Ursolic acid inhibits cell migration and promotes JNK-dependent lysosomal associated cell death in Glioblastoma multiforme cells

Ursolic acid (UA) is a bioactive compound which has demonstrated therapeutic efficacy in a variety of cancer cell lines. UA activates various signalling pathways in Glioblastoma multiforme (GBM), however, the relationship between cell death and migration has yet to be elucidated. UA induces a dose dependent cytotoxic response demonstrated by flow cytometry and biochemical cytotoxicity assays. Inhibitor and fluorescent probe studies demonstrated that UA induces a caspase independent, JNK dependent, mechanism of cell death. Migration studies established that UA inhibits GBM cell migration in a time dependent manner that is independent of the JNK signalling pathway. The cytotoxic insult induced by UA resulted in the formation of acidic vesicle organelles (AVOs), speculating activation of autophagy. However, inhibitor and spectrophotometric analysis demonstrated that autophagy was not responsible for the formation of the AVOs and confocal microscopy identified the AVO as lysosomes. Further investigation using isosurface visualisation of confocal imaging determined co-localisation of lysosomes with the previously identified acidic vesicles, thus providing evidence that lysosomes are likely to be playing a role in UA induced cell death. Collectively, our data identifies that UA rapidly induces a lysosomal associated mechanism of cell death in addition to UA acting as an inhibitor of GBM cell migration.