA1B and TUBB3, CLDN11 blocks the polymerization of tubulins and cell migration activity. Thus, CLDN11 functions as a potential tumor suppressor gene and silencing of CLDN11 by DNA hypermethylation promotes NPC progression.

Methylation of the claudin‑3 promoter predicts the prognosis of advanced gastric adenocarcinoma

Claudin-3 expression is associated with gastric cancer progression, but the role of epigenetic modifications remains unclear. We investigated methylation of the claudin-3 promoter and expression profiles in gastric adenocarcinoma and their associations with clinicopathological characteristics and prognosis of the patients. A total of 122 patients with advanced gastric cancer [stage IIB-IV, with lymph node (LN) metastasis] were enrolled. Each patient provided 4 tissue samples: normal gastric epithelium, intestinal metaplasia, primary tumor and metastatic LN. Claudin-3 protein expression was examined by immunohistochemistry. Claudin-3 promoter methylation was determined by methylation-specific PCR and verified by bisulfite sequencing PCR. Claudin-3 mRNA expression was measured by real-time PCR in a subset of cases, and its correlation with protein expression was analyzed using Spearman correlation. Kaplan-Meier survival analysis was performed (log-rank test). Factors associated with survival were identified by Cox regression. The strong expression rate of claudin-3 in intestinal metaplasia, primary tumor, metastatic LN and normal gastric epithelium was 91.8, 58.2, 30.3 and 13.9%, respectively. The promoter hypermethylation rate in intestinal metaplasia, primary tumor, normal gastric epithelium and metastatic LN was 5.7, 27.9, 36.9 and 49.2%, respectively. Claudin-3 mRNA and protein expression were positively correlated (P<0.001) with normal gastric epithelium (r_s=0.745), intestinal metaplasia (r_s=0.876), primary gastric adenocarcinoma (r_s=0.915) and metastatic LN (r_s=0.819). Claudin-3 mRNA expression was negatively correlated with claudin-3 promoter methylation. Median patient survival was 38, 22 and 11 months in the hypomethylated, partially methylated and hypermethylated groups, respectively (P<0.001). Claudin-3 promoter methylation status (HR: 5.67; 95% CI: 2.27–14.17) but not claudin-3 expression was an independent predictor of survival. Claudin-3 promoter hypermethylation reduces claudin-3 expression and independently predicts poor prognosis.

Significant Down-Regulation of "Biological Adhesion" Genes in Porcine Oocytes after IVM

Proper maturation of the mammalian oocyte is a compound processes determining successful monospermic fertilization, however the number of fully mature porcine oocytes is still unsatisfactory. Since oocytes’ maturation and fertilization involve cellular adhesion and membranous contact, the aim was to investigate cell adhesion ontology group in porcine oocytes. The oocytes were collected from ovaries of 45 pubertal crossbred Landrace gilts and subjected to two BCB tests. After the first test, only granulosa cell-free BCB⁺ oocytes were directly exposed to microarray assays and RT-qPCR (“before IVM” group), or first in vitro matured and then if classified as BCB⁺ passed to molecular analyses (“after IVM” group). As a result, we have discovered substantial down-regulation of genes involved in adhesion processes, such as: organization of actin cytoskeleton, migration, proliferation, differentiation, apoptosis, survival or angiogenesis in porcine oocytes after IVM, compared to oocytes analyzed before IVM. In conclusion, we found that biological adhesion may be recognized as the process involved in porcine oocytes’ successful IVM. Down-regulation of genes included in this ontology group in immature oocytes after IVM points to their unique function in oocyte’s achievement of fully mature stages. Thus, results indicated new molecular markers involved in porcine oocyte IVM, displaying essential roles in biological adhesion processes.

SMAD2 Inactivation Inhibits CLDN6 Methylation to Suppress Migration and Invasion of Breast Cancer Cells

The downregulation of tight junction protein CLDN6 promotes breast cancer cell migration and invasion; however, the exact mechanism underlying CLDN6 downregulation remains unclear. CLDN6 silence is associated with DNA methyltransferase 1 (DNMT1) mediated DNA methylation, and DNMT1 is regulated by the transforming growth factor beta (TGFβ)/SMAD pathway. Therefore, we hypothesized that TGFβ/SMAD pathway, specifically SMAD2, may play a critical role for CLDN6 downregulation through DNA methyltransferase 1 (DNMT1) mediated DNA methylation. To test this hypothesis, we blocked the SMAD2 pathway with SB431542 in two human breast cancer cell lines (MCF-7 and SKBR-3). Our results showed that treatment with SB431542 led to a decrease of DNMT1 expression and the binding activity for CLDN6 promoter. The methylation level of CLDN6 promoter was decreased, and simultaneously CLDN6 protein expression increased. Upregulation of CLDN6 inhibited epithelial to mesenchymal transition (EMT) and reduced the migration and invasion ability of both MCF-7 and SKBR-3 cells. Furthermore, knocked down of CLDN6 abolished SB431542 effects on suppression of EMT associated gene expression and inhibition of migration and invasion. Thus, we demonstrated that the downregulation of CLDN6 is regulated through promoter methylation by DNMT1, which depends on the SMAD2 pathway, and that CLDN6 is a key regulator in the SMAD2/DNMT1/CLDN6 pathway to inhibit EMT, migration and invasion of breast cancer cells.

Autocrine Human Growth Hormone Promotes Invasive and Cancer Stem Cell-Like Behavior of Hepatocellular Carcinoma Cells by STAT3 Dependent Inhibition of CLAUDIN-1 Expression

Despite progress in diagnosis and treatment of hepatocellular carcinoma (HCC), the clinical outcome is still unsatisfactory. Increased expression of human growth hormone (hGH) in HCC has been reported and is associated with poor survival outcome in HCC patients. Herein, we investigated the mechanism of the oncogenic effects of hGH in HCC cell lines. In vitro functional assays demonstrated that forced expression of hGH in these HCC cell lines promoted cell proliferation, cell survival, anchorage-independent growth, cell migration, and invasion, as previously reported. In addition, forced expression of hGH promoted cancer stem cell (CSC)-like properties of HCC cells. The increased invasive and CSC-like properties of HCC cells with forced expression of hGH were mediated by inhibition of the expression of the tight junction component CLAUDIN-1. Consistently, depletion of CLAUDIN-1 expression increased the invasive and CSC-like properties of HCC cell lines. Moreover, forced expression of CLAUDIN-1 abrogated the acquired invasive and CSC-like properties of HCC cell lines with forced expression of hGH. We further demonstrated that forced expression of hGH inhibited CLAUDIN-1 expression in HCC cell lines via signal transducer and activator of transcription 3 (STAT3) mediated inhibition of CLAUDIN-1 transcription. Hence, we have elucidated a novel hGH-STAT3-CLAUDIN-1 axis responsible for invasive and CSC-like properties in HCC. Inhibition of hGH should be considered as a therapeutic option to hinder progression and relapse of HCC.

Claudin-targeted drug development using anti-claudin monoclonal antibodies to treat hepatitis and cancer

The 27-member family of tetraspan membrane proteins known as claudins (CLDNs) is a major component of tight junctions. A series of studies elucidating the relationship between CLDNs and various pathological conditions has provided new insights into drug development. For instance, CLDN-1 may be a potent target for epidermal absorption of drugs and for treating hepatitis C virus (HCV) infection. CLDN-4 may be a target for treating cancer. Because CLDNs are also expressed in various normal tissues, safety and efficacy evaluations are critical for translational research. We previously developed several anti-CLDN antibodies and have established proof of concept for CLDN-targeted drug development using these reagents. Here, we provide an overview of CLDN-1 as a target for improving epidermal drug absorption and preventing HCV infection and of CLDN-4 as a target for anticancer therapeutics.

An emerging role for IQGAP1 in tight junction control

IQGAP1 is a scaffold protein involved in the assembly of adherens junctions. Our work has recently revealed a novel role for IQGAP1 in the regulation of tight junctions (TJ) through differential recruitment of claudins to the nascent TJ. Here, we discuss the potential mechanisms of this regulation, including IQGAP1 effects on CDC42, and IQGAP1 interactions with sorting/trafficking molecules (e.g. Exo70). Given the many roles of IQGAP1 and the large number of interacting partners, we focus our discussion of these functions in the context of junction formation, trafficking, growth factor signaling and cancer. We also propose a potential role for IQGAP1 in regulating epithelial integrity and compartmentalized signaling in epithelia.

Willing to Be Involved in Cancer

Genome sequencing is now a common procedure, but prior to this, screening experiments using protein baits was one of the routinely used methods that, occasionally, allowed the identification of new gene products. One such experiment uncovered the gene product called willin/human Expanded/FRMD6. Initial characterization studies found that willin bound phospholipids and was strongly co-localised with actin. However, subsequently, willin was found to be the closest human sequence homologue of the Drosophila protein Expanded (Ex), sharing 60% homology with the Ex FERM domain. This in turn suggested, and then was proven that willin could activate the Hippo signalling pathway. This review describes the increasing body of knowledge about the actions of willin in a number of cellular functions related to cancer. However, like many gene products involved in aspects of cell signalling, a convincing direct role for willin in cancer remains tantalisingly elusive, at present.

The role of barrier genes in epidermal malignancy

The outermost layer of the mammalian skin, the epidermis, forms a protective barrier against pathogenic microbes and tissue dehydration. This barrier is formed and maintained by complex genetic networks that connect cellular differentiation processes, enzymatic activities and cellular junctions. Disruption in these networks affects the balance between keratinocyte proliferation and differentiation resulting in barrier function impairment, epidermal hyperproliferation and in some cases, squamous cell carcinoma (SCC). Recent studies in wound-induced inflammation-mediated cancers in mice have identified dysregulation of core barrier components as tumor drivers. We therefore propose a hypothesis in which loss of key barrier genes, induce barrier dysfunction, and promote inflammation-driven epidermal hyperplasia and carcinogenesis over time. This emerging vision suggests that under specific genetic circumstances, localized barrier impairment could be considered as a hallmark of initiating lesions in epidermal SCC.

Tight junctions in inflammatory bowel diseases and inflammatory bowel disease associated colorectal cancer

Inflammatory bowel diseases are characterised by inflammation that compromises the integrity of the epithelial barrier. The intestinal epithelium is not only a static barrier but has evolved complex mechanisms to control and regulate bacterial interactions with the mucosal surface. Apical tight junction proteins are critical in the maintenance of epithelial barrier function and control of paracellular permeability. The characterisation of alterations in tight junction proteins as key players in epithelial barrier function in inflammatory bowel diseases is rapidly enhancing our understanding of critical mechanisms in disease pathogenesis as well as novel therapeutic opportunities. Here we give an overview of recent literature focusing on the role of tight junction proteins, in particular claudins, in inflammatory bowel diseases and inflammatory bowel disease associated colorectal cancer.

Claudin-4 is required for vasculogenic mimicry formation in human breast cancer cells

Vasculogenic mimicry (VM) refers to the unique capability of aggressive tumor cells to mimic the pattern of embryonic vasculogenic networks. Claudins are aberrantly expressed in aggressive breast cancer. However, the relationship between claudins and VM formation is not clear. We examined VM in two human breast cancer cell lines with different aggressive capabilities (MDA-MB-231 and MCF-7 cells) and one human umbilical vein endothelial cell line (HUVEC). Both HUVEC and MDA-MB-231 cells formed vascular channels in Matrigel cultures, while MCF-7 cells did not. Western blot analysis revealed a possible correlation between claudin-4 and -6 expression in breast cancer cell lines and tumor aggressiveness, with protein levels correlating with the ability to form vascular channels. Treatment of MDA-MB-231 and HUVEC cells with claudin-4 monoclonal antibodies completely inhibited the ability of cells to form vascular channels. Moreover, knockdown of claudin-4 by short hairpin RNA completely inhibited tubule formation in MDA-MB-231 cells. Overexpression of claudin-4 in MCF-7 cells induced formation of vascular channels. Immunocytochemistry revealed that membranous claudin-4 protein was significantly associated with vascular channel formation. Collectively, these results indicate that claudin-4 may play a critical role in VM in human breast cancer cells, opening new opportunities to improve aggressive breast cancer therapy.

Effects of Hydrostatic Pressure on Carcinogenic Properties of Epithelia

The relationship between chronic inflammation and cancer is well known. The inflammation increases the permeability of blood vessels and consequently elevates pressure in the interstitial tissues. However, there have been only a few reports on the effects of hydrostatic pressure on cultured cells, and the relationship between elevated hydrostatic pressure and cell properties related to malignant tumors is less well understood. Therefore, we investigated the effects of hydrostatic pressure on the cultured epithelial cells seeded on permeable filters. Surprisingly, hydrostatic pressure from basal to apical side induced epithelial stratification in Madin-Darby canine kidney (MDCK) I and Caco-2 cells, and cavities with microvilli and tight junctions around their surfaces were formed within the multi-layered epithelia. The hydrostatic pressure gradient also promoted cell proliferation, suppressed cell apoptosis, and increased transepithelial ion permeability. The inhibition of protein kinase A (PKA) promoted epithelial stratification by the hydrostatic pressure whereas the activation of PKA led to suppressed epithelial stratification. These results indicate the role of the hydrostatic pressure gradient in the regulation of various epithelial cell functions. The findings in this study may provide clues for the development of a novel strategy for the treatment of the carcinoma.

Claudin-1 enhances tumor proliferation and metastasis by regulating cell anoikis in gastric cancer

Claudin-1 (CLDN1) is overexpressed in gastric cancer and correlated with tumor invasion, metastasis and poor outcome. Here, we both down and up regulated CLDN1 expression in gastric cancer cells to elucidate its role in gastric carcinogenesis and tumor progression. We found that deficiency of CLDN1 inhibited cells migration, invasion, and colony formation in vitro and tumorigenicity, metastasis in vivo. Also, CLDN1 promoted cell aggregation and increased anoikis resistance. Down or up regulation of CLDN1 was accompanied with changes of membrane β-catenin expression as well as Akt and Src activities. When β-catenin was up-regulated in CLDN1-KD cells, cell aggregation and anoikis resistance were restored, and Akt and Src signal pathways were re-activated. Taken together, these findings suggest that CLDN1 is oncogenic in gastric cancer and its malignant potential may be attributed in part to regulation of anoikis, by mediating membrane β-catenin-regulated cell-cell adhesion and cell survival.

Claudin-3, claudin-7, and claudin-10 show different distribution patterns during decidualization and trophoblast invasion in mouse and human

Implantation of the mammalian embryo requires profound endometrial changes for successful pregnancy, including epithelial-mesenchymal transition of the luminal epithelium and stromal-epithelial transition of the stromal cells resulting in decidualization. Claudins (Cldn) determine the variability in tight junction paracellular permeability and may play a role during these epithelial and decidual changes. We here localized Cldn3, Cldn7 and Cldn10 proteins in the different compartments of murine endometrium up to day 8.5 of pregnancy (dpc) as well as in human endometrium and first trimester decidua. In murine estrous endometrium, luminal and glandular epithelium exhibited Cldn3 and Cldn7, whereas Cldn10 was only detectable in glandular epithelium. At 4.5 dpc, Cldn3 protein shifted to an apical localization, whereas Cldn7 vanished in the epithelium of the implantation chamber. At this stage, there was no stromal signal for Cldn3 and Cldn7, but a strong induction of Cldn10 in the primary decidual zone. Cldn3 proteins emerged at 5.5 dpc spreading considerably from 6.5 dpc onward in the endothelial cells of the decidual blood sinusoids and in the decidual cells of the compact antimesometrial region. In addition to Cldn3, Cldn10 was identified in human endometrial epithelia. Both proteins were not detected in human first trimester decidual cells. Cldn3 was shown in murine trophoblast giant cells as well as in human extravillous trophoblast cells and thus may have an impact on trophoblast invasion in both species. We here showed a specific claudin signature during early decidualization pointing to a role in decidual angiogenesis and regulation of trophoblast invasion.

CITED4 gene silencing in colorectal cancer cells modulates adherens/tight junction gene expression and reduces cell proliferation

Purpose

CITED4 is one member of a family of transcriptional cofactors, several of which are deregulated in a variety of tumors, including colorectal cancer (CRC). We modulated CITED4 expression, in vitro, and analyzed the associated phenotypic and gene expression changes.

Methods

CITED4-overexpressing and shRNA-mediated knockdown cell lines and control cell lines were established in the CRC cell line SW480. The cells were analyzed for changes in proliferation, apoptosis/cell cycle, migration, invasion, colony formation and adhesion. mRNA expression changes were determined by microarray and pathway analysis, and several deregulated genes were validated by qRT-PCR and Western blotting. Based on results obtained from these studies, the status of the actin cytoskeleton was evaluated by phalloidin/vinculin staining.

Results

Phenotypically, the CITED4-overexpressing cell line showed only moderate changes in adhesion. Microarray analysis identified several deregulated genes, including several G protein-coupled receptors. Phenotypic analysis of the CITED4 shRNA knockdown cell line demonstrated decreased cell proliferation and G2 cell cycle blockage. Microarray analysis identified many deregulated genes, and pathway analysis discovered genes linked to actin-associated adherens junctions/tight junctions (claudin-4, claudin-7, ezrin, MET, ß-catenin). Phenotypically, no morphological changes of the actin cytoskeleton were seen.

Conclusions

Upregulation of CITED4 in SW480 resulted in no obvious phenotype. CITED4 shRNA-mediated knockdown led to decreased cellular proliferation and modulation of a large number of genes, including the c-MET tyrosine kinase and several actin-associated adherens junctions/tight junction genes.

Electronic supplementary material

The online version of this article (doi:10.1007/s00432-015-2011-5) contains supplementary material, which is available to authorized users.

Expression changes of cell-cell adhesion-related genes in colorectal tumors

Epithelial tissues achieve a highly organized structure due to cell-cell junction complexes. Carcinogenesis is accompanied by changes in cell interactions and tissue morphology, which appear in the early stages of benign tumors and progress along with invasive potential. The aim of the present study was to analyze the changes in expression levels of genes encoding intercellular junction proteins that have been previously identified to be differentially expressed in colorectal tumors compared with normal mucosa samples (fold change, >2.5) in genome-wide expression profiling. The expression of 20 selected genes was assessed using quantitative reverse transcription polymerase chain reaction in 26 colorectal cancer, 42 adenoma and 24 normal mucosa samples. Between these tissue types, differences were observed in the mRNA levels of genes encoding adherens junction proteins (upregulation of CDH3 and CDH11, and downregulation of CDH19 and PTPRF), tight junction proteins (upregulation of CLDN1 and CLDN2, and downregulation of CLDN5, CLDN8, CLDN23, CLDN15, JAM2 and CGN) and desmosomes (upregulation of DSC3 and DSG3, and downregulation of DSC2), in addition to a decrease in the expression of certain other genes involved in intercellular connections: PCDHB14, PCDH7, MUPCDH and NEO1. The differences between tissue types were statistically significant, and separate clustering of normal adenoma and carcinoma samples was observed in a hierarchical clustering analysis. These results indicate that the morphological changes in neoplastic colon tissue that occur during the 'adenoma-carcinoma sequence' are accompanied by specific changes in the expression of multiple genes encoding the majority of cell-cell junction complexes. The particular differential expression patterns appear to be consistent among patients with cancer and adenoma, in addition to normal mucosa samples.

Classifying ten types of major cancers based on reverse phase protein array profiles

Gathering vast data sets of cancer genomes requires more efficient and autonomous procedures to classify cancer types and to discover a few essential genes to distinguish different cancers. Because protein expression is more stable than gene expression, we chose reverse phase protein array (RPPA) data, a powerful and robust antibody-based high-throughput approach for targeted proteomics, to perform our research. In this study, we proposed a computational framework to classify the patient samples into ten major cancer types based on the RPPA data using the SMO (Sequential minimal optimization) method. A careful feature selection procedure was employed to select 23 important proteins from the total of 187 proteins by mRMR (minimum Redundancy Maximum Relevance Feature Selection) and IFS (Incremental Feature Selection) on the training set. By using the 23 proteins, we successfully classified the ten cancer types with an MCC (Matthews Correlation Coefficient) of 0.904 on the training set, evaluated by 10-fold cross-validation, and an MCC of 0.936 on an independent test set. Further analysis of these 23 proteins was performed. Most of these proteins can present the hallmarks of cancer; Chk2, for example, plays an important role in the proliferation of cancer cells. Our analysis of these 23 proteins lends credence to the importance of these genes as indicators of cancer classification. We also believe our methods and findings may shed light on the discoveries of specific biomarkers of different types of cancers.

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 involvement of JAK-STAT3 in cell motility, invasion, and metastasis

JAK-STAT3 signaling, while regulating many aspects of cancer development and progression, promotes invasion and metastasis through activation of key metastasis promoting genes such as WASF3. STAT3 promotes WASF3 expression and JAK2 independently activates it, which is required for invasion. JAK-STAT3 signaling is dependent on WASF3 function, since its inactivation in cells expressing JAK-STAT3 suppresses invasion. WASF3 overexpression leads to activation of NFκB and ZEB1 which also promote invasion through regulation of target genes involved in metastasis. NFκB frequently cooperates with STAT3 to upregulate metastasis promoting genes such as matrix metalloproteinases and cytokines, as well as to suppress microRNAs which can suppresses invasion. This better understanding of the complex role played by JAK-STAT3 in the regulation of cell movement, invasion, and metastasis provides opportunities to suppress this lethal aspect of cancer progression by not only targeting the JAK and STAT3 proteins directly, but also some of the downstream effectors of JAK-STAT3 signaling.

HGF signaling regulates Claudin-3 dynamics through its C-terminal tyrosine residues

The hormone HGF regulates morphogenesis and regeneration of multiple organs and increased HGF signaling is strongly associated with metastatic cancer. At the cellular level, one of the distinct effects of HGF is the de-stabilization of cell-cell junctions. Several molecular mechanisms have been shown to be involved that mostly culminate at the E-cadherin adhesion complex. One of the key determinants in HGF-driven morphological changes is the actomyosin cytoskeleton whose organization and physical parameters changes upon stimulation. Here we have investigated how HGF affects the different actomyosin-associated cell-cell junction complexes, Nectin Junctions, Adherens Junctions and Tight Junctions in MDCK cells. We find that components of all complexes stay present at cell-cell contacts until their physical dissociation. We find that at cell-cell junctions, the mobility of Claudin-3, but not that of other cell-cell adhesion receptors, is affected by HGF. This depends on tyrosine residues that likely affect PDZ-domain interactions at the C-terminal tail of Claudin-3, although their phosphorylation is not directly regulated by HGF. Thus we uncovered Claudins as novel targets of HGF signaling at cell-cell junctions.

Tight junction protein claudin-1 is differentially expressed in craniopharyngioma subtypes and indicates invasive tumor growth

BACKGROUND

Claudins are tight junction proteins expressed in epithelial tissues that play important roles in cell polarity and adhesion. Altered distribution of claudin-1(CLDN1) affects cell mobility and tumor invasiveness. Craniopharyngiomas (CPs) represent epithelial tumors of the sellar region, consisting of adamantinomatous (adaCP) and papillary (papCP) variants. Their tendency to infiltrate surrounding brain structures complicates successful surgery. Reliable markers are required to predict tumor behavior and to establish individualized treatment protocols.

METHODS

We describe the distribution pattern of CLDN1 in a large cohort of 66 adaCPs, 21 papCPs, and 24 Rathke`s cleft cyst (RCC) cases using immunohistochemistry. CLDN1 mRNA levels were analyzed with qRT-PCR in 33 CP samples. The impact on the migration potential was studied in primary adaCP cell cultures (n = 11) treated with small interfering RNA (siRNA) for CLDN1. Furthermore, CLDN1 distribution patterns and expression levels were compared between invasive (n = 16) and noninvasive (n = 17) tumor groups.

RESULTS

PapCPs and RCCs exhibited a distinct homogenous and membranous expression pattern, whereas CLDN1 immunoreactivity appeared weaker and more heterogeneous in adaCPs. In the latter cases, whirl-like cell clusters showed complete absence of CLDN1. mRNA analysis confirmed reduced CLDN1 levels in adaCPs versus papCPs. Interestingly, invasive tumors exhibited significantly lower CLDN1 expression compared with noninvasive counterparts regardless of CP subtype. Accordingly, siRNA treatment for CLDN1 altered tumor cell migration in vitro.

CONCLUSION

CLDN1 represents a novel marker in the differential diagnosis of CP variants and RCCs. Low CLDN1 expression levels correlate with an invasive CP growth pattern and may serve as a prognostic marker.

All about claudins

Since the discovery of Claudins more than a decade ago, much has been learned about their structure-function relationships. Claudins are tetraspan membrane proteins responsible for the formation of tight junctions. In this capacity, Claudins form a tissue-specific selective permeability barrier that is critical for the function of the tissue. Claudins are developmentally regulated and expressed in a tissue- and cell-specific manner; chronic changes in their expression are associated with various disease states. The studies that have been put together in this Special Issue provide updates on both current knowledge as well as some of the unanswered questions and challenges in the field.

Inhibiting invasion into human bladder carcinoma 5637 cells with diallyl trisulfide by inhibiting matrix metalloproteinase activities and tightening tight junctions

Diallyl trisulfide (DATS), an organosulfur compound in garlic, possesses pronounced anti-cancer potential. However, the anti-invasive mechanism of this compound in human bladder carcinoma is not fully understood. In this study, we evaluated the anti-invasive effects of DATS on a human bladder carcinoma (5637) cell line and investigated the underlying mechanism. The results indicated that DATS suppressed migration and invasion of 5637 cells by reducing the activities and expression of matrix metalloproteinase (MMP)-2 and MMP-9 at both the protein and mRNA levels. DATS treatment up-regulated expression of tissue inhibitor of metalloproteinase (TIMP)-1 and TIMP-2 in 5637 cells. The inhibitory effects of DATS on invasiveness were associated with an increase in transepithelial electrical resistance and repression of the levels of claudin family members. Although further studies are needed, our data demonstrate that DATS exhibits anti-invasive effects in 5637 cells by down-regulating the activity of tight junctions and MMPs. DATS may have future utility in clinical applications for treating bladder cancer.

Mechanisms that link the oncogenic epithelial-mesenchymal transition to suppression of anoikis

The oncogenic epithelial-mesenchymal transition (EMT) contributes to tumor progression in various context-dependent ways, including increased metastatic potential, expansion of cancer stem cell subpopulations, chemo-resistance and disease recurrence. One of the hallmarks of EMT is resistance of tumor cells to anoikis. This resistance contributes to metastasis and is a defining property not only of EMT but also of cancer stem cells. Here, we review the mechanistic coupling between EMT and resistance to anoikis. The discussion focuses on several key aspects. First, we provide an update on new pathways that lead from the loss of E-cadherin to anoikis resistance. We then discuss the relevance of transcription factors that are crucial in wound healing in the context of oncogenic EMT. Next, we explore the consequences of the breakdown of cell-polarity complexes upon anoikis sensitivity, through the Hippo, Wnt and transforming growth factor β (TGF-β) pathways, emphasizing points of crossregulation. Finally, we summarize the direct regulation of cell survival genes through EMT-inducing transcription factors, and the roles of the tyrosine kinases focal adhesion kinase (FAK) and TrkB neurotrophin receptor in EMT-related regulation of anoikis. Emerging from these studies are unifying principles that will lead to improvements in cancer therapy by reprogramming sensitivity of anoikis.