Putting the brakes on cancer cell migration: JAM-A restrains integrin activation

The Roles of Junctional Adhesion Molecules (JAMs) in Cell Migration

The review briefly summarizes the role of the family of adhesion molecules, JAMs (junctional adhesion molecules), in various cell migration, covering germ cells, epithelial cells, endothelial cells, several leukocytes, and different cancer cells. These functions affect multiple diseases, including reproductive diseases, inflammation-related diseases, cardiovascular diseases, and cancers. JAMs bind to both similar and dissimilar proteins and take both similar and dissimilar effects on different cells. Concluding relevant results provides a reference to further research.

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.

ZO-1 controls endothelial adherens junctions, cell-cell tension, angiogenesis, and barrier formation

Intercellular junctions are crucial for mechanotransduction, but whether tight junctions contribute to the regulation of cell-cell tension and adherens junctions is unknown. Here, we demonstrate that the tight junction protein ZO-1 regulates tension acting on VE-cadherin-based adherens junctions, cell migration, and barrier formation of primary endothelial cells, as well as angiogenesis in vitro and in vivo. ZO-1 depletion led to tight junction disruption, redistribution of active myosin II from junctions to stress fibers, reduced tension on VE-cadherin and loss of junctional mechanotransducers such as vinculin and PAK2, and induced vinculin dissociation from the α-catenin-VE-cadherin complex. Claudin-5 depletion only mimicked ZO-1 effects on barrier formation, whereas the effects on mechanotransducers were rescued by inhibition of ROCK and phenocopied by JAM-A, JACOP, or p114RhoGEF down-regulation. ZO-1 was required for junctional recruitment of JACOP, which, in turn, recruited p114RhoGEF. ZO-1 is thus a central regulator of VE-cadherin-dependent endothelial junctions that orchestrates the spatial actomyosin organization, tuning cell-cell tension, migration, angiogenesis, and barrier formation.

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.

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.

CD146 expression in human breast cancer cell lines induces phenotypic and functional changes observed in Epithelial to Mesenchymal Transition

BACKGROUND

Metastasis is an important step in tumor progression leading to a disseminated and often incurable disease. First steps of metastasis include down-regulation of cell adhesion molecules, alteration of cell polarity and reorganization of cytoskeleton, modifications associated with enhanced migratory properties and resistance of tumor cells to anoikis. Such modifications resemble Epithelial to Mesenchymal Transition (EMT). In breast cancer CD146 expression is associated with poor prognosis and enhanced motility.

METHODOLOGY/PRINCIPAL FINDINGS

On 4 different human breast cancer cell lines, we modified CD146 expression either with shRNA technology in CD146 positive cells or with stable transfection of CD146 in negative cells. Modifications in morphology, growth and migration were evaluated. Using Q-RT-PCR, we analyzed the expression of different EMT markers. We demonstrate that high levels of CD146 are associated with loss of cell-cell contacts, expression of EMT markers, increased cell motility and increased resistance to doxorubicin or docetaxel. Experimental modulation of CD146 expression induces changes consistent with the above described characteristics: morphology, motility, growth in anchorage independent conditions and Slug mRNA variations are strictly correlated with CD146 expression. These changes are associated with modifications of ER (estrogen receptor) and Erb receptors and are enhanced by simultaneous and opposite modulation of JAM-A, or exposure to heregulin, an erb-B4 ligand.

CONCLUSIONS

CD146 expression is associated with an EMT phenotype. Several molecules are affected by CD146 expression: direct or indirect signaling contributes to EMT by increasing Slug expression. CD146 may also interact with Erb signaling by modifying cell surface expression of ErbB3 and ErbB4 and increased resistance to chemotherapy. Antagonistic effects of JAM-A, a tight junction-associated protein, on CD146 promigratory effects underline the complexity of the adhesion molecules network in tumor cell migration and metastasis.

Tight junctions in lung cancer and lung metastasis: a review

Tight junctions are structures located in the apicobasal region of the cell membranes. They regulate paracellular solute and electrical permeability of cell layers. Additionally, they influence cellular polarity, form a paracellular fence to molecules and pathogens and divide the cell membranes to apical and lateral compartments. Tight junctions adhere to the corresponding ones of neighbouring cells and by this way also mediate attachment of the cells to one other. Molecules forming the membranous part of tight junctions include occludin, claudins, tricellulin and junctional adhesion molecules. These molecules are attached to scaffolding proteins such as ZO-1, ZO-2 and ZO-3 through which signals are mediated to the cell interior. Expression of tight junction proteins, such as claudins, may be up- or downregulated in cancer and they are involved in EMT thus influencing tumor spread. Like in tumors of other sites, lung tumors show changes in the expression in tight junction proteins. In this review the significance of tight junctions and its proteins in lung cancer is discussed with a focus on the proteins forming the membranous part of these structures.

Expression of tight junction molecules in breast carcinomas analysed by array PCR and immunohistochemistry

In the past few decades an enormous amount of data became known to clarify the molecular composition and architecture of tight junctions (TJs). Despite the efforts, the expression and function of several TJ genes and proteins in breast carcinoma are still not known and some of the data are contradictory. The expression of forty-four TJ associated genes was examined at mRNA level in eighteen invasive ductal breast carcinoma samples and corresponding normal breast tissues by using low density array PCR. Expressions of claudins (CLDNs) 5, 10, 16, 17, and 18, and ZO-1, ZO-2 were evaluated by immunohistochemistry as well. Using immunohistochemical phenotype as a surrogate for the genetic subtype, 11 luminal A, 3 luminal B, 3 triple negative and one HER2+ cases were included. Ten genes were significantly downregulated in tumors compared with normal breast tissues (CLDNs 5, 10, 16, 18, 19, CTNNAL1, JAM-B, ZO-1, ZO-2 and PARD3), whereas one gene (CLDN17) was significantly up-regulated in tumors when compared with normal breast. At protein level CLDNs 5, 10, 16, 18, ZO-1 and ZO-2 were downregulated in tumors as compared with normal breast tissue. CLDN17 showed variable expression in tumor tissues in comparison to normal breast. In the single HER2+ tumor when compared with the other subtypes CLDNs 5, 16, 17, 18, CTNNAL1, JAM-B, ZO-1, ZO-2 and PARD3 genes were found to be upregulated. We found altered TJ genes and proteins whose expression has not yet been associated with breast carcinoma. Our findings show a tendency of TJ genes and proteins to be downregulated in breast cancer. Further studies are necessary to examine whether the downregulation of the above mentioned TJ associated genes and proteins may contribute to the malignant progression of invasive ductal breast carcinomas.