The extracellular domain of
receptor protein tyrosine phosphatase beta (
RPTPbeta) is composed of several domains which mediate its interactions with distinct
ligands present on the surface of either neurons or glial cells. Here, we demonstrate that the fibronectin type III domain (FNIII) of
RPTPbeta binds to glial
tumor-derived cell lines and primary astrocytes. We used affinity purification to isolate several
proteins that specifically bind to the FNIII domain of
RPTPbeta. One of these, a 240 kDa
protein that was purified from U118MG
glioblastoma cell, was identified as
tenascin C based on the amino acid sequence of several tryptic
peptides. The interaction of
RPTPbeta with
tenascin C was found to mediate cell adhesion. Adhesion and spreading of SF763T
astrocytoma cells expressing
RPTPbeta on
tenascin C was specifically abolished by the addition of a soluble fragment containing the FNIII domain of the receptor.
RPTPbeta-dependent cell adhesion was mediated by binding to the alternatively spliced FNIII repeats A1,2,4 (TnfnA1,2,4) of
tenascin C. Furthermore, COS cells expressing
RPTPbeta adhere to TnfnA1,2,4, while the parental cells did not. These results demonstrate that the FNIII domain of
RPTPbeta binds to
tenascin C and suggest that
RPTPbeta present on glial
tumor cells is a primary
adhesion receptor system to the extracellular matrix.