Active caspase-8 translocates into the nucleus of apoptotic cells to inactivate poly(ADP-ribose) polymerase-2

pADP-ribosylation regulates the cytoplasmic localization, cleavage, and pro-apoptotic function of HuR

HuR (ElavL1) is one of the main post-transcriptional regulators that determines cell fate. Although the role of HuR in apoptosis is well established, the post-translational modifications that govern this function remain elusive. In this study, we show that PARP1/2-mediated poly(ADP)-ribosylation (PARylation) is instrumental in the pro-apoptotic function of HuR. During apoptosis, a substantial reduction in HuR PARylation is observed. This results in the cytoplasmic accumulation and the cleavage of HuR, both of which are essential events for apoptosis. These effects are mediated by a pADP-ribose-binding motif within the HuR-HNS region (HuR PAR-binding site). Under normal conditions, the association of the HuR PAR-binding site with pADP-ribose is responsible for the nuclear retention of HuR. Mutations within this motif prevent the binding of HuR to its import factor TRN2, leading to its cytoplasmic accumulation and cleavage. Collectively, our findings underscore the role of PARylation in controlling the pro-apoptotic function of HuR, offering insight into the mechanism by which PARP1/2 enzymes regulate cell fate and adaptation to various assaults.

Specific and shared biological functions of PARP2 - is PARP2 really a lil' brother of PARP1?

PARP2, that belongs to the family of ADP-ribosyl transferase enzymes (ART), is a discovery of the millennium, as it was identified in 1999. Although PARP2 was described initially as a DNA repair factor, it is now evident that PARP2 partakes in the regulation or execution of multiple biological processes as inflammation, carcinogenesis and cancer progression, metabolism or oxidative stress-related diseases. Hereby, we review the involvement of PARP2 in these processes with the aim of understanding which processes are specific for PARP2, but not for other members of the ART family. A better understanding of the specific functions of PARP2 in all of these biological processes is crucial for the development of new PARP-centred selective therapies.

Acylated ghrelin protection inhibits apoptosis in the remote myocardium post-myocardial infarction by inhibiting calcineurin and activating ARC

This study investigated if acylated ghrelin (AG) could inhibit myocardial infarction (MI)-induced apoptosis in the left ventricles (LV) of male rats and tested if this protection involves modulating ARC anti-apoptotic protein. Rats (n = 12/group) were assigned as a sham-operated, a sham + AG (100 µg/kg, 2x/d, S.C.), MI, and MI + AG. With no antioxidant activity or expression of FAS, AG inhibited caspase-3, 8, and 9 and decreased cytosolic/mitochondrial levels of cytochrome-c, Bax, Bad, and Bad-BCL-2 complex in the LVs of the sham-operated and MI-treated rats. Concomitantly, AG preserved the mitochondria structure, decreased mtPTP, and enhanced state-3 respiration in the LVs of both treated groups. These effects were associated with increased mitochondrial levels of ARC and a reduction in the activity of calcineurin. Overall, AG suppresses MI-induced ventricular apoptosis by inhibition of calcineurin, activation of ARC, and preserving mitochondria integrity.

Polystyrene microplastics induce apoptosis in chicken testis via crosstalk between NF-κB and Nrf2 pathways

Microplastics (MPs) are a new type of pollutants that are widespread in nature, and their toxic effects on humans or animals are receiving attention. Birds are in a higher ecological niche in nature, and MPs may have potential bioaccumulation and biomagnification risks to birds. The mechanisms underlying the reproductive toxicity of MPs to birds are mainly unknown. To study the reproductive toxicity of MPs to birds, we randomly divided chickens into six groups and exposed polystyrene microplastics (PS-MPs) through drinking water (0, 1, and 100 mg/L) for 28 and 42 days. We found that PS-MPs caused testicular inflammatory infiltration and interstitial hemorrhage, resulting in testicular tissue damage; the expression of Claudin3 and Occludin in the blood-testis barrier (BTB) decreased and may damage the integrity of the BTB. PS-MPs exposure inhibited the expression of the Nrf2-Keap1 pathway, which in turn reduced HO-1 and NQO1, simultaneous GSH and T-AOC were also reduced, resulting in an imbalance of the redox system; in addition, the NF-κB signaling pathway was activated, increasing the expression of TNF-α, COX-2 and iNOS. Under redox system imbalance and inflammatory stress, exposure to PS-MPs led to decreased expression of Bcl-2 and increased Bax, cytc, caspase-8, and caspase-3, etc., activating apoptosis, and ultimately causing testicular damage. These results suggested that PS-MPs exposure led to an imbalance of the redox system and an inflammatory response, inducing both endogenous and exogenous apoptosis, resulting in testicular tissue damage. Our study provides a theoretical basis for reproductive injury mechanisms in chicken.

Clostridioides difficile toxin B alone and with pro-inflammatory cytokines induces apoptosis in enteric glial cells by activating three different signalling pathways mediated by caspases, calpains and cathepsin B

Clostridioides difficile infection (CDI) causes nosocomial/antibiotic-associated gastrointestinal diseases with dramatically increasing global incidence and mortality rates. The main C. difficile virulence factors, toxins A and B (TcdA/TcdB), cause cytopathic/cytotoxic effects and inflammation. We demonstrated that TcdB induces caspase-dependent, mitochondria-independent enteric glial cell (EGC) apoptosis that is enhanced by the pro-inflammatory cytokines TNF-α and IFN-γ (CKs) by increasing caspase-3/7/9 and PARP activation. Because this cytotoxic synergism is important for CDI pathogenesis, we investigated the apoptotic pathways involved in TcdB- and TcdB + CK-induced apoptosis indepth. EGCs were pre-treated with the inhibitors BAF or Q-VD-OPh (pan-caspase), Z-DEVD-fmk (caspase-3/7), Z-IETD-fmk (caspase-8), PD150606 (calpains), and CA-074Me (cathepsin B) 1 h before TcdB exposure, while CKs were given 1.5 h after TcdB exposure, and assays were performed at 24 h. TcdB and TcdB + CKs induced apoptosis through three signalling pathways activated by calpains, caspases and cathepsins, which all are involved both in induction and execution apoptotic signalling under both conditions but to different degrees in TcdB and TcdB + CKs especially as regards to signal transduction mediated by these proteases towards downstream effects (apoptosis). Calpain activation by Ca²⁺ influx is the first pro-apoptotic event in TcdB- and TcdB + CK-induced EGC apoptosis and causes caspase-3, caspase-7 and PARP activation. PARP is also directly activated by calpains which are responsible of about 75% of apoptosis in TcdB and 62% in TcdB + CK which is both effector caspase-dependent and -independent. Initiator caspase-8 activation mediated by TcdB contributes to caspase-3/caspase-7 and PARP activation and is responsible of about 28% of apoptosis in both conditions. Caspase-3/caspase-7 activation is weakly responsible of apoptosis, indeed we found that it mediates 27% of apoptosis only in TcdB. Cathepsin B contributes to triggering pro-apoptotic signal and is responsible in both conditions of about 35% of apoptosis by a caspase-independent manner, and seems to regulate the caspase-3 and caspase-7 cleaved fragment levels, highlighting the complex interaction between these cysteine protease families activated during TcdB-induced apoptosis. Further a relevant difference between TcdB- and TcdB + CK-induced apoptosis is that TcdB-induced apoptosis increased slowly reaching at 72 h the value of 18.7%, while TcdB + CK-induced apoptosis increased strongly reaching at 72 h the value of 60.6%. Apoptotic signalling activation by TcdB + CKs is enriched by TNF-α-induced NF-κB signalling, inhibition of JNK activation and activation of AKT. In conclusion, the ability of C. difficile to activate three apoptotic pathways represents an important strategy to overcome resistance against its cytotoxic activity.

Poly (ADP-ribose) polymerase: An Overview of Mechanistic Approaches and Therapeutic Opportunities in the Management of Stroke

Stroke is one of the leading causes of morbidity and mortality accompanied by blood supply loss to a particular brain area. Several mechanistic approaches such as inhibition of poly (ADP-ribose) polymerase, therapies against tissue thrombosis, and neutrophils lead to stroke's therapeutic intervention. Evidence obtained with the poly (ADP-ribose) polymerase (PARP) inhibition and animals having a deficiency of PARP enzymes; represented the role of PARP in cerebral stroke, ischemia/reperfusion, and neurotrauma. PARP is a nuclear enzyme superfamily with various isoforms, each with different structural domains and functions, and out of all, PARP-1 is the best-characterized member. It has been shown to perform multiple physiological as well as pathological processes, including its role in inflammation, oxidative stress, apoptosis, and mitochondrial dysfunction. The enzyme interacts with NF-κB, p53, and other transcriptional factors to regulate survival and cell death and modulates multiple downstream signaling pathways. Clinical trials have also been conducted using PARP inhibitors for numerous disorders and have shown positive results. However, additional information is yet to be established for the therapeutic intervention of PARP inhibitors in stroke. These agents' utilization appears to be challenging due to their unknown potential long-term side effects. PARP activity increased during ischemia, but its inhibition provided significant neuroprotection. Despite the increased interest in PARP as a pharmacological modulator for novel therapeutic therapies, the current review focused on stroke and poly ADP-ribosylation.

Predicted coronavirus Nsp5 protease cleavage sites in the human proteome

Background

The coronavirus nonstructural protein 5 (Nsp5) is a cysteine protease required for processing the viral polyprotein and is therefore crucial for viral replication. Nsp5 from several coronaviruses have also been found to cleave host proteins, disrupting molecular pathways involved in innate immunity. Nsp5 from the recently emerged SARS-CoV-2 virus interacts with and can cleave human proteins, which may be relevant to the pathogenesis of COVID-19. Based on the continuing global pandemic, and emerging understanding of coronavirus Nsp5-human protein interactions, we set out to predict what human proteins are cleaved by the coronavirus Nsp5 protease using a bioinformatics approach.

Results

Using a previously developed neural network trained on coronavirus Nsp5 cleavage sites (NetCorona), we made predictions of Nsp5 cleavage sites in all human proteins. Structures of human proteins in the Protein Data Bank containing a predicted Nsp5 cleavage site were then examined, generating a list of 92 human proteins with a highly predicted and accessible cleavage site. Of those, 48 are expected to be found in the same cellular compartment as Nsp5. Analysis of this targeted list of proteins revealed molecular pathways susceptible to Nsp5 cleavage and therefore relevant to coronavirus infection, including pathways involved in mRNA processing, cytokine response, cytoskeleton organization, and apoptosis.

Conclusions

This study combines predictions of Nsp5 cleavage sites in human proteins with protein structure information and protein network analysis. We predicted cleavage sites in proteins recently shown to be cleaved in vitro by SARS-CoV-2 Nsp5, and we discuss how other potentially cleaved proteins may be relevant to coronavirus mediated immune dysregulation. The data presented here will assist in the design of more targeted experiments, to determine the role of coronavirus Nsp5 cleavage of host proteins, which is relevant to understanding the molecular pathology of coronavirus infection.

Interleukin 1β Blockade Reduces Intestinal Inflammation in a Murine Model of Tumor Necrosis Factor-Independent Ulcerative Colitis

BACKGROUND & AIMS

Inflammatory bowel diseases are multifactorial diseases commonly treated with either immunomodulatory drugs or anti-tumor necrosis factor (TNF). Currently, failure to respond to anti-TNF therapy (assessed no earlier than 8-12 weeks after starting treatment) occurs in 20%-40% of patients enrolled in clinical trials and in 10%-20% in clinical practice. Murine models of inflammatory bowel disease provide important tools to better understand disease mechanism(s). In this context and among the numerous models available, Winnie-TNF-knockout (KO) mice recently were reported to show characteristics of ulcerative colitis (UC) that are independent of TNF, and with increased interleukin (IL)1β production.

METHODS

Herein, the efficacy of recombinant IL1-receptor antagonist (anakinra) administration was evaluated in Winnie-TNF-KO mice, used as a UC model of primary anti-TNF nonresponders.

RESULTS

We analyzed gut mucosal biopsy specimens and circulating cytokine profiles of a cohort of 30 UC patients; approximately 75% of primary nonresponders were characterized by abundant IL1β in both the serum and local intestinal tissues. In Winnie-TNF-KO mice, administration of anakinra efficiently reduced the histologic score of the distal colon, which represents the most common site of inflammation in Winnie mice. Furthermore, among lamina propria and mesenteric lymph node-derived T cells, interferon γ-expressing CD8⁺ T cells were reduced significantly after anakinra administration.

CONCLUSIONS

Our study provides new insight and alternative approaches to treat UC patients, and points to anti-IL1 strategies (ie, anakinra) that may be a more effective therapeutic option for primary nonresponders to anti-TNF therapy.

Exogenous Introduction of Initiator and Executioner Caspases Results in Different Apoptotic Outcomes

The balance of pro-apoptotic and pro-survival proteins defines a cell's fate. These processes are controlled through an interdependent and finely tuned protein network that enables survival or leads to apoptotic cell death. The caspase family of proteases is central to this apoptotic network, with initiator and executioner caspases, and their interaction partners, regulating and executing apoptosis. In this work, we interrogate and modulate this network by exogenously introducing specific initiator or executioner caspase proteins. Each caspase is exogenously introduced using redox-responsive polymeric nanogels. Although caspase-3 might be expected to be the most effective due to the centrality of its role in apoptosis and its heightened catalytic efficiency relative to other family members, we observed that caspase-7 and caspase-9 are the most effective at inducing apoptotic cell death. By critically analyzing the introduced activity of the delivered caspase, the pattern of substrate cleavage, as well as the ability to activate endogenous caspases, we conclude that the efficacy of each caspase correlated with the levels of pro-survival factors that both directly and indirectly impact the introduced caspase. These findings lay the groundwork for developing methods for exogenous introduction of caspases as a therapeutic option that can be tuned to the apoptotic balance in a proliferating cell.

miRNA-149 targets PARP-2 in endometrial epithelial and stromal cells to regulate the trophoblast attachment process

Embryo implantation is a highly complex process involving many regulatory factors, including several micro RNAs (miRNAs/miRs). One miRNA present in the stromal cells of normal endometrium is miR-149, which targets poly (ADP-ribose) polymerase 2 (PARP-2), a gene involved in endometrial receptivity for trophoblast implantation. However, the precise role of miR-149 in the endometrial receptivity during blastocyst implantation is still unknown. We studied miR-149-dependent PARP-2 regulation during trophoblast attachment to endometrial epithelial cells. Using FISH, we found that miR-149 is expressed in mouse endometrial epithelial and stromal cells at implantation and inter-implantation sites. Endometrial receptivity for embryo implantation and attachment is inhibited by the upregulation of miR-149 in the endometrium. Our RT-PCR analysis revealed downregulation of miR-149 in the implantation region of the uterus during the receptive stage (Day 5, 0500 h, p.c.) in the mouse. Under in-vitro conditions, miR-149 overexpression in human endometrial epithelial cells (hEECs) abrogated the human trophoblastic cells spheroid and mouse blastocyst attachment. Subsequently, miR-149 also regulates transformed human endometrial stromal cell (T-hESCs) decidualization by downregulating PARP-2 and upregulating caspase-8 proteins. Overexpression of miR-149 in hEECs and downregulated PARP-2 protein expression, reconfirming that PARP-2 is a downstream target of miR-149 in endometrial cells as well. miR-149 is also able to alter the expression of caspase-8, another PARP-2 regulator. In conclusion, our data indicate that miR-149 is one of the regulators of endometrial receptivity and decidualization for trophoblast implantation, and it exerts the effects by acting on the downstream targets PARP-2 and caspase-8.

Poly(ADP-ribose) polymerase-2 is essential for endometrial receptivity and blastocyst implantation, and regulated by caspase-8

Embryo implantation is a very complex process and several factors play important roles. Using a mouse model, we investigated the functions of PARP-2 and caspase-8 during endometrial receptivity for blastocyst implantation. We found that PARP-2 was upregulated at the receptive stage's implantation region and predominantly expressed in the endometrial stromal region, but downregulated during pregnancy failure and pseudopregnancy. To reinforce the necessity of PARP-2 for embryo implantation, we pharmacologically inhibited PARP-2 'before' & 'after' embryo arrival and observed a reduction in blastocyst implantation. Conversely, elevated caspase-8 expression and activity during pseudopregnancy, delayed implantation, and embryo implantation failure conditions and decreased levels in the decidualization exhibited an inverse pattern with PARP-2, suggesting caspase-8 as a negative regulator for embryo implantation. In vitro caspase-8 downregulates the PARP-2 activity in the mouse endometrial epithelial and stromal cells. These data suggest that PARP-2 and its negative regulation by caspase-8 constitute a crucial step in embryo implantation.

Indomethacin can induce cell death in rat gastric parietal cells through alteration of some apoptosis- and autophagy-associated molecules

In clinical medicine, indomethacin (IND, a non-steroidal anti-inflammatory drug) is used variously in the treatment of severe osteoarthritis, rheumatoid arthritis, gouty arthritis or ankylosing spondylitis. A common complication found alongside the therapeutic characteristics is gastric mucosal damage. This complication is mediated through apoptosis and autophagy of the gastrointestinal mucosal epithelium. Apoptosis and autophagy are critical homeostatic pathways catalysed by caspases downstream of the gastrointestinal mucosal epithelial injury. Both act through molecular signalling pathways characterized by the initiation, mediation, execution and regulation of the cell regulatory cycle. In this study we hypothesized that dysregulated apoptosis and autophagy are associated with IND-induced gastric damage. We examined the spectra of in vivo experimental gastric ulcers in male Sprague-Dawley rats through gastric gavage of IND. Following an 18-hour fast, IND was administered to experimental rats. They were sacrificed at 3-, 6- and 12-hour intervals. Parietal cells (H⁺ , K⁺ -ATPase β-subunit assay) and apoptosis (TUNEL assay) were determined. The expression of apoptosis-signalling caspase (caspases 3, 8, 9 and 12), DNA damage (anti-phospho-histone H2A.X) and autophagy (MAP-LC3, LAMP-1 and cathepsin B)-related molecules in gastric mucosal cells was examined. The administration of IND was associated with gastric mucosal erosions and ulcerations mainly involving the gastric parietal cells (PCs) of the isthmic and upper neck regions and a time-dependent gradual increase in the number of apoptotic PCs with the induction of both apoptotic (upregulation of caspases 3 and 8) cell death and autophagic (MAP-LC3-II, LAMP-1 and cathepsin B) cell death. Autophagy induced by fasting and IND 3 hours initially prompted the degradation of caspase 8. After 6 and 12 hours, damping down of autophagic activity occurred, resulting in the upregulation of active caspase 8 and its nuclear translocation. In conclusion we report that IND can induce time-dependent apoptotic and autophagic cell death of PCs. Our study provides the first indication of the interactions between these two homeostatic pathways in this context.

Differential regulation of breast cancer bone metastasis by PARP1 and PARP2

PARP1 and PARP2 dual inhibitors, such as olaparib, have been recently FDA approved for the treatment of advanced breast and ovarian cancers. However, their effects on bone mass and bone metastasis are unknown. Here we show that olaparib increases breast cancer bone metastasis through PARP2, but not PARP1, specifically in the myeloid lineage, but not in the cancer cells. Olaparib treatment or PARP1/2 deletion promotes osteoclast differentiation and bone loss. Intriguingly, myeloid deletion of PARP2, but not PARP1, increases the population of immature myeloid cells in bone marrow, and impairs the expression of chemokines such as CCL3 through enhancing the transcriptional repression by β-catenin. Compromised CCL3 production in turn creates an immune-suppressive milieu by altering T cell subpopulations. Our findings warrant careful examination of current PARP inhibitors on bone metastasis and bone loss, and suggest cotreatment with CCL3, β-catenin inhibitors, anti-RANKL or bisphosphonates as potential combination therapy for PARP inhibitors.

TRAIL Induces Nuclear Translocation and Chromatin Localization of TRAIL Death Receptors

Binding of tumor necrosis factor-related apoptosis-inducing ligand (TRAIL) to the plasma membrane TRAIL-R1/-R2 selectively kills tumor cells. This discovery led to evaluation of TRAIL-R1/-R2 as targets for anti-cancer therapy, yet the corresponding clinical trials were disappointing. Meanwhile, it emerged that many cancer cells are TRAIL-resistant and that TRAIL-R1/-R2-triggering may lead to tumor-promoting effects. Intriguingly, recent studies uncovered specific functions of long ignored intracellular TRAIL-R1/-R2, with tumor-promoting functions of nuclear (n)TRAIL-R2 as the regulator of let-7-maturation. As nuclear trafficking of TRAIL-Rs is not well understood, we addressed this issue in our present study. Cell surface biotinylation and tracking of biotinylated proteins in intracellular compartments revealed that nTRAIL-Rs originate from the plasma membrane. Nuclear TRAIL-Rs-trafficking is a fast process, requiring clathrin-dependent endocytosis and it is TRAIL-dependent. Immunoprecipitation and immunofluorescence approaches revealed an interaction of nTRAIL-R2 with the nucleo-cytoplasmic shuttle protein Exportin-1/CRM-1. Mutation of a putative nuclear export sequence (NES) in TRAIL-R2 or the inhibition of CRM-1 by Leptomycin-B resulted in the nuclear accumulation of TRAIL-R2. In addition, TRAIL-R1 and TRAIL-R2 constitutively localize to chromatin, which is strongly enhanced by TRAIL-treatment. Our data highlight the novel role for surface-activated TRAIL-Rs by direct trafficking and signaling into the nucleus, a previously unknown signaling principle for cell surface receptors that belong to the TNF-superfamily.

Serum-dependent and -independent regulation of PARP2

PARP2 belongs to a family of proteins involved in cell differentiation, DNA damage repair, cellular energy expenditure, and chromatin modeling. In addition to these overlapping functions with PARP1, PARP2 participates in spermatogenesis, T-cell maturation, extra-embryonic endoderm formation, adipogenesis, lipid metabolism, and cholesterol homeostasis. Knowledge of the functions of PARP2 is far from complete, and the mechanism(s) by which the gene and protein are regulated are unknown. In this study, we found that two different mechanisms are used in vitro to regulate PARP2 levels. In the presence of serum, PARP2 is degraded through the ubiquitin-proteasome pathway; however, when serum is removed or dialyzed with a 3.5 kDa molecular cut membrane, PARP2 rapidly becomes sodium dodecyl sulphate- and urea-insoluble. Despite the presence of a putative serum response element in the PARP2 gene, transcription is not affected by serum deprivation, and PARP2 levels are restored when serum is replaced. The loss of PARP2 affects cell differentiation and gene expression linked to cholesterol and lipid metabolism. These observations highlight the critical roles that PARP2 plays under different physiological conditions, and reveal that PARP2 is tightly regulated by distinct pathways.

Apoptosis regulation by subcellular relocation of caspases

The cleavage of nuclear proteins by caspases promotes nuclear breakdown and, therefore, plays a key role in apoptosis execution. However, the detailed molecular mechanisms of these events remain unclear. To get more insights into the mechanisms of nuclear events during apoptosis we set up a rapid fractionation protocol for the separation of the cytoplasmic and nuclear fractions of cells undergoing cisplatin-induced apoptosis. Importantly, nuclear accumulation of effector caspase-3 as well as initiator caspase-2, -8 and -9 was observed using the developed protocol and immunofluorescence microscopy. The detection of caspases and their cleavage products in the nucleus occurred within the same time interval after cisplatin treatment and took place shortly before nuclear fragmentation. The entry of initiator caspases to the nucleus was independent of caspase-3. Given that all three initiator caspases had catalytic activity in the nuclei, our findings indicate that initiator caspases might participate in the proteolysis of nuclear components during apoptosis, promoting its disintegration and apoptotic cell death.

Alterations in the nucleocytoplasmic transport in apoptosis: Caspases lead the way

Apoptosis is a mode of regulated cell death that is indispensable for the morphogenesis, development and homeostasis of multicellular organisms. Caspases are cysteine-dependent aspartate-specific proteases, which function as initiators and executors of apoptosis. Caspases are cytosolic proteins that can cleave substrates located in different intracellular compartments during apoptosis. Many years ago, the involvement of caspases in the regulation of nuclear changes, a hallmark of apoptosis, was documented. Accumulated data suggest that apoptosis-associated alterations in nucleocytoplasmic transport are also linked to caspase activity. Here, we aim to discuss the current state of knowledge regarding this process. Particular attention will be focused on caspase nuclear entry and their functions in the demolition of the nucleus upon apoptotic stimuli.

Asthma and poly(ADP-ribose) polymerase inhibition: a new therapeutic approach

Asthma is a chronic lung disease affecting people of all ages worldwide, and it frequently begins in childhood. Because of its chronic nature, it is characterized by pathological manifestations, including airway inflammation, remodeling, and goblet cell hyperplasia. Current therapies for asthma, including corticosteroids and beta-2 adrenergic agonists, are directed toward relieving the symptoms of the asthmatic response, with poor effectiveness against the underlying causes of the disease. Asthma initiation and progression depends on the T helper (Th) 2 type immune response carried out by a complex interplay of cytokines, such as interleukin (IL) 4, IL5, and IL13, and the signal transducer and activator of transcription 6. Much of the data resulting from different laboratories support the role of poly(ADP-ribose) polymerase (PARP) 1 and PARP14 activation in asthma. Indeed, PARP enzymes play key roles in the regulation and progression of the inflammatory asthma process because they affect the expression of genes and chemokines involved in the immune response. Consistently, PARP inhibition achievable either upon genetic ablation or by using pharmacological agents has shown a range of therapeutic effects against the disease. Indeed, in the last two decades, several preclinical studies highlighted the protective effects of PARP inhibition in various animal models of asthma. PARP inhibitors showed the ability to reduce the overall lung inflammation acting with a specific effect on immune cell recruitment and through the modulation of asthma-associated cytokines production. PARP inhibition has been shown to affect the Th1–Th2 balance and, at least in some aspects, the airway remodeling. In this review, we summarize and discuss the steps that led PARP inhibition to become a possible future therapeutic strategy against allergic asthma.

Imbalance between pro-apoptotic and pro-survival factors in human retinal pericytes in diabetic-like conditions

PURPOSE

Loss of pericytes is one the key events in the pathogenesis of diabetic retinopathy. We have previously demonstrated that human retinal pericytes (HRP) are more vulnerable to intermittent than stable high glucose concentrations, with an increase in apoptosis. Our aim was to explore the expression of molecules involved in pro-apoptotic and survival pathways in pericytes cultured in stable/intermittent high glucose and/or hypoxia, to clarify the mechanisms of action of these diabetic-like stressing stimuli.

METHODS

Human retinal pericytes (HRP) were exposed intermittently at 48-hr intervals to high/physiological glucose for 8 days (intHG) and/or hypoxia over the last 48 hr. Control cells were kept in stable physiological and high glucose. Cell proliferation and apoptosis were assessed. The expression of pro-apoptotic and pro-survival molecules was evaluated by Western blotting. Caspase-8 translocation from the cytoplasm into the nucleus was checked by Western blotting of nuclear versus cytoplasmic fractions and immunofluorescence.

RESULTS

Hypoxia, alone and combined with intHG, increased HRP apoptosis and decreased proliferation. Pro-apoptotic molecules increased in HRP cultured in these conditions, while some survival markers decreased. Conversely, in stable HG, pro-apoptotic molecules were stable or even decreased, and survival factors increased. Translocation of caspase-8 from cytoplasm into nucleus indicates a primary role for this molecule in inducing apoptosis.

CONCLUSION

Diabetic-like conditions are able to stimulate pericyte apoptosis through activation of pro-apoptotic molecules, leading to an imbalance between pro-apoptotic and survival signalling pathways, with caspase-8 playing a pivotal role. Our identification of such intermediates could help finding new therapeutic approaches for the prevention of diabetic retinopathy.

Increased oxidative stress and apoptosis in the hypothalamus of diabetic male mice in the insulin receptor substrate-2 knockout model

Insulin receptor substrate-2-deficient (IRS2(-/-)) mice are considered a good model to study the development of diabetes because IRS proteins mediate the pleiotropic effects of insulin-like growth factor-I (IGF-I) and insulin on metabolism, mitogenesis and cell survival. The hypothalamus might play a key role in the early onset of diabetes, owing to its involvement in the control of glucose homeostasis and energy balance. Because some inflammatory markers are elevated in the hypothalamus of diabetic IRS2(-/-) mice, our aim was to analyze whether the diabetes associated with the absence of IRS2 results in hypothalamic injury and to analyze the intracellular mechanisms involved. Only diabetic IRS2(-/-) mice showed increased cell death and activation of caspase-8 and -3 in the hypothalamus. Regulators of apoptosis such as FADD, Bcl-2, Bcl-xL and p53 were also increased, whereas p-IκB and c-FLIPL were decreased. This was accompanied by increased levels of Nox-4 and catalase, enzymes involved in oxidative stress. In summary, the hypothalamus of diabetic IRS2(-/-) mice showed an increase in oxidative stress and inflammatory markers that finally resulted in cell death via substantial activation of the extrinsic apoptotic pathway. Conversely, non-diabetic IRS2(-/-) mice did not show cell death in the hypothalamus, possibly owing to an increase in the levels of circulating IGF-I and in the enhanced hypothalamic IGF-IR phosphorylation that would lead to the stimulation of survival pathways. In conclusion, diabetes in IRS2-deficient male mice is associated with increased oxidative stress and apoptosis in the hypothalamus.

Iridovirus CARD Protein Inhibits Apoptosis through Intrinsic and Extrinsic Pathways

Grouper iridovirus (GIV) belongs to the genus Ranavirus of the family Iridoviridae; the genomes of such viruses contain an anti-apoptotic caspase recruitment domain (CARD) gene. The GIV-CARD gene encodes a protein of 91 amino acids with a molecular mass of 10,505 Daltons, and shows high similarity to other viral CARD genes and human ICEBERG. In this study, we used Northern blot to demonstrate that GIV-CARD transcription begins at 4 h post-infection; furthermore, we report that its transcription is completely inhibited by cycloheximide but not by aphidicolin, indicating that GIV-CARD is an early gene. GIV-CARD-EGFP and GIV-CARD-FLAG recombinant proteins were observed to translocate from the cytoplasm into the nucleus, but no obvious nuclear localization sequence was observed within GIV-CARD. RNA interference-mediated knockdown of GIV-CARD in GK cells infected with GIV inhibited expression of GIV-CARD and five other viral genes during the early stages of infection, and also reduced GIV infection ability. Immunostaining was performed to show that apoptosis was effectively inhibited in cells expressing GIV-CARD. HeLa cells irradiated with UV or treated with anti-Fas antibody will undergo apoptosis through the intrinsic and extrinsic pathways, respectively. However, over-expression of recombinant GIV-CARD protein in HeLa cells inhibited apoptosis induced by mitochondrial and death receptor signaling. Finally, we report that expression of GIV-CARD in HeLa cells significantly reduced the activities of caspase-8 and -9 following apoptosis triggered by anti-Fas antibody. Taken together, these results demonstrate that GIV-CARD inhibits apoptosis through both intrinsic and extrinsic pathways.

NLRX1 acts as tumor suppressor by regulating TNF-α induced apoptosis and metabolism in cancer cells

Chronic inflammation in tumor microenvironment plays an important role at different stages of tumor development. The specific mechanisms of the association and its role in providing a survival advantage to the tumor cells are not well understood. Mitochondria are emerging as a central platform for the assembly of signaling complexes regulating inflammatory pathways, including the activation of type-I IFN and NF-κB. These complexes in turn may affect metabolic functions of mitochondria and promote tumorigenesis. NLRX1, a mitochondrial NOD-like receptor protein, regulate inflammatory pathways, however its role in regulation of cross talk of cell death and metabolism and its implication in tumorigenesis is not well understood. Here we demonstrate that NLRX1 sensitizes cells to TNF-α induced cell death by activating Caspase-8. In the presence of TNF-α, NLRX1 and active subunits of Caspase-8 are preferentially localized to mitochondria and regulate the mitochondrial ROS generation. NLRX1 regulates mitochondrial Complex I and Complex III activities to maintain ATP levels in the presence of TNF-α. The expression of NLRX1 compromises clonogenicity, anchorage-independent growth, migration of cancer cells in vitro and suppresses tumorigenicity in vivo in nude mice. We conclude that NLRX1 acts as a potential tumor suppressor by regulating the TNF-α induced cell death and metabolism.

Herpesvirus entry mediator (HVEM) attenuates signals mediated by the lymphotoxin β receptor (LTβR) in human cells stimulated by the shared ligand LIGHT

Signals mediated by members of the tumor necrosis factor receptor superfamily modulate a network of diverse processes including initiation of inflammatory responses and altering cell fate between pathways favoring survival and death. Although such pathways have been well-described for the TNF-α receptor, less is known about signaling induced by the TNF superfamily member LIGHT and how it is differentially altered by expression of its two receptors LTβR and HVEM in the same cell. We used cell lines with different relative expression of HVEM and LTβR to show that LIGHT-induced signals mediated by these receptors were associated with altered TRAF2 stability and RelA nuclear translocation. Production of the inflammatory chemokine CXCL10 was primarily mediated by LTβR. Higher expression of HVEM was associated with cell survival, while unopposed LTβR signaling favored pathways leading to apoptosis. Importantly, restoring HVEM expression in cells with low endogenous expression recapitulated the phenotype of cells with higher endogenous expression. Together, our data provide evidence that relative expression of HVEM and LTβR modulates canonical NF-κB and pro-apoptotic signals stimulated by LIGHT.

Selenium attenuates high glucose-induced ROS/TLR-4 involved apoptosis of rat cardiomyocyte

The potential mechanism of high glucose-induced cardiomyocyte apoptosis and selenium's protective effects were investigated in this study. Myocytes isolated from neonate rats were cultured in high-glucose medium (25.5 mmol/L glucose) to mimic sustained hyperglycemia. Before high-glucose incubation, myocytes were pretreated by sodium selenite solution. Cell apoptosis was evaluated by annexin V/propidium iodide (PI) staining and caspase activation. Expression of Toll-like receptor 4 (TLR-4) and myeloid differentiation factor 88 (MyD-88) was examined at both mRNA and protein levels. The intracellular reactive oxygen species (ROS) production and glutathione peroxidase (GPx) activity in myocytes were also detected. We found high glucose-induced cell apoptosis and activation of TLR-4/MyD-88/caspase-8/caspase-3 signaling, accompanied by increased production of ROS. Selenium pretreatment attenuated apoptosis in high glucose-incubated myocytes, and mechanically, this protective effect was found to be associated with attenuating oxidative status by increasing activity of GPx, decreasing the generation of ROS, as well as inhibition of the activation of TLR-4/MyD-88/caspase-8/caspase-3 signaling in myocytes. These results suggest that activation of TLR-4/MyD-88 signaling pathway plays an important role in high glucose-induced cardiomyocyte apoptosis. Additionally, by modulating TLR-4/MyD-88 signaling pathway, which is linked to ROS formation, selenium exerts its antioxidative and antiapoptotic effects in high glucose-incubated myocytes.

Cytosolic and nuclear caspase-8 have opposite impact on survival after liver resection for hepatocellular carcinoma

Background

An imbalance between proliferation and apoptosis is one of the main features of carcinogenesis. TRAIL (TNF-related apoptosis-inducing ligand) induces apoptosis upon binding to the TRAIL death receptors, TRAIL receptor 1 (TRAIL-R1) and TRAIL-R2, whereas binding to TRAIL-R3 and TRAIL-R4 might promote cell survival and proliferation. The anti-tumor activity of TRAIL-R1 and TRAIL-R2 agonists is currently investigated in clinical trials. To gain further insight into the regulation of apoptosis in hepatocellular carcinoma (HCC), we investigated the TRAIL pathway and the regulators of apoptosis caspase-8, Bcl-xL and Mcl-1 in patients with HCC regarding patient survival.

Methods

We analyzed 157 hepatocellular carcinoma patients who underwent partial liver resection or orthotopic liver transplantation and healthy control liver tissue using immunohistochemistry on tissue microarrays for the expression of TRAIL-R1 to TRAIL-R4, caspase-8, Bcl-xL and Mcl-1. Immunohistochemical data were evaluated for potential associations with clinico-pathological parameters and survival.

Results

Whereas TRAIL-R1 was downregulated in HCC in comparison to normal liver tissue, TRAIL-R2 and –R4 were upregulated in HCC, especially in G2 and G3 tumors. TRAIL-R1 downregulation and upregulation of TRAIL-R2 and TRAIL-R4 correlated with tumor dedifferentiation (G2/G3). TRAIL-R3, Bcl-xL and Mcl-1 showed no differential expression in tumor tissue compared to normal tissue. The expression levels of TRAIL receptors did not correlate with patient survival after partial hepatectomy. Interestingly, in tumor tissue, but not in normal hepatocytes, caspase-8 showed a strong nuclear staining. Low cytosolic and high nuclear staining intensity of caspase-8 significantly correlated with impaired survival after partial hepatectomy, which, for cytosolic caspase-8, was independent from tumor grade.

Conclusions

Assessment of TRAIL-receptor expression patterns may have therapeutic implications for the use of TRAIL receptor agonists in HCC therapy. Tumor-specific nuclear localisation of caspase-8 in HCC suggests an apoptosis-independent function of caspase-8 and correlates with patient survival.

Roles of poly(ADP-ribose) glycohydrolase in DNA damage and apoptosis

Poly(ADP-ribose) glycohydrolase (PARG) is the primary enzyme that catalyzes the hydrolysis of poly(ADP-ribose) (PAR), an essential biopolymer that is synthesized by poly(ADP-ribose) polymerases (PARPs) in the cell. By regulating the hydrolytic arm of poly(ADP-ribosyl)ation, PARG participates in a number of biological processes, including the repair of DNA damage, chromatin dynamics, transcriptional regulation, and cell death. Collectively, the research investigating the roles of PARG in the cell has identified the importance of PARG and its value as a therapeutic target. However, the biological role of PARG remains less understood than the role of PAR synthesis by the PARPs. Further complicating the study of PARG is the existence of multiple PARG isoforms in the cell, the lack of optimal PARG inhibitors, and the lack of viable PARG-null animals. This review will present our current knowledge of PARG, with a focus on its roles in DNA-damage repair and cell death.

Poly(ADP-ribose) polymerase-2: emerging transcriptional roles of a DNA-repair protein

Poly(ADP-ribose) polymerase (PARP)-2 is a nuclear enzyme that belongs to the PARP family and PARP-2 is responsible for 5-15 % of total cellular PARP activity. PARP-2 was originally described in connection to DNA repair and in physiological and pathophysiological processes associated with genome maintenance (e.g., centromere and telomere protection, spermiogenesis, thymopoiesis, azoospermia, and tumorigenesis). Recent reports have identified important rearrangements in gene expression upon the knockout of PARP-2. Such rearrangements heavily impact inflammation and metabolism. Metabolic effects are mediated through modifying PPARγ and SIRT1 function. Altered gene expression gives rise to a complex phenotype characterized primarily by enhanced mitochondrial activity that results both in beneficial (loss of fat, enhanced insulin sensitivity) and in disadvantageous (pancreatic beta cell hypofunction upon high fat feeding) consequences. Enhanced mitochondrial biogenesis provides protection in oxidative stress-related diseases. Hereby, we review the recent developments in PARP-2 research with special attention to the involvement of PARP-2 in transcriptional and metabolic regulation.

Role of poly(ADP-ribose) polymerases in the regulation of inflammatory processes

PARP enzymes influence the immune system at several key points and thus modulate inflammatory diseases. PARP enzymes affect immune cell maturation and differentiation and regulate the expression of inflammatory mediators such as cytokines, chemokines, inducible nitric oxide synthase and adhesion molecules. Moreover, PARP enzymes are key regulators of cell death during inflammation-related oxidative and nitrosative stress. Here we provide an overview of the different inflammatory diseases regulated by PARP enzymes.

PARPs and the DNA damage response

Adenosine diphosphate (ADP)-ribosylation is an important posttranslational modification catalyzed by a variety of enzymes, including poly (ADP ribose) polymerases (PARPs), which use nicotinamide adenine dinucleotide (NAD(+)) as a substrate to synthesize and transfer ADP-ribose units to acceptor proteins. The PARP family members possess a variety of structural domains, span a wide range of functions and localize to various cellular compartments. Among the molecular actions attributed to PARPs, their role in the DNA damage response (DDR) has been widely documented. In particular, PARPs 1-3 are involved in several cellular processes that respond to DNA lesions, which include DNA damage recognition, signaling and repair as well as local transcriptional blockage, chromatin remodeling and cell death induction. However, how these enzymes are able to participate in such numerous and diverse mechanisms in response to DNA damage is not fully understood. Herein, the DDR functions of PARPs 1-3 and the emerging roles of poly (ADP ribose) polymers in DNA damage are reviewed. The development of PARP inhibitors, their applications and mechanisms of action are also discussed in the context of the DDR.

Sex-specific activation of cell death signalling pathways in cerebellar granule neurons exposed to oxygen glucose deprivation followed by reoxygenation

Neuronal death pathways following hypoxia-ischaemia are sexually dimorphic, but the underlying mechanisms are unclear. We examined cell death mechanisms during OGD (oxygen-glucose deprivation) followed by Reox (reoxygenation) in segregated male (XY) and female (XX) mouse primary CGNs (cerebellar granule neurons) that are WT (wild-type) or Parp-1 [poly(ADP-ribose) polymerase 1] KO (knockout). Exposure of CGNs to OGD (1.5 h)/Reox (7 h) caused cell death in XY and XX neurons, but cell death during Reox was greater in XX neurons. ATP levels were significantly lower after OGD/Reox in WT-XX neurons than in XY neurons; this difference was eliminated in Parp-1 KO-XX neurons. AIF (apoptosis-inducing factor) was released from mitochondria and translocated to the nucleus by 1 h exclusively in WT-XY neurons. In contrast, there was a release of Cyt C (cytochrome C) from mitochondria in WT-XX and Parp-1 KO neurons of both sexes; delayed activation of caspase 3 was observed in the same three groups. Thus deletion of Parp-1 shunted cell death towards caspase 3-dependent apoptosis. Delayed activation of caspase 8 was also observed in all groups after OGD/Reox, but was much greater in XX neurons, and caspase 8 translocated to the nucleus in XX neurons only. Caspase 8 activation may contribute to increased XX neuronal death during Reox, via caspase 3 activation. Thus, OGD/Reox induces death of XY neurons via a PARP-1-AIF-dependent mechanism, but blockade of PARP-1-AIF pathway shifts neuronal death towards a caspase-dependent mechanism. In XX neurons, OGD/Reox caused prolonged depletion of ATP and delayed activation of caspase 8 and caspase 3, culminating in greater cell death during Reox.

Sex differences in caspase activation after stroke

BACKGROUND AND PURPOSE

Over the past 5 years, experimental data have emerged that ischemia-induced cell death pathways may differ in males and females. Cell death in males is triggered by poly(ADP-ribose) polymerase activation and nuclear translocation of apoptosis-inducing factor. We have previously shown that interference with this pathway benefits males but not females after an experimental stroke. In contrast, caspase activation may be the major pathway activated after ischemic injury in females. The aim of this study is to examine whether sex differences exist in caspase activation in adult mice after stroke and to determine if interference with stroke-induced caspase activation preferentially protects females.

METHODS

Focal stroke was induced by reversible middle cerebral artery occlusion (90 minutes) in young and aging C57BL/6 mice of both sexes. The pan-caspase inhibitor, quinoline-Val-Asp(Ome)-CH2-O-phenoxy was administered at reperfusion. Histological outcomes were assessed 48 hours after middle cerebral artery occlusion. Separate cohorts were used for protein analysis of key cell death proteins, including caspase-3, caspase-8, cytochrome C, and apoptosis-inducing factor.

RESULTS

Drug-treated female mice had significantly decreased infarct volumes and improved neurological deficits after stroke compared to vehicle-treated mice. Quinoline-Val-Asp(Ome)-CH2-O-phenoxy administration had no effect in male mice. The expression of cytochrome C and nuclear caspase-8 levels were increased in females after stroke.

CONCLUSIONS

Female mice had an early release of cytochrome C and enhanced caspase activation after middle cerebral artery occlusion. Caspase inhibition benefited females but not males. Sex differences exist in both the response to ischemic injury and the efficacy of neuroprotective agents.

Parp and cell death or protection in rat primary astroglial cell cultures under LPS/IFNgamma induced proinflammatory conditions

The enzyme poly(ADP-ribose)polymerase (PARP) has a leader role in the DNA damage survey mechanisms by its nick-sensor function, but it is also involved in the early events of the programmed cell death, particularly during inflammatory injury, as a coactivator of NF-kB. In the present study, we evaluated the PARP involvement in the mechanisms of protection and/or cell death in rat astroglial cell cultures during the early phase of proinflammatory commitment after lipopolysaccharide and interferon gamma treatment. According with the recent findings that PARP-1 phosphorylation by MAPK/ERK-2 pathway seems to modulate PARP activation, in time course experiments we demonstrated that a very early PARP activation and expression is able to trigger a cell death pathway, DNA damage independent, during strong proinflammatory insults, maintaining its role of guardian of the genome stability only during the normal cell cycling.

Nonisotopic methods for determination of poly(ADP-ribose) levels and detection of poly(ADP-ribose) polymerase

Poly(ADP-ribosyl)ation is a post-translational modification catalyzed mostly by the 116-kDa enzyme poly(ADP-ribose) polymerase-1 (PARP-1), a nuclear enzyme that transfers an ADP-ribose moiety onto a limited number of nuclear proteins, including itself. When cells are exposed to environmental stresses such as alkylating agents or free radicals, there is up to a 500-fold increase in net poly(ADP-ribose) synthesis in response to DNA strand breaks. The enzyme responsible for 80% to 90% of this stimulated poly(ADP-ribose) synthesis is PARP-1, while other PARPs are responsible for the remaining 10% to 20%. The physiological meaning of these phenomena is not clear; however, it can be interpreted as a way of translating an event occurring on DNA to the nucleus by protein modification and finally to the cytoplasm via NAD(+) depletion. It has also been proposed that the presence of negatively charged poly(ADP-ribose) at the site of DNA damage may play several roles in regulation of base excision repair, p53 functions, and apoptosis. This unit describes protocols for measuring the levels of poly(ADP-ribose) in cells using nonisotopic reagents and for identifying the poly(ADP-ribose) polymerase enzymes present in cells.

Involvement of mitochondrial complex II defects in neuronal death produced by N-terminus fragment of mutated huntingtin

Alterations of mitochondrial function may play a central role in neuronal death in Huntington's disease (HD). However, the molecular mechanisms underlying such functional deficits of mitochondria are not elucidated yet. We herein showed that the expression of two important constituents of mitochondrial complex II, the 30-kDa iron-sulfur (Ip) subunit and the 70-kDa FAD (Fp) subunit, was preferentially decreased in the striatum of HD patients compared with controls. We also examined several mitochondrial proteins in striatal neurons that were infected with lentiviral vectors coding for the N-terminus part of huntingtin (Htt) with either a pathological (Htt171-82Q) or physiological (Htt171-19Q) polyglutamine tract. Compared with Htt171-19Q, expression of Htt171-82Q preferentially decreased the levels of Ip and Fp subunits and affected the dehydrogenase activity of the complex. The Htt171-82Q-induced preferential loss of complex II was not associated with a decrease in mRNA levels, suggesting the involvement of a posttranscriptional mechanism. Importantly, the overexpression of either Ip or Fp subunit restored complex II levels and blocked mitochondrial dysfunction and striatal cell death induced by Htt171-82Q in striatal neurons. The present results strongly suggest that complex II defects in HD may be instrumental in striatal cell death.

Apoptotic cell death progression after photothrombotic focal cerebral ischaemia: effects of the lipophilic iron chelator 2,2'-dipyridyl

Two different forms of cell death have been distinguished morphologically following cerebral ischaemia: necrotic and apoptotic cell death. The aim of this study was to investigate the contribution of apoptosis to ischaemic damage by carefully depicting the temporal and spatial neuronal death following focal ischaemia. For this purpose, rats were subjected to chemical photothrombosis, and histological and biochemical analyses were performed over a period of 24 h after the onset of ischaemia. In addition, the effects of the lipophilic antioxidant iron chelator 2,2'-dipyridyl (DP) were evaluated 24 h after photothrombosis when the lesion volume was maximal. Our results showed two separate waves of neuronal death. In the first wave, shrunken dark neurons were massively present as early as 2 h after photothrombosis in the infarct core. From this initial neuronal abnormal population, progressive and time-dependent changes of both necrotic and apoptotic cell death were observed, leading to ghost neurons and apoptotic bodies after 24 h. The extension of the lesion coincided with a second wave of cell death. Massive and rapid neuronal loss occurred at the infarct border, which appeared as a sharply demarcated pale region. Procaspase and poly(ADP-ribose) polymerase-1 (PARP-1) cleavages were also detected in the infarct core and surrounding damaged tissue. DP treatment markedly blocked the enlargement of the lesion, the infarct border being rescued from infarction. Furthermore, a large decrease of apoptotic bodies was associated with a significant drop of caspase and PARP-1 cleavages, suggesting that the protective effect of DP closely correlates with limitation of apoptosis expansion.

Nucleocytoplasmic transport in apoptosis

The apoptotic demolition of the nucleus is accomplished by diverse proapoptotic factors, most of which are activated in the cytoplasm and gain access to the nucleoplasm during the cell death process. The nucleus is also the main target for genotoxic insult, a potent apoptotic trigger. Signals generated in the nucleus by DNA damage have to propagate to all cellular compartments to ensure the coordinated execution of cell demise. The nucleocytoplasmic shuttling of signalling and execution factors is thus an integral part of the apoptotic programme. Several proteins implicated in apoptotic cell death have been shown to migrate in and out of the nucleus following apoptosis induction. This review summarises the current knowledge on nucleocytoplasmic trafficking of apoptosis-relevant proteins. The effects of apoptosis induction on the nucleocytoplasmic transport machinery are also discussed. Finally, a potential role of nuclear transport as a critical control point of the apoptotic signal cascade is proposed.

Activation of caspase 8 in the pituitaries of streptozotocin-induced diabetic rats: implication in increased apoptosis of lactotrophs

Lactotroph cell death is increased in streptozotocin-induced diabetic rats. To determine the mechanism involved, cell death proteins were accessed in pituitaries of diabetic (streptozotocin at 65 mg/kg, 2 months evolution) and control male rats by Western blot analysis and double immunohistochemistry. The intact and cleaved forms of caspase 9 were increased in diabetic rat pituitaries compared with controls. Although the proforms of caspases 3, 6, and 7 were increased in diabetic rat pituitaries, their activated forms were either unchanged or decreased. Activation of these effector caspases may be blocked by the increased expression of X-chromosome-linked inhibitor of apoptosis protein (XIAP) in diabetic rat pituitaries. However, in diabetic rats, XIAP expression in lactotrophs was decreased, suggesting that this cell type is not protected. Caspase 8, p53, and nuclear factor kappaB were more highly activated in diabetic rat pituitaries, with caspase 8 colocalization in lactotrophs being increased. These results suggest that, in the pituitaries of diabetic rats, the cascades of normal cell turnover are partially inhibited, possibly via XIAP, and this may be cell specific. Furthermore, activation of the extrinsic cell-death pathway, including activation of caspase 8, may underlie the diabetes-associated increase in lactotroph death.

CD437, a synthetic retinoid, induces apoptosis in human respiratory epithelial cells via caspase-independent mitochondrial and caspase-8-dependent pathways both up-regulated by JNK signaling pathway

The synthetic retinoid-related molecule CD437-induced apoptosis in human epithelial airway respiratory cells: the 16HBE bronchial cell line and normal nasal epithelial cells. CD437 caused apoptosis in S-phase cells and cell cycle arrest in S phase. Apoptosis was abolished by caspase-8 inhibitor z-IETD-fmk which preserved S-phase cells but was weakly inhibited by others selective caspase-inhibitors, indicating that caspase-8 activation was involved. z-VAD and z-IETD prevented the nuclear envelope fragmentation but did not block the chromatin condensation. The disruption of mitochondrial transmembrane potential was also induced by CD437 treatment. The translocation of Bax to mitochondria was demonstrated, as well as the release of cytochrome c into the cytosol and of apoptosis-inducing factor (AIF) translocated into the nucleus. z-VAD and z-IETD did not inhibit mitochondrial depolarization, Bax translocation or release of cytochrome c and AIF from mitochondria. These results suggest that CD437-induced apoptosis is executed by two converging pathways. AIF release is responsible for chromatin condensation, the first stage of apoptotic cell, via a mitochondrial pathway independent of caspase. But final stage of apoptosis requires the caspase-8-dependent nuclear envelope fragmentation. In addition, using SP600125, JNK inhibitor, we demonstrated that CD437 activates the JNK-MAP kinase signaling pathway upstream to mitochondrial and caspase-8 pathways. Conversely, JNK pathway inhibition, which suppresses S-phase apoptosis, did not prevent cell cycle arrest within S phase, confirming that these processes are triggered by distinct mechanisms.

Caspase-8 sumoylation is associated with nuclear localization

The cysteine protease caspase-8 plays a pivotal role in the initiation of different apoptotic pathways and controls the maturation and differentiation of various cell types including neurons, fibroblasts and lymphocytes. Specific substrates of caspase-8 are present in both the cytoplasm and the nucleus, which may determine the ultimate biological effect of caspase-8. However, the mechanisms regulating the cellular localization of caspase-8 are still unknown. We show here that, in contrast to other caspases such as caspase-9 and -3, caspase-8 can be sumoylated at lysine 156. This sumoylation (i) is associated with the nuclear localization of caspase-8 and (ii) did not impair caspase-8 activation.

Poly(ADP-ribose) polymerases: homology, structural domains and functions. Novel therapeutical applications

Poly(ADP-ribose) polymerases (PARPs) are a family of enzymes, which show differences in structure, cellular location and functions. However, all these enzymes possess poly(ADP-ribosyl)ation activity. Overactivation of PARP enzymes has been implicated in the pathogenesis of several diseases, including stroke, myocardial infarction, diabetes, shock, neurodegenerative disorder and allergy. The best studied of these enzymes (PARP-1) is involved in the cellular response to DNA damage so that in the event of irreparable DNA damage overactivation of PARP-1 leads to necrotic cell death. Inhibitors of PARP-1 activity in combination with DNA-binding antitumor drugs may constitute a suitable strategy in cancer chemotherapy. In addition, PARP inhibitors may be also useful to restore cellular functions in several pathophysiological states and diseases. This review gives an update of the state-of-the-art concerning PARP enzymes and their exploitation as pharmacological targets in several illnesses.

Tumour necrosis factor-mediated cell death pathways do not contribute to muscle fibre death in dystrophinopathies

There is evidence that apoptotic cell death mechanisms contribute to muscle fibre loss in dystrophinopathies, but little knowledge about the activators of the final degrading caspase cascade in muscle fibre apoptosis. As mitochondria-related activation of this caspase cascade, through e.g. APAF-1, could not be proven in dystrophin-deficient muscle, this study searches for other prospective candidates that may directly trigger apoptotic cell degradation by mitochondria-independent pathways involving the interaction of tumour necrosis factor-alpha (TNF-alpha) and TRAIL with death receptors and subsequent activation of caspase-8. The expression of TNF-alpha, TNF-R1, TRAIL, NF-(kappa)B and caspase-8 were studied in muscle biopsy specimens from 14 patients with a dystrophinopathy [10 Duchenne muscular dystrophies (DMD), 2 Becker MD, and 2 DMD carriers] by immunohistochemistry and Western blotting. In all types of dystrophinopathies, necrotic muscle fibres undergoing myophagocytosis displayed strong expression of TNF-alpha, TNF-R1, and TRAIL, which, however, was attributed to phagocytosing cells and not to the muscle fibres themselves. There was no up-regulation in normal-shaped or atrophic non-necrotic muscle fibres, or in intact muscle fibre segments adjacent to segmental necrosis and myophagocytosis. The expression profiles of caspase-8 and NF-(kappa)B resembled that of normal control muscle. There were likewise no significant differences in the Western blot analyses between normal control and dystrophin-deficient muscle. Based on these findings, a contribution of TNF-alpha or TRAIL-mediated cell death pathways to muscle fibre apoptosis or necrosis in dystrophinopathies could not be confirmed.

Activation of proinflammatory caspases by cathepsin B in focal cerebral ischemia

Cathepsins and caspases are two families of proteases that play pivotal roles in ischemic cell death. This study investigated the existence of a cross-talk between cathepsin B and proinflammatory caspases in stroke-induced cell death, as recently suggested by in vitro data. Cortical ischemic damage was induced in mice by distal and permanent occlusion of the middle cerebral artery. Cytoplasmic activation of cathepsin B was observed from the early stages of infarction, and displayed an activation pattern parallel to the activation pattern of caspase-1 and -11. Immunohistochemistry revealed the colocalization of cathepsin B with each caspase in cells of the infarct core. The apical position of cathepsin B in both caspase-activation cascades was confirmed by pretreatment of the animals with the cathepsin B inhibitor CA-074, which also potently protected cortical structures from ischemic damage, indicating involvement of the proteases in the lesion process. The results show that cathepsin B release is an early event following occlusion of cerebral arteries, which eventually triggers the activation of proinflammatory caspases in the absence of reperfusion. This new pathway may play a critical role in brain infarction by promoting inflammatory responses, and/or by amplifying the apoptotic process.

The mechanisms of cell death in focal cerebral ischemia highlight neuroprotective perspectives by anti-caspase therapy

A number of studies have validated the importance of caspase activation in ischemia-induced brain damage. Caspases participate in both the initiation and execution phases of apoptosis, and play a central role in neuronal death after global cerebral ischemia. In focal ischemia, apoptosis occurs in the penumbra during the secondary phase of expansion of the lesion. However, ultrastructural and biochemical analysis have also shown signs of apoptosis in the initial lesion, or infarct core, which is traditionally considered necrotic. Specific caspase pathways are activated in the core and in the penumbra, and participate in both cytoplasmic and nuclear apoptotic events, notwithstanding their initial classification as activator or initiator caspases. This confirms previous suggestions that caspase inhibition holds tremendous neuroprotective potential in stroke and other apoptosis-related degenerative diseases. Consequently, two new approaches, aimed at treating stroke-induced brain damage by anti-apoptotic molecules, are being developed in academic and industrial laboratories. These are based, respectively, on the use of small peptide sequences corresponding to the preferred cleavage site of a caspase, and on genomic constructions derived from the fusion of endogenous anti-caspase molecules with a protein transduction domain from the human immunodeficiency virus-1. Fusion proteins containing endogenous caspases inhibitors efficiently counteract apoptosis in vitro. In in vivo models of focal cerebral ischemia, fusion proteins successfully cross the blood brain barrier and protect cells from ischemic death. This new approach by protein therapy could prove to be an interesting alternative for the reduction of the dramatic consequences of stroke, provided that the long-term efficiency of this protection in terms of functional recovery is demonstrated.