Regulation of autophagy, endoplasmic reticulum and unfolded protein response by glucocorticoids in physiology and disease

Acute lymphoblastic leukemia (ALL) is the most frequent cancer in children, and although highly treatable, challenges remain due to significant side effects of therapy and the poor outcome for some patients. Synthetic glucocorticoid, Dexamethasone (Dex), has been used to treat several haematological malignancies including ALL. To understand better how GC-resistant leukemic cells respond to Dex treatment, combination treatment of Dexamethasone with Chloroquine (CLQ), Thapsigargin (TG), Rotenone (ROT) and Bortezomib (BTZ) were used to investigate the role of autophagy, endoplasmic reticulum stress (ER stress) and unfolded protein response (UPR) respectively, in acute lymphoblastic leukemia cell lines including CEM-C1-15, CEM-C7-14 and Molt4. The results showed that autophagy inhibition by CLQ increased cell death and combination treatment with Dex exerted cytotoxic effect in all cells. These findings suggest that autophagy may play the important role to protect the ALL cells from GC-induced cell apoptosis, especially in GC-resistant cells. Furthermore, ER stress inducer, TG, treatment in the absence and presence of dexamethasone resulted in increase of ER chaperone proteins GRP78 and GRP94 in CEM-C7-14 cells. This is potentially related to increased cell death and may play a role in ER stress mediated cell apoptosis. Protein degradation inhibition by BTZ sensitised the ALL cells to the treatments and combination conditions had synergistic effect in all leukemic cells. Reactive oxygen species assay indicated that increased ROS levels correlate with the increase in CEM cells death in ROT only and combination treatment with Dex. Interestingly, ER chaperone proteins GRP78 and GRP94 increase in the protein but not mRNA expression levels in Dexamethasone treated glucocorticoid-sensitive cells. These results suggested that GR regulated chaperone protein levels by indirect mechanism. Taken together, these findings suggest that autophagy may be acting as pro survival process in glucocorticoid resistant leukemia. In GC sensitive leukemia, mitochondria and ER are important for GCs dependent cell death and GCs mediated increase in the GRPs protein levels that could lead to cell apoptosis. These results, if confirmed in clinical samples may have prognostic, diagnostic and therapeutic future use in medicine