A novel protein with homology to the junctional adhesion molecule. Characterization of leukocyte interactions

JAM2 is a prognostic biomarker and inhibits proliferation, metastasis and epithelial-mesenchymal transition in lung adenocarcinoma

BACKGROUND

Junctional adhesion molecule 2 (JAM2) plays a pivotal role in various biological processes, including proliferation, metastasis and angiogenesis, contributing to tumor progression. While previous studies have highlighted the polarizing functions of JAM2 in different cancer types, its specific role in lung adenocarcinoma (LUAD) remains unclear.

METHODS

In this study, we harnessed multiple public databases to analyze the expression and prognostic significance of JAM2 in LUAD. Using the Linkedomics database, Matescape database and R package, we explored the associated genes, the potential biological functions and the impact of JAM2 on the tumor microenvironment. Our findings from public databases were further validated using real-time quantitative PCR, western blot and immunohistochemistry. Additionally, in vitro experiments were conducted to assess the influence of JAM2 on LUAD cell proliferation, invasion, migration, apoptosis and epithelial-mesenchymal transition. Furthermore, we established a xenograft model to investigate the in vivo effects of JAM2 on tumorigenesis.

RESULTS

Our results revealed a significant downregulation of JAM2 in LUAD, and patients with low JAM2 expression exhibited unfavorable overall survival outcomes. Functional enrichment analysis indicated that JAM2 may be associated with processes such as cell adhesion, extracellular matrix, cell junctions and regulation of proliferation. Notably, increased JAM2 expression correlated with higher tumor microenvironment scores and reduced immune cell abundance. Furthermore, overexpression of JAM2 induced apoptosis, suppressed tumor proliferation and exhibited potential inhibitory effects on tumor invasion and migration through the modulation of epithelial-mesenchymal transition. Additionally, in vivo experiments confirmed that JAM2 overexpression led to a reduction in tumor growth.

CONCLUSION

Overall, our study highlights the clinical significance of low JAM2 expression as a predictor of poor prognosis in LUAD patients. Moreover, JAM2 was found to exert inhibitory effects on various aspects of tumor progression. Consequently, JAM2 emerges as a promising prognostic biomarker and a potential therapeutic target for LUAD patients.

Impact of the Junction Adhesion Molecule-A on Asthma

PURPOSE

Junctional adhesion molecule (JAM)-A is an immunoglobulin-like molecule that colocalizes with tight junctions (TJs) in the endothelium and epithelium. It is also found in blood leukocytes and platelets. The biological significance of JAM-A in asthma, as well as its clinical potential as a therapeutic target, are not well understood. The aim of this study was to elucidate the role of JAM-A in a mouse model of asthma, and to determine blood levels of JAM-A in asthmatic patients.

MATERIALS AND METHODS

Mice sensitized and challenged with ovalbumin (OVA) or saline were used to investigate the role of JAM-A in the pathogenesis of bronchial asthma. In addition, JAM-A levels were measured in the plasma of asthmatic patients and healthy controls. The relationships between JAM-A and clinical variables in patients with asthma were also examined.

RESULTS

Plasma JAM-A levels were higher in asthma patients (n=19) than in healthy controls (n=12). In asthma patients, the JAM-A levels correlated with forced expiratory volume in 1 second (FEV₁%), FEV₁/forced vital capacity (FVC), and the blood lymphocyte proportion. JAM-A, phospho-JNK, and phospho-ERK protein expressions in lung tissue were significantly higher in OVA/OVA mice than in control mice. In human bronchial epithelial cells treated with house dust mite extracts for 4 h, 8 h, and 24 h, the JAM-A, phospho-JNK, and phospho-ERK expressions were increased, as shown by Western blotting, while the transepithelial electrical resistance was reduced.

CONCLUSION

These results suggest that JAM-A is involved in the pathogenesis of asthma, and may be a marker for asthma.

Epigenetic silencing of JAM3 promotes esophageal cancer development by activating Wnt signaling

BACKGROUND

The role of JAM3 in different tumors is controversial. The epigenetic regulation and the mechanism of JAM3 remain to be elucidated in human esophageal cancer (EC).

METHODS

Eleven EC cell lines, 49 cases of esophageal intraepithelial neoplasia (EIN) and 760 cases of primary EC samples were employed. Methylation-specific polymerase chain reaction, immunohistochemistry, MTT, western blot and xenograft mouse models were applied in this study.

RESULTS

The inverse association between RNA expression and promoter region methylation of JAM3 was found by analyzing 185 cases of EC samples extracted from the TCGA database (p < 0.05). JAM3 was highly expressed in KYSE450, KYSE520, TE1 and YES2 cells, low level expressed in KYSE70 cells and unexpressed in KYSE30, KYSE150, KYSE410, KYSE510, TE13 and BIC1 cells. JAM3 was unmethylated in KYSE450, KYSE520, TE1 and YES2 cells, partial methylated in KYSE70 cells and completely methylated in KYSE30, KYSE150, KYSE410, KYSE510, TE13 and BIC1 cells. The expression of JAM3 is correlated with methylation status. The levels of JAM3 were unchanged in KYSE450, KYSE520, TE1 and YES2 cells, increased in KYSE70 cells and restored expression in KYSE30, KYSE150, KYSE410, KYSE510, TE13 and BIC1 cells after 5-aza-2'-deoxycytidine treatment, suggesting that the expression of JAM3 is regulated by promoter region methylation. JAM3 was methylated in 26.5% (13/49) of EIN and 51.1% (388/760) of primary EC, and methylation of JAM3 was associated significantly with tumor differentiation and family history (all p < 0.05). Methylation of JAM3 is an independent prognostic factor of poor 5-year overall survival (p < 0.05). JAM3 suppresses cell proliferation, colony formation, migration and invasion and induces G1/S arrest and apoptosis in EC. Further study demonstrated that JAM3 suppressed EC cells and xenograft tumor growth by inhibiting Wnt/β-catenin signaling.

CONCLUSION

JAM3 is frequently methylated in human EC, and the expression of JAM3 is regulated by promoter region methylation. JAM3 methylation is an early detection and prognostic marker of EC. JAM3 suppresses EC growth both in vitro and in vivo by inhibiting Wnt signaling.

Transcriptional and Post-Translational Regulation of Junctional Adhesion Molecule-B (JAM-B) in Leukocytes under Inflammatory Stimuli

Junctional adhesion molecules (JAMs; comprising JAM-A, -B and -C) act as receptors for viruses, mediate cell permeability, facilitate leukocyte migration during sterile and non-sterile inflammation and are important for the maintenance of epithelial barrier integrity. As such, they are implicated in the development of both communicable and non-communicable chronic diseases. Here, we investigated the expression and regulation of JAM-B in leukocytes under pathogen- and host-derived inflammatory stimuli using immunoassays, qPCR and pharmacological inhibitors of inflammatory signalling pathways. We show that JAM-B is expressed at both the mRNA and protein level in leukocytes. JAM-B protein is localised to the cytoplasm, Golgi apparatus and in the nucleus around ring-shaped structures. We also provide evidence that JAM-B nuclear localisation occurs via the classical importin-α/β pathway, which is likely mediated through JAM-B protein nuclear localisation signals (NLS) and export signals (NES). In addition, we provide evidence that under both pathogen- and host-derived inflammatory stimuli, JAM-B transcription is regulated via the NF-κB-dependent pathways, whereas at the post-translational level JAM-B is regulated by ubiquitin-proteosome pathways. Anaphase-promoting ubiquitin ligase complex (APC/C) and herpes simplex virus-associated ubiquitin-specific protease (HAUSP/USP) were identified as candidates for JAM-B ubiquitination and de-ubiquitination, respectively. The expression and regulation of JAM-B in leukocytes reported here is a novel observation and contrasts with previous reports. The data reported here suggest that JAM-B expression in leukocytes is under the control of common inflammatory pathways.

Junctional Adhesion Molecules: Potential Proteins in Atherosclerosis

Junctional adhesion molecules (JAMs) are cell-cell adhesion molecules of the immunoglobulin superfamily and are involved in the regulation of diverse atherosclerosis-related processes such as endothelial barrier maintenance, leucocytes transendothelial migration, and angiogenesis. To combine and further broaden related results, this review concluded the recent progress in the roles of JAMs and predicted future studies of JAMs in the development of atherosclerosis.

Junctional Adhesion Molecule 3 Expression in the Mouse Airway Epithelium Is Linked to Multiciliated Cells

Tight-junction (TJ) proteins are essential for establishing the barrier function between neighbor epithelial cells, but also for recognition of pathogens or cell migration. Establishing the expression pattern and localization of different TJ proteins will help to understand the development and physiology of the airway. Here we identify that the junctional adhesion molecule 3 (Jam3) expression is restricted to multiciliated cells (MCCs) in the airway epithelium. In vitro, Jam3 expression varies along airway basal stem cell (BSC) differentiation and upon DAPT treatment or IL6 exposure. However, Jam3 is not required for BSC differentiation to specific cell types. In addition, we found that MCC lacking Jam3 display normal cilia morphology and cilia beating frequency with a delay in BB assembly/positioning in MCCs during differentiation. Remarkably, Jam3 in MCC is mostly localized to subapical organelles, which are negative for the apical recycling endosome marker Rab11 and positive for EEA1. Our data show that Jam3 expression is connected to mature MCC in the airway epithelium and suggest a Jam3 role unrelated to its known barrier function.

Endothelial tight junctions and their regulatory signaling pathways in vascular homeostasis and disease

Endothelial tight junctions (TJs) regulate the transport of water, ions, and molecules through the paracellular pathway, serving as an important barrier in blood vessels and maintaining vascular homeostasis. In endothelial cells (ECs), TJs are highly dynamic structures that respond to multiple external stimuli and pathological conditions. Alterations in the expression, distribution, and structure of endothelial TJs may lead to many related vascular diseases and pathologies. In this review, we provide an overview of the assessment methods used to evaluate endothelial TJ barrier function both in vitro and in vivo and describe the composition of endothelial TJs in diverse vascular systems and ECs. More importantly, the direct phosphorylation and dephosphorylation of TJ proteins by intracellular kinases and phosphatases, as well as the signaling pathways involved in the regulation of TJs, including and the protein kinase C (PKC), PKA, PKG, Ras homolog gene family member A (RhoA), mitogen-activated protein kinase (MAPK), phosphatidylinositol 3-kinase (PI3K)/Akt, and Wnt/β-catenin pathways, are discussed. With great advances in this area, targeting endothelial TJs may provide novel treatment for TJ-related vascular pathologies.

Essential Roles of Tbr1 in the Formation and Maintenance of the Orientation-Selective J-RGCs and a Group of OFF-Sustained RGCs in Mouse

In the mouse retina, more than 30 retinal ganglion cell (RGC) subtypes have been classified based on a combined metric of morphological and functional characteristics. RGCs arise from a common pool of retinal progenitor cells during embryonic stages and differentiate into mature subtypes in adult retinas. However, the cellular and molecular mechanisms controlling formation and maturation of such remarkable cellular diversity remain unknown. Here, we demonstrate that T-box transcription factor T-brain 1 (Tbr1) is expressed in two groups of morphologically and functionally distinct RGCs: the orientation-selective J-RGCs and a group of OFF-sustained RGCs with symmetrical dendritic arbors. When Tbr1 is genetically ablated during retinal development, these two RGC groups cannot develop. Ectopically expressing Tbr1 in M4 ipRGCs during development alters dendritic branching and density but not the inner plexiform layer stratification level. Our data indicate that Tbr1 plays critical roles in regulating the formation and dendritic morphogenesis of specific RGC types.

Survey of Human Chromosome 21 Gene Expression Effects on Early Development in Danio rerio

Trisomy for human chromosome 21 (Hsa21) results in Down syndrome (DS), one of the most genetically complex conditions compatible with human survival. Assessment of the physiological consequences of dosage-driven overexpression of individual Hsa21 genes during early embryogenesis and the resulting contributions to DS pathology in mammals are not tractable in a systematic way. A recent study looked at loss-of-function of a subset of Caenorhabditis elegans orthologs of Hsa21 genes and identified ten candidates with behavioral phenotypes, but the equivalent over-expression experiment has not been done. We turned to zebrafish as a developmental model and, using a number of surrogate phenotypes, we screened Hsa21 genes for effects on early embyrogenesis. We prepared a library of 164 cDNAs of conserved protein coding genes, injected mRNA into early embryos and evaluated up to 5 days post-fertilization (dpf). Twenty-four genes produced a gross morphological phenotype, 11 of which could be reproduced reliably. Seven of these gave a phenotype consistent with down regulation of the sonic hedgehog (Shh) pathway; two showed defects indicative of defective neural crest migration; one resulted consistently in pericardial edema; and one was embryonic lethal. Combinatorial injections of multiple Hsa21 genes revealed both additive and compensatory effects, supporting the notion that complex genetic relationships underlie end phenotypes of trisomy that produce DS. Together, our data suggest that this system is useful in the genetic dissection of dosage-sensitive gene effects on early development and can inform the contribution of both individual loci and their combinatorial effects to phenotypes relevant to the etiopathology of DS.

Junctional Adhesion Molecules (JAMs): The JAM-Integrin Connection

Junctional adhesion molecules (JAMs) are cell surface adhesion receptors of the immunoglobulin superfamily. JAMs are involved in a variety of biological processes both in the adult organism but also during development. These include processes such as inflammation, angiogenesis, hemostasis, or epithelial barrier formation, but also developmental processes such as hematopoiesis, germ cell development, and development of the nervous system. Several of these functions of JAMs depend on a physical and functional interaction with integrins. The JAM – integrin interactions in trans regulate cell-cell adhesion, their interactions in cis regulate signaling processes originating at the cell surface. The JAM – integrin interaction can regulate the function of the JAM as well as the function of the integrin. Beyond the physical interaction with integrins, JAMs can regulate integrin function through intracellular signaling indicating an additional level of JAM – integrin cross-talk. In this review, we describe the various levels of the functional interplay between JAMs and integrins and the role of this interplay during different physiological processes.

Cellular and Molecular Analysis of Dendritic Morphogenesis in a Retinal Cell Type That Senses Color Contrast and Ventral Motion

As neuronal dendrites develop, they acquire cell-type-specific features including characteristic size, shape, arborization, location and synaptic patterns. These features, in turn, are major determinants of type-specific neuronal function. Because neuronal diversity complicates the task of relating developmental programs to adult structure and function, we analyzed dendritic morphogenesis in a single retinal ganglion cell (RGC) type in mouse called J-RGC. We documented the emergence of five dendritic features that underlie J-RGC physiology: (1) dendritic field size, which approximate receptive field size; (2) dendritic complexity, which affects how J-RGCs sample space; (3) asymmetry, which contributes to direction-selectivity; (4) restricted lamination within the inner plexiform layer (IPL), which renders J-RGCs responsive to light decrements; and (5) distribution of synaptic inputs, which generate a color-opponent receptive field. We found dendritic growth in J-RGCs is accompanied by a refinement in dendritic self-crossing. Asymmetry arises by a combination of selective pruning and elaboration, whereas laminar restriction results from biased outgrowth toward the outermost IPL. Interestingly, asymmetry develops in a protracted dorsoventral wave, whereas lamination does so in a rapid centrifugal wave. As arbors mature, they acquire excitatory and inhibitory synapses, with the latter forming first and being concentrated in proximal dendrites. Thus, distinct mechanisms operate in different spatiotemporal dimensions of J-RGC dendritic patterning to generate the substrate for specific patterns of synaptogenesis. Finally, we asked whether the defining molecular signature of J-RGCs, the adhesion molecule JAM-B, regulates morphogenesis, and showed that it promotes dendro-dendritic interactions. Our results reveal multiple mechanisms that shape a dendritic arbor.SIGNIFICANCE STATEMENT Visual perception begins in the retina, where distinct types of retinal ganglion cells (RGCs) are tuned to specific visual features such as direction of motion. The features to which each RGC type responds are determined largely by the number and type of synaptic inputs it receives, and these, in turn, are greatly influenced by the size, shape, arborization pattern, and location of its dendrites. We analyzed dendritic morphogenesis in a functionally characterized RGC type, the J-RGC, demonstrating distinct mechanisms that operate in different dimensions to generate the dendritic scaffold and synaptic patterns for feature detection. Our work elucidates cellular and molecular mechanisms that shape dendritic arbors and synaptic distribution, enabling J-RGC connectivity and thus, function.

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.

The role of JAM-B in cancer and cancer metastasis (Review)

The junctional adhesion molecule B (JAM-B) is a multifunctional transmembrane protein, which belongs to the immunoglobulin superfamily (IgSF). JAM-B is localized to cell-cell contacts and enriched at cell junctions in epithelial and endothelial cells, as well as on the surface of erythrocytes, leukocytes, and platelets. Recent research in this field has shown that JAM-B plays an important role in numerous cellular processes, such as tight junction assembly, spermatogenesis, regulation of paracellular permeability, leukocytic transmigration, angiogenesis, tumor metastasis and cell proliferation. This study provides a new research direction for the diagnosis and treatment of relevant diseases. In this review, we briefly focus on what is currently known about the structure, function, and mechanism of JAM-B, with particular emphasis on cancer.

Penetrance of Congenital Heart Disease in a Mouse Model of Down Syndrome Depends on a Trisomic Potentiator of a Disomic Modifier

Down syndrome (DS) is a significant risk factor for congenital heart disease (CHD), increasing the incidence 50 times over the general population. However, half of people with DS have a normal heart and thus trisomy 21 is not sufficient to cause CHD by itself. Ts65Dn mice are trisomic for orthologs of >100 Hsa21 genes, and their heart defect frequency is significantly higher than their euploid littermates. Introduction of a null allele of Creld1 into Ts65Dn increases the penetrance of heart defects significantly. However, this increase was not seen when the Creld1 null allele was introduced into Ts1Cje, a mouse that is trisomic for about two thirds of the Hsa21 orthologs that are triplicated in Ts65Dn. Among the 23 genes present in three copies in Ts65Dn but not Ts1Cje, we identified Jam2 as necessary for the increased penetrance of Creld1-mediated septal defects in Ts65Dn. Thus, overexpression of the trisomic gene, Jam2, is a necessary potentiator of the disomic genetic modifier, Creld1 No direct physical interaction between Jam2 and Creld1 was identified by several methods. Regions of Hsa21 containing genes that are risk factors of CHD have been identified, but Jam2 (and its environs) has not been linked to heart formation previously. The complexity of this interaction may be more representative of the clinical situation in people than consideration of simple single-gene models.

Identification of neutrophil surface marker changes in health and inflammation using high-throughput screening flow cytometry

Neutrophils are the most abundant white blood cell and are an essential component of the innate immune system. A complete cataloguing of cell surface markers has not been undertaken for neutrophils isolated from circulation as well as healthy and inflamed tissues. To identify cell-surface markers specific to human neutrophils, we used high-throughput flow cytometry to screen neutrophil populations isolated from blood and oral rinses from healthy and chronic periodontitis patients against a panel of 374 known cluster of differentiation (CD) antibodies. This screen identified CD11b, CD16, and CD66b as markers that are consistently expressed on neutrophils independent of the cell location, level of activation and disease state. Cell sorting against CD11b, CD16 and CD66b allowed for the enrichment of mature neutrophils, yielding neutrophil populations with up to 99% purity. These findings suggest an ideal surface marker set for isolating mature neutrophils from humans. The screen also demonstrated that tissue neutrophils from chronically inflamed tissue display a unique surface marker set compared to tissue neutrophils present in healthy, non-inflamed tissues.

Changes of junctions of endothelial cells in coronary sclerosis: A review

Atherosclerosis, the major cause of cardiovascular diseases, has been a leading contributor to morbidity and mortality in the United States and it has been on the rise globally. Endothelial cell-cell junctions are critical for vascular integrity and maintenance of vascular function. Endothelial cell junctions dysfunction is the onset step of future coronary events and coronary artery disease.

A novel junctional adhesion molecule A (CgJAM-A-L) from oyster (Crassostrea gigas) functions as pattern recognition receptor and opsonin

Junctional adhesion molecule (JAM), a subfamily of immunoglobulin superfamily (IgSF) with a couple of immunoglobulin domains, can act as regulator in homeostasis and inflammation of vertebrates. In the present study, a structural homolog of JAM-A (designated CgJAM-A-L) was screened out from oyster, Crassostrea gigas, through a search of JAM-A D1 domain (N-terminal Ig domain in JAM-A). The cDNA of CgJAM-A-L was of 1188 bp encoding a predicted polypeptide of 395 amino acids. The immunoreactive area of CgJAM-A-L mainly distributed over the plasma membrane of hemocytes. After Vibro splendidus or tumor necrosis factor (CgTNF-1) stimulation, the mRNA transcripts of CgJAM-A-L in hemocytes increased significantly by 4.46-fold and 9.00-fold (p < 0.01) of those in control group, respectively. The recombinant CgJAM-A-L protein (rCgJAM-A-L) could bind multiple PAMPs including lipopolysaccharides (LPS), peptidoglycan (PGN), lipoteichoic acid (LTA), mannose (MAN), β-glucan (GLU) and poly(I:C), and various microorganisms including Micrococcus luteus, Staphylococcus aureus, Escherichia coli, Vibro anguillarum, V. splendidus, Pastoris pastoris and Yarrowia lipolytica. The phagocytic rates of oyster hemocytes towards Gram-negative bacteria V. anguillarum and yeast P. pastoris were significantly enhanced after the incubation of rCgJAM-A-L, and even increased more significantly after the pre-incubation of rCgJAM-A-L with microbes (p < 0.01). The results collectively indicated that CgJAM-A-L functioned as an important pattern recognition receptor (PRR) and opsonin in the immune defense against invading pathogen in oyster. Moreover, as the most primitive specie with homolog of JAMs, the information of CgJAM-A-L in oyster would provide useful clues for the evolutionary study of JAMs and immunoglobulins.

Function of Jam-B/Jam-C interaction in homing and mobilization of human and mouse hematopoietic stem and progenitor cells

The junctional adhesion molecules Jam-b and Jam-c interact together at interendothelial junctions and have been involved in the regulation of immune response, inflammation, and leukocyte migration. More recently, Jam-c has been found to be expressed by hematopoietic stem and progenitor cells (HSPC) in mouse. Conversely, we have reported that Jam-b is present on bone marrow stromal cells and that Jam-b-deficient mice have defects in the regulation of hematopoietic stem cell pool. In this study, we have addressed whether interaction between Jam-b and Jam-c participates to HSPC mobilization or hematopoietic reconstitution after irradiation. We show that a blocking monoclonal antibody directed against Jam-c inhibits hematopoietic reconstitution, progenitor homing to the bone marrow, and induces HSPC mobilization in a Jam-b dependent manner. In the latter setting, antibody treatment over a period of 3 days does not alter hematopoietic differentiation nor induce leukocytosis. Results are translated to human hematopoietic system in which a functional adhesive interaction between JAM-B and JAM-C is found between human HSPC and mesenchymal stem cells. Such an interaction does not occur between HSPC and human endothelial cells or osteoblasts. It is further shown that anti-JAM-C blocking antibody interferes with CD34(+) hematopoietic progenitor homing in mouse bone marrow suggesting that monoclonal antibodies inhibiting JAM-B/JAM-C interaction may represent valuable therapeutic tools to improve stem cell mobilization protocols.

Intestinal permeability regulation by tight junction: implication on inflammatory bowel diseases

Epithelial tight junctions (TJs) are the key structures regulating paracellular trafficking of macromolecules. The TJ is multi-protein complex that forms a selective permeable seal between adjacent epithelial cells and demarcates the boundary between apical and basolateral membrane domains. Disruption of the intestinal TJ barrier, followed by permeation of luminal noxious molecules, induces a perturbation of the mucosal immune system and inflammation, which can act as a trigger for the development of intestinal and systemic diseases. Inflammatory bowel disease (IBD) patients demonstrate increased intestinal paracellular permeability. Although it remains unclear whether barrier dysfunction precedes disease or results from active inflammation, increased intestinal TJ disruption is observed in IBD patients suggest that dysregulation of TJ barrier integrity may predispose or enhance IBD progression. Therefore, therapeutic target to restore the TJ barrier integrity may provide effective therapeutic and preventive approaches against IBD. This review discusses the molecular structure and regulation of intestinal TJs and the involvement of intestinal TJs in IBD pathogenesis.

"You Shall Not Pass"-tight junctions of the blood brain barrier

The structure and function of the barrier layers restricting the free diffusion of substances between the central nervous system (brain and spinal cord) and the systemic circulation is of great medical interest as various pathological conditions often lead to their impairment. Excessive leakage of blood-borne molecules into the parenchyma and the concomitant fluctuations in the microenvironment following a transient breakdown of the blood-brain barrier (BBB) during ischemic/hypoxic conditions or because of an autoimmune disease are detrimental to the physiological functioning of nervous tissue. On the other hand, the treatment of neurological disorders is often hampered as only minimal amounts of therapeutic agents are able to penetrate a fully functional BBB or blood cerebrospinal fluid barrier. An in-depth understanding of the molecular machinery governing the establishment and maintenance of these barriers is necessary to develop rational strategies allowing a controlled delivery of appropriate drugs to the CNS. At the basis of such tissue barriers are intimate cell-cell contacts (zonulae occludentes, tight junctions) which are present in all polarized epithelia and endothelia. By creating a paracellular diffusion constraint TJs enable the vectorial transport across cell monolayers. More recent findings indicate that functional barriers are already established during development, protecting the fetal brain. As an understanding of the biogenesis of TJs might reveal the underlying mechanisms of barrier formation during ontogenic development numerous in vitro systems have been developed to study the assembly and disassembly of TJs. In addition, monitoring the stage-specific expression of TJ-associated proteins during development has brought much insight into the “developmental tightening” of tissue barriers. Over the last two decades a detailed molecular map of transmembrane and cytoplasmic TJ-proteins has been identified. These proteins not only form a cell-cell adhesion structure, but integrate various signaling pathways, thereby directly or indirectly impacting upon processes such as cell-cell adhesion, cytoskeletal rearrangement, and transcriptional control. This review will provide a brief overview on the establishment of the BBB during embryonic development in mammals and a detailed description of the ultrastructure, biogenesis, and molecular composition of epithelial and endothelial TJs will be given.

JAM-related proteins in mucosal homeostasis and inflammation

Mucosal surfaces are lined by epithelial cells that form a physical barrier protecting the body against external noxious substances and pathogens. At a molecular level, the mucosal barrier is regulated by tight junctions (TJs) that seal the paracellular space between adjacent epithelial cells. Transmembrane proteins within TJs include junctional adhesion molecules (JAMs) that belong to the cortical thymocyte marker for Xenopus family of proteins. JAM family encompasses three classical members (JAM-A, JAM-B, and JAM-C) and related molecules including JAM4, JAM-like protein, Coxsackie and adenovirus receptor (CAR), CAR-like membrane protein and endothelial cell-selective adhesion molecule. JAMs have multiple functions that include regulation of endothelial and epithelial paracellular permeability, leukocyte recruitment during inflammation, angiogenesis, cell migration, and proliferation. In this review, we summarize the current knowledge regarding the roles of the JAM family members in the regulation of mucosal homeostasis and leukocyte trafficking with a particular emphasis on barrier function and its perturbation during pathological inflammation.

JAM-C promotes lymphangiogenesis and nodal metastasis in non-small cell lung cancer

This study aims to investigate lymphatic metastasis-related genes in non-small cell lung carcinomas (NSCLC). NSCLC tissue was analyzed for expression of junctional adhesion molecule-C (JAM-C) protein. Our data revealed novel associations between JAM-C overexpression in primary tumors and lymphatic microvessel density (LMVD), lymph node metastasis, and poorer overall survival and recurrence-free survival. We used the highly metastatic human lung adenocarcinoma cell line Anip973 and its parental line AGZY83-a, which has a low metastatic capacity, in vivo and vitro. We found that JAM-C played an important role in different metastasis capacity of lymph node. JAM-C affected tumor growth, LNM, JAM-C, VEGF-C, vasculature, and ERK1/2 phosphorylation (p-ERK1/2). β1 integrin was involved in lymph node metastasis. Moreover, JAM-C knockdown in highly metastatic Anip973 decreased cell migration in scratch-wound assays. The JAM-C knockdown in Anip973 cells and JAM-C cDNA in AGZY83-a cells regulated the vascular endothelial growth factor C (VEGF-C) expression. Immunofluorescence showed that blocked VEGF-C expression in JAM-C shRNA Anip973 cells were restored after JAM-C treatment. JAM-C-induced VEGF-C in JAM-C cDNA AGZY83-a cells was also effectively inhibited by treatment with an antibody specifically against JAM-C. Use of media from Anip973 cells, AGZY83-a, and A549cells lung cancer cells that overexpressed or downregulated JAM-C was demonstrated to affect activity of VEGF-C-induced β1 integrin subunit or ERK activity in human dermal lymphatic endothelial cells (HDLEC) treated with VEGF-C or inhibitory antibody to JAM-C. Overall, these results indicate that JAM-C could mediate metastasis as it contributes to VEGF-C expression in cancer cells. JAM-C affects β1and ERK activation in HDLEC, thus promoting lymphangiogenesis and nodal metastasis. Our findings indicate that JAM-C may be a therapeutic target for preventing and treating lymphatic metastases.

Regulation of intestinal epithelial permeability by tight junctions

The gastrointestinal epithelium forms the boundary between the body and external environment. It effectively provides a selective permeable barrier that limits the permeation of luminal noxious molecules, such as pathogens, toxins, and antigens, while allowing the appropriate absorption of nutrients and water. This selective permeable barrier is achieved by intercellular tight junction (TJ) structures, which regulate paracellular permeability. Disruption of the intestinal TJ barrier, followed by permeation of luminal noxious molecules, induces a perturbation of the mucosal immune system and inflammation, and can act as a trigger for the development of intestinal and systemic diseases. In this context, much effort has been taken to understand the roles of extracellular factors, including cytokines, pathogens, and food factors, for the regulation of the intestinal TJ barrier. Here, I discuss the regulation of the intestinal TJ barrier together with its implications for the pathogenesis of diseases.

The Junctional Adhesion Molecule-B regulates JAM-C-dependent melanoma cell metastasis

Metastasis is a major clinical issue and results in poor prognosis for most cancers. The Junctional Adhesion Molecule-C (JAM-C) expressed by B16 melanoma and endothelial cells has been involved in metastasis of tumor cells through homophilic JAM-C/JAM-C trans-interactions. Here, we show that JAM-B expressed by endothelial cells contributes to murine B16 melanoma cells metastasis through its interaction with JAM-C on tumor cells. We further show that this adhesion molecular pair mediates melanoma cell adhesion to primary Lung Microvascular Endothelial Cells and that it is functional in vivo as demonstrated by the reduced metastasis of B16 cells in Jam-b deficient mice.

Function of junctional adhesion molecules (JAMs) in leukocyte migration and homeostasis

Homeostasis is a word widely used in the scientific community to refer to the property of a system to maintain its uniformity and functionality. In living organisms, the word refers to the concept enunciated 150 years ago by C. Bernard by which external variations must be compensated for in order to maintain internal conditions compatible with life. This is especially true in the case of highly dynamic system such as the hematopoietic system that requires the coordinated control of cell proliferation and death within specialized microenvironments that are anatomically distinct. As a consequence, hematopoietic cell adhesion and migration must be tightly controlled in order for hematopoietic cells to reach and to be maintained in appropriate microenvironments. The junctional adhesion molecules (JAMs) are adhesion molecules that belong to the immunoglobulin superfamily (IgSf) and that have been initially identified as important players controlling vascular permeability and leukocyte transendothelial migration. This involves the regulated localization of the JAMs at lateral endothelial cell/cell borders and their interaction with leukocyte integrins. More recently, some of the JAM family members have also been found to be expressed by stromal cells and to regulate chemokine secretion within lymphoid organs, acting not only on leukocyte transendothelial migration, but also on hematopoietic cell retention within specialized microenvironments. This review summarizes recent progress in understanding the role of the JAMs in leukocyte adhesion and migration to tentatively draw an integrated view of the homeostatic function of the JAMs within the hematopoietic system.

Genomic organisation, embryonic expression and biochemical interactions of the zebrafish junctional adhesion molecule family of receptors

The mammalian JAM family is composed of three cell surface receptors. Interactions between the proteins have well-characterised roles in inflammation and tight junction formation, but little is known about their function in early development. Recently, we identified a role for jamb and jamc in zebrafish myocyte fusion. Genome duplication in the teleost lineage raised the possibility that additional JAM family paralogues may also function in muscle development. To address this, we searched the zebrafish genome to identify potential paralogues and confirmed their homology, bringing the total number of zebrafish jam family members to six. We then compared the physical binding properties of each paralogue by surface plasmon resonance and determined the gene expression patterns of all zebrafish jam genes at different stages of development. Our results suggest a significant sub-functionalisation of JAM-B and JAM-C orthologues with respect to binding strength (but not specificity) and gene expression. The paralogous genes, jamb2 and jamc2, were not detected in the somites or myotome of wild-type embryos. We conclude that it is unlikely that the paralogues have a function in primary myogenesis.

Junctional adhesion molecule 2 mediates the interaction between hatched blastocyst and luminal epithelium: induction by progesterone and LIF

Background

Junctional adhesion molecule 2 (Jam2) is a member of the JAM superfamily. JAMs are localized at intercellular contacts and participated in the assembly and maintenance of junctions, and control of cell permeability. Because Jam2 is highly expressed in the luminal epithelium on day 4 of pregnancy, this study was to determine whether Jam2 plays a role in uterine receptivity and blastocyst attachment in mouse uterus.

Methodology/Principal Findings

Jam2 is highly expressed in the uterine luminal epithelium on days 3 and 4 of pregnancy. Progesterone induces Jam2 expression in ovariectomized mice, which is blocked by progesterone antagonist RU486. Jam2 expression on day 4 of pregnancy is also inhibited by RU486 treatment. Leukemia inhibitory factor (LIF) up-regulates Jam2 protein in isolated luminal epithelium from day 4 uterus, which is blocked by S3I-201, a cell-permeable inhibitor for Stat3 phosphorylation. Under adhesion assay, recombinant Jam2 protein increases the rate of blastocyst adhesion. Both soluble recombinant Jam2 and Jam3 can reverse this process.

Conclusion

Jam2 is highly expressed in the luminal epithelium of receptive uterus and up-regulated by progesterone and LIF via tyrosine phosphorylation of Stat3. Jam2 may play a role in the interaction between hatched blastocyst and receptive uterus.

Enterocytes’ tight junctions: From molecules to diseases

Tight junctions (TJs) are structures between cells where cells appear in the closest possible contact. They are responsible for sealing compartments when epithelial sheets are generated. They regulate the permeability of ions, (macro) molecules and cells via the paracellular pathway. Their structure at the electron microscopic level has been well known since the 1970s; however, only recently has their macromolecular composition been revealed. This review first examines the major macromolecular components of the TJs (occludin, claudins, junctional adhesion molecule and tricellulin) and then the associated macromolecules at the intracellular plaque [zonula occludens (ZO)-1, ZO-2, ZO-3, AF-6, cingulin, 7H6]. Emphasis is given to their interactions in order to begin to understand the mode of assembly of TJs. The functional significance of TJs is detailed and several mechanisms and factors involved are discussed briefly. Emphasis is given to the role of intestinal TJs and the alterations observed or speculated in diverse disease states. Specifically, intestinal TJs may exert a pathogenetic role in intestinal (inflammatory bowel disease, celiac disease) and extraintestinal diseases (diabetes type 1, food allergies, autoimmune diseases). Additionally, intestinal TJs may be secondarily disrupted during the course of diverse diseases, subsequently allowing the bacterial translocation phenomenon and promoting the systemic inflammatory response, which is often associated with clinical deterioration. The major questions in the field are highlighted.

Jamb and jamc are essential for vertebrate myocyte fusion

Jamb and Jamc are an essential cell surface receptor pair that interact to drive fusion between muscle precursor cells during zebrafish development.

Cellular fusion is required in the development of several tissues, including skeletal muscle. In vertebrates, this process is poorly understood and lacks an in vivo-validated cell surface heterophilic receptor pair that is necessary for fusion. Identification of essential cell surface interactions between fusing cells is an important step in elucidating the molecular mechanism of cellular fusion. We show here that the zebrafish orthologues of JAM-B and JAM-C receptors are essential for fusion of myocyte precursors to form syncytial muscle fibres. Both jamb and jamc are dynamically co-expressed in developing muscles and encode receptors that physically interact. Heritable mutations in either gene prevent myocyte fusion in vivo, resulting in an overabundance of mononuclear, but otherwise overtly normal, functional fast-twitch muscle fibres. Transplantation experiments show that the Jamb and Jamc receptors must interact between neighbouring cells (in trans) for fusion to occur. We also show that jamc is ectopically expressed in prdm1a mutant slow muscle precursors, which inappropriately fuse with other myocytes, suggesting that control of myocyte fusion through regulation of jamc expression has important implications for the growth and patterning of muscles. Our discovery of a receptor-ligand pair critical for fusion in vivo has important implications for understanding the molecular mechanisms responsible for myocyte fusion and its regulation in vertebrate myogenesis.

The fusion of precursor cells is a crucial step in many biological processes, one of which is the development of skeletal muscle. The molecular and cell biology of fusion of muscle precursors has been well described in Drosophila melanogaster larvae, leading to insights into the process in vertebrates. However, the identity and mechanism of action of essential cell surface proteins for fusion between vertebrate muscle precursors has previously been lacking. Here, we describe a vertebrate-specific cell surface receptor pair that is essential for fusion in zebrafish: Jamb and Jamc. Loss of function of either receptor causes a near-complete block in fusion, resulting in an overabundance of mononucleate muscle fibres that are otherwise overtly normal. We demonstrate that Jamb and Jamc physically interact and are co-expressed by muscle precursors. Moreover, we show that the interaction between them is essential for fusion between neighbouring precursors in an embryo. We hypothesise that binding of Jamb to Jamc is a necessary recognition and adhesion step permissive for, but not sufficient to cause, myocyte fusion. Knowledge of these molecular components in vertebrates will lead to better understanding of how fusion is controlled to pattern skeletal muscle tissue.

Pathobiology of junctional adhesion molecules

Junctional adhesion molecules are transmembrane proteins that belong to the immunoglobulin superfamily. In addition to their localization in close proximity to the tight junctions in endothelial and epithelial cells, junctional adhesion molecules are also expressed in circulating cells that do not form junctions, such as leukocytes and platelets. As a consequence, these proteins are associated not only with the permeability-regulating barrier function of the tight junctions, but also with other biologic processes, such as inflammatory reactions, responses to vascular injury, and tumor angiogenesis. Furthermore, because of their transmembrane topology, junctional adhesion molecules are poised both for receiving inputs from the cell interior (their expression, localization, and function being regulated in response to inflammatory cytokines and growth factors) and for translating extracellular adhesive events into functional responses. This review focuses on the different roles of junctional adhesion molecules in normal and pathologic conditions, with emphasis on inflammatory reactions and vascular responses to injury.

A look at tricellulin and its role in tight junction formation and maintenance

Tight junctions are elaborate networks of transmembrane and cytosolic proteins that regulate epithelial permeability. Tricellulin was the first tight junction protein found at tricellular tight junctions, the specialized structures occurring where three cells meet together. Here, we summarize the current knowledge about tricellulin (marvelD2), a MARVEL domain protein. We address tricellulin location at tricellular junctions, and establish the comparison with the other members of the MARVEL family, occludin (marvelD1) and marvelD3. The structure of tricellulin and its membrane folding, as well as the proposed molecular interactions of tricellulin with other tight junction proteins, together with the interplay between those proteins are also discussed. In addition, we address the role of tricellulin in barrier properties, discriminating the involvement of the protein in paracellular permeability at bicellular and at tricellular tight junctions. Moreover, the key importance of the protein for hearing is highlighted based on the fact that mutations in TRIC, the human tricellulin gene, lead to deafness. Furthermore, this review points to some of the aspects that still deserve clarification for a better understanding of the biology of tight junctions in general and of tricellulin in particular.

CRTAM: A molecule involved in epithelial cell adhesion

Class I-restricted T cell associated molecule (CRTAM) is a member of the immunoglobulin superfamily that complies with the structural characteristics of the JAM family of proteins and is phylogenetically more closely related to nectin-like proteins. Here we demonstrate for the first time, that CRTAM is expressed in epithelial cells along the lateral membrane and is important for early cell-cell contacts and cell-substrate interactions. CRTAM is sensitive to intermediate filament disruption and treatment of monolayers with soluble CRTAM enhances cell-cell dissociation and lowers transepithelial electrical resistance. Incubation of newly plated cells with anti-CRTAM antibody decreases the formation of cell aggregates and promotes cell detachment. Co-cultures of epithelial cells and fibroblasts that lack CRTAM expression and in vitro binding assays, demonstrate the participation of CRTAM in homotypic and heterotypic trans-interactions. Hence we conclude that CRTAM is a molecule involved in epithelial cell adhesion.

Junctional adhesion molecule-C is a soluble mediator of angiogenesis

Junctional adhesion molecule-C (JAM-C) is an adhesion molecule expressed by endothelial cells (ECs) that plays a role in tight junction formation, leukocyte adhesion, and transendothelial migration. In the current study, we investigated whether JAM-C is found in soluble form and whether soluble JAM-C (sJAM-C) mediates angiogenesis. We found that JAM-C is present in soluble form in normal serum and elevated in rheumatoid arthritis (RA) serum. The concentration of sJAM-C is also elevated locally in RA synovial fluid compared with RA serum or osteoarthritis synovial fluid. sJAM-C was also present in the culture supernatant of human microvascular ECs (HMVECs) and immortalized human dermal microvascular ECs, and its concentration was increased following cytokine stimulation. In addition, sJAM-C cleavage from the cell surface was mediated in part by a disintegrin and metalloproteinases 10 and 17. In functional assays, sJAM-C was both chemotactic and chemokinetic for HMVECs and induced HMVEC tube formation on Matrigel in vitro. Neutralizing anti-JAM-C Abs inhibited RA synovial fluid-induced HMVEC chemotaxis and sJAM-C-induced HMVEC tube formation on Matrigel. sJAM-C also induced angiogenesis in vivo in the Matrigel plug and sponge granuloma models. Moreover, sJAM-C-mediated HMVEC chemotaxis was dependent on Src, p38, and PI3K. Our results show that JAM-C exists in soluble form and suggest that modulation of sJAM-C may provide a novel route for controlling pathological angiogenesis.

Cooperative expression of junctional adhesion molecule-C and -B supports growth and invasion of glioma

Brain invasion is a biological hallmark of glioma that contributes to its aggressiveness and limits the potential of surgery and irradiation. Deregulated expression of adhesion molecules on glioma cells is thought to contribute to this process. Junctional adhesion molecules (JAMs) include several IgSF members involved in leukocyte trafficking, angiogenesis, and cell polarity. They are expressed mainly by endothelial cells, white blood cells, and platelets. Here, we report JAM-C expression by human gliomas, but not by their normal cellular counterpart. This expression correlates with the expression of genes involved in cytoskeleton remodeling and cell migration. These genes, identified by a transcriptomic approach, include poliovirus receptor and cystein-rich 61, both known to promote glioma invasion, as well as actin filament associated protein, a c-Src binding partner. Gliomas also aberrantly express JAM-B, a high affinity JAM-C ligand. Their interaction activates the c-Src proto-oncogene, a central upstream molecule in the pathways regulating cell migration and invasion. In the tumor microenvironment, this co-expression may thus promote glioma invasion through paracrine stimuli from both tumor cells and endothelial cells. Accordingly, JAM-C/B blocking antibodies impair in vivo glioma growth and invasion, highlighting the potential of JAM-C and JAM-B as new targets for the treatment of human gliomas.

Investigation of the binding preference of reovirus sigma1 for junctional adhesion molecule A by classical and steered molecular dynamics

Biochemical studies have determined that reoviruses attach to cells by combining attachment protein sigma1 to the binding interface of its receptor protein junctional adhesion molecule A (JAM-A), and the interface normally takes care of the homodimerization of JAM-A. Tighter binding and slower dissociation of for the sigma1-JAM complex than for the JAM-JAM complex have been probed by both biological and atomic force microscopy experiments; however, the mechanism of the binding preference of the attachment protein for JAM-A still remains unclear. With the help of classical and steered molecular dynamics and energy calculations, the unbinding forces and kinetic properties of the complexes are investigated, together with detailed structural information analyses. A multireceptor mechanism is proposed for the binding preference, which can be helpful for future viral infection and vector targeting studies.

JAM-A is a novel surface marker for NG2-Glia in the adult mouse brain

Background

Junctional adhesion molecule-A (JAM-A) is an adhesive protein expressed in various cell types. JAM-A localizes to the tight junctions between contacting endothelial and epithelial cells, where it contributes to cell-cell adhesion and to the control of paracellular permeability.

Results

So far, the expression pattern of JAM-A has not been described in detail for the different cell types of the adult brain. Here we show that a subset of proliferating cells in the adult mouse brain express JAM-A. We further clarify that these cells belong to the lineage of NG2-glia cells. Although these mitotic NG2-glia cells express JAM-A, the protein never shows a polarized subcellular distribution. Also non-mitotic NG2-glia cells express JAM-A in a non-polarized pattern on their surface.

Conclusions

Our data show that JAM-A is a novel surface marker for NG2-glia cells of the adult brain.

The role of JAM-A in inflammatory bowel disease: unrevealing the ties that bind

Tight junctions (TJ) are junctional proteins whose function is to maintain an intact intestinal epithelial barrier and regulate the paracellular movement of water and solutes. Altered TJ structure and epithelial permeability are observed in inflammatory bowel disease and seem to have an important role in the pathogenesis of these diseases. Junctional adhesion molecule-A (JAM-A) is a protein expressed at tight junctions of epithelial and endothelial cells, as well as on circulating leukocytes. Its function at tight junctions appears to be crucial as an extracellular adhesive molecule in the direct regulation of intestinal barrier function. This review focuses on the role of JAM-A in controlling mucosal homeostasis by regulating the integrity and permeability of epithelial barrier function.

Junctional Adhesion Molecules (JAMs) are Differentially Expressed in Fibroblasts and Co-Localize with ZO-1 to Adherens-Like Junctions

Junctional Adhesion Molecules (JAMs) are components and regulators of the well-characterized epithelial and endothelial tight junction. Since the molecular components of native fibroblast adherens-like junctions remain poorly described we determined JAM expression profiles in fibroblasts. We found JAM-C on human dermal, lung, and corneal primary fibroblast cultures. Within murine lines, JAM-A was found in L-cells, JAM-C in 3T3 L1 cells, and both JAM-A and JAM-C were co-expressed in NIH 3T3 fibroblasts. In primary dermal fibroblasts, JAM-C concentrated at zipper-like junctions that formed between apposing cells. Dual immunostaining showed JAM-C co-localization with the ZO-1 intracellular scaffolding molecule at cell contacts that ranged from 7 microm to over 25 microm in length. JAM-C also labeled similar zipper-like junctions detected with N-Cadherin and Cadherin-11 antibodies. We conclude that endogenous JAM-C is an integral component of the dermal fibroblast adherens-like junction, and our data extend the expression and potential function of JAMs into mesenchymal tissues.

Evidence for cross-reactivity of JAM-C antibodies: implications for cellular localization studies

BACKGROUND INFORMATION

JAM-C (junctional adhesion molecule C) has been implicated in the regulation of leukocyte migration, cell polarity, spermatogenesis, angiogenesis and nerve conduction. JAM-C has been also reported to concentrate at TJs (tight junctions) and desmosomes, although detailed localization studies remain incomplete.

RESULTS

Monoclonal (LUCA14, MAB1189, Gi11, and PACA4) and polyclonal (40-9000) antibodies were employed to evaluate JAM-C expression/localization in various epithelial cell lines. However, RT-PCR (reverse transcription-PCR) assays revealed no JAM-C mRNA in SK-CO15, HeLa and HPAF-II cells, whereas abundant mRNA was detected in platelets, Caco-2 and ARPE cells. Interestingly, immunofluorescence localization in all cells revealed strong intercellular junctional staining with all of the above antibodies, except PACA4. Given the positive staining results in cells lacking JAM-C mRNA, immunoblot analyses were performed. Western blots revealed a prominent protein band at 52 kDa in all cells tested with all antibodies except PACA4. However, the correct size of JAM-C (37 kDa) was only detected in cells containing JAM-C mRNA. Immunofluorescence staining of JAM-C mRNA-expressing Caco-2 cells using mAb PACA4 revealed co-localization with occludin and ZO-1 (zonula occludens 1) at TJs. Analyses by MS identified the cross-reactive 52 kDa protein band as K8 (keratin 8). Furthermore, siRNA (small interfering RNA)-mediated downregulation of K8 in JAM-C mRNA-negative cells resulted in diminished junctional staining along with a reduction in the intensity of the 52 kDa protein band. Using an antibody specific for K8 phosphorylated at Ser73, the 52 kDa protein was identified as this phosphorylated form of K8.

CONCLUSIONS

The results from the present study demonstrate that a majority of available anti-human JAM-C antibodies cross-react with phosphorylated K8 and suggest that cellular localization studies using these reagents should be interpreted with caution. Of the JAM-C antibodies tested, only mAb PACA4 is monospecific for human JAM-C. Analyses using PACA4 reveal that JAM-C expression is variable in different epithelial cell lines with co-localization at TJs.

Adaptive immune response in JAM-C-deficient mice: normal initiation but reduced IgG memory

We have recently shown that junctional adhesion molecule (JAM)-C-deficient mice have leukocytic pulmonary infiltrates, disturbed neutrophil homeostasis, and increased postnatal mortality. This phenotype was partially rescued when mice were housed in ventilated isolators, suggesting an inability to cope with opportunistic infections. In the present study, we further examined the adaptive immune responses in JAM-C(-/-) mice. We found that murine conventional dendritic cells express in addition to Mac-1 and CD11c also JAM-B as ligand for JAM-C. By in vitro adhesion assay, we show that murine DCs can interact with recombinant JAM-C via Mac-1. However, this interaction does not seem to be necessary for dendritic cell migration and function in vivo, even though JAM-C is highly expressed by lymphatic sinuses of lymph nodes. Nevertheless, upon immunization and boosting with a protein Ag, JAM-C-deficient mice showed decreased persistence of specific circulating Abs although the initial response was normal. Such a phenotype has also been observed in a model of Ag-induced arthritis, showing that specific IgG2a Ab titers are reduced in the serum of JAM-C(-/-) compared with wild-type mice. Taken together, these data suggest that JAM-C deficiency affects the adaptive humoral immune response against pathogens, in addition to the innate immune system.

JAM-L-mediated leukocyte adhesion to endothelial cells is regulated in cis by alpha4beta1 integrin activation

Junctional adhesion molecules (JAMs) are endothelial and epithelial adhesion molecules involved in the recruitment of circulating leukocytes to inflammatory sites. We show here that JAM-L, a protein related to the JAM family, is restricted to leukocytes and promotes their adhesion to endothelial cells. Cis dimerization of JAM-L is required to engage in heterophilic interactions with its cognate counter-receptor CAR (coxsackie and adenovirus receptor). Interestingly, JAM-L expressed on neutrophils binds CAR independently of integrin activation. However, on resting monocytes and T lymphocytes, which express the integrin VLA-4, JAM-L molecules engage in complexes with VLA-4 and mainly accumulate in their monomeric form. Integrin activation is required for the dissociation of JAM-L–VLA-4 complexes and the accumulation of functional JAM-L dimers, which indicates that the leukocyte integrin VLA-4 controls JAM-L function in cis by controlling its dimerization state. This provides a mechanism through which VLA-4 and JAM-L functions are coordinately regulated, allowing JAM-L to strengthen integrin-dependent adhesion of leukocytes to endothelial cells.

Junctional adhesion molecule C mediates leukocyte adhesion to rheumatoid arthritis synovium

OBJECTIVE

Leukocyte infiltration into the rheumatoid arthritis (RA) synovium is a multistep process in which leukocytes leave the bloodstream and invade the synovial tissue (ST). Leukocyte transendothelial migration and adhesion to RA ST requires adhesion molecules on the surface of endothelial cells and RA ST fibroblasts. This study was undertaken to investigate the role of junctional adhesion molecule C (JAM-C) in mediating leukocyte recruitment and retention in the RA joint.

METHODS

Immunohistologic analysis was performed on RA, osteoarthritis (OA), and normal ST samples to quantify JAM-C expression. Fibroblast JAM-C expression was also analyzed using Western blotting, cell surface enzyme-linked immunosorbent assay, and immunofluorescence. To determine the role of JAM-C in leukocyte retention in the RA synovium, in vitro and in situ adhesion assays and RA ST fibroblast transmigration assays were performed.

RESULTS

JAM-C was highly expressed by RA ST lining cells, and its expression was increased in OA ST and RA ST endothelial cells compared with normal ST endothelial cells. JAM-C was also expressed on the surface of OA ST and RA ST fibroblasts. Furthermore, we demonstrated that myeloid U937 cell adhesion to both OA ST and RA ST fibroblasts and to RA ST was dependent on JAM-C. U937 cell migration through an RA ST fibroblast monolayer was enhanced in the presence of neutralizing antibodies against JAM-C.

CONCLUSION

Our results highlight the novel role of JAM-C in recruiting and retaining leukocytes in the RA synovium and suggest that targeting JAM-C may be important in combating inflammatory diseases such as RA.

Vascular and epithelial junctions: a barrier for leucocyte migration

Rapid mobilization of leucocytes through endothelial and epithelial barriers is key in immune system reactivity. The underlying mechanisms that regulate these processes have been the basis for many recent studies. Traditionally, leucocyte extravasation had been believed to occur through a paracellular route, which involves localized disruption of endothelial cell junctions. However, more recently, a transcellular route has been described involving the passage through the endothelial cell body. Leucocytes are also able to migrate through epithelium to monitor mucosal tissues and microenvironments. A number of adhesion molecules are known to regulate transmigration of leucocytes through epithelial and endothelial layers. Paracellular and transcellular leucocyte transmigration are regulated by adhesion molecules such as PECAM-1 (platelet-endothelial cell adhesion molecule 1), CD99, VE-cadherin (vascular endothelial cadherin) and JAM (junctional adhesion molecule) proteins. The purpose of this review is to discuss the role of these molecules in leucocyte transmigration and how they contribute to the different mechanisms that regulate leucocyte trafficking.

DICAM, a novel dual immunoglobulin domain containing cell adhesion molecule interacts with alphavbeta3 integrin

Immunoglobulin (Ig) superfamily members are abundant with diverse functions including cell adhesion in various tissues. Here, we identified and characterized a novel adhesion molecule that belongs to the CTX protein family and named as DICAM (Dual Ig domain containing cell adhesion molecule). DICAM is a type I transmembrane protein with two V-type Ig domains in the extracellular region and a short cytoplasmic tail of 442 amino acids. DICAM is found to be expressed ubiquitously in various organs and cell lines. Subcellular localization of DICAM was observed in the cell-cell contact region and nucleus of cultured epithelial cells. Cell-cell contact region was colocalized with tight junction protein, ZO-1. The DICAM increased MDCK cell adhesion to 60% levels of fibronectin. DICAM mediated cell adhesion was specific for the alphavbeta3 integrin; other integrins, alpha2, alpha5, beta1, alpha2beta1, alpha5beta1, were not involved in cell adhesion. In identifying the interacting domain of DICAM with alphavbeta3, the Ig domain 2 showed higher cell adhesion activity than that of Ig domain 1. Although RGD motif in Ig domain 2 was engaged in cell adhesion, it was not participated in DICAM-alphavbeta3 mediated cell adhesion. Furthermore, differentially expressing DICAM stable cells showed well correlated cell to cell adhesion capability with integrin beta3-overexpressing cells. Collectively, these results indicate that DICAM, a novel dual Ig domain containing adhesion molecule, mediates cell adhesion via alphavbeta3 integrin.

Cell surface proteomics identifies molecules functionally linked to tumor cell intravasation

In order to better understand the molecular and cellular determinants of tumor cell intravasation, our laboratory has generated a pair of congenic human HT-1080 fibrosarcoma variants (i.e. HT-hi/diss and HT-lo/diss) differing 50-100-fold in their ability to intravasate and disseminate. To investigate the molecular differences underlying the distinct dissemination capacities of these HT-1080 variants, we performed a comparative analysis of the cell surface proteomes of HT-hi/diss and HT-lo/diss. Cell membrane proteins were enriched by biotinylation and avidin precipitation and analyzed by tandem mass spectrometry employing multidimensional protein identification technology. By this approach, 47 cell surface-associated molecules were identified as differentially expressed between the HT-1080 intravasation variants. From these candidates, four targets (i.e. TIMP-2, NCAM-1, JAM-C, and tissue factor (TF)) were selected for further biochemical validation and in vivo functional verification. Western blot analysis of the cell surface enriched fractions confirmed the proteomic array data, demonstrating that, in vitro, TIMP-2 protein was increased in the HT-lo/diss variant, whereas NCAM-1, JAM-C, and TF levels were increased in the HT-hi/diss variant. Corresponding in vivo differences in levels of TIMP-2, JAM-C, and TF were demonstrated in primary tumors grown in the chick embryo. Finally, functional inhibition of one selected protein (i.e. TF) by small interfering RNA silencing or ligation with a function-blocking antibody significantly reduced HT-hi/diss intravasation, thus clearly implicating TF in the early steps of tumor cell dissemination. Overall, our cell surface proteomic analysis provides a powerful tool for identification of specific cell membrane molecules that contribute functionally to intravasation and metastasis in vivo.

A comparative molecular force spectroscopy study of homophilic JAM-A interactions and JAM-A interactions with reovirus attachment protein sigma1

JAM-A belongs to a family of immunoglobulin-like proteins called junctional adhesion molecules (JAMs) that localize at epithelial and endothelial intercellular tight junctions. JAM-A is also expressed on dendritic cells, neutrophils, and platelets. Homophilic JAM-A interactions play an important role in regulating paracellular permeability and leukocyte transmigration across epithelial monolayers and endothelial cell junctions, respectively. In addition, JAM-A is a receptor for the reovirus attachment protein, sigma1. In this study, we used single molecular force spectroscopy to compare the kinetics of JAM-A interactions with itself and sigma1. A chimeric murine JAM-A/Fc fusion protein and the purified sigma1 head domain were used to probe murine L929 cells, which express JAM-A and are susceptible to reovirus infection. The bond half-life (t(1/2)) of homophilic JAM-A interactions was found to be shorter (k(off)(o) = 0.688 +/- 0.349 s(-1)) than that of sigma1/JAM-A interactions (k(off)(o) = 0.067 +/- 0.041 s(-1)). These results are in accordance with the physiological functions of JAM-A and sigma1. A short bond lifetime imparts a highly dynamic nature to homophilic JAM-A interactions for regulating tight junction permeability while stable interactions between sigma1 and JAM-A likely anchor the virus to the cell surface and facilitate viral entry.