MicroRNA-210 Regulates Mitochondrial Free Radical Response to Hypoxia and Krebs Cycle in Cancer Cells by Targeting Iron Sulfur Cluster Protein ISCU

Abstract

BackgroundHypoxia in cancers results in the upregulation of hypoxia inducible factor 1 (HIF-1) and a microRNA, hsa-miR-210 (miR-210) which is associated with a poor prognosis.Methods and FindingsIn human cancer cell lines and tumours, we found that miR-210 targets the mitochondrial iron sulfur scaffold protein ISCU, required for assembly of iron-sulfur clusters, cofactors for key enzymes involved in the Krebs cycle, electron transport, and iron metabolism. Down regulation of ISCU was the major cause of induction of reactive oxygen species (ROS) in hypoxia. ISCU suppression reduced mitochondrial complex 1 activity and aconitase activity, caused a shift to glycolysis in normoxia and enhanced cell survival. Cancers with low ISCU had a worse prognosis.ConclusionsInduction of these major hallmarks of cancer show that a single microRNA, miR-210, mediates a new mechanism of adaptation to hypoxia, by regulating mitochondrial function via iron-sulfur cluster metabolism and free radical generation.

miR-210 is overexpressed in late stages of lung cancer and mediates mitochondrial alterations associated with modulation of HIF-1 activity

“…These apparently contradictory results highlight the complex processes involved in the regulation of mitochondrial respiration and energy production in the hypoxic cell. 32 On the basis of this model, miR-210 overexpression in normoxia would create a mitochondrial dysfunction including a mismatch in electron transport that could lead notably to an increase in toxic reactive oxygen species as recently suggested 24 and increased apoptosis as corroborated by our data (Figures 2d, 5b and c). In contrast, during hypoxia, the miR-210-dependent repression of the ETC via SDHD, NDUFA4 or ISCU1/2 and other validated or yet unknown targets would be protective by participating in the homeostatic downregulation of mitochondrial respiration.…”

“…Notably, these effects can be recapitulated in clonogenic assays (Figure 6b) and are in agreement with similar data published during the revision of this paper. 24 Overall, these data strongly suggest that although miR-210 exerts a maladaptive role in normoxia, its induction following hypoxia would, in contrast, be protective, as suggested by other studies. 17,18,33 As the respiratory chain also serves as an intracellular O 2 sensor, miR-210-mediated targeting of SDHD is likely to have direct functional consequences on HIF-1a activation.…”

“…Accordingly, SDHD inhibition mimicked several miR-210-mediated cellular effects, including alteration of mitochondrial ultrastructure (Figure 5a), decrease of cell viability ( Figure 5b) and activation of caspases ( Figure 5c). Our findings appear particularly interesting in the light of the report published during the preparation 18 and revision 24,31 of this paper, showing that miR-210 also targets the transcript coding for ISCU1/2. ISCU1/2 facilitate the assembly of ironsulfur clusters that are incorporated into enzymes involved in energy production, including mitochondrial respiratory complexes I, II and III.…”

“…Finally, using TaqMan quantitative (q)RT-PCR, miR-210 was significantly induced in A549 cells under hypoxic condition (Figure 1c), and this hypoxic induction was dependent on HIF-1a but not HIF-2a (Supplementary Figure S1) as previously reported in other models. 12,24 miR-210 alters cell viability and enhances caspase-3/7 activity in A549 cells in normoxia. Giannakakis et al, 11 using several bioinformatic predictions of miRNA targets, reported that miR-210 can target the transcript coding for the E2F family protein E2F3.…”

The Intermediate Filament Vimentin Mediates MicroRNA miR-378 Function in Cellular Self-renewal by Regulating the Expression of the Sox2 Transcription Factor

“…It is highly expressed in neural stem cells, where it maintains the neural stem cell properties (30,31). Sox2 is also required to maintain neural stem cells in the eyes and brain and facilitates neuronal differentiation (32). By acting together with other transcription factors, Sox2 can re-establish pluripotency in terminally differentiated cells, resulting in reprogramming them to become pluripotent stem cells for further differentia-tion (33).…”