SignificanceIncreasing evidence suggests that extracellular vesicles (EVs) can transfer genetic material to recipient cells. However, the mechanism and role of this phenomenon are largely unknown. Here we have made a remarkable discovery: EVs can harbor the full mitochondrial genome. These extracellular vesicles can in turn transfer their mtDNA to cells with impaired metabolism, leading to restoration of metabolic activity. We determined that hormonal therapy induces oxidative phosphorylation-deficient breast cancer cells, which can be rescued via the transfer of mtDNA-laden extracellular vesicles. Horizontal transfer of mtDNA occurred in cancer stem-like cells and was associated with increased self-renewal potential of these cells, leading to resistance to hormonal therapy. We propose that mtDNA transfer occurs in human cancer via EVs.

Data availability The RNA sequencing datasets (GSE117930) and the single cell RNA sequencing datasets (GSE131508) are deposited in the Gene Expression Omnibus (GEO, NCBI) repository. The proteomic datasets are deposited in PRoteomics IDEntifications (PRIDE) repository (PXD010597). Author Contribution L.O. designed and performed most of the experiments, analysed and interpreted the data and contributed to the manuscript preparation. E.N. assisted with data collection, performed all the 3D-scaffold co-culture experiments, the in vivo Wisp1 experiments, the scRNA sequencing, interpreted and analysed the data and contributed to the manuscript preparation. I.K. performed the qPCR analysis, some of the tissue IF staining and analysed the data. A.M. and J.H.L. performed some of the tissue IF staining, all the lung organoid experiments, interpreted and analysed the data. V.B. performed some of the tissue IF staining. P.C. and S. H. performed bioinformatics analysis. I.H., J.K. and A.O. performed the proteomic and analysed the data. E.G.G. helped with the collection of Ly6G + cells for proteomics. G.M. performed the 3D-scaffold co-culture to analyse CD104 + cells. A.W. and L.C. performed the electron microscopy experiments. E.H. and V.S. provided human samples. L.O., E.N., I.K., V.B. and J.H.L., critically reviewed the manuscript. J.H.L., supervised the lung organoid experiments. I.M. designed and supervised the study, interpreted the data and wrote the manuscript.

Hypoxia-inducible factor 1 alpha (HIF-1α) orchestrates cellular adaptation to low oxygen and nutrient-deprived environment and drives progression to malignancy in human solid cancers. Its canonical regulation involves prolyl hydroxylases (PHDs), which in normoxia induce degradation, whereas in hypoxia allow stabilization of HIF-1α. However, in certain circumstances, HIF-1α regulation goes beyond the actual external oxygen levels and involves PHD-independent mechanisms. Here, we gather and discuss the evidence on the non-canonical HIF-1α regulation, focusing in particular on the consequences of mitochondrial respiratory complexes damage on stabilization of this pleiotropic transcription factor.

The oncogenic versus suppressor roles of mitochondrial genes have long been debated. Peculiar features of mitochondrial genetics such as hetero/homoplasmy and mutation threshold are seldom taken into account in this debate. Mitochondrial DNA (mtDNA) mutations generally have been claimed to be protumorigenic, but they are also hallmarks of mostly benign oncocytic tumors wherein they help reduce adaptation to hypoxia by destabilizing hypoxia-inducible factor-1a (HIF1a). To determine the influence of a disassembling mtDNA mutation and its hetero/homoplasmy on tumorigenic and metastatic potential, we injected mice with tumor cells harboring different loads of the gene MTND1 m.3571insC. Cell cultures obtained from tumor xenografts were then analyzed to correlate energetic competence, apoptosis, a-ketoglutarate (a-KG)/succinate (SA) ratio, and HIF1a stabilization with the mutation load. A threshold level for the antitumorigenic effect of MTND1 m.3571insC mutation was defined, above which tumor growth and invasiveness were reduced significantly. Notably, HIF1a destabilization and downregulation of HIF1a-dependent genes occurred in cells and tumors lacking complex I (CI), where there was an associated imbalance of a-KG/SA despite the presence of an actual hypoxic environment. These results strongly implicate mtDNA mutations as a cause of oncocytic transformation. Thus, the antitumorigenic and antimetastatic effects of high loads of MTND1 m.3571insC, following CI disassembly, define a novel threshold-regulated class of cancer genes. We suggest these genes be termed oncojanus genes to recognize their ability to contribute either oncogenic or suppressive functions in mitochondrial settings during tumorigenesis.