Quantitative increase of neuroglia-specific GFA protein in rat C-6 glioma cells in vitro.

Abstract

AMONG neural cell lines the C-6 glioma, a cell line cloned from an N-methylnitrosourea (MNU)-induced experimental glioma in rat, has generated considerable interest as a model system for the study of neuroglia1. The clone was originally selected on the basis of a high production of the protein S-100, a protein believed to be characteristic of glial cells in vivo2. Since its introduction, the line has been further characterised with regard to a number of other biochemical features3. Among these is the recent demonstration of the glial fibrillary acidic (GFA) protein by immunofluorescent staining of C-6 cells maintained in certain in vitro conditions4. The GFA protein, isolated from multiple sclerosis plaques and areas of sub-ependymal gliosis in the central nervous system, has been shown to be a specific marker for fibrillary astrocytes, is believed to be a component of the 80–90 A diameter glial filaments5–8, and has not been reported in non-glial neural cell lines. It is, therefore, a useful biochemical marker for the differentiation of a type of mature astrocyte. In previous work with the C-6 line, GFA protein was found to be present by immunofluorescence in only an occasional C-6 cell maintained in monolayer or suspension cultures, and to be markedly increased in many C-6 cells when they were maintained for 12–14 d in an organ culture system using Gelfoam matrices4. Such a system is known to favour structural differentiation in vitro9. No increase of filaments was observed, however, in any of the in vitro systems used, suggesting that the synthesis of GFA protein could proceed without the formation of intracytoplasmic glial filaments4. We compared the quantitative levels of GFA protein in C-6 and other cell types in various culture conditions, using a “two-site” immunoradiometric assay recently developed in this laboratory10.