Claudin-1 induces epithelial-mesenchymal transition through activation of the c-Abl-ERK signaling pathway in human liver cells

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.

Novel roles for HMGA2 isoforms in regulating oxidative stress and sensitizing to RSL3-Induced ferroptosis in prostate cancer cells

Oxidative stress is increased in several cancers including prostate cancer, and is currently being exploited in cancer therapy to induce ferroptosis, a novel nonapoptotic form of cell death. High mobility group A2 (HMGA2), a non-histone protein up-regulated in several cancers, can be truncated due to chromosomal rearrangement or alternative splicing of HMGA2 gene. The purpose of this study is to investigate the role of wild-type vs. truncated HMGA2 in prostate cancer (PCa). We analyzed the expression of wild-type vs. truncated HMGA2 and showed that prostate cancer patient tissue and some cell lines expressed increasing amounts of both wild-type and truncated HMGA2 with increasing tumor grade, compared to normal epithelial cells. RNA-Seq analysis of LNCaP prostate cancer cells stably overexpressing wild-type HMGA2 (HMGA2-WT), truncated HMGA2 (HMGA2-TR) or empty vector (Neo) control revealed that HMGA2-TR cells exhibited higher oxidative stress compared to HMGA2-WT or Neo control cells, which was also confirmed by analysis of basal reactive oxygen species (ROS) levels using 2', 7'-dichlorofluorescin diacetate (DCFDA) dye, the ratio of reduced glutathione/oxidized glutathione (GSH/GSSG) and NADP/NADPH using metabolomics. This was associated with increased sensitivity to RAS-selective lethal 3 (RSL3)-induced ferroptosis that could be antagonized by ferrostatin-1. Additionally, proteomic and immunoprecipitation analyses showed that cytoplasmic HMGA2 protein interacted with Ras GTPase-activating protein-binding protein 1 (G3BP1), a cytoplasmic stress granule protein that responds to oxidative stress, and that G3BP1 transient knockdown increased sensitivity to ferroptosis even further. Endogenous knockdown of HMGA2 or G3BP1 in PC3 cells reduced proliferation which was reversed by ferrostatin-1. In conclusion, we show a novel role for HMGA2 in oxidative stress, particularly the truncated HMGA2, which may be a therapeutic target for ferroptosis-mediated prostate cancer therapy.

Claudins: The Newly Emerging Targets in Breast Cancer

Claudin-low breast cancers are recently described entities showing low expression of certain claudins and cell adhesion molecules. Claudins constitute the backbone of tight junctions (TJs) formed between 2 cells. Their dysregulation plays a vital role in tumorigenesis. First part of the article focuses on the role of claudins in the TJ organization, their structural-functional characteristics, and post-transcriptional and translational modifications. The latter part of the review attempts to summarize existing knowledge regarding the status of claudins in breast cancer. The article also provides an overview of the effect of claudins on tumor progression, metastasis, stemness, chemotherapy resistance, and their crosstalk with relevant signaling pathways in breast cancer. Claudins can act as 2-edged swords in tumors. Some claudins have either tumor-suppressive/ promoting action, while others work as both in a context-dependent manner. Claudins regulate many important events in breast cancer. However, the intricacies involved in their activity are poorly understood. Post-translational modifications in claudins and their impact on TJ integrity, function, and tumor behavior are still unclear. Although their role in adverse events in breast cancer is recognized, their potential to serve as relevant targets for future therapeutics, especially for difficult-to-treat subtypes of the above malignancy, remains to be explored.

Differential Expression of Claudin in Odontogenic Cysts

Objective  This study aimed to analyze claudin-1, -4, and -7 expression in different types of odontogenic cysts (odontogenic keratocysts [OKCs], dentigerous cysts [DCs], calcifying odontogenic cysts [COCs], and radicular cysts [RCs]) as well as its association with OKC recurrence.

Materials and Methods  Seventy samples of odontogenic cysts samples were immunohistochemically stained to detect claudin-1, -4, and -7 expression. Patient information and OKC recurrence data were recorded. The staining was analyzed semiquantitatively and categorized based on the pattern and percentage of positively stained cystic epithelial cells.

Statistical Analysis  Expression of different claudins between groups was analyzed using the Kruskal–Wallis test with Dunn's test, followed by post hoc pairwise comparison. The association between claudin expression and OKC recurrence was analyzed by the Mann–Whitney U test. Correlations among claudin expression were examined with Spearman's correlation coefficient. Level of significance was at p  < 0.005.

Results  Claudin-1 was widely expressed in every odontogenic cyst. Most DCs (50%) expressed claudin-1 in more than 75% of cells, as did RCs (65%), while most OKCs (50%) expressed claudin-1 in 26 to 50% of cells. Most COCs (50%) expressed claudin-1 in 51 to 75% of cells. Every sample of OKC and RC was positive for claudin-4, but no sample showed staining in more than 51% of cells. Every odontogenic cyst was positive for claudin-7. DCs (35%), OKCs (55%), and RCs (40%) mostly showed staining in 26 to 50% of cells. High claudin-1 expression was shown in COCs, DCs, and RCs, while low expression of claudin-4 was shown in every odontogenic cyst. For claudin-7, the expression is high only in COCs. Claudin-1 and -4 was significantly different among each odontogenic cyst. High expression of claudin-1 was correlated with OKC recurrence. The correlations of claudin-1 with claudin-7 expression and claudin-4 with claudin-7 expression were significant in DCs. In COCs, claudin-1 and claudin-7 expression was significantly correlated.

Conclusions  The expression of claudin-1, -4, and -7 was present in every odontogenic cyst, but the proportion of positive staining cells was different. Expression of claudin-1 is associated with OKC recurrence. Dysregulation of claudin expression may play a pathogenic role in cyst pathogenesis.

Recent Advances in Liver Cancer Stem Cells: Non-coding RNAs, Oncogenes and Oncoproteins

Hepatocellular carcinoma (HCC) is one of the most prevalent malignancies worldwide, with high morbidity, relapse, metastasis and mortality rates. Although liver surgical resection, transplantation, chemotherapy, radiotherapy and some molecular targeted therapeutics may prolong the survival of HCC patients to a certain degree, the curative effect is still poor, primarily because of tumor recurrence and the drug resistance of HCC cells. Liver cancer stem cells (LCSCs), also known as liver tumor-initiating cells, represent one small subset of cancer cells that are responsible for disease recurrence, drug resistance and death. Therefore, understanding the regulatory mechanism of LCSCs in HCC is of vital importance. Thus, new studies that present gene regulation strategies to control LCSC differentiation and replication are under development. In this review, we provide an update on the latest advances in experimental studies on non-coding RNAs (ncRNAs), oncogenes and oncoproteins. All the articles addressed the crosstalk between different ncRNAs, oncogenes and oncoproteins, as well as their upstream and downstream products targeting LCSCs. In this review, we summarize three pathways, the Wnt/β-catenin signaling pathway, phosphatidylinositol 3-kinase (PI3K)/protein kinase B (Akt) signaling pathway, and interleukin 6/Janus kinase 2/signal transducer and activator of transcription 3 (IL6/JAK2/STAT3) signaling pathway, and their targeting gene, c-Myc. Furthermore, we conclude that octamer 4 (OCT4) and Nanog are two important functional genes that play a pivotal role in LCSC regulation and HCC prognosis.

Claudin-9 enhances the metastatic potential of hepatocytes via Tyk2/Stat3 signaling

BACKGROUND/AIMS

We have previously identified a tight junction protein claudin-9 (CLDN9) as an upregulated gene in hepatocellular carcinoma (HCC) through an immunohistochemistry analysis. Here, we explore its function and clinical relevance in human HCC.

MATERIALS AND METHODS

Stable transfection of the hepatocyte line HL7702 with CLDN9 was confirmed by the real-time polymerase chain reaction (PCR), western blotting, and immunofluorescence. The impact of CLDN9 on the cell invasion and migration was assessed in vitro by a transwell assay and wound-healing experiment. Western blotting was used to determine the activation state of the Tyk2 (tyrosine kinase 2)/Stat3 (signal transducer and activator of transcription 3) pathway. Moreover, we used a Tyk2-RNAi assay to silence the expression of Tyk2 in CLDN9 expressing hepatocytes; subsequently, the impact of the Tyk2/Stat3 signaling pathway on the cell invasion and migration in vitro was assessed by a transwell assay and a wound-healing experiment. Furthermore, an immunohistochemistry method was utilized to explore the expression levels of CLDN9 and p-Stat3 in the HCC tissues and histologically non-neoplastic hepatic tissues.

RESULTS

We confirmed that the expression of CLDN9 significantly enhanced the metastatic ability of hepatocytes in vitro, and the activation of the Stat3 pathway by Tyk2 was an important mechanism by which CLDN9 promoted hepatocyte aggressiveness in HCC.

CONCLUSION

As an HCC proto-oncogene, CLDN9 affected the Stat3 signaling pathway via Tyk2 and ultimately enhanced the metastatic ability of hepatocytes.

PRPF4 is a novel therapeutic target for the treatment of breast cancer by influencing growth, migration, invasion, and apoptosis of breast cancer cells via p38 MAPK signaling pathway

Pre-mRNA processing factor 4 (PRPF4), a core protein in U4/U6 snRNP, maintains snRNP structures by interacting with PRPF3 and cyclophilin H. Expression of the PRPF4 gene affects cell survival as well as apoptosis and is responsible for retinitis pigmentosa (RP). Proteomics analysis shows that PRPF4 may be a therapeutic target in human cancers. Nevertheless, the exact function and role of the PRPF4 gene are unclear. In this study, we assessed the expression of PRPF4 gene in human breast cancer cells. First, we confirmed that the PRPF4 gene was overexpressed in various breast cancer cell lines. Next, using breast cancer cell lines MCF7 and MDA-MB-468, we established stable cell lines with PRPF4 gene knockdown. We also performed microarray analysis to investigate molecular mechanisms underlying PRPF4 activity. All cell lines with PRPF4 gene knockdown exhibited reduced cell proliferation, remarkable reduction in anchorage-independent colony formation capacity, and reduction of PCNA protein, which is a marker cell of proliferation. Reduced expression of the PRPF4 gene induced apoptosis and changes in the expression of associated apoptotic markers in breast cancer cell lines. Knockdown of the PRPF4 gene reduced cellular capacity for migration and invasion (the key hallmarks of human cancers) and decreased the expression of genes involved in epithelial-mesenchymal transition (EMT). Microarray results showed that the expression of PPIP5K1, PPIPK2, and YWHAE genes was reduced at the transcriptional level, leading to reduced phosphorylation of p38 MAPK. These findings suggest that knockdown of PRPF4 gene slows down breast cancer progression via suppression of p38 MAPK phosphorylation. In conclusion, the PRPF4 gene plays an important role in the growth of breast cancer cells and is therefore a potential therapeutic target.

CLDN10 promotes a malignant phenotype of osteosarcoma cells via JAK1/Stat1 signaling

In our previous study, the expression profile of tight junction (TJ) protein claudins (CLDNs) in human osteosarcoma (OS) cells was examined, and the data found the CLDN10 was high expressed in OS cells versus fetal osteoblast cells. Hence, we aim to determine the impacts and the molecular mechanisms of CLDN10 in the metastatic phenotype of OS. The exact expression profiles of CLDN10 and phosphorylated Janus kinase 1 (JAK1) in noncancerous bone tissues and OS tissues were detected via a western blotting and immunohistochemistry method. The OS cells with CLDN10 or JAK1 silencing was established via an RNA interference (RNAi) method, and an osteoblast cell line stably expressing CLDN10 was established via cell transfection. Then, the transfection effects and activation states of JAK1/ signal transducer and activator of transcription1 (Stat1) pathway in OS and osteoblast cells were detected via a western blotting assay. Moreover, the metastatic ability of osteoblast cells and OS cells in vitro were evaluated by means of a cell counting kit-8 (CCK8) assay, colony formation assay in soft agar, transwell assay and wound-healing experiment. The present data revealed that CLDN10 and phospho-JAK1 were up-regulated in OS tissues compared with noncancerous bone tissues. Genetic loss of CLDN10 or JAK1 inhibited the activation of the Stat1 and the malignant phenotype in OS cells. To sum up, our study suggested the CLDN10 enhanced the metastatic phenotype of OS cells via the activation of the JAK1/Stat1 signaling pathway.

CLDN2 inhibits the metastasis of osteosarcoma cells via down-regulating the afadin/ERK signaling pathway

Background

In an earlier study, we investigated the expression of tight junction protein claudins (CLDNs) in human osteosarcoma (OS) cells, and the CLDN2 was found to be down-regulated in primary tumor cells compared with normal osteoblast cells. Here, we sought to explore the effects of CLDN2 on the malignant phenotype of OS and the underlying molecular mechanisms.

Methods

The expression patterns of CLDN2 and afadin in OS tissues and histologically non-neoplastic bone tissues were explored via immunohistochemistry and western blotting. CLDN2 expression levels in an OS cell line stably expressing CLDN2 and an osteoblast cell line with a CLDN2 knockout were confirmed by western blotting and immunofluorescence staining. The malignant phenotype of OS cells and osteoblast cells in vitro was assessed using a cell counting kit-8 assay, transwell assay and wound-healing experiment. Western blotting was utilized to detect the activation state of Ras/Raf/MEK/ERK pathway. Moreover, an RNA interference method were used to silence afadin in CLDN2-expressing OS cells.

Results

Our research group found that CLDN2 and afadin was underexpressed in OS tissues, and the overexpression of CLDN2 significantly inhibited the migration abilities of OS cells. Genetic silencing of afadin in CLDN2-overexpressing OS cells promoted U2OS cell motility and activation of the Ras/Raf/MEK/ERK pathway.

Conclusions

In this study, we confirmed that CLDN2 expression significantly inhibited the malignant phenotype of OS cells in vitro. Inhibition of the ERK pathway by afadin may be one of the mechanisms by which CLDN2 blocks the metastasis phenotype of OS cells.

Increased expression of claudin-17 promotes a malignant phenotype in hepatocyte via Tyk2/Stat3 signaling and is associated with poor prognosis in patients with hepatocellular carcinoma

Background

Hepatocellular carcinoma (HCC) is the second leading cause of cancer death in Asia; however, the molecular mechanism in its tumorigenesis remains unclear. Abnormal expression of claudins (CLDNs), a family of tight junction (TJ) proteins, plays an important role in the metastatic phenotype of epithelial-derived tumors by affecting tight junction structure, function and related cellular signaling pathways. In a previous study, we used a tissue chip assay to identify CLDN17 as an upregulated gene in HCC. Here we aimed to use molecular biology technology to explore the effect of CLDN17 on the malignant phenotype of HCC and the underlying molecular mechanism, with the objective of identifying a new target for HCC treatment and the control of HCC metastasis.

Method

The expression levels of CLDN17 in HCC tissues and histologically non-neoplastic hepatic tissues were explored by immunohistochemistry. Stable transfection of the hepatocyte line HL7702 with CLDN17 was detected by real-time polymerase chain reaction (PCR), western blotting and immunofluorescence. The impact of CLDN17 on the malignant phenotype of HL7702 cells in vitro was assessed by a Cell Counting Kit-8 (CCK8) assay, a Transwell assay and a wound-healing experiment. Western blotting was utilized to detect the activation state of Tyrosine kinase 2 (Tyk2) / signal transducer and activator of transcription3 (Stat3) pathway. A Tyk2 RNA interference (RNAi) was utilized to determine the impact of the Tyk2/Stat3 signaling pathway on the malignant phenotype of hepatocytes.

Results

In this work, our research group first found that CLDN17 was highly expressed in HCC tissues and was associated with poor prognosis. In addition, we demonstrated that CLDN17 affected the Stat3 signaling pathway via Tyk2 and ultimately enhanced the migration ability of hepatocytes.

Conclusion

In conclusion, we confirmed that the upregulated expression of CLDN17 significantly enhances the migration ability of hepatocytes in vitro and we found that the activation of the Stat3 pathway by Tyk2 may an important mechanism by which CLDN17 promotes aggressiveness in hepatocytes.

TMPRSS4 promotes cancer stem cell traits by regulating CLDN1 in hepatocellular carcinoma

Encouraging advances in the treatment of hepatocellular carcinoma(HCC) have been achieved; however, a considerable part of patients still relapse or metastasize after therapy, and the underlying mechanisms have not been clarified yet. Here, we found that CLDN1 was markedly up-regulated in HCC tissues, and correlated with poor prognosis. Overexpression of CLDN1 dramatically promoted the capability of tumorsphere formation and cancer stem cell (CSC) traits. Furthermore, we found that TMPRSS4 was up-regulated in HCC tissues and there was a positive correlation between TMPRSS4 and CLDN1. In addition, the expression of CLDN1 was regulated by TMPRSS4. Moreover, TMPRSS4 mediated CSC properties and up-regulated CLDN1 by activating ERK1/2 signaling pathway. Taken together, our results revealed that CLDN1 contributed to CSC features of HCC, which was altered by TMPRSS4 expression via ERK1/2 signaling pathway, providing promising targets for novel specific therapies.

Long non-coding RNA HOTAIR functions as miRNA sponge to promote the epithelial to mesenchymal transition in esophageal cancer

BACKGROUND

Accumulating evidence indicates dysregulated expression of the long non-coding RNA HOTAIR (lncRNA-HOTAIR) may play a significant role in tumor progression. LncRNA-HOTAIR promotes several processes in esophageal cancer (EC), including cell growth, differentiation, invasion and migration. However, the mechanisms by which lncRNA-HOTAIR promotes invasion and migration EC remain unclear.

METHODS

LncRNA-HOTAIR and miR-148a expression were quantified in 40 paired human EC and tumor-adjacent tissues and EC cell lines by quantitative real-time PCR (qRT-PCR). The CCK8 assay was used to quantify cell proliferation. Transwell invasion and migration assays were performed to assess cell invasion and migration. Western blot analysis was used to quantify E-cadherin, N-cadherin, Vimentin, and Snail2 expression. StarBase V2.0 was used to identify putative miRNA binding sites in lncRNA-HOTAIR; luciferase reporter assays were performed to validate the function of the predicted binding sites.

RESULT

High lncRNA-HOTAIR expression was associated with significantly poorer overall survival in EC. In vitro analysis showed lncRNA-HOTAIR enhanced EC cell proliferation, invasion and migration, and promoted the EMT. Mechanistic investigations revealed lncRNA-HOTAIR promotes the EMT by acting as a miR-148a sponge to positively regulate Snail2 expression.

CONCLUSIONS

LncRNA-HOTAIR acts as a miR-148a sponge to positively regulate Snail2 expression, enhance cell invasion and metastasis, and promote the EMT in EC. LncRNA-HOTAIR may play an important role in tumor development and progression and represent a novel therapeutic target for EC.

Claudin proteins, outside-in signaling, and carcinogenesis

Environment affects an individual's development and disease risk which then suggest that the environmental cues must have ways of reaching to the cellular nuclei to orchestrate desired genetic changes. Polarized and differentiated epithelial cells join together by cell-cell adhesions to create a protective sheet which separates body's internal milieu from its environment, albeit in highly regulated manner. Among these cell-cell adhesions, a key role of tight junction, the apical cell-cell adhesion, in maintaining epithelial cell polarity and differentiation is well recognized. Moreover, significant changes in expression and cellular distribution of claudin proteins, integral component of the tight junction, characterize pathophysiological changes including neoplastic growth and progression. Studies have further confirmed existence of complex claudin-based interactomes and demonstrated that changes in such protein partnering can influence barrier integrity and communication between a cell and its environment to produce undesired outcome. Cell signaling is the process by which cells respond to their environment to make dynamic decisions to live, grow and proliferate, or die. Thus, pivotal role of the deregulated tight junction structure/function in influencing cellular signaling cascades to alter cellular phenotype can be envisaged, however, is not well understood. Needless to mention that advanced knowledge in this area can help improve therapeutic considerations and preventive measures. Here, we discuss potential role of the tight junction in the regulation of "outside-in" signaling to regulate cancer growth, with specific focus upon the claudin family of proteins.

Gefitinib inhibits invasive phenotype and epithelial-mesenchymal transition in drug-resistant NSCLC cells with MET amplification

Despite the initial response, all patients with epidermal growth factor receptor (EGFR)-mutant non-small cell lung cancer (NSCLC) eventually develop acquired resistance to EGFR tyrosine kinase inhibitors (TKIs). The EGFR-T790M secondary mutation is responsible for half of acquired resistance cases, while MET amplification has been associated with acquired resistance in about 5-15% of NSCLCs. Clinical findings indicate the retained addiction of resistant tumors on EGFR signaling. Therefore, we evaluated the molecular mechanisms supporting the therapeutic potential of gefitinib maintenance in the HCC827 GR5 NSCLC cell line harbouring MET amplification as acquired resistance mechanism. We demonstrated that resistant cells can proliferate and survive regardless of the presence of gefitinib, whereas the absence of the drug significantly enhanced cell migration and invasion. Moreover, the continuous exposure to gefitinib prevented the epithelial-mesenchymal transition (EMT) with increased E-cadherin expression and down-regulation of vimentin and N-cadherin. Importantly, the inhibition of cellular migration was correlated with the suppression of EGFR-dependent Src, STAT5 and p38 signaling as assessed by a specific kinase array, western blot analysis and silencing functional studies. On the contrary, the lack of effect of gefitinib on EGFR phosphorylation in the H1975 cells (EGFR-T790M) correlated with the absence of effects on cell migration and invasion. In conclusion, our findings suggest that certain EGFR-mutated patients may still benefit from a second-line therapy including gefitinib based on the specific mechanism underlying tumor cell resistance.