Loss of claudin-7 is a negative prognostic factor for invasion and metastasis in oral squamous cell carcinoma

A Review of a Breakdown in the Barrier: Tight Junction Dysfunction in Dental Diseases

The tight junction (TJ), a type of cell-cell junction, regulates the permeability of solutes across epithelial and endothelial cellular sheets and is believed to maintain cell polarity. However, recent studies have provided conflicting views on the roles of TJs in epithelial polarity. Membrane proteins, including occludin, claudin, and the junction adhesion molecule, have been identified as TJ components. TJs are predominantly found at the stratum granulosum and stratum corneum. Although it remains unclear whether the disruption of TJs is the cause or consequence of certain dental diseases, evidence suggests that TJ dysfunction may be a crucial factor in gingival epithelial barrier impairment and the progression of oral diseases. Bacterial infection is among the most specific factors we found that may contribute to the breakdown of the epithelial barrier formed by TJs in dental diseases. Bacteria and their products may weaken the epithelial barrier by directly destroying intercellular junctions or altering the expression of junctional proteins. Additionally, they may induce the production of inflammatory cytokines, which could lead to the downregulation of TJ proteins and, consequently, impair the epithelial barrier. This review introduces a novel perspective by exploring, for the first time, the role of TJs dysfunction in the breakdown of the oral epithelial barrier and its potential link to the progression of dental diseases such as gingivitis, periodontitis, Sjӧgren syndrome, and oral squamous cell carcinoma.

High expression of MARVELD3 as a potential prognostic biomarker for oral squamous cell carcinoma

Objectives: Tight junction-associated marvel proteins (TAMP) is a transmembrane protein whose members are associated with tight junctions between cells and epithelial remodeling. MARVEL domain containing 3 (MARVELD3) is one of the members of the TAMP. MARVELD3, as a novel tight junction protein involved in bicellular tight junction assembly, has attracted growing attention in the field of oncology. This study aimed to investigate the prognostic role of MARVELD3 and to determine how it functions in tumorigenesis in oral squamous cell carcinoma (OSCC), thus providing additional data to help the guidance of clinical practice.

Materials and Methods: RNA-seq data and relevant clinical information were obtained from TCGA. Bioinformatics means used in this study included differential gene expression analysis, KM survival curve analysis, univariate and multivariate Cox regression analyses, nomogram analysis, ROC curve analysis, methylation level analysis, gene function enrichment analysis, and immune cell infiltration analysis.

Results:MARVELD3 was significantly higher expressed in OSCC tissue than in normal tissue, and the overall survival of the high expression group was significantly lower than that of the normal group. Univariate and multivariate Cox regression analyses showed that MARVELD3 could serve as an independent contributing factor to poor OSCC prognosis. The nomograms and ROC curves supported the results above. Its expression was negatively correlated with DNA methylation sites. Analysis of PPI networking and gene functional enrichment showed that MARVELD3 was involved in the functional activities of DNA and RNA and was associated with immune cell infiltration.

Conclusion: The high expression of MARVELD3 is associated with poor prognosis in OSCC, and MARVELD3 could be recognized as a novel independent prognostic factor for OSCC.

Clinical Significance of Claudin Expression in Oral Squamous Cell Carcinoma

A change in claudin expression has been demonstrated in various tumors. The present study specifically compares claudin expression in oral squamous cell carcinoma (OSCC) with healthy oral epithelium from the same individual and analyzes the association between claudin expression and the clinically relevant course parameters. Our study includes tissue samples and clinically relevant follow-up data from 60 patients with primary and untreated OSCC. The oral mucosa was analyzed via Western blot for the expression of claudin-1, -2, -3, -4, -5, and -7. Importantly, the tumor and healthy tissues were obtained pairwise from patients, allowing for intraindividual comparisons. Both the healthy and tumor epithelium from the oral cavity did not express the claudin-3 protein. The intraindividual comparison revealed that, in OSCC, claudin-2 expression was higher, and the expression of claudin-4, -5, and -7 was lower than in healthy epithelium. An association was found between increased claudin-2 expression and shorter relapse-free survival. In addition, the reduced expression of claudin-4 had a negative impact on relapse-free survival. Furthermore, associations between the reduced expression of claudin-7 and the stage of a tumor, or the presence of lymph node metastases, were found. Thus, the expression level of claudin-2, -4, and -7 appears to be predictive of the diagnosis and prognosis of OSCC.

Loss of intercellular bridges in the depth of invasion measurement area is a novel negative prognostic factor for oral squamous cell carcinoma: A retrospective study

OBJECTIVE

This study aimed to evaluate intercellular bridges in the depth of invasion (DOI) measurement area as prognostic factors in oral squamous cell carcinoma (OSCC).

STUDY DESIGN

The mode of invasion was determined based on the Yamamoto-Kohama classification system by observing the hematoxylin-eosin-stained whole-slide images of specimens obtained from 78 patients with OSCC, and the clinicopathologic features were characterized. The presence of intercellular bridges was analyzed in 46 patients with Yamamoto-Kohama classification grade ≥3 whose DOI was measured by dividing the measurement area into 3 parts: the surface, center, and front of the tumor.

RESULTS

Univariate analyses identified lymph node metastasis, loss of intercellular bridges in the DOI measurement area, DOI of ≥4500 µm, and pattern of invasion 4C-4D as negative prognostic factors. Multivariate analyses revealed that lymph node metastasis and the loss of intercellular bridges in the entire area were independent factors, with hazard ratios of 9.34 (95% confidence interval, 2.09-42.03; P = .003) and 3.64 (95% confidence interval, 1.10-11.99; P = .045), respectively.

CONCLUSIONS

Loss of intercellular bridges in the DOI measurement area is a negative prognostic factor for OSCC and may be useful in selecting treatment.

Automatic discrimination of Yamamoto-Kohama classification by machine learning approach for invasive pattern of oral squamous cell carcinoma using digital microscopic images: a retrospective study

OBJECTIVE

The Yamamoto-Kohama criteria are clinically useful for determining the mode of tumor invasion, especially in Japan. However, this evaluation method is based on subjective visual findings and has led to significant differences in determinations between evaluators and facilities. In this retrospective study, we aimed to develop an automatic method of determining the mode of invasion based on the processing of digital medical images.

STUDY DESIGN

Using 101 digitized photographic images of anonymized stained specimen slides, we created a classifier that allowed clinicians to introduce feature values and subjected the cases to machine learning using a random forest approach. We then compared the Yamamoto-Kohama grades (1, 2, 3, 4C, 4D) determined by a human oral and maxillofacial surgeon with those determined using the machine learning approach.

RESULTS

The input of multiple test images into the newly created classifier yielded an overall F-measure value of 87% (grade 1, 93%; grade 2, 67%; grade 3, 89%; grade 4C, 83%; grade 4D, 94%). These results suggest that the output of the classifier was very similar to the judgments of the clinician.

CONCLUSIONS

This system may be valuable for diagnostic support to provide an accurate determination of the mode of invasion.

High expression of protein tyrosine kinase 7 in oral squamous cell carcinoma: Clinicopathological correlation and prognosis relevance

Background

The purpose of this study was to evaluate the association between the　immunohistochemistry (IHC) of protein tyrosine kinase 7 (PTK7) expression and clinicopathological factors of oral squamous cell carcinoma (OSCC).

Methods

Tissue specimens were obtained from 80 patients with primary OSCC. IHC scoring was conducted according to the rate of positive cell and staining intensity. We used the IHC score to classify the degree of PTK7 expression and evaluate clinicopathological factors and prognosis.

Results

The number of the high expression group (IHC Score 2 or 3) was 45 cases and that of the low expression group (IHC Score 0 or 1) was 35 cases. A significant difference between high expression and low expression groups was found in the N category (p = .008), degree of differentiation (p < .001), and pattern of invasion (p < .001). In accordance with the exacerbation of OSCC with respect to three parameters (N category, degree of differentiation, and pattern of invasion), the ratio of high expression of PTK7 increased. The overall 5‐year survival rate was 59.3% in the high expression group and 87.3% in the low expression group (p < .05). The pathological prognostic signs affecting overall survival were evaluated by univariate analysis and multivariate analysis with Cox proportional hazards model and showed an association with lymph node metastasis and invasion patterns.

Conclusion

This study suggests that a high IHC score of PTK7 is a potential biomarker for predicting potential metastasis.

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

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

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.

Intestinal Barrier, Claudins and Mycotoxins

The intestinal barrier is the main barrier against all of the substances that enter the body. Proper functioning of this barrier guarantees maintained balance in the organism. Mycotoxins are toxic, secondary fungi metabolites, that have a negative impact both on human and animal health. It was postulated that various mycotoxins may affect homeostasis by disturbing the intestinal barrier. Claudins are proteins that are involved in creating tight junctions between epithelial cells. A growing body of evidence underlines their role in molecular response to mycotoxin-induced cytotoxicity. This review summarizes the information connected with claudins, their association with an intestinal barrier, physiological conditions in general, and with gastrointestinal cancers. Moreover, this review also includes information about the changes in claudin expression upon exposition to various mycotoxins.

TNF-α-induced miR-450a mediates TMEM182 expression to promote oral squamous cell carcinoma motility

Distant metastasis leads oral cancer patients into a poor survival rate and a high recurrence stage. During tumor progression, dysregulated microRNAs (miRNAs) have been reported to involve tumor initiation and modulate oral cancer malignancy. MiR-450a was significantly upregulated in oral squamous cell carcinoma (OSCC) patients without functional reports. This study was attempted to uncover the molecular mechanism of novel miR-450a in OSCC. Mir-450a expression was examined by quantitative RT-PCR, both in OSCC cell lines and patients. Specific target of miR-450a was determined by software prediction, luciferase reporter assay, and correlation with target protein expression. The functions of miR-450a and TMEM182 were accessed by adhesion and transwell invasion analyses. Determination of the expression and cellular localization of TMEM182 was examined by RT-PCR and by immunofluorescence staining. The signaling pathways involved in regulation of miR-450a were investigated using the kinase inhibitors. Overexpression of miR-450a in OSCC cells impaired cell adhesion ability and induced invasiveness, which demonstrated the functional role of miR-450a as an onco-miRNA. Interestingly, tumor necrosis factor alpha (TNF-α)-mediated expression of TMEM182 was regulated by miR-450a induction. MiR-450a-reduced cellular adhesion was abolished by TMEM182 restoration. Furthermore, the oncogenic activity of TNF-α/miR-450a/TMEM182 axis was primarily through activating extracellular signal-regulated kinase 1/2 (ERK1/2) signaling pathway. ERK1/2 inhibitor prevented the TNF-α-induced miR-450a expression and enhanced adhesion ability. Our data suggested that TNF-α-induced ERK1/2-dependent miR-450a against TMEM182 expression exerted a great influence on increasing OSCC motility. Overall, our results provide novel molecular insights into how TNF-α contributes to oral carcinogenesis through miR-450a that targets TMEM182.

High-level cytoplasmic claudin 3 expression is an independent predictor of poor survival in triple-negative breast cancer

Background

The subtype of claudin-low breast cancer can be reliably determined only by gene-expression profiling. Attempts have been made to develop immunohistochemical surrogates, which nearly always focus on membranous claudin expression.

Methods

We assessed the immunohistochemical expression of both membranous and cytoplasmic claudins 3, 4 and 7 in a series of 197 non-metastatic breast cancers, enriched with triple-negative breast cancers (TNBCs; 60%). The expression of epithelial-to-mesenchymal transition-regulating transcription factors Sip1, Zeb1 and vimentin had previously been determined in the same material.

Results

In multivariate analysis, strong cytoplasmic claudin 3 expression was associated with poor relapse-free survival (RFS), disease-free survival, distant disease-free survival, breast cancer-specific survival and overall survival among TNBC patients (for RFS, RR 5.202, 95% CI 1.210–22.369, p = 0.027, vs. T-class, RR 0.663, 95% CI 0.168–2.623, p = 0.558, and N-class, RR 3.940, 95% CI 0.933–16.631, p = 0.062). Cytoplasmic claudin 3 expression was also associated with strong nuclear Sip1 expression (p = 0.000053), TNBC phenotype (p = 0.012) and within them, non-basal-like phenotype (p = 0.026). Cytoplasmic claudin 7 was associated with dismal RFS (RR 6.328, 95% CI 1.401–28.593, p = 0.016, vs. T-class, RR 0.692, 95% CI 0.242–1.982, p = 0.493, and N-class, RR 2.981, 95% CI 1.1016–8.749, p = 0.047). Low cytoplasmic expression of claudins 3, 4 and 7 together also predicted poor RFS (RR 6.070, 95% CI 1.347–27.363, p = 0.019, vs. T-class, RR 0.677, 95% CI 0.237–1.934, p = 0.467, and N-class, RR 3.167, 95% CI 1.079–9.290, p = 0.036).

Conclusions

Immunohistochemical expression levels of cytoplasmic claudins 3 and 7 appear to be novel prognostic factors in TNBC.

Integrative analyses of transcriptome sequencing identify novel functional lncRNAs in esophageal squamous cell carcinoma

Long non-coding RNAs (lncRNAs) have a critical role in cancer initiation and progression, and thus may mediate oncogenic or tumor suppressing effects, as well as be a new class of cancer therapeutic targets. We performed high-throughput sequencing of RNA (RNA-seq) to investigate the expression level of lncRNAs and protein-coding genes in 30 esophageal samples, comprised of 15 esophageal squamous cell carcinoma (ESCC) samples and their 15 paired non-tumor tissues. We further developed an integrative bioinformatics method, denoted URW-LPE, to identify key functional lncRNAs that regulate expression of downstream protein-coding genes in ESCC. A number of known onco-lncRNA and many putative novel ones were effectively identified by URW-LPE. Importantly, we identified lncRNA625 as a novel regulator of ESCC cell proliferation, invasion and migration. ESCC patients with high lncRNA625 expression had significantly shorter survival time than those with low expression. LncRNA625 also showed specific prognostic value for patients with metastatic ESCC. Finally, we identified E1A-binding protein p300 (EP300) as a downstream executor of lncRNA625-induced transcriptional responses. These findings establish a catalog of novel cancer-associated functional lncRNAs, which will promote our understanding of lncRNA-mediated regulation in this malignancy.

Expression of claudin-5, claudin-7 and occludin in oral squamous cell carcinoma and their clinico-pathological significance

Background

Claudin and occludin are the important tight junctions protein in human. The downregulation or upregulation of claudins and occludin might have a role in cancer development. The objective of this study was to investigate the expression of claudin-5, claudin-7 and occludin in oral squamous cell carcinoma (OSCC) and their relationships with the prognostically-related clinico-pathologic features.

Material and Methods

Standard indirect immunohistochemical technique using anti-claudin-5, anti-claudin-7 and anti-occludin was performed in formalin-fixed paraffin-embedded tissue sections of 66 OSCC samples from Faculty of Dentistry, Chulalongkorn University. The positive cases were divided into 2 groups, the low expression group (cases with less than 50% of positive cancer cells) and the high expression group for statistical analysis. Categorical analysis of the clinico-pathologic parameters together with univariate analysis using the Kaplan-Meier method and the log rank test were performed.

Results

There were 22 male and 23 female patients enrolled in this study, with a mean age of 65.82+12.10 years. The claudin-5 immunoreactivity was observed in 26.6% of cases. The positive immunoreactivity of claudin-7 is more noted (93.3%). Only 4 cases showed occludin immunoreactivity (8.9%) and all of them show positivity less than 25% of cancer cells. Only loss of claudin-7 expression was associated with the high pathologic grade, advanced TNM staging, large tumor size, the presence of microscopic perineural, vascular invasions and regional lymph node involvement. There is a tendency towards the association of the higher claudin-7 expression and a longer survival time (P=0.012).

Conclusions

The results showed expression of claudin-5, claudin-7 and low expression of occludin in OSCC. Only claudin-7 expression showed impact on clinic-pathological parameter of OSCC.

Key words:Claudin, occludin, oral squamous cell carcinoma, tight junctions, oral cancer.

Helicobacter pylori targets cancer-associated apical-junctional constituents in gastroids and gastric epithelial cells

OBJECTIVE

Helicobacter pylori strains that express the oncoprotein CagA augment risk for gastric cancer. However, the precise mechanisms through which cag(+) strains heighten cancer risk have not been fully delineated and model systems that recapitulate the gastric niche are critical for understanding pathogenesis. Gastroids are three-dimensional organ-like structures that provide unique opportunities to study host-H. pylori interactions in a preclinical model. We used gastroids to inform and direct in vitro studies to define mechanisms through which H. pylori modulates expression of the cancer-associated tight junction protein claudin-7.

DESIGN

Gastroids were infected by luminal microinjection, and MKN28 gastric epithelial cells were cocultured with H. pylori wild-type cag(+) strains or isogenic mutants. β-catenin, claudin-7 and snail localisation was determined by immunocytochemistry. Proliferation was assessed using 5-ethynyl-2'-deoxyuridine, and levels of claudin-7 and snail were determined by western blot and flow cytometry.

RESULTS

Gastroids developed into a self-organising differentiation axis and H. pylori induced mislocalisation of claudin-7 and increased proliferation in a CagA- and β-catenin-dependent manner. In MKN28 cells, H pylori-induced suppression of claudin-7 was regulated by β-catenin and snail. Similarly, snail expression was increased and claudin-7 levels were decreased among H. pylori-infected individuals.

CONCLUSIONS

H. pylori increase proliferation in a strain-specific manner in a novel gastroid system. H. pylori also alter expression and localisation of claudin-7 in gastroids and human epithelial cells, which is mediated by β-catenin and snail activation. These data provide new insights into molecular interactions with carcinogenic potential that occur between H. pylori and epithelial cells within the gastric niche.

Computational analysis identifies invasion-associated genes in pituitary adenomas

Pituitary adenomas are considered to be benign tumours. However, they can infiltrate surrounding tissues, which may cause a failure of complete removal during surgical resection. Thus far, no molecular biomarkers have been identified, which are able to reliably predict the behaviour of this type of tumour. In the present study, a list of differentially expressed genes in invasive pituitary adenomas was obtained using a computational bioinformatics analysis on the DNA microarray expression profiles. The gene expression datasets of a total of 16 samples were retrieved from the National Center for Biotechnology Information Gene Expression Omnibus database. The gene set enrichment analysis was later conducted on the significantly (FDR<0.05) differentially expressed genes. A total of 194 genes were identified as differentially expressed. The pathway impact analysis revealed that cell adhesion molecules may be vital in the progression of pituitary adenoma invasion. A total of six genes, claudin 7, contactin associated protein-like 2, integrin α6, junctional adhesion molecule 3, protein tyrosine phosphatase, receptor type C and cadherin-associated protein α1 were identified as molecular biomarkers for pituitary adenoma invasion. The present study identified six novel molecular biomarkers, which may be used for diagnostic or therapeutic purposes. However, further experimental investigations are required to validate the present findings.

Claudin-7 expression induces mesenchymal to epithelial transformation (MET) to inhibit colon tumorigenesis

In normal colon, claudin-7 is one of the highly expressed claudin proteins and its knockdown in mice results in altered epithelial cell homeostasis and neonatal death. Notably, dysregulation of the epithelial homeostasis potentiates oncogenic transformation and growth. However, the role of claudin-7 in the regulation of colon tumorigenesis remains poorly understood. Using a large colorectal cancer (CRC) patient database and mouse models of colon cancer, we found claudin-7 expression to be significantly downregulated in cancer samples. Most notably, forced claudin-7 expression in poorly differentiated and highly metastatic SW620 colon cancer cells induced epithelial characteristics and inhibited their growth in soft agar and tumor growth in vivo. By contrast, knockdown of claudin-7 in HT-29 or DLD-1 cells induced epithelial-to-mesenchymal transition (EMT), colony formation, xenograft-tumor growth in athymic mice and invasion. Importantly, a claudin-7 signature gene profile generated by overlapping the DEGs (differentially expressed genes in a high-throughput transcriptome analysis using claudin-7-manipulated cells) with human claudin-7 signature genes identified high-risk CRC patients. Furthermore, Rab25, a colon cancer suppressor and regulator of the polarized cell trafficking constituted one of the highly upregulated DEGs in claudin-7 overexpressing cells. Notably, silencing of Rab25 expression counteracted the effects of claudin-7 expression and not only increased proliferation and cell invasion but also increased the expression of p-Src and mitogen-activated protein kinase-extracellular signal-regulated kinase 1/2 that were suppressed upon claudin-7 overexpression. Of interest, CRC cell lines, which exhibited decreased claudin-7 expression, also exhibited promoter DNA hypermethylation, a modification associated with transcriptional silencing. Taken together, our data demonstrate a previously undescribed role of claudin-7 as a colon cancer suppressor and suggest that loss of claudin-7 potentiates EMT to promote colon cancer, in a manner dependent on Rab25.

Overexpression of the cell adhesion molecule claudin-9 is associated with invasion in pituitary oncocytomas

Pituitary oncocytoma is a subtype of nonfunctioning pituitary adenomas with the potential to be locally invasive. Currently, surgery is the most effective treatment, whereas functional pituitary adenomas can be treated by drugs. We analyzed the invasiveness of pituitary oncocytomas to identify biomarkers that may be useful for guiding future therapeutic decision making. To identify important biomarkers of pituitary oncocytomas, 20 oncocytomas that were negative for hormone-specific immunostaining were confirmed by anti-mitochondria antibody immunostaining and electron microscopy. Our clinical phenotype data showed a prominent male predilection (85%). These tumors were classified as invasive or noninvasive based on preoperative magnetic resonance imaging, intraoperative records, and pathology slide. We observed significantly different expression profiles between pituitary oncocytomas (n = 3) and normal pituitary glands (n = 3). A total of 1937 genes were differentially expressed between the pituitary oncocytomas and normal pituitary glands. Among these 1937 genes, 954 were up-regulated and 983 were down-regulated in pituitary oncocytomas. The most significantly altered gene, claudin-9 (CLDN9), was further confirmed by quantitative real-time polymerase chain reaction, Western blot, and immunohistochemical staining in 10 invasive pituitary oncocytoma samples and 10 noninvasive pituitary oncocytoma samples. High levels of CLDN9 were found in the pituitary oncocytomas, whereas low levels were detected in normal pituitary glands. In addition, the CLDN9 expression level was higher in invasive oncocytomas compared with noninvasive oncocytomas. Bioinformatics Gene Ontology analysis was performed to better understand the critical role of CLDN9 in the development and progression of oncocytomas. Consequently, CLDN9 may be an important biomarker for invasive pituitary oncocytomas.

Emerging roles of claudins in human cancer

Claudins are major integral membrane proteins of tight junctions. Altered expression of several claudin proteins, in particular claudin-1, -3, -4 and -7, has been linked to the development of various cancers. Although their dysregulation in cancer suggests that claudins play a role in tumorigenesis, the exact underlying mechanism remains unclear. The involvement of claudins in tumor progression was suggested by their important role in the migration, invasion and metastasis of cancer cells in a tissue-dependent manner. Recent studies have shown that they play a role in epithelial to mesenchymal transition (EMT), the formation of cancer stem cells or tumor-initiating cells (CSCs/TICs), and chemoresistance, suggesting that claudins are promising targets for the treatment of chemoresistant and recurrent tumors. A recently identified claudin-low breast cancer subtype that is characterized by the enrichment of EMT and stem cell-like features is significantly associated with disease recurrence, underscoring the importance of claudins as predictors of tumor recurrence. The critical role of epigenetic mechanisms in the regulation of claudin expression indicates the possible application of epigenetic therapy to target claudins. A better understanding of the emerging role of claudins in CSC/TICs and chemoresistance may help to develop therapies against recurrent cancers.