To begin understanding the regulation and biological significance of changes in the expression of intermediate filament proteins in astrocytic tumors, we have recently shown that TGF-alpha alters the protein level of glial fibrillary acidic protein (GFAP), nestin, and vimentin in U-373 MG glioblastoma cells. Here, we have determined the molecular mechanisms regulating these changes. In addition, to evaluate the significance of these changes we have examined whether TGF-alpha affects various cellular properties related to differentiation. Our results show that, in U-373 MG cells treated with TGF-alpha, GFAP gene transcription, mRNA level, and specific protein synthesis decrease by approximately 50%. This suggests that, in U-373 MG cells, TGF-alpha down-regulates the expression of this marker of astrocytic differentiation at the transcriptional level, resulting in decreased GFAP mRNA level and specific protein synthesis. In contrast, TGF-alpha does not change vimentin gene transcription, but increases by about 50% the transcription of the gene for nestin, a marker for undifferentiated astrocytic precursors. This differential regulation of GFAP, nestin, and vimentin gene expression indicates that TGF-alpha induces further dedifferentiation of U-373 MG cells. This notion is also supported by our findings that TGF-alpha increases the motility of U-373 MG cells and induces a less stellate morphology.
Copyright 2000 Academic Press.