Downregulation of CLDN6 inhibits cell proliferation, migration, and invasion via regulating EGFR/AKT/mTOR signalling pathway in hepatocellular carcinoma

Role of tight junction proteins in shaping the immune milieu of malignancies

INTRODUCTION

Tight junctions (TJs) and their constituent proteins play pivotal roles in cellular physiology and anatomy by establishing functional boundaries within and between neighboring cells. While the involvement of TJ proteins, such as claudins, in cancer is extensively studied, studies highlighting their interaction with immune system are still meager. Studies indicate that alterations in cytokines and immune cell populations can affect TJ proteins, compromising TJ barrier function and exacerbating pro-inflammatory conditions, potentially leading to epithelial cell malignancy. Disrupted TJs in established tumors may foster a pro-tumor immune microenvironment, facilitating tumor progression, invasion, epithelial-to-mesenchymal transition and metastasis. Although previous literature contains many studies describing the involvement of TJs in pathogenesis of malignancies their role in modulating the immune microenvironment of tumors is just beginning to be unleashed.

AREAS COVERED

This article for the first time attempts to discern the importance of interaction between TJs and immune microenvironment in malignancies. To achieve the above aim a thorough search of databases like PubMed and Google Scholar was conducted to identify the recent and relevant articles on the topic.

EXPERT OPINION

Breaking the vicious cycle of dysbiosis/infections/chemical/carcinogen-induced inflammation-TJ remodeling-malignancy-TJ dysregulation-more inflammation can be used as a strategy to complement the effect of immunotherapies in various malignancies.

CLDN6 inhibited cellular biological function of nonsmall cell lung cancer cells through suppressing aerobic glycolysis via the RIP1/ASK1/JNK axis

Claudin-6 (CLDN6) has been extensively studied in different tumors to date. However, in the case of nonsmall cell lung cancer (NSCLC), CLDN6 has a largely unknown role and molecular mechanism. We detected the expression of CLDN6 in NSCLC tissues and cells using reverse transcription-quantitative polymerase chain reaction (PCR) and western blot assays. A gain-of-function experiment was performed to evaluate the biological effects of CLDN6 on NSCLC cell behaviors. Methylation-specific PCR was utilized to detect the DNA methylation of CLDN6 gene promoter region. The interaction of CLDN6 and receptor interacting protein 1 (RIP1) was determined by coimmunoprecipitation assay. Furthermore, the modulation of CLDN6 on RIP1/apoptosis signal-regulating kinase 1 (ASK1)/c-Jun N-terminal kinase (JNK) axis was confirmed. The results showed that in NSCLC tissues and cells, CLDN6 expression level was declined, and was associated with a high level of DNA methylation. CLDN6 overexpression suppressed the viability, invasion, migration, and promoted cell apoptosis. Besides, the enhanced expression of CLDN6 reduced the glycolysis and the dysfunction of mitochondrial respiration of NSCLC cells. Mechanistic investigation confirmed that CLDN6 interacted with RIP1 and inhibited cellular biological function of NSCLC cells via RIP1/ASK1/JNK axis. Besides, CLDN6 overexpression inhibited tumor growth in vivo. In conclusion, CLDN6 inhibited NSCLC cell proliferation through inactivating aerobic glycolysis via the RIP1/ASK1/JNK axis.

Claudins and hepatocellular carcinoma

Hepatocellular carcinoma (HCC) has a high incidence and dismal prognosis, making it a significant global health burden. To change this, the development of new therapeutic strategies is imminent. The claudin (CLDN) family, as key components of tight junctions (TJs), plays an important role in the initiation and development of cancer. Dysregulated expression of CLDNs leads to loss of intercellular adhesion and aberrant cell signaling, which are closely related to cancer cell invasion, migration, and epithelial-mesenchymal transition (EMT). CLDN1, CLDN3, CLDN4, CLDN5, CLDN6, CLDN7, CLDN9, CLDN10, CLDN11, CLDN14, and CLDN17 are aberrantly expressed in HCC, which drives the progression of the disease. Consequently, they have tremendous potential as prognostic indicators and therapeutic targets. This article summarizes the aberrant expression, molecular mechanisms, and clinical application studies of different subtypes of CLDNs in HCC, with a particular emphasis on CLDN1.

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.

Targeting EGFR/PI3K/AKT/mTOR Signaling in Hepatocellular Carcinoma

Hepatocellular carcinoma (HCC) poses a significant global health concern, with its incidence steadily increasing. The development of HCC is a multifaceted, multi-step process involving alterations in various signaling cascades. In recent years, significant progress has been made in understanding the molecular signaling pathways that play central roles in hepatocarcinogenesis. In particular, the EGFR/PI3K/AKT/mTOR signaling pathway in HCC has garnered renewed attention from both basic and clinical researchers. Preclinical studies in vitro and in vivo have shown the effectiveness of targeting the key components of this signaling pathway in human HCC cells. Thus, targeting these signaling pathways with small molecule inhibitors holds promise as a potential therapeutic option for patients with HCC. In this review, we explore recent advancements in understanding the role of the EGFR/PI3K/AKT/mTOR signaling pathway in HCC and assess the effectiveness of targeting this signaling cascade as a potential strategy for HCC therapy based on preclinical studies.

Claudin-6 enhances the malignant progression of gestational trophoblastic neoplasm by promoting proliferation and metastasis

PURPOSE

Choriocarcinoma (CC) is a rare and highly malignant epithelial tumour. However, the mechanism underlying its occurrence and development remains unknown. We aimed to reveal the biological significance and prognostic value of Claudin-6 (CLDN6) in gestational trophoblastic disease (GTD).

PATIENTS AND METHODS

We collected clinical GTD specimens from 2011 to 2019 and measured CLDN6 gene expression by immunohistochemistry (IHC). High-throughput mRNA sequencing (RNA-seq) revealed a GTD progression-associated gene. CCK-8, wound healing, and flow cytometry assays were used to assess the biological effects of CLDN6 overexpression and knockdown. The medical records of 118 GTD patients from 2011 to 2019 were retrospectively analysed to identify correlations between CLDN6 expression and GTD patient clinical-pathological parameters; these correlations were analysed using the chi-square test and one-way ANOVA. Univariate logistic regression was used to analyse various prognostic parameters of patients with post-molar GTN.

RESULTS

CLDN6 had the second highest fold change in gene expression between GTN and normal samples. CLDN6 was highly expressed in GTN tissues and CC cell lines, and silencing CLDN6 inhibited the proliferation and migration and promoted the apoptosis of CC cells. CLDN6 overexpression was significantly correlated with uterine size (p = 0.01) and ovarian cysts > 6 cm (p = 0.027), CLDN6 expression was significantly higher in HR-GTNs than in low-risk GTNs (LR-GTNs) (p = 0.008), and logistic regression analysis showed that CLDN6 expression in hydatidiform moles (HMs) was related to a high risk of developing post-molar GTN (OR = 2.393, p = 0.03).

CONCLUSION

We propose that CLDN6 participates in the development of GTD and may become a new therapeutic target for CC.

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.

Investigation of Anti-Liver Cancer Activity of the Herbal Drug FDY003 Using Network Pharmacology

Globally, liver cancer (LC) is the sixth-most frequently occurring and the second-most fatal malignancy, responsible for 0.83 million deaths annually. Although the application of herbal drugs in cancer therapies has increased, their anti-LC activity and relevant mechanisms have not been fully studied from a systems perspective. To address these issues, we conducted a system-perspective network pharmacological investigation into the activity and mechanisms underlying the action of the herbal drug. FDY003 reduced the viability of human LC treatment. FDY003 reduced the viability of human LC cells and elevated their chemosensitivity. There were a total of 16 potential bioactive chemical components in FDY003 and they had 91 corresponding targets responsible for the pathological processes in LC. These FDY003 targets were functionally involved in regulating the survival, proliferation, apoptosis, and cell cycle of LC cells. Additionally, we found that FDY003 may target key signaling cascades connected to diverse LC pathological mechanisms, namely, PI3K-Akt, focal adhesion, IL-17, FoxO, MAPK, and TNF pathways. Overall, this study contributed to integrative mechanistic insights into the anti-LC potential of FDY003.

Multi-omics data identified TP53 and LRP1B as key regulatory gene related to immune phenotypes via EPCAM in HCC

Background

Many studies showed that the prognosis of hepatocellular carcinoma (HCC) was significantly associated with the expressions of TP53 and LRP1B. However, the potential influence of the two genes on the malignant progression of HCC is still to be expounded.

Methods

According to the correlation analysis between immune cells and expression levels of TP53 and LRP1B, we filtered the immune cells to perform unsupervised clustering analysis. Integration of multi‐omic data analysis identified genetic alteration and epigenetic alteration. In addition, pathway analysis was used to explore the potential function of the differentially expressed mRNAs. According to the differentially expressed genes, we established an interaction network to seek the hub gene. Least absolute shrinkage and selection operator (LASSO) regression analysis was used to build a prognosis model.

Results

The unsupervised clustering analysis showed that the cluster A1 showed the highest immune cell levels and the cluster B2 showed the lowest immune cell levels. Multi‐omics data analysis identified that somatic mutations, copy number variations, and DNA methylation levels had significant differences between cluster A1 and cluster B2. Gene Ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG) analysis found that the upregulated mRNAs in the cluster A1 were mainly concentrated in T cell activation, external side of plasma membrane, receptor ligand activity, and cytokine−cytokine receptor interaction. Importantly, the EPCAM was identified as a critical node in the lncRNAs–miRNAs–mRNAs regulatory network correlated with the immune phenotypes. In addition, based on differentially expressed genes between cluster A1 and cluster B2, the prognostic model established by LASSO could predict the overall survival (OS) of HCC accurately.

Conclusions

The results indicated that the TP53 and LRP1B acted as the key genes in regulating the immune phenotypes of HCC via EPCAM.

Recent advances in systemic therapy for hepatocellular carcinoma

Hepatocellular carcinoma (HCC) is one of the most common and lethal malignant tumors in the world. Therapeutic options for advanced HCC are limited. Systemic treatment, especially with conventional cytotoxic drugs, is usually ineffective. For more than a decade, sorafenib has been the only systemic drug that has been proven to be clinically effective for treating advanced HCC. However, over the past three years, the rapid progress of molecular targeted therapies has dramatically changed the treatment landscape for advanced HCC. Immune checkpoint therapies are now being incorporated into HCC therapies, and their combination with molecular targeted therapy is emerging as a tool to enhance the immune response. In this review, we summarize the development and progress of molecular targeted agents and immunotherapies in HCC.

CLDN6 Suppresses c-MYC-Mediated Aerobic Glycolysis to Inhibit Proliferation by TAZ in Breast Cancer

Claudin 6 (CLDN6) was found to be a breast cancer suppressor gene, which is lowly expressed in breast cancer and inhibits breast cancer cell proliferation upon overexpression. However, the mechanism by which CLDN6 inhibits breast cancer proliferation is unclear. Here, we investigated this issue and elucidated the molecular mechanisms by which CLDN6 inhibits breast cancer proliferation. First, we verified that CLDN6 was lowly expressed in breast cancer tissues and that patients with lower CLDN6 expression had a worse prognosis. Next, we confirmed that CLDN6 inhibited breast cancer proliferation through in vitro and in vivo experiments. As for the mechanism, we found that CLDN6 inhibited c-MYC-mediated aerobic glycolysis based on a metabolomic analysis of CLDN6 affecting cellular lactate levels. CLDN6 interacted with a transcriptional co-activator with PDZ-binding motif (TAZ) and reduced the level of TAZ, thereby suppressing c-MYC transcription, which led to a reduction in glucose uptake and lactate production. Considered together, our results suggested that CLDN6 suppressed c-MYC-mediated aerobic glycolysis to inhibit the proliferation of breast cancer by TAZ, which indicated that CLDN6 acted as a novel regulator of aerobic glycolysis and provided a theoretical basis for CLDN6 as a biomarker of progression in breast cancer.

CLDN6: From Traditional Barrier Function to Emerging Roles in Cancers

Claudins (CLDNs) are the most important tight junction proteins, which are mainly expressed in endothelial cells or epithelial cells in a tissue-specific manner. As a member of the CLDNs family, CLDN6 is highly expressed in fetal tissues such as the stomach, pancreas, lung, and kidney, but is not expressed in corresponding adult tissues. The expression of CLDN6 is regulated by a variety of factors, including but not limited to stimuli and transcription factors, DNA methylation, and post-translational modifications. CLDN6 has been found to have a key role in the formation of barriers, especially the lung epithelial barrier and the epidermal permeability barrier (EPB). Importantly, the roles of CLDN6 in cancers have gained focus and are being investigated in recent years. Strong evidence indicates that the altered expression of CLDN6 is linked to the development of various cancers. Malignant phenotypes of tumors affected by CLDN6 include proliferation and apoptosis, migration and invasion, and drug resistance, which are regulated by CLDN6-mediated key signaling pathways. Given the important role in tumors and its low or no expression in normal tissues, CLDN6 is an ideal target for tumor therapy. This review aims to provide an overview of the structure and regulation of CLDN6, and its traditional barrier function, with a special emphasis on its emerging roles in cancers, including its impact on the malignant phenotypes, signal-modulating effects, the prognosis of tumor patients, and clinical applications in cancers.

Identification of Claudin-6 as a Molecular Biomarker in Pan-Cancer Through Multiple Omics Integrative Analysis

Claudin-6 (CLDN6) is one of the 27 family members of claudins and majorly involved in the tight junction and cell-to-cell adhesion of epithelial cell sheets, playing a significant role in cancer initiation and progression. To provide a more systematic and comprehensive dimension of identifying the diverse significance of CLDN6 in a variety of malignant tumors, we explored CLDN6 through multiple omics data integrative analysis, including gene expression level in pan-cancer and comparison of CLDN6 expression in different molecular subtypes and immune subtypes of pan-cancer, targeted protein, biological functions, molecular signatures, diagnostic value, and prognostic value in pan-cancer. Furthermore, we focused on uterine corpus endometrial carcinoma (UCEC) and further investigated CLDN6 from the perspective of the correlations with clinical characteristics, prognosis in different clinical subgroups, co-expression genes, and differentially expressed genes (DEGs), basing on discussing the validation of its established monoclonal antibody by immunohistochemical staining and semi-quantification reported in the previous study. As a result, CLDN6 expression differs significantly not only in most cancers but also in different molecular and immune subtypes of cancers. Besides, high accuracy in predicting cancers and notable correlations with prognosis of certain cancers suggest that CLDN6 might be a potential diagnostic and prognostic biomarker of cancers. Additionally, CLDN6 is identified to be significantly correlated with age, stage, weight, histological type, histologic grade, and menopause status in UCEC. Moreover, CLDN6 high expression can lead to a worse overall survival (OS), disease-specific survival (DSS), and progression-free interval (PFI) in UCEC, especially in different clinical subgroups of UCEC. Taken together, CLDN6 may be a remarkable molecular biomarker for diagnosis and prognosis in pan-cancer and an independent prognostic risk factor of UCEC, presenting to be a promising molecular target for cancer therapy.

The Expression of CLDN6 in Hepatocellular Carcinoma Tissue and the Effects of CLDN6 on Biological Phenotypes of Hepatocellular Carcinoma Cells

CLDN6, a member of claudin (CLDN) family, was found to be a breast cancer suppressor gene in our early experiments. However, CLDN6 was highly expressed in human hepatocellular carcinoma (hHCC) (TCGA database), and the role of CLDN6 in hHCC is still unclear. To investigate the expression of CLDN6, immunohistochemical staining was performed in hHCC tissues. As a result, hHCC tissues highly expressed CLDN6, and the expression was related to the degree of tumor's differentiation. To research the role of CLDN6 in hHCC cells, CLDN6 was silenced in HepG2 and Hep3B cells which highly expressed CLDN6 through liposome transfection. Results showed that after silencing of CLDN6, the proliferation, migration and invasion abilities of hHCC cells were inhibited. Meanwhile, the expression of E-cadherin was upregulated, and the expression of N-cadherin and Vimentin was downregulated. All the results above indicated that CLDN6 promoted the development of hHCC, and could be a potential target for the treatment of it.

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.