Poster Presentation Australasian Extracellular Vesicles Conference 2018

Proteome profiling of extracellular vesicles from neurosurgical aspirates identifies Chaperonin Containing TCP1 Subunit 6A (CCT6A) as a potential glioblastoma biomarker with prognostic significance (#61)

Susannah Hallal 1 , Benjamin P Russell 2 , Heng Wei 3 , Maggie Lee 3 , Christopher Toon 2 , Joanne Sy 3 , Brindha Shivalingam 4 , Michael E Buckland 1 3 , Kimberley L Kaufman 3 5
  1. Discipline of Pathology, Brain and Mind Centre, The University of Sydney, Camperdown, NSW, Australia
  2. Sydney Medical School, The University of Sydney, Camperdown, NSW, Australia
  3. Department of Neuropathology, Royal Prince Alfred Hospital, Camperdown, NSW, Australia
  4. Department of Surgery, Chris O'Brien Lifehouse, Camperdown, NSW, Australia
  5. School of Life and Environmental Science, Brain and Mind Centre, The University of Sydney, Camperdown, NSW, Australia

Glioblastoma (GBM), WHO-grade IV glioma, carries a dismal prognosis owing to its infiltrative growth and limited treatment options. GBM-derived extracellular vesicles (EVs; 30-1000nm membranous particles) influence the microenvironment to mediate tumour aggressiveness and carry oncogenic cargo across the blood-brain-barrier into the circulation. As such, EVs represent biomarker reservoirs with enormous potential for assessing glioblastoma tumours in situ. We have shown that neurosurgical aspirates are rich sources of EVs, isolated directly from glioma micro-environments. Using quantitative LC-MS/MS, we compared EV proteomes enriched from GBM (n=15) and glioma grade II-III (n=7) aspirates and identified 298 differentially-abundant proteins (p-value<0.00496; Benjamini-Hochber­­g correction for multiple comparisons). These included previously identified putative EV biomarkers for GBM invasiveness (ANXA1, ITGB1, ACTR3 and PSMD2) among many other interesting targets. Levels of all eight subunits of the key molecular chaperone, T-complex protein 1 Ring complex (TRiC), were higher in GBM-EVs, including CCT2, CCT3, CCT5, CCT6A, CCT7 and TCP1 (p<0.00496). Analogous increases in TRiC transcript levels and DNA copy numbers were detected in silico, where CCT6A had the greatest induction of expression and amplification in glioblastoma and showed a negative association with survival (p=0.006). CCT6A is co-localised with EGFR at 7p11.2, with a strong tendency for co-amplification (p<0.001). Immunohistochemistry corroborated the CCT6A proteomics measurements and indicated a potential link between EGFR and CCT6A tissue expression. Further studies are needed to better understand this molecular interplay and may reveal EV-associated CCT6A as a proxy for EGFR testing. Putative EV-biomarkers described here will be further assessed in EVs captured from peripheral blood.