Identification and characterization of the human cell adhesion molecule contactin

Proteinuria is a key to suspect autoimmune nodopathies

BACKGROUND AND PURPOSE

Reports of patients who have autoimmune nodopathies concurrent with nephrotic syndrome are increasing. We investigated whether proteinuria could be a biomarker of autoimmune nodopathies.

METHODS

Qualitative urinalysis results were retrospectively obtained from 69 patients who were diagnosed with chronic inflammatory demyelinating polyneuropathy (CIDP) at a hospital in Japan. Proteinuria was graded as mild to severe (i.e., mild, 30-99; moderate, 100-299; severe, 300 mg/dL or more) according to the results of the urine dipstick test. Autoantibodies against the paranodal proteins contactin 1 (CNTN1), neurofascin 155 (NF155), and contactin-associated protein 1 (Caspr1) and the nodal protein neurofascin 186 (NF186) were measured, and the predominant IgG subclass was determined by enzyme-linked immunosorbent assay in sera from the 69 patients.

RESULTS

Four patients (6%), five patients (7%), and one (1%) patient were positive for anti-CNTN1, anti-NF155, and anti-Caspr1 IgG4 antibodies, respectively. No patients had IgG4 antibodies against NF186. Proteinuria of mild or greater levels was found in three patients with anti-CNTN1 IgG4 and two patients with anti-NF155 IgG4 antibodies. The autoantibody-positive patients more frequently had proteinuria of mild or greater levels than the seronegative patients (p = 0.01).

CONCLUSIONS

Proteinuria is a possible biomarker of autoimmune nodopathies associated with autoantibodies targeting CNTN1 or NF155. Urinalysis results should be carefully checked for quick differentiation of autoimmune nodopathies from CIDP. Patients who present with nephrotic syndrome should be tested for anti-CNTN1 IgG4 antibodies, and patients who exhibit mild proteinuria should be tested for anti-NF155 IgG4 antibodies.

Characteristics of anti-contactin1 antibody positive autoimmune nodopathies combined with membranous nephropathy

BACKGROUND

Autoimmune nodopathy (AN) is a very rare new disease entity, especially when combined with membranous nephropathy (MN).

METHODS

Antibodies against nodal-paranodal cell adhesion molecules in the serum were detected using cell-based assays. Antibody subtypes against contactin-1 (CNTN1) were confirmed. Cases of anti-CNTN1 antibody-positive AN with and without MN were retrieved through a literature search to compare clinical and electrophysiological characteristics.

RESULTS

A 65-year-old male patient with MN developed limb numbness and weakness, along with walking instability. Serum CNTN1 antibodies were positive, primarily those of the IgG4 subtype. Electromyography showed prominent demyelination patterns in both the proximal and distal segments of the nerves compared to the middle nerve trunk. Magnetic resonance imaging revealed enlargement of the bilateral brachial and lumbosacral plexuses and local hyperintensity of the right C5-C6 nerve roots. Thirty-five cases with anti-CNTN1 antibody-positive AN with MN and 51 cases with anti-CNTN1 antibody-positive AN without MN were compared. Furthermore, the proportion of patients with MN combined with AN presenting with acute or subacute onset was higher than that observed in the MN without AN group. Nevertheless, no substantial differences were noted between the two groups concerning the clinical and electrophysiological characteristics, which were mainly elderly men, manifested as sensory ataxia, IgG4 antibody subtype, electrophysiological demyelination, and a certain effect on immunotherapy.

CONCLUSION

In cases of electrophysiological manifestation of demyelinating peripheral neuropathy, especially in distal and poximal segments of nerves, AN should be considered, and further screening for renal function should be performed. Concomitant MN does not aggravate or alleviate peripheral nerve symptoms.

Neuronal Proteins as Antigenic Targets in Membranous Nephropathy

CONTEXT

The discovery of new target antigens in membranous nephropathy (MN) has revealed new disease phenotypes and, in some cases, has suggested mechanisms of disease shared by two concurrent autoimmune diseases. Subject of Review: Several recent reports and an accompanying editorial describe the association of anti-contactin-1 (CNTN1) autoantibodies of the IgG4 subclass with a novel subtype of MN that co-occurs with a form of chronic inflammatory demyelinating polyradiculoneuropathy caused by anti-CNTN1 antibodies. CNTN1, the cellular source of which is still undetermined, is identified as the target antigen in the kidney since it is present within glomerular subepithelial deposits and anti-CNTN1 IgG4 antibodies can be eluted from the corresponding kidney biopsy tissue. Second Opinion: These new reports reinforce recent findings that many proteins targeted in several other types of primary and secondary MN are proteins whose expression is shared by podocytes and neurons. While complement-mediated podocyte damage represents a well-established paradigm in the pathogenesis of MN, interference with the normal functions of these shared proteins by autoantibodies should be considered as another potential mechanism of glomerular injury to be explored in future research.

Contactin 1, a Potential New Antigen Target in Membranous Nephropathy: A Case Report

Several novel antigens have recently been characterized in membranous nephropathy (MN), but those involved in the rare cases of MN associated with inflammatory neuropathies remain elusive. Although several antibodies have been identified in the serum, there is no evidence so far for their deposition in glomeruli. We report the case of a 73-year-old woman who was referred because of subacute onset of proximal asymmetric lower limb weakness together with ataxic gait. She was diagnosed with inflammatory neuropathy. Testing showed an estimated glomerular filtration rate of 73mL/min/1.73m², hypoalbuminemia (2.89g/dL), and proteinuria (3.6g/d). Autoantibodies (antinuclear antibody, anti-extractable nuclear antigen antibody, anti-double stranded DNA antibody, lupus anticoagulant, anticardiolipin antibody, antineutrophil cytoplasmic antibody) were undetectable. Serum immunoglobulin and complement levels were normal. A kidney biopsy with electron microscopy examination showed a classical picture of MN. Testing for antibodies to phospholipase A₂ receptor (PLA₂R) gave negative results in the serum, and PLA₂R and THSD7A antigens were not detected in kidney tissue. Anti-contactin 1 (CNTN1) antibody was detected by enzyme-linked immunosorbent assay at a 1:100 dilution of serum and shown to be mostly of IgG4 subclass by Western blot. CNTN1 antigen was colocalized with IgG4 within immune deposits by confocal microscopy. This observation suggests a pathophysiological link between inflammatory neuropathies and MN. CNTN1 should be considered as a potential candidate antigen involved in MN and tested in PLA₂R-negative forms associated with inflammatory neuropathies.

Rituximab Responsive Relapsing-Remitting IgG4 Anticontactin 1 Chronic Inflammatory Demyelinating Polyradiculoneuropathy Associated With Membranous Nephropathy: A Case Description and Brief Review

ABSTRACT

Nodal/paranodal IgG4-related chronic inflammatory demyelinating polyradiculoneuropathy (CIDP) rarely involves anticontactin (CNTN1) subtype and exceptionally complicates with nephrotic syndrome. A 65-year-old man developed weakness, facial palsy, and balance impairment; after spontaneous recovery, he severely relapsed 1 month later. Electroneuromyography confirmed CIDP. Proteinorachy (462 mg/dL; N < 45), proteinuria (3.5 g/g creatine), and biopsy-proven membranous nephropathy were identified. Intravenous immunoglobulins, corticosteroids, and plasmaphereses did not allow recovery. Anti-CNTN1 immunoglobulin G4 (IgG4) assay was positive. Rituximab (375 mg/m2/week, 4 weeks) provided obvious improvement. Relapsing-remitting anti-CNTN1-CIDP co-occurring with nephrotic syndrome is exceptional, and its identification is essential because efficient therapies such as rituximab are available for this severe condition.

Anti-Neuronal IgG4 Autoimmune Diseases and IgG4-Related Diseases May Not Be Part of the Same Spectrum: A Comparative Study

Background

IgG4 is associated with two emerging groups of rare diseases: 1) IgG4 autoimmune diseases (IgG4-AID) and 2) IgG4-related diseases (IgG4-RLD). Anti-neuronal IgG4-AID include MuSK myasthenia gravis, LGI1- and Caspr2-encephalitis and autoimmune nodo-/paranodopathies (CNTN1/Caspr1 or NF155 antibodies). IgG4-RLD is a multiorgan disease hallmarked by tissue-destructive fibrotic lesions with lymphocyte and IgG4 plasma cell infiltrates and increased serum IgG4 concentrations. It is unclear whether IgG4-AID and IgG4-RLD share relevant clinical and immunopathological features.

Methods

We collected and analyzed clinical, serological, and histopathological data in 50 patients with anti-neuronal IgG4-AID and 19 patients with IgG4-RLD.

Results

A significantly higher proportion of IgG4-RLD patients had serum IgG4 elevation when compared to IgG4-AID patients (52.63% vs. 16%, p = .004). Moreover, those IgG4-AID patients with elevated IgG4 did not meet the diagnostic criteria of IgG4-RLD, and their autoantibody titers did not correlate with their serum IgG4 concentrations. In addition, patients with IgG4-RLD were negative for anti-neuronal/neuromuscular autoantibodies and among these patients, men showed a significantly higher propensity for IgG4 elevation, when compared to women (p = .005). Last, a kidney biopsy from a patient with autoimmune paranodopathy due to CNTN1/Caspr1-complex IgG4 autoantibodies and concomitant nephrotic syndrome did not show fibrosis or IgG4+ plasma cells, which are diagnostic hallmarks of IgG4-RLD.

Conclusion

Our observations suggest that anti-neuronal IgG4-AID and IgG4-RLD are most likely distinct disease entities.

When contactin antibodies hit the podocyte: a new neurorenal syndrome

Membranous nephropathy can be associated with various etiologies and antigens. In this issue of Kidney International, Le Quintrec et al. described contactin-1 cell adhesion molecule as a novel target antigen shared by the peripheral nerve and podocyte in patients with neurological disease and membranous nephropathy.

Characteristics of Anti-Contactin1 Antibody-Associated Autoimmune Nodopathies With Concomitant Membranous Nephropathy

Background

The concurrence of anti-contactin 1 (CNTN1) antibody-associated chronic inflammatory demyelinating polyneuropathy (CIDP) and membranous nephropathy (MN) has previously been reported in the literature. CIDP with autoantibodies against paranodal proteins are defined as autoimmune nodopathies (AN) in the latest research. In view of the unclear relationship between CIDP and MN, we performed a case study and literature review to investigate the clinical characteristics of anti-CNTN antibody-associated AN with MN.

Methods

We detected antibodies against NF155, NF186, CNTN1, CNTN2, CASPR1 and PLA2R in blood samples of a patient with clinically manifested MN and concomitant peripheral neuropathy via double immunofluorescence staining and conducted a quantitative measurement of anti-PLA2R IgG antibodies via enzyme-linked immunosorbent assay (ELISA). Case reports of anti-CNTN1 antibody-associated AN, anti-CNTN1 antibody-associated AN with MN, and CIDP with MN were retrieved through a literature search for a comparative analysis of clinical characteristics. The cases were grouped according to the chronological order of CIDP and MN onset for the comparison of clinical characteristics.

Results

A 57-year-old man with anti-PLA2R positive MN was admitted to the hospital due to limb numbness, weakness, and proprioceptive sensory disorder. He was diagnosed with anti-CNTN1 antibody-associated AN and recovered well after immunotherapy. Our literature search returned 22 cases of CIDP with MN that occurred before, after, or concurrently with CIDP. Good responses were achieved with early single-agent or combination immunotherapy, but eight out of the 22 patients with CIDP and concomitant MN ultimately developed different motor sequelae. Five patients had anti-CNTN1 antibody-associated AN with MN. Among these patients, males accounted for the majority of cases (male:female=4:1), the mean age at onset was late (60.2 ± 15.7 years, range 43–78 years), and 40% had acute to subacute onset. Clinical manifestations included sensory-motor neuropathy, sensory ataxia caused by proprioceptive impairment, and elevated cerebrospinal fluid protein levels.

Conclusion

The age at onset of CIDP with MN was earlier than that of anti-CNTN1 antibody-associated AN. MN may occur before, after or concurrently with CIDP. The early detection and isotyping of anti-CNTN1 and anti-PLA2R antibodies and the monitoring of isotype switching may be essential for suspected CIDP patients.

Contactin-1 is a novel target antigen in membranous nephropathy associated with chronic inflammatory demyelinating polyneuropathy

Primary membranous nephropathy (MN) is an autoimmune glomerular disease in which autoantibodies are directed against podocyte proteins. In about 80% of cases the main targeted antigen is the phospholipase A2 receptor 1 (PLA2R1). Anti-PLA2R1 antibodies are mainly immunoglobulin G type 4 (IgG4). However, the antigenic target remains to be defined in 20% of cases. MN can be associated with chronic inflammatory demyelinating polyneuropathy, an autoimmune disease of the peripheral nervous system where a common antigenic target has yet to be identified. To ascertain a possible novel target antigen, we analyzed kidney biopsies from five patients positive for anti-contactin 1 antibodies and presenting with MN combined with chronic inflammatory demyelinating polyneuropathy. Eluted IgG from biopsy sections against contactin 1 and nerve tissue were screened. Western blot revealed contactin 1 expression in normal kidney glomeruli. Confocal microscopic analysis showed the presence and colocalization of contactin 1 and IgG4 on the glomerular basement membrane of these patients. Glomerular contactin 1 was absent in patients with anti-PLA2R1-associated MN or membranous lupus nephritis or a healthy control. The eluted IgG from contactin 1-positive biopsy sections but not the IgG eluted from patients with PLA2R1 MN bound contactin 1 with the main eluted subclass IgG4. Eluted IgG could bind paranodal tissue (myelinated axon) and colocalized with commercial anti-contactin 1 antibody. Thus, contactin 1 is a novel common antigenic target in MN associated with chronic inflammatory demyelinating polyneuropathy. However, the precise pathophysiology remains to be elucidated.

Mechanisms of Primary Membranous Nephropathy

Membranous nephropathy (MN) is an autoimmune disease of the kidney glomerulus and one of the leading causes of nephrotic syndrome. The disease exhibits heterogenous outcomes with approximately 30% of cases progressing to end-stage renal disease. The clinical management of MN has steadily advanced owing to the identification of autoantibodies to the phospholipase A2 receptor (PLA2R) in 2009 and thrombospondin domain-containing 7A (THSD7A) in 2014 on the podocyte surface. Approximately 50–80% and 3–5% of primary MN (PMN) cases are associated with either anti-PLA2R or anti-THSD7A antibodies, respectively. The presence of these autoantibodies is used for MN diagnosis; antibody levels correlate with disease severity and possess significant biomarker values in monitoring disease progression and treatment response. Importantly, both autoantibodies are causative to MN. Additionally, evidence is emerging that NELL-1 is associated with 5–10% of PMN cases that are PLA2R- and THSD7A-negative, which moves us one step closer to mapping out the full spectrum of PMN antigens. Recent developments suggest exostosin 1 (EXT1), EXT2, NELL-1, and contactin 1 (CNTN1) are associated with MN. Genetic factors and other mechanisms are in place to regulate these factors and may contribute to MN pathogenesis. This review will discuss recent developments over the past 5 years.

Update on IgG4-mediated autoimmune diseases: New insights and new family members

Antibodies of IgG4 subclass are exceptional players of the immune system, as they are considered to be immunologically inert and functionally monovalent, and as such may be part of classical tolerance mechanisms. IgG4 antibodies are found in a range of different diseases, including IgG4-related diseases, allergy, cancer, rheumatoid arthritis, helminth infection and IgG4 autoimmune diseases, where they may be pathogenic or protective. IgG4 autoimmune diseases are an emerging new group of diseases that are characterized by pathogenic, antigen-specific autoantibodies of IgG4 subclass, such as MuSK myasthenia gravis, pemphigus vulgaris and thrombotic thrombocytopenic purpura. The list of IgG4 autoantigens is rapidly growing and to date contains 29 candidate antigens. Interestingly, IgG4 autoimmune diseases are restricted to four distinct organs: 1) the central and peripheral nervous system, 2) the kidney, 3) the skin and mucous membranes and 4) the vascular system and soluble antigens in the blood circulation. The pathogenicity of IgG4 can be validated using our classification system, and is usually excerted by functional blocking of protein-protein interaction.

Antibodies against the node of Ranvier: a real-life evaluation of incidence, clinical features and response to treatment based on a prospective analysis of 1500 sera

INTRODUCTION

IgG4 antibodies against neurofascin (Nfasc155 and Nfasc140/186), contactin (CNTN1) and contactin-associated protein (Caspr1) are described in specific subtypes of chronic inflammatory demyelinating polyradiculoneuropathy (CIDP). Our objective was to assess, in a real-life practice, the incidence, the clinical features and the response to treatment of these forms of CIDP.

METHODS

1500 sera of patients suspected of having CIDP from France, Belgium and Switzerland were prospectively tested using a flow cytometry technique. The characteristics of patients with antibodies against the node of Ranvier were compared to 100 seronegative CIDP from our department.

RESULTS

IgG4 antibodies against Nfasc155, CNTN1, and Caspr1 were, respectively, detected in 15 (prevalence 1%), 10 (0.7%) and 2 (0.2%) sera. Antibodies specific of the Nfasc140/186 were not detected. All subjects with antibodies against the node of Ranvier fulfilled diagnostic criteria for CIDP. CIDP with anti-Nfasc155 were younger, had more sensory ataxia and postural tremor than seronegative CIDP. CIDP with anti-CNTN1 had more frequent subacute onset and facial paralysis, commoner renal involvement with membranous glomerulonephritis and greater disability, than seronegative CIDP. CIDP with anti-Caspr1 had more frequent respiratory failure and cranial nerve involvement but not more neuropathic pain than seronegative CIDP. Intravenous immunoglobulins were ineffective in most seropositive patients. Rituximab produced dramatic improvement in disability and decreased antibodies titres in 13 seropositive patients (8 with anti-Nfasc155 and 5 with anti-CNTN1 antibodies).

CONCLUSIONS

Although rare, anti-paranodal antibodies are clinically valuable, because they are associated with specific phenotypes and therapeutic response.

Distinguish CIDP with autoantibody from that without autoantibody: pathogenesis, histopathology, and clinical features

Chronic inflammatory demyelinating polyradiculoneuropathy (CIDP) is considered to be an immune-mediated heterogeneous disease involving cellular and humoral immunity. In recent years, autoantibodies against nodal/paranodal protein neurofascin155 (NF155), neurofascin186 (NF186), contactin-1 (CNTN1), and contactin-associated protein 1 (CASPR1) have been identified in a small subset of patients with CIDP, which disrupt axo-glial interactions at nodes/paranodes. Although CIDP electrodiagnosis was made in patients with anti-nodal/paranodal component autoantibodies, macrophage-induced demyelination, the characteristic of typical CIDP, was not observed. Apart from specific histopathology, the pathogenic mechanisms and clinical manifestations of CIDP with autoantibody are also distinct. We herein compared pathogenesis, histopathology, clinical manifestations, and therapeutic response in CIDP with autoantibody vs. CIDP without autoantibody. CIDP with autoantibodies should be considered as an independent disease entity, not a subtype of CIDP due to many differences. They possibly should be classified as CIDP-like chronic nodo-paranodopathy, which can better characterize these disorders, help diagnose and make the most effective therapeutic decisions.

Metabolic reprogramming by tobacco-specific nitrosamines (TSNAs) in cancer

Metabolic reprogramming is a hallmark of cancer and the link between oncogenes activation, tumor supressors inactivation and bioenergetics modulation is well established. However, numerous carcinogenic environmental factors are responsible for early cancer initiation and their impact on metabolic reprogramming just starts to be deciphered. For instance, it was recently shown that UVB irradiation triggers metabolic reprogramming at the pre-cancer stage with implication for skin cancer detection and therapy. These observations foster the need to study the early changes in tissue metabolism following exposure to other carcinogenic events. According to the International Agency for Research on Cancer (IARC), tobacco smoke is a major class I-carcinogenic environmental factor that contains different carcinogens, but little is known on the impact of tobacco smoke on tissue metabolism and its participation to cancer initiation. In particular, tobacco-specific nitrosamines (TSNAs) play a central role in tobacco-smoke mediated cancer initiation. Here we describe the recent advances that have led to a new hypothesis regarding the link between nitrosamines signaling and metabolic reprogramming in cancer.

Chronic Inflammatory Demyelinating Polyneuropathy With Concurrent Membranous Nephropathy: An Anti-paranode and Podocyte Protein Antibody Study and Literature Survey

Background: Several case reports have described the concurrence of chronic inflammatory demyelinating polyneuropathy (CIDP) and membranous nephropathy (MN). The presence of autoantibodies against podocyte antigens phospholipase A2 receptor (PLA2R) and thrombospondin type 1 domain containing 7A (THSD7A) in MN suggests an autoimmune mechanism. Some CIDP patients also harbor autoantibodies against paranodal proteins such as neurofascin 155 (NF155) and contactin-1 (CNTN1). We investigated the relationship between CIDP and MN by assaying autoantibodies against paranodal and podocyte antigens in a CIDP patient with MN, and by a literature survey on the clinical features of CIDP with MN.

Methods: Anti-CNTN1 and NF155 antibodies were measured by flow cytometry using HEK293 cell lines stably expressing human CNTN1 or NF155. Binding capacity of antibodies was validated by immunostaining mouse teased sciatic nerve fibers. Anti-PLA2R antibodies were measured by enzyme-linked sorbent assay and anti-THSD7A antibodies by indirect immunofluorescence assay. Clinical features between 14 CIDP with MN cases including two with anti-CNTN1 antibodies and 20 anti-CNTN1 antibody-positive CIDP cases were compared.

Results: A patient whose ages was in the late 70 s complained of progressive weakness and superficial and deep sensory impairment in four extremities over 6 months. Nerve conduction studies showed prominent demyelination patterns. The patient presented with nephrotic syndrome. Renal biopsy disclosed basement membrane thickening with local subepithelial projections and glomerular deposits of IgG4, compatible with MN. Autoantibody assays revealed the presence of IgG4 and IgG1 anti-CNTN1 antibodies, but an absence of anti-NF155, anti-PLA2R, and anti-THSD7A antibodies. The patient's serum stained paranodes of teased sciatic nerves. CIDP with MN and anti-CNTN1 antibody-positive CIDP commonly showed male preponderance, relatively higher age of onset, acute to subacute onset in 35–50% of cases, distal dominant sensorimotor neuropathy, proprioceptive impairment leading to sensory ataxia, and very high cerebrospinal fluid protein levels. However, 11 of 13 CIDP patients with MN had a favorable response to mono- or combined immunotherapies whereas anti-CNTN1 antibody-positive CIDP was frequently refractory to corticosteroids and intravenous immunoglobulin administration.

Conclusion: CIDP with MN and anti-CNTN1 antibody-positive CIDP show considerable overlap but are not identical. CIDP with MN is probably heterogeneous and some cases harbor anti-CNTN1 antibodies.

Tobacco carcinogen NNK-induced lung cancer animal models and associated carcinogenic mechanisms

Tobacco usage is a major risk factor in the development, progression, and outcomes for lung cancer. Of the carcinogens associated with lung cancer, tobacco-specific nitrosamines 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone (NNK) is among the most potent ones. The oncogenic mechanisms of NNK are not entirely understood, hindering the development of effective strategies for preventing and treating smoking-associated lung cancers. Here, we introduce the NNK-induced lung cancer animal models in different species and its potential mechanisms. Finally, we summarize several chemopreventive agents developed from these animal models.

Destruction of paranodal architecture in inflammatory neuropathy with anti-contactin-1 autoantibodies

OBJECTIVE

Autoantibodies against paranodal proteins have been described in patients with inflammatory neuropathies, but their association with pathology of nodes of Ranvier is unclear. We describe the clinical phenotype and histopathological changes of paranodal architecture of patients with autoantibodies against contactin-1, identified from a cohort with chronic inflammatory demyelinating polyradiculoneuropathy (n=53) and Guillain-Barré syndrome (n=21).

METHODS

We used ELISA to detect autoantibodies against contactin-1. Specificity of the autoantibodies was confirmed by immunoblot assay, binding to contactin-1-transfected human embryonic kidney cells, binding to paranodes of murine teased fibres and preabsorption experiments. Paranodal pathology was investigated by immunofluorescence labelling of dermal myelinated fibres.

RESULTS

High reactivity to contactin-1 by ELISA was found in four patients with chronic inflammatory demyelinating polyradiculoneuropathy and in none of the patients with Guillain-Barré syndrome, which was confirmed by cell binding assays in all four patients. The four patients presented with a typical clinical picture, namely acute onset of disease and severe motor symptoms, with three patients manifesting action tremor. Immunofluorescence-labelling of paranodal proteins of dermal myelinated fibres revealed disruption of paranodal architecture. Semithin sections showed axonal damage but no classical signs of demyelination.

INTERPRETATION

We conclude that anti-contactin-1-related neuropathy constitutes a presumably autoantibody-mediated form of inflammatory neuropathy with distinct clinical symptoms and disruption of paranodal architecture as a pathological correlate. Anti-contactin-1-associated neuropathy does not meet morphological criteria of demyelinating neuropathy and therefore, might rather be termed a 'paranodopathy' rather than a subtype of demyelinating inflammatory neuropathy.

Contactin-1 reduces E-cadherin expression via activating AKT in lung cancer

Contactin-1 has been shown to promote cancer metastasis. However, the underlying mechanisms remain unclear. We report here that knockdown of contactin-1 in A549 lung cancer cells reduced A549 cell invasion and the cell's ability to grow in soft agar without affecting cell proliferation. Reduction of contactin-1 resulted in upregulation of E-cadherin, consistent with E-cadherin being inhibitive of cancer cell invasion. In an effort to investigate the mechanisms whereby contactin-1 reduces E-cadherin expression, we observed that contactin-1 plays a role in AKT activation, as knockdown of contactin-1 attenuated AKT activation. Additionally, inhibition of AKT activation significantly enhanced E-cadherin expression, an observation that mimics the situation observed in contactin-1 knockdown, suggesting that activation of AKT plays a role in contactin-1-mediated downregulation of E-cadherin. In addition, we were able to show that knockdown of contactin-1 did not further reduce A549 cell's invasion ability, when AKT activation was inhibited by an AKT inhibitor. To further support our findings, we overexpressed CNTN-1 in two CNTN-1 null breast cancer cell lines expressing E-cadherin. Upon overexpression, CNTN-1 reduced E-cadherin levels in one cell line and increased AKT activation in the other. Furthermore, in our study of 63 primary lung cancers, we observed 65% of primary lung cancers being contactin-1 positive and in these carcinomas, 61% were E-cadherin negative. Collectively, we provide evidence that contactin-1 plays a role in the downregulation of E-cadherin in lung cancer and that AKT activation contributes to this process. In a study of mechanisms responsible for contactin-1 to activate AKT, we demonstrated that knockdown of CNTN-1 in A549 cells did not enhance PTEN expression but upregulated PHLPP2, a phosphatase that dephosphorylates AKT. These observations thus suggest that contactin-1 enhances AKT activation in part by preventing PHLPP2-mediated AKT dephosphrorylation.

Expression and significances of contactin-1 in human gastric cancer

Background. This study aimed at determining the relationship between vascular endothelial growth factor-C (VEGF-C), vascular endothelial growth factor receptor-3 (VEGFR-3), and contactin-1 (CNTN-1) expression in gastric cancer (GC). Methods. The expression level of CNTN-1 mRNA and CNTN-1 protein of 33 cases was determined using RT-PCR and Western Blot. And 105 cases were immunohistochemically examined for VEGF-C, VEGFR-3, and CNTN-1 expressions. Assessment of lymphatic vessel density (LVD) was also performed by D2-40 immunostaining. Then we analyzed the relationships between VEGF-C, VEGFR-3, and CNTN-1, as well as their correlations with clinicopathologic features, LVD, and survival time. Results. The positivity rate of VEGF-C, VEGFR-3, and CNTN-1 in primary tumor was 56.19%, 64.76%, and 58.09%. The expression of CNTN-1 significantly correlated with VEGF-C (P < 0.001) and VEGFR-3 (P < 0.001). All of them were closely related to TNM stage, lymphatic invasion, and lymph node involvement (P < 0.05). LVD was significantly correlated with VEGF-C (P = 0.001), VEGFR-3 (P = 0.011), and CNTN-1 expression (P < 0.001). VEGF-C, VEGFR-3, and CNTN-1 expression significantly associated with poorer prognosis (P < 0.001, P = 0.034, P = 0.012, resp.). Conclusion. CNTN-1 associated with VEGF-C and VEGFR-3 expression in GC. All of them correlated with lymphatic metastasis, which might play an important role in the lymphatic invasion via lymphangiogenesis pathway in GC.

Contactin 1 (CNTN1) expression associates with regional lymph node metastasis and is a novel predictor of prognosis in patients with oral squamous cell carcinoma

The contactin 1 (CNTN1) gene exerts oncogene‑like activities and its expression has been linked to several human malignancies. In this study, a possible association between CNTN1 expression and clinicopathological parameters and clinical outcomes in patients with oral squamous cell carcinoma (OSCC) was examined. CNTN1 protein expression was evaluated by immunohistochemistry in OSCC tissues of 45 patients. For the immunohistochemical assessment of CNTN1 expression, the cytoplasmic staining labeling index was analyzed using a semiquantitative score. The association between CNTN1 protein levels and clinicopathological factors was analyzed using the Mann-Whitney U test for categorical variables and the Kruskal-Wallis test for continuous variables. The effects of CNTN1 expression on overall and disease-free survival were assessed by using univariate survival analysis. The transcript levels of CNTN1 were detected in OSCC cell lines. In addition, specific siRNA against CNTN1 was applied to investigate the effect exerted by CNTN1 ablation on OSCC cell lines by proliferation and invasion assays in vitro. During follow-up, 16 patients (35.56%) had succumbed to OSCC; the median follow-up of patients was 5.0 years (range, 0.2-8.3). A high expression of CNTN1 was markedly associated with the regional lymph node metastasis of patients with OSCC (P=0.006). CNTN1 expression was significantly associated with overall survival of patients with OSCC (P=0.032; log-rank test) and disease-free survival of patients with OSCC (P=0.038; log-rank test). In addition, CNTN1 ablation notably suppressed the invasion potential of OSCC cell lines, but there was no significant change in the proliferation of OSCC cell lines by CNTN1 knockdown in vitro. The study supports CNTN1 as a novel predictor of regional lymph node metastasis in patients with OSCC and a prognostic marker for OSCC in patients.

Contactin-1 (CNTN-1) overexpression is correlated with advanced clinical stage and lymph node metastasis in oesophageal squamous cell carcinomas

OBJECTIVE

Oesophageal squamous cell carcinoma is one of the deadliest malignancies worldwide. Contactin-1, a neural adhesion molecule, is implicated in tumour invasion and metastasis. The purpose of this study was to investigate the expression of CNTN-1 in normal and cancerous oesophageal tissue, and the potential relevance to clinicopathological features.

METHODS

Thirty normal oesophageal tissue samples and 82 primary oesophageal squamous cell carcinoma tissue samples were included in this study. The expression levels of CNTN-1, VEGF-C and HIF-1α messenger RNA were determined using reverse transcriptase-polymerase chain reaction and quantitative real-time polymerase chain reaction. The expression of the CNTN-1 protein was measured using immunohistochemistry.

RESULTS

The expression of CNTN-1 messenger RNA was significantly increased in the tumour tissue compared with the normal oesophageal tissue (P=0.001). The oesophageal squamous cell carcinoma tissue consistently showed higher CNTN-1 protein levels. The CNTN-1 expression correlated with the oesophageal squamous cell carcinoma stage (P=0.006), lymph node metastasis (P=0.018) and lymphatic invasion (P=0.035). The messenger RNA level of CNTN-1 correlated significantly with those of VEGF-C and HIF-1α.

CONCLUSIONS

The expression of CNTN-1 is upregulated in the oesophageal squamous cell carcinoma tissue and related to stage, lymph node metastasis and lymphatic invasion. Thus, CNTN-1 may be involved in the progression and pathogenesis of oesophageal squamous cell carcinoma.

VEGF-C promotes the development of esophageal cancer via regulating CNTN-1 expression

Vascular endothelial growth factor C (VEGF-C) is a key regulator of angiogenesis and lymphangiogenesis. VEGF-C is also implicated in the development of esophageal cancer. We investigated the mRNA levels of VEGF-C and its receptors in 38 esophageal squamous cell carcinoma specimens (ESCCs) and matched adjacent normal esophageal tissues via real-time PCR. The mRNA levels of VEGF-C, VEGFR-2 and VEGFR-3 were significantly upregulated in ESCCs versus respective side normal tissues. To explore the influence of VEGF-C on esophageal cancer progression, the expression of VEGF-C was manipulated in esophageal cancer cell lines TE-1 and Eca-109. VEGF-C transcription, translation and secretion were significantly enhanced in cells stably transfected with a VEGF-C overexpression vector or attenuated in VEGF-C shRNA-transfected cell lines. In vitro, TE-1 cells stably transfected with a VEGF-C overexpression vector exhibited an increased rate of cell proliferation, migration and focus formation, whereas knockdown of VEGF-C inhibited cell proliferation, migration and focus formation. Similar results were obtained for Eca-109 cells. VEGF-C mediated biological function through transcription of CNTN-1, which is implicated in tumor invasion and metastasis. The expression of VEGF-C was correlated with that of CNTN-1 and cell proliferation and migration induced by VEGF-C were reversed by silencing of CNTN-1. In addition, nude mice inoculated with VEGF-C shRNA-transfected cells exhibited a significantly decreased tumor size in vivo via reduced VEGFR-2 and VEGFR-3 phosphorylation and microvessel formation. VEGF-C upregulation may be involved in esophageal tumor progression. Vector-based RNA interference (RNAi) targeting VEGF-C is a potential therapeutic method for human esophageal carcinoma.

Tissue-specific and ubiquitous expression patterns from alternative promoters of human genes

BACKGROUND

Transcriptome diversity provides the key to cellular identity. One important contribution to expression diversity is the use of alternative promoters, which creates mRNA isoforms by expanding the choice of transcription initiation sites of a gene. The proximity of the basal promoter to the transcription initiation site enables prediction of a promoter's location based on the gene annotations. We show that annotation of alternative promoters regulating expression of transcripts with distinct first exons enables a novel methodology to quantify expression levels and tissue specificity of mRNA isoforms.

PRINCIPAL FINDINGS

The use of distinct alternative first exons in 3,296 genes was examined using exon-microarray data from 11 human tissues. Comparing two transcripts from each gene we found that the activity of alternative promoters (i.e., P1 and P2) was not correlated through tissue specificity or level of expression. Furthermore neither P1 nor P2 conferred any bias for tissue-specific or ubiquitous expression. Genes associated with specific diseases produced transcripts whose limited expression patterns were consistent with the tissue affected in disease. Notably, genes that were historically designated as tissue-specific or housekeeping had alternative isoforms that showed differential expression. Furthermore, only a small number of alternative promoters showed expression exclusive to a single tissue indicating that "tissue preference" provides a better description of promoter activity than tissue specificity. When compared to gene expression data in public databases, as few as 22% of the genes had detailed information for more than one isoform, whereas the remainder collapsed the expression patterns from individual transcripts into one profile.

CONCLUSIONS

We describe a computational pipeline that uses microarray data to assess the level of expression and breadth of tissue profiles for transcripts with distinct first exons regulated by alternative promoters. We conclude that alternative promoters provide individualized regulation that is confirmed through expression levels, tissue preference and chromatin modifications. Although the selective use of alternative promoters often goes uncharacterized in gene expression analyses, transcripts produced in this manner make unique contributions to the cell that requires further exploration.

Myelination and regional domain differentiation of the axon

During evolution, as organisms increased in complexity and function, the need for the ensheathment and insulation of axons by glia became vital for faster conductance of action potentials in nerves. Myelination, as the process is termed, facilitates the formation of discrete domains within the axolemma that are enriched in ion channels, and macromolecular complexes consisting of cell adhesion molecules and cytoskeletal regulators. While it is known that glia play a substantial role in the coordination and organization of these domains, the mechanisms involved and signals transduced between the axon and glia, as well as the proteins regulating axo-glial junction formation remain elusive. Emerging evidence has shed light on the processes regulating myelination and domain differentiation, and key molecules have been identified that are required for their assembly and maintenance. This review highlights these recent findings, and relates their significance to domain disorganization as seen in several demyelinating disorders and other neuropathies.

Mutations in contactin-1, a neural adhesion and neuromuscular junction protein, cause a familial form of lethal congenital myopathy

We have previously reported a group of patients with congenital onset weakness associated with a deficiency of members of the syntrophin-alpha-dystrobrevin subcomplex and have demonstrated that loss of syntrophin and dystrobrevin from the sarcolemma of skeletal muscle can also be associated with denervation. Here, we have further studied four individuals from a consanguineous Egyptian family with a lethal congenital myopathy inherited in an autosomal-recessive fashion and characterized by a secondary loss of beta2-syntrophin and alpha-dystrobrevin from the muscle sarcolemma, central nervous system involvement, and fetal akinesia. We performed homozygosity mapping and candidate gene analysis and identified a mutation that segregates with disease within CNTN1, the gene encoding for the neural immunoglobulin family adhesion molecule, contactin-1. Contactin-1 transcripts were markedly decreased on gene-expression arrays of muscle from affected family members compared to controls. We demonstrate that contactin-1 is expressed at the neuromuscular junction (NMJ) in mice and man in addition to the previously documented expression in the central and peripheral nervous system. In patients with secondary dystroglycanopathies, we show that contactin-1 is abnormally localized to the sarcolemma instead of exclusively at the NMJ. The cntn1 null mouse presents with ataxia, progressive muscle weakness, and postnatal lethality, similar to the affected members in this family. We propose that loss of contactin-1 from the NMJ impairs communication or adhesion between nerve and muscle resulting in the severe myopathic phenotype. This disorder is part of the continuum in the clinical spectrum of congenital myopathies and congenital myasthenic syndromes.

Early coevolution of adhesive but not antiadhesive tenascin-R ligand-receptor pairs in vertebrates: A phylogenetic study

Axon growth inhibitory CNS matrix proteins, such as tenascin-R (TN-R), have been supposed to contribute to the poor regenerative capacity of adult mammalian CNS. With regard to TN-R function in low vertebrates capable of CNS regeneration, questions of particular interest concern the (co)evolution of ligand-receptor pairs and cellular response mechanisms associated with axon growth inhibition and oligodendrocyte differentiation. We address here these questions in a series of comparative in vivo and in vitro analyses using TN-R proteins purified from different vertebrates (from fish to human). Our studies provide strong evidence that unlike TN-R of higher vertebrates, fish TN-R proteins are not repellent for fish and less repellent for mammalian neurons and do not interfere with F3/contactin- and fibronectin-mediated mammalian cell adhesion and axon growth. However, axonal repulsion is induced in fish neurons by mammalian TN-R proteins, suggesting that the intracellular inhibitory machinery induced by TN-R-F3 interactions is already present during early vertebrate evolution. In contrast to TN-R-F3, TN-R-sulfatide interactions, mediating oligodendrocyte adhesion and differentiation, are highly conserved during vertebrate evolution. Our findings thus indicate the necessity of being cautious about extrapolations of the function of ligand-receptor pairs beyond a species border and, therefore, about the phylogenetic conservation of a molecular function at the cellular/tissue level.

Knockdown of contactin-1 expression suppresses invasion and metastasis of lung adenocarcinoma

Numerous genetic changes are associated with cancer cell metastasis and invasion. In search for key regulators of invasion and metastasis, a panel of lung cancer cell lines with different invasive ability was screened. The gene for contactin-1 was found to play an essential role in tumor invasion and metastasis. Suppression of contactin-1 expression abolished the ability of lung adenocarcinoma cells to invade Matrigel in vitro as well as the polymerization of filamentous-actin and the formation of focal adhesion structures. Furthermore, knockdown of contactin-1 resulted in extensive inhibition of tumor metastasis and in increased survival in an animal model. RhoA but not Cdc42 or Rac1 was found to serve a critical role in contactin-1-mediated invasion and metastasis. Contactin-1-specific RNA interference resulted in loss of metastatic and invasive capacity in both in vitro and in vivo models. This loss was overturned by constitutive expression of the active form of RhoA. Contactin-1 was differentially expressed in tumor tissues, and its expression correlated with tumor stage, lymph node metastasis, and patient survival. Contactin-1 is proposed to function importantly in the invasion and metastasis of lung adenocarcinoma cells via RhoA-mediated mechanisms.

Contactin is expressed in human astrocytic gliomas and mediates repulsive effects

Contactin is a cell surface adhesion molecule that is normally expressed by neurons and oligodendrocytes. Particularly high levels of contactin are present during brain development. Using subtractive cloning, we identified contactin transcripts as overexpressed in glioblastomas compared with normal brain. We confirmed contactin overexpression in glioblastomas at the protein level, and localized contactin to the surface of glial fibrillary acidic protein (GFAP)-expressing glioblastoma cells. In contrast, normal astrocytes did not express contactin. Analyzing different types of astrocytic tumors, we detected an association between increasing malignancy grade and contactin expression. Functionally, contactin had repellent effects on glioma cells in vitro, as demonstrated by adhesion and migration assays. Overexpression of contactin by transfection into glioblastoma cells did not alter the proliferation rate or adhesion to various extracellular matrix proteins as well as adhesion to cells expressing the specific contactin ligand the protein tyrosine phosphatase zeta (PTPzeta). Our findings suggest that contactin has repellent effects on glioma cells to which it is presented as a ligand, but it does not alter the proliferative or adhesive capacities of cells that overexpress the molecule. The repulsive properties of contactin may be a key factor in glioma disaggregation, and may contribute to the diffuse infiltration pattern characteristic of glioma cells in human brain.

Contactin-associated protein (Caspr) and contactin form a complex that is targeted to the paranodal junctions during myelination

Specialized paranodal junctions form between the axon and the closely apposed paranodal loops of myelinating glia. They are interposed between sodium channels at the nodes of Ranvier and potassium channels in the juxtaparanodal regions; their precise function and molecular composition have been elusive. We previously reported that Caspr (contactin-associated protein) is a major axonal constituent of these junctions (Einheber et al., 1997). We now report that contactin colocalizes and forms a cis complex with Caspr in the paranodes and juxtamesaxon. These proteins coextract and coprecipitate from neurons, myelinating cultures, and myelin preparations enriched in junctional markers; they fractionate on sucrose gradients as a high-molecular-weight complex, suggesting that other proteins may also be associated with this complex. Neurons express two contactin isoforms that differ in their extent of glycosylation: a lower-molecular-weight phosphatidylinositol phospholipase C (PI-PLC)-resistant form is associated specifically with Caspr in the paranodes, whereas a higher-molecular-weight form of contactin, not associated with Caspr, is present in central nodes of Ranvier. These results suggest that the targeting of contactin to different axonal domains may be determined, in part, via its association with Caspr. Treatment of myelinating cocultures of Schwann cells and neurons with RPTPbeta-Fc, a soluble construct containing the carbonic anhydrase domain of the receptor protein tyrosine phosphatase beta (RPTPbeta), a potential glial receptor for contactin, blocks the localization of the Caspr/contactin complex to the paranodes. These results strongly suggest that a preformed complex of Caspr and contactin is targeted to the paranodal junctions via extracellular interactions with myelinating glia.

Identification of proteins in the postsynaptic density fraction by mass spectrometry

Our understanding of the organization of postsynaptic signaling systems at excitatory synapses has been aided by the identification of proteins in the postsynaptic density (PSD) fraction, a subcellular fraction enriched in structures with the morphology of PSDs. In this study, we have completed the identification of most major proteins in the PSD fraction with the use of an analytical method based on mass spectrometry coupled with searching of the protein sequence databases. At least one protein in each of 26 prominent protein bands from the PSD fraction has now been identified. We found 7 proteins not previously known to be constituents of the PSD fraction and 24 that had previously been associated with the PSD by other methods. The newly identified proteins include the heavy chain of myosin-Va (dilute myosin), a motor protein thought to be involved in vesicle trafficking, and the mammalian homolog of the yeast septin protein cdc10, which is important for bud formation in yeast. Both myosin-Va and cdc10 are threefold to fivefold enriched in the PSD fraction over brain homogenates. Immunocytochemical localization of myosin-Va in cultured hippocampal neurons shows that it partially colocalizes with PSD-95 at synapses and is also diffusely localized in cell bodies, dendrites, and axons. Cdc10 has a punctate distribution in cell bodies and dendrites, with some of the puncta colocalizing with PSD-95. The results support a role for myosin-Va in transport of materials into spines and for septins in the formation or maintenance of spines.

An essential role of the neuronal cell adhesion molecule contactin in development of the Xenopus primary sensory system

Contactin is a glycosylphosphatidylinositol-anchored immunoglobulin-like neuronal cell adhesion molecule that has been implicated in cellular interaction during development of the vertebrate central nervous system. Here we report evidence for an essential role of contactin in development of the Xenopus nervous system. Contactin mRNA is detectable by in situ hybridization in subsets of neurons in the brain, primary sensory neurons in the spinal cord, and cells along the trigeminal nerves of tailbud embryos. Contactin immunoreactivities preferentially distribute on axon tracts of the brain, the spinal cord, and the trigeminal sensory nerves. Most prominently, cell bodies and peripheral and spinal axons of primary sensory neurons, Rohon-Beard (RB) cells, are strongly contactin positive. Injection of the contactin overexpression vector into one blastomere of two-cell stage embryos leads to misdirected elongation of the peripheral axons of RB neurons in the injected half. Overexpression of antisense transcript causes depletion of contactin mRNA accumulation and abnormal development of RB neurons. In 52.3% of the injected embryos, RB neurons decrease in number and their peripheral axons in dorsal lateral tracts are defasciculated. These results demonstrate that contactin plays an essential role in development of the Xenopus primary sensory system.

Ataxia and abnormal cerebellar microorganization in mice with ablated contactin gene expression

Axon guidance and target recognition depend on neuronal cell surface receptors that recognize and elicit selective growth cone responses to guidance cues in the environment. Contactin, a cell adhesion/recognition molecule of the immunoglobulin gene superfamily, regulates axon growth and fasciculation in vitro, but its role in vivo is unknown. To assess its function in the developing nervous system, we have ablated contactin gene expression in mice. Contactin-/- mutants displayed a severe ataxic phenotype consistent with defects in the cerebellum and survived only until postnatal day 18. Analysis of the contactin-/- mutant cerebellum revealed defects in granule cell axon guidance and in dendritic projections from granule and Golgi cells. These results demonstrate that contactin controls axonal and dendritic interactions of cerebellar interneurons and contributes to cerebellar microorganization.

Recombinant human nerve growth factor in the treatment of diabetic polyneuropathy. NGF Study Group

BACKGROUND

Preclinical studies have demonstrated that nerve growth factor may prevent or reverse peripheral neuropathy. We have therefore tested the effects of recombinant human nerve growth factor in patients with diabetic polyneuropathy.

METHODS

A total of 250 patients with symptomatic diabetic polyneuropathy randomly received either placebo or one of two doses of recombinant human nerve growth factor for 6 months. Patients were assessed for symptoms and signs of polyneuropathy before and after treatment.

RESULTS

Compared with placebo, recombinant human nerve growth factor led to significant improvement after 6 months of treatment, as measured by the sensory component of the neurologic examination, two quantitative sensory tests, and the impression of most subjects that their neuropathy had improved. Three prospectively identified multiple endpoint analyses indicated improvements in the nerve growth factor treatment groups over the placebo group in all three analyses (p = 0.032; p = 0.008; p = 0.005). Recombinant human nerve growth factor was well tolerated, with injection site discomfort reported as the most frequent adverse event.

CONCLUSIONS

Recombinant human nerve growth factor appears to be safe and shows preliminary evidence of efficacy in patients with symptomatic diabetic polyneuropathy.

The role of glycoproteins in neural development function, and disease

Glycoproteins play key roles in the development, structuring, and subsequent functioning of the nervous system. However, the complex glycosylation process is a critical component in the biosynthesis of CNS glycoproteins that may be susceptible to the actions of toxicological agents or may be altered by genetic defects. This review will provide an outline of the complexity of this glycosylation process and of some of the key neural glycoproteins that play particular roles in neural development and in synaptic plasticity in the mature CNS. Finally, the potential of glycoproteins as targets for CNS disorders will be discussed.

cDNA cloning and chromosomal localization of neural adhesion molecule NB-3 in human

Neural adhesion molecules in the immunoglobulin superfamily play essential roles in axonal guidance during development, plasticity, and maintenance of synaptic connections in the adult brain. Recently, we reported two novel cDNAs encoding adhesion molecules, NB-2 and NB-3, in the contactin/F3 subgroup of the immunoglobulin superfamily from rat brain. We have now isolated cDNA encoding human NB-3. The cDNA clone, hNB-3, consists of 3,530 nucleotides with an open reading frame of 3,084 nucleotides encoding 1,028 amino acids. It shares with rat NB-3 86% identity in nucleotide sequences and 90% identity in amino acid sequences. Likewise, hNB-3 exhibits 53% and 51% identity in nucleotide sequences and 43% and 44% identity in amino acid sequences with human contactin/F3 and human TAG-1/axonin-1, respectively. Northern blot analysis of mRNA isolated from different regions of the adult human nervous system showed that the hNB-3 mRNA content was regionally different by dozens-fold, although the mRNA was detected in all regions, as a transcript of 3.7 kb. The cerebellum showed the highest expression of hNB-3 mRNA among various regions of the nervous system. Chromosomal localization of hNB-3, using fluorescence in situ hybridization, was assigned to 3p25-26.

The gene of the neural cell recognition molecule F11: conserved exon-intron arrangement in genes of neural members of the immunoglobulin superfamily

The chicken neural glycoprotein F11 is a cell recognition molecule implicated in neurohistogenesis, in particular in the context of neurite outgrowth and fasciculation. F11 is a glycosyl-phosphatidylinositol-linked member of the immunoglobulin superfamily that is also termed contactin or F3 in humans and rodents, respectively. In this study, we report the complete structure of the F11 gene. It is composed of 23 exons distributed over more than 100 kb of genomic DNA and each of the ten domains of the F11 protein is encoded by two exons. The sizes of the introns vary by two orders of magnitude ranging from 150 bp to more than 15 kb. All interdomain introns are in phase one, i.e. are inserted after the first nucleotide of a codon, being consistent with assembly of a F11 progenitor gene via exon shuffling. The intradomain introns are localized at variable sites within the domains and have different intron phases. This study reveals a remarkable similarity of the F11 gene with the gene of axonin-1, a related neural immunoglobulin superfamily member which is also implicated in neurite outgrowth and fasciculation. The intron positions with respect to the protein domain organization are found to be identical, strongly suggesting that both genes are derived from a common ancestor that already had this exon-intron structure.

Induction of neurite outgrowth through contactin and Nr-CAM by extracellular regions of glial receptor tyrosine phosphatase beta

Receptor protein tyrosine phosphatase beta (RPTPbeta) is expressed as soluble and receptor forms with common extracellular regions consisting of a carbonic anhydrase domain (C), a fibronectin type III repeat (F), and a unique region called S. We showed previously that a recombinant Fc fusion protein with the C domain (beta C) binds to contactin and supports neuronal adhesion and neurite growth. As a substrate, betaCFS was less effective in supporting cell adhesion, but it was a more effective promoter of neurite outgrowth than betaCF. betaS had no effect by itself, but it potentiated neurite growth when mixed with betaCF. Neurite outgrowth induced by betaCFS was inhibited by antibodies against Nr-CAM and contactin, and these cell adhesion molecules formed a complex that bound betaCFS. NIH-3T3 cells transfected to express betaCFS on their surfaces induced neuronal differentiation in culture. These results suggest that binding of glial RPTPbeta to the contactin/Nr-CAM complex is important for neurite growth and neuronal differentiation.

cDNA cloning and expression of the Xenopus homologue of the neural adhesion molecule, contactin (F3/F11)

Contactin (F3/F11) is an immunoglobulin superfamily cell surface glycoprotein predominantly expressed in the nervous system. To examine the structure and tissue distribution of Xenopus contactin, a cDNA clone was isolated based on the amino acid sequences conserved among chicken and mammalian contactin proteins. The conceptual translate of the cDNA consists of 1005 amino acid residues that have 70% identity to those of chicken and mammalian contactin. Northern blot hybridization using a labeled cDNA fragment revealed specific expression of 6.5 kb mRNA in the brain. Monoclonal and polyclonal antibodies prepared to the recombinant Xenopus contactin peptides detected a single 135 kD band on Western blots of the brain and spinal cord extracts. Differential extraction and phosphatidylinositol-specific phospholipase C (PI-PLC) digestion experiments showed that the immunoreactive 135 kD proteins bind, at least in part to the membrane by GPI anchor. On brain tissue sections, strong contactin immunoreactivities were detected on nerve fibers of a subset of cerebral and cerebellar neurons. These results suggest that the basic structure and tissue distribution of Xenopus contactin are similar to those in other vertebrates.

Overlapping and differential expression of BIG-2, BIG-1, TAG-1, and F3: four members of an axon-associated cell adhesion molecule subgroup of the immunoglobulin superfamily

Axon-associated cell adhesion molecules (AxCAMs) play crucial roles in the formation, maintenance, and plasticity of functional neuronal networks. We report here a molecular cloning of a novel AxCAM, BIG-2. BIG-2 is a member of TAG-1/F3 subgroup of the immunoglobulin (Ig) superfamily, with six Ig-like domains, four fibronectin type III-like repeats, and a glycosyl phosphatidylinositol-anchoring domain. Recombinant BIG-2 protein had a neurite outgrowth-promoting activity when used as a substrate for neurons in vitro. To survey the spatial expression pattern of BIG-2 in comparison with other TAG-1/F3 subgroup members, an in situ hybridization analysis was performed in adult and developing rat brain sections with riboprobes specific for BIG-2, BIG-1, TAG-1, and F3. The four AxCAM transcripts displayed cell type-specific expression patterns with overlapping and distinct profiles. In adult hippocampus, for example, we observed BIG-1 mRNA specifically in granule cells of the dentate gyrus, BIG-2 mRNA highly in the CA1 pyramidal cells, TAG-1 mRNA predominantly in the CA3 pyramidal cells, and F3 mRNA in neurons in all of these fields. These results suggest that BIG-2, BIG-1, TAG-1, and F3 may play important roles in the formation and maintenance of specific neuronal networks in the brain.

Cloning of the cDNA encoding neural adhesion molecule F3 from bovine brain

We cloned a bovine cDNA encoding the neural adhesion molecule F3 and analyzed its nucleotide sequence. The coding region consisted of 3054 bp encoding 1018 amino acid (aa) residues. The M(r) calculated from the deduced aa sequence was 113,383. Bovine F3 had 93, 94 and 77% aa identity with the mouse, human and chicken homologs, respectively. Bovine F3, similar to those of chicken and human, was devoid of two aa residues (Ile-Thr) in the sixth immunoglobulin type C2-like domain, as compared with the mouse homolog. Parts of bovine F3 protein were overproduced in Escherichia coli. The antibodies raised against the recombinant proteins in rabbits reacted specifically with F3. F3 protein was detected in cerebellum, cerebrum and spinal cord in Western blot analysis.

The carbonic anhydrase domain of receptor tyrosine phosphatase beta is a functional ligand for the axonal cell recognition molecule contactin

Receptor-type protein tyrosine phosphatase beta (RPTP beta) is expressed in the developing nervous system and contains a carbonic anhydrase (CAH) domain as well as a fibronectin type III repeat in its extracellular domain. Fusion proteins containing these domains were used to search for ligands of RPTP beta. The CAH domain bound specifically to a 140 kDa protein expressed on the surface of neuronal cells. Expression cloning in COS7 cells revealed that this protein is contactin, a GPI membrane-anchored neuronal cell recognition molecule. The CAH domain of RPTP beta induced cell adhesion and neurite growth of primary tectal neurons, and differentiation of neuroblastoma cells. These responses were blocked by antibodies against contactin, demonstrating that contactin is a neuronal receptor for RPTP beta. These experiments show that an individual domain of RPTP beta acts as a functional ligand for the neuronal receptor contactin. The interaction between contactin and RPTP beta may generate unidirectional or bidirectional signals during neural development.