The presence of neuron-associated microtubule proteins in the human U-251 MG cell line. A comparative immunoblot and immunohistochemical study.

U-251 MG, a permanent cell line derived from human glioblastoma multiforme with the capacity to maintain glial fibrillary acidic protein (GFAP) production over repeated in vitro passages, was evaluated for the expression of three neuron-associated proteins (Class III beta-tubulin, MAP2, and tau) in three different in vitro systems: as free-floating suspensions, on coverslips, and on a gelatin foam (Gelfoam) matrix. Cells grown under the three in vitro conditions were analyzed by immunoblotting techniques, whereas immunohistochemical analyses were performed on cells grown on Gelfoam. By immunohistochemistry, cells were positive for Class III beta-tubulin isotype, a neuron-associated beta-tubulin, for microtubule-associated protein 2 (MAP2), but not for tau. Immunoblotting studies confirmed the presence of Class III beta-tubulin in extracts of cells grown under the three in vitro conditions. MAP2 and tau were clearly evident only in cell extracts grown in Gelfoam cultures. GFAP expression was observed in all three in vitro conditions by immunoblotting and also in foam matrix cultures by immunohistochemistry. In matrix cultures, Class III beta-tubulin- and GFAP-positive cells were found immediately adjacent to each other, but coexpression of these proteins was not observed, and the cells were morphologically indistinguishable. Our findings confirm the heterogeneity of malignant gliomas in vitro, and the implications of these observations require further study.