Glioblastoma (GBM) is the most common and malignant primary tumor in adults. When GBM tumors are located close to the lateral ventricle they display a more aggressive recurrence pattern and negatively impact patient survival. These findings suggest the involvement of the subventricular zone neurogenic niche in GBM malignancy. To define the inter-cellular communication between neural stem cells and GBM cells, we optimized a tool to determine cell-specific proteomic changes of GBM cells in response to neural stem cell proximity.
We cloned the mutated methionyl-tRNA synthetase (MetRS) gene into the lentiviral plasmid MetRS puro. MetRS allows for incorporation of azide-tagged methionine analog azidonorleucine (ANL) into newly formed proteins, effectively labeling proteins synthesized by expressing cells. We utilized the pLKO.1 vector backbone allowing puromycin resistance as a selection method. The MetRS L274 modification was confirmed, as only MetRS-transduced cells of both commercial HEK and primary GBM1A cell lines selectively incorporated ANL. Following verification, we successfully packaged the plasmid into a lentivirus. We transduced primary human fetal neural stem cell (hfNSC) and GBM lines and selected the MetRS-expressing cells by puromycin exposure. After 96 hours, wild type (WT) cells died while successfully transduced cells exhibited resistance and the ANL-compatible MetRS enzyme.
Co-cultures consisting of MetRS-transduced GBM and WT hfNSCs were used to simulate a similar environment of glioblastoma neighboring lateral ventricles. Proteome Profiler results showed a significant downregulation of an angiogenesis inhibitor and upregulation of malignancy promoting proteins in GBM1A. Going forward, this analysis method will be used for cell-specific proteomics in vivo
