INTERACTIONS WITH TENASCIN AND DIFFERENTIAL-EFFECTS ON CELL-ADHESION OF NEUROCAN AND PHOSPHACAN, 2 MAJOR CHONDROITIN SULFATE PROTEOGLYCANS OF NERVOUS-TISSUE

We have studied interactions of tenascin with two chondroitin sulfate proteoglycans, neurocan and phosphacan. Neurocan is a multi-domain pro teoglycan with a 136-kDa core protein that is synthesized by neurons a nd binds to hyaluronic acid, whereas the 173-kDa core protein of phosp hacan, which is synthesized by glia, represents an extracellular varia nt of the receptor-type protein tyrosine phosphatase RPTP zeta/beta. K eratan sulfate-containing glycoforms of phosphacan (designated phospha can-KS) are also present in brain. Immunocytochemical studies of early postnatal rat cerebellum demonstrated that the localization of neuroc an, phosphacan, and phosphacan-KS all overlap extensively with that of tenascin, an extracellular matrix protein that modulates cell adhesio n and migration. Binding studies using purified proteins covalently at tached to fluorescent microbeads demonstrated that proteoglycan-coated beads co-aggregated with differently fluorescing beads coated with te nascin. The co-aggregation was specifically inhibited by Fab' fragment s of antibodies against tenascin or the proteoglycans and by soluble n eurocan, phosphacan, and tenascin. A solid phase radioligand binding a ssay confirmed that neurocan, phosphacan, and phosphacan-KS bind to te nascin but not to laminin and fibronectin. Chondroitinase treatment of the proteoglycans or addition of free chondroitin sulfate had no sign ificant effect, indicating that the binding activity is mediated large ly via the core glycoproteins. Scatchard analysis demonstrated high af finity binding of I-125-phosphacan, phosphacan-KS, and neurocan to a s ingle site in tenascin, and neurocan and various glycoforms of phospha can all inhibited binding of I-125-phosphacan to tenascin. In studies of cell adhesion to proteins adsorbed to Petri dishes, phosphacan inhi bited adhesion of C6 glioma cells to tenascin whereas neurocan had no effect. Our results suggest that tenascin binds phosphacan and neuroca n in vivo and that interactions between chondroitin sulfate proteoglyc ans and tenascin may play important roles in nervous tissue histogenes is, possibly by modulating signal transduction across the plasma membr ane.