Functional and physical interaction between Bcl-X(L) and a BH3-like domain in Beclin-1

The Viral Bcl-2 Homologs of Kaposi's Sarcoma-Associated Herpesvirus and Rhesus Rhadinovirus Share an Essential Role for Viral Replication

KS-Bcl-2 is a Kaposi's sarcoma-associated herpesvirus (KSHV)-encoded viral Bcl-2 (vBcl-2) homolog which has apoptosis- and autophagy-inhibiting activity when expressed in transfected cells. However, little is known about its function during viral infection. As KS-Bcl-2 is expressed during the lytic replication cycle, we used constitutively lytic and inducibly lytic KSHV mutants to investigate the role of KS-Bcl-2 during the lytic cycle. We show that KSHV cannot complete the lytic replication cycle and produce infectious progeny in the absence of KS-Bcl-2, indicating that the protein is essential for KSHV replication. Replacement of the KS-Bcl-2 coding sequence, ORF16, by sequences encoding a potent cellular apoptosis and autophagy inhibitor, Bcl-XL, or the cytomegalovirus mitochondrial inhibitor of apoptosis, vMIA, did not rescue KSHV replication, suggesting that KS-Bcl-2 has a function that goes beyond apoptosis and autophagy inhibition. Strikingly, the vBcl-2 proteins of the related γ₂-herpesviruses murine herpesvirus 68 and herpesvirus saimiri did not rescue the replication of a KS-Bcl-2 deletion mutant, but rhesus rhadinovirus (RRV) vBcl-2 did. Deletion of ORF16 from the RRV genome abrogated viral replication, but its replacement by KSHV ORF16 rescued RRV replication, indicating that the essential vBcl-2 function is conserved between these two primate rhadinoviruses. We further show that the KSHV and RRV Bcl-2 homologs localize to the mitochondria and nuclei of infected cells. Deletion of 17 amino acids from the N terminus of KS-Bcl-2 abrogates nuclear localization and KSHV replication, suggesting that KS-Bcl-2 might execute its essential function in the nuclei of infected cells.IMPORTANCE Several viruses express proteins homologous to cellular Bcl-2. Viral Bcl-2 proteins have functions similar to those of cellular Bcl-2: they can inhibit apoptosis, a form of programmed cell death, and autophagy, a self-degradative process for the disposal of dysfunctional or unwanted components. This study shows that the vBcl-2 proteins of KSHV and RRV differ from other vBcl-2 proteins in that they are essential for viral replication. The essential function is separate from the apoptosis- and autophagy-inhibiting activity but correlates with an unusual localization within the cell nucleus, suggesting that these proteins exert a novel function in the nucleus.

The microRNA-423-3p-Bim Axis Promotes Cancer Progression and Activates Oncogenic Autophagy in Gastric Cancer

Human serum microRNAs (miRNAs) have been shown to serve as disease fingerprints for predicting survival of cancer patients. However, the roles of specific miRNAs involved in gastric cancer (GC) are largely unknown. In this study, miRNA profiling was performed on sera obtained from six patients in good- and poor-survival groups. Expression of miR-423-3p was validated by quantitative RT-PCR in another 67 GC serum samples and paired normal and cancerous gastric tissues. Luciferase reporter assays were used to identify the target gene Bcl-2-interacting mediator of cell death (Bim). As a result, between the good-survival and poor-survival groups, the expression of nine serum miRNAs was altered more than two-fold. Among these, miR-423-3p was significantly increased in the poor-survival group, and its overexpression in GC tissues predicted poor survival in 119 patients with GC. miR-423-3p was found to promote cell proliferation, migration, and invasion in cell lines and animal models. Mechanistically, knockdown of the autophagy-related gene (Atg) 7 rescued the GC-promoting effect of miR-423-3p. In conclusion, miR-423-3p activates oncogenic and Beclin-1-dependent autophagy and promotes GC progression by reducing the expression of Bim. The newly identified miR-423-3p-Bim axis might be a potential therapeutic target in GC.

Propylene Glycol Alginate Sodium Sulfate Alleviates Cerulein-Induced Acute Pancreatitis by Modulating the MEK/ERK Pathway in Mice

Previous studies have focused on the effects of propylene glycol alginate sodium sulfate  (PSS)  against  thrombosis,  but  the  anti-inflammatory  potential  is  unknown.  Therefore,  we  specifically focused on the protective effects of PSS on cerulein-induced acute pancreatitis (AP)  using a mouse model, and investigated the mechanism of PSS on autophagy and apoptosis via the  Mitogen-activated  protein  kinase  (MEK)/extracellular  signal-regulated  kinase  (ERK)  pathway.  Cerulein (100 ug/kg) was used to induce AP by ten intraperitoneal injections at hourly intervals in  Balb/C mice. Pretreatment with vehicle or PSS was carried out 1 h before the first cerulein injection  and two doses (25 mg/kg and 50 mg/kg) of PSS were injected intraperitoneally. The severity of AP was  assessed by pathological score, biochemistry, pro-inflammatory cytokine levels, myeloperoxidase  (MPO) activity and MEK/ERK activity. Furthermore, pancreatic histological scores, serum amylase  and lipase activities, tumor necrosis factor-α (TNF-α), interleukin (IL)-1β interleukin (IL)-6 levels, and  MPO activity were significantly reduced by PSS via up-regulated MEK/ERK activity. The representative  molecules of apoptosis and autophagy, such as Bcl-2, Bax, Lc-3, Beclin-1, P62, were remarkably reduced.  Taken together, these results indicate that PSS attenuates pancreas injury by inhibiting autophagy and  apoptosis through a mechanism involving the MEK/ERK signaling pathway.

Interplay between autophagy and apoptosis in selenium deficient cardiomyocytes in chicken

Dietary selenium (Se) deficiency can cause heart dysfunction, however the exact mechanism remains unclear. To understand this mechanism, 180day-old chicks, divided into two groups, C (control group) and L (low Se group), were fed with either a Se-sufficient (0.23mg/kg) or Se-deficient (0.033mg/kg) diets for 25days, respectively. Heart tissues and blood samples were collected. In L group, the activities of serum creatine kinase (CK) and creatine kinase-myoglobin (CK-MB) increased and typical ultrastructural apoptotic features were observed. Se deficiency up-regulated the mRNA levels of Cysteinyl aspartate specific proteinase 3 (Caspase-3), Cysteinyl aspartate specific proteinase 8 (Caspase-8), Cysteinyl aspartate specific proteinase 9 (Caspase-9), B cell lymphoma/leukemia 2 (Bcl-2), Bcl-2 Associated X Protein (Bax), (P<0.05), whereas, the mRNA levels of Microtubuleassociated protein light chains 3-1 (LC3-1), Autophagy associated gene 5 (ATG-5), Mammalian target of rapamycin (mTOR), Dynein and Becline-1 were down-regulated (P<0.05). Noticeably, Microtubuleassociated protein light chains 3-2 (LC3-2) mRNA level increased (P<0.05) by 20%. Western blot results showed that Se deficiency decreased the expression of Becline-1 and LC3-1 protein, however, the expression of Bax, Caspase-3 and Cysteinyl aspartate specific proteinase 12 (Caspase-12) increased at protein levels. The present study revealed that Se deficiency induced apoptosis while inhibited autophagy in chicken cardiomyocytes through Bax/Bcl-2 inhibition and caspases-mediated cleavage of Becline-1. Moreover, correlation analysis illustrates that apoptosis and autophagy might function contradictorily. Altogether we conclude that Se deficient chicken cardiomyocytes experienced apoptosis rather than autophagy which is considered to be more pro-survival.

Bcl-2 family proteins: master regulators of cell survival

The most prominent function of proteins of the Bcl-2 family is regulation of the initiation of intrinsic (mitochondrial) pathways of apoptosis. However, recent research has revealed that in addition to regulation of mitochondrial apoptosis, proteins of the Bcl-2 family play important roles in regulating other cellular pathways with a strong impact on cell survival like autophagy, endoplasmic reticulum (ER) stress response, intracellular calcium dynamics, cell cycle progression, mitochondrial dynamics and energy metabolism. This review summarizes the recent knowledge about functions of Bcl-2 family proteins that are related to cell survival.

Norcantharidin Inhibits SK-N-SH Neuroblastoma Cell Growth by Induction of Autophagy and Apoptosis

Norcantharidin, a low-toxic analog of the active anticancer compound cantharidin in Mylabris, can inhibit proliferation and induce apoptosis of multiple types of cancer cells. However, the anticancer activities of norcantharidin with respect to neuroblastoma, and its underlying mechanisms, have not been investigated. Therefore, our study was designed to determine the efficacy of norcantharidin on SK-N-SH neuroblastoma cell death and to elucidate detailed mechanisms of activity. In the present study, norcantharidin suppressed the proliferation and cloning ability of SK-N-SH cells in a dose-dependent manner, apparently by reducing the mitochondrial membrane potential and arresting SK-N-SH cells at the G2/M stage, accompanied by elevated expressions of p21 and decreased expressions of cyclin B1 and cell division control 2. Treatment by norcantharidin induced significant mitophagy and autophagy, as demonstrated by a decrease in Translocase Of Outer Mitochondrial Membrane 20 (TOM20), increased beclin1 and LC3-II protein expression, reduced protein SQSTM1/p62 expression, and accumulation of punctate LC3 in the cytoplasm of SK-N-SH cells. In addition, norcantharidin induced apoptosis through regulating the expression of B-cell lymphoma 2-associated X protein/B-cell lymphoma 2 and B-cell lymphoma 2-associated X protein/myeloid cell leukemia 1 and activating caspase-3 and caspase-9-dependent endogenous mitochondrial pathways. We also observed an increase in phosphor-AMP-activated protein kinase accompanied with a decrease in phosphor-protein kinase B and mammalian target of rapamycin expression after treatment with norcantharidin. Subsequent studies indicated that norcantharidin participates in cellular autophagy and apoptosis via activation of the c-Jun NH2-terminal kinases/c-Jun pathway. In conclusion, our results demonstrate that norcantharidin can reduce the mitochondrial membrane potential, induce mitophagy, and subsequently arouse cellular autophagy and apoptosis; the AMP-activated protein kinase, protein kinase B/mammalian target of rapamycin, and c-Jun NH2-terminal kinases/c-Jun signaling pathways are widely involved in these processes. Thus, the traditional Chinese medicine norcantharidin could be a novel therapeutic strategy for treating neuroblastoma.

Autophagy Is Impaired in Neutrophils from Streptozotocin-Induced Diabetic Rats

We tested the hypothesis that changes reported on functions of neutrophils from streptozotocin-induced diabetic rats involve autophagy impairment. Wistar rats were rendered diabetic by streptozotocin injection (65 mg/kg, i.v.), and the measurements were carried out 2 weeks afterward. Neutrophils were collected through intraperitoneal cavity lavage after 4 h of i.p. oyster glycogen type 2 injection. Neutrophils cultured with PMA (20 nM) for 1 h were used for analysis of plasma membrane integrity, DNA fragmentation, and mitochondrial depolarization by flow cytometry; expression of Atg5, Atg14, Beclin1, LC3BII, and Rab9 by RT-PCR; the contents of caspase 3, LC3BII/LC3BI, and pS6 by western blotting; ATP content by fluorescence essay; reactive oxygen species production by chemiluminescence (Luminol), and autophagy by immunofluorescence tracking LC3B cleavage. Herein, neutrophils from diabetic rats had high DNA fragmentation, depolarization of mitochondrial membrane, low content of ATP, and high content of cleaved caspase 3 after PMA stimulation. Neutrophils from diabetic rats also had low expression of LC3B, failed to increase the expression of Rab9 and Atg14 induced by PMA stimulation. Neutrophils from diabetic animals also had low cleavage of LC3BI to LC3BII and do not present punctate structures that label autophagosomal membranes after stimulus. The changes of neutrophil function reported in diabetic rats do involve impaired autophagy. The suppression of autophagy in neutrophils from diabetic rats may be associated with the activation of the mTOR signaling as indicated by the high content of pS6.

Autophagy, Metabolic Disease, and Pathogenesis of Heart Dysfunction

In normal physiology, autophagy is recognized as a protective housekeeping mechanism that enables elimination of unhealthy organelles, protein aggregates, and invading pathogens, as well as recycling cell components and producing new building blocks and energy for cellular renovation and homeostasis. However, overactive or depressed autophagy is often associated with the pathogenesis of multiple disorders, including cardiac disease. During metabolic disorders, such as diabetes and obesity, dysregulation of autophagy frequently leads to cell death, cardiomyopathy, and cardiac dysfunction. In this article, we summarize the current understanding of autophagy-its classification, progression, and regulation; its roles in both physiological and pathophysiological conditions; and the balance between autophagy and apoptosis. We also explore how dysregulation of autophagy leads to cell death in models of metabolic disease and its contributing factors-including nutrient state, hyperglycemia, dyslipidemia, insulin inefficiency, and oxidative stress-and outline some recent efforts to restore normal autophagy in pathophysiological states. This information could provide potential targets for the prevention of, or intervention in, cardiac failure in metabolic disorders such as diabetes and obesity.

Bcl-xL Affects Group A Streptococcus-Induced Autophagy Directly, by Inhibiting Fusion between Autophagosomes and Lysosomes, and Indirectly, by Inhibiting Bacterial Internalization via Interaction with Beclin 1-UVRAG

Anti-apoptotic Bcl-2 and Bcl-xL are proposed to regulate starvation-induced autophagy by directly interacting with Beclin 1. Beclin 1 is also thought to be involved in multiple vesicle trafficking pathways such as endocytosis by binding to Atg14L and UVRAG. However, how the interaction of Bcl-2 family proteins and Beclin 1 regulates anti-bacterial autophagy (xenophagy) is still unclear. In this study, we analyzed these interactions using Group A Streptococcus (GAS; Streptococcus pyogenes) infection as a model. GAS is internalized into epithelial cells through endocytosis, while the intracellular fate of GAS is degradation by autophagy. Here, we found that Bcl-xL but not Bcl-2 regulates GAS-induced autophagy. Autophagosome-lysosome fusion and the internalization process during GAS infection were promoted in Bcl-xL knockout cells. In addition, knockout of Beclin 1 phenocopied the internalization defect of GAS. Furthermore, UVRAG interacts not only with Beclin 1 but also with Bcl-xL, and overexpression of UVRAG partially rescued the internalization defect of Beclin 1 knockout cells during GAS infection. Thus, our results indicate that Bcl-xL inhibits GAS-induced autophagy directly by suppressing autophagosome-lysosome fusion and indirectly by suppressing GAS internalization via interaction with Beclin 1-UVRAG.

Autophagy Is an Innate Mechanism Associated with Leprosy Polarization

Leprosy is a chronic infectious disease that may present different clinical forms according to the immune response of the host. Levels of IFN-γ are significantly raised in paucibacillary tuberculoid (T-lep) when compared with multibacillary lepromatous (L-lep) patients. IFN-γ primes macrophages for inflammatory activation and induces the autophagy antimicrobial mechanism. The involvement of autophagy in the immune response against Mycobacterium leprae remains unexplored. Here, we demonstrated by different autophagic assays that LC3-positive autophagosomes were predominantly observed in T-lep when compared with L-lep lesions and skin-derived macrophages. Accumulation of the autophagic receptors SQSTM1/p62 and NBR1, expression of lysosomal antimicrobial peptides and colocalization analysis of autolysosomes revealed an impairment of the autophagic flux in L-lep cells, which was restored by IFN-γ or rapamycin treatment. Autophagy PCR array gene-expression analysis revealed a significantly upregulation of autophagy genes (BECN1, GPSM3, ATG14, APOL1, and TPR) in T-lep cells. Furthermore, an upregulation of autophagy genes (TPR, GFI1B and GNAI3) as well as LC3 levels was observed in cells of L-lep patients that developed type 1 reaction (T1R) episodes, an acute inflammatory condition associated with increased IFN-γ levels. Finally, we observed increased BCL2 expression in L-lep cells that could be responsible for the blockage of BECN1-mediated autophagy. In addition, in vitro studies demonstrated that dead, but not live M. leprae can induce autophagy in primary and lineage human monocytes, and that live mycobacteria can reduce the autophagy activation triggered by dead mycobacteria, suggesting that M. leprae may hamper the autophagic machinery as an immune escape mechanism. Together, these results indicate that autophagy is an important innate mechanism associated with the M. leprae control in skin macrophages.

Leprosy is an interesting model to study immune responses in humans due to the dichotomy observed among the poles of the disease. While in the self-limited tuberculoid form (T-lep) there are high systemic levels of the cytokine IFN-γ, in the clinically progressive lepromatous form (L-lep) low IFN-γ levels are found. IFN-γ activates an antimicrobial mechanism called autophagy, which has been implicated in control of Mycobacterium tuberculosis infection. However, the role played by autophagy in the immunopathogenesis of leprosy remains unknown. Here we show that autophagy was differentially regulated in T-lep and L-lep patients. In T-lep skin lesion cells autophagy contributes for bacilli control, whereas in L-lep cells the BCL2-mediated block of autophagy promotes the mycobacterial persistence. We also observed that IFN-γ may counteract the inhibition of autophagy triggered by M. leprae infection in L-lep macrophages. In addition, the levels of autophagy were restored in L-lep patients who developed the reversal reaction, an inflammatory state associated with augmented IFN-γ, which is the most important cause of nerve damage and deformities in leprosy. These findings suggest that the modulation of autophagy has the potential to be useful in the treatment of the disease, and provides new insights to prevent leprosy reactional episodes.

Inflammatory Bowel Disease Drugs: A Focus on Autophagy

Inflammatory bowel disease [IBD] is characterized by chronic inflammation of the gastrointestinal tract. Medications such as corticosteroids, thiopurines, immunomodulators and biologic agents are used to induce and maintain remission; however, response to these drugs is variable and can diminish over time. Defective autophagy has been strongly linked to IBD pathogenesis, with evidence showing that enhancing autophagy may be therapeutically beneficial by regulating inflammation and clearing intestinal pathogens. It is plausible that the therapeutic effects of some IBD drugs are mediated in part through modulation of the autophagy pathway, with studies investigating a wide range of diseases and cell types demonstrating autophagy pathway regulation by these agents. This review will highlight the current evidence, both in vitro and in vivo, for the modulation of autophagy by drugs routinely used in IBD. A clearer understanding of their mechanisms of action will be invaluable to utilize these drugs in a more targeted and personalized manner in this diverse and often complex group of patients.

Beginning to Understand the Role of the Type IV Secretion System Effector Proteins in Coxiella burnetii Pathogenesis

Coxiella burnetii is the etiological agent of the zoonotic disease Q fever, which manifests in severe outbreaks and is associated with important health and economic burden. Moreover, C. burnetii belongs to the list of class B bioterrorism organisms, as it is an airborne and highly infective pathogen with remarkable resistance to environmental stresses. Detailed study of the host-pathogen interaction during C. burnetii infection has been hampered due to the obligate intracellular nature of this pathogen. However, the development of an axenic culture medium, together with the implementation of bioinformatics tools and high-content screening approaches, have significantly progressed C. burnetii research in the last decade. This has facilitated identification of the Dot/Icm type IV secretion system (T4SS) as an essential virulence factor. T4SS is used to deliver an arsenal of effector proteins into the cytoplasm of the host cell. These effectors mediate the survival of the host cell and the development of very large replicative compartments called Coxiella-containing vacuoles (CCVs). Biogenesis of the CCV relies on T4SS-dependent re-routing of numerous intracellular trafficking pathways to deliver membranes and nutrients that are essential for bacterial replication. This review aims to illustrate the key milestones that have contributed to ascribe C. burnetii as a model organism for the study of host/pathogen interactions as well as presenting an up-to-date description of our knowledge of the cell biology of C. burnetii infections.

ΔN-Bcl-xL, a therapeutic target for neuroprotection

The B-cell lymphoma-extra large (Bcl-xL) is a mitochondrial anti-apoptotic protein that plays a role in neuroprotection. However, during excitotoxic stimulation, Bcl-xL undergoes caspase-dependent cleavage and produces a fragmented form, ΔN-Bcl-xL. Accumulation of ΔN-Bcl-xL is associated with mitochondrial dysfunction and neuronal death. Therefore, strategies to inhibit the activity or formation of ΔN-Bcl-xL protect the brain against excitotoxic injuries. Our team found that the pharmacological inhibitor ABT-737 exerts dose dependent effects in primary neurons. When primary hippocampal neurons were treated with 1 μM ABT-737, glutamate-mediated mitochondrial damage and neuronal death were exacerbated, whereas 10 nM ABT-737, a 100-fold lower concentration, protected mitochondrial function and enhanced neuronal viability against glutamate toxicity. In addition, we suggested acute vs. prolonged formation of ΔN-Bcl-xL may have different effects on mitochondrial or neuronal functions. Unlike acute production of ΔN-Bcl-xL by glutamate, overexpression of ΔN-Bcl-xL did not cause drastic changes in neuronal viability. We predicted that neurons undergo adaptation and may activate altered metabolism to compensate for ΔN-Bcl-xL-mediated mitochondrial dysfunction. Although the detailed mechanism of ABT-mediated neurotoxicity neuroprotection is still unclear, our study shows that the mitochondrial membrane protein ΔN-Bcl-xL is a central target for interventions.

Reduction of neuronal damage and promotion of locomotor recovery after spinal cord injury by early administration of methylprednisolone: possible involvement of autophagy pathway

Interaction between autophagy and apoptosis participates in the neuroprotective effect of methylprednisolone on spinal cord injury.

Autophagy modulators from traditional Chinese medicine: Mechanisms and therapeutic potentials for cancer and neurodegenerative diseases

ETHNOPHARMACOLOGICAL RELEVANCE

Traditional Chinese medicine (TCM), an ancient yet still alive medicinal system widely used in East Asia, has played an essential role in health maintenance and diseases control, for a wide range of human chronic diseases like cancers and neurodegenerative diseases. TCM-derived compounds and extracts attract wide attention for their potential application as therapeutic agents against above mentioned diseases.

AIM OF REVIEW

Recent years the enthusiasm in searching for autophagy regulators for human diseases has yielded many positive hits. TCM-derived compounds as important sources for drug discovery have been widely tested in different models for autophagy modulation. Here we summarize the current progress in the discovery of natural autophagy regulators from TCM for the therapeutic application in cancer and neurodegenerative disease models, aiming to provide the direct link from traditional use to new pharmacological application.

METHODS

The present review collected the literature published during the recent 10 years which studied the effect of TCM-derived compounds or extracts on autophagy regulation from PubMed, Web of Science, Google Scholar and Science Direct. The names of chemical compounds studied in this article are corresponding to the information in journal plant list.

RESULTS

In this review, we give a brief introduction about the autophagy and its roles in cancer and neurodegenerative disease models and describe the molecular mechanisms of autophagy modulation. We also make comprehensive lists to summarize the effects and underlying mechanisms of TCM-derived autophagy regulators in cancer and neurodegenerative disease models. In the end of the review, we discuss the current strategies, problems and future direction for TCM-derived autophagy regulators in the treatment of human diseases.

CONCLUSIONS

A number of data from in vivo and in vitro models indicated TCM derived compounds and extracts hold great potential for the treatment of human diseases including cancers and neurodegenerative diseases. Autophagy, as a novel and promising drug target involved in a wide range of human diseases, can be modulated by many TCM derived agents, indicating autophagy modulation may be an important mechanism underlying the therapeutic effect of TCM in treating diseases. Furthermore, we look forward to seeing the discovery of ideal autophagy modulators from TCM with considerably higher selectivity for the treatment of human diseases.

mTORC1 activation decreases autophagy in aging and idiopathic pulmonary fibrosis and contributes to apoptosis resistance in IPF fibroblasts

Idiopathic pulmonary fibrosis (IPF) is a chronic, progressive, and usually lethal disease associated with aging. However, the molecular mechanisms of the aging process that contribute to the pathogenesis of IPF have not been elucidated. IPF is characterized by abundant foci of highly active fibroblasts and myofibroblasts resistant to apoptosis. Remarkably, the role of aging in the autophagy activity of lung fibroblasts and its relationship with apoptosis, as adaptive responses, has not been evaluated previously in this disease. In the present study, we analyzed the dynamics of autophagy in primary lung fibroblasts from IPF compared to young and age‐matched normal lung fibroblasts. Our results showed that aging contributes for a lower induction of autophagy on basal conditions and under starvation which is mediated by mTOR pathway activation. Treatment with rapamycin and PP242, that target the PI3K/AKT/mTOR signaling pathway, modified starvation‐induced autophagy and apoptosis in IPF fibroblasts. Interestingly, we found a persistent activation of this pathway under starvation that contributes to the apoptosis resistance in IPF fibroblasts. These findings indicate that aging affects adaptive responses to stress decreasing autophagy through activation of mTORC1 in lung fibroblasts. The activation of this pathway also contributes to the resistance to cell death in IPF lung fibroblasts.

AMBRA1, a Novel BH3-Like Protein: New Insights Into the AMBRA1-BCL2-Family Proteins Relationship

Cellular homeostasis swings like a pendulum backward and forward between life and death. Two of the main processes, which regulate this equilibrium, are autophagy and apoptosis. While autophagy is a highly conserved self-digestion mechanism that mediates degradation of damaged or surplus components, apoptosis is a programmed cell suicide in which typical death signals induce the elimination of undesired cells. Both these processes are highly regulated by complex molecular machineries, including some common proteins whose "dual role" favors one process or the other. Among these proteins, the well-known antiapoptotic factor BCL2 downregulates autophagy through interactions with the essential autophagic effectors, BECN1/BECLIN 1 and AMBRA1. Recently, we have demonstrated that the proautophagic protein AMBRA1 contains a BH3 domain necessary for AMBRA1 binding with the antiapoptotic factor BCL2. We found that the AMBRA1-BCL2 couple have a "dual role" in autophagy and apoptosis: the mitochondrial pool of BCL2 is able to inhibit AMBRA1-dependent autophagy, whereas in cell death conditions, the cleaved form of AMBRA1 (AMBRA1^CT), resulting from CASP/CASPASES-cleavage, abrogates the prosurvival activity of BCL2 and promotes a proapoptotic amplification loop. The CASP-cleaved form of AMBRA1 bound other antiapoptotic members of the BCL2 family proteins such as MCL1 and BCL2L1/BCL-X; by contrast, no binding could be detected with the proapoptotic-BCL2 factors such as BAK1/BAK and BAX. These findings underline an intricate interplay between autophagy and cell death in which the proautophagic protein AMBRA1 and the antiapoptotic BCL2 family members are the major players. Here, we give an overview of the AMBRA1-BCL2 family proteins interactome and its involvement in controlling life and cell death. We discuss a putative therapeutic target which offers the novel BH3 motif identified in the C-terminal part of AMBRA1.

MST1 coordinately regulates autophagy and apoptosis in diabetic cardiomyopathy in mice

AIMS/HYPOTHESIS

Diabetic cardiomyopathy (DCM) is associated with suppressed autophagy and augmented apoptosis in the heart although the interplay between the two remains elusive. The ability of mammalian sterile 20-like kinase 1 to regulate both autophagy and apoptosis prompted us to investigate it as a possible candidate in the progression of DCM.

METHODS

Wild-type, Mst1 (also known as Stk4) transgenic and Mst1-knockout mice were challenged with streptozotocin to induce experimental diabetes. In addition, cultured neonatal mouse cardiomyocytes were subjected to simulated diabetes to probe mechanisms.

RESULTS

Mst1 knockout alleviated while Mst1 overexpression aggravated cardiac dysfunction in diabetes. Diabetic Mst1 transgenic mice exhibited decreased LC3 expression and enhanced protein aggregation. In contrast, typical autophagosomes were observed in diabetic Mst1-knockout mice with increased LC3 expression and reduced protein aggregation. Mst1 downregulation promoted autophagic flux as demonstrated by increased LC3-II and decreased p62 expression in the presence of bafilomycin A1. Furthermore, Mst1 overexpression increased, while Mst1 knockout decreased, cardiomyocyte apoptosis both in vivo and in vitro. Co-immunoprecipitation assays showed that Mst1 overexpression promoted Beclin1 binding to B cell lymphoma 2 (Bcl-2) and induced dissociation of Bcl-2 from Bax in diabetic mice. Conversely, Mst1 knockout disrupted the Beclin1-Bcl-2 complex and enhanced the interaction between Bcl-2 and Bax.

CONCLUSIONS/INTERPRETATION

Mst1 knockout restores autophagy and protects against apoptosis in cardiomyocytes, en route to the rescue against DCM.

Celastrus orbiculatus extract triggers apoptosis and autophagy via PI3K/Akt/mTOR inhibition in human colorectal cancer cells

Celastrus orbiculatus is used as a folk medicine in China for the treatment of numerous diseases. The ethyl acetate extract of Celastrus orbiculatus (COE) also displays a wide range of anti-cancer activities in the laboratory. However, the effectiveness of COE-induced autophagy and its mechanism of action in colorectal cancer cells have not been investigated thus far. The present study analyzed the effect of COE on HT-29 cell viability, apoptosis and autophagy using MTT assay, flow cytometry, transmission electron microscopy and western blotting. Additionally, the autophagy inhibitor 3-methyladenine and the autophagy inducer rapamycin were used to further explore the effects of COE-induced autophagy in HT-29 cells. The present study also examined whether the phosphatidylinositol-4,5-bisphosphate 3-kinase (PI3K)/Akt/mechanistic target of rapamycin (mTOR)/p70 ribosomal protein S6 kinase (p70S6K) signaling pathway was involved in the regulation of COE-induced autophagy. The results revealed that COE inhibited HT-29 cell proliferation and decreased cell survival in a time- and dose-dependent manner, and that COE possessed the ability to induce both apoptosis and autophagy in HT-29 cells. Furthermore, autophagy and apoptosis induced by COE synergized to inhibit colorectal cancer growth. In addition, COE treatment decreased the phosphorylation of Akt and its downstream effectors mTOR and p70S6K. Taken together, these results demonstrate that both autophagy and apoptosis were activated during COE treatment of HT-29 cells, and that COE-induced autophagy decreases the viability of HT-29 cells via a mechanism that may depend on the PI3K/Akt/mTOR/p70S6K signaling pathway. Furthermore, compounds that induce autophagy administered in combination with COE may be an attractive strategy for enhancing the anti-tumor potency of COE in colorectal cancer.

Autophagy mediated CoCrMo particle-induced peri-implant osteolysis by promoting osteoblast apoptosis

Wear particle-induced osteolysis is the leading cause of aseptic loosening, which is the most common reason for THA (total hip arthroplasty) failure and revision surgery. Although existing studies suggest that osteoblast apoptosis induced by wear debris is involved in aseptic loosening, the underlying mechanism linking wear particles to osteoblast apoptosis remains almost totally unknown. In the present study, we investigated the effect of autophagy on osteoblast apoptosis induced by CoCrMo metal particles (CoPs) in vitro and in a calvarial resorption animal model. Our study demonstrated that CoPs stimulated autophagy in osteoblasts and PIO (particle-induced osteolysis) animal models. Both autophagy inhibitor 3-MA (3-methyladenine) and siRNA of Atg5 could dramatically reduce CoPs-induced apoptosis in osteoblasts. Further, inhibition of autophagy with 3-MA ameliorated the severity of osteolysis in PIO animal models. Moreover, 3-MA also prevented osteoblast apoptosis in an antiautophagic way when tested in PIO model. Collectively, these results suggest that autophagy plays a key role in CoPs-induced osteolysis and that targeting autophagy-related pathways may represent a potential therapeutic approach for treating particle-induced peri-implant osteolysis.

Therapeutic Targeting of Autophagy

Autophagy is a catabolic process that facilitates nutrient recycling via degradation of damaged organelles and proteins through lysosomal mediated degradation. Alterations in this complex, and tightly regulated process, lead to disease. Autophagy is widely accepted as cytoprotective against neurodegenerative diseases and a variety of clinical interventions are moving forward to increase autophagy as a therapeutic intervention. Autophagy has both positive and negative roles in cancer and this has led to controversy over whether or how autophagy manipulation should be attempted in cancer therapy. Nevertheless, cancer is the disease where most current activity in trying to manipulate autophagy for therapy is taking place and dozens of clinical trials are using autophagy inhibition with Chloroquine or Hydroxychloroquine in combination with other drugs for the treatment of multiple neoplasms. Here, we review recent literature implicating autophagy in neurodegenerative diseases and cancer and highlight some of the opportunities, controversies and potential pitfalls of therapeutically targeting autophagy.

Caspase-mediated cleavage of Beclin1 inhibits autophagy and promotes apoptosis induced by S1 in human ovarian cancer SKOV3 cells

S1, a novel BH3 mimetic, can induce apoptosis dependent on Bax/Bak through inhibition of Bcl-2 in various tumors. S1 also induces autophagy through interrupting the interaction of Bcl-2 and Beclin1. Our results showed that S1 induces apoptosis in human ovarian cancer SKOV3 cells in a time- and dose-dependent manner. Autophagy precedes apoptosis, in SKOV3 cells treated with S1 (6 μmol/L), autophagy reached the maximum peak at 12 h after treatment and decreased to 24 h. In SKOV3 cells treated with different concentrations of S1 for 24 h, the highest level of autophagy was observed with 5 μmol/L and decreased to 10 μmol/L. Autophagy inhibitors 3-MA and CQ enhanced apoptosis induced by S1 in SKOV3 cells. However, overactivation of caspases in apoptosis induced by S1 may inhibit the autophagy-inducing function of Beclin1. Because the pan-caspase inhibitor Z-VAD recovered the autophagy-inducing function of Beclin1 through reduction of activated caspase-mediated cleavage of Beclin1. Furthermore, the Beclin1 cleavage products could further increase apoptosis induced by S1 in SKOV3 cells. This indicates that apoptosis induced by high doses and long exposure of S1 causes the overactivation of caspases and subsequent cleavage of Beclin1, and inhibits the protection of autophagy. Moreover, the cleaved product of Beclin1 further promotes apoptosis induced by S1 in SKOV3 cells. Our results suggest this may be a molecular mechanism for enhancing the sensitivity of cancer cells to apoptosis induced by small molecular compound targeting Bcl-2.

Electroacupuncture Ameliorates Cerebral Ischemia-Reperfusion Injury by Regulation of Autophagy and Apoptosis

Background. The therapeutic mechanisms of cerebral ischemia treatment by acupuncture are yet not well addressed. Objective. We investigated the effects of electroacupuncture (EA) at GV26 observing the expression of autophagy-related proteins Beclin-1 and LC3B and proportion of apoptotic cells and Bcl-2 positive cells in MCAO/R model rats. Methods. Sprague-Dawley (SD) male rats were randomly assigned to 7 groups: model groups (M6h, M24h, and M72h), EA treatment groups (T6h, T24h, and T72h), and sham operation group (S). Neurological deficit and cerebral infarction volume were measured to assess the improvement effect, while the expression of Beclin-1 and LC3B and proportion of Tunel-positive and Bcl-2 positive cells were examined to explore EA effect on autophagy and apoptosis. Results. EA significantly decreased neurological deficit scores and the volume of cerebral infarction. Beclin-1 was significantly decreased in T24h, while LC3B-II/LC3B-I ratio markedly reduced in 6th hour. EA groups markedly reduced the number of Tunel positive cells, especially in T24h. Meanwhile, the number of Bcl-2 positive cells obviously increased after EA treatment, especially in T6h and T24h. Conclusions. The alleviation of inadequate autophagy and apoptosis may be a key mechanism involved in the reflex regulation of EA at GV26 to treat cerebral ischemia.

Metabolomic Analysis of Mouse Embryonic Fibroblast Cells in Response to Autophagy Induced by Acute Starvation

Autophagy-related protein 7 (Atg7) is essential in the formation of the autophagophore and is indispensable for autophagy induction. Autophagy will exist in lower level or even be blocked in cells without Atg7. Even though the possible signaling pathways of Atg7 have been proposed, the metabolomic responses under acute starvation in cells with and without Atg7 have not been elucidated. This study therefore was designed and aimed to reveal the metabolomics of Atg7-dependent autophagy through metabolomic analysis of Atg7^-/- mouse embryonic fibroblast cells (MEFs) and wild-type MEFs along with the starvation time. 30 significantly altered metabolites were identified in response to nutrient stress, which were mainly associated with amino acid, energy, carbohydrate, and lipid metabolism. For the wild-type MEFs, the induction of autophagy protected cell survival with some up-regulated lipids during the first two hours' starvation, while the subsequent apoptosis resulted in the decrease of cell viability after four hours' starvation. For the Atg7^-/- MEFs, apoptosis perhaps led to the deactivation of tricarboxylic acid (TCA) cycle due to the lack of autophagy, which resulted in the immediate drop of cellular viability under starvation. These results contributed to the metabolomic study and provided new insights into the mechanism associated with Atg7-dependent autophagy.

Parkin and mitophagy in cancer

Mitophagy, the selective engulfment and clearance of mitochondria, is essential for the homeostasis of a healthy network of functioning mitochondria and prevents excessive production of cytotoxic reactive oxygen species from damaged mitochondria. The mitochondrially targeted PTEN-induced kinase-1 (PINK1) and the E3 ubiquitin ligase Parkin are well-established synergistic mediators of the mitophagy of dysfunctional mitochondria. This pathway relies on the ubiquitination of a number of mitochondrial outer membrane substrates and subsequent docking of autophagy receptor proteins to selectively clear mitochondria. There are also alternate Parkin-independent mitophagy pathways mediated by BCL2/adenovirus E1B 19 kDa protein-interacting protein 3 and Nip-3 like protein X as well as other effectors. There is increasing evidence that ablation of mitophagy accelerates a number of pathologies. Familial Parkinsonism is associated with loss-of-function mutations in PINK1 and Parkin. A growing number of studies have observed a correlation between impaired Parkin activity and enhanced cancer development, leading to the emerging concept that Parkin activity, or mitophagy in general, is a tumour suppression mechanism. This review examines the molecular mechanisms of mitophagy and highlights the potential links between Parkin and the hallmarks of cancer that may influence tumour development and progression.

Cocaine-Mediated Autophagy in Astrocytes Involves Sigma 1 Receptor, PI3K, mTOR, Atg5/7, Beclin-1 and Induces Type II Programed Cell Death

Cocaine, a commonly used drug of abuse, has been shown to cause neuropathological dysfunction and damage in the human brain. However, the role of autophagy in this process is not defined. Autophagy, generally protective in nature, can also be destructive leading to autophagic cell death. This study was designed to investigate whether cocaine induces autophagy in the cells of CNS origin. We employed astrocyte, the most abundant cell in the CNS, to define the effects of cocaine on autophagy. We measured levels of the autophagic marker protein LC3II in SVGA astrocytes after exposure with cocaine. The results showed that cocaine caused an increase in LC3II level in a dose- and time-dependent manner, with the peak observed at 1 mM cocaine after 6-h exposure. This result was also confirmed by detecting LC3II in SVGA astrocytes using confocal microscopy and transmission electron microscopy. Next, we sought to explore the mechanism by which cocaine induces the autophagic response. We found that cocaine-induced autophagy was mediated by sigma 1 receptor, and autophagy signaling proteins p-mTOR, Atg5, Atg7, and p-Bcl-2/Beclin-1 were also involved, and this was confirmed by using selective inhibitors and small interfering RNAs (siRNAs). In addition, we found that chronic treatment with cocaine resulted in cell death, which is caspase-3 independent and can be ameliorated by autophagy inhibitor. Therefore, this study demonstrated that cocaine induces autophagy in astrocytes and is associated with autophagic cell death.

The critical roles of mitophagy in cerebral ischemia

Mitochondria play a key role in various cell processes including ATP production, Ca²⁺ homeostasis, reactive oxygen species (ROS) generation, and apoptosis. The selective removal of impaired mitochondria by autophagosome is known as mitophagy. Cerebral ischemia is a common form of stroke caused by insufficient blood supply to the brain. Emerging evidence suggests that mitophagy plays important roles in the pathophysiological process of cerebral ischemia. This review focuses on the relationship between ischemic brain injury and mitophagy. Based on the latest research, it describes how the signaling pathways of mitophagy appear to be involved in cerebral ischemia.

Conformational flexibility of BECN1: Essential to its key role in autophagy and beyond

BECN1 (Beclin 1), a highly conserved eukaryotic protein, is a key regulator of autophagy, a cellular homeostasis pathway, and also participates in vacuolar protein sorting, endocytic trafficking, and apoptosis. BECN1 is important for embryonic development, the innate immune response, tumor suppression, and protection against neurodegenerative disorders, diabetes, and heart disease. BECN1 mediates autophagy as a core component of the class III phosphatidylinositol 3-kinase complexes. However, the exact mechanism by which it regulates the activity of these complexes, or mediates its other diverse functions is unclear. BECN1 interacts with several diverse protein partners, perhaps serving as a scaffold or interaction hub for autophagy. Based on extensive structural, biophysical and bioinformatics analyses, BECN1 consists of an intrinsically disordered region (IDR), which includes a BH3 homology domain (BH3D); a flexible helical domain (FHD); a coiled-coil domain (CCD); and a β-α-repeated autophagy-specific domain (BARAD). Each of these BECN1 domains mediates multiple diverse interactions that involve concomitant conformational changes. Thus, BECN1 conformational flexibility likely plays a key role in facilitating diverse protein interactions. Further, BECN1 conformation and interactions are also modulated by numerous post-translational modifications. A better structure-based understanding of the interplay between different BECN1 conformational and binding states, and the impact of post-translational modifications will be essential to elucidating the mechanism of its multiple biological roles.

A model-driven methodology for exploring complex disease comorbidities applied to autism spectrum disorder and inflammatory bowel disease

We propose a model-driven methodology aimed to shed light on complex disorders. Our approach enables exploring shared etiologies of comorbid diseases at the molecular pathway level. The method, Comparative Comorbidities Simulation (CCS), uses stochastic Petri net simulation for examining the phenotypic effects of perturbation of a network known to be involved in comorbidities to predict new roles for mutations in comorbid conditions. To demonstrate the utility of our novel methodology, we investigated the molecular convergence of autism spectrum disorder (ASD) and inflammatory bowel disease (IBD) on the autophagy pathway. In addition to validation by domain experts, we used formal analyses to demonstrate the model's self-consistency. We then used CCS to compare the effects of loss of function (LoF) mutations previously implicated in either ASD or IBD on the autophagy pathway. CCS identified similar dynamic consequences of these mutations in the autophagy pathway. Our method suggests that two LoF mutations previously implicated in IBD may contribute to ASD, and one ASD-implicated LoF mutation may play a role in IBD. Future targeted genomic or functional studies could be designed to directly test these predictions.

Autophagy is induced in the skeletal muscle of cachectic cancer patients

Basal rates of autophagy can be markedly accelerated by environmental stresses. Recently, autophagy has been involved in cancer-induced muscle wasting. Aim of this study has been to evaluate if autophagy is induced in the skeletal muscle of cancer patients. The expression (mRNA and protein) of autophagic markers has been evaluated in intraoperative muscle biopsies. Beclin-1 protein levels were increased in cachectic cancer patients, suggesting autophagy induction. LC3B-I protein levels were not significantly modified. LC3B-II protein levels were significantly increased in cachectic cancer patients suggesting either increased autophagosome formation or reduced autophagosome turnover. Conversely, p62 protein levels were increased in cachectic and non-cachectic cancer patients, suggesting impaired autophagosome clearance. As for mitophagy, both Bnip3 and Nix/Bnip3L show a trend to increase in cachectic patients. In the same patients, Parkin levels significantly increased, while PINK1 was unchanged. At gene level, Beclin-1, p-62, BNIP3, NIX/BNIP3L and TFEB mRNAs were not significantly modulated, while LC3B and PINK1 mRNA levels were increased and decreased, respectively, in cachectic cancer patients. Autophagy is induced in the skeletal muscle of cachectic cancer patients, although autophagosome clearance appears to be impaired. Further studies should evaluate whether modulation of autophagy could represent a relevant therapeutic strategy in cancer cachexia.

Glutaminolysis and autophagy in cancer

The remarkable metabolic differences between cancer cells and normal cells result in the potential for targeted cancer therapy. The upregulation of glutaminolysis provides energetic advantages to cancer cells. The recently described link between glutaminolysis and autophagy, mediated by MTORC1, may constitute an attractive target for therapeutic strategies. A combination of therapies targeting simultane-ously cell signaling, cancer metabolism, and autophagy can solve therapy resistance and tumor relapse problems, commonly observed in patients treated with most of the current targeted therapies. In this review we summarize the mechanistic link between glutaminolysis and autophagy, and discuss the impacts of these processes on cancer progression and the potential for therapeutic intervention.

Functional Implications of the spectrum of BCL2 mutations in Lymphoma

Mutations in the translocated BCL2 gene are often detected in diffuse large B-cell lymphomas (DLBCLs), indicating both their significance and pervasiveness. Large series genome sequencing of more than 200 DLBCLs has identified frequent BCL2 mutations clustered in the exons coding for the BH4 domain and the folded loop domain (FLD) of the protein. However, BCL2 mutations are mostly contemplated to represent bystander events with negligible functional impact on the pathogenesis of DLBCL. BCL2 arbitrates apoptosis through a classic interaction between its hydrophobic groove forming BH1-3 domains and the BH3 domain of pro-apoptotic members of the BCL2 family. The effects of mutations are mainly determined by the ability of the mutated BCL2 to mediate apoptosis by this inter-member protein binding. Nevertheless, BCL2 regulates diverse non-canonical pathways that are unlikely to be explained by canonical interactions. In this review, first, we identify recurrent missense mutations in the BH4 domain and the FLD reported in independent lymphoma sequencing studies. Second, we discuss the probable consequences of mutations on the binding ability of BCL2 to non-BCL2 family member proteins crucial for 1) maintaining mitochondrial energetics and calcium hemostasis such as VDAC, IP3R, and RyR and 2) oncogenic pathways implicated in the acquisition of the 'hallmarks of cancer' such as SOD, Raf-1, NFAT, p53, HIF-1α, and gelsolin. The study also highlights the likely ramifications of mutations on binding of BCL2 antagonists and BH3 profiling. Based on our analysis, we believe that an in-depth focus on BCL2 interactions mediated by these domains is warranted to elucidate the functional significance of missense mutations in DLBCL. In summary, we provide an extensive overview of the pleiotropic functions of BCL2 mediated by its physical binding interaction with other proteins and the various ways BCL2 mutations would affect the normal function of the cell leading to the development of DLBCL.

Autophagy is not uniformly cytoprotective: a personalized medicine approach for autophagy inhibition as a therapeutic strategy in non-small cell lung cancer

BACKGROUND

Lung cancer is the leading cause of cancer-related death worldwide. In addition to surgical resection, which is considered first-line treatment at early stages of the disease, chemotherapy and radiation are widely used when the disease is advanced. Of multiple responses that may occur in the tumor cells in response to cancer therapy, the functional importance of autophagy remains equivocal; this is likely to restrict current efforts to sensitize this malignancy to chemotherapy and/or radiation by pharmacological interference with the autophagic response.

SCOPE OF REVIEW

In this review, we attempt to summarize the current state of knowledge based on studies that evaluated the function of autophagy in non-small cell lung cancer (NSCLC) cells in response to radiation and the most commonly used chemotherapeutic agents.

MAJOR CONCLUSIONS

In addition to the expected prosurvival function of autophagy, where autophagy inhibition enhances the response to therapy, autophagy appears also to have a "non-cytoprotective" function, where autophagy blockade does not affect cell viability, clonogenicity or tumor volume in response to therapy. In other cases, autophagy may actually mediate drug action via expression of its cytotoxic function.

GENERAL SIGNIFICANCE

These observations emphasize the complexity of autophagy function when examined in different tumor cell lines and in response to different chemotherapeutic agents. A more in-depth understanding of the conditions that promote the unique functions of autophagy is required in order to translate preclinical findings of autophagy inhibition to the clinic for the purpose of improving patient response to chemotherapy and radiation.

Characterisation of the conformational preference and dynamics of the intrinsically disordered N-terminal region of Beclin 1 by NMR spectroscopy

Beclin 1 is a 450 amino acid protein that plays critical roles in the early stages of autophagosome formation. We recently reported the successful expression, purification and structural characterisation of the entire N-terminal region of Beclin 1 (residues 1-150), including its backbone NMR chemical shift assignments. Based on assigned backbone NMR chemical shifts, it has been established that the N-terminal region of Beclin 1 (1-150), including the BH3 domain (112-123), is intrinsically disordered in the absence of its interaction partners. Here, a detailed study of its conformational preference and backbone dynamics obtained from an analysis of its secondary structure populations using the δ2D method, and the measurements of effective hydrodynamic radius as well as (1)H temperature coefficients, (1)H solvent exchange rates, and (15)N relaxation parameters of backbone amides using NMR spectroscopy is reported. These data provide further evidence for the intrinsically disordered nature of the N-terminal region of Beclin 1 and support the view that the helical conformation adopted by the Beclin 1 BH3 domain upon interaction with binding partners such as BCL-2 pro-survival proteins is likely induced rather than pre-existing.

Inhibition of mitochondrial calcium uniporter protects neurocytes from ischemia/reperfusion injury via the inhibition of excessive mitophagy

Mitophagy plays an important role in mitochondrial quality control and cell survival during the process of ischemia/reperfusion (I/R) injury. Mitochondrial calcium uniporter (MCU) is the most important channel responsible for Ca(2+) influx into mitochondria and Ca(2+) signal plays a potential role in modulating mitophagy. However, the effect of MCU on mitophagy during the process of I/R injury remains unknown. This study constructed an in vitro I/R model by subjecting oxygen and glucose deprivation/reperfusion (OGD/RP) model to SH-SY5Y cells to mimic the cerebral I/R injury and aimed to explore the exact effect of MCU on I/R induced mitophagy. The results showed that OGD/RP induced autophagy and mitophagy in SH-SY5Y cells. Ru360, the inhibitor of MCU, improved mitochondrial morphology and fuctional stability as well as cell viability, significantly reduced OGD/RP induced mitophagy as evidenced by the decrease in Beclin-1 and the increase in Tom20 and P62 expression. Whereas spermine, the agonist of MCU, had no significant impact on the expression of those mitophagy related proteins compared with OGD/RP group. This study indicates that inhibition of MCU can inhibit excessive mitophagy and protect the neurocytes from I/R injury.

Role of Autophagy in Hypoxia-Induced Angiogenesis of RF/6A Cells in vitro

PURPOSE

Autophagy plays a role in the pathogenesis of tumor angiogenesis and cardiovascular diseases. The autophagy level in mammalian cells was found to increase in the state of hypoxia or ischemia reperfusion. However, the role of autophagy in ocular angiogenesis has not yet been elucidated. The aim of this study was to investigate the effects of autophagy on hypoxia-induced choroidal and retinal angiogenesis in vitro using a rhesus macaque choroid-retinal endothelial (RF/6A) cell line.

MATERIALS AND METHODS

RF/6A cells were cultured and randomly divided into three groups according to the different culture media: control, hypoxia model[adding 125μMcobalt chloride (CoCl₂) to the culture medium], and hypoxia with an autophagy inhibition group [pretreatment with 5 mmol/L 3-methyladenine (3-MA) for 1.5 h and then adding125μmol/LCoCl₂ to the culture medium]. The impact of 3-MA's effect on the level of autophagy proteins (Beclin-1 and LC3) was tested by Western blot analysis. The cell proliferation was assessed using the chromogenicmethylthiazol tetrazolium bromide (MTT) dye after 24 and 48 hours. Cell migration was investigated by wound assay. The tube formation was measured on Matrigel.

RESULTS

Under chemical hypoxia conditions, Beclin-1 and LC3 levels increased and this change can be inhibited by 3-MA. Cell viability was decreased in cells treated with CoCl₂ for 24 and 48 h compared with the control, and pretreatment with 3-MA slightly promoted CoCl₂-inhibited cell proliferation. Cell migration and tube formation were increased in cells treated with CoCl₂ for 24 and 48 h compared with the control. Pretreatment with 3-MA significantly inhibited CoCl₂-induced cell migration and tube formation.

CONCLUSIONS

Hypoxia-induced autophagy decreased the cell viability and increased the cell migration and tube formation of RF/6A cells. 3-MA can inhibit hypoxia-induced angiogenesis of RF/6A cells in vitro. The present study suggests that autophagy plays a role in retinal and choroidal angiogenesis and the autophagy inhibitor can be a potential candidate for the treatment of choroidal or retinal neovascularization.

Combination of Eribulin and Aurora A Inhibitor MLN8237 Prevents Metastatic Colonization and Induces Cytotoxic Autophagy in Breast Cancer

Recent findings suggest that the inhibition of Aurora A (AURKA) kinase may offer a novel treatment strategy against metastatic cancers. In the current study, we determined the effects of AURKA inhibition by the small molecule inhibitor MLN8237 both as a monotherapy and in combination with the microtubule-targeting drug eribulin on different stages of metastasis in triple-negative breast cancer (TNBC) and defined the potential mechanism of its action. MLN8237 as a single agent and in combination with eribulin affected multiple steps in the metastatic process, including migration, attachment, and proliferation in distant organs, resulting in suppression of metastatic colonization and recurrence of cancer. Eribulin application induces accumulation of active AURKA in TNBC cells, providing foundation for the combination therapy. Mechanistically, AURKA inhibition induces cytotoxic autophagy via activation of the LC3B/p62 axis and inhibition of pAKT, leading to eradication of metastases, but has no effect on growth of mammary tumor. Combination of MLN8237 with eribulin leads to a synergistic increase in apoptosis in mammary tumors, as well as cytotoxic autophagy in metastases. These preclinical data provide a new understanding of the mechanisms by which MLN8237 mediates its antimetastatic effects and advocates for its combination with eribulin in future clinical trials for metastatic breast cancer and early-stage solid tumors. Mol Cancer Ther; 15(8); 1809-22. ©2016 AACR.

Ginsenoside Rg1 protects starving H9c2 cells by dissociation of Bcl-2-Beclin1 complex

Background

Autophagy can result in cellular adaptation, as well as cell survival or cell death. We investigated how ginsenoside Rg1(G-Rg1) regulates the relationship between autophagy and apoptosis induced by continuous starvation.

Methods

H9c2 cells under continuous starvation were treated with or without ginsenoside Rg1, and autophagy and apoptosis related proteins were assessed over a continuous time course by Western blot. Dynamic fluorescence intensity of green fluorescent protein (GFP)-LC3 was used to assess autophagosome formation by live cell imaging. Cyan fluorescent protein (CFP) -Beclin1(BECN1) and yellow fluorescent protein (YFP) -Bcl-2 were co-transfected into cells to observe ginsenoside Rg1 regulation of BECN1/Bcl-2 interaction using Fluorescence Resonance Energy Transfer (FRET). Immunoprecipitation was also used to assess BECN1/Bcl-2 interaction over a continuous time course.

Results

In H9c2 cells, starvation induced both apoptosis and autophagy. Cell apoptosis was significantly attenuated in ginsenoside Rg1-treated conditions, while autophagy was promoted. Ginsenoside Rg1 weakened the interaction between Beclin1 and Bcl-2, inhibiting apoptosis while promoting autophagy. Our results suggest that autophagy is beneficial to starved cardiac cells over a period of time. Furthermore, we describe the effect of ginsenoside Rg1 on the relationship between autophagy and apoptosis during starvation.

Conclusions

Our findings provide valuable evidence for employing ginsenoside Rg1 as a specific promoter of autophagy and inhibitor of apoptosis.

Electronic supplementary material

The online version of this article (doi:10.1186/s12906-016-1112-2) contains supplementary material, which is available to authorized users.

BAX-BAK1-independent LC3B lipidation by BH3 mimetics is unrelated to BH3 mimetic activity and has only minimal effects on autophagic flux

Inhibition of prosurvival BCL2 family members can induce autophagy, but the mechanism is controversial. We have provided genetic evidence that BCL2 family members block autophagy by inhibiting BAX and BAK1, but others have proposed they instead inhibit BECN1. Here we confirm that small molecule BH3 mimetics can induce BAX- and BAK1-independent MAP1LC3B/LC3B lipidation, but this only occurred at concentrations far greater than required to induce apoptosis and dissociate canonical BH3 domain-containing proteins that bind more tightly than BECN1. Because high concentrations of a less-active enantiomer of ABT-263 also induced BAX- and BAK1-independent LC3B lipidation, induction of this marker of autophagy appears to be an off-target effect. Indeed, robust autophagic flux was not induced by BH3 mimetic compounds in the absence of BAX and BAK1. Therefore at concentrations that are on target and achievable in vivo, BH3 mimetics only induce autophagy in a BAX- and BAK1-dependent manner.

Paris Saponin II induced apoptosis via activation of autophagy in human lung cancer cells

Paris Saponin II (PSII) has been shown anticancer activity against several cancer lines through the pro-apoptotic pathway. The aim of the study was to investigate the relationship between apoptosis and autophagy taking part in the anti-cancer mechanisms of PSII. In this study, PSII induced autophagy and apoptosis in dose- and time-dependent manners. Meanwhile, it induced autophagy as early as 2 h after exposure to 1 μM of PSII accompanying with apoptosis. Blockade of autophagy with chloroquine (CQ) attenuated apoptosis, while regulation of reactive oxygen species (ROS) by N-acetyl cysteine (NAC), gallic acid (GA) and H2O2 could not influence autophagy. In addition, PSII induced apoptosis via activation of autophagy, which might be associated with the activation of JNK and inhibition of PI3K/AKT/mTOR pathway. All in all, our research increased the understanding of the role of PSII regulating autophagy and apoptosis, which would hopefully provide prospective strategies for cancer therapy.

Organelle-Specific Initiation of Autophagy

Autophagy constitutes a prominent mechanism through which eukaryotic cells preserve homeostasis in baseline conditions and in response to perturbations of the intracellular or extracellular microenvironment. Autophagic responses can be relatively non-selective or target a specific subcellular compartment. At least in part, this depends on the balance between the availability of autophagic substrates ("offer") and the cellular need of autophagic products or functions for adaptation ("demand"). Irrespective of cargo specificity, adaptive autophagy relies on a panel of sensors that detect potentially dangerous cues and convert them into signals that are ultimately relayed to the autophagic machinery. Here, we summarize the molecular systems through which specific subcellular compartments-including the nucleus, mitochondria, plasma membrane, reticular apparatus, and cytosol-convert homeostatic perturbations into an increased offer of autophagic substrates or an accrued cellular demand for autophagic products or functions.

Gene expression profiles of autophagy-related genes in multiple sclerosis

Multiple sclerosis (MS) is an imflammatory disease of central nervous system caused by genetic and environmental factors that remain largely unknown. Autophagy is the process of degradation and recycling of damaged cytoplasmic organelles, macromolecular aggregates, and long-lived proteins. Malfunction of autophagy contributes to the pathogenesis of neurological diseases, and autophagy genes may modulate the T cell survival. We aimed to examine the expression levels of autophagy-related genes. The blood samples of 95 unrelated patients (aged 17-65years, 37 male, 58 female) diagnosed as MS and 95 healthy controls were used to extract the RNA samples. After conversion to single stranded cDNA using polyT priming: the targeted genes were pre-amplified, and 96×78 (samples×primers) qRT-PCR reactions were performed for each primer pair on each sample on a 96.96 array of Fluidigm BioMark™. Compared to age- and sex-matched controls, gene expression levels of ATG16L2, ATG9A, BCL2, FAS, GAA, HGS, PIK3R1, RAB24, RGS19, ULK1, FOXO1, HTT were significantly altered (false discovery rate<0.05). Thus, altered expression levels of several autophagy related genes may affect protein levels, which in turn would influence the activity of autophagy, or most probably, those genes might be acting independent of autophagy and contributing to MS pathogenesis as risk factors. The indeterminate genetic causes leading to alterations in gene expressions require further analysis.

A brewing understanding of the regulation of Bax function by Bcl-xL and Bcl-2

Bcl-2 family members form a network of protein-protein interactions that regulate apoptosis through permeabilization of the mitochondrial outer membrane. Deciphering this intricate network requires streamlined experimental models, including the heterologous expression in yeast. This approach had previously enabled researchers to identify domains and residues that underlie the conformational changes driving the translocation, the insertion and the oligomerization of the pro-apoptotic protein Bax at the level of the mitochondrial outer membrane. Recent studies that combine experiments in yeast and in mammalian cells have shown the unexpected effect of the anti-apoptotic protein Bcl-xL on the priming of Bax. As demonstrated with the BH3-mimetic molecule ABT-737, this property of Bcl-xL, and of Bcl-2, is crucial to elaborate about how apoptosis could be reactivated in tumoral cells.

MYBL2 guides autophagy suppressor VDAC2 in the developing ovary to inhibit autophagy through a complex of VDAC2-BECN1-BCL2L1 in mammals

Oogenesis is essential for female gamete production in mammals. The total number of ovarian follicles is determined early in life and production of ovarian oocytes is thought to stop during the lifetime. However, the molecular mechanisms underling oogenesis, particularly autophagy regulation in the ovary, remain largely unknown. Here, we reveal an important MYBL2-VDAC2-BECN1-BCL2L1 pathway linking autophagy suppression in the developing ovary. The transcription factors GATA1 and MYBL2 can bind to and activate the Vdac2 promoter. MYBL2 regulates the spatiotemporal expression of VDAC2 in the developing ovary. Strikingly, in the VDAC2 transgenic pigs (Sus scrofa/Ss), VDAC2 exerts its function by inhibiting autophagy in the ovary. In contrast, Vdac2 knockout promotes autophagy. Moreover, VDAC2-mediated autophagy suppression is dependent on its interactions with both BECN1 and BCL2L1 to stabilize the BECN1 and BCL2L1 complex, suggesting VDAC2 as an autophagy suppressor in the pathway. Our findings provide a functional connection among the VDAC2, MYBL2, the BECN1-BCL2L1 pathway and autophagy suppression in the developing ovary, which is implicated in improving female fecundity.

Regulation of cardiomyocyte autophagy by calcium

Calcium signaling plays a crucial role in a multitude of events within the cardiomyocyte, including cell cycle control, growth, apoptosis, and autophagy. With respect to calcium-dependent regulation of autophagy, ion channels and exchangers, receptors, and intracellular mediators play fundamental roles. In this review, we discuss calcium-dependent regulation of cardiomyocyte autophagy, a lysosomal mechanism that is often cytoprotective, serving to defend against disease-related stress and nutrient insufficiency. We also highlight the importance of the subcellular distribution of calcium and related proteins, interorganelle communication, and other key signaling events that govern cardiomyocyte autophagy.

Rapamycin Inhibits Cardiac Hypertrophy by Promoting Autophagy via the MEK/ERK/Beclin-1 Pathway

Rapamycin, also known as sirolimus, is an antifungal agent and immunosuppressant drug used to prevent organ rejection in transplantation. However, little is known about the role of rapamycin in cardiac hypertrophy and the signaling pathways involved. Here, the effect of rapamycin was examined using phenylephrine (PE) induced cardiomyocyte hypertrophy in vitro and in a rat model of aortic banding (AB) - induced hypertrophy in vivo. Inhibition of MEK/ERK signaling reversed the effect of rapamycin on the up-regulation of LC3-II, Beclin-1 and Noxa, and the down-regulation of Mcl-1 and p62. Silencing of Noxa or Beclin-1 suppressed rapamycin-induced autophagy, and co-immunoprecipitation experiments showed that Noxa abolishes the inhibitory effect of Mcl-1 on Beclin-1, promoting autophagy. In vivo experiments showed that rapamycin decreased AB-induced cardiac hypertrophy in a MEK/ERK dependent manner. Taken together, our results indicate that rapamycin attenuates cardiac hypertrophy by promoting autophagy through a mechanism involving the modulation of Noxa and Beclin-1 expression by the MEK/ERK signaling pathway.

Autophagy and Apoptotic Crosstalk: Mechanism of Therapeutic Resistance in HER2-Positive Breast Cancer

While breast cancer patients benefit from the use of HER2 inhibitors, many fail therapy and become resistant to treatment, indicating a critical need to prevent treatment failure. A number of studies have emerged that highlight the catabolic process of autophagy in breast cancer as a mechanism of resistance to chemotherapy and targeted inhibitors. Furthermore, recent research has begun to dissect how autophagy signaling crosstalks with apoptotic signaling. Thus, a possible strategy in fighting resistance is to couple targeting of apoptotic and autophagy signaling pathways. In this review, we discuss how cellular response by autophagy circumvents cell death to promote resistance of breast cancers to HER2 inhibitors, as well as the potential avenues of therapeutic intervention.