Apoptosis signal-regulating kinase 1 is associated with the effect of claudin-6 in breast cancer

Expression patterns of claudins in cancer

Claudins are four-transmembrane proteins, which were found in tight junctions. They maintain cell barriers and regulate cell differentiation and proliferation. They are involved in maintaining cellular polarity and normal functions. Different claudins show different expression patterns. The expression level and localization of claudins are altered in various cancers. They promote or inhibit proliferation, invasion, and migration of cancer cells through multiple signaling pathways. Therefore, claudins may serve as diagnostic markers, novel therapeutic targets, and prognostic risk factors. The important roles of claudins in cancer aroused our great interest. In the present review, we provide a summary of insights into expression patterns of claudins in cancer, which is more comprehensive and provides new ideas for further research.

Binding of YY1/CREB to an Enhancer Region Triggers Claudin 6 Expression in H. pylori LPS-Stimulated AGS Cells

Aberrant expression of the tight junction protein claudin 6 (CLDN6) is a hallmark of gastric cancer progression. Its expression is regulated by the cAMP response element-binding protein (CREB). In gastric cancer induced by Helicobacter pylori (H. pylori) there is no information regarding what transcription factors induce/upregulate the expression of CLDN6. We aimed to identify whether CREB and Yin Yang1 (YY1) regulate the expression of CLDN6 and the site where they bind to the promoter sequence. Bioinformatics analysis, H. pylori lipopolysaccharide (LPS), YY1 and CREB silencing, Western blot, luciferase assays, and chromatin immunoprecipitation experiments were performed using the stomach gastric adenocarcinoma cell line AGS. A gen reporter assay suggested that the initial 2000 bp contains the regulatory sequence associated with CLDN6 transcription; the luciferase assay demonstrated three different regions with transcriptional activity, but the -901 to -1421 bp region displayed the maximal transcriptional activity in response to LPS. Fragment 1279-1421 showed CREB and, surprisingly, YY1 occupancy. Sequential Chromatin Immunoprecipitation (ChIP) experiments confirmed that YY1 and CREB interact in the 1279-1421 region. Our results suggest that CLDN6 expression is regulated by the binding of YY1 and CREB in the 901-1421 enhancer, in which a non-described interaction of YY1 with CREB was established in the 1279-1421 region.

The role and mechanism of claudins in cancer

Claudins are a tetraspan membrane protein multigene family that plays a structural and functional role in constructing tight junctions. Claudins perform crucial roles in maintaining cell polarity in epithelial and endothelial cell sheets and controlling paracellular permeability. In the last two decades, increasing evidence indicates that claudin proteins play a major role in controlling paracellular permeability and signaling inside cells. Several types of claudins are dysregulated in various cancers. Depending on where the tumor originated, claudin overexpression or underexpression has been shown to regulate cell proliferation, cell growth, metabolism, metastasis and cell stemness. Epithelial-to-mesenchymal transition is one of the most important functions of claudin proteins in disease progression. However, the exact molecular mechanisms and signaling pathways that explain why claudin proteins are so important to tumorigenesis and progression have not been determined. In addition, claudins are currently being investigated as possible diagnostic and treatment targets. Here, we discuss how claudin-related signaling pathways affect tumorigenesis, tumor progression, and treatment sensitivity.

Knockdown of CLAUDIN-6 Inhibited Apoptosis and Induced Proliferation of Bovine Cumulus Cells

This study aims to investigate the effects of CLAUDIN-6 (CLDN6) on cell apoptosis and proliferation of bovine cumulus cells (CCs). Immunofluorescence staining was used to localize CLDN6 protein in CCs. Three pairs of siRNA targeting CLDN6 and one pair of siRNA universal negative sequence as control were transfected into bovine CCs. Then, the effective siRNA was screened by real-time quantitative PCR (RT-qPCR) and Western blotting. The mRNA expression levels of apoptosis related genes (CASPASE-3, BAX and BCL-2) and proliferation related genes (PCNA, CDC42 and CCND2) were evaluated by RT-qPCR in CCs with CLDN6 knockdown. Cell proliferation, apoptosis and cell cycle were detected by flow cytometry with CCK-8 staining, Annexin V-FITC staining and propidium iodide staining, respectively. Results showed that the CLDN6 gene was expressed in bovine CCs and the protein was localized in cell membranes and cytoplasms. After CLDN6 was knocked down in CCs, the cell apoptosis rate significantly decreased and the pro-apoptotic genes BAX and CASPASE-3 were down-regulated significantly, whereas the anti-apoptotic gene BCL-2 was markedly up-regulated (p < 0.05). Additionally, CLDN6 knockdown significantly enhanced cell proliferation of CCs at 72 h after siRNA transfection. The mRNA levels of proliferation-related genes PCNA, CCND2 and CDC42 increased obviously in CCs with CLDN6 knockdown (p < 0.05). After CLDN6 was down-regulated, the percentage of CCs at S phase was significantly increased (p < 0.05). However, there was no remarkable difference in the percentages of cells at the G0/G1 phase and G2/M phase between CCs with or without CLDN6 knockdown (p > 0.05). Therefore, the expression of CLDN6 and its effects on cell proliferation, apoptosis and cell cycle of bovine CCs were first studied. CLDN6 low expression inhibited cell apoptosis, induced cell proliferation and cell cycle arrest of bovine CCs.

CLDN6 inhibits breast cancer cell malignant behavior by suppressing ERK signaling

Claudin 6 (CLDN6) is an important component of tight junctions. Through the PDZ binding motif, CLDN6 binds to a variety of signaling proteins that contain the PDZ domain to regulate different signaling pathways, and plays an important role in the occurrence and development of tumors. Our previous work showed that CLDN6 was expressed at low levels in breast cancer cells, and overexpression of CLDN6 inhibited breast cancer cell proliferation, migration and invasion. However, the mechanism of how CLDN6 works remains unclear. In this study, we aimed to explore the mechanism by which CLDN6 inhibits breast cancer cell malignant behavior. As a result, overexpression of CLDN6 inhibited the proliferation of breast cancer cells along with the downregulation of cyclin D1, which plays an important role in regulating cell proliferation. After overexpression of Sp1 in CLDN6-overexpressing cells, the expression of cyclin D1 was upregulated. On the other hand, CLDN6 inhibited breast cancer cell migration and invasion along with the downregulation of IL-8, CXCR2 and FAK. When treated with IL-8, the migration and invasion ability were promoted along with the upregulation of CXCR2 and p-FAK, and the cytoskeleton was rearranged in CLDN6-overexpressing cells. Furthermore, when treated with the ERK signaling activator PMA, the proliferation, migration and invasion abilities were promoted along with the upregulation of Sp1, cyclin D1 and IL-8 in CLDN6-overexpressin cells. In conclusion, CLDN6 suppressed ERK/Sp1/cyclin D1 and ERK/IL-8 signaling to inhibit proliferation, migration and invasion in breast cancer cells. The mechanism may provide experimental evidence for the treatment of breast cancer targeting CLDN6.

Claudin 6: Therapeutic prospects for tumours, and mechanisms of expression and regulation (Review)

Tight junctions (TJs) are an important component of cell connectivity; they maintain cell polarity, permeability and adhesion, and participate in the regulation of cell proliferation and differentiation. The claudin (CLDN) family is integral to TJs, and CLDN6 is an important member of this family. Abnormal expression of CLDN6 can destroy the integrity of TJs through various mechanisms and can serve multiple roles in the occurrence and development of tumours. CLDN6 is widely expressed in various tumours but rarely expressed in healthy adult tissues. The aim of this review is to critically examine the recent literature on CLDN6, including its structure, expression in different tumours, regulatory mechanisms and therapeutic prospects. Although some conclusions are controversial, in certain tumours, such as liver, ovarian, endometrial and oesophageal cancer, and atypical teratoid/rhabdoid tumours, research consistently shows that CLDN6 is expressed in tumour tissues but is not expressed or is expressed at low levels in surrounding tissues. In these tumours, CLDN6 has potential as a carcinoembryonic antigen and a therapeutic target.

Effect of CXCR4 silencing with shRNA on MAPK signaling in ovarian cancer

Our previous study demonstrated that short hairpin RNA (shRNA) targeting of C-X-C chemokine receptor type 4 (CXCR4) significantly inhibited cell proliferation, metastasis and invasion. On the basis of these results, the aim of the present study was to determine the effects of shRNA-CXCR4 silencing on mitogen-activated protein kinase (MAPK) signaling in human SW626 ovarian cancer cells. Following silencing the CXCR4 gene with shRNA, the mRNA expression of apoptosis signal-regulating kinase 1 (ASK1) was determined using the reverse transcription-quantitative polymerase chain reaction, whereas the protein expression of extracellular-signal-regulated kinase (ERK)1/2 and phosphorylated (p)-c-Jun were determined using immunocytochemistry and western blotting. SW626 cells transfected with shRNA-CXCR4 exhibited significantly increased ASK1 mRNA expression (P<0.05), significantly increased p-c-Jun protein expression (P<0.05), and significantly decreased ERK1/2 protein expression (P<0.05). Silencing the CXCR4 gene with shRNA significantly inhibited cell proliferation, promoted cell apoptosis and may be mediated by the MAPK signaling pathway.

ASK family and cancer

Cancer is a major problem in public health and is one of the leading causes of mortality worldwide. Many types of cancer cells exhibit aberrant cellular signal transduction in response to stress, which often leads to oncogenesis. Mitogen-activated protein kinase (MAPK) signal cascades are one of the important intracellular stress signaling pathways closely related to cancer. The key molecules in MAPK signal cascades that respond to various types of stressors are apoptosis signal-regulating kinase (ASK) family members; ASK1, ASK2 and ASK3. ASK family members are activated by a wide variety of stressors, and they regulate various cellular responses, such as cell proliferation, inflammation and apoptosis. In this review, we will discuss both the oncogenic and anti-oncogenic roles of the ASK family members in various contexts of cancer development with deeper insights into the involvement of ASK family members in cancer pathology.

Bioinformatic analysis reveals potential properties of human Claudin-6 regulation and functions

Claudin-6 (CLDN6) is an integral component of the tight junction proteins in polarized epithelial and endothelial cells and plays a crucial role in maintaining cell integrity. Deregulation of CLDN6 expression and distribution in tumor tissues have been widely documented and correlated with cancer progression and metastasis. However, a complete mechanistic understanding of CLDN6 regulation and function remains to be studied. Herein, we show new potential properties of CLDN6 regulation and functions from bioinformatics analysis. Using numerous algorithms to characterize the CLDN6 gene promoter elements and the CLDN6 protein structure, physio-chemical and localization properties, and its evolutionary relationships. CLDN6 is regulated by a diverse set of transcription factors (SP1, SPR, AML-1a, CdxA, CRE-BP and CREB) and associated with the levels of methylation of CpG islands in promoters. The structural properties of CLDN6 indicate that it promotes cancer cell behavior via the ASK1-p38/JNK MAPK secretory signaling pathway. In conclusion, this information from bioinformatics analysis will help future attempts to better understand CLDN6 regulation and functions.

Claudin-4 controls the proliferation, apoptosis, migration and in vivo growth of MCF-7 breast cancer cells

Previous studies have shown that the expression of claudin-4 is upregulated in breast cancer. The aim of the present study was to investigate the role and the regulation of claudin-4 in MCF-7 breast cancer cells. For the in vitro experiments, MCF-7 cells were treated with recombinant vectors carrying cDNA for claudin-4 overexpression or short hairpin RNAs (shRNAs) for claudin-4 silencing. Cell proliferation was determined by an MTT assay and cell migration ability was measured by a wound-healing assay. The cell cycle profile and apoptotic rate were analyzed using flow cytometry. The effect of methylation status on claudin-4 expression was determined by PCR and western blotting. For the in vivo tumorigenesis analysis, MCF-7 cells with or without claudin-4 silencing were transplanted into nude mice. In vivo cell growth was evaluated 14 days after transplantation. We found that claudin-4 overexpression increased MCF-7 cell proliferation and migration, and reduced the rate of cell apoptosis. Silencing of claudin-4 induced the opposite effects in MCF-7 cells. In addition, claudin-4 expression was upregulated by demethylation. Moreover, the size of tumor formation was reduced in nude mice transplanted with claudin-4 silenced MCF-7 cells. These observations suggested that claudin-4, which was regulated by methylation status, plays an important role in breast cancer growth and malignancy via the control of cell proliferation, migration and apoptosis.

Expression of apoptosis signal-regulating kinase 1 is associated with tight junction protein claudin-6 in cervical carcinoma

In our previous work, apoptosis signal-regulating kinase 1 (ASK1), a member of the mitogen-activated protein kinase (MAPK) kinase family has been proved to be associated with the pro-apoptosis effect of tight junction protein claudin-6 in breast cancer. However, its expression in cervical carcinoma has not been reported. The ASK1 and claudin-6 expression in cervical carcinoma tissues and adjacent non-neoplastic tissues was examined by immunohistochemistry. The mRNA and protein expression of ASK1 and claudin-6 in cervical cancer carcinoma cells was detected by reverse transcription (RT)-PCR and western blot. The expression level of ASK1 was down-regulated in cervical carcinoma tissues compared with the adjacent non-neoplastic tissues and positively correlated with the level of claudin-6 in cervical carcinoma cells and tissues. Our present study reveals that ASK1 protein expression altered between human cervical carcinoma and adjacent non-neoplastic tissues. The expression of ASK1 is correlated with the level of claudin-6 in cervical carcinoma cells and tissues.

The expression patterns of tight junction protein claudin-1, -3, and -4 in human gastric neoplasms and adjacent non-neoplastic tissues

Recently, there is growing evidence that tight junction proteins are often abnormally regulated in human tumors. The function of tight junction proteins in the maintenance of normal epithelial physiology has been well discussed, but their role in the tumorigenesis of gastric cancer is less well defined. To explore the expression distinction of the tight junction proteins claudin-1, -3, and -4 expression in the gastric cancer, the expression of claudin-1, -3, and -4 in 92 gastric cancer tissues and the non-neoplastic tissues adjacent to the tumors were examined by immunohistochemistry. Compared with adjacent non-neoplastic tissues, the expression of claudin-1 was down regulated. However, the expression of claudin-3 and claudin-4 were up-regulated in gastric cancer tissue. In addition, the expression of claudin-3 is correlated with claudin-4 expression in gastric cancer. Our present study reveals that claudin-1, -3, and -4 protein expression altered between human gastric cancers and adjacent non-neoplastic tissues.

Emerging multifunctional roles of Claudin tight junction proteins in bone

The imbalance between bone formation and resorption during bone remodeling has been documented to be a major factor in the pathogenesis of osteoporosis. Recent evidence suggests a significant role for the tight junction proteins, Claudins (Cldns), in the regulation of bone remodeling processes. In terms of function, whereas Cldns act "canonically" as key determinants of paracellular permeability, there is considerable recent evidence to suggest that Cldns also participate in cell signaling, ie, a "noncanonical function". To this end, Cldns have been shown to regulate cell proliferation, differentiation, and gene expression in a variety of cell types. The present review will discuss Cldns' structure, their expression profile, regulation of expression, and their canonical and non- canonical functions in general with special emphasis on bone cells. In order to shed light on the noncanonical functions of Cldns in bone, we will highlight the role of Cldn-18 in regulating bone resorption and osteoclast differentiation. Collectively, we hope to provide a framework for guiding future research on understanding how Cldns modulate osteoblast and osteoclast function and overall bone homeostasis. Such studies should provide valuable insights into the pathogenesis of osteoporosis, and may highlight Cldns as novel targets for the diagnosis and therapeutic management of osteoporosis.

Expression of glucosylceramide synthase in invasive ductal breast cancer may be correlated with high estrogen receptor status and low HER-2 status

Abstract

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The distinct expression patterns of claudin-2, -6, and -11 between human gastric neoplasms and adjacent non-neoplastic tissues

Background

Cancers have a multifactorial etiology a part of which is genetic. Recent data indicate that expression of the tight junction claudin proteins is involved in the etiology and progression of cancer.

Methods

To explore the correlations of the tight junction proteins claudin-2,-6, and −11 in the pathogenesis and clinical behavior of gastric cancer, 40 gastric cancer tissues and 28 samples of non-neoplastic tissues adjacent to the tumors were examined for expression of claudin-2,-6, and −11 by streptavidin-perosidase immunohistochemical staining method.

Results

The positive expression rates of claudin-2 in gastric cancer tissues and adjacent tissues were 25% and 68% respectively (P < 0.001). The positive expression rates of claudin-6 in gastric cancer tissues and adjacent tissues were 55% and 79% respectively (P = 0.045 < 0.05). In contrast, the positive expression rates of claudin-11 in gastric cancer tissues and gastric cancer adjacent tissues were 80% and 46% (P = 0.004 < 0.01). Thus in our study, the expression of claudin-2, and claudin-6 was down regulated in gastric cancer tissue while the expression of claudin-11 was up regulated. Correlations between claudin expression and clinical behavior were not observed.

Conclusion

Our study provides the first evidence that claudin-2,-6, and −11 protein expression varies between human gastric cancers and adjacent non-neoplastic tissues.

Virtual slides

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