Cloning of a soluble isoform of the SgIGSF adhesion molecule that binds the extracellular domain of the membrane-bound isoform

Clinical significance of soluble CADM1 as a novel marker for adult T-cell leukemia/lymphoma

Adult T-cell leukemia/leukemia (ATLL) is an aggressive peripheral T-cell malignancy, caused by infection with the human T-cell leukemia virus type 1 (HTLV-1). We recently showed that the cell adhesion molecule 1 (CADM1), a member of the immunoglobulin superfamily, is specifically and consistently overexpressed in ATLL cells, and functions as a novel cell surface marker. In this study, we first show that a soluble form of CADM1 (sCADM1) is secreted from ATLL cells by mainly alternative splicing. After developing the Alpha linked immunosorbent assay (AlphaLISA) for sCADM1, we show that plasma sCADM1 concentrations gradually increased during disease progression from indolent to aggressive ATLL. Although other known biomarkers of tumor burden such as soluble interleukin-2 receptor α (sIL-2Rα) also increased with sCADM1 during ATLL progression, multivariate statistical analysis of biomarkers revealed that only plasma sCADM1 was selected as a specific biomarker for aggressive ATLL, suggesting that plasma sCADM1 may be a potential risk factor for aggressive ATLL. In addition, plasma sCADM1 is a useful marker for monitoring response to chemotherapy as well as for predicting relapse of ATLL. Furthermore, the change in sCADM1 concentration between indolent and aggressive type ATLL was more prominent than the change in the percentage of CD4⁺CADM1⁺ ATLL cells. As plasma sCADM1 values fell within normal ranges in HTLV-1-associated myelopathy/tropical spastic paraparesis (HAM/TSP) patients with higher levels of serum sIL-2Rα, the measurement of sCADM1 may become a useful tool to discriminate between ATLL and other inflammatory diseases, including HAM/TSP.

CADM1 suppresses c-Src activation by binding with Cbp on membrane lipid rafts and intervenes colon carcinogenesis

Cell adhesion molecules act as tumor suppressors primarily by cell attachment activity, but additional mechanisms modifying signal transduction are suggested in some cases. Cell adhesion molecule 1 (CADM1), a membrane-spanning immunoglobulin superfamily, mediates intercellular adhesion by trans-homophilic interaction and acts as a tumor suppressor. Here, we investigated CADM1-associated proteins comprehensively using proteomic analysis of immune-precipitates of CADM1 by mass spectrometry and identified a transmembrane adaptor protein, Csk-binding protein (Cbp), known to suppress Src-mediated transformation, as a binding partner of CADM1. CADM1 localizes to detergent-resistant membrane fractions and co-immunoprecipitated with Cbp and c-Src. Suppression of CADM1 expression using siRNA reduces the amount of co-immunoprecipitated c-Src with Cbp and activates c-Src in colon cancer cells expressing both CADM1 and Cbp. On the other hand, co-replacement of CADM1 and Cbp in colon cancer cells lacking CADM1 and Cbp expression suppresses c-Src activation, wound healing and tumorigenicity in nude mice. Furthermore, expression of Cbp and CADM1 was lost in 55% and 83% of human colon cancer, respectively, preferentially in tumors with larger size and/or lymph node metastasis. CADM1 would act as a colon tumor suppressor by intervening oncogenic c-Src signaling through binding with Cbp besides its authentic cell adhesion activity.

Urinary Cell Adhesion Molecule 1 Is a Novel Biomarker That Links Tubulointerstitial Damage to Glomerular Filtration Rates in Chronic Kidney Disease

Cell adhesion molecule 1 (CADM1) is an immunoglobulin superfamily member strongly expressed on renal tubular epithelia in the urinary tract. Enzymatic cleavage of its ectodomain increases in chronic kidney disease (CKD), and is assumed to contribute to tubulointerstitial lesion formation. Because the cleaved ectodomain fragments are likely to be released into the urine, a sandwich enzyme-linked immunosorbent assay (ELISA) system for urinary CADM1 was developed using two anti-ectodomain antibodies. Urinary CADM1 concentrations in patients with CKD based on various forms of glomerulonephritis and nephropathy (n = 127) were measured. A total of 44 patients (35%) had elevated CADM1 concentrations over the normal upper limit (362 pg/mL), with a mean of 1,727 pg/mL. Renal biopsy specimens of all patients were pathologically scored for tubulointerstitial lesions using epithelial degeneration, interstitial inflammation, and fibrosis. There were no correlations between urinary CADM1 concentrations and pathological scores or any widely used renal markers, including glomerular filtration rate (GFR), but there was a weak inverse correlation between pathological scores and GFR (R² = 0.292). Notably, this correlation gradually increased in patients with increasing CADM1 concentrations, and reached a maximum R² (0.899) at a cutoff of 1,569 pg/mL. The results of this study suggest that urinary CADM1 is a useful marker indicating tubulointerstitial damage from elevated GFR levels in CKD.

MiR-128-1-5p regulates tight junction induced by selenium deficiency via targeting cell adhesion molecule 1 in broilers vein endothelial cells

Vein endothelial cells (VECs) constitute an important barrier for macromolecules and circulating cells from the blood to the tissues, stabilizing the colloid osmotic pressure of the blood, regulating the vascular tone, and rapidly changing the intercellular connection, and maintaining normal physiological function. Tight junction has been discovered as an important structural basis of intercellular connection and may play a key role in intercellular connection injuries or vascular diseases and selenium (Se) deficiency symptoms. Hence, we replicated the Se-deficient broilers model and detected the specific microRNA in response to Se-deficient vein by using quantitative real time-PCR (qRT-PCR) analysis. Also, we selected miR-128-1-5p based on differential expression in vein tissue and confirmed its target gene cell adhesion molecule 1 (CADM1) by the dual luciferase reporter assay and qRT-PCR in VECs. We made the ectopic miR-128-1-5p expression for the purpose of validating its function on tight junction. The result showed that miR-128-1-5p and CADM1 were involved in the ZO-1-mediated tight junction, increased paracellular permeability, and arrested cell cycle. We presumed that miR-128-1-5p and Se deficiency might trigger tight junction. Interestingly, miR-128-1-5p inhibitor and fasudil in part hinder the destruction of the intercellular structure caused by Se deficiency. The miR-128-1-5p/CADM1/tight junction axis provides a new avenue toward understanding the mechanism of Se deficiency, revealing a novel regulation model of tight junction injury in vascular diseases.

Mast cells in asthma--state of the art

Mast cells (MCs) play a central role in tissue homoeostasis, sensing the local environment through numerous innate cell surface receptors. This enables them to respond rapidly to perceived tissue insults with a view to initiating a co-ordinated programme of inflammation and repair. However, when the tissue insult is chronic, the ongoing release of multiple pro-inflammatory mediators, proteases, cytokines and chemokines leads to tissue damage and remodelling. In asthma, there is strong evidence of ongoing MC activation, and their mediators and cell-cell signals are capable of regulating many facets of asthma pathophysiology. This article reviews the evidence behind this.

Tumor Necrosis Factor α Regulates Endothelial Progenitor Cell Migration via CADM1 and NF-kB

Shortly after the discovery of endothelial progenitor cells (EPCs) in 1997, many clinical trials were conducted using EPCs as a cellular based therapy with the goal of restoring damaged organ function by inducing growth of new blood vessels (angiogenesis). Results were disappointing, largely because the cellular and molecular mechanisms of EPC-induced angiogenesis were not clearly understood. Following injection, EPCs must migrate to the target tissue and engraft prior to induction of angiogenesis. In this study EPC migration was investigated in response to tumor necrosis factor α (TNFα), a pro-inflammatory cytokine, to test the hypothesis that organ damage observed in ischemic diseases induces an inflammatory signal that is important for EPC homing. In this study, EPC migration and incorporation were modeled in vitro using a coculture assay where TNFα treated EPCs were tracked while migrating toward vessel-like structures. It was found that TNFα treatment of EPCs increased migration and incorporation into vessel-like structures. Using a combination of genomic and proteomic approaches, NF-kB mediated upregulation of CADM1 was identified as a mechanism of TNFα induced migration. Inhibition of NF-kB or CADM1 significantly decreased migration of EPCs in vitro suggesting a role for TNFα signaling in EPC homing during tissue repair. Stem Cells 2016;34:1922-1933.

Splicing Regulation of Pro-Inflammatory Cytokines and Chemokines: At the Interface of the Neuroendocrine and Immune Systems

Alternative splicing plays a key role in posttranscriptional regulation of gene expression, allowing a single gene to encode multiple protein isoforms. As such, alternative splicing amplifies the coding capacity of the genome enormously, generates protein diversity, and alters protein function. More than 90% of human genes undergo alternative splicing, and alternative splicing is especially prevalent in the nervous and immune systems, tissues where cells need to react swiftly and adapt to changes in the environment through carefully regulated mechanisms of cell differentiation, migration, targeting, and activation. Given its prevalence and complexity, this highly regulated mode of gene expression is prone to be affected by disease. In the following review, we look at how alternative splicing of signaling molecules—cytokines and their receptors—changes in different pathological conditions, from chronic inflammation to neurologic disorders, providing means of functional interaction between the immune and neuroendocrine systems. Switches in alternative splicing patterns can be very dynamic and can produce signaling molecules with distinct or antagonistic functions and localization to different subcellular compartments. This newly discovered link expands our understanding of the biology of immune and neuroendocrine cells, and has the potential to open new windows of opportunity for treatment of neurodegenerative disorders.

The intracellular domain of cell adhesion molecule 1 is present in emphysematous lungs and induces lung epithelial cell apoptosis

Background

Pulmonary emphysema is characterized histologically by destruction of alveolar walls and enlargement of air spaces due to lung epithelial cell apoptosis. Cell adhesion molecule 1 (CADM1) is an immunoglobulin superfamily member expressed in lung epithelial cells. CADM1 generates a membrane-associated C-terminal fragment, αCTF, through A disintegrin- and metalloprotease-10-mediated ectodomain shedding, subsequently releasing the intracellular domain (ICD) through γ-secretase-mediated intramembrane shedding of αCTF. αCTF localizes to mitochondria and induces apoptosis in lung epithelial cells. αCTF contributes to the development and progression of emphysema as a consequence of increased CADM1 ectodomain shedding. The purpose of this study was to examine whether the ICD makes a similar contribution.

Results

The ICD was synthesized as a 51-amino acid peptide, and its mutant was synthesized by substituting seven amino acids and deleting two amino acids. These peptides were labeled with fluorescein isothiocyanate and were introduced into various cell lines. ICD peptide-derived fluorescence was well visualized in lung epithelial cells at the site of Mitotracker mitochondrial labeling, but was detected in locations other than mitochondria in other cell types. Mutant peptide-derived fluorescence was detected in locations other than mitochondria, even in lung epithelial cells. Terminal deoxynucleotidyl transferase-mediated dUTP nick-end labeling assays revealed that transduction of the ICD peptide increased the proportion of apoptotic cells 2- to 5-fold in the lung epithelial cell lines, whereas the mutant peptide did not. Abundance of the ICD was below the Western blot detection limit in emphysematous (n = 4) and control (n = 4) human lungs. However, the ICD was detected only in emphysematous lungs when it was immunoprecipitated with anti-CADM1 antibody (4/4 vs. 0/4, P = 0.029).

Conclusions

As the abundance of ICD molecules was sparse but present, increased CADM1 shedding appeared to contribute to the development of emphysema by generating αCTF and the ICD in lung epithelial cells.

Electronic supplementary material

The online version of this article (doi:10.1186/s12929-015-0173-8) contains supplementary material, which is available to authorized users.

CADM1 is expressed as multiple alternatively spliced functional and dysfunctional isoforms in human mast cells

Cell adhesion molecule 1 (CADM1) is implicated in the pathogenesis of several diseases and is responsible for adhesion and survival of mast cells (MCs). Differential expression of CADM1 isoforms was found in different species. We previously cloned SP4, SP1, SP6 and a dysfunctional isoform from human lung MCs (HLMCs) and the MC line HMC-1. The aim of this study was to identify all isoforms expressed in human MCs. The functional isoforms SP4, SP1, SP6 and SP3, with alternative splicing between exons 7/11, were detected in human MCs by RT-PCR. Two dysfunctional isoforms with alternative splicing of cryptic exons A and B between exons 1/2, leading to premature termination of translation, were found in ∼40% of MC specimens. Sequencing of genomic DNA showed that splicing of cryptic exon B did not result from specific SNPs within this exon or its putative splice branch point. Highly glycosylated CADM1 (∼105 kDa) was detected by western blotting, but an extracellular domain (∼95 kDa) was found only in the culture medium from HLMCs, but not HMC-1 cells, indicating differential protein expression. Transfection of SP1 and SP6, but not SP4, reduced adhesion of HMC-1 cells to human lung fibroblasts but not airway smooth muscle cells. Hence, dysfunctional and functional CADM1 isoforms are found in human MCs. The longer SP1 and SP6 were most evident in differentiated HLMCs and displayed differential adhesion compared to SP4. These multiple isoforms are likely to contribute to MC function in both health and disease.

Polysialylation of the synaptic cell adhesion molecule 1 (SynCAM 1) depends exclusively on the polysialyltransferase ST8SiaII in vivo

Polysialic acid is a unique carbohydrate polymer specifically attached to a limited number of glycoproteins. Among them is synaptic cell adhesion molecule 1 (SynCAM 1), a member of the immunoglobulin (Ig) superfamily composed of three extracellular Ig-like domains. Polysialylation of SynCAM 1 is cell type-specific and was exclusively found in NG2 cells, a class of multifunctional progenitor cells that form specialized synapses with neurons. Here, we studied the molecular requirements for SynCAM 1 polysialylation. Analysis of mice lacking one of the two polysialyltransferases, ST8SiaII or ST8SiaIV, revealed that polysialylation of SynCAM 1 is exclusively mediated by ST8SiaII throughout postnatal brain development. Alternative splicing of the three variable exons 8a, 8b, and 8c can theoretically give rise to eight transmembrane isoforms of SynCAM 1. We detected seven transcript variants in the developing mouse brain, including three variants containing exon 8c, which was so far regarded as a cryptic exon in mice. Polysialylation of SynCAM 1 was restricted to four isoforms in perinatal brain. However, cell culture experiments demonstrated that all transmembrane isoforms of SynCAM 1 can be polysialylated by ST8SiaII. Moreover, analysis of domain deletion constructs revealed that Ig1, which harbors the polysialylation site, is not sufficient as an acceptor for ST8SiaII. The minimal polypeptide required for polysialylation contained Ig1 and Ig2, suggesting an important role for Ig2 as a docking site for ST8SiaII.

CADM1 isoforms differentially regulate human mast cell survival and homotypic adhesion

Cell adhesion molecule 1 (CADM1), expressed by human lung mast cells (HLMCs), mediates their adhesion to airway smooth muscle (ASM), and contributes to ASM-dependent HLMC proliferation and survival. CADM1 is expressed in alternatively spliced isoforms, but those present in HLMCs and their function are not known. We cloned three functional and one cryptic non-functional isoform with alternative splicing between exons 7/11 and 1/2, respectively, from HLMCs and human MC lines (HMC-1 and LAD2). Differentiated HLMCs and LAD2 cells expressed the functional isoform SP4 containing exons 7/8/11 (~80% of clones), as well as SP1 (exons 7/8/9/11) and a novel SP6 (exons 7/8/9/10/11). In contrast, immature HMC-1 cells expressed only functional SP4. SP4 overexpression in HMC-1 cells and HLMCs augmented homotypic adhesion to a greater extent than SP1 in various conditions. In contrast, CADM1 downregulation abolished homotypic adhesion, indicating that CADM1 is the sole receptor mediating mast cell aggregation. CADM1-mediated adhesion was enhanced by the presence of cell survival factors. SP1 overexpression in HMC-1 cells compromised survival compared to SP4 overexpression or control. CADM1 downregulation resulted in reduced viability and decreased expression of the pro-survival protein Mcl-1_L, but not Blc-2 or Bcl-X_L, and increased caspase-3/7 activity in both HMC-1 cells and HLMCs. This coincided with decreased basal Kit levels in HLMCs. In summary, human MCs express multiple CADM1 isoforms which exhibit differential regulation of survival and homotypic adhesion. The most highly expressed SP4 isoform is likely to contribute to MC aggregation and longevity in mastocytosis, and augment the pathophysiology of allergic diseases.

Clinical significance of CADM1/TSLC1/IgSF4 expression in adult T-cell leukemia/lymphoma

Cell adhesion molecule 1 (CADM1/TSLC1) was recently identified as a novel cell surface marker for adult T-cell leukemia/lymphoma (ATLL). In this study, we developed various antibodies as diagnostic tools to identify CADM1-positive ATLL leukemia cells. In flow cytometric analysis, the percentages of CD4(+)CADM1(+) double-positive cells correlated well with both the percentages of CD4(+)CD25(+) cells and with abnormal lymphocytes in the peripheral blood of patients with various types of ATLL. Moreover, the degree of CD4(+)CADM1(+) cells over 1% significantly correlated with the copy number of the human T-lymphotropic virus type 1 (HTLV-1) provirus in the peripheral blood of HTLV-1 carriers and ATLL patients. We also identified a soluble form of CADM1 in the peripheral blood of ATLL patients, and the expression levels of this form were correlated with the levels of soluble interleukin 2 receptor alpha. Moreover, lymphomas derived from ATLL were strongly and specifically stained with a CADM1 antibody. Thus, detection of CD4(+)CADM1(+) cells in the peripheral blood, measurement of serum levels of soluble CADM1 and immunohistochemical detection of CADM1 in lymphomas would be a useful set of markers for disease progression in ATLL and may aid in both the early diagnosis and measurement of treatment efficacy for ATLL.

Adhesion molecule CADM1 contributes to gap junctional communication among pancreatic islet α-cells and prevents their excessive secretion of glucagon

Cell adhesion molecule-1 (CADM1) is a recently identified adhesion molecule of pancreatic islet α-cells that mediates nerve-α-cell interactions via trans-homophilic binding and serves anatomical units for the autonomic control of glucagon secretion. CADM1 also mediates attachment between adjacent α-cells. Since gap junctional intercellular communication (GJIC) among islet cells is essential for islet hormone secretion, we examined whether CADM1 promotes GJIC among α-cells and subsequently participates in glucagon secretion regulation. Dye transfer assays using αTC6 mouse α-cells, which endogenously express CADM1, supported this possibility; efficient cell-to-cell spread of gap junction-permeable dye was detected in clusters of αTC6 cells transfected with nonspecific, but not with CADM1-targeting, siRNA. Immunocytochemical analysis of connexin 36, a major component of the gap junction among αTC6 cells, revealed that it was localized exclusively to the cell membrane in CADM1-non-targeted αTC6 cells, but diffusely to the cytoplasm in CADM1-targeted cells. Next, we incubated CADM1-targeted and non-targeted αTC6 cells in a medium containing 1 mM glucose and 200 mM arginine for 30 min to induce glucagon secretion, and found that the targeted cells secreted three times more glucagon than did the non-targeted. We conducted similar experiments using pancreatic islets that were freshly isolated from wild-type and CADM1-knockout mice, and expressed glucagon secretion as ratios relative to baseline values. The increase in ratio was larger in CADM1-knockout islets than in wild-type islets. These results suggest that CADM1 may serve as a volume limiter of glucagon secretion by sustaining α-cell attachment necessary for efficient GJIC.

Tumor suppressor cell adhesion molecule 1 (CADM1) is cleaved by a disintegrin and metalloprotease 10 (ADAM10) and subsequently cleaved by γ-secretase complex

Cell adhesion molecule 1 (CADM1) is a type I transmembrane glycoprotein expressed in various tissues. CADM1 is a cell adhesion molecule with many functions, including roles in tumor suppression, apoptosis, mast cell survival, synapse formation, and spermatogenesis. CADM1 undergoes membrane-proximal cleavage called shedding, but the sheddase and mechanisms of CADM1 proteolysis have not been reported. We determined the cleavage site involved in CADM1 shedding by LC/MS/MS and showed that CADM1 shedding occurred in the membrane fraction and was inhibited by tumor necrosis factor-α protease inhibitor-1 (TAPI-1). An siRNA experiment revealed that ADAM10 mediates endogenous CADM1 shedding. In addition, the membrane-bound fragment generated by shedding was further cleaved by γ-secretase and generated CADM1-intracellular domain (ICD) in a mechanism called regulated intramembrane proteolysis (RIP). These results clarify the detailed mechanism of membrane-proximal cleavage of CADM1, suggesting the possibility of RIP-mediated CADM1 signaling.

Enhanced nerve-mast cell interaction by a neuronal short isoform of cell adhesion molecule-1

Close apposition of nerve and mast cells is viewed as a functional unit of neuro-immune mechanisms, and it is sustained by trans-homophilic binding of cell adhesion molecule-1 (CADM1), an Ig superfamily member. Cerebral nerve-mast cell interaction might be developmentally modulated, because the alternative splicing pattern of four (a-d) types of CADM1 transcripts drastically changed during development of the mouse cerebrum: developing cerebrums expressed CADM1b and CADM1c exclusively, while mature cerebrums expressed CADM1d additionally and predominantly. To probe how individual isoforms are involved in nerve-mast cell interaction, Neuro2a neuroblastoma cells that express CADM1c endogenously were modified to express additionally either CADM1b (Neuro2a-CADM1b) or CADM1d (Neuro2a-CADM1d), and they were cocultured with mouse bone marrow-derived mast cells (BMMCs) and BMMC-derived cell line IC-2 cells, both of which expressed CADM1c. BMMCs were found to adhere to Neuro2a-CADM1d neurites more firmly than to Neuro2a-CADM1b neurites when the adhesive strengths were estimated from the femtosecond laser-induced impulsive forces minimally required for detaching BMMCs. GFP-tagging and crosslinking experiments revealed that the firmer adhesion site consisted of an assembly of CADM1d cis-homodimers. When Neuro2a cells were specifically activated by histamine, intracellular Ca(2+) concentration was increased in 63 and 38% of CADM1c-expressing IC-2 cells that attached to the CADM1d assembly site and elsewhere, respectively. These results indicate that CADM1d is a specific neuronal isoform that enhances nerve-mast cell interaction, and they suggest that nerve-mast cell interaction may be reinforced as the brain grows mature because CADM1d becomes predominant.

Cadm1 expression and function in the mouse lens

PURPOSE

The immunoglobulin superfamily member Cadm1 is a single-pass, type 1 membrane protein that mediates calcium-independent, cell-cell adhesion. Cadm1 has been implicated in tumor formation and synaptogenesis. A recent analysis of mouse lens cell membranes identified Cadm1 as a major constituent of the fiber cell membrane proteome. Here the authors examined the expression and function of Cadm1 in the mouse lens.

METHODS

Cadm1 expression was analyzed by Western blotting and immunofluorescence. The morphology of individual wild-type and Cadm1-null lens cells was visualized by confocal microscopy.

RESULTS

Cadm1 was present in epithelial and superficial fiber cells as a heavily glycosylated protein with an apparent molecular mass of ≈80 kDa. Analysis of proteins extracted from various strata of the lens indicated that Cadm1 was degraded during fiber cell differentiation, at approximately the same time as the lens organelles, an observation confirmed by confocal microscopy. In epithelial cells, Cadm1 was enriched in basolateral membranes, whereas, in fiber cells, expression was restricted to the lateral membranes. Lenses from Cadm1-null mice were of normal size and transparency. The three-dimensional morphology of the cells in the epithelial layer was unaltered in the absence of Cadm1. However, in contrast to wild-type lens fiber cells, Cadm1-null fiber cells had an irregular, highly undulating morphology.

CONCLUSIONS

Cadm1 is an abundant component of the lens fiber cell membrane. Although not essential for lens transparency, Cadm1 has an indispensable role in establishing and maintaining the characteristic three-dimensional architecture of the lens fiber cell mass.

Noncontact estimation of intercellular breaking force using a femtosecond laser impulse quantified by atomic force microscopy

When a femtosecond laser pulse (fsLP) is focused through an objective lens into a culture medium, an impulsive force (fsLP-IF) is generated that propagates from the laser focal point (O(f)) in a micron-sized space. This force can detach individual adherent cells without causing considerable cell damage. In this study, an fsLP-IF was reflected in the vibratory movement of an atomic force microscopy (AFM) cantilever. Based on the magnitude of the vibration and the geometrical relationship between O(f) and the cantilever, the fsLP-IF generated at O(f) was calculated as a unit of impulse [N-s]. This impulsive force broke adhesion molecule-mediated intercellular interactions in a manner that depended on the adhesion strength that was estimated by the cell aggregation assay. The force also broke the interactions between streptavidin-coated microspheres and a biotin-coated substrate with a measurement error of approximately 7%. These results suggest that fsLP-IF can be used to break intermolecular and intercellular interactions and estimate the adhesion strength. The fsLP-IF was used to break intercellular contacts in two biologically relevant cultures: a coculture of leukocytes seeded over on an endothelial cell monolayer, and a polarized monolayer culture of epithelial cells. The impulses needed to break leukocyte-endothelial and interepithelial interactions, which were calculated based on the geometrical relationship between O(f) and the adhesive interface, were on the order of 10(-13) and 10(-12) N-s, respectively. When the total impulse at O(f) is well-defined, fsLP-IF can be used to estimate the force required to break intercellular adhesions in a noncontact manner under biologically relevant conditions.

TSLC1 tumour-suppressor gene expression in canine mast cell tumours

Tumour suppressor in lung cancer-1 (TSLC1) is a tumour-suppressor gene coding for an adhesion molecule that is expressed by mast cells. Reduced TSLC1 expression is associated with a poor prognosis in several human tumours, and this study sought to investigate if TSLC1 expression could be used to predict outcome in dogs with mast cell tumours (MCTs). Sections of MCTs of different tumour grades from 45 dogs (Group 1) were immunohistochemically assessed for TSLC1 and Ki67 expression. In addition, 35 intermediate-grade MCTs (Group 2) from dogs with known clinical follow-up were immunohistochemically stained for TSLC1 and Ki67. The TSLC1 staining intensity was found to strongly inversely correlate with tumour grade for Group 1 (P = 0.002857). For Group 2 there was a trend towards dogs with lower TSLC1 scores being more likely to die from MCT-related disease (P = 0.058). The intensity of TSLC1 staining inversely correlated with Ki67 expression for both groups.

Expression of a soluble isoform of cell adhesion molecule 1 in the brain and its involvement in directional neurite outgrowth

Cell adhesion molecule 1 (CADM1), an immunoglobulin superfamily member, is expressed on superior cervical ganglion neurites and mediates cell-cell adhesion by trans-homophilic binding. In addition to the membrane-bound form, we have previously shown that a soluble form (sCADM1) generated by alternative splicing possesses a stop codon immediately downstream of the immunoglobulin-like domain. Here, we demonstrate the presence of sCADM1 in vivo and its possible role in neurite extension. sCADM1 appears to be a stromal protein because extracellular-restricted, but not intracellular-restricted, anti-CADM1 antibody stained stromal protein-rich extract from mouse brains. Murine plasmacytoma cells, P3U1, were modified to secrete sCADM1 fused with either immunoglobulin (Ig)G Fc portion (sCADM1-Fc) or its deletion form that lacks the immunoglobulin-like domain (DeltasCADM1-Fc). When P3U1 derivatives expressing sCADM1-Fc or DeltasCADM1-Fc were implanted into collagen gels, Fc-fused proteins were present more abundantly around the cells. Superior cervical ganglion neurons, parental P3U1, and either derivative were implanted into collagen gels separately, and co-cultured for 4 days. Bodian staining of the gel sections revealed that most superior cervical ganglion neurites turned toward the source of sCADM1-Fc, but not DeltasCADM1-Fc. Furthermore, immunofluorescence signals for sCADM1-Fc and membrane-bound CADM1 were co-localized on the neurite surface. These results show that sCADM1 appears to be involved in directional neurite extension by serving as an anchor to which membrane-bound CADM1 on the neurites can bind.

Association between dense CADM1 promoter methylation and reduced protein expression in high-grade CIN and cervical SCC

We previously showed that silencing of TSLC1, recently renamed CADM1, is functionally involved in high-risk HPV-mediated cervical carcinogenesis. CADM1 silencing often results from promoter methylation. Here, we determined the extent of CADM1 promoter methylation in cervical (pre)malignant lesions and its relation to anchorage-independent growth and gene silencing to select a CADM1-based methylation marker for identification of women at risk of cervical cancer. Methylation-specific PCRs targeting three regions within the CADM1 promoter were performed on high-risk HPV-containing cell lines, PBMCs, normal cervical smears, and (pre)malignant lesions. CADM1 protein expression in cervical tissues was analysed by immunohistochemistry. All statistical tests were two-sided. Density of methylation was associated with the degree of anchorage-independent growth and CADM1 gene silencing in vitro. In cervical squamous lesions, methylation frequency and density increased with severity of disease. Dense methylation (defined as >or= 2 methylated regions) increased from 5% in normal cervical samples to 30% in CIN3 lesions and 83% in squamous cell carcinomas (SCCs) and was significantly associated with decreased CADM1 protein expression (p < 0.00005). The frequency of dense methylation was significantly higher in >or= CIN3 compared with <or= CIN1 (p = 0.005), as well as in SCCs compared with adenocarcinomas (83% versus 23%; p = 0.002). Detection of dense CADM1 promoter methylation will contribute to the assembly of a valuable marker panel for the triage of high-risk HPV-positive women at risk of >or= CIN3.

SgIGSF is a novel biliary-epithelial cell adhesion molecule mediating duct/ductule development

Spermatogenic immunoglobulin superfamily (SgIGSF) is an intercellular adhesion molecule of the nectin-like family. While screening its tissue distribution, we found that it was expressed in fetal liver but not adult liver. In the present study, we examined which cells in developing and regenerating liver express SgIGSF via immunohistochemistry and Western blot analysis. In developing mouse liver, SgIGSF expression was transiently upregulated at perinatal ages and was restricted to the lateral membrane of biliary epithelial cells (BECs). In regenerating rat livers from the 2-acetylaminofluorene/partial hepatectomy model, SgIGSF was detected exclusively in oval cells that aligned in ductal and trabecular patterns by the second week posthepatectomy. In human livers, fetal and newborn bile ducts and cirrhotic bile ductules were clearly positive for SgIGSF, whereas disease-free adult bile ducts were negative. To investigate the role of SgIGSF in bile duct/ductule formation, we used an in vitro model in which rat hepatocyte aggregates embedded in collagen gels containing insulin and epidermal growth factor extend epithelial sheets and processes in the first week and form ductules within a month. The process and ductular cells were continuously positive for SgIGSF and cytokeratin 19, a BEC marker. When the aggregate culture was started in the presence of a function-blocking anti-SgIGSF antibody, the number of epithelial processes per aggregate was reduced by 80%.

CONCLUSION

We propose that SgIGSF is a novel and functional BEC adhesion molecule that is expressed for a limited time during active bile duct/ductule formation.

Heterophilic binding of the adhesion molecules poliovirus receptor and immunoglobulin superfamily 4A in the interaction between mouse spermatogenic and Sertoli cells

The cell adhesion protein immunoglobulin superfamily 4A (IGSF4A) is expressed on the surfaces of spermatogenic cells in the mouse testis. During spermatogenesis, IGSF4A is considered to bind to the surface of Sertoli cells in a heterophilic manner. To identify this unknown partner of IGSF4A, we generated rat monoclonal antibodies against the membrane proteins of mouse Sertoli cells grown in primary culture. Using these monoclonal antibodies, we isolated a clone that immunostained Sertoli cells and reacted with the product of immunoprecipitation of the homogenate of mouse testis with anti-IGSF4A antibody. Subsequently, to identify the Sertoli cell membrane protein that is recognized by this monoclonal antibody, we performed expression cloning of a cDNA library from the mouse testis. As a result, we identified poliovirus receptor (PVR), which is another IGSF-type cell adhesion molecule, as the binding partner of IGSF4A. The antibodies raised against PVR and IGSF4A immunoprecipitated both antigens in the homogenate of mouse testis. Immunoreactivity for PVR was present in Sertoli cells but not in spermatogenic cells at all stages of spermatogenesis. Overexpression of PVR in TM4, a mouse Sertoli cell line, increased more than three-fold its capacity to adhere to Tera-2, which is a human cell line that expresses IGSF4A. These findings suggest that the heterophilic binding of PVR to IGSF4A is responsible, at least in part, for the interaction between Sertoli and spermatogenic cells during mouse spermatogenesis.

Direct Interaction Between Nerves and Mast Cells Mediated by the SgIGSF/SynCAM Adhesion Molecule

Accumulating evidence has so far indicated that cross-talk between the nervous and immune systems plays a pivotal role in the pathophysiology of various diseases. As a prototypic demonstration of neuro-immune systems, the interaction between nerves and mast cells has been examined intensively. Anatomically, mast cells are often located in close proximity to nerves. Functionally, both cells communicate with each other in a bi-directional manner. Substance P released from nerves and proteases and cytokines from mast cells have proved to be important mediators in such communication. On the other hand, the molecules involved in membrane-membrane contacts between nerves and mast cells were largely unknown. In 2003, both cells were found to express the identical adhesion molecule, named SynCAM (synaptic cell adhesion molecule) or SgIGSF (spermatogenic immunoglobulin superfamily). Since SgIGSF/SynCAM binds homophilically, its involvement in nerve-mast cell interaction was examined in vitro. Superior cervical ganglia expressed SgIGSF/SynCAM along their neurites. Adhesion to these neurites of mast cells lacking SgIGSF/SynCAM was poor, and this was normalized by ectopic expression of SgIGSF/SynCAM. Moreover, SgIGSF/SynCAM-expressing mast cells were more competent in communicating with the neurites. Further understanding of the adhesion molecule-dependent interaction will be expected to open a new avenue in the field of neuro-immune cross-talk.

Bioinformatic characterization of the SynCAM family of immunoglobulin-like domain-containing adhesion molecules

SynCAM 1 (synaptic cell adhesion molecule 1, alternatively named Tslc1 and nectin-like protein 3) belongs to the immunoglobulin superfamily and is an adhesion molecule that operates in a variety of important contexts. Exemplary are its roles in adhesion at synapses in the central nervous system and as tumor suppressor. Here, I describe a family of genes homologous to SynCAM 1 comprising four genes found solely in vertebrates. All SynCAM genes encode proteins with three immunoglobulin-like domains of the V-set, C1-set, and I-set subclasses. Comparison of genomic with cDNA sequences provides their exon-intron structure. Alternative splicing generates isoforms of SynCAM proteins, and diverse SynCAM 1 and 2 isoforms are created in an extracellular region rich in predicted O-glycosylation sites. Protein interaction motifs in the cytosolic sequence are highly conserved among all four SynCAM proteins, indicating their critical functional role. These findings aim to facilitate the understanding of SynCAM genes and provide the framework to examine the physiological functions of this family of vertebrate-specific adhesion molecules.

The Spermatogenic Ig Superfamily/Synaptic Cell Adhesion Molecule Mast-Cell Adhesion Molecule Promotes Interaction with Nerves

Nerve-mast cell interaction is involved in both homeostatic and pathologic regulations. The molecules that sustain this association have not been identified. Because synaptic cell adhesion molecule (SynCAM), alternatively named spermatogenic Ig superfamily (SgIGSF), is expressed on both nerves and mast cells and because it binds homophilically, this molecule may be a candidate. To examine this possibility, mast cells with or without SgIGSF/SynCAM were cocultured with superior cervical ganglion neurons that express SgIGSF/SynCAM, and the number of mast cells attached to neurites was counted. The attachment of mast cells with SgIGSF/SynCAM, i.e., bone marrow-derived mast cells (BMMC) from wild-type mice, was inhibited dose-dependently by blocking Ab to SgIGSF/SynCAM. Mast cells without SgIGSF/SynCAM, i.e., BMMC from microphthalmia transcription factor-deficient mice and BMMC-derived cell line IC-2 cells, were defective in attachment to neurite, and transfection with SgIGSF/SynCAM normalized this. When the nerves were specifically activated by scorpion venom, one-quarter of the attached IC-2 cells mobilized Ca(2+) after a few dozen seconds, and ectopic SgIGSF/SynCAM doubled this proportion. At points of contact between neurites and wild-type BMMC, SgIGSF/SynCAM was locally concentrated in both neurites and BMMC. SgIGSF/SynCAM on mast cells appeared to predominantly mediate attachment and promote communication with nerves.

Distinct role for c-kit receptor tyrosine kinase and SgIGSF adhesion molecule in attachment of mast cells to fibroblasts

Binding of stem cell factor (SCF) to c-kit receptor tyrosine kinase (KIT) transduces signals essential for mast cell development via several pathways including activation of phosphatidylinositol 3-kinase (PI3-K). When cultured mast cells (CMCs) are cocultured with fibroblasts expressing membrane-bound SCF, CMCs with normal KIT adhere to fibroblasts and proliferate, whereas CMCs lacking cell surface expression of KIT do neither. Spermatogenic immunoglobulin superfamily (SgIGSF) was identified as another molecule that participates in mast cell adhesion to fibroblasts. Since the IC-2 mast cell line expressed neither KIT nor SgIGSF, the effect of ectopic expression of KIT or SgIGSF on the adhesion of IC-2 cells was examined. Three forms of KIT with the normal ectodomain were used: wild-type (KIT-WT) and two mutant types with a phenylalanine substitution at the tyrosine residue 719 (KIT-Y719F) or 821 (KIT-Y821F). KIT-Y719F does not activate PI3-K, whereas KIT-Y821F does. Firstly, KIT or SgIGSF was expressed singly in IC-2 cells. All three forms of KIT increased the adhesion level of IC-2 cells, whereas SgIGSF did not. Secondly, SgIGSF was coexpressed with one of the three forms of KIT. Coexpression of SgIGSF with KIT-WT or KIT-Y821F increased the adhesion level more markedly than was achieved by KIT-WT or KIT-Y821F alone. The effect was abolished by an antibody that blocks SCF-KIT interaction. In contrast, coexpression of SgIGSF with KIT-Y719F did not increase the adhesion level induced by KIT-Y719F alone. In adhesion of mast cells to fibroblasts, KIT appeared to behave as an adhesion molecule and as an activator of other adhesion molecules through phosphorylating PI3-K.