Mitochondrial ATP synthase inhibitory factor 1 interacts with the p53-cyclophilin D complex and promotes opening of the permeability transition pore.

The mitochondrial permeability transition pore (PTP) is a Ca2+-dependent megachannel that plays an important role in mitochondrial physiology and cell fate. Cyclophilin D (CyPD) is a well-characterized PTP regulator, and its binding to the PTP favors pore opening. It has previously been shown that p53 physically interacts with CyPD and opens the PTP during necrosis. Accumulating studies also suggest that the F-ATP synthase contributes to the regulation and formation of the PTP. F-ATP synthase IF1 (mitochondrial ATP synthase inhibitory factor 1) is a natural inhibitor of F-ATP synthase activity; however, whether IF1 participates in the modulation of PTP opening is basically unknown. Here, we demonstrate using calcium retention capacity assay that IF1 overexpression promotes mitochondrial permeability transition via opening of the PTP. Intriguingly, we show that IF1 can interact with the p53-CyPD complex and facilitate cell death. We also demonstrate that the presence of IF1 is necessary for the formation of p53-CyPD complex. Therefore, we suggest that IF1 regulates the PTP via interaction with the p53-CyPD complex, and that IF1 is necessary for the inducing effect of p53-CyPD complex on PTP opening.

A Novel Method for Recognizing Space Radiation Sources Based on Multi-Scale Residual Prototype Learning Network.

As a basic task and key link of space situational awareness, space target recognition has become crucial in threat analysis, communication reconnaissance and electronic countermeasures. Using the fingerprint features carried by the electromagnetic signal to recognize is an effective method. Because traditional radiation source recognition technologies are difficult to obtain satisfactory expert features, automatic feature extraction methods based on deep learning have become popular. Although many deep learning schemes have been proposed, most of them are only used to solve the inter-class separable problem and ignore the intra-class compactness. In addition, the openness of the real space may invalidate the existing closed-set recognition methods. In order to solve the above problems, inspired by the application of prototype learning in image recognition, we propose a novel method for recognizing space radiation sources based on a multi-scale residual prototype learning network (MSRPLNet). The method can be used for both the closed- and open-set recognition of space radiation sources. Furthermore, we also design a joint decision algorithm for an open-set recognition task to identify unknown radiation sources. To verify the effectiveness and reliability of the proposed method, we built a set of satellite signal observation and receiving systems in a real external environment and collected eight Iridium signals. The experimental results show that the accuracy of our proposed method can reach 98.34% and 91.04% for the closed- and open-set recognition of eight Iridium targets, respectively. Compared to similar research works, our method has obvious advantages.

Arg-8 of yeast subunit e contributes to the stability of F-ATP synthase dimers and to the generation of the full-conductance mitochondrial megachannel.

The mitochondrial F-ATP synthase is a complex molecular motor arranged in V-shaped dimers that is responsible for most cellular ATP synthesis in aerobic conditions. In the yeast F-ATP synthase, subunits e and g of the FO sector constitute a lateral domain, which is required for dimer stability and cristae formation. Here, by using site-directed mutagenesis, we identified Arg-8 of subunit e as a critical residue in mediating interactions between subunits e and g, most likely through an interaction with Glu-83 of subunit g. Consistent with this hypothesis, (i) the substitution of Arg-8 in subunit e (eArg-8) with Ala or Glu or of Glu-83 in subunit g (gGlu-83) with Ala or Lys destabilized the digitonin-extracted F-ATP synthase, resulting in decreased dimer formation as revealed by blue-native electrophoresis; and (ii) simultaneous substitution of eArg-8 with Glu and of gGlu-83 with Lys rescued digitonin-stable F-ATP synthase dimers. When tested in lipid bilayers for generation of Ca2+-dependent channels, WT dimers displayed the high-conductance channel activity expected for the mitochondrial megachannel/permeability transition pore, whereas dimers obtained at low digitonin concentrations from the Arg-8 variants displayed currents of strikingly small conductance. Remarkably, double replacement of eArg-8 with Glu and of gGlu-83 with Lys restored high-conductance channels indistinguishable from those seen in WT enzymes. These findings suggest that the interaction of subunit e with subunit g is important for generation of the full-conductance megachannel from F-ATP synthase.

Arginine 107 of yeast ATP synthase subunit g mediates sensitivity of the mitochondrial permeability transition to phenylglyoxal.

Modification with arginine-specific glyoxals modulates the permeability transition (PT) of rat liver mitochondria, with inhibitory or inducing effects that depend on the net charge of the adduct(s). Here, we show that phenylglyoxal (PGO) affects the PT in a species-specific manner (inhibition in mouse and yeast, induction in human and Drosophila mitochondria). Following the hypotheses (i) that the effects are mediated by conserved arginine(s) and (ii) that the PT is mediated by the F-ATP synthase, we have narrowed the search to 60 arginines. Most of these residues are located in subunits α, ß, γ, ϵ, a, and c and were excluded because PGO modification did not significantly affect enzyme catalysis. On the other hand, yeast mitochondria lacking subunit g or bearing a subunit g R107A mutation were totally resistant to PT inhibition by PGO. Thus, the effect of PGO on the PT is specifically mediated by Arg-107, the only subunit g arginine that has been conserved across species. These findings are evidence that the PT is mediated by F-ATP synthase.

Synergistic antitumor activity of vitamin D3 combined with metformin in human breast carcinoma MDA-MB-231 cells involves m-TOR related signaling pathways.

Metformin is usually used for the treatment of type 2 diabetes. Recently, many studies suggest that metformin and vitamin D have broad-spectrum antitumor activities. Our aim in this research was to study the effects of vitamin D3 combined with metformin on the apoptosis induction and its mechanisms in the human breast cancer cell line MDA-MB-231. Cell proliferation was measured by methylthiazol tetrazolium (MTT) assay. The morphology of cell apoptosis was observed after Hoechst 33342 staining. Here we show that vitamin D3 280 µg/ml or vitamin D3 300 µg/ml or vitamin D3 320 µg/ml seperately combined with metformin 15000 µg/ml exhibited synergistic effects on cell proliferation and apoptosis. The underlying anti-tumor mechanisms may involve m-TOR related pathways, which are related to activating expression of cleaved caspase-3, Bax and p-AMPK, as well as inhibiting expressions of p-Bcl-2, c-Myc, p-IGF-IR, p-mTOR, p-P70S6K, p-S6.

Vitamin D3 enhances antitumor activity of metformin in human bladder carcinoma SW-780 cells.

OBJECTIVE: To study the effects of vitamin D3 combined with metformin on the proliferation and apoptosis in human bladder cancer cell line SW-780 and its possible mechanism. METHODS: MTT assay and fluorescence microscope observations were used to study the effects of vitamin D3 combined with metformin on the proliferation and apoptosis of SW-780 cells in vitro. Western blot was used to detect the expression of apoptosis-related proteins p-Bcl-2, Bax, Cyclin D1, c-Myc and related signaling pathways activated proteins p-IGF-IR, p-mTOR, p-P70S6K, p-S6. RESULTS: MTT results showed that 320 µg/ml vitamin D3 combined with 620 µg/ml metformin acting on cells for 48h had a significant synergistic effect on proliferation. Fluorescence microscope observations showed that compared with negative control group and monotherapy treatment group, the apoptosis features of combination treatment group were obvious and the apoptosis rate increased greatly. Western blot showed that compared with the negative control group and monotherapy treatment group, the expression levels of p-Bcl-2, Cyclin D1 and c-Myc in combination treatment group significantly decreased, whereas the expression level of Bax significantly increased, and the expression levels of p-IGF-IR, p-mTOR, p-P70S6K and p-S6 in combination treatment group significantly decreased. CONCLUSION: Vitamin D3 combined with metformin exhibited obvious inhibitory effects on the cell proliferation and apoptosis induction in SW-780 cells. The underlying anti-tumor mechanism might be related to inhibiting the expressions of p-Bcl-2, Cyclin D1, c-Myc, p-IGF-IR, p-mTOR, p-P70S6K, p-S6 and activating the expression of Bax.

F-ATP synthase inhibitory factor 1 regulates metabolic reprogramming involving its interaction with c-Myc and PGC1α.

F-ATP synthase inhibitory factor 1 (IF1) is an intrinsic inhibitor of F-ATP synthase. It is known that IF1 mediates metabolic phenotypes and cell fate, yet the molecular mechanisms through which IF1 fulfills its physiological functions are not fully understood. Ablation of IF1 favors metabolic switch to oxidative metabolism from glycolysis. c-Myc and PGC1α are critical for metabolic reprogramming. This work identified that IF1 interacted with Thr-58 phosphorylated c-Myc, which might thus mediate the activity of c-Myc and promote glycolysis. The interaction of IF1 with PGC1α inhibited oxidative respiration. c-Myc and PGC1α were localized to mitochondria under mitochondrial stress in an IF1-dependent manner. Furthermore, IF1 was found to be required for the protective effect of hypoxia on c-Myc- and PGC1α-induced cell death. This study suggested that the interactions of IF1 with transcription factors c-Myc and PGC1α might be involved in IF1-regulatory metabolic reprogramming and cell fate.

Mitochondria and the permeability transition pore in cancer metabolic reprogramming.

Mitochondria are a major source of ATP provision as well as cellular suicidal weapon store. Accumulating evidences demonstrate that mitochondrial bioenergetics, biosynthesis and signaling are important mediators of tumorigenesis. Metabolic plasticity enables cancer cell reprogramming to cope with cellular and environmental alterations, a process requires mitochondria biology. Mitochondrial metabolism emerges to be a promising arena for cancer therapeutic targets. The permeability transition pore (PTP) participates in physiological Ca2+ and ROS homeostasis as well as cell death depending on the open state. The hypothesis that PTP forms from F-ATP synthase provides clues to the potential collaborative role of mitochondrial respiration and PTP in regulating cancer cell fate and metabolic reprogramming.

Calcium and regulation of the mitochondrial permeability transition.

Recent years have seen renewed interest in the permeability transition pore, a high conductance channel responsible for permeabilization of the inner mitochondrial membrane, a process that leads to depolarization and Ca2+ release. Transient openings may be involved in physiological Ca2+ homeostasis while long-lasting openings may trigger and/or execute cell death. In this review we specifically focus (i) on the hypothesis that the PTP forms from the F-ATP synthase and (ii) on the mechanisms through which Ca2+ can reversibly switch this energy-conserving nanomachine into an energy-dissipating device.

Combined use of vitamin D3 and metformin exhibits synergistic chemopreventive effects on colorectal neoplasia in rats and mice.

Vitamin D3 and metformin are widely used in humans for regulating mineral metabolism and as an antidiabetic drug, respectively; and both of them have been shown to have chemopreventive effects against various tumors. This study was designed to investigate the potential synergistic chemopreventive effects of vitamin D3 and metformin against the development of early colon neoplasia in two models. The first model was a 1,2-dimethylhydrazine dihydrochloride (DMH)-induced colon cancer rat model and the second, a DMH-dextran sodium sulfate (DSS)-induced colitis-associated colon neoplasia mouse model. Compared with either vitamin D3 or metformin alone, combined use of vitamin D3 and metformin showed more pronounced effect in reducing the numbers of aberrant crypt foci (ACF) and tumor in the colon. The most prominent inhibitory effects were observed in the vitamin D3 medium dose (100 IU/kg/d) and metformin medium dose (120 mg/kg/d) combination group. Furthermore, our results showed that enhancement of metformin's chemopreventive effects by vitamin D3 was associated with downregulation of S6P expression, via the AMPK (IGFI)/mTOR pathway. In addition, enhancement of vitamin D3's chemopreventive effects by metformin was associated with inhibition of the protein expressions of c-Myc and Cyclin D1, via the vitamin D receptor/ß-catenin pathway. These findings show that the combined use of vitamin D3 and metformin exhibits synergistic effects against the development of early colon neoplasia. They suggest that the combined use of vitamin D3 and metformin may represent a novel strategy for chemoprevention of colorectal cancer.