Occurrence of Total and Proteinase K-Resistant Alpha-Synuclein in Glioblastoma Cells Depends on mTOR Activity

Alpha-synuclein (-syn) is a protein considered to be detrimental in a number of degenerative disorders (synucleinopathies) of which -syn aggregates are considered a pathological hallmark. The clearance of -syn strongly depends on autophagy, which can be stimulated by inhibiting the mechanistic target of rapamycin (mTOR). Thus, the overexpression of mTOR and severe autophagy suppression may produce -syn accumulation, including the proteinase K-resistant protein isoform. Glioblastoma multiforme (GBM) is a lethal brain tumor that features mTOR overexpression and severe autophagy inhibition. Cell pathology in GBM is reminiscent of a fast, progressive degenerative disorder. Therefore, the present work questions whether, as is analogous to neurons during degenerative disorders, an overexpression of -syn occurs within GBM cells. A high amount of -syn was documented in GBM cells via real-time PCR (RT-PCR), Western blotting, immunohistochemistry, immuno-fluorescence, and ultrastructural stoichiometry, compared with the amount of a e b -synucleins and compared with the amount of -syn counted within astrocytes. The present study indicates that (i) -syn is overexpressed in GBM cells, (ii) -syn expression includes a proteinase-K resistant isoform, (iii) -syn is dispersed from autophagy-like vacuoles to the cytosol, (iv) -syn overexpression and cytosol dispersion are mitigated by rapamycin, and (v) the -syn-related GBM-like phenotype is mitigated by silencing the SNCA gene.