The ubiquitously expressed ATPase inhibitory factor 1 (IF1) is a mitochondrial protein that blocks the reversal of the F1Fo-ATPsynthase, preventing dissipation of cellular ATP and ischemic damage. IF1 suppresses programmed cell death, enhancing tumor invasion and chemoresistance, and is expressed in various types of human cancers. In this study, we examined its effect on mitochondrial redox balance and apoptotic cristae remodeling, finding that, by maintaining ATP levels, IF1 reduces glutathione (GSH) consumption and inactivation of peroxiredoxin 3 (Prx3) during apoptosis. This correlates with inhibition of metallopeptidase OMA1-mediated processing of the pro-fusion dynamin-related protein optic atrophy 1 (OPA1). Stabilization of OPA1 impedes cristae remodeling and completion of apoptosis. Taken together, these data suggest that IF1 acts on both mitochondrial bioenergetics and structure, is involved in mitochondrial signaling in tumor cells, and may underlie their proliferative capacity.

The role of reactive oxygen species (ROS) in the metabolic reprogramming of cells adapted to hypoxia and the interplay between ROS and hypoxia in malignancy is under debate. Here, we examined how ROS levels are modulated by hypoxia in human cancer compared to untransformed cells. Short time exposure (20 min) of either fibroblasts or 143B osteosarcoma cells to low oxygen tension down to 0.5% induced a significant decrease of the cellular ROS level, as detected by the CellROX fluorescent probe (−70%). Prolonging the cells’ exposure to hypoxia for 24 h, ROS decreased further, reaching nearly 20% of the normoxic value. In this regard, due to the debated role of the endogenous inhibitor protein (IF₁) of the ATP synthase complex in cancer cell bioenergetics, we investigated whether IF₁ is involved in the control of ROS generation under severe hypoxic conditions. A significant ROS content decrease was observed in hypoxia in both IF₁-expressing and IF₁- silenced cells compared to normoxia. However, IF₁-silenced cells showed higher ROS levels compared to IF1-containing cells. In addition, the MitoSOX Red-measured superoxide level of all the hypoxic cells was significantly lower compared to normoxia; however, the decrease was milder than the marked drop of ROS content. Accordingly, the difference between IF₁-expressing and IF₁-silenced cells was smaller but significant in both normoxia and hypoxia. In conclusion, the interplay between ROS and hypoxia and its modulation by IF₁ have to be taken into account to develop therapeutic strategies against cancer.

The growing use of fluorescent biosensors to directly probe the spatiotemporal dynamics of biochemical processes in living cells has revolutionized the study of intracellular signaling. In this review, we summarize recent developments in the use of biosensors to illuminate the molecular details of G-protein-coupled receptor (GPCR) signaling pathways, which have long served as the model for our understanding of signal transduction, while also offering our perspectives on the future of this exciting field. Specifically, we highlight several ways in which biosensor-based single-cell analyses are being used to unravel many of the enduring mysteries that surround these diverse signaling pathways.

Au₂phen ((2,9-dimethyl-1,10-phenanthroline)₂Au₂(µ-O)₂)(PF₆)₂ and Auoxo6 ((6,6′-dimethyl-2,2′-bipyridine)₂Au₂(µ-O)₂)(PF₆)₂ are two structurally related gold(III) complexes that were previously reported to display relevant and promising anticancer properties in vitro toward a large number of human cancer cell lines. To expand the knowledge on the molecular mechanisms through which these gold(III) complexes trigger apoptosis in cancer cells, further studies have been performed using A2780 ovarian cancer cells as reference models. For comparative purposes, parallel studies were carried out on the gold(III) complex AuL12 (dibromo(ethylsarcosinedithiocarbamate)gold(III)), whose proapoptotic profile had been earlier characterized in several cancer cell lines. Our results pointed out that all these gold(III) compounds manifest a significant degree of similarity in their cellular and proapoptotic effects; the main observed perturbations consist of potent thioredoxin reductase inhibition, disruption of the cell redox balance, impairment of the mitochondrial membrane potential, and induction of associated metabolic changes. In addition, evidence was gained of the remarkable contribution of ASK1 (apoptosis-signal-regulating kinase-1) and AKT pathways to gold(III)-induced apoptotic signaling. Overall, the observed effects may be traced back to gold(III) reduction and subsequent formation and release of gold(I) species that are able to bind and inhibit several enzymes responsible for the intracellular redox homeostasis, in particular the selenoenzyme thioredoxin reductase.