ALTERED STRESS GRANULES DYNAMIC MODULATES CELL FATE IN BORTEZOMIB-TREATED HUMAN GLIOMA CELLS

LAURA V. BONNET; JESICA FLORES-MARTIN; MAURICIO R. GALIANO; MARTA E. HALLAK

Buenos Aires

Congreso; Reunión Conjunta de Sociedades de Biociencias; 2017

Sociedad Argentina de Investigación en Bioquímica y Biología Molecular

Among different human glioma cells, we determined a differential susceptibility to Bortezomib treatment (BT) that correlates with variable expression levels and subcellular localization of arginylated calreticulin (R-CRT), together with ER stress induction. Those cells (MO59K) that are resistant to BT showed a small variation of R-CRT, which appears confined to increased stress granules (SGs) formation and sharp ER stress. Whereas those cells (HOG) that are susceptible to BT showed intracellular increased levels and plasma membrane enrichment of R-CRT, where it participates in a caspase 3 dependent pro-apoptotic signaling, after strong ER stress induced by the drug. Co-treatment of HOG cells with BT and Tannic Acid (TA, Ate1 inhibitor) reverts the cytotoxicity shown by BT alone. Since the formation of SGs is associated with a greater resistance to chemotherapy, we evaluate how its dynamism is affected in both HOG and MO59K. Firstly, by immunofluorescence, we determined that HOG exposed to both BT and TA showed an increase of SGs formation in agreement with enhanced resistance of these cells to BT, change that is not shown by co-treated MO59K. However, the later showed the formation of smaller SGs after co-treatment. Secondly, as autophagy is known to degrade SGs, we also evaluate whether it is induced in both cell types during BT. After BT treatment MO59K showed a clear induction of LC3 II. By contrast, a strong activation of autophagy was shown by HOG even in control condition (non-treated cells), what may correspond with a reduced number of SGs in these cells. Hence, the increased susceptibility of HOG cells to BT is associated with a markedly active autophagy and robust induction of ER stress, which strongly promotes arginylation of CRT and R-CRT exposure at plasma membrane. By contrast, in MO59K cells a controlled induction of both autophagy and ER stress maintains reduced levels of R-CRT that mainly associates with SGs, as a hallmark of BT resistance.