BH3-only proteins target BCL-xL/MCL-1, not BAX/BAK, to initiate apoptosis.

It has been widely accepted that mitochondria-dependent apoptosis initiates when select BH3-only proteins (BID, BIM, etc.) directly engage and allosterically activate effector proteins BAX/BAK. Here, through reconstitution of cells lacking all eight pro-apoptotic BH3-only proteins, we demonstrate that all BH3-only proteins primarily target the anti-apoptotic BCL-2 proteins BCL-xL/MCL-1, whose simultaneous suppression enables membrane-mediated spontaneous activation of BAX/BAK. BH3-only proteins' apoptotic activities correlate with affinities for BCL-xL/MCL-1 instead of abilities to directly activate BAX/BAK. Further, BID and BIM do not distinguish BAX from BAK or accelerate BAX/BAK activation following inactivation of BCL-xL/MCL-1. Remarkably, death ligand-induced apoptosis in cells lacking BH3-only proteins and MCL-1 is fully restored by BID mutants capable of neutralizing BCL-xL, but not direct activation of BAX/BAK. Taken together, our findings provide a "Membrane-mediated Permissive" model, in which the BH3-only proteins only indirectly activate BAX/BAK by neutralizing the anti-apoptotic BCL-2 proteins, and thus allowing BAX/BAK to undergo unimpeded, spontaneous activation in the mitochondrial outer membrane milieu, leading to apoptosis initiation.

Increased Ripk1-mediated bone marrow necroptosis leads to myelodysplasia and bone marrow failure in mice.

Hematopoiesis is a dynamic system that requires balanced cell division, differentiation, and death. The 2 major modes of programmed cell death, apoptosis and necroptosis, share molecular machinery but diverge in outcome with important implications for the microenvironment; apoptotic cells are removed in an immune silent process, whereas necroptotic cells leak cellular contents that incite inflammation. Given the importance of cytokine-directed cues for hematopoietic cell survival and differentiation, the impact on hematopoietic homeostasis of biasing cell death fate to necroptosis is substantial and poorly understood. Here, we present a mouse model with increased bone marrow necroptosis. Deletion of the proapoptotic Bcl-2 family members Bax and Bak inhibits bone marrow apoptosis. Further deletion of the BH3-only member Bid (to generate Vav CreBaxBakBid triple-knockout [TKO] mice) leads to unrestrained bone marrow necroptosis driven by increased Rip1 kinase (Ripk1). TKO mice display loss of progenitor cells, leading to increased cytokine production and increased stem cell proliferation and exhaustion and culminating in bone marrow failure. Genetically restoring Ripk1 to wild-type levels restores peripheral red cell counts as well as normal cytokine production. TKO bone marrow is hypercellular with abnormal differentiation, resembling the human disorder myelodysplastic syndrome (MDS), and we demonstrate increased necroptosis in MDS bone marrow. Finally, we show that Bid impacts necroptotic signaling through modulation of caspase-8-mediated Ripk1 degradation. Thus, we demonstrate that dysregulated necroptosis in hematopoiesis promotes bone marrow progenitor cell death that incites inflammation, impairs hematopoietic stem cells, and recapitulates the salient features of the bone marrow failure disorder MDS.

Differential role of FL-BID and t-BID during verotoxin-1-induced apoptosis in Burkitt's lymphoma cells.

The globotriaosylceramide Gb3 is a glycosphingolipid expressed on a subpopulation of germinal center B lymphocytes which has been recognized as the B cell differentiation antigen CD77. Among tumoral cell types, Gb3/CD77 is strongly expressed in Burkitt's lymphoma (BL) cells as well as other solid tumors including breast, testicular and ovarian carcinomas. One known ligand of Gb3/CD77 is Verotoxin-1 (VT-1), a Shiga toxin produced in specific E. coli strains. Previously, we have reported that in BL cells, VT-1 induces apoptosis via a caspase-dependent and mitochondria-dependent pathway. Yet, the respective roles of various apoptogenic factors remained to be deciphered. Here, this apoptotic pathway was found to require cleavage of the BID protein by caspase-8 as well as activation of two other apoptogenic proteins, BAK and BAX. Surprisingly however, t-BID, the truncated form of BID resulting from caspase-8 cleavage, played no role in the conformational changes of BAK and BAX. Rather, their activation occurred under the control of full length BID (FL-BID). Indeed, introducing a non-cleavable form of BID (BID-D59A) into BID-deficient BL cells restored BAK and BAX activation following VT-1 treatment. Still, t-BID was involved along with FL-BID in the BAK-dependent and BAX-dependent cytosolic release of CYT C and SMAC/DIABLO from the mitochondrial intermembrane space: FL-BID was found to control the homo-oligomerization of both BAK and BAX, likely contributing to the initial release of CYT C and SMAC/DIABLO, while t-BID was needed for their hetero-oligomerization and ensuing release amplification. Together, our results reveal a functional cooperation between BAK and BAX during VT-1-induced apoptosis and, unexpectedly, that activation of caspase-8 and production of t-BID were not mandatory for initiation of the cell death process.

BCL9L Dysfunction Impairs Caspase-2 Expression Permitting Aneuploidy Tolerance in Colorectal Cancer.

Chromosomal instability (CIN) contributes to cancer evolution, intratumor heterogeneity, and drug resistance. CIN is driven by chromosome segregation errors and a tolerance phenotype that permits the propagation of aneuploid genomes. Through genomic analysis of colorectal cancers and cell lines, we find frequent loss of heterozygosity and mutations in BCL9L in aneuploid tumors. BCL9L deficiency promoted tolerance of chromosome missegregation events, propagation of aneuploidy, and genetic heterogeneity in xenograft models likely through modulation of Wnt signaling. We find that BCL9L dysfunction contributes to aneuploidy tolerance in both TP53-WT and mutant cells by reducing basal caspase-2 levels and preventing cleavage of MDM2 and BID. Efforts to exploit aneuploidy tolerance mechanisms and the BCL9L/caspase-2/BID axis may limit cancer diversity and evolution.

Caspase-3 feedback loop enhances Bid-induced AIF/endoG and Bak activation in Bax and p53-independent manner.

Chemoresistance in cancer has previously been attributed to gene mutations or deficiencies. Bax or p53 deficiency can lead to resistance to cancer drugs. We aimed to find an agent to overcome chemoresistance induced by Bax or p53 deficiency. Here, we used immunoblot, flow-cytometry analysis, gene interference, etc. to show that genistein, a major component of isoflavone that is known to have anti-tumor activities in a variety of models, induces Bax/p53-independent cell death in HCT116 Bax knockout (KO), HCT116 p53 KO, DU145 Bax KO, or DU145 p53 KO cells that express wild-type (WT) Bak. Bak knockdown (KD) only partially attenuated genistein-induced apoptosis. Further results indicated that the release of AIF and endoG also contributes to genistein-induced cell death, which is independent of Bak activation. Conversely, AIF and endoG knockdown had little effect on Bak activation. Knockdown of either AIF or endoG alone could not efficiently inhibit apoptosis in cells treated with genistein, whereas an AIF, endoG, and Bak triple knockdown almost completely attenuated apoptosis. Next, we found that the Akt-Bid pathway mediates Bak-induced caspase-dependent and AIF- and endoG-induced caspase-independent cell death. Moreover, downstream caspase-3 could enhance the release of AIF and endoG as well as Bak activation via a positive feedback loop. Taken together, our data elaborate the detailed mechanisms of genistein in Bax/p53-independent apoptosis and indicate that caspase-3-enhanced Bid activation initiates the cell death pathway. Our results also suggest that genistein may be an effective agent for overcoming chemoresistance in cancers with dysfunctional Bax and p53.

Sevoflurane Post-conditioning Protects Primary Rat Cortical Neurons Against Oxygen-Glucose Deprivation/Resuscitation: Roles of Extracellular Signal-Regulated Kinase 1/2 and Bid, Bim, Puma.

Temporal post-conditioning to induce neuroprotection against brain ischemia-reperfusion injury insult is considered to be an effective intervention, but the exact mechanisms of sevoflurane post-conditioning are poorly understood. Extracellular signal-related kinases 1/2 (Erk1/2) play a pivotal role in the cell growth and proliferation. The essential axis of activator Bid, Bim, Puma (BH3s) and BAX, BAK in activating the mitochondrial death program might offer common ground for cell death signal. We hypothesized that, sevoflurane post-conditioning might inhibit the expression of Bid, Bim and Puma and is activated by phosphor-Erk1/2 to reduce neuronal death. To test this hypothesis, we exposed primary cultured cortical neurons to oxygen-glucose deprivation for 1 h and resuscitation for 24 h (OGD/R). The assays of MTT, propidium iodide uptake, JC-1 fluorescence and western blot demonstrated that OGD/R exposure reduced cell viability, increased cell death, decreased mitochondrial membrane potential and the expressions of Bid, Bim, and Puma. Inhibition of Erk1/2 phosphorylation could partially attenuate 2 % of sevoflurane post-conditioning mediated increase in neuronal viability and mitochondrial membrane potential, and also a decrease in cell death and expression of Bid, Bim and Puma after OGD/R treatment. The results demonstrated that, the protection of sevoflurane post-conditioning markedly reducing death of cortical neurons exposed to OGD/R could be correlated with down-regulation of Bid, Bim and Puma expression mediated by phosphorylation/activation of Erk1/2.

Activation of the Mitochondrial Apoptotic Pathway Produces Reactive Oxygen Species and Oxidative Damage in Hepatocytes That Contribute to Liver Tumorigenesis.

Chronic hepatitis, including viral hepatitis and steatihepatitis, is a well-known high-risk condition for hepatocellular carcinoma. We previously reported that continuous hepatocyte apoptosis drives liver tumors in hepatocyte-specific Bcl-xL or Mcl-1 knockout mice. In this study, we further examine the underlying cellular mechanisms of generating tumors in apoptosis-prone liver. In cultured hepatocytes, the administration of ABT-737, a Bcl-xL/-2/-w inhibitor, led to production of reactive oxygen species (ROS) as well as activation of caspases. Mitochondria isolated from murine liver, upon administration of truncated-Bid, a proapoptotic Bcl-2 family protein, released cytochrome c and produced ROS, which was dependent on mitochondrial respiration. Hepatic apoptosis, regeneration, accumulation of oxidative damages, and tumorigenesis observed in hepatocyte-specific Mcl-1 knockout mice were substantially attenuated by further deficiency of Bax or Bid, suggesting that a balance of mitochondrial Bcl-2 family proteins governs generation of oxidative stress and other pathologies. Whole-exome sequencing clarified that C>A/G>T transversion, which is often caused by oxidative DNA damage in proliferating cells, was a frequently observed mutation pattern in liver tumors of Mcl-1 knockout mice. The administration of antioxidant L-N-acetylcysteine did not affect apoptosis, compensatory regeneration, or fibrotic responses but significantly reduced oxidative DNA damage and incidence and multiplicity of live tumors in Mcl-1 knockout mice. In conclusion, activation of the mitochondrial apoptotic pathway in hepatocytes accumulates intracellular oxidative damages, leading to liver tumorigenesis, independently of liver regeneration or fibrosis. This study supports a concept that antioxidant therapy may be useful for suppressing liver carcinogenesis in patients with chronic liver disease.

Hepatocyte autophagy is linked to C/EBP-homologous protein, Bcl2-interacting mediator of cell death, and BH3-interacting domain death agonist gene expression.

BACKGROUND: Endoplasmic reticulum (ER) stress and autophagy each play important roles in hepatocyte cell injury. We hypothesized that gene expression of C/EBP-homologous protein (CHOP) and the BH3 proteins Bcl2-interacting mediator of cell death (BIM) and BH3-interacting domain death agonist (BID) are involved in a complex interplay that regulates ER stress-induced autophagy and cell death. MATERIALS AND METHODS: Hepatocytes were cultured from lean Zucker rats. Confluent hepatocytes were incubated with single or combined small interfering RNA for CHOP, BIM, and/or BID for 24 h providing gene inhibition. Incubation with tunicamycin (TM) for another 24 h stimulated ER stress. Quantitative real-time polymerase chain reaction determined the expression levels of CHOP, BIM, and BID. Immunostaining with microtubule-associated protein 1 light chain 3 measured autophagy activity. Trypan blue exclusion determined the cell viability. RESULTS: TM treatment increased the messenger RNA levels of CHOP and BIM but decreased the messenger RNA levels of BID. TM increased autophagy and decreased cell viability. Individual inhibition of CHOP, BIM, or BID protected against autophagy and cell death. However, simultaneous treatment with any combination of CHOP, BIM, and BID small interfering RNAs reduced autophagy activity but increased cell death independent of ER stress induction. CONCLUSIONS: Autophagy in hepatocytes results from acute ER stress and involves interplay, at the gene expression level, of CHOP, BIM, and BID. Inhibition of any one of these individual genes during acute ER stress is protective against cell death. Conversely, inhibition of any two of the three genes results in increased nonautophagic cell death independent of ER stress induction. This study suggests interplay between CHOP, BIM, and BID expression that can be leveraged for protection against ER stress-related cell death. However, disruption of the CHOP/BH3 gene expression homeostasis is detrimental to cell survival independent of other cellular stress.

BID mediates selective killing of APC-deficient cells in intestinal tumor suppression by nonsteroidal antiinflammatory drugs.

Colorectal tumorigenesis is driven by genetic alterations in the adenomatous polyposis coli (APC) tumor suppressor pathway and effectively inhibited by nonsteroidal antiinflammatory drugs (NSAIDs). However, how NSAIDs prevent colorectal tumorigenesis has remained obscure. We found that the extrinsic apoptotic pathway and the BH3 interacting-domain death agonist (BID) are activated in adenomas from NSAID-treated patients. Loss of BID abolishes NSAID-mediated tumor suppression, survival benefit, and apoptosis in tumor-initiating stem cells in APC(Min/+) mice. BID-mediated cross-talk between the extrinsic and intrinsic apoptotic pathways is responsible for selective killing of neoplastic cells by NSAIDs. We further demonstrate that NSAIDs induce death receptor signaling in both cancer and normal cells, but only activate BID in cells with APC deficiency and ensuing c-Myc activation. Our results suggest that NSAIDs suppress intestinal tumorigenesis through BID-mediated synthetic lethality triggered by death receptor signaling and gatekeeper mutations, and provide a rationale for developing more effective cancer prevention strategies and agents.

A near death experience: Shigella manipulates host death machinery to silence innate immunity.

Release of mitochondrial contents often triggers inflammation and cell death, and modulating this process can be advantageous to invading pathogens. In this issue of The EMBO Journal, Andree and colleagues reveal new findings that an intracellular bacterial pathogen exploits apoptotic machinery to suppress host immune signaling, yet avoids cell death. This study emphasizes the need to expand our understanding of the roles played by pro­apoptotic proteins in non­death scenarios.

B cell lymphoma-2 (BCL-2) homology domain 3 (BH3) mimetics demonstrate differential activities dependent upon the functional repertoire of pro- and anti-apoptotic BCL-2 family proteins.

The B cell lymphoma-2 (BCL-2) family is the key mediator of cellular sensitivity to apoptosis during pharmacological interventions for numerous human pathologies, including cancer. There is tremendous interest to understand how the proapoptotic BCL-2 effector members (e.g. BCL-2-associated X protein, BAX) cooperate with the BCL-2 homology domain only (BH3-only) subclass (e.g. BCL-2 interacting mediator of death, BIM; BCL-2 interacting-domain death agonist, BID) to induce mitochondrial outer membrane permeabilization (MOMP) and apoptosis and whether these mechanisms may be pharmacologically exploited to enhance the killing of cancer cells. Indeed, small molecule inhibitors of the anti-apoptotic BCL-2 family members have been designed rationally. However, the success of these "BH3 mimetics" in the clinic has been limited, likely due to an incomplete understanding of how these drugs function in the presence of multiple BCL-2 family members. To increase our mechanistic understanding of how BH3 mimetics cooperate with multiple BCL-2 family members in vitro, we directly compared the activity of several BH3-mimetic compounds (i.e. ABT-263, ABT-737, GX15-070, HA14.1, TW-37) in biochemically defined large unilamellar vesicle model systems that faithfully recapitulate BAX-dependent mitochondrial outer membrane permeabilization. Our investigations revealed that the presence of BAX, BID, and BIM differentially regulated the ability of BH3 mimetics to derepress proapoptotic molecules from anti-apoptotic proteins. Using mitochondria loaded with fluorescent BH3 peptides and cells treated with inducers of cell death, these differences were supported. Together, these data suggest that although the presence of anti-apoptotic BCL-2 proteins primarily dictates cellular sensitivity to BH3 mimetics, additional specificity is conferred by proapoptotic BCL-2 proteins.

BID-dependent release of mitochondrial SMAC dampens XIAP-mediated immunity against Shigella.

The X-linked inhibitor of apoptosis protein (XIAP) is a potent caspase inhibitor, best known for its anti-apoptotic function in cancer. During apoptosis, XIAP is antagonized by SMAC, which is released from the mitochondria upon caspase-mediated activation of BID. Recent studies suggest that XIAP is involved in immune signaling. Here, we explore XIAP as an important mediator of an immune response against the enteroinvasive bacterium Shigella flexneri, both in vitro and in vivo. Our data demonstrate for the first time that Shigella evades the XIAP-mediated immune response by inducing the BID-dependent release of SMAC from the mitochondria. Unlike apoptotic stimuli, Shigella activates the calpain-dependent cleavage of BID to trigger the release of SMAC, which antagonizes the inflammatory action of XIAP without inducing apoptosis. Our results demonstrate how the cellular death machinery can be subverted by an invasive pathogen to ensure bacterial colonization.

Dexamethasone differentially regulates Bcl-2 family proteins in human proliferative chondrocytes: role of pro-apoptotic Bid.

Glucocorticoids (GCs) are widely used to treat inflammatory diseases and cancers. A multitude of undesired side effects have been reported in GC-treated patients including decreased linear bone growth. We have previously reported that GCs activate the caspase cascade and trigger Bax-mediated mitochondrial apoptosis in growth plate chondrocytes causing growth retardation in young mice. To further explore the role of mitochondrial apoptosis in GC-induced bone growth retardation, a number of pro- and anti-apoptotic proteins were studied in ex vivo cultures of human growth plate cartilage and human HCS-2/8 proliferative chondrocytes exposed to dexamethasone. Dexamethasone was found to increase the pro-apoptotic proteins Bcl-xS, Bad, and Bak as well as the proteolysis of Bid. Anti-Bid small interfering RNA partially rescued the chondrocytes from dexamethasone-induced apoptosis. Taken together, our data suggest that GC treatment differentially regulates Bcl-2 family member proteins to facilitate mitochondrial apoptosis in proliferative chondrocytes thereby contributing to GC-induced bone growth impairment. Prevention of this imbalance between pro- and anti-apoptotic Bcl-2 family proteins may provide a new strategy to protect from adverse effects of GCs on bone growth.

Is suppression of apoptosis a new therapeutic target in sepsis?

Sepsis remains as a leading cause of death in critically ill patients. Unfortunately, there have been very few successful specific therapeutic agents that can significantly reduce the attributable mortality and morbidity of sepsis. Developing novel therapeutic strategies to improve outcomes of sepsis remains an important focus of ongoing research in the field of critical care medicine. Apoptosis has recently been identified as an important mechanism of cell death and evidence suggests that prevention of cell apoptosis can improve survival in animal models of sepsis and endotoxaemia. In this review article, we summarise the critical role of apoptosis of the immune cells in the pathophysiology of sepsis and propose that blocking cell-signaling pathways leading to apoptosis may present a promising specific therapy for sepsis. Various methods to inhibit apoptosis including the cell surface Fas receptor pathway inhibitors, caspase inhibitors, over-expression of anti-apoptotic genes and small interfering ribonucleic acid therapy are discussed.

The loss of the BH3-only Bcl-2 family member Bid delays T-cell leukemogenesis in Atm-/- mice.

Multicellular organisms maintain genomic integrity and resist tumorigenesis through a tightly regulated DNA damage response (DDR) that prevents propagation of deleterious mutations either through DNA repair or programmed cell death. An impaired DDR leads to tumorigenesis that is accelerated when programmed cell death is prevented. Loss of the ATM (ataxia telangiectasia mutated)-mediated DDR in mice results in T-cell leukemia driven by accumulation of DNA damage accrued during normal T-cell development. Pro-apoptotic BH3-only Bid is a substrate of Atm, and Bid phosphorylation is required for proper cell cycle checkpoint control and regulation of hematopoietic function. In this report, we demonstrate that, surprisingly, loss of Bid increases the latency of leukemogenesis in Atm-/- mice. Bid-/-Atm-/- mice display impaired checkpoint control and increased cell death of DN3 thymocytes. Loss of Bid thus inhibits T-cell tumorigenesis by increasing clearance of damaged cells, and preventing propagation of deleterious mutations.

Rejuvenating Bi(d)ology.

The BH3-only Bid protein is a critical sentinel of cellular stress in the liver and the hematopoietic system. Bid's initial 'claim to fame' came from its ability-as a caspase-truncated product-to trigger the mitochondrial apoptotic program following death receptor activation. Today we know that Bid can response to multiple types of proteases, which are activated under different conditions such as T-cell activation, ischemical reperfusion injury and lysosomal injury. Activation of the mitochondrial apoptotic program by Bid-via its recently identified receptor mitochondrial carrier homolog 2-involves multiple mechanisms, including release of cytochrome c and second mitochondria-derived activator of caspase (Smac), alteration of mitochondrial cristae organization, generation of reactive oxygen species and engagement of the permeability transition pore. Bid is also emerging-in its full-length form-as a pivotal sentinel of DNA damage in the bone marrow regulated by the ataxia telangiectasia mutated (ATM)/ataxia telangiectasia and Rad3-related (ATR) kinases. The ATM/ATR-Bid pathway is critically involved in preserving the quiescence and survival of hematopoietic stem cells both in the absence and presence of external stress, and a large part of this review will be dedicated to recent advances in this area of research.

Bid signal pathway components are identified in the temporal cortex with Parkinson disease.

OBJECTIVE: Parkinson disease (PD), a devastating neurodegenerative disorder, affects motor abilities and cognition as well. It is not clear whether the proapoptotic protein, Bid, is involved in tumor necrosis factor death receptor I (TNFRI)-mediated destructive signal transduction pathways such as cell dysfunction or neurodegeneration in the temporal cortex of patients with PD. METHODS: Molecular and biochemical approaches were used to dissect mitochondrial related components of the destructive signaling pathway in the temporal cortex from rapidly autopsied brains (postmortem interval mean 2.6 hours). Brains from patients with PD (n = 15) had an average age of 81.4 years, compared to the average age of 84.36 years in age-matched control patient brains (n = 15). RESULTS: TNFRI and its adaptor protein, TRADD, were not only present in the cytoplasm of the temporal cortex, but were significantly elevated (42.3% and 136.1%, respectively) in PD brains compared to age-matched control brains. Bid in the PD temporal cortex could be further cleaved into tBid in the cytosol, which is translocated into the mitochondria, where cytochrome c is then released and caspase-3 is subsequently activated. CONCLUSION: Patients with PD have an activated Bid-mediated destructive signal pathway via TNFRI in the temporal cortex. Such deficits are pervasive, suggesting that they might contribute to cortex degeneration as PD manifests.

The ATM-BID pathway regulates quiescence and survival of haematopoietic stem cells.

BID, a BH3-only BCL2 family member, functions in apoptosis as well as the DNA-damage response. Our previous data demonstrated that BID is an ATM effector acting to induce cell-cycle arrest and inhibition of apoptosis following DNA damage. Here we show that ATM-mediated BID phosphorylation plays an unexpected role in maintaining the quiescence of haematopoietic stem cells (HSCs). Loss of BID phosphorylation leads to escape from quiescence of HSCs, resulting in exhaustion of the HSC pool and a marked reduction of HSC repopulating potential in vivo. We also demonstrate that BID phosphorylation plays a role in protecting HSCs from irradiation, and that regulating both quiescence and survival of HSCs depends on BID's ability to regulate oxidative stress. Moreover, loss of BID phosphorylation, ATM knockout or exposing mice to irradiation leads to an increase in mitochondrial BID, which correlates with an increase in mitochondrial oxidative stress. These results show that the ATM-BID pathway serves as a critical checkpoint for coupling HSC homeostasis and the DNA-damage stress response to enable long-term regenerative capacity.

Lysosomes and lysosomal cathepsins in cell death.

Lysosomes are the key degradative compartments of the cell. Lysosomal cathepsins, which are enclosed in the lysosomes, help to maintain the homeostasis of the cell's metabolism by participating in the degradation of heterophagic and autophagic material. Following the targeted lysosomal membrane's destabilization, the cathepsins can be released into the cytosol and initiate the lysosomal pathway of apoptosis through the cleavage of Bid and the degradation of the anti-apoptotic Bcl-2 homologues. Cathepsins can also amplify the apoptotic signaling, when the lysosomal membranes are destabilized at a later stage of apoptosis, initiated by other stimuli. However, the functional integrity of the lysosomal compartment during apoptosis enables efficient autophagy, which can counteract apoptosis by providing the energy source and by disposing the damaged mitochondria, which generate the ROS. Impairing autophagy by disabling the lysosome function is being investigated as an adjuvant therapeutic approach to sensitize cells to apoptosis-inducing agents. Destabilization of the lysosomal membranes by the lysosomotropic detergents seems to be a promising strategy in this context as it would not only disable autophagy, but also promote apoptosis through the initiation of the lysosomal pathway. In contrast, the impaired autophagy and lysosomal degradation linked with the increased oxidative stress underlie degenerative changes in the aging neurons. This further suggests that lysosomes and lysosomal cathepsins have a dual role in cell death. This article is part of a Special Issue entitled: Proteolysis 50 years after the discovery of lysosome.

Intracellular pathways of pancreatic ß-cell apoptosis in type 1 diabetes.

BACKGROUND: Apoptosis of ß cells is a feature of type 1 diabetes. It is also increasingly recognized in type 2 diabetes and islet graft rejection. METHODS: We have studied the intracellular pathways that regulate ß-cell apoptosis in type 1 and 2 diabetes. We have examined the role of Bid, a pro-apoptotic member of the Bcl-2 family, using islets from mice deficient in Bid. We also studied the Bcl-2 family molecules involved in killing by using high concentrations of reducing sugars such as glucose or ribose. RESULTS: We found that Bid-deficient islets are protected from recombinant human perforin and granzyme B, as well as from Fas-mediated killing. This makes Bid a target for protection of ß cells from multiple insults relevant to type 1 diabetes. In contrast to granzyme B and death receptor signalling, we found that islets lacking Bim or Puma were protected from glucose toxicity. CONCLUSIONS: Our data indicate that different stimuli activate different initiator molecules in the Bcl-2-regulated pathway in ß cells.