Retinoic acid-induced alterations enhance eATP-mediated anti-cancer effects in glioma cells: Implications for P2X7 receptor variants as key players

Retinoic acid (RA) is a small, lipophilic molecule that inhibits cell proliferation and induces differentiation through activation of a family of nuclear receptors (RARs). The therapeutic potential of RA in the treatment of glioma was first evaluated two decades ago, but these attempts were considered not conclusive. Based on the complexity of tumor microenvironment and the role of purinergic signals within TME, we aimed to support RA-induced alterations in glioma cells with extracellular ATP. Our experiments focused on defining the purinergic signaling dynamics of two different human glioma cell lines M059K and M059J subjected to RA-based differentiation protocol. The applied procedure caused considerable modulation in P2X7 receptor variants expression at the gene and protein level, and decrease in ecto-nucleotidase activity. Collectively, it led to the decrease in cell proliferation rate and migration, as well as boosted sensitivity to cytotoxic eATP influence. We confirmed that micromolar concentrations of ATP decreased cell viability by 40 and 20 % in RA-treated M059K and M059J cells, respectively. Moreover, the decrease in migration capability up to 60 % in the presence of 100 μM ATP was observed. Both effects were mediated by P2X7R activation and reversed in the presence of A740003 antagonist, confirming the role of P2X7 receptor. We postulate that retinoic acid-induced changes coupled with micromolar eATP could be effective as anti-cancer treatment affecting the purinergic signaling. The obtained results point out the role of P2X7R variants in influencing potential of glioma cells, as well as the possibility of using these isoforms as therapeutic targets.