RECEPTOR TYROSINE PHOSPHATASE-BETA IS EXPRESSED IN THE FORM OF PROTEOGLYCAN AND BINDS TO THE EXTRACELLULAR-MATRIX PROTEIN TENASCIN

The extracellular domain of receptor type protein tyrosine phosphatase beta (RPTP beta) exhibits striking sequence similarity with a soluble , rat brain chondroitin sulfate proteoglycan (3F8 PG). Immunoprecipita tion experiments of cells transfected with RPTP beta expression vector and metabolically labeled with [S-35]sulfate and [S-35]methionine ind icate that the transmembrane form of RPTP beta is indeed a chondroitin sulfate proteoglycan. The 3F8 PG is therefore a variant form composed of the entire extracellular domain of RPTP beta probably generated by alternative RNA splicing. Previous immunohistochemical studies indica ted that both RPTP beta and the extracellular matrix protein tenascin are localized in similar regions of the central nervous system. We hav e performed co-aggregation assays with red and green Covaspheres coate d with tenascin and 3F8 PG, respectively, showing that the extracellul ar domain of RPTP beta (3F8 PG) binds specifically to tenascin. The in teraction between a receptor tyrosine phosphatase and an extracellular matrix protein may have a role in development of the mammalian centra l nervous system.