CONICET | Buscador de Institutos y Recursos Humanos

Among different human glioma cells, we determined a differentialsusceptibility to Bortezomib treatment (BT) that correlates withvariable expression levels and subcellular localization of arginylatedcalreticulin (R-CRT), together with ER stress induction. Thosecells (MO59K) that are resistant to BT showed a small variation ofR-CRT, which appears confined to increased stress granules (SGs)formation and sharp ER stress. Whereas those cells (HOG) that aresusceptible to BT showed intracellular increased levels and plasmamembrane enrichment of R-CRT, where it participates in a caspase3 dependent pro-apoptotic signaling, after strong ER stress inducedby the drug. Co-treatment of HOG cells with BT and Tannic Acid(TA, Ate1 inhibitor) reverts the cytotoxicity shown by BT alone. Sincethe formation of SGs is associated with a greater resistance to chemotherapy,we evaluate how its dynamism is affected in both HOGand MO59K. Firstly, by immunofluorescence, we determined thatHOG exposed to both BT and TA showed an increase of SGs formationin agreement with enhanced resistance of these cells to BT,change that is not shown by co-treated MO59K. However, the latershowed the formation of smaller SGs after co-treatment. Secondly,as autophagy is known to degrade SGs, we also evaluate whetherit is induced in both cell types during BT. After BT treatment MO59Kshowed a clear induction of LC3 II. By contrast, a strong activation ofautophagy was shown by HOG even in control condition (non-treatedcells), what may correspond with a reduced number of SGs inthese cells. Hence, the increased susceptibility of HOG cells to BT isassociated with a markedly active autophagy and robust induction ofER stress, which strongly promotes arginylation of CRT and R-CRTexposure at plasma membrane. By contrast, in MO59K cells a controlledinduction of both autophagy and ER stress maintains reducedlevels of R-CRT that mainly associates with SGs, as a hallmark ofBT resistance.