Identification of glial filament protein and vimentin in the same intermediate filament system in human glioma cells.

We have used a human glioma cell line (U-251MG) to study the expression and cytoplasmic organization of vimentin (decamin) and the glial filament protein (GFP). Four clones of the parental U-251 cultures were isolated and found to express GFP from 1-2% to 99% of the cells in the population. Double immunofluorescence microscopy with antibodies to vimentin and GFP has shown that, in all four clonal cell lines, vimentin-containing filaments are expressed in most cells as an organized network and, in GFP-positive cells, GFP and vimentin are associated with the same filament network. Immunoelectron microscopy with specific antibodies labeled with colloidal gold particles of various sizes shows that GFP and vimentin are localized in the same filaments. These findings confirm in vitro studies of the copolymerization of subunits of different biochemical nature into the same intermediate filament and suggest the in vivo probability of the coassembly of GFP and vimentin from a possible soluble pool of monomers.