Inactivation of prosurvival Bcl-2 proteins activates Bax/Bak through the outer mitochondrial membrane

BH3 mimetics as anti-fibrotic therapy: Unleashing the mitochondrial pathway of apoptosis in myofibroblasts

Organs and tissues in mammals can undergo self-repair following injury. However, chronic or severe tissue injury leads to the development of dense scar tissue or fibrosis at the expense of regeneration. The identification of novel therapeutic strategies aiming at reversing fibrosis is therefore a major clinical unmet need in regenerative medicine. Persistent activation of scar-forming myofibroblasts distinguishes non-resolving pathological fibrosis from self-limited physiological wound healing. Thus, therapeutic strategies selectively inducing myofibroblast apoptosis could prevent progression and potentially reverse established fibrosis in fibrotic diseases. In this Review, we discuss recent findings that have demonstrated that activated myofibroblasts, traditionally viewed as apoptosis-resistant cells, are actually "primed for death". In this state, mitochondria of activated myofibroblasts are loaded with proapoptotic BH3 proteins, which creates a cellular "addiction" to individual antiapoptotic proteins to block prodeath signaling and ensure survival. This creates a novel therapeutic opportunity to treat organ fibrosis by inducing myofibroblast apoptosis with the so-called BH3 mimetic drugs, which have recently shown potent antifibrotic activities in experimental models. Finally, we discuss the potential use of BH3 profiling as a functional tool to diagnose myofibroblast addiction to individual antiapoptotic proteins, which may serve to guide and assign the most effective BH3 mimetic drug for patients with fibrotic disease.

Cell Death or Survival Against Oxidative Stress

Peroxisomes contain anabolic and catabolic enzymes including oxidases that produce hydrogen peroxide as a by-product. Peroxisomes also contain catalase to metabolize hydrogen peroxide. It has been recognized that catalase is localized to cytosol in addition to peroxisomes. A recent study has revealed that loss of VDAC2 shifts localization of BAK, a pro-apoptotic member of Bcl-2 family, from mitochondria to peroxisomes and cytosol, thereby leading to release of peroxisomal matrix proteins including catalase to the cytosol. A subset of BAK is localized to peroxisomes even in wild-type cells, regulating peroxisomal membrane permeability and catalase localization. The cytosolic catalase potentially acts as an antioxidant to eliminate extra-peroxisomal hydrogen peroxide.

The dietary compound luteolin inhibits pancreatic cancer growth by targeting BCL-2

Luteolin, a bioactive flavonoid from celery (Apium graveolens), has been rationally proved to trigger SW1990 cells to apoptosis by targeting BCL-2, and may serve as a potential agent for this cancer therapy.

MOMP, cell suicide as a BCL-2 family business

Apoptosis shapes development and differentiation, has a key role in tissue homeostasis, and is deregulated in cancer. In most cases, successful apoptosis is triggered by mitochondrial outer membrane permeabilization (MOMP), which defines the mitochondrial or intrinsic pathway and ultimately leads to caspase activation and protein substrate cleavage. The mitochondrial apoptotic pathway centered on MOMP is controlled by an intricate network of events that determine the balance of the cell fate choice between survival and death. Here we will review how MOMP proceeds and how the main effectors cytochrome c, a heme protein that has a crucial role in respiration, and second mitochondria-derived activator of caspase (SMAC), as well as other intermembrane space proteins, orchestrate caspase activation. Moreover, we discuss recent insights on the interplay of the upstream coordinators and initiators of MOMP, the BCL-2 family. This review highlights how our increasing knowledge on the regulation of critical checkpoints of apoptosis integrates with understanding of cancer development and has begun to translate into therapeutic clinical benefit.

Upregulation of BAG3 with apoptotic and autophagic activities in maggot extract‑promoted rat skin wound healing

Maggot extract (ME) accelerates rat skin wound healing, however its effect on cell maintenance in wound tissues remains unclear. B‑cell lymphoma (Bcl) 2‑associated athanogene (BAG)3 inhibits apoptosis and promotes autophagy by associating with Bcl‑2 or Beclin 1. Bcl‑2, the downstream effector of signal transducer and activator of transcription 3 signaling, is enhanced in ME‑treated wound tissues, which may reinforce the Bcl‑2 anti‑apoptotic activity and/or cooperate with Beclin 1 to regulate autophagy during wound healing. The present study investigated expression levels of BAG3, Bcl‑2, Beclin 1 and light chain (LC)3 levels in rat skin wound tissues in the presence and absence of ME treatment. The results revealed frequent TUNEL‑negative cell death in the wound tissues in the early three days following injury, irrespective to ME treatment. TUNEL‑positive cells appeared in the wound tissues following 4 days of injury and 150 µg/ml ME efficiently reduced apoptotic rate and enhanced BAG3 and Bcl‑2 expression. Elevated Beclin 1 and LC3 levels and an increased LC3 II ratio were revealed in the ME‑treated tissues during the wound healing. The results of the present study demonstrate the anti‑apoptotic effects of BAG3 and Bcl‑2 in ME‑promoted wound healing. Beclin 1/LC3 mediated autophagy may be favorable in maintaining cell survival in the damaged tissues and ME‑upregulated BAG3 may enhance its activity.

[Effects of simvastatin on aortic vascular endothelial cell apoptosis and Bcl-2 protein expression in a rat model of atherosclerosis]

OBJECTIVE

To explore the effects of simvastatin on vascular endothelial cell apoptosis and Bcl-2 protein expression in the aorta in a rat model of atherosclerosis.

METHODS

Thirty-six rats were randomized into control group (n=10), atherosclerosis model group (n=13) and simvastatin intervention group (n=13). In the latter two groups, rat models of atherosclerosis were established by intraperitoneal injection of vitamin D3 combined with high-fat feeding for 6 weeks, and the control rats were fed with regular diet. In the intervention group, the rats were further fed with high-fat diet with daily simvastatin treatment for 4 weeks. After the treatments, the pathological changes and plaque in the thoracic aorta were observed, and the expression of Bcl-2 protein was detected with immunohistochemistry. TUNEL assay was used to determine the apoptosis index (AI) of the vascular endothelial cells.

RESULTS

Compared with that in the control group, Bcl-2 protein expression in the aorta of atherosclerotic rats was significantly decreased (P<0.05); simvastatin treatment obviously increased the expression of Bcl-2 protein in atherosclerotic rats (P<0.05) to a level similar to that in the control group. The AI was the highest in the model group (P<0.05) and comparable between the control and simvastatin treatment group.

CONCLUSION

The therapeutic effect of simvastatin against atherosclerosis is probably mediated by up-regulation of Bcl-2 protein, which inhibits vascular endothelial cell apoptosis in rats with aortic atherosclerosis.

BCL-2 family proteins: changing partners in the dance towards death

The BCL-2 family of proteins controls cell death primarily by direct binding interactions that regulate mitochondrial outer membrane permeabilization (MOMP) leading to the irreversible release of intermembrane space proteins, subsequent caspase activation and apoptosis. The affinities and relative abundance of the BCL-2 family proteins dictate the predominate interactions between anti-apoptotic and pro-apoptotic BCL-2 family proteins that regulate MOMP. We highlight the core mechanisms of BCL-2 family regulation of MOMP with an emphasis on how the interactions between the BCL-2 family proteins govern cell fate. We address the critical importance of both the concentration and affinities of BCL-2 family proteins and show how differences in either can greatly change the outcome. Further, we explain the importance of using full-length BCL-2 family proteins (versus truncated versions or peptides) to parse out the core mechanisms of MOMP regulation by the BCL-2 family. Finally, we discuss how post-translational modifications and differing intracellular localizations alter the mechanisms of apoptosis regulation by BCL-2 family proteins. Successful therapeutic intervention of MOMP regulation in human disease requires an understanding of the factors that mediate the major binding interactions between BCL-2 family proteins in cells.

Viewing BCL2 and cell death control from an evolutionary perspective

The last 30 years of studying BCL2 have brought cell death research into the molecular era, and revealed its relevance to human pathophysiology. Most, if not all metazoans use an evolutionarily conserved process for cellular self destruction that is controlled and implemented by proteins related to BCL2. We propose the anti-apoptotic BCL2-like and pro-apoptotic BH3-only members of the family arose through duplication and modification of genes for the pro-apoptotic multi-BH domain family members, such as BAX and BAK1. In that way, a cell suicide process that initially evolved as a mechanism for defense against intracellular parasites was then also used in multicellular organisms for morphogenesis and to maintain the correct number of cells in adults by balancing cell production by mitosis.

The BCL-2 arbiters of apoptosis and their growing role as cancer targets

Impaired apoptosis plays a central role in cancer development and limits the efficacy of conventional cytotoxic therapies. Deepening understanding of how opposing factions of the BCL-2 protein family switch on apoptosis and of their structures has driven development of a new class of cancer drugs that targets various pro-survival members by mimicking their natural inhibitors, the BH3-only proteins. These ‘BH3 mimetic’ drugs seem destined to become powerful new weapons in the arsenal against cancer. Successful clinical trials of venetoclax/ABT-199, a specific inhibitor of BCL-2, have led to its approval for a refractory form of chronic lymphocytic leukaemia and to scores of on-going trials for other malignancies. Furthermore, encouraging preclinical studies of BH3 mimetics that target other BCL-2 pro-survival members, particularly MCL-1, offer promise for cancers resistant to venetoclax. This review sketches the impact of the BCL-2 family on cancer development and therapy, describes how interactions of family members trigger apoptosis and discusses the potential of BH3 mimetic drugs to advance cancer therapy.

Bcl-2 proteins: Unraveling the details of a complex and dynamic network

Apoptosis regulation by Bcl-2 proteins is pivotal for mammalians, not only because it is key for development but also because aberrant apoptosis is prerequisite to severe diseases, like cancer. Recently, we quantified interactions within the Bcl-2 protein network in solution and membranes, and addressed membrane recruitment, preference of interaction partners and the consequences for Bax activation and inhibition.

Resveratrol enhances anticancer effects of paclitaxel in HepG2 human liver cancer cells

BACKGROUND

The aim of this in vitro study was to measure the enhanced anticancer effects of Res (resveratrol) on PA (paclitaxel) in HepG2 human liver cancer cells.

METHODS

The MTT (thiazolyl blue tetrazolium bromide, 3-(4,5-Dimethylthiazol-2-yl)-2,5-Diphenyltetrazolium Bromide), flow cytometry, qPCR (real-time quantitative polymerase chain reaction) and western blot assay were used for cells growth inhibitory effects, cells apoptosis (DNA content of sub-G1), mRNA and protein expressions, respectively.

RESULTS

The 10 μg/mL of Res had no growth inhibitory effect on Nthy-ori 3-1 normal cells or HepG2 cancer cells meanwhile the 5 or 10 μg/mL of PA also had no growth inhibitory effect on Nthy-ori 3-1 normal cells. Where as PA-L (5 μg/mL) and PA-H (10 μg/mL) had the growth inhibitory effects in HepG2 cancer cells, and Res increase these growth inhibitory effects. By flow cytometry experiment, after Res (5 μg/mL) + PA-H (10 μg/mL) treatment, the HepG2 cells showed the most apoptosis in cells as compared to other treatments groups, and after additionally treated with Res, both the apoptosis cells of two concentrations PA were raised. As PA raised it also raised the mRNA and protein expressions of caspase-3, caspase-8, caspase-9, Bax (Bcl-2 assaciated X protein), p53, p21, IκB-α (inhibitor of NF-κB alpha), Fas (factor associated suicide), FasL (factor associated suicide ligand), TIMP-1 (tissue inhibitor of metalloproteinases 1), TIMP-2 (tissue inhibitor of metalloproteinases 2) and decrease Bcl-2 (B cell leukemia 2), Bcl-xL (B cell leukemia extra large), HIAP-1 (cIAP-1, cellular inhibitor of apoptosis 1), HIAP-2 (cIAP-2, cellular inhibitor of apoptosis 2), NF-κB (nuclear factor kappa B), COX-2 (cyclooxygenase 2), iNOS (inducible nitric oxide synthase), MMP-2 (metalloproteinase 2), MMP-9 (metalloproteinase 9), EGF (epidermal growth factor), EGFR (epidermal growth factor receptor), VEGF (vascular endothelial growth factor), Fit-1 (VEGFR-1, vascular endothelial growth factor receptor 1). Meanwhile, the 5 μg/mL of Res could enhance these mRNA expressions changes as compared to the control cells.

CONCLUSION

From these results, we can conclude that Res could raise the anticancer effects of PA in HepG2 cells, Res could be used as a good sensitizing agent for PA.

The 2-oxoglutarate carrier promotes liver cancer by sustaining mitochondrial GSH despite cholesterol loading

Cancer cells exhibit mitochondrial cholesterol (mt-cholesterol) accumulation, which contributes to cell death resistance by antagonizing mitochondrial outer membrane (MOM) permeabilization. Hepatocellular mt-cholesterol loading, however, promotes steatohepatitis, an advanced stage of chronic liver disease that precedes hepatocellular carcinoma (HCC), by depleting mitochondrial GSH (mGSH) due to a cholesterol-mediated impairment in mGSH transport. Whether and how HCC cells overcome the restriction of mGSH transport imposed by mt-cholesterol loading to support mGSH uptake remains unknown. Although the transport of mGSH is not fully understood, SLC25A10 (dicarboxylate carrier, DIC) and SLC25A11 (2-oxoglutarate carrier, OGC) have been involved in mGSH transport, and therefore we examined their expression and role in HCC. Unexpectedly, HCC cells and liver explants from patients with HCC exhibit divergent expression of these mitochondrial carriers, with selective OGC upregulation, which contributes to mGSH maintenance. OGC but not DIC downregulation by siRNA depleted mGSH levels and sensitized HCC cells to hypoxia-induced ROS generation and cell death as well as impaired cell growth in three-dimensional multicellular HCC spheroids, effects that were reversible upon mGSH replenishment by GSH ethyl ester, a membrane permeable GSH precursor. We also show that OGC regulates mitochondrial respiration and glycolysis. Moreover, OGC silencing promoted hypoxia-induced cardiolipin peroxidation, which reversed the inhibition of cholesterol on the permeabilization of MOM-like liposomes induced by Bax or Bak. Genetic OGC knockdown reduced the ability of tumor-initiating stem-like cells to induce liver cancer. These findings underscore the selective overexpression of OGC as an adaptive mechanism of HCC to provide adequate mGSH levels in the face of mt-cholesterol loading and suggest that OGC may be a novel therapeutic target for HCC treatment.

The life and death of immune cell types: the role of BCL-2 anti-apoptotic molecules

Targeting survival mechanisms of immune cells may provide an avenue for immune intervention to dampen unwanted responses (e.g. autoimmunity, immunopathology and transplant rejection) or enhance beneficial ones (e.g. immune deficiency, microbial defence and cancer immunotherapy). The selective survival mechanisms of the various immune cell types also avails the possibility of specific tailoring of such interventions. Here, we review the role of the BCL-2 anti-apoptotic family members (BCL-2, BCL-XL, BCL-W, MCL-1 and A1) on cell death/survival of the major immune cell types, for example, T, NK, B, dendritic cell (DC) lineages. There is both selectivity and redundancy among this family. Selectivity comes partly from the expression levels in each of the cell types. For example, plasmacytoid DC express abundant BCL-2 and are susceptible to BCL-2 antagonism or deficiency, whereas conventional DC express abundant A1 and are susceptible to A1 deficiency. There is, however, also functional redundancy; for example, overexpression of MCL-1 can override BCL-2 antagonism in plasmacytoid DC. Moreover, susceptibility to another anti-apoptotic family member can be unmasked, when one or other member is removed. These dual principles of selectivity and redundancy should guide the use of antagonists for manipulating immune cells.

Lactobacillus raises in vitro anticancer effect of geniposide in HSC-3 human oral squamous cell carcinoma cells

The present study determined the ability of the Lactobacillus rhamnosus GG strain (LGG) to enhance the anticancer effects of geniposide on HSC-3 human oral squamous carcinoma cells. LGG (1.0×10³ CFU/ml) on its own had no impact on human oral keratinocytes and HSC-3 cancer cells. Geniposide (25 or 50 µg/ml) had no impact on human oral keratinocytes, but exerted growth inhibitory effects on HSC-3 cancer cells, which were increased in the presence of LGG. Flow cytometric analysis and a nuclear staining assay with DAPI revealed that HSC-3 cancer cells treated with LGG-geniposide (1.0×10³ CFU/ml LGG and 50 µg/ml geniposide) had a higher apoptotic rate than cells in other treatment groups, particularly that treated with geniposide (50 µg/ml) only. Geniposide also increased the mRNA and protein expression of caspase-3, -8 and -9 as well as B-cell lymphoma 2 (Bcl-2)-associated X protein, p53, p21, inhibitor of nuclear factor-κB (NF-κB) α, Fas and Fas ligand, while decreasing Bcl-2, Bcl extra large protein, inhibitor of apoptosis-1 and -2, NF-κB, cyclooxigenase-2 and inducible nitric oxide synthase in HSC-3 cells, which was increased in the presence of LGG. These results indicated that LGG enhanced the anticancer effects of geniposide in HSC-3 cells.

The protective effects of ischemic preconditioning on rats with renal ischemia-reperfusion injury and the effects on the expression of Bcl-2 and Bax

The aim of the present study was to investigate the protective effects of ischemic preconditioning on rats with renal ischemia-reperfusion injury and the effects on the expression of Bcl-2 and Bax. Thirty-six SD rats were randomly divided into three groups (n=12) including sham operation (S) group, ischemia-reperfusion group (I/R) group and ischemic preconditioning (IP) group. After anesthesia with intraperitoneal injection of chloral hydrate, bilateral renal pedicles were clipped for 45 min, followed by perfusion for 6 h to establish the I/R model. Both kidneys in rats of S group were separated and exposed for 45 min, but renal pedicles were not clipped. In IP group, bilateral renal pedicles were clipped for 5 min, followed by perfusion for 5 min, this procedure was repeated 3 times. Then bilateral renal pedicles were clipped for 45 min, followed by perfusion for 6 h. Blood samples were collected and rats were sacrificed to collect renal tissue. Levels of serum creatinine (Cr) and blood urea nitrogen (BUN) were measured. Activity of superoxide dismutase (SOD) was measured by xanthine oxidase assay. Degree of renal injury was evaluated by H&E staining. TUNEL kit was used to detect the number of apoptotic cells in renal tissue. Expression levels of Bcl-2 and Bax were detected by semi-quantitative PCR and western blot analysis at mRNA and protein levels, respectively. Results showed that levels of Cr and BUN in I/R and IP groups were significantly higher than those in S group, and levels of Cr and BUN in I/R group were significantly higher than that in IP group (P<0.05). Activity of SOD in I/R group and IP group were significantly lower than those in S group, and activity of SOD in I/R group were significantly lower than those in IP group (P<0.05). H&E staining showed that, compared with S group, renal injury in the I/R and IP groups was more serious than that in the S group, and I/R group was more serious than the IP group (P<0.05). TUNEL apoptosis assay showed that number of apoptotic cells in IP and I/R groups were significantly higher than that in the S group (P<0.01). Semi-quantitative PCR and western blot analysis showed that, compared with the S group, expression levels of Bcl-2 mRNA and protein were significantly decreased, expression levels of Bax mRNA and protein were significantly increased, and the ratio of Bcl-2/Bax was significantly decreased in the IP and I/R groups (P<0.01). Compared with the I/R group, expression level of Bcl-2 was significantly increased, the level of Bax was significantly deceased, and the ratio of Bcl-2/Bax was significantly increased in the IP group (P<0.01). As a result, ischemic preconditioning can protect rats with renal ischemia-reperfusion injury possibly by increasing the expression level of Bcl-2 and decreasing the expression level of Bax.

Quantitative interactome of a membrane Bcl-2 network identifies a hierarchy of complexes for apoptosis regulation

The Bcl-2 proteins form a complex interaction network that controls mitochondrial permeabilization and apoptosis. The relative importance of different Bcl-2 complexes and their spatio-temporal regulation is debated. Using fluorescence cross-correlation spectroscopy to quantify the interactions within a minimal Bcl-2 network, comprised by cBid, Bax, and Bcl-xL, we show that membrane insertion drastically alters the pattern of Bcl-2 complexes, and that the C-terminal helix of Bcl-xL determines its binding preferences. At physiological temperature, Bax can spontaneously activate in a self-amplifying process. Strikingly, Bax also recruits Bcl-xL to membranes, which is sufficient to retrotranslocate Bax back into solution to secure membrane integrity. Our study disentangles the hierarchy of Bcl-2 complex formation in relation to their environment: Bcl-xL association with cBid occurs in solution and in membranes, where the complex is stabilized, whereas Bcl-xL binding to Bax occurs only in membranes and with lower affinity than to cBid, leading instead to Bax retrotranslocation.

The permeabilization of the mitochondrial outer membrane to induce apoptosis is regulated by complex interactions between Bcl-2 family members. Here the authors develop a quantitative interactome of a membrane Bcl-2 network and identify a hierarchy of protein complexes in apoptosis induction.

The BH3-only proteins BIM and PUMA are not critical for the reticulocyte apoptosis caused by loss of the pro-survival protein BCL-XL

Anaemia is a major global health problem arising from diverse causes and for which improved therapeutic strategies are needed. Erythroid cells can undergo apoptotic cell death and loss of pro-survival BCL-XL is known to trigger apoptosis during late-stage erythroid development. However, the mechanism by which loss or pharmacological blockade of BCL-XL leads to erythroid cell apoptosis remains unclear. Here we sought to identify the precise stage of erythropoiesis that depends on BCL-XL. We also tested whether deficiency of BIM or PUMA, the two main pro-apoptotic antagonists of BCL-XL, could prevent reticulocyte death and anaemia caused by BCL-XL loss. Using an in vivo mouse model of tamoxifen-inducible Bclx gene deletion and in vitro assays with a BCL-XL-selective inhibitor, we interrogated each stage of erythrocyte differentiation for BCL-XL dependency. This revealed that reticulocytes, but not orthochromatic erythroblasts, require BCL-XL for their survival. Surprisingly, concurrent loss of BIM or PUMA had no significant impact on the development of anemia following acute BCL-XL deletion in vivo. However, analysis of mixed bone marrow chimaeric mice revealed that loss of PUMA, but not loss of BIM, partially alleviated impaired erythropoiesis caused by BCL-XL deficiency. Insight into how the network of pro-survival and pro-apoptotic proteins works will assist the development of strategies to mitigate the effects of abnormal cell death during erythropoiesis and prevent anaemia in patients treated with BCL-XL-specific BH3-mimetic drugs.

Interrogating the relevance of mitochondrial apoptosis for vertebrate development and postnatal tissue homeostasis

"Programmed cell death or 'apoptosis' is critical for organogenesis during embryonic development and tissue homeostasis in the adult. Its deregulation can contribute to a broad range of human pathologies, including neurodegeneration, cancer, or autoimmunity…" These or similar phrases have become generic opening statements in many reviews and textbooks describing the physiological relevance of apoptotic cell death. However, while the role in disease has been documented beyond doubt, facilitating innovative drug discovery, we wonder whether the former is really true. What goes wrong in vertebrate development or in adult tissue when the main route to apoptotic cell death, controlled by the BCL2 family, is impaired? Such scenarios have been mimicked by deletion of one or more prodeath genes within the BCL2 family, and gene targeting studies in mice exploring the consequences have been manifold. Many of these studies were geared toward understanding the role of BCL2 family proteins and mitochondrial apoptosis in disease, whereas fewer focused in detail on their role during normal development or tissue homeostasis, perhaps also due to an irritating lack of phenotype. Looking at these studies, the relevance of classical programmed cell death by apoptosis for development appears rather limited. Together, these many studies suggest either highly selective and context-dependent contributions of mitochondrial apoptosis or significant redundancy with alternative cell death mechanisms, as summarized and discussed here.

Anti-apoptotic proteins BCL-2, MCL-1 and A1 summate collectively to maintain survival of immune cell populations both in vitro and in vivo

Survival of various immune cell populations has been proposed to preferentially rely on a particular anti-apoptotic BCL-2 family member, for example, naive T cells require BCL-2, while regulatory T cells require MCL-1. Here we examined the survival requirements of multiple immune cell subsets in vitro and in vivo, using both genetic and pharmacological approaches. Our findings support a model in which survival is determined by quantitative participation of multiple anti-apoptotic proteins rather than by a single anti-apoptotic protein. This model provides both an insight into how the sum of relative levels of anti-apoptotic proteins BCL-2, MCL-1 and A1 influence survival of T cells, B cells and dendritic cells, and a framework for ascertaining how these different immune cells can be optimally targeted in treatment of immunopathology, transplantation rejection or hematological cancers.

Wogonoside exerts growth-suppressive effects against T acute lymphoblastic leukemia through the STAT3 pathway

Wogonoside is the main flavonoid of the traditional Chinese medicinal herb Scutellaria baicalensis Georgi and has been found to induce growth suppression in myelogenous leukemia cells. However, its activity in T acute lymphoblastic leukemia (T-ALL) is still unclear. In this study, T-ALL cell lines MOLT-3 and Jurkat were exposed to different concentrations of wogonoside for 48 h, and cell viability, cell cycle distribution, and apoptosis were measured. The involvement of signal transducers and activators of transcription 3 (STAT3) signaling in the activity of wogonoside was checked. The in vivo effect of wogonoside on T-ALL growth was investigated in a xenograft mouse model. Wogonoside significantly inhibited the viability of MOLT-3 and Jurkat cells, with the IC₅₀ (the half maximal concentration) of 68.5 ± 3.8 and 52.6 ± 4.3 μM, respectively. However, healthy T lymphocytes were unaffected. Wogonoside-treated Jurkat cells exhibited a G1-phase cell cycle arrest and significant apoptosis, which was coupled with inactivation of STAT3 signaling. Overexpression of constitutively active STAT3 reversed wogonoside-mediated growth suppression and apoptosis and restored the expression of cyclin D1, Mcl-1, and Bcl-xL. In vivo studies demonstrated that wogonoside retarded tumor growth and suppressed STAT3 phosphorylation in Jurkat xenografts. In conclusion, wogonoside suppresses the growth of T-ALL through the STAT3 pathway and may have therapeutic benefits in this disease.

Induction of cell death by pyropheophorbide-α methyl ester-mediated photodynamic therapy in lung cancer A549 cells

Pyropheophorbide‐α methyl ester (MPPa) was a promising photosensitizer with stable chemical structure, strong absorption, higher tissue selectivity and longer activation wavelengths. The present study investigated the effect of MPPa‐mediated photodynamic treatment on lung cancer A549 cells as well as the underlying mechanisms. Cell Counting Kit‐8 was employed for cell viability assessment. Reactive oxygen species levels were determined by fluorescence microscopy and flow cytometry. Cell morphology was evaluated by Hoechst staining and transmission electron microscopy. Mitochondrial membrane potential, cellular apoptosis and cell cycle distribution were evaluated flow‐cytometrically. The protein levels of apoptotic effectors were examined by Western blot. We found that the photocytotoxicity of MPPa showed both drug‐ and light‐ dose dependent characteristics in A549 cells. Additionally, MPPa‐PDT caused cell apoptosis by reducing mitochondrial membrane potential, increasing reactive oxygen species (ROS) production, inducing caspase‐9/caspase‐3 signaling activation as well as cell cycle arrest at G₀/G₁ phase. These results suggested that MPPa‐PDT mainly kills cells by apoptotic mechanisms, with overt curative effects, indicating that MPPa should be considered a potent photosensitizer for lung carcinoma treatment.

The VDAC2-BAK axis regulates peroxisomal membrane permeability

Peroxisomal biogenesis disorders (PBDs) are fatal genetic diseases consisting of 14 complementation groups (CGs). We previously isolated a peroxisome-deficient Chinese hamster ovary cell mutant, ZP114, which belongs to none of these CGs. Using a functional screening strategy, VDAC2 was identified as rescuing the peroxisomal deficiency of ZP114 where VDAC2 expression was not detected. Interestingly, knockdown of BAK or overexpression of the BAK inhibitors BCL-X_L and MCL-1 restored peroxisomal biogenesis in ZP114 cells. Although VDAC2 is not localized to the peroxisome, loss of VDAC2 shifts the localization of BAK from mitochondria to peroxisomes, resulting in peroxisomal deficiency. Introduction of peroxisome-targeted BAK harboring the Pex26p transmembrane region into wild-type cells resulted in the release of peroxisomal matrix proteins to cytosol. Moreover, overexpression of BAK activators PUMA and BIM permeabilized peroxisomes in a BAK-dependent manner. Collectively, these findings suggest that BAK plays a role in peroxisomal permeability, similar to mitochondrial outer membrane permeabilization.

BCL-2: Long and winding path from discovery to therapeutic target

In 1988, the BCL-2 protein was found to promote cancer by limiting cell death rather than enhancing proliferation. This discovery set the wheels in motion for an almost 30 year journey involving many international research teams that has recently culminated in the approval for a drug, ABT-199/venetoclax/Venclexta that targets this protein in the treatment of cancer. This review will describe the long and winding path from the discovery of this protein and understanding the fundamental process of apoptosis that BCL-2 and its numerous homologues control, through to its exploitation as a drug target that is set to have significant benefit for cancer patients.

Cell cycle progression dictates the requirement for BCL2 in natural killer cell survival

Natural killer (NK) cells are innate lymphoid cells with antitumor functions. Using an N-ethyl-N-nitrosourea (ENU)-induced mutagenesis screen in mice, we identified a strain with an NK cell deficiency caused by a hypomorphic mutation in the Bcl2 (B cell lymphoma 2) gene. Analysis of these mice and the conditional deletion of Bcl2 in NK cells revealed a nonredundant intrinsic requirement for BCL2 in NK cell survival. In these mice, NK cells in cycle were protected against apoptosis, and NK cell counts were restored in inflammatory conditions, suggesting a redundant role for BCL2 in proliferating NK cells. Consistent with this, cycling NK cells expressed higher MCL1 (myeloid cell leukemia 1) levels in both control and BCL2-null mice. Finally, we showed that deletion of BIM restored survival in BCL2-deficient but not MCL1-deficient NK cells. Overall, these data demonstrate an essential role for the binding of BCL2 to BIM in the survival of noncycling NK cells. They also favor a model in which MCL1 is the dominant survival protein in proliferating NK cells.

Bax and Bak Pores: Are We Closing the Circle?

Bax and its homolog Bak are key regulators of the mitochondrial pathway of apoptosis. On cell stress Bax and Bak accumulate at distinct foci on the mitochondrial surface where they undergo a conformational change, oligomerize, and mediate cytochrome c release, leading to cell death. The molecular mechanisms of Bax and Bak assembly and mitochondrial permeabilization have remained a longstanding question in the field. Recent structural and biophysical studies at several length scales have shed light on key aspects of Bax and Bak function that have shifted how we think this process occurs. These discoveries reveal an unexpected molecular mechanism in which Bax (and likely Bak) dimers assemble into oligomers with an even number of molecules that fully or partially delineate pores of different sizes to permeabilize the mitochondrial outer membrane (MOM) during apoptosis.

Mitochondrial apoptosis and BH3 mimetics

The BCL2-selective BH3 mimetic venetoclax was recently approved for the treatment of relapsed, chromosome 17p-deleted chronic lymphocytic leukemia (CLL) and is undergoing extensive testing, alone and in combination, in lymphomas, acute leukemias, and solid tumors. Here we summarize recent advances in understanding of the biology of BCL2 family members that shed light on the action of BH3 mimetics, review preclinical and clinical studies leading to the regulatory approval of venetoclax, and discuss future investigation of this new class of antineoplastic agent.

MLL-AF4 binds directly to a BCL-2 specific enhancer and modulates H3K27 acetylation

Survival rates for children and adults carrying mutations in the Mixed Lineage Leukemia (MLL) gene continue to have a very poor prognosis. The most common MLL mutation in acute lymphoblastic leukemia is the t(4;11)(q21;q23) chromosome translocation that fuses MLL in-frame with the AF4 gene producing MLL-AF4 and AF4-MLL fusion proteins. Previously, we found that MLL-AF4 binds to the BCL-2 gene and directly activates it through DOT1L recruitment and increased H3K79me2/3 levels. In the study described here, we performed a detailed analysis of MLL-AF4 regulation of the entire BCL-2 family. By measuring nascent RNA production in MLL-AF4 knockdowns, we found that of all the BCL-2 family genes, MLL-AF4 directly controls the active transcription of both BCL-2 and MCL-1 and also represses BIM via binding of the polycomb group repressor 1 (PRC1) complex component CBX8. We further analyzed MLL-AF4 activation of the BCL-2 gene using Capture-C and identified a BCL-2-specific enhancer, consisting of two clusters of H3K27Ac at the 3' end of the gene. Loss of MLL-AF4 activity results in a reduction of H3K79me3 levels in the gene body and H3K27Ac levels at the 3' BCL-2 enhancer, revealing a novel regulatory link between these two histone marks and MLL-AF4-mediated activation of BCL-2.

Inhibition of CDK9 induces apoptosis and potentiates the effect of cisplatin in hypopharyngeal carcinoma cells

Myeloid cell leukemia-1 (Mcl-1) plays an important role in survival, chemo- and radioresistance of head and neck squamous cell carcinoma (HNSCC). Cyclin-dependent kinase 9/cyclin T (CDK9) promotes excessive production of multiple pro-survival proteins including Mcl-1, leading to impaired apoptosis of cancer cells. As such, CDK9 is an emerging therapeutic target in cancer therapy. We herein report the first study of targeting CDK9 as a treatment strategy for hypopharyngeal squamous cell carcinoma (HSCC), an aggressive malignancy associated with one of the worst prognoses within HNSCC. We showed that mRNA levels of Mcl-1 were significantly higher in HSCC tumor tissues than in the adjacent non-tumor mucosae. In addition, the levels of Mcl-1 mRNA correlated with the tumor size and clinical stage of HSCC patients. CDKI-73, a potent CDK9 inhibitor, was capable of downregulating the expression of Mcl-1 in the HSCC cells by suppression of the CDK9 mediated phosphorylation of RNA polymerase II. CDKI-73 effectively induced apoptosis as a single agent and synergized anti-tumor activity of cisplatin in HSCC cells. Taken together, our study presents compelling evidence for developing CDK9 inhibitors, such as CDKI-73, as new therapeutic strategy for HSCC.

Overexpression of Mcl-1 exacerbates lymphocyte accumulation and autoimmune kidney disease in lpr mice

Cell death by apoptosis has a critical role during embryonic development and in maintaining tissue homeostasis. In mammals, there are two converging apoptosis pathways: the 'extrinsic' pathway, which is triggered by engagement of cell surface 'death receptors' such as Fas/APO-1; and the 'intrinsic' pathway, which is triggered by diverse cellular stresses, and is regulated by pro-survival and pro-apoptotic members of the Bcl-2 family of proteins. Pro-survival Mcl-1, which can block activation of the pro-apoptotic proteins, Bax and Bak, appears critical for the survival and maintenance of multiple haemopoietic cell types. To investigate the impact on haemopoiesis of simultaneously inhibiting both apoptosis pathways, we introduced the vavP-Mcl-1 transgene, which causes overexpression of Mcl-1 protein in all haemopoietic lineages, into Fas^lpr/lpr mice, which lack functional Fas and are prone to autoimmunity. The combined mutations had a modest impact on myelopoiesis, primarily an increase in the macrophage/monocyte population in Mcl-1tg/lpr mice compared with lpr or Mcl-1tg mice. The impact on lymphopoiesis was striking, with a marked elevation in all major lymphoid subsets, including the non-conventional double-negative (DN) T cells (TCRβ⁺CD4^-CD8^-B220⁺) characteristic of Fas^lpr/lpr mice. Of note, the onset of autoimmunity was markedly accelerated in Mcl-1tg/lpr mice compared with lpr mice, and this was preceded by an increase in immunoglobulin (Ig)-producing cells and circulating autoantibodies. This degree of impact was surprising, given the relatively mild phenotype conferred by the vavP-Mcl-1 transgene by itself: a two- to threefold elevation of peripheral B and T cells, no significant increase in the non-conventional DN T-cell population and no autoimmune disease. Comparison of the phenotype with that of other susceptible mice suggests that the development of autoimmune disease in Mcl-1tg/lpr mice may be influenced not only by Ig-producing cells but also other haemopoietic cell types.

Cycloheximide Can Induce Bax/Bak Dependent Myeloid Cell Death Independently of Multiple BH3-Only Proteins

Apoptosis mediated by Bax or Bak is usually thought to be triggered by BH3-only members of the Bcl-2 protein family. BH3-only proteins can directly bind to and activate Bax or Bak, or indirectly activate them by binding to anti-apoptotic Bcl-2 family members, thereby relieving their inhibition of Bax and Bak. Here we describe a third way of activation of Bax/Bak dependent apoptosis that does not require triggering by multiple BH3-only proteins. In factor dependent myeloid (FDM) cell lines, cycloheximide induced apoptosis by a Bax/Bak dependent mechanism, because Bax^-/-Bak^-/- lines were profoundly resistant, whereas FDM lines lacking one or more genes for BH3-only proteins remained highly sensitive. Addition of cycloheximide led to the rapid loss of Mcl-1 but did not affect the expression of other Bcl-2 family proteins. In support of these findings, similar results were observed by treating FDM cells with the CDK inhibitor, roscovitine. Roscovitine reduced Mcl-1 abundance and caused Bax/Bak dependent cell death, yet FDM lines lacking one or more genes for BH3-only proteins remained highly sensitive. Therefore Bax/Bak dependent apoptosis can be regulated by the abundance of anti-apoptotic Bcl-2 family members such as Mcl-1, independently of several known BH3-only proteins.

Bcl-2 proteins bid and bax form a network to permeabilize the mitochondria at the onset of apoptosis

The most critical step in the initiation of apoptosis is the activation of the Bcl-2 family of proteins to oligomerize and permeabilize the outer-mitochondrial membrane (OMM). As this step results in the irreversible release of factors that enhance cellular degradation, it is the point of no return in programmed cell death and would be an ideal therapeutic target. However, the arrangement of the Bcl-2 proteins in the OMM during permeabilization still remains unknown. It is also unclear whether the Bcl-2 protein, Bid, directly participates in the formation of the oligomers in live cells, even though it is cleaved and translocates to the OMM at the initiation of apoptosis. Therefore, we utilized confocal microscopy to measure Förster resonance energy transfer (FRET) efficiencies in live cells to determine the conformation(s) and intermolecular contacts of Bid within these Bcl-2 oligomers. We found that Bid adopts an extended conformation, which appears to be critical for its association with the mitochondrial membrane. This conformation is also important for intermolecular contacts within the Bid oligomer. More importantly for the first time, direct intermolecular contacts between Bid and Bax were observed, thereby, confirming Bid as a key component of these oligomers. Furthermore, the observed FRET efficiencies allowed us to propose an oligomeric arrangement of Bid, Bax, and possibly other members of the Bcl-2 family of proteins that form a self-propagating network that permeabilizes the OMM.

The high expression of long non-coding RNA PANDAR indicates a poor prognosis for colorectal cancer and promotes metastasis by EMT pathway

BACKGROUND

Long non-coding RNAs (lncRNAs) have been shown to have crucial regulatory roles in human cancer biology. LncRNA PANDAR is a novel identified lncRNA that was previously reported to be increased in various cancers; however, its effect in colorectal cancer (CRC) remains unknown. The aim of this study was to explore the expression and role of lncRNA PANDAR in CRC.

METHODS

The expression of lncRNA PANDAR was examined in CRC samples and cell lines by qRT-PCR. Kaplan-Meier survival analysis and univariate and multivariate Cox proportional hazards model were performed to evaluate the clinical and prognostic significance of lncRNA PANDAR in CRC patients. Furthermore, the biological function of lncRNA PANDAR on tumor cell growth, apoptosis and mobility was investigated through CCK-8, soft agar colony formation, flow cytometry, transwell migration and invasion assays in vitro. The potential mechanism of lncRNA PANDAR was demonstrated by Western blot and qRT-PCR.

RESULTS

The expression level of PANDAR was higher in CRC tissues and cells compared to adjacent non-tumor tissues and normal colonic epithelial cells. Patients with high PANDAR expression level had poorer overall survival than those with low PANDAR expression. Moreover, multivariate analysis showed that the status of PANDAR expression was an independent prognostic indicator for CRC. Knockdown of PANDAR could inhibit cell growth, migration and invasion, arrest cell cycle as well as induce apoptosis of CRC cells in vitro study. In addition, PANDAR could affect epithelial-mesenchymal transition through inhibiting N-cadherin, vimentin, β-catenin, Snail and Twist expression and increasing the expression levels of E-cadherin.

CONCLUSION

Our data suggested that lncRNA PANDAR was a novel molecule involved in CRC progression, which provided a potential prognostic biomarker and therapeutic target for new therapies in patients with CRC.

MOMP in the absence of BH3-only proteins

This Outlook discusses O'Neill et al.’s use of CRISPR/Cas9 to generate cells lacking the entire Bcl-2 family in an effort to identify the minimal requirement for direct activation of Bax/Bak and mitochondrial outer membrane permeabilization.

The minimum requirement for mitochondrial apoptosis has been controversial ever since the discovery of BCL-2 as a cell death regulator. In this issue of Genes & Development, O'Neill and colleagues (pp. 973–988) end a long-standing debate by creating a cellular system free of BCL-2 family proteins, thereby identifying the outer mitochondrial membrane rather than BH3-only proteins as the only requirement for BAX/BAK activation and mitochondrial outer membrane permeabilization (MOMP).

Physiological and Pharmacological Control of BAK, BAX, and Beyond

Cellular commitment to the mitochondrial pathway of apoptosis is accomplished when proapoptotic B cell chronic lymphocytic leukemia/lymphoma (BCL)-2 proteins compromise mitochondrial integrity through the process of mitochondrial outer membrane permeabilization (MOMP). For nearly three decades, intensive efforts focused on the identification and interactions of two key proapoptotic BCL-2 proteins: BCL-2 antagonist killer (BAK) and BCL-2-associated X (BAX). Indeed, we now have critical insights into which BCL-2 proteins interact with BAK/BAX to either preserve survival or initiate MOMP. In contrast, while mitochondria are targeted by BAK/BAX, a molecular understanding of how these organelles govern BAK/BAX function remains less clear. Here, we integrate recent mechanistic insights of proapoptotic BCL-2 protein function in the context of mitochondrial environment, and discuss current and potential pharmacological opportunities to control MOMP in disease.

Targeting BCL-2-like Proteins to Kill Cancer Cells

Mutations that impair apoptosis contribute to cancer development and reduce the effectiveness of conventional anti-cancer therapies. These insights and understanding of how the B cell lymphoma (BCL)-2 protein family governs apoptosis have galvanized the search for a new class of cancer drugs that target its pro-survival members by mimicking their natural antagonists, the BCL-2 homology (BH)3-only proteins. Successful initial clinical trials of the BH3 mimetic venetoclax/ABT-199, specific for BCL-2, have led to its recent licensing for refractory chronic lymphocytic leukemia and to multiple ongoing trials for other malignancies. Moreover, preclinical studies herald the potential of emerging BH3 mimetics targeting other BCL-2 pro-survival members, particularly myeloid cell leukemia (MCL)-1, for multiple cancer types. Thus, BH3 mimetics seem destined to become powerful new weapons in the arsenal against cancer. This review sketches the discovery of the BCL-2 family and its impact on cancer development and therapy; describes how interactions of family members trigger apoptosis; outlines the development of BH3 mimetic drugs; and discusses their potential to advance cancer therapy.