gms | German Medical Science

Using subtractive cloning we identified contactin as overexpressed in glioblastomas compared with normal brain. Contactin is a cell surface adhesion molecule that is normally not expressed by astrocytes. It is expressed by neurons and oligodendrocytes at particularly high levels during development. Contactin can mediate adhesive or repulsive intercellular interactions depending on the molecular context. We analyzed the expression of contactin in human astrocytomas and determined its functional relevance for glioma cells.

Western blotting, immunohistochemistry and confocal immunocytochemistry were used to analyze contactin expression in astrocytomas and astrocytes. Adhesion and migration assays were performed to study effects of contactin on glioma cells. Contactin cDNA was transfected into glioma cells to determine the effect of contactin overexpression on attachment to extracellular matrix (ECM) molecules. Expression of the receptor-type protein tyrosine phosphatase β (RPTPβ), a specific contactin ligand that is also overexpressed in glioblastomas, was downregulated by stable siRNA transfection to study interactions with contactin overexpressing cells.

Contactin expression was detected in GFAP positive tumor cells but was absent in normal astrocytes. Levels of contactin in gliomas were associated with increasing malignancy grade. None of 10 glioblastoma cell lines adhered to contactin or was stimulated in its motility by contactin. In contrast, increasing coating concentrations of contactin caused progressive cell repellence. Co-presentation with contactin reduced the haptotactic migration induced by fibronectin in several cell lines. Overexpression of contactin in human glioblastoma cells by cDNA transfection had no effect on cell proliferation or adhesion to various ECM molecules. Contactin expression also did not alter the adhesion to cells expressing normal or downregulated levels of RPTPβ.

The expresssion of astrocytic as well as neuronal markers within glioma cells may reflect an ability of these cells for multilineage differentiation, a phenomenon that has recently been described also for the so-called glioma stem cells. While adhesive and proliferative properties of glioma cells are unaltered by contactin overexpression, confrontation of glioma cells with contactin has repulsive effects, which may contribute to the diffuse infiltration pattern characteristic of these cells in human brain.