Borankova, K. | Search bioRxiv

bioRxiv2024

Depletion of chemoresponsive mitochondrial fission mediator DRP1 does not mitigate sarcoma resistance

Specific patterns of mitochondrial dynamics have been repeatedly reported to promote drug resistance in cancer. However, whether targeting mitochondrial fission- and fusion-related proteins could be leveraged to combat multidrug-resistant pediatric sarcomas is poorly understood. Here, we demonstrated that the expression and activation of the mitochondrial fission mediator DRP1 are affected by chemotherapy exposure in common pediatric sarcomas, i.e., rhabdomyosarcoma and osteosarcoma. Unexpectedly, decreasing DRP1 activity through stable DRP1 knockdown did not attenuate sarcoma drug resistance or affect growth rate or the mitochondrial network morphology. The minimal impact on sarcoma cell physiology, combined with the upregulation of fission adaptor proteins (MFF and FIS1) detected in rhabdomyosarcoma cells, indicates that an alternative DRP1-independent mitochondrial fission mechanism may efficiently compensate for the lack of DRP1 activity. By exploring the upstream mitophagy and mitochondrial fission regulator, AMPK1, we found that markedly reduced AMPK1 levels are sufficient to maintain AMPK signaling capacity without affecting chemosensitivity. Collectively, our findings challenge the direct involvement of DRP1 in pediatric sarcoma drug resistance and highlight the complexity of yet-to-be-characterized noncanonical regulators of mitochondrial dynamics. SUMMARY BLURBThe mitochondrial fission mediator DRP1 levels and activation are modulated upon chemotherapy exposure, yet depleting DRP1 does not restore chemosensitivity in the most common pediatric sarcomas.

cancer biology↗

bioRxiv2023

Inhibiting mitochondrial translation overcomes multidrug resistance in MYC-driven neuroblastoma via OMA1-mediated integrated stress response

High-risk neuroblastoma remains a clinically challenging childhood tumor with a 5-year survival of only 50%. Tumors overexpressing N-MYC or c-MYC oncoproteins define a group of MYC-driven high-risk neuroblastoma with the most dismal outcomes, mainly caused by treatment failure due to the emergence and regrowth of multidrug-resistant cancer cells. Specific mitochondrial processes have been implicated in the maintenance of aggressive stem-like phenotypes in various cancers. We have recently identified a novel mitochondria-mediated mechanism of neuroblastoma multidrug resistance. However, the potential of pharmacological targeting of mitochondria to overcome therapy resistance and stemness in neuroblastoma remains unclear. Here, we show that c-MYC/N-MYC-driven multidrug-resistant neuroblastoma cells are highly vulnerable to cell death induced by the inhibition of mitochondrial translation. In contrast with normal fibroblasts, doxycycline (DOXY)-mediated inhibition of mitochondrial ribosomes efficiently impaired the survival of neuroblastoma cells regardless of their multidrug resistance and stem-like phenotypes. Mechanistically, inhibiting mitochondrial translation induced the mitochondrial stress-activated integrated stress response (ISR) via the OMA1-eIF2 axis, which preceded neuroblastoma cell death. Strikingly, several oncoproteins associated with poor neuroblastoma prognosis, including c-MYC and N-MYC, were markedly downregulated upon ISR activation. Comparing models of various neuroectodermal tumors and normal fibroblasts, we identified high levels of phosphorylated c-MYC and N-MYC (indicating their activity and rapid turnover) as a factor that predetermines susceptibility of neuroblastoma cells to DOXY-induced cell death. Neuroblastoma cells failed to develop significant DOXY resistance over a long-term repeated (pulsed) selection pressure, further demonstrating mitochondrial protein balance as a clinically relevant vulnerability of cancer cells that rely on high MYC activity. Together, our findings provide insight into mitochondrial retrograde regulatory networks in the context of MYC dependence and demonstrate the mitochondrial translation machinery as a promising therapeutic target in multidrug-resistant MYC-driven neuroblastoma.

cancer biology↗