Ubiquitin in normal, reactive and neoplastic human astrocytes

Ubiquitin, a protein important in regulating non-lysosomal proteolysis, has previously been shown to be present in cytoskeletal inclusions of the neurodegenerative diseases. Its role in other pathological processes of the central nervous system, such as neoplastic transformation of cells, is not known. The astrocytoma, a tumor of complex biology derived from the astrocyte, is the most common primary parenchymal human brain tumor in both children and adults. Until recently, ubiquitin was not known to form stable conjugates in cells. We have shown using immunocytochemistry on sections of astrocytomas that both glial fibrillary acidic protein (GFAP) (the major intermediate filament protein present in normal, reactive and neoplastic astrocytes) and ubiquitin are simultaneously present in the cytoplasm and cell processes of tumor cells. The presence of ubiquitin and GFAP was also found in astrocytoma cells in short- and long-term culture, and confirmed by immunostaining of blots of tumor homogenates subjected to sodium dodecyl sulfate polyacrylamide gel electrophoresis.