Stem-16. promoting the cancer stem cell subpopulation and phenotype in glioblastoma via extracellular vesicle cross-talk

INTRODUCTION Extracellular vesicles (EVs) released from cancer cells contain bioactive molecules that have been long implicated in tumorigenesis. In glioblastoma (GBM), there is mounting evidence that EVs play a role in critical processes including angiogenesis, immune suppression, and invasion. GBM secreted EVs have also been demonstrated to promote a cancer stem cell (CSC) phenotype by transporting stemness markers and proteins (I.e. Notch-1) involved in stem-cell activating pathways. Understanding the maintenance of CSCs, which contributes to tumor proliferation, treatment resistance, and re-expansion of the tumor bulk, can offer insight into new therapeutic drug targets that can disrupt this subpopulation. METHODS EVs were isolated from patient-derived primary GBM cell lines maintained as adherent cultures and free floating spheres (n = 3) using a staged ultracentrifugation technique. Normal astrocytes were used as the control group (n = 1). Protein expression profiles were then generated via high-throughput mass spectrometry for both EVs and whole cell lysate samples from the same cell line and compared against each other. RESULTS EGF-containing fibulin extracellular matrix protein 1 (EFEMP1) was shown to be upregulated in GBM derived EVs compared to control. Further analysis shows that EFEMP1 is enhanced in adherent cultures compared to free floating sphere cultures. CONCLUSION EFEMP1 is an extracellular matrix protein that has been identified as an oncogenic protein in GBM by activating Notch-1, Akt, and NF-Kb signaling pathways resulting in increased Temozolomide resistance, cellular proliferation, and invasion, all of which are hallmark characteristics of CSCs. EFEMP1 is also a downstream effector in the HIF-1 pathway, which has been strongly correlated in the maintenance of CSCs. Our results therefore demonstrate a possible EV mediated mechanism for the maintenance of the CSC population and phenotype in GBM.