Role of Claudin Proteins in Regulating Cancer Stem Cells and Chemoresistance-Potential Implication in Disease Prognosis and Therapy

Diversity of Intercellular Communication Modes: A Cancer Biology Perspective

From the moment a cell is on the path to malignant transformation, its interaction with other cells from the microenvironment becomes altered. The flow of molecular information is at the heart of the cellular and systemic fate in tumors, and various processes participate in conveying key molecular information from or to certain cancer cells. For instance, the loss of tight junction molecules is part of the signal sent to cancer cells so that they are no longer bound to the primary tumors and are thus free to travel and metastasize. Upon the targeting of a single cell by a therapeutic drug, gap junctions are able to communicate death information to by-standing cells. The discovery of the importance of novel modes of cell-cell communication such as different types of extracellular vesicles or tunneling nanotubes is changing the way scientists look at these processes. However, are they all actively involved in different contexts at the same time or are they recruited to fulfill specific tasks? What does the multiplicity of modes mean for the overall progression of the disease? Here, we extend an open invitation to think about the overall significance of these questions, rather than engage in an elusive attempt at a systematic repertory of the mechanisms at play.

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.

Antibody-mediated targeting of Claudins in cancer

Tight junctions (TJs) are large intercellular adhesion complexes that maintain cell polarity in normal epithelia and endothelia. Claudins are critical components of TJs, forming homo- and heteromeric interaction between adjacent cells, which have emerged as key functional modulators of carcinogenesis and metastasis. Numerous epithelial-derived cancers display altered claudin expression patterns, and these aberrantly expressed claudins have been shown to regulate cancer cell proliferation/growth, metabolism, metastasis and cell stemness. Certain claudins can now be used as biomarkers to predict patient prognosis in a variety of solid cancers. Our understanding of the distinct roles played by claudins during the cancer progression has progressed significantly over the last decade and claudins are now being investigated as possible diagnostic markers and therapeutic targets. In this review, we will summarize recent progress in the use of antibody-based or related strategies for targeting claudins in cancer treatment. We first describe pre-clinical studies that have facilitated the development of neutralizing antibodies and antibody-drug-conjugates targeting Claudins (Claudins-1, -3, -4, -6 and 18.2). Next, we summarize clinical trials assessing the efficacy of antibodies targeting Claudin-6 or Claudin-18.2. Finally, emerging strategies for targeting Claudins, including Chimeric Antigen Receptor (CAR)-T cell therapy and Bi-specific T cell engagers (BiTEs), are also discussed.

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.

Immunohistochemical Expression of Claudin-1 and Claudin-4 in Urothelial Carcinoma of the Urinary Bladder

BACKGROUND

In Egypt, bladder cancer occupies the second rankamong reported cancers in men. Claudins are tight junctions that have a critical role in tumor pathogenesis, invasion, progression, and metastasis and currentlyare a focus of interest for targeting therapies.

OBJECTIVES

We aimed to evaluatethe immunohistochemical expression of Claudin-1 and Claudin-4 in urinary bladder urothelial carcinoma and investigate the relationshipbetweenthe expressed Claudins with differentclinicopathological parameters.

METHODS

Claudin-1 and Claudin-4 immunohistochemical expression was studied in 62 cases of urinary bladder urothelial carcinomas. The cases were classified into two categories; low and high Claudin-1 and Claudin-4 expression.

RESULTS

High Claudin-1 expression was detected in67.7% of the studied urothelial carcinomas while 32.3% showed low expression. Claudin-1 expression was reduced significantly with high tumor grade, non-papillary tumors, muscle invasion, schistosomal infestation, and perineural invasion (p-value < 0.05). Claudin-4 high expression was detected in 82.3% of our cases while low expression was detected in 17.7%. Claudin-4 reduced expression was significantly associated with non-papillary tumors, muscle invasion, advanced T stages, and associated lympho-vascular emboli (P-value < 0.05).

CONCLUSION

According to the results ofthe present study, the reduced expressions of Claudin-1 and Claudin-4 provide clues concerning the progression of urothelial carcinoma. Consequently, it is thought that Claudin-1 and Claudin-4 could help to differentiatelow-grade from high-grade and muscle-invasive from non-muscle-invasive urothelial carcinomas. In addition, it can be introduced as a possible therapeutic target.

Emerging roles of transmembrane-type tight junction proteins in cancers

Tight junctions (TJs) are the most apical components of the cell-cell adhesion machinery in epithelial and endothelial cells and they play essential roles in homeostasis. Recent studies have revealed that aberrant expression of tight junction proteins (TJPs) is frequently observed in various type of cancers. Here we review cancer-associated aberrant expression of TJPs with focus on transmembrane-type TJPs including claudins, junctional adhesion molecule-A (JAM-A), and occludin. Some transmembrane-type TJPs are upregulated at the early neoplastic stage and their expression persists during dedifferentiation. Aberrant expression of TJPs contributes to proliferation, invasion, and dysregulated signaling of cancer cells. In addition to an increase in their expression level, their localization is altered from a TJ-restricted pattern to distribution throughout the whole cell membrane, making them suitable as therapeutic targets. Extracellular domains of transmembrane-type TJPs can be approached by target drugs not only from the lumen side (apical side) but also from the extracellular matrix side (basal side), including blood vessels. Aberrantly expressed TJPs are potential useful diagnostic markers as well as therapeutic targets for cancers.

Endorsement of TNBC Biomarkers in Precision Therapy by Nanotechnology

Breast cancer is a heterogeneous disease which accounts globally for approximately 1 million new cases annually, wherein more than 200,000 of these cases turn out to be cases of triple-negative breast cancer (TNBC). TNBC is an aggressive and rare breast cancer subtype that accounts for 10-15% of all breast cancer cases. Chemotherapy remains the only therapy regimen against TNBC. However, the emergence of innate or acquired chemoresistance has hindered the chemotherapy used to treat TNBC. The data obtained from molecular technologies have recognized TNBC with various gene profiling and mutation settings that have helped establish and develop targeted therapies. New therapeutic strategies based on the targeted delivery of therapeutics have relied on the application of biomarkers derived from the molecular profiling of TNBC patients. Several biomarkers have been found that are targets for the precision therapy in TNBC, such as EGFR, VGFR, TP53, interleukins, insulin-like growth factor binding proteins, c-MET, androgen receptor, BRCA1, glucocorticoid, PTEN, ALDH1, etc. This review discusses the various candidate biomarkers identified in the treatment of TNBC along with the evidence supporting their use. It was established that nanoparticles had been considered a multifunctional system for delivering therapeutics to target sites with increased precision. Here, we also discuss the role of biomarkers in nanotechnology translation in TNBC therapy and management.

Carbon nanomaterial-involved EMT and CSC in cancer

Carbon nanomaterials (CNMs) are ubiquitous in our daily lives because of the outstanding physicochemical properties. CNMs play curial parts in industrial and medical fields, however, the risks of CNMs exposure to human health are still not fully understood. In view of, it is becoming extremely difficult to ignore the existence of the toxicity of CNMs. With the increasing exploitation of CNMs, it's necessary to evaluate the potential impact of these materials on human health. In recent years, more and more researches have shown that CNMs are contributed to the cancer formation and metastasis after long-term exposure through epithelial-mesenchymal transition (EMT) and cancer stem cells (CSCs) which is associated with cancer progression and invasion. This review discusses CNMs properties and applications in industrial and medical fields, adverse effects on human health, especially the induction of tumor initiation and metastasis through EMT and CSCs procedure.

Overexpression of CLDN16 in ovarian cancer is modulated by PI3K and PKC pathways

Epithelial ovarian cancer (EOC) is the gynecological malignant tumor of poorest prognosis and higher mortality rate. Chemotherapy is the base of high-grade serous ovarian cancer (HGSOC) treatment; however, it favors the emergence of chemoresistance and metastasis. Thus, there is an urge to search for new therapeutic targets, such as proteins related to cellular proliferation and invasion. Herein, we investigated the expression profile of claudin-16 (CLDN16 protein and CLDN16 transcript) and its possible functions in EOC. In silico analysis of CLDN16 expression profile was performed using data extracted from GENT2 and GEPIA2 platforms. A retrospective study was carried out with 55 patients to evaluate the expression of CLDN16. The samples were evaluated by immunohistochemistry, immunofluorescence, qRT-PCR, molecular docking, sequencing, and immunoblotting assays. Statistical analyzes were performed using Kaplan-Meier curves, one-way ANOVA, Turkey posttest. Data were analyzed using GraphPad Prism 8.0. In silico experiments showed that CLDN16 is overexpressed in EOC. 80.0% of all EOC types overexpressed CLDN16, of which in 87% of the cases the protein is restricted to cellular cytoplasm. CLDN16 expression was not related to tumor stage, tumor cells differentiation status, tumor responsiveness to cisplatin, or patients' survival rate. When compared to data obtained from in silico analysis regarding EOC stage and degree of differentiation, differences were found in the former but not in the later, neither in survival curves. CLDN16 expression in HGSOC OVCAR-3 cells increased by 1.95-fold (p < 0.001), 2.32-fold (p < 0.001), and 6.57-fold (p < 0.001) via PKC, PI3K, and estrogen pathways, respectively. Altogether, our results suggest that despite the low number of samples included in our in vitro studies, adding to the expression profile findings, we provided a comprehensive study of CLDN16 expression in EOC. Therefore, we hypothesize that CLDN16 is a potential target in the diagnosis and treatment of the disease.

Galangin-Loaded Gold Nanoparticles: Molecular Mechanisms of Antiangiogenesis Properties in Breast Cancer

Angiogenesis is important for tissue during normal physiological processes as well as in a number of diseases, including cancer. Drug resistance is one of the largest difficulties to antiangiogenesis therapy. Due to their lower cytotoxicity and stronger pharmacological advantage, phytochemical anticancer medications have a number of advantages over chemical chemotherapeutic drugs. In the current study, the effectiveness of AuNPs, AuNPs-GAL, and free galangin as an antiangiogenesis agent was evaluated. Different physicochemical and molecular approaches have been used including the characterization, cytotoxicity, scratch wound healing assay, and gene expression of VEGF and ERKI in MCF-7 and MDA-MB-231 human breast cancer cell line. Results obtained from MTT assay show cell growth reduction in a time- and dose-dependent aspect; also, in comparison to individual treatment, a synergistic impact was indicated. CAM assay results demonstrated galangin-gold nanoparticle capacity to suppress angiogenesis in chick embryo. Additionally, altering VEGF and ERKI gene expression was recorded. Taken together, all the results can conclude that galangin-conjugated gold nanoparticles can be a promising antiangiogenesis supplemental drug in breast cancer treatment.

Tight Junction Protein Signaling and Cancer Biology

Tight junctions (TJs) are intercellular protein complexes that preserve tissue homeostasis and integrity through the control of paracellular permeability and cell polarity. Recent findings have revealed the functional role of TJ proteins outside TJs and beyond their classical cellular functions as selective gatekeepers. This is illustrated by the dysregulation in TJ protein expression levels in response to external and intracellular stimuli, notably during tumorigenesis. A large body of knowledge has uncovered the well-established functional role of TJ proteins in cancer pathogenesis. Mechanistically, TJ proteins act as bidirectional signaling hubs that connect the extracellular compartment to the intracellular compartment. By modulating key signaling pathways, TJ proteins are crucial players in the regulation of cell proliferation, migration, and differentiation, all of which being essential cancer hallmarks crucial for tumor growth and metastasis. TJ proteins also promote the acquisition of stem cell phenotypes in cancer cells. These findings highlight their contribution to carcinogenesis and therapeutic resistance. Moreover, recent preclinical and clinical studies have used TJ proteins as therapeutic targets or prognostic markers. This review summarizes the functional role of TJ proteins in cancer biology and their impact for novel strategies to prevent and treat cancer.

A gene expression signature in HER2+ breast cancer patients related to neoadjuvant chemotherapy resistance, overall survival, and disease-free survival

Breast cancer ranks first in terms of mortality and incidence rates worldwide among women. The HER2+ molecular subtype is one of the most aggressive subtypes; its treatment includes neoadjuvant chemotherapy and the use of a HER2 antibody. Some patients develop resistance despite positive results obtained using this therapeutic strategy. Objective. To identify prognostic markers for treatment and survival in HER2+ patients. Methods. Patients treated with neoadjuvant chemotherapy were assigned to sensitive and resistant groups based on their treatment response. Differentially expressed genes (DEGs) were identified using RNA-seq analysis. KEGG pathway, gene ontology, and interactome analyses were performed for all DEGs. An enrichment analysis Gene set enrichment analysis was performed. All DEGs were analyzed for overall (OS) and disease-free survival (DFS). Results. A total of 94 DEGs were related to treatment resistance. Survival analysis showed that 12 genes (ATF6B, DHRS13, DIRAS1, ERAL1, GRIN2B, L1CAM, IRX3, PRTFDC1, PBX2, S100B, SLC9A3R2, and TNXB) were good predictors of disease-free survival, and eight genes (GNG4, IL22RA2, MICA, S100B, SERPINF2, HLA-A, DIRAS1, and TNXB) were good predictors of overall survival (OS). Conclusion: We highlighted a molecular expression signature that can differentiate the treatment response, overall survival, and DFS of patients with HER2+ breast cancer.

Claudin-6 increases SNAI1, NANOG and SOX2 gene expression in human gastric adenocarcinoma AGS cells

BACKGROUND

Gastric cancer is a heterogeneous disease associated to deregulated gastric epithelia tight junction barrier function and di novo expression of claudin-6; these changes are associated with epithelial-mesenchymal transition, enhanced invasiveness, metastatic progression, resistance to chemotherapy, and poor prognosis. Gastric cancer stem cells represent a rare population of cells within the tumor implicated in tumor growth and higher tumorigenic capacity. The possible relation between claudin-6 expression and the expression of some markers associated to epithelial mesenchymal transition and cancer stem cells in gastric cancer cells have never been explored.

METHODS AND RESULTS

CD44, CD24, Twist, Villin, DCLK1, claudin-6, NANOG, E-Cadherin, SOX2, and SNAI1 expression was evaluated by immunofluorescence and cytofluorometry in wild type and Claudin-6 transfected AGS cells. Cell migration assays were also performed. Differentially expressed genes and biological processes analysis was performed to determine gene preponderance. The results showed that claudin-6 overexpression enriched the CD44 + /CD24- subpopulation with an overall increase in the expression and the number of CD44 + cells. A significant increase in NANOG, SOX2 and SNAI1 expression and enhanced cell migration was observed in claudin-6 transfected cells. Transcriptome analysis revealed 271 genes involved in enhanced biological processes with only 31 with a significantly p value; thirteen of those genes are closely associated to epithelial mesenchymal transition processes and folding and unfolding processes of proteins in the endoplasmic reticulum.

CONCLUSIONS

The pro-tumorigenic effect of claudin-6 in gastric cancer could be associated to dedifferentiation of epithelial cells and an increase in di novo cancer stem cell genesis.

Gastric cancer with enhanced apical junction pathway has increased metastatic potential and worse clinical outcomes

Excessive intercellular connection at confluency may be limiting further cell growth or a sign of aggressive biology in the cell culture. As apical junction complex is a main component of cell-to-cell connection, we aimed to investigate gastric cancer biology using Apical Junction Pathway score that we generated using Gene set variant analysis (GSVA) of the "Hallmark Apical Junction" gene set. 1,239 gastric cancer patients from the Cancer Genome Atlas (TCGA) and two GSE cohorts were included in this study. The cohorts were dichotomized using the median of the score. Apical Junction Pathway score high gastric cancer was not consistently associated with increased cell proliferation or immune cell infiltration. On the other hand, Apical Junction Pathway score high gastric cancer was associated with significantly higher infiltration of stromal cells, such as endothelial cells; hence, increased neovascularization and angiogenesis in the tumor microenvironment (TME) were speculated. Gene set enrichment analysis (GSEA) confirmed increased expression of epithelial mesenchymal transition (EMT) and angiogenesis in the high Apical Junction Pathway score group (false discovery rate (FDR) <0.25). Lastly, the high Apical Junction Pathway score group was associated with more aggressive clinicopathological characteristics, such as significantly higher American Joint Committee on Cancer (AJCC) T-category and higher pathological stage, leading to worse disease-specific survival and overall survival (P<0.05, respectively). In conclusion, enhanced Apical Junction Pathway score gastric cancer was associated with aggressive clinical characteristics leading to shorter survival likely due to increased metastatic potential from EMT and angiogenesis.

Claudin1 decrease induced by 1,25-dihydroxy-vitamin D3 potentiates gefitinib resistance therapy through inhibiting AKT activation-mediated cancer stem-like properties in NSCLC cells

Claudins, the integral tight junction proteins that regulate paracellular permeability and cell polarity, are frequently dysregulated in cancer; however, their roles in regulating EGFR tyrosine kinase inhibitors (EGFR-TKIs) resistance in non-small cell lung cancer (NSCLC) are unknown. To this end, we performed GEO dataset analysis and identified that claudin1 was a critical regulator of EGFR-TKI resistance in NSCLC cells. We also found that claudin1, which was highly induced by continuous gefitinib treatment, was significantly upregulated in EGFR-TKI-resistant NSCLC cells. By knocking down claudin1 in cell lines and xenograft models, we established that gefitinib resistance was decreased. Moreover, claudin1 knockdown suppressed the expression levels of pluripotency markers (Oct4, Nanog, Sox2, CD133, and ALDH1A1). Claudin1 loss inhibited phosphorylated AKT (p-AKT) expression and reduced cancer cell stemness by suppressing AKT activation. Furthermore, SKL2001, a β-catenin agonist, upregulated the expression levels of claudin1, p-AKT, and pluripotency markers, and 1,25-dihydroxy-vitamin D3 (1,25(OH)₂D₃) reduced claudin1 expression, AKT activation, and cancer cell stemness by inhibiting β-catenin, and suppressed claudin1/AKT pathway mediated cancer stem-like properties and gefitinib resistance. Collectively, inhibition of claudin1-mediated cancer stem-like properties by 1,25(OH)₂D₃ may decrease gefitinib resistance through the AKT pathway, which may be a promising therapeutic strategy for inhibiting gefitinib resistance in EGFR-mutant lung adenocarcinoma.

Disruption of Claudin-Made Tight Junction Barriers by Clostridium perfringens Enterotoxin: Insights from Structural Biology

Claudins are a family of integral membrane proteins that enable epithelial cell/cell interactions by localizing to and driving the formation of tight junctions. Via claudin self-assembly within the membranes of adjoining cells, their extracellular domains interact, forming barriers to the paracellular transport of small molecules and ions. The bacterium Clostridium perfringens causes prevalent gastrointestinal disorders in mammals by employing an enterotoxin (CpE) that targets claudins. CpE binds to claudins at or near tight junctions in the gut and disrupts their barrier function, potentially by disabling their assembly or via cell signaling means—the mechanism(s) remain unclear. CpE ultimately destroys claudin-expressing cells through the formation of a cytotoxic membrane-penetrating β-barrel pore. Structures obtained by X-ray crystallography of CpE, claudins, and claudins in complex with CpE fragments have provided the structural bases of claudin and CpE functions, revealing potential mechanisms for the CpE-mediated disruption of claudin-made tight junctions. This review highlights current progress in this space—what has been discovered and what remains unknown—toward efforts to elucidate the molecular mechanism of CpE disruption of tight junction barriers. It further underscores the key insights obtained through structure that are being applied to develop CpE-based therapeutics that combat claudin-overexpressing cancers or modulate tight junction barriers.

Immunoexpression of E-cadherin, CD44 and Claudin 7 in gastric adenocarcinomas

Gastric adenocarcinomas represent frequent malignant tumors in the digestive tract, with a high and constant mortality rate in last decades. The disturbance of the adhesion molecules expression, which normally is essential in maintaining epithelial homeostasis, has a critical role in the initiation and progression of tumors. In this study, we analyzed the immunoexpression of E-cadherin, cluster of differentiation 44 (CD44), and Claudin 7 in 58 cases of gastric adenocarcinomas, in relation to the histopathological parameters of the lesions' aggressiveness. Increased E-cadherin immunoexpression was observed in tubular adenocarcinomas, those of low grade and in stages I-III. CD44 presented high scores in discohesive, hepatoid, tubular, and tubulopapillary adenocarcinomas, those of high grade and in advanced stages. Claudin 7 associated increased scores for tubular, tubulopapillary and micropapillary tumors, those of low grade and mainly in stage I. The markers used in the study can be useful for assessing the aggressiveness of gastric adenocarcinomas, in the context of specific adapted therapy.

An Update on the Molecular and Clinical Characteristics of Apocrine Carcinoma of the Breast

Apocrine carcinoma of the breast is a rare malignancy. According to 2019 WHO classification, apocrine cellular features and a characteristic steroid receptor profile (Estrogen receptor (ER)-negative and androgen receptor (AR)-positive) define apocrine carcinoma. Her-2/neu protein expression is reported in ∼30-50% of apocrine carcinomas, while NGS analysis showed frequent PIK3CA/PTEN/AKT and TP53 mutations Followed by deregulation in the mitogen-activated protein kinase pathway components (mutations of KRAS, NRAS, BRAF). A recent miRNA study indicates various miRNAs (downregulated hsa-miR-145-5p and upregulated 14 miRNAs such as hsa-miR-182-5p, hsa-miR-3135b, and hsa-miR-4417) may target the commonly altered pathways in apocrine carcinomas such as ERBB2/HER2 and mitogen-activated protein kinase signaling pathway. Although AR expression is a hallmark of apocrine carcinoma, little is known regarding the efficacy/resistance to antiandrogens. Success of bicalutamide, a non-steroidal anti-androgen, was reported in a case of Her2-negative apocrine carcinoma. Two recent studies, however, described presence of anti-androgen resistance biomarkers (a splice variant ARv7 and AR/NCOA2 co-amplification) in a subset of AR+ apocrine carcinomas, cautioning the use of anti-androgens in AR+ triple-negative breast carcinomas. Apocrine carcinomas rarely show biomarkers predictive of response to immune checkpoint inhibitors (PD-L1 expression, MSI-H status, and TMB-high). Therefore, a comprehensive cancer profiling of apocrine carcinomas is necessary to identify potential therapeutic targets for a truly individualized treatment approach.

Unveiling the tumour-regulatory roles of miR-1275 in cancer

The rapid development of small RNA and molecular biology research in the past 20 years has enabled scientists to discover many new miRNAs that are proven to play essential roles in regulating the development of different cancer types. Among these miRNAs, miR-1275 is one of the well-studied miRNAs that has been described to act as a tumour-promoting or tumour-suppressing miRNA in various cancer types. Even though miR-1275 has been widely reported in different original research articles on its roles in modulating the progression of different cancer types, however, there is scarce an in-depth review that could constructively summarize the findings from different studies on the regulatory roles of miR-1275 in different cancer types. To fill up this literature gap, therefore, this review was aimed to provide an overview and summary of the roles of miR-1275 in modulating the development of different cancers and to unravel the mechanism of how miR-1275 regulates cancer progression. Based on the findings summarized from various sources, it was found that miR-1275 plays a vital role in regulating various cellular signaling pathways like the PI3K/AKT, ERK/JNK, MAPK, and Wnt signaling pathways, and the dysregulation of this miRNA has been shown to contribute to the development of multiple cancer types such as cancers of the liver, breast, lung, gastrointestinal tract and genitourinary tract. Therefore, miR-1275 has great potential to be employed as a biomarker to diagnose cancer and to predict the prognosis of cancer patients. In addition, by inhibiting the expression of its unique downstream targets that are involved in regulating the mentioned cellular pathways, this miRNA could also be utilized as a novel therapeutic agent to halt cancer development.

Transcriptional and Epigenetic Bioinformatic Analysis of Claudin-9 Regulation in Gastric Cancer

Gastric cancer is a heterogeneous disease that represents 5% to 10% of all new cancer cases worldwide. Advances in histological diagnosis and the discovery of new genes have admitted new genomic classifications. Nevertheless, the bioinformatic analysis of gastric cancer databases has favored the detection of specific differentially expressed genes with biological significance. Claudins, a family of proteins involved in tight junction physiology, have emerged as the key regulators of cellular processes, such as growth, proliferation, and migration, associated with cancer progression. The expression of Claudin-9 in the gastric cancer tissue has been linked to poor prognosis, however, its transcriptional and epigenetic regulations demand a more comprehensive analysis. Using the neural network promoter prediction, TransFact, Uniprot-KB, Expasy-SOPMA, protein data bank, proteomics DB, Interpro, BioGRID, String, and the FASTA protein sequence databases and software, we found the following: (1) the promoter sequence has an unconventional structure, including different transcriptional regulation elements distributed throughout it, (2) GATA 4, GATA 6, and KLF5 are the key regulators of Claudin-9 expression, (3) Oct1, NF-κB, AP-1, c-Ets-1, and HNF-3β have the higher binding affinity to the CLDN9 promoter, (4) Claudin-9 interacts with cell differentiation and development proteins, (5) CLDN9 is highly methylated, and (6) Claudin-9 expression is associated with poor survival. In conclusion, Claudin-9 is a protein that should be considered a diagnostic marker as its gene promoter region binds to the transcription factors associated with the deregulation of cell control, enhanced cell proliferation, and metastasis.

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.

Emerging agents for metastatic pancreatic cancer: spotlight on early phase clinical trials

INTRODUCTION

Despite the recent development of new chemotherapeutic regimens and combination strategies, metastatic pancreatic cancer (mPC) still shows only a modest response to conventional cytotoxic agents. However, several novel therapeutic agents targeting the unique features of mPC are showing promise in clinical trials.

AREA COVERED

This article reviews the current state of development of new agents targeting various systems and molecular pathways. We searched PubMed and clinicaltrials.gov in September 2021 with a special focus on ongoing early phase clinical trials to identify the promising therapeutic strategies for mPC.

EXPERT OPINION

Extensive tumor heterogeneity, complex tumor microenvironment, genetic alterations of the oncogenic signaling pathways, metabolic dysregulation, and a low immunogenicity are hurdles for current treatment approaches. Ongoing research efforts strive to overcome these hurdles and are showing some promising early results.

Tight junction protein CLDN17 serves as a tumor suppressor to reduce the invasion and migration of oral cancer cells by inhibiting epithelial-mesenchymal transition

OBJECTIVE

To investigate claudin-17 (CLDN17) expression in oral cancer and its effect on epithelial-mesenchymal transition (EMT), invasion and migration in oral cancer cells.

METHODS

The GEO2R tool was used to analyze gene expression in two microarray datasets (GSE74530 and GSE146483) derived from the Gene Expression Omnibus (GEO) database. Gene Expression Profiling Interactive Analysis (GEPIA) verified CLDN17 expression in head and neck squamous cell carcinoma (HNSC) patients. Moreover, oral cancer cells were transfected with CLDN17 overexpression plasmid or CLDN17 shRNA to evaluate cell invasion and migration. Gene and protein expression was detected by qRT-PCR, immunohistochemistry and western blotting.

RESULTS

CLDN17 was one of the top 200 differentially expressed genes in the GSE74530 and GSE146483 datasets and was downregulated in oral cancer. CLDN17 expression was higher in HNSC tissues, and it was related to TNM staging. In HNSC tumors, CLDN17 expression was positively correlated with CDH1 but negatively related to VIM, SNAIL1, SNAIL2, and TWIST1. Meanwhile, we found that CLDN17 expression was lower in oral cancer tissues; it declined with higher T status, N status, M status and staging, lower differentiation grade, and a worse prognosis. Upregulation of CLDN17 inhibited the invasion and migration of oral cancer cells, with elevated CDH1 and reduced VIM, SNAIL1, SNAIL2, and TWIST1, while CLDN17 downregulation had the opposite effects.

CONCLUSION

CLDN17 may serve as a tumor suppressor in oral cancer since it could reduce the invasion and migration of cells by inhibiting the EMT process, thus becoming a potential therapeutic target in oral cancer.

Cell polarity and cell adhesion associated gene expression differences between invasive micropapillary and no special type breast carcinomas and their prognostic significance

Invasive micropapillary carcinoma of the breast (IMPC) has been in the focus of several studies given its specific histology and clinicopathological course. We analysed mRNA expression profiles and the prognostic value of 43 genes involved in cell polarity, cell-adhesion and epithelial-mesenchymal transition (EMT) in IMPC tumors and compared them to invasive breast carcinomas of no special type (IBC-NST). IMPCs (36 cases), IBC-NSTs (36 cases) and mixed IMPC-IBC NSTs (8 cases) were investigated. mRNA expression level of selected genes were analysed using the NanoString nCounter Analysis System. Distant metastases free survival (DMFS) intervals were determined. Statistical analysis was performed using Statistica 13.5 software. Twelve genes showed significantly different expression in the IMPC group. There was no difference in DMFS according to histological type (IBC-NST vs. IMPC). High CLDN3, PALS1 and low PAR6 expression levels in the entire cohort were associated with shorter DMFS, and PALS1 was proven to be grade independent prognostic factor. Positive lymph node status was associated with higher levels of AKT1 expression. Differences in gene expression in IMPC versus IBC-NST may contribute to the unique histological appearance of IMPCs. No marked differences were observed in DMFS of the two groups. Altered gene expression in the mTOR signaling pathway in both tumor subtypes highlights the potential benefit from AKT/mTOR inhibitors in IMPCs similarly to IBC-NSTs.

A Claudin-Based Molecular Signature Identifies High-Risk, Chemoresistant Colorectal Cancer Patients

Identifying molecular characteristics that are associated with aggressive cancer phenotypes through gene expression profiling can help predict treatment responses and clinical outcomes. Claudins are deregulated in colorectal cancer (CRC). In CRC, increased claudin-1 expression results in epithelial-to-mesenchymal transition and metastasis, while claudin-7 functions as a tumor suppressor. In this study, we have developed a molecular signature based on claudin-1 and claudin-7 associated with poor patient survival and chemoresistance. This signature was validated using an integrated approach including publicly available datasets and CRC samples from patients who either responded or did not respond to standard-of-care treatment, CRC cell lines, and patient-derived rectal and colon tumoroids. Transcriptomic analysis from a patient dataset initially yielded 23 genes that were differentially expressed along with higher claudin-1 and decreased claudin-7. From this analysis, we selected a claudins-associated molecular signature including PIK3CA, SLC6A6, TMEM43, and ASAP-1 based on their importance in CRC. The upregulation of these genes and their protein products was validated using multiple CRC patient datasets, in vitro chemoresistant cell lines, and patient-derived tumoroid models. Additionally, blocking these genes improved 5-FU sensitivity in chemoresistant CRC cells. Our findings propose a new claudin-based molecular signature that associates with poor prognosis as well as characteristics of treatment-resistant CRC including chemoresistance, metastasis, and relapse.

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.

Targeting claudins in cancer: diagnosis, prognosis and therapy

Increasing evidence has linked claudins to signal transduction and tumorigenesis. The expression of claudins is frequently dysregulated in the context of neoplastic transformation, suggesting their promise as biomarkers for diagnosis and prognosis or targets for treatment. Claudin binders (Clostridium perfringens enterotoxin and monoclonal antibody) have been tested in preclinical experiments, and some of them have progressed into clinical trials involving patients with certain cancers. However, the clinical development of many of these agents has not advanced to clinical applications. Herein, I review the current status of preclinical and clinical investigations of agents targeting claudins for diagnosis, prognosis and therapy. I also discuss the potential of combining claudin binders with other currently approved therapeutic agents.

Trimethylamine/Trimethylamine-N-Oxide as a Key Between Diet and Cardiovascular Diseases

Trimethylamine (TMA) is a gut microbiota-derived metabolite which comes from diets rich of choline, betaine or L-carnitine and could be further converted to Trimethylamine-N-oxide (TMAO) in the liver. As the function of gut microbiota and its metabolites being explored so far, studies suggest that TMAO may be a potential risk factor of cardiovascular diseases independent of other traditional risk factors. However, the precise role of TMAO is controversial as some converse results were discovered. In recent studies, it is hypothesized that TMA may also participate in the progression of cardiovascular diseases and some cytotoxic effect of TMA has been discovered. Thus, exploring the relationship between TMA, TMAO and CVD may bring a novel insight into the diagnosis and therapy of cardiovascular diseases. In this review, we discussed the factors which influence the TMA/TMAO's process of metabolism in the human body. We have also summarized the pathogenic effect of TMA/TMAO in cardiovascular diseases, as well as the limitation of some controversial discoveries.

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.

Context-Dependent Roles of Claudins in Tumorigenesis

The barrier and fence functions of the claudin protein family are fundamental to tissue integrity and human health. Increasing evidence has linked claudins to signal transduction and tumorigenesis. The expression of claudins is frequently dysregulated in the context of neoplastic transformation. Studies have uncovered that claudins engage in nearly all aspects of tumor biology and steps of tumor development, suggesting their promise as targets for treatment or biomarkers for diagnosis and prognosis. However, claudins can be either tumor promoters or tumor suppressors depending on the context, which emphasizes the importance of taking various factors, including organ type, environmental context and genetic confounders, into account when studying the biological functions and targeting of claudins in cancer. This review discusses the complicated roles and intrinsic and extrinsic determinants of the context-specific effects of claudins in cancer.

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.

Target specific tight junction modulators

Intercellular tight junctions represent a formidable barrier against paracellular drug absorption at epithelia (e.g., nasal, intestinal) and the endothelium (e.g., blood-brain barrier). In order to enhance paracellular transport of drugs and increase their bioavailability and organ deposition, active excipients modulating tight junctions have been applied. First-generation of permeation enhancers (PEs) acted by unspecific interactions, while recently developed PEs address specific physiological mechanisms. Such target specific tight junction modulators (TJMs) have the advantage of a defined specific mechanism of action. To date, merely a few of these novel active excipients has entered into clinical trials, as their lack in safety and efficiency in vivo often impedes their commercialisation. A stronger focus on the development of such active excipients would result in an economic and therapeutic improvement of current and future drugs.

Involvement of mTOR/Survivin signaling pathway in TUA(2β, 3β, 23-trihydroxy-urs-12-ene-28-olic acid)-induced apoptosis in human gastric cancer cell line BGC823 cells

ETHNO-PHARMACOLOGICAL RELEVANCE

A natural ursolic compound, 2β,3β,23-trihydroxy-urs-12-ene-28-olic acid (TUA) was isolated from the root of Actinidiafulvicoma Hance. (A.fulvicoma Radix), which is used as a traditional hebal medicine to cure innominate inflammation of unknown origin of the digestive tract in the She nationality.

AIM OF THE STUDY

The aim of present study was to investigate the effects of TUA on gastric cancer and to clarify the potential mechanisms in human gastric cancer cell line BGC823 cells in vitro and in vivo.

MATERIALS AND METHODS

Cell proliferation, apoptosis, cell cycle, autophagy were all measured by MTS assay, flow cytometry following exposure to TUA. The mRNA expressions of PI3K, AKT, mTOR, P70S6K, Survivin and the protein expressions of p-PI3K, p-AKT, p-mTOR, p-P70S6K, Survivin were determined by qRT-PCR and Western blotting analysis, respectively. In vivo antitumor activity of TUA was assessed in a xenograft model.

RESULTS

In vitro studies showed that TUA significantly suppressed the viability of BGC823 cells in a concentration- and time-dependent manner but not GES-1 non-tumorigenic human gastric epithelial cells. TUA also significantly increased the apoptosis rate and the sub G2 population by cell cycle analysis in a concentration dependent manner. Exposure to TUA decreased PI3K, AKT, mTOR, P70S6K, Survivin mRNA, inhibited the phosphorylation of major receptors involved in autophagy and apoptosis, such as PI3K, AKT, mTOR and P70S6K, while reduced the expression of Survivin in BGC cells. In vivo studies showed that TUA decreased tumor volume and tumor weight and also down regulated the autophagy-related proteins expression.

CONCLUSIONS

TUA occupies underlying antitumor effects, the potential mechanisms may involve the suppression of mTOR/Survivin pathways connected to autophagy and the activation of apoptotic pathways in gastric cancer cells.

Comprehensive Analysis of the Expression and Prognostic Value of SPINT1/2 in Breast Carcinoma

BACKGROUND

Hepatocyte growth factor (HGF) signaling plays a plethora of roles in tumorigenesis and progression in many cancer types. As HGF activator inhibitors, serine protease inhibitor, Kunitz types 1 and 2 (SPINT1 and SPINT2) have been reported to be differentially expressed in breast cancer, but their prognostic significance and functioning mechanism remain unclear.

METHODS

In our study, multiple databases and bioinformatics tools were used to investigate SPINT1/2 expression profiles, prognostic significance, genetic alteration, methylation, and regulatory network in breast carcinoma.

RESULTS

SPINT1/2 expression was upregulated in breast cancer, and was relatively higher in human epidermal growth factor receptor 2 (HER2) and node positive patients. Elevated SPINT1/2 expression was significantly correlated with a poorer prognosis. Genetic alterations and SPINT1/2 hypomethylation were observed. In breast carcinoma, SPINT1/2 were reciprocally correlated and shared common co-expressed genes. Gene ontology (GO) and the Kyoto Encyclopedia of Genes and Genomes (KEGG) enrichment analysis showed that their common co-expressed genes were primarily involved in regulating cell attachment and migration.

CONCLUSIONS

Our study identified the expression profiles, prognostic significance and potential roles of SPINT1/2 in breast carcinoma. These study results showed that the SPINT1/2 were potential prognostic biomarker for patients with breast cancer.

Cell-cell junctions: structure and regulation in physiology and pathology

Epithelial and endothelial cell-cell contacts are established and maintained by several intercellular junctional complexes. These structurally and biochemically differentiated regions on the plasma membrane primarily include tight junctions (TJs), and anchoring junctions. While the adherens junctions (AJs) provide essential adhesive and mechanical properties, TJs hold the cells together and form a near leak-proof intercellular seal by the fusion of adjacent cell membranes. AJs and TJs play essential roles in vascular permeability. Considering their involvement in several key cellular functions such as barrier formation, proliferation, migration, survival, and differentiation, further research is warranted on the composition and signaling pathways regulating cell-cell junctions to develop novel therapeutics for diseases such as organ injuries. The current review article presents our current state of knowledge on various cell-cell junctions, their molecular composition, and mechanisms regulating their expression and function in endothelial and epithelial cells.

Special Issue on "The Tight Junction and Its Proteins: More than Just a Barrier"

For a long time, the tight junction (TJ) was known to form and regulate the paracellular barrier between epithelia and endothelial cell sheets. Starting shortly after the discovery of the proteins forming the TJ—mainly, the two families of claudins and TAMPs—several other functions have been discovered, a striking one being the surprising finding that some claudins form paracellular channels for small ions and/or water. This Special Issue covers numerous dedicated topics including pathogens affecting the TJ barrier, TJ regulation via immune cells, the TJ as a therapeutic target, TJ and cell polarity, the function of and regulation by proteins of the tricellular TJ, the TJ as a regulator of cellular processes, organ- and tissue-specific functions, TJs as sensors and reactors to environmental conditions, and last, but not least, TJ proteins and cancer. It is not surprising that due to this diversity of topics and functions, the still-young field of TJ research is growing fast. This Editorial gives an introduction to all 43 papers of the Special Issue in a structured topical order.

Ruffles and spikes: Control of tight junction morphology and permeability by claudins

Epithelial barrier function is regulated by a family of transmembrane proteins known as claudins. Functional tight junctions are formed when claudins interact with other transmembrane proteins, cytosolic scaffold proteins and the actin cytoskeleton. The predominant scaffold protein, zonula occludens-1 (ZO-1), directly binds to most claudin C-terminal domains, crosslinking them to the actin cytoskeleton. When imaged by immunofluorescence microscopy, tight junctions most frequently are linear structures that form between tricellular junctions. However, tight junctions also adapt non-linear architectures exhibiting either a ruffled or spiked morphology, which both are responses to changes in claudin engagement of actin filaments. Other terms for ruffled tight junctions include wavy, tortuous, undulating, serpentine or zig-zag junctions. Ruffling is under the control of hypoxia induced factor (HIF) and integrin-mediated signaling, as well as direct mechanical stimulation. Tight junction ruffling is specifically enhanced by claudin-2, antagonized by claudin-1 and requires claudin binding to ZO-1. Tight junction spikes are sites of active vesicle budding and fusion that appear as perpendicular projections oriented towards the nucleus. Spikes share molecular features with focal adherens junctions and tubulobulbar complexes found in Sertoli cells. Lung epithelial cells under stress form spikes due to an increase in claudin-5 expression that directly disrupts claudin-18/ZO-1 interactions. Together this suggests that claudins are not simply passive cargoes controlled by scaffold proteins. We propose a model where claudins specifically influence tight junction scaffold proteins to control interactions with the cytoskeleton as a mechanism that regulates tight junction assembly and function.