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

Abstract

Alpha‐synuclein (α‐syn) is a protein considered to be detrimental in a number of degenerative disorders (synucleinopathies) of which α‐syn aggregates are considered a pathological hallmark. The clearance of α‐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 α‐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 α‐syn occurs within GBM cells. A high amount of α‐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 β‐ and γ‐synucleins and compared with the amount of α‐syn counted within astrocytes. The present study indicates that (i) α‐syn is overexpressed in GBM cells, (ii) α‐syn expression includes a proteinase‐K resistant isoform, (iii) α‐syn is dispersed from autophagy‐like vacuoles to the cytosol, (iv) α‐syn overexpression and cytosol dispersion are mitigated by rapamycin, and (v) the α‐syn‐related GBM‐like phenotype is mitigated by silencing the SNCA gene.