Conformational modification of serpins transforms leukocyte elastase inhibitor into an endonuclease involved in apoptosis

RNA Binding by Plant Serpins in vitro

Serpins constitute a large family of protease inhibitors with regulatory functions found in all living organisms. Most plant serpins have not been functionally characterized, with the exception of Arabidopsis thaliana AtSerpin1, an inhibitor of pro-apoptotic proteases, which is involved in the regulation of the programmed cell death induction, and Cucurbita maxima CmPS1, a phloem protein, which presumably inhibits insect digestive proteases and binds RNA. CmPS1 interacts most efficiently with highly structured RNA; in particular, it forms a specific complex with tRNA. Here, we demonstrated that AtSerpin1 also forms a complex with tRNA. Analysis of tRNA species bound by AtSerpin1 and CmPS1 in the presence of tRNA excess revealed that both proteins have no strict selectivity for individual tRNAs, suggesting specific interaction of AtSerpin1 and CmPS1 proteins with elements of the secondary/tertiary structure universal for all tRNAs. Analysis of CmPS1 binding of the microRNA precursor pre-miR390 and its mutants demonstrated that the pre-miR390 mutant with a perfect duplex in the hairpin stem lost the ability to form a discrete complex with CmPS1, whereas another variant of pre-miR390 with the native unpaired nucleotide residues in the stem retained this ability. These data indicate that specific interactions of plant serpins with structured RNA are based on the recognition of structurally unique spatial motifs formed with the participation of unpaired nucleotide residues in the RNA duplexes.

Cell Death Mechanisms in a Mouse Model of Retinal Degeneration in Spinocerebellar Ataxia 7

Spino-cerebellar ataxia type 7 (SCA7) is a polyglutamine (polyQ) disorder characterized by neurodegeneration of the brain, cerebellum, and retina caused by a polyglutamine expansion in ataxin7. The presence of an expanded polyQ tract in a mutant protein is known to induce protein aggregation, cellular stress, toxicity, and finally cell death. However, the consequences of the presence of mutant ataxin7 in the retina and the mechanisms underlying photoreceptor degeneration remain poorly understood. In this study, we show that in a retinal SCA7 mouse model, polyQ ataxin7 induces stress within the retina and activates Muller cells. Moreover, unfolded protein response and autophagy are activated in SCA7 photoreceptors. We have also shown that the photoreceptor death does not involve a caspase-dependent apoptosis but instead involves apoptosis inducing factor (AIF) and Leukocyte Elastase Inhibitor (LEI/L-DNase II). When these two cell death effectors are downregulated by their siRNA, a significant reduction in photoreceptor death is observed. These results highlight the consequences of polyQ protein expression in the retina and the role of caspase-independent pathways involved in photoreceptor cell death.

Effects of white light-emitting diode (LED) exposure on retinal pigment epithelium in vivo

Ageing and alteration of the functions of the retinal pigment epithelium (RPE) are at the origin of lost of vision seen in age-related macular degeneration (AMD). The RPE is known to be vulnerable to high-energy blue light. The white light-emitting diodes (LED) commercially available have relatively high content of blue light, a feature that suggest that they could be deleterious for this retinal cell layer. The aim of our study was to investigate the effects of "white LED" exposure on RPE. For this, commercially available white LEDs were used for exposure experiments on Wistar rats. Immunohistochemical stain on RPE flat mount, transmission electron microscopy and Western blot were used to exam the RPE. LED-induced RPE damage was evaluated by studying oxidative stress, stress response pathways and cell death pathways as well as the integrity of the outer blood-retinal barrier (BRB). We show that white LED light caused structural alterations leading to the disruption of the outer blood-retinal barrier. We observed an increase in oxidized molecules, disturbance of basal autophagy and cell death by necrosis. We conclude that white LEDs induced strong damages in rat RPE characterized by the breakdown of the BRB and the induction of necrotic cell death.

Schistosoma japonicum serine protease inhibitor increases endothelial barrier function

Schistosomiasis remains the second most prevalent zoonotic disease after malaria in veterinary medicine. The egg lodgement in target host tissue plays important roles in pathogenesis of this disease, but the process prior to egg-laying is still elusive. Surely, investigation of how this parasite invades and moves inside corresponding host will probably improve our understanding of homeostasis and maintenance of animal health, further, of related pathogenesis and thus potential intervention against schistosomiasis. TNT-coupled transcription/translation-expressed Sj serpin was employed for the protease inhibition assay. Transendothelial resistance (TER), its charge selectivity and size selectivity, were measured by the ussing chamber technique in serpin-transfected or recombinant serpin-treated HUVEC monolayer. The expressions of junction proteins were assayed using real-time PCR, Western blot and immunostaining. Sj serpin blocks the protease activity of elastase in a time-dependent manner; and Sj serpin can increase TER ofendothelial monolayer by decreasing its paracellular size selectivity, but not by interfere with the charge selectivity. Altered expression of tight junction protein claudin-2 was not observed at either RNA or protein levels; however, we found a marked increase in the expression of occludin, ZO-1,VE-cadherin and beta-catenin. Sj serpin can increase the transendothelial barrier function by decreasing the transendothelial permeability, implying serpin as a potential target to limit the invasion of schistosome into animal blood vessel.

Dnases in health and disease

DNA degradation is critical to healthy organism development and survival. Two nuclease families that play key roles in development and in disease are the Dnase1 and Dnase2 families. While these two families were initially characterized by biochemical function, it is now clear that multiple enzymes in each family perform similar, non-redundant roles in many different tissues. Most Dnase1 and Dnase2 family members are poorly characterized, yet their elimination can lead to a wide range of diseases, including lethal anemia, parakeratosis, cataracts and systemic lupus erythematosus. Therefore, understanding these enzyme families represents a critical field of emerging research. This review explores what is currently known about Dnase1 and Dnase2 family members, highlighting important questions about the structure and function of family members, and how their absence translates to disease.

Channel catfish granzyme-like I is a highly specific serine protease with metase activity that is expressed by fish NK-like cells

Here we present the extended cleavage specificity of catfish granzyme-like I, previously identified in fish NK-like cells. This protease has been characterised using substrate phage display and further validated by using a panel of recombinant substrates. A strict preference for Met in the P1 (cleavage) position, indicating metase specificity was observed. A screening of potential in vivo substrates was performed based on the derived P5-P3' consensus: Arg-Val-Thr-Gly-Met(↓)Ser-Leu-Val. Channel catfish caspase 6 was one very interesting potential target identified. This site was present in an adjacent position to the classic caspase activation site (Asp179 in human caspase 6). Cleavage of this site (hence potential activation) by the catfish granzyme-like I could reveal a novel mechanism of caspase 6 activation. This poses an interesting idea that the role of granzyme-like proteases in the activation of caspase dependent apoptosis mechanisms has been conserved for over 400 million years.

The hidden side of SERPINB1/Leukocyte Elastase Inhibitor

SERPINB1, also called Leukocyte Elastase Inhibitor (LEI) is a member of the clade B of SERPINS. It is an intracellular protein and acts primarily to protect the cell from proteases released into the cytoplasm during stress. Its role in inflammation is clear due to its involvement in the resolution of chronic inflammatory lung and bowel diseases. LEI/SERPINB1 intrinsically possesses two enzymatic activities: an antiprotease activity dependent on its reactive site loop, which is analogous to the other proteins of the family and an endonuclease activity which is unveiled by the cleavage of the reactive site loop. The conformational change induced by this cleavage also unveils a bipartite nuclear localization signal allowing the protein to translocate to the nucleus. Recent data indicate that it has also a role in cell migration suggesting that it could be involved in diverse processes like wound healing and malignant metastases.

Inhibitors of Serine Proteases in Regulating the Production and Function of Neutrophil Extracellular Traps

Neutrophil extracellular traps (NETs), DNA webs released into the extracellular environment by activated neutrophils, are thought to play a key role in the entrapment and eradication of microbes. However, NETs are highly cytotoxic and a likely source of autoantigens, suggesting that NET release is tightly regulated. NET formation involves the activity of neutrophil elastase (NE), which cleaves histones, leading to chromatin decondensation. We and others have recently demonstrated that inhibitors of NE, such as secretory leukocyte protease inhibitor (SLPI) and SerpinB1, restrict NET production in vitro and in vivo. SLPI was also identified as a NET component in the lesional skin of patients suffering from the autoinflammatory skin disease psoriasis. SLPI-competent NET-like structures (a mixture of SLPI with neutrophil DNA and NE) stimulated the synthesis of interferon type I (IFNI) in plasmacytoid dendritic cells (pDCs) in vitro. pDCs uniquely respond to viral or microbial DNA/RNA but also to nucleic acids of “self” origin with the production of IFNI. Although IFNIs are critical in activating the antiviral/antimicrobial functions of many cells, IFNIs also play a role in inducing autoimmunity. Thus, NETs decorated by SLPI may regulate skin immunity through enhancing IFNI production in pDCs. Here, we review key aspects of how SLPI and SerpinB1 can control NET production and immunogenic function.

Retinal damage induced by commercial light emitting diodes (LEDs)

Spectra of "white LEDs" are characterized by an intense emission in the blue region of the visible spectrum, absent in daylight spectra. This blue component and the high intensity of emission are the main sources of concern about the health risks of LEDs with respect to their toxicity to the eye and the retina. The aim of our study was to elucidate the role of blue light from LEDs in retinal damage. Commercially available white LEDs and four different blue LEDs (507, 473, 467, and 449nm) were used for exposure experiments on Wistar rats. Immunohistochemical stain, transmission electron microscopy, and Western blot were used to exam the retinas. We evaluated LED-induced retinal cell damage by studying oxidative stress, stress response pathways, and the identification of cell death pathways. LED light caused a state of suffering of the retina with oxidative damage and retinal injury. We observed a loss of photoreceptors and the activation of caspase-independent apoptosis, necroptosis, and necrosis. A wavelength dependence of the effects was observed. Phototoxicity of LEDs on the retina is characterized by a strong damage of photoreceptors and by the induction of necrosis.

On the use of an appropriate TdT-mediated dUTP-biotin nick end labeling assay to identify apoptotic cells

Apoptosis is an essential cellular mechanism involved in many processes such as embryogenesis, metamorphosis, and tissue homeostasis. DNA fragmentation is one of the key markers of this form of cell death. DNA fragmentation is executed by endogenous endonucleases such as caspase-activated DNase (CAD) in caspase-dependent apoptosis. The TUNEL (TdT-mediated dUTP-biotin nick end labeling) technique is the most widely used method to identify apoptotic cells in a tissue or culture and to assess drug toxicity. It is based on the detection of 3'-OH termini that are labeled with dUTP by the terminal deoxynucleotidyl transferase. Although the test is very reliable and sensitive in caspase-dependent apoptosis, it is completely useless when cell death is mediated by pathways involving DNA degradation that generates 3'-P ends as in the LEI/L-DNase II pathway. Here, we propose a modification in the TUNEL protocol consisting of a dephosphorylation step prior to the TUNEL labeling. This allows the detection of both types of DNA breaks induced during apoptosis caspase-dependent and independent pathways, avoiding underestimating the cell death induced by the treatment of interest.

The activation of the atypical PKC zeta in light-induced retinal degeneration and its involvement in L-DNase II control

Light-induced retinal degeneration is characterized by photoreceptor cell death. Many studies showed that photoreceptor demise is caspase-independent. In our laboratory we showed that leucocyte elastase inhibitor/LEI-derived DNase II (LEI/L-DNase II), a caspase-independent apoptotic pathway, is responsible for photoreceptor death. In this work, we investigated the activation of a pro-survival kinase, the protein kinase C (PKC) zeta. We show that light exposure induced PKC zeta activation. PKC zeta interacts with LEI/L-DNase II and controls its DNase activity by impairing its nuclear translocation. These results highlight the role of PKC zeta in retinal physiology and show that this kinase can control caspase-independent pathways.

Apoptosis-inducing factor (AIF) and leukocyte elastase inhibitor/L-DNase II (LEI/LDNaseII), can interact to conduct caspase-independent cell death

Programmed cell death is an important factor in tissue homeostasis. Lot of work has been performed to characterize the caspase-dependent cell death. Caspase-independent cell death, although important in many physiological situations, is less investigated. In this work we show that two caspase-independent effectors of cell death, namely apoptosis-inducing factor and leukocyte elastase inhibitor derived DNase II interact and can cooperate to induce cell death. These results contribute to the knowledge of molecular pathways of cell death, an important issue in the development of new therapeutic strategies for the treatment of cancer or neurodegenerative diseases.

Endonucleases and apoptosis in animals

Endonucleases are the main instruments of obligatory DNA degradation in apoptosis. Many endonucleases have marked processive action; initially they split DNA in chromatin into very large domains, and then they perform in it internucleosomal fragmentation of DNA followed by its hydrolysis to small fragments (oligonucleotides). During apoptosis, DNA of chromatin is attacked by many nucleases that are different in activity, specificity, and order of action. The activity of every endonuclease is regulated in the cell through its own regulatory mechanism (metal ions and other effectors, possibly also S-adenosylmethionine). Apoptosis is impossible without endonucleases as far as it leads to accumulation of unnecessary (defective) DNA, disorders in cell differentiation, embryogenesis, the organism's development, and is accompanied by various severe diseases. The interpretation of the structure and functions of endonucleases and of the nature and action of their modulating effectors is important not only for elucidation of mechanisms of apoptosis, but also for regulation and control of programmed cell death, cell differentiation, and development of organisms.

Proteomic analysis of rainbow trout (Oncorhynchus mykiss) intestinal epithelia: physiological acclimation to short-term starvation

The intestinal epithelia form the first line of defense against harmful agents in the gut lumen of most monogastric vertebrates, including teleost fishes. Previous investigations into the effect of starvation on the intestinal epithelia of teleost fishes have focused primarily on changes in morphological characteristics and targeted molecular analysis of specific enzymes. The goal of this study was to use a comprehensive approach to help reveal how the intestinal epithelia of carnivorous teleost fishes acclimate to short-term nutrient deprivation. We utilized two-dimensional gel electrophoresis (2-DE) to conduct the proteomic analysis of the mucosal and epithelial layer of the anterior gut intestinal tract (GIT) from satiation fed vs. 4 week starved rainbow trout (Oncorhynchus mykiss). A total of 40 proteins were determined to be differentially expressed and were subsequently picked for in-gel trypsin digestion. Peptide mass fingerprint analysis was conducted using matrix assisted laser desorption time-of-flight/time-of-flight. Nine of the 11 positively identified proteins were directly related to innate immunity. The expression of α-1 proteinase inhibitor decreased in starved vs. fed fish. Also, the concentration of one leukocyte elastase inhibitor (LEI) isomer decreased in starved fish, though the concentration of another LEI isomer increased in due to starvation. In addition, starvation promoted an increased concentration of the important xenobiotic-transporter p-glycoprotein. Finally, starvation resulted in a significant increase in type II keratin E2. Overall, our results indicate that starvation promoted a reduced capacity to inhibit enzymatic stress but increased xenobiotic resistance and paracellular permeability of epithelial cells in the anterior intestine of rainbow trout.

Functional specific roles of H-ras and N-ras. A proteomic approach using knockout cell lines

Ras small GTPases function as transducers of extracellular signals regulating cell survival, growth and differentiation. There are three major ras isoforms: H-, N- and K-Ras. To improve the understanding of H- and N-Ras protein signalling networks, we compared total proteome changes in mouse embryonic fibroblasts knock out for H-ras and/or N-ras, using proteomics tools combining 2DE, semi-quantitative image analysis, in-gel trypsin digestion and mass spectrometry. There are four up-regulated proteins due to the loss of expression of H-Ras (including cyclin-dependent kinase inhibitor 2A) and eight down-regulated (including stress-70 protein, dihydropyrimidinase-related-protein 3, heat shock cognate 71 kDa protein, tropomyosin beta chain, Rho GDP-dissociation inhibitor 1) and six up-regulated proteins (e.g. leukocyte elastase inhibitor A, L-lactate dehydrogenase B chain, c-Myc-responsive protein Rcl, interleukin-1 receptor antagonist protein) due to the loss of expression of both N- and H-Ras. Most of these proteins are related to Ras signalling in one way or another. Changes in expression of some of these proteins were further confirmed by Western blot. This proteomic comparative analysis from loss of function of H- and N-Ras knockout fibroblasts yields interpretable data to elucidate the differential protein expression, and contributes to evaluate the possibilities for physiological and therapeutic targets.

An emerging role for the nuclear localization of maspin in the suppression of tumor progression and metastasis

Maspin, a member of the serpin family of serine protease inhibitors, was originally identified as a tumor suppressor that is expressed in normal mammary epithelial cells but is reduced or absent in breast carcinomas. Early enthusiasm for maspin as a biomarker for disease progression has been tempered by clinical data that associates maspin with favourable outcomes in some studies and poor prognosis in others. Here, we review all of the published clinical studies for maspin in breast and ovarian cancers and propose that the apparent discordance between clinical reports is a consequence of differential cellular distribution of maspin. Indeed, it was thought that an extracellular pool of maspin possessed tumor suppressor activity, acting by inhibiting migration and increasing cell adhesion. Recent evidence from our group and others indicates, however, that the nuclear localization of maspin in cancer cells is necessary for its tumor suppressor activity. We provide additional data here to demonstrate that nuclear-localized maspin binds to chromatin and is required to effectively prevent cells from metastasizing. Our knowledge of other serpins that localize to the nucleus should help to inform future studies of nuclear maspin. Elucidation of the molecular mechanisms regulating the localization and activities of maspin should pave the way for the development of improved diagnostics and therapies for cancer.

Ocular biocompatibility of novel Cyclosporin A formulations based on methoxy poly(ethylene glycol)-hexylsubstituted poly(lactide) micelle carriers

Topical ocular drug delivery has always been a challenge for pharmaceutical technology scientists. In the last two decades, many nano-systems have been studied to find ways to overcome the typical problems of topical ocular therapy, such as difficult corneal penetration and poor drug availability. In this study, methoxy poly(ethylene glycol)-hexylsubstituted poly(lactides) (MPEG-hexPLA) micelle formulations, which are promising nanocarriers for poorly water soluble drugs, were investigated for the delivery of Cyclosporin A (CsA) to the eye. As a new possible pharmaceutical excipient, the ocular compatibility of MPEG-hexPLA micelle formulations was evaluated. An in vitro biocompatibility assessment on human corneal epithelial cells was carried out using different tests. Cytotoxicity was studied by using the [3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyl tetrazolium bromide] (MTT), and clonogenic tests and revealed that the CsA formulations and copolymer solutions were not toxic. After incubation with MPEG-hexPLA micelle formulations, the activation of caspase-dependent and -independent apoptosis as well as autophagy was evaluated using immunohistochemistry by analyzing the localization of four antibodies: (1) anti-caspase 3; (2) anti-apoptotic inducing factor (AIF); (3) anti-IL-Dnase II and (4) anti-microtubule-associated protein 1 light chain 3 (LC3). No apoptosis was induced when the cells were treated with the micelle solutions that were either unloaded or loaded with CsA. The ocular tolerance was assessed in vivo on rabbit eyes by Confocal Laser Scanning Ophthalmoscopy (CLSO), and very good tolerability was seen. The observed corneal surface was comparable to a control surface that was treated with a 0.9% NaCl solution. In conclusion, these results demonstrate that MPEG-hexPLA micelles are promising drug carriers for ocular diseases involving the activation of cytokines, such as dry eye syndrome and autoimmune uveitis, or for the prevention of corneal graft rejection.

Leukocyte elastase inhibitor: a new regulator of PARP-1

Poly(ADP-ribose) polymerase-1 (PARP-1) uses NAD(+) as a substrate to form ADP-ribose. During apoptosis, caspases cleave PARP-1 to avoid excessive NAD consumption. Because PARP-1 is a key regulator of the activity of DNases involved in caspase-dependent apoptosis, its cleavage is required to promote DNA degradation. To explore the situation in caspase-independent cell death, we investigated the effect of PARP-1 on the acid endonuclease leukocyte elastase inhibitor (LEI)-derived DNase II (L-DNase II). We found for the first time an association between PARP-1 and LEI/L-DNase II. Unexpectedly, we observed that LEI influenced the automodification of PARP-1.

Regulation of poly(ADP-ribose) polymerase-1 functions by leukocyte elastase inhibitor/LEI-derived DNase II during caspase-independent apoptosis

Poly(ADP-ribose) polymerase-1 (PARP-1) is an important regulator of apoptosis. Its over-activation at the onset of apoptosis can inhibit the action of apoptotic endonucleases like caspase-activated DNase and DNAS1L3. Therefore, controlled PARP-1 proteolysis during caspase-dependent apoptosis is considered essential to promote DNA degradation. Yet, little is known about the interplay of PARP-1 and endonucleases that operate during caspase-independent cell death. Here we show that in the long-term cultured HeLa cells which undergo caspase-independent death, PARP-1 co-immunoprecipitates with leukocyte elastase inhibitor-derived DNase II (L-DNase II), an acid DNase implicated in this death pathway and activated by serine proteases. Our results indicate that, despite having putative poly(ADP-ribose)-acceptor sites, LEI/L-DNase II is neither significantly poly(ADP-ribosyl)ated nor inhibited by PARP-1 during caspase-independent apoptosis. Unexpectedly, caspase-independent apoptosis induced by hexa-methylene amiloride, LEI/L-DNase II can activate PARP-1 and promote its auto-poly(ADP-ribosyl)ation, thus inhibiting PARP-1 activity. Moreover, overexpression of LEI blocks the pro-survival effect of PARP-1 in this model of cell death. Our results provide the original evidence for a new mechanism of PARP-1 activity regulation in the caspase-independent death pathway involving LEI/L-DNase II.

The functions of Deoxyribonuclease II in immunity and development

Apoptosis, which is usually accompanied by DNA degradation, is important not only for the homeostasis of metazoans but also for mammalian development. If DNA is not properly degraded in these processes, it can cause diverse diseases, such as anemia, cataracts, and some autoimmune diseases. A large effort has been made to identify these nucleases that are responsible for these effects. In contrast to Deoxyribonuclease I (DNase I), Deoxyribonuclease II (DNase II) has been less well characterized in these processes. Additionally, enzymes of DNase II family in Trichinella spiralis, which is an intracellular parasitic nematode, are also considered involved in the development of the nematode. We have compiled information from studies on DNase II from various organisms and found some nonclassic features in these enzymes of T. spiralis. Here we have reviewed the characterization and functions of DNase II in these processes and predicted the functions of these enzymes in T. spiralis during host invasion and development.

Nuclear export of LEI/L-DNase II by Crm1 is essential for cell survival

LEI/L-DNase II is the key protein of a caspase-independent pathway activated by serine proteases. LEI (Leukocyte elastase inhibitor), L-DNase II precursor, is a member of the clade B serpins (also called serpin b1). In its native conformation it inhibits several intracellular proteases and has an anti-apoptotic activity. Following a metabolic stress and the increase of protease activity in the cell, LEI is cleaved and transformed into L-DNase II (LEI-derived DNase II). This transformation is due to a conformational modification that exposes a nuclear localization signal and an endonuclease active site. In this paper we show that LEI can bind the exportin Crm1, and we identify on LEI a nuclear export signal involved in the control of LEI/L-DNase II nuclearization in healthy cells. Point mutation of this site increases the accumulation of the molecule in the nucleus and triggers cell death.

Functional diversification of a protease inhibitor gene in the genus Drosophila and its molecular basis

The mutually exclusive use of alternative reactive site loop (RSL) cassettes due to alternative splicing of serpin (serine protease inhibitor) gene transcripts is a widespread strategy to create target-selective protease inhibitors in the animal kingdom. Since molecular basis and evolution of serpin RSL cassette exon amplification and diversification are unexplored, the exon-intron organization of the serpin gene spn4 from 12 species of the genus Drosophila was studied. The analysis of the gene structures shows that both number and target enzyme specificities of Spn4 RSL cassettes are highly variable in fruit flies and includes inhibitor variants with novel antiproteolytic activities in some species, indicating that RSL diversity is the result of adaptive evolution. Comparative genomics suggests that interallelic gene conversion and/or recombination events contribute to RSL cassette exon amplification. Due to an intron that is located at the most suitable position within the RSL region, multiple inhibitors can be formed in an economic manner that are both efficient and target-selective, allowing fruit flies to control an astonishing variety of proteases with different cleavage chemistry and evolutionary ancestry.