Claudin-1 expression in squamous cell carcinomas of different organs: comparative study of cancerous tissues and normal controls

Aberrant Expression of Claudins in Head and Neck Carcinomas and Their Prognostic and Therapeutic Value: A Narrative Review

Head and neck carcinomas have been associated with poor prognosis. Recent studies have highlighted the role of claudins' expression in tumors throughout the body, and their prognostic and therapeutic role. Understanding the role of claudins and how their expression affects the progression of carcinomas in the head and neck region may allow for advances in the prognosis and management of this type of cancer. Several studies have highlighted the aberrant expression of the proteins in carcinomas in this region. Specifically, the overexpression of claudin-1 and downregulation of claudins-4, -7, and -17 have been linked with poor survival in oral squamous cell carcinoma patients. In laryngeal squamous cell carcinoma, increased levels of claudins-1 and reduced levels of claudins-3, -8, and -11 have been linked with poor outcomes. Targeting these proteins has shown promising outcomes as therapeutic in preclinical studies. However, studies remain extremely limited in nasal and hypopharyngeal carcinomas. In this review, we survey the available literature describing the aberrant expression of various claudins in carcinomas in this region, while highlighting their potential prognostic and therapeutic value. Then, we describe some molecular mechanisms involved in the aberrant expression of claudins and how they can be utilized as therapeutic targets.

Expression of Claudins in Preneoplastic Conditions of the Gastrointestinal Tract: A Review

Premalignant lesions of the gastrointestinal tract are a group of disorders which act as the harbinger of malignant tumors. They are the ground-zero of neoplastic transformation, and their identification and management offer patients the best opportunity of blocking the progress of cancer. However, diagnoses of some of these conditions are hard to make, and their clinical importance is difficult to assess. Recent reports indicated that several claudin proteins have altered expressions in many cancers, including esophageal, gastric, colon, liver, and pancreatic cancers. The early identification of the aberrant expression of these proteins could lead to the early diagnosis and management of gastrointestinal tumors. Specifically, claudins -1, -2, -3, -4, and -18 are frequently overexpressed in gastrointestinal preneoplastic lesions. These altered expressions have shown clinical value in several tumors, providing diagnostic and prognostic information. In this article, we review the literature on the aberrant expression of claudins in preneoplastic lesions of the gastrointestinal tract. Additionally, we summarize their diagnostic and prognostic implications.

Differential Expression of Claudin 1 and 4 in Basal Cell Carcinoma of the Skin

Basal cell carcinoma (BCC) is the most common human malignancy. The biological behavior of this entity is remarkably indolent. Claudin plays an important role in tight junctions, regulating paracellular passage of variable substance including growth factors and maintaining the polarity of epithelia. Up- or downregulated claudin expression has been reported in many cancers. Nevertheless, claudin expression in BCC of the skin remains unclear. We therefore examined the status of claudin 1 and 4 expressions in BCC and adjacent normal skin by immunohistochemistry (IHC). Our IHC results demonstrated high claudin 1 expression and low claudin 4 expression in 33 of 34 lower-grade BCCs. In lower-grade BCC, claudin 1 was increased and claudin 4 was decreased compared with the normal skin. Claudin 1 was inclined to be highly expressed in the membrane and cytoplasm of tumour cells in the periphery of tumour nest. Conversely, almost all lower-grade BCCs (33/34) and one of two higher-grade BCC lacked or showed focal positivity for claudin 4. These results imply that the expression pattern is characteristics of lower-risk BCC. Interestingly, one of the two higher-grade BCCs demonstrated the converse expression patterns of claudins, with decreased claudin 1 and increased claudin 4. The combination of immunohistochemical claudin 1 and 4 expression may offer a useful ancillary tool for the pathological diagnosis of BCC. Furthermore, membranous and intracellular claudins may present future therapeutic targets for uncontrollable BCC.

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.

Digital Image Analysis-Based Evaluation of Claudin-1 and Claudin-7 Delocalization in Cutaneous Squamous Cell Carcinoma and in Its Precancerous State

Accumulating evidence has revealed that delocalization of the transmembrane proteins, Claudin-1 and Claudin-7, to the cytoplasm and/or nucleus occurs in various tumors. However, their subcellular distribution in terms of the membrane, cytoplasm, and nucleus and relationship with signaling pathways have not been elucidated during carcinogenesis. We first determined the expression of these proteins in the membrane, cytoplasm, and nucleus using ImageJ software and automatically collected the immunohistochemical quantification of dysplasia (actinic keratosis (AK)), carcinoma in situ (CIS; Bowen’s disease (BD)), and invasive cutaneous squamous cell carcinoma (SCC) for digital image analysis (DIA). The activity of p-ERK, p-AKT, and p-mTOR and their correlation with subcellular Claudin-1 and Claudin-7 were also performed. Finally, we validated Claudin-1 and Claudin-7 delocalization at the cytoplasm and nucleus in cultured human normal keratinocytes and cutaneous SCC cells. Claudin-1 and Claudin-7 were delocalized as revealed by membranous, cytoplasmic, and nuclear staining in sun-exposed skin, AK, BD, and SCC. In BD, both membranous and cytoplasmic Claudin-1 (nuclear Claudin-1 decrease but no significant difference) were higher than AK, while Claudin-7 almost had the opposite situation. In SCC, cytoplasmic and nuclear Claudin-1 (membranous Claudin-1 no significant difference) was lower than in AK and sun-exposed skin, while Claudin-7 had higher membranous and cytoplasmic but lower nuclear expression. Moreover, p-AKT and p-mTOR (but not p-ERK) were downregulated in the SCC. Subcellular Claudin-1 and Claudin-7 were not only correlated with each other, but also correlated with p-ERK in BD and p-AKT and p-mTOR in SCC. Together, these results imply the delocalization of Claudin-1 and Claudin-7 and their correlation with MAPK/ERK and PI3K-AKT-mTOR signaling pathways in tumorigenesis and infiltration in cutaneous SCC.

Claudin expression profile in flat wart and cutaneous squamous cell carcinoma in epidermodysplasia verruciformis

Epidermodysplasia verruciformis (EV) is a genodermatosis related to human beta-papillomavirus (beta-HPV), with a high risk of cutaneous squamous cell carcinoma (cSCC). Claudins are transmembrane proteins expressed in epithelia and may be altered during carcinogenesis. For a better understanding of the role of beta-HPV in cutaneous carcinogenesis, this claudin expression study was conducted on lesions of patients with and without EV. In this study, claudins-1, -2, -3, -4, -5, -7 and -11 expressions were analyzed by applying the immunohistochemistry technique, in samples of 108 normal skin, 39 flat warts and 174 cSCC. The cSCC samples were organized in tissue microarrays. We found that claudin-1 and claudin-3 focal expressions were associated with cSCC (p < 0.001), and claudin-2 focal or negative expression with flat wart (p < 0.001), in EV and NEV (non-EV) groups. For claudin-5, EV group showed a lower chance of focal and negative expression (p < 0.001), and its negative expression was associated with flat wart (p < 0.001) and lower mean age (p < 0.001). Claudins-4, -7 and -11 showed a diffuse expression in almost all studied samples. Our findings suggest that claudin-5 increased expression observed on normal skin, flat wart and cSCC showed association with EV. Claudin-1 and -3 down expression were also observed, but they could not be related to beta-HPV infection.

Claudin-1, A Double-Edged Sword in Cancer

Claudins, a group of membrane proteins involved in the formation of tight junctions, are mainly found in endothelial or epithelial cells. These proteins have attracted much attention in recent years and have been implicated and studied in a multitude of diseases. Claudins not only regulate paracellular transepithelial/transendothelial transport but are also critical for cell growth and differentiation. Not only tissue-specific but the differential expression in malignant tumors is also the focus of claudin-related research. In addition to up- or down-regulation, claudin proteins also undergo delocalization, which plays a vital role in tumor invasion and aggressiveness. Claudin (CLDN)-1 is the most-studied claudin in cancers and to date, its role as either a tumor promoter or suppressor (or both) is not established. In some cancers, lower expression of CLDN-1 is shown to be associated with cancer progression and invasion, while in others, loss of CLDN-1 improves the patient survival. Another topic of discussion regarding the significance of CLDN-1 is its localization (nuclear or cytoplasmic vs perijunctional) in diseased states. This article reviews the evidence regarding CLDN-1 in cancers either as a tumor promoter or suppressor from the literature and we also review the literature regarding the pattern of CLDN-1 distribution in different cancers, focusing on whether this localization is associated with tumor aggressiveness. Furthermore, we utilized expression data from The Cancer Genome Atlas (TCGA) to investigate the association between CLDN-1 expression and overall survival (OS) in different cancer types. We also used TCGA data to compare CLDN-1 expression in normal and tumor tissues. Additionally, a pathway interaction analysis was performed to investigate the interaction of CLDN-1 with other proteins and as a future therapeutic target.

Claudin-1 expression decreases with increasing pathological grade in actinic keratosis and may be a marker of high-risk actinic keratosis

BACKGROUND

Actinic keratosis (AK) is a common sun-induced skin disorder that can progress to invasive squamous cell carcinoma. However, there is still no reliable method to predict high-risk AK.

AIM

To identify markers that reflect the biological behaviour of AK and to understand the pathogenesis of AK.

METHODS

In total, 52 patients with AK and 17 site-matched healthy controls (HCs) were enrolled. We evaluated solar elastosis and immunohistochemical features using antibodies to p53, vitamin D receptor (VDR), claudin-1 and Langerin (CD207). Comparisons between AK and HC skin were performed and analyses carried out according to the pathological grade of AK.

RESULTS

We found that in both patients and HCs, solar elastosis increased and Langerhans cell (LC) density decreased with ageing. Solar elastosis and p53 expression were higher and VDR expression was lower in patients than in HCs; however, there was no statistical difference between them in relation to the pathological grade of AK. Claudin-1 expression gradually decreased from HC skin to severe AK, and particularly decreased in areas with epidermal atypia. LC density in severe AK was significantly lower than in HC skin and mild AK, while there was no difference in LC density between HC skin, mild AK and moderate AK.

CONCLUSIONS

Claudin-1 could be a useful marker of the pathological severity of AK. In addition, p53 increases and VDR decreases in AK, not in a gradual manner but in the early steps of carcinogenesis. LC density is relatively maintained in AK until it reaches severe dysplasia.

Aberrant expression of the tight junction molecules claudin-1 and zonula occludens-1 mediates cell growth and invasion in oral squamous cell carcinoma

We reported that altered cell contact mediated by E-cadherin is an initial event in the pathogenesis of oral epithelial malignancies. To assess other effects of cell adhesion, we examined the expression levels of tight junction (TJ) molecules in oral carcinoma in situ (CIS) and squamous cell carcinoma (SCC). To identify changes in the expression of TJ molecules, we conducted an analysis of the immunohistochemical profiles of claudin-1 (CLDN-1) and zonula occludens-1 (ZO-1) in surgical specimens acquired from patients with oral SCC containing foci of epithelial dysplasia or from patients with CIS. We used immunofluorescence, Western blotting, reverse-transcription polymerase chain reaction, and RNA interference to evaluate the functions of CLDN-1 and ZO-1 in cultured oral SCC cells. TJ molecules were not detected in normal oral epithelial tissues but were expressed in SCC/CIS cells. ZO-1 was localized within the nucleus of proliferating cells. When CLDN-1 expression was inhibited by transfecting cells with specific small interference RNAs, SCC cells dissociated, and their ability to proliferate and invade Matrigel was inhibited. In contrast, although RNA interference-mediated inhibition of ZO-1 expression did not affect cell morphology, it inhibited cell proliferation and invasiveness. Our findings indicated that the detection of TJ molecules in the oral epithelia may serve as a marker for the malignant phenotype of cells in which CLDN-1 regulates proliferation and invasion.

Claudin-1 correlates with poor prognosis in lung adenocarcinoma

BACKGROUND

This study was conducted to investigate the clinical significance of claudin-1 (CLDN1) expression in patients with lung adenocarcinoma.

METHODS

We examined CLDN1 protein expression by immunohistochemistry in a tissue microarray from 258 patients with lung adenocarcinoma. We investigated messenger ribonucleic acid (mRNA) expression in H358 (formerly bronchioloalveolar carcinoma) and lung adenocarcinoma cell lines (A549) by real-time reverse transcriptase-polymerase chain reaction.

RESULTS

Multivariate analysis showed that prognostic factors for lung adenocarcinoma were histologic type, CLDN1, T stage and N stage. Patients with positive CLDN1 expression had a poorer prognosis than patients with negative CLDN1 expression. CLDN1 expression was correlated with Ras and epidermal growth factor receptor (EGFR) expression. Patients with positive expressions of both CLDN1 and Ras/EGFR had a poorer prognosis than patients with CLDN1 (+) Ras/EGFR(-) or CLDN1 (-) Ras/EGFR(+) and patients with negative expressions of both CLDN1 and Ras/EGFR. CLDN1 mRNA expression was lower in the H358 compared with the lung adenocarcinoma cell line (A549).

CONCLUSION

The combination of CLDN1 and Ras/EGFR is a valuable independent prognostic predictor for lung adenocarcinoma.

Analysis of the distribution and expression of claudin-1 tight junction protein in the oral cavity

BACKGROUND

Claudins are the main sealing proteins of the intercellular tight junctions and play an important role in cancer cell progression and dissemination. The authors have previously shown that overexpression of claudin-1 is associated with angiolymphatic and perineural invasion, consistent with aggressive tumor behavior and with advanced stage disease in oral squamous cell carcinomas (OSCCs). Our goal in this study was to examine claudin-1 expression in a tissue microarray of OSCCs taken from multiple sites within the oral cavity.

MATERIALS AND METHODS

This study examined and compared the expression of claudin-1 by immunohistochemistry in 60 tissue samples (49 OSCCs and 10 cases of non-neoplastic tissue, single core per case) were analyzed for claudin-1 expression by immunohistochemistry. The tumors included SCCs from the tongue (n=28), the cheek (n=9), gingival (n=4), lip (n=3), and oral cavity (n=5). Nonmalignant normal oral mucosa from the tongue (unmatched cases, n=2). Cancer adjacent tissue samples were taken from the tongue (n=6), gingival (n=2), and palate (n=1).

RESULTS

This study demonstrates the expression of claudin-1 protein across a sample of OSCCs originating from multiple locations in the oral cavity. The highest expression of claudin-1 was observed in well-differentiated OSCCs, whereas poorly differentiated OSCCs exhibited mostly negative staining for claudin-1. In addition, we hereby report differential pattern of expression among tumors of different sites within the oral cavity, and between benign and cancerous samples. Our understanding of the exact function and role of claudin-1 in tumorigenesis is expanding exponentially.

Diverse regulation of claudin-1 and claudin-4 in atopic dermatitis

Tight junctions are important for skin barrier function. The tight junction protein claudin 1 (Cldn-1) has been reported to be down-regulated in nonlesional skin of atopic dermatitis (AD) patients. In contrast, we did not observe a significant down-regulation of Cldn-1 in nonlesional skin of the AD cohort used in this study. However, for the first time, a significant down-regulation of Cldn-1 in the upper and lower epidermal layers of lesional skin was detected. In addition, there was a significant up-regulation of Cldn-4 in nonlesional, but not lesional, AD skin. For occludin, no significant alterations were observed. In an AD-like allergic dermatitis mouse model, Cldn-1 down-regulation in eczema was significantly influenced by dermal inflammation, and significantly correlated with hallmarks of eczema (ie, increased keratinocyte proliferation, altered keratinocyte differentiation, increased epidermal thickness, and impaired barrier function). In human epidermal equivalents, the addition of IL-4, IL-13, and IL-31 resulted in a down-regulation of Cldn-1, and Cldn1 knockdown in keratinocytes resulted in abnormal differentiation. In summary, we provide the first evidence that Cldn-1 and Cldn-4 are differentially involved in AD pathogenesis. Our data suggest a role of Cldn-1 in AD eczema formation triggered by inflammation.

Overexpression of Claudin-1 is Associated with Advanced Clinical Stage and Invasive Pathologic Characteristics of Oral Squamous Cell Carcinoma

Claudins constitute a group of principal proteins forming the tight junctional complex. The altered expression of selected claudins has been reported in several human cancers. The purpose of this study was to investigate the expression of claudin-1 and claudin-4 in oral squamous cell carcinoma (OSCC) and examine its relationship with patient clinical-pathologic features. Forty-five OSCC cases were enrolled. Patient clinical, pathologic and follow-up data were reviewed and the claudin-1 and claudin-4 expression was analyzed immunohistochemically. Positive claudin-1 and claudin-4 immunoreactivities were noted in 86.7 and 80 % of cases, respectively. The majority of cases showed the staining in less than 25 % of cancer cells. The increased claudin-1 expression was significantly associated with the high pathologic grade, the presence of microscopic perineural invasion, vascular invasion, nodal metastasis, and advanced clinical stage. No relationship between various clinico-pathologic parameters and differential claudin-4 expression was observed. Claudin-1 may play a role in OSCC progression and could serve as a prognostic marker of advanced disease.

The claudin family of proteins in human malignancy: a clinical perspective

Tight junctions, or zonula occludens, are the most apical component of the junctional complex and provide one form of cell-cell adhesion in epithelial and endothelial cells. Nearly 90% of malignant tumors are derived from the epithelium. Loss of cell-cell adhesion is one of the steps in the progression of cancer to metastasis. At least three main tight junction family proteins have been discovered: occludin, claudin, and junctional adhesion molecule (JAM). Claudins are the most important structural and functional components of tight junction integral membrane proteins, with at least 24 members in mammals. They are crucial for the paracellular flux of ions and small molecules. Overexpression or downregulation of claudins is frequently observed in epithelial-derived cancers. However, molecular mechanisms by which claudins affect tumorigenesis remain largely unknown. As the pivotal proteins in epithelial cells, altered expression and distribution of different claudins have been reported in a wide variety of human malignancies, including pancreatic, colonic, lung, ovarian, thyroid, prostate, esophageal, and breast cancers. In this review, we will give the readers an overall picture of the changes in claudin expression observed in various cancers and their mechanisms of regulation. Downregulation of claudins contributes to epithelial transformation by increasing the paracellular permeability of nutrients and growth factors to cancerous cells. In the cases of upregulation of claudin expression, the barrier function of the cancerous epithelia changes, as they often display a disorganized arrangement of tight junction strands with increased permeability to paracellular markers. Finally, we will summarize the literature suggesting that claudins may become useful biomarkers for cancer detection and diagnosis as well as possible therapeutic targets for cancer treatment.

Trichostatin-A modulates claudin-1 mRNA stability through the modulation of Hu antigen R and tristetraprolin in colon cancer cells

Expression of claudin-1, a tight junction protein, is highly upregulated in colon cancer. We have reported that claudin-1 expression in colon cancer cells is epigenetically regulated as histone deacetylase (HDAC) inhibitors decrease claudin-1 messenger RNA (mRNA) stability and thus expression. In this regard, our data suggested a role of the 3'-untranslated region (UTR) in the regulation of HDAC-dependent regulation of claudin-1 mRNA stability. In the current study, we demonstrate, based on our continued investigation, that the ELAV-like RNA-binding proteins (RBPs), human antigen R (HuR) and tristetraprolin (TTP) associate with the 3'-UTR of claudin-1 mRNA to modulate the latter's stability. Ribonomic and site-directed mutagenesis approaches were used to confirm the binding of HuR and TTP to the 3'-UTR of claudin-1. We further confirmed their roles in the stabilization of claudin-1 mRNA, under conditions of HDAC inhibition. In summary, we report that HuR and TTP are the critical regulators of the posttranscriptional regulation of claudin-1 expression in colon cancer cells. We also demonstrate that inhibition of HDACs by trichostatin treatment decreased the binding of HuR while increasing the binding of TTP to the 3'-UTR of claudin-1. Additionally, we provide data showing transcriptional regulation of claudin-1 expression, through the regulation of transcription factor Sp1. Taken together, we demonstrate epigenetic regulation of claudin-1 expression in colon cancer cells at the transcriptional and posttranscriptional levels.

Occludin is involved in adhesion, apoptosis, differentiation and Ca2+-homeostasis of human keratinocytes: implications for tumorigenesis

Tight junction (TJ) proteins are involved in a number of cellular functions, including paracellular barrier formation, cell polarization, differentiation, and proliferation. Altered expression of TJ proteins was reported in various epithelial tumors. Here, we used tissue samples of human cutaneous squamous cell carcinoma (SCC), its precursor tumors, as well as sun-exposed and non-sun-exposed skin as a model system to investigate TJ protein alteration at various stages of tumorigenesis. We identified that a broader localization of zonula occludens protein (ZO)-1 and claudin-4 (Cldn-4) as well as downregulation of Cldn-1 in deeper epidermal layers is a frequent event in all the tumor entities as well as in sun-exposed skin, suggesting that these changes result from chronic UV irradiation. In contrast, SCC could be distinguished from the precursor tumors and sun-exposed skin by a frequent complete loss of occludin (Ocln). To elucidate the impact of down-regulation of Ocln, we performed Ocln siRNA experiments in human keratinocytes and uncovered that Ocln downregulation results in decreased epithelial cell-cell adhesion and reduced susceptibility to apoptosis induction by UVB or TNF-related apoptosis-inducing ligand (TRAIL), cellular characteristics for tumorigenesis. Furthermore, an influence on epidermal differentiation was observed, while there was no change of E-cadherin and vimentin, markers for epithelial-mesenchymal transition. Ocln knock-down altered Ca²⁺-homeostasis which may contribute to alterations of cell-cell adhesion and differentiation. As downregulation of Ocln is also seen in SCC derived from other tissues, as well as in other carcinomas, we suggest this as a common principle in tumor pathogenesis, which may be used as a target for therapeutic intervention.