Reduced ER-mitochondria connectivity promotes neuroblastoma multidrug resistance

Most cancer deaths result from progression of therapy resistant disease, yet our understanding of this phenotype is limited. Cancer therapies generate stress signals that act upon mitochondria to initiate apoptosis. Mitochondria isolated from neuroblastoma cells were exposed to tBid or Bim, death effectors activated by therapeutic stress. Multidrug-resistant tumor cells obtained from children at relapse had markedly attenuated Bak and Bax oligomerization and cytochrome c release (surrogates for apoptotic commitment) in comparison with patient-matched tumor cells obtained at diagnosis. Electron microscopy identified reduced ER-mitochondria-associated membranes (MAMs; ER-mitochondria contacts, ERMCs) in therapy-resistant cells, and genetically or biochemically reducing MAMs in therapy-sensitive tumors phenocopied resistance. MAMs serve as platforms to transfer Ca2+ and bioactive lipids to mitochondria. Reduced Ca2+ transfer was found in some but not all resistant cells, and inhibiting transfer did not attenuate apoptotic signaling. In contrast, reduced ceramide synthesis and transfer was common to resistant cells and its inhibition induced stress resistance. We identify ER-mitochondria-associated membranes as physiologic regulators of apoptosis via ceramide transfer and uncover a previously unrecognized mechanism for cancer multidrug resistance.

Automated summary

Most cancer deaths occur due to the progression of therapy resistant disease, however, our understanding of this phenotype is limited. Cancer therapies generate stress signals that trigger cell apoptosis. Our study showed that resistance to therapy is associated with reduced Bak and Bax oligomerization and cytochrome c release in tumor cells. We also found that reducing ER-mitochondria-associated membranes (MAMs) in therapy-sensitive tumors can mimic resistance. MAMs serve as platforms for transferring Ca2+ and bioactive lipids to mitochondria. In addition, we discovered that reduced ceramide synthesis and transfer in resistant cells is common and its inhibition induces stress resistance.