Natural diterpenoid compound elevates expression of Bim protein, which interacts with antiapoptotic protein Bcl-2, converting it to proapoptotic Bax-like molecule

Synergistic effect of venetoclax and ibrutinib on ibrutinib-resistant ABC-type DLBCL cells

Despite the widespread use of R-CHOP therapy in diffuse large B-cell lymphoma (DLBCL), the therapeutic efficacy for this disease remains suboptimal, primarily due to the heterogeneity of refractory and/or relapsed diseases. To address this challenge, optimization of DLBCL treatment regimens has focused on the strategy of combining an additional drug "X" with R-CHOP to enhance efficacy. However, the failure of R-CHOP combined with the BTK inhibitor ibrutinib in treating ABC-type DLBCL patients has raised significant concerns regarding ibrutinib resistance. While some studies suggest that venetoclax may synergize with ibrutinib to kill ibrutinib-resistant cells, the underlying mechanisms remain unclear. Our study aimed to validate the enhanced tumor-suppressive effect of combining ibrutinib with venetoclax against ibrutinib-resistant cells and elucidate its potential mechanisms. Our experimental results demonstrated that ibrutinib-resistant cells exhibited significant cytotoxicity to the combination therapy of ibrutinib and venetoclax, inducing cell apoptosis through activation of the mitochondrial pathway and inhibition of aerobic respiration. Furthermore, we validated the inhibitory effect of this combination therapy on tumor growth in in vivo models. Therefore, our study proposes that the combination therapy of ibrutinib and venetoclax is a promising treatment strategy that can be applied in clinical practice for ABC-type DLBCL, offering a new solution to overcome the urgent challenge of ibrutinib resistance.

Baicalin and baicalein in modulating tumor microenvironment for cancer treatment: A comprehensive review with future perspectives

Cancer is a leading cause of death worldwide. The burden of cancer incidence and mortality is increasing rapidly. New approaches to cancer prevention and treatment are urgently needed. Natural products are reliable and powerful sources for anticancer drug discovery. Baicalin and baicalein, two major flavones isolated from Scutellaria baicalensis Georgi, a multi-purpose traditional medicinal plant in China, exhibit anticancer activities against multiple cancers. Of note, these phytochemicals exhibit extremely low toxicity to normal cells. Besides their cytotoxic and cytostatic activities toward diverse tumor cells, recent studies demonstrated that baicalin and baicalein modulate a variety of tumor stromal cells and extracellular matrix (ECM) in the tumor microenvironment (TME), which is essential for tumorigenesis, cancer progression and metastasis. In this review, we summarize the therapeutic potential and the mechanism of action of baicalin and baicalein in the regulation of tumor microenvironmental immune cells, endothelial cells, fibroblasts, and ECM that reshape the TME and cancer signaling, leading to inhibition of tumor angiogenesis, progression, and metastasis. In addition, we discuss the biotransformation pathways of baicalin and baicalein, related therapeutic challenges and the future research directions to improve their bioavailability and clinical anticancer applications. Recent advances of baicalin and baicalein warrant their continued study as important natural ways for cancer interception and therapy.

Role of Txnrd3 in NiCl2-induced kidney cell apoptosis in mice: Potential therapeutic effect of melatonin

Nickel (Ni) exposure is a significant risk factor for kidney dysfunction and oxidative stress injury in humans. Thioredoxin reductase 3 (Txnrd3), an important enzyme in animals, plays a role in maintaining cellular homeostasis and regulating oxidative stress. However, its protective effect against kidney injury has been determined. Melatonin (Mel) has antioxidant and anti-apoptotic effects and therefore may be a preventive and therapeutic agent for kidney injury. Our study aimed to investigate the roles of Mel and Txnrd3 in the treatment of nickel-induced renal injury. We divided 80 wild-type mice and 80 Txnrd3 -/- mice (C57BL/6 N) into a control group treated with saline, Ni group treated with 10 mg/kg NiCl2, Mel group treated with 2 mg/kg Mel, and Ni + Mel group given NiCl2 and Mel for 21 days. Histopathological and ultrastructural observation of the kidney showed that nuclei were wrinkled and mitochondrial cristae were broken in the Ni group, and these changes were significantly attenuated by Mel treatment. Mitochondrial and nuclear damage improved significantly in the Ni + Mel and Txnrd3-/- Ni + Mel groups. Furthermore, NiCl2 exposure decreased T-AOC, SOD, and GSH activities in the kidney. The decreases in antioxidant enzyme activity were attenuated by Mel, and these improvements were abolished by Txnrd3 knockout. NiCl2-induced increases in the mRNA and protein levels of apoptosis factors (Bax, Cyt-c, caspase-3, and caspase-9) were attenuated by Mel treatment, and Txnrd3 knockout abolished the repressive effect of Mel on apoptosis genes. Overall, we concluded that Mel improves oxidative stress and apoptosis induced by NiCl2 by regulating Txnrd3 expression in the kidney. Our results provide evidence for the role of Mel in NiCl2-induced kidney injury and identify Txnrd3 as a potential therapeutic target for renal injury.

Effects of toxicants on endoplasmic reticulum stress and hepatic cell fate determination

Toxicant-induced injury is a significant global health issue. However, the mechanisms through which toxicants such as carbon tetrachloride, acetaminophen, dimethylformamide, cocaine, and morphine induce the death of multiple cell types and contribute to liver toxicity are highly complex. This phenomenon involves intricate signaling pathways in association with oxidative stress, inflammation, and activation of death receptors, which are closely linked to endoplasmic reticulum (ER) stress. ER stress initially triggers the unfolded protein response, which either promotes cell survival or causes cell death at later times, depending on the severity and duration of the stress. Thus, comprehending the molecular basis governing cell fate determination in the context of ER stress may provide key insights into the prevention and treatment of toxicant-induced injury. This review summarizes our current understanding of agents that trigger different forms of ER stress-mediated cell death, necroptosis, ferroptosis, pyroptosis, and apoptosis, and covers the underlying molecular basis of toxicant-induced ER stress, as well as potential target molecules.

Structure-destabilizing mutations unleash an intrinsic perforation activity of antiapoptotic Bcl-2 in the mitochondrial membrane enabling apoptotic cell death

Bcl-2 and Bax share a similar structural fold in solution, yet function oppositely in the mitochondrial outer membrane (MOM) during apoptosis. The proapoptotic Bax forms pores in the MOM to trigger cell death, whereas Bcl-2 inhibits the Bax pore formation to prevent cell death. Intriguingly both proteins can switch to a similar conformation after activation by BH3-only proteins, with multiple regions embedded in the MOM. Here we tested a hypothesis that destabilization of the Bcl-2 structure might convert Bcl-2 to a Bax-like perforator. We discovered that mutations of glutamate 152 which eliminate hydrogen bonds in the protein core and thereby reduce the Bcl-2 structural stability. These Bcl-2 mutants induced apoptosis by releasing cytochrome c from the mitochondria in the cells that lack Bax and Bak, the other proapoptotic perforator. Using liposomal membranes made with typical mitochondrial lipids and reconstituted with purified proteins we revealed this perforation activity was intrinsic to Bcl-2 and could be unleashed by a BH3-only protein, similar to the perforation activity of Bax. Our study thus demonstrated a structural conversion of antiapoptotic Bcl-2 to a proapoptotic perforator through a simple molecular manipulation or interaction that is worthy to explore further for eradicating cancer cells that are resistant to a current Bcl-2-targeting drug.

The pro-apoptotic activity of sinueracasbanone D isolated from Sinularia Leptoclados in hepatocellular carcinoma cells

The soft-bodied corals of the genera Sarcophyton and Sinularia (Alcyoniidae) are known as a warehouse of casbane and cembranoid diterpenoids with remarkable antitumor effects. Two casbane-type diterpenoids (1, 2) along with four cembrane-type diterpenoids (3-6) were isolated from the diethyl ether soluble fraction of the organic extracts of the Red Sea soft corals Sinularia leptoclados and Sarcophyton glaucum, respectively. The antiproliferative activity of all isolated compounds (1-6) against three hepatocellular carcinoma cells, namely, Huh-7, SNU 499, and HepG2, along with the normal cells EA.hy 926, was evaluated. Sinueracabanone D (1) displayed a remarkable antiproliferative effect against the examined cancer cell lines, especially HepG2 cells with IC₅₀ of 4.0 ± 0.37 µM. Cell cycle analysis indicated compound 1 caused the accumulation of HepG2 cells in the G2/M-phase. Further, compound 1 exhibited significant pro-apoptotic activities in HepG2 cells as evidenced by annexin V staining, enhanced mRNA expression of Bax, cytochrome C, and caspase 3, as well as inhibition of Bcl2 expression. Also, challenging HepG2 cells with sinueracabanone D (1) enhanced the active oxygen species generation and decreased mitochondrial membrane potential. In conclusion, compound 1 possesses potent antiproliferative activities against HepG2 cells. These antiproliferative activities are mediated, at least partly, by their ability to induce apoptosis, mitochondrial dysfunction, and oxidative stress.

Pharmacological Progress of Mitophagy Regulation

With the advancement in novel drug discovery, biologically active compounds are considered pharmacological tools to understand complex biological mechanisms and the identification of potent therapeutic agents. Mitochondria boast a central role in different integral biological processes and mitochondrial dysfunction is associated with multiple pathologies. It is, therefore, prudent to target mitochondrial quality control mechanisms by using pharmacological approaches. However, there is a scarcity of biologically active molecules, which can interact with mitochondria directly. Currently, the chemical compounds used to induce mitophagy include oligomycin and antimycin A for impaired respiration and acute dissipation of mitochondrial membrane potential by using CCCP/FCCP, the mitochondrial uncouplers. These chemical probes alter the homeostasis of the mitochondria and limit our understanding of the energy regulatory mechanisms. Efforts are underway to find molecules that can bring about selective removal of defective mitochondria without compromising normal mitochondrial respiration. In this report, we have tried to summarize and status of the recently reported modulators of mitophagy.

Effect of Modified Levopimaric Acid Diene Adducts on Mitochondrial and Liposome Membranes

This paper demonstrates the membranotropic effect of modified levopimaric acid diene adducts on liver mitochondria and lecithin liposomes. We found that the derivatives dose-dependently reduced the efficiency of oxidative phosphorylation of mitochondria due to inhibition of the activity of complexes III and IV of the respiratory chain and protonophore action. This was accompanied by a decrease in the membrane potential in the case of organelle energization both by glutamate/malate (complex I substrates) and succinate (complex II substrate). Compounds 1 and 2 reduced the generation of H₂O₂ by mitochondria, while compound 3 exhibited a pronounced antioxidant effect on glutamate/malate-driven respiration and, on the other hand, caused ROS overproduction when organelles are energized with succinate. All tested compounds exhibited surface-active properties, reducing the fluidity of mitochondrial membranes and contributing to nonspecific permeabilization of the lipid bilayer of mitochondrial membranes and swelling of the organelles. Modified levopimaric acid diene adducts also induced nonspecific permeabilization of unilamellar lecithin liposomes, which confirmed their membranotropic properties. We discuss the mechanisms of action of the tested compounds on the mitochondrial OXPHOS system and the state of the lipid bilayer of membranes, as well as the prospects for the use of new modified levopimaric acid diene adducts in medicine.

Natural product sciences: an integrative approach to the innovations of plant natural products

The study on plant natural products not only helps us understand that their structural diversity is the inevitable result of plant species diversity, but also helps us understand certain rules and unity of the inevitable connection between the two. The diversity and complexity of chemical structures of many natural products are beyond imagination before we elucidated their structures. The question that follows is what is the biological significance of these natural products. Intrigued by the relationship between plant resources, natural products and biological functions, the Hao laboratory has taken an integrative approach that employs tools and knowledge from multi-disciplines, including natural product chemistry, chemical ecology and chemical biology, to unveil the effects of plant natural products on plant resistance to diseases, and environmental acclimations. Collaborating with cell biologists, the research has resulted in discovery of new mechanisms of cellular signaling and lead compounds.

Glucocorticoids can induce BIM to trigger apoptosis in the absence of BAX and BAK1

Cells from two murine lymphoid lines died 24-48 h after treatment with the glucocorticoid dexamethasone. Deletion of Bax and Bak1 prevented rapid apoptosis, but treatment with dexamethasone for greater 6 days still led to cell death that was characterized by release of cytochrome c into the cytosol, activation of caspases, and loss of cell membrane integrity. In WEHI7 thymoma cells, this did not occur when Bcl2l11 (Bim) was deleted in addition to Bax and Bak1. When these triple mutant lines were exposed to dexamethasone for 10 days, they arrested, but after dexamethasone was removed, they had 10-fold higher clone forming efficiency than Bax/Bak1 double knock-out cells. Although induced over-expression of BIMs alone was not sufficient to induce the death of Bax^-/-Bak1^-/-Bim^-/- cells, they did die when BIMs was induced in the presence of dexamethasone. These results suggest that dexamethasone induces production of BIM together with other, as yet unidentified proteins, that cause release of cytochrome c and apoptosis in the absence of BAX and BAK1.

[Physiological Function and Structural Basis of Bcl-2 Family Proteins]

Apoptosis is an important biological process that plays a key role in the regulation of cell fate and homeostasis. The B-cell lymphoma-2 (Bcl-2) family proteins are important regulators of the apoptotic pathway, and their dysfunction is associated with a variety of diseases, including cancer, neurodegenerative and autoimmune diseases. In the past decade, a large number of research work on the physiological functions and atomic structures of Bcl-2 family proteins have been reported, which has deepened our understanding of the molecular mechanism and pathological significance of Bcl-2 family proteins. Recently, new drugs targeting different Bcl-2 proteins have been developed and used in clinics or tested in clinical trials. However, the complexity and diversity in functions and structures of Bcl-2 family have left many unsolved problems. This article summarizes current knowledge of the structure and function of Bcl-2 family proteins and discusses the pharmacological significance of Bcl-2 proteins as effective therapeutic targets.

An Explorer of Chemical Biology of Plant Natural Products in Southwest China, Xiaojiang Hao

Xiaojiang Hao, who obtained Master Degree from Kunming Institute of Botany (KIB), Chinese Academy of Sciences (CAS) in 1985, and Doctor in Pharmacy degree in Pharmacy from Institute for Chemical Research, Kyoto University, in 1990, was born in Chongqing in July, 1951. In 1991, he returned to KIB, CAS, as an Associate professor and served as the chair of the Department of Phytochemistry. In 1994, he was promoted to a full professor at the current institute. He served as the Deputy Director of KIB and the Director of Open Laboratory of Phytochemistry from 1995 to 1997, and the Director of KIB from 1997 to 2005. Professor Hao has published more than 450 peer-reviewed SCI papers, which have been cited over 6000 times. He has obtained one PCT patent and 23 patents in China. Due to his tremendous efforts, one candidate drug, phenchlobenpyrrone, has entered the Phase II clinical trail for the treatment of Alzheimer's disease. Moreover, he won the First Prize of Natural Sciences in Yunnan Province for three times, and Ho Leung Ho Lee Fund Science and Technology Innovation Award in 2017.

Molecular elucidation of a new allelic variation at the Sg-5 gene associated with the absence of group A saponins in wild soybean

In soybean, triterpenoid saponin is one of the major secondary metabolites and is further classified into group A and DDMP saponins. Although they have known health benefits for humans and animals, acetylation of group A saponins causes bitterness and gives an astringent taste to soy products. Therefore, several studies are being conducted to eliminate acetylated group A saponins. Previous studies have isolated and characterized the Sg-5 (Glyma.15g243300) gene, which encodes the cytochrome P450 72A69 enzyme and is responsible for soyasapogenol A biosynthesis. In this study, we elucidated the molecular identity of a novel mutant of Glycine soja, 'CWS5095'. Phenotypic analysis using TLC and LC-PDA/MS/MS showed that the mutant 'CWS5095' did not produce any group A saponins. Segregation analysis showed that the absence of group A saponins is controlled by a single recessive allele. The locus was mapped on chromosome 15 (4.3 Mb) between Affx-89193969 and Affx-89134397 where the previously identified Glyma.15g243300 gene is positioned. Sequence analysis of the coding region for the Glyma.15g243300 gene revealed the presence of four SNPs in 'CWS5095' compared to the control lines. One of these four SNPs (G1127A) leads to the amino acid change Arg376Lys in the EXXR motif, which is invariably conserved among the CYP450 superfamily proteins. Co-segregation analysis showed that the missense mutation (Arg376Lys) was tightly linked with the absence of group A saponins in 'CWS5095'. Even though Arg and Lys have similar chemical features, the 3D modelled protein structure indicates that the replacement of Arg with Lys may cause a loss-of-function of the Sg-5 protein by inhibiting the stable binding of a heme cofactor to the CYP72A69 apoenzyme.

Mitochondrial ATF2 translocation contributes to apoptosis induction and BRAF inhibitor resistance in melanoma through the interaction of Bim with VDAC1

BACKGROUND

The mitochondrial accumulation of ATF2 is involved in tumor suppressor activities via cytochrome c release in melanoma cells. However, the signaling pathways that connect mitochondrial ATF2 accumulation and cytochrome c release are not well documented.

METHODS

Several melanoma cell lines, B16F10, K1735M2, A375 and A375-R1, were treated with paclitaxel and vemurafenib to test the function of mitochondrial ATF2 and its connection to Bim and voltage-dependent anion channel 1 (VDAC1). Immunoprecipitation analysis was performed to investigate the functional interaction between the involved proteins. VDAC1 oligomerization was evaluated using an EGS-based crosslinking assay.

RESULTS

The expression and migration of ATF2 to the mitochondria accounted for paclitaxel stimuli and acquired resistance to BRAF inhibitors. Mitochondrial ATF2 facilitated Bim stabilization through the inhibition of its degradation by the proteasome, thereby promoting cytochrome c release and inducing apoptosis in B16F10 and A375 cells. Studies using B16F10 and A375 cells genetically modified for ATF2 indicated that mitochondrial ATF2 was able to dissociate Bim from the Mcl-1/Bim complex to trigger VDAC1 oligomerization. Immunoprecipitation analysis revealed that Bim interacts with VDAC1, and this interaction was remarkably enhanced during apoptosis.

CONCLUSION

These results reveal that mitochondrial ATF2 is associated with the induction of apoptosis and BRAF inhibitor resistance through Bim activation, which might suggest potential novel therapies for the targeted induction of apoptosis in melanoma therapy.

Reduction of myeloid-derived suppressor cells and lymphoma growth by a natural triterpenoid

Lymphoma is a potentially life threatening disease. The goal of this study was to investigate the therapeutic potential of a natural triterpenoid, Ganoderic acid A (GA-A) in controlling lymphoma growth both in vitro and in vivo. Here, we show that GA-A treatment induces caspase-dependent apoptotic cell death characterized by a dose-dependent increase in active caspases 9 and 3, up-regulation of pro-apoptotic BIM and BAX proteins, and a subsequent loss of mitochondrial membrane potential with release of cytochrome c. In addition to GA-A's anti-growth activity, we show that lower doses of GA-A enhance HLA class II-mediated antigen (Ag) presentation and CD4+ T cell recognition of lymphoma cells in vitro. The therapeutic relevance of GA-A treatment was also tested in vivo using the EL4 syngeneic mouse model of metastatic lymphoma. GA-A-treatment significantly prolonged survival of EL4 challenged mice and decreased tumor metastasis to the liver, an outcome accompanied by a marked down-regulation of STAT3 phosphorylation, reduction myeloid-derived suppressor cells (MDSCs), and enhancement of cytotoxic CD8+ T cells in the host. Thus, GA-A not only selectively induces apoptosis in lymphoma cells, but also enhances cell-mediated immune responses by attenuating MDSCs, and elevating Ag presentation and T cell recognition. The demonstrated therapeutic benefit indicates that GA-A is a candidate for future drug design for the treatment of lymphoma.

A bio-inspired synthetic route to the core ring systems of Spiraea atisine-type diterpenoid alkaloids and related diterpenes

A bio-inspired synthetic strategy for the construction of the complex substructures of biologically active atisine-type diterpenoid alkaloids and related diterpenes was successfully developed.

Diterpene alkaloids and diterpenes from Spiraea japonica and their anti-tobacco mosaic virus activity

Five new naturally occurring natural products, including two atisine-type diterpene alkaloids (1 and 2), two atisane-type diterpenes (3 and 4), and a new natural product spiramine C2 (5), along with nine known ones (6-14), were isolated from the ethanolic extracts of the whole plant of Spiraea japonica var. acuminata Franch. Their structures were elucidated by extensive spectroscopic analysis. The anti-tobacco mosaic virus (TMV) activities of all the compounds were evaluated by the conventional half-leaf method. Six compounds (2, 3, 6, 7, 11, and 12) exhibited moderate activities at 100 μg/mL with inhibition rates in the range of 69.4-92.9%, which were higher than that of the positive control, ningnanmycin. Their preliminary structure-activity relationships were also discussed.

A New Fungal Diterpene Induces VDAC1-dependent Apoptosis in Bax/Bak-deficient Cells

The pro-apoptotic Bax and Bak proteins are considered central to apoptosis, yet apoptosis occurs in their absence. Here, we asked whether the mitochondrial protein VDAC1 mediates apoptosis independently of Bax/Bak. Upon screening a fungal secondary metabolite library for compounds inducing apoptosis in Bax/Bak-deficient mouse embryonic fibroblasts, we identified cyathin-R, a new cyathane diterpenoid compound able to activate apoptosis in the absence of Bax/Bak via promotion of the VDAC1 oligomerization that mediates cytochrome c release. Diphenylamine-2-carboxilic acid, an inhibitor of VDAC1 conductance and oligomerization, inhibited cyathin-R-induced VDAC1 oligomerization and apoptosis. Similarly, Bcl-2 overexpression conferred resistance to cyathin-R-induced apoptosis and VDAC1 oligomerization. Silencing of VDAC1 expression prevented cyathin-R-induced apoptosis. Finally, cyathin-R effectively attenuated tumor growth and induced apoptosis in Bax/Bak-deficient cells implanted into a xenograft mouse model. Hence, this study identified a new compound promoting VDAC1-dependent apoptosis as a potential therapeutic option for cancerous cells lacking or presenting inactivated Bax/Bak.

Spiramine derivatives induce apoptosis of Bax(-/-)/Bak(-/-) cell and cancer cells

Spiramine C-D, the atisine-type diterpenoid alkaloids isolated from the Chinese herbal medicine Spiraea japonica complex, are shown to have anti-inflammatory effects in vitro. In this study, we report that spiramine derivatives of spiramine C-D bearing α,β-unsaturated ketone induce apoptosis of Bax(-/-)/Bak(-/-) MEFs cell, which is positively corresponding their cytotoxicity of tumor cell lines including multidrug resistance MCF-7/ADR. The results indicated that oxazolidine ring is necessary, and derivatives bearing double 'Michael reaction acceptor' group would significantly increased activities both of inducing apoptosis of Bax(-/-)/Bak(-/-) cells and cytotoxicity of tumor cells. The result indicated that spiramine derivative with α,β-unsaturated ketone group is a new anti-cancer agent with a capability of inducing apoptosis of cancer cells in Bax/Bak-independent manner.

After embedding in membranes antiapoptotic Bcl-XL protein binds both Bcl-2 homology region 3 and helix 1 of proapoptotic Bax protein to inhibit apoptotic mitochondrial permeabilization

Bcl-XL binds to Bax, inhibiting Bax oligomerization required for mitochondrial outer membrane permeabilization (MOMP) during apoptosis. How Bcl-XL binds to Bax in the membrane is not known. Here, we investigated the structural organization of Bcl-XL·Bax complexes formed in the MOM, including the binding interface and membrane topology, using site-specific cross-linking, compartment-specific labeling, and computational modeling. We found that one heterodimer interface is formed by a specific interaction between the Bcl-2 homology 1-3 (BH1-3) groove of Bcl-XL and the BH3 helix of Bax, as defined previously by the crystal structure of a truncated Bcl-XL protein and a Bax BH3 peptide (Protein Data Bank entry 3PL7). We also discovered a novel interface in the heterodimer formed by equivalent interactions between the helix 1 regions of Bcl-XL and Bax when their helical axes are oriented either in parallel or antiparallel. The two interfaces are located on the cytosolic side of the MOM, whereas helix 9 of Bcl-XL is embedded in the membrane together with helices 5, 6, and 9 of Bax. Formation of the helix 1·helix 1 interface partially depends on the formation of the groove·BH3 interface because point mutations in the latter interface and the addition of ABT-737, a groove-binding BH3 mimetic, blocked the formation of both interfaces. The mutations and ABT-737 also prevented Bcl-XL from inhibiting Bax oligomerization and subsequent MOMP, suggesting that the structural organization in which interactions at both interfaces contribute to the overall stability and functionality of the complex represents antiapoptotic Bcl-XL·Bax complexes in the MOM.

Mitofusins: ubiquitylation promotes fusion

Mitochondrial genes including Mfn2 are at the center of many diseases, underscoring their potential as a therapeutical target. The Chen group now identified 15-oxospiramilactone as a chemical inhibitor of the mammalian deubiquitylase USP30, acting on Mfn1 and Mfn2.

A small natural molecule promotes mitochondrial fusion through inhibition of the deubiquitinase USP30

Mitochondrial fusion is a highly coordinated process that mixes and unifies the mitochondrial compartment for normal mitochondrial functions and mitochondrial DNA inheritance. Dysregulated mitochondrial fusion causes mitochondrial fragmentation, abnormal mitochondrial physiology and inheritance, and has been causally linked with a number of neuronal diseases. Here, we identified a diterpenoid derivative 15-oxospiramilactone (S3) that potently induced mitochondrial fusion to restore the mitochondrial network and oxidative respiration in cells that are deficient in either Mfn1 or Mfn2. A mitochondria-localized deubiquitinase USP30 is a target of S3. The inhibition of USP30 by S3 leads to an increase of non-degradative ubiquitination of Mfn1/2, which enhances Mfn1 and Mfn2 activity and promotes mitochondrial fusion. Thus, through the use of an inhibitor of USP30, our study uncovers an unconventional function of non-degradative ubiquitination of Mfns in promoting mitochondrial fusion.

A diterpenoid derivate compound targets selenocysteine of thioredoxin reductases and induces Bax/Bak-independent apoptosis

We have previously shown that the natural diterpenoid derivative S3 induced Bim upregulation and apoptosis in a Bax/Bak-independent manner. However, the exact molecular target(s) of S3 and the mechanism controlling Bim upregulation are still not clear. Here, we identify that S3 targets the selenoproteins TrxR1 and TrxR2 at the selenocysteine residue of the reactive center of the enzymes and inhibits their antioxidant activities. Consequently, cellular ROS is elevated, leading to the activation of FOXO3a, which contributes to Bim upregulation in Bax/Bak-deficient cells. Moreover, S3 retards tumor growth in subcutaneous xenograft tumors by inhibiting TrxR activity in vivo. Our studies delineate the signaling pathway controlling Bim upregulation, which results in Bax/Bak-independent apoptosis and provide evidence that the compounds can act as anticancer agents based on mammalian TrxRs inhibition.

17β-estradiol impedes Bax-involved mitochondrial apoptosis of retinal nerve cells induced by oxidative damage via the phosphatidylinositol 3-kinase/Akt signal pathway

Oxidative stress leading to retinal nerve cells (RNCs) apoptosis is a major cause of neurodegenerative disorders of the retina. 17β-Estradiol (E2) has been suggested to be a neuroprotective agent in the central nervous system; however, at present, the underlying mechanisms are not well understood, and the related research on the RNCs is less reported. Here, in order to investigate the protective role and mechanism of E2 against oxidative stress-induced damage on RNCs, the transmission electron microscopy and annexin V-FITC/propidium iodide assay were applied to detect the RNCs apoptosis. Western blot and real-time PCR were used to determine the expression of the critical molecules in Bcl-2 and caspase family associated with apoptosis. The transmission electron microscopy results showed that H(2)O(2) could induce typical features of apoptosis in RNCs, including formation of the apoptosome. E2 could, however, suppress the H(2)O(2)-induced morphological changes of apoptosis. Intriguingly, we observed E2-mediated phagocytic scavenging of apoptosome. In response to H(2)O(2)-induced apoptosis, Bax, acting as one of the pivotal pro-apoptotic members of Bcl-2 family, increased significantly, which directly resulted in an increased ratio of Bax to anti-apoptotic protein Bcl-2 (Bax/Bcl-2). Additionally, caspases 9 and 3, which are the critical molecules of the mitochondrial apoptosis pathway, were activated by H(2)O(2). In contrast, E2 exerted anti-apoptotic effects by reducing the expression of Bax to decrease the ratio of Bax/Bcl-2 and impeded the caspases 9/3 activation. Moreover, LY294002, a phosphatidylinositol 3-kinase (PI3K) inhibitor, could sharply block the effect of E2 in reducing the percentage of apoptotic cells resistance to H(2)O(2). And the attenuation of Bax, the reduced activities of caspases 9/3 and the impeded release of mitochondrial cytochrome c mediated by E2 resistance to H(2)O(2) damage were significantly retrieved by LY294002 administration. Taken together, E2 protects the RNCs against H(2)O(2)-induced apoptosis by significantly inhibiting the Bax-involved mitochondrial apoptosis via the activation of PI3K/Akt signal pathway.

Phosphorylation of Rad9 at serine 328 by cyclin A-Cdk2 triggers apoptosis via interfering Bcl-xL

Cyclin A-Cdk2, a cell cycle regulated Ser/Thr kinase, plays important roles in a variety of apoptoticprocesses. However, the mechanism of cyclin A-Cdk2 regulated apoptosis remains unclear. Here, we demonstrated that Rad9, a member of the BH3-only subfamily of Bcl-2 proteins, could be phosphorylated by cyclin A-Cdk2 in vitro and in vivo. Cyclin A-Cdk2 catalyzed the phosphorylation of Rad9 at serine 328 in HeLa cells during apoptosis induced by etoposide, an inhibitor of topoisomeraseII. The phosphorylation of Rad9 resulted in its translocation from the nucleus to the mitochondria and its interaction with Bcl-xL. The forced activation of cyclin A-Cdk2 in these cells by the overexpression of cyclin A,triggered Rad9 phosphorylation at serine 328 and thereby promoted the interaction of Rad9 with Bcl-xL and the subsequent initiation of the apoptotic program. The pro-apoptotic effects regulated by the cyclin A-Cdk2 complex were significantly lower in cells transfected with Rad9S328A, an expression vector that encodes a Rad9 mutant that is resistant to cyclin A-Cdk2 phosphorylation. These findings suggest that cyclin A-Cdk2 regulates apoptosis through a mechanism that involves Rad9phosphorylation.

Methanol extract of Sanguisorba officinalis L. with cytotoxic activity against PC3 human prostate cancer cells

Sanguisorba officinalis is a natural plant that has been traditionally used for the treatment of inflammatory and metabolic diseases. Several studies have reported that its extracts exhibit anticancer, antioxidative and anti-lipid peroxidation activities. However, the effects of this plant on human prostate cancer cells have not yet been investigated. In the present study, we investigated the inhibitory effects and underlying mechanisms of a methanol extract of Sanguisorba officinalis (MESO) in PC3 human prostate cancer cells. MESO significantly decreased cell growth and induced apoptosis through the intrinsic apoptosis pathway. MESO decreased the expression levels of myeloid cell leukemia-1 (Mcl-1), a Bcl‑2‑like anti-apoptotic protein that is highly expressed in various cancer cell lines. Expression levels of the pro-apoptotic protein Bax were increased by MESO whereas those of Bak and Bcl-xL were unchanged. In addition, MESO induced the oligomerization of Bax in the mitochondrial outer membrane. These results suggest that MESO inhibits the growth of prostate cancer cells and induces apoptotic cell death by the downregulation of Mcl-1 protein expression and the oligomerization of Bax. Therefore, MESO has potential as a drug candidate for the treatment of prostate cancer.