The protein structures that shape caspase activity, specificity, activation and inhibition

Effects of maslinic acid on the proliferation and apoptosis of A549 lung cancer cells

Maslinic acid (MA) is a pentacyclic triterpene acid that is present in numerous dietary plants. Although certain studies have demonstrated that MA has anti-cancer properties in different cell types, the effect of MA on lung cancer cell proliferation and apoptosis and the potential underlying mechanisms remain to be elucidated. In the present study, A549 lung cancer cells were treated with different doses of MA and it was found that MA significantly inhibited A549 cell growth in a dose-dependent manner. In addition, Annexin V/propidium iodide flow cytometric analysis demonstrated that MA induced apoptosis of A549 cells. The present study also confirmed that MA induced apoptosis by observing morphological alterations. In addition, the effect of MA treatment on the levels of apoptosis-associated proteins was examined. The results demonstrated that MA treatment suppressed the expression of caspase-3, -8 and -9, and increased the expression of cleaved caspase-3, -8 and -9 in a dose-dependent manner. The level of inhibitors of apoptosis (IAPs) and Smac, which are possible upstream factors of caspase proteins, were also examined. It was found that MA treatment increased the protein expression of Smac and decreased the protein levels of c-IAP1, c-IAP2, X-linked inhibitor of apoptosis protein (XIAP) and Survivin in a dose-dependent manner. These results suggested that MA inhibited proliferation and induced apoptosis of A549 cells through regulation of caspase cleavage as well as Smac, c-IAP1, c-IAP2, XIAP and Survivin.

Small Molecule Active Site Directed Tools for Studying Human Caspases

Caspases are proteases of clan CD and were described for the first time more than two decades ago. They play critical roles in the control of regulated cell death pathways including apoptosis and inflammation. Due to their involvement in the development of various diseases like cancer, neurodegenerative diseases, or autoimmune disorders, caspases have been intensively investigated as potential drug targets, both in academic and industrial laboratories. This review presents a thorough, deep, and systematic assessment of all technologies developed over the years for the investigation of caspase activity and specificity using substrates and inhibitors, as well as activity based probes, which in recent years have attracted considerable interest due to their usefulness in the investigation of biological functions of this family of enzymes.

Structural Insights into Separase Architecture and Substrate Recognition through Computational Modelling of Caspase-Like and Death Domains

Separases are large proteins that mediate sister chromatid disjunction in all eukaryotes. They belong to clan CD of cysteine peptidases and contain a well-conserved C-terminal catalytic protease domain similar to caspases and gingipains. However, unlike other well-characterized groups of clan CD peptidases, there are no high-resolution structures of separases and the details of their regulation and substrate recognition are poorly understood. Here we undertook an in-depth bioinformatical analysis of separases from different species with respect to their similarity in amino acid sequence and protein fold in comparison to caspases, MALT-1 proteins (mucosa-associated lymphoidtissue lymphoma translocation protein 1) and gingipain-R. A comparative model of the single C-terminal caspase-like domain in separase from C. elegans suggests similar binding modes of substrate peptides between these protein subfamilies, and enables differences in substrate specificity of separase proteins to be rationalised. We also modelled a newly identified putative death domain, located N-terminal to the caspase-like domain. The surface features of this domain identify potential sites of protein-protein interactions. Notably, we identified a novel conserved region with the consensus sequence WWxxRxxLD predicted to be exposed on the surface of the death domain, which we termed the WR motif. We envisage that findings from our study will guide structural and functional studies of this important protein family.

The separation of sister chromatids is a crucial step in cell division and is triggered by the activation of separase, a protease that cleaves the proteins that maintain the cohesion between sister chromatids. Knowledge of the molecular structure and activation mechanism of separase is limited by the difficulty of obtaining structural information on this large and flexible protein. Sequence conservation between separase homologues from diverse species is limited to the C-terminal region that contains the catalytically active protease domain. We conducted an in-depth bioinformatical analysis of separase and generated structural models of the two conserved domains that comprise the C-terminal region: a caspase-like domain and a putative death domain. This analysis provided insights into substrate recognition and identified potential sites of protein-protein interactions. Both the death domain and caspase-like domain are well-conserved in separases, which suggests an evolutionary pressure to keep these two domains together, perhaps to enable separase activity and/or provide stability. Insights into the molecular structures of separase gained in this study may provide a starting point for experimental structural studies on this protein and may aid therapeutic development against cancers where chromosomes are improperly segregated.

Molecular architecture of the DED chains at the DISC: regulation of procaspase-8 activation by short DED proteins c-FLIP and procaspase-8 prodomain

The CD95/Fas/APO-1 death-inducing signaling complex (DISC), comprising CD95, FADD, procaspase-8, procaspase-10, and c-FLIP, has a key role in apoptosis induction. Recently, it was demonstrated that procaspase-8 activation is driven by death effector domain (DED) chains at the DISC. Here, we analyzed the molecular architecture of the chains and the role of the short DED proteins in regulating procaspase-8 activation in the chain model. We demonstrate that the DED chains are largely composed of procaspase-8 cleavage products and, in particular, of its prodomain. The DED chain also comprises c-FLIP and procaspase-10 that are present in 10 times lower amounts compared with procaspase-8. We show that short c-FLIP isoforms can inhibit CD95-induced cell death upon overexpression, likely by forming inactive heterodimers with procaspase-8. Furthermore, we have addressed mechanisms of the termination of chain elongation using experimental and mathematical modeling approaches. We show that neither c-FLIP nor procaspase-8 prodomain terminates the DED chain, but rather the dissociation/association rates of procaspase-8 define the stability of the chain and thereby its length. In addition, we provide evidence that procaspase-8 prodomain generated at the DISC constitutes a negative feedback loop in procaspase-8 activation. Overall, these findings provide new insights into caspase-8 activation in DED chains and apoptosis initiation.

Zinc pyrithione inhibits caspase-3 activity, promotes ErbB1-ErbB2 heterodimerization and suppresses ErbB2 downregulation in cardiomyocytes subjected to ischemia/reperfusion

Heart tissue becomes zinc-depleted and the capacity to mobilize labile zinc is diminished, indicating zinc dyshomeostasis during ischemia/reperfusion (I/R). Apparently, zinc pyrithione restores the basal zinc levels during I/R and prevents apoptosis by activating phosphatidyl inositol-3-kinase/Akt and targeting mitochondrial permeability transition. Receptor tyrosine kinases of the ErbB family (ErbB1 to ErbB4) are cell surface proteins that can regulate cell growth, proliferation and survival. Previous studies have shown that zinc pyrithione-induced activation of PI3kinase/Akt requires ErbB2 expression. On the other hand, while I/R decreases ErbB2 levels causing cardiomyocyte dysfunction and cell death, zinc pyrithione restores ErbB2 levels and maintains cardiomyocyte function. H9c2 cells expressed all the four ErbBs, although the expression of ErbB1 and ErbB2 were higher compared to ErbB3 and ErbB4. Hypoxia/Reoxygenation (H/R) had opposing effects on the mRNA expression of ErbB1 and ErbB2. ErbB2 mRNA levels were enhanced, but corresponding ErbB2 protein levels decreased after reoxygenation. H/R induced the degradation of ErbB2 in caspase-3 dependent manner, with the formation of a 25kDa fragment. This fragment could be detected after H/R only upon treatment of the cells with a proteasomal inhibitor, ALLN, suggesting that caspase-mediated cleavage of 185kDa ErbB2 results in C-terminal cleavage and formation of 25kDa fragment, which is further degraded by proteasome. Heterodimerization and phosphorylation of ErbB2/ErbB1 which decreased upon reoxygenation, was promoted by zinc pyrithione. Zinc pyrithione effectively suppressed the caspase activation, decreased the proteolytic cleavage of ErbB2, enhanced the phosphorylation and activation of ErbB1-ErbB2 complexes and improved the cell survival after hypoxia/reoxygenation.

Structure and function of legumain in health and disease

The last years have seen a steady increase in our understanding of legumain biology that is driven from two largely uncoupled research arenas, the mammalian and the plant legumain field. Research on legumain, which is also referred to as asparaginyl endopeptidase (AEP) or vacuolar processing enzyme (VPE), is slivered, however. Here we summarise recent important findings and put them into a common perspective. Legumain is usually associated with its cysteine endopeptidase activity in lysosomes where it contributes to antigen processing for class II MHC presentation. However, newly recognized functions disperse previously assumed boundaries with respect to their cellular compartmentalisation and enzymatic activities. Legumain is also found extracellularly and even translocates to the cytosol and the nucleus, with seemingly incompatible pH and redox potential. These different milieus translate into changes of legumain's molecular properties, including its (auto-)activation, conformational stability and enzymatic functions. Contrasting its endopeptidase activity, legumain can develop a carboxypeptidase activity which remains stable at neutral pH. Moreover, legumain features a peptide ligase activity, with intriguing mechanistic peculiarities in plant and human isoforms. In pathological settings, such as cancer or Alzheimer's disease, the proper association of legumain activities with the corresponding cellular compartments is breached. Legumain's increasingly recognized physiological and pathological roles also indicate future research opportunities in this vibrant field.

Methylene Blue Inhibits Caspases by Oxidation of the Catalytic Cysteine

Methylene blue, currently in phase 3 clinical trials against Alzheimer Disease, disaggregates the Tau protein of neurofibrillary tangles by oxidizing specific cysteine residues. Here, we investigated if methylene blue can inhibit caspases via the oxidation of their active site cysteine. Methylene blue, and derivatives, azure A and azure B competitively inhibited recombinant Caspase-6 (Casp6), and inhibited Casp6 activity in transfected human colon carcinoma cells and in serum-deprived primary human neuron cultures. Methylene blue also inhibited recombinant Casp1 and Casp3. Furthermore, methylene blue inhibited Casp3 activity in an acute mouse model of liver toxicity. Mass spectrometry confirmed methylene blue and azure B oxidation of the catalytic Cys163 cysteine of Casp6. Together, these results show a novel inhibitory mechanism of caspases via sulfenation of the active site cysteine. These results indicate that methylene blue or its derivatives could (1) have an additional effect against Alzheimer Disease by inhibiting brain caspase activity, (2) be used as a drug to prevent caspase activation in other conditions, and (3) predispose chronically treated individuals to cancer via the inhibition of caspases.

The Paracaspase MALT1

The human paracaspase MALT1 is a caspase homolog that plays a central role in NF-κB signaling. Over the past few years it has become clear that this is due to a combination of its scaffolding and proteolytic function. Knockout mice and mice expressing a catalytically dead variant of the protease have provided valuable information. This review aims to provide an overview of recent developments regarding the enzymatic mechanism and specificity of MALT1, its substrates discovered to date, different mouse models, as well as the role of MALT1 in NF-κB signaling downstream of a variety of different receptors.

Aluminum doping tunes band gap energy level as well as oxidative stress-mediated cytotoxicity of ZnO nanoparticles in MCF-7 cells

We investigated whether Aluminum (Al) doping tunes band gap energy level as well as selective cytotoxicity of ZnO nanoparticles in human breast cancer cells (MCF-7). Pure and Al-doped ZnO nanoparticles were prepared by a simple sol-gel method. Characterization study confirmed the formation of single phase of Al_xZn_1-xO nanocrystals with the size range of 33–55 nm. Al-doping increased the band gap energy of ZnO nanoparticles (from 3.51 eV for pure to 3.87 eV for Al-doped ZnO). Al-doping also enhanced the cytotoxicity and oxidative stress response of ZnO nanoparticles in MCF-7 cells. The IC50 for undoped ZnO nanoparticles was 44 μg/ml while for the Al-doped ZnO counterparts was 31 μg/ml. Up-regulation of apoptotic genes (e.g. p53, bax/bcl2 ratio, caspase-3 & caspase-9) along with loss of mitochondrial membrane potential suggested that Al-doped ZnO nanoparticles induced apoptosis in MCF-7 cells through mitochondrial pathway. Importantly, Al-doping did not change the benign nature of ZnO nanoparticles towards normal cells suggesting that Al-doping improves the selective cytotoxicity of ZnO nanoparticles toward MCF-7 cells without affecting the normal cells. Our results indicated a novel approach through which the inherent selective cytotoxicity of ZnO nanoparticles against cancer cells can be further improved.

Gallic acid ameliorates renal functions by inhibiting the activation of p38 MAPK in experimentally induced type 2 diabetic rats and cultured rat proximal tubular epithelial cells

Diabetic nephropathy (DN) is one of the leading causes of morbidity and mortality in diabetic patients that accounts for about 40% of deaths in type 2 diabetes. p38 mitogen activated protein kinase (p38 MAPK), a serine-threonine kinase, plays an important role in tissue inflammation and is known to be activated under conditions of oxidative stress and hyperglycemia. The role of p38 MAPK has been demonstrated in DN, and its inhibition has been suggested as an alternative approach in the treatment of DN. In the present study, we investigated the nephroprotective effects of an anti-inflammatory phenolic compound, gallic acid (GA, 3,4,5-trihydroxybenzoic acid), in high fat diet/streptozotocin (HFD/STZ) induce type 2 diabetic wistar albino rats. GA (25 mg/kgbw and 50 mg/kgbw, p.o.) treatment for 16 weeks post induction of diabetes led to a significant reduction in the levels of blood glucose, HbA1c, serum creatinine, blood urea nitrogen and proteinuria as well as a significant reduction in the levels of creatinine clearance. GA significantly inhibited the renal p38 MAPK and nuclear factor kappa B (N-κB) activation as well as significantly reduced the levels of renal transforming growth factor beta (TGF-β) and fibronectin. Treatment with GA resulted in a significant reduction in the serum levels of proinflammatory cytokines viz. interleukin 1 beta (IL-1β), IL-6 and tumor necrosis factor alpha (TNF-α). Moreover, GA significantly lowered renal pathology and attenuated renal oxidative stress. In cultured rat NRK 52E proximal tubular epithelial cells, GA treatment inhibited high glucose induced activation of p38 MAPK and NF-κB as well as suppressed proinflammatory cytokine synthesis. The results of the present study provide in vivo and in vitro evidences that the p38 MAPK pathway plays an important role in the pathogenesis of DN, and GA attenuates the p38 MAPK-mediated renal dysfunction in HFD/STZ induced type 2 diabetic rats.

Substrate Specificity and Possible Heterologous Targets of Phytaspase, a Plant Cell Death Protease

Plants lack aspartate-specific cell death proteases homologous to animal caspases. Instead, a subtilisin-like serine-dependent plant protease named phytaspase shown to be involved in the accomplishment of programmed death of plant cells is able to hydrolyze a number of peptide-based caspase substrates. Here, we determined the substrate specificity of rice (Oryza sativa) phytaspase by using the positional scanning substrate combinatorial library approach. Phytaspase was shown to display an absolute specificity of hydrolysis after an aspartic acid residue. The preceding amino acid residues, however, significantly influence the efficiency of hydrolysis. Efficient phytaspase substrates demonstrated a remarkable preference for an aromatic amino acid residue in the P3 position. The deduced optimum phytaspase recognition motif has the sequence IWLD and is strikingly hydrophobic. The established pattern was confirmed through synthesis and kinetic analysis of cleavage of a set of optimized peptide substrates. An amino acid motif similar to the phytaspase cleavage site is shared by the human gastrointestinal peptide hormones gastrin and cholecystokinin. In agreement with the established enzyme specificity, phytaspase was shown to hydrolyze gastrin-1 and cholecystokinin at the predicted sites in vitro, thus destroying the active moieties of the hormones.

Caspases and Thrombin Activity Regulation by Specific Serpin Inhibitors in Bovine Skeletal Muscle

In living cells, after activation, protein inhibitors constitute the last step of proteases activity regulation. This review intends to provide original information about a group of bovine muscle serine proteases inhibitors belonging to the Serpin superfamily and characterized at the gene and protein level. This report is the only one and the first to provide much information on this group of proteases inhibitors of the serpin type and their potential biological functions. Amongst the eight genes identified in bovine, three serpins were purified from the muscle tissue and characterized. These are two members of the bovSERPINA3 family, i.e., bovSERPINA3-1 and A3-3, and the last one is antithrombin III (AT-III or BovSERPINC1). BovSERPINA3 family comprises at least eight protein members encoded by different genes mapped on chromosome 7q23-q26 cluster. BovSERPINA3-1 and A3-3 were shown to locate within muscle cells and are cross-class inhibitors strongly active against trypsin as well as against human initiator and effector caspases 8 and 3. They constitute a key apoptosis control in mammals. They were thus expressed in proliferating and confluent myoblasts phases where cells must be alive but not in myotubes. Antithrombin III inhibits trypsin and, in a heparin dependent manner, thrombin. AT-III and its mRNA were expressed in muscle cells and in differentiating primary myoblasts in culture.

New Insights into the Role of Ubiquitin Networks in the Regulation of Antiapoptosis Pathways

Ubiquitin is a small modifier protein that conjugates on lysine (Lys) residues of substrates, and it can be targeted by another ubiquitin molecule to form chains through conjugation on the intrinsic Lys residues and methionine (Met) 1 residue. Ubiquitination of substrates by such chains determines the fate of substrates, thereby influencing various biological processes. In this chapter, we focus on apoptosis with an emphasis on the regulation by ubiquitination. The signal transduction of apoptosis is governed not only by the classical function of ubiquitin, which is proteasome-dependent degradation of substrates, but also by the apoptosis signaling complex formation guided by different types of ubiquitin chains. Ubiquitinations of pro- and antiapoptotic proteins are tightly regulated by particular sets of enzymes, such as ubiquitin E3 ligases and deubiquitinases (DUBs). We further discuss ubiquitination in the tumor necrosis factor (TNF) signaling pathway as an example for the ubiquitin-dependent regulation of apoptosis and cell survival.

Endogenous and Uric Acid-Induced Activation of NLRP3 Inflammasome in Pregnant Women with Preeclampsia

Preeclampsia (PE) is a specific syndrome of pregnancy, characterized by hypertension and proteinuria. This pathology is associated with hyperuricemia and elevated serum levels of inflammatory cytokines. Uric acid crystals may activate an intracellular complex called inflammasome, which is important for processing and release of inflammatory cytokines. This study investigated the state of monocyte activation, both endogenous and stimulated with monosodium urate (MSU), by gene expression of NLRP1 and NLRP3 receptors as well as their association with inflammatory cytokines expression. Monocytes were obtained from peripheral blood of 23 preeclamptic pregnant women, 23 normotensive pregnant women (NT) and 23 healthy non-pregnant women (NP). Inflammasome activation was evaluated by the gene expression of NLRP1, NLRP3, caspase-1, IL-1β, IL-18 and TNF-α by RT-qPCR in unstimulated monocytes (endogenous expression), or after cell stimulation with MSU (stimulated expression). The concentration of cytokines was assessed by ELISA. In preeclamptic pregnant women, gene expression of NLRP1, NLRP3, caspase-1, IL-1β and TNF-α by monocytes stimulated or not with MSU was significantly higher than in NT and NP groups. Stimulation of monocytes from preeclamptic and non-pregnant women with MSU induced increased gene expression of NLRP3, caspase-1 and TNF-α in relation to the endogenous expression in these groups, while this was not observed in the NT group. The cytokine determination showed that monocytes from women with PE produced higher endogenous levels of IL-1β, IL-18 and TNF-α compared to the other groups, while the stimulus with MSU led to higher production of these cytokines in preeclamptic group than in the NT group. In conclusion, the results showed increased basal gene expression of NLRP1 and NLRP3 receptors in monocytes from PE group. These cells stimulation with MSU demonstrates that uric acid plays a role in NLRP3 inflammasome activation, suggesting the participation of this inflammatory complex in the pathogenesis of preeclampsia.

Propeptides as modulators of functional activity of proteases

Most proteases are synthesized in the cell as precursor-containing propeptides. These structural elements can determine the folding of the cognate protein, function as an inhibitor/activator peptide, mediate enzyme sorting, and mediate the protease interaction with other molecules and supramolecular structures. The data presented in this review demonstrate modulatory activity of propeptides irrespective of the specific mechanism of action. Changes in propeptide structure, sometimes minor, can crucially alter protein function in the living organism. Modulatory activity coupled with high variation allows us to consider propeptides as specific evolutionary modules that can transform biological properties of proteases without significant changes in the highly conserved catalytic domains. As the considered properties of propeptides are not unique to proteases, propeptide-mediated evolution seems to be a universal biological mechanism.

[Phytaspases: aspartate-specific proteases involved in plant cell death]

Structure and properties of the recently discovered aspartate-specific cell death-related plant proteases named phytaspases are reviewed and compared to those of animal apoptotic proteases, caspases. Caspases (cysteine-dependent proteases) and phytaspases (serine-dependent proteases) are structurally very different, yet they share cleavage specificity and a role in programmed cell death. We demonstrate here that the distinctions in structural organization of animal and plant death proteases define differences in the strategies to regulate functioning of these proteolytic enzymes in the two kingdoms.

Implication of Caspase-3 as a Common Therapeutic Target for Multineurodegenerative Disorders and Its Inhibition Using Nonpeptidyl Natural Compounds

Caspase-3 has been identified as a key mediator of neuronal apoptosis. The present study identifies caspase-3 as a common player involved in the regulation of multineurodegenerative disorders, namely, Alzheimer's disease (AD), Parkinson's disease (PD), Huntington's disease (HD), and amyotrophic lateral sclerosis (ALS). The protein interaction network prepared using STRING database provides a strong evidence of caspase-3 interactions with the metabolic cascade of the said multineurodegenerative disorders, thus characterizing it as a potential therapeutic target for multiple neurodegenerative disorders. In silico molecular docking of selected nonpeptidyl natural compounds against caspase-3 exposed potent leads against this common therapeutic target. Rosmarinic acid and curcumin proved to be the most promising ligands (leads) mimicking the inhibitory action of peptidyl inhibitors with the highest Gold fitness scores 57.38 and 53.51, respectively. These results were in close agreement with the fitness score predicted using X-score, a consensus based scoring function to calculate the binding affinity. Nonpeptidyl inhibitors of caspase-3 identified in the present study expeditiously mimic the inhibitory action of the previously identified peptidyl inhibitors. Since, nonpeptidyl inhibitors are preferred drug candidates, hence, discovery of natural compounds as nonpeptidyl inhibitors is a significant transition towards feasible drug development for neurodegenerative disorders.

The multifaceted activity of insect caspases

Caspases are frequently considered synonymous with apoptotic cell death. Increasing evidence demonstrates that these proteases may exert their activities in non-apoptotic functions. The non-apoptotic roles of caspases may include developmentally regulated autophagy during insect metamorphosis, as well as neuroblast self-renewal and the immune response. Here, we summarize the established knowledge and the recent advances in the multiple roles of insect caspases to highlight their relevance for physiological processes and survival.

RSV P-protein impairs extrinsic apoptosis pathway in a macrophage-like cell line persistently infected with respiratory syncytial virus

Disabling apoptosis is practically a mandatory step for establishing and maintaining viral persistence in host cells. Thus, persisting viruses have evolved strategies to impair apoptosis mechanisms. Apoptosis can be induced through either the intrinsic or the extrinsic pathway. Previously, we reported that staurosporine-induced intrinsic apoptotic pathway was down-regulated in a macrophage cell line persistently infected with respiratory syncytial virus (RSV, MΦP). In the present study, our results showed that the extrinsic apoptotic pathway was also impaired in this cell line and that RSV P-protein interfered with the onset of the extrinsic apoptotic process. In this work, we analyzed and compared the expression of several components of the DISC complex (i.e., TNF-α, TNFR1, caspase-8, and cIAP2) in MΦP cells with that in mock-infected macrophages. Additionally, by using DNA sequence analysis in silico, we searched for an RSV protein putatively interfering with the triggering of the extrinsic apoptotic process. The analysis showed that viral P-protein shared a 52% homology with the caspase-8 death domain. Subsequently, the nucleic acid sequence of the viral P-protein was cloned and transfected into the macrophage cell line; the effect of this transfection on staurosporine-induced apoptosis was evaluated by assaying for cell viability and caspases-8 and -9 activity. The results revealed that although caspase-9 was activated, the activity of the caspase-8 was impaired in the RSV P-protein transfected cells; more of these cells survived than did mock-transfected cells. These findings suggest that P-protein impaired the extrinsic pathway of apoptosis. Our findings contribute to the understanding of the mechanism by which viral proteins subvert the extrinsic apoptosis process in cells persistently infected with RSV.

Apoptosis induced by sonodynamic therapy in human osteosarcoma cells in vitro

The aim of the present study was to investigate the potential effect of hematoporphyrin monomethyl ether-sonodynamic therapy (HMME-SDT) on MG-63 osteosarcoma cells. The HMME concentration was kept constant at 20 µg/ml and the MG-63 osteosarcoma cell line was exposed to ultrasound with an intensity of 1.0 W/cm2 for 30 sec. Cell cytotoxicity was quantified using an MTT assay 6 h after HMME-SDT. The intracellular localization of HMME was imaged using inverted confocal laser scanning microscopy. Apoptosis was investigated using flow cytometry with Annexin V-fluorescein isothiocyanate and propidium iodine staining. The cytotoxicity of HMME-mediated sonodynamic action on MG-63 cells was significantly higher than that of other treatments, including ultrasound alone, HMME alone and sham treatment. Flow cytometry demonstrated that HMME‑SDT action markedly enhanced the apoptotic rate of MG-63 cells. The mechanisms of apoptosis were analyzed by measuring the protein expression of poly ADP-ribose polymerase (PARP), cleaved PARP, procaspase-3, cleaved caspase-3 and cleaved caspase-9. The data demonstrated that HMME-SDT action markedly induced the apoptosis of MG-63 cells.

Cytochrome c oxidase deficiency accelerates mitochondrial apoptosis by activating ceramide synthase 6

Although numerous pathogenic changes within the mitochondrial respiratory chain (RC) have been associated with an elevated occurrence of apoptosis within the affected tissues, the mechanistic insight into how mitochondrial dysfunction initiates apoptotic cell death is still unknown. In this study, we show that the specific alteration of the cytochrome c oxidase (COX), representing a common defect found in mitochondrial diseases, facilitates mitochondrial apoptosis in response to oxidative stress. Our data identified an increased ceramide synthase 6 (CerS6) activity as an important pro-apoptotic response to COX dysfunction induced either by chemical or genetic approaches. The elevated CerS6 activity resulted in accumulation of the pro-apoptotic C_16 : 0 ceramide, which facilitates the mitochondrial apoptosis in response to oxidative stress. Accordingly, inhibition of CerS6 or its specific knockdown diminished the increased susceptibility of COX-deficient cells to oxidative stress. Our results provide new insights into how mitochondrial RC dysfunction mechanistically interferes with the apoptotic machinery. On the basis of its pivotal role in regulating cell death upon COX dysfunction, CerS6 might potentially represent a novel target for therapeutic intervention in mitochondrial diseases caused by COX dysfunction.

Oxidative stress, unfolded protein response, and apoptosis in developmental toxicity

Physiological development requires precise spatiotemporal regulation of cellular and molecular processes. Disruption of these key events can generate developmental toxicity in the form of teratogenesis or mortality. The mechanism behind many developmental toxicants remains unknown. While recent work has focused on the unfolded protein response (UPR), oxidative stress, and apoptosis in the pathogenesis of disease, few studies have addressed their relationship in developmental toxicity. Redox regulation, UPR, and apoptosis are essential for physiological development and can be disturbed by a variety of endogenous and exogenous toxicants to generate lethality and diverse malformations. This review examines the current knowledge of the role of oxidative stress, UPR, and apoptosis in physiological development as well as in developmental toxicity, focusing on studies and advances in vertebrates model systems.

Comparative structural analysis of the caspase family with other clan CD cysteine peptidases

Clan CD forms a structural group of cysteine peptidases, containing seven individual families and two subfamilies of structurally related enzymes. Historically, it is most notable for containing the mammalian caspases, on which the structures of the clan were founded. Interestingly, the caspase family is split into two subfamilies: the caspases, and a second subfamily containing both the paracaspases and the metacaspases. Structural data are now available for both the paracaspases and the metacaspases, allowing a comprehensive structural analysis of the entire caspase family. In addition, a relative plethora of structural data has recently become available for many of the other families in the clan, allowing both the structures and the structure-function relationships of clan CD to be fully explored. The present review compares the enzymes in the caspase subfamilies with each other, together with a comprehensive comparison of all the structural families in clan CD. This reveals a diverse group of structures with highly conserved structural elements that provide the peptidases with a variety of substrate specificities and activation mechanisms. It also reveals conserved structural elements involved in substrate binding, and potential autoinhibitory functions, throughout the clan, and confirms that the metacaspases are structurally diverse from the caspases (and paracaspases), suggesting that they should form a distinct family of clan CD peptidases.

Sam68 is cleaved by caspases under apoptotic cell death induced by ionizing radiation

The RNA-binding protein Sam68, a mitotic substrate of tyrosine kinases, has been reported to participate in the cell cycle, apoptosis, and signaling. In particular, overexpression of Sam68 protein is known to suppress cell growth and cell cycle progression in NIH3T3 cells. Although Sam68 is involved in many cellular activities, the function of Sam68, especially in response to apoptotic stimulation, is not well understood. In this study, we found that Sam68 protein is cleaved in immune cells undergoing apoptosis induced by γ-radiation. Moreover, we found that Sam68 cleavage was induced by apoptotic stimuli containing γ-radiation in a caspase-dependent manner. In particular, we showed that activated casepase-3, 7, 8 and 9 can directly cleave Sam68 protein through in vitro protease cleavage assay. Finally, we found that the knockdown of Sam68 attenuated γ-radiation-induced cell death and growth suppression. Conclusively, the cleavage of Sam68 is a new indicator for the cell damaging effects of ionizing radiation.

Biological functions of thyroid hormone in placenta

The thyroid hormone, 3,3,5-triiodo-l-thyronine (T₃), modulates several physiological processes, including cellular growth, differentiation, metabolism, inflammation and proliferation, via interactions with thyroid hormone response elements (TREs) in the regulatory regions of target genes. Infection and inflammation are critical processes in placental development and pregnancy-related diseases. In particular, infection is the leading cause of neonatal mortality and morbidity worldwide. However, to date, no successful approach has been developed for the effective diagnosis of infection in preterm infants. Pre-eclampsia (PE) is a serious disorder that adversely affects ~5% of human pregnancies. Recent studies identified a multiprotein complex, the inflammasome, including the Nod-like receptor (NLR) family of cytosolic pattern recognition receptors, the adaptor protein apoptosis-associated speck-like protein containing a caspase recruitment domain (ASC) and caspase-1, which plays a vital role in the placenta. The thyroid hormone modulates inflammation processes and is additionally implicated in placental development and disease. Therefore, elucidation of thyroid hormone receptor-regulated inflammation-related molecules, and their underlying mechanisms in placenta, should facilitate the identification of novel predictive and therapeutic targets for placental disorders. This review provides a detailed summary of current knowledge with respect to identification of useful biomarkers and their physiological significance in placenta.

Breakdown of coral colonial form under reduced pH conditions is initiated in polyps and mediated through apoptosis

Certain stony corals can alternate between a calcifying colonial form and noncalcifying solitary polyps, supporting the hypothesis that corals have survived through geologic timescale periods of unfavorable calcification conditions. However, the mechanisms enabling this biological plasticity are yet to be identified. Here we show that incubation of two coral species (Pocillopora damicornis and Oculina patagonica) under reduced pH conditions (pH 7.2) simulating past ocean acidification induce tissue-specific apoptosis that leads to the dissociation of polyps from coenosarcs. This in turn leads to the breakdown of the coenosarc and, as a consequence, to loss of coloniality. Our data show that apoptosis is initiated in the polyps and that once dissociation between polyp and coenosarc terminates, apoptosis subsides. After reexposure of the resulting solitary polyps to normal pH (pH 8.2), both coral species regenerated coenosarc tissues and resumed calcification. These results indicate that regulation of coloniality is under the control of the polyp, the basic modular unit of the colony. A mechanistic explanation for several key evolutionarily important phenomena that occurred throughout coral evolution is proposed, including mechanisms that permitted species to survive the third tier of mass extinctions.

Structure and mechanism of an aspartimide-dependent peptide ligase in human legumain

Peptide ligases expand the repertoire of genetically encoded protein architectures by synthesizing new peptide bonds, energetically driven by ATP or NTPs. Here, we report the discovery of a genuine ligase activity in human legumain (AEP) which has important roles in immunity and tumor progression that were believed to be due to its established cysteine protease activity. Defying dogma, the ligase reaction is independent of the catalytic cysteine but exploits an endogenous energy reservoir that results from the conversion of a conserved aspartate to a metastable aspartimide. Legumain's dual protease-ligase activities are pH- and thus localization controlled, dominating at acidic and neutral pH, respectively. Their relevance includes reversible on-off switching of cystatin inhibitors and enzyme (in)activation, and may affect the generation of three-dimensional MHC epitopes. The aspartate-aspartimide (succinimide) pair represents a new paradigm of coupling endergonic reactions in ATP-scarce environments.

Caspase-3 and caspase-6 cleave STAT1 in leukemic cells

Signal Transducer and Activator of Transcription-1 (STAT1) is phosphorylated upon interferon (IFN) stimulation, which can restrict cell proliferation and survival. Nevertheless, in some cancers STAT1 can act in an anti-apoptotic manner. Moreover, certain malignancies are characterized by the overexpression and constitutive activation of STAT1. Here, we demonstrate that the treatment of transformed hematopoietic cells with epigenetic drugs belonging to the class of histone deacetylase inhibitors (HDACi) leads to the cleavage of STAT1 at multiple sites by caspase-3 and caspase-6. This process does not occur in solid tumor cells, normal hematopoietic cells, and leukemic cells that underwent granulocytic or monocytic differentiation. STAT1 cleavage was studied under cell free conditions with purified STAT1 and a set of candidate caspases as well as with mass spectrometry. These assays indicate that unmodified STAT1 is cleaved at multiple sites by caspase-3 and caspase-6. Our study shows that STAT1 is targeted by caspases in malignant undifferentiated hematopoietic cells. This observation may provide an explanation for the selective toxicity of HDACi against rapidly proliferating leukemic cells.

Targeting apoptosis in autoimmune hepatitis

Apoptosis is the predominant mechanism of liver cell death in autoimmune hepatitis, and interventions that can modulate this activity are emerging. The aim of this review was to describe the apoptotic mechanisms, possible aberrations, and opportunities for intervention in autoimmune hepatitis. Studies cited in PubMed from 1972 to 2014 for autoimmune hepatitis, apoptosis in liver disease, apoptosis mechanisms, and apoptosis treatment were examined. Apoptosis is overactive in autoimmune hepatitis, and the principal pathway of cell death is receptor mediated. Surface death receptors are activated by extrinsic factors including liver-infiltrating cytotoxic T cells and the cytokine milieu. The executioner caspases 3 and 7 cleave nuclear deoxyribonucleic acid, and the release of apoptotic bodies can stimulate inflammatory, immune, and fibrotic responses. Changes in mitochondrial membrane permeability can be initiated by caspase 8, and an intrinsic pathway of apoptosis can complement the extrinsic pathway. Defects in the apoptosis of activated effector cells can prolong their survival and sustain the immune response. Caspase inhibitors have been used in diverse experimental and human diseases to retard apoptosis. Oligonucleotides that inhibit the signaling of toll-like receptors can limit the presentation of auto-antigens, and inhibitors of apoptosis that extend the survival of effector cells can be blocked by antisense oligonucleotides. Mechanisms that enhance the clearance of apoptotic bodies and affect key signaling pathways are also feasible. Interventions that influence the survival of liver and effector cells by altering their apoptosis are candidates for study in autoimmune hepatitis.

Revisiting caspases in sepsis

Sepsis is a life-threatening illness that occurs due to an abnormal host immune network which extends through the initial widespread and overwhelming inflammation, and culminates at the late stage of immunosupression. Recently, interest has been shifted toward therapies aimed at reversing the accompanying periods of immune suppression. Studies in experimental animals and critically ill patients have demonstrated that increased apoptosis of lymphoid organs and some parenchymal tissues contributes to this immune suppression, anergy and organ dysfunction. Immediate to the discoveries of the intracellular proteases, caspases for the induction of apoptosis and inflammation, and their striking roles in sepsis have been focused elaborately in a number of original and review articles. Here we revisited the different aspects of caspases in terms of apoptosis, pyroptosis, necroptosis and inflammation and focused their links in sepsis by reviewing several recent findings. In addition, we have documented striking perspectives which not only rewrite the pathophysiology, but also modernize our understanding for developing novel therapeutics against sepsis.

A clear and present danger: inflammasomes DAMPing down disorders of pregnancy

BACKGROUND

When the normal progression of pregnancy is threatened, inflammatory processes are often amplified in order to minimize detrimental effects and eliminate noxious agents. Inflammasomes are unique, intracellular, multiprotein assemblies that enable caspase-1 mediated proteolytic processing of the proinflammatory cytokine interleukin-1β, levels of which are elevated in some forms of preterm birth and maternal metabolic disorders.

METHODS

A comprehensive review based on a search of PubMed and Medline for terms and combinations of terms incorporating 'inflammation', 'inflammasome', 'pregnancy', 'preterm birth', 'pre-eclampsia', 'interleukin-1', 'caspase-1' and others selected to capture key articles.

RESULTS

In the decade since the discovery of the inflammasome, between January 2002 and June 2014 over 2200 articles have been published. Articles in the reproductive field are scarce but there is clear evidence for a role of the inflammasome axis in pregnancy, preterm birth and the maternal metabolic syndrome.

CONCLUSION

Further investigations on the inflammasome in pregnancy are needed in order to elucidate the biology of this unique structure in reproduction. Coordination of maternal, fetal and placental aspects of inflammasome function will potentially yield new information on the detection and transduction of host and non-host signals in the inflammatory response.

The actin cytoskeleton as a sensor and mediator of apoptosis

Apoptosis is an important biological process required for the removal of unwanted or damaged cells. Mounting evidence implicates the actin cytoskeleton as both a sensor and mediator of apoptosis. Studies also suggest that actin binding proteins (ABPs) significantly contribute to apoptosis and that actin dynamics play a key role in regulating apoptosis signaling. Changes in the organization of the actin cytoskeleton has been attributed to the process of malignant transformation and it is hypothesized that remodeling of the actin cytoskeleton may enable tumor cells to evade normal apoptotic signaling. This review aims to illuminate the role of the actin cytoskeleton in apoptosis by systematically analyzing how actin and ABPs regulate different apoptosis pathways and to also highlight the potential for developing novel compounds that target tumor-specific actin filaments.

Baculovirus resistance in codling moth is virus isolate-dependent and the consequence of a mutation in viral gene pe38

The baculovirus Cydia pomonella granulovirus (CpGV) is widely applied as a biocontrol agent of codling moth. After field resistance of codling moth populations had been observed against the commercially used Mexican (M) isolate of CpGV, infection experiments of larvae of the resistant codling moth strain CpRR1 showed that several other naturally occurring CpGV isolates (I12, S, E2, and I07) from different geographic origins are still infectious to resistant CpRR1. Whole-genome sequencing and phylogenetic analyses of these geographic CpGV variants revealed that their genomes share only a single common difference from that of CpGV-M, which is a mutation coding for a repeat of 24 nucleotides within the gene pe38; this mutation results in an additional repeat of eight amino acids that appears to be inserted to PE38 of CpGV-M only. Deletion of pe38 from CpGV-M totally abolished virus infection in codling moth cells and larvae, demonstrating that it is an essential gene. When the CpGV-M deletion mutant was repaired with pe38 from isolate CpGV-S, which originated from the commercial product Virosoft and is infectious for the resistant codling moth strain CpRR1, the repaired CpGV-M mutant was found to be fully infectious for CpRR1. Repair using pe38 from CpGV-M restored infectivity for the virus in sensitive codling moth strains, but not in CpRR1. Therefore, we conclude that CpGV resistance of codling moth is directed to CpGV-M but not to other virus isolates. The viral gene pe38 is not only essential for the infectivity of CpGV but it is also the key factor in overcoming CpGV resistance in codling moth.

Activation and regulation of caspase-6 and its role in neurodegenerative diseases

Caspases, a family of cysteine proteases, are major mediators of apoptosis and inflammation. Caspase-6 is classified as an apoptotic effector, and it mediates nuclear shrinkage during apoptosis, but it possesses unique activation and regulation mechanisms that differ from those of other effector caspases. Furthermore, increasing evidence has shown that caspase-6 is highly involved in axon degeneration and neurodegenerative diseases, such as Huntington's disease and Alzheimer's disease. Cleavage at the caspase-6 site in mutated huntingtin protein is a prerequisite for the development of the characteristic behavioral and neuropathological features of Huntington's disease. Active caspase-6 is present in early stages of Alzheimer's disease, and caspase-6 activity is associated with the disease's pathological lesions. In this review, we discuss the evidence relevant to the role of caspase-6 in neurodegenerative diseases and summarize its activation and regulation mechanisms. In doing so, we provide new insight about potential therapeutic approaches that incorporate the modulation of caspase-6 function for the treatment of neurodegenerative diseases.

Apoptosis block as a barrier to effective therapy in non small cell lung cancer

Lung cancer, is the most common cause of cancer death in men and second only to breast cancer in women. Currently, the first line therapy of choice is platinum-based combination chemotherapy. A therapeutic plateau has been reached with the prognosis for patients with advanced non-small cell lung cancer (NSCLC) remaining poor. New biomarkers of prognosis as well as new therapies focusing on molecular targets are emerging helping to identify patients who are likely to benefit from therapy. Despite this, drug resistance remains the major cause for treatment failure. In this article we review the role of apoptosis in mediating drug resistance in NSCLC. Better understanding of this fundamental biological process may provide a rationale for overcoming the current therapeutic plateau.

Anthraquinone G503 induces apoptosis in gastric cancer cells through the mitochondrial pathway

G503 is an anthraquinone compound isolated from the secondary metabolites of a mangrove endophytic fungus from the South China Sea. The present study elucidates the anti-tumor activity and the underlying mechanism of G503. Cell viability assay performed in nine cancer cell lines and two normal cell lines demonstrated that the gastric cancer cell line SGC7901 is the most G503-sensitive cancer cells. G503 induced SGC7901 cell death via apoptosis. G503 exposure activated caspases-3, -8 and -9. Pretreatment with the pan-caspase inhibitor Z-VAD-FMK and caspase-9 inhibitor Z-LEHD-FMK, but not caspase-8 inbibitor Z-IETD-FMK, attenuated the effect of G503. These results suggested that the intrinsic mitochondrial apoptosis pathway, rather than the extrinsic pathway, was involved in G503-induced apoptosis. Furthermore, G503 increased the ratio of Bax to Bcl-2 in the mitochondria and decreased the ratio in the cytosol. G503 treatment resulted in mitochondrial depolarization, cytochrome c release and the subsequent cleavage of caspase -9 and -3. Moreover, it is reported that the endoplasmic reticulum apoptosis pathway may also be activated by G503 by inducing capase-4 cleavage. In consideration of the lower 50% inhibitory concentration for gastric cancer cells, G503 may serve as a promising candidate for gastric cancer chemotherapy.

Combined inhibition of caspase 3 and caspase 7 by two highly selective DARPins slows down cellular demise

Caspases play important roles during apoptosis, inflammation and proliferation. The high homology among family members makes selective targeting of individual caspases difficult, which is necessary to precisely define the role of these enzymes. We have selected caspase-7-specific binders from a library of DARPins (designed ankyrin repeat proteins). The DARPins D7.18 and D7.43 bind specifically to procaspase 7 and active caspase 7, but not to other members of the family. Binding of the DARPins does not affect the active enzyme, but interferes with its activation by other caspases. The crystal structure of the caspase 7-D7.18 complex elucidates the high selectivity and the mode of inhibition. Combining these caspase-7-specific DARPins with the previously reported caspase-3-inhibitory DARPin D3.4S76R reduces the activity of caspase 3 and 7 in double-transfected HeLa cells during apoptosis. In addition, these cells showed less susceptibility to TRAIL (tumour-necrosis-factor-related apoptosis-inducing ligand)-induced apoptosis in living cell experiments. D7.18 and D7.43 are therefore novel tools for in vitro studies on procaspase 7 activation as well as for clarifying the role of its activation in different cellular processes. If applied in combination with D3.4S76R, they represent an excellent instrument to increase our understanding of these enzymes during various cellular processes.

A fluorescent protein scaffold for presenting structurally constrained peptides provides an effective screening system to identify high affinity target-binding peptides

Peptides that have high affinity for target molecules on the surface of cancer cells are crucial for the development of targeted cancer therapies. However, unstructured peptides often fail to bind their target molecules with high affinity. To efficiently identify high-affinity target-binding peptides, we have constructed a fluorescent protein scaffold, designated gFPS, in which structurally constrained peptides are integrated at residues K131-L137 of superfolder green fluorescent protein. Molecular dynamics simulation supported the suitability of this site for presentation of exogenous peptides with a constrained structure. gFPS can present 4 to 12 exogenous amino acids without a loss of fluorescence. When gFPSs presenting human epidermal growth factor receptor type 2 (HER2)-targeting peptides were added to the culture medium of HER2-expressing cells, we could easily identify the peptides with high HER2-affinity and -specificity based on gFPS fluorescence. In addition, gFPS could be expressed on the yeast cell surface and applied for a high-throughput screening. These results demonstrate that gFPS has the potential to serve as a powerful tool to improve screening of structurally constrained peptides that have a high target affinity, and suggest that it could expedite the one-step identification of clinically applicable cancer cell-binding peptides.

Zinc oxide quantum dots: a potential candidate to detain liver cancer cells

The term cancer is used for diseases in which abnormal cells proliferate without control and are able to attack with other tissues. Over various types of cancers, liver cancer is the most hurtful disease, which affects the whole body system. The aim of the present study was to investigate the efficiency against cancer cells of HepG2 cells, with quantum dots of ZnO. The cytotoxic effects were analyzed with MTT assays in range of 1-100 μg/ml. The cells were exposed to ZnO-QDs and it exhibit significant reduction, which starts from concentration 5 μg/ml (4 %; p < 0.05). The assay was justified with quantitative RT-PCR and it demonstrates, exposure of ZnO-QDs on HepG2 cells. The level of mRNA expressions was significantly up-regulated (Bax, P53, and Caspase-3), whereas the anti-apoptotic gene (Bcl-2) was down-regulated. The QDs (5 ± 2 nm) were prepared via soft chemical solution process and analyzed using FESEM, TEM and HR-TEM.

Real-time detection of CTL function reveals distinct patterns of caspase activation mediated by Fas versus granzyme B

Activation of caspase-mediated apoptosis is reported to be a hallmark of both granzyme B- and Fas-mediated pathways of killing by CTLs; however, the kinetics of caspase activation remain undefined owing to an inability to monitor target cell-specific apoptosis in real time. We have overcome this limitation by developing a novel biosensor assay that detects continuous, protease-specific activity in target cells. Biosensors were engineered from a circularly permuted luciferase, linked internally by either caspase 3/7 or granzyme B/caspase 8 cleavage sites, thus allowing activation upon proteolytic cleavage by the respective proteases. Coincubation of murine CTLs with target cells expressing either type of biosensor led to a robust luminescent signal within minutes of cell contact. The signal was modulated by the strength of TCR signaling, the ratio of CTL/target cells, and the type of biosensor used. Additionally, the luciferase signal at 30 min correlated with target cell death, as measured by a (51)Cr-release assay. The rate of caspase 3/7 biosensor activation was unexpectedly rapid following granzyme B- compared with Fas-mediated signal induction in murine CTLs; the latter appeared gradually after a 90-min delay in perforin- or granzyme B-deficient CTLs. Remarkably, the Fas-dependent, caspase 3/7 biosensor signal induced by perforin-deficient human CTLs was also detectable after a 90-min delay when measured by redirected killing. Thus, we have used a novel, real-time assay to demonstrate the distinct pattern of caspase activation induced by granzyme B versus Fas in human and murine CTLs.

The caspase-8 homolog Dredd cleaves Imd and Relish but is not inhibited by p35

In Drosophila, the Imd pathway is activated by diaminopimelic acid-type peptidoglycan and triggers the humoral innate immune response, including the robust induction of antimicrobial peptide gene expression. Imd and Relish, two essential components of this pathway, are both endoproteolytically cleaved upon immune stimulation. Genetic analyses have shown that these cleavage events are dependent on the caspase-8 like Dredd, suggesting that Imd and Relish are direct substrates of Dredd. Among the seven Drosophila caspases, we find that Dredd uniquely promotes Imd and Relish processing, and purified recombinant Dredd cleaves Imd and Relish in vitro. In addition, interdomain cleavage of Dredd is not required for Imd or Relish processing and is not observed during immune stimulation. Baculovirus p35, a suicide substrate of executioner caspases, is not cleaved by purified Dredd in vitro. Consistent with this biochemistry but contrary to earlier reports, p35 does not interfere with Imd signaling in S2* cells or in vivo.

Caspase 3 inactivation protects against hepatic cell death and ameliorates fibrogenesis in a diet-induced NASH model

BACKGROUND/AIMS

Hepatocyte cell death is a key feature of nonalcoholic steatohepatitis (NASH). As the contribution of specific caspases remains unclear, our aim was to ascertain the effect of caspase 3 suppression on liver injury and fibrogenesis.

METHODS

C57BL/6 wild-type (WT) and caspase 3 knock out (Casp3 (-/-)) mice were placed on a methionine- and choline-deficient (MCD) diet for 6 weeks to induce steatohepatitis and liver fibrosis. Thereafter, liver injury, liver fibrosis and hepatocellular apoptosis were quantified in liver sections. Additionally, expression of proteins associated with liver inflammation and fibrogenesis was analyzed.

RESULTS

WT mice fed MCD diet showed marked activation of caspase 3 in hepatocytes, in conjunction with steatohepatitis and increased hepatic triglyceride levels, hepatocyte ballooning, inflammation and fibrosis. Casp3 (-/-) mice fed the MCD diet showed similar serum aminotransferase levels and NAFLD activity scores (NAS) compared with WT MCD-fed mice. However, Casp3 (-/-) mice on the MCD diet showed a marked reduction in expression of transcripts for profibrogenic genes, which translated into reduced hepatic collagen deposition. These changes were associated with decreased levels of apoptosis, and a significant reduction in the expression of cytokines involved in inflammatory signaling. Casp3 (-/-) mice on the MCD showed a reduction in expression of chemokine receptor 2 (CCR2) leading to ameliorated infiltration of inflammatory lymphocyte antigen 6 complex, locus C1 (Ly6c) positive monocytes.

CONCLUSION

These findings support a prominent role for hepatocyte caspase 3 activation in NASH-related apoptosis, fibrogenesis and fibrosis which in part is mediated via CCR2-dependent infiltration of Ly6c positive monocytes.

Association of caspase9 promoter polymorphisms with the susceptibility of AML in south Indian subjects

Abnormal apoptosis is one of the hallmarks of cancers including acute myeloid leukemia (AML), as it plays a pivotal role in precisely maintaining self-renewal, proliferation, and differentiation properties of hematopoietic stem cells (HSCs). Caspase9 (CASP9), an initiator caspase activated by mitochondrial-mediated apoptotic pathway (intrinsic pathway), triggers cascade of effector caspases and executes apoptosis. Functional SNPs in CASP9 might influence the gene expression leading to altered apoptosis which confer the risk to AML. To test this hypothesis, we have analyzed four CASP9 gene polymorphisms [CASP9 - 1263A > G (rs4645978), CASP9 - 712C > T (rs4645981), CASP9 - 293_275del CGTGAGGTC AGTGCGGGGA (-293del) (rs4645982), and CASP9 Ex5 + 32G > A (rs1052576)] in 180 AML cases and 304 age- and sex-matched healthy controls. We performed various statistical analyses to determine the potential interactions between these SNPs and AML. The study revealed that presence of G allele at CASP9 - 1263 position elevates the risk of AML 1.53-fold and CT/TT genotype at CASP9 - 712 position by 2.60-fold under dominant model of inheritance. Two CASP9 haplotypes, G-del(+)-C-A and G-del(+)-T-A, were found to be significantly associated with increased AML risk by 2.19- (95 % confidence interval (CI), 1.09-4.39; p = 0.028) and 11.75-fold (95 % CI, 1.01-136.57; p = 0.05), respectively. Further, multidimensionality reduction (MDR) analysis had revealed single locus CASP9 - 712C > T SNP and four loci CASP9 - 1263A > G, CASP9 - 293del, CASP9 - 712C > T, and CASP9 Ex5 + 32G > A SNPs as highest predicting models for AML development. Our results revealed a significant association of two SNPs in CASP9 (-1263A > G and -712C > T) and two haplotypes of the four SNP combinations with AML susceptibility.

The unique regulation of iron-sulfur cluster biogenesis in a Gram-positive bacterium

Iron-sulfur clusters function as cofactors of a wide range of proteins, with diverse molecular roles in both prokaryotic and eukaryotic cells. Dedicated machineries assemble the clusters and deliver them to the final acceptor molecules in a tightly regulated process. In the prototypical Gram-negative bacterium Escherichia coli, the two existing iron-sulfur cluster assembly systems, iron-sulfur cluster (ISC) and sulfur assimilation (SUF) pathways, are closely interconnected. The ISC pathway regulator, IscR, is a transcription factor of the helix-turn-helix type that can coordinate a [2Fe-2S] cluster. Redox conditions and iron or sulfur availability modulate the ligation status of the labile IscR cluster, which in turn determines a switch in DNA sequence specificity of the regulator: cluster-containing IscR can bind to a family of gene promoters (type-1) whereas the clusterless form recognizes only a second group of sequences (type-2). However, iron-sulfur cluster biogenesis in Gram-positive bacteria is not so well characterized, and most organisms of this group display only one of the iron-sulfur cluster assembly systems. A notable exception is the unique Gram-positive dissimilatory metal reducing bacterium Thermincola potens, where genes from both systems could be identified, albeit with a diverging organization from that of Gram-negative bacteria. We demonstrated that one of these genes encodes a functional IscR homolog and is likely involved in the regulation of iron-sulfur cluster biogenesis in T. potens. Structural and biochemical characterization of T. potens and E. coli IscR revealed a strikingly similar architecture and unveiled an unforeseen conservation of the unique mechanism of sequence discrimination characteristic of this distinctive group of transcription regulators.