Interactions of the chondroitin sulfate proteoglycan phosphacan, the extracellular domain of a receptor-type protein tyrosine phosphatase, with neurons, glia, and neural cell adhesion molecules.

Abstract

Abstract. Phosphacan is a chondroitin sulfate proteoglycan produced by glial cells in the central nervous system, and represents the extracellular domain of a receptor-type protein tyrosine phosphatase (RPTPg'/B). We previously demonstrated that soluble phosphacan inhibited the aggregation of microbeads coated with N-CAM or Ng-CAM, and have now found that soluble ~25I-phosphacan bound reversibly to these neural cell adhesion molecules, but not to a number of other cell surface and extracellular matrix proteins. The binding was saturable, and Scatchard plots indicated a single high affinity binding site with a Kd of ,~0.1 nM. Binding was reduced by "~15% after chondroitinase treatment, and free chondroitin sulfate was only moderately inhibitory, indicating that the phosphacan core glycoprotein accounts for most of the binding activity.Immunocytochemical studies of embryonic rat spinal cord and early postnatal cerebellum demonstrated that phosphacan, Ng-CAM, and N-CAM have overlapping distributions. When dissociated neurons were incubated on dishes coated with combinations of phosphacan and Ng-CAM, neuronal adhesion and neurite growth were inhibited. 125I-phosphacan bound to neurons, and the binding was inhibited by antibodies against Ng-CAM and N-CAM, suggesting that these CAMs are major receptors for phosphacan on neurons. C6 glioma cells, which express phosphacan, adhered to dishes coated with Ng-CAM, and low concentrations of phosphacan inhibited adhesion to Ng-CAM but not to laminin and fibronectin. Our studies suggest that by binding to neural cell adhesion molecules, and possibly also by competing for ligands of the transmembrane phosphatase, phosphacan may play a major role in modulating neuronal and glial adhesion, neurite growth, and signal transduction during the development of the central nervous system.

Molecular dissection of NRG1-ERBB4 signaling implicates PTPRZ1 as a potential schizophrenia susceptibility gene

“…44 The carbonic anhydrase domain interacts with the cell recognition molecule contactin, 51 whereas the spacer region can interact with several other cell adhesion molecules including NrCAM, L1CAM, NCAM, contactin-1 and contactin-2/TAG-1. [52][53][54][55][56] PTPRZ1 gene products are expressed from early developmental to adulthood in glial cells 47,[57][58][59] as well as in certain population of neurons [60][61][62][63] and are implicated in neuron-glial cell interactions that involve on bi-directional signaling, including myelination and node of Ranvier formation, through interactions with neuronal cell adhesion molecules. 55,56 Interestingly, in situ hybridization analysis has shown that PTPRZ1 is expressed in the subventricular zone of the lateral ventricles in early embryos and in adults, in the subgranular zone in the dentate gyrus of the hippocampus of adults, 57,64 and in adult glial progenitor cells, 65 suggesting that PTPRZ1 also has a function in adult stem/progenitor cells.…”

The Fibrinogen-like Globe of Tenascin-C Mediates Its Interactions with Neurocan and Phosphacan/Protein-tyrosine Phosphatase-ζ/β

“…The effects of phosphacan on C6 cell adhesion to tenascin-C are similar to the previously observed inhibition of neuronal adhesion to the neural cell adhesion molecule Ng-CAM/L1. It was concluded from these studies that inhibition of neuronal adhesion by both neurocan and phosphacan (which bind to Ng-CAM/ L1) is mediated by direct effects on the cells rather than via binding to the substrate, since the proteoglycans also inhibited adhesion to a substrate consisting of anti-Ng-CAM antibodies, to which the proteoglycans do not bind (9,10). Phosphacan also inhibited the adhesion of C6 cells to Ng-CAM (7) but not to laminin (1).…”

“…Binding assays were performed as described previously (10). Briefly, proteins at a concentration of 1-12 nM were coated in removable Immulon-4 wells, and binding of 125 I-labeled neurocan and phosphacan was measured in 20 mM Tris, pH 7.4, containing 150 mM NaCl, 2 mM CaCl 2, 2 mM MgCl 2, 0.02% NaN 3 , and 1 mg/ml heat-treated BSA, following incubation with gentle shaking (45 rpm) for 9 -12 h at room temperature.…”

“…Immunocytochemical studies of embryonic and early postnatal nervous tissue showed an overlapping localization of the proteoglycans with all of their identified ligands, further supporting the biological significance of their ability to interact in vitro. In addition to their demonstrated high-affinity interactions with neural cell adhesion and extracellular matrix proteins, neurocan and phosphacan are also potent inhibitors of cell adhesion and inhibit or stimulate neurite outgrowth depending on the cell type and other factors (1,9,10,12,13). Our data therefore suggest that these two chondroitin sulfate proteoglycans are components of a multidimensional mechanism for the regulation of cell-cell and cell-matrix interactions at different sites and periods during nervous tissue histogenesis and that the multiplicity of ligands with differing affinities and properties could provide a means for the fine tuning of various regulatory processes.…”

The effects of proteoglycan surface patterning on neuronal pathfinding

“…It has also been found that aggrecan affects laminin activity on neuron cell body substratum attachment depending on the order in which the two molecules are adsorbed, providing evidence that the effect of aggrecan is not simply additive [132]. It has thus been suggested that aggrecan and other CSPGs may exert their inhibitory effect by adversely changing the activity of laminin and other growth promoting molecules through protein-protein interactions and conformational changes.Interactions between proteoglycans and laminins have been elucidated including CSPG direct binding to and masking of laminin integrin sites [133][134][135]. It has also been found that certain CSPGs appear to affect only particular growth promoting molecules.…”