We report that tumor cells without mitochondrial DNA (mtDNA) show delayed tumor growth, and that tumor formation is associated with acquisition of mtDNA from host cells. This leads to partial ...recovery of mitochondrial function in cells derived from primary tumors grown from cells without mtDNA and a shorter lag in tumor growth. Cell lines from circulating tumor cells showed further recovery of mitochondrial respiration and an intermediate lag to tumor growth, while cells from lung metastases exhibited full restoration of respiratory function and no lag in tumor growth. Stepwise assembly of mitochondrial respiratory (super)complexes was correlated with acquisition of respiratory function. Our findings indicate horizontal transfer of mtDNA from host cells in the tumor microenvironment to tumor cells with compromised respiratory function to re-establish respiration and tumor-initiating efficacy. These results suggest pathophysiological processes for overcoming mtDNA damage and support the notion of high plasticity of malignant cells.
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•Tumor cells lacking mtDNA form tumors only after acquiring host mtDNA•Tumor microenvironment instructs stepwise recovery of respiration•Recovery of mitochondrial function aligns with efficient tumor formation•Functional respirasome and complex II assembly occur in metastatic cells
Mitochondrial genome acquisition from cells in the tumor microenvironment restores tumorigenicity and respiration in cells lacking mtDNA. Cell lines derived from primary and circulating tumor cells and lung metastases that grew from these cells showed stepwise recovery of tumorigenicity and respiration that was associated with respirasome and complex II assembly.
p53-mutated tumors often exhibit increased resistance to standard chemotherapy and enhanced metastatic potential. Here we demonstrate that inhibition of dihydroorotate dehydrogenase (DHODH), a key ...enzyme of the de novo pyrimidine synthesis pathway, effectively decreases proliferation of cancer cells via induction of replication and ribosomal stress in a p53- and checkpoint kinase 1 (Chk1)-dependent manner. Mechanistically, a block in replication and ribosomal biogenesis result in p53 activation paralleled by accumulation of replication forks that activate the ataxia telangiectasia and Rad3-related kinase/Chk1 pathway, both of which lead to cell cycle arrest. Since in the absence of functional p53 the cell cycle arrest fully depends on Chk1, combined DHODH/Chk1 inhibition in p53-dysfunctional cancer cells induces aberrant cell cycle re-entry and erroneous mitosis, resulting in massive cell death. Combined DHODH/Chk1 inhibition effectively suppresses p53-mutated tumors and their metastasis, and therefore presents a promising therapeutic strategy for p53-mutated cancers.
Recently, we showed that generation of tumours in syngeneic mice by cells devoid of mitochondrial (mt) DNA (ρ
cells) is linked to the acquisition of the host mtDNA. However, the mechanism of mtDNA ...movement between cells remains unresolved. To determine whether the transfer of mtDNA involves whole mitochondria, we injected B16ρ
mouse melanoma cells into syngeneic C57BL/6N
mice that express red fluorescent protein in their mitochondria. We document that mtDNA is acquired by transfer of whole mitochondria from the host animal, leading to normalisation of mitochondrial respiration. Additionally, knockdown of key mitochondrial complex I (NDUFV1) and complex II (SDHC) subunits by shRNA in B16ρ
cells abolished or significantly retarded their ability to form tumours. Collectively, these results show that intact mitochondria with their mtDNA payload are transferred in the developing tumour, and provide functional evidence for an essential role of oxidative phosphorylation in cancer.
Malignant mesothelioma (MM) is an aggressive type of tumour causing high mortality. One reason for this paradigm may be the existence of a subpopulation of tumour-initiating cells (TICs) that endow ...MM with drug resistance and recurrence. The objective of this study was to identify and characterise a TIC subpopulation in MM cells, using spheroid cultures, mesospheres, as a model of MM TICs. Mesospheres, typified by the stemness markers CD24, ABCG2 and OCT4, initiated tumours in immunodeficient mice more efficiently than adherent cells. CD24 knock-down cells lost the sphere-forming capacity and featured lower tumorigenicity. Upon serial transplantation, mesospheres were gradually more efficiently tumrigenic with increased level of stem cell markers. We also show that mesospheres feature mitochondrial and metabolic properties similar to those of normal and cancer stem cells. Finally, we show that mesothelioma-initiating cells are highly susceptible to mitochondrially targeted vitamin E succinate. This study documents that mesospheres can be used as a plausible model of mesothelioma-initiating cells and that they can be utilised in the search for efficient agents against MM.
We synthesized a mitochondria-targeted honokiol (Mito-HNK) that facilitates its mitochondrial accumulation; this dramatically increases its potency and efficacy against highly metastatic lung cancer ...lines in vitro, and in orthotopic lung tumor xenografts and brain metastases in vivo. Mito-HNK is >100-fold more potent than HNK in inhibiting cell proliferation, inhibiting mitochondrial complex ǀ, stimulating reactive oxygen species generation, oxidizing mitochondrial peroxiredoxin-3, and suppressing the phosphorylation of mitoSTAT3. Within lung cancer brain metastases in mice, Mito-HNK induced the mediators of cell death and decreased the pathways that support invasion and proliferation. In contrast, in the non-malignant stroma, Mito-HNK suppressed pathways that support metastatic lesions, including those involved in inflammation and angiogenesis. Mito-HNK showed no toxicity and targets the metabolic vulnerabilities of primary and metastatic lung cancers. Its pronounced anti-invasive and anti-metastatic effects in the brain are particularly intriguing given the paucity of treatment options for such patients either alone or in combination with standard chemotherapeutics.
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•Synthesis of mitochondria-targeted honokiol (Mito-HNK);•Mito-HNK inhibits mitochondrial complex I, and stimulates oxidizing peroxiredoxin-3•Mito-HNK suppresses the phosphorylation of mitoSTAT3•Mito-HNK has pronounced activity against lung cancer and its brain metastases
Natural Product Chemistry; Immunology; Medicinal and Aromatic Plants
Highlights • Mitochondrial transfer between mammalian cells has been demonstrated in cell co-culture experiments. • Mitochondrial transfer between cells has been shown in mouse models of lung injury ...and inflammation. • mtDNA transfer to tumor cells without mtDNA has been unequivocally documented in mouse models. • Mitochondrial transfer between neurons and astrocytes has been shown to occur in mouse retinal ganglion axons at the optic nerve head. • Mitochondrial transfer to transmissible canine venereal tumors is implied from phylogenetic approaches.
Cancer cells without mitochondrial DNA (mtDNA) do not form tumors unless they reconstitute oxidative phosphorylation (OXPHOS) by mitochondria acquired from host stroma. To understand why functional ...respiration is crucial for tumorigenesis, we used time-resolved analysis of tumor formation by mtDNA-depleted cells and genetic manipulations of OXPHOS. We show that pyrimidine biosynthesis dependent on respiration-linked dihydroorotate dehydrogenase (DHODH) is required to overcome cell-cycle arrest, while mitochondrial ATP generation is dispensable for tumorigenesis. Latent DHODH in mtDNA-deficient cells is fully activated with restoration of complex III/IV activity and coenzyme Q redox-cycling after mitochondrial transfer, or by introduction of an alternative oxidase. Further, deletion of DHODH interferes with tumor formation in cells with fully functional OXPHOS, while disruption of mitochondrial ATP synthase has little effect. Our results show that DHODH-driven pyrimidine biosynthesis is an essential pathway linking respiration to tumorigenesis, pointing to inhibitors of DHODH as potential anti-cancer agents.
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•Tumorigenesis depends on functional OXPHOS•OXPHOS-derived ATP is not required for tumor formation•DHODH-driven pyrimidine biosynthesis requires CoQ redox-cycling•CoQ redox-cycling via OXPHOS drives tumorigenesis through pyrimidine biosynthesis
Cancer cells without mitochondrial DNA (mtDNA) do not form tumors unless they can highjack host mitochondria. Bajzikova et al. show that the acquired mitochondrial electron transport is necessary to drive de novo pyrimidine synthesis to overcome cell-cycle arrest. Surprisingly, ATP generation is dispensable for tumorigenesis in this context.
Recently, we showed that ρ0 cancer cells devoid of mitochondrial DNA (mtDNA) recover tumour formation ability only after acquisition of host mtDNA. In order to restore respiration, mtDNA moves ...between cells in whole mitochondria. While it is now clear that recovery respiration is essential for tumour formation, its functional link to the process is unclear. It includes gradual increase in mtDNA level of homoplasmic host polymorphism, followed by binding of mtDNA-processing enzymes to its regulatory domain, replication and transcription of mtDNA, increased expression of components of respiratory complexes, resulting in full restoration of respiration. We found that pyrimidine biosynthesis, supported by the respiration-linked enzyme dihydroorotate dehydrogenase (DHODH), is critically required to overcome cell cycle arrest. We further confirmed that efficient de novo pyrimidine synthesis, necessary for tumour cell proliferation, is the key event for triggering tumour growth. Moreover, respiration recovery, which is necessary for tumour formation, is associated with efficient de novo pyrimidine synthesis. In conclusion, we propose that DHODH is a critical link between de novo pyrimidine synthesis and respiration, and that it is a promising target for broad-spectrum cancer therapy.
In our previous work, we showed that mtDNA-devoid cancer cells (ρ0 cells) form tumors in mice only after a respiration recovery following acquisition of whole mitochondria from the host animal. In ...the current study, we investigated the role of respiration in tumor growth, using time-resolved analysis of tumor formation from ρ0 cells. ATP levels were stable during the whole time, indicating that the absence of mitochondrial ATP production may not be limiting for tumorigenesis. To confirm this, we prepared ATP5BKO cells. These ATP synthase-deficient cells formed tumors, albeit with a delay, documenting that mitochondrial ATP generation is dispensable for tumorigenesis. In contrast, knocking out of dihydroorotate dehydrogenase (DHODH) completely blocked tumor development. DHODH was non-functional in ρ0 cells and was reactivated after the recovery of complex III/IV respiration by mitochondrial transfer. DHODH activity in ρ0 cells was suppressed due to the absence of oxidized coenzyme Q (CoQ), the electron acceptor for DHODH. The recovery of CoQ redox-cycling by introduction of alternative oxidase into ρ0 cells restored DHODH activity, pyrimidine biosynthesis and allowed tumor growth. Hence, DHODH-driven pyrimidine biosynthesis is a crucial link between respiration and tumorigenesis.
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