Investigating mitochondrial stress signalling and the integrated stress response.

Vollständiger Abstract

Worum geht es in dieser Arbeit?

Mitochondria produce cellular energy, but because most mitochondrial proteins are stored in the nucleus, they also function as signalling centres that regulate homeostasis and stress responses. In response to stressors, including DNA damage and amino acid imbalance, mitochondria communicate with the nucleus through mito-nuclear signalling pathways. One such pathway is the mitochondrial integrated stress response (mtISR), although the mechanisms by which mitochondrial stressors activate this response remain unclear. Our goal is to define the mtISR signalling pathways activated by different mitochondrial stressors and determine whether responses are stress-specific. Using K562 cells, a model of chronic myelogenous leukemia, we aimed to clarify the mechanisms underlying mtISR activation. This work seeks to advance our understanding of mitochondrial stress responses and mechanisms involved in cancer cell adaptation and therapeutic resistance. K562 cells were treated with the BH3 mimetics ABT-199, ABT-263, and ABT-737, chemotherapeutic agents that engage apoptosis, as well as electron transport chain inhibitors oligomycin, a complex V inhibitor, rotenone/antimycin, a complex I/III inhibitor, and IACS, a complex I inhibitor. Flow cytometry assessed mitochondrial membrane potential, and western blotting measured apoptosis markers and ISR-associated proteins, including cleaved PARP, phosphorylated eIF2α and ATF4, which assess ISR activation, and GADD34, which mediates a negative-feedback loop that resolves prolonged ISR activation. ABT-199 strongly activated the ISR, whereas ABT-263 and ABT-737 produced minimal activation. Despite this, ABT-199 was the least lethal to K562 cells, suggesting that ISR activation does not directly correlate with cell death. The ISR was also activated by oligomycin and rotenone/antimycin, but not IACS, indicating that mitochondrial dysfunction can produce distinct responses. Future work will investigate the role of ISR activation in promoting survival following ABT-199 treatment and establish the signalling pathways engaged by mitochondrial stressors such as electron transport chain inhibition. These findings may help improve cancer therapies by targeting mtISR-dependent survival mechanisms.Supervisors: Dr. Edmond Chan and Dr. Sheela Abraham