Upregulation of Epithelial-To-Mesenchymal Transition Markers and P2X7 Receptors Is Associated to Increased Invasiveness Caused by P2X7 Receptor Stimulation in Human Glioblastoma Stem Cells

Abstract

Glioblastoma (GBM) stem cells (GSCs), which contribute to GBM unfavorable prognosis, show high expression levels of ATP/P2X7 receptors (P2X7R). Here, we reported that cells exposure to 2’(3’)-O-(4-benzoylbenzoyl)-ATP (BzATP), a P2X7R agonist, up-regulated the expression of markers associated to epithelial-to-mesenchymal transition (EMT), a process likely contributing to GSC malignancy, and increased GSC migration/invasiveness like the known EMT inducer, Transforming Growth Factor β1 (TGFβ1). These effects were coupled to phosphorylation of SMAD2, a downstream effector in the TGFβ pathway, suggesting its involvement in P2X7R-mediated activity in GSCs. All BzATP effects, including a decrease in the caspase 3/7 activity in GSC medium, were mostly counteracted by the P2X7R antagonist A438079. Finally, BzATP increased the subunit expression of two main human P2X7R splice variants, the full-length P2X7A and the truncated P2X7B, lacking the carboxylic tail, which have different functional properties depending on their arrangement. Since up-regulation of A/B subunits might favor their assembly into a heterotrimeric P2X7R with great sensitivity towards agonists and cell energy support, this is in line with increased EMT markers expression, cell migration/invasion and GSC survival observed following P2X7R stimulation. As in GBM microenvironment extracellular ATP levels may activate P2X7R, our data suggest a P2X7R role in GBM recurrence/invasiveness.