Abrogation of junctional adhesion molecule-A expression induces cell apoptosis and reduces breast cancer progression

Multilayered proteomics reveals that JAM-A promotes breast cancer progression via regulation of amino acid transporter LAT1

Recent studies have shown that transmembrane-type tight junction proteins are upregulated in various cancers compared with their levels in normal tissues and are involved in cancer progression, suggesting that they are potential therapeutic targets. Here, we demonstrated the expression profile and a novel role of junctional adhesion molecule-A (JAM-A) in breast cancer. Immunohistochemistry of surgical specimens showed that JAM-A was highly expressed from carcinoma in situ lesions, as in other adenocarcinomas, with higher expression in invasive carcinomas. High expression of JAM-A contributed to malignant aspects such as lymph node metastasis and lymphatic involvement positivity. In breast cancer cells, JAM-A expression status affects malignant potentials including proliferation and migration. Multilayered proteomics revealed that JAM-A interacts with the amino acid transporter LAT1 in breast cancer cells. JAM-A regulates the expression of LAT1 and interacts with it on the whole cell membrane, leading to enhanced amino acid uptake to promote tumor growth. Double high expression of JAM-A and LAT1 predicts poor prognosis in patients with breast cancer. Of note, an antibody against an extracellular domain of JAM-A suppressed the proliferation of breast cancer cells. Our findings indicate the possibility of JAM-A-targeted therapy ideally combined with LAT1-targeted therapy as a new therapeutic strategy against breast cancer.

Generation and characterization of mAb 61H9 against junctional adhesion molecule-a with potent antitumor activity

Junctional adhesion molecule-A (JAM-A) is an adhesion molecule that exists on the surface of certain types of cells, including white blood cells, endothelial cells, and dendritic cells. In this study, the cDNA sequences of JAM-A-Fc were chemically synthesized with optimization for mammalian expression. Afterward, we analyzed JAM-A protein expression through transient transfection in HEK293 cell lines. Mice were immunized with JAM-A-Fc protein, and hybridoma was prepared by fusing myeloma cells and mouse spleen cells. Antibodies were purified from the hybridoma supernatant and four monoclonal strains were obtained and numbered 61H9, 70E5, 71A8, and 74H3 via enzyme-linked immunosorbent assay screening. Immunofluorescence staining assay showed 61H9 was the most suitable cell line for mAb production due to its fluorescence signal being the strongest. Flow cytometric analysis proved that 61H9 possessed high affinity. Moreover, antagonism of JAM-A mAb could attenuate the proliferative, migrative, and invasive abilities of ESCC cells and significantly inhibit tumor growth in mice. By examining hematoxylin-eosin staining mice tumor tissues, we found inflammatory cells infiltrated lightly in the anti-JAM-A group. The expression of BCL-2 and IκBα in the anti-JAM-A group were decreased in mice tumor tissues compared to the control group. Ultimately, a method for preparing high-yield JAM-A-Fc protein was created and a high affinity mAb against JAM-A with an antitumor effect was prepared.

Triple negative breast cancer metastasis is hindered by a peptide antagonist of F11R/JAM‑A protein

BACKGROUND

The F11R/JAM-A cell adhesion protein was examined as the therapeutic target in triple negative breast cancer (TNBC) with the use of the peptide antagonist to F11R/JAM-A, that previously inhibited the early stages of breast cancer metastasis in vitro.

METHODS

The online in silico analysis was performed by TNMPlot, UALCAN, and KM plotter. The in vitro experiments were performed to verify the effect of peptide 4D (P4D) on human endothelial cell lines EA.hy926 and HMEC-1 as well as on human TNBC cell line MDA-MB-231. The cell morphology upon P4D treatment was verified by light microscopy, while the cell functions were assessed by colony forming assay, MTT cell viability assay, BrdU cell proliferation assay, and Transepithelial/Endothelial Electrical Resistance measurements. The in vivo experiments on 4T1 murine breast cancer model were followed by histopathological analysis and a series of quantitative analyses of murine tissues.

RESULTS

By in silico analysis we have found the elevated gene expression in breast cancer with particular emphasis on TNBC. The elevated F11R expression in TNBC was related with poorer survival prognosis. Peptide 4D has altered the morphology and increased the permeability of endothelial monolayers. The colony formation, viability, and proliferation of MDA-MB-231 cells were decreased. P4D inhibited the metastasis in 4T1 breast cancer murine model in a statistically significant manner that was demonstrated by the resampling bootstrap technique.

CONCLUSIONS

The P4D peptide antagonist to F11R/JAM-A is able to hinder the metastasis in TNBC. This assumption needs to be confirmed by additional 4T1 mouse model study performed on larger group size, before making the decision on human clinical trials.

The activation of EP300 by F11R leads to EMT and acts as a prognostic factor in triple-negative breast cancers

Cancer progression is influenced by junctional adhesion molecule (JAM) family members. The relationship between JAM family members and different types of cancer was examined using The Cancer Genome Atlas dataset. mRNA levels of the F11R (F11 receptor) in tumours were inversely correlated to the expression of JAM-2 and JAM-3. This relationship was unique to breast cancer (BCa) and was associated with poor prognosis (p = 0.024, hazard ratio = 1.44 [1.05-1.99]). A 50-gene molecular signature (prediction analysis of microarray 50) was used to subtype BCa. F11R mRNA expression significantly increased in human epidermal growth factor receptor 2 (HER2)-enriched (p = 0.0035) and basal-like BCa tumours (p = 0.0005). We evaluated F11R protein levels in two different compositions of BCa subtype patient tissue array cohorts to determine the relationship between BCa subtype and prognosis. Immunohistochemistry staining revealed that a high F11R protein level was associated with poor overall survival (p < 0.001; Taipei Medical University [TMU] cohort, p < 0.001; Kaohsiung Veterans General Hospital [KVGH] cohort) or disease-free survival (p < 0.001 [TMU cohort], p = 0.034 [KVGH cohort]) in patients with BCa. Comparison of F11R levels in different subtypes revealed the association of poor prognosis with high levels of F11R among luminal (p < 0.001 [TMU cohort], p = 0.027 [KVGH cohort]), HER2 positive (p = 0.018 [TMU cohort], p = 0.037 [KVGH cohort]), and triple-negative (p = 0.013 [TMU cohort], p = 0.037 [KVGH cohort]) BCa. F11R-based RNA microarray analysis and Ingenuity Pathway Analysis were successful in profiling the detailed gene ontology of triple-negative BCa cells regulated by F11R. The EP300 transcription factor was highly correlated with F11R in BCa (R = 0.51, p < 0.001). By analysing these F11R-affected molecules with the L1000CDs datasets, we were able to predict some repurposing drugs for potential application in F11R-positive BCa treatment.

Epithelial-Mesenchymal Transition-Based Gene Signature and Distinct Molecular Subtypes for Predicting Clinical Outcomes in Breast Cancer

Purpose

Regulation of inducers and transcription factor families influence epithelial–mesenchymal transition (EMT), a contributing factor to breast cancer invasion and progression.

Methods

Molecular subtypes were classified based on EMT-related mRNAs using ConsensusClusterPlus package. Differences in tumor immune microenvironment and prognosis were assessed among subtypes. Based on EMT genes, a gene signature for prognosis was built using TCGA training set by performing multivariate and univariate Cox regression analyses. Prediction accuracy of the signature was validated by receiver operating characteristic (ROC) curves and overall survival analysis on internal and external datasets. By conducting univariate and multivariate Cox regression analyses, the risk signature as an independent prognostic indicator was assessed. A nomogram was constructed and validated by calibration analysis and decision curve analysis (DCA).

Results

Five molecular subtypes were characterized based on EMT genes. Patients in Cluster 2 exhibited an activated immune state and a better prognosis. An 11-EMT gene-signature was built to predict breast cancer prognosis. After validation, the signature showed independence and robustness in predicting clinical outcomes of patients. A nomogram combining the RiskScore and pTNM_stage accurately predicted 1-, 2-, 3-, and 5-year survival chance. In comparison with published model, the current model showed a higher area under the curve (AUC).

Conclusion

We characterized five breast cancer subtypes with distinct clinical outcomes and immune status. The study developed an 11-EMT gene-signature as an independent prognostic factor for predicting clinical outcomes of breast cancer.

Functional Antagonism of Junctional Adhesion Molecule-A (JAM-A), Overexpressed in Breast Ductal Carcinoma In Situ (DCIS), Reduces HER2-Positive Tumor Progression

Simple Summary

Specific drug targets for breast ductal carcinoma in situ (DCIS) remain elusive, despite increasing disease prevalence and burden to healthcare services. Estrogen receptor (ER)-negative HER2-positive DCIS, associated with the poorest patient prognosis, is in particular need of novel therapeutic avenues. This report provides the first evidence that a cell surface protein called JAM-A is upregulated on human DCIS patient tissues and can be readily targeted by a novel JAM-A-binding peptide inhibitor in separate in vivo models of DCIS. The anti-tumor efficacy and lack of systemic toxicity of this lead inhibitor, coupled with early indications of potential signaling pathways implicated, support the value of future studies investigating JAM-A as a novel drug target in DCIS patients.

Abstract

Breast ductal carcinoma in situ (DCIS) is clinically challenging, featuring high diagnosis rates and few targeted therapies. Expression/signaling from junctional adhesion molecule-A (JAM-A) has been linked to poor prognosis in invasive breast cancers, but its role in DCIS is unknown. Since progression from DCIS to invasive cancer has been linked with overexpression of the human epidermal growth factor receptor-2 (HER2), and JAM-A regulates HER2 expression, we evaluated JAM-A as a therapeutic target in DCIS. JAM-A expression was immunohistochemically assessed in patient DCIS tissues. A novel JAM-A antagonist (JBS2) was designed and tested alone/in combination with the HER2 kinase inhibitor lapatinib, using SUM-225 cells in vitro and in vivo as validated DCIS models. Murine tumors were proteomically analyzed. JAM-A expression was moderate/high in 96% of DCIS patient tissues, versus 23% of normal adjacent tissues. JBS2 bound to recombinant JAM-A, inhibiting cell viability in SUM-225 cells and a primary DCIS culture in vitro and in a chick embryo xenograft model. JBS2 reduced tumor progression in in vivo models of SUM-225 cells engrafted into mammary fat pads or directly injected into the mammary ducts of NOD-SCID mice. Preliminary proteomic analysis revealed alterations in angiogenic and apoptotic pathways. High JAM-A expression in aggressive DCIS lesions and their sensitivity to treatment by a novel JAM-A antagonist support the viability of testing JAM-A as a novel therapeutic target in DCIS.

Circulating proteins reveal prior use of menopausal hormonal therapy and increased risk of breast cancer

Accessible risk predictors are crucial for improving the early detection and prognosis of breast cancer. Blood samples are widely available and contain proteins that provide important information about human health and disease, however, little is still known about the contribution of circulating proteins to breast cancer risk prediction. We profiled EDTA plasma samples collected before diagnosis from the Swedish KARMA breast cancer cohort to evaluate circulating proteins as molecular predictors. A data-driven analysis strategy was applied to the molecular phenotypes built on 700 circulating proteins to identify and annotate clusters of women. The unsupervised analysis of 183 future breast cancer cases and 366 age-matched controls revealed five stable clusters with distinct proteomic plasma profiles. Among these women, those in the most stable cluster (N = 19; mean Jaccard index: 0.70 ± 0.29) were significantly more likely to have used menopausal hormonal therapy (MHT), get a breast cancer diagnosis, and were older compared to the remaining clusters. The circulating proteins associated with this cluster (FDR < 0.001) represented physiological processes related to cell junctions (F11R, CLDN15, ITGAL), DNA repair (RBBP8), cell replication (TJP3), and included proteins found in female reproductive tissue (PTCH1, ZP4). Using a data-driven approach on plasma proteomics data revealed the potential long-lasting molecular effects of menopausal hormonal therapy (MHT) on the circulating proteome, even after women had ended their treatment. This provides valuable insights concerning proteomics efforts to identify molecular markers for breast cancer risk prediction.

A Transcriptional Link between HER2, JAM-A and FOXA1 in Breast Cancer

Overexpression of the human epidermal growth factor receptor-2 (HER2) is associated with aggressive disease in breast and certain other cancers. At a cellular level, the adhesion protein Junctional Adhesion Molecule-A (JAM-A) has been reported to regulate the expression of HER3 via a transcriptional pathway involving FOXA1. Since FOXA1 is also a suggested transcription factor for HER2, this study set out to determine if JAM-A regulates HER2 expression via a similar mechanism. An integrated tripartite approach was taken, involving cellular expression studies after targeted disruption of individual players in the putative pathway, in silico identification of relevant HER2 promoter regions and, finally, interrogation of cancer patient survival databases to deconstruct functionally important links between HER2, JAM-A and FOXA1 gene expression. The outcome of these investigations revealed a unidirectional pathway in which JAM-A expression transcriptionally regulates that of HER2 by influencing the binding of FOXA1 to a specific site in the HER2 gene promoter. Moreover, a correlation between JAM-A and HER2 gene expression was identified in 75% of a sample of 40 cancer types from The Cancer Genome Atlas, and coincident high mean mRNA expression of JAM-A, HER2 and FOXA1 was associated with poorer survival outcomes in HER2-positive (but not HER2-negative) patients with either breast or gastric tumors. These investigations provide the first evidence of a transcriptional pathway linking JAM-A, HER2 and FOXA1 in cancer settings, and support potential future pharmacological targeting of JAM-A as an upstream regulator of HER2.

JAM-A interacts with α3β1 integrin and tetraspanins CD151 and CD9 to regulate collective cell migration of polarized epithelial cells

Junctional adhesion molecule (JAM)-A is a cell adhesion receptor localized at epithelial cell–cell contacts with enrichment at the tight junctions. Its role during cell–cell contact formation and epithelial barrier formation has intensively been studied. In contrast, its role during collective cell migration is largely unexplored. Here, we show that JAM-A regulates collective cell migration of polarized epithelial cells. Depletion of JAM-A in MDCK cells enhances the motility of singly migrating cells but reduces cell motility of cells embedded in a collective by impairing the dynamics of cryptic lamellipodia formation. This activity of JAM-A is observed in cells grown on laminin and collagen-I but not on fibronectin or vitronectin. Accordingly, we find that JAM-A exists in a complex with the laminin- and collagen-I-binding α3β1 integrin. We also find that JAM-A interacts with tetraspanins CD151 and CD9, which both interact with α3β1 integrin and regulate α3β1 integrin activity in different contexts. Mapping experiments indicate that JAM-A associates with α3β1 integrin and tetraspanins CD151 and CD9 through its extracellular domain. Similar to depletion of JAM-A, depletion of either α3β1 integrin or tetraspanins CD151 and CD9 in MDCK cells slows down collective cell migration. Our findings suggest that JAM-A exists with α3β1 integrin and tetraspanins CD151 and CD9 in a functional complex to regulate collective cell migration of polarized epithelial cells.

MIR21-induced loss of junctional adhesion molecule A promotes activation of oncogenic pathways, progression and metastasis in colorectal cancer

Junctional adhesion molecules (JAMs) play a critical role in cell permeability, polarity and migration. JAM-A, a key protein of the JAM family, is altered in a number of conditions including cancer; however, consequences of JAM-A dysregulation on carcinogenesis appear to be tissue dependent and organ dependent with significant implications for the use of JAM-A as a biomarker or therapeutic target. Here, we test the expression and prognostic role of JAM-A downregulation in primary and metastatic colorectal cancer (CRC) (n = 947). We show that JAM-A downregulation is observed in ~60% of CRC and correlates with poor outcome in four cohorts of stages II and III CRC (n = 1098). Using JAM-A knockdown, re-expression and rescue experiments in cell line monolayers, 3D spheroids, patient-derived organoids and xenotransplants, we demonstrate that JAM-A silencing promotes proliferation and migration in 2D and 3D cell models and increases tumour volume and metastases in vivo. Using gene-expression and proteomic analyses, we show that JAM-A downregulation results in the activation of ERK, AKT and ROCK pathways and leads to decreased bone morphogenetic protein 7 expression. We identify MIR21 upregulation as the cause of JAM-A downregulation and show that JAM-A rescue mitigates the effects of MIR21 overexpression on cancer phenotype. Our results identify a novel molecular loop involving MIR21 dysregulation, JAM-A silencing and activation of multiple oncogenic pathways in promoting invasiveness and metastasis in CRC.

The F11 Receptor (F11R)/Junctional Adhesion Molecule-A (JAM-A) (F11R/JAM-A) in cancer progression

The F11 Receptor (F11R), also called Junctional Adhesion Molecule-A (JAM-A) (F11R/JAM-A), is a transmembrane glycoprotein of the immunoglobulin superfamily, which is mainly located in epithelial and endothelial cell tight junctions and also expressed on circulating platelets and leukocytes. It participates in the regulation of various biological processes, as diverse as paracellular permeability, tight junction formation and maintenance, leukocyte transendothelial migration, epithelial-to-mesenchymal transition, angiogenesis, reovirus binding, and platelet activation. Dysregulation of F11R/JAM-A may result in pathological consequences and disorders in normal cell function. A growing body of evidence points to its role in carcinogenesis and invasiveness, but its tissue-specific pro- or anti-tumorigenic role remains a debated issue. The following review focuses on the F11R/JAM-A tissue-dependent manner in tumorigenesis and metastasis and also discusses the correlation between poor patient clinical outcomes and its aberrant expression. In the future, it will be required to clarify the signaling pathways that are activated or suppressed via the F11R/JAM-A protein in various cancer types to understand its multiple roles in cancer progression and further use it as a novel direct target for cancer treatment.

A ligand-insensitive UNC5B splicing isoform regulates angiogenesis by promoting apoptosis

The Netrin-1 receptor UNC5B is an axon guidance regulator that is also expressed in endothelial cells (ECs), where it finely controls developmental and tumor angiogenesis. In the absence of Netrin-1, UNC5B induces apoptosis that is blocked upon Netrin-1 binding. Here, we identify an UNC5B splicing isoform (called UNC5B-Δ8) expressed exclusively by ECs and generated through exon skipping by NOVA2, an alternative splicing factor regulating vascular development. We show that UNC5B-Δ8 is a constitutively pro-apoptotic splicing isoform insensitive to Netrin-1 and required for specific blood vessel development in an apoptosis-dependent manner. Like NOVA2, UNC5B-Δ8 is aberrantly expressed in colon cancer vasculature where its expression correlates with tumor angiogenesis and poor patient outcome. Collectively, our data identify a mechanism controlling UNC5B’s necessary apoptotic function in ECs and suggest that the NOVA2/UNC5B circuit represents a post-transcriptional pathway regulating angiogenesis.

UNC5B is a Netrin-1 receptor expressed in endothelial cells that in the absence of ligand induces apoptosis. Here the authors identify an UNC5B splicing isoform that is insensitive to the pro-survival ligand Netrin-1 and is required for apoptosis-dependent blood vessel development.

Development of a Novel Weighted Ranking Method for Immunohistochemical Quantification of a Heterogeneously Expressed Protein in Gastro-Esophageal Cancers

Simple Summary

High levels of the protein Junctional Adhesion Molecule-A (JAM-A) have been linked with aggressive disease in patients with several different cancers. However, its distribution is often non-uniform (heterogeneous) across tumors, and can be difficult to quantify. JAM-A has also been linked with high levels of HER2 (an important oncogene) in breast tumors, and the development of resistance to HER2-targeted drugs in those patients. Since gastro-esophageal (GE) cancers are often high in HER2 and have also been approved for HER2-targeted drugs, the aim of this study was to investigate if levels of JAM-A and HER2 are linked in GE cancer. JAM-A was expressed very heterogeneously across miniaturized tissue sections called tissue microarrays (TMAs) of GE cancer patients. In this model, therefore, there was no correlation between JAM-A and HER2 expression. However, when we used larger tissue sections and developed a scoring system to account for heterogeneity, a significant correlation between JAM-A and HER2 levels emerged. This work illustrates the importance of taking intra-tumor heterogeneity into account, particularly in an era when analysis of protein levels by this method is increasingly used to select patients for targeted cancer drugs.

Abstract

High expression of Junctional Adhesion Molecule-A (JAM-A) has been linked with poor prognosis in several cancers, including breast cancers overexpressing the human epidermal growth factor receptor-2 (HER2). Furthermore, JAM-A expression has been linked with regulating that of HER2, and associated with the development of resistance to HER2-targeted therapies in breast cancer patients. The purpose of this study was to establish a potential relationship between JAM-A and HER2 in HER2-overexpressing gastro-esophageal (GE) cancers. Interrogation of gene expression datasets revealed that high JAM-A mRNA expression was associated with poorer survival in HER2-positive gastric cancer patients. However, high intra-tumoral heterogeneity of JAM-A protein expression was noted upon immunohistochemical scoring of a GE cancer tissue microarray (TMA), precluding a simple confirmation of any relationship between JAM-A and HER2 at protein level. However, in a test-set of 25 full-face GE cancer tissue sections, a novel weighted ranking system proved effective in capturing JAM-A intra-tumoral heterogeneity and confirming statistically significant correlations between JAM-A/HER2 expression. Given the growing importance of immunohistochemistry in stratifying cancer patients for the receipt of new targeted therapies, this may sound a cautionary note against over-relying on cancer TMAs in biomarker discovery studies of heterogeneously expressed proteins. It also highlights a timely need to develop validated mechanisms of capturing intra-tumoral heterogeneity to aid in future biomarker/therapeutic target development for the benefit of cancer patients.

Human Epidermal Growth Factor Receptor-3 Expression Is Regulated at Transcriptional Level in Breast Cancer Settings by Junctional Adhesion Molecule-A via a Pathway Involving Beta-Catenin and FOXA1

Simple Summary

Signaling from the human epidermal growth factor receptor (HER) family of proteins increases in many cancers, including breast. HER2-high breast cancers are successfully treated with anti-HER2 therapies, but these drugs are limited by the fact that patients frequently develop resistance to them. One common mechanism by which resistance develops is when tumors acquire high levels of a family member called HER3. We had previously shown that a protein called JAM-A regulates the level of HER2 in breast cancer cells, and is associated with the development of resistance to HER2-targeted therapies. In this study we show for the first time that JAM-A levels also regulate those of HER3. Using breast cancer cell and tissue models and culminating in patient tissue material, we provide evidence that JAM-A regulates HER3 expression via a pathway involving the transcription factors β-catenin and FOXA1. We suggest that JAM-A merits future investigation as a novel drug target for its potential to reduce HER3 tumorigenic signaling and to offset the development of resistance to HER2-targeted therapies.

Abstract

The success of breast cancer therapies targeting the human epidermal growth factor receptor-2 (HER2) is limited by the development of drug resistance by mechanisms including upregulation of HER3. Having reported that HER2 expression and resistance to HER2-targeted therapies can be regulated by Junctional Adhesion Molecule-A (JAM-A), this study investigated if JAM-A regulates HER3 expression. Expressional alteration of JAM-A in breast cancer cells was used to test expressional effects on HER3 and its effectors, alongside associated functional behaviors, in vitro and semi-in vivo. HER3 transcription factors were identified and tested for regulation by JAM-A. Finally a patient tissue microarray was used to interrogate connections between putative pathway components connecting JAM-A and HER3. This study reveals for the first time that HER3 and its effectors are regulated at gene/protein expression level by JAM-A in breast cancer cell lines; with functional consequences in in vitro and semi-in vivo models. In bioinformatic, cellular and patient tissue models, this was associated with regulation of the HER3 transcription factor FOXA1 by JAM-A via a pathway involving β-catenin. Our data suggest a novel model whereby JAM-A expression regulates β-catenin localization, in turn regulating FOXA1 expression, which could drive HER3 gene transcription. JAM-A merits investigation as a novel target to prevent upregulation of HER3 during the development of resistance to HER2-targeted therapies, or to reduce HER3-dependent tumorigenic signaling.

Development of near-infrared imaging agents for detection of junction adhesion molecule-A protein

•

Anti-junctional adhesion molecule-A (JAM-A) monoclonal antibodies (mAb) conjugated with near infra-red fluorescent dye, IR700 – as a JAM-A mAb/IR700 agent was developed.

•

An in vivo JAM-A mAb/IR700-specific near infra-red imaging of human-derived prostate and breast cancer xenograft is presented.

•

A single injection of the agent is diminished number of mitotic cells in cancerous tissue of mice bearing heterotopic tumors.

•

Since, our agent depicts the specific accumulation within the targeted tumors, this agent may be adapted to solid tumor targeted photoimmunotherapy.

Introduction

Prostate and breast cancer are the most prevalent primary malignant human tumors globally. Prostatectomy and breast conservative surgery remain the most common definitive treatment option for the >500,000 men and women newly diagnosed with localized prostate and breast cancer each year only in the US. Morphological examination is the mainstay of diagnosis but margin under-sampling of the excised cancer tissue may lead to local recurrence. In despite of the progress of non-invasive optical imaging, there is still a clinical need for targeted optical imaging probes that could rapidly and globally visualize cancerous tissues.

Methods

Elevated expression of junctional adhesion molecule-A (JAM-A) on tumor cells and its multiple pro-tumorigenic activity make the JAM-A a candidate for molecular imaging. Near-infrared imaging probe, which employed anti-JAM-A monoclonal antibody (mAb) phthalocyanine dye IR700 conjugates (JAM-A mAb/IR700), was synthesized and used to identify and visualize heterotopic human prostate and breast tumor mouse xenografts in vivo.

Results

The intravenously injected JAM-A mAb/IR700 conjugates enabled the non-invasive detection of prostate and breast cancerous tissue by fluorescence imaging. A single dose of JAM-A mAb/IR700 reduced number of mitotic cancer cells in vivo, indicating theranostic ability of this imaging agent. The JAM-A mAb/IR700 conjugates allowed us to image a specific receptor expression in prostate and breast tumors without post-image processing.

Conclusion

This agent demonstrates promise as a method to image the extent of prostate and breast cancer in vivo and could assist with real-time visualization of extracapsular extension of cancerous tissue.

Targeting Opposing Immunological Roles of the Junctional Adhesion Molecule-A in Autoimmunity and Cancer

The junctional adhesion molecule-A (JAM-A) is a cell surface adhesion molecule expressed on platelets, epithelial cells, endothelial cells and leukocytes (e. g. monocytes and dendritic cells). JAM-A plays a relevant role in leukocyte trafficking and its therapeutic potential has been studied in several pathological conditions due to its capacity to induce leukocyte migration out of inflamed sites or infiltration into tumor sites. However, disruption of JAM-A pathways may worsen clinical pathology in some cases. As such, the effects of JAM-A manipulation on modulating immune responses in the context of different diseases must be better understood. In this mini-review, we discuss the potential of JAM-A as a therapeutic target, summarizing findings from studies manipulating JAM-A in the context of inflammatory diseases (e.g. autoimmune diseases) and cancer and highlighting described mechanisms.

Low junctional adhesion molecule-A expression is associated with an epithelial to mesenchymal transition and poorer outcomes in high-grade serous carcinoma of uterine adnexa

High-grade serous carcinoma of uterine adnexa (HGSC) is the most frequent histotype of epithelial ovarian cancer and has a poor 5-year survival rate due to late-stage diagnosis and the poor efficacy of standard treatments. Novel biomarkers of cancer outcome are needed to identify new targetable pathways and improve personalized treatments. Cell-surface screening of 26 HGSC cell lines by high-throughput flow cytometry identified junctional adhesion molecule 1 (JAM-A, also known as F11R) as a potential biomarker. Using a multi-labeled immunofluorescent staining coupled with digital image analysis, protein levels of JAM-A were quantified in tissue microarrays from three HGSC patient cohorts: a discovery cohort (n = 101), the Canadian Ovarian Experimental Unified Resource cohort (COEUR, n = 1158), and the Canadian Cancer Trials Group OV16 cohort (n = 267). Low JAM-A level was associated with poorer outcome in the three cohorts by Kaplan-Meier (p = 0.023, p < 0.001, and p = 0.036, respectively) and was an independent marker of shorter survival in the COEUR cohort (HR = 0.517 (0.381-703), p < 0.001). When analyses were restricted to patients treated by taxane-platinum-based chemotherapy, low JAM-A protein expression was associated with poorer responses in the COEUR (p < 0.001) and OV16 cohorts (p = 0.006) by Kaplan-Meier. Decreased JAM-A gene expression was an indicator of poor outcome in gene expression datasets including The Cancer Genome Atlas (n = 606, p = 0.002) and Kaplan-Meier plotter (n = 1816, p = 0.024). Finally, we observed that tumors with decreased JAM-A expression exhibited an enhanced epithelial to mesenchymal transition (EMT) signature. Our results demonstrate that JAM-A expression is a robust prognostic biomarker of HGSC and may be used to discriminate tumors responsive to therapies targeting EMT.

Junctional Adhesion Molecules in Cancer: A Paradigm for the Diverse Functions of Cell-Cell Interactions in Tumor Progression

Tight junction (TJ) proteins are essential for mediating interactions between adjacent cells and coordinating cellular and organ responses. Initial investigations into TJ proteins and junctional adhesion molecules (JAM) in cancer suggested a tumor-suppressive role where decreased expression led to increased metastasis. However, recent studies of the JAM family members JAM-A and JAM-C have expanded the roles of these proteins to include protumorigenic functions, including inhibition of apoptosis and promotion of proliferation, cancer stem cell biology, and epithelial-to-mesenchymal transition. JAM function by interacting with other proteins through three distinct molecular mechanisms: direct cell-cell interaction on adjacent cells, stabilization of adjacent cell surface receptors on the same cell, and interactions between JAM and cell surface receptors expressed on adjacent cells. Collectively, these diverse interactions contribute to both the pro- and antitumorigenic functions of JAM. In this review, we discuss these context-dependent functions of JAM in a variety of cancers and highlight key areas that remain poorly understood, including their potentially diverse intracellular signaling networks, their roles in the tumor microenvironment, and the consequences of posttranslational modifications on their function. These studies have implications in furthering our understanding of JAM in cancer and provide a paradigm for exploring additional roles of TJ proteins.

Relationship between apical junction proteins, gene expression and cancer

The apical junctional complex (AJC) is a cell-cell adhesion system present at the upper portion of the lateral membrane of epithelial cells integrated by the tight junction (TJ) and the adherens junction (AJ). This complex is crucial to initiate and stabilize cell-cell adhesion, to regulate the paracellular transit of ions and molecules and to maintain cell polarity. Moreover, we now consider the AJC as a hub of signal transduction that regulates cell-cell adhesion, gene transcription and cell proliferation and differentiation. The molecular components of the AJC are multiple and diverse and depending on the cellular context some of the proteins in this complex act as tumor suppressors or as promoters of cell transformation, migration and metastasis outgrowth. Here, we describe these new roles played by TJ and AJ proteins and their potential use in cancer diagnostics and as targets for therapeutic intervention.

Functional inhibition of F11 receptor (F11R/junctional adhesion molecule-A/JAM-A) activity by a F11R-derived peptide in breast cancer and its microenvironment

Purpose

To examine the involvement of the F11R/JAM-A protein in breast cancer metastasis, we utilized the F11R/JAM-A antagonistic peptide 4D (P4D) in experiments of transendothelial migration (TEM) of breast cancer cells.

Methods

Experiments were conducted in the mouse 4T1 breast cancer model utilizing the human mammary epithelial cell and endothelial cell lines. The levels of soluble F11R/JAM-A (sJAM-A) in the murine plasmas were measured by ELISA. Levels of F11R/JAM-A mRNA and protein in cell lines were assessed by qRT-PCR and Western blot, respectively. Cell surface expression of F11R/JAM-A was demonstrated by flow cytometry. Functional tests included the TEM of breast cancer cells and adhesion of breast cancer cells to the endothelium. The endothelial permeability was studied by fluorescent tracer assay and by the Real-Time Cell Analysis (RTCA).

Results

The tumor inducers Tβ4 and TGF-β1 reduced the levels of sJAM-A in murine plasma, and reduced the F11R/JAM-A protein levels in the human microvascular endothelial cell line HMEC-1. The adhesion and TEM measured between breast cancer cells and inflamed or Tβ4-treated endothelium were inhibited by P4D. The presence of P4D did not destabilize the pre-existing tight junctions in the endothelial monolayer. The barrier-protecting effect of P4D was stronger than that of forskolin, when a booster dose of P4D was applied to the inflamed endothelium.

Conclusions

F11R/JAM-A protein can be considered as a novel target in the treatment of breast cancer metastasis. In vivo and clinical studies are needed to further investigate the effectiveness of F11R/JAM-A-derived peptide as a possible anti-metastatic drug.

Electronic supplementary material

The online version of this article (10.1007/s10549-019-05471-x) contains supplementary material, which is available to authorized users.

High expression of junctional adhesion molecule-A is associated with poor survival in patients with epithelial ovarian cancer

PURPOSE

Aberrant expression of different tight junction proteins, including the junctional adhesion molecule-A (JAM-A), has been frequently reported in association with tumor progression of several malignancies. To our knowledge, this is the first study examining the clinical significance of JAM-A gene expression in epithelial ovarian cancer.

METHODS

JAM-A expression levels in 44 epithelial ovarian cancer and 12 benign formalin-fixed paraffin-embedded samples were determined by reverse transcription quantitative polymerase chain reaction. Receiver operating characteristic (ROC) curve analysis was used to determine the diagnostic and prognostic potential of JAM-A. Associations between JAM-A expression and clinicopathological characteristics of epithelial ovarian cancer were analyzed using Fisher's exact test. The Kaplan-Meier method and univariate Cox regression analysis were used for the survival analysis. P ⩽ 0.05 was considered statistically significant.

RESULTS

ROC curve analyses showed that JAM-A gene expression exhibits both diagnostic and prognostic performance in epithelial ovarian cancer (area under the curve (AUC) 0.640, 95% confidence interval (CI) 0.488, 0.792, sensitivity 43.18%, specificity 100% and AUC 0.621, 95% CI 0.427, 0.816, sensitivity 52.63%, specificity 85%, respectively). JAM-A expression was significantly associated with International Federation of Gynecologists and Obstetricians (FIGO) stage (P =0.049) and the Kaplan-Meier method demonstrated that patients with high expression of JAM-A had significantly worse overall survival compared to patients with low JAM-A expression (P =0.004). Moreover, univariate Cox regression analysis showed that FIGO stage, peritoneal metastasis, residual tumor and JAM-A expression were significantly associated with reduced overall survival in epithelial ovarian cancer.

CONCLUSIONS

Our results indicate that high levels of JAM-A expression are associated with an advanced clinicopathological feature and may have diagnostic potential; also, it could be a predictor of poor overall survival in patients with epithelial ovarian cancer.

Junctional adhesion molecule-A is down-regulated in anaplastic thyroid carcinomas and reduces cancer cell aggressiveness by modulating p53 and GSK3 α/β pathways

Junctional adhesion molecule A (JAM-A) is a transmembrane protein that contributes to different biological process, including the epithelial to mesenchymal transition (EMT). Through an EMT profiler array, we explored the molecular players associated with human thyroid cancer progression and identified JAM-A as one of the genes mostly deregulated. The quantitative real-time polymerase chain reaction and immunohistochemistry analyses showed that downregulation of JAM-A occurred in anaplastic thyroid carcinoma (ATC) compared with normal thyroid (NT) and papillary thyroid carcinoma (PTC) tissues and correlated with extrathyroid infiltration, tumor size, and ATC histotype. In ATC cell lines, JAM-A restoration suppressed malignant hallmarks of transformation including cell proliferation, motility, and transendothelial migration. Accordingly, knockdown of JAM-A enhanced thyroid cancer cell proliferation and motility in PTC cells. Through the proteome profiler human phospho-kinase array, we demonstrated that higher expression of JAM-A was associated with a significant increased level of phosphorylation of p53 and GSK3 α/β proteins. In conclusion, our findings highlight a novel role of JAM-A in thyroid cancer progression and suggest that JAM-A restoration could have potential clinical relevance in thyroid cancer treatment.

Cleavage of the extracellular domain of junctional adhesion molecule-A is associated with resistance to anti-HER2 therapies in breast cancer settings

BACKGROUND

Junctional adhesion molecule-A (JAM-A) is an adhesion molecule whose overexpression on breast tumor tissue has been associated with aggressive cancer phenotypes, including human epidermal growth factor receptor-2 (HER2)-positive disease. Since JAM-A has been described to regulate HER2 expression in breast cancer cells, we hypothesized that JAM-dependent stabilization of HER2 could participate in resistance to HER2-targeted therapies.

METHODS

Using breast cancer cell line models resistant to anti-HER2 drugs, we investigated JAM-A expression and the effect of JAM-A silencing on biochemical/functional parameters. We also tested whether altered JAM-A expression/processing underpinned differences between drug-sensitive and -resistant cells and acted as a biomarker of patients who developed resistance to HER2-targeted therapies.

RESULTS

Silencing JAM-A enhanced the anti-proliferative effects of anti-HER2 treatments in trastuzumab- and lapatinib-resistant breast cancer cells and further reduced HER2 protein expression and Akt phosphorylation in drug-treated cells. Increased epidermal growth factor receptor expression observed in drug-resistant models was normalized upon JAM-A silencing. JAM-A was highly expressed in all of a small cohort of HER2-positive patients whose disease recurred following anti-HER2 therapy. High JAM-A expression also correlated with metastatic disease at the time of diagnosis in another patient cohort resistant to trastuzumab therapy. Importantly, cleavage of JAM-A was increased in drug-resistant cell lines in conjunction with increased expression of ADAM-10 and -17 metalloproteases. Pharmacological inhibition or genetic silencing studies suggested a particular role for ADAM-10 in reducing JAM-A cleavage and partially re-sensitizing drug-resistant cells to the anti-proliferative effects of HER2-targeted drugs. Functionally, recombinant cleaved JAM-A enhanced breast cancer cell invasion in vitro and both invasion and proliferation in a semi-in vivo model. Finally, cleaved JAM-A was detectable in the serum of a small cohort of HER2-positive patients and correlated significantly with resistance to HER2-targeted therapy.

CONCLUSIONS

Collectively, our data suggest a novel model whereby increased expression and cleavage of JAM-A drive tumorigenic behavior and act as a biomarker and potential therapeutic target for resistance to HER2-targeted therapies.

Natural compound Tetrocarcin-A downregulates Junctional Adhesion Molecule-A in conjunction with HER2 and inhibitor of apoptosis proteins and inhibits tumor cell growth

Overexpression of the tight junction protein Junctional Adhesion Molecule-A (JAM-A) has been linked to aggressive disease in breast and other cancers, but JAM-targeting drugs remain elusive. Screening of a natural compound library identified the antibiotic Tetrocarcin-A as a novel downregulator of JAM-A and human epidermal growth factor receptor-2 (HER2) protein expression in breast cancer cells. Lysosomal inhibition partially rescued the downregulation of JAM-A and HER2 caused by Tetrocarcin-A, and attenuated its cytotoxic activity. Tetrocarcin-A treatment or JAM-A silencing reduced AKT and ERK phosphorylation, inhibited c-FOS phosphorylation at Threonine-232 (its transcriptional regulation site), inhibited nuclear localization of c-FOS, and downregulated expression of the inhibitor of apoptosis proteins (IAP). This was accompanied by Tetrocarcin-A-induced caspase-dependent apoptosis. To begin evaluating the potential clinical relevance of our findings, we extended our studies to other models. Encouragingly, Tetrocarcin-A downregulated JAM-A expression and caused cytotoxicity in primary breast cells and lung cancer stem cells, and inhibited the growth of xenografts in a semi-in vivo model involving invasion across the chicken egg chorioallantoic membrane. Taken together, our data suggest that Tetrocarcin-A warrants future evaluation as a novel cancer therapeutic by virtue of its ability to downregulate JAM-A expression, reduce tumorigenic signaling and induce apoptosis.

Unravelling subclonal heterogeneity and aggressive disease states in TNBC through single-cell RNA-seq

Triple-negative breast cancer (TNBC) is an aggressive subtype characterized by extensive intratumoral heterogeneity. To investigate the underlying biology, we conducted single-cell RNA-sequencing (scRNA-seq) of >1500 cells from six primary TNBC. Here, we show that intercellular heterogeneity of gene expression programs within each tumor is variable and largely correlates with clonality of inferred genomic copy number changes, suggesting that genotype drives the gene expression phenotype of individual subpopulations. Clustering of gene expression profiles identified distinct subgroups of malignant cells shared by multiple tumors, including a single subpopulation associated with multiple signatures of treatment resistance and metastasis, and characterized functionally by activation of glycosphingolipid metabolism and associated innate immunity pathways. A novel signature defining this subpopulation predicts long-term outcomes for TNBC patients in a large cohort. Collectively, this analysis reveals the functional heterogeneity and its association with genomic evolution in TNBC, and uncovers unanticipated biological principles dictating poor outcomes in this disease.

Immunoreactivity patterns of tight junction proteins are useful for differential diagnosis of human salivary gland tumors

The expression pattern of tight junction proteins (TJPs) varies among organs and tumor types. In this study, we examined the immunoreactivity of claudin (CLDN)-1, -4, and -7, and JAM-A in salivary gland tumors (SGTs) by histological types and cell types to estimate their usefulness as differential diagnostic markers. Immunoreactivity of CLDN1 was higher in ductal epithelium cells of SGTs than in non-tumor tissues. Conversely, immunoreactivity of CLDN1 was significantly decreased in basal/myoepithelium cells of SGTs compared with that in non-tumor tissues. There was no significant difference between the immunoreactivity of CLDN1 in benign tumors and that in malignant tumors. Immunoreactivity of CLDN4, CLDN7, and JAM-A in ductal epithelium cells was higher in many SGTs than in non-tumor tissues. There was a difference depending on the histological type of SGT in immunoreactivity of CLDN4, CLDN7, and JAM-A in basaloid/myoepithelial cells. It was possible to classify SGTs by a hierarchical clustering using immunoreactivity of TJPs. The results suggest that an immunohistochemical marker panel including these TJPs may be useful for differential diagnosis of SGTs and that CLDN1 is associated with tumorigenesis of SGTs.

Expression and prognostic value of JAM-A in gliomas

Gliomas are among the most lethal cancers, being highly resistant to both chemo- and radiotherapy. The expression of junctional adhesion molecule-A (JAM-A) was recently identified on the surface of stem cell-like brain tumor-initiating cells and suggested to function as a unique glioblastoma niche adhesion factor influencing the tumorigenic potential of brain tumor-initiating cells. We have recently identified high JAM-A expression to be associated with poor outcome in glioblastomas, and our aim was to further investigate the expression of JAM-A in gliomas focusing especially on the prognostic value in WHO grade II and III gliomas. JAM-A protein expression was evaluated by immunohistochemistry and advanced quantitative image analysis with continuous estimates of staining intensity. The JAM-A antibody stained tumor cell membranes and cytoplasm to various extent in different glioma subtypes, and the intensity was higher in glioblastomas than low-grade gliomas. We could not detect an association with overall survival in patients with grade II and III tumors. Double-immunofluorescence stainings in glioblastomas revealed co-expression of JAM-A with CD133, SOX2, nestin, and GFAP in tumor cells as well as some co-expression with the microglial/macrophage marker IBA-1. In conclusion, JAM-A expression was higher in glioblastomas compared to low-grade gliomas and co-localized with recognized stem cell markers suggesting an association of JAM-A with glioma aggressiveness. No significant association between JAM-A expression and overall survival was found in grade II and III gliomas. Further research is needed to determine the function and clinical impact of JAM-A in gliomas.

Junctional Adhesion Molecules (JAMs): Cell Adhesion Receptors With Pleiotropic Functions in Cell Physiology and Development

Junctional adhesion molecules (JAM)-A, -B and -C are cell-cell adhesion molecules of the immunoglobulin superfamily which are expressed by a variety of tissues, both during development and in the adult organism. Through their extracellular domains, they interact with other adhesion receptors on opposing cells. Through their cytoplasmic domains, they interact with PDZ domain-containing scaffolding and signaling proteins. In combination, these two properties regulate the assembly of signaling complexes at specific sites of cell-cell adhesion. The multitude of molecular interactions has enabled JAMs to adopt distinct cellular functions such as the regulation of cell-cell contact formation, cell migration, or mitotic spindle orientation. Not surprisingly, JAMs regulate diverse processes such as epithelial and endothelial barrier formation, hemostasis, angiogenesis, hematopoiesis, germ cell development, and the development of the central and peripheral nervous system. This review summarizes the recent progress in the understanding of JAMs, including their characteristic structural features, their molecular interactions, their cellular functions, and their contribution to a multitude of processes during vertebrate development and homeostasis.

New Monoclonal Antibodies to Defined Cell Surface Proteins on Human Pluripotent Stem Cells

The study and application of human pluripotent stem cells (hPSCs) will be enhanced by the availability of well‐characterized monoclonal antibodies (mAbs) detecting cell‐surface epitopes. Here, we report generation of seven new mAbs that detect cell surface proteins present on live and fixed human ES cells (hESCs) and human iPS cells (hiPSCs), confirming our previous prediction that these proteins were present on the cell surface of hPSCs. The mAbs all show a high correlation with POU5F1 (OCT4) expression and other hPSC surface markers (TRA‐160 and SSEA‐4) in hPSC cultures and detect rare OCT4 positive cells in differentiated cell cultures. These mAbs are immunoreactive to cell surface protein epitopes on both primed and naive state hPSCs, providing useful research tools to investigate the cellular mechanisms underlying human pluripotency and states of cellular reprogramming. In addition, we report that subsets of the seven new mAbs are also immunoreactive to human bone marrow‐derived mesenchymal stem cells (MSCs), normal human breast subsets and both normal and tumorigenic colorectal cell populations. The mAbs reported here should accelerate the investigation of the nature of pluripotency, and enable development of robust cell separation and tracing technologies to enrich or deplete for hPSCs and other human stem and somatic cell types. Stem Cells2017;35:626–640

Junctional adhesion molecule-A is overexpressed in advanced multiple myeloma and determines response to oncolytic reovirus

Despite the development of several new agents for multiple myeloma (MM) therapy over the last decade, drug resistance continues to be a significant problem. Patients with relapsed/refractory disease have high mortality rates and desperately need new precision approaches that directly target specific molecular features that are prevalent in the refractory setting. Reolysin is a proprietary formulation of reovirus for cancer therapy that has demonstrated efficacy in multiple clinical trials. Its selective effects against solid tumors have been largely attributed to RAS-mediated control of reovirus replication. However, the mechanisms regulating its preferential anti-neoplastic effects in MM and other hematological malignancies have not been rigorously studied. Here we report that the reovirus receptor, junctional adhesion molecule-A (JAM-A) is highly expressed in primary cells from patients with MM and the majority of MM cell lines compared to normal controls. A series of experiments demonstrated that JAM-A expression, rather than RAS, was required for Reolysin-induced cell death in MM models. Notably, analysis of paired primary MM specimens revealed that JAM-A expression was significantly increased at relapse compared to diagnosis. Two different models of acquired resistance to bortezomib also displayed both higher JAM-A expression and elevated sensitivity to Reolysin compared to parental cells, suggesting that Reolysin may be an effective agent for patients with relapsed/refractory disease due to their high JAM-A levels. Taken together, these findings support further investigation of Reolysin for the treatment of patients with relapsed/refractory MM and of JAM-A as a predictive biomarker for sensitivity to Reolysin-induced cell death.

Tension on JAM-A activates RhoA via GEF-H1 and p115 RhoGEF

Forces on JAM-A activate RhoA to increase cell stiffness. Activation of RhoA requires GEF-H1 and p115 RhoGEF activation downstream of FAK/ERK and Src family kinases, respectively.

Junctional adhesion molecule A (JAM-A) is a broadly expressed adhesion molecule that regulates cell–cell contacts and facilitates leukocyte transendothelial migration. The latter occurs through interactions with the integrin LFA-1. Although we understand much about JAM-A, little is known regarding the protein’s role in mechanotransduction or as a modulator of RhoA signaling. We found that tension imposed on JAM-A activates RhoA, which leads to increased cell stiffness. Activation of RhoA in this system depends on PI3K-mediated activation of GEF-H1 and p115 RhoGEF. These two GEFs are further regulated by FAK/ERK and Src family kinases, respectively. Finally, we show that phosphorylation of JAM-A at Ser-284 is required for RhoA activation in response to tension. These data demonstrate a direct role of JAM-A in mechanosignaling and control of RhoA and implicate Src family kinases in the regulation of p115 RhoGEF.

Potential for Improving Potency and Specificity of Reovirus Oncolysis with Next-Generation Reovirus Variants

Viruses that specifically replicate in tumor over normal cells offer promising cancer therapies. Oncolytic viruses (OV) not only kill the tumor cells directly; they also promote anti-tumor immunotherapeutic responses. Other major advantages of OVs are that they dose-escalate in tumors and can be genetically engineered to enhance potency and specificity. Unmodified wild type reovirus is a propitious OV currently in phase I–III clinical trials. This review summarizes modifications to reovirus that may improve potency and/or specificity during oncolysis. Classical genetics approaches have revealed reovirus variants with improved adaptation towards tumors or with enhanced ability to establish specific steps of virus replication and cell killing among transformed cells. The recent emergence of a reverse genetics system for reovirus has provided novel strategies to fine-tune reovirus proteins or introduce exogenous genes that could promote oncolytic activity. Over the next decade, these findings are likely to generate better-optimized second-generation reovirus vectors and improve the efficacy of oncolytic reotherapy.

Paradigms lost-an emerging role for over-expression of tight junction adhesion proteins in cancer pathogenesis

Tight junctions (TJ) are multi-protein complexes located at the apicalmost tip of the lateral membrane in polarised epithelial and endothelial cells. Their principal function is in mediating intercellular adhesion and polarity. Accordingly, it has long been a paradigm that loss of TJ proteins and consequent deficits in cell-cell adhesion are required for tumour cell dissemination in the early stages of the invasive/metastatic cascade. However it is becoming increasingly apparent that TJ proteins play important roles in not just adhesion but also intracellular signalling events, activation of which can contribute to, or even drive, tumour progression and metastasis. In this review, we shall therefore highlight cases wherein the gain of TJ proteins has been associated with signals promoting tumour progression. We will also discuss the potential of overexpressed TJ proteins to act as therapeutic targets in cancer treatment. The overall purpose of this review is not to disprove the fact that loss of TJ-based adhesion contributes to the progression of several cancers, but rather to introduce the growing body of evidence that gain of TJ proteins may have adhesion-independent consequences for promoting progression in other cancers.

N-glycosylation controls the function of junctional adhesion molecule-A

Junctional adhesion molecule-A (JAM-A) is an adherens and tight junction protein expressed by endothelial and epithelial cells. JAM-A serves many roles and contributes to barrier function and cell migration and motility, and it also acts as a ligand for the leukocyte receptor LFA-1. JAM-A is reported to contain N-glycans, but the extent of this modification and its contribution to the protein's functions are unknown. We show that human JAM-A contains a single N-glycan at N185 and that this residue is conserved across multiple mammalian species. A glycomutant lacking all N-glycans, N185Q, is able to reach the cell surface but exhibits decreased protein half-life compared with the wild- type protein. N-glycosylation of JAM-A is required for the protein's ability to reinforce barrier function and contributes to Rap1 activity. We further show that glycosylation of N185 is required for JAM-A-mediated reduction of cell migration. Finally, we show that N-glycosylation of JAM-A regulates leukocyte adhesion and LFA-1 binding. These findings identify N-glycosylation as critical for JAM-A's many functions.

Development of a Fluorescent Reporter System to Delineate Cancer Stem Cells in Triple-Negative Breast Cancer

Advanced cancers display cellular heterogeneity driven by self-renewing, tumorigenic cancer stem cells (CSCs). The use of cell lines to model CSCs is challenging due to the difficulty of identifying and isolating cell populations that possess differences in self-renewal and tumor initiation. To overcome these barriers in triple-negative breast cancer (TNBC), we developed a CSC system using a green fluorescent protein (GFP) reporter for the promoter of the well-established pluripotency gene NANOG. NANOG-GFP+ cells gave rise to both GFP+ and GFP(-) cells, and GFP+ cells possessed increased levels of the embryonic stem cell transcription factors NANOG, SOX2, and OCT4 and elevated self-renewal and tumor initiation capacities. GFP+ cells also expressed mesenchymal markers and demonstrated increased invasion. Compared with the well-established CSC markers CD24(-) /CD44(+) , CD49f, and aldehyde dehydrogenase (ALDH) activity, our NANOG-GFP reporter system demonstrated increased enrichment for CSCs. To explore the utility of this system as a screening platform, we performed a flow cytometry screen that confirmed increased CSC marker expression in the GFP+ population and identified new cell surface markers elevated in TNBC CSCs, including junctional adhesion molecule-A (JAM-A). JAM-A was highly expressed in GFP+ cells and patient-derived xenograft ALDH+ CSCs compared with the GFP(-) and ALDH(-) cells, respectively. Depletion of JAM-A compromised self-renewal, whereas JAM-A overexpression induced self-renewal in GFP(-) cells. Our data indicate that we have defined and developed a robust system to monitor differences between CSCs and non-CSCs in TNBC that can be used to identify CSC-specific targets for the development of future therapeutic strategies.

Dysregulation of JAM-A plays an important role in human tumor progression

Junctional adhesion molecule A (JAM-A) is a transmembrane protein that belongs to the immunoglobulin (Ig) superfamily. Evidence determines that JAM-A plays a role in numerous cellular processes, including tight junction assembly, leukocyte migration, platelet activation, angiogenesis and virus binding. Recent research suggests that JAM-A is dysregulated in various cancers and is vital for tumor progression. JAM-A is implicated in carcinogenesis via different signal pathways such as TGF-β1 signaling. Furthermore, JAM-A expression in cancers is usually associated with certain outcome of patients and might be a prognostic indicator. In this review, the correlation between JAM-A expression and human cancers will be described.

Inhibition of glioma proliferation and migration by magnetic nanoparticle mediated JAM-2 silencing

Brain invasion is a biological hallmark of glioma that leads to its aggressiveness and prognosis.

High-throughput flow cytometry screening reveals a role for junctional adhesion molecule a as a cancer stem cell maintenance factor

Stem cells reside in niches that regulate the balance between self-renewal and differentiation. The identity of a stem cell is linked with the ability to interact with its niche through adhesion mechanisms. To identify targets that disrupt cancer stem cell (CSC) adhesion, we performed a flow cytometry screen on patient-derived glioblastoma (GBM) cells and identified junctional adhesion molecule A (JAM-A) as a CSC adhesion mechanism essential for self-renewal and tumor growth. JAM-A was dispensable for normal neural stem/progenitor cell (NPC) function, and JAM-A expression was reduced in normal brain versus GBM. Targeting JAM-A compromised the self-renewal of CSCs. JAM-A expression negatively correlated to GBM patient prognosis. Our results demonstrate that GBM-targeting strategies can be identified through screening adhesion receptors and JAM-A represents a mechanism for niche-driven CSC maintenance.

Overexpression of JAM-A in non-small cell lung cancer correlates with tumor progression

The objective of the current study was to determine the clinical significance of junctional adhesion molecule A (JAM-A) in patients with non-small cell lung cancer (NSCLC) and the biological function of JAM-A in NSCLC cell lines. We showed that JAM-A is predominantly expressed in cell membranes and high expression of JAM-A occurred in 37% of lung tumor specimens compared to corresponding normal tissues. High expression of JAM-A was significantly correlated with TNM stage (P = 0.021), lymph node metastasis (P = 0.007), and decreased overall survival (P = 0.02), In addition, we observed that silencing JAM-A by small interfering RNA inhibited tumor cell proliferation and induced cell cycle arrest at the G1/S boundary. Western blotting analysis revealed that knockdown of JAM-A decreased the protein levels of cyclin D1, CDK4, 6, and P-Rb. Thus, JAM-A plays an important role in NSCLC progression.

Ductal barriers in mammary epithelium

Tissue barriers play an integral role in the biology and pathobiology of mammary ductal epithelium. In normal breast physiology, tight and adherens junctions undergo dynamic changes in permeability in response to hormonal and other stimuli, while several of their proteins are directly involved in mammary tumorigenesis. This review describes first the structure of mammary ductal epithelial barriers and their role in normal mammary development, examining the cyclical changes in response to puberty, pregnancy, lactation and involution. It then examines the role of adherens and tight junctions and the participation of their constituent proteins in mammary tumorigenic functions such as migration, invasion and metastasis. Finally, it discusses the potential of these adhesion proteins as both prognostic biomarkers and potential therapeutic targets in breast cancer.

A novel role for junctional adhesion molecule-A in tumor proliferation: modulation by an anti-JAM-A monoclonal antibody

To identify new potential targets in oncology, functional approaches were developed using tumor cells as immunogens to select monoclonal antibodies targeting membrane receptors involved in cell proliferation. For that purpose cancer cells were injected into mice and resulting hybridomas were screened for their ability to inhibit cell proliferation in vitro. Based on this functional approach coupled to proteomic analysis, a monoclonal antibody specifically recognizing the human junctional adhesion molecule-A (JAM-A) was defined. Interestingly, compared to both normal and tumor tissues, we observed that JAM-A was mainly overexpressed on breast, lung and kidney tumor tissues. In vivo experiments demonstrated that injections of anti-JAM-A antibody resulted in a significant tumor growth inhibition of xenograft human tumors. Treatment with monoclonal antibody induced a decrease of the Ki67 expression and downregulated JAM-A levels. All together, our results show for the first time that JAM-A can interfere with tumor proliferation and suggest that JAM-A is a potential novel target in oncology. The results also demonstrate that a functional approach coupled to a robust proteomic analysis can be successful to identify new antibody target molecules that lead to promising new antibody-based therapies against cancers.

Junctional adhesion molecule-A is co-expressed with HER2 in breast tumors and acts as a novel regulator of HER2 protein degradation and signaling

Junctional adhesion molecule-A (JAM-A) is a membranous cell-cell adhesion protein involved in tight-junction formation in epithelial and endothelial cells. Its overexpression in breast tumors has recently been linked with increased risk of metastasis. We sought to identify if JAM-A overexpression was associated with specific subtypes of breast cancer as defined by the expression of human epidermal growth factor receptor-2 (HER2), estrogen receptor (ER) and progesterone receptor. To this end, JAM-A immunohistochemistry was performed in two breast cancer tissue microarrays. In parallel, cross-talk between JAM-A, HER2 and ER was examined in several breast cell lines, using complementary genetic and pharmacological approaches. High JAM-A expression correlated significantly with HER2 protein expression, ER negativity, lower patient age, high-grade breast cancers, and aggressive luminal B, HER2 and basal subtypes of breast cancer. JAM-A and HER2 were co-expressed at high levels in vitro in SKBR3, UACC-812, UACC-893 and MCF7-HER2 cells. Knockdown or functional antagonism of HER2 did not alter JAM-A expression in any cell line tested. Interestingly, however, JAM-A knockdown decreased HER2 and ER-α expression, resulting in reduced levels of phospho-(active) AKT without an effect on the extracellular signal-related kinase phosphorylation. The downstream effects of JAM-A knockdown on HER2 and phospho-AKT were partially reversed upon treatment with the proteasomal inhibitor MG132. We conclude that JAM-A is co-expressed with HER2 and associates with aggressive breast cancer phenotypes. Furthermore, we speculate that JAM-A may regulate HER2 proteasomal degradation and activity, potentially offering a promise as a therapeutic target in HER2-positive breast cancers.