Bcl-2 family member Bfl-1/A1 sequesters truncated bid to inhibit is collaboration with pro-apoptotic Bak or Bax

Retinoic acid determines life span of leukemic cells by inducing antagonistic apoptosis-regulatory programs

As a single signal, retinoids induce terminal differentiation. This implies that they activate differentiation and apoptosis in a temporally defined order to allow expression of the differentiated phenotype well before death. We report that two apparently contradictory retinoid-induced programs have the capacity to define cellular life span. Anti-apoptotic factors are activated concomitantly with differentiation, while retinoids induce at the same time also pro-apoptotic signaling. We have assessed the roles of two key factors, Bcl2A1 and TRAIL, in the temporal programming of cell death and differentiation. We demonstrate that PLB985 are type II cells in which TRAIL induces apoptosis through the extrinsic and--via Bid activation--also the intrinsic death pathways. Bcl2A1, ectopically over-expressed, or endogenously induced by retinoic acid receptor agonists, protected cells from apoptosis triggered by TRAIL, whose induction required the activation of both the retinoic acid and retinoid X receptors. Bcl2A1 prevented loss of mitochondrial membrane potential and caspase-9, but not caspase-8, activation. The expression of anti-sense Bcl2A1 sensitized PLB985 cells to TRAIL. Co-culture experiments revealed protection from fraternicide if sister cells were pre-exposed to retinoic acid. Collectively, our data support a model in which retinoids orchestrate a life span-regulatory program comprising Bcl2A1 induction to temporally protect against concomitantly induced TRAIL death signaling. Termination of this life span in presence of Bcl2A1 is most likely a consequence of the Bid-independent TRAIL action. Thus, depending on the retinoic acid and retinoid X receptor activation potential of a ligand and the relative efficacies of the intrinsic and extrinsic death pathways in a given cell, a single retinoid triggers the life span of a differentiated phenotype.

Interleukin-10 enhances the oxidized LDL-induced foam cell formation of macrophages by antiapoptotic mechanisms

Interleukin (IL)-10 may have a therapeutic potential in atherosclerosis, but its mechanisms of action have not been clarified. Foam cell formation is a key event in atherogenesis, and apoptosis of these lipid-laden cells may promote plaque destabilization. We sought to explore whether IL-10 could have plaque-stabilizing properties in acute coronary syndromes (ACS). We studied the effect of IL-10 on oxidized low density lipoprotein (oxLDL)-stimulated THP-1 cells and monocyte-derived macrophages from ACS patients and healthy controls using different experimental approaches. Our main findings were: i) IL-10 enhances lipid accumulation in oxLDL-stimulated THP-1 macrophages, at least partly by counteracting oxLDL-induced apoptosis; ii) This antiapoptotic effect of IL-10 involves increased expression of the antiapoptotic genes Bfl-1 and Mcl-1, accompanied by protective effects on mitochondria function; iii) By silencing Bfl-1 and Mcl-1 genes using siRNAs, we were able to abolish this IL-10-mediated effect on lipid accumulation; iv) IL-10 also induced lipid accumulation in oxLDL-stimulated macrophages from patients with ACS, but not in macrophages from healthy controls; v) In ACS patients, this enhancing effect of IL-10 on lipid accumulation was accompanied by enhanced Mcl-1 expression. No such antiapoptotic effect was seen in macrophages from healthy controls. These findings suggest a new mechanism for the effect of IL-10 in atherosclerosis, possibly contributing to plaque stabilization.

Mechanism of action of Drosophila Reaper in mammalian cells: Reaper globally inhibits protein synthesis and induces apoptosis independent of mitochondrial permeability

Drosophila Reaper can bind inhibitor of apoptosis proteins (IAP) and thereby rescue caspases from proteasomal degradation. In insect cells, this is sufficient to induce apoptosis. Reaper can also induce apoptosis in mammalian cells, in which caspases need to be activated, usually via the mitochondrial pathway. Nevertheless, we find that Reaper efficiently induces apoptosis in mammalian cells in the absence of mitochondrial permeabilisation and cytochrome c release. Moreover, this capacity was only marginally affected by deletion of Reaper's amino-terminal IAP-binding motif. Independent of this motif, Reaper could globally suppress protein synthesis. Deletion of 20 amino acids from the carboxy-terminus of Reaper fully abrogated its potential to inhibit protein synthesis and to induce apoptosis in the absence of IAP-binding. Our findings indicate that the newly identified capacity of Reaper to suppress protein translation can operate in mammalian cells and may be key to its pro-apoptotic activity.

Eosinophil adhesion to cholinergic IMR-32 cells protects against induced neuronal apoptosis

Eosinophils release a number of mediators that are potentially toxic to nerve cells. However, in a number of inflammatory conditions, such as asthma and inflammatory bowel disease, it has been shown that eosinophils localize to nerves, and this is associated with enhanced nerve activity. In in vitro studies, we have shown that eosinophil adhesion via neuronal ICAM-1 leads to activation of neuronal NF-kappaB via an ERK1/2-dependent pathway. In this study, we tested the hypothesis that eosinophil adhesion to nerves promotes neural survival by protection from inflammation-associated apoptosis. Exposure of differentiated IMR-32 cholinergic nerve cells to IL-1beta, TNF-alpha, and IFN-gamma, or culture in serum-deprived medium, induced neuronal apoptosis, as detected by annexin V staining, caspase-3 activation, and DNA laddering. Addition of human eosinophils to IMR-32 nerve cells completely prevented all these features of apoptosis. The mechanism of protection by eosinophils was by an adhesion-dependent activation of ERK1/2, which led to the induced expression of the antiapoptotic gene bfl-1. Adhesion to nerve cells did not influence the expression of the related genes bax and bad. Thus, prevention of apoptosis by eosinophils may be a mechanism by which these cells regulate neural plasticity in the peripheral nervous system.

Oxidative stress attenuates Fas-mediated apoptosis in Jurkat T cell line through Bfl-1 induction

Many types of mammalian cells produce ROS in response to many different stimuli to modulate a number of cellular functions, including apoptosis. However, the correlation between ROS and apoptosis remains controversial, and the mechanisms whereby ROS-induced signals are propagated to critical downstream targets remain largely undefined. Here, we demonstrate that hydrogen peroxide (H2O2) upregulates the expression of Bfl-1, an antiapoptotic member of the Bcl-2 family, and that this is responsible for the antiapoptotic activity of ROS. When Jurkat, human leukemic T cells, were pretreated with 100 microM H2O2 and then treated with anti-Fas antibody, apoptosis was impaired without change of cell surface Fas expression. An investigation of the expression patterns of Bcl-2 family genes revealed that H2O2 treatment induced Bfl-1 gene expression, but left other genes unchanged, and this Bfl-1 expression and H2O2 -induced antiapoptotic effect was inhibited by antioxidants or NF-kappaB inhibitor. In addition, an electromobility shift assay revealed that the p65/p50 subunits of NF-kappaB activated by H2O2 bound to a bfl-1 promoter. Neither the induction of Bfl-1 nor the antiapoptotic effect of H2O2 was detected in Bfl-1-knockdown Jurkat cell line containing Bfl-1 antisense (Bfl-1AS). These data indicate that oxidative stress induces the expression of Bfl-1 via NF-kappaB activation, and this early-response gene protects cells from Fas-mediated apoptosis. This may be a cellular survival mechanism of cells exposed to phagocytes-derived ROS.

Gonococcal porin IB activates NF-kappaB in human urethral epithelium and increases the expression of host antiapoptotic factors

Infection of human urethral epithelial cells (UECs) with Neisseria gonorrhoeae increases the transcription of several host antiapoptotic genes, including bfl-1, cox-2, and c-IAP-2. In order to identify the bacterial factor(s) responsible for eliciting these changes, the transcriptional status of apoptotic machinery was monitored in UECs challenged with certain gonococcal membrane components. Initially, we observed that infection of UECs with gentamicin-killed gonococci increased the expression of the antiapoptotic Bcl-2 family member, bfl-1. This observation indicated that viable, replicating bacteria are not required for induction of antiapoptotic gene expression. Confirming this observation, treatment of UECs with purified gonococcal membrane increased the expression of bfl-1, cox-2, and c-IAP-2. This finding suggested that a factor or multiple factors present in the outer membrane (OM) are responsible for altering UEC antiapoptotic gene expression. Interestingly, treatment of UECs with gonococcal porin IB (PorB IB), a major constituent of the OM, significantly increased the transcription of bfl-1, cox-2, and c-IAP-2. The upregulation of these genes by PorB IB was determined to be dependent on NF-kappaB activation, as inhibiting NF-kappaB blocked induced expression of these genes. This work demonstrates the altered expression of host apoptotic factors in response to gonococcal PorB IB and supports a model whereby UEC cell death may be modulated as a potential mechanism of bacterial survival and proliferation.

p38alpha, but not p38beta, inhibits the phosphorylation and presence of c-FLIPS in DISC to potentiate Fas-mediated caspase-8 activation and type I apoptotic signaling

Pharmacological inhibitors of JNK (SP600125) and p38 (PD169316) sensitize tumor cells to Fas-mediated apoptosis. PD169316 is less potent than SP600125 and diminishes its effect when present together. Because the p38 isoforms that promote (p38alpha) or inhibit (p38beta) apoptosis are both suppressed by PD169316, we investigated their regulatory involvement in Fas-signaling. We report here, that p38alpha, but not p38beta, exerts its proapoptotic effect by inhibiting the phosphorylation and presence of c-FLIPS, but not c-FLIPL, in the DISC to promote caspase-8 activation and type I signaling in Fas-activated Jurkat cells. Its effect was enhanced by enforced expression of Flag-tagged p38alpha and was attenuated by its inactive mutant (p38alpha-AGF) or by translational silencing. By contrast, type II signaling was facilitated by p38alpha-dependent mitochondrial presence of tBid and inhibition of Bcl-2 (Ser70) phosphorylation as well as by p38alpha/beta-dependent mitochondrial localization of Bax and inhibition of phosphorylation of Bad (Ser112/Ser155). Potentiation of Fas-mediated apoptosis by the inhibition of JNK1/2 correlated with the loss of Bad (Ser136) phosphorylation and was dependent on the stimulatory effect of p38alpha on DISC and the downstream effects of both p38alpha and p38beta. These data underscore the need to reassess the findings obtained with pan-p38 inhibitors and suggest that activation of p38alpha coupled with targeted inhibition of p38beta and JNK1/2 should optimally sensitize tumor cells to Fas-mediated apoptosis.

Defying death: the hepatocyte's survival kit

Acute liver injury can develop as a consequence of viral hepatitis, drug- or toxin-induced toxicity or rejection after liver transplantation, whereas chronic liver injury can be due to long-term exposure to alcohol, chemicals, chronic viral hepatitis, metabolic or cholestatic disorders. During liver injury, liver cells are exposed to increased levels of cytokines, bile acids and oxidative stress. This results in death of hepatocytes. In contrast, stellate cells become active and are resistant against cell death. Eventually, acute and chronic liver injury is followed by loss of liver function for which no effective therapies are available. Hepatocytes are well equipped with protective mechanisms to prevent cell death. As long as these protective mechanisms can be activated, the balance will be in favour of cell survival. However, the balance between cell survival and cell death is delicate and can be easily tipped towards cell death during liver injury. Therefore understanding the cellular mechanisms controlling death of liver cells is of clinical and scientific importance and can lead to the identification of novel intervention targets. This review describes some of the mechanisms that determine the balance between cell death and cell survival during liver diseases. The strict regulation of apoptotic cell death allows therapeutic intervention strategies. In this light, receptor-mediated apoptosis and mitochondria-mediated cell death are discussed and strategies are provided to selectively interfere with these processes.

The Transcriptional Activation Program of Human Neutrophils in Skin Lesions Supports Their Important Role in Wound Healing

To investigate the cellular fate and function of polymorphonuclear neutrophilic granulocytes (PMNs) attracted to skin wounds, we used a human skin-wounding model and microarray technology to define differentially expressed genes in PMNs from peripheral blood, and PMNs that had transmigrated to skin lesions. After migration to skin lesions, PMNs demonstrated a significant transcriptional response including genes from several different functional categories. The up-regulation of anti-apoptotic genes concomitant with the down-regulation of proapoptotic genes suggested a transient anti-apoptotic priming of PMNs. Among the up-regulated genes were cytokines and chemokines critical for chemotaxis of macrophages, T cells, and PMNs, and for the modulation of their inflammatory responses. PMNs in skin lesions down-regulated receptors mediating chemotaxis and anti-microbial activity, but up-regulated other receptors involved in inflammatory responses. These findings indicate a change of responsiveness to chemotactic and immunoregulatory mediators once PMNs have migrated to skin lesions and have been activated. Other effects of the up-regulated cytokines/chemokines/enzymes were critical for wound healing. These included the breakdown of fibrin clots and degradation of extracellular matrix, the promotion of angiogenesis, the migration and proliferation of keratinocytes and fibroblasts, the adhesion of keratinocytes to the dermal layer, and finally, the induction of anti-microbial gene expression in keratinocytes. Notably, the up-regulation of genes, which activate lysosomal proteases, indicate a priming of skin lesion-PMNs for degradation of phagocytosed material. These findings demonstrate that migration of PMNs to skin lesions induces a transcriptional activation program, which regulates cellular fate and function, and promotes wound healing.

The Bcl-2 family member Bfl-1/A1 is strongly repressed in normal and malignant plasma cells but is a potent anti-apoptotic factor for myeloma cells

Terminal B-cell differentiation is a multi-step process, from short-lived plasmablasts to mature long-lived plasma cells (PC). The anti-apoptotic Bcl-2 family member Bfl-1/A1 plays a critical role in the survival of mature B cells. However, its potential involvement at the later stages of B-cell development remains highly controversial. Our aim was thus to clarify the place of Bfl-1/A1 in the biology of normal PC and in the pathogenesis of multiple myeloma (MM), the major PC dyscrasia. Using gene expression profiling and quantifiable reverse transcription polymerase chain reaction experiments, we found a similar down-regulation of Bfl-1/A1 in both normal immature plasmablasts and mature PC when compared with B cells. In myeloma cells, the level of Bfl-1/A1 was low and Bfl-1/A1 was not a nuclear factor kappaB-inducible gene. Collectively, these data demonstrate that Bfl-1/A1 is not involved in the prolonged survival of normal mature PC, and that Bfl-1/A1 deregulation is not a common oncogenic event in MM. However, overexpression of Bfl-1/A1 by retroviral transduction promoted autonomous survival of an interleukin-6-dependent myeloma cell line and rendered it less sensitive to dexamethasone. Thus, Bfl-1/A1 transduction could be an interesting tool to obtain myeloma cell lines from primary samples and to favour the in vitro generation of antibody-secreting, long-lived normal PC.

Effects of BAK gene over-expression on apoptosis in gastric cancer cells and its molecular mechanisms

AIM: To explore the apoptosis-inducing effects of extrinsic BAK gene transfer and its over-expression on gastric cancer cells and its molecular mechanisms.

METHODS: The eukaryotic expression for BAK gene was constructed and transferred into gastric cancer MKN-45 cell line. After being transferred for 1 to 5 d, cellular BAK gene expression was detected by RT-PCR and Western blotting methods. The growth activities of cancer cells were detected by cell count and MTT colorimetry. Cell cycle changes were assayed by flow cytometry. Cellular apoptosis was assayed by electronic microscopy and in situ terminally labeled transferase technique (TUNEL). Cellular caspase-3 activities were observed by colorimetric method.

RESULTS: After being transferred for 1 to 5 d, cellular BAK mRNA and protein expression levels were significantly increased (P < 0.01). In vitro growth of gastric cancer cells was inhibited by 11.6-35.3% (P < 0.01). The cellular proliferation activities were decreased by 10.2-32.4% (P < 0.01), with cell cycle being blocked at G0/G1 phase. Partial cancer cells presented the characteristic morphological changes of apoptosis, with the apoptotic rates being 21.4% (P < 0.01). The cellular caspase-3 activities were enhanced by 4.45 times (P < 0.01).

CONCLUSION: Transfection of extrinsic BAK gene, resulting in its over-expression, can significantly induce apoptosis of gastric cancer MKN-45 cells through activating caspase-3, which is a potential strategy for gene therapy of gastric cancer.

Comparison of mammary gland involution between 129S1 and C57BL/6 inbred mouse strains: differential regulation of Bcl2a1, Trp53, Cebpb, and Cebpd expression

Genetic engineering has made the mouse an invaluable tool to address the function of individual genes in a targeted manner. Over the last decade it has become apparent that the genetic mouse strain background can significantly influence the phenotype of an engineered mouse. Therefore, it is essential to characterize the biology of the different wild-type background strains. In this study, we have compared mouse mammary gland involution in the 129S1 and C57BL/6 inbred strains and report significant differences at the molecular level with differential expression of Bcl2a1 (Bfl1), Trp53 (p53), Cebpb (C/EBP beta), and Cebpd (C/EBP delta). The C57BL/6 strain exhibits dynamic responses with induction of Trp53 and Cebpd and concomitant downregulation of Bcl2a1 during the first phase of involution. In contrast, expression of these genes does not change significantly in 129S1 mice. During the second phase, C57BL/6 glands contain more Cebpb than 129S1 glands. Nevertheless, involution proceeds morphologically with similar kinetics in both strains. The data demonstrate that the genetic response of mammary tissue varies significantly between 129S1 and C57BL/6. These results may provide a basis for the interpretation of strain-specific phenotypes in engineered mice and underline the importance of pure strains for large-scale expression studies with mutant mice.

The role of Bcl-2 family members in tumorigenesis

The Bcl-2 family consists of about 20 homologues of important pro- and anti-apoptotic regulators of programmed cell death. The established mode of function of the individual members is to either preserve or disturb mitochondrial integrity, thereby inducing or preventing release of apoptogenic factors like Cytochrome c (Cyt c) from mitochondria. Recent findings also indicate further Bcl-2-controlled mitochondria-independent apoptosis pathways. Bcl-2 represents the founding member of the new and growing class of cell death inhibiting oncoproteins. In this review, we try to briefly summarize current models of Bcl-2 family function and to outline the work demonstrating the influence of deregulated Bcl-2 family member expression on tumorigenesis and cancer therapy. Since several Bcl-2 homologues, in addition to influencing apoptotic behaviour, also impinge on cell cycle progression, we discuss possible implications of this additional role for the expression of Bcl-2 family members in tumor cells.

Estrogen stimulates microglia and brain recovery from hypoxia-ischemia in normoglycemic but not diabetic female mice

Diabetic hyperglycemia increases ischemic brain damage in experimental animals and humans. The mechanisms are unclear but may involve enhanced apoptosis in penumbral regions. Estrogen is an established neuroprotectant in experimental stroke. Our previous study demonstrated that female diabetic db/db mice suffered less damage following cerebral hypoxia-ischemia (H/I) than male db/db mice. Here we investigated the effects of diabetes and estrogen apoptotic gene expression following H/I. Female db/db and nondiabetic (+/?) mice were ovariectomized (OVX) and treated with estrogen or vehicle prior to H/I; brains were analyzed for damage and bcl-2 family gene expression. OVX increased ischemic damage in +/? mice; estrogen reduced tissue injury and enhanced antiapoptotic gene expression (bcl-2 and bfl-1). db/db mice demonstrated more damage, without increased bcl-2 mRNA; bfl-1 expression appeared at 48 hours of recovery associated with infarction. To our knowledge, this is the first description of bfl-1 in the brain with localization to microglia and macrophages. Early induction of bfl-1 expression in +/? mouse brain was associated with microglia; delayed bfl-1 expression in diabetic brain was in macrophages bordering the infarct. Furthermore, estrogen replacement stimulated early postischemic expression of bcl-2 and bfl-1 and reduced damage in normoglycemic animals but failed to protect the diabetic brain.

Estrogen stimulates microglia and brain recovery from hypoxia-ischemia in normoglycemic but not diabetic female mice

Diabetic hyperglycemia increases ischemic brain damage in experimental animals and humans. The mechanisms are unclear but may involve enhanced apoptosis in penumbral regions. Estrogen is an established neuroprotectant in experimental stroke. Our previous study demonstrated that female diabetic db/db mice suffered less damage following cerebral hypoxia-ischemia (H/I) than male db/db mice. Here we investigated the effects of diabetes and estrogen apoptotic gene expression following H/I. Female db/db and nondiabetic (+/?) mice were ovariectomized (OVX) and treated with estrogen or vehicle prior to H/I; brains were analyzed for damage and bcl-2 family gene expression. OVX increased ischemic damage in +/? mice; estrogen reduced tissue injury and enhanced antiapoptotic gene expression (bcl-2 and bfl-1). db/db mice demonstrated more damage, without increased bcl-2 mRNA; bfl-1 expression appeared at 48 hours of recovery associated with infarction. To our knowledge, this is the first description of bfl-1 in the brain with localization to microglia and macrophages. Early induction of bfl-1 expression in +/? mouse brain was associated with microglia; delayed bfl-1 expression in diabetic brain was in macrophages bordering the infarct. Furthermore, estrogen replacement stimulated early postischemic expression of bcl-2 and bfl-1 and reduced damage in normoglycemic animals but failed to protect the diabetic brain.

tBid forms a pore in the liposome membrane

We investigated the ability of tBid (truncated form of Bid) to bind and permeabilize the liposomes (large unilamellar vesicles, LUVs) and release fluorescent marker molecules (fluorescein-isothiocyanate-conjugated dextrans, FITC-dextrans) of various molecular diameters (FD-20, FD-70, FD-250S) from LUVs. Obtained data showed that tBid was more efficient in promoting leakage of FITC-dextrans from LUVs composed of cardiolipin and dioleoylphosphatidylcholine (DOPC) than LUVs made of dioleoylphosphatidic acid or dioleoylphosphatidylglycerol and DOPC. The leakage efficiency was reduced with increasing amount of dioleoylphosphatidylethanolamine or dielaidoylphosphatidylethanolamine. Phospholipid monolayer assay and fluorescence quenching measurements revealed that tBid inserted deeply into the hydrophobic acyl chain of acidic phospholipids. Taking into account the tBid three-dimensional structure, we propose that tBid could penetrate into the hydrophobic core of membrane, resulting in the leakage of entrapped content from LUVs via a pore-forming mechanism.

A dominant role of Toll-like receptor 4 in the signaling of apoptosis in bacteria-faced macrophages

Conserved bacterial components potently activate host immune cells through transmembrane Toll-like receptors (TLRs), which trigger a protective immune response but also may signal apoptosis. In this study, we investigated the roles of TLR2 and TLR4 as inducers of apoptosis in Yersinia enterocolitica-infected macrophages. Yersiniae suppress activation of the antiapoptotic NF-kappaB signaling pathway in host cells by inhibiting inhibitory kappaB kinase-beta. This leads to macrophage apoptosis under infection conditions. Experiments with mouse macrophages deficient for TLR2, TLR4, or both receptors showed that, although yersiniae could activate signaling through both TLR2 and TLR4, loss of TLR4 solely diminished Yersinia-induced apoptosis. This suggests implication of TLR4, but not of TLR2, as a proapoptotic signal transducer in Yersinia-conferred cell death. In the same manner, agonist-specific activation of TLR4 efficiently mediated macrophage apoptosis in the presence of the proteasome inhibitor MG-132, an effect that was less pronounced for activation through TLR2. Furthermore, the extended stimulation of overexpressed TLR4 elicited cellular death in epithelial cells. A dominant-negative mutant of Fas-associated death domain protein could suppress TLR4-mediated cell death, which indicates that TLR4 may signal apoptosis through a Fas-associated death domain protein-dependent pathway. Together, these data show that TLR4 could act as a potent inducer of apoptosis in macrophages that encounter a bacterial pathogen.

TRAIL and NFkappaB signaling--a complex relationship

Tumor necrosis factor (TNF)-related apoptosis-inducing ligand (TRAIL) or Apo2L is a ligand of the TNF family interacting with five different receptors of the TNF receptor superfamily, including two death receptors. It has attracted wide interest as a potential anticancer therapy because some recombinant soluble forms of TRAIL induce cell death predominantly in transformed cells. The nuclear factor-kappaB (NFkappaB)?Rel family of proteins are composed of a group of dimeric transcription factors that have an outstanding role in the regulation of inflammation and immunity. Control of transcription by NFkappaB proteins can be of relevance to the function of TRAIL in three ways. First, induction of antiapoptotic NFkappaB dependent genes critically determines cellular susceptibility toward apoptosis induction by TRAIL-R1, TRAIL-R2, and other death receptors. Each of the multiple of known NFkappaB inducers therefore has the potential to interfere with TRAIL-induced cell death. Second, TRAIL and some of its receptors are inducible by NFkappaB, disclosing the possibility of autoamplifying TRAIL signaling loops. Third, the TRAIL death receptors can activate the NFkappaB pathway. This chapter summarizes basic knowledge regarding the understanding of the NFkappaB pathway and focuses on its multiple roles in TRAIL signaling.

TRAIL induces apoptosis of chondrocytes and influences the pathogenesis of experimentally induced rat osteoarthritis

OBJECTIVE

To investigate whether TRAIL influences the pathogenesis of osteoarthritis (OA).

METHODS

A recombinant adenoviral vector system (Ad-TRAIL) was used. Expression of TRAIL in a rat chondrocyte cell line (RCJ3.1C.18) and alterations in the expression of death and decoy receptors after Ad-TRAIL infection were measured by Western blot assay. To explore the underlying mechanism, Western blot assays (to detect caspase 8, poly[ADP-ribose] polymerase [PARP], and caspase 3 activation), mitochondrial membrane potential (DeltaPsim) measurement, Hoechst staining, and DNA electrophoresis were conducted. Next, expression of TRAIL and death and decoy receptors was examined by immunochemistry in primary cultured chondrocytes and on cartilage obtained from rats with experimentally induced OA.

RESULTS

Ad-TRAIL infection induced expression of TRAIL in RCJ3.1C.18 cells, increased expression of death receptor 4 (DR4), and decreased expression of DR5 and decoy receptor 1 (DcR1). Ad-TRAIL, at doses of 10 and 100 multiplicities of infection, decreased the viability of chondrocytes 4 days after infection. Reduction of DeltaPsim, cytochrome c release, nuclear condensation, activation of caspase 3 and PARP, and DNA fragmentation proved the induction of apoptosis. Activation of caspase 8 was also observed. Ad-TRAIL also induced apoptosis in primary cultured chondrocytes, in which alterations in expression of TRAIL and death receptors were similar to those observed in RCJ3.1C.18 cells. Cartilage obtained from rats with experimentally induced OA showed increased expression of TRAIL and DR4 and decreased expression of DR5 and DcR1 compared with control cartilage.

CONCLUSION

TRAIL induces chondrocyte apoptosis, and TRAIL-induced chondrocyte apoptosis may play a role in the pathogenesis of OA.

Multiple and synergistic deregulations of apoptosis-controlling genes in pancreatic carcinoma cells

Inability to die by apoptosis is one of the reasons for the deregulated growth of tumour cells and the frequently observed failure of chemotherapy. In this study we thought to identify the common and functionally important characteristics responsible for the apoptosis resistance of pancreatic tumour cells. We analysed cell surface expression level of death receptors CD95 and TRAIL-R1-4 as well as the expression profile of sixteen apoptosis-relevant proteins in five pancreatic carcinoma cell lines Capan1, Colo357, PancTuI, Panc89 and Panc1. These data were evaluated in the context of sensitivity towards anti-CD95 and TRAIL-mediated apoptosis. Here we report that except for resistant Panc1 cells, which only marginally expressed CD95, all other cell lines showed comparable levels of CD95 and TRAIL receptors irrespectively of their apoptotic phenotype. Interestingly, we found that the elevated expression of FLIP, Bcl-x_L and IAP in parallel with a downregulation of FADD and Bid was common for the resistant cell lines. Consequently, stable overexpression of XIAP, Bcl-x_L or dominant negative FADD in sensitive cells significantly reduced the death receptor mediated apoptosis while the overexpression of Bid rendered the resistant cells sensitive.

Conversion of Bfl-1, an anti-apoptotic Bcl-2 family protein, to a potent pro-apoptotic protein by fusion with green fluorescent protein (GFP)

Human Bfl-1 is an anti-apoptotic Bcl-2 family member. Here, we found that Bfl-1 was converted into a potent death-promoting protein by green fluorescent protein (GFP) fusion with its N-terminus. The transient expression of GFP-Bfl-1 induced cytochrome c release and triggered apoptosis in 293T cells, which depended on the mitochondrial localization of GFP-Bfl-1. Apoptosis induced by GFP-Bfl-1 was significantly blocked by the pan-caspase inhibitor carbobenzoxy-Val-Ala-Asp-fluoromethyl ketone, but was not blocked by either Bcl-xL or Bfl-1. Our findings provide a useful model for understanding the structural basis of Bcl-2 family proteins that act in an opposite way despite sharing structural similarity between anti-apoptotic and pro-apoptotic proteins.

A1/Bfl-1 expression is restricted to TCR engagement in T lymphocytes

We analyzed regulation of the prosurvival Bcl-2 homologue A1, following T-cell receptor (TCR) or cytokine receptor engagement. Activation of CD4(+) or CD8(+) T cells by antigenic peptides induced an early but transient IL-2-independent expression of A1 and Bcl-xl mRNA and proteins, whereas expression of Bcl-2 was delayed and required IL-2. Cytokines such as IL-2, IL-4, IL-7 or IL-15 prevented apoptosis of activated T cells that effect being associated with the maintenance of Bcl-2, but not of A1 expression. However, restimulation of activated or posteffector T cells with antigenic peptide strongly upregulated A1 mRNA and maintained A1 protein expression. IL-4, IL-7 or IL-15 also prevented cell death of naive T cells. In those cells, cytokines upregulated Bcl-2, but not A1 expression. Therefore, in naive, activated and posteffector T cells, expression of A1 is dependent on TCR but not on cytokine receptor engagement, indicating that A1 is differently regulated from Bcl-xl and Bcl-2.

Infection of human urethral epithelium with Neisseria gonorrhoeae elicits an upregulation of host anti-apoptotic factors and protects cells from staurosporine-induced apoptosis

In order to better understand the host response to an infection with Neisseria gonorrhoeae, microarray technology was used to analyse the gene expression profile between uninfected and infected human urethral epithelium. The anti-apoptotic genes bfl-1, cox-2 and c-IAP-2 were identified to be upregulated approximately eight-, four- or twofold, respectively, following infection. Subsequent assays including RT-PCR, real time RT-PCR and RNase protection confirmed the increased expression of these apoptotic regulators, and identified that a fourth anti-apoptotic factor, mcl-1, is also upregulated. RT-PCR and RNase protection also showed that key pro-apoptotic factors including bax, bad and bak do not change in expression. Furthermore, our studies demonstrated that infection with the gonococcus partially protects urethral epithelium from apoptosis induced by the protein kinase inhibitor, staurosporine (STS). This work shows that following infection with Neisseria gonorrhoeae, several host anti-apoptotic factors are upregulated. In addition, a gonococcal infection protects host cells from subsequent STS-induced death. The regulation of host cell death by the gonococcus may represent a mechanism employed by this pathogen to survive and proliferate in host epithelium.

Overexpression of the transgene for manganese superoxide dismutase (MnSOD) in 32D cl 3 cells prevents apoptosis induction by TNF-alpha, IL-3 withdrawal, and ionizing radiation

OBJECTIVE

Stabilization of the mitochondria in IL-3-dependent hematopoietic progenitor cell line 32D cl 3 by overexpression of the transgene for manganese superoxide dismutase (MnSOD) prior to ionizing radiation prevents apoptosis. We now demonstrate that overexpression of the MnSOD transgene also protects 32D cl 3 cells from apoptosis caused by exposure to tumor necrosis factor-alpha (TNF-alpha) or withdrawal of interleukin (IL)-3.

MATERIALS AND METHODS

The hematopoietic progenitor cell line, 32D cl 3, and subclones overexpressing the human MnSOD transgene, 1F2 or 2C6, were radiated to 1000 cGy or were exposed to TNF-alpha (0 to 100 etag/mL) or were subjected to IL-3 withdrawal. The cells were then examined at several time points for DNA strand breaks using a comet assay, depolarization of the mitochondrial membrane, activation of caspase-3, PARP cleavage, and apoptosis, and also for changes in cell cycle distribution.

RESULTS

Overexpression of the transgene for MnSOD resulted in increased survival following exposure to radiation, exposure to TNF-alpha, or IL-3 withdrawal. The cell lines overexpressing MnSOD (1F2 or 2C6) displayed decreased radiation-induced, TNF-alpha-induced, or IL-3 withdrawal-induced mitochondrial membrane permeability, caspase-3 and PARP activation, and apoptosis.

CONCLUSIONS

Overexpression of the human MnSOD transgene in 32D cl 3 cells results in stabilization of the mitochondria and reduction in radiation-, TNF-alpha-, or IL-3 withdrawal-induced damage. Thus, MnSOD stabilization of the mitochondrial membrane is relevant to reduction of apoptosis by several classes of oxidative stress inducers.

Bfl-1S, a novel alternative splice variant of Bfl-1, localizes in the nucleus via its C-terminus and prevents cell death

Bfl-1 is an antiapoptotic Bcl-2 family member and a mouse A1 homologue. The mouse A1 has been reported to have three isoforms, but little is known about human Bfl-1. By reverse-transcriptase polymerase chain reaction analysis, we have identified Bfl-1S (short form), an alternative splice variant of Bfl-1. The Bfl-1S primary sequence contains four conserved Bcl-2 homology (BH) domains and a positive-charged C-terminus containing KKRK amino acids. The expression of Bfl-1S mRNA was detected predominantly in normal lymph nodes and in B-lymphoid leukemia cells. Confocal microscopic analysis using green fluorescence protein fusion proteins demonstrated that Bfl-1S is localized in the nucleus by its C-terminus as an intrinsic nuclear localization sequence. Bfl-1S acts as an antiapoptotic agent in coexpression experiments with Bax, a proapoptotic molecule. The expression of Bfl-1S provided significant resistance against staurosporine (STS) treatments in Molt-4 human T-leukemia cells. Bfl-1S also significantly inhibited the cleavage of Bid, and of caspases 3 and 8 against STS treatment. These results indicate that Bfl-1S is a novel human Bcl-2 family member that possesses antiapoptotic function.

Induction of hepatocyte proliferation and death by modulation of T-Antigen expression

Mice expressing SV40 T-Antigen in liver under control of the phosphoenolpyruvate carboxykinase promoter were generated. By altering the carbohydrate content of the diet, TAg expression, the rate of hepatocyte proliferation and apoptosis, and hence hepatocarcinogenesis, could be regulated. Carbohydrate-mediated suppression of TAg resulted in slow hepatic growth that progressed to focal hepatocellular carcinoma (HCC) after a long latency period. In contrast, induction of TAg by feeding mice a low carbohydrate diet resulted in massive hepatomegaly that progressed rapidly to diffuse multifocal HCC. Hepatic TAg expression could be efficiently repressed by switching mice from the low to the high-carbohydrate diet, which if instigated prior to the development of HCC, resulted in rapid regression through a p53-independent reduction in hepatocyte proliferation and an increase in hepatocyte apoptosis. Although liver growth was accompanied by compensatory hepatocyte apoptosis, an apoptotic deficit developed following chronic exposure to high levels of TAg. This was associated with Akt phosphorylation and increased expression of the antiapoptotic molecules bfl-1/A1, TIAP, and A20. Mice were resistant to Fas-induced hepatocellular apoptosis due to severely impaired caspase activation and failed activation of the mitochondrial amplification loop. This model will be useful to investigate oncogene-mediated disruption of the cell cycle and apoptosis, and to determine which processes constitute fixed, or reversible aspects of the tumorigenic process.

Apoptosis or growth arrest: modulation of the cellular response to p53 by proliferative signals

Activation of the tumor suppressor p53 after genotoxic insults may result in two different responses: growth arrest or apoptosis. In this study, we analysed how mitogenic stimulation of primary mouse lymphocytes influences p53 signaling upon gamma-irradiation. We found that G(0) lymphocytes rapidly went into p53-dependent apoptosis, whereas stimulated lymphocytes went into a p53-dependent, p21-mediated growth arrest. The switch in p53 response upon stimulation did neither result from a switch in transcriptional activation of major p53 target genes, nor from the high level of p21 expressed in stimulated, irradiated cells. Growth stimulation, however, led to the upregulation of the antiapoptotic factors Bcl-x(L) and Bfl-1. In resting cells, p53 induced apoptosis after gamma-irradiation was accompanied by a breakdown of the mitochondrial membrane potential (psi(m)) that was counteracted by growth stimulation. We propose that growth stimulation intercepted p53 proapoptotic signaling at the level of mitochondrial integrity, most likely by upregulating the antiapoptotic factors Bcl-x(L) and Bfl-1. Upregulation of Bcl-x(L) and of Bfl-1 upon growth stimulation was mediated by the PKC-dependent activation of NF-kappaB. Consequently, blocking PKC activity restored apoptosis in stimulated, irradiated splenocytes. The inherent coupling of growth stimulation with antiapoptotic signaling in primary lymphocytes might provide hints as to how precancerous lymphocytes bypass the need for mutational inactivation of p53. Thus, our findings might explain the relatively low frequency of p53 mutations in lymphomas in comparison to other tumor entities.

Inhibition of glucocorticoid-induced apoptosis in 697 pre-B lymphocytes by the mineralocorticoid receptor N-terminal domain

The glucocorticoid and mineralocorticoid receptors (GR and MR) share considerable structural and functional homology and bind as homodimers to hormone-response elements. We have shown previously that MR and GR can form heterodimers that inhibit transcription from a glucocorticoid (GC)-responsive gene and that this inhibition was mediated by the N-terminal domain (NTD) of MR. In this report, we examined the effect of NTD-MR on GC-induced apoptosis in the GC-sensitive pre-B lymphoma cell line, 697. In GC-treated 697 cells, we demonstrated that stable expression of NTD-MR blocks apoptosis and inhibits proteolytic processing of pro-caspases-3, -8, and -9 and poly(ADP-ribose) polymerase. Importantly, gel shift and immunoprecipitation analyses revealed a direct association between the GR and amino acids 203-603 of NTD-MR. We observed down-regulation of c-Myc and of the anti-apoptotic proteins Bcl-2 and Bfl-1 as well as high levels of the pro-apoptotic proteins Bax and Bid. Conversely, cells stably expressing NTD-MR exhibited increased expression of Bcl-2 and Bfl-1 and diminished levels of Bid and Bax. These data provide a potential mechanism for the observed inhibition of cytochrome c and Smac release from the mitochondria of NTD-MR cells and resultant resistance to GC-induced apoptosis. Thus, NTD-MR may mediate GC effects through heterodimerization with GR and ensuing inhibition of GC-regulated gene transcription.

TRAIL receptor and CD95 signal to mitochondria via FADD, caspase-8/10, Bid, and Bax but differentially regulate events downstream from truncated Bid

The death receptor ligand TRAIL arouses much interest for clinical application. We found that TRAIL receptor could induce cytochrome c (Cyt c) release from mitochondria in cells that failed to respond to CD95. Therefore, we examined whether these two closely related death receptors use different intermediates to convey the apoptotic signal to mitochondria. Dominant negative FADD, FLIP(L), or a Bid mutant lacking cleavage sites for caspase-8/10 completely inhibited Cyt c release in response to either receptor. Depletion of Bid from TRAIL- or CD95-activated cytosols blocked their capacity to mediate Cyt c release from mitochondria in vitro, whereas Bax depletion reduced it. We conclude that FADD, caspase-8/10, and caspase-cleaved Bid are required for TRAIL receptor and CD95 signaling to mitochondria, whereas Bax is a common accessory. In vitro, caspase-8 treatment of cytosol from CD95-resistant cells permitted generation of truncated Bid and its association with mitochondria. However, this cytosol impaired the ability of truncated Bid to liberate Cyt c from exogenous mitochondria. We conclude that the TRAIL receptor can bypass or neutralize the activity of cytosolic factor that blocks truncated Bid function. This may benefit the capacity of TRAIL to break apoptosis resistance in tumor cells.

BH3 domains: intracellular death-ligands critical for initiating apoptosis

Recent studies have clarified how the BH3 domain, a short peptide motif found in certain BCL-2 family proteins, triggers key mitochondrial events associated with apoptosis.