Extracellular vesicles (EVs) play key roles in
glioblastoma (GBM) biology and represent novel sources of
biomarkers that are detectable in the peripheral circulation. Despite this notionally non-invasive approach to assess GBM tumours in situ, a comprehensive GBM EV
protein signature has not been described. Here, EVs secreted by six GBM cell lines were isolated and analysed by quantitative high-resolution mass spectrometry. Overall, 844
proteins were identified in the GBM EV
proteome, of which 145
proteins were common to EVs secreted by all cell lines examined; included in the curated EV compendium (Vesiclepedia_559; http://microvesicles.org ). Levels of 14 EV
proteins significantly correlated with cell invasion (invadopodia production; r2 > 0.5, p < 0.05), including several
proteins that interact with molecules responsible for regulating invadopodia formation. Invadopodia, actin-rich membrane protrusions with proteolytic activity, are associated with more aggressive disease and are sites of EV release. Gene levels corresponding to invasion-related EV
proteins showed that five genes (
annexin A1,
actin-related protein 3,
integrin-β1,
insulin-like growth factor 2 receptor and programmed cell death 6-interacting
protein) were significantly higher in GBM tumours compared to normal brain in silico, with common functions relating to actin polymerisation and endosomal sorting. We also show that Cavitron Ultrasonic Surgical Aspirator (CUSA) washings are a novel source of brain tumour-derived EVs, demonstrated by particle tracking analysis, TEM and
proteome profiling. Quantitative proteomics corroborated the high levels of proposed invasion-related
proteins in EVs enriched from a GBM compared to low-grade
astrocytoma tumour. Large-scale clinical follow-up of putative
biomarkers, particularly the proposed survival marker
annexin A1, is warranted.