Glial tumor cell adhesion is mediated by binding of the FNIII domain of receptor protein tyrosine phosphatase β (RPTPβ) to tenascin C

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Abstract
The extracellular domain of receptor protein tyrosine phosphatase β (RPTPβ) 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 RPTPβ 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 RPTPβ. 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 RPTPβ with tenascin C was found to mediate cell adhesion. Adhesion and spreading of SF763T astrocytoma cells expressing RPTPβ on tenascin C was specifically abolished by the addition of a soluble fragment containing the FNIII domain of the receptor. RPTPβ-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 RPTPβ adhere to TnfnA1,2,4, while the parental cells did not. These results demonstrate that the FNIII domain of RPTPβ binds to tenascin C and suggest that RPTPβ present on glial tumor cells is a primary adhesion receptor system to the extracellular matrix.

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