Distinct Sites on Tenascin-C Mediate Repellent or Adhesive Interactions with Different Neuronal Cell Types

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Abstract
In this study we have determined the binding specificities of four different neuronal cell types to tenascin-C (TN-C) and laminin using a cell adhesion assay. TN-C was repulsive for small cerebellar neurons and PC12 phaeochromocytoma cells, since after short-term adhesion to the substrate-bound molecule with a maximum of cell binding at 45 min, the cells detached from the substrate and after 22 h only about 25% of the originally adherent cells were still bound. For N2A neuroblastoma cells and retinal cells TN-C was an adhesive substrate, since the number of adherent cells did not decrease after the initial attachment period. All four cell types adhered well to laminin at all time points studied. For short-term adhesion of small cerebellar neurons and PC12 cells two binding sites were identified on TN-C, one being localized within the epidermal growth factor-like repeats three to five and the second within fibronectin type III-like repeats three and four. One binding site for N2A and retinal cells was localized within fibronectin type III-like repeat seven. Binding of small cerebellar neurons to TN-C was dependent on Ca2+, but not on Mg2+ and was inhibitable by polyclonal antibodies to beta 1 integrin. Short-term adhesion of small cerebellar neurons was also inhibitable with a mixture of recombinant fragments of TN-C encompassing the whole molecule, although the specific inhibitory activity of this mixture was ten-fold lower on a molar basis when compared to the native molecule. Our observations indicate that different neuronal cell types use distinct binding sites on TN-C for repellent or adhesive interactions and that beta 1 integrin is involved in the recognition event leading to repulsion of small cerebellar neurons.

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