Desmoid tumour biology in patients with familial adenomatous polyposis coli.

BACKGROUND: Familial adenomatous polyposis (FAP) is caused by mutations in the adenomatous polyposis coli (APC) gene. Desmoid tumours affect up to 26 per cent of patients and contribute significantly to death. This study aimed to assess the influence of sex and mutation site on desmoid tumour development and sex-specific genetic differences in patients with FAP with and without desmoid tumours. METHODS: Patients with FAP-associated desmoid tumours recorded in the Heidelberg Polyposis Register between 1991 and 2010 were identified. These patients were analysed with respect to clinical parameters and possible risk factors. RESULTS: Some 105 patients with FAP-associated desmoid tumours of a total of 585 patients with FAP were analysed. Male patients had a significantly greater number of desmoid tumours and a larger tumour mass, although tumours were more common in female patients. Desmoid tumours in male patients were located more often in the abdominal wall. Seventy-nine (75.2 per cent) of the 105 patients demonstrated a clear temporal association between a previous operation and subsequent desmoid tumour development; most of these patients were female. Mutation sites in male patients were limited to exons 5, 14 and 15, whereas female patients carried mutations along the entire coding region of the APC gene. Twenty-one per cent of patients with desmoid tumours carried mutations within the 'desmoid region', compared with only 4.1 per cent of the control group without desmoids. CONCLUSION: There are significant sex differences concerning desmoid tumour manifestation. Female patients appear to have a higher risk of desmoid tumour occurrence independent of the mutation site, whereas in male patients the mutation site seems to exert more influence.

[Who will be a good physician? Admission procedures for medical and dental students]. / Wer wird ein guter Arzt? Verfahren zur Auswahl von Studierenden der Human- und Zahnmedizin.

Since 2005, German universities are free to select 60% of their freshmen according to their own admission processes. In 2008, selection of medical students in Germany was mainly based on grades achieved in final school examinations (Abiturnote). Further criteria were used in various combinations: some medical schools conducted interviews or tests, while others rewarded work experience, research awards, or cultural and social dedication. However, solely high school grades and some measures of ability show acceptable validity coefficients with regard to academic and professional success. Evidence for the prognostic validity of interviews and other noncognitive criteria cannot be regarded as sufficient. Recent studies conducted in Hamburg and Heidelberg attempt to validate selection criteria such as a test of natural sciences, final school examination grades, work experience, and voluntary work in the social sector. For the selection of medical students, we recommend the use of final school examination grades in combination with special written test results or, in the case of dentistry, a test of manual dexterity. Interviews might be beneficial to emphasize the importance of non-academic skills and to strengthen the ties of students to their faculty.

L1 makes immunological progress by expanding its relations.

The cell-adhesion molecule L1 was originally described in the nervous system. It has recently been detected in CD4+ T lymphocytes, peripheral B lymphocytes, and granulocytes in the human immune system and in similar leucocyte types in the murine immune system. L1 mediates neural recognition by Ca+2, Mg+2-independent homophilic binding. In the human and murine immune systems, L1 binds to the "classical" vitronectin receptor, alphaVbeta3, and fibronectin receptor, alpha5beta1, respectively, and abstains from homophilic binding. Homophilic L1 binding probably involves antiparallel alignment of several interactive domains. Integrin binding is mediated by a short segment of immunoglobulinlike domain 6, which includes two RGD repeats in rodent L1 and one RGD motif in human L1. L1 is modulated in activated leucocytes in vitro in parallel to L-selectin, and diverse cell types release intact L1 in vivo and in vitro. Released L1 can bind to laminin and adheres to the extracellular matrix of sciatic nerve, M21 melanoma, and possibly spleen and other tissues. It can support integrin-dependent cell migration and preliminary data implicate it in tumor development and transnodal lymphocyte migration.

The cell adhesion molecule L1: species- and cell-type-dependent multiple binding mechanisms.

The cell adhesion molecule L1 is known to mediate neuronal adhesion, neurite fasciculation, and stimulation of fibroblastin growth factor (FGF)-receptor-dependent neurite outgrowth by homophilic interaction. Recent findings have also revealed heterophilic interactions between L1 and two "classical" integrin matrix receptors, murine alpha 5 beta 1 and human alpha V beta 3. The homophilic binding mechanism of L1 involves multiple domains and has been conserved in chicken neuron-glia cell adhesion molecule (NgCAM) and mammalian L1. The integrin-binding site of L1 contains the tripeptide Arg-Gly-Asp but varies among different species. L1-integrin binding predominates in leucocyte subsets and in several tumours. It can mediate homotypic and heterotypic cell-cell adhesion and haptotactic cell movement on substrate-embedded L1. L1 is released in response to cytokines by at least some neuronal and leucocyte types. It can be detected in the extracellular matrix and conceivably contributes to cell and axonal navigation. Antibody perturbation studies indicate that the integrin-binding site of L1 is important for granule cell migration and neurite outgrowth in postnatal murine cerebellum, possibly via modulation of the src signal transduction pathway. The model of L1 binding seems to be governed by the cell, but it does not correlate with known alternative splicing or glycosylation patterns of L1.

Adhesive hierarchy involving the cell adhesion molecules L1, CD24, and alpha 6 integrin in murine neuroblastoma N2A cells.

The aggregation rate of resuspended neuroblastoma N2A cells depends on the density of the cells in culture prior to their resuspension: isolated, fast growing cells have a weak tendency to aggregate whereas confluent, slowly growing cells reaggregate very strongly. L1 antibody 557 strongly inhibited the slow aggregation of isolated, fast growing cells but not the reaggregation of confluent cells. CD24 (nectadrin) antibodies did not affect the aggregation of isolated or confluent cells but stimulated the aggregation of subconfluent cells. In all stages aggregation was not inhibited when antibody 557 was used together with CD24 antibodies at 37 degrees C in the presence of divalent cations. EA-1 antibody to alpha 6 integrin chain stimulated the aggregation of subconfluent cells but inhibited the reaggregation of confluent cells. Therefore, L1 appears to be an early recognition molecule mediating weak primary adhesion. CD24 appears to participate in activating secondary adhesion mechanisms during primary adhesion, possibly in cooperation with L1, and alpha 6 integrin seems to serve as a secondary, strong adhesion molecule that in early adhesion phases also mediates the activation of itself or of other adhesion mechanisms. These results indicate that neural cells might employ a strategy of adhesion cascade in establishing stable contacts.

Evidence for cis interaction and cooperative signalling by the heat-stable antigen nectadrin (murine CD24) and the cell adhesion molecule L1 in neurons.

L1 is a transmembranal homophilic cell adhesion molecule of the immunoglobulin superfamily expressed by neural and lymphoid cells. The heat-stable antigen (HSA, murine CD24) nectadrin is a highly and heterogeneously glycosylated glycophosphatidylinositol-linked differentiation antigen of haematopoietic and neural cells. L1 and nectadrin have been shown to mediate cell adhesion and intracellular Ca2+ signals in neurons and B lymphoblasts, respectively. Here we show that nectadrin is co-expressed with L1 in murine cerebellar granule cell neurons and neuroblastoma N2A cells. Purified nectadrin bound to L1 with an apparent binding ratio of five nectadrin molecules to one L1 molecule at saturation. Binding between nectadrin and purified N-CAM was not observed. In co-capping experiments nectadrin co-redistributed with L1 and N-CAM. Since in these cells N-CAM and L1 cohere by cis-binding nectadrin appears to join the L1-N-CAM complex through binding to L1. Antibodies to each L1 and nectadrin evoked small increases in the intracellular Ca2+ concentration. However, when both antibodies were added together or in tandem to the cells, a strong intracellular Ca2+ signal was measured that was at least 6- and 10-fold stronger than the signal separately induced by L1 and nectadrin antibodies respectively. Such a cooperative effect was not observed in B lymphoblasts, using the same antibodies, or in neurons, using a combination of L1 and Thy-1 antibodies. Both the weak Ca2+ signal mediated by L1 alone and the enhanced signal jointly triggered by antibodies to L1 and nectadrin were inhibited by phorbol 12-myristate 13-acetate and were not significantly affected by Ni2+ and Cd2+ cations, suggesting that they are related to one another and involve recruitment of intracellular Ca2+. Nectadrin therefore appears to join a functional complex of neuronal adhesion molecules and to potentiate the signal transduction pathway of L1, possibly in response to neuron-neuron contact formation.

Differential, LFA-1-sensitive effects of antibodies to nectadrin, the heat-stable antigen, on B lymphoblast aggregation and signal transduction.

Nectadrin, the heat-stable antigen (HSA), is a highly glycosylated GPI-linked glycoprotein that can undergo homophilic and heterophilic binding. In the present work we have examined short-term effects of nectadrin antibodies on splenic B lymphoblast aggregation and signal transduction. Monoclonal antibody 79 inhibited cell aggregation and induced an intracellular Ca++ signal in the absence of cross-linking. Both these effects were perturbed in the presence of LFA-1 antibodies. Nectadrin antibody M1/69 and polyclonal nectadrin antibodies stimulated cell aggregation, did not induce a Ca++ signal, and their effects were functionally independent of LFA-1. These results suggest that nectadrin may concomitantly mediate primary and activate secondary adhesion mechanisms whereby each of these processes may be related to a different signal transduction pathway.

Expression of L1 cell adhesion molecule is associated with lymphoma growth and metastasis.

The cell adhesion molecule (CAM) L1 is involved in homotypic and heterotypic adhesion between neural cells. It has recently also been identified on leucocytes. We have investigated the expression of L1 on hematopoietic tumor cell lines and found that several tumors including the ESb-MP lymphoma are positive for L1. A potential role for L1 in spontaneous metastasis formation was examined using these cells. From wild-type (wt) L1high lymphoma cells we selected by a fluorescence-activated cell sorter (FACS) stable L1low expression variants. Syngeneic DBA/2 mice injected subcutaneously with L1low clones showed faster primary tumor growth, developed visceral metastases significantly faster and died earlier than animals carrying L1high wt cells. L1 high revertants from the L1low variants showed again a reduced metastatic capacity and a malignancy similar to the wt cells. Expression of L1 on the tumor variants and revertants correlated directly with their homotypic aggregation behaviour in vitro. L1 expression correlated negatively with metastatic capacity. These results suggest that L1 molecules may contribute to the overall malignant potential of the lymphoma cells, presumably by interfering with cell-cell interactions critical for tumor growth and dissemination.

Nectadrin, the heat-stable antigen, is a cell adhesion molecule.

Nectadrin, the cell surface glycoprotein recognized by the novel mAb 79, was found to be immunologically identical to the heat-stable antigen (HSA). It is a glycoprotein with a polypeptide core of only 30 amino acids and a very high carbohydrate content (Wenger, R. H., M. Ayane, R. Bose, G. Köhler, and P. J. Nielsen. 1991. Eur. J. Immunol. 21:1039-1046). Immunocytological studies using cultured splenic B-lymphocytes, neuroblastoma cells, and cerebellar cells indicated that nectadrin is preferentially expressed at sites of cell-cell contact. Purified nectadrin and monoclonal nectadrin antibody 79, but not other monoclonal nectadrin antibodies, inhibited the aggregation of B-lymphocytes by 70%, suggesting that nectadrin may act as a cell adhesion molecule. Nectadrin was purified from a mouse lymphoma cell line in two forms of 40-60 and 23-30 kD. The lower molecular weight form appears to be generated from the higher molecular weight form by degradative removal of saccharide residues characteristic of complex type oligosaccharide side chains. Latex beads coated with purified nectadrin aggregated and the rate of their aggregation depended on the molecular form of nectadrin, with the larger form being more potent than the smaller one in mediating bead aggregation. Nectadrin thus appears to be a self-binding cell adhesion molecule of a structurally novel type in that its extensive glycan structures may be implicated in mediating cell adhesion.

Expression and function of the neural cell adhesion molecule L1 in mouse leukocytes.

The neural cell adhesion molecule L1 is a cell surface glycoprotein of the immunoglobulin superfamily which mediates adhesion between neural cells. The possibility that similar cell-cell recognition mechanisms may be shared by the nervous and immune systems prompted us to study the expression and function of L1 in cells of the hematopoietic system. Immunofluorescence analysis using monoclonal L1 antibody revealed that the molecule is expressed in the bone marrow, spleen, and thymus of the mouse. This observation was confirmed by amplifying cDNA derived from these organs by the polymerase chain reaction with L1-specific oligonucleotide primers. Two-color fluorescence analysis indicated that bone marrow lymphoid and granulocyte precursor cells express low and high levels of L1, respectively. In the thymus L1 is primarily expressed by mature cells that have a strong expression of CD3 and in the spleen both B cells and T cells express L1. The possible function of L1 in lymphoid cells was studied using subcloned ESb-MP lymphoma cells having high or low densities of L1 on the cell surface as well as activated splenic B lymphoblasts. Parental and subcloned ESb-MP cells that strongly expressed L1 could form homotypic aggregates in the presence of low Ca2+ levels, whereas subcloned ESb-MP cells with a weak expression of L1 did not aggregate, suggesting that L1 mediates the Ca(2+)-independent aggregation of the parental ESb-MP cells. Furthermore, the aggregation of activated B lymphoblasts under physiological concentrations of Ca2+ and Mg2+ was inhibited by 30% in the presence of Fab fragments of polyclonal L1 antibodies, implying that L1 also mediates adhesion among normal lymphoid cells. A possible role of L1 on lymphocytes in stimulating the innervation of lymphoid organs is discussed.

Retention of J1/tenascin and the polysialylated form of the neural cell adhesion molecule (N-CAM) in the adult olfactory bulb.

To gain insight into the cellular and molecular mechanisms underlying neurogenesis in adult mouse olfactory bulb, several adhesion molecules expressed by glial cells and neurons were investigated. In the germinal zone of the olfactory bulb, the subependymal layer of the rostral region of the lateral ventricles, two adhesion molecules are detectable that are characteristic of early morphogenetic events: J1/tenascin and the polysialylated form, the so-called embryonic form, of N-CAM. The polysialylated form of N-CAM is expressed by most cells in the subependymal layer, and by some astrocytes and neurons in the granular layer adjacent to the subependymal layer. This suggests that bipotential precursor cells retain expression of the embryonic form during their migration from the subependymal layer and during the first stages of differentiation into neurons and glia. Expression of the polysialylated form of N-CAM is also retained in monolayer cultures of six-day-old olfactory bulbs, 55 days after seeding in vitro. J1/tenascin was detectable in the subependymal layer using two monoclonal antibodies. The immunostaining pattern was different between the two antibodies and more restricted to the subependymal layer than when staining with polyclonal J1 antibodies was performed, indicating that J1/tenascin exists in distinct isoforms. Finally, our observations suggest that, in the adult olfactory bulb, L1 is not only a neuron-neuron adhesion molecule, but it may also be involved in neuron-glia interactions, since it is found at contact sites between these two cell types. L1, therefore, may be a neuron-glia adhesion molecule in some parts of the CNS, while it is not in others.

The neural cell adhesion molecule N-CAM enhances L1-dependent cell-cell interactions.

On neural cells, the cell adhesion molecule L1 is generally found coexpressed with N-CAM. The two molecules have been suggested, but not directly shown, to affect each other's function. To investigate the possible functional relationship between the two molecules, we have characterized the adhesive interactions between the purified molecules and between cultured cells expressing them. Latex beads were coated with purified L1 and found to aggregate slowly. N-CAM-coated beads did not aggregate, but did so after addition of heparin. Beads coated with both L1 and N-CAM aggregated better than L1-coated beads. Strongest aggregation was achieved when L1-coated beads were incubated together with beads carrying both L1 and N-CAM. In a binding assay, the complex of L1 and N-CAM bound strongly to immobilized L1, but not to the cell adhesion molecules J1 or myelin-associated glycoprotein. N-CAM alone did not bind to these glycoproteins. Cerebellar neurones adhered to and sent out processes on L1 immobilized on nitrocellulose. N-CAM was less effective as substrate. Neurones interacted most efficiently with the immobilized complex of L1 and N-CAM. They adhered to this complex even when its concentration was at least 10 times lower than the lowest concentration of L1 found to promote adhesion. The complex became adhesive for cells only when the two glycoproteins were preincubated together for approximately 30 min before their immobilization on nitrocellulose. The adhesive properties between cells that express L1 only or both L1 and N-CAM were also studied. ESb-MP cells, which are L1-positive, but N-CAM negative, aggregated slowly under low Ca2+. Their aggregation could be completely inhibited by antibodies to L1 and enhanced by addition of soluble N-CAM to the cells before aggregation. N2A cells, which are L1 and N-CAM positive aggregated well under low Ca2+. Their aggregation was partially inhibited by either L1 or N-CAM antibodies and almost completely by the combination of both antibodies. N2A and ESb-MP cells coaggregated rapidly and their interaction was similarly inhibited by L1 and N-CAM antibodies. These results indicate that L1 is involved in two types of binding mechanisms. In one type, L1 serves as its own receptor with slow binding kinetics. In the other, L1 is modulated in the presence of N-CAM on one cell (cis-binding) to form a more potent receptor complex for L1 on another cell (trans-binding).

Functional cooperation between the neural adhesion molecules L1 and N-CAM is carbohydrate dependent.

The neural cell adhesion molecules L1 and N-CAM have been suggested to interact functionally by formation of a complex between the two molecules (Kadmon, G., A. Kowitz, P. Altevogt, and M. Schachner. 1990. J. Cell Biol. 110:193-208). To determine the molecular mechanisms underlying this functional cooperation, we have studied the contribution of carbohydrates to the association of the two molecules at the cell surface. Aggregation or adhesion between L1- and N-CAM-positive neuroblastoma N2A cells was reduced when the synthesis of complex and/or hybrid glycans was modified by castanospermine. Fab fragments of polyclonal antibodies to L1 inhibited aggregation and adhesion of castanospermine-treated cells almost completely, whereas untreated cells were inhibited by approximately 50%. Fab fragments of polyclonal antibodies to N-CAM did not interfere with the interaction between castanospermine-treated cells, whereas they inhibited aggregation or adhesion of untreated cells by approximately 50%. These findings indicate that cell interactions depending both on L1 and N-CAM ("assisted homophilic" binding) can be reduced to an L1-dominated interaction ("homophilic binding"). Treatment of cells with the carbohydrate synthesis inhibitor swainsonine did not modify cell aggregation in the absence or presence of antibodies compared with untreated cells, indicating that castanospermine-sensitive, but swainsonine-insensitive glycans are involved. To investigate whether the appropriate carbohydrate composition is required for an association of L1 and N-CAM in the surface membrane (cis-interaction) or between L1 on one side and L1 and N-CAM on the other side of interacting partner cells (trans-interaction), an L1-positive lymphoid tumor cell line was coaggregated with and adhered to neuroblastoma cells in the various combinations of castanospermine-treated and untreated cells. The results show that it is the cis-interaction between L1 and N-CAM that depends on the appropriate carbohydrate structures.

Expression of L1 and N-CAM cell adhesion molecules during development of the mouse olfactory system.

The expression of the neural adhesion molecules L1 and N-CAM has been studied in the embryonic and early postnatal olfactory system of the mouse in order to gain insight into the function of these molecules during development of a neural structure which retains neuronal turnover capacities throughout adulthood. N-CAM was slightly expressed and L1 was not significantly expressed in the olfactory placode on Embryonic Day 9, the earliest stage tested. Rather, N-CAM was strongly expressed in the mesenchyme underlying the olfactory placode. In the developing nasal pit, L1 and N-CAM were detectable in the developing olfactory epithelium, but not in regions developing into the respiratory epithelium. At early developmental stages, expression of the so-called embryonic form of N-CAM (E-N-CAM) coincides with the expression of N-CAM, whereas at later developmental stages and in the adult it is restricted to a smaller number of sensory cell bodies and axons, suggesting that the less adhesive embryonic form is characteristic of morphogenetically dynamic neuronal structures. Moreover, E-N-CAM is highly expressed at contact sites between olfactory axons and their target cells in the glomeruli of the olfactory bulb. L1 and N-CAM 180, the component of N-CAM that accumulates at cell contacts by interaction with the cytoskeleton are detectable as early as the first axons extend toward the primordial olfactory bulb. L1 remains prominent throughout development on axonal processes, both at contacts with other axons and with ensheathing cells. Contrary to N-CAM 180 which remains detectable on differentiating sensory neuronal cell bodies, L1 is only transiently expressed on these and is no longer detectable on primary olfactory neuronal cell bodies in the adult. Furthermore, whereas throughout development L1 has a molecular form similar to that seen in other parts of the developing and adult central nervous systems, N-CAM and, in particular, N-CAM 180 retain their highly sialylated form at least partially throughout all ages studied. These observations suggest that E-N-CAM and N-CAM 180 are characteristic of developmentally active structures and L1 may not only be involved in neurite outgrowth, but also in stabilization of contacts among fasciculating axons and between axons and ensheathing cells, as it has previously been found in the developing peripheral nervous system.

Expression of cell adhesion molecules in the olfactory system of the adult mouse: presence of the embryonic form of N-CAM.

The expression of the neural cell adhesion molecules N-CAM and L1 was investigated in the olfactory system of the mouse using immunocytochemical and immunochemical techniques. In the olfactory epithelium, globose basal cells and olfactory neurons were stained by the polyclonal N-CAM antibody reacting with all three components of N-CAM (N-CAM total) in their adult and embryonic states. Dark basal cells and supporting cells were not found positive for N-CAM total. The embryonic form of N-CAM (E-N-CAM) was only observed on the majority of globose basal cells, the precursor cells of olfactory neurons, and some neuronal elements, probably immature neurons, since they were localized adjacent to the basal cell layer. Differentiated neurons in the olfactory epithelium did not express E-N-CAM. In contrast to N-CAM total, the 180-kDa component of N-CAM (N-CAM180) and E-N-CAM, L1 was not detectable on cell bodies in the olfactory epithelium. L1 and N-CAM180 were strongly expressed on axons leaving the olfactory epithelium. Olfactory axons were also labeled by antibodies to N-CAM180 and L1 in the lamina propria and the nerve fiber and glomerular layers of the olfactory bulb, but only some axons showed a positive immunoreaction for E-N-CAM. Ensheathing cells in the olfactory nerve were observed to bear some labeling for N-CAM total, L1, and N-CAM180, but not E-N-CAM. In the olfactory bulb, L1 was not present on glial cells. In contrast, N-CAM180 was detectable on some glia and N-CAM total on virtually all glia. Glia in the nerve fiber layer were labeled by E-N-CAM antibody only at the external glial limiting membrane. In the glomerular layer, E-N-CAM expression was particularly pronounced at contacts between olfactory axons and target cells. The presence of E-N-CAM in the adult olfactory epithelium and bulb was confirmed by Western blot analysis. The continued presence of E-N-CAM in adulthood on neuronal precursor cells, a subpopulation of olfactory axons, glial cells at the glia limitans, and contacts between olfactory axons and their target cells indicates the retention of embryonic features in the mammalian olfactory system, which may underlie its remarkable regenerative capacity.