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.