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

Possible Therapeutic Utility of anti-Cell Adhesion Molecule 1 Antibodies for Malignant Pleural Mesothelioma

Malignant pleural mesothelioma (MPM) is a highly aggressive malignant tumor, and the effective therapeutic drugs are limited. Thus, the establishment of novel therapeutic method is desired. Considerable proportion of MPMs are shown to express cell adhesion molecule 1 (CADM1), and to use CADM1 to bind to and proliferate on the pleural mesothelial surface, suggesting that CADM1 is a possible therapeutic target. Here, anti-CADM1 ectodomain chicken monoclonal antibodies, 3E1 and 9D2, were examined for their possible therapeutic utility. The full-length form of CADM1 was expressed in eight out of twelve human MPM cell lines. MPM cell lines were cultured on a confluent monolayer of mesothelial MeT-5A cells in the presence of 9D2, the neutralizing antibody. 9D2 suppressed the cell growth of CADM1-positive MPM cells with the loss and aggregation of CADM1 molecules on the MPM cell membrane, but not of CADM1-negative MPM cells. Co-addition of 3E1, lacking the neutralizing action, enhanced the growth-suppressive effect of 9D2. The two antibodies were tested as drug delivery vectors. 3E1 was converted into a humanized antibody (h3E1) and conjugated with monomethyl auristatin E (MMAE), a tubulin polymerization inhibitor. When the resulting h3E1–MMAE antibody-drug conjugate (ADC) was added to the standard cultures of CADM1-positive MPM cells, it suppressed the cell growth in a dose-dependent manner. Co-addition of 9D2 enhanced the growth-suppressive effect of h3E1–MMAE ADC. Anti-CADM1 ectodomain antibodies were suggested to serve as both antibody drugs and drug vectors in the treatment of MPM.

Expression of cell adhesion molecule 1 in human and murine endometrial glandular cells and its increase during the proliferative phase by estrogen and cell density

AIMS

Cell adhesion molecule 1 (CADM1) mediates interepithelial adhesion and is upregulated in crowded epithelial monolayers. This study aimed to examine CADM1 expression in the human endometrium of proliferative and secretory phases, and its transcriptional regulation in terms of estrogen stimuli and higher cellularity.

MAIN METHODS

CADM1 immunohistochemistry was conducted on endometrial tissues from women in their 40s and adult mice subcutaneously injected with estradiol following ovariectomy. Dual-luciferase reporter assays were conducted using human endometrial HEC-50B and HEC-1B cells and reporter plasmids harboring the human CADM1 3.4-kb promoter and its deleted and mutated forms. Cells were transfected with estrogen receptor α cDNA and reporter plasmids, and treated with estradiol before luciferase activity measurement.

KEY FINDINGS

Immunohistochemistry revealed that CADM1 was clearly expressed on the lateral membranes of the simple columnar glandular cells in the proliferative phase, but not in the secretory phase, from both women and the mouse model. The glandular cell density increased two-fold in the proliferative phase. Reporter assays identified three Sp1-binding sites as estradiol-responsive elements in the proximal region (from -223 to -84) of the transcription start site (+1) in HEC-50B cells. When the cell culture was started at eight-fold higher cell density, the CADM1 3.4-kb promoter was transactivated at a two-fold higher level in HEC-50B cells. This cell density effect was not detected for the CADM1 2.3-kb or 1.6-kb promoter.

SIGNIFICANCE

Two (proximal and distal) promoter regions are suggested to function additively to transactivate CADM1 in endometrial glandular cells that crowd in the proliferative phase.

Cell Adhesion Molecule 1 Contributes to Cell Survival in Crowded Epithelial Monolayers

When epithelial cells in vivo are stimulated to proliferate, they crowd and often grow in height. These processes are likely to implicate dynamic interactions among lateral membranous proteins, such as cell adhesion molecule 1 (CADM1), an immunoglobulin superfamily member. Pulmonary epithelial cell lines that express CADM1, named NCI-H441 and RLE-6TN, were grown to become overconfluent in the polarized 2D culture system, and were examined for the expression of CADM1. Western analyses showed that the CADM1 expression levels increased gradually up to 3 times in a cell density-dependent manner. Confocal microscopic observations revealed dense immunostaining for CADM1 on the lateral membrane. In the overconfluent monolayers, CADM1 knockdown was achieved by two methods using CADM1-targeting siRNA and an anti-CADM1 neutralizing antibody. Antibody treatment experiments were also done on 6 other epithelial cell lines expressing CADM1. The CADM1 expression levels were reduced roughly by half, in association with cell height decrease by half in 3 lines. TUNEL assays revealed that the CADM1 knockdown increased the proportion of TUNEL-positive apoptotic cells approximately 10 folds. Increased expression of CADM1 appeared to contribute to cell survival in crowded epithelial monolayers.

Comparison of SynCAM1/CADM1 PDZ interactions with MUPP1 using mammalian and bacterial pull-down systems

BACKGROUND

Synaptic cell adhesion molecule 1 (SynCAM1) also known as cell adhesion molecule 1 (CADM1) is a transmembrane cell adhesion protein that operates in a variety of physiological and pathological cellular contexts, and its interaction with the PDZ signalling protein MUPP1 have been previously implicated in autism spectrum disorder (ASD).

METHODS

We used in vitro pull-down systems based on the bacterial and mammalian extracts to study SynCAM1/CADM1 PDZ interactions with MUPP1 at various conditions.

RESULTS

So far, the investigated interaction of SynCAM1/CADM1 with MUPP1 has been mostly attributed to an unspecified region of MUPP1 PDZ domains 1-5 or exclusively to domain 2, using a yeast two-hybrid system. We also confirmed the single interaction of native synaptosomal CADM1 with PDZ domain 2. However, in this work, using recombinant proteins overexpressed in bacteria, we found an in vitro pull-down conditions in which all first five domains and, to a much lesser extent, MUPP1 domains 7 and 11 significantly interacted with the whole C-terminal domain of SynCAM1/CADM1. These PDZ interactions were confirmed by a pull-down assay using the last seven amino acids of the SynCAM1/CADM1 PDZ motif and using two fusion partners. Multiple interactions were additionally replicated using the continuous N-terminal MUPP1 protein fragment, which included first five PDZ domains, containing either intact or mutated domain 2.

CONCLUSIONS

We hypothesize that multiple interactions might exist in vivo, representing transient low-affinity interactions or alternative binding sites on MUPP1 when domain 2 is occupied or occluded by the interaction with other ligands. This newly identified interactions extend the potential genetic mutations, possibly affecting SynCAM1/CADM1/MUPP1 function. Possible reasons for the absence of some of the identified CADM1 PDZ interactions in mammalian extracts are discussed.

The Many Roles of Cell Adhesion Molecules in Hepatic Fibrosis

Fibrogenesis is a progressive scarring event resulting from disrupted regular wound healing due to repeated tissue injury and can end in organ failure, like in liver cirrhosis. The protagonists in this process, either liver-resident cells or patrolling leukocytes attracted to the site of tissue damage, interact with each other by soluble factors but also by direct cell–cell contact mediated by cell adhesion molecules. Since cell adhesion molecules also support binding to the extracellular matrix, they represent excellent biosensors, which allow cells to modulate their behavior based on changes in the surrounding microenvironment. In this review, we focus on selectins, cadherins, integrins and members of the immunoglobulin superfamily of adhesion molecules as well as some non-classical cell adhesion molecules in the context of hepatic fibrosis. We describe their liver-specific contributions to leukocyte recruitment, cell differentiation and survival, matrix remodeling or angiogenesis and touch on their suitability as targets in antifibrotic therapies.

Expression of cell adhesion molecule 1 in gastric neck and base glandular cells: Possible involvement in peritoneal dissemination of signet ring cells

AIMS

To determine cellular distribution of cell adhesion molecule 1 (CADM1), an immunoglobulin superfamily member, in the human oxyntic gastric mucosa, and to explore possible involvement in the development and peritoneal dissemination of signet ring cell (SRC) gastric carcinoma, which often develops in the oxyntic mucosa.

MAIN METHODS

Immunohistochemistry and double immunofluorescence were conducted on surgical specimens of normal and SRC-bearing stomachs and peritoneal metastatic foci of SRCs. KATO-III (lacking CADM1) and HSC-43 (expressing CADM1) SRC cell lines were cocultured on a Met-5A mesothelial or TIG-1 fibroblastic cell monolayer.

KEY FINDINGS

In the oxyntic gland, some neck and nearly all base glandular cells were CADM1-positive, and mucin 5AC-positive cells were CADM1-negative, while some mucin 6-positive neck cells were CADM1-positive. Foveolar-epithelial, parietal, and endocrine cells were CADM1-negative. CADM1 was negative in all SRC carcinomas that were confined within the submucosa (n = 11) and all but one of those invading deeper (n = 15). In contrast, peritoneal metastatic foci of SRCs were CADM1-positive in five out of eleven cases (P < 0.01). In the cocultures, exogenous CADM1 made KATO-III cells adhere more and grow faster on a Met-5A monolayer, not on TIG-1 monolayers. HSC-43 cells adhered more and grew faster on Met-5A than on TIG-1 monolayers, which were partly counteracted by a function-neutralizing anti-CADM1 antibody.

SIGNIFICANCE

Nearly all chief cells and a part of mucous neck cells express CADM1. SRC gastric carcinoma appears to emerge as a CADM1-negative tumor, but CADM1 may help SRCs develop peritoneal dissemination through promoting their adhesion and growth in the serosal tissue.

Modest Static Pressure Can Cause Enteric Nerve Degeneration Through Ectodomain Shedding of Cell Adhesion Molecule 1

Internal pressure is often involved in neurodegeneration; intraocular and intraventricular pressure elevations over 20-30 cmH₂O cause glaucoma and hydrocephalus, respectively. Here, we investigated enteric nerve degeneration in colon segments having tumor-induced stenosis and dilation and examined the mechanism of intraluminal pressure involvement. Histological examination revealed that the enteric ganglion neurons and neurites decreased in density in the dilated colons proportionate to the degree of dilation. Western blot analysis for cell adhesion molecule 1 (CADM1), an immunoglobulin superfamily member expressed in enteric neurons, revealed that ectodomain shedding of CADM1 increased proportionate to colon dilation, with increased production of its C-terminal fragment αCTF, a proapoptotic intracellular molecule. To link these neurodegenerative events to increased intraluminal pressure, we devised a two-chamber culture system wherein cells cultured on a semipermeable membrane were subjected to increased medium height (water pressure up to 50 cmH₂O). Mouse dorsal root ganglion (DRG) neurons were examined for expansion of their neurite networks in this system. As the pressure increased to 15, 30, and 45 cmH₂O, the neurites decreased in density and became thinner. In addition, CADM1 shedding increased with more αCTF production. CADM1 immunofluorescence and Mitotracker mitochondrial labeling revealed that as the pressure increased, neuritic CADM1 distribution changed from uniform to punctate staining patterns, and neuritic mitochondria decreased in number and appeared as course particles. These pressure-induced phenotypes were reproduced by exogenous expression of αCTF in standard DRG neuron cultures. Therefore, increases in colonic intraluminal pressure might cause enteric nerve degeneration by inducing CADM1 shedding and αCTF production.

Pathogenic Actions of Cell Adhesion Molecule 1 in Pulmonary Emphysema and Atopic Dermatitis

Cell adhesion mediated by adhesion molecules is of central importance in the maintenance of tissue homeostasis. Therefore, altered expression of adhesion molecules leads to the development of various tissue disorders involving cell activation, degeneration, and apoptosis. Nevertheless, it still remains unclear what initiates the altered expression of adhesion molecules and how the subsequent pathological cascades proceed. In this regard, cell adhesion molecule 1 (CADM1) is one of the candidates that is involved in the development of pathological lesions; it is an intercellular adhesion molecule that is expressed in various types of cells such as pulmonary cells, neurons, and mast cells. Recent studies have revealed that alterations in the transcriptional or post-transcriptional expressions of CADM1 correlate with the pathogenesis of pulmonary diseases and allergic diseases. In this review, we specifically focus on how CADM1 is involved in the development of pathological lesions in pulmonary emphysema and atopic dermatitis.

Increased ectodomain shedding of cell adhesion molecule 1 as a cause of type II alveolar epithelial cell apoptosis in patients with idiopathic interstitial pneumonia

BACKGROUND

Lung alveolar epithelial cell (AEC) apoptosis has attracted attention as an early pathogenic event in the development of idiopathic interstitial pneumonia (IIP); however, the causative mechanism remains unclear. Cell adhesion molecule 1 (CADM1) is an AEC adhesion molecule in the immunoglobulin superfamily. It generates a membrane-associated C-terminal fragment, αCTF, through protease-mediated ectodomain shedding, termed α-shedding. Increased CADM1 α-shedding contributes to AEC apoptosis in emphysematous lungs.

METHODS

Formalin-fixed, paraffin-embedded lung lobes (n = 39) from 36 autopsied patients with IIP were classified as acute IIP (n = 10), fibrosing-type nonspecific IIP (f-NSIP, n = 10), cryptogenic organizing IIP (n = 9), and usual IIP (n = 10). CADM1 expression in the lung sections was examined by western blotting and compared with control lungs (n = 10). The rate of CADM1 α-shedding was calculated as the relative amount of αCTF to full-length CADM1, and the full-length CADM1 level was estimated per epithelial cell by normalization to cytokeratin 7, a lung epithelial marker. Apoptotic AECs were detected by immunohistochemistry for single-stranded DNA (ssDNA). NCI-H441 and A549 human lung epithelial cells were transfected with small interfering RNA (siRNA) to silence CADM1 expression and analyzed by terminal nucleotide nick end labeling assays.

RESULTS

The rate of CADM1 α-shedding was higher in all IIP subtypes than in the control (P ≤ 0.019), and the full-length CADM1 level was lower in f-NSIP (P = 0.007). The α-shedding rate and full-length CADM1 level were correlated with each other (P = 0.015) and with the proportion of ssDNA-positive AECs (P ≤ 0.024). NCI-H441 cells transfected with siRNA exhibited a 61 % lower rate of expression of full-length CADM1 and a 17-fold increased proportion of apoptotic cells. Similar results were obtained with A549 cells.

CONCLUSIONS

CADM1 α-shedding appeared to be increased in all four IIP subtypes and consequently contributed to AEC apoptosis by decreasing the full-length CADM1 level. This mechanism particularly impacted f-NSIP. The molecular mechanism causing AEC apoptosis may be similar between IIP and emphysema.

Increased ectodomain shedding of cell adhesion molecule 1 from pancreatic islets in type 2 diabetic pancreata: correlation with hemoglobin A1c levels

Pulmonary emphysema and type 2 diabetes mellitus (T2DM), both caused by lifestyle factors, frequently concur. Respectively, the diseases affect lung alveolar and pancreatic islet cells, which express cell adhesion molecule 1 (CADM1), an immunoglobulin superfamily member. Protease-mediated ectodomain shedding of full-length CADM1 produces C-terminal fragments (CTFs) with proapoptotic activity. In emphysematous lungs, the CADM1 shedding rate and thus the level of CTFs in alveolar cells increase. In this study, CADM1 expression in islet cells was examined by western blotting. Protein was extracted from formalin-fixed, paraffin-embedded sections of pancreata isolated from patients with T2DM (n = 12) or from patients without pancreatic disease (n = 8) at autopsy. After adjusting for the number of islet cells present in the adjacent section, we found that full-length CADM1 decreased in T2DM islets, while ectodomain shedding increased. Hemoglobin A1c levels, measured when patients were alive, correlated inversely with full-length CADM1 levels (P = 0.041) and positively with ectodomain shedding rates (P = 0.001). In immunofluorescence images of T2DM islet cells, CADM1 was detected in the cytoplasm, but not on the cell membrane. Consistently, when MIN6-m9 mouse beta cells were treated with phorbol ester and trypsin to induce shedding, CADM1 immunostaining was diffuse in the cytoplasm. When a form of CTFs was exogenously expressed in MIN6-m9 cells, it localized diffusely in the cytoplasm and increased the number of apoptotic cells. These results suggest that increased CADM1 ectodomain shedding contributes to blood glucose dysregulation in T2DM by decreasing full-length CADM1 and producing CTFs that accumulate in the cytoplasm and promote apoptosis of beta cells. Thus, this study has identified a molecular alteration shared by pulmonary emphysema and T2DM.

Increased ectodomain shedding of lung epithelial cell adhesion molecule 1 as a cause of increased alveolar cell apoptosis in emphysema

Rationale

Alveolar epithelial cell apoptosis and protease/antiprotease imbalance based proteolysis play central roles in the pathogenesis of pulmonary emphysema but molecular mechanisms underlying these two events are not yet clearly understood. Cell adhesion molecule 1 (CADM1) is a lung epithelial cell adhesion molecule in the immunoglobulin superfamily. It generates two membrane associated C terminal fragments (CTFs), αCTF and βCTF, through protease mediated ectodomain shedding.

Objective

To explore the hypothesis that more CADM1-CTFs are generated in emphysematous lungs through enhanced ectodomain shedding, and cause increased apoptosis of alveolar epithelial cells.

Methods and results

Western blot analyses revealed that CADM1-CTFs increased in human emphysematous lungs in association with increased ectodomain shedding. Increased apoptosis of alveolar epithelial cells in emphysematous lungs was confirmed by terminal nucleotide nick end labelling (TUNEL) assays. NCI-H441 lung epithelial cells expressing mature CADM1 but not CTFs were induced to express αCTF both endogenously (by shedding inducers phorbol ester and trypsin) and exogenously (by transfection). Cell fractionation, immunofluorescence, mitochondrial membrane potentiometric JC-1 dye labelling and TUNEL assays revealed that CADM1-αCTF was localised to mitochondria where it decreased mitochondrial membrane potential and increased cell apoptosis. A mutation in the intracytoplasmic domain abrogated all three abilities of αCTF.

Conclusions

CADM1 ectodomain shedding appeared to cause alveolar cell apoptosis in emphysematous lungs by producing αCTF that accumulated in mitochondria. These data link proteolysis to apoptosis, which are two landmark events in emphysema.

Tumor necrosis factor-α promotes bile ductular transdifferentiation of mature rat hepatocytes in vitro

We previously showed that mature hepatocytes could transdifferentiate into bile ductular cells when placed in a collagen-rich microenvironment. To explore the mechanism of transdifferentiation, we examined whether inflammatory cytokines affected the phenotype of hepatocytes in a three-dimensional culture system. Spheroidal aggregates of rat hepatocytes were embedded within a type I collagen gel matrix and cultured in the presence of various cytokines. In the control, hepatocytes gradually lost expression of albumin, tyrosine aminotransferase, and hepatocyte nuclear factor (HNF)-4α, while aberrantly expressed bile ductular markers, including cytokeratin 19 (CK 19) and spermatogenic immunoglobulin superfamily (SgIGSF). Among the cytokines examined, tumor necrosis factor (TNF)-α inhibited expression of albumin and HNF-4α, both at mRNA and protein levels. After culturing for 2 weeks with TNF-α, hepatocytic spheroids were transformed into extensively branching tubular structures composed of CK 19- and SgIGSF-positive small cuboidal cells. These cells responded to secretin with an increase in secretion and expressed functional bile duct markers. TNF-α also induced the phosphorylation of Jun N-terminal kinase (JNK) and c-Jun, and the morphogenesis was inhibited by SP600125, a specific JNK inhibitor. Furthermore, in chronic rat liver injury induced by CCl(4) , ductular reaction in the centrilobular area demonstrated strong nuclear staining of phosphorylated c-Jun. Our results demonstrate that TNF-α promotes the ductular transdifferentiation of hepatocytes and suggest a role of TNF-α in the pathogenesis of ductular reaction.

Cell adhesion molecule 1 is a new osteoblastic cell adhesion molecule and a diagnostic marker for osteosarcoma

AIMS

An immunohistochemical screen for mouse embryos showed that cell adhesion molecule 1 (CADM1), which is an immunoglobulin superfamily member, was expressed in developing bones. Here, we determined the cell types expressing CADM1 and examined its usefulness in the differential diagnosis of osteosarcoma.

MAIN METHODS

Serial sections of murine developing mandibles were stained with anti-CADM1 antibody, by a coloring substrate reactive to alkaline phosphatase (ALP), a broad osteoblastic marker for preosteoblasts to osteoblasts, and by in situ hybridization for osteopontin (OPN), a marker for mature osteoblasts. CADM1 immunohistochemistry was also performed on human remodeling bones, osteosarcomas and other soft tissue tumors.

KEY FINDINGS

CADM1 immunohistochemistry for the mandible revealed that morphologically identifiable osteoblasts expressed CADM1 on their plasma membranes, but neither osteocytes nor bone lining cells did. At the mandibular margin, not only OPN-positive cells but also OPN-negative, ALP-positive cells were CADM1-positive, whereas inside the mandible, OPN-positive cells were often CADM1-negative. Clear membranous staining was detected in the majority of osteosarcomas (46/57), whereas only 13% (6/46) of the other soft tissue tumors were CADM1-positive (P<0.001).

SIGNIFICANCE

These results indicated that CADM1 was a novel osteoblastic adhesion molecule that is expressed transiently during osteoblastic maturation, and a useful diagnostic marker for osteosarcoma cells.

Temporal and Spatial Cellular Distribution of Neural Crest Derivatives and Alpha Cells during Islet Development

Recent studies have revealed that signals from neural crest (NC) derivatives regulate the mass, proliferation, and maturation of beta cells in developing fetal pancreas. However, little is known about the cellular distribution of NC derivatives during pancreatic development or the process whereby the developing islets are enclosed. We studied the temporal and spatial distribution of NC derivatives and endocrine cells at each developmental stage. At embryonic day 10.5 (E10.5) of mouse embryo, NC derivatives that migrated to the prospective pancreatic region were distributed in close proximity to pancreatic epithelial cells. As development advanced, most NC derivatives progressively surrounded endocrine rather than exocrine cells, and were distributed in closer proximity to alpha cells rather than to beta cells. At E20, approximately 70% of the NC derivatives enclosing endocrine cells were distributed in close proximity to alpha cells. Moreover, the expression of SynCAM, a Ca(2+)-independent homophilic trans-cell adhesion molecule, was confirmed from E16.5 on and was more remarkable at the cell boundaries of alpha cells and NC derivatives. These findings suggest that NC derivatives might be distributed in close proximity to alpha cells as a result of homophilic binding of SynCAM expressed by alpha cells and NC derivatives during islet development.

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.

Localization of Cadm2a and Cadm3 proteins during development of the zebrafish nervous system

Members of the Cadm/SynCAM/Necl/IGSF/TSLC family of cell adhesion molecules are known to have diverse functions during development of the nervous system, but information regarding their role during central nervous system (CNS) development in vivo is scarce. The rapid development of a relatively simple nervous system in larval zebrafish makes them a highly tractable model organism for studying gene function during nervous system development. An essential prerequisite for functional studies is a description of protein localization. To address this we have generated subtype-specific antibodies to two members of the zebrafish cell adhesion molecule family: cadm2a and cadm3. Using these novel antibodies we show that cadm3 and cadm2a are expressed throughout the nervous system of larval stage zebrafish. Particularly striking, and largely nonoverlapping expression of cadm2a and cadm3 is observed in the developing retina and spinal cord. Using in vitro binding assays we show that cadm2a and cadm3 bind heterophilically and preferentially to cadm1 and cadm4, respectively. These binding preferences are very similar to those seen for tetrapod Cadms but our study of protein localization suggests novel and diverse functions of cadms during nervous system development.

Developmental changes of cell adhesion molecule expression in the fetal mouse liver

Developmental changes of cell adhesion molecule expression, especially in nonparenchymal cells, have hardly ever been analyzed in the murine liver. The present study was undertaken to immunohistochemically examine the expression of NCAM, ICAM, VCAM, and N-cadherin during mouse liver development and in fetal liver cell cultures. NCAM was transiently expressed in mesenchymal cells of the septum transversum and sinusoidal cells in liver development. In vitro studies demonstrated that desmin-positive stellate cells expressed this cell adhesion molecule. NCAM expression in periportal biliary epithelial cells and connective tissue cells also coincided well with bile duct remodeling processes in the perinatal periods. Expression of ICAM and VCAM was transiently restricted to hepatoblasts, hepatocytes and hemopoietic cells in fetal stages. N-cadherin was expressed not only in hepatoblasts and hepatocytes, but also in nonparenchymal cells such as endothelial cells, stellate cells and connective tissue cells, however the expression was weak. These results suggest that each cell adhesion molecule may play an important role during development in hepatic histogenesis, including hepatoblast/hepatocyte-stellate cell interactions, hemopoiesis, and bile duct morphogenesis.

CADM1 interacts with Tiam1 and promotes invasive phenotype of human T-cell leukemia virus type I-transformed cells and adult T-cell leukemia cells

CADM1 encodes a multifunctional immunoglobulin-like cell adhesion molecule whose cytoplasmic domain contains a type II PSD95/Dlg/ZO-1 (PDZ)-binding motif (BM) for associating with other intracellular proteins. Although CADM1 lacks expression in T lymphocytes of healthy individuals, it is overexpressed in adult T-cell leukemia-lymphoma (ATL) cells. It has been suggested that the expression of CADM1 protein promotes infiltration of leukemic cells into various organs and tissues, which is one of the frequent clinical manifestations of ATL. Amino acid sequence alignment revealed that Tiam1 (T-lymphoma invasion and metastasis 1), a Rac-specific guanine nucleotide exchange factor, has a type II PDZ domain similar to those of membrane-associated guanylate kinase homologs (MAGUKs) that are known to bind to the PDZ-BM of CADM1. In this study, we demonstrated that the cytoplasmic domain of CADM1 directly interacted with the PDZ domain of Tiam1 and induced formation of lamellipodia through Rac activation in HTLV-I-transformed cell lines as well as ATL cell lines. Our results indicate that Tiam1 integrates signals from CADM1 to regulate the actin cytoskeleton through Rac activation, which may lead to tissue infiltration of leukemic cells in ATL patients.

Expression of contactin associated protein-like 2 in a subset of hepatic progenitor cell compartment identified by gene expression profiling in hepatitis B virus-positive cirrhosis

BACKGROUND

Hepatic progenitor cells (HPC), a cell compartment capable of differentiating into hepatocytic and biliary lineages, may give rise to the formation of intermediate hepatobiliary cells (IHBC) or ductular reactions (DR).

AIMS

The aim of this study was to analyse the gene expression profiles of DR in cirrhosis and further investigate novel proteins expressed by HPC and their intermediate progeny.

METHODS

DR in hepatitis B virus (HBV)-positive cirrhotic liver tissues adjacent to hepatocellular carcinoma and interlobular bile ducts (ILBDs) in normal liver tissues were isolated by laser capture microdissection and then subjected to microarray analysis. Differential gene expression patterns were verified by quantitative reverse transcriptase-polymerase chain reaction and immunohistochemistry on serial sections. HPC and their intermediate progeny were recognized by immunostaining with hepatocytic and biliary markers [HepPar1, cytokeratin (CK)7, CK19, neural cell adhesion molecule (NCAM), epithelial cell adhesion molecule (EpCAM)].

RESULTS

A total of 88 genes showed upregulation in DR compared with ILBDs. Gene ontology analyses revealed that these upregulated genes were mostly associated with cell adhesion, immune response and the metabolic process. Contactin associated protein-like 2 (CNTNAP2) was first confirmed to be a novel protein expressed in a subpopulation of DR that was positive for CK7, NCAM or EpCAM. In addition, immunoreactivity for CNTNAP2 was also noted in a subset of isolated CK7-positive HPC as well as some ductular IHBC positive for CK19 and HepPar1 in DR.

CONCLUSION

CNTNAP2 is specifically associated with the emergence of ductular populations and may be identified as a novel protein for defining a subset of HPC and their intermediate progeny in cirrhosis.

Necl2 regulates epidermal adhesion and wound repair

Differential expression of cell adhesion molecules regulates stem cell location, self-renewal and lineage selection under steady state conditions and during tissue repair. We show that the intercellular adhesion protein nectin-like molecule 2 (Necl2) is highly expressed in bulge stem cells of adult human and mouse hair follicles. Overexpression of Necl2 in cultured human keratinocytes led to upregulation of calcium/calmodulin-associated Ser/Thr kinase (CASK), increased calcium-independent intercellular adhesion, and inhibition of cell motility and in vitro wound healing. Although the rate of cell proliferation was reduced, terminal differentiation was unaffected. To assess the role of Necl2 in vivo, we examined the epidermis of Necl2-null mice and developed transgenic mice that expressed Necl2 in the basal layer of murine epidermis. Necl2 overexpression led to a reduction in S-phase cells and an increase in quiescent cells retaining DNA label in the bulge. Although epidermal homeostasis appeared normal in both transgenic and knockout mice, wound healing was markedly delayed. Necl2 overexpression resulted in reduced proliferation and increased levels of CASK and E-cadherin at the leading edge of healing wounds, consistent with its effects in culture. Our results demonstrate that Necl2 is involved in regulating epidermal stem cell quiescence and location.

Mechanisms of liver development: concepts for understanding liver disorders and design of novel therapies

The study of liver development has significantly contributed to developmental concepts about morphogenesis and differentiation of other organs. Knowledge of the mechanisms that regulate hepatic epithelial cell differentiation has been essential in creating efficient cell culture protocols for programmed differentiation of stem cells to hepatocytes as well as developing cell transplantation therapies. Such knowledge also provides a basis for the understanding of human congenital diseases. Importantly, much of our understanding of organ development has arisen from analyses of patients with liver deficiencies. We review how the liver develops in the embryo and discuss the concepts that operate during this process. We focus on the mechanisms that control the differentiation and organization of the hepatocytes and cholangiocytes and refer to other reviews for the development of nonepithelial tissue in the liver. Much progress in the characterization of liver development has been the result of genetic studies of human diseases; gaining a better understanding of these mechanisms could lead to new therapeutic approaches for patients with liver disorders.

Nerve-mast cell and smooth muscle-mast cell interaction mediated by cell adhesion molecule-1, CADM1

Mast cells are a native composer of connective tissue of the skin dermis and intestinal and respiratory mucosa. Independent lines of accumulated evidence indicate the existence of an intensive bidirectional crosstalk between mast cells and sensory nerves and suggest that mast cells and sensory nerves may be viewed as a functional unit, which could be of crucial importance in neuroimmunological pathways. Mast cells appear to have a property of influencing smooth muscle function via not only such nerve-mast cell effects, but also direct pathways. In bronchial asthma, mast cells infiltrate the airway smooth muscle layer, and interact directly with smooth muscle cells, suggesting pathogenic roles for mast cells in airway obstruction. Current studies on mast cell biology identified a novel adhesion molecule of mast cells, namely cell adhesion molecule-1, CADM1. This molecule is unique, because it serves as not only simple glue but also appears to promote functional communication between nerve and mast cells and between smooth muscle and mast cells.

Six cadm/SynCAM genes are expressed in the nervous system of developing zebrafish

The Cadm (cell adhesion molecule) family of cell adhesion molecules (also known as IGSF4, SynCAM, Necl and TSLC) has been implicated in a multitude of physiological and pathological processes, such as spermatogenesis, synapse formation and lung cancer. The precise mechanisms by which these adhesion molecules mediate these diverse functions remain unknown. To investigate mechanisms of action of these molecules during development, we have identified zebrafish orthologs of Cadm family members and have examined their expression patterns during development and in the adult. Zebrafish possess six cadm genes. Sequence comparisons and phylogenetic analysis suggest that four of the zebrafish cadm genes represent duplicates of two tetrapod Cadm genes, whereas the other two cadm genes are single orthologs of tetrapod Cadm genes. All six zebrafish cadms are expressed throughout the nervous system both during development and in the adult. The spatial and temporal patterns of expression suggest multiple roles for Cadms during nervous system development.

Cell adhesion molecule 1 is a novel pancreatic-islet cell adhesion molecule that mediates nerve-islet cell interactions

BACKGROUND & AIMS

Cell adhesion molecule 1 (CADM1), mediates nerve-mast cell attachment and communication through homophilic binding. An immunohistochemical screen showed that CADM1 is expressed in pancreatic islets. Here, we determined the cell types expressing CADM1 and examined its role in nerve-islet cell interactions.

METHODS

Immunohistochemistry and double-staining immunofluorescence were performed on murine and human pancreases and on islet cell tumors (ICTs). alphaTC6 cells, a murine alpha cell line, were cultured on neurite networks of superior cervical ganglia. Neurite-alphaTC6 cell attachment and communication were examined after nerves were activated specifically by scorpion venom.

RESULTS

CADM1 was expressed on the plasma membrane in all 4 major types of islet cells, alpha, beta, D, and pancreatic polypeptide in human beings, but primarily in alpha cells in mice. In cocultures, alphaTC6 cell to neurite attachment was inhibited dose-dependently by an anti-CADM1 function-blocking antibody. In response to scorpion venom-evoked nerve activation, 36% of the alphaTC6 cells mobilized Ca(2+), and introduction of a CADM1-targeting small interfering RNA reduced the fraction of responding cells to 7%. In 21 human ICTs, CADM1 was present in the plasma membrane of 7, and the others were negative for CADM1. Six of the CADM1-expressing tumors were functional hormonally, whereas all but 2 of the CADM1-negative tumors were nonfunctional (P = .0032).

CONCLUSIONS

CADM1 is a novel islet cell adhesion molecule mediating nerve-islet cell interactions. The strong correlation between CADM1 expression and hormonally functional phenotypes suggests that CADM1 is involved in hormone secretion from ICTs.

Expression of cell adhesion molecule 1 in malignant pleural mesothelioma as a cause of efficient adhesion and growth on mesothelium

Cell adhesion molecule 1 (CADM1), formerly referred to as SgIGSF, TSLC1, or Necl-2, has been characterized as a mast-cell adhesion molecule that mediates efficient interactions with mesothelial cells. Here, we examined whether CADM1 might be involved in the diffuse tumor growth over the pleural surface that characterizes malignant pleural mesothelioma (MPM). Immunohistochemical and western blot analyses revealed that 14 (25%) of 57 MPMs expressed the full-length form of CADM1 on the cell membrane, but non-neoplastic mesothelial cells did not express it at all. The majority of available MPM cell lines also expressed the full-length form of CADM1. We compared CADM1-positive and -negative MPM cells in culture within soft agar and in coculture on mesothelial or fibroblastic monolayers. Within soft agar, CADM1-negative MPM cells were capable of forming colonies, whereas CADM1-positive cells were not, suggesting that CADM1 is a potential tumor suppressor of MPM, consistent with the past characterization of this molecule in other types of tumors. However, in coculture on mesothelial cell monolayers lacking full-length CADM1, CADM1-positive MPM cells spread more widely and grew more quickly, whereas the CADM1-negative cells piled up. Transfection of the CADM1-negative cells with CADM1 cDNA caused them to behave like the CADM1-positive cells, with faster, more widespread growth. These phenotypic differences were not detectable in cocultures on lung fibroblastic monolayers, in which all MPM cells grew much more slowly than on mesothelial cells, irrespective of CADM1 positivity. CADM1 thus appears to mediate efficient adhesion and growth of MPM cells specifically on mesothelial cells, probably via trans-heterophilic binding, and thus may be involved in the manifestation of a considerable subset of MPMs as diffusely growing tumors disseminated over the pleural surface.

Activation of stem cells in hepatic diseases

The liver has enormous regenerative capacity. Following acute liver injury, hepatocyte division regenerates the parenchyma but, if this capacity is overwhelmed during massive or chronic liver injury, the intrinsic hepatic progenitor cells (HPCs) termed oval cells are activated. These HPCs are bipotential and can regenerate both biliary epithelia and hepatocytes. Multiple signalling pathways contribute to the complex mechanism controlling the behaviour of the HPCs. These signals are delivered primarily by the surrounding microenvironment. During liver disease, stem cells extrinsic to the liver are activated and bone-marrow-derived cells play a role in the generation of fibrosis during liver injury and its resolution. Here, we review our current understanding of the role of stem cells during liver disease and their mechanisms of activation.